From 1952e2e1c1be6f107fa3ce8b10025cfd1cd7943b Mon Sep 17 00:00:00 2001 From: "David E. O'Brien" Date: Fri, 1 Feb 2002 18:16:02 +0000 Subject: Enlist the FreeBSD-CURRENT users as testers of what is to become Gcc 3.1.0. These bits are taken from the FSF anoncvs repo on 1-Feb-2002 08:20 PST. --- contrib/gcc/doc/bugreport.texi | 394 ++ contrib/gcc/doc/c-tree.texi | 2307 +++++++ contrib/gcc/doc/collect2.texi | 85 + contrib/gcc/doc/configfiles.texi | 74 + contrib/gcc/doc/configterms.texi | 61 + contrib/gcc/doc/contrib.texi | 712 ++ contrib/gcc/doc/contribute.texi | 25 + contrib/gcc/doc/cpp.texi | 4302 ++++++++++++ contrib/gcc/doc/cppinternals.texi | 1065 +++ contrib/gcc/doc/extend.texi | 6616 +++++++++++++++++++ contrib/gcc/doc/fragments.texi | 190 + contrib/gcc/doc/frontends.texi | 70 + contrib/gcc/doc/gcc.texi | 234 + contrib/gcc/doc/gccint.texi | 236 + contrib/gcc/doc/gcov.texi | 406 ++ contrib/gcc/doc/gnu.texi | 20 + contrib/gcc/doc/headerdirs.texi | 33 + contrib/gcc/doc/hostconfig.texi | 130 + contrib/gcc/doc/include/fdl.texi | 434 ++ contrib/gcc/doc/include/funding.texi | 60 + contrib/gcc/doc/include/gcc-common.texi | 36 + contrib/gcc/doc/include/gpl.texi | 409 ++ contrib/gcc/doc/install-old.texi | 725 +++ contrib/gcc/doc/install.texi | 3823 +++++++++++ contrib/gcc/doc/install.texi2html | 31 + contrib/gcc/doc/interface.texi | 102 + contrib/gcc/doc/invoke.texi | 10463 ++++++++++++++++++++++++++++++ contrib/gcc/doc/languages.texi | 36 + contrib/gcc/doc/makefile.texi | 102 + contrib/gcc/doc/md.texi | 5303 +++++++++++++++ contrib/gcc/doc/objc.texi | 458 ++ contrib/gcc/doc/passes.texi | 659 ++ contrib/gcc/doc/portability.texi | 38 + contrib/gcc/doc/rtl.texi | 3401 ++++++++++ contrib/gcc/doc/service.texi | 30 + contrib/gcc/doc/sourcebuild.texi | 875 +++ contrib/gcc/doc/standards.texi | 178 + contrib/gcc/doc/tm.texi | 8614 ++++++++++++++++++++++++ contrib/gcc/doc/trouble.texi | 1462 +++++ contrib/gcc/doc/vms.texi | 331 + 40 files changed, 54530 insertions(+) create mode 100644 contrib/gcc/doc/bugreport.texi create mode 100644 contrib/gcc/doc/c-tree.texi create mode 100644 contrib/gcc/doc/collect2.texi create mode 100644 contrib/gcc/doc/configfiles.texi create mode 100644 contrib/gcc/doc/configterms.texi create mode 100644 contrib/gcc/doc/contrib.texi create mode 100644 contrib/gcc/doc/contribute.texi create mode 100644 contrib/gcc/doc/cpp.texi create mode 100644 contrib/gcc/doc/cppinternals.texi create mode 100644 contrib/gcc/doc/extend.texi create mode 100644 contrib/gcc/doc/fragments.texi create mode 100644 contrib/gcc/doc/frontends.texi create mode 100644 contrib/gcc/doc/gcc.texi create mode 100644 contrib/gcc/doc/gccint.texi create mode 100644 contrib/gcc/doc/gcov.texi create mode 100644 contrib/gcc/doc/gnu.texi create mode 100644 contrib/gcc/doc/headerdirs.texi create mode 100644 contrib/gcc/doc/hostconfig.texi create mode 100644 contrib/gcc/doc/include/fdl.texi create mode 100644 contrib/gcc/doc/include/funding.texi create mode 100644 contrib/gcc/doc/include/gcc-common.texi create mode 100644 contrib/gcc/doc/include/gpl.texi create mode 100644 contrib/gcc/doc/install-old.texi create mode 100644 contrib/gcc/doc/install.texi create mode 100755 contrib/gcc/doc/install.texi2html create mode 100644 contrib/gcc/doc/interface.texi create mode 100644 contrib/gcc/doc/invoke.texi create mode 100644 contrib/gcc/doc/languages.texi create mode 100644 contrib/gcc/doc/makefile.texi create mode 100644 contrib/gcc/doc/md.texi create mode 100644 contrib/gcc/doc/objc.texi create mode 100644 contrib/gcc/doc/passes.texi create mode 100644 contrib/gcc/doc/portability.texi create mode 100644 contrib/gcc/doc/rtl.texi create mode 100644 contrib/gcc/doc/service.texi create mode 100644 contrib/gcc/doc/sourcebuild.texi create mode 100644 contrib/gcc/doc/standards.texi create mode 100644 contrib/gcc/doc/tm.texi create mode 100644 contrib/gcc/doc/trouble.texi create mode 100644 contrib/gcc/doc/vms.texi (limited to 'contrib/gcc/doc') diff --git a/contrib/gcc/doc/bugreport.texi b/contrib/gcc/doc/bugreport.texi new file mode 100644 index 000000000000..1ac26c5fa5df --- /dev/null +++ b/contrib/gcc/doc/bugreport.texi @@ -0,0 +1,394 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Bugs +@chapter Reporting Bugs +@cindex bugs +@cindex reporting bugs + +Your bug reports play an essential role in making GCC reliable. + +When you encounter a problem, the first thing to do is to see if it is +already known. @xref{Trouble}. If it isn't known, then you should +report the problem. + +Reporting a bug may help you by bringing a solution to your problem, or +it may not. (If it does not, look in the service directory; see +@ref{Service}.) In any case, the principal function of a bug report is +to help the entire community by making the next version of GCC work +better. Bug reports are your contribution to the maintenance of GCC@. + +Since the maintainers are very overloaded, we cannot respond to every +bug report. However, if the bug has not been fixed, we are likely to +send you a patch and ask you to tell us whether it works. + +In order for a bug report to serve its purpose, you must include the +information that makes for fixing the bug. + +@menu +* Criteria: Bug Criteria. Have you really found a bug? +* Where: Bug Lists. Where to send your bug report. +* Reporting: Bug Reporting. How to report a bug effectively. +* GNATS: gccbug. You can use a bug reporting tool. +* Known: Trouble. Known problems. +* Help: Service. Where to ask for help. +@end menu + +@node Bug Criteria,Bug Lists,,Bugs +@section Have You Found a Bug? +@cindex bug criteria + +If you are not sure whether you have found a bug, here are some guidelines: + +@itemize @bullet +@cindex fatal signal +@cindex core dump +@item +If the compiler gets a fatal signal, for any input whatever, that is a +compiler bug. Reliable compilers never crash. + +@cindex invalid assembly code +@cindex assembly code, invalid +@item +If the compiler produces invalid assembly code, for any input whatever +(except an @code{asm} statement), that is a compiler bug, unless the +compiler reports errors (not just warnings) which would ordinarily +prevent the assembler from being run. + +@cindex undefined behavior +@cindex undefined function value +@cindex increment operators +@item +If the compiler produces valid assembly code that does not correctly +execute the input source code, that is a compiler bug. + +However, you must double-check to make sure, because you may have run +into an incompatibility between GNU C and traditional C +(@pxref{Incompatibilities}). These incompatibilities might be considered +bugs, but they are inescapable consequences of valuable features. + +Or you may have a program whose behavior is undefined, which happened +by chance to give the desired results with another C or C++ compiler. + +For example, in many nonoptimizing compilers, you can write @samp{x;} +at the end of a function instead of @samp{return x;}, with the same +results. But the value of the function is undefined if @code{return} +is omitted; it is not a bug when GCC produces different results. + +Problems often result from expressions with two increment operators, +as in @code{f (*p++, *p++)}. Your previous compiler might have +interpreted that expression the way you intended; GCC might +interpret it another way. Neither compiler is wrong. The bug is +in your code. + +After you have localized the error to a single source line, it should +be easy to check for these things. If your program is correct and +well defined, you have found a compiler bug. + +@item +If the compiler produces an error message for valid input, that is a +compiler bug. + +@cindex invalid input +@item +If the compiler does not produce an error message for invalid input, +that is a compiler bug. However, you should note that your idea of +``invalid input'' might be my idea of ``an extension'' or ``support +for traditional practice''. + +@item +If you are an experienced user of one of the languages GCC supports, your +suggestions for improvement of GCC are welcome in any case. +@end itemize + +@node Bug Lists,Bug Reporting,Bug Criteria,Bugs +@section Where to Report Bugs +@cindex bug report mailing lists +@kindex gcc-bugs@@gcc.gnu.org or bug-gcc@@gnu.org +Send bug reports for the GNU Compiler Collection to +@email{gcc-bugs@@gcc.gnu.org}. In accordance with the GNU-wide +convention, in which bug reports for tool ``foo'' are sent +to @samp{bug-foo@@gnu.org}, the address @email{bug-gcc@@gnu.org} +may also be used; it will forward to the address given above. + +Please read @uref{http://gcc.gnu.org/bugs.html} for additional and/or +more up-to-date bug reporting instructions before you post a bug report. + +@node Bug Reporting,gccbug,Bug Lists,Bugs +@section How to Report Bugs +@cindex compiler bugs, reporting + +The fundamental principle of reporting bugs usefully is this: +@strong{report all the facts}. If you are not sure whether to state a +fact or leave it out, state it! + +Often people omit facts because they think they know what causes the +problem and they conclude that some details don't matter. Thus, you might +assume that the name of the variable you use in an example does not matter. +Well, probably it doesn't, but one cannot be sure. Perhaps the bug is a +stray memory reference which happens to fetch from the location where that +name is stored in memory; perhaps, if the name were different, the contents +of that location would fool the compiler into doing the right thing despite +the bug. Play it safe and give a specific, complete example. That is the +easiest thing for you to do, and the most helpful. + +Keep in mind that the purpose of a bug report is to enable someone to +fix the bug if it is not known. It isn't very important what happens if +the bug is already known. Therefore, always write your bug reports on +the assumption that the bug is not known. + +Sometimes people give a few sketchy facts and ask, ``Does this ring a +bell?'' This cannot help us fix a bug, so it is basically useless. We +respond by asking for enough details to enable us to investigate. +You might as well expedite matters by sending them to begin with. + +Try to make your bug report self-contained. If we have to ask you for +more information, it is best if you include all the previous information +in your response, as well as the information that was missing. + +Please report each bug in a separate message. This makes it easier for +us to track which bugs have been fixed and to forward your bugs reports +to the appropriate maintainer. + +To enable someone to investigate the bug, you should include all these +things: + +@itemize @bullet +@item +The version of GCC@. You can get this by running it with the +@option{-v} option. + +Without this, we won't know whether there is any point in looking for +the bug in the current version of GCC@. + +@item +A complete input file that will reproduce the bug. If the bug is in the +C preprocessor, send a source file and any header files that it +requires. If the bug is in the compiler proper (@file{cc1}), send the +preprocessor output generated by adding @option{-save-temps} to the +compilation command (@pxref{Debugging Options}). When you do this, use +the same @option{-I}, @option{-D} or @option{-U} options that you used in +actual compilation. Then send the @var{input}.i or @var{input}.ii files +generated. + +A single statement is not enough of an example. In order to compile it, +it must be embedded in a complete file of compiler input; and the bug +might depend on the details of how this is done. + +Without a real example one can compile, all anyone can do about your bug +report is wish you luck. It would be futile to try to guess how to +provoke the bug. For example, bugs in register allocation and reloading +frequently depend on every little detail of the function they happen in. + +Even if the input file that fails comes from a GNU program, you should +still send the complete test case. Don't ask the GCC maintainers to +do the extra work of obtaining the program in question---they are all +overworked as it is. Also, the problem may depend on what is in the +header files on your system; it is unreliable for the GCC maintainers +to try the problem with the header files available to them. By sending +CPP output, you can eliminate this source of uncertainty and save us +a certain percentage of wild goose chases. + +@item +The command arguments you gave GCC to compile that example +and observe the bug. For example, did you use @option{-O}? To guarantee +you won't omit something important, list all the options. + +If we were to try to guess the arguments, we would probably guess wrong +and then we would not encounter the bug. + +@item +The type of machine you are using, and the operating system name and +version number. + +@item +The operands you gave to the @code{configure} command when you installed +the compiler. + +@item +A complete list of any modifications you have made to the compiler +source. (We don't promise to investigate the bug unless it happens in +an unmodified compiler. But if you've made modifications and don't tell +us, then you are sending us on a wild goose chase.) + +Be precise about these changes. A description in English is not +enough---send a context diff for them. + +Adding files of your own (such as a machine description for a machine we +don't support) is a modification of the compiler source. + +@item +Details of any other deviations from the standard procedure for installing +GCC@. + +@item +A description of what behavior you observe that you believe is +incorrect. For example, ``The compiler gets a fatal signal,'' or, +``The assembler instruction at line 208 in the output is incorrect.'' + +Of course, if the bug is that the compiler gets a fatal signal, then one +can't miss it. But if the bug is incorrect output, the maintainer might +not notice unless it is glaringly wrong. None of us has time to study +all the assembler code from a 50-line C program just on the chance that +one instruction might be wrong. We need @emph{you} to do this part! + +Even if the problem you experience is a fatal signal, you should still +say so explicitly. Suppose something strange is going on, such as, your +copy of the compiler is out of synch, or you have encountered a bug in +the C library on your system. (This has happened!) Your copy might +crash and the copy here would not. If you @i{said} to expect a crash, +then when the compiler here fails to crash, we would know that the bug +was not happening. If you don't say to expect a crash, then we would +not know whether the bug was happening. We would not be able to draw +any conclusion from our observations. + +If the problem is a diagnostic when compiling GCC with some other +compiler, say whether it is a warning or an error. + +Often the observed symptom is incorrect output when your program is run. +Sad to say, this is not enough information unless the program is short +and simple. None of us has time to study a large program to figure out +how it would work if compiled correctly, much less which line of it was +compiled wrong. So you will have to do that. Tell us which source line +it is, and what incorrect result happens when that line is executed. A +person who understands the program can find this as easily as finding a +bug in the program itself. + +@item +If you send examples of assembler code output from GCC, +please use @option{-g} when you make them. The debugging information +includes source line numbers which are essential for correlating the +output with the input. + +@item +If you wish to mention something in the GCC source, refer to it by +context, not by line number. + +The line numbers in the development sources don't match those in your +sources. Your line numbers would convey no useful information to the +maintainers. + +@item +Additional information from a debugger might enable someone to find a +problem on a machine which he does not have available. However, you +need to think when you collect this information if you want it to have +any chance of being useful. + +@cindex backtrace for bug reports +For example, many people send just a backtrace, but that is never +useful by itself. A simple backtrace with arguments conveys little +about GCC because the compiler is largely data-driven; the same +functions are called over and over for different RTL insns, doing +different things depending on the details of the insn. + +Most of the arguments listed in the backtrace are useless because they +are pointers to RTL list structure. The numeric values of the +pointers, which the debugger prints in the backtrace, have no +significance whatever; all that matters is the contents of the objects +they point to (and most of the contents are other such pointers). + +In addition, most compiler passes consist of one or more loops that +scan the RTL insn sequence. The most vital piece of information about +such a loop---which insn it has reached---is usually in a local variable, +not in an argument. + +@findex debug_rtx +What you need to provide in addition to a backtrace are the values of +the local variables for several stack frames up. When a local +variable or an argument is an RTX, first print its value and then use +the GDB command @code{pr} to print the RTL expression that it points +to. (If GDB doesn't run on your machine, use your debugger to call +the function @code{debug_rtx} with the RTX as an argument.) In +general, whenever a variable is a pointer, its value is no use +without the data it points to. +@end itemize + +Here are some things that are not necessary: + +@itemize @bullet +@item +A description of the envelope of the bug. + +Often people who encounter a bug spend a lot of time investigating +which changes to the input file will make the bug go away and which +changes will not affect it. + +This is often time consuming and not very useful, because the way we +will find the bug is by running a single example under the debugger with +breakpoints, not by pure deduction from a series of examples. You might +as well save your time for something else. + +Of course, if you can find a simpler example to report @emph{instead} of +the original one, that is a convenience. Errors in the output will be +easier to spot, running under the debugger will take less time, etc. +Most GCC bugs involve just one function, so the most straightforward +way to simplify an example is to delete all the function definitions +except the one where the bug occurs. Those earlier in the file may be +replaced by external declarations if the crucial function depends on +them. (Exception: inline functions may affect compilation of functions +defined later in the file.) + +However, simplification is not vital; if you don't want to do this, +report the bug anyway and send the entire test case you used. + +@item +In particular, some people insert conditionals @samp{#ifdef BUG} around +a statement which, if removed, makes the bug not happen. These are just +clutter; we won't pay any attention to them anyway. Besides, you should +send us cpp output, and that can't have conditionals. + +@item +A patch for the bug. + +A patch for the bug is useful if it is a good one. But don't omit the +necessary information, such as the test case, on the assumption that a +patch is all we need. We might see problems with your patch and decide +to fix the problem another way, or we might not understand it at all. + +Sometimes with a program as complicated as GCC it is very hard to +construct an example that will make the program follow a certain path +through the code. If you don't send the example, we won't be able to +construct one, so we won't be able to verify that the bug is fixed. + +And if we can't understand what bug you are trying to fix, or why your +patch should be an improvement, we won't install it. A test case will +help us to understand. + +See @uref{http://gcc.gnu.org/contribute.html} +for guidelines on how to make it easy for us to +understand and install your patches. + +@item +A guess about what the bug is or what it depends on. + +Such guesses are usually wrong. Even I can't guess right about such +things without first using the debugger to find the facts. + +@item +A core dump file. + +We have no way of examining a core dump for your type of machine +unless we have an identical system---and if we do have one, +we should be able to reproduce the crash ourselves. +@end itemize + +@node gccbug,, Bug Reporting, Bugs +@section The gccbug script +@cindex gccbug script + +To simplify creation of bug reports, and to allow better tracking of +reports, we use the GNATS bug tracking system. Part of that system is +the @code{gccbug} script. This is a Unix shell script, so you need a +shell to run it. It is normally installed in the same directory where +@code{gcc} is installed. + +The gccbug script is derived from send-pr, @pxref{using +send-pr,,Creating new Problem Reports,send-pr,Reporting Problems}. When +invoked, it starts a text editor so you can fill out the various fields +of the report. When the you quit the editor, the report is automatically +send to the bug reporting address. + +A number of fields in this bug report form are specific to GCC, and are +explained at @uref{http://gcc.gnu.org/gnats.html}. diff --git a/contrib/gcc/doc/c-tree.texi b/contrib/gcc/doc/c-tree.texi new file mode 100644 index 000000000000..cbf01967dfa1 --- /dev/null +++ b/contrib/gcc/doc/c-tree.texi @@ -0,0 +1,2307 @@ +@c Copyright (c) 1999, 2000, 2001 Free Software Foundation, Inc. +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@c --------------------------------------------------------------------- +@c Trees +@c --------------------------------------------------------------------- + +@node Trees +@chapter Trees: The intermediate representation used by the C and C++ front ends +@cindex Trees +@cindex C/C++ Internal Representation + +This chapter documents the internal representation used by GCC to +represent C and C++ source programs. When presented with a C or C++ +source program, GCC parses the program, performs semantic analysis +(including the generation of error messages), and then produces the +internal representation described here. This representation contains a +complete representation for the entire translation unit provided as +input to the front end. This representation is then typically processed +by a code-generator in order to produce machine code, but could also be +used in the creation of source browsers, intelligent editors, automatic +documentation generators, interpreters, and any other programs needing +the ability to process C or C++ code. + +This chapter explains the internal representation. In particular, it +documents the internal representation for C and C++ source +constructs, and the macros, functions, and variables that can be used to +access these constructs. The C++ representation which is largely a superset +of the representation used in the C front end. There is only one +construct used in C that does not appear in the C++ front end and that +is the GNU ``nested function'' extension. Many of the macros documented +here do not apply in C because the corresponding language constructs do +not appear in C@. + +If you are developing a ``back end'', be it is a code-generator or some +other tool, that uses this representation, you may occasionally find +that you need to ask questions not easily answered by the functions and +macros available here. If that situation occurs, it is quite likely +that GCC already supports the functionality you desire, but that the +interface is simply not documented here. In that case, you should ask +the GCC maintainers (via mail to @email{gcc@@gcc.gnu.org}) about +documenting the functionality you require. Similarly, if you find +yourself writing functions that do not deal directly with your back end, +but instead might be useful to other people using the GCC front end, you +should submit your patches for inclusion in GCC@. + +@menu +* Deficiencies:: Topics net yet covered in this document. +* Tree overview:: All about @code{tree}s. +* Types:: Fundamental and aggregate types. +* Scopes:: Namespaces and classes. +* Functions:: Overloading, function bodies, and linkage. +* Declarations:: Type declarations and variables. +* Attributes:: Declaration and type attributes. +* Expression trees:: From @code{typeid} to @code{throw}. +@end menu + +@c --------------------------------------------------------------------- +@c Deficiencies +@c --------------------------------------------------------------------- + +@node Deficiencies +@section Deficiencies + +There are many places in which this document is incomplet and incorrekt. +It is, as of yet, only @emph{preliminary} documentation. + +@c --------------------------------------------------------------------- +@c Overview +@c --------------------------------------------------------------------- + +@node Tree overview +@section Overview +@cindex tree +@findex TREE_CODE + +The central data structure used by the internal representation is the +@code{tree}. These nodes, while all of the C type @code{tree}, are of +many varieties. A @code{tree} is a pointer type, but the object to +which it points may be of a variety of types. From this point forward, +we will refer to trees in ordinary type, rather than in @code{this +font}, except when talking about the actual C type @code{tree}. + +You can tell what kind of node a particular tree is by using the +@code{TREE_CODE} macro. Many, many macros take a trees as input and +return trees as output. However, most macros require a certain kinds of +tree node as input. In other words, there is a type-system for trees, +but it is not reflected in the C type-system. + +For safety, it is useful to configure GCC with @option{--enable-checking}. +Although this results in a significant performance penalty (since all +tree types are checked at run-time), and is therefore inappropriate in a +release version, it is extremely helpful during the development process. + +Many macros behave as predicates. Many, although not all, of these +predicates end in @samp{_P}. Do not rely on the result type of these +macros being of any particular type. You may, however, rely on the fact +that the type can be compared to @code{0}, so that statements like +@example +if (TEST_P (t) && !TEST_P (y)) + x = 1; +@end example +@noindent +and +@example +int i = (TEST_P (t) != 0); +@end example +@noindent +are legal. Macros that return @code{int} values now may be changed to +return @code{tree} values, or other pointers in the future. Even those +that continue to return @code{int} may return multiple nonzero codes +where previously they returned only zero and one. Therefore, you should +not write code like +@example +if (TEST_P (t) == 1) +@end example +@noindent +as this code is not guaranteed to work correctly in the future. + +You should not take the address of values returned by the macros or +functions described here. In particular, no guarantee is given that the +values are lvalues. + +In general, the names of macros are all in uppercase, while the names of +functions are entirely in lower case. There are rare exceptions to this +rule. You should assume that any macro or function whose name is made +up entirely of uppercase letters may evaluate its arguments more than +once. You may assume that a macro or function whose name is made up +entirely of lowercase letters will evaluate its arguments only once. + +The @code{error_mark_node} is a special tree. Its tree code is +@code{ERROR_MARK}, but since there is only ever one node with that code, +the usual practice is to compare the tree against +@code{error_mark_node}. (This test is just a test for pointer +equality.) If an error has occurred during front-end processing the +flag @code{errorcount} will be set. If the front end has encountered +code it cannot handle, it will issue a message to the user and set +@code{sorrycount}. When these flags are set, any macro or function +which normally returns a tree of a particular kind may instead return +the @code{error_mark_node}. Thus, if you intend to do any processing of +erroneous code, you must be prepared to deal with the +@code{error_mark_node}. + +Occasionally, a particular tree slot (like an operand to an expression, +or a particular field in a declaration) will be referred to as +``reserved for the back end.'' These slots are used to store RTL when +the tree is converted to RTL for use by the GCC back end. However, if +that process is not taking place (e.g., if the front end is being hooked +up to an intelligent editor), then those slots may be used by the +back end presently in use. + +If you encounter situations that do not match this documentation, such +as tree nodes of types not mentioned here, or macros documented to +return entities of a particular kind that instead return entities of +some different kind, you have found a bug, either in the front end or in +the documentation. Please report these bugs as you would any other +bug. + +@menu +* Macros and Functions::Macros and functions that can be used with all trees. +* Identifiers:: The names of things. +* Containers:: Lists and vectors. +@end menu + +@c --------------------------------------------------------------------- +@c Trees +@c --------------------------------------------------------------------- + +@node Macros and Functions +@subsection Trees +@cindex tree + +This section is not here yet. + +@c --------------------------------------------------------------------- +@c Identifiers +@c --------------------------------------------------------------------- + +@node Identifiers +@subsection Identifiers +@cindex identifier +@cindex name +@tindex IDENTIFIER_NODE + +An @code{IDENTIFIER_NODE} represents a slightly more general concept +that the standard C or C++ concept of identifier. In particular, an +@code{IDENTIFIER_NODE} may contain a @samp{$}, or other extraordinary +characters. + +There are never two distinct @code{IDENTIFIER_NODE}s representing the +same identifier. Therefore, you may use pointer equality to compare +@code{IDENTIFIER_NODE}s, rather than using a routine like @code{strcmp}. + +You can use the following macros to access identifiers: +@ftable @code +@item IDENTIFIER_POINTER +The string represented by the identifier, represented as a +@code{char*}. This string is always @code{NUL}-terminated, and contains +no embedded @code{NUL} characters. + +@item IDENTIFIER_LENGTH +The length of the string returned by @code{IDENTIFIER_POINTER}, not +including the trailing @code{NUL}. This value of +@code{IDENTIFIER_LENGTH (x)} is always the same as @code{strlen +(IDENTIFIER_POINTER (x))}. + +@item IDENTIFIER_OPNAME_P +This predicate holds if the identifier represents the name of an +overloaded operator. In this case, you should not depend on the +contents of either the @code{IDENTIFIER_POINTER} or the +@code{IDENTIFIER_LENGTH}. + +@item IDENTIFIER_TYPENAME_P +This predicate holds if the identifier represents the name of a +user-defined conversion operator. In this case, the @code{TREE_TYPE} of +the @code{IDENTIFIER_NODE} holds the type to which the conversion +operator converts. + +@end ftable + +@c --------------------------------------------------------------------- +@c Containers +@c --------------------------------------------------------------------- + +@node Containers +@subsection Containers +@cindex container +@cindex list +@cindex vector +@tindex TREE_LIST +@tindex TREE_VEC +@findex TREE_PURPOSE +@findex TREE_VALUE +@findex TREE_VEC_LENGTH +@findex TREE_VEC_ELT + +Two common container data structures can be represented directly with +tree nodes. A @code{TREE_LIST} is a singly linked list containing two +trees per node. These are the @code{TREE_PURPOSE} and @code{TREE_VALUE} +of each node. (Often, the @code{TREE_PURPOSE} contains some kind of +tag, or additional information, while the @code{TREE_VALUE} contains the +majority of the payload. In other cases, the @code{TREE_PURPOSE} is +simply @code{NULL_TREE}, while in still others both the +@code{TREE_PURPOSE} and @code{TREE_VALUE} are of equal stature.) Given +one @code{TREE_LIST} node, the next node is found by following the +@code{TREE_CHAIN}. If the @code{TREE_CHAIN} is @code{NULL_TREE}, then +you have reached the end of the list. + +A @code{TREE_VEC} is a simple vector. The @code{TREE_VEC_LENGTH} is an +integer (not a tree) giving the number of nodes in the vector. The +nodes themselves are accessed using the @code{TREE_VEC_ELT} macro, which +takes two arguments. The first is the @code{TREE_VEC} in question; the +second is an integer indicating which element in the vector is desired. +The elements are indexed from zero. + +@c --------------------------------------------------------------------- +@c Types +@c --------------------------------------------------------------------- + +@node Types +@section Types +@cindex type +@cindex pointer +@cindex reference +@cindex fundamental type +@cindex array +@tindex VOID_TYPE +@tindex INTEGER_TYPE +@tindex TYPE_MIN_VALUE +@tindex TYPE_MAX_VALUE +@tindex REAL_TYPE +@tindex COMPLEX_TYPE +@tindex ENUMERAL_TYPE +@tindex BOOLEAN_TYPE +@tindex POINTER_TYPE +@tindex REFERENCE_TYPE +@tindex FUNCTION_TYPE +@tindex METHOD_TYPE +@tindex ARRAY_TYPE +@tindex RECORD_TYPE +@tindex UNION_TYPE +@tindex UNKNOWN_TYPE +@tindex OFFSET_TYPE +@tindex TYPENAME_TYPE +@tindex TYPEOF_TYPE +@findex CP_TYPE_QUALS +@findex TYPE_UNQUALIFIED +@findex TYPE_QUAL_CONST +@findex TYPE_QUAL_VOLATILE +@findex TYPE_QUAL_RESTRICT +@findex TYPE_MAIN_VARIANT +@cindex qualified type +@findex TYPE_SIZE +@findex TYPE_ALIGN +@findex TYPE_PRECISION +@findex TYPE_ARG_TYPES +@findex TYPE_METHOD_BASETYPE +@findex TYPE_PTRMEM_P +@findex TYPE_OFFSET_BASETYPE +@findex TREE_TYPE +@findex TYPE_CONTEXT +@findex TYPE_NAME +@findex TYPENAME_TYPE_FULLNAME +@findex TYPE_FIELDS +@findex TYPE_PTROBV_P + +All types have corresponding tree nodes. However, you should not assume +that there is exactly one tree node corresponding to each type. There +are often several nodes each of which correspond to the same type. + +For the most part, different kinds of types have different tree codes. +(For example, pointer types use a @code{POINTER_TYPE} code while arrays +use an @code{ARRAY_TYPE} code.) However, pointers to member functions +use the @code{RECORD_TYPE} code. Therefore, when writing a +@code{switch} statement that depends on the code associated with a +particular type, you should take care to handle pointers to member +functions under the @code{RECORD_TYPE} case label. + +In C++, an array type is not qualified; rather the type of the array +elements is qualified. This situation is reflected in the intermediate +representation. The macros described here will always examine the +qualification of the underlying element type when applied to an array +type. (If the element type is itself an array, then the recursion +continues until a non-array type is found, and the qualification of this +type is examined.) So, for example, @code{CP_TYPE_CONST_P} will hold of +the type @code{const int ()[7]}, denoting an array of seven @code{int}s. + +The following functions and macros deal with cv-qualification of types: +@ftable @code +@item CP_TYPE_QUALS +This macro returns the set of type qualifiers applied to this type. +This value is @code{TYPE_UNQUALIFIED} if no qualifiers have been +applied. The @code{TYPE_QUAL_CONST} bit is set if the type is +@code{const}-qualified. The @code{TYPE_QUAL_VOLATILE} bit is set if the +type is @code{volatile}-qualified. The @code{TYPE_QUAL_RESTRICT} bit is +set if the type is @code{restrict}-qualified. + +@item CP_TYPE_CONST_P +This macro holds if the type is @code{const}-qualified. + +@item CP_TYPE_VOLATILE_P +This macro holds if the type is @code{volatile}-qualified. + +@item CP_TYPE_RESTRICT_P +This macro holds if the type is @code{restrict}-qualified. + +@item CP_TYPE_CONST_NON_VOLATILE_P +This predicate holds for a type that is @code{const}-qualified, but +@emph{not} @code{volatile}-qualified; other cv-qualifiers are ignored as +well: only the @code{const}-ness is tested. + +@item TYPE_MAIN_VARIANT +This macro returns the unqualified version of a type. It may be applied +to an unqualified type, but it is not always the identity function in +that case. +@end ftable + +A few other macros and functions are usable with all types: +@ftable @code +@item TYPE_SIZE +The number of bits required to represent the type, represented as an +@code{INTEGER_CST}. For an incomplete type, @code{TYPE_SIZE} will be +@code{NULL_TREE}. + +@item TYPE_ALIGN +The alignment of the type, in bits, represented as an @code{int}. + +@item TYPE_NAME +This macro returns a declaration (in the form of a @code{TYPE_DECL}) for +the type. (Note this macro does @emph{not} return a +@code{IDENTIFIER_NODE}, as you might expect, given its name!) You can +look at the @code{DECL_NAME} of the @code{TYPE_DECL} to obtain the +actual name of the type. The @code{TYPE_NAME} will be @code{NULL_TREE} +for a type that is not a built-in type, the result of a typedef, or a +named class type. + +@item CP_INTEGRAL_TYPE +This predicate holds if the type is an integral type. Notice that in +C++, enumerations are @emph{not} integral types. + +@item ARITHMETIC_TYPE_P +This predicate holds if the type is an integral type (in the C++ sense) +or a floating point type. + +@item CLASS_TYPE_P +This predicate holds for a class-type. + +@item TYPE_BUILT_IN +This predicate holds for a built-in type. + +@item TYPE_PTRMEM_P +This predicate holds if the type is a pointer to data member. + +@item TYPE_PTR_P +This predicate holds if the type is a pointer type, and the pointee is +not a data member. + +@item TYPE_PTRFN_P +This predicate holds for a pointer to function type. + +@item TYPE_PTROB_P +This predicate holds for a pointer to object type. Note however that it +does not hold for the generic pointer to object type @code{void *}. You +may use @code{TYPE_PTROBV_P} to test for a pointer to object type as +well as @code{void *}. + +@item same_type_p +This predicate takes two types as input, and holds if they are the same +type. For example, if one type is a @code{typedef} for the other, or +both are @code{typedef}s for the same type. This predicate also holds if +the two trees given as input are simply copies of one another; i.e., +there is no difference between them at the source level, but, for +whatever reason, a duplicate has been made in the representation. You +should never use @code{==} (pointer equality) to compare types; always +use @code{same_type_p} instead. +@end ftable + +Detailed below are the various kinds of types, and the macros that can +be used to access them. Although other kinds of types are used +elsewhere in G++, the types described here are the only ones that you +will encounter while examining the intermediate representation. + +@table @code +@item VOID_TYPE +Used to represent the @code{void} type. + +@item INTEGER_TYPE +Used to represent the various integral types, including @code{char}, +@code{short}, @code{int}, @code{long}, and @code{long long}. This code +is not used for enumeration types, nor for the @code{bool} type. Note +that GCC's @code{CHAR_TYPE} node is @emph{not} used to represent +@code{char}. The @code{TYPE_PRECISION} is the number of bits used in +the representation, represented as an @code{unsigned int}. (Note that +in the general case this is not the same value as @code{TYPE_SIZE}; +suppose that there were a 24-bit integer type, but that alignment +requirements for the ABI required 32-bit alignment. Then, +@code{TYPE_SIZE} would be an @code{INTEGER_CST} for 32, while +@code{TYPE_PRECISION} would be 24.) The integer type is unsigned if +@code{TREE_UNSIGNED} holds; otherwise, it is signed. + +The @code{TYPE_MIN_VALUE} is an @code{INTEGER_CST} for the smallest +integer that may be represented by this type. Similarly, the +@code{TYPE_MAX_VALUE} is an @code{INTEGER_CST} for the largest integer +that may be represented by this type. + +@item REAL_TYPE +Used to represent the @code{float}, @code{double}, and @code{long +double} types. The number of bits in the floating-point representation +is given by @code{TYPE_PRECISION}, as in the @code{INTEGER_TYPE} case. + +@item COMPLEX_TYPE +Used to represent GCC built-in @code{__complex__} data types. The +@code{TREE_TYPE} is the type of the real and imaginary parts. + +@item ENUMERAL_TYPE +Used to represent an enumeration type. The @code{TYPE_PRECISION} gives +(as an @code{int}), the number of bits used to represent the type. If +there are no negative enumeration constants, @code{TREE_UNSIGNED} will +hold. The minimum and maximum enumeration constants may be obtained +with @code{TYPE_MIN_VALUE} and @code{TYPE_MAX_VALUE}, respectively; each +of these macros returns an @code{INTEGER_CST}. + +The actual enumeration constants themselves may be obtained by looking +at the @code{TYPE_VALUES}. This macro will return a @code{TREE_LIST}, +containing the constants. The @code{TREE_PURPOSE} of each node will be +an @code{IDENTIFIER_NODE} giving the name of the constant; the +@code{TREE_VALUE} will be an @code{INTEGER_CST} giving the value +assigned to that constant. These constants will appear in the order in +which they were declared. The @code{TREE_TYPE} of each of these +constants will be the type of enumeration type itself. + +@item BOOLEAN_TYPE +Used to represent the @code{bool} type. + +@item POINTER_TYPE +Used to represent pointer types, and pointer to data member types. The +@code{TREE_TYPE} gives the type to which this type points. If the type +is a pointer to data member type, then @code{TYPE_PTRMEM_P} will hold. +For a pointer to data member type of the form @samp{T X::*}, +@code{TYPE_PTRMEM_CLASS_TYPE} will be the type @code{X}, while +@code{TYPE_PTRMEM_POINTED_TO_TYPE} will be the type @code{T}. + +@item REFERENCE_TYPE +Used to represent reference types. The @code{TREE_TYPE} gives the type +to which this type refers. + +@item FUNCTION_TYPE +Used to represent the type of non-member functions and of static member +functions. The @code{TREE_TYPE} gives the return type of the function. +The @code{TYPE_ARG_TYPES} are a @code{TREE_LIST} of the argument types. +The @code{TREE_VALUE} of each node in this list is the type of the +corresponding argument; the @code{TREE_PURPOSE} is an expression for the +default argument value, if any. If the last node in the list is +@code{void_list_node} (a @code{TREE_LIST} node whose @code{TREE_VALUE} +is the @code{void_type_node}), then functions of this type do not take +variable arguments. Otherwise, they do take a variable number of +arguments. + +Note that in C (but not in C++) a function declared like @code{void f()} +is an unprototyped function taking a variable number of arguments; the +@code{TYPE_ARG_TYPES} of such a function will be @code{NULL}. + +@item METHOD_TYPE +Used to represent the type of a non-static member function. Like a +@code{FUNCTION_TYPE}, the return type is given by the @code{TREE_TYPE}. +The type of @code{*this}, i.e., the class of which functions of this +type are a member, is given by the @code{TYPE_METHOD_BASETYPE}. The +@code{TYPE_ARG_TYPES} is the parameter list, as for a +@code{FUNCTION_TYPE}, and includes the @code{this} argument. + +@item ARRAY_TYPE +Used to represent array types. The @code{TREE_TYPE} gives the type of +the elements in the array. If the array-bound is present in the type, +the @code{TYPE_DOMAIN} is an @code{INTEGER_TYPE} whose +@code{TYPE_MIN_VALUE} and @code{TYPE_MAX_VALUE} will be the lower and +upper bounds of the array, respectively. The @code{TYPE_MIN_VALUE} will +always be an @code{INTEGER_CST} for zero, while the +@code{TYPE_MAX_VALUE} will be one less than the number of elements in +the array, i.e., the highest value which may be used to index an element +in the array. + +@item RECORD_TYPE +Used to represent @code{struct} and @code{class} types, as well as +pointers to member functions and similar constructs in other languages. +@code{TYPE_FIELDS} contains the items contained in this type, each of +which can be a @code{FIELD_DECL}, @code{VAR_DECL}, @code{CONST_DECL}, or +@code{TYPE_DECL}. You may not make any assumptions about the ordering +of the fields in the type or whether one or more of them overlap. If +@code{TYPE_PTRMEMFUNC_P} holds, then this type is a pointer-to-member +type. In that case, the @code{TYPE_PTRMEMFUNC_FN_TYPE} is a +@code{POINTER_TYPE} pointing to a @code{METHOD_TYPE}. The +@code{METHOD_TYPE} is the type of a function pointed to by the +pointer-to-member function. If @code{TYPE_PTRMEMFUNC_P} does not hold, +this type is a class type. For more information, see @pxref{Classes}. + +@item UNION_TYPE +Used to represent @code{union} types. Similar to @code{RECORD_TYPE} +except that all @code{FIELD_DECL} nodes in @code{TYPE_FIELD} start at +bit position zero. + +@item QUAL_UNION_TYPE +Used to represent part of a variant record in Ada. Similar to +@code{UNION_TYPE} except that each @code{FIELD_DECL} has a +@code{DECL_QUALIFIER} field, which contains a boolean expression that +indicates whether the field is present in the object. The type will only +have one field, so each field's @code{DECL_QUALIFIER} is only evaluated +if none of the expressions in the previous fields in @code{TYPE_FIELDS} +are nonzero. Normally these expressions will reference a field in the +outer object using a @code{PLACEHOLDER_EXPR}. + +@item UNKNOWN_TYPE +This node is used to represent a type the knowledge of which is +insufficient for a sound processing. + +@item OFFSET_TYPE +This node is used to represent a data member; for example a +pointer-to-data-member is represented by a @code{POINTER_TYPE} whose +@code{TREE_TYPE} is an @code{OFFSET_TYPE}. For a data member @code{X::m} +the @code{TYPE_OFFSET_BASETYPE} is @code{X} and the @code{TREE_TYPE} is +the type of @code{m}. + +@item TYPENAME_TYPE +Used to represent a construct of the form @code{typename T::A}. The +@code{TYPE_CONTEXT} is @code{T}; the @code{TYPE_NAME} is an +@code{IDENTIFIER_NODE} for @code{A}. If the type is specified via a +template-id, then @code{TYPENAME_TYPE_FULLNAME} yields a +@code{TEMPLATE_ID_EXPR}. The @code{TREE_TYPE} is non-@code{NULL} if the +node is implicitly generated in support for the implicit typename +extension; in which case the @code{TREE_TYPE} is a type node for the +base-class. + +@item TYPEOF_TYPE +Used to represent the @code{__typeof__} extension. The +@code{TYPE_FIELDS} is the expression the type of which is being +represented. +@end table + +There are variables whose values represent some of the basic types. +These include: +@table @code +@item void_type_node +A node for @code{void}. + +@item integer_type_node +A node for @code{int}. + +@item unsigned_type_node. +A node for @code{unsigned int}. + +@item char_type_node. +A node for @code{char}. +@end table +@noindent +It may sometimes be useful to compare one of these variables with a type +in hand, using @code{same_type_p}. + +@c --------------------------------------------------------------------- +@c Scopes +@c --------------------------------------------------------------------- + +@node Scopes +@section Scopes +@cindex namespace, class, scope + +The root of the entire intermediate representation is the variable +@code{global_namespace}. This is the namespace specified with @code{::} +in C++ source code. All other namespaces, types, variables, functions, +and so forth can be found starting with this namespace. + +Besides namespaces, the other high-level scoping construct in C++ is the +class. (Throughout this manual the term @dfn{class} is used to mean the +types referred to in the ANSI/ISO C++ Standard as classes; these include +types defined with the @code{class}, @code{struct}, and @code{union} +keywords.) + +@menu +* Namespaces:: Member functions, types, etc. +* Classes:: Members, bases, friends, etc. +@end menu + +@c --------------------------------------------------------------------- +@c Namespaces +@c --------------------------------------------------------------------- + +@node Namespaces +@subsection Namespaces +@cindex namespace +@tindex NAMESPACE_DECL + +A namespace is represented by a @code{NAMESPACE_DECL} node. + +However, except for the fact that it is distinguished as the root of the +representation, the global namespace is no different from any other +namespace. Thus, in what follows, we describe namespaces generally, +rather than the global namespace in particular. + +The following macros and functions can be used on a @code{NAMESPACE_DECL}: + +@ftable @code +@item DECL_NAME +This macro is used to obtain the @code{IDENTIFIER_NODE} corresponding to +the unqualified name of the name of the namespace (@pxref{Identifiers}). +The name of the global namespace is @samp{::}, even though in C++ the +global namespace is unnamed. However, you should use comparison with +@code{global_namespace}, rather than @code{DECL_NAME} to determine +whether or not a namespaces is the global one. An unnamed namespace +will have a @code{DECL_NAME} equal to @code{anonymous_namespace_name}. +Within a single translation unit, all unnamed namespaces will have the +same name. + +@item DECL_CONTEXT +This macro returns the enclosing namespace. The @code{DECL_CONTEXT} for +the @code{global_namespace} is @code{NULL_TREE}. + +@item DECL_NAMESPACE_ALIAS +If this declaration is for a namespace alias, then +@code{DECL_NAMESPACE_ALIAS} is the namespace for which this one is an +alias. + +Do not attempt to use @code{cp_namespace_decls} for a namespace which is +an alias. Instead, follow @code{DECL_NAMESPACE_ALIAS} links until you +reach an ordinary, non-alias, namespace, and call +@code{cp_namespace_decls} there. + +@item DECL_NAMESPACE_STD_P +This predicate holds if the namespace is the special @code{::std} +namespace. + +@item cp_namespace_decls +This function will return the declarations contained in the namespace, +including types, overloaded functions, other namespaces, and so forth. +If there are no declarations, this function will return +@code{NULL_TREE}. The declarations are connected through their +@code{TREE_CHAIN} fields. + +Although most entries on this list will be declarations, +@code{TREE_LIST} nodes may also appear. In this case, the +@code{TREE_VALUE} will be an @code{OVERLOAD}. The value of the +@code{TREE_PURPOSE} is unspecified; back ends should ignore this value. +As with the other kinds of declarations returned by +@code{cp_namespace_decls}, the @code{TREE_CHAIN} will point to the next +declaration in this list. + +For more information on the kinds of declarations that can occur on this +list, @xref{Declarations}. Some declarations will not appear on this +list. In particular, no @code{FIELD_DECL}, @code{LABEL_DECL}, or +@code{PARM_DECL} nodes will appear here. + +This function cannot be used with namespaces that have +@code{DECL_NAMESPACE_ALIAS} set. + +@end ftable + +@c --------------------------------------------------------------------- +@c Classes +@c --------------------------------------------------------------------- + +@node Classes +@subsection Classes +@cindex class +@tindex RECORD_TYPE +@tindex UNION_TYPE +@findex CLASSTYPE_DECLARED_CLASS +@findex TYPE_BINFO +@findex BINFO_TYPE +@findex TREE_VIA_PUBLIC +@findex TREE_VIA_PROTECTED +@findex TREE_VIA_PRIVATE +@findex TYPE_FIELDS +@findex TYPE_VFIELD +@findex TYPE_METHODS + +A class type is represented by either a @code{RECORD_TYPE} or a +@code{UNION_TYPE}. A class declared with the @code{union} tag is +represented by a @code{UNION_TYPE}, while classes declared with either +the @code{struct} or the @code{class} tag are represented by +@code{RECORD_TYPE}s. You can use the @code{CLASSTYPE_DECLARED_CLASS} +macro to discern whether or not a particular type is a @code{class} as +opposed to a @code{struct}. This macro will be true only for classes +declared with the @code{class} tag. + +Almost all non-function members are available on the @code{TYPE_FIELDS} +list. Given one member, the next can be found by following the +@code{TREE_CHAIN}. You should not depend in any way on the order in +which fields appear on this list. All nodes on this list will be +@samp{DECL} nodes. A @code{FIELD_DECL} is used to represent a non-static +data member, a @code{VAR_DECL} is used to represent a static data +member, and a @code{TYPE_DECL} is used to represent a type. Note that +the @code{CONST_DECL} for an enumeration constant will appear on this +list, if the enumeration type was declared in the class. (Of course, +the @code{TYPE_DECL} for the enumeration type will appear here as well.) +There are no entries for base classes on this list. In particular, +there is no @code{FIELD_DECL} for the ``base-class portion'' of an +object. + +The @code{TYPE_VFIELD} is a compiler-generated field used to point to +virtual function tables. It may or may not appear on the +@code{TYPE_FIELDS} list. However, back ends should handle the +@code{TYPE_VFIELD} just like all the entries on the @code{TYPE_FIELDS} +list. + +The function members are available on the @code{TYPE_METHODS} list. +Again, subsequent members are found by following the @code{TREE_CHAIN} +field. If a function is overloaded, each of the overloaded functions +appears; no @code{OVERLOAD} nodes appear on the @code{TYPE_METHODS} +list. Implicitly declared functions (including default constructors, +copy constructors, assignment operators, and destructors) will appear on +this list as well. + +Every class has an associated @dfn{binfo}, which can be obtained with +@code{TYPE_BINFO}. Binfos are used to represent base-classes. The +binfo given by @code{TYPE_BINFO} is the degenerate case, whereby every +class is considered to be its own base-class. The base classes for a +particular binfo can be obtained with @code{BINFO_BASETYPES}. These +base-classes are themselves binfos. The class type associated with a +binfo is given by @code{BINFO_TYPE}. It is always the case that +@code{BINFO_TYPE (TYPE_BINFO (x))} is the same type as @code{x}, up to +qualifiers. However, it is not always the case that @code{TYPE_BINFO +(BINFO_TYPE (y))} is always the same binfo as @code{y}. The reason is +that if @code{y} is a binfo representing a base-class @code{B} of a +derived class @code{D}, then @code{BINFO_TYPE (y)} will be @code{B}, and +@code{TYPE_INFO (BINFO_TYPE (y))} will be @code{B} as its own +base-class, rather than as a base-class of @code{D}. + +The @code{BINFO_BASETYPES} is a @code{TREE_VEC} (@pxref{Containers}). +Base types appear in left-to-right order in this vector. You can tell +whether or @code{public}, @code{protected}, or @code{private} +inheritance was used by using the @code{TREE_VIA_PUBLIC}, +@code{TREE_VIA_PROTECTED}, and @code{TREE_VIA_PRIVATE} macros. Each of +these macros takes a @code{BINFO} and is true if and only if the +indicated kind of inheritance was used. If @code{TREE_VIA_VIRTUAL} +holds of a binfo, then its @code{BINFO_TYPE} was inherited from +virtually. + +The following macros can be used on a tree node representing a class-type. + +@ftable @code +@item LOCAL_CLASS_P +This predicate holds if the class is local class @emph{i.e.} declared +inside a function body. + +@item TYPE_POLYMORPHIC_P +This predicate holds if the class has at least one virtual function +(declared or inherited). + +@item TYPE_HAS_DEFAULT_CONSTRUCTOR +This predicate holds whenever its argument represents a class-type with +default constructor. + +@item CLASSTYPE_HAS_MUTABLE +@item TYPE_HAS_MUTABLE_P +These predicates hold for a class-type having a mutable data member. + +@item CLASSTYPE_NON_POD_P +This predicate holds only for class-types that are not PODs. + +@item TYPE_HAS_NEW_OPERATOR +This predicate holds for a class-type that defines +@code{operator new}. + +@item TYPE_HAS_ARRAY_NEW_OPERATOR +This predicate holds for a class-type for which +@code{operator new[]} is defined. + +@item TYPE_OVERLOADS_CALL_EXPR +This predicate holds for class-type for which the function call +@code{operator()} is overloaded. + +@item TYPE_OVERLOADS_ARRAY_REF +This predicate holds for a class-type that overloads +@code{operator[]} + +@item TYPE_OVERLOADS_ARROW +This predicate holds for a class-type for which @code{operator->} is +overloaded. + +@end ftable + +@c --------------------------------------------------------------------- +@c Declarations +@c --------------------------------------------------------------------- + +@node Declarations +@section Declarations +@cindex declaration +@cindex variable +@cindex type declaration +@tindex LABEL_DECL +@tindex CONST_DECL +@tindex TYPE_DECL +@tindex VAR_DECL +@tindex PARM_DECL +@tindex FIELD_DECL +@tindex NAMESPACE_DECL +@tindex RESULT_DECL +@tindex TEMPLATE_DECL +@tindex THUNK_DECL +@tindex USING_DECL +@findex THUNK_DELTA +@findex DECL_INITIAL +@findex DECL_SIZE +@findex DECL_ALIGN +@findex DECL_EXTERNAL + +This section covers the various kinds of declarations that appear in the +internal representation, except for declarations of functions +(represented by @code{FUNCTION_DECL} nodes), which are described in +@ref{Functions}. + +Some macros can be used with any kind of declaration. These include: +@ftable @code +@item DECL_NAME +This macro returns an @code{IDENTIFIER_NODE} giving the name of the +entity. + +@item TREE_TYPE +This macro returns the type of the entity declared. + +@item DECL_SOURCE_FILE +This macro returns the name of the file in which the entity was +declared, as a @code{char*}. For an entity declared implicitly by the +compiler (like @code{__builtin_memcpy}), this will be the string +@code{""}. + +@item DECL_SOURCE_LINE +This macro returns the line number at which the entity was declared, as +an @code{int}. + +@item DECL_ARTIFICIAL +This predicate holds if the declaration was implicitly generated by the +compiler. For example, this predicate will hold of an implicitly +declared member function, or of the @code{TYPE_DECL} implicitly +generated for a class type. Recall that in C++ code like: +@example +struct S @{@}; +@end example +@noindent +is roughly equivalent to C code like: +@example +struct S @{@}; +typedef struct S S; +@end example +The implicitly generated @code{typedef} declaration is represented by a +@code{TYPE_DECL} for which @code{DECL_ARTIFICIAL} holds. + +@item DECL_NAMESPACE_SCOPE_P +This predicate holds if the entity was declared at a namespace scope. + +@item DECL_CLASS_SCOPE_P +This predicate holds if the entity was declared at a class scope. + +@item DECL_FUNCTION_SCOPE_P +This predicate holds if the entity was declared inside a function +body. + +@end ftable + +The various kinds of declarations include: +@table @code +@item LABEL_DECL +These nodes are used to represent labels in function bodies. For more +information, see @ref{Functions}. These nodes only appear in block +scopes. + +@item CONST_DECL +These nodes are used to represent enumeration constants. The value of +the constant is given by @code{DECL_INITIAL} which will be an +@code{INTEGER_CST} with the same type as the @code{TREE_TYPE} of the +@code{CONST_DECL}, i.e., an @code{ENUMERAL_TYPE}. + +@item RESULT_DECL +These nodes represent the value returned by a function. When a value is +assigned to a @code{RESULT_DECL}, that indicates that the value should +be returned, via bitwise copy, by the function. You can use +@code{DECL_SIZE} and @code{DECL_ALIGN} on a @code{RESULT_DECL}, just as +with a @code{VAR_DECL}. + +@item TYPE_DECL +These nodes represent @code{typedef} declarations. The @code{TREE_TYPE} +is the type declared to have the name given by @code{DECL_NAME}. In +some cases, there is no associated name. + +@item VAR_DECL +These nodes represent variables with namespace or block scope, as well +as static data members. The @code{DECL_SIZE} and @code{DECL_ALIGN} are +analogous to @code{TYPE_SIZE} and @code{TYPE_ALIGN}. For a declaration, +you should always use the @code{DECL_SIZE} and @code{DECL_ALIGN} rather +than the @code{TYPE_SIZE} and @code{TYPE_ALIGN} given by the +@code{TREE_TYPE}, since special attributes may have been applied to the +variable to give it a particular size and alignment. You may use the +predicates @code{DECL_THIS_STATIC} or @code{DECL_THIS_EXTERN} to test +whether the storage class specifiers @code{static} or @code{extern} were +used to declare a variable. + +If this variable is initialized (but does not require a constructor), +the @code{DECL_INITIAL} will be an expression for the initializer. The +initializer should be evaluated, and a bitwise copy into the variable +performed. If the @code{DECL_INITIAL} is the @code{error_mark_node}, +there is an initializer, but it is given by an explicit statement later +in the code; no bitwise copy is required. + +GCC provides an extension that allows either automatic variables, or +global variables, to be placed in particular registers. This extension +is being used for a particular @code{VAR_DECL} if @code{DECL_REGISTER} +holds for the @code{VAR_DECL}, and if @code{DECL_ASSEMBLER_NAME} is not +equal to @code{DECL_NAME}. In that case, @code{DECL_ASSEMBLER_NAME} is +the name of the register into which the variable will be placed. + +@item PARM_DECL +Used to represent a parameter to a function. Treat these nodes +similarly to @code{VAR_DECL} nodes. These nodes only appear in the +@code{DECL_ARGUMENTS} for a @code{FUNCTION_DECL}. + +The @code{DECL_ARG_TYPE} for a @code{PARM_DECL} is the type that will +actually be used when a value is passed to this function. It may be a +wider type than the @code{TREE_TYPE} of the parameter; for example, the +ordinary type might be @code{short} while the @code{DECL_ARG_TYPE} is +@code{int}. + +@item FIELD_DECL +These nodes represent non-static data members. The @code{DECL_SIZE} and +@code{DECL_ALIGN} behave as for @code{VAR_DECL} nodes. The +@code{DECL_FIELD_BITPOS} gives the first bit used for this field, as an +@code{INTEGER_CST}. These values are indexed from zero, where zero +indicates the first bit in the object. + +If @code{DECL_C_BIT_FIELD} holds, this field is a bit-field. + +@item NAMESPACE_DECL +@xref{Namespaces}. + +@item TEMPLATE_DECL + +These nodes are used to represent class, function, and variable (static +data member) templates. The @code{DECL_TEMPLATE_SPECIALIZATIONS} are a +@code{TREE_LIST}. The @code{TREE_VALUE} of each node in the list is a +@code{TEMPLATE_DECL}s or @code{FUNCTION_DECL}s representing +specializations (including instantiations) of this template. Back ends +can safely ignore @code{TEMPLATE_DECL}s, but should examine +@code{FUNCTION_DECL} nodes on the specializations list just as they +would ordinary @code{FUNCTION_DECL} nodes. + +For a class template, the @code{DECL_TEMPLATE_INSTANTIATIONS} list +contains the instantiations. The @code{TREE_VALUE} of each node is an +instantiation of the class. The @code{DECL_TEMPLATE_SPECIALIZATIONS} +contains partial specializations of the class. + +@item USING_DECL + +Back ends can safely ignore these nodes. + +@end table + +@c --------------------------------------------------------------------- +@c Functions +@c --------------------------------------------------------------------- + +@node Functions +@section Functions +@cindex function +@tindex FUNCTION_DECL +@tindex OVERLOAD +@findex OVL_CURRENT +@findex OVL_NEXT + +A function is represented by a @code{FUNCTION_DECL} node. A set of +overloaded functions is sometimes represented by a @code{OVERLOAD} node. + +An @code{OVERLOAD} node is not a declaration, so none of the +@samp{DECL_} macros should be used on an @code{OVERLOAD}. An +@code{OVERLOAD} node is similar to a @code{TREE_LIST}. Use +@code{OVL_CURRENT} to get the function associated with an +@code{OVERLOAD} node; use @code{OVL_NEXT} to get the next +@code{OVERLOAD} node in the list of overloaded functions. The macros +@code{OVL_CURRENT} and @code{OVL_NEXT} are actually polymorphic; you can +use them to work with @code{FUNCTION_DECL} nodes as well as with +overloads. In the case of a @code{FUNCTION_DECL}, @code{OVL_CURRENT} +will always return the function itself, and @code{OVL_NEXT} will always +be @code{NULL_TREE}. + +To determine the scope of a function, you can use the +@code{DECL_REAL_CONTEXT} macro. This macro will return the class +(either a @code{RECORD_TYPE} or a @code{UNION_TYPE}) or namespace (a +@code{NAMESPACE_DECL}) of which the function is a member. For a virtual +function, this macro returns the class in which the function was +actually defined, not the base class in which the virtual declaration +occurred. If a friend function is defined in a class scope, the +@code{DECL_CLASS_CONTEXT} macro can be used to determine the class in +which it was defined. For example, in +@example +class C @{ friend void f() @{@} @}; +@end example +the @code{DECL_REAL_CONTEXT} for @code{f} will be the +@code{global_namespace}, but the @code{DECL_CLASS_CONTEXT} will be the +@code{RECORD_TYPE} for @code{C}. + +The @code{DECL_REAL_CONTEXT} and @code{DECL_CLASS_CONTEXT} are not +available in C; instead you should simply use @code{DECL_CONTEXT}. In C, +the @code{DECL_CONTEXT} for a function maybe another function. This +representation indicates that the GNU nested function extension is in +use. For details on the semantics of nested functions, see the GCC +Manual. The nested function can refer to local variables in its +containing function. Such references are not explicitly marked in the +tree structure; back ends must look at the @code{DECL_CONTEXT} for the +referenced @code{VAR_DECL}. If the @code{DECL_CONTEXT} for the +referenced @code{VAR_DECL} is not the same as the function currently +being processed, and neither @code{DECL_EXTERNAL} nor @code{DECL_STATIC} +hold, then the reference is to a local variable in a containing +function, and the back end must take appropriate action. + +@menu +* Function Basics:: Function names, linkage, and so forth. +* Function Bodies:: The statements that make up a function body. +@end menu + +@c --------------------------------------------------------------------- +@c Function Basics +@c --------------------------------------------------------------------- + +@node Function Basics +@subsection Function Basics +@cindex constructor +@cindex destructor +@cindex copy constructor +@cindex assignment operator +@cindex linkage +@findex DECL_NAME +@findex DECL_ASSEMBLER_NAME +@findex TREE_PUBLIC +@findex DECL_LINKONCE_P +@findex DECL_FUNCTION_MEMBER_P +@findex DECL_CONSTRUCTOR_P +@findex DECL_DESTRUCTOR_P +@findex DECL_OVERLOADED_OPERATOR_P +@findex DECL_CONV_FN_P +@findex DECL_ARTIFICIAL +@findex DECL_GLOBAL_CTOR_P +@findex DECL_GLOBAL_DTOR_P +@findex GLOBAL_INIT_PRIORITY + +The following macros and functions can be used on a @code{FUNCTION_DECL}: +@ftable @code +@item DECL_MAIN_P +This predicate holds for a function that is the program entry point +@code{::code}. + +@item DECL_NAME +This macro returns the unqualified name of the function, as an +@code{IDENTIFIER_NODE}. For an instantiation of a function template, +the @code{DECL_NAME} is the unqualified name of the template, not +something like @code{f}. The value of @code{DECL_NAME} is +undefined when used on a constructor, destructor, overloaded operator, +or type-conversion operator, or any function that is implicitly +generated by the compiler. See below for macros that can be used to +distinguish these cases. + +@item DECL_ASSEMBLER_NAME +This macro returns the mangled name of the function, also an +@code{IDENTIFIER_NODE}. This name does not contain leading underscores +on systems that prefix all identifiers with underscores. The mangled +name is computed in the same way on all platforms; if special processing +is required to deal with the object file format used on a particular +platform, it is the responsibility of the back end to perform those +modifications. (Of course, the back end should not modify +@code{DECL_ASSEMBLER_NAME} itself.) + +@item DECL_EXTERNAL +This predicate holds if the function is undefined. + +@item TREE_PUBLIC +This predicate holds if the function has external linkage. + +@item DECL_LOCAL_FUNCTION_P +This predicate holds if the function was declared at block scope, even +though it has a global scope. + +@item DECL_ANTICIPATED +This predicate holds if the function is a built-in function but its +prototype is not yet explicitly declared. + +@item DECL_EXTERN_C_FUNCTION_P +This predicate holds if the function is declared as an +`@code{extern "C"}' function. + +@item DECL_LINKONCE_P +This macro holds if multiple copies of this function may be emitted in +various translation units. It is the responsibility of the linker to +merge the various copies. Template instantiations are the most common +example of functions for which @code{DECL_LINKONCE_P} holds; G++ +instantiates needed templates in all translation units which require them, +and then relies on the linker to remove duplicate instantiations. + +FIXME: This macro is not yet implemented. + +@item DECL_FUNCTION_MEMBER_P +This macro holds if the function is a member of a class, rather than a +member of a namespace. + +@item DECL_STATIC_FUNCTION_P +This predicate holds if the function a static member function. + +@item DECL_NONSTATIC_MEMBER_FUNCTION_P +This macro holds for a non-static member function. + +@item DECL_CONST_MEMFUNC_P +This predicate holds for a @code{const}-member function. + +@item DECL_VOLATILE_MEMFUNC_P +This predicate holds for a @code{volatile}-member function. + +@item DECL_CONSTRUCTOR_P +This macro holds if the function is a constructor. + +@item DECL_NONCONVERTING_P +This predicate holds if the constructor is a non-converting constructor. + +@item DECL_COMPLETE_CONSTRUCTOR_P +This predicate holds for a function which is a constructor for an object +of a complete type. + +@item DECL_BASE_CONSTRUCTOR_P +This predicate holds for a function which is a constructor for a base +class sub-object. + +@item DECL_COPY_CONSTRUCTOR_P +This predicate holds for a function which is a copy-constructor. + +@item DECL_DESTRUCTOR_P +This macro holds if the function is a destructor. + +@item DECL_COMPLETE_DESTRUCTOR_P +This predicate holds if the function is the destructor for an object a +complete type. + +@item DECL_OVERLOADED_OPERATOR_P +This macro holds if the function is an overloaded operator. + +@item DECL_CONV_FN_P +This macro holds if the function is a type-conversion operator. + +@item DECL_GLOBAL_CTOR_P +This predicate holds if the function is a file-scope initialization +function. + +@item DECL_GLOBAL_DTOR_P +This predicate holds if the function is a file-scope finalization +function. + +@item DECL_THUNK_P +This predicate holds if the function is a thunk. + +These functions represent stub code that adjusts the @code{this} pointer +and then jumps to another function. When the jumped-to function +returns, control is transferred directly to the caller, without +returning to the thunk. The first parameter to the thunk is always the +@code{this} pointer; the thunk should add @code{THUNK_DELTA} to this +value. (The @code{THUNK_DELTA} is an @code{int}, not an +@code{INTEGER_CST}.) + +Then, if @code{THUNK_VCALL_OFFSET} (an @code{INTEGER_CST}) is nonzero +the adjusted @code{this} pointer must be adjusted again. The complete +calculation is given by the following pseudo-code: + +@example +this += THUNK_DELTA +if (THUNK_VCALL_OFFSET) + this += (*((ptrdiff_t **) this))[THUNK_VCALL_OFFSET] +@end example + +Finally, the thunk should jump to the location given +by @code{DECL_INITIAL}; this will always be an expression for the +address of a function. + +@item DECL_NON_THUNK_FUNCTION_P +This predicate holds if the function is @emph{not} a thunk function. + +@item GLOBAL_INIT_PRIORITY +If either @code{DECL_GLOBAL_CTOR_P} or @code{DECL_GLOBAL_DTOR_P} holds, +then this gives the initialization priority for the function. The +linker will arrange that all functions for which +@code{DECL_GLOBAL_CTOR_P} holds are run in increasing order of priority +before @code{main} is called. When the program exits, all functions for +which @code{DECL_GLOBAL_DTOR_P} holds are run in the reverse order. + +@item DECL_ARTIFICIAL +This macro holds if the function was implicitly generated by the +compiler, rather than explicitly declared. In addition to implicitly +generated class member functions, this macro holds for the special +functions created to implement static initialization and destruction, to +compute run-time type information, and so forth. + +@item DECL_ARGUMENTS +This macro returns the @code{PARM_DECL} for the first argument to the +function. Subsequent @code{PARM_DECL} nodes can be obtained by +following the @code{TREE_CHAIN} links. + +@item DECL_RESULT +This macro returns the @code{RESULT_DECL} for the function. + +@item TREE_TYPE +This macro returns the @code{FUNCTION_TYPE} or @code{METHOD_TYPE} for +the function. + +@item TYPE_RAISES_EXCEPTIONS +This macro returns the list of exceptions that a (member-)function can +raise. The returned list, if non @code{NULL}, is comprised of nodes +whose @code{TREE_VALUE} represents a type. + +@item TYPE_NOTHROW_P +This predicate holds when the exception-specification of its arguments +if of the form `@code{()}'. + +@item DECL_ARRAY_DELETE_OPERATOR_P +This predicate holds if the function an overloaded +@code{operator delete[]}. + +@end ftable + +@c --------------------------------------------------------------------- +@c Function Bodies +@c --------------------------------------------------------------------- + +@node Function Bodies +@subsection Function Bodies +@cindex function body +@cindex statements +@tindex ASM_STMT +@findex ASM_STRING +@findex ASM_CV_QUAL +@findex ASM_INPUTS +@findex ASM_OUTPUTS +@findex ASM_CLOBBERS +@tindex BREAK_STMT +@tindex CLEANUP_STMT +@findex CLEANUP_DECL +@findex CLEANUP_EXPR +@tindex COMPOUND_STMT +@findex COMPOUND_BODY +@tindex CONTINUE_STMT +@tindex DECL_STMT +@findex DECL_STMT_DECL +@tindex DO_STMT +@findex DO_BODY +@findex DO_COND +@tindex EMPTY_CLASS_EXPR +@tindex EXPR_STMT +@findex EXPR_STMT_EXPR +@tindex FOR_STMT +@findex FOR_INIT_STMT +@findex FOR_COND +@findex FOR_EXPR +@findex FOR_BODY +@tindex FILE_STMT +@findex FILE_STMT_FILENAME +@tindex GOTO_STMT +@findex GOTO_DESTINATION +@findex GOTO_FAKE_P +@tindex HANDLER +@tindex IF_STMT +@findex IF_COND +@findex THEN_CLAUSE +@findex ELSE_CLAUSE +@tindex LABEL_STMT +@tindex LABEL_STMT_LABEL +@tindex RETURN_INIT +@tindex RETURN_STMT +@findex RETURN_EXPR +@tindex SCOPE_STMT +@findex SCOPE_BEGIN_P +@findex SCOPE_END_P +@findex SCOPE_NULLIFIED_P +@tindex SUBOBJECT +@findex SUBOBJECT_CLEANUP +@tindex SWITCH_STMT +@findex SWITCH_COND +@findex SWITCH_BODY +@tindex TRY_BLOCK +@findex TRY_STMTS +@findex TRY_HANDLERS +@findex HANDLER_PARMS +@findex HANDLER_BODY +@findex USING_STMT +@tindex WHILE_STMT +@findex WHILE_BODY +@findex WHILE_COND + +A function that has a definition in the current translation unit will +have a non-@code{NULL} @code{DECL_INITIAL}. However, back ends should not make +use of the particular value given by @code{DECL_INITIAL}. + +The @code{DECL_SAVED_TREE} macro will give the complete body of the +function. This node will usually be a @code{COMPOUND_STMT} representing +the outermost block of the function, but it may also be a +@code{TRY_BLOCK}, a @code{RETURN_INIT}, or any other valid statement. + +@subsubsection Statements + +There are tree nodes corresponding to all of the source-level statement +constructs. These are enumerated here, together with a list of the +various macros that can be used to obtain information about them. There +are a few macros that can be used with all statements: + +@ftable @code +@item STMT_LINENO +This macro returns the line number for the statement. If the statement +spans multiple lines, this value will be the number of the first line on +which the statement occurs. Although we mention @code{CASE_LABEL} below +as if it were a statement, they do not allow the use of +@code{STMT_LINENO}. There is no way to obtain the line number for a +@code{CASE_LABEL}. + +Statements do not contain information about +the file from which they came; that information is implicit in the +@code{FUNCTION_DECL} from which the statements originate. + +@item STMT_IS_FULL_EXPR_P +In C++, statements normally constitute ``full expressions''; temporaries +created during a statement are destroyed when the statement is complete. +However, G++ sometimes represents expressions by statements; these +statements will not have @code{STMT_IS_FULL_EXPR_P} set. Temporaries +created during such statements should be destroyed when the innermost +enclosing statement with @code{STMT_IS_FULL_EXPR_P} set is exited. + +@end ftable + +Here is the list of the various statement nodes, and the macros used to +access them. This documentation describes the use of these nodes in +non-template functions (including instantiations of template functions). +In template functions, the same nodes are used, but sometimes in +slightly different ways. + +Many of the statements have substatements. For example, a @code{while} +loop will have a body, which is itself a statement. If the substatement +is @code{NULL_TREE}, it is considered equivalent to a statement +consisting of a single @code{;}, i.e., an expression statement in which +the expression has been omitted. A substatement may in fact be a list +of statements, connected via their @code{TREE_CHAIN}s. So, you should +always process the statement tree by looping over substatements, like +this: +@example +void process_stmt (stmt) + tree stmt; +@{ + while (stmt) + @{ + switch (TREE_CODE (stmt)) + @{ + case IF_STMT: + process_stmt (THEN_CLAUSE (stmt)); + /* More processing here. */ + break; + + @dots{} + @} + + stmt = TREE_CHAIN (stmt); + @} +@} +@end example +In other words, while the @code{then} clause of an @code{if} statement +in C++ can be only one statement (although that one statement may be a +compound statement), the intermediate representation will sometimes use +several statements chained together. + +@table @code +@item ASM_STMT + +Used to represent an inline assembly statement. For an inline assembly +statement like: +@example +asm ("mov x, y"); +@end example +The @code{ASM_STRING} macro will return a @code{STRING_CST} node for +@code{"mov x, y"}. If the original statement made use of the +extended-assembly syntax, then @code{ASM_OUTPUTS}, +@code{ASM_INPUTS}, and @code{ASM_CLOBBERS} will be the outputs, inputs, +and clobbers for the statement, represented as @code{STRING_CST} nodes. +The extended-assembly syntax looks like: +@example +asm ("fsinx %1,%0" : "=f" (result) : "f" (angle)); +@end example +The first string is the @code{ASM_STRING}, containing the instruction +template. The next two strings are the output and inputs, respectively; +this statement has no clobbers. As this example indicates, ``plain'' +assembly statements are merely a special case of extended assembly +statements; they have no cv-qualifiers, outputs, inputs, or clobbers. +All of the strings will be @code{NUL}-terminated, and will contain no +embedded @code{NUL}-characters. + +If the assembly statement is declared @code{volatile}, or if the +statement was not an extended assembly statement, and is therefore +implicitly volatile, then the predicate @code{ASM_VOLATILE_P} will hold +of the @code{ASM_STMT}. + +@item BREAK_STMT + +Used to represent a @code{break} statement. There are no additional +fields. + +@item CASE_LABEL + +Use to represent a @code{case} label, range of @code{case} labels, or a +@code{default} label. If @code{CASE_LOW} is @code{NULL_TREE}, then this is a +@code{default} label. Otherwise, if @code{CASE_HIGH} is @code{NULL_TREE}, then +this is an ordinary @code{case} label. In this case, @code{CASE_LOW} is +an expression giving the value of the label. Both @code{CASE_LOW} and +@code{CASE_HIGH} are @code{INTEGER_CST} nodes. These values will have +the same type as the condition expression in the switch statement. + +Otherwise, if both @code{CASE_LOW} and @code{CASE_HIGH} are defined, the +statement is a range of case labels. Such statements originate with the +extension that allows users to write things of the form: +@example +case 2 ... 5: +@end example +The first value will be @code{CASE_LOW}, while the second will be +@code{CASE_HIGH}. + +@item CLEANUP_STMT + +Used to represent an action that should take place upon exit from the +enclosing scope. Typically, these actions are calls to destructors for +local objects, but back ends cannot rely on this fact. If these nodes +are in fact representing such destructors, @code{CLEANUP_DECL} will be +the @code{VAR_DECL} destroyed. Otherwise, @code{CLEANUP_DECL} will be +@code{NULL_TREE}. In any case, the @code{CLEANUP_EXPR} is the +expression to execute. The cleanups executed on exit from a scope +should be run in the reverse order of the order in which the associated +@code{CLEANUP_STMT}s were encountered. + +@item COMPOUND_STMT + +Used to represent a brace-enclosed block. The first substatement is +given by @code{COMPOUND_BODY}. Subsequent substatements are found by +following the @code{TREE_CHAIN} link from one substatement to the next. +The @code{COMPOUND_BODY} will be @code{NULL_TREE} if there are no +substatements. + +@item CONTINUE_STMT + +Used to represent a @code{continue} statement. There are no additional +fields. + +@item CTOR_STMT + +Used to mark the beginning (if @code{CTOR_BEGIN_P} holds) or end (if +@code{CTOR_END_P} holds of the main body of a constructor. See also +@code{SUBOBJECT} for more information on how to use these nodes. + +@item DECL_STMT + +Used to represent a local declaration. The @code{DECL_STMT_DECL} macro +can be used to obtain the entity declared. This declaration may be a +@code{LABEL_DECL}, indicating that the label declared is a local label. +(As an extension, GCC allows the declaration of labels with scope.) In +C, this declaration may be a @code{FUNCTION_DECL}, indicating the +use of the GCC nested function extension. For more information, +@pxref{Functions}. + +@item DO_STMT + +Used to represent a @code{do} loop. The body of the loop is given by +@code{DO_BODY} while the termination condition for the loop is given by +@code{DO_COND}. The condition for a @code{do}-statement is always an +expression. + +@item EMPTY_CLASS_EXPR + +Used to represent a temporary object of a class with no data whose +address is never taken. (All such objects are interchangeable.) The +@code{TREE_TYPE} represents the type of the object. + +@item EXPR_STMT + +Used to represent an expression statement. Use @code{EXPR_STMT_EXPR} to +obtain the expression. + +@item FILE_STMT + +Used to record a change in filename within the body of a function. +Use @code{FILE_STMT_FILENAME} to obtain the new filename. + +@item FOR_STMT + +Used to represent a @code{for} statement. The @code{FOR_INIT_STMT} is +the initialization statement for the loop. The @code{FOR_COND} is the +termination condition. The @code{FOR_EXPR} is the expression executed +right before the @code{FOR_COND} on each loop iteration; often, this +expression increments a counter. The body of the loop is given by +@code{FOR_BODY}. Note that @code{FOR_INIT_STMT} and @code{FOR_BODY} +return statements, while @code{FOR_COND} and @code{FOR_EXPR} return +expressions. + +@item GOTO_STMT + +Used to represent a @code{goto} statement. The @code{GOTO_DESTINATION} will +usually be a @code{LABEL_DECL}. However, if the ``computed goto'' extension +has been used, the @code{GOTO_DESTINATION} will be an arbitrary expression +indicating the destination. This expression will always have pointer type. +Additionally the @code{GOTO_FAKE_P} flag is set whenever the goto statement +does not come from source code, but it is generated implicitly by the compiler. +This is used for branch prediction. + +@item HANDLER + +Used to represent a C++ @code{catch} block. The @code{HANDLER_TYPE} +is the type of exception that will be caught by this handler; it is +equal (by pointer equality) to @code{CATCH_ALL_TYPE} if this handler +is for all types. @code{HANDLER_PARMS} is the @code{DECL_STMT} for +the catch parameter, and @code{HANDLER_BODY} is the +@code{COMPOUND_STMT} for the block itself. + +@item IF_STMT + +Used to represent an @code{if} statement. The @code{IF_COND} is the +expression. + +If the condition is a @code{TREE_LIST}, then the @code{TREE_PURPOSE} is +a statement (usually a @code{DECL_STMT}). Each time the condition is +evaluated, the statement should be executed. Then, the +@code{TREE_VALUE} should be used as the conditional expression itself. +This representation is used to handle C++ code like this: + +@example +if (int i = 7) @dots{} +@end example + +where there is a new local variable (or variables) declared within the +condition. + +The @code{THEN_CLAUSE} represents the statement given by the @code{then} +condition, while the @code{ELSE_CLAUSE} represents the statement given +by the @code{else} condition. + +@item LABEL_STMT + +Used to represent a label. The @code{LABEL_DECL} declared by this +statement can be obtained with the @code{LABEL_STMT_LABEL} macro. The +@code{IDENTIFIER_NODE} giving the name of the label can be obtained from +the @code{LABEL_DECL} with @code{DECL_NAME}. + +@item RETURN_INIT + +If the function uses the G++ ``named return value'' extension, meaning +that the function has been defined like: +@example +S f(int) return s @{@dots{}@} +@end example +then there will be a @code{RETURN_INIT}. There is never a named +returned value for a constructor. The first argument to the +@code{RETURN_INIT} is the name of the object returned; the second +argument is the initializer for the object. The object is initialized +when the @code{RETURN_INIT} is encountered. The object referred to is +the actual object returned; this extension is a manual way of doing the +``return-value optimization.'' Therefore, the object must actually be +constructed in the place where the object will be returned. + +@item RETURN_STMT + +Used to represent a @code{return} statement. The @code{RETURN_EXPR} is +the expression returned; it will be @code{NULL_TREE} if the statement +was just +@example +return; +@end example + +@item SCOPE_STMT + +A scope-statement represents the beginning or end of a scope. If +@code{SCOPE_BEGIN_P} holds, this statement represents the beginning of a +scope; if @code{SCOPE_END_P} holds this statement represents the end of +a scope. On exit from a scope, all cleanups from @code{CLEANUP_STMT}s +occurring in the scope must be run, in reverse order to the order in +which they were encountered. If @code{SCOPE_NULLIFIED_P} or +@code{SCOPE_NO_CLEANUPS_P} holds of the scope, back ends should behave +as if the @code{SCOPE_STMT} were not present at all. + +@item SUBOBJECT + +In a constructor, these nodes are used to mark the point at which a +subobject of @code{this} is fully constructed. If, after this point, an +exception is thrown before a @code{CTOR_STMT} with @code{CTOR_END_P} set +is encountered, the @code{SUBOBJECT_CLEANUP} must be executed. The +cleanups must be executed in the reverse order in which they appear. + +@item SWITCH_STMT + +Used to represent a @code{switch} statement. The @code{SWITCH_COND} is +the expression on which the switch is occurring. See the documentation +for an @code{IF_STMT} for more information on the representation used +for the condition. The @code{SWITCH_BODY} is the body of the switch +statement. + +@item TRY_BLOCK +Used to represent a @code{try} block. The body of the try block is +given by @code{TRY_STMTS}. Each of the catch blocks is a @code{HANDLER} +node. The first handler is given by @code{TRY_HANDLERS}. Subsequent +handlers are obtained by following the @code{TREE_CHAIN} link from one +handler to the next. The body of the handler is given by +@code{HANDLER_BODY}. + +If @code{CLEANUP_P} holds of the @code{TRY_BLOCK}, then the +@code{TRY_HANDLERS} will not be a @code{HANDLER} node. Instead, it will +be an expression that should be executed if an exception is thrown in +the try block. It must rethrow the exception after executing that code. +And, if an exception is thrown while the expression is executing, +@code{terminate} must be called. + +@item USING_STMT +Used to represent a @code{using} directive. The namespace is given by +@code{USING_STMT_NAMESPACE}, which will be a NAMESPACE_DECL@. This node +is needed inside template functions, to implement using directives +during instantiation. + +@item WHILE_STMT + +Used to represent a @code{while} loop. The @code{WHILE_COND} is the +termination condition for the loop. See the documentation for an +@code{IF_STMT} for more information on the representation used for the +condition. + +The @code{WHILE_BODY} is the body of the loop. + +@end table + +@c --------------------------------------------------------------------- +@c Attributes +@c --------------------------------------------------------------------- +@node Attributes +@section Attributes in trees +@cindex attributes + +Attributes, as specified using the @code{__attribute__} keyword, are +represented internally as a @code{TREE_LIST}. The @code{TREE_PURPOSE} +is the name of the attribute, as an @code{IDENTIFIER_NODE}. The +@code{TREE_VALUE} is a @code{TREE_LIST} of the arguments of the +attribute, if any, or @code{NULL_TREE} if there are no arguments; the +arguments are stored as the @code{TREE_VALUE} of successive entries in +the list, and may be identifiers or expressions. The @code{TREE_CHAIN} +of the attribute is the next attribute in a list of attributes applying +to the same declaration or type, or @code{NULL_TREE} if there are no +further attributes in the list. + +Attributes may be attached to declarations and to types; these +attributes may be accessed with the following macros. All attributes +are stored in this way, and many also cause other changes to the +declaration or type or to other internal compiler data structures. + +@deftypefn {Tree Macro} tree DECL_ATTRIBUTES (tree @var{decl}) +This macro returns the attributes on the declaration @var{decl}. +@end deftypefn + +@deftypefn {Tree Macro} tree TYPE_ATTRIBUTES (tree @var{type}) +This macro returns the attributes on the type @var{type}. +@end deftypefn + +@c --------------------------------------------------------------------- +@c Expressions +@c --------------------------------------------------------------------- + +@node Expression trees +@section Expressions +@cindex expression +@findex TREE_OPERAND +@tindex INTEGER_CST +@findex TREE_INT_CST_HIGH +@findex TREE_INT_CST_LOW +@findex tree_int_cst_lt +@findex tree_int_cst_equal +@tindex REAL_CST +@tindex COMPLEX_CST +@tindex STRING_CST +@findex TREE_STRING_LENGTH +@findex TREE_STRING_POINTER +@tindex PTRMEM_CST +@findex PTRMEM_CST_CLASS +@findex PTRMEM_CST_MEMBER +@tindex VAR_DECL +@tindex NEGATE_EXPR +@tindex BIT_NOT_EXPR +@tindex TRUTH_NOT_EXPR +@tindex ADDR_EXPR +@tindex INDIRECT_REF +@tindex FIX_TRUNC_EXPR +@tindex FLOAT_EXPR +@tindex COMPLEX_EXPR +@tindex CONJ_EXPR +@tindex REALPART_EXPR +@tindex IMAGPART_EXPR +@tindex NOP_EXPR +@tindex CONVERT_EXPR +@tindex THROW_EXPR +@tindex LSHIFT_EXPR +@tindex RSHIFT_EXPR +@tindex BIT_IOR_EXPR +@tindex BIT_XOR_EXPR +@tindex BIT_AND_EXPR +@tindex TRUTH_ANDIF_EXPR +@tindex TRUTH_ORIF_EXPR +@tindex TRUTH_AND_EXPR +@tindex TRUTH_OR_EXPR +@tindex TRUTH_XOR_EXPR +@tindex PLUS_EXPR +@tindex MINUS_EXPR +@tindex MULT_EXPR +@tindex TRUNC_DIV_EXPR +@tindex TRUNC_MOD_EXPR +@tindex RDIV_EXPR +@tindex LT_EXPR +@tindex LE_EXPR +@tindex GT_EXPR +@tindex GE_EXPR +@tindex EQ_EXPR +@tindex NE_EXPR +@tindex INIT_EXPR +@tindex MODIFY_EXPR +@tindex COMPONENT_REF +@tindex COMPOUND_EXPR +@tindex COND_EXPR +@tindex CALL_EXPR +@tindex CONSTRUCTOR +@tindex COMPOUND_LITERAL_EXPR +@tindex STMT_EXPR +@tindex BIND_EXPR +@tindex LOOP_EXPR +@tindex EXIT_EXPR +@tindex CLEANUP_POINT_EXPR +@tindex ARRAY_REF +@tindex VTABLE_REF + +The internal representation for expressions is for the most part quite +straightforward. However, there are a few facts that one must bear in +mind. In particular, the expression ``tree'' is actually a directed +acyclic graph. (For example there may be many references to the integer +constant zero throughout the source program; many of these will be +represented by the same expression node.) You should not rely on +certain kinds of node being shared, nor should rely on certain kinds of +nodes being unshared. + +The following macros can be used with all expression nodes: + +@ftable @code +@item TREE_TYPE +Returns the type of the expression. This value may not be precisely the +same type that would be given the expression in the original program. +@end ftable + +In what follows, some nodes that one might expect to always have type +@code{bool} are documented to have either integral or boolean type. At +some point in the future, the C front end may also make use of this same +intermediate representation, and at this point these nodes will +certainly have integral type. The previous sentence is not meant to +imply that the C++ front end does not or will not give these nodes +integral type. + +Below, we list the various kinds of expression nodes. Except where +noted otherwise, the operands to an expression are accessed using the +@code{TREE_OPERAND} macro. For example, to access the first operand to +a binary plus expression @code{expr}, use: + +@example +TREE_OPERAND (expr, 0) +@end example +@noindent +As this example indicates, the operands are zero-indexed. + +The table below begins with constants, moves on to unary expressions, +then proceeds to binary expressions, and concludes with various other +kinds of expressions: + +@table @code +@item INTEGER_CST +These nodes represent integer constants. Note that the type of these +constants is obtained with @code{TREE_TYPE}; they are not always of type +@code{int}. In particular, @code{char} constants are represented with +@code{INTEGER_CST} nodes. The value of the integer constant @code{e} is +given by @example +((TREE_INT_CST_HIGH (e) << HOST_BITS_PER_WIDE_INT) ++ TREE_INST_CST_LOW (e)) +@end example +@noindent +HOST_BITS_PER_WIDE_INT is at least thirty-two on all platforms. Both +@code{TREE_INT_CST_HIGH} and @code{TREE_INT_CST_LOW} return a +@code{HOST_WIDE_INT}. The value of an @code{INTEGER_CST} is interpreted +as a signed or unsigned quantity depending on the type of the constant. +In general, the expression given above will overflow, so it should not +be used to calculate the value of the constant. + +The variable @code{integer_zero_node} is an integer constant with value +zero. Similarly, @code{integer_one_node} is an integer constant with +value one. The @code{size_zero_node} and @code{size_one_node} variables +are analogous, but have type @code{size_t} rather than @code{int}. + +The function @code{tree_int_cst_lt} is a predicate which holds if its +first argument is less than its second. Both constants are assumed to +have the same signedness (i.e., either both should be signed or both +should be unsigned.) The full width of the constant is used when doing +the comparison; the usual rules about promotions and conversions are +ignored. Similarly, @code{tree_int_cst_equal} holds if the two +constants are equal. The @code{tree_int_cst_sgn} function returns the +sign of a constant. The value is @code{1}, @code{0}, or @code{-1} +according on whether the constant is greater than, equal to, or less +than zero. Again, the signedness of the constant's type is taken into +account; an unsigned constant is never less than zero, no matter what +its bit-pattern. + +@item REAL_CST + +FIXME: Talk about how to obtain representations of this constant, do +comparisons, and so forth. + +@item COMPLEX_CST +These nodes are used to represent complex number constants, that is a +@code{__complex__} whose parts are constant nodes. The +@code{TREE_REALPART} and @code{TREE_IMAGPART} return the real and the +imaginary parts respectively. + +@item STRING_CST +These nodes represent string-constants. The @code{TREE_STRING_LENGTH} +returns the length of the string, as an @code{int}. The +@code{TREE_STRING_POINTER} is a @code{char*} containing the string +itself. The string may not be @code{NUL}-terminated, and it may contain +embedded @code{NUL} characters. Therefore, the +@code{TREE_STRING_LENGTH} includes the trailing @code{NUL} if it is +present. + +For wide string constants, the @code{TREE_STRING_LENGTH} is the number +of bytes in the string, and the @code{TREE_STRING_POINTER} +points to an array of the bytes of the string, as represented on the +target system (that is, as integers in the target endianness). Wide and +non-wide string constants are distinguished only by the @code{TREE_TYPE} +of the @code{STRING_CST}. + +FIXME: The formats of string constants are not well-defined when the +target system bytes are not the same width as host system bytes. + +@item PTRMEM_CST +These nodes are used to represent pointer-to-member constants. The +@code{PTRMEM_CST_CLASS} is the class type (either a @code{RECORD_TYPE} +or @code{UNION_TYPE} within which the pointer points), and the +@code{PTRMEM_CST_MEMBER} is the declaration for the pointed to object. +Note that the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is in +general different from the @code{PTRMEM_CST_CLASS}. For example, +given: +@example +struct B @{ int i; @}; +struct D : public B @{@}; +int D::*dp = &D::i; +@end example +@noindent +The @code{PTRMEM_CST_CLASS} for @code{&D::i} is @code{D}, even though +the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is @code{B}, +since @code{B::i} is a member of @code{B}, not @code{D}. + +@item VAR_DECL + +These nodes represent variables, including static data members. For +more information, @pxref{Declarations}. + +@item NEGATE_EXPR +These nodes represent unary negation of the single operand, for both +integer and floating-point types. The type of negation can be +determined by looking at the type of the expression. + +@item BIT_NOT_EXPR +These nodes represent bitwise complement, and will always have integral +type. The only operand is the value to be complemented. + +@item TRUTH_NOT_EXPR +These nodes represent logical negation, and will always have integral +(or boolean) type. The operand is the value being negated. + +@item PREDECREMENT_EXPR +@itemx PREINCREMENT_EXPR +@itemx POSTDECREMENT_EXPR +@itemx POSTINCREMENT_EXPR +These nodes represent increment and decrement expressions. The value of +the single operand is computed, and the operand incremented or +decremented. In the case of @code{PREDECREMENT_EXPR} and +@code{PREINCREMENT_EXPR}, the value of the expression is the value +resulting after the increment or decrement; in the case of +@code{POSTDECREMENT_EXPR} and @code{POSTINCREMENT_EXPR} is the value +before the increment or decrement occurs. The type of the operand, like +that of the result, will be either integral, boolean, or floating-point. + +@item ADDR_EXPR +These nodes are used to represent the address of an object. (These +expressions will always have pointer or reference type.) The operand may +be another expression, or it may be a declaration. + +As an extension, GCC allows users to take the address of a label. In +this case, the operand of the @code{ADDR_EXPR} will be a +@code{LABEL_DECL}. The type of such an expression is @code{void*}. + +If the object addressed is not an lvalue, a temporary is created, and +the address of the temporary is used. + +@item INDIRECT_REF +These nodes are used to represent the object pointed to by a pointer. +The operand is the pointer being dereferenced; it will always have +pointer or reference type. + +@item FIX_TRUNC_EXPR +These nodes represent conversion of a floating-point value to an +integer. The single operand will have a floating-point type, while the +the complete expression will have an integral (or boolean) type. The +operand is rounded towards zero. + +@item FLOAT_EXPR +These nodes represent conversion of an integral (or boolean) value to a +floating-point value. The single operand will have integral type, while +the complete expression will have a floating-point type. + +FIXME: How is the operand supposed to be rounded? Is this dependent on +@option{-mieee}? + +@item COMPLEX_EXPR +These nodes are used to represent complex numbers constructed from two +expressions of the same (integer or real) type. The first operand is the +real part and the second operand is the imaginary part. + +@item CONJ_EXPR +These nodes represent the conjugate of their operand. + +@item REALPART_EXPR +@item IMAGPART_EXPR +These nodes represent respectively the real and the imaginary parts +of complex numbers (their sole argument). + +@item NON_LVALUE_EXPR +These nodes indicate that their one and only operand is not an lvalue. +A back end can treat these identically to the single operand. + +@item NOP_EXPR +These nodes are used to represent conversions that do not require any +code-generation. For example, conversion of a @code{char*} to an +@code{int*} does not require any code be generated; such a conversion is +represented by a @code{NOP_EXPR}. The single operand is the expression +to be converted. The conversion from a pointer to a reference is also +represented with a @code{NOP_EXPR}. + +@item CONVERT_EXPR +These nodes are similar to @code{NOP_EXPR}s, but are used in those +situations where code may need to be generated. For example, if an +@code{int*} is converted to an @code{int} code may need to be generated +on some platforms. These nodes are never used for C++-specific +conversions, like conversions between pointers to different classes in +an inheritance hierarchy. Any adjustments that need to be made in such +cases are always indicated explicitly. Similarly, a user-defined +conversion is never represented by a @code{CONVERT_EXPR}; instead, the +function calls are made explicit. + +@item THROW_EXPR +These nodes represent @code{throw} expressions. The single operand is +an expression for the code that should be executed to throw the +exception. However, there is one implicit action not represented in +that expression; namely the call to @code{__throw}. This function takes +no arguments. If @code{setjmp}/@code{longjmp} exceptions are used, the +function @code{__sjthrow} is called instead. The normal GCC back end +uses the function @code{emit_throw} to generate this code; you can +examine this function to see what needs to be done. + +@item LSHIFT_EXPR +@itemx RSHIFT_EXPR +These nodes represent left and right shifts, respectively. The first +operand is the value to shift; it will always be of integral type. The +second operand is an expression for the number of bits by which to +shift. Right shift should be treated as arithmetic, i.e., the +high-order bits should be zero-filled when the expression has unsigned +type and filled with the sign bit when the expression has signed type. +Note that the result is undefined if the second operand is larger +than the first operand's type size. + + +@item BIT_IOR_EXPR +@itemx BIT_XOR_EXPR +@itemx BIT_AND_EXPR +These nodes represent bitwise inclusive or, bitwise exclusive or, and +bitwise and, respectively. Both operands will always have integral +type. + +@item TRUTH_ANDIF_EXPR +@itemx TRUTH_ORIF_EXPR +These nodes represent logical and and logical or, respectively. These +operators are not strict; i.e., the second operand is evaluated only if +the value of the expression is not determined by evaluation of the first +operand. The type of the operands, and the result type, is always of +boolean or integral type. + +@item TRUTH_AND_EXPR +@itemx TRUTH_OR_EXPR +@itemx TRUTH_XOR_EXPR +These nodes represent logical and, logical or, and logical exclusive or. +They are strict; both arguments are always evaluated. There are no +corresponding operators in C or C++, but the front end will sometimes +generate these expressions anyhow, if it can tell that strictness does +not matter. + +@itemx PLUS_EXPR +@itemx MINUS_EXPR +@itemx MULT_EXPR +@itemx TRUNC_DIV_EXPR +@itemx TRUNC_MOD_EXPR +@itemx RDIV_EXPR +These nodes represent various binary arithmetic operations. +Respectively, these operations are addition, subtraction (of the second +operand from the first), multiplication, integer division, integer +remainder, and floating-point division. The operands to the first three +of these may have either integral or floating type, but there will never +be case in which one operand is of floating type and the other is of +integral type. + +The result of a @code{TRUNC_DIV_EXPR} is always rounded towards zero. +The @code{TRUNC_MOD_EXPR} of two operands @code{a} and @code{b} is +always @code{a - a/b} where the division is as if computed by a +@code{TRUNC_DIV_EXPR}. + +@item ARRAY_REF +These nodes represent array accesses. The first operand is the array; +the second is the index. To calculate the address of the memory +accessed, you must scale the index by the size of the type of the array +elements. The type of these expressions must be the type of a component of +the array. + +@item ARRAY_RANGE_REF +These nodes represent access to a range (or ``slice'') of an array. The +operands are the same as that for @code{ARRAY_REF} and have the same +meanings. The type of these expressions must be an array whose component +type is the same as that of the first operand. The range of that array +type determines the amount of data these expressions access. + +@item EXACT_DIV_EXPR +Document. + +@item LT_EXPR +@itemx LE_EXPR +@itemx GT_EXPR +@itemx GE_EXPR +@itemx EQ_EXPR +@itemx NE_EXPR + +These nodes represent the less than, less than or equal to, greater +than, greater than or equal to, equal, and not equal comparison +operators. The first and second operand with either be both of integral +type or both of floating type. The result type of these expressions +will always be of integral or boolean type. + +@item MODIFY_EXPR +These nodes represent assignment. The left-hand side is the first +operand; the right-hand side is the second operand. The left-hand side +will be a @code{VAR_DECL}, @code{INDIRECT_REF}, @code{COMPONENT_REF}, or +other lvalue. + +These nodes are used to represent not only assignment with @samp{=} but +also compound assignments (like @samp{+=}), by reduction to @samp{=} +assignment. In other words, the representation for @samp{i += 3} looks +just like that for @samp{i = i + 3}. + +@item INIT_EXPR +These nodes are just like @code{MODIFY_EXPR}, but are used only when a +variable is initialized, rather than assigned to subsequently. + +@item COMPONENT_REF +These nodes represent non-static data member accesses. The first +operand is the object (rather than a pointer to it); the second operand +is the @code{FIELD_DECL} for the data member. + +@item COMPOUND_EXPR +These nodes represent comma-expressions. The first operand is an +expression whose value is computed and thrown away prior to the +evaluation of the second operand. The value of the entire expression is +the value of the second operand. + +@item COND_EXPR +These nodes represent @code{?:} expressions. The first operand +is of boolean or integral type. If it evaluates to a nonzero value, +the second operand should be evaluated, and returned as the value of the +expression. Otherwise, the third operand is evaluated, and returned as +the value of the expression. As a GNU extension, the middle operand of +the @code{?:} operator may be omitted in the source, like this: + +@example +x ? : 3 +@end example +@noindent +which is equivalent to + +@example +x ? x : 3 +@end example + +@noindent +assuming that @code{x} is an expression without side-effects. However, +in the case that the first operation causes side effects, the +side-effects occur only once. Consumers of the internal representation +do not need to worry about this oddity; the second operand will be +always be present in the internal representation. + +@item CALL_EXPR +These nodes are used to represent calls to functions, including +non-static member functions. The first operand is a pointer to the +function to call; it is always an expression whose type is a +@code{POINTER_TYPE}. The second argument is a @code{TREE_LIST}. The +arguments to the call appear left-to-right in the list. The +@code{TREE_VALUE} of each list node contains the expression +corresponding to that argument. (The value of @code{TREE_PURPOSE} for +these nodes is unspecified, and should be ignored.) For non-static +member functions, there will be an operand corresponding to the +@code{this} pointer. There will always be expressions corresponding to +all of the arguments, even if the function is declared with default +arguments and some arguments are not explicitly provided at the call +sites. + +@item STMT_EXPR +These nodes are used to represent GCC's statement-expression extension. +The statement-expression extension allows code like this: +@example +int f() @{ return (@{ int j; j = 3; j + 7; @}); @} +@end example +In other words, an sequence of statements may occur where a single +expression would normally appear. The @code{STMT_EXPR} node represents +such an expression. The @code{STMT_EXPR_STMT} gives the statement +contained in the expression; this is always a @code{COMPOUND_STMT}. The +value of the expression is the value of the last sub-statement in the +@code{COMPOUND_STMT}. More precisely, the value is the value computed +by the last @code{EXPR_STMT} in the outermost scope of the +@code{COMPOUND_STMT}. For example, in: +@example +(@{ 3; @}) +@end example +the value is @code{3} while in: +@example +(@{ if (x) @{ 3; @} @}) +@end example +(represented by a nested @code{COMPOUND_STMT}), there is no value. If +the @code{STMT_EXPR} does not yield a value, it's type will be +@code{void}. + +@item BIND_EXPR +These nodes represent local blocks. The first operand is a list of +temporary variables, connected via their @code{TREE_CHAIN} field. These +will never require cleanups. The scope of these variables is just the +body of the @code{BIND_EXPR}. The body of the @code{BIND_EXPR} is the +second operand. + +@item LOOP_EXPR +These nodes represent ``infinite'' loops. The @code{LOOP_EXPR_BODY} +represents the body of the loop. It should be executed forever, unless +an @code{EXIT_EXPR} is encountered. + +@item EXIT_EXPR +These nodes represent conditional exits from the nearest enclosing +@code{LOOP_EXPR}. The single operand is the condition; if it is +nonzero, then the loop should be exited. An @code{EXIT_EXPR} will only +appear within a @code{LOOP_EXPR}. + +@item CLEANUP_POINT_EXPR +These nodes represent full-expressions. The single operand is an +expression to evaluate. Any destructor calls engendered by the creation +of temporaries during the evaluation of that expression should be +performed immediately after the expression is evaluated. + +@item CONSTRUCTOR +These nodes represent the brace-enclosed initializers for a structure or +array. The first operand is reserved for use by the back end. The +second operand is a @code{TREE_LIST}. If the @code{TREE_TYPE} of the +@code{CONSTRUCTOR} is a @code{RECORD_TYPE} or @code{UNION_TYPE}, then +the @code{TREE_PURPOSE} of each node in the @code{TREE_LIST} will be a +@code{FIELD_DECL} and the @code{TREE_VALUE} of each node will be the +expression used to initialize that field. You should not depend on the +fields appearing in any particular order, nor should you assume that all +fields will be represented. Unrepresented fields may be assigned any +value. + +If the @code{TREE_TYPE} of the @code{CONSTRUCTOR} is an +@code{ARRAY_TYPE}, then the @code{TREE_PURPOSE} of each element in the +@code{TREE_LIST} will be an @code{INTEGER_CST}. This constant indicates +which element of the array (indexed from zero) is being assigned to; +again, the @code{TREE_VALUE} is the corresponding initializer. If the +@code{TREE_PURPOSE} is @code{NULL_TREE}, then the initializer is for the +next available array element. + +Conceptually, before any initialization is done, the entire area of +storage is initialized to zero. + +@item COMPOUND_LITERAL_EXPR +@findex COMPOUND_LITERAL_EXPR_DECL_STMT +@findex COMPOUND_LITERAL_EXPR_DECL +These nodes represent ISO C99 compound literals. The +@code{COMPOUND_LITERAL_EXPR_DECL_STMT} is a @code{DECL_STMT} +containing an anonymous @code{VAR_DECL} for +the unnamed object represented by the compound literal; the +@code{DECL_INITIAL} of that @code{VAR_DECL} is a @code{CONSTRUCTOR} +representing the brace-enclosed list of initializers in the compound +literal. That anonymous @code{VAR_DECL} can also be accessed directly +by the @code{COMPOUND_LITERAL_EXPR_DECL} macro. + +@item SAVE_EXPR + +A @code{SAVE_EXPR} represents an expression (possibly involving +side-effects) that is used more than once. The side-effects should +occur only the first time the expression is evaluated. Subsequent uses +should just reuse the computed value. The first operand to the +@code{SAVE_EXPR} is the expression to evaluate. The side-effects should +be executed where the @code{SAVE_EXPR} is first encountered in a +depth-first preorder traversal of the expression tree. + +@item TARGET_EXPR +A @code{TARGET_EXPR} represents a temporary object. The first operand +is a @code{VAR_DECL} for the temporary variable. The second operand is +the initializer for the temporary. The initializer is evaluated, and +copied (bitwise) into the temporary. + +Often, a @code{TARGET_EXPR} occurs on the right-hand side of an +assignment, or as the second operand to a comma-expression which is +itself the right-hand side of an assignment, etc. In this case, we say +that the @code{TARGET_EXPR} is ``normal''; otherwise, we say it is +``orphaned''. For a normal @code{TARGET_EXPR} the temporary variable +should be treated as an alias for the left-hand side of the assignment, +rather than as a new temporary variable. + +The third operand to the @code{TARGET_EXPR}, if present, is a +cleanup-expression (i.e., destructor call) for the temporary. If this +expression is orphaned, then this expression must be executed when the +statement containing this expression is complete. These cleanups must +always be executed in the order opposite to that in which they were +encountered. Note that if a temporary is created on one branch of a +conditional operator (i.e., in the second or third operand to a +@code{COND_EXPR}), the cleanup must be run only if that branch is +actually executed. + +See @code{STMT_IS_FULL_EXPR_P} for more information about running these +cleanups. + +@item AGGR_INIT_EXPR +An @code{AGGR_INIT_EXPR} represents the initialization as the return +value of a function call, or as the result of a constructor. An +@code{AGGR_INIT_EXPR} will only appear as the second operand of a +@code{TARGET_EXPR}. The first operand to the @code{AGGR_INIT_EXPR} is +the address of a function to call, just as in a @code{CALL_EXPR}. The +second operand are the arguments to pass that function, as a +@code{TREE_LIST}, again in a manner similar to that of a +@code{CALL_EXPR}. The value of the expression is that returned by the +function. + +If @code{AGGR_INIT_VIA_CTOR_P} holds of the @code{AGGR_INIT_EXPR}, then +the initialization is via a constructor call. The address of the third +operand of the @code{AGGR_INIT_EXPR}, which is always a @code{VAR_DECL}, +is taken, and this value replaces the first argument in the argument +list. In this case, the value of the expression is the @code{VAR_DECL} +given by the third operand to the @code{AGGR_INIT_EXPR}; constructors do +not return a value. + +@item VTABLE_REF +A @code{VTABLE_REF} indicates that the interior expression computes +a value that is a vtable entry. It is used with @option{-fvtable-gc} +to track the reference through to front end to the middle end, at +which point we transform this to a @code{REG_VTABLE_REF} note, which +survives the balance of code generation. + +The first operand is the expression that computes the vtable reference. +The second operand is the @code{VAR_DECL} of the vtable. The third +operand is an @code{INTEGER_CST} of the byte offset into the vtable. + +@end table diff --git a/contrib/gcc/doc/collect2.texi b/contrib/gcc/doc/collect2.texi new file mode 100644 index 000000000000..2cd1d3c0d5a1 --- /dev/null +++ b/contrib/gcc/doc/collect2.texi @@ -0,0 +1,85 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Collect2 +@chapter @code{collect2} + +GNU CC uses a utility called @code{collect2} on nearly all systems to arrange +to call various initialization functions at start time. + +The program @code{collect2} works by linking the program once and +looking through the linker output file for symbols with particular names +indicating they are constructor functions. If it finds any, it +creates a new temporary @samp{.c} file containing a table of them, +compiles it, and links the program a second time including that file. + +@findex __main +@cindex constructors, automatic calls +The actual calls to the constructors are carried out by a subroutine +called @code{__main}, which is called (automatically) at the beginning +of the body of @code{main} (provided @code{main} was compiled with GNU +CC)@. Calling @code{__main} is necessary, even when compiling C code, to +allow linking C and C++ object code together. (If you use +@option{-nostdlib}, you get an unresolved reference to @code{__main}, +since it's defined in the standard GCC library. Include @option{-lgcc} at +the end of your compiler command line to resolve this reference.) + +The program @code{collect2} is installed as @code{ld} in the directory +where the passes of the compiler are installed. When @code{collect2} +needs to find the @emph{real} @code{ld}, it tries the following file +names: + +@itemize @bullet +@item +@file{real-ld} in the directories listed in the compiler's search +directories. + +@item +@file{real-ld} in the directories listed in the environment variable +@code{PATH}. + +@item +The file specified in the @code{REAL_LD_FILE_NAME} configuration macro, +if specified. + +@item +@file{ld} in the compiler's search directories, except that +@code{collect2} will not execute itself recursively. + +@item +@file{ld} in @code{PATH}. +@end itemize + +``The compiler's search directories'' means all the directories where +@code{gcc} searches for passes of the compiler. This includes +directories that you specify with @option{-B}. + +Cross-compilers search a little differently: + +@itemize @bullet +@item +@file{real-ld} in the compiler's search directories. + +@item +@file{@var{target}-real-ld} in @code{PATH}. + +@item +The file specified in the @code{REAL_LD_FILE_NAME} configuration macro, +if specified. + +@item +@file{ld} in the compiler's search directories. + +@item +@file{@var{target}-ld} in @code{PATH}. +@end itemize + +@code{collect2} explicitly avoids running @code{ld} using the file name +under which @code{collect2} itself was invoked. In fact, it remembers +up a list of such names---in case one copy of @code{collect2} finds +another copy (or version) of @code{collect2} installed as @code{ld} in a +second place in the search path. + +@code{collect2} searches for the utilities @code{nm} and @code{strip} +using the same algorithm as above for @code{ld}. diff --git a/contrib/gcc/doc/configfiles.texi b/contrib/gcc/doc/configfiles.texi new file mode 100644 index 000000000000..c6c60bbe802a --- /dev/null +++ b/contrib/gcc/doc/configfiles.texi @@ -0,0 +1,74 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001, 2002 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Configuration Files +@subsubsection Files Created by @code{configure} + +Here we spell out what files will be set up by @file{configure} in the +@file{gcc} directory. Some other files are created as temporary files +in the configuration process, and are not used in the subsequent +build; these are not documented. + +@itemize @bullet +@item +@file{Makefile} is constructed from @file{Makefile.in}, together with +the host and target fragments (@pxref{Fragments, , Makefile +Fragments}) @file{t-@var{target}} and @file{x-@var{host}} from +@file{config}, if any, and language Makefile fragments +@file{@var{language}/Make-lang.in}. +@item +@file{auto-host.h} contains information about the host machine +determined by @file{configure}. If the host machine is different from +the build machine, then @file{auto-build.h} is also created, +containing such information about the build machine. +@item +@file{config.status} is a script that may be run to recreate the +current configuration. +@item +@file{configargs.h} is a header containing details of the arguments +passed to @file{configure} to configure GCC, and of the thread model +used. +@item +@file{cstamp-h} is used as a timestamp. +@item +@file{fixinc/Makefile} is constructed from @file{fixinc/Makefile.in}. +@item +@file{gccbug}, a script for reporting bugs in GCC, is constructed from +@file{gccbug.in}. +@item +@file{intl/Makefile} is constructed from @file{intl/Makefile.in}. +@item +@file{mklibgcc}, a shell script to create a Makefile to build libgcc, +is constructed from @file{mklibgcc.in}. +@item +If a language @file{config-lang.in} file (@pxref{Front End Config, , +The Front End @file{config-lang.in} File}) sets @code{outputs}, then +the files listed in @code{outputs} there are also generated. +@end itemize + +The following configuration headers are created from the Makefile, +using @file{mkconfig.sh}, rather than directly by @file{configure}. +@file{config.h}, @file{hconfig.h} and @file{tconfig.h} all contain the +@file{xm-@var{machine}.h} header, if any, appropriate to the host, +build and target machines respectively, the configuration headers for +the target, and some definitions; for the host and build machines, +these include the autoconfigured headers generated by +@file{configure}. The other configuration headers are determined by +@file{config.gcc}. They also contain the typedefs for @code{rtx}, +@code{rtvec} and @code{tree}. + +@itemize @bullet +@item +@file{config.h}, for use in programs that run on the host machine. +@item +@file{hconfig.h}, for use in programs that run on the build machine. +@item +@file{tconfig.h}, for use in programs and libraries for the target +machine. +@item +@file{tm_p.h}, which includes the header @file{@var{machine}-protos.h} +that contains prototypes for functions in the target @file{.c} file. +FIXME: why is such a separate header necessary? +@end itemize diff --git a/contrib/gcc/doc/configterms.texi b/contrib/gcc/doc/configterms.texi new file mode 100644 index 000000000000..39b3152d5286 --- /dev/null +++ b/contrib/gcc/doc/configterms.texi @@ -0,0 +1,61 @@ +@c Copyright (C) 2001, 2002 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Configure Terms +@section Configure Terms and History +@cindex configure terms +@cindex canadian + +The configure and build process has a long and colorful history, and can +be confusing to anyone who doesn't know why things are the way they are. +While there are other documents which describe the configuration process +in detail, here are a few things that everyone working on GCC should +know. + +There are three system names that the build knows about: the machine you +are building on (@dfn{build}), the machine that you are building for +(@dfn{host}), and the machine that GCC will produce code for +(@dfn{target}). When you configure GCC, you specify these with +@option{--build=}, @option{--host=}, and @option{--target=}. + +Specifying the host without specifying the build should be avoided, as +@command{configure} may (and once did) assume that the host you specify +is also the build, which may not be true. + +If build, host, and target are all the same, this is called a +@dfn{native}. If build and host are the same but target is different, +this is called a @dfn{cross}. If build, host, and target are all +different this is called a @dfn{canadian} (for obscure reasons dealing +with Canada's political party and the background of the person working +on the build at that time). If host and target are the same, but build +is different, you are using a cross-compiler to build a native for a +different system. Some people call this a @dfn{host-x-host}, +@dfn{crossed native}, or @dfn{cross-built native}. If build and target +are the same, but host is different, you are using a cross compiler to +build a cross compiler that produces code for the machine you're +building on. This is rare, so there is no common way of describing it +(although I propose calling it a @dfn{crossback}). + +If build and host are the same, the GCC you are building will also be +used to build the target libraries (like @code{libstdc++}). If build and host +are different, you must have already build and installed a cross +compiler that will be used to build the target libraries (if you +configured with @option{--target=foo-bar}, this compiler will be called +@command{foo-bar-gcc}). + +In the case of target libraries, the machine you're building for is the +machine you specified with @option{--target}. So, build is the machine +you're building on (no change there), host is the machine you're +building for (the target libraries are built for the target, so host is +the target you specified), and target doesn't apply (because you're not +building a compiler, you're building libraries). The configure/make +process will adjust these variables as needed. It also sets +@code{$with_cross_host} to the original @option{--host} value in case you +need it. + +The @code{libiberty} support library is built up to three times: once +for the host, once for the target (even if they are the same), and once +for the build if build and host are different. This allows it to be +used by all programs which are generated in the course of the build +process. diff --git a/contrib/gcc/doc/contrib.texi b/contrib/gcc/doc/contrib.texi new file mode 100644 index 000000000000..966d3ec3e0de --- /dev/null +++ b/contrib/gcc/doc/contrib.texi @@ -0,0 +1,712 @@ +@c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001 +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Contributors +@unnumbered Contributors to GCC +@cindex contributors + +The GCC project would like to thank its many contributors. Without them the +project would not have been nearly as successful as it has been. Any omissions +in this list are accidental. Feel free to contact +@email{law@@redhat.com} if you have been left out +or some of your contributions are not listed. Please keep this list in +alphabetical order. + +Some projects operating under the GCC project maintain their own list +of contributors, such as +@uref{http://gcc.gnu.org/libstdc++/,the C++ library}. + +@itemize @bullet + +@item +Analog Devices helped implement the support for complex data types +and iterators. + +@item +James van Artsdalen wrote the code that makes efficient use of +the Intel 80387 register stack. + +@item +Alasdair Baird for various bugfixes. + +@item +Gerald Baumgartner added the signature extension to the C++ front end. + +@item +Neil Booth for various work on cpplib. + +@item +Per Bothner for his direction via the steering committee and various +improvements to our infrastructure for supporting new languages. Chill +and Java front end implementations. Initial implementations of +cpplib, fix-header, config.guess, libio, and past C++ library +(libg++) maintainer. + +@item +Devon Bowen helped port GCC to the Tahoe. + +@item +Don Bowman for mips-vxworks contributions. + +@item +Dave Brolley for work on cpplib and Chill. + +@item +Robert Brown implemented the support for Encore 32000 systems. + +@item +Christian Bruel for improvements to local store elimination. + +@item +Herman A.J. ten Brugge for various fixes. + +@item +Joe Buck for his direction via the steering committee. + +@item +Craig Burley for leadership of the Fortran effort. + +@item +John Carr for his alias work, SPARC hacking, infrastructure improvements, +previous contributions to the steering committee, loop optimizations, etc. + +@item +Steve Chamberlain wrote the support for the Hitachi SH and H8 processors +and the PicoJava processor. + +@item +Scott Christley for his ObjC contributions. + +@item +Branko Cibej for more warning contributions. + +@item +Nick Clifton for arm, mcore, fr30, v850, m32r work, @option{--help}, and other random +hacking. + +@item +Ralf Corsepius for SH testing and minor bugfixing. + +@item +Stan Cox for care and feeding of the x86 port and lots of behind +the scenes hacking. + +@item +Alex Crain provided changes for the 3b1. + +@item +Ian Dall for major improvements to the NS32k port. + +@item +Dario Dariol contributed the four varieties of sample programs +that print a copy of their source. + +@item +Ulrich Drepper for his work on the C++ runtime libraries, glibc, + testing of GCC using glibc, ISO C99 support, CFG dumping support, etc. + +@item +Richard Earnshaw for his ongoing work with the ARM@. + +@item +David Edelsohn for his direction via the steering committee, +ongoing work with the RS6000/PowerPC port, and help cleaning up Haifa +loop changes. + +@item +Paul Eggert for random hacking all over GCC@. + +@item +Mark Elbrecht for various DJGPP improvements. + +@item +Ben Elliston for his work to move the Objective-C runtime into its +own subdirectory and for his work on autoconf. + +@item +Marc Espie for OpenBSD support. + +@item +Doug Evans for much of the global optimization framework, arc, m32r, +and SPARC work. + +@item +Fred Fish for BeOS support and Ada fixes. + +@item +Peter Gerwinski for various bugfixes and the Pascal front end. + +@item +Kaveh Ghazi for his direction via the steering committee and +amazing work to make @samp{-W -Wall} useful. + +@item +Judy Goldberg for c++ contributions. + +@item +Torbjorn Granlund for various fixes and the c-torture testsuite, +multiply- and divide-by-constant optimization, improved long long +support, improved leaf function register allocation, and his direction +via the steering committee. + +@item +Anthony Green for his @option{-Os} contributions and Java front end work. + +@item +Michael K. Gschwind contributed the port to the PDP-11. + +@item +Ron Guilmette implemented the @command{protoize} and @command{unprotoize} +tools, the support for Dwarf symbolic debugging information, and much of +the support for System V Release 4. He has also worked heavily on the +Intel 386 and 860 support. + +@item +Bruno Haible for improvements in the runtime overhead for EH, new +warnings and assorted bugfixes. + +@item +Andrew Haley for his Java work. + +@item +Chris Hanson assisted in making GCC work on HP-UX for the 9000 series 300. + +@item +Michael Hayes for various thankless work he's done trying to get +the c30/c40 ports functional. Lots of loop and unroll improvements and +fixes. + +@item +Kate Hedstrom for staking the g77 folks with an initial testsuite. + +@item +Richard Henderson for his ongoing SPARC and alpha work, loop opts, and +generally fixing lots of old problems we've ignored for years, flow +rewrite and lots of stuff I've forgotten. + +@item +Nobuyuki Hikichi of Software Research Associates, Tokyo, contributed +the support for the Sony NEWS machine. + +@item +Manfred Hollstein for his ongoing work to keep the m88k alive, lots +of testing an bugfixing, particularly of our configury code. + +@item +Steve Holmgren for MachTen patches. + +@item +Jan Hubicka for his x86 port improvements. + +@item +Christian Iseli for various bugfixes. + +@item +Kamil Iskra for general m68k hacking. + +@item +Lee Iverson for random fixes and mips testing. + +@item +Andreas Jaeger for various fixes to the MIPS port + +@item +Jakub Jelinek for his SPARC work and sibling call optimizations. + +@item +J. Kean Johnston for OpenServer support. + +@item +Klaus Kaempf for his ongoing work to make alpha-vms a viable target. + +@item +David Kashtan of SRI adapted GCC to VMS@. + +@item +Geoffrey Keating for his ongoing work to make the PPC work for Linux. + +@item +Brendan Kehoe for his ongoing work with g++. + +@item +Oliver M. Kellogg of Deutsche Aerospace contributed the port to the +MIL-STD-1750A@. + +@item +Richard Kenner of the New York University Ultracomputer Research +Laboratory wrote the machine descriptions for the AMD 29000, the DEC +Alpha, the IBM RT PC, and the IBM RS/6000 as well as the support for +instruction attributes. He also made changes to better support RISC +processors including changes to common subexpression elimination, +strength reduction, function calling sequence handling, and condition +code support, in addition to generalizing the code for frame pointer +elimination and delay slot scheduling. Richard Kenner was also the +head maintainer of GCC for several years. + +@item +Mumit Khan for various contributions to the cygwin and mingw32 ports and +maintaining binary releases for Windows hosts. + +@item +Robin Kirkham for cpu32 support. + +@item +Mark Klein for PA improvements. + +@item +Thomas Koenig for various bugfixes. + +@item +Bruce Korb for the new and improved fixincludes code. + +@item +Benjamin Kosnik for his g++ work. + +@item +Charles LaBrec contributed the support for the Integrated Solutions +68020 system. + +@item +Jeff Law for his direction via the steering committee, coordinating the +entire egcs project and GCC 2.95, rolling out snapshots and releases, +handling merges from GCC2, reviewing tons of patches that might have +fallen through the cracks else, and random but extensive hacking. + +@item +Marc Lehmann for his direction via the steering committee and helping +with analysis and improvements of x86 performance. + +@item +Ted Lemon wrote parts of the RTL reader and printer. + +@item +Kriang Lerdsuwanakij for improvements to demangler and various c++ fixes. + +@item +Warren Levy major work on libgcj (Java Runtime Library) and random +work on the Java front end. + +@item +Alain Lichnewsky ported GCC to the Mips cpu. + +@item +Robert Lipe for OpenServer support, new testsuites, testing, etc. + +@item +Weiwen Liu for testing and various bugfixes. + +@item +Dave Love for his ongoing work with the Fortran front end and +runtime libraries. + +@item +Martin von L@"owis for internal consistency checking infrastructure, +and various C++ improvements including namespace support. + +@item +H.J. Lu for his previous contributions to the steering committee, many x86 +bug reports, prototype patches, and keeping the Linux ports working. + +@item +Greg McGary for random fixes and (someday) bounded pointers. + +@item +Andrew MacLeod for his ongoing work in building a real EH system, +various code generation improvements, work on the global optimizer, etc. + +@item +Vladimir Makarov for hacking some ugly i960 problems, PowerPC +hacking improvements to compile-time performance and overall knowledge +and direction in the area of instruction scheduling. + +@item +Bob Manson for his behind the scenes work on dejagnu. + +@item +Michael Meissner for LRS framework, ia32, m32r, v850, m88k, MIPS powerpc, haifa, +ECOFF debug support, and other assorted hacking. + +@item +Jason Merrill for his direction via the steering committee and leading +the g++ effort. + +@item +David Miller for his direction via the steering committee, lots of +SPARC work, improvements in jump.c and interfacing with the Linux kernel +developers. + +@item +Gary Miller ported GCC to Charles River Data Systems machines. + +@item +Mark Mitchell for his direction via the steering committee, mountains of +C++ work, load/store hoisting out of loops, alias analysis improvements, +ISO C @code{restrict} support, and serving as release manager for GCC 3.0. + +@item +Alan Modra for various Linux bits and testing. + +@item +Toon Moene for his direction via the steering committee, Fortran +maintenance, and his ongoing work to make us make Fortran run fast. + +@item +Jason Molenda for major help in the care and feeding of all the services +on the gcc.gnu.org (formerly egcs.cygnus.com) machine---mail, web +services, ftp services, etc etc. + +@item +Catherine Moore for fixing various ugly problems we have sent her +way, including the haifa bug which was killing the Alpha & PowerPC Linux +kernels. + +@item +David Mosberger-Tang for various Alpha improvements. + +@item +Stephen Moshier contributed the floating point emulator that assists in +cross-compilation and permits support for floating point numbers wider +than 64 bits and for ISO C99 support. + +@item +Bill Moyer for his behind the scenes work on various issues. + +@item +Philippe De Muyter for his work on the m68k port. + +@item +Joseph S. Myers for his work on the PDP-11 port, format checking and ISO +C99 support, and continuous emphasis on (and contributions to) documentation. + +@item +Nathan Myers for his work on libstdc++-v3. + +@item +NeXT, Inc.@: donated the front end that supports the Objective-C +language. + +@item +Hans-Peter Nilsson for the CRIS and MMIX ports, improvements to the search +engine setup, various documentation fixes and other small fixes. + +@item +Geoff Noer for this work on getting cygwin native builds working. + +@item +Alexandre Oliva for various build infrastructure improvements, scripts and +amazing testing work. + +@item +Melissa O'Neill for various NeXT fixes. + +@item +Rainer Orth for random MIPS work, including improvements to our o32 +ABI support, improvements to dejagnu's MIPS support, etc. + +@item +Paul Petersen wrote the machine description for the Alliant FX/8. + +@item +Alexandre Petit-Bianco for his Java work. + +@item +Matthias Pfaller for major improvements to the NS32k port. + +@item +Gerald Pfeifer for his direction via the steering committee, pointing +out lots of problems we need to solve, maintenance of the web pages, and +taking care of documentation maintenance in general. + +@item +Ovidiu Predescu for his work on the ObjC front end and runtime libraries. + +@item +Ken Raeburn for various improvements to checker, mips ports and various +cleanups in the compiler. + +@item +David Reese of Sun Microsystems contributed to the Solaris on PowerPC +port. +@item +Gabriel Dos Reis for contributions and maintenance of libstdc++-v3, +including valarray implementation and limits support. + +@item +Joern Rennecke for maintaining the sh port, loop, regmove & reload +hacking. + +@item +Gavin Romig-Koch for lots of behind the scenes MIPS work. + +@item +Ken Rose for fixes to our delay slot filling code. + +@item +Paul Rubin wrote most of the preprocessor. + +@item +Juha Sarlin for improvements to the H8 code generator. + +@item +Greg Satz assisted in making GCC work on HP-UX for the 9000 series 300. + +@item +Peter Schauer wrote the code to allow debugging to work on the Alpha. + +@item +William Schelter did most of the work on the Intel 80386 support. + +@item +Bernd Schmidt for various code generation improvements and major +work in the reload pass as well a serving as release manager for +GCC 2.95.3. + +@item +Andreas Schwab for his work on the m68k port. + +@item +Joel Sherrill for his direction via the steering committee, RTEMS +contributions and RTEMS testing. + +@item +Nathan Sidwell for many C++ fixes/improvements. + +@item +Jeffrey Siegal for helping RMS with the original design of GCC, some +code which handles the parse tree and RTL data structures, constant +folding and help with the original VAX & m68k ports. + +@item +Franz Sirl for his ongoing work with making the PPC port stable +for linux. + +@item +Andrey Slepuhin for assorted AIX hacking. + +@item +Christopher Smith did the port for Convex machines. + +@item +Randy Smith finished the Sun FPA support. + +@item +Scott Snyder for various fixes. + +@item +Richard Stallman, for writing the original gcc and launching the GNU project. + +@item +Jan Stein of the Chalmers Computer Society provided support for +Genix, as well as part of the 32000 machine description. + +@item +Nigel Stephens for various mips16 related fixes/improvements. + +@item +Jonathan Stone wrote the machine description for the Pyramid computer. + +@item +Graham Stott for various infrastructure improvements. + +@item +Mike Stump for his Elxsi port, g++ contributions over the years and more +recently his vxworks contributions + +@item +Shigeya Suzuki for this fixes for the bsdi platforms. + +@item +Ian Lance Taylor for his mips16 work, general configury hacking, +fixincludes, etc. + +@item +Holger Teutsch provided the support for the Clipper cpu. + +@item +Gary Thomas for his ongoing work to make the PPC work for Linux. + +@item +Philipp Thomas for random bugfixes throughout the compiler + +@item +Kresten Krab Thorup wrote the run time support for the Objective-C +language. + +@item +Michael Tiemann for random bugfixes the first instruction scheduler, +initial C++ support, function integration, NS32k, sparc and M88k +machine description work, delay slot scheduling. + +@item +Teemu Torma for thread safe exception handling support. + +@item +Leonard Tower wrote parts of the parser, RTL generator, and RTL +definitions, and of the VAX machine description. + +@item +Tom Tromey for internationalization support and his Java work. + +@item +Lassi Tuura for improvements to config.guess to determine HP processor +types. + +@item +Todd Vierling for contributions for NetBSD ports. + +@item +Dean Wakerley for converting the install documentation from HTML to texinfo +in time for GCC 3.0. + +@item +Krister Walfridsson for random bugfixes. + +@item +John Wehle for various improvements for the x86 code generator, +related infrastructure improvements to help x86 code generation, +value range propagation and other work, WE32k port. + +@item +Zack Weinberg for major work on cpplib and various other bugfixes. + +@item +Dale Wiles helped port GCC to the Tahoe. + +@item +Bob Wilson from Tensilica, Inc.@: for the Xtensa port. + +@item +Jim Wilson for his direction via the steering committee, tackling hard +problems in various places that nobody else wanted to work on, strength +reduction and other loop optimizations. + +@item +Carlo Wood for various fixes. + +@item +Tom Wood for work on the m88k port. + +@item +Masanobu Yuhara of Fujitsu Laboratories implemented the machine +description for the Tron architecture (specifically, the Gmicro). + +@item +Kevin Zachmann helped ported GCC to the Tahoe. + +@end itemize + + +We'd also like to thank the folks who have contributed time and energy in +testing GCC: + +@itemize @bullet +@item +David Billinghurst + +@item +Horst von Brand + +@item +Rodney Brown + +@item +Joe Buck + +@item +Craig Burley + +@item +Ulrich Drepper + +@item +David Edelsohn + +@item +Yung Shing Gene + +@item +Kaveh Ghazi + +@item +Kate Hedstrom + +@item +Richard Henderson + +@item +Manfred Hollstein + +@item +Kamil Iskra + +@item +Christian Joensson + +@item +Jeff Law + +@item +Robert Lipe + +@item +Damon Love + +@item +Dave Love + +@item +H.J. Lu + +@item +Mumit Khan + +@item +Matthias Klose + +@item +Martin Knoblauch + +@item +David Miller + +@item +Toon Moene + +@item +Matthias Mueller + +@item +Alexandre Oliva + +@item +Richard Polton + +@item +David Rees + +@item +Peter Schmid + +@item +David Schuler + +@item +Vin Shelton + +@item +Franz Sirl + +@item +Mike Stump + +@item +Carlo Wood + +@item +And many others +@end itemize + +And finally we'd like to thank everyone who uses the compiler, submits bug +reports and generally reminds us why we're doing this work in the first place. diff --git a/contrib/gcc/doc/contribute.texi b/contrib/gcc/doc/contribute.texi new file mode 100644 index 000000000000..f9a5f970af28 --- /dev/null +++ b/contrib/gcc/doc/contribute.texi @@ -0,0 +1,25 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Contributing +@chapter Contributing to GCC Development + +If you would like to help pretest GCC releases to assure they work well, +our current development sources are available by CVS (see +@uref{http://gcc.gnu.org/cvs.html}). Source and binary snapshots are +also available for FTP; see @uref{http://gcc.gnu.org/snapshots.html}. + +If you would like to work on improvements to GCC, please read the +advice at these URLs: + +@smallexample +@uref{http://gcc.gnu.org/contribute.html} +@uref{http://gcc.gnu.org/contributewhy.html} +@end smallexample + +@noindent +for information on how to make useful contributions and avoid +duplication of effort. Suggested projects are listed at +@uref{http://gcc.gnu.org/projects/}. diff --git a/contrib/gcc/doc/cpp.texi b/contrib/gcc/doc/cpp.texi new file mode 100644 index 000000000000..3572384613cf --- /dev/null +++ b/contrib/gcc/doc/cpp.texi @@ -0,0 +1,4302 @@ +\input texinfo +@setfilename cpp.info +@settitle The C Preprocessor +@setchapternewpage off +@c @smallbook +@c @cropmarks +@c @finalout + +@macro copyrightnotice +@c man begin COPYRIGHT +Copyright @copyright{} 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, +1997, 1998, 1999, 2000, 2001 +Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation. A copy of +the license is included in the +@c man end +section entitled ``GNU Free Documentation License''. +@ignore +@c man begin COPYRIGHT +man page gfdl(7). +@c man end +@end ignore +@end macro + +@macro covertexts +@c man begin COPYRIGHT +This manual contains no Invariant Sections. The Front-Cover Texts are +(a) (see below), and the Back-Cover Texts are (b) (see below). + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@end macro + +@macro gcctabopt{body} +@code{\body\} +@end macro + +@ifinfo +@dircategory Programming +@direntry +* Cpp: (cpp). The GNU C preprocessor. +@end direntry +@end ifinfo + +@titlepage +@title The C Preprocessor +@subtitle Last revised April 2001 +@subtitle for GCC version 3 +@author Richard M. Stallman +@author Zachary Weinberg +@page +@c There is a fill at the bottom of the page, so we need a filll to +@c override it. +@vskip 0pt plus 1filll +@copyrightnotice{} +@covertexts{} +@end titlepage +@contents +@page + +@node Top +@top +The C preprocessor implements the macro language used to transform C, +C++, and Objective-C programs before they are compiled. It can also be +useful on its own. + +@menu +* Overview:: +* Header Files:: +* Macros:: +* Conditionals:: +* Diagnostics:: +* Line Control:: +* Pragmas:: +* Other Directives:: +* Preprocessor Output:: +* Traditional Mode:: +* Implementation Details:: +* Invocation:: +* GNU Free Documentation License:: +* Index of Directives:: +* Concept Index:: + +@detailmenu + --- The Detailed Node Listing --- + +Overview + +* Initial processing:: +* Tokenization:: +* The preprocessing language:: + +Header Files + +* Include Syntax:: +* Include Operation:: +* Search Path:: +* Once-Only Headers:: +* Computed Includes:: +* Wrapper Headers:: +* System Headers:: + +Macros + +* Object-like Macros:: +* Function-like Macros:: +* Macro Arguments:: +* Stringification:: +* Concatenation:: +* Variadic Macros:: +* Predefined Macros:: +* Undefining and Redefining Macros:: +* Macro Pitfalls:: + +Predefined Macros + +* Standard Predefined Macros:: +* Common Predefined Macros:: +* System-specific Predefined Macros:: +* C++ Named Operators:: + +Macro Pitfalls + +* Misnesting:: +* Operator Precedence Problems:: +* Swallowing the Semicolon:: +* Duplication of Side Effects:: +* Self-Referential Macros:: +* Argument Prescan:: +* Newlines in Arguments:: + +Conditionals + +* Conditional Uses:: +* Conditional Syntax:: +* Deleted Code:: + +Conditional Syntax + +* Ifdef:: +* If:: +* Defined:: +* Else:: +* Elif:: + +Implementation Details + +* Implementation-defined behavior:: +* Implementation limits:: +* Obsolete Features:: +* Differences from previous versions:: + +Obsolete Features + +* Assertions:: +* Obsolete once-only headers:: +* Miscellaneous obsolete features:: + +@end detailmenu +@end menu + +@ifnottex +@copyrightnotice{} +@covertexts{} +@end ifnottex + +@node Overview +@chapter Overview +@c man begin DESCRIPTION +The C preprocessor, often known as @dfn{cpp}, is a @dfn{macro processor} +that is used automatically by the C compiler to transform your program +before compilation. It is called a macro processor because it allows +you to define @dfn{macros}, which are brief abbreviations for longer +constructs. + +The C preprocessor is intended to be used only with C, C++, and +Objective-C source code. In the past, it has been abused as a general +text processor. It will choke on input which does not obey C's lexical +rules. For example, apostrophes will be interpreted as the beginning of +character constants, and cause errors. Also, you cannot rely on it +preserving characteristics of the input which are not significant to +C-family languages. If a Makefile is preprocessed, all the hard tabs +will be removed, and the Makefile will not work. + +Having said that, you can often get away with using cpp on things which +are not C@. Other Algol-ish programming languages are often safe +(Pascal, Ada, etc.) So is assembly, with caution. @option{-traditional} +mode preserves more white space, and is otherwise more permissive. Many +of the problems can be avoided by writing C or C++ style comments +instead of native language comments, and keeping macros simple. + +Wherever possible, you should use a preprocessor geared to the language +you are writing in. Modern versions of the GNU assembler have macro +facilities. Most high level programming languages have their own +conditional compilation and inclusion mechanism. If all else fails, +try a true general text processor, such as GNU M4. + +C preprocessors vary in some details. This manual discusses the GNU C +preprocessor, which provides a small superset of the features of ISO +Standard C@. In its default mode, the GNU C preprocessor does not do a +few things required by the standard. These are features which are +rarely, if ever, used, and may cause surprising changes to the meaning +of a program which does not expect them. To get strict ISO Standard C, +you should use the @option{-std=c89} or @option{-std=c99} options, depending +on which version of the standard you want. To get all the mandatory +diagnostics, you must also use @option{-pedantic}. @xref{Invocation}. +@c man end + +@menu +* Initial processing:: +* Tokenization:: +* The preprocessing language:: +@end menu + +@node Initial processing +@section Initial processing + +The preprocessor performs a series of textual transformations on its +input. These happen before all other processing. Conceptually, they +happen in a rigid order, and the entire file is run through each +transformation before the next one begins. GNU CPP actually does them +all at once, for performance reasons. These transformations correspond +roughly to the first three ``phases of translation'' described in the C +standard. + +@enumerate +@item +@cindex character sets +@cindex line endings +The input file is read into memory and broken into lines. + +GNU CPP expects its input to be a text file, that is, an unstructured +stream of ASCII characters, with some characters indicating the end of a +line of text. Extended ASCII character sets, such as ISO Latin-1 or +Unicode encoded in UTF-8, are also acceptable. Character sets that are +not strict supersets of seven-bit ASCII will not work. We plan to add +complete support for international character sets in a future release. + +Different systems use different conventions to indicate the end of a +line. GCC accepts the ASCII control sequences @kbd{LF}, @kbd{@w{CR +LF}}, @kbd{CR}, and @kbd{@w{LF CR}} as end-of-line markers. The first +three are the canonical sequences used by Unix, DOS and VMS, and the +classic Mac OS (before OSX) respectively. You may therefore safely copy +source code written on any of those systems to a different one and use +it without conversion. (GCC may lose track of the current line number +if a file doesn't consistently use one convention, as sometimes happens +when it is edited on computers with different conventions that share a +network file system.) @kbd{@w{LF CR}} is included because it has been +reported as an end-of-line marker under exotic conditions. + +If the last line of any input file lacks an end-of-line marker, the end +of the file is considered to implicitly supply one. The C standard says +that this condition provokes undefined behavior, so GCC will emit a +warning message. + +@item +@cindex trigraphs +If trigraphs are enabled, they are replaced by their corresponding +single characters. + +These are nine three-character sequences, all starting with @samp{??}, +that are defined by ISO C to stand for single characters. They permit +obsolete systems that lack some of C's punctuation to use C@. For +example, @samp{??/} stands for @samp{\}, so @t{'??/n'} is a character +constant for a newline. By default, GCC ignores trigraphs, but if you +request a strictly conforming mode with the @option{-std} option, then +it converts them. + +Trigraphs are not popular and many compilers implement them incorrectly. +Portable code should not rely on trigraphs being either converted or +ignored. If you use the @option{-Wall} or @option{-Wtrigraphs} options, +GCC will warn you when a trigraph would change the meaning of your +program if it were converted. + +In a string constant, you can prevent a sequence of question marks from +being confused with a trigraph by inserting a backslash between the +question marks. @t{"(??\?)"} is the string @samp{(???)}, not +@samp{(?]}. Traditional C compilers do not recognize this idiom. + +The nine trigraphs and their replacements are + +@example +Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- +Replacement: [ ] @{ @} # \ ^ | ~ +@end example + +@item +@cindex continued lines +@cindex backslash-newline +Continued lines are merged into one long line. + +A continued line is a line which ends with a backslash, @samp{\}. The +backslash is removed and the following line is joined with the current +one. No space is inserted, so you may split a line anywhere, even in +the middle of a word. (It is generally more readable to split lines +only at white space.) + +The trailing backslash on a continued line is commonly referred to as a +@dfn{backslash-newline}. + +If there is white space between a backslash and the end of a line, that +is still a continued line. However, as this is usually the result of an +editing mistake, and many compilers will not accept it as a continued +line, GCC will warn you about it. + +@item +@cindex comments +@cindex line comments +@cindex block comments +All comments are replaced with single spaces. + +There are two kinds of comments. @dfn{Block comments} begin with +@samp{/*} and continue until the next @samp{*/}. Block comments do not +nest: + +@example +/* @r{this is} /* @r{one comment} */ @r{text outside comment} +@end example + +@dfn{Line comments} begin with @samp{//} and continue to the end of the +current line. Line comments do not nest either, but it does not matter, +because they would end in the same place anyway. + +@example +// @r{this is} // @r{one comment} +@r{text outside comment} +@end example +@end enumerate + +It is safe to put line comments inside block comments, or vice versa. + +@example +@group +/* @r{block comment} + // @r{contains line comment} + @r{yet more comment} + */ @r{outside comment} + +// @r{line comment} /* @r{contains block comment} */ +@end group +@end example + +But beware of commenting out one end of a block comment with a line +comment. + +@example +@group + // @r{l.c.} /* @r{block comment begins} + @r{oops! this isn't a comment anymore} */ +@end group +@end example + +Comments are not recognized within string literals. @t{@w{"/* blah +*/"}} is the string constant @samp{@w{/* blah */}}, not an empty string. + +Line comments are not in the 1989 edition of the C standard, but they +are recognized by GCC as an extension. In C++ and in the 1999 edition +of the C standard, they are an official part of the language. + +Since these transformations happen before all other processing, you can +split a line mechanically with backslash-newline anywhere. You can +comment out the end of a line. You can continue a line comment onto the +next line with backslash-newline. You can even split @samp{/*}, +@samp{*/}, and @samp{//} onto multiple lines with backslash-newline. +For example: + +@example +@group +/\ +* +*/ # /* +*/ defi\ +ne FO\ +O 10\ +20 +@end group +@end example + +@noindent +is equivalent to @code{@w{#define FOO 1020}}. All these tricks are +extremely confusing and should not be used in code intended to be +readable. + +There is no way to prevent a backslash at the end of a line from being +interpreted as a backslash-newline. + +@example +"foo\\ +bar" +@end example + +@noindent +is equivalent to @code{"foo\bar"}, not to @code{"foo\\bar"}. To avoid +having to worry about this, do not use the deprecated GNU extension +which permits multi-line strings. Instead, use string literal +concatenation: + +@example + "foo\\" + "bar" +@end example + +@noindent +Your program will be more portable this way, too. + +@node Tokenization +@section Tokenization + +@cindex tokens +@cindex preprocessing tokens +After the textual transformations are finished, the input file is +converted into a sequence of @dfn{preprocessing tokens}. These mostly +correspond to the syntactic tokens used by the C compiler, but there are +a few differences. White space separates tokens; it is not itself a +token of any kind. Tokens do not have to be separated by white space, +but it is often necessary to avoid ambiguities. + +When faced with a sequence of characters that has more than one possible +tokenization, the preprocessor is greedy. It always makes each token, +starting from the left, as big as possible before moving on to the next +token. For instance, @code{a+++++b} is interpreted as +@code{@w{a ++ ++ + b}}, not as @code{@w{a ++ + ++ b}}, even though the +latter tokenization could be part of a valid C program and the former +could not. + +Once the input file is broken into tokens, the token boundaries never +change, except when the @samp{##} preprocessing operator is used to paste +tokens together. @xref{Concatenation}. For example, + +@example +@group +#define foo() bar +foo()baz + @expansion{} bar baz +@emph{not} + @expansion{} barbaz +@end group +@end example + +The compiler does not re-tokenize the preprocessor's output. Each +preprocessing token becomes one compiler token. + +@cindex identifiers +Preprocessing tokens fall into five broad classes: identifiers, +preprocessing numbers, string literals, punctuators, and other. An +@dfn{identifier} is the same as an identifier in C: any sequence of +letters, digits, or underscores, which begins with a letter or +underscore. Keywords of C have no significance to the preprocessor; +they are ordinary identifiers. You can define a macro whose name is a +keyword, for instance. The only identifier which can be considered a +preprocessing keyword is @code{defined}. @xref{Defined}. + +This is mostly true of other languages which use the C preprocessor. +However, a few of the keywords of C++ are significant even in the +preprocessor. @xref{C++ Named Operators}. + +In the 1999 C standard, identifiers may contain letters which are not +part of the ``basic source character set,'' at the implementation's +discretion (such as accented Latin letters, Greek letters, or Chinese +ideograms). This may be done with an extended character set, or the +@samp{\u} and @samp{\U} escape sequences. GCC does not presently +implement either feature in the preprocessor or the compiler. + +As an extension, GCC treats @samp{$} as a letter. This is for +compatibility with some systems, such as VMS, where @samp{$} is commonly +used in system-defined function and object names. @samp{$} is not a +letter in strictly conforming mode, or if you specify the @option{-$} +option. @xref{Invocation}. + +@cindex numbers +@cindex preprocessing numbers +A @dfn{preprocessing number} has a rather bizarre definition. The +category includes all the normal integer and floating point constants +one expects of C, but also a number of other things one might not +initially recognize as a number. Formally, preprocessing numbers begin +with an optional period, a required decimal digit, and then continue +with any sequence of letters, digits, underscores, periods, and +exponents. Exponents are the two-character sequences @samp{e+}, +@samp{e-}, @samp{E+}, @samp{E-}, @samp{p+}, @samp{p-}, @samp{P+}, and +@samp{P-}. (The exponents that begin with @samp{p} or @samp{P} are new +to C99. They are used for hexadecimal floating-point constants.) + +The purpose of this unusual definition is to isolate the preprocessor +from the full complexity of numeric constants. It does not have to +distinguish between lexically valid and invalid floating-point numbers, +which is complicated. The definition also permits you to split an +identifier at any position and get exactly two tokens, which can then be +pasted back together with the @samp{##} operator. + +It's possible for preprocessing numbers to cause programs to be +misinterpreted. For example, @code{0xE+12} is a preprocessing number +which does not translate to any valid numeric constant, therefore a +syntax error. It does not mean @code{@w{0xE + 12}}, which is what you +might have intended. + +@cindex string literals +@cindex string constants +@cindex character constants +@cindex header file names +@c the @: prevents makeinfo from turning '' into ". +@dfn{String literals} are string constants, character constants, and +header file names (the argument of @samp{#include}).@footnote{The C +standard uses the term @dfn{string literal} to refer only to what we are +calling @dfn{string constants}.} String constants and character +constants are straightforward: @t{"@dots{}"} or @t{'@dots{}'}. In +either case embedded quotes should be escaped with a backslash: +@t{'\'@:'} is the character constant for @samp{'}. There is no limit on +the length of a character constant, but the value of a character +constant that contains more than one character is +implementation-defined. @xref{Implementation Details}. + +Header file names either look like string constants, @t{"@dots{}"}, or are +written with angle brackets instead, @t{<@dots{}>}. In either case, +backslash is an ordinary character. There is no way to escape the +closing quote or angle bracket. The preprocessor looks for the header +file in different places depending on which form you use. @xref{Include +Operation}. + +In standard C, no string literal may extend past the end of a line. GNU +CPP accepts multi-line string constants, but not multi-line character +constants or header file names. This extension is deprecated and will +be removed in GCC 3.1. You may use continued lines instead, or string +constant concatenation. @xref{Differences from previous versions}. + +@cindex punctuators +@cindex digraphs +@cindex alternative tokens +@dfn{Punctuators} are all the usual bits of punctuation which are +meaningful to C and C++. All but three of the punctuation characters in +ASCII are C punctuators. The exceptions are @samp{@@}, @samp{$}, and +@samp{`}. In addition, all the two- and three-character operators are +punctuators. There are also six @dfn{digraphs}, which the C++ standard +calls @dfn{alternative tokens}, which are merely alternate ways to spell +other punctuators. This is a second attempt to work around missing +punctuation in obsolete systems. It has no negative side effects, +unlike trigraphs, but does not cover as much ground. The digraphs and +their corresponding normal punctuators are: + +@example +Digraph: <% %> <: :> %: %:%: +Punctuator: @{ @} [ ] # ## +@end example + +@cindex other tokens +Any other single character is considered ``other.'' It is passed on to +the preprocessor's output unmolested. The C compiler will almost +certainly reject source code containing ``other'' tokens. In ASCII, the +only other characters are @samp{@@}, @samp{$}, @samp{`}, and control +characters other than NUL (all bits zero). (Note that @samp{$} is +normally considered a letter.) All characters with the high bit set +(numeric range 0x7F--0xFF) are also ``other'' in the present +implementation. This will change when proper support for international +character sets is added to GCC@. + +NUL is a special case because of the high probability that its +appearance is accidental, and because it may be invisible to the user +(many terminals do not display NUL at all). Within comments, NULs are +silently ignored, just as any other character would be. In running +text, NUL is considered white space. For example, these two directives +have the same meaning. + +@example +#define X^@@1 +#define X 1 +@end example + +@noindent +(where @samp{^@@} is ASCII NUL)@. Within string or character constants, +NULs are preserved. In the latter two cases the preprocessor emits a +warning message. + +@node The preprocessing language +@section The preprocessing language +@cindex directives +@cindex preprocessing directives +@cindex directive line +@cindex directive name + +After tokenization, the stream of tokens may simply be passed straight +to the compiler's parser. However, if it contains any operations in the +@dfn{preprocessing language}, it will be transformed first. This stage +corresponds roughly to the standard's ``translation phase 4'' and is +what most people think of as the preprocessor's job. + +The preprocessing language consists of @dfn{directives} to be executed +and @dfn{macros} to be expanded. Its primary capabilities are: + +@itemize @bullet +@item +Inclusion of header files. These are files of declarations that can be +substituted into your program. + +@item +Macro expansion. You can define @dfn{macros}, which are abbreviations +for arbitrary fragments of C code. The preprocessor will replace the +macros with their definitions throughout the program. Some macros are +automatically defined for you. + +@item +Conditional compilation. You can include or exclude parts of the +program according to various conditions. + +@item +Line control. If you use a program to combine or rearrange source files +into an intermediate file which is then compiled, you can use line +control to inform the compiler where each source line originally came +from. + +@item +Diagnostics. You can detect problems at compile time and issue errors +or warnings. +@end itemize + +There are a few more, less useful, features. + +Except for expansion of predefined macros, all these operations are +triggered with @dfn{preprocessing directives}. Preprocessing directives +are lines in your program that start with @samp{#}. Whitespace is +allowed before and after the @samp{#}. The @samp{#} is followed by an +identifier, the @dfn{directive name}. It specifies the operation to +perform. Directives are commonly referred to as @samp{#@var{name}} +where @var{name} is the directive name. For example, @samp{#define} is +the directive that defines a macro. + +The @samp{#} which begins a directive cannot come from a macro +expansion. Also, the directive name is not macro expanded. Thus, if +@code{foo} is defined as a macro expanding to @code{define}, that does +not make @samp{#foo} a valid preprocessing directive. + +The set of valid directive names is fixed. Programs cannot define new +preprocessing directives. + +Some directives require arguments; these make up the rest of the +directive line and must be separated from the directive name by +whitespace. For example, @samp{#define} must be followed by a macro +name and the intended expansion of the macro. + +A preprocessing directive cannot cover more than one line. The line +may, however, be continued with backslash-newline, or by a block comment +which extends past the end of the line. In either case, when the +directive is processed, the continuations have already been merged with +the first line to make one long line. + +@node Header Files +@chapter Header Files + +@cindex header file +A header file is a file containing C declarations and macro definitions +(@pxref{Macros}) to be shared between several source files. You request +the use of a header file in your program by @dfn{including} it, with the +C preprocessing directive @samp{#include}. + +Header files serve two purposes. + +@itemize @bullet +@item +@cindex system header files +System header files declare the interfaces to parts of the operating +system. You include them in your program to supply the definitions and +declarations you need to invoke system calls and libraries. + +@item +Your own header files contain declarations for interfaces between the +source files of your program. Each time you have a group of related +declarations and macro definitions all or most of which are needed in +several different source files, it is a good idea to create a header +file for them. +@end itemize + +Including a header file produces the same results as copying the header +file into each source file that needs it. Such copying would be +time-consuming and error-prone. With a header file, the related +declarations appear in only one place. If they need to be changed, they +can be changed in one place, and programs that include the header file +will automatically use the new version when next recompiled. The header +file eliminates the labor of finding and changing all the copies as well +as the risk that a failure to find one copy will result in +inconsistencies within a program. + +In C, the usual convention is to give header files names that end with +@file{.h}. It is most portable to use only letters, digits, dashes, and +underscores in header file names, and at most one dot. + +@menu +* Include Syntax:: +* Include Operation:: +* Search Path:: +* Once-Only Headers:: +* Computed Includes:: +* Wrapper Headers:: +* System Headers:: +@end menu + +@node Include Syntax +@section Include Syntax + +@findex #include +Both user and system header files are included using the preprocessing +directive @samp{#include}. It has two variants: + +@table @code +@item #include <@var{file}> +This variant is used for system header files. It searches for a file +named @var{file} in a standard list of system directories. You can prepend +directories to this list with the @option{-I} option (@pxref{Invocation}). + +@item #include "@var{file}" +This variant is used for header files of your own program. It searches +for a file named @var{file} first in the directory containing the +current file, then in the same directories used for @code{<@var{file}>}. +@end table + +The argument of @samp{#include}, whether delimited with quote marks or +angle brackets, behaves like a string constant in that comments are not +recognized, and macro names are not expanded. Thus, @code{@w{#include +}} specifies inclusion of a system header file named @file{x/*y}. + +However, if backslashes occur within @var{file}, they are considered +ordinary text characters, not escape characters. None of the character +escape sequences appropriate to string constants in C are processed. +Thus, @code{@w{#include "x\n\\y"}} specifies a filename containing three +backslashes. (Some systems interpret @samp{\} as a pathname separator. +All of these also interpret @samp{/} the same way. It is most portable +to use only @samp{/}.) + +It is an error if there is anything (other than comments) on the line +after the file name. + +@node Include Operation +@section Include Operation + +The @samp{#include} directive works by directing the C preprocessor to +scan the specified file as input before continuing with the rest of the +current file. The output from the preprocessor contains the output +already generated, followed by the output resulting from the included +file, followed by the output that comes from the text after the +@samp{#include} directive. For example, if you have a header file +@file{header.h} as follows, + +@example +char *test (void); +@end example + +@noindent +and a main program called @file{program.c} that uses the header file, +like this, + +@example +int x; +#include "header.h" + +int +main (void) +@{ + puts (test ()); +@} +@end example + +@noindent +the compiler will see the same token stream as it would if +@file{program.c} read + +@example +int x; +char *test (void); + +int +main (void) +@{ + puts (test ()); +@} +@end example + +Included files are not limited to declarations and macro definitions; +those are merely the typical uses. Any fragment of a C program can be +included from another file. The include file could even contain the +beginning of a statement that is concluded in the containing file, or +the end of a statement that was started in the including file. However, +a comment or a string or character constant may not start in the +included file and finish in the including file. An unterminated +comment, string constant or character constant in an included file is +considered to end (with an error message) at the end of the file. + +To avoid confusion, it is best if header files contain only complete +syntactic units---function declarations or definitions, type +declarations, etc. + +The line following the @samp{#include} directive is always treated as a +separate line by the C preprocessor, even if the included file lacks a +final newline. + +@node Search Path +@section Search Path + +GCC looks in several different places for headers. On a normal Unix +system, if you do not instruct it otherwise, it will look for headers +requested with @code{@w{#include <@var{file}>}} in: + +@example +/usr/local/include +/usr/lib/gcc-lib/@var{target}/@var{version}/include +/usr/@var{target}/include +/usr/include +@end example + +For C++ programs, it will also look in @file{/usr/include/g++-v3}, +first. In the above, @var{target} is the canonical name of the system +GCC was configured to compile code for; often but not always the same as +the canonical name of the system it runs on. @var{version} is the +version of GCC in use. + +You can add to this list with the @option{-I@var{dir}} command line +option. All the directories named by @option{-I} are searched, in +left-to-right order, @emph{before} the default directories. You can +also prevent GCC from searching any of the default directories with the +@option{-nostdinc} option. This is useful when you are compiling an +operating system kernel or some other program that does not use the +standard C library facilities, or the standard C library itself. + +GCC looks for headers requested with @code{@w{#include "@var{file}"}} +first in the directory containing the current file, then in the same +places it would have looked for a header requested with angle brackets. +For example, if @file{/usr/include/sys/stat.h} contains +@code{@w{#include "types.h"}}, GCC looks for @file{types.h} first in +@file{/usr/include/sys}, then in its usual search path. + +If you name a search directory with @option{-I@var{dir}} that is also a +system include directory, the @option{-I} wins; the directory will be +searched according to the @option{-I} ordering, and it will not be +treated as a system include directory. GCC will warn you when a system +include directory is hidden in this way. + +@samp{#line} (@pxref{Line Control}) does not change GCC's idea of the +directory containing the current file. + +You may put @option{-I-} at any point in your list of @option{-I} options. +This has two effects. First, directories appearing before the +@option{-I-} in the list are searched only for headers requested with +quote marks. Directories after @option{-I-} are searched for all +headers. Second, the directory containing the current file is not +searched for anything, unless it happens to be one of the directories +named by an @option{-I} switch. + +@option{-I. -I-} is not the same as no @option{-I} options at all, and does +not cause the same behavior for @samp{<>} includes that @samp{""} +includes get with no special options. @option{-I.} searches the +compiler's current working directory for header files. That may or may +not be the same as the directory containing the current file. + +If you need to look for headers in a directory named @file{-}, write +@option{-I./-}. + +There are several more ways to adjust the header search path. They are +generally less useful. @xref{Invocation}. + +@node Once-Only Headers +@section Once-Only Headers +@cindex repeated inclusion +@cindex including just once +@cindex wrapper @code{#ifndef} + +If a header file happens to be included twice, the compiler will process +its contents twice. This is very likely to cause an error, e.g.@: when the +compiler sees the same structure definition twice. Even if it does not, +it will certainly waste time. + +The standard way to prevent this is to enclose the entire real contents +of the file in a conditional, like this: + +@example +@group +/* File foo. */ +#ifndef FILE_FOO_SEEN +#define FILE_FOO_SEEN + +@var{the entire file} + +#endif /* !FILE_FOO_SEEN */ +@end group +@end example + +This construct is commonly known as a @dfn{wrapper #ifndef}. +When the header is included again, the conditional will be false, +because @code{FILE_FOO_SEEN} is defined. The preprocessor will skip +over the entire contents of the file, and the compiler will not see it +twice. + +GNU CPP optimizes even further. It remembers when a header file has a +wrapper @samp{#ifndef}. If a subsequent @samp{#include} specifies that +header, and the macro in the @samp{#ifndef} is still defined, it does +not bother to rescan the file at all. + +You can put comments outside the wrapper. They will not interfere with +this optimization. + +@cindex controlling macro +@cindex guard macro +The macro @code{FILE_FOO_SEEN} is called the @dfn{controlling macro} or +@dfn{guard macro}. In a user header file, the macro name should not +begin with @samp{_}. In a system header file, it should begin with +@samp{__} to avoid conflicts with user programs. In any kind of header +file, the macro name should contain the name of the file and some +additional text, to avoid conflicts with other header files. + +@node Computed Includes +@section Computed Includes +@cindex computed includes +@cindex macros in include + +Sometimes it is necessary to select one of several different header +files to be included into your program. They might specify +configuration parameters to be used on different sorts of operating +systems, for instance. You could do this with a series of conditionals, + +@example +#if SYSTEM_1 +# include "system_1.h" +#elif SYSTEM_2 +# include "system_2.h" +#elif SYSTEM_3 +@dots{} +#endif +@end example + +That rapidly becomes tedious. Instead, the preprocessor offers the +ability to use a macro for the header name. This is called a +@dfn{computed include}. Instead of writing a header name as the direct +argument of @samp{#include}, you simply put a macro name there instead: + +@example +#define SYSTEM_H "system_1.h" +@dots{} +#include SYSTEM_H +@end example + +@noindent +@code{SYSTEM_H} will be expanded, and the preprocessor will look for +@file{system_1.h} as if the @samp{#include} had been written that way +originally. @code{SYSTEM_H} could be defined by your Makefile with a +@option{-D} option. + +You must be careful when you define the macro. @samp{#define} saves +tokens, not text. The preprocessor has no way of knowing that the macro +will be used as the argument of @samp{#include}, so it generates +ordinary tokens, not a header name. This is unlikely to cause problems +if you use double-quote includes, which are close enough to string +constants. If you use angle brackets, however, you may have trouble. + +The syntax of a computed include is actually a bit more general than the +above. If the first non-whitespace character after @samp{#include} is +not @samp{"} or @samp{<}, then the entire line is macro-expanded +like running text would be. + +If the line expands to a single string constant, the contents of that +string constant are the file to be included. CPP does not re-examine the +string for embedded quotes, but neither does it process backslash +escapes in the string. Therefore + +@example +#define HEADER "a\"b" +#include HEADER +@end example + +@noindent +looks for a file named @file{a\"b}. CPP searches for the file according +to the rules for double-quoted includes. + +If the line expands to a token stream beginning with a @samp{<} token +and including a @samp{>} token, then the tokens between the @samp{<} and +the first @samp{>} are combined to form the filename to be included. +Any whitespace between tokens is reduced to a single space; then any +space after the initial @samp{<} is retained, but a trailing space +before the closing @samp{>} is ignored. CPP searches for the file +according to the rules for angle-bracket includes. + +In either case, if there are any tokens on the line after the file name, +an error occurs and the directive is not processed. It is also an error +if the result of expansion does not match either of the two expected +forms. + +These rules are implementation-defined behavior according to the C +standard. To minimize the risk of different compilers interpreting your +computed includes differently, we recommend you use only a single +object-like macro which expands to a string constant. This will also +minimize confusion for people reading your program. + +@node Wrapper Headers +@section Wrapper Headers +@cindex wrapper headers +@cindex overriding a header file +@findex #include_next + +Sometimes it is necessary to adjust the contents of a system-provided +header file without editing it directly. GCC's @command{fixincludes} +operation does this, for example. One way to do that would be to create +a new header file with the same name and insert it in the search path +before the original header. That works fine as long as you're willing +to replace the old header entirely. But what if you want to refer to +the old header from the new one? + +You cannot simply include the old header with @samp{#include}. That +will start from the beginning, and find your new header again. If your +header is not protected from multiple inclusion (@pxref{Once-Only +Headers}), it will recurse infinitely and cause a fatal error. + +You could include the old header with an absolute pathname: +@example +#include "/usr/include/old-header.h" +@end example +@noindent +This works, but is not clean; should the system headers ever move, you +would have to edit the new headers to match. + +There is no way to solve this problem within the C standard, but you can +use the GNU extension @samp{#include_next}. It means, ``Include the +@emph{next} file with this name.'' This directive works like +@samp{#include} except in searching for the specified file: it starts +searching the list of header file directories @emph{after} the directory +in which the current file was found. + +Suppose you specify @option{-I /usr/local/include}, and the list of +directories to search also includes @file{/usr/include}; and suppose +both directories contain @file{signal.h}. Ordinary @code{@w{#include +}} finds the file under @file{/usr/local/include}. If that +file contains @code{@w{#include_next }}, it starts searching +after that directory, and finds the file in @file{/usr/include}. + +@samp{#include_next} does not distinguish between @code{<@var{file}>} +and @code{"@var{file}"} inclusion, nor does it check that the file you +specify has the same name as the current file. It simply looks for the +file named, starting with the directory in the search path after the one +where the current file was found. + +The use of @samp{#include_next} can lead to great confusion. We +recommend it be used only when there is no other alternative. In +particular, it should not be used in the headers belonging to a specific +program; it should be used only to make global corrections along the +lines of @command{fixincludes}. + +@node System Headers +@section System Headers +@cindex system header files + +The header files declaring interfaces to the operating system and +runtime libraries often cannot be written in strictly conforming C@. +Therefore, GCC gives code found in @dfn{system headers} special +treatment. All warnings, other than those generated by @samp{#warning} +(@pxref{Diagnostics}), are suppressed while GCC is processing a system +header. Macros defined in a system header are immune to a few warnings +wherever they are expanded. This immunity is granted on an ad-hoc +basis, when we find that a warning generates lots of false positives +because of code in macros defined in system headers. + +Normally, only the headers found in specific directories are considered +system headers. These directories are determined when GCC is compiled. +There are, however, two ways to make normal headers into system headers. + +The @option{-isystem} command line option adds its argument to the list of +directories to search for headers, just like @option{-I}. Any headers +found in that directory will be considered system headers. + +All directories named by @option{-isystem} are searched @emph{after} all +directories named by @option{-I}, no matter what their order was on the +command line. If the same directory is named by both @option{-I} and +@option{-isystem}, @option{-I} wins; it is as if the @option{-isystem} option +had never been specified at all. GCC warns you when this happens. + +@findex #pragma GCC system_header +There is also a directive, @code{@w{#pragma GCC system_header}}, which +tells GCC to consider the rest of the current include file a system +header, no matter where it was found. Code that comes before the +@samp{#pragma} in the file will not be affected. @code{@w{#pragma GCC +system_header}} has no effect in the primary source file. + +On very old systems, some of the pre-defined system header directories +get even more special treatment. GNU C++ considers code in headers +found in those directories to be surrounded by an @code{@w{extern "C"}} +block. There is no way to request this behavior with a @samp{#pragma}, +or from the command line. + +@node Macros +@chapter Macros + +A @dfn{macro} is a fragment of code which has been given a name. +Whenever the name is used, it is replaced by the contents of the macro. +There are two kinds of macros. They differ mostly in what they look +like when they are used. @dfn{Object-like} macros resemble data objects +when used, @dfn{function-like} macros resemble function calls. + +You may define any valid identifier as a macro, even if it is a C +keyword. The preprocessor does not know anything about keywords. This +can be useful if you wish to hide a keyword such as @code{const} from an +older compiler that does not understand it. However, the preprocessor +operator @code{defined} (@pxref{Defined}) can never be defined as a +macro, and C++'s named operators (@pxref{C++ Named Operators}) cannot be +macros when you are compiling C++. + +@menu +* Object-like Macros:: +* Function-like Macros:: +* Macro Arguments:: +* Stringification:: +* Concatenation:: +* Variadic Macros:: +* Predefined Macros:: +* Undefining and Redefining Macros:: +* Macro Pitfalls:: +@end menu + +@node Object-like Macros +@section Object-like Macros +@cindex object-like macro +@cindex symbolic constants +@cindex manifest constants + +An @dfn{object-like macro} is a simple identifier which will be replaced +by a code fragment. It is called object-like because it looks like a +data object in code that uses it. They are most commonly used to give +symbolic names to numeric constants. + +@findex #define +You create macros with the @samp{#define} directive. @samp{#define} is +followed by the name of the macro and then the token sequence it should +be an abbreviation for, which is variously referred to as the macro's +@dfn{body}, @dfn{expansion} or @dfn{replacement list}. For example, + +@example +#define BUFFER_SIZE 1024 +@end example + +@noindent +defines a macro named @code{BUFFER_SIZE} as an abbreviation for the +token @code{1024}. If somewhere after this @samp{#define} directive +there comes a C statement of the form + +@example +foo = (char *) malloc (BUFFER_SIZE); +@end example + +@noindent +then the C preprocessor will recognize and @dfn{expand} the macro +@code{BUFFER_SIZE}. The C compiler will see the same tokens as it would +if you had written + +@example +foo = (char *) malloc (1024); +@end example + +By convention, macro names are written in upper case. Programs are +easier to read when it is possible to tell at a glance which names are +macros. + +The macro's body ends at the end of the @samp{#define} line. You may +continue the definition onto multiple lines, if necessary, using +backslash-newline. When the macro is expanded, however, it will all +come out on one line. For example, + +@example +#define NUMBERS 1, \ + 2, \ + 3 +int x[] = @{ NUMBERS @}; + @expansion{} int x[] = @{ 1, 2, 3 @}; +@end example + +@noindent +The most common visible consequence of this is surprising line numbers +in error messages. + +There is no restriction on what can go in a macro body provided it +decomposes into valid preprocessing tokens. Parentheses need not +balance, and the body need not resemble valid C code. (If it does not, +you may get error messages from the C compiler when you use the macro.) + +The C preprocessor scans your program sequentially. Macro definitions +take effect at the place you write them. Therefore, the following input +to the C preprocessor + +@example +foo = X; +#define X 4 +bar = X; +@end example + +@noindent +produces + +@example +foo = X; +bar = 4; +@end example + +When the preprocessor expands a macro name, the macro's expansion +replaces the macro invocation, then the expansion is examined for more +macros to expand. For example, + +@example +@group +#define TABLESIZE BUFSIZE +#define BUFSIZE 1024 +TABLESIZE + @expansion{} BUFSIZE + @expansion{} 1024 +@end group +@end example + +@noindent +@code{TABLESIZE} is expanded first to produce @code{BUFSIZE}, then that +macro is expanded to produce the final result, @code{1024}. + +Notice that @code{BUFSIZE} was not defined when @code{TABLESIZE} was +defined. The @samp{#define} for @code{TABLESIZE} uses exactly the +expansion you specify---in this case, @code{BUFSIZE}---and does not +check to see whether it too contains macro names. Only when you +@emph{use} @code{TABLESIZE} is the result of its expansion scanned for +more macro names. + +This makes a difference if you change the definition of @code{BUFSIZE} +at some point in the source file. @code{TABLESIZE}, defined as shown, +will always expand using the definition of @code{BUFSIZE} that is +currently in effect: + +@example +#define BUFSIZE 1020 +#define TABLESIZE BUFSIZE +#undef BUFSIZE +#define BUFSIZE 37 +@end example + +@noindent +Now @code{TABLESIZE} expands (in two stages) to @code{37}. + +If the expansion of a macro contains its own name, either directly or +via intermediate macros, it is not expanded again when the expansion is +examined for more macros. This prevents infinite recursion. +@xref{Self-Referential Macros}, for the precise details. + +@node Function-like Macros +@section Function-like Macros +@cindex function-like macros + +You can also define macros whose use looks like a function call. These +are called @dfn{function-like macros}. To define a function-like macro, +you use the same @samp{#define} directive, but you put a pair of +parentheses immediately after the macro name. For example, + +@example +#define lang_init() c_init() +lang_init() + @expansion{} c_init() +@end example + +A function-like macro is only expanded if its name appears with a pair +of parentheses after it. If you write just the name, it is left alone. +This can be useful when you have a function and a macro of the same +name, and you wish to use the function sometimes. + +@example +extern void foo(void); +#define foo() /* optimized inline version */ +@dots{} + foo(); + funcptr = foo; +@end example + +Here the call to @code{foo()} will use the macro, but the function +pointer will get the address of the real function. If the macro were to +be expanded, it would cause a syntax error. + +If you put spaces between the macro name and the parentheses in the +macro definition, that does not define a function-like macro, it defines +an object-like macro whose expansion happens to begin with a pair of +parentheses. + +@example +#define lang_init () c_init() +lang_init() + @expansion{} () c_init()() +@end example + +The first two pairs of parentheses in this expansion come from the +macro. The third is the pair that was originally after the macro +invocation. Since @code{lang_init} is an object-like macro, it does not +consume those parentheses. + +@node Macro Arguments +@section Macro Arguments +@cindex arguments +@cindex macros with arguments +@cindex arguments in macro definitions + +Function-like macros can take @dfn{arguments}, just like true functions. +To define a macro that uses arguments, you insert @dfn{parameters} +between the pair of parentheses in the macro definition that make the +macro function-like. The parameters must be valid C identifiers, +separated by commas and optionally whitespace. + +To invoke a macro that takes arguments, you write the name of the macro +followed by a list of @dfn{actual arguments} in parentheses, separated +by commas. The invocation of the macro need not be restricted to a +single logical line---it can cross as many lines in the source file as +you wish. The number of arguments you give must match the number of +parameters in the macro definition. When the macro is expanded, each +use of a parameter in its body is replaced by the tokens of the +corresponding argument. (You need not use all of the parameters in the +macro body.) + +As an example, here is a macro that computes the minimum of two numeric +values, as it is defined in many C programs, and some uses. + +@example +#define min(X, Y) ((X) < (Y) ? (X) : (Y)) + x = min(a, b); @expansion{} x = ((a) < (b) ? (a) : (b)); + y = min(1, 2); @expansion{} y = ((1) < (2) ? (1) : (2)); + z = min(a + 28, *p); @expansion{} z = ((a + 28) < (*p) ? (a + 28) : (*p)); +@end example + +@noindent +(In this small example you can already see several of the dangers of +macro arguments. @xref{Macro Pitfalls}, for detailed explanations.) + +Leading and trailing whitespace in each argument is dropped, and all +whitespace between the tokens of an argument is reduced to a single +space. Parentheses within each argument must balance; a comma within +such parentheses does not end the argument. However, there is no +requirement for square brackets or braces to balance, and they do not +prevent a comma from separating arguments. Thus, + +@example +macro (array[x = y, x + 1]) +@end example + +@noindent +passes two arguments to @code{macro}: @code{array[x = y} and @code{x + +1]}. If you want to supply @code{array[x = y, x + 1]} as an argument, +you can write it as @code{array[(x = y, x + 1)]}, which is equivalent C +code. + +All arguments to a macro are completely macro-expanded before they are +substituted into the macro body. After substitution, the complete text +is scanned again for macros to expand, including the arguments. This rule +may seem strange, but it is carefully designed so you need not worry +about whether any function call is actually a macro invocation. You can +run into trouble if you try to be too clever, though. @xref{Argument +Prescan}, for detailed discussion. + +For example, @code{min (min (a, b), c)} is first expanded to + +@example + min (((a) < (b) ? (a) : (b)), (c)) +@end example + +@noindent +and then to + +@example +@group +((((a) < (b) ? (a) : (b))) < (c) + ? (((a) < (b) ? (a) : (b))) + : (c)) +@end group +@end example + +@noindent +(Line breaks shown here for clarity would not actually be generated.) + +@cindex empty macro arguments +You can leave macro arguments empty; this is not an error to the +preprocessor (but many macros will then expand to invalid code). +You cannot leave out arguments entirely; if a macro takes two arguments, +there must be exactly one comma at the top level of its argument list. +Here are some silly examples using @code{min}: + +@example +min(, b) @expansion{} (( ) < (b) ? ( ) : (b)) +min(a, ) @expansion{} ((a ) < ( ) ? (a ) : ( )) +min(,) @expansion{} (( ) < ( ) ? ( ) : ( )) +min((,),) @expansion{} (((,)) < ( ) ? ((,)) : ( )) + +min() @error{} macro "min" requires 2 arguments, but only 1 given +min(,,) @error{} macro "min" passed 3 arguments, but takes just 2 +@end example + +Whitespace is not a preprocessing token, so if a macro @code{foo} takes +one argument, @code{@w{foo ()}} and @code{@w{foo ( )}} both supply it an +empty argument. Previous GNU preprocessor implementations and +documentation were incorrect on this point, insisting that a +function-like macro that takes a single argument be passed a space if an +empty argument was required. + +Macro parameters appearing inside string literals are not replaced by +their corresponding actual arguments. + +@example +#define foo(x) x, "x" +foo(bar) @expansion{} bar, "x" +@end example + +@node Stringification +@section Stringification +@cindex stringification +@cindex @samp{#} operator + +Sometimes you may want to convert a macro argument into a string +constant. Parameters are not replaced inside string constants, but you +can use the @samp{#} preprocessing operator instead. When a macro +parameter is used with a leading @samp{#}, the preprocessor replaces it +with the literal text of the actual argument, converted to a string +constant. Unlike normal parameter replacement, the argument is not +macro-expanded first. This is called @dfn{stringification}. + +There is no way to combine an argument with surrounding text and +stringify it all together. Instead, you can write a series of adjacent +string constants and stringified arguments. The preprocessor will +replace the stringified arguments with string constants. The C +compiler will then combine all the adjacent string constants into one +long string. + +Here is an example of a macro definition that uses stringification: + +@example +@group +#define WARN_IF(EXP) \ +do @{ if (EXP) \ + fprintf (stderr, "Warning: " #EXP "\n"); @} \ +while (0) +WARN_IF (x == 0); + @expansion{} do @{ if (x == 0) + fprintf (stderr, "Warning: " "x == 0" "\n"); @} while (0); +@end group +@end example + +@noindent +The argument for @code{EXP} is substituted once, as-is, into the +@code{if} statement, and once, stringified, into the argument to +@code{fprintf}. If @code{x} were a macro, it would be expanded in the +@code{if} statement, but not in the string. + +The @code{do} and @code{while (0)} are a kludge to make it possible to +write @code{WARN_IF (@var{arg});}, which the resemblance of +@code{WARN_IF} to a function would make C programmers want to do; see +@ref{Swallowing the Semicolon}. + +Stringification in C involves more than putting double-quote characters +around the fragment. The preprocessor backslash-escapes the quotes +surrounding embedded string constants, and all backslashes within string and +character constants, in order to get a valid C string constant with the +proper contents. Thus, stringifying @code{@w{p = "foo\n";}} results in +@t{@w{"p = \"foo\\n\";"}}. However, backslashes that are not inside string +or character constants are not duplicated: @samp{\n} by itself +stringifies to @t{"\n"}. + +All leading and trailing whitespace in text being stringified is +ignored. Any sequence of whitespace in the middle of the text is +converted to a single space in the stringified result. Comments are +replaced by whitespace long before stringification happens, so they +never appear in stringified text. + +There is no way to convert a macro argument into a character constant. + +If you want to stringify the result of expansion of a macro argument, +you have to use two levels of macros. + +@example +#define xstr(s) str(s) +#define str(s) #s +#define foo 4 +str (foo) + @expansion{} "foo" +xstr (foo) + @expansion{} xstr (4) + @expansion{} str (4) + @expansion{} "4" +@end example + +@code{s} is stringified when it is used in @code{str}, so it is not +macro-expanded first. But @code{s} is an ordinary argument to +@code{xstr}, so it is completely macro-expanded before @code{xstr} +itself is expanded (@pxref{Argument Prescan}). Therefore, by the time +@code{str} gets to its argument, it has already been macro-expanded. + +@node Concatenation +@section Concatenation +@cindex concatenation +@cindex token pasting +@cindex token concatenation +@cindex @samp{##} operator + +It is often useful to merge two tokens into one while expanding macros. +This is called @dfn{token pasting} or @dfn{token concatenation}. The +@samp{##} preprocessing operator performs token pasting. When a macro +is expanded, the two tokens on either side of each @samp{##} operator +are combined into a single token, which then replaces the @samp{##} and +the two original tokens in the macro expansion. Usually both will be +identifiers, or one will be an identifier and the other a preprocessing +number. When pasted, they make a longer identifier. This isn't the +only valid case. It is also possible to concatenate two numbers (or a +number and a name, such as @code{1.5} and @code{e3}) into a number. +Also, multi-character operators such as @code{+=} can be formed by +token pasting. + +However, two tokens that don't together form a valid token cannot be +pasted together. For example, you cannot concatenate @code{x} with +@code{+} in either order. If you try, the preprocessor issues a warning +and emits the two tokens. Whether it puts white space between the +tokens is undefined. It is common to find unnecessary uses of @samp{##} +in complex macros. If you get this warning, it is likely that you can +simply remove the @samp{##}. + +Both the tokens combined by @samp{##} could come from the macro body, +but you could just as well write them as one token in the first place. +Token pasting is most useful when one or both of the tokens comes from a +macro argument. If either of the tokens next to an @samp{##} is a +parameter name, it is replaced by its actual argument before @samp{##} +executes. As with stringification, the actual argument is not +macro-expanded first. If the argument is empty, that @samp{##} has no +effect. + +Keep in mind that the C preprocessor converts comments to whitespace +before macros are even considered. Therefore, you cannot create a +comment by concatenating @samp{/} and @samp{*}. You can put as much +whitespace between @samp{##} and its operands as you like, including +comments, and you can put comments in arguments that will be +concatenated. However, it is an error if @samp{##} appears at either +end of a macro body. + +Consider a C program that interprets named commands. There probably +needs to be a table of commands, perhaps an array of structures declared +as follows: + +@example +@group +struct command +@{ + char *name; + void (*function) (void); +@}; +@end group + +@group +struct command commands[] = +@{ + @{ "quit", quit_command @}, + @{ "help", help_command @}, + @dots{} +@}; +@end group +@end example + +It would be cleaner not to have to give each command name twice, once in +the string constant and once in the function name. A macro which takes the +name of a command as an argument can make this unnecessary. The string +constant can be created with stringification, and the function name by +concatenating the argument with @samp{_command}. Here is how it is done: + +@example +#define COMMAND(NAME) @{ #NAME, NAME ## _command @} + +struct command commands[] = +@{ + COMMAND (quit), + COMMAND (help), + @dots{} +@}; +@end example + +@node Variadic Macros +@section Variadic Macros +@cindex variable number of arguments +@cindex macros with variable arguments +@cindex variadic macros + +A macro can be declared to accept a variable number of arguments much as +a function can. The syntax for defining the macro is similar to that of +a function. Here is an example: + +@example +#define eprintf(@dots{}) fprintf (stderr, __VA_ARGS__) +@end example + +This kind of macro is called @dfn{variadic}. When the macro is invoked, +all the tokens in its argument list after the last named argument (this +macro has none), including any commas, become the @dfn{variable +argument}. This sequence of tokens replaces the identifier +@code{@w{__VA_ARGS__}} in the macro body wherever it appears. Thus, we +have this expansion: + +@example +eprintf ("%s:%d: ", input_file, lineno) + @expansion{} fprintf (stderr, "%s:%d: ", input_file, lineno) +@end example + +The variable argument is completely macro-expanded before it is inserted +into the macro expansion, just like an ordinary argument. You may use +the @samp{#} and @samp{##} operators to stringify the variable argument +or to paste its leading or trailing token with another token. (But see +below for an important special case for @samp{##}.) + +If your macro is complicated, you may want a more descriptive name for +the variable argument than @code{@w{__VA_ARGS__}}. GNU CPP permits +this, as an extension. You may write an argument name immediately +before the @samp{@dots{}}; that name is used for the variable argument. +The @code{eprintf} macro above could be written + +@example +#define eprintf(args@dots{}) fprintf (stderr, args) +@end example + +@noindent +using this extension. You cannot use @code{__VA_ARGS__} and this +extension in the same macro. + +You can have named arguments as well as variable arguments in a variadic +macro. We could define @code{eprintf} like this, instead: + +@example +#define eprintf(format, @dots{}) fprintf (stderr, format, __VA_ARGS__) +@end example + +@noindent +This formulation looks more descriptive, but unfortunately it is less +flexible: you must now supply at least one argument after the format +string. In standard C, you cannot omit the comma separating the named +argument from the variable arguments. Furthermore, if you leave the +variable argument empty, you will get a syntax error, because +there will be an extra comma after the format string. + +@example +eprintf("success!\n", ); + @expansion{} fprintf(stderr, "success!\n", ); +@end example + +GNU CPP has a pair of extensions which deal with this problem. First, +you are allowed to leave the variable argument out entirely: + +@example +eprintf ("success!\n") + @expansion{} fprintf(stderr, "success!\n", ); +@end example + +@noindent +Second, the @samp{##} token paste operator has a special meaning when +placed between a comma and a variable argument. If you write + +@example +#define eprintf(format, @dots{}) fprintf (stderr, format, ##__VA_ARGS__) +@end example + +@noindent +and the variable argument is left out when the @code{eprintf} macro is +used, then the comma before the @samp{##} will be deleted. This does +@emph{not} happen if you pass an empty argument, nor does it happen if +the token preceding @samp{##} is anything other than a comma. + +@example +eprintf ("success!\n") + @expansion{} fprintf(stderr, "success!\n"); +@end example + +C99 mandates that the only place the identifier @code{@w{__VA_ARGS__}} +can appear is in the replacement list of a variadic macro. It may not +be used as a macro name, macro argument name, or within a different type +of macro. It may also be forbidden in open text; the standard is +ambiguous. We recommend you avoid using it except for its defined +purpose. + +Variadic macros are a new feature in C99. GNU CPP has supported them +for a long time, but only with a named variable argument +(@samp{args@dots{}}, not @samp{@dots{}} and @code{@w{__VA_ARGS__}}). If you are +concerned with portability to previous versions of GCC, you should use +only named variable arguments. On the other hand, if you are concerned +with portability to other conforming implementations of C99, you should +use only @code{@w{__VA_ARGS__}}. + +Previous versions of GNU CPP implemented the comma-deletion extension +much more generally. We have restricted it in this release to minimize +the differences from C99. To get the same effect with both this and +previous versions of GCC, the token preceding the special @samp{##} must +be a comma, and there must be white space between that comma and +whatever comes immediately before it: + +@example +#define eprintf(format, args@dots{}) fprintf (stderr, format , ##args) +@end example + +@noindent +@xref{Differences from previous versions}, for the gory details. + +@node Predefined Macros +@section Predefined Macros + +@cindex predefined macros +Several object-like macros are predefined; you use them without +supplying their definitions. They fall into three classes: standard, +common, and system-specific. + +In C++, there is a fourth category, the named operators. They act like +predefined macros, but you cannot undefine them. + +@menu +* Standard Predefined Macros:: +* Common Predefined Macros:: +* System-specific Predefined Macros:: +* C++ Named Operators:: +@end menu + +@node Standard Predefined Macros +@subsection Standard Predefined Macros +@cindex standard predefined macros. + +The standard predefined macros are specified by the C and/or C++ +language standards, so they are available with all compilers that +implement those standards. Older compilers may not provide all of +them. Their names all start with double underscores. + +@table @code +@item __FILE__ +This macro expands to the name of the current input file, in the form of +a C string constant. This is the path by which the preprocessor opened +the file, not the short name specified in @samp{#include} or as the +input file name argument. For example, +@code{"/usr/local/include/myheader.h"} is a possible expansion of this +macro. + +@item __LINE__ +This macro expands to the current input line number, in the form of a +decimal integer constant. While we call it a predefined macro, it's +a pretty strange macro, since its ``definition'' changes with each +new line of source code. +@end table + +@code{__FILE__} and @code{__LINE__} are useful in generating an error +message to report an inconsistency detected by the program; the message +can state the source line at which the inconsistency was detected. For +example, + +@example +fprintf (stderr, "Internal error: " + "negative string length " + "%d at %s, line %d.", + length, __FILE__, __LINE__); +@end example + +An @samp{#include} directive changes the expansions of @code{__FILE__} +and @code{__LINE__} to correspond to the included file. At the end of +that file, when processing resumes on the input file that contained +the @samp{#include} directive, the expansions of @code{__FILE__} and +@code{__LINE__} revert to the values they had before the +@samp{#include} (but @code{__LINE__} is then incremented by one as +processing moves to the line after the @samp{#include}). + +A @samp{#line} directive changes @code{__LINE__}, and may change +@code{__FILE__} as well. @xref{Line Control}. + +C99 introduces @code{__func__}, and GCC has provided @code{__FUNCTION__} +for a long time. Both of these are strings containing the name of the +current function (there are slight semantic differences; see the GCC +manual). Neither of them is a macro; the preprocessor does not know the +name of the current function. They tend to be useful in conjunction +with @code{__FILE__} and @code{__LINE__}, though. + +@table @code + +@item __DATE__ +This macro expands to a string constant that describes the date on which +the preprocessor is being run. The string constant contains eleven +characters and looks like @code{@w{"Feb 12 1996"}}. If the day of the +month is less than 10, it is padded with a space on the left. + +@item __TIME__ +This macro expands to a string constant that describes the time at +which the preprocessor is being run. The string constant contains +eight characters and looks like @code{"23:59:01"}. + +@item __STDC__ +In normal operation, this macro expands to the constant 1, to signify +that this compiler conforms to ISO Standard C@. If GNU CPP is used with +a compiler other than GCC, this is not necessarily true; however, the +preprocessor always conforms to the standard, unless the +@option{-traditional} option is used. + +This macro is not defined if the @option{-traditional} option is used. + +On some hosts, the system compiler uses a different convention, where +@code{__STDC__} is normally 0, but is 1 if the user specifies strict +conformance to the C Standard. GNU CPP follows the host convention when +processing system header files, but when processing user files +@code{__STDC__} is always 1. This has been reported to cause problems; +for instance, some versions of Solaris provide X Windows headers that +expect @code{__STDC__} to be either undefined or 1. You may be able to +work around this sort of problem by using an @option{-I} option to +cancel treatment of those headers as system headers. @xref{Invocation}. + +@item __STDC_VERSION__ +This macro expands to the C Standard's version number, a long integer +constant of the form @code{@var{yyyy}@var{mm}L} where @var{yyyy} and +@var{mm} are the year and month of the Standard version. This signifies +which version of the C Standard the compiler conforms to. Like +@code{__STDC__}, this is not necessarily accurate for the entire +implementation, unless GNU CPP is being used with GCC@. + +The value @code{199409L} signifies the 1989 C standard as amended in +1994, which is the current default; the value @code{199901L} signifies +the 1999 revision of the C standard. Support for the 1999 revision is +not yet complete. + +This macro is not defined if the @option{-traditional} option is used, nor +when compiling C++ or Objective-C@. + +@item __STDC_HOSTED__ +This macro is defined, with value 1, if the compiler's target is a +@dfn{hosted environment}. A hosted environment has the complete +facilities of the standard C library available. + +@item __cplusplus +This macro is defined when the C++ compiler is in use. You can use +@code{__cplusplus} to test whether a header is compiled by a C compiler +or a C++ compiler. This macro is similar to @code{__STDC_VERSION__}, in +that it expands to a version number. A fully conforming implementation +of the 1998 C++ standard will define this macro to @code{199711L}. The +GNU C++ compiler is not yet fully conforming, so it uses @code{1} +instead. We hope to complete our implementation in the near future. + +@end table + +@node Common Predefined Macros +@subsection Common Predefined Macros +@cindex common predefined macros + +The common predefined macros are GNU C extensions. They are available +with the same meanings regardless of the machine or operating system on +which you are using GNU C@. Their names all start with double +underscores. + +@table @code + +@item __GNUC__ +@itemx __GNUC_MINOR__ +@itemx __GNUC_PATCHLEVEL__ +These macros are defined by all GNU compilers that use the C +preprocessor: C, C++, and Objective-C@. Their values are the major +version, minor version, and patch level of the compiler, as integer +constants. For example, GCC 3.2.1 will define @code{__GNUC__} to 3, +@code{__GNUC_MINOR__} to 2, and @code{__GNUC_PATCHLEVEL__} to 1. They +are defined only when the entire compiler is in use; if you invoke the +preprocessor directly, they are not defined. + +@code{__GNUC_PATCHLEVEL__} is new to GCC 3.0; it is also present in the +widely-used development snapshots leading up to 3.0 (which identify +themselves as GCC 2.96 or 2.97, depending on which snapshot you have). + +If all you need to know is whether or not your program is being compiled +by GCC, you can simply test @code{__GNUC__}. If you need to write code +which depends on a specific version, you must be more careful. Each +time the minor version is increased, the patch level is reset to zero; +each time the major version is increased (which happens rarely), the +minor version and patch level are reset. If you wish to use the +predefined macros directly in the conditional, you will need to write it +like this: + +@example +/* @r{Test for GCC > 3.2.0} */ +#if __GNUC__ > 3 || \ + (__GNUC__ == 3 && (__GNUC_MINOR__ > 2 || \ + (__GNUC_MINOR__ == 2 && \ + __GNUC_PATCHLEVEL__ > 0)) +@end example + +@noindent +Another approach is to use the predefined macros to +calculate a single number, then compare that against a threshold: + +@example +#define GCC_VERSION (__GNUC__ * 10000 \ + + __GNUC_MINOR__ * 100 \ + + __GNUC_PATCHLEVEL__) +@dots{} +/* @r{Test for GCC > 3.2.0} */ +#if GCC_VERSION > 30200 +@end example + +@noindent +Many people find this form easier to understand. + +@item __OBJC__ +This macro is defined, with value 1, when the Objective-C compiler is in +use. You can use @code{__OBJC__} to test whether a header is compiled +by a C compiler or a Objective-C compiler. + +@item __GNUG__ +The GNU C++ compiler defines this. Testing it is equivalent to +testing @code{@w{(__GNUC__ && __cplusplus)}}. + +@item __STRICT_ANSI__ +GCC defines this macro if and only if the @option{-ansi} switch, or a +@option{-std} switch specifying strict conformance to some version of ISO C, +was specified when GCC was invoked. It is defined to @samp{1}. +This macro exists primarily to direct GNU libc's header files to +restrict their definitions to the minimal set found in the 1989 C +standard. + +@item __BASE_FILE__ +This macro expands to the name of the main input file, in the form +of a C string constant. This is the source file that was specified +on the command line of the preprocessor or C compiler. + +@item __INCLUDE_LEVEL__ +This macro expands to a decimal integer constant that represents the +depth of nesting in include files. The value of this macro is +incremented on every @samp{#include} directive and decremented at the +end of every included file. It starts out at 0, it's value within the +base file specified on the command line. + +@item __VERSION__ +This macro expands to a string constant which describes the version of +the compiler in use. You should not rely on its contents having any +particular form, but it can be counted on to contain at least the +release number. + +@item __OPTIMIZE__ +@itemx __OPTIMIZE_SIZE__ +@itemx __NO_INLINE__ +These macros describe the compilation mode. @code{__OPTIMIZE__} is +defined in all optimizing compilations. @code{__OPTIMIZE_SIZE__} is +defined if the compiler is optimizing for size, not speed. +@code{__NO_INLINE__} is defined if no functions will be inlined into +their callers (when not optimizing, or when inlining has been +specifically disabled by @option{-fno-inline}). + +These macros cause certain GNU header files to provide optimized +definitions, using macros or inline functions, of system library +functions. You should not use these macros in any way unless you make +sure that programs will execute with the same effect whether or not they +are defined. If they are defined, their value is 1. + +@item __CHAR_UNSIGNED__ +GCC defines this macro if and only if the data type @code{char} is +unsigned on the target machine. It exists to cause the standard header +file @file{limits.h} to work correctly. You should not use this macro +yourself; instead, refer to the standard macros defined in @file{limits.h}. + +@item __REGISTER_PREFIX__ +This macro expands to a single token (not a string constant) which is +the prefix applied to CPU register names in assembly language for this +target. You can use it to write assembly that is usable in multiple +environments. For example, in the @code{m68k-aout} environment it +expands to nothing, but in the @code{m68k-coff} environment it expands +to a single @samp{%}. + +@item __USER_LABEL_PREFIX__ +This macro expands to a single token which is the prefix applied to +user labels (symbols visible to C code) in assembly. For example, in +the @code{m68k-aout} environment it expands to an @samp{_}, but in the +@code{m68k-coff} environment it expands to nothing. + +This macro will have the correct definition even if +@option{-f(no-)underscores} is in use, but it will not be correct if +target-specific options that adjust this prefix are used (e.g.@: the +OSF/rose @option{-mno-underscores} option). + +@item __SIZE_TYPE__ +@itemx __PTRDIFF_TYPE__ +@itemx __WCHAR_TYPE__ +@itemx __WINT_TYPE__ +These macros are defined to the correct underlying types for the +@code{size_t}, @code{ptrdiff_t}, @code{wchar_t}, and @code{wint_t} +typedefs, respectively. They exist to make the standard header files +@file{stddef.h} and @file{wchar.h} work correctly. You should not use +these macros directly; instead, include the appropriate headers and use +the typedefs. + +@item __USING_SJLJ_EXCEPTIONS__ +This macro is defined, with value 1, if the compiler uses the old +mechanism based on @code{setjmp} and @code{longjmp} for exception +handling. +@end table + +@node System-specific Predefined Macros +@subsection System-specific Predefined Macros + +@cindex system-specific predefined macros +@cindex predefined macros, system-specific +@cindex reserved namespace + +The C preprocessor normally predefines several macros that indicate what +type of system and machine is in use. They are obviously different on +each target supported by GCC@. This manual, being for all systems and +machines, cannot tell you what their names are, but you can use +@command{cpp -dM} to see them all. @xref{Invocation}. All system-specific +predefined macros expand to the constant 1, so you can test them with +either @samp{#ifdef} or @samp{#if}. + +The C standard requires that all system-specific macros be part of the +@dfn{reserved namespace}. All names which begin with two underscores, +or an underscore and a capital letter, are reserved for the compiler and +library to use as they wish. However, historically system-specific +macros have had names with no special prefix; for instance, it is common +to find @code{unix} defined on Unix systems. For all such macros, GCC +provides a parallel macro with two underscores added at the beginning +and the end. If @code{unix} is defined, @code{__unix__} will be defined +too. There will never be more than two underscores; the parallel of +@code{_mips} is @code{__mips__}. + +When the @option{-ansi} option, or any @option{-std} option that +requests strict conformance, is given to the compiler, all the +system-specific predefined macros outside the reserved namespace are +suppressed. The parallel macros, inside the reserved namespace, remain +defined. + +We are slowly phasing out all predefined macros which are outside the +reserved namespace. You should never use them in new programs, and we +encourage you to correct older code to use the parallel macros whenever +you find it. We don't recommend you use the system-specific macros that +are in the reserved namespace, either. It is better in the long run to +check specifically for features you need, using a tool such as +@command{autoconf}. + +@node C++ Named Operators +@subsection C++ Named Operators +@cindex named operators +@cindex C++ named operators +@cindex iso646.h + +In C++, there are eleven keywords which are simply alternate spellings +of operators normally written with punctuation. These keywords are +treated as such even in the preprocessor. They function as operators in +@samp{#if}, and they cannot be defined as macros or poisoned. In C, you +can request that those keywords take their C++ meaning by including +@file{iso646.h}. That header defines each one as a normal object-like +macro expanding to the appropriate punctuator. + +These are the named operators and their corresponding punctuators: + +@multitable {Named Operator} {Punctuator} +@item Named Operator @tab Punctuator +@item @code{and} @tab @code{&&} +@item @code{and_eq} @tab @code{&=} +@item @code{bitand} @tab @code{&} +@item @code{bitor} @tab @code{|} +@item @code{compl} @tab @code{~} +@item @code{not} @tab @code{!} +@item @code{not_eq} @tab @code{!=} +@item @code{or} @tab @code{||} +@item @code{or_eq} @tab @code{|=} +@item @code{xor} @tab @code{^} +@item @code{xor_eq} @tab @code{^=} +@end multitable + +@node Undefining and Redefining Macros +@section Undefining and Redefining Macros +@cindex undefining macros +@cindex redefining macros +@findex #undef + +If a macro ceases to be useful, it may be @dfn{undefined} with the +@samp{#undef} directive. @samp{#undef} takes a single argument, the +name of the macro to undefine. You use the bare macro name, even if the +macro is function-like. It is an error if anything appears on the line +after the macro name. @samp{#undef} has no effect if the name is not a +macro. + +@example +#define FOO 4 +x = FOO; @expansion{} x = 4; +#undef FOO +x = FOO; @expansion{} x = FOO; +@end example + +Once a macro has been undefined, that identifier may be @dfn{redefined} +as a macro by a subsequent @samp{#define} directive. The new definition +need not have any resemblance to the old definition. + +However, if an identifier which is currently a macro is redefined, then +the new definition must be @dfn{effectively the same} as the old one. +Two macro definitions are effectively the same if: +@itemize @bullet +@item Both are the same type of macro (object- or function-like). +@item All the tokens of the replacement list are the same. +@item If there are any parameters, they are the same. +@item Whitespace appears in the same places in both. It need not be +exactly the same amount of whitespace, though. Remember that comments +count as whitespace. +@end itemize + +@noindent +These definitions are effectively the same: +@example +#define FOUR (2 + 2) +#define FOUR (2 + 2) +#define FOUR (2 /* two */ + 2) +@end example +@noindent +but these are not: +@example +#define FOUR (2 + 2) +#define FOUR ( 2+2 ) +#define FOUR (2 * 2) +#define FOUR(score,and,seven,years,ago) (2 + 2) +@end example + +If a macro is redefined with a definition that is not effectively the +same as the old one, the preprocessor issues a warning and changes the +macro to use the new definition. If the new definition is effectively +the same, the redefinition is silently ignored. This allows, for +instance, two different headers to define a common macro. The +preprocessor will only complain if the definitions do not match. + +@node Macro Pitfalls +@section Macro Pitfalls +@cindex problems with macros +@cindex pitfalls of macros + +In this section we describe some special rules that apply to macros and +macro expansion, and point out certain cases in which the rules have +counter-intuitive consequences that you must watch out for. + +@menu +* Misnesting:: +* Operator Precedence Problems:: +* Swallowing the Semicolon:: +* Duplication of Side Effects:: +* Self-Referential Macros:: +* Argument Prescan:: +* Newlines in Arguments:: +@end menu + +@node Misnesting +@subsection Misnesting + +When a macro is called with arguments, the arguments are substituted +into the macro body and the result is checked, together with the rest of +the input file, for more macro calls. It is possible to piece together +a macro call coming partially from the macro body and partially from the +arguments. For example, + +@example +#define twice(x) (2*(x)) +#define call_with_1(x) x(1) +call_with_1 (twice) + @expansion{} twice(1) + @expansion{} (2*(1)) +@end example + +Macro definitions do not have to have balanced parentheses. By writing +an unbalanced open parenthesis in a macro body, it is possible to create +a macro call that begins inside the macro body but ends outside of it. +For example, + +@example +#define strange(file) fprintf (file, "%s %d", +@dots{} +strange(stderr) p, 35) + @expansion{} fprintf (stderr, "%s %d", p, 35) +@end example + +The ability to piece together a macro call can be useful, but the use of +unbalanced open parentheses in a macro body is just confusing, and +should be avoided. + +@node Operator Precedence Problems +@subsection Operator Precedence Problems +@cindex parentheses in macro bodies + +You may have noticed that in most of the macro definition examples shown +above, each occurrence of a macro argument name had parentheses around +it. In addition, another pair of parentheses usually surround the +entire macro definition. Here is why it is best to write macros that +way. + +Suppose you define a macro as follows, + +@example +#define ceil_div(x, y) (x + y - 1) / y +@end example + +@noindent +whose purpose is to divide, rounding up. (One use for this operation is +to compute how many @code{int} objects are needed to hold a certain +number of @code{char} objects.) Then suppose it is used as follows: + +@example +a = ceil_div (b & c, sizeof (int)); + @expansion{} a = (b & c + sizeof (int) - 1) / sizeof (int); +@end example + +@noindent +This does not do what is intended. The operator-precedence rules of +C make it equivalent to this: + +@example +a = (b & (c + sizeof (int) - 1)) / sizeof (int); +@end example + +@noindent +What we want is this: + +@example +a = ((b & c) + sizeof (int) - 1)) / sizeof (int); +@end example + +@noindent +Defining the macro as + +@example +#define ceil_div(x, y) ((x) + (y) - 1) / (y) +@end example + +@noindent +provides the desired result. + +Unintended grouping can result in another way. Consider @code{sizeof +ceil_div(1, 2)}. That has the appearance of a C expression that would +compute the size of the type of @code{ceil_div (1, 2)}, but in fact it +means something very different. Here is what it expands to: + +@example +sizeof ((1) + (2) - 1) / (2) +@end example + +@noindent +This would take the size of an integer and divide it by two. The +precedence rules have put the division outside the @code{sizeof} when it +was intended to be inside. + +Parentheses around the entire macro definition prevent such problems. +Here, then, is the recommended way to define @code{ceil_div}: + +@example +#define ceil_div(x, y) (((x) + (y) - 1) / (y)) +@end example + +@node Swallowing the Semicolon +@subsection Swallowing the Semicolon +@cindex semicolons (after macro calls) + +Often it is desirable to define a macro that expands into a compound +statement. Consider, for example, the following macro, that advances a +pointer (the argument @code{p} says where to find it) across whitespace +characters: + +@example +#define SKIP_SPACES(p, limit) \ +@{ char *lim = (limit); \ + while (p < lim) @{ \ + if (*p++ != ' ') @{ \ + p--; break; @}@}@} +@end example + +@noindent +Here backslash-newline is used to split the macro definition, which must +be a single logical line, so that it resembles the way such code would +be laid out if not part of a macro definition. + +A call to this macro might be @code{SKIP_SPACES (p, lim)}. Strictly +speaking, the call expands to a compound statement, which is a complete +statement with no need for a semicolon to end it. However, since it +looks like a function call, it minimizes confusion if you can use it +like a function call, writing a semicolon afterward, as in +@code{SKIP_SPACES (p, lim);} + +This can cause trouble before @code{else} statements, because the +semicolon is actually a null statement. Suppose you write + +@example +if (*p != 0) + SKIP_SPACES (p, lim); +else @dots{} +@end example + +@noindent +The presence of two statements---the compound statement and a null +statement---in between the @code{if} condition and the @code{else} +makes invalid C code. + +The definition of the macro @code{SKIP_SPACES} can be altered to solve +this problem, using a @code{do @dots{} while} statement. Here is how: + +@example +#define SKIP_SPACES(p, limit) \ +do @{ char *lim = (limit); \ + while (p < lim) @{ \ + if (*p++ != ' ') @{ \ + p--; break; @}@}@} \ +while (0) +@end example + +Now @code{SKIP_SPACES (p, lim);} expands into + +@example +do @{@dots{}@} while (0); +@end example + +@noindent +which is one statement. The loop executes exactly once; most compilers +generate no extra code for it. + +@node Duplication of Side Effects +@subsection Duplication of Side Effects + +@cindex side effects (in macro arguments) +@cindex unsafe macros +Many C programs define a macro @code{min}, for ``minimum'', like this: + +@example +#define min(X, Y) ((X) < (Y) ? (X) : (Y)) +@end example + +When you use this macro with an argument containing a side effect, +as shown here, + +@example +next = min (x + y, foo (z)); +@end example + +@noindent +it expands as follows: + +@example +next = ((x + y) < (foo (z)) ? (x + y) : (foo (z))); +@end example + +@noindent +where @code{x + y} has been substituted for @code{X} and @code{foo (z)} +for @code{Y}. + +The function @code{foo} is used only once in the statement as it appears +in the program, but the expression @code{foo (z)} has been substituted +twice into the macro expansion. As a result, @code{foo} might be called +two times when the statement is executed. If it has side effects or if +it takes a long time to compute, the results might not be what you +intended. We say that @code{min} is an @dfn{unsafe} macro. + +The best solution to this problem is to define @code{min} in a way that +computes the value of @code{foo (z)} only once. The C language offers +no standard way to do this, but it can be done with GNU extensions as +follows: + +@example +#define min(X, Y) \ +(@{ typeof (X) x_ = (X); \ + typeof (Y) y_ = (Y); \ + (x_ < y_) ? x_ : y_; @}) +@end example + +The @samp{(@{ @dots{} @})} notation produces a compound statement that +acts as an expression. Its value is the value of its last statement. +This permits us to define local variables and assign each argument to +one. The local variables have underscores after their names to reduce +the risk of conflict with an identifier of wider scope (it is impossible +to avoid this entirely). Now each argument is evaluated exactly once. + +If you do not wish to use GNU C extensions, the only solution is to be +careful when @emph{using} the macro @code{min}. For example, you can +calculate the value of @code{foo (z)}, save it in a variable, and use +that variable in @code{min}: + +@example +@group +#define min(X, Y) ((X) < (Y) ? (X) : (Y)) +@dots{} +@{ + int tem = foo (z); + next = min (x + y, tem); +@} +@end group +@end example + +@noindent +(where we assume that @code{foo} returns type @code{int}). + +@node Self-Referential Macros +@subsection Self-Referential Macros +@cindex self-reference + +A @dfn{self-referential} macro is one whose name appears in its +definition. Recall that all macro definitions are rescanned for more +macros to replace. If the self-reference were considered a use of the +macro, it would produce an infinitely large expansion. To prevent this, +the self-reference is not considered a macro call. It is passed into +the preprocessor output unchanged. Let's consider an example: + +@example +#define foo (4 + foo) +@end example + +@noindent +where @code{foo} is also a variable in your program. + +Following the ordinary rules, each reference to @code{foo} will expand +into @code{(4 + foo)}; then this will be rescanned and will expand into +@code{(4 + (4 + foo))}; and so on until the computer runs out of memory. + +The self-reference rule cuts this process short after one step, at +@code{(4 + foo)}. Therefore, this macro definition has the possibly +useful effect of causing the program to add 4 to the value of @code{foo} +wherever @code{foo} is referred to. + +In most cases, it is a bad idea to take advantage of this feature. A +person reading the program who sees that @code{foo} is a variable will +not expect that it is a macro as well. The reader will come across the +identifier @code{foo} in the program and think its value should be that +of the variable @code{foo}, whereas in fact the value is four greater. + +One common, useful use of self-reference is to create a macro which +expands to itself. If you write + +@example +#define EPERM EPERM +@end example + +@noindent +then the macro @code{EPERM} expands to @code{EPERM}. Effectively, it is +left alone by the preprocessor whenever it's used in running text. You +can tell that it's a macro with @samp{#ifdef}. You might do this if you +want to define numeric constants with an @code{enum}, but have +@samp{#ifdef} be true for each constant. + +If a macro @code{x} expands to use a macro @code{y}, and the expansion of +@code{y} refers to the macro @code{x}, that is an @dfn{indirect +self-reference} of @code{x}. @code{x} is not expanded in this case +either. Thus, if we have + +@example +#define x (4 + y) +#define y (2 * x) +@end example + +@noindent +then @code{x} and @code{y} expand as follows: + +@example +@group +x @expansion{} (4 + y) + @expansion{} (4 + (2 * x)) + +y @expansion{} (2 * x) + @expansion{} (2 * (4 + y)) +@end group +@end example + +@noindent +Each macro is expanded when it appears in the definition of the other +macro, but not when it indirectly appears in its own definition. + +@node Argument Prescan +@subsection Argument Prescan +@cindex expansion of arguments +@cindex macro argument expansion +@cindex prescan of macro arguments + +Macro arguments are completely macro-expanded before they are +substituted into a macro body, unless they are stringified or pasted +with other tokens. After substitution, the entire macro body, including +the substituted arguments, is scanned again for macros to be expanded. +The result is that the arguments are scanned @emph{twice} to expand +macro calls in them. + +Most of the time, this has no effect. If the argument contained any +macro calls, they are expanded during the first scan. The result +therefore contains no macro calls, so the second scan does not change +it. If the argument were substituted as given, with no prescan, the +single remaining scan would find the same macro calls and produce the +same results. + +You might expect the double scan to change the results when a +self-referential macro is used in an argument of another macro +(@pxref{Self-Referential Macros}): the self-referential macro would be +expanded once in the first scan, and a second time in the second scan. +However, this is not what happens. The self-references that do not +expand in the first scan are marked so that they will not expand in the +second scan either. + +You might wonder, ``Why mention the prescan, if it makes no difference? +And why not skip it and make the preprocessor faster?'' The answer is +that the prescan does make a difference in three special cases: + +@itemize @bullet +@item +Nested calls to a macro. + +We say that @dfn{nested} calls to a macro occur when a macro's argument +contains a call to that very macro. For example, if @code{f} is a macro +that expects one argument, @code{f (f (1))} is a nested pair of calls to +@code{f}. The desired expansion is made by expanding @code{f (1)} and +substituting that into the definition of @code{f}. The prescan causes +the expected result to happen. Without the prescan, @code{f (1)} itself +would be substituted as an argument, and the inner use of @code{f} would +appear during the main scan as an indirect self-reference and would not +be expanded. + +@item +Macros that call other macros that stringify or concatenate. + +If an argument is stringified or concatenated, the prescan does not +occur. If you @emph{want} to expand a macro, then stringify or +concatenate its expansion, you can do that by causing one macro to call +another macro that does the stringification or concatenation. For +instance, if you have + +@example +#define AFTERX(x) X_ ## x +#define XAFTERX(x) AFTERX(x) +#define TABLESIZE 1024 +#define BUFSIZE TABLESIZE +@end example + +then @code{AFTERX(BUFSIZE)} expands to @code{X_BUFSIZE}, and +@code{XAFTERX(BUFSIZE)} expands to @code{X_1024}. (Not to +@code{X_TABLESIZE}. Prescan always does a complete expansion.) + +@item +Macros used in arguments, whose expansions contain unshielded commas. + +This can cause a macro expanded on the second scan to be called with the +wrong number of arguments. Here is an example: + +@example +#define foo a,b +#define bar(x) lose(x) +#define lose(x) (1 + (x)) +@end example + +We would like @code{bar(foo)} to turn into @code{(1 + (foo))}, which +would then turn into @code{(1 + (a,b))}. Instead, @code{bar(foo)} +expands into @code{lose(a,b)}, and you get an error because @code{lose} +requires a single argument. In this case, the problem is easily solved +by the same parentheses that ought to be used to prevent misnesting of +arithmetic operations: + +@example +#define foo (a,b) +@exdent or +#define bar(x) lose((x)) +@end example + +The extra pair of parentheses prevents the comma in @code{foo}'s +definition from being interpreted as an argument separator. + +@end itemize + +@node Newlines in Arguments +@subsection Newlines in Arguments +@cindex newlines in macro arguments + +The invocation of a function-like macro can extend over many logical +lines. However, in the present implementation, the entire expansion +comes out on one line. Thus line numbers emitted by the compiler or +debugger refer to the line the invocation started on, which might be +different to the line containing the argument causing the problem. + +Here is an example illustrating this: + +@example +#define ignore_second_arg(a,b,c) a; c + +ignore_second_arg (foo (), + ignored (), + syntax error); +@end example + +@noindent +The syntax error triggered by the tokens @code{syntax error} results in +an error message citing line three---the line of ignore_second_arg--- +even though the problematic code comes from line five. + +We consider this a bug, and intend to fix it in the near future. + +@node Conditionals +@chapter Conditionals +@cindex conditionals + +A @dfn{conditional} is a directive that instructs the preprocessor to +select whether or not to include a chunk of code in the final token +stream passed to the compiler. Preprocessor conditionals can test +arithmetic expressions, or whether a name is defined as a macro, or both +simultaneously using the special @code{defined} operator. + +A conditional in the C preprocessor resembles in some ways an @code{if} +statement in C, but it is important to understand the difference between +them. The condition in an @code{if} statement is tested during the +execution of your program. Its purpose is to allow your program to +behave differently from run to run, depending on the data it is +operating on. The condition in a preprocessing conditional directive is +tested when your program is compiled. Its purpose is to allow different +code to be included in the program depending on the situation at the +time of compilation. + +However, the distinction is becoming less clear. Modern compilers often +do test @code{if} statements when a program is compiled, if their +conditions are known not to vary at run time, and eliminate code which +can never be executed. If you can count on your compiler to do this, +you may find that your program is more readable if you use @code{if} +statements with constant conditions (perhaps determined by macros). Of +course, you can only use this to exclude code, not type definitions or +other preprocessing directives, and you can only do it if the code +remains syntactically valid when it is not to be used. + +GCC version 3 eliminates this kind of never-executed code even when +not optimizing. Older versions did it only when optimizing. + +@menu +* Conditional Uses:: +* Conditional Syntax:: +* Deleted Code:: +@end menu + +@node Conditional Uses +@section Conditional Uses + +There are three general reasons to use a conditional. + +@itemize @bullet +@item +A program may need to use different code depending on the machine or +operating system it is to run on. In some cases the code for one +operating system may be erroneous on another operating system; for +example, it might refer to data types or constants that do not exist on +the other system. When this happens, it is not enough to avoid +executing the invalid code. Its mere presence will cause the compiler +to reject the program. With a preprocessing conditional, the offending +code can be effectively excised from the program when it is not valid. + +@item +You may want to be able to compile the same source file into two +different programs. One version might make frequent time-consuming +consistency checks on its intermediate data, or print the values of +those data for debugging, and the other not. + +@item +A conditional whose condition is always false is one way to exclude code +from the program but keep it as a sort of comment for future reference. +@end itemize + +Simple programs that do not need system-specific logic or complex +debugging hooks generally will not need to use preprocessing +conditionals. + +@node Conditional Syntax +@section Conditional Syntax + +@findex #if +A conditional in the C preprocessor begins with a @dfn{conditional +directive}: @samp{#if}, @samp{#ifdef} or @samp{#ifndef}. + +@menu +* Ifdef:: +* If:: +* Defined:: +* Else:: +* Elif:: +@end menu + +@node Ifdef +@subsection Ifdef +@findex #ifdef +@findex #endif + +The simplest sort of conditional is + +@example +@group +#ifdef @var{MACRO} + +@var{controlled text} + +#endif /* @var{MACRO} */ +@end group +@end example + +@cindex conditional group +This block is called a @dfn{conditional group}. @var{controlled text} +will be included in the output of the preprocessor if and only if +@var{MACRO} is defined. We say that the conditional @dfn{succeeds} if +@var{MACRO} is defined, @dfn{fails} if it is not. + +The @var{controlled text} inside of a conditional can include +preprocessing directives. They are executed only if the conditional +succeeds. You can nest conditional groups inside other conditional +groups, but they must be completely nested. In other words, +@samp{#endif} always matches the nearest @samp{#ifdef} (or +@samp{#ifndef}, or @samp{#if}). Also, you cannot start a conditional +group in one file and end it in another. + +Even if a conditional fails, the @var{controlled text} inside it is +still run through initial transformations and tokenization. Therefore, +it must all be lexically valid C@. Normally the only way this matters is +that all comments and string literals inside a failing conditional group +must still be properly ended. + +The comment following the @samp{#endif} is not required, but it is a +good practice if there is a lot of @var{controlled text}, because it +helps people match the @samp{#endif} to the corresponding @samp{#ifdef}. +Older programs sometimes put @var{MACRO} directly after the +@samp{#endif} without enclosing it in a comment. This is invalid code +according to the C standard. GNU CPP accepts it with a warning. It +never affects which @samp{#ifndef} the @samp{#endif} matches. + +@findex #ifndef +Sometimes you wish to use some code if a macro is @emph{not} defined. +You can do this by writing @samp{#ifndef} instead of @samp{#ifdef}. +One common use of @samp{#ifndef} is to include code only the first +time a header file is included. @xref{Once-Only Headers}. + +Macro definitions can vary between compilations for several reasons. +Here are some samples. + +@itemize @bullet +@item +Some macros are predefined on each kind of machine +(@pxref{System-specific Predefined Macros}). This allows you to provide +code specially tuned for a particular machine. + +@item +System header files define more macros, associated with the features +they implement. You can test these macros with conditionals to avoid +using a system feature on a machine where it is not implemented. + +@item +Macros can be defined or undefined with the @option{-D} and @option{-U} +command line options when you compile the program. You can arrange to +compile the same source file into two different programs by choosing a +macro name to specify which program you want, writing conditionals to +test whether or how this macro is defined, and then controlling the +state of the macro with command line options, perhaps set in the +Makefile. @xref{Invocation}. + +@item +Your program might have a special header file (often called +@file{config.h}) that is adjusted when the program is compiled. It can +define or not define macros depending on the features of the system and +the desired capabilities of the program. The adjustment can be +automated by a tool such as @command{autoconf}, or done by hand. +@end itemize + +@node If +@subsection If + +The @samp{#if} directive allows you to test the value of an arithmetic +expression, rather than the mere existence of one macro. Its syntax is + +@example +@group +#if @var{expression} + +@var{controlled text} + +#endif /* @var{expression} */ +@end group +@end example + +@var{expression} is a C expression of integer type, subject to stringent +restrictions. It may contain + +@itemize @bullet +@item +Integer constants. + +@item +Character constants, which are interpreted as they would be in normal +code. + +@item +Arithmetic operators for addition, subtraction, multiplication, +division, bitwise operations, shifts, comparisons, and logical +operations (@code{&&} and @code{||}). The latter two obey the usual +short-circuiting rules of standard C@. + +@item +Macros. All macros in the expression are expanded before actual +computation of the expression's value begins. + +@item +Uses of the @code{defined} operator, which lets you check whether macros +are defined in the middle of an @samp{#if}. + +@item +Identifiers that are not macros, which are all considered to be the +number zero. This allows you to write @code{@w{#if MACRO}} instead of +@code{@w{#ifdef MACRO}}, if you know that MACRO, when defined, will +always have a nonzero value. Function-like macros used without their +function call parentheses are also treated as zero. + +In some contexts this shortcut is undesirable. The @option{-Wundef} +option causes GCC to warn whenever it encounters an identifier which is +not a macro in an @samp{#if}. +@end itemize + +The preprocessor does not know anything about types in the language. +Therefore, @code{sizeof} operators are not recognized in @samp{#if}, and +neither are @code{enum} constants. They will be taken as identifiers +which are not macros, and replaced by zero. In the case of +@code{sizeof}, this is likely to cause the expression to be invalid. + +The preprocessor calculates the value of @var{expression}. It carries +out all calculations in the widest integer type known to the compiler; +on most machines supported by GCC this is 64 bits. This is not the same +rule as the compiler uses to calculate the value of a constant +expression, and may give different results in some cases. If the value +comes out to be nonzero, the @samp{#if} succeeds and the @var{controlled +text} is included; otherwise it is skipped. + +If @var{expression} is not correctly formed, GCC issues an error and +treats the conditional as having failed. + +@node Defined +@subsection Defined + +@cindex @code{defined} +The special operator @code{defined} is used in @samp{#if} and +@samp{#elif} expressions to test whether a certain name is defined as a +macro. @code{defined @var{name}} and @code{defined (@var{name})} are +both expressions whose value is 1 if @var{name} is defined as a macro at +the current point in the program, and 0 otherwise. Thus, @code{@w{#if +defined MACRO}} is precisely equivalent to @code{@w{#ifdef MACRO}}. + +@code{defined} is useful when you wish to test more than one macro for +existence at once. For example, + +@example +#if defined (__vax__) || defined (__ns16000__) +@end example + +@noindent +would succeed if either of the names @code{__vax__} or +@code{__ns16000__} is defined as a macro. + +Conditionals written like this: + +@example +#if defined BUFSIZE && BUFSIZE >= 1024 +@end example + +@noindent +can generally be simplified to just @code{@w{#if BUFSIZE >= 1024}}, +since if @code{BUFSIZE} is not defined, it will be interpreted as having +the value zero. + +If the @code{defined} operator appears as a result of a macro expansion, +the C standard says the behavior is undefined. GNU cpp treats it as a +genuine @code{defined} operator and evaluates it normally. It will warn +wherever your code uses this feature if you use the command-line option +@option{-pedantic}, since other compilers may handle it differently. + +@node Else +@subsection Else + +@findex #else +The @samp{#else} directive can be added to a conditional to provide +alternative text to be used if the condition fails. This is what it +looks like: + +@example +@group +#if @var{expression} +@var{text-if-true} +#else /* Not @var{expression} */ +@var{text-if-false} +#endif /* Not @var{expression} */ +@end group +@end example + +@noindent +If @var{expression} is nonzero, the @var{text-if-true} is included and +the @var{text-if-false} is skipped. If @var{expression} is zero, the +opposite happens. + +You can use @samp{#else} with @samp{#ifdef} and @samp{#ifndef}, too. + +@node Elif +@subsection Elif + +@findex #elif +One common case of nested conditionals is used to check for more than two +possible alternatives. For example, you might have + +@example +#if X == 1 +@dots{} +#else /* X != 1 */ +#if X == 2 +@dots{} +#else /* X != 2 */ +@dots{} +#endif /* X != 2 */ +#endif /* X != 1 */ +@end example + +Another conditional directive, @samp{#elif}, allows this to be +abbreviated as follows: + +@example +#if X == 1 +@dots{} +#elif X == 2 +@dots{} +#else /* X != 2 and X != 1*/ +@dots{} +#endif /* X != 2 and X != 1*/ +@end example + +@samp{#elif} stands for ``else if''. Like @samp{#else}, it goes in the +middle of a conditional group and subdivides it; it does not require a +matching @samp{#endif} of its own. Like @samp{#if}, the @samp{#elif} +directive includes an expression to be tested. The text following the +@samp{#elif} is processed only if the original @samp{#if}-condition +failed and the @samp{#elif} condition succeeds. + +More than one @samp{#elif} can go in the same conditional group. Then +the text after each @samp{#elif} is processed only if the @samp{#elif} +condition succeeds after the original @samp{#if} and all previous +@samp{#elif} directives within it have failed. + +@samp{#else} is allowed after any number of @samp{#elif} directives, but +@samp{#elif} may not follow @samp{#else}. + +@node Deleted Code +@section Deleted Code +@cindex commenting out code + +If you replace or delete a part of the program but want to keep the old +code around for future reference, you often cannot simply comment it +out. Block comments do not nest, so the first comment inside the old +code will end the commenting-out. The probable result is a flood of +syntax errors. + +One way to avoid this problem is to use an always-false conditional +instead. For instance, put @code{#if 0} before the deleted code and +@code{#endif} after it. This works even if the code being turned +off contains conditionals, but they must be entire conditionals +(balanced @samp{#if} and @samp{#endif}). + +Some people use @code{#ifdef notdef} instead. This is risky, because +@code{notdef} might be accidentally defined as a macro, and then the +conditional would succeed. @code{#if 0} can be counted on to fail. + +Do not use @code{#if 0} for comments which are not C code. Use a real +comment, instead. The interior of @code{#if 0} must consist of complete +tokens; in particular, single-quote characters must balance. Comments +often contain unbalanced single-quote characters (known in English as +apostrophes). These confuse @code{#if 0}. They don't confuse +@samp{/*}. + +@node Diagnostics +@chapter Diagnostics +@cindex diagnostic +@cindex reporting errors +@cindex reporting warnings + +@findex #error +The directive @samp{#error} causes the preprocessor to report a fatal +error. The tokens forming the rest of the line following @samp{#error} +are used as the error message. + +You would use @samp{#error} inside of a conditional that detects a +combination of parameters which you know the program does not properly +support. For example, if you know that the program will not run +properly on a VAX, you might write + +@example +@group +#ifdef __vax__ +#error "Won't work on VAXen. See comments at get_last_object." +#endif +@end group +@end example + +If you have several configuration parameters that must be set up by +the installation in a consistent way, you can use conditionals to detect +an inconsistency and report it with @samp{#error}. For example, + +@example +#if !defined(UNALIGNED_INT_ASM_OP) && defined(DWARF2_DEBUGGING_INFO) +#error "DWARF2_DEBUGGING_INFO requires UNALIGNED_INT_ASM_OP." +#endif +@end example + +@findex #warning +The directive @samp{#warning} is like @samp{#error}, but causes the +preprocessor to issue a warning and continue preprocessing. The tokens +following @samp{#warning} are used as the warning message. + +You might use @samp{#warning} in obsolete header files, with a message +directing the user to the header file which should be used instead. + +Neither @samp{#error} nor @samp{#warning} macro-expands its argument. +Internal whitespace sequences are each replaced with a single space. +The line must consist of complete tokens. It is wisest to make the +argument of these directives be a single string constant; this avoids +problems with apostrophes and the like. + +@node Line Control +@chapter Line Control +@cindex line control + +The C preprocessor informs the C compiler of the location in your source +code where each token came from. Presently, this is just the file name +and line number. All the tokens resulting from macro expansion are +reported as having appeared on the line of the source file where the +outermost macro was used. We intend to be more accurate in the future. + +If you write a program which generates source code, such as the +@command{bison} parser generator, you may want to adjust the preprocessor's +notion of the current file name and line number by hand. Parts of the +output from @command{bison} are generated from scratch, other parts come +from a standard parser file. The rest are copied verbatim from +@command{bison}'s input. You would like compiler error messages and +symbolic debuggers to be able to refer to @code{bison}'s input file. + +@findex #line +@command{bison} or any such program can arrange this by writing +@samp{#line} directives into the output file. @samp{#line} is a +directive that specifies the original line number and source file name +for subsequent input in the current preprocessor input file. +@samp{#line} has three variants: + +@table @code +@item #line @var{linenum} +@var{linenum} is a non-negative decimal integer constant. It specifies +the line number which should be reported for the following line of +input. Subsequent lines are counted from @var{linenum}. + +@item #line @var{linenum} @var{filename} +@var{linenum} is the same as for the first form, and has the same +effect. In addition, @var{filename} is a string constant. The +following line and all subsequent lines are reported to come from the +file it specifies, until something else happens to change that. + +@item #line @var{anything else} +@var{anything else} is checked for macro calls, which are expanded. +The result should match one of the above two forms. +@end table + +@samp{#line} directives alter the results of the @code{__FILE__} and +@code{__LINE__} predefined macros from that point on. @xref{Standard +Predefined Macros}. They do not have any effect on @samp{#include}'s +idea of the directory containing the current file. + +@node Pragmas +@chapter Pragmas + +The @samp{#pragma} directive is the method specified by the C standard +for providing additional information to the compiler, beyond what is +conveyed in the language itself. Three forms of this directive +(commonly known as @dfn{pragmas}) are specified by the 1999 C standard. +A C compiler is free to attach any meaning it likes to other pragmas. + +GCC has historically preferred to use extensions to the syntax of the +language, such as @code{__attribute__}, for this purpose. However, GCC +does define a few pragmas of its own. These mostly have effects on the +entire translation unit or source file. + +In GCC version 3, all GNU-defined, supported pragmas have been given a +@code{GCC} prefix. This is in line with the @code{STDC} prefix on all +pragmas defined by C99. For backward compatibility, pragmas which were +recognized by previous versions are still recognized without the +@code{GCC} prefix, but that usage is deprecated. Some older pragmas are +deprecated in their entirety. They are not recognized with the +@code{GCC} prefix. @xref{Obsolete Features}. + +@cindex @code{_Pragma} +C99 introduces the @code{@w{_Pragma}} operator. This feature addresses a +major problem with @samp{#pragma}: being a directive, it cannot be +produced as the result of macro expansion. @code{@w{_Pragma}} is an +operator, much like @code{sizeof} or @code{defined}, and can be embedded +in a macro. + +Its syntax is @code{@w{_Pragma (@var{string-literal})}}, where +@var{string-literal} can be either a normal or wide-character string +literal. It is destringized, by replacing all @samp{\\} with a single +@samp{\} and all @samp{\"} with a @samp{"}. The result is then +processed as if it had appeared as the right hand side of a +@samp{#pragma} directive. For example, + +@example +_Pragma ("GCC dependency \"parse.y\"") +@end example + +@noindent +has the same effect as @code{#pragma GCC dependency "parse.y"}. The +same effect could be achieved using macros, for example + +@example +#define DO_PRAGMA(x) _Pragma (#x) +DO_PRAGMA (GCC dependency "parse.y") +@end example + +The standard is unclear on where a @code{_Pragma} operator can appear. +The preprocessor does not accept it within a preprocessing conditional +directive like @samp{#if}. To be safe, you are probably best keeping it +out of directives other than @samp{#define}, and putting it on a line of +its own. + +This manual documents the pragmas which are meaningful to the +preprocessor itself. Other pragmas are meaningful to the C or C++ +compilers. They are documented in the GCC manual. + +@ftable @code +@item #pragma GCC dependency +@code{#pragma GCC dependency} allows you to check the relative dates of +the current file and another file. If the other file is more recent than +the current file, a warning is issued. This is useful if the current +file is derived from the other file, and should be regenerated. The +other file is searched for using the normal include search path. +Optional trailing text can be used to give more information in the +warning message. + +@example +#pragma GCC dependency "parse.y" +#pragma GCC dependency "/usr/include/time.h" rerun fixincludes +@end example + +@item #pragma GCC poison +Sometimes, there is an identifier that you want to remove completely +from your program, and make sure that it never creeps back in. To +enforce this, you can @dfn{poison} the identifier with this pragma. +@code{#pragma GCC poison} is followed by a list of identifiers to +poison. If any of those identifiers appears anywhere in the source +after the directive, it is a hard error. For example, + +@example +#pragma GCC poison printf sprintf fprintf +sprintf(some_string, "hello"); +@end example + +@noindent +will produce an error. + +If a poisoned identifier appears as part of the expansion of a macro +which was defined before the identifier was poisoned, it will @emph{not} +cause an error. This lets you poison an identifier without worrying +about system headers defining macros that use it. + +For example, + +@example +#define strrchr rindex +#pragma GCC poison rindex +strrchr(some_string, 'h'); +@end example + +@noindent +will not produce an error. + +@item #pragma GCC system_header +This pragma takes no arguments. It causes the rest of the code in the +current file to be treated as if it came from a system header. +@xref{System Headers}. + +@end ftable + +@node Other Directives +@chapter Other Directives + +@findex #ident +The @samp{#ident} directive takes one argument, a string constant. On +some systems, that string constant is copied into a special segment of +the object file. On other systems, the directive is ignored. + +This directive is not part of the C standard, but it is not an official +GNU extension either. We believe it came from System V@. + +@findex #sccs +The @samp{#sccs} directive is recognized on some systems, because it +appears in their header files. It is a very old, obscure, extension +which we did not invent, and we have been unable to find any +documentation of what it should do, so GCC simply ignores it. + +@cindex null directive +The @dfn{null directive} consists of a @samp{#} followed by a newline, +with only whitespace (including comments) in between. A null directive +is understood as a preprocessing directive but has no effect on the +preprocessor output. The primary significance of the existence of the +null directive is that an input line consisting of just a @samp{#} will +produce no output, rather than a line of output containing just a +@samp{#}. Supposedly some old C programs contain such lines. + +@node Preprocessor Output +@chapter Preprocessor Output + +When the C preprocessor is used with the C, C++, or Objective-C +compilers, it is integrated into the compiler and communicates a stream +of binary tokens directly to the compiler's parser. However, it can +also be used in the more conventional standalone mode, where it produces +textual output. +@c FIXME: Document the library interface. + +@cindex output format +The output from the C preprocessor looks much like the input, except +that all preprocessing directive lines have been replaced with blank +lines and all comments with spaces. Long runs of blank lines are +discarded. + +The ISO standard specifies that it is implementation defined whether a +preprocessor preserves whitespace between tokens, or replaces it with +e.g.@: a single space. In GNU CPP, whitespace between tokens is collapsed +to become a single space, with the exception that the first token on a +non-directive line is preceded with sufficient spaces that it appears in +the same column in the preprocessed output that it appeared in the +original source file. This is so the output is easy to read. +@xref{Differences from previous versions}. CPP does not insert any +whitespace where there was none in the original source, except where +necessary to prevent an accidental token paste. + +@cindex linemarkers +Source file name and line number information is conveyed by lines +of the form + +@example +# @var{linenum} @var{filename} @var{flags} +@end example + +@noindent +These are called @dfn{linemarkers}. They are inserted as needed into +the output (but never within a string or character constant). They mean +that the following line originated in file @var{filename} at line +@var{linenum}. + +After the file name comes zero or more flags, which are @samp{1}, +@samp{2}, @samp{3}, or @samp{4}. If there are multiple flags, spaces +separate them. Here is what the flags mean: + +@table @samp +@item 1 +This indicates the start of a new file. +@item 2 +This indicates returning to a file (after having included another file). +@item 3 +This indicates that the following text comes from a system header file, +so certain warnings should be suppressed. +@item 4 +This indicates that the following text should be treated as being +wrapped in an implicit @code{extern "C"} block. +@c maybe cross reference NO_IMPLICIT_EXTERN_C +@end table + +As an extension, the preprocessor accepts linemarkers in non-assembler +input files. They are treated like the corresponding @samp{#line} +directive, (@pxref{Line Control}), except that trailing flags are +permitted, and are interpreted with the meanings described above. If +multiple flags are given, they must be in ascending order. + +Some directives may be duplicated in the output of the preprocessor. +These are @samp{#ident} (always), @samp{#pragma} (only if the +preprocessor does not handle the pragma itself), and @samp{#define} and +@samp{#undef} (with certain debugging options). If this happens, the +@samp{#} of the directive will always be in the first column, and there +will be no space between the @samp{#} and the directive name. If macro +expansion happens to generate tokens which might be mistaken for a +duplicated directive, a space will be inserted between the @samp{#} and +the directive name. + +@node Traditional Mode +@chapter Traditional Mode + +Traditional (pre-standard) C preprocessing is rather different from +the preprocessing specified by the standard. When GCC is given the +@option{-traditional} option, it attempts to emulate a traditional +preprocessor. We do not guarantee that GCC's behavior under +@option{-traditional} matches any pre-standard preprocessor exactly. + +Traditional mode exists only for backward compatibility. We have no +plans to augment it in any way nor will we change it except to fix +catastrophic bugs. You should be aware that modern C libraries often +have header files which are incompatible with traditional mode. + +This is a list of the differences. It may not be complete, and may not +correspond exactly to the behavior of either GCC or a true traditional +preprocessor. + +@itemize @bullet +@item +Traditional macro expansion pays no attention to single-quote or +double-quote characters; macro argument symbols are replaced by the +argument values even when they appear within apparent string or +character constants. + +@item +Traditionally, it is permissible for a macro expansion to end in the +middle of a string or character constant. The constant continues into +the text surrounding the macro call. + +@item +However, the end of the line terminates a string or character constant, +with no error. (This is a kluge. Traditional mode is commonly used to +preprocess things which are not C, and have a different comment syntax. +Single apostrophes often appear in comments. This kluge prevents the +traditional preprocessor from issuing errors on such comments.) + +@item +Preprocessing directives are recognized in traditional C only when their +leading @samp{#} appears in the first column. There can be no +whitespace between the beginning of the line and the @samp{#}. + +@item +In traditional C, a comment is equivalent to no text at all. (In ISO +C, a comment counts as whitespace.) It can be used sort of the same way +that @samp{##} is used in ISO C, to paste macro arguments together. + +@item +Traditional C does not have the concept of a preprocessing number. + +@item +A macro is not suppressed within its own definition, in traditional C@. +Thus, any macro that is used recursively inevitably causes an error. + +@item +The @samp{#} and @samp{##} operators are not available in traditional +C@. + +@item +In traditional C, the text at the end of a macro expansion can run +together with the text after the macro call, to produce a single token. +This is impossible in ISO C@. + +@item +None of the GNU extensions to the preprocessor are available in +traditional mode, with the exception of a partial implementation of +assertions, and those may be removed in the future. + +@item +A true traditional C preprocessor does not recognize @samp{#elif}, +@samp{#error}, or @samp{#pragma}. GCC supports @samp{#elif} and +@samp{#error} even in traditional mode, but not @samp{#pragma}. + +@item +Traditional mode is text-based, not token-based, and comments are +stripped after macro expansion. Therefore, @samp{/**/} can be used to +paste tokens together provided that there is no whitespace between it +and the tokens to be pasted. + +@item +Traditional mode preserves the amount and form of whitespace provided by +the user. Hard tabs remain hard tabs. This can be useful, e.g.@: if you +are preprocessing a Makefile (which we do not encourage). +@end itemize + +You can request warnings about features that did not exist, or worked +differently, in traditional C with the @option{-Wtraditional} option. +This works only if you do @emph{not} specify @option{-traditional}. GCC +does not warn about features of ISO C which you must use when you are +using a conforming compiler, such as the @samp{#} and @samp{##} +operators. + +Presently @option{-Wtraditional} warns about: + +@itemize @bullet +@item +Macro parameters that appear within string literals in the macro body. +In traditional C macro replacement takes place within string literals, +but does not in ISO C@. + +@item +In traditional C, some preprocessor directives did not exist. +Traditional preprocessors would only consider a line to be a directive +if the @samp{#} appeared in column 1 on the line. Therefore +@option{-Wtraditional} warns about directives that traditional C +understands but would ignore because the @samp{#} does not appear as the +first character on the line. It also suggests you hide directives like +@samp{#pragma} not understood by traditional C by indenting them. Some +traditional implementations would not recognize @samp{#elif}, so it +suggests avoiding it altogether. + +@item +A function-like macro that appears without an argument list. In +traditional C this was an error. In ISO C it merely means that the +macro is not expanded. + +@item +The unary plus operator. This did not exist in traditional C@. + +@item +The @samp{U} and @samp{LL} integer constant suffixes, which were not +available in traditional C@. (Traditional C does support the @samp{L} +suffix for simple long integer constants.) You are not warned about +uses of these suffixes in macros defined in system headers. For +instance, @code{UINT_MAX} may well be defined as @code{4294967295U}, but +you will not be warned if you use @code{UINT_MAX}. + +You can usually avoid the warning, and the related warning about +constants which are so large that they are unsigned, by writing the +integer constant in question in hexadecimal, with no U suffix. Take +care, though, because this gives the wrong result in exotic cases. +@end itemize + +@node Implementation Details +@chapter Implementation Details + +Here we document details of how the preprocessor's implementation +affects its user-visible behavior. You should try to avoid undue +reliance on behavior described here, as it is possible that it will +change subtly in future implementations. + +Also documented here are obsolete features and changes from previous +versions of GNU CPP@. + +@menu +* Implementation-defined behavior:: +* Implementation limits:: +* Obsolete Features:: +* Differences from previous versions:: +@end menu + +@node Implementation-defined behavior +@section Implementation-defined behavior +@cindex implementation-defined behavior + +This is how GNU CPP behaves in all the cases which the C standard +describes as @dfn{implementation-defined}. This term means that the +implementation is free to do what it likes, but must document its choice +and stick to it. +@c FIXME: Check the C++ standard for more implementation-defined stuff. + +@itemize @bullet +@need 1000 +@item The mapping of physical source file multi-byte characters to the +execution character set. + +Currently, GNU cpp only supports character sets that are strict supersets +of ASCII, and performs no translation of characters. + +@item Non-empty sequences of whitespace characters. + +In textual output, each whitespace sequence is collapsed to a single +space. For aesthetic reasons, the first token on each non-directive +line of output is preceded with sufficient spaces that it appears in the +same column as it did in the original source file. + +@item The numeric value of character constants in preprocessor expressions. + +The preprocessor and compiler interpret character constants in the same +way; escape sequences such as @samp{\a} are given the values they would +have on the target machine. + +Multi-character character constants are interpreted a character at a +time, shifting the previous result left by the number of bits per +character on the host, and adding the new character. For example, 'ab' +on an 8-bit host would be interpreted as @w{'a' * 256 + 'b'}. If there +are more characters in the constant than can fit in the widest native +integer type on the host, usually a @code{long}, the excess characters +are ignored and a diagnostic is given. + +@item Source file inclusion. + +For a discussion on how the preprocessor locates header files, +@ref{Include Operation}. + +@item Interpretation of the filename resulting from a macro-expanded +@samp{#include} directive. + +@xref{Computed Includes}. + +@item Treatment of a @samp{#pragma} directive that after macro-expansion +results in a standard pragma. + +No macro expansion occurs on any @samp{#pragma} directive line, so the +question does not arise. + +Note that GCC does not yet implement any of the standard +pragmas. + +@end itemize + +@node Implementation limits +@section Implementation limits +@cindex implementation limits + +GNU CPP has a small number of internal limits. This section lists the +limits which the C standard requires to be no lower than some minimum, +and all the others we are aware of. We intend there to be as few limits +as possible. If you encounter an undocumented or inconvenient limit, +please report that to us as a bug. (See the section on reporting bugs in +the GCC manual.) + +Where we say something is limited @dfn{only by available memory}, that +means that internal data structures impose no intrinsic limit, and space +is allocated with @code{malloc} or equivalent. The actual limit will +therefore depend on many things, such as the size of other things +allocated by the compiler at the same time, the amount of memory +consumed by other processes on the same computer, etc. + +@itemize @bullet + +@item Nesting levels of @samp{#include} files. + +We impose an arbitrary limit of 200 levels, to avoid runaway recursion. +The standard requires at least 15 levels. + +@item Nesting levels of conditional inclusion. + +The C standard mandates this be at least 63. GNU CPP is limited only by +available memory. + +@item Levels of parenthesised expressions within a full expression. + +The C standard requires this to be at least 63. In preprocessor +conditional expressions, it is limited only by available memory. + +@item Significant initial characters in an identifier or macro name. + +The preprocessor treats all characters as significant. The C standard +requires only that the first 63 be significant. + +@item Number of macros simultaneously defined in a single translation unit. + +The standard requires at least 4095 be possible. GNU CPP is limited only +by available memory. + +@item Number of parameters in a macro definition and arguments in a macro call. + +We allow @code{USHRT_MAX}, which is no smaller than 65,535. The minimum +required by the standard is 127. + +@item Number of characters on a logical source line. + +The C standard requires a minimum of 4096 be permitted. GNU CPP places +no limits on this, but you may get incorrect column numbers reported in +diagnostics for lines longer than 65,535 characters. + +@item Maximum size of a source file. + +The standard does not specify any lower limit on the maximum size of a +source file. GNU cpp maps files into memory, so it is limited by the +available address space. This is generally at least two gigabytes. +Depending on the operating system, the size of physical memory may or +may not be a limitation. + +@end itemize + +@node Obsolete Features +@section Obsolete Features + +GNU CPP has a number of features which are present mainly for +compatibility with older programs. We discourage their use in new code. +In some cases, we plan to remove the feature in a future version of GCC@. + +@menu +* Assertions:: +* Obsolete once-only headers:: +* Miscellaneous obsolete features:: +@end menu + +@node Assertions +@subsection Assertions +@cindex assertions + +@dfn{Assertions} are a deprecated alternative to macros in writing +conditionals to test what sort of computer or system the compiled +program will run on. Assertions are usually predefined, but you can +define them with preprocessing directives or command-line options. + +Assertions were intended to provide a more systematic way to describe +the compiler's target system. However, in practice they are just as +unpredictable as the system-specific predefined macros. In addition, they +are not part of any standard, and only a few compilers support them. +Therefore, the use of assertions is @strong{less} portable than the use +of system-specific predefined macros. We recommend you do not use them at +all. + +@cindex predicates +An assertion looks like this: + +@example +#@var{predicate} (@var{answer}) +@end example + +@noindent +@var{predicate} must be a single identifier. @var{answer} can be any +sequence of tokens; all characters are significant except for leading +and trailing whitespace, and differences in internal whitespace +sequences are ignored. (This is similar to the rules governing macro +redefinition.) Thus, @code{(x + y)} is different from @code{(x+y)} but +equivalent to @code{@w{( x + y )}}. Parentheses do not nest inside an +answer. + +@cindex testing predicates +To test an assertion, you write it in an @samp{#if}. For example, this +conditional succeeds if either @code{vax} or @code{ns16000} has been +asserted as an answer for @code{machine}. + +@example +#if #machine (vax) || #machine (ns16000) +@end example + +@noindent +You can test whether @emph{any} answer is asserted for a predicate by +omitting the answer in the conditional: + +@example +#if #machine +@end example + +@findex #assert +Assertions are made with the @samp{#assert} directive. Its sole +argument is the assertion to make, without the leading @samp{#} that +identifies assertions in conditionals. + +@example +#assert @var{predicate} (@var{answer}) +@end example + +@noindent +You may make several assertions with the same predicate and different +answers. Subsequent assertions do not override previous ones for the +same predicate. All the answers for any given predicate are +simultaneously true. + +@cindex assertions, cancelling +@findex #unassert +Assertions can be cancelled with the @samp{#unassert} directive. It +has the same syntax as @samp{#assert}. In that form it cancels only the +answer which was specified on the @samp{#unassert} line; other answers +for that predicate remain true. You can cancel an entire predicate by +leaving out the answer: + +@example +#unassert @var{predicate} +@end example + +@noindent +In either form, if no such assertion has been made, @samp{#unassert} has +no effect. + +You can also make or cancel assertions using command line options. +@xref{Invocation}. + +@node Obsolete once-only headers +@subsection Obsolete once-only headers + +GNU CPP supports two more ways of indicating that a header file should be +read only once. Neither one is as portable as a wrapper @samp{#ifndef}, +and we recommend you do not use them in new programs. + +@findex #import +In the Objective-C language, there is a variant of @samp{#include} +called @samp{#import} which includes a file, but does so at most once. +If you use @samp{#import} instead of @samp{#include}, then you don't +need the conditionals inside the header file to prevent multiple +inclusion of the contents. GCC permits the use of @samp{#import} in C +and C++ as well as Objective-C@. However, it is not in standard C or C++ +and should therefore not be used by portable programs. + +@samp{#import} is not a well designed feature. It requires the users of +a header file to know that it should only be included once. It is much +better for the header file's implementor to write the file so that users +don't need to know this. Using a wrapper @samp{#ifndef} accomplishes +this goal. + +In the present implementation, a single use of @samp{#import} will +prevent the file from ever being read again, by either @samp{#import} or +@samp{#include}. You should not rely on this; do not use both +@samp{#import} and @samp{#include} to refer to the same header file. + +Another way to prevent a header file from being included more than once +is with the @samp{#pragma once} directive. If @samp{#pragma once} is +seen when scanning a header file, that file will never be read again, no +matter what. + +@samp{#pragma once} does not have the problems that @samp{#import} does, +but it is not recognized by all preprocessors, so you cannot rely on it +in a portable program. + +@node Miscellaneous obsolete features +@subsection Miscellaneous obsolete features + +Here are a few more obsolete features. + +@itemize @bullet +@cindex invalid token paste +@item Attempting to paste two tokens which together do not form a valid +preprocessing token. + +The preprocessor currently warns about this and outputs the two tokens +adjacently, which is probably the behavior the programmer intends. It +may not work in future, though. + +Most of the time, when you get this warning, you will find that @samp{##} +is being used superstitiously, to guard against whitespace appearing +between two tokens. It is almost always safe to delete the @samp{##}. + +@cindex pragma poison +@item @code{#pragma poison} + +This is the same as @code{#pragma GCC poison}. The version without the +@code{GCC} prefix is deprecated. @xref{Pragmas}. + +@cindex multi-line string constants +@item Multi-line string constants + +GCC currently allows a string constant to extend across multiple logical +lines of the source file. This extension is deprecated and will be +removed in a future version of GCC@. Such string constants are already +rejected in all directives apart from @samp{#define}. + +Instead, make use of ISO C concatenation of adjacent string literals, or +use @samp{\n} followed by a backslash-newline. + +@end itemize + +@node Differences from previous versions +@section Differences from previous versions +@cindex differences from previous versions + +This section details behavior which has changed from previous versions +of GNU CPP@. We do not plan to change it again in the near future, but +we do not promise not to, either. + +The ``previous versions'' discussed here are 2.95 and before. The +behavior of GCC 3.0 is mostly the same as the behavior of the widely +used 2.96 and 2.97 development snapshots. Where there are differences, +they generally represent bugs in the snapshots. + +@itemize @bullet + +@item Order of evaluation of @samp{#} and @samp{##} operators + +The standard does not specify the order of evaluation of a chain of +@samp{##} operators, nor whether @samp{#} is evaluated before, after, or +at the same time as @samp{##}. You should therefore not write any code +which depends on any specific ordering. It is possible to guarantee an +ordering, if you need one, by suitable use of nested macros. + +An example of where this might matter is pasting the arguments @samp{1}, +@samp{e} and @samp{-2}. This would be fine for left-to-right pasting, +but right-to-left pasting would produce an invalid token @samp{e-2}. + +GCC 3.0 evaluates @samp{#} and @samp{##} at the same time and strictly +left to right. Older versions evaluated all @samp{#} operators first, +then all @samp{##} operators, in an unreliable order. + +@item The form of whitespace betwen tokens in preprocessor output + +@xref{Preprocessor Output}, for the current textual format. This is +also the format used by stringification. Normally, the preprocessor +communicates tokens directly to the compiler's parser, and whitespace +does not come up at all. + +Older versions of GCC preserved all whitespace provided by the user and +inserted lots more whitespace of their own, because they could not +accurately predict when extra spaces were needed to prevent accidental +token pasting. + +@item Optional argument when invoking rest argument macros + +As an extension, GCC permits you to omit the variable arguments entirely +when you use a variable argument macro. This is forbidden by the 1999 C +standard, and will provoke a pedantic warning with GCC 3.0. Previous +versions accepted it silently. + +@item @samp{##} swallowing preceding text in rest argument macros + +Formerly, in a macro expansion, if @samp{##} appeared before a variable +arguments parameter, and the set of tokens specified for that argument +in the macro invocation was empty, previous versions of GNU CPP would +back up and remove the preceding sequence of non-whitespace characters +(@strong{not} the preceding token). This extension is in direct +conflict with the 1999 C standard and has been drastically pared back. + +In the current version of the preprocessor, if @samp{##} appears between +a comma and a variable arguments parameter, and the variable argument is +omitted entirely, the comma will be removed from the expansion. If the +variable argument is empty, or the token before @samp{##} is not a +comma, then @samp{##} behaves as a normal token paste. + +@item Traditional mode and GNU extensions + +Traditional mode used to be implemented in the same program as normal +preprocessing. Therefore, all the GNU extensions to the preprocessor +were still available in traditional mode. It is now a separate program +and does not implement any of the GNU extensions, except for a partial +implementation of assertions. Even those may be removed in a future +release. +@end itemize + +@node Invocation +@chapter Invocation +@cindex invocation +@cindex command line + +Most often when you use the C preprocessor you will not have to invoke it +explicitly: the C compiler will do so automatically. However, the +preprocessor is sometimes useful on its own. All the options listed +here are also acceptable to the C compiler and have the same meaning, +except that the C compiler has different rules for specifying the output +file. + +@strong{Note:} Whether you use the preprocessor by way of @command{gcc} +or @command{cpp}, the @dfn{compiler driver} is run first. This +program's purpose is to translate your command into invocations of the +programs that do the actual work. Their command line interfaces are +similar but not identical to the documented interface, and may change +without notice. + +@ignore +@c man begin SYNOPSIS +cpp [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] + [@option{-I}@var{dir}@dots{}] [@option{-W}@var{warn}@dots{}] + [@option{-M}|@option{-MM}] [@option{-MG}] [@option{-MF} @var{filename}] + [@option{-MP}] [@option{-MQ} @var{target}@dots{}] [@option{-MT} @var{target}@dots{}] + [@option{-x} @var{language}] [@option{-std=}@var{standard}] + @var{infile} @var{outfile} + +Only the most useful options are listed here; see below for the remainder. +@c man end +@c man begin SEEALSO +gpl(7), gfdl(7), fsf-funding(7), +gcc(1), as(1), ld(1), and the Info entries for @file{cpp}, @file{gcc}, and +@file{binutils}. +@c man end +@end ignore + +@c man begin OPTIONS +The C preprocessor expects two file names as arguments, @var{infile} and +@var{outfile}. The preprocessor reads @var{infile} together with any +other files it specifies with @samp{#include}. All the output generated +by the combined input files is written in @var{outfile}. + +Either @var{infile} or @var{outfile} may be @option{-}, which as +@var{infile} means to read from standard input and as @var{outfile} +means to write to standard output. Also, if either file is omitted, it +means the same as if @option{-} had been specified for that file. + +Unless otherwise noted, or the option ends in @samp{=}, all options +which take an argument may have that argument appear either immediately +after the option, or with a space between option and argument: +@option{-Ifoo} and @option{-I foo} have the same effect. + +@cindex grouping options +@cindex options, grouping +Many options have multi-letter names; therefore multiple single-letter +options may @emph{not} be grouped: @option{-dM} is very different from +@w{@samp{-d -M}}. + +@cindex options +@table @gcctabopt +@item -D @var{name} +Predefine @var{name} as a macro, with definition @code{1}. + +@item -D @var{name}=@var{definition} +Predefine @var{name} as a macro, with definition @var{definition}. +There are no restrictions on the contents of @var{definition}, but if +you are invoking the preprocessor from a shell or shell-like program you +may need to use the shell's quoting syntax to protect characters such as +spaces that have a meaning in the shell syntax. If you use more than +one @option{-D} for the same @var{name}, the rightmost definition takes +effect. + +If you wish to define a function-like macro on the command line, write +its argument list with surrounding parentheses before the equals sign +(if any). Parentheses are meaningful to most shells, so you will need +to quote the option. With @command{sh} and @command{csh}, +@option{-D'@var{name}(@var{args@dots{}})=@var{definition}'} works. + +@item -U @var{name} +Cancel any previous definition of @var{name}, either built in or +provided with a @option{-D} option. + +All @option{-imacros @var{file}} and @option{-include @var{file}} options +are processed after all @option{-D} and @option{-U} options. + +@item -undef +Do not predefine any system-specific macros. The common predefined +macros remain defined. + +@item -I @var{dir} +Add the directory @var{dir} to the list of directories to be searched +for header files. @xref{Search Path}. Directories named by @option{-I} +are searched before the standard system include directories. + +It is dangerous to specify a standard system include directory in an +@option{-I} option. This defeats the special treatment of system +headers (@pxref{System Headers}). It can also defeat the repairs to +buggy system headers which GCC makes when it is installed. + +@item -o @var{file} +Write output to @var{file}. This is the same as specifying @var{file} +as the second non-option argument to @command{cpp}. @command{gcc} has a +different interpretation of a second non-option argument, so you must +use @option{-o} to specify the output file. + +@item -Wall +Turns on all optional warnings which are desirable for normal code. At +present this is @option{-Wcomment} and @option{-Wtrigraphs}. Note that +many of the preprocessor's warnings are on by default and have no +options to control them. + +@item -Wcomment +@itemx -Wcomments +Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} +comment, or whenever a backslash-newline appears in a @samp{//} comment. +(Both forms have the same effect.) + +@item -Wtrigraphs +Warn if any trigraphs are encountered. This option used to take effect +only if @option{-trigraphs} was also specified, but now works +independently. Warnings are not given for trigraphs within comments, as +they do not affect the meaning of the program. + +@item -Wtraditional +Warn about certain constructs that behave differently in traditional and +ISO C@. Also warn about ISO C constructs that have no traditional C +equivalent, and problematic constructs which should be avoided. +@xref{Traditional Mode}. + +@item -Wimport +Warn the first time @samp{#import} is used. + +@item -Wundef +Warn whenever an identifier which is not a macro is encountered in an +@samp{#if} directive, outside of @samp{defined}. Such identifiers are +replaced with zero. + +@item -Werror +Make all warnings into hard errors. Source code which triggers warnings +will be rejected. + +@item -Wsystem-headers +Issue warnings for code in system headers. These are normally unhelpful +in finding bugs in your own code, therefore suppressed. If you are +responsible for the system library, you may want to see them. + +@item -w +Suppress all warnings, including those which GNU CPP issues by default. + +@item -pedantic +Issue all the mandatory diagnostics listed in the C standard. Some of +them are left out by default, since they trigger frequently on harmless +code. + +@item -pedantic-errors +Issue all the mandatory diagnostics, and make all mandatory diagnostics +into errors. This includes mandatory diagnostics that GCC issues +without @samp{-pedantic} but treats as warnings. + +@item -M +Instead of outputting the result of preprocessing, output a rule +suitable for @command{make} describing the dependencies of the main +source file. The preprocessor outputs one @command{make} rule containing +the object file name for that source file, a colon, and the names of all +the included files, including those coming from @option{-include} or +@option{-imacros} command line options. + +Unless specified explicitly (with @option{-MT} or @option{-MQ}), the +object file name consists of the basename of the source file with any +suffix replaced with object file suffix. If there are many included +files then the rule is split into several lines using @samp{\}-newline. +The rule has no commands. + +@item -MM +Like @option{-M}, but mention only the files included with @code{@w{#include +"@var{file}"}} or with @option{-include} or @option{-imacros} command line +options. System header files included with @code{@w{#include <@var{file}>}} +are omitted. + +@item -MF @var{file} +When used with @option{-M} or @option{-MM}, specifies a file to write the +dependencies to. This allows the preprocessor to write the preprocessed +file to stdout normally. If no @option{-MF} switch is given, CPP sends +the rules to stdout and suppresses normal preprocessed output. + +@item -MG +When used with @option{-M} or @option{-MM}, @option{-MG} says to treat missing +header files as generated files and assume they live in the same +directory as the source file. It suppresses preprocessed output, as a +missing header file is ordinarily an error. + +This feature is used in automatic updating of makefiles. + +@item -MP +This option instructs CPP to add a phony target for each dependency +other than the main file, causing each to depend on nothing. These +dummy rules work around errors @command{make} gives if you remove header +files without updating the @file{Makefile} to match. + +This is typical output: + +@example +test.o: test.c test.h + +test.h: +@end example + +@item -MT @var{target} + +Change the target of the rule emitted by dependency generation. By +default CPP takes the name of the main input file, including any path, +deletes any file suffix such as @samp{.c}, and appends the platform's +usual object suffix. The result is the target. + +An @option{-MT} option will set the target to be exactly the string you +specify. If you want multiple targets, you can specify them as a single +argument to @option{-MT}, or use multiple @option{-MT} options. + +For example, @option{@w{-MT '$(objpfx)foo.o'}} might give + +@example +$(objpfx)foo.o: foo.c +@end example + +@item -MQ @var{target} + +Same as @option{-MT}, but it quotes any characters which are special to +Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives + +@example +$$(objpfx)foo.o: foo.c +@end example + +The default target is automatically quoted, as if it were given with +@option{-MQ}. + +@item -MD @var{file} +@itemx -MMD @var{file} +@option{-MD @var{file}} is equivalent to @option{-M -MF @var{file}}, and +@option{-MMD @var{file}} is equivalent to @option{-MM -MF @var{file}}. + +Due to limitations in the compiler driver, you must use these switches +when you want to generate a dependency file as a side-effect of normal +compilation. + +@item -x c +@itemx -x c++ +@itemx -x objective-c +@itemx -x assembler-with-cpp +Specify the source language: C, C++, Objective-C, or assembly. This has +nothing to do with standards conformance or extensions; it merely +selects which base syntax to expect. If you give none of these options, +cpp will deduce the language from the extension of the source file: +@samp{.c}, @samp{.cc}, @samp{.m}, or @samp{.S}. Some other common +extensions for C++ and assembly are also recognized. If cpp does not +recognize the extension, it will treat the file as C; this is the most +generic mode. + +@strong{Note:} Previous versions of cpp accepted a @option{-lang} option +which selected both the language and the standards conformance level. +This option has been removed, because it conflicts with the @option{-l} +option. + +@item -std=@var{standard} +@itemx -ansi +Specify the standard to which the code should conform. Currently cpp +only knows about the standards for C; other language standards will be +added in the future. + +@var{standard} +may be one of: +@table @code +@item iso9899:1990 +@itemx c89 +The ISO C standard from 1990. @samp{c89} is the customary shorthand for +this version of the standard. + +The @option{-ansi} option is equivalent to @option{-std=c89}. + +@item iso9899:199409 +The 1990 C standard, as amended in 1994. + +@item iso9899:1999 +@itemx c99 +@itemx iso9899:199x +@itemx c9x +The revised ISO C standard, published in December 1999. Before +publication, this was known as C9X@. + +@item gnu89 +The 1990 C standard plus GNU extensions. This is the default. + +@item gnu99 +@itemx gnu9x +The 1999 C standard plus GNU extensions. +@end table + +@item -I- +Split the include path. Any directories specified with @option{-I} +options before @option{-I-} are searched only for headers requested with +@code{@w{#include "@var{file}"}}; they are not searched for +@code{@w{#include <@var{file}>}}. If additional directories are +specified with @option{-I} options after the @option{-I-}, those +directories are searched for all @samp{#include} directives. + +In addition, @option{-I-} inhibits the use of the directory of the current +file directory as the first search directory for @code{@w{#include +"@var{file}"}}. @xref{Search Path}. + +@item -nostdinc +Do not search the standard system directories for header files. +Only the directories you have specified with @option{-I} options +(and the directory of the current file, if appropriate) are searched. + +@item -nostdinc++ +Do not search for header files in the C++-specific standard directories, +but do still search the other standard directories. (This option is +used when building the C++ library.) + +@item -include @var{file} + +Process @var{file} as if @code{#include "file"} appeared as the first +line of the primary source file. However, the first directory searched +for @var{file} is the preprocessor's working directory @emph{instead of} +the directory containing the main source file. If not found there, it +is searched for in the remainder of the @code{#include "@dots{}"} search +chain as normal. + +If multiple @option{-include} options are given, the files are included +in the order they appear on the command line. + +@item -imacros @var{file} + +Exactly like @option{-include}, except that any output produced by +scanning @var{file} is thrown away. Macros it defines remain defined. +This allows you to acquire all the macros from a header without also +processing its declarations. + +All files specified by @option{-imacros} are processed before all files +specified by @option{-include}. + +@item -idirafter @var{dir} +Search @var{dir} for header files, but do it @emph{after} all +directories specified with @option{-I} and the standard system directories +have been exhausted. @var{dir} is treated as a system include directory. + +@item -iprefix @var{prefix} +Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix} +options. If the prefix represents a directory, you should include the +final @samp{/}. + +@item -iwithprefix @var{dir} +@itemx -iwithprefixbefore @var{dir} + +Append @var{dir} to the prefix specified previously with +@option{-iprefix}, and add the resulting directory to the include search +path. @option{-iwithprefixbefore} puts it in the same place @option{-I} +would; @option{-iwithprefix} puts it where @option{-idirafter} would. + +Use of these options is discouraged. + +@item -isystem @var{dir} +Search @var{dir} for header files, after all directories specified by +@option{-I} but before the standard system directories. Mark it +as a system directory, so that it gets the same special treatment as +is applied to the standard system directories. @xref{System Headers}. + +@item -fpreprocessed +Indicate to the preprocessor that the input file has already been +preprocessed. This suppresses things like macro expansion, trigraph +conversion, escaped newline splicing, and processing of most directives. +The preprocessor still recognizes and removes comments, so that you can +pass a file preprocessed with @option{-C} to the compiler without +problems. In this mode the integrated preprocessor is little more than +a tokenizer for the front ends. + +@option{-fpreprocessed} is implicit if the input file has one of the +extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the +extensions that GCC uses for preprocessed files created by +@option{-save-temps}. + +@item -ftabstop=@var{width} +Set the distance between tab stops. This helps the preprocessor report +correct column numbers in warnings or errors, even if tabs appear on the +line. If the value is less than 1 or greater than 100, the option is +ignored. The default is 8. + +@item -fno-show-column +Do not print column numbers in diagnostics. This may be necessary if +diagnostics are being scanned by a program that does not understand the +column numbers, such as @command{dejagnu}. + +@item -A @var{predicate}=@var{answer} +Make an assertion with the predicate @var{predicate} and answer +@var{answer}. This form is preferred to the older form @option{-A +@var{predicate}(@var{answer})}, which is still supported, because +it does not use shell special characters. @xref{Assertions}. + +@item -A -@var{predicate}=@var{answer} +Cancel an assertion with the predicate @var{predicate} and answer +@var{answer}. + +@item -A- +Cancel all predefined assertions and all assertions preceding it on +the command line. Also, undefine all predefined macros and all +macros preceding it on the command line. (This is a historical wart and +may change in the future.) + +@item -dCHARS +@var{CHARS} is a sequence of one or more of the following characters, +and must not be preceded by a space. Other characters are interpreted +by the compiler proper, or reserved for future versions of GCC, and so +are silently ignored. If you specify characters whose behavior +conflicts, the result is undefined. + +@table @samp +@item M +Instead of the normal output, generate a list of @samp{#define} +directives for all the macros defined during the execution of the +preprocessor, including predefined macros. This gives you a way of +finding out what is predefined in your version of the preprocessor. +Assuming you have no file @file{foo.h}, the command + +@example +touch foo.h; cpp -dM foo.h +@end example + +@noindent +will show all the predefined macros. + +@item D +Like @samp{M} except in two respects: it does @emph{not} include the +predefined macros, and it outputs @emph{both} the @samp{#define} +directives and the result of preprocessing. Both kinds of output go to +the standard output file. + +@item N +Like @samp{D}, but emit only the macro names, not their expansions. + +@item I +Output @samp{#include} directives in addition to the result of +preprocessing. +@end table + +@item -P +Inhibit generation of linemarkers in the output from the preprocessor. +This might be useful when running the preprocessor on something that is +not C code, and will be sent to a program which might be confused by the +linemarkers. @xref{Preprocessor Output}. + +@item -C +Do not discard comments. All comments are passed through to the output +file, except for comments in processed directives, which are deleted +along with the directive. + +You should be prepared for side effects when using @option{-C}; it +causes the preprocessor to treat comments as tokens in their own right. +For example, comments appearing at the start of what would be a +directive line have the effect of turning that line into an ordinary +source line, since the first token on the line is no longer a @samp{#}. + +@item -gcc +Define the macros @sc{__gnuc__}, @sc{__gnuc_minor__} and +@sc{__gnuc_patchlevel__}. These are defined automatically when you use +@command{gcc -E}; you can turn them off in that case with +@option{-no-gcc}. + +@item -traditional +Try to imitate the behavior of old-fashioned C, as opposed to ISO +C@. @xref{Traditional Mode}. + +@item -trigraphs +Process trigraph sequences. @xref{Initial processing}. + +@item -remap +Enable special code to work around file systems which only permit very +short file names, such as MS-DOS@. + +@item -$ +Forbid the use of @samp{$} in identifiers. The C standard allows +implementations to define extra characters that can appear in +identifiers. By default GNU CPP permits @samp{$}, a common extension. + +@item -h +@itemx --help +@itemx --target-help +Print text describing all the command line options instead of +preprocessing anything. + +@item -v +Verbose mode. Print out GNU CPP's version number at the beginning of +execution, and report the final form of the include path. + +@item -H +Print the name of each header file used, in addition to other normal +activities. Each name is indented to show how deep in the +@samp{#include} stack it is. + +@item -version +@itemx --version +Print out GNU CPP's version number. With one dash, proceed to +preprocess as normal. With two dashes, exit immediately. +@end table +@c man end + +@include fdl.texi + +@page +@node Index of Directives +@unnumbered Index of Directives +@printindex fn + +@node Concept Index +@unnumbered Concept Index +@printindex cp + +@bye diff --git a/contrib/gcc/doc/cppinternals.texi b/contrib/gcc/doc/cppinternals.texi new file mode 100644 index 000000000000..3f3d9af00517 --- /dev/null +++ b/contrib/gcc/doc/cppinternals.texi @@ -0,0 +1,1065 @@ +\input texinfo +@setfilename cppinternals.info +@settitle The GNU C Preprocessor Internals + +@ifinfo +@dircategory Programming +@direntry +* Cpplib: (cppinternals). Cpplib internals. +@end direntry +@end ifinfo + +@c @smallbook +@c @cropmarks +@c @finalout +@setchapternewpage odd +@ifinfo +This file documents the internals of the GNU C Preprocessor. + +Copyright 2000, 2001, 2002 Free Software Foundation, Inc. + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +@ignore +Permission is granted to process this file through Tex and print the +results, provided the printed document carries copying permission +notice identical to this one except for the removal of this paragraph +(this paragraph not being relevant to the printed manual). + +@end ignore +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that +the entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. +@end ifinfo + +@titlepage +@c @finalout +@title Cpplib Internals +@subtitle Last revised January 2002 +@subtitle for GCC version 3.1 +@author Neil Booth +@page +@vskip 0pt plus 1filll +@c man begin COPYRIGHT +Copyright @copyright{} 2000, 2001, 2002 +Free Software Foundation, Inc. + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that +the entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. +@c man end +@end titlepage +@contents +@page + +@node Top +@top +@chapter Cpplib---the GNU C Preprocessor + +The GNU C preprocessor in GCC 3.x has been completely rewritten. It is +now implemented as a library, @dfn{cpplib}, so it can be easily shared between +a stand-alone preprocessor, and a preprocessor integrated with the C, +C++ and Objective-C front ends. It is also available for use by other +programs, though this is not recommended as its exposed interface has +not yet reached a point of reasonable stability. + +The library has been written to be re-entrant, so that it can be used +to preprocess many files simultaneously if necessary. It has also been +written with the preprocessing token as the fundamental unit; the +preprocessor in previous versions of GCC would operate on text strings +as the fundamental unit. + +This brief manual documents the internals of cpplib, and explains some +of the tricky issues. It is intended that, along with the comments in +the source code, a reasonably competent C programmer should be able to +figure out what the code is doing, and why things have been implemented +the way they have. + +@menu +* Conventions:: Conventions used in the code. +* Lexer:: The combined C, C++ and Objective-C Lexer. +* Hash Nodes:: All identifiers are entered into a hash table. +* Macro Expansion:: Macro expansion algorithm. +* Token Spacing:: Spacing and paste avoidance issues. +* Line Numbering:: Tracking location within files. +* Guard Macros:: Optimizing header files with guard macros. +* Files:: File handling. +* Index:: Index. +@end menu + +@node Conventions +@unnumbered Conventions +@cindex interface +@cindex header files + +cpplib has two interfaces---one is exposed internally only, and the +other is for both internal and external use. + +The convention is that functions and types that are exposed to multiple +files internally are prefixed with @samp{_cpp_}, and are to be found in +the file @file{cpphash.h}. Functions and types exposed to external +clients are in @file{cpplib.h}, and prefixed with @samp{cpp_}. For +historical reasons this is no longer quite true, but we should strive to +stick to it. + +We are striving to reduce the information exposed in @file{cpplib.h} to the +bare minimum necessary, and then to keep it there. This makes clear +exactly what external clients are entitled to assume, and allows us to +change internals in the future without worrying whether library clients +are perhaps relying on some kind of undocumented implementation-specific +behavior. + +@node Lexer +@unnumbered The Lexer +@cindex lexer +@cindex newlines +@cindex escaped newlines + +@section Overview +The lexer is contained in the file @file{cpplex.c}. It is a hand-coded +lexer, and not implemented as a state machine. It can understand C, C++ +and Objective-C source code, and has been extended to allow reasonably +successful preprocessing of assembly language. The lexer does not make +an initial pass to strip out trigraphs and escaped newlines, but handles +them as they are encountered in a single pass of the input file. It +returns preprocessing tokens individually, not a line at a time. + +It is mostly transparent to users of the library, since the library's +interface for obtaining the next token, @code{cpp_get_token}, takes care +of lexing new tokens, handling directives, and expanding macros as +necessary. However, the lexer does expose some functionality so that +clients of the library can easily spell a given token, such as +@code{cpp_spell_token} and @code{cpp_token_len}. These functions are +useful when generating diagnostics, and for emitting the preprocessed +output. + +@section Lexing a token +Lexing of an individual token is handled by @code{_cpp_lex_direct} and +its subroutines. In its current form the code is quite complicated, +with read ahead characters and such-like, since it strives to not step +back in the character stream in preparation for handling non-ASCII file +encodings. The current plan is to convert any such files to UTF-8 +before processing them. This complexity is therefore unnecessary and +will be removed, so I'll not discuss it further here. + +The job of @code{_cpp_lex_direct} is simply to lex a token. It is not +responsible for issues like directive handling, returning lookahead +tokens directly, multiple-include optimization, or conditional block +skipping. It necessarily has a minor r@^ole to play in memory +management of lexed lines. I discuss these issues in a separate section +(@pxref{Lexing a line}). + +The lexer places the token it lexes into storage pointed to by the +variable @code{cur_token}, and then increments it. This variable is +important for correct diagnostic positioning. Unless a specific line +and column are passed to the diagnostic routines, they will examine the +@code{line} and @code{col} values of the token just before the location +that @code{cur_token} points to, and use that location to report the +diagnostic. + +The lexer does not consider whitespace to be a token in its own right. +If whitespace (other than a new line) precedes a token, it sets the +@code{PREV_WHITE} bit in the token's flags. Each token has its +@code{line} and @code{col} variables set to the line and column of the +first character of the token. This line number is the line number in +the translation unit, and can be converted to a source (file, line) pair +using the line map code. + +The first token on a logical, i.e.@: unescaped, line has the flag +@code{BOL} set for beginning-of-line. This flag is intended for +internal use, both to distinguish a @samp{#} that begins a directive +from one that doesn't, and to generate a call-back to clients that want +to be notified about the start of every non-directive line with tokens +on it. Clients cannot reliably determine this for themselves: the first +token might be a macro, and the tokens of a macro expansion do not have +the @code{BOL} flag set. The macro expansion may even be empty, and the +next token on the line certainly won't have the @code{BOL} flag set. + +New lines are treated specially; exactly how the lexer handles them is +context-dependent. The C standard mandates that directives are +terminated by the first unescaped newline character, even if it appears +in the middle of a macro expansion. Therefore, if the state variable +@code{in_directive} is set, the lexer returns a @code{CPP_EOF} token, +which is normally used to indicate end-of-file, to indicate +end-of-directive. In a directive a @code{CPP_EOF} token never means +end-of-file. Conveniently, if the caller was @code{collect_args}, it +already handles @code{CPP_EOF} as if it were end-of-file, and reports an +error about an unterminated macro argument list. + +The C standard also specifies that a new line in the middle of the +arguments to a macro is treated as whitespace. This white space is +important in case the macro argument is stringified. The state variable +@code{parsing_args} is nonzero when the preprocessor is collecting the +arguments to a macro call. It is set to 1 when looking for the opening +parenthesis to a function-like macro, and 2 when collecting the actual +arguments up to the closing parenthesis, since these two cases need to +be distinguished sometimes. One such time is here: the lexer sets the +@code{PREV_WHITE} flag of a token if it meets a new line when +@code{parsing_args} is set to 2. It doesn't set it if it meets a new +line when @code{parsing_args} is 1, since then code like + +@smallexample +#define foo() bar +foo +baz +@end smallexample + +@noindent would be output with an erroneous space before @samp{baz}: + +@smallexample +foo + baz +@end smallexample + +This is a good example of the subtlety of getting token spacing correct +in the preprocessor; there are plenty of tests in the test suite for +corner cases like this. + +The lexer is written to treat each of @samp{\r}, @samp{\n}, @samp{\r\n} +and @samp{\n\r} as a single new line indicator. This allows it to +transparently preprocess MS-DOS, Macintosh and Unix files without their +needing to pass through a special filter beforehand. + +We also decided to treat a backslash, either @samp{\} or the trigraph +@samp{??/}, separated from one of the above newline indicators by +non-comment whitespace only, as intending to escape the newline. It +tends to be a typing mistake, and cannot reasonably be mistaken for +anything else in any of the C-family grammars. Since handling it this +way is not strictly conforming to the ISO standard, the library issues a +warning wherever it encounters it. + +Handling newlines like this is made simpler by doing it in one place +only. The function @code{handle_newline} takes care of all newline +characters, and @code{skip_escaped_newlines} takes care of arbitrarily +long sequences of escaped newlines, deferring to @code{handle_newline} +to handle the newlines themselves. + +The most painful aspect of lexing ISO-standard C and C++ is handling +trigraphs and backlash-escaped newlines. Trigraphs are processed before +any interpretation of the meaning of a character is made, and unfortunately +there is a trigraph representation for a backslash, so it is possible for +the trigraph @samp{??/} to introduce an escaped newline. + +Escaped newlines are tedious because theoretically they can occur +anywhere---between the @samp{+} and @samp{=} of the @samp{+=} token, +within the characters of an identifier, and even between the @samp{*} +and @samp{/} that terminates a comment. Moreover, you cannot be sure +there is just one---there might be an arbitrarily long sequence of them. + +So, for example, the routine that lexes a number, @code{parse_number}, +cannot assume that it can scan forwards until the first non-number +character and be done with it, because this could be the @samp{\} +introducing an escaped newline, or the @samp{?} introducing the trigraph +sequence that represents the @samp{\} of an escaped newline. If it +encounters a @samp{?} or @samp{\}, it calls @code{skip_escaped_newlines} +to skip over any potential escaped newlines before checking whether the +number has been finished. + +Similarly code in the main body of @code{_cpp_lex_direct} cannot simply +check for a @samp{=} after a @samp{+} character to determine whether it +has a @samp{+=} token; it needs to be prepared for an escaped newline of +some sort. Such cases use the function @code{get_effective_char}, which +returns the first character after any intervening escaped newlines. + +The lexer needs to keep track of the correct column position, including +counting tabs as specified by the @option{-ftabstop=} option. This +should be done even within C-style comments; they can appear in the +middle of a line, and we want to report diagnostics in the correct +position for text appearing after the end of the comment. + +@anchor{Invalid identifiers} +Some identifiers, such as @code{__VA_ARGS__} and poisoned identifiers, +may be invalid and require a diagnostic. However, if they appear in a +macro expansion we don't want to complain with each use of the macro. +It is therefore best to catch them during the lexing stage, in +@code{parse_identifier}. In both cases, whether a diagnostic is needed +or not is dependent upon the lexer's state. For example, we don't want +to issue a diagnostic for re-poisoning a poisoned identifier, or for +using @code{__VA_ARGS__} in the expansion of a variable-argument macro. +Therefore @code{parse_identifier} makes use of state flags to determine +whether a diagnostic is appropriate. Since we change state on a +per-token basis, and don't lex whole lines at a time, this is not a +problem. + +Another place where state flags are used to change behavior is whilst +lexing header names. Normally, a @samp{<} would be lexed as a single +token. After a @code{#include} directive, though, it should be lexed as +a single token as far as the nearest @samp{>} character. Note that we +don't allow the terminators of header names to be escaped; the first +@samp{"} or @samp{>} terminates the header name. + +Interpretation of some character sequences depends upon whether we are +lexing C, C++ or Objective-C, and on the revision of the standard in +force. For example, @samp{::} is a single token in C++, but in C it is +two separate @samp{:} tokens and almost certainly a syntax error. Such +cases are handled by @code{_cpp_lex_direct} based upon command-line +flags stored in the @code{cpp_options} structure. + +Once a token has been lexed, it leads an independent existence. The +spelling of numbers, identifiers and strings is copied to permanent +storage from the original input buffer, so a token remains valid and +correct even if its source buffer is freed with @code{_cpp_pop_buffer}. +The storage holding the spellings of such tokens remains until the +client program calls cpp_destroy, probably at the end of the translation +unit. + +@anchor{Lexing a line} +@section Lexing a line +@cindex token run + +When the preprocessor was changed to return pointers to tokens, one +feature I wanted was some sort of guarantee regarding how long a +returned pointer remains valid. This is important to the stand-alone +preprocessor, the future direction of the C family front ends, and even +to cpplib itself internally. + +Occasionally the preprocessor wants to be able to peek ahead in the +token stream. For example, after the name of a function-like macro, it +wants to check the next token to see if it is an opening parenthesis. +Another example is that, after reading the first few tokens of a +@code{#pragma} directive and not recognizing it as a registered pragma, +it wants to backtrack and allow the user-defined handler for unknown +pragmas to access the full @code{#pragma} token stream. The stand-alone +preprocessor wants to be able to test the current token with the +previous one to see if a space needs to be inserted to preserve their +separate tokenization upon re-lexing (paste avoidance), so it needs to +be sure the pointer to the previous token is still valid. The +recursive-descent C++ parser wants to be able to perform tentative +parsing arbitrarily far ahead in the token stream, and then to be able +to jump back to a prior position in that stream if necessary. + +The rule I chose, which is fairly natural, is to arrange that the +preprocessor lex all tokens on a line consecutively into a token buffer, +which I call a @dfn{token run}, and when meeting an unescaped new line +(newlines within comments do not count either), to start lexing back at +the beginning of the run. Note that we do @emph{not} lex a line of +tokens at once; if we did that @code{parse_identifier} would not have +state flags available to warn about invalid identifiers (@pxref{Invalid +identifiers}). + +In other words, accessing tokens that appeared earlier in the current +line is valid, but since each logical line overwrites the tokens of the +previous line, tokens from prior lines are unavailable. In particular, +since a directive only occupies a single logical line, this means that +the directive handlers like the @code{#pragma} handler can jump around +in the directive's tokens if necessary. + +Two issues remain: what about tokens that arise from macro expansions, +and what happens when we have a long line that overflows the token run? + +Since we promise clients that we preserve the validity of pointers that +we have already returned for tokens that appeared earlier in the line, +we cannot reallocate the run. Instead, on overflow it is expanded by +chaining a new token run on to the end of the existing one. + +The tokens forming a macro's replacement list are collected by the +@code{#define} handler, and placed in storage that is only freed by +@code{cpp_destroy}. So if a macro is expanded in our line of tokens, +the pointers to the tokens of its expansion that we return will always +remain valid. However, macros are a little trickier than that, since +they give rise to three sources of fresh tokens. They are the built-in +macros like @code{__LINE__}, and the @samp{#} and @samp{##} operators +for stringification and token pasting. I handled this by allocating +space for these tokens from the lexer's token run chain. This means +they automatically receive the same lifetime guarantees as lexed tokens, +and we don't need to concern ourselves with freeing them. + +Lexing into a line of tokens solves some of the token memory management +issues, but not all. The opening parenthesis after a function-like +macro name might lie on a different line, and the front ends definitely +want the ability to look ahead past the end of the current line. So +cpplib only moves back to the start of the token run at the end of a +line if the variable @code{keep_tokens} is zero. Line-buffering is +quite natural for the preprocessor, and as a result the only time cpplib +needs to increment this variable is whilst looking for the opening +parenthesis to, and reading the arguments of, a function-like macro. In +the near future cpplib will export an interface to increment and +decrement this variable, so that clients can share full control over the +lifetime of token pointers too. + +The routine @code{_cpp_lex_token} handles moving to new token runs, +calling @code{_cpp_lex_direct} to lex new tokens, or returning +previously-lexed tokens if we stepped back in the token stream. It also +checks each token for the @code{BOL} flag, which might indicate a +directive that needs to be handled, or require a start-of-line call-back +to be made. @code{_cpp_lex_token} also handles skipping over tokens in +failed conditional blocks, and invalidates the control macro of the +multiple-include optimization if a token was successfully lexed outside +a directive. In other words, its callers do not need to concern +themselves with such issues. + +@node Hash Nodes +@unnumbered Hash Nodes +@cindex hash table +@cindex identifiers +@cindex macros +@cindex assertions +@cindex named operators + +When cpplib encounters an ``identifier'', it generates a hash code for +it and stores it in the hash table. By ``identifier'' we mean tokens +with type @code{CPP_NAME}; this includes identifiers in the usual C +sense, as well as keywords, directive names, macro names and so on. For +example, all of @code{pragma}, @code{int}, @code{foo} and +@code{__GNUC__} are identifiers and hashed when lexed. + +Each node in the hash table contain various information about the +identifier it represents. For example, its length and type. At any one +time, each identifier falls into exactly one of three categories: + +@itemize @bullet +@item Macros + +These have been declared to be macros, either on the command line or +with @code{#define}. A few, such as @code{__TIME__} are built-ins +entered in the hash table during initialization. The hash node for a +normal macro points to a structure with more information about the +macro, such as whether it is function-like, how many arguments it takes, +and its expansion. Built-in macros are flagged as special, and instead +contain an enum indicating which of the various built-in macros it is. + +@item Assertions + +Assertions are in a separate namespace to macros. To enforce this, cpp +actually prepends a @code{#} character before hashing and entering it in +the hash table. An assertion's node points to a chain of answers to +that assertion. + +@item Void + +Everything else falls into this category---an identifier that is not +currently a macro, or a macro that has since been undefined with +@code{#undef}. + +When preprocessing C++, this category also includes the named operators, +such as @code{xor}. In expressions these behave like the operators they +represent, but in contexts where the spelling of a token matters they +are spelt differently. This spelling distinction is relevant when they +are operands of the stringizing and pasting macro operators @code{#} and +@code{##}. Named operator hash nodes are flagged, both to catch the +spelling distinction and to prevent them from being defined as macros. +@end itemize + +The same identifiers share the same hash node. Since each identifier +token, after lexing, contains a pointer to its hash node, this is used +to provide rapid lookup of various information. For example, when +parsing a @code{#define} statement, CPP flags each argument's identifier +hash node with the index of that argument. This makes duplicated +argument checking an O(1) operation for each argument. Similarly, for +each identifier in the macro's expansion, lookup to see if it is an +argument, and which argument it is, is also an O(1) operation. Further, +each directive name, such as @code{endif}, has an associated directive +enum stored in its hash node, so that directive lookup is also O(1). + +@node Macro Expansion +@unnumbered Macro Expansion Algorithm +@cindex macro expansion + +Macro expansion is a tricky operation, fraught with nasty corner cases +and situations that render what you thought was a nifty way to +optimize the preprocessor's expansion algorithm wrong in quite subtle +ways. + +I strongly recommend you have a good grasp of how the C and C++ +standards require macros to be expanded before diving into this +section, let alone the code!. If you don't have a clear mental +picture of how things like nested macro expansion, stringification and +token pasting are supposed to work, damage to your sanity can quickly +result. + +@section Internal representation of macros +@cindex macro representation (internal) + +The preprocessor stores macro expansions in tokenized form. This +saves repeated lexing passes during expansion, at the cost of a small +increase in memory consumption on average. The tokens are stored +contiguously in memory, so a pointer to the first one and a token +count is all you need to get the replacement list of a macro. + +If the macro is a function-like macro the preprocessor also stores its +parameters, in the form of an ordered list of pointers to the hash +table entry of each parameter's identifier. Further, in the macro's +stored expansion each occurrence of a parameter is replaced with a +special token of type @code{CPP_MACRO_ARG}. Each such token holds the +index of the parameter it represents in the parameter list, which +allows rapid replacement of parameters with their arguments during +expansion. Despite this optimization it is still necessary to store +the original parameters to the macro, both for dumping with e.g., +@option{-dD}, and to warn about non-trivial macro redefinitions when +the parameter names have changed. + +@section Macro expansion overview +The preprocessor maintains a @dfn{context stack}, implemented as a +linked list of @code{cpp_context} structures, which together represent +the macro expansion state at any one time. The @code{struct +cpp_reader} member variable @code{context} points to the current top +of this stack. The top normally holds the unexpanded replacement list +of the innermost macro under expansion, except when cpplib is about to +pre-expand an argument, in which case it holds that argument's +unexpanded tokens. + +When there are no macros under expansion, cpplib is in @dfn{base +context}. All contexts other than the base context contain a +contiguous list of tokens delimited by a starting and ending token. +When not in base context, cpplib obtains the next token from the list +of the top context. If there are no tokens left in the list, it pops +that context off the stack, and subsequent ones if necessary, until an +unexhausted context is found or it returns to base context. In base +context, cpplib reads tokens directly from the lexer. + +If it encounters an identifier that is both a macro and enabled for +expansion, cpplib prepares to push a new context for that macro on the +stack by calling the routine @code{enter_macro_context}. When this +routine returns, the new context will contain the unexpanded tokens of +the replacement list of that macro. In the case of function-like +macros, @code{enter_macro_context} also replaces any parameters in the +replacement list, stored as @code{CPP_MACRO_ARG} tokens, with the +appropriate macro argument. If the standard requires that the +parameter be replaced with its expanded argument, the argument will +have been fully macro expanded first. + +@code{enter_macro_context} also handles special macros like +@code{__LINE__}. Although these macros expand to a single token which +cannot contain any further macros, for reasons of token spacing +(@pxref{Token Spacing}) and simplicity of implementation, cpplib +handles these special macros by pushing a context containing just that +one token. + +The final thing that @code{enter_macro_context} does before returning +is to mark the macro disabled for expansion (except for special macros +like @code{__TIME__}). The macro is re-enabled when its context is +later popped from the context stack, as described above. This strict +ordering ensures that a macro is disabled whilst its expansion is +being scanned, but that it is @emph{not} disabled whilst any arguments +to it are being expanded. + +@section Scanning the replacement list for macros to expand +The C standard states that, after any parameters have been replaced +with their possibly-expanded arguments, the replacement list is +scanned for nested macros. Further, any identifiers in the +replacement list that are not expanded during this scan are never +again eligible for expansion in the future, if the reason they were +not expanded is that the macro in question was disabled. + +Clearly this latter condition can only apply to tokens resulting from +argument pre-expansion. Other tokens never have an opportunity to be +re-tested for expansion. It is possible for identifiers that are +function-like macros to not expand initially but to expand during a +later scan. This occurs when the identifier is the last token of an +argument (and therefore originally followed by a comma or a closing +parenthesis in its macro's argument list), and when it replaces its +parameter in the macro's replacement list, the subsequent token +happens to be an opening parenthesis (itself possibly the first token +of an argument). + +It is important to note that when cpplib reads the last token of a +given context, that context still remains on the stack. Only when +looking for the @emph{next} token do we pop it off the stack and drop +to a lower context. This makes backing up by one token easy, but more +importantly ensures that the macro corresponding to the current +context is still disabled when we are considering the last token of +its replacement list for expansion (or indeed expanding it). As an +example, which illustrates many of the points above, consider + +@smallexample +#define foo(x) bar x +foo(foo) (2) +@end smallexample + +@noindent which fully expands to @samp{bar foo (2)}. During pre-expansion +of the argument, @samp{foo} does not expand even though the macro is +enabled, since it has no following parenthesis [pre-expansion of an +argument only uses tokens from that argument; it cannot take tokens +from whatever follows the macro invocation]. This still leaves the +argument token @samp{foo} eligible for future expansion. Then, when +re-scanning after argument replacement, the token @samp{foo} is +rejected for expansion, and marked ineligible for future expansion, +since the macro is now disabled. It is disabled because the +replacement list @samp{bar foo} of the macro is still on the context +stack. + +If instead the algorithm looked for an opening parenthesis first and +then tested whether the macro were disabled it would be subtly wrong. +In the example above, the replacement list of @samp{foo} would be +popped in the process of finding the parenthesis, re-enabling +@samp{foo} and expanding it a second time. + +@section Looking for a function-like macro's opening parenthesis +Function-like macros only expand when immediately followed by a +parenthesis. To do this cpplib needs to temporarily disable macros +and read the next token. Unfortunately, because of spacing issues +(@pxref{Token Spacing}), there can be fake padding tokens in-between, +and if the next real token is not a parenthesis cpplib needs to be +able to back up that one token as well as retain the information in +any intervening padding tokens. + +Backing up more than one token when macros are involved is not +permitted by cpplib, because in general it might involve issues like +restoring popped contexts onto the context stack, which are too hard. +Instead, searching for the parenthesis is handled by a special +function, @code{funlike_invocation_p}, which remembers padding +information as it reads tokens. If the next real token is not an +opening parenthesis, it backs up that one token, and then pushes an +extra context just containing the padding information if necessary. + +@section Marking tokens ineligible for future expansion +As discussed above, cpplib needs a way of marking tokens as +unexpandable. Since the tokens cpplib handles are read-only once they +have been lexed, it instead makes a copy of the token and adds the +flag @code{NO_EXPAND} to the copy. + +For efficiency and to simplify memory management by avoiding having to +remember to free these tokens, they are allocated as temporary tokens +from the lexer's current token run (@pxref{Lexing a line}) using the +function @code{_cpp_temp_token}. The tokens are then re-used once the +current line of tokens has been read in. + +This might sound unsafe. However, tokens runs are not re-used at the +end of a line if it happens to be in the middle of a macro argument +list, and cpplib only wants to back-up more than one lexer token in +situations where no macro expansion is involved, so the optimization +is safe. + +@node Token Spacing +@unnumbered Token Spacing +@cindex paste avoidance +@cindex spacing +@cindex token spacing + +First, let's look at an issue that only concerns the stand-alone +preprocessor: we want to guarantee that re-reading its preprocessed +output results in an identical token stream. Without taking special +measures, this might not be the case because of macro substitution. +For example: + +@smallexample +#define PLUS + +#define EMPTY +#define f(x) =x= ++PLUS -EMPTY- PLUS+ f(=) + @expansion{} + + - - + + = = = +@emph{not} + @expansion{} ++ -- ++ === +@end smallexample + +One solution would be to simply insert a space between all adjacent +tokens. However, we would like to keep space insertion to a minimum, +both for aesthetic reasons and because it causes problems for people who +still try to abuse the preprocessor for things like Fortran source and +Makefiles. + +For now, just notice that when tokens are added (or removed, as shown by +the @code{EMPTY} example) from the original lexed token stream, we need +to check for accidental token pasting. We call this @dfn{paste +avoidance}. Token addition and removal can only occur because of macro +expansion, but accidental pasting can occur in many places: both before +and after each macro replacement, each argument replacement, and +additionally each token created by the @samp{#} and @samp{##} operators. + +Let's look at how the preprocessor gets whitespace output correct +normally. The @code{cpp_token} structure contains a flags byte, and one +of those flags is @code{PREV_WHITE}. This is flagged by the lexer, and +indicates that the token was preceded by whitespace of some form other +than a new line. The stand-alone preprocessor can use this flag to +decide whether to insert a space between tokens in the output. + +Now consider the result of the following macro expansion: + +@smallexample +#define add(x, y, z) x + y +z; +sum = add (1,2, 3); + @expansion{} sum = 1 + 2 +3; +@end smallexample + +The interesting thing here is that the tokens @samp{1} and @samp{2} are +output with a preceding space, and @samp{3} is output without a +preceding space, but when lexed none of these tokens had that property. +Careful consideration reveals that @samp{1} gets its preceding +whitespace from the space preceding @samp{add} in the macro invocation, +@emph{not} replacement list. @samp{2} gets its whitespace from the +space preceding the parameter @samp{y} in the macro replacement list, +and @samp{3} has no preceding space because parameter @samp{z} has none +in the replacement list. + +Once lexed, tokens are effectively fixed and cannot be altered, since +pointers to them might be held in many places, in particular by +in-progress macro expansions. So instead of modifying the two tokens +above, the preprocessor inserts a special token, which I call a +@dfn{padding token}, into the token stream to indicate that spacing of +the subsequent token is special. The preprocessor inserts padding +tokens in front of every macro expansion and expanded macro argument. +These point to a @dfn{source token} from which the subsequent real token +should inherit its spacing. In the above example, the source tokens are +@samp{add} in the macro invocation, and @samp{y} and @samp{z} in the +macro replacement list, respectively. + +It is quite easy to get multiple padding tokens in a row, for example if +a macro's first replacement token expands straight into another macro. + +@smallexample +#define foo bar +#define bar baz +[foo] + @expansion{} [baz] +@end smallexample + +Here, two padding tokens are generated with sources the @samp{foo} token +between the brackets, and the @samp{bar} token from foo's replacement +list, respectively. Clearly the first padding token is the one we +should use, so our output code should contain a rule that the first +padding token in a sequence is the one that matters. + +But what if we happen to leave a macro expansion? Adjusting the above +example slightly: + +@smallexample +#define foo bar +#define bar EMPTY baz +#define EMPTY +[foo] EMPTY; + @expansion{} [ baz] ; +@end smallexample + +As shown, now there should be a space before @samp{baz} and the +semicolon in the output. + +The rules we decided above fail for @samp{baz}: we generate three +padding tokens, one per macro invocation, before the token @samp{baz}. +We would then have it take its spacing from the first of these, which +carries source token @samp{foo} with no leading space. + +It is vital that cpplib get spacing correct in these examples since any +of these macro expansions could be stringified, where spacing matters. + +So, this demonstrates that not just entering macro and argument +expansions, but leaving them requires special handling too. I made +cpplib insert a padding token with a @code{NULL} source token when +leaving macro expansions, as well as after each replaced argument in a +macro's replacement list. It also inserts appropriate padding tokens on +either side of tokens created by the @samp{#} and @samp{##} operators. +I expanded the rule so that, if we see a padding token with a +@code{NULL} source token, @emph{and} that source token has no leading +space, then we behave as if we have seen no padding tokens at all. A +quick check shows this rule will then get the above example correct as +well. + +Now a relationship with paste avoidance is apparent: we have to be +careful about paste avoidance in exactly the same locations we have +padding tokens in order to get white space correct. This makes +implementation of paste avoidance easy: wherever the stand-alone +preprocessor is fixing up spacing because of padding tokens, and it +turns out that no space is needed, it has to take the extra step to +check that a space is not needed after all to avoid an accidental paste. +The function @code{cpp_avoid_paste} advises whether a space is required +between two consecutive tokens. To avoid excessive spacing, it tries +hard to only require a space if one is likely to be necessary, but for +reasons of efficiency it is slightly conservative and might recommend a +space where one is not strictly needed. + +@node Line Numbering +@unnumbered Line numbering +@cindex line numbers + +@section Just which line number anyway? + +There are three reasonable requirements a cpplib client might have for +the line number of a token passed to it: + +@itemize @bullet +@item +The source line it was lexed on. +@item +The line it is output on. This can be different to the line it was +lexed on if, for example, there are intervening escaped newlines or +C-style comments. For example: + +@smallexample +foo /* A long +comment */ bar \ +baz +@result{} +foo bar baz +@end smallexample + +@item +If the token results from a macro expansion, the line of the macro name, +or possibly the line of the closing parenthesis in the case of +function-like macro expansion. +@end itemize + +The @code{cpp_token} structure contains @code{line} and @code{col} +members. The lexer fills these in with the line and column of the first +character of the token. Consequently, but maybe unexpectedly, a token +from the replacement list of a macro expansion carries the location of +the token within the @code{#define} directive, because cpplib expands a +macro by returning pointers to the tokens in its replacement list. The +current implementation of cpplib assigns tokens created from built-in +macros and the @samp{#} and @samp{##} operators the location of the most +recently lexed token. This is a because they are allocated from the +lexer's token runs, and because of the way the diagnostic routines infer +the appropriate location to report. + +The diagnostic routines in cpplib display the location of the most +recently @emph{lexed} token, unless they are passed a specific line and +column to report. For diagnostics regarding tokens that arise from +macro expansions, it might also be helpful for the user to see the +original location in the macro definition that the token came from. +Since that is exactly the information each token carries, such an +enhancement could be made relatively easily in future. + +The stand-alone preprocessor faces a similar problem when determining +the correct line to output the token on: the position attached to a +token is fairly useless if the token came from a macro expansion. All +tokens on a logical line should be output on its first physical line, so +the token's reported location is also wrong if it is part of a physical +line other than the first. + +To solve these issues, cpplib provides a callback that is generated +whenever it lexes a preprocessing token that starts a new logical line +other than a directive. It passes this token (which may be a +@code{CPP_EOF} token indicating the end of the translation unit) to the +callback routine, which can then use the line and column of this token +to produce correct output. + +@section Representation of line numbers + +As mentioned above, cpplib stores with each token the line number that +it was lexed on. In fact, this number is not the number of the line in +the source file, but instead bears more resemblance to the number of the +line in the translation unit. + +The preprocessor maintains a monotonic increasing line count, which is +incremented at every new line character (and also at the end of any +buffer that does not end in a new line). Since a line number of zero is +useful to indicate certain special states and conditions, this variable +starts counting from one. + +This variable therefore uniquely enumerates each line in the translation +unit. With some simple infrastructure, it is straight forward to map +from this to the original source file and line number pair, saving space +whenever line number information needs to be saved. The code the +implements this mapping lies in the files @file{line-map.c} and +@file{line-map.h}. + +Command-line macros and assertions are implemented by pushing a buffer +containing the right hand side of an equivalent @code{#define} or +@code{#assert} directive. Some built-in macros are handled similarly. +Since these are all processed before the first line of the main input +file, it will typically have an assigned line closer to twenty than to +one. + +@node Guard Macros +@unnumbered The Multiple-Include Optimization +@cindex guard macros +@cindex controlling macros +@cindex multiple-include optimization + +Header files are often of the form + +@smallexample +#ifndef FOO +#define FOO +@dots{} +#endif +@end smallexample + +@noindent +to prevent the compiler from processing them more than once. The +preprocessor notices such header files, so that if the header file +appears in a subsequent @code{#include} directive and @code{FOO} is +defined, then it is ignored and it doesn't preprocess or even re-open +the file a second time. This is referred to as the @dfn{multiple +include optimization}. + +Under what circumstances is such an optimization valid? If the file +were included a second time, it can only be optimized away if that +inclusion would result in no tokens to return, and no relevant +directives to process. Therefore the current implementation imposes +requirements and makes some allowances as follows: + +@enumerate +@item +There must be no tokens outside the controlling @code{#if}-@code{#endif} +pair, but whitespace and comments are permitted. + +@item +There must be no directives outside the controlling directive pair, but +the @dfn{null directive} (a line containing nothing other than a single +@samp{#} and possibly whitespace) is permitted. + +@item +The opening directive must be of the form + +@smallexample +#ifndef FOO +@end smallexample + +or + +@smallexample +#if !defined FOO [equivalently, #if !defined(FOO)] +@end smallexample + +@item +In the second form above, the tokens forming the @code{#if} expression +must have come directly from the source file---no macro expansion must +have been involved. This is because macro definitions can change, and +tracking whether or not a relevant change has been made is not worth the +implementation cost. + +@item +There can be no @code{#else} or @code{#elif} directives at the outer +conditional block level, because they would probably contain something +of interest to a subsequent pass. +@end enumerate + +First, when pushing a new file on the buffer stack, +@code{_stack_include_file} sets the controlling macro @code{mi_cmacro} to +@code{NULL}, and sets @code{mi_valid} to @code{true}. This indicates +that the preprocessor has not yet encountered anything that would +invalidate the multiple-include optimization. As described in the next +few paragraphs, these two variables having these values effectively +indicates top-of-file. + +When about to return a token that is not part of a directive, +@code{_cpp_lex_token} sets @code{mi_valid} to @code{false}. This +enforces the constraint that tokens outside the controlling conditional +block invalidate the optimization. + +The @code{do_if}, when appropriate, and @code{do_ifndef} directive +handlers pass the controlling macro to the function +@code{push_conditional}. cpplib maintains a stack of nested conditional +blocks, and after processing every opening conditional this function +pushes an @code{if_stack} structure onto the stack. In this structure +it records the controlling macro for the block, provided there is one +and we're at top-of-file (as described above). If an @code{#elif} or +@code{#else} directive is encountered, the controlling macro for that +block is cleared to @code{NULL}. Otherwise, it survives until the +@code{#endif} closing the block, upon which @code{do_endif} sets +@code{mi_valid} to true and stores the controlling macro in +@code{mi_cmacro}. + +@code{_cpp_handle_directive} clears @code{mi_valid} when processing any +directive other than an opening conditional and the null directive. +With this, and requiring top-of-file to record a controlling macro, and +no @code{#else} or @code{#elif} for it to survive and be copied to +@code{mi_cmacro} by @code{do_endif}, we have enforced the absence of +directives outside the main conditional block for the optimization to be +on. + +Note that whilst we are inside the conditional block, @code{mi_valid} is +likely to be reset to @code{false}, but this does not matter since the +the closing @code{#endif} restores it to @code{true} if appropriate. + +Finally, since @code{_cpp_lex_direct} pops the file off the buffer stack +at @code{EOF} without returning a token, if the @code{#endif} directive +was not followed by any tokens, @code{mi_valid} is @code{true} and +@code{_cpp_pop_file_buffer} remembers the controlling macro associated +with the file. Subsequent calls to @code{stack_include_file} result in +no buffer being pushed if the controlling macro is defined, effecting +the optimization. + +A quick word on how we handle the + +@smallexample +#if !defined FOO +@end smallexample + +@noindent +case. @code{_cpp_parse_expr} and @code{parse_defined} take steps to see +whether the three stages @samp{!}, @samp{defined-expression} and +@samp{end-of-directive} occur in order in a @code{#if} expression. If +so, they return the guard macro to @code{do_if} in the variable +@code{mi_ind_cmacro}, and otherwise set it to @code{NULL}. +@code{enter_macro_context} sets @code{mi_valid} to false, so if a macro +was expanded whilst parsing any part of the expression, then the +top-of-file test in @code{push_conditional} fails and the optimization +is turned off. + +@node Files +@unnumbered File Handling +@cindex files + +Fairly obviously, the file handling code of cpplib resides in the file +@file{cppfiles.c}. It takes care of the details of file searching, +opening, reading and caching, for both the main source file and all the +headers it recursively includes. + +The basic strategy is to minimize the number of system calls. On many +systems, the basic @code{open ()} and @code{fstat ()} system calls can +be quite expensive. For every @code{#include}-d file, we need to try +all the directories in the search path until we find a match. Some +projects, such as glibc, pass twenty or thirty include paths on the +command line, so this can rapidly become time consuming. + +For a header file we have not encountered before we have little choice +but to do this. However, it is often the case that the same headers are +repeatedly included, and in these cases we try to avoid repeating the +filesystem queries whilst searching for the correct file. + +For each file we try to open, we store the constructed path in a splay +tree. This path first undergoes simplification by the function +@code{_cpp_simplify_pathname}. For example, +@file{/usr/include/bits/../foo.h} is simplified to +@file{/usr/include/foo.h} before we enter it in the splay tree and try +to @code{open ()} the file. CPP will then find subsequent uses of +@file{foo.h}, even as @file{/usr/include/foo.h}, in the splay tree and +save system calls. + +Further, it is likely the file contents have also been cached, saving a +@code{read ()} system call. We don't bother caching the contents of +header files that are re-inclusion protected, and whose re-inclusion +macro is defined when we leave the header file for the first time. If +the host supports it, we try to map suitably large files into memory, +rather than reading them in directly. + +The include paths are internally stored on a null-terminated +singly-linked list, starting with the @code{"header.h"} directory search +chain, which then links into the @code{} directory chain. + +Files included with the @code{} syntax start the lookup directly +in the second half of this chain. However, files included with the +@code{"foo.h"} syntax start at the beginning of the chain, but with one +extra directory prepended. This is the directory of the current file; +the one containing the @code{#include} directive. Prepending this +directory on a per-file basis is handled by the function +@code{search_from}. + +Note that a header included with a directory component, such as +@code{#include "mydir/foo.h"} and opened as +@file{/usr/local/include/mydir/foo.h}, will have the complete path minus +the basename @samp{foo.h} as the current directory. + +Enough information is stored in the splay tree that CPP can immediately +tell whether it can skip the header file because of the multiple include +optimization, whether the file didn't exist or couldn't be opened for +some reason, or whether the header was flagged not to be re-used, as it +is with the obsolete @code{#import} directive. + +For the benefit of MS-DOS filesystems with an 8.3 filename limitation, +CPP offers the ability to treat various include file names as aliases +for the real header files with shorter names. The map from one to the +other is found in a special file called @samp{header.gcc}, stored in the +command line (or system) include directories to which the mapping +applies. This may be higher up the directory tree than the full path to +the file minus the base name. + +@node Index +@unnumbered Index +@printindex cp + +@bye diff --git a/contrib/gcc/doc/extend.texi b/contrib/gcc/doc/extend.texi new file mode 100644 index 000000000000..ad88a2a83afc --- /dev/null +++ b/contrib/gcc/doc/extend.texi @@ -0,0 +1,6616 @@ +@c Copyright (C) 1988,1989,1992,1993,1994,1996,1998,1999,2000,2001,2002 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node C Implementation +@chapter C Implementation-defined behavior +@cindex implementation-defined behavior, C language + +A conforming implementation of ISO C is required to document its +choice of behavior in each of the areas that are designated +``implementation defined.'' The following lists all such areas, +along with the section number from the ISO/IEC 9899:1999 standard. + +@menu +* Translation implementation:: +* Environment implementation:: +* Identifiers implementation:: +* Characters implementation:: +* Integers implementation:: +* Floating point implementation:: +* Arrays and pointers implementation:: +* Hints implementation:: +* Structures unions enumerations and bit-fields implementation:: +* Qualifiers implementation:: +* Preprocessing directives implementation:: +* Library functions implementation:: +* Architecture implementation:: +* Locale-specific behavior implementation:: +@end menu + +@node Translation implementation +@section Translation + +@itemize @bullet +@item +@cite{How a diagnostic is identified (3.10, 5.1.1.3).} + +@item +@cite{Whether each nonempty sequence of white-space characters other than +new-line is retained or replaced by one space character in translation +phase 3 (5.1.1.2).} +@end itemize + +@node Environment implementation +@section Environment + +The behavior of these points are dependent on the implementation +of the C library, and are not defined by GCC itself. + +@node Identifiers implementation +@section Identifiers + +@itemize @bullet +@item +@cite{Which additional multibyte characters may appear in identifiers +and their correspondence to universal character names (6.4.2).} + +@item +@cite{The number of significant initial characters in an identifier +(5.2.4.1, 6.4.2).} +@end itemize + +@node Characters implementation +@section Characters + +@itemize @bullet +@item +@cite{The number of bits in a byte (3.6).} + +@item +@cite{The values of the members of the execution character set (5.2.1).} + +@item +@cite{The unique value of the member of the execution character set produced +for each of the standard alphabetic escape sequences (5.2.2).} + +@item +@cite{The value of a @code{char} object into which has been stored any +character other than a member of the basic execution character set (6.2.5).} + +@item +@cite{Which of @code{signed char} or @code{unsigned char} has the same range, +representation, and behavior as ``plain'' @code{char} (6.2.5, 6.3.1.1).} + +@item +@cite{The mapping of members of the source character set (in character +constants and string literals) to members of the execution character +set (6.4.4.4, 5.1.1.2).} + +@item +@cite{The value of an integer character constant containing more than one +character or containing a character or escape sequence that does not map +to a single-byte execution character (6.4.4.4).} + +@item +@cite{The value of a wide character constant containing more than one +multibyte character, or containing a multibyte character or escape +sequence not represented in the extended execution character set (6.4.4.4).} + +@item +@cite{The current locale used to convert a wide character constant consisting +of a single multibyte character that maps to a member of the extended +execution character set into a corresponding wide character code (6.4.4.4).} + +@item +@cite{The current locale used to convert a wide string literal into +corresponding wide character codes (6.4.5).} + +@item +@cite{The value of a string literal containing a multibyte character or escape +sequence not represented in the execution character set (6.4.5).} +@end itemize + +@node Integers implementation +@section Integers + +@itemize @bullet +@item +@cite{Any extended integer types that exist in the implementation (6.2.5).} + +@item +@cite{Whether signed integer types are represented using sign and magnitude, +two's complement, or one's complement, and whether the extraordinary value +is a trap representation or an ordinary value (6.2.6.2).} + +@item +@cite{The rank of any extended integer type relative to another extended +integer type with the same precision (6.3.1.1).} + +@item +@cite{The result of, or the signal raised by, converting an integer to a +signed integer type when the value cannot be represented in an object of +that type (6.3.1.3).} + +@item +@cite{The results of some bitwise operations on signed integers (6.5).} +@end itemize + +@node Floating point implementation +@section Floating point + +@itemize @bullet +@item +@cite{The accuracy of the floating-point operations and of the library +functions in @code{} and @code{} that return floating-point +results (5.2.4.2.2).} + +@item +@cite{The rounding behaviors characterized by non-standard values +of @code{FLT_ROUNDS} @gol +(5.2.4.2.2).} + +@item +@cite{The evaluation methods characterized by non-standard negative +values of @code{FLT_EVAL_METHOD} (5.2.4.2.2).} + +@item +@cite{The direction of rounding when an integer is converted to a +floating-point number that cannot exactly represent the original +value (6.3.1.4).} + +@item +@cite{The direction of rounding when a floating-point number is +converted to a narrower floating-point number (6.3.1.5).} + +@item +@cite{How the nearest representable value or the larger or smaller +representable value immediately adjacent to the nearest representable +value is chosen for certain floating constants (6.4.4.2).} + +@item +@cite{Whether and how floating expressions are contracted when not +disallowed by the @code{FP_CONTRACT} pragma (6.5).} + +@item +@cite{The default state for the @code{FENV_ACCESS} pragma (7.6.1).} + +@item +@cite{Additional floating-point exceptions, rounding modes, environments, +and classifications, and their macro names (7.6, 7.12).} + +@item +@cite{The default state for the @code{FP_CONTRACT} pragma (7.12.2).} + +@item +@cite{Whether the ``inexact'' floating-point exception can be raised +when the rounded result actually does equal the mathematical result +in an IEC 60559 conformant implementation (F.9).} + +@item +@cite{Whether the ``underflow'' (and ``inexact'') floating-point +exception can be raised when a result is tiny but not inexact in an +IEC 60559 conformant implementation (F.9).} + +@end itemize + +@node Arrays and pointers implementation +@section Arrays and pointers + +@itemize @bullet +@item +@cite{The result of converting a pointer to an integer or +vice versa (6.3.2.3).} + +A cast from pointer to integer discards most-significant bits if the +pointer representation is larger than the integer type, +sign-extends@footnote{Future versions of GCC may zero-extend, or use +a target-defined @code{ptr_extend} pattern. Do not rely on sign extension.} +if the pointer representation is smaller than the integer type, otherwise +the bits are unchanged. +@c ??? We've always claimed that pointers were unsigned entities. +@c Shouldn't we therefore be doing zero-extension? If so, the bug +@c is in convert_to_integer, where we call type_for_size and request +@c a signed integral type. On the other hand, it might be most useful +@c for the target if we extend according to POINTERS_EXTEND_UNSIGNED. + +A cast from integer to pointer discards most-significant bits if the +pointer representation is smaller than the integer type, extends according +to the signedness of the integer type if the pointer representation +is larger than the integer type, otherwise the bits are unchanged. + +When casting from pointer to integer and back again, the resulting +pointer must reference the same object as the original pointer, otherwise +the behavior is undefined. That is, one may not use integer arithmetic to +avoid the undefined behavior of pointer arithmetic as proscribed in 6.5.6/8. + +@item +@cite{The size of the result of subtracting two pointers to elements +of the same array (6.5.6).} + +@end itemize + +@node Hints implementation +@section Hints + +@itemize @bullet +@item +@cite{The extent to which suggestions made by using the @code{register} +storage-class specifier are effective (6.7.1).} + +@item +@cite{The extent to which suggestions made by using the inline function +specifier are effective (6.7.4).} + +@end itemize + +@node Structures unions enumerations and bit-fields implementation +@section Structures, unions, enumerations, and bit-fields + +@itemize @bullet +@item +@cite{Whether a ``plain'' int bit-field is treated as a @code{signed int} +bit-field or as an @code{unsigned int} bit-field (6.7.2, 6.7.2.1).} + +@item +@cite{Allowable bit-field types other than @code{_Bool}, @code{signed int}, +and @code{unsigned int} (6.7.2.1).} + +@item +@cite{Whether a bit-field can straddle a storage-unit boundary (6.7.2.1).} + +@item +@cite{The order of allocation of bit-fields within a unit (6.7.2.1).} + +@item +@cite{The alignment of non-bit-field members of structures (6.7.2.1).} + +@item +@cite{The integer type compatible with each enumerated type (6.7.2.2).} + +@end itemize + +@node Qualifiers implementation +@section Qualifiers + +@itemize @bullet +@item +@cite{What constitutes an access to an object that has volatile-qualified +type (6.7.3).} + +@end itemize + +@node Preprocessing directives implementation +@section Preprocessing directives + +@itemize @bullet +@item +@cite{How sequences in both forms of header names are mapped to headers +or external source file names (6.4.7).} + +@item +@cite{Whether the value of a character constant in a constant expression +that controls conditional inclusion matches the value of the same character +constant in the execution character set (6.10.1).} + +@item +@cite{Whether the value of a single-character character constant in a +constant expression that controls conditional inclusion may have a +negative value (6.10.1).} + +@item +@cite{The places that are searched for an included @samp{<>} delimited +header, and how the places are specified or the header is +identified (6.10.2).} + +@item +@cite{How the named source file is searched for in an included @samp{""} +delimited header (6.10.2).} + +@item +@cite{The method by which preprocessing tokens (possibly resulting from +macro expansion) in a @code{#include} directive are combined into a header +name (6.10.2).} + +@item +@cite{The nesting limit for @code{#include} processing (6.10.2).} + +@item +@cite{Whether the @samp{#} operator inserts a @samp{\} character before +the @samp{\} character that begins a universal character name in a +character constant or string literal (6.10.3.2).} + +@item +@cite{The behavior on each recognized non-@code{STDC #pragma} +directive (6.10.6).} + +@item +@cite{The definitions for @code{__DATE__} and @code{__TIME__} when +respectively, the date and time of translation are not available (6.10.8).} + +@end itemize + +@node Library functions implementation +@section Library functions + +The behavior of these points are dependent on the implementation +of the C library, and are not defined by GCC itself. + +@node Architecture implementation +@section Architecture + +@itemize @bullet +@item +@cite{The values or expressions assigned to the macros specified in the +headers @code{}, @code{}, and @code{} +(5.2.4.2, 7.18.2, 7.18.3).} + +@item +@cite{The number, order, and encoding of bytes in any object +(when not explicitly specified in this International Standard) (6.2.6.1).} + +@item +@cite{The value of the result of the sizeof operator (6.5.3.4).} + +@end itemize + +@node Locale-specific behavior implementation +@section Locale-specific behavior + +The behavior of these points are dependent on the implementation +of the C library, and are not defined by GCC itself. + +@node C Extensions +@chapter Extensions to the C Language Family +@cindex extensions, C language +@cindex C language extensions + +@opindex pedantic +GNU C provides several language features not found in ISO standard C@. +(The @option{-pedantic} option directs GCC to print a warning message if +any of these features is used.) To test for the availability of these +features in conditional compilation, check for a predefined macro +@code{__GNUC__}, which is always defined under GCC@. + +These extensions are available in C and Objective-C@. Most of them are +also available in C++. @xref{C++ Extensions,,Extensions to the +C++ Language}, for extensions that apply @emph{only} to C++. + +Some features that are in ISO C99 but not C89 or C++ are also, as +extensions, accepted by GCC in C89 mode and in C++. + +@menu +* Statement Exprs:: Putting statements and declarations inside expressions. +* Local Labels:: Labels local to a statement-expression. +* Labels as Values:: Getting pointers to labels, and computed gotos. +* Nested Functions:: As in Algol and Pascal, lexical scoping of functions. +* Constructing Calls:: Dispatching a call to another function. +* Naming Types:: Giving a name to the type of some expression. +* Typeof:: @code{typeof}: referring to the type of an expression. +* Lvalues:: Using @samp{?:}, @samp{,} and casts in lvalues. +* Conditionals:: Omitting the middle operand of a @samp{?:} expression. +* Long Long:: Double-word integers---@code{long long int}. +* Complex:: Data types for complex numbers. +* Hex Floats:: Hexadecimal floating-point constants. +* Zero Length:: Zero-length arrays. +* Variable Length:: Arrays whose length is computed at run time. +* Variadic Macros:: Macros with a variable number of arguments. +* Escaped Newlines:: Slightly looser rules for escaped newlines. +* Multi-line Strings:: String literals with embedded newlines. +* Subscripting:: Any array can be subscripted, even if not an lvalue. +* Pointer Arith:: Arithmetic on @code{void}-pointers and function pointers. +* Initializers:: Non-constant initializers. +* Compound Literals:: Compound literals give structures, unions + or arrays as values. +* Designated Inits:: Labeling elements of initializers. +* Cast to Union:: Casting to union type from any member of the union. +* Case Ranges:: `case 1 ... 9' and such. +* Mixed Declarations:: Mixing declarations and code. +* Function Attributes:: Declaring that functions have no side effects, + or that they can never return. +* Attribute Syntax:: Formal syntax for attributes. +* Function Prototypes:: Prototype declarations and old-style definitions. +* C++ Comments:: C++ comments are recognized. +* Dollar Signs:: Dollar sign is allowed in identifiers. +* Character Escapes:: @samp{\e} stands for the character @key{ESC}. +* Variable Attributes:: Specifying attributes of variables. +* Type Attributes:: Specifying attributes of types. +* Alignment:: Inquiring about the alignment of a type or variable. +* Inline:: Defining inline functions (as fast as macros). +* Extended Asm:: Assembler instructions with C expressions as operands. + (With them you can define ``built-in'' functions.) +* Constraints:: Constraints for asm operands +* Asm Labels:: Specifying the assembler name to use for a C symbol. +* Explicit Reg Vars:: Defining variables residing in specified registers. +* Alternate Keywords:: @code{__const__}, @code{__asm__}, etc., for header files. +* Incomplete Enums:: @code{enum foo;}, with details to follow. +* Function Names:: Printable strings which are the name of the current + function. +* Return Address:: Getting the return or frame address of a function. +* Vector Extensions:: Using vector instructions through built-in functions. +* Other Builtins:: Other built-in functions. +* Target Builtins:: Built-in functions specific to particular targets. +* Pragmas:: Pragmas accepted by GCC. +* Unnamed Fields:: Unnamed struct/union fields within structs/unions. +@end menu + +@node Statement Exprs +@section Statements and Declarations in Expressions +@cindex statements inside expressions +@cindex declarations inside expressions +@cindex expressions containing statements +@cindex macros, statements in expressions + +@c the above section title wrapped and causes an underfull hbox.. i +@c changed it from "within" to "in". --mew 4feb93 + +A compound statement enclosed in parentheses may appear as an expression +in GNU C@. This allows you to use loops, switches, and local variables +within an expression. + +Recall that a compound statement is a sequence of statements surrounded +by braces; in this construct, parentheses go around the braces. For +example: + +@example +(@{ int y = foo (); int z; + if (y > 0) z = y; + else z = - y; + z; @}) +@end example + +@noindent +is a valid (though slightly more complex than necessary) expression +for the absolute value of @code{foo ()}. + +The last thing in the compound statement should be an expression +followed by a semicolon; the value of this subexpression serves as the +value of the entire construct. (If you use some other kind of statement +last within the braces, the construct has type @code{void}, and thus +effectively no value.) + +This feature is especially useful in making macro definitions ``safe'' (so +that they evaluate each operand exactly once). For example, the +``maximum'' function is commonly defined as a macro in standard C as +follows: + +@example +#define max(a,b) ((a) > (b) ? (a) : (b)) +@end example + +@noindent +@cindex side effects, macro argument +But this definition computes either @var{a} or @var{b} twice, with bad +results if the operand has side effects. In GNU C, if you know the +type of the operands (here let's assume @code{int}), you can define +the macro safely as follows: + +@example +#define maxint(a,b) \ + (@{int _a = (a), _b = (b); _a > _b ? _a : _b; @}) +@end example + +Embedded statements are not allowed in constant expressions, such as +the value of an enumeration constant, the width of a bit-field, or +the initial value of a static variable. + +If you don't know the type of the operand, you can still do this, but you +must use @code{typeof} (@pxref{Typeof}) or type naming (@pxref{Naming +Types}). + +Statement expressions are not supported fully in G++, and their fate +there is unclear. (It is possible that they will become fully supported +at some point, or that they will be deprecated, or that the bugs that +are present will continue to exist indefinitely.) Presently, statement +expressions do not work well as default arguments. + +In addition, there are semantic issues with statement-expressions in +C++. If you try to use statement-expressions instead of inline +functions in C++, you may be surprised at the way object destruction is +handled. For example: + +@example +#define foo(a) (@{int b = (a); b + 3; @}) +@end example + +@noindent +does not work the same way as: + +@example +inline int foo(int a) @{ int b = a; return b + 3; @} +@end example + +@noindent +In particular, if the expression passed into @code{foo} involves the +creation of temporaries, the destructors for those temporaries will be +run earlier in the case of the macro than in the case of the function. + +These considerations mean that it is probably a bad idea to use +statement-expressions of this form in header files that are designed to +work with C++. (Note that some versions of the GNU C Library contained +header files using statement-expression that lead to precisely this +bug.) + +@node Local Labels +@section Locally Declared Labels +@cindex local labels +@cindex macros, local labels + +Each statement expression is a scope in which @dfn{local labels} can be +declared. A local label is simply an identifier; you can jump to it +with an ordinary @code{goto} statement, but only from within the +statement expression it belongs to. + +A local label declaration looks like this: + +@example +__label__ @var{label}; +@end example + +@noindent +or + +@example +__label__ @var{label1}, @var{label2}, @dots{}; +@end example + +Local label declarations must come at the beginning of the statement +expression, right after the @samp{(@{}, before any ordinary +declarations. + +The label declaration defines the label @emph{name}, but does not define +the label itself. You must do this in the usual way, with +@code{@var{label}:}, within the statements of the statement expression. + +The local label feature is useful because statement expressions are +often used in macros. If the macro contains nested loops, a @code{goto} +can be useful for breaking out of them. However, an ordinary label +whose scope is the whole function cannot be used: if the macro can be +expanded several times in one function, the label will be multiply +defined in that function. A local label avoids this problem. For +example: + +@example +#define SEARCH(array, target) \ +(@{ \ + __label__ found; \ + typeof (target) _SEARCH_target = (target); \ + typeof (*(array)) *_SEARCH_array = (array); \ + int i, j; \ + int value; \ + for (i = 0; i < max; i++) \ + for (j = 0; j < max; j++) \ + if (_SEARCH_array[i][j] == _SEARCH_target) \ + @{ value = i; goto found; @} \ + value = -1; \ + found: \ + value; \ +@}) +@end example + +@node Labels as Values +@section Labels as Values +@cindex labels as values +@cindex computed gotos +@cindex goto with computed label +@cindex address of a label + +You can get the address of a label defined in the current function +(or a containing function) with the unary operator @samp{&&}. The +value has type @code{void *}. This value is a constant and can be used +wherever a constant of that type is valid. For example: + +@example +void *ptr; +@dots{} +ptr = &&foo; +@end example + +To use these values, you need to be able to jump to one. This is done +with the computed goto statement@footnote{The analogous feature in +Fortran is called an assigned goto, but that name seems inappropriate in +C, where one can do more than simply store label addresses in label +variables.}, @code{goto *@var{exp};}. For example, + +@example +goto *ptr; +@end example + +@noindent +Any expression of type @code{void *} is allowed. + +One way of using these constants is in initializing a static array that +will serve as a jump table: + +@example +static void *array[] = @{ &&foo, &&bar, &&hack @}; +@end example + +Then you can select a label with indexing, like this: + +@example +goto *array[i]; +@end example + +@noindent +Note that this does not check whether the subscript is in bounds---array +indexing in C never does that. + +Such an array of label values serves a purpose much like that of the +@code{switch} statement. The @code{switch} statement is cleaner, so +use that rather than an array unless the problem does not fit a +@code{switch} statement very well. + +Another use of label values is in an interpreter for threaded code. +The labels within the interpreter function can be stored in the +threaded code for super-fast dispatching. + +You may not use this mechanism to jump to code in a different function. +If you do that, totally unpredictable things will happen. The best way to +avoid this is to store the label address only in automatic variables and +never pass it as an argument. + +An alternate way to write the above example is + +@example +static const int array[] = @{ &&foo - &&foo, &&bar - &&foo, + &&hack - &&foo @}; +goto *(&&foo + array[i]); +@end example + +@noindent +This is more friendly to code living in shared libraries, as it reduces +the number of dynamic relocations that are needed, and by consequence, +allows the data to be read-only. + +@node Nested Functions +@section Nested Functions +@cindex nested functions +@cindex downward funargs +@cindex thunks + +A @dfn{nested function} is a function defined inside another function. +(Nested functions are not supported for GNU C++.) The nested function's +name is local to the block where it is defined. For example, here we +define a nested function named @code{square}, and call it twice: + +@example +@group +foo (double a, double b) +@{ + double square (double z) @{ return z * z; @} + + return square (a) + square (b); +@} +@end group +@end example + +The nested function can access all the variables of the containing +function that are visible at the point of its definition. This is +called @dfn{lexical scoping}. For example, here we show a nested +function which uses an inherited variable named @code{offset}: + +@example +@group +bar (int *array, int offset, int size) +@{ + int access (int *array, int index) + @{ return array[index + offset]; @} + int i; + @dots{} + for (i = 0; i < size; i++) + @dots{} access (array, i) @dots{} +@} +@end group +@end example + +Nested function definitions are permitted within functions in the places +where variable definitions are allowed; that is, in any block, before +the first statement in the block. + +It is possible to call the nested function from outside the scope of its +name by storing its address or passing the address to another function: + +@example +hack (int *array, int size) +@{ + void store (int index, int value) + @{ array[index] = value; @} + + intermediate (store, size); +@} +@end example + +Here, the function @code{intermediate} receives the address of +@code{store} as an argument. If @code{intermediate} calls @code{store}, +the arguments given to @code{store} are used to store into @code{array}. +But this technique works only so long as the containing function +(@code{hack}, in this example) does not exit. + +If you try to call the nested function through its address after the +containing function has exited, all hell will break loose. If you try +to call it after a containing scope level has exited, and if it refers +to some of the variables that are no longer in scope, you may be lucky, +but it's not wise to take the risk. If, however, the nested function +does not refer to anything that has gone out of scope, you should be +safe. + +GCC implements taking the address of a nested function using a technique +called @dfn{trampolines}. A paper describing them is available as + +@noindent +@uref{http://people.debian.org/~karlheg/Usenix88-lexic.pdf}. + +A nested function can jump to a label inherited from a containing +function, provided the label was explicitly declared in the containing +function (@pxref{Local Labels}). Such a jump returns instantly to the +containing function, exiting the nested function which did the +@code{goto} and any intermediate functions as well. Here is an example: + +@example +@group +bar (int *array, int offset, int size) +@{ + __label__ failure; + int access (int *array, int index) + @{ + if (index > size) + goto failure; + return array[index + offset]; + @} + int i; + @dots{} + for (i = 0; i < size; i++) + @dots{} access (array, i) @dots{} + @dots{} + return 0; + + /* @r{Control comes here from @code{access} + if it detects an error.} */ + failure: + return -1; +@} +@end group +@end example + +A nested function always has internal linkage. Declaring one with +@code{extern} is erroneous. If you need to declare the nested function +before its definition, use @code{auto} (which is otherwise meaningless +for function declarations). + +@example +bar (int *array, int offset, int size) +@{ + __label__ failure; + auto int access (int *, int); + @dots{} + int access (int *array, int index) + @{ + if (index > size) + goto failure; + return array[index + offset]; + @} + @dots{} +@} +@end example + +@node Constructing Calls +@section Constructing Function Calls +@cindex constructing calls +@cindex forwarding calls + +Using the built-in functions described below, you can record +the arguments a function received, and call another function +with the same arguments, without knowing the number or types +of the arguments. + +You can also record the return value of that function call, +and later return that value, without knowing what data type +the function tried to return (as long as your caller expects +that data type). + +@deftypefn {Built-in Function} {void *} __builtin_apply_args () +This built-in function returns a pointer to data +describing how to perform a call with the same arguments as were passed +to the current function. + +The function saves the arg pointer register, structure value address, +and all registers that might be used to pass arguments to a function +into a block of memory allocated on the stack. Then it returns the +address of that block. +@end deftypefn + +@deftypefn {Built-in Function} {void *} __builtin_apply (void (*@var{function})(), void *@var{arguments}, size_t @var{size}) +This built-in function invokes @var{function} +with a copy of the parameters described by @var{arguments} +and @var{size}. + +The value of @var{arguments} should be the value returned by +@code{__builtin_apply_args}. The argument @var{size} specifies the size +of the stack argument data, in bytes. + +This function returns a pointer to data describing +how to return whatever value was returned by @var{function}. The data +is saved in a block of memory allocated on the stack. + +It is not always simple to compute the proper value for @var{size}. The +value is used by @code{__builtin_apply} to compute the amount of data +that should be pushed on the stack and copied from the incoming argument +area. +@end deftypefn + +@deftypefn {Built-in Function} {void} __builtin_return (void *@var{result}) +This built-in function returns the value described by @var{result} from +the containing function. You should specify, for @var{result}, a value +returned by @code{__builtin_apply}. +@end deftypefn + +@node Naming Types +@section Naming an Expression's Type +@cindex naming types + +You can give a name to the type of an expression using a @code{typedef} +declaration with an initializer. Here is how to define @var{name} as a +type name for the type of @var{exp}: + +@example +typedef @var{name} = @var{exp}; +@end example + +This is useful in conjunction with the statements-within-expressions +feature. Here is how the two together can be used to define a safe +``maximum'' macro that operates on any arithmetic type: + +@example +#define max(a,b) \ + (@{typedef _ta = (a), _tb = (b); \ + _ta _a = (a); _tb _b = (b); \ + _a > _b ? _a : _b; @}) +@end example + +@cindex underscores in variables in macros +@cindex @samp{_} in variables in macros +@cindex local variables in macros +@cindex variables, local, in macros +@cindex macros, local variables in + +The reason for using names that start with underscores for the local +variables is to avoid conflicts with variable names that occur within the +expressions that are substituted for @code{a} and @code{b}. Eventually we +hope to design a new form of declaration syntax that allows you to declare +variables whose scopes start only after their initializers; this will be a +more reliable way to prevent such conflicts. + +@node Typeof +@section Referring to a Type with @code{typeof} +@findex typeof +@findex sizeof +@cindex macros, types of arguments + +Another way to refer to the type of an expression is with @code{typeof}. +The syntax of using of this keyword looks like @code{sizeof}, but the +construct acts semantically like a type name defined with @code{typedef}. + +There are two ways of writing the argument to @code{typeof}: with an +expression or with a type. Here is an example with an expression: + +@example +typeof (x[0](1)) +@end example + +@noindent +This assumes that @code{x} is an array of pointers to functions; +the type described is that of the values of the functions. + +Here is an example with a typename as the argument: + +@example +typeof (int *) +@end example + +@noindent +Here the type described is that of pointers to @code{int}. + +If you are writing a header file that must work when included in ISO C +programs, write @code{__typeof__} instead of @code{typeof}. +@xref{Alternate Keywords}. + +A @code{typeof}-construct can be used anywhere a typedef name could be +used. For example, you can use it in a declaration, in a cast, or inside +of @code{sizeof} or @code{typeof}. + +@itemize @bullet +@item +This declares @code{y} with the type of what @code{x} points to. + +@example +typeof (*x) y; +@end example + +@item +This declares @code{y} as an array of such values. + +@example +typeof (*x) y[4]; +@end example + +@item +This declares @code{y} as an array of pointers to characters: + +@example +typeof (typeof (char *)[4]) y; +@end example + +@noindent +It is equivalent to the following traditional C declaration: + +@example +char *y[4]; +@end example + +To see the meaning of the declaration using @code{typeof}, and why it +might be a useful way to write, let's rewrite it with these macros: + +@example +#define pointer(T) typeof(T *) +#define array(T, N) typeof(T [N]) +@end example + +@noindent +Now the declaration can be rewritten this way: + +@example +array (pointer (char), 4) y; +@end example + +@noindent +Thus, @code{array (pointer (char), 4)} is the type of arrays of 4 +pointers to @code{char}. +@end itemize + +@node Lvalues +@section Generalized Lvalues +@cindex compound expressions as lvalues +@cindex expressions, compound, as lvalues +@cindex conditional expressions as lvalues +@cindex expressions, conditional, as lvalues +@cindex casts as lvalues +@cindex generalized lvalues +@cindex lvalues, generalized +@cindex extensions, @code{?:} +@cindex @code{?:} extensions +Compound expressions, conditional expressions and casts are allowed as +lvalues provided their operands are lvalues. This means that you can take +their addresses or store values into them. + +Standard C++ allows compound expressions and conditional expressions as +lvalues, and permits casts to reference type, so use of this extension +is deprecated for C++ code. + +For example, a compound expression can be assigned, provided the last +expression in the sequence is an lvalue. These two expressions are +equivalent: + +@example +(a, b) += 5 +a, (b += 5) +@end example + +Similarly, the address of the compound expression can be taken. These two +expressions are equivalent: + +@example +&(a, b) +a, &b +@end example + +A conditional expression is a valid lvalue if its type is not void and the +true and false branches are both valid lvalues. For example, these two +expressions are equivalent: + +@example +(a ? b : c) = 5 +(a ? b = 5 : (c = 5)) +@end example + +A cast is a valid lvalue if its operand is an lvalue. A simple +assignment whose left-hand side is a cast works by converting the +right-hand side first to the specified type, then to the type of the +inner left-hand side expression. After this is stored, the value is +converted back to the specified type to become the value of the +assignment. Thus, if @code{a} has type @code{char *}, the following two +expressions are equivalent: + +@example +(int)a = 5 +(int)(a = (char *)(int)5) +@end example + +An assignment-with-arithmetic operation such as @samp{+=} applied to a cast +performs the arithmetic using the type resulting from the cast, and then +continues as in the previous case. Therefore, these two expressions are +equivalent: + +@example +(int)a += 5 +(int)(a = (char *)(int) ((int)a + 5)) +@end example + +You cannot take the address of an lvalue cast, because the use of its +address would not work out coherently. Suppose that @code{&(int)f} were +permitted, where @code{f} has type @code{float}. Then the following +statement would try to store an integer bit-pattern where a floating +point number belongs: + +@example +*&(int)f = 1; +@end example + +This is quite different from what @code{(int)f = 1} would do---that +would convert 1 to floating point and store it. Rather than cause this +inconsistency, we think it is better to prohibit use of @samp{&} on a cast. + +If you really do want an @code{int *} pointer with the address of +@code{f}, you can simply write @code{(int *)&f}. + +@node Conditionals +@section Conditionals with Omitted Operands +@cindex conditional expressions, extensions +@cindex omitted middle-operands +@cindex middle-operands, omitted +@cindex extensions, @code{?:} +@cindex @code{?:} extensions + +The middle operand in a conditional expression may be omitted. Then +if the first operand is nonzero, its value is the value of the conditional +expression. + +Therefore, the expression + +@example +x ? : y +@end example + +@noindent +has the value of @code{x} if that is nonzero; otherwise, the value of +@code{y}. + +This example is perfectly equivalent to + +@example +x ? x : y +@end example + +@cindex side effect in ?: +@cindex ?: side effect +@noindent +In this simple case, the ability to omit the middle operand is not +especially useful. When it becomes useful is when the first operand does, +or may (if it is a macro argument), contain a side effect. Then repeating +the operand in the middle would perform the side effect twice. Omitting +the middle operand uses the value already computed without the undesirable +effects of recomputing it. + +@node Long Long +@section Double-Word Integers +@cindex @code{long long} data types +@cindex double-word arithmetic +@cindex multiprecision arithmetic +@cindex @code{LL} integer suffix +@cindex @code{ULL} integer suffix + +ISO C99 supports data types for integers that are at least 64 bits wide, +and as an extension GCC supports them in C89 mode and in C++. +Simply write @code{long long int} for a signed integer, or +@code{unsigned long long int} for an unsigned integer. To make an +integer constant of type @code{long long int}, add the suffix @samp{LL} +to the integer. To make an integer constant of type @code{unsigned long +long int}, add the suffix @samp{ULL} to the integer. + +You can use these types in arithmetic like any other integer types. +Addition, subtraction, and bitwise boolean operations on these types +are open-coded on all types of machines. Multiplication is open-coded +if the machine supports fullword-to-doubleword a widening multiply +instruction. Division and shifts are open-coded only on machines that +provide special support. The operations that are not open-coded use +special library routines that come with GCC@. + +There may be pitfalls when you use @code{long long} types for function +arguments, unless you declare function prototypes. If a function +expects type @code{int} for its argument, and you pass a value of type +@code{long long int}, confusion will result because the caller and the +subroutine will disagree about the number of bytes for the argument. +Likewise, if the function expects @code{long long int} and you pass +@code{int}. The best way to avoid such problems is to use prototypes. + +@node Complex +@section Complex Numbers +@cindex complex numbers +@cindex @code{_Complex} keyword +@cindex @code{__complex__} keyword + +ISO C99 supports complex floating data types, and as an extension GCC +supports them in C89 mode and in C++, and supports complex integer data +types which are not part of ISO C99. You can declare complex types +using the keyword @code{_Complex}. As an extension, the older GNU +keyword @code{__complex__} is also supported. + +For example, @samp{_Complex double x;} declares @code{x} as a +variable whose real part and imaginary part are both of type +@code{double}. @samp{_Complex short int y;} declares @code{y} to +have real and imaginary parts of type @code{short int}; this is not +likely to be useful, but it shows that the set of complex types is +complete. + +To write a constant with a complex data type, use the suffix @samp{i} or +@samp{j} (either one; they are equivalent). For example, @code{2.5fi} +has type @code{_Complex float} and @code{3i} has type +@code{_Complex int}. Such a constant always has a pure imaginary +value, but you can form any complex value you like by adding one to a +real constant. This is a GNU extension; if you have an ISO C99 +conforming C library (such as GNU libc), and want to construct complex +constants of floating type, you should include @code{} and +use the macros @code{I} or @code{_Complex_I} instead. + +@cindex @code{__real__} keyword +@cindex @code{__imag__} keyword +To extract the real part of a complex-valued expression @var{exp}, write +@code{__real__ @var{exp}}. Likewise, use @code{__imag__} to +extract the imaginary part. This is a GNU extension; for values of +floating type, you should use the ISO C99 functions @code{crealf}, +@code{creal}, @code{creall}, @code{cimagf}, @code{cimag} and +@code{cimagl}, declared in @code{} and also provided as +built-in functions by GCC@. + +@cindex complex conjugation +The operator @samp{~} performs complex conjugation when used on a value +with a complex type. This is a GNU extension; for values of +floating type, you should use the ISO C99 functions @code{conjf}, +@code{conj} and @code{conjl}, declared in @code{} and also +provided as built-in functions by GCC@. + +GCC can allocate complex automatic variables in a noncontiguous +fashion; it's even possible for the real part to be in a register while +the imaginary part is on the stack (or vice-versa). None of the +supported debugging info formats has a way to represent noncontiguous +allocation like this, so GCC describes a noncontiguous complex +variable as if it were two separate variables of noncomplex type. +If the variable's actual name is @code{foo}, the two fictitious +variables are named @code{foo$real} and @code{foo$imag}. You can +examine and set these two fictitious variables with your debugger. + +A future version of GDB will know how to recognize such pairs and treat +them as a single variable with a complex type. + +@node Hex Floats +@section Hex Floats +@cindex hex floats + +ISO C99 supports floating-point numbers written not only in the usual +decimal notation, such as @code{1.55e1}, but also numbers such as +@code{0x1.fp3} written in hexadecimal format. As a GNU extension, GCC +supports this in C89 mode (except in some cases when strictly +conforming) and in C++. In that format the +@samp{0x} hex introducer and the @samp{p} or @samp{P} exponent field are +mandatory. The exponent is a decimal number that indicates the power of +2 by which the significant part will be multiplied. Thus @samp{0x1.f} is +@tex +$1 {15\over16}$, +@end tex +@ifnottex +1 15/16, +@end ifnottex +@samp{p3} multiplies it by 8, and the value of @code{0x1.fp3} +is the same as @code{1.55e1}. + +Unlike for floating-point numbers in the decimal notation the exponent +is always required in the hexadecimal notation. Otherwise the compiler +would not be able to resolve the ambiguity of, e.g., @code{0x1.f}. This +could mean @code{1.0f} or @code{1.9375} since @samp{f} is also the +extension for floating-point constants of type @code{float}. + +@node Zero Length +@section Arrays of Length Zero +@cindex arrays of length zero +@cindex zero-length arrays +@cindex length-zero arrays +@cindex flexible array members + +Zero-length arrays are allowed in GNU C@. They are very useful as the +last element of a structure which is really a header for a variable-length +object: + +@example +struct line @{ + int length; + char contents[0]; +@}; + +struct line *thisline = (struct line *) + malloc (sizeof (struct line) + this_length); +thisline->length = this_length; +@end example + +In ISO C89, you would have to give @code{contents} a length of 1, which +means either you waste space or complicate the argument to @code{malloc}. + +In ISO C99, you would use a @dfn{flexible array member}, which is +slightly different in syntax and semantics: + +@itemize @bullet +@item +Flexible array members are written as @code{contents[]} without +the @code{0}. + +@item +Flexible array members have incomplete type, and so the @code{sizeof} +operator may not be applied. As a quirk of the original implementation +of zero-length arrays, @code{sizeof} evaluates to zero. + +@item +Flexible array members may only appear as the last member of a +@code{struct} that is otherwise non-empty. +@end itemize + +GCC versions before 3.0 allowed zero-length arrays to be statically +initialized, as if they were flexible arrays. In addition to those +cases that were useful, it also allowed initializations in situations +that would corrupt later data. Non-empty initialization of zero-length +arrays is now treated like any case where there are more initializer +elements than the array holds, in that a suitable warning about "excess +elements in array" is given, and the excess elements (all of them, in +this case) are ignored. + +Instead GCC allows static initialization of flexible array members. +This is equivalent to defining a new structure containing the original +structure followed by an array of sufficient size to contain the data. +I.e.@: in the following, @code{f1} is constructed as if it were declared +like @code{f2}. + +@example +struct f1 @{ + int x; int y[]; +@} f1 = @{ 1, @{ 2, 3, 4 @} @}; + +struct f2 @{ + struct f1 f1; int data[3]; +@} f2 = @{ @{ 1 @}, @{ 2, 3, 4 @} @}; +@end example + +@noindent +The convenience of this extension is that @code{f1} has the desired +type, eliminating the need to consistently refer to @code{f2.f1}. + +This has symmetry with normal static arrays, in that an array of +unknown size is also written with @code{[]}. + +Of course, this extension only makes sense if the extra data comes at +the end of a top-level object, as otherwise we would be overwriting +data at subsequent offsets. To avoid undue complication and confusion +with initialization of deeply nested arrays, we simply disallow any +non-empty initialization except when the structure is the top-level +object. For example: + +@example +struct foo @{ int x; int y[]; @}; +struct bar @{ struct foo z; @}; + +struct foo a = @{ 1, @{ 2, 3, 4 @} @}; // @r{Valid.} +struct bar b = @{ @{ 1, @{ 2, 3, 4 @} @} @}; // @r{Invalid.} +struct bar c = @{ @{ 1, @{ @} @} @}; // @r{Valid.} +struct foo d[1] = @{ @{ 1 @{ 2, 3, 4 @} @} @}; // @r{Invalid.} +@end example + +@node Variable Length +@section Arrays of Variable Length +@cindex variable-length arrays +@cindex arrays of variable length +@cindex VLAs + +Variable-length automatic arrays are allowed in ISO C99, and as an +extension GCC accepts them in C89 mode and in C++. (However, GCC's +implementation of variable-length arrays does not yet conform in detail +to the ISO C99 standard.) These arrays are +declared like any other automatic arrays, but with a length that is not +a constant expression. The storage is allocated at the point of +declaration and deallocated when the brace-level is exited. For +example: + +@example +FILE * +concat_fopen (char *s1, char *s2, char *mode) +@{ + char str[strlen (s1) + strlen (s2) + 1]; + strcpy (str, s1); + strcat (str, s2); + return fopen (str, mode); +@} +@end example + +@cindex scope of a variable length array +@cindex variable-length array scope +@cindex deallocating variable length arrays +Jumping or breaking out of the scope of the array name deallocates the +storage. Jumping into the scope is not allowed; you get an error +message for it. + +@cindex @code{alloca} vs variable-length arrays +You can use the function @code{alloca} to get an effect much like +variable-length arrays. The function @code{alloca} is available in +many other C implementations (but not in all). On the other hand, +variable-length arrays are more elegant. + +There are other differences between these two methods. Space allocated +with @code{alloca} exists until the containing @emph{function} returns. +The space for a variable-length array is deallocated as soon as the array +name's scope ends. (If you use both variable-length arrays and +@code{alloca} in the same function, deallocation of a variable-length array +will also deallocate anything more recently allocated with @code{alloca}.) + +You can also use variable-length arrays as arguments to functions: + +@example +struct entry +tester (int len, char data[len][len]) +@{ + @dots{} +@} +@end example + +The length of an array is computed once when the storage is allocated +and is remembered for the scope of the array in case you access it with +@code{sizeof}. + +If you want to pass the array first and the length afterward, you can +use a forward declaration in the parameter list---another GNU extension. + +@example +struct entry +tester (int len; char data[len][len], int len) +@{ + @dots{} +@} +@end example + +@cindex parameter forward declaration +The @samp{int len} before the semicolon is a @dfn{parameter forward +declaration}, and it serves the purpose of making the name @code{len} +known when the declaration of @code{data} is parsed. + +You can write any number of such parameter forward declarations in the +parameter list. They can be separated by commas or semicolons, but the +last one must end with a semicolon, which is followed by the ``real'' +parameter declarations. Each forward declaration must match a ``real'' +declaration in parameter name and data type. ISO C99 does not support +parameter forward declarations. + +@node Variadic Macros +@section Macros with a Variable Number of Arguments. +@cindex variable number of arguments +@cindex macro with variable arguments +@cindex rest argument (in macro) +@cindex variadic macros + +In the ISO C standard of 1999, a macro can be declared to accept a +variable number of arguments much as a function can. The syntax for +defining the macro is similar to that of a function. Here is an +example: + +@example +#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__) +@end example + +Here @samp{@dots{}} is a @dfn{variable argument}. In the invocation of +such a macro, it represents the zero or more tokens until the closing +parenthesis that ends the invocation, including any commas. This set of +tokens replaces the identifier @code{__VA_ARGS__} in the macro body +wherever it appears. See the CPP manual for more information. + +GCC has long supported variadic macros, and used a different syntax that +allowed you to give a name to the variable arguments just like any other +argument. Here is an example: + +@example +#define debug(format, args...) fprintf (stderr, format, args) +@end example + +This is in all ways equivalent to the ISO C example above, but arguably +more readable and descriptive. + +GNU CPP has two further variadic macro extensions, and permits them to +be used with either of the above forms of macro definition. + +In standard C, you are not allowed to leave the variable argument out +entirely; but you are allowed to pass an empty argument. For example, +this invocation is invalid in ISO C, because there is no comma after +the string: + +@example +debug ("A message") +@end example + +GNU CPP permits you to completely omit the variable arguments in this +way. In the above examples, the compiler would complain, though since +the expansion of the macro still has the extra comma after the format +string. + +To help solve this problem, CPP behaves specially for variable arguments +used with the token paste operator, @samp{##}. If instead you write + +@example +#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__) +@end example + +and if the variable arguments are omitted or empty, the @samp{##} +operator causes the preprocessor to remove the comma before it. If you +do provide some variable arguments in your macro invocation, GNU CPP +does not complain about the paste operation and instead places the +variable arguments after the comma. Just like any other pasted macro +argument, these arguments are not macro expanded. + +@node Escaped Newlines +@section Slightly Looser Rules for Escaped Newlines +@cindex escaped newlines +@cindex newlines (escaped) + +Recently, the non-traditional preprocessor has relaxed its treatment of +escaped newlines. Previously, the newline had to immediately follow a +backslash. The current implementation allows whitespace in the form of +spaces, horizontal and vertical tabs, and form feeds between the +backslash and the subsequent newline. The preprocessor issues a +warning, but treats it as a valid escaped newline and combines the two +lines to form a single logical line. This works within comments and +tokens, including multi-line strings, as well as between tokens. +Comments are @emph{not} treated as whitespace for the purposes of this +relaxation, since they have not yet been replaced with spaces. + +@node Multi-line Strings +@section String Literals with Embedded Newlines +@cindex multi-line string literals + +As an extension, GNU CPP permits string literals to cross multiple lines +without escaping the embedded newlines. Each embedded newline is +replaced with a single @samp{\n} character in the resulting string +literal, regardless of what form the newline took originally. + +CPP currently allows such strings in directives as well (other than the +@samp{#include} family). This is deprecated and will eventually be +removed. + +@node Subscripting +@section Non-Lvalue Arrays May Have Subscripts +@cindex subscripting +@cindex arrays, non-lvalue + +@cindex subscripting and function values +In ISO C99, arrays that are not lvalues still decay to pointers, and +may be subscripted, although they may not be modified or used after +the next sequence point and the unary @samp{&} operator may not be +applied to them. As an extension, GCC allows such arrays to be +subscripted in C89 mode, though otherwise they do not decay to +pointers outside C99 mode. For example, +this is valid in GNU C though not valid in C89: + +@example +@group +struct foo @{int a[4];@}; + +struct foo f(); + +bar (int index) +@{ + return f().a[index]; +@} +@end group +@end example + +@node Pointer Arith +@section Arithmetic on @code{void}- and Function-Pointers +@cindex void pointers, arithmetic +@cindex void, size of pointer to +@cindex function pointers, arithmetic +@cindex function, size of pointer to + +In GNU C, addition and subtraction operations are supported on pointers to +@code{void} and on pointers to functions. This is done by treating the +size of a @code{void} or of a function as 1. + +A consequence of this is that @code{sizeof} is also allowed on @code{void} +and on function types, and returns 1. + +@opindex Wpointer-arith +The option @option{-Wpointer-arith} requests a warning if these extensions +are used. + +@node Initializers +@section Non-Constant Initializers +@cindex initializers, non-constant +@cindex non-constant initializers + +As in standard C++ and ISO C99, the elements of an aggregate initializer for an +automatic variable are not required to be constant expressions in GNU C@. +Here is an example of an initializer with run-time varying elements: + +@example +foo (float f, float g) +@{ + float beat_freqs[2] = @{ f-g, f+g @}; + @dots{} +@} +@end example + +@node Compound Literals +@section Compound Literals +@cindex constructor expressions +@cindex initializations in expressions +@cindex structures, constructor expression +@cindex expressions, constructor +@cindex compound literals +@c The GNU C name for what C99 calls compound literals was "constructor expressions". + +ISO C99 supports compound literals. A compound literal looks like +a cast containing an initializer. Its value is an object of the +type specified in the cast, containing the elements specified in +the initializer; it is an lvalue. As an extension, GCC supports +compound literals in C89 mode and in C++. + +Usually, the specified type is a structure. Assume that +@code{struct foo} and @code{structure} are declared as shown: + +@example +struct foo @{int a; char b[2];@} structure; +@end example + +@noindent +Here is an example of constructing a @code{struct foo} with a compound literal: + +@example +structure = ((struct foo) @{x + y, 'a', 0@}); +@end example + +@noindent +This is equivalent to writing the following: + +@example +@{ + struct foo temp = @{x + y, 'a', 0@}; + structure = temp; +@} +@end example + +You can also construct an array. If all the elements of the compound literal +are (made up of) simple constant expressions, suitable for use in +initializers of objects of static storage duration, then the compound +literal can be coerced to a pointer to its first element and used in +such an initializer, as shown here: + +@example +char **foo = (char *[]) @{ "x", "y", "z" @}; +@end example + +Compound literals for scalar types and union types are is +also allowed, but then the compound literal is equivalent +to a cast. + +As a GNU extension, GCC allows initialization of objects with static storage +duration by compound literals (which is not possible in ISO C99, because +the initializer is not a constant). +It is handled as if the object was initialized only with the bracket +enclosed list if compound literal's and object types match. +The initializer list of the compound literal must be constant. +If the object being initialized has array type of unknown size, the size is +determined by compound literal size. + +@example +static struct foo x = (struct foo) @{1, 'a', 'b'@}; +static int y[] = (int []) @{1, 2, 3@}; +static int z[] = (int [3]) @{1@}; +@end example + +@noindent +The above lines are equivalent to the following: +@example +static struct foo x = @{1, 'a', 'b'@}; +static int y[] = @{1, 2, 3@}; +static int z[] = @{1, 0, 0@}; +@end example + +@node Designated Inits +@section Designated Initializers +@cindex initializers with labeled elements +@cindex labeled elements in initializers +@cindex case labels in initializers +@cindex designated initializers + +Standard C89 requires the elements of an initializer to appear in a fixed +order, the same as the order of the elements in the array or structure +being initialized. + +In ISO C99 you can give the elements in any order, specifying the array +indices or structure field names they apply to, and GNU C allows this as +an extension in C89 mode as well. This extension is not +implemented in GNU C++. + +To specify an array index, write +@samp{[@var{index}] =} before the element value. For example, + +@example +int a[6] = @{ [4] = 29, [2] = 15 @}; +@end example + +@noindent +is equivalent to + +@example +int a[6] = @{ 0, 0, 15, 0, 29, 0 @}; +@end example + +@noindent +The index values must be constant expressions, even if the array being +initialized is automatic. + +An alternative syntax for this which has been obsolete since GCC 2.5 but +GCC still accepts is to write @samp{[@var{index}]} before the element +value, with no @samp{=}. + +To initialize a range of elements to the same value, write +@samp{[@var{first} ... @var{last}] = @var{value}}. This is a GNU +extension. For example, + +@example +int widths[] = @{ [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 @}; +@end example + +@noindent +If the value in it has side-effects, the side-effects will happen only once, +not for each initialized field by the range initializer. + +@noindent +Note that the length of the array is the highest value specified +plus one. + +In a structure initializer, specify the name of a field to initialize +with @samp{.@var{fieldname} =} before the element value. For example, +given the following structure, + +@example +struct point @{ int x, y; @}; +@end example + +@noindent +the following initialization + +@example +struct point p = @{ .y = yvalue, .x = xvalue @}; +@end example + +@noindent +is equivalent to + +@example +struct point p = @{ xvalue, yvalue @}; +@end example + +Another syntax which has the same meaning, obsolete since GCC 2.5, is +@samp{@var{fieldname}:}, as shown here: + +@example +struct point p = @{ y: yvalue, x: xvalue @}; +@end example + +@cindex designators +The @samp{[@var{index}]} or @samp{.@var{fieldname}} is known as a +@dfn{designator}. You can also use a designator (or the obsolete colon +syntax) when initializing a union, to specify which element of the union +should be used. For example, + +@example +union foo @{ int i; double d; @}; + +union foo f = @{ .d = 4 @}; +@end example + +@noindent +will convert 4 to a @code{double} to store it in the union using +the second element. By contrast, casting 4 to type @code{union foo} +would store it into the union as the integer @code{i}, since it is +an integer. (@xref{Cast to Union}.) + +You can combine this technique of naming elements with ordinary C +initialization of successive elements. Each initializer element that +does not have a designator applies to the next consecutive element of the +array or structure. For example, + +@example +int a[6] = @{ [1] = v1, v2, [4] = v4 @}; +@end example + +@noindent +is equivalent to + +@example +int a[6] = @{ 0, v1, v2, 0, v4, 0 @}; +@end example + +Labeling the elements of an array initializer is especially useful +when the indices are characters or belong to an @code{enum} type. +For example: + +@example +int whitespace[256] + = @{ [' '] = 1, ['\t'] = 1, ['\h'] = 1, + ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 @}; +@end example + +@cindex designator lists +You can also write a series of @samp{.@var{fieldname}} and +@samp{[@var{index}]} designators before an @samp{=} to specify a +nested subobject to initialize; the list is taken relative to the +subobject corresponding to the closest surrounding brace pair. For +example, with the @samp{struct point} declaration above: + +@example +struct point ptarray[10] = @{ [2].y = yv2, [2].x = xv2, [0].x = xv0 @}; +@end example + +@noindent +If the same field is initialized multiple times, it will have value from +the last initialization. If any such overridden initialization has +side-effect, it is unspecified whether the side-effect happens or not. +Currently, gcc will discard them and issue a warning. + +@node Case Ranges +@section Case Ranges +@cindex case ranges +@cindex ranges in case statements + +You can specify a range of consecutive values in a single @code{case} label, +like this: + +@example +case @var{low} ... @var{high}: +@end example + +@noindent +This has the same effect as the proper number of individual @code{case} +labels, one for each integer value from @var{low} to @var{high}, inclusive. + +This feature is especially useful for ranges of ASCII character codes: + +@example +case 'A' ... 'Z': +@end example + +@strong{Be careful:} Write spaces around the @code{...}, for otherwise +it may be parsed wrong when you use it with integer values. For example, +write this: + +@example +case 1 ... 5: +@end example + +@noindent +rather than this: + +@example +case 1...5: +@end example + +@node Cast to Union +@section Cast to a Union Type +@cindex cast to a union +@cindex union, casting to a + +A cast to union type is similar to other casts, except that the type +specified is a union type. You can specify the type either with +@code{union @var{tag}} or with a typedef name. A cast to union is actually +a constructor though, not a cast, and hence does not yield an lvalue like +normal casts. (@xref{Compound Literals}.) + +The types that may be cast to the union type are those of the members +of the union. Thus, given the following union and variables: + +@example +union foo @{ int i; double d; @}; +int x; +double y; +@end example + +@noindent +both @code{x} and @code{y} can be cast to type @code{union foo}. + +Using the cast as the right-hand side of an assignment to a variable of +union type is equivalent to storing in a member of the union: + +@example +union foo u; +@dots{} +u = (union foo) x @equiv{} u.i = x +u = (union foo) y @equiv{} u.d = y +@end example + +You can also use the union cast as a function argument: + +@example +void hack (union foo); +@dots{} +hack ((union foo) x); +@end example + +@node Mixed Declarations +@section Mixed Declarations and Code +@cindex mixed declarations and code +@cindex declarations, mixed with code +@cindex code, mixed with declarations + +ISO C99 and ISO C++ allow declarations and code to be freely mixed +within compound statements. As an extension, GCC also allows this in +C89 mode. For example, you could do: + +@example +int i; +@dots{} +i++; +int j = i + 2; +@end example + +Each identifier is visible from where it is declared until the end of +the enclosing block. + +@node Function Attributes +@section Declaring Attributes of Functions +@cindex function attributes +@cindex declaring attributes of functions +@cindex functions that never return +@cindex functions that have no side effects +@cindex functions in arbitrary sections +@cindex functions that behave like malloc +@cindex @code{volatile} applied to function +@cindex @code{const} applied to function +@cindex functions with @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style arguments +@cindex functions that are passed arguments in registers on the 386 +@cindex functions that pop the argument stack on the 386 +@cindex functions that do not pop the argument stack on the 386 + +In GNU C, you declare certain things about functions called in your program +which help the compiler optimize function calls and check your code more +carefully. + +The keyword @code{__attribute__} allows you to specify special +attributes when making a declaration. This keyword is followed by an +attribute specification inside double parentheses. The following +attributes are currently defined for functions on all targets: +@code{noreturn}, @code{noinline}, @code{pure}, @code{const}, +@code{format}, @code{format_arg}, @code{no_instrument_function}, +@code{section}, @code{constructor}, @code{destructor}, @code{used}, +@code{unused}, @code{deprecated}, @code{weak}, @code{malloc}, and +@code{alias}. Several other attributes are defined for functions on +particular target systems. Other attributes, including @code{section} +are supported for variables declarations (@pxref{Variable Attributes}) +and for types (@pxref{Type Attributes}). + +You may also specify attributes with @samp{__} preceding and following +each keyword. This allows you to use them in header files without +being concerned about a possible macro of the same name. For example, +you may use @code{__noreturn__} instead of @code{noreturn}. + +@xref{Attribute Syntax}, for details of the exact syntax for using +attributes. + +@table @code +@cindex @code{noreturn} function attribute +@item noreturn +A few standard library functions, such as @code{abort} and @code{exit}, +cannot return. GCC knows this automatically. Some programs define +their own functions that never return. You can declare them +@code{noreturn} to tell the compiler this fact. For example, + +@smallexample +@group +void fatal () __attribute__ ((noreturn)); + +void +fatal (@dots{}) +@{ + @dots{} /* @r{Print error message.} */ @dots{} + exit (1); +@} +@end group +@end smallexample + +The @code{noreturn} keyword tells the compiler to assume that +@code{fatal} cannot return. It can then optimize without regard to what +would happen if @code{fatal} ever did return. This makes slightly +better code. More importantly, it helps avoid spurious warnings of +uninitialized variables. + +Do not assume that registers saved by the calling function are +restored before calling the @code{noreturn} function. + +It does not make sense for a @code{noreturn} function to have a return +type other than @code{void}. + +The attribute @code{noreturn} is not implemented in GCC versions +earlier than 2.5. An alternative way to declare that a function does +not return, which works in the current version and in some older +versions, is as follows: + +@smallexample +typedef void voidfn (); + +volatile voidfn fatal; +@end smallexample + +@cindex @code{noinline} function attribute +@item noinline +This function attribute prevents a function from being considered for +inlining. + +@cindex @code{pure} function attribute +@item pure +Many functions have no effects except the return value and their +return value depends only on the parameters and/or global variables. +Such a function can be subject +to common subexpression elimination and loop optimization just as an +arithmetic operator would be. These functions should be declared +with the attribute @code{pure}. For example, + +@smallexample +int square (int) __attribute__ ((pure)); +@end smallexample + +@noindent +says that the hypothetical function @code{square} is safe to call +fewer times than the program says. + +Some of common examples of pure functions are @code{strlen} or @code{memcmp}. +Interesting non-pure functions are functions with infinite loops or those +depending on volatile memory or other system resource, that may change between +two consecutive calls (such as @code{feof} in a multithreading environment). + +The attribute @code{pure} is not implemented in GCC versions earlier +than 2.96. +@cindex @code{const} function attribute +@item const +Many functions do not examine any values except their arguments, and +have no effects except the return value. Basically this is just slightly +more strict class than the @code{pure} attribute above, since function is not +allowed to read global memory. + +@cindex pointer arguments +Note that a function that has pointer arguments and examines the data +pointed to must @emph{not} be declared @code{const}. Likewise, a +function that calls a non-@code{const} function usually must not be +@code{const}. It does not make sense for a @code{const} function to +return @code{void}. + +The attribute @code{const} is not implemented in GCC versions earlier +than 2.5. An alternative way to declare that a function has no side +effects, which works in the current version and in some older versions, +is as follows: + +@smallexample +typedef int intfn (); + +extern const intfn square; +@end smallexample + +This approach does not work in GNU C++ from 2.6.0 on, since the language +specifies that the @samp{const} must be attached to the return value. + + +@item format (@var{archetype}, @var{string-index}, @var{first-to-check}) +@cindex @code{format} function attribute +@opindex Wformat +The @code{format} attribute specifies that a function takes @code{printf}, +@code{scanf}, @code{strftime} or @code{strfmon} style arguments which +should be type-checked against a format string. For example, the +declaration: + +@smallexample +extern int +my_printf (void *my_object, const char *my_format, ...) + __attribute__ ((format (printf, 2, 3))); +@end smallexample + +@noindent +causes the compiler to check the arguments in calls to @code{my_printf} +for consistency with the @code{printf} style format string argument +@code{my_format}. + +The parameter @var{archetype} determines how the format string is +interpreted, and should be @code{printf}, @code{scanf}, @code{strftime} +or @code{strfmon}. (You can also use @code{__printf__}, +@code{__scanf__}, @code{__strftime__} or @code{__strfmon__}.) The +parameter @var{string-index} specifies which argument is the format +string argument (starting from 1), while @var{first-to-check} is the +number of the first argument to check against the format string. For +functions where the arguments are not available to be checked (such as +@code{vprintf}), specify the third parameter as zero. In this case the +compiler only checks the format string for consistency. For +@code{strftime} formats, the third parameter is required to be zero. + +In the example above, the format string (@code{my_format}) is the second +argument of the function @code{my_print}, and the arguments to check +start with the third argument, so the correct parameters for the format +attribute are 2 and 3. + +@opindex ffreestanding +The @code{format} attribute allows you to identify your own functions +which take format strings as arguments, so that GCC can check the +calls to these functions for errors. The compiler always (unless +@option{-ffreestanding} is used) checks formats +for the standard library functions @code{printf}, @code{fprintf}, +@code{sprintf}, @code{scanf}, @code{fscanf}, @code{sscanf}, @code{strftime}, +@code{vprintf}, @code{vfprintf} and @code{vsprintf} whenever such +warnings are requested (using @option{-Wformat}), so there is no need to +modify the header file @file{stdio.h}. In C99 mode, the functions +@code{snprintf}, @code{vsnprintf}, @code{vscanf}, @code{vfscanf} and +@code{vsscanf} are also checked. Except in strictly conforming C +standard modes, the X/Open function @code{strfmon} is also checked as +are @code{printf_unlocked} and @code{fprintf_unlocked}. +@xref{C Dialect Options,,Options Controlling C Dialect}. + +@item format_arg (@var{string-index}) +@cindex @code{format_arg} function attribute +@opindex Wformat-nonliteral +The @code{format_arg} attribute specifies that a function takes a format +string for a @code{printf}, @code{scanf}, @code{strftime} or +@code{strfmon} style function and modifies it (for example, to translate +it into another language), so the result can be passed to a +@code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style +function (with the remaining arguments to the format function the same +as they would have been for the unmodified string). For example, the +declaration: + +@smallexample +extern char * +my_dgettext (char *my_domain, const char *my_format) + __attribute__ ((format_arg (2))); +@end smallexample + +@noindent +causes the compiler to check the arguments in calls to a @code{printf}, +@code{scanf}, @code{strftime} or @code{strfmon} type function, whose +format string argument is a call to the @code{my_dgettext} function, for +consistency with the format string argument @code{my_format}. If the +@code{format_arg} attribute had not been specified, all the compiler +could tell in such calls to format functions would be that the format +string argument is not constant; this would generate a warning when +@option{-Wformat-nonliteral} is used, but the calls could not be checked +without the attribute. + +The parameter @var{string-index} specifies which argument is the format +string argument (starting from 1). + +The @code{format-arg} attribute allows you to identify your own +functions which modify format strings, so that GCC can check the +calls to @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} +type function whose operands are a call to one of your own function. +The compiler always treats @code{gettext}, @code{dgettext}, and +@code{dcgettext} in this manner except when strict ISO C support is +requested by @option{-ansi} or an appropriate @option{-std} option, or +@option{-ffreestanding} is used. @xref{C Dialect Options,,Options +Controlling C Dialect}. + +@item no_instrument_function +@cindex @code{no_instrument_function} function attribute +@opindex finstrument-functions +If @option{-finstrument-functions} is given, profiling function calls will +be generated at entry and exit of most user-compiled functions. +Functions with this attribute will not be so instrumented. + +@item section ("@var{section-name}") +@cindex @code{section} function attribute +Normally, the compiler places the code it generates in the @code{text} section. +Sometimes, however, you need additional sections, or you need certain +particular functions to appear in special sections. The @code{section} +attribute specifies that a function lives in a particular section. +For example, the declaration: + +@smallexample +extern void foobar (void) __attribute__ ((section ("bar"))); +@end smallexample + +@noindent +puts the function @code{foobar} in the @code{bar} section. + +Some file formats do not support arbitrary sections so the @code{section} +attribute is not available on all platforms. +If you need to map the entire contents of a module to a particular +section, consider using the facilities of the linker instead. + +@item constructor +@itemx destructor +@cindex @code{constructor} function attribute +@cindex @code{destructor} function attribute +The @code{constructor} attribute causes the function to be called +automatically before execution enters @code{main ()}. Similarly, the +@code{destructor} attribute causes the function to be called +automatically after @code{main ()} has completed or @code{exit ()} has +been called. Functions with these attributes are useful for +initializing data that will be used implicitly during the execution of +the program. + +These attributes are not currently implemented for Objective-C@. + +@cindex @code{unused} attribute. +@item unused +This attribute, attached to a function, means that the function is meant +to be possibly unused. GCC will not produce a warning for this +function. GNU C++ does not currently support this attribute as +definitions without parameters are valid in C++. + +@cindex @code{used} attribute. +@item used +This attribute, attached to a function, means that code must be emitted +for the function even if it appears that the function is not referenced. +This is useful, for example, when the function is referenced only in +inline assembly. + +@cindex @code{deprecated} attribute. +@item deprecated +The @code{deprecated} attribute results in a warning if the function +is used anywhere in the source file. This is useful when identifying +functions that are expected to be removed in a future version of a +program. The warning also includes the location of the declaration +of the deprecated function, to enable users to easily find further +information about why the function is deprecated, or what they should +do instead. Note that the warnings only occurs for uses: + +@smallexample +int old_fn () __attribute__ ((deprecated)); +int old_fn (); +int (*fn_ptr)() = old_fn; +@end smallexample + +results in a warning on line 3 but not line 2. + +The @code{deprecated} attribute can also be used for variables and +types (@pxref{Variable Attributes}, @pxref{Type Attributes}.) + +@item weak +@cindex @code{weak} attribute +The @code{weak} attribute causes the declaration to be emitted as a weak +symbol rather than a global. This is primarily useful in defining +library functions which can be overridden in user code, though it can +also be used with non-function declarations. Weak symbols are supported +for ELF targets, and also for a.out targets when using the GNU assembler +and linker. + +@item malloc +@cindex @code{malloc} attribute +The @code{malloc} attribute is used to tell the compiler that a function +may be treated as if it were the malloc function. The compiler assumes +that calls to malloc result in a pointers that cannot alias anything. +This will often improve optimization. + +@item alias ("@var{target}") +@cindex @code{alias} attribute +The @code{alias} attribute causes the declaration to be emitted as an +alias for another symbol, which must be specified. For instance, + +@smallexample +void __f () @{ /* do something */; @} +void f () __attribute__ ((weak, alias ("__f"))); +@end smallexample + +declares @samp{f} to be a weak alias for @samp{__f}. In C++, the +mangled name for the target must be used. + +Not all target machines support this attribute. + +@item regparm (@var{number}) +@cindex functions that are passed arguments in registers on the 386 +On the Intel 386, the @code{regparm} attribute causes the compiler to +pass up to @var{number} integer arguments in registers EAX, +EDX, and ECX instead of on the stack. Functions that take a +variable number of arguments will continue to be passed all of their +arguments on the stack. + +@item stdcall +@cindex functions that pop the argument stack on the 386 +On the Intel 386, the @code{stdcall} attribute causes the compiler to +assume that the called function will pop off the stack space used to +pass arguments, unless it takes a variable number of arguments. + +The PowerPC compiler for Windows NT currently ignores the @code{stdcall} +attribute. + +@item cdecl +@cindex functions that do pop the argument stack on the 386 +@opindex mrtd +On the Intel 386, the @code{cdecl} attribute causes the compiler to +assume that the calling function will pop off the stack space used to +pass arguments. This is +useful to override the effects of the @option{-mrtd} switch. + +The PowerPC compiler for Windows NT currently ignores the @code{cdecl} +attribute. + +@item longcall +@cindex functions called via pointer on the RS/6000 and PowerPC +On the RS/6000 and PowerPC, the @code{longcall} attribute causes the +compiler to always call the function via a pointer, so that functions +which reside further than 64 megabytes (67,108,864 bytes) from the +current location can be called. + +@item long_call/short_call +@cindex indirect calls on ARM +This attribute allows to specify how to call a particular function on +ARM@. Both attributes override the @option{-mlong-calls} (@pxref{ARM Options}) +command line switch and @code{#pragma long_calls} settings. The +@code{long_call} attribute causes the compiler to always call the +function by first loading its address into a register and then using the +contents of that register. The @code{short_call} attribute always places +the offset to the function from the call site into the @samp{BL} +instruction directly. + +@item dllimport +@cindex functions which are imported from a dll on PowerPC Windows NT +On the PowerPC running Windows NT, the @code{dllimport} attribute causes +the compiler to call the function via a global pointer to the function +pointer that is set up by the Windows NT dll library. The pointer name +is formed by combining @code{__imp_} and the function name. + +@item dllexport +@cindex functions which are exported from a dll on PowerPC Windows NT +On the PowerPC running Windows NT, the @code{dllexport} attribute causes +the compiler to provide a global pointer to the function pointer, so +that it can be called with the @code{dllimport} attribute. The pointer +name is formed by combining @code{__imp_} and the function name. + +@item exception (@var{except-func} [, @var{except-arg}]) +@cindex functions which specify exception handling on PowerPC Windows NT +On the PowerPC running Windows NT, the @code{exception} attribute causes +the compiler to modify the structured exception table entry it emits for +the declared function. The string or identifier @var{except-func} is +placed in the third entry of the structured exception table. It +represents a function, which is called by the exception handling +mechanism if an exception occurs. If it was specified, the string or +identifier @var{except-arg} is placed in the fourth entry of the +structured exception table. + +@item function_vector +@cindex calling functions through the function vector on the H8/300 processors +Use this attribute on the H8/300 and H8/300H to indicate that the specified +function should be called through the function vector. Calling a +function through the function vector will reduce code size, however; +the function vector has a limited size (maximum 128 entries on the H8/300 +and 64 entries on the H8/300H) and shares space with the interrupt vector. + +You must use GAS and GLD from GNU binutils version 2.7 or later for +this attribute to work correctly. + +@item interrupt +@cindex interrupt handler functions +Use this attribute on the ARM, AVR, M32R/D and Xstormy16 ports to indicate +that the specified function is an interrupt handler. The compiler will +generate function entry and exit sequences suitable for use in an +interrupt handler when this attribute is present. + +Note, interrupt handlers for the H8/300, H8/300H and SH processors can +be specified via the @code{interrupt_handler} attribute. + +Note, on the AVR interrupts will be enabled inside the function. + +Note, for the ARM you can specify the kind of interrupt to be handled by +adding an optional parameter to the interrupt attribute like this: + +@smallexample +void f () __attribute__ ((interrupt ("IRQ"))); +@end smallexample + +Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF@. + +@item interrupt_handler +@cindex interrupt handler functions on the H8/300 and SH processors +Use this attribute on the H8/300, H8/300H and SH to indicate that the +specified function is an interrupt handler. The compiler will generate +function entry and exit sequences suitable for use in an interrupt +handler when this attribute is present. + +@item sp_switch +Use this attribute on the SH to indicate an @code{interrupt_handler} +function should switch to an alternate stack. It expects a string +argument that names a global variable holding the address of the +alternate stack. + +@smallexample +void *alt_stack; +void f () __attribute__ ((interrupt_handler, + sp_switch ("alt_stack"))); +@end smallexample + +@item trap_exit +Use this attribute on the SH for an @code{interrupt_handle} to return using +@code{trapa} instead of @code{rte}. This attribute expects an integer +argument specifying the trap number to be used. + +@item eightbit_data +@cindex eight bit data on the H8/300 and H8/300H +Use this attribute on the H8/300 and H8/300H to indicate that the specified +variable should be placed into the eight bit data section. +The compiler will generate more efficient code for certain operations +on data in the eight bit data area. Note the eight bit data area is limited to +256 bytes of data. + +You must use GAS and GLD from GNU binutils version 2.7 or later for +this attribute to work correctly. + +@item tiny_data +@cindex tiny data section on the H8/300H +Use this attribute on the H8/300H to indicate that the specified +variable should be placed into the tiny data section. +The compiler will generate more efficient code for loads and stores +on data in the tiny data section. Note the tiny data area is limited to +slightly under 32kbytes of data. + +@item signal +@cindex signal handler functions on the AVR processors +Use this attribute on the AVR to indicate that the specified +function is an signal handler. The compiler will generate function +entry and exit sequences suitable for use in an signal handler when this +attribute is present. Interrupts will be disabled inside function. + +@item naked +@cindex function without a prologue/epilogue code +Use this attribute on the ARM or AVR ports to indicate that the specified +function do not need prologue/epilogue sequences generated by the +compiler. It is up to the programmer to provide these sequences. + +@item model (@var{model-name}) +@cindex function addressability on the M32R/D +Use this attribute on the M32R/D to set the addressability of an object, +and the code generated for a function. +The identifier @var{model-name} is one of @code{small}, @code{medium}, +or @code{large}, representing each of the code models. + +Small model objects live in the lower 16MB of memory (so that their +addresses can be loaded with the @code{ld24} instruction), and are +callable with the @code{bl} instruction. + +Medium model objects may live anywhere in the 32-bit address space (the +compiler will generate @code{seth/add3} instructions to load their addresses), +and are callable with the @code{bl} instruction. + +Large model objects may live anywhere in the 32-bit address space (the +compiler will generate @code{seth/add3} instructions to load their addresses), +and may not be reachable with the @code{bl} instruction (the compiler will +generate the much slower @code{seth/add3/jl} instruction sequence). + +@end table + +You can specify multiple attributes in a declaration by separating them +by commas within the double parentheses or by immediately following an +attribute declaration with another attribute declaration. + +@cindex @code{#pragma}, reason for not using +@cindex pragma, reason for not using +Some people object to the @code{__attribute__} feature, suggesting that +ISO C's @code{#pragma} should be used instead. At the time +@code{__attribute__} was designed, there were two reasons for not doing +this. + +@enumerate +@item +It is impossible to generate @code{#pragma} commands from a macro. + +@item +There is no telling what the same @code{#pragma} might mean in another +compiler. +@end enumerate + +These two reasons applied to almost any application that might have been +proposed for @code{#pragma}. It was basically a mistake to use +@code{#pragma} for @emph{anything}. + +The ISO C99 standard includes @code{_Pragma}, which now allows pragmas +to be generated from macros. In addition, a @code{#pragma GCC} +namespace is now in use for GCC-specific pragmas. However, it has been +found convenient to use @code{__attribute__} to achieve a natural +attachment of attributes to their corresponding declarations, whereas +@code{#pragma GCC} is of use for constructs that do not naturally form +part of the grammar. @xref{Other Directives,,Miscellaneous +Preprocessing Directives, cpp, The C Preprocessor}. + +@node Attribute Syntax +@section Attribute Syntax +@cindex attribute syntax + +This section describes the syntax with which @code{__attribute__} may be +used, and the constructs to which attribute specifiers bind, for the C +language. Some details may vary for C++ and Objective-C@. Because of +infelicities in the grammar for attributes, some forms described here +may not be successfully parsed in all cases. + +There are some problems with the semantics of attributes in C++. For +example, there are no manglings for attributes, although they may affect +code generation, so problems may arise when attributed types are used in +conjunction with templates or overloading. Similarly, @code{typeid} +does not distinguish between types with different attributes. Support +for attributes in C++ may be restricted in future to attributes on +declarations only, but not on nested declarators. + +@xref{Function Attributes}, for details of the semantics of attributes +applying to functions. @xref{Variable Attributes}, for details of the +semantics of attributes applying to variables. @xref{Type Attributes}, +for details of the semantics of attributes applying to structure, union +and enumerated types. + +An @dfn{attribute specifier} is of the form +@code{__attribute__ ((@var{attribute-list}))}. An @dfn{attribute list} +is a possibly empty comma-separated sequence of @dfn{attributes}, where +each attribute is one of the following: + +@itemize @bullet +@item +Empty. Empty attributes are ignored. + +@item +A word (which may be an identifier such as @code{unused}, or a reserved +word such as @code{const}). + +@item +A word, followed by, in parentheses, parameters for the attribute. +These parameters take one of the following forms: + +@itemize @bullet +@item +An identifier. For example, @code{mode} attributes use this form. + +@item +An identifier followed by a comma and a non-empty comma-separated list +of expressions. For example, @code{format} attributes use this form. + +@item +A possibly empty comma-separated list of expressions. For example, +@code{format_arg} attributes use this form with the list being a single +integer constant expression, and @code{alias} attributes use this form +with the list being a single string constant. +@end itemize +@end itemize + +An @dfn{attribute specifier list} is a sequence of one or more attribute +specifiers, not separated by any other tokens. + +An attribute specifier list may appear after the colon following a +label, other than a @code{case} or @code{default} label. The only +attribute it makes sense to use after a label is @code{unused}. This +feature is intended for code generated by programs which contains labels +that may be unused but which is compiled with @option{-Wall}. It would +not normally be appropriate to use in it human-written code, though it +could be useful in cases where the code that jumps to the label is +contained within an @code{#ifdef} conditional. + +An attribute specifier list may appear as part of a @code{struct}, +@code{union} or @code{enum} specifier. It may go either immediately +after the @code{struct}, @code{union} or @code{enum} keyword, or after +the closing brace. It is ignored if the content of the structure, union +or enumerated type is not defined in the specifier in which the +attribute specifier list is used---that is, in usages such as +@code{struct __attribute__((foo)) bar} with no following opening brace. +Where attribute specifiers follow the closing brace, they are considered +to relate to the structure, union or enumerated type defined, not to any +enclosing declaration the type specifier appears in, and the type +defined is not complete until after the attribute specifiers. +@c Otherwise, there would be the following problems: a shift/reduce +@c conflict between attributes binding the struct/union/enum and +@c binding to the list of specifiers/qualifiers; and "aligned" +@c attributes could use sizeof for the structure, but the size could be +@c changed later by "packed" attributes. + +Otherwise, an attribute specifier appears as part of a declaration, +counting declarations of unnamed parameters and type names, and relates +to that declaration (which may be nested in another declaration, for +example in the case of a parameter declaration), or to a particular declarator +within a declaration. Where an +attribute specifier is applied to a parameter declared as a function or +an array, it should apply to the function or array rather than the +pointer to which the parameter is implicitly converted, but this is not +yet correctly implemented. + +Any list of specifiers and qualifiers at the start of a declaration may +contain attribute specifiers, whether or not such a list may in that +context contain storage class specifiers. (Some attributes, however, +are essentially in the nature of storage class specifiers, and only make +sense where storage class specifiers may be used; for example, +@code{section}.) There is one necessary limitation to this syntax: the +first old-style parameter declaration in a function definition cannot +begin with an attribute specifier, because such an attribute applies to +the function instead by syntax described below (which, however, is not +yet implemented in this case). In some other cases, attribute +specifiers are permitted by this grammar but not yet supported by the +compiler. All attribute specifiers in this place relate to the +declaration as a whole. In the obsolescent usage where a type of +@code{int} is implied by the absence of type specifiers, such a list of +specifiers and qualifiers may be an attribute specifier list with no +other specifiers or qualifiers. + +An attribute specifier list may appear immediately before a declarator +(other than the first) in a comma-separated list of declarators in a +declaration of more than one identifier using a single list of +specifiers and qualifiers. Such attribute specifiers apply +only to the identifier before whose declarator they appear. For +example, in + +@smallexample +__attribute__((noreturn)) void d0 (void), + __attribute__((format(printf, 1, 2))) d1 (const char *, ...), + d2 (void) +@end smallexample + +@noindent +the @code{noreturn} attribute applies to all the functions +declared; the @code{format} attribute only applies to @code{d1}. + +An attribute specifier list may appear immediately before the comma, +@code{=} or semicolon terminating the declaration of an identifier other +than a function definition. At present, such attribute specifiers apply +to the declared object or function, but in future they may attach to the +outermost adjacent declarator. In simple cases there is no difference, +but, for example, in + +@smallexample +void (****f)(void) __attribute__((noreturn)); +@end smallexample + +@noindent +at present the @code{noreturn} attribute applies to @code{f}, which +causes a warning since @code{f} is not a function, but in future it may +apply to the function @code{****f}. The precise semantics of what +attributes in such cases will apply to are not yet specified. Where an +assembler name for an object or function is specified (@pxref{Asm +Labels}), at present the attribute must follow the @code{asm} +specification; in future, attributes before the @code{asm} specification +may apply to the adjacent declarator, and those after it to the declared +object or function. + +An attribute specifier list may, in future, be permitted to appear after +the declarator in a function definition (before any old-style parameter +declarations or the function body). + +Attribute specifiers may be mixed with type qualifiers appearing inside +the @code{[]} of a parameter array declarator, in the C99 construct by +which such qualifiers are applied to the pointer to which the array is +implicitly converted. Such attribute specifiers apply to the pointer, +not to the array, but at present this is not implemented and they are +ignored. + +An attribute specifier list may appear at the start of a nested +declarator. At present, there are some limitations in this usage: the +attributes correctly apply to the declarator, but for most individual +attributes the semantics this implies are not implemented. +When attribute specifiers follow the @code{*} of a pointer +declarator, they may be mixed with any type qualifiers present. +The following describes the formal semantics of this syntax. It will make the +most sense if you are familiar with the formal specification of +declarators in the ISO C standard. + +Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration @code{T +D1}, where @code{T} contains declaration specifiers that specify a type +@var{Type} (such as @code{int}) and @code{D1} is a declarator that +contains an identifier @var{ident}. The type specified for @var{ident} +for derived declarators whose type does not include an attribute +specifier is as in the ISO C standard. + +If @code{D1} has the form @code{( @var{attribute-specifier-list} D )}, +and the declaration @code{T D} specifies the type +``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then +@code{T D1} specifies the type ``@var{derived-declarator-type-list} +@var{attribute-specifier-list} @var{Type}'' for @var{ident}. + +If @code{D1} has the form @code{* +@var{type-qualifier-and-attribute-specifier-list} D}, and the +declaration @code{T D} specifies the type +``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then +@code{T D1} specifies the type ``@var{derived-declarator-type-list} +@var{type-qualifier-and-attribute-specifier-list} @var{Type}'' for +@var{ident}. + +For example, + +@smallexample +void (__attribute__((noreturn)) ****f) (void); +@end smallexample + +@noindent +specifies the type ``pointer to pointer to pointer to pointer to +non-returning function returning @code{void}''. As another example, + +@smallexample +char *__attribute__((aligned(8))) *f; +@end smallexample + +@noindent +specifies the type ``pointer to 8-byte-aligned pointer to @code{char}''. +Note again that this does not work with most attributes; for example, +the usage of @samp{aligned} and @samp{noreturn} attributes given above +is not yet supported. + +For compatibility with existing code written for compiler versions that +did not implement attributes on nested declarators, some laxity is +allowed in the placing of attributes. If an attribute that only applies +to types is applied to a declaration, it will be treated as applying to +the type of that declaration. If an attribute that only applies to +declarations is applied to the type of a declaration, it will be treated +as applying to that declaration; and, for compatibility with code +placing the attributes immediately before the identifier declared, such +an attribute applied to a function return type will be treated as +applying to the function type, and such an attribute applied to an array +element type will be treated as applying to the array type. If an +attribute that only applies to function types is applied to a +pointer-to-function type, it will be treated as applying to the pointer +target type; if such an attribute is applied to a function return type +that is not a pointer-to-function type, it will be treated as applying +to the function type. + +@node Function Prototypes +@section Prototypes and Old-Style Function Definitions +@cindex function prototype declarations +@cindex old-style function definitions +@cindex promotion of formal parameters + +GNU C extends ISO C to allow a function prototype to override a later +old-style non-prototype definition. Consider the following example: + +@example +/* @r{Use prototypes unless the compiler is old-fashioned.} */ +#ifdef __STDC__ +#define P(x) x +#else +#define P(x) () +#endif + +/* @r{Prototype function declaration.} */ +int isroot P((uid_t)); + +/* @r{Old-style function definition.} */ +int +isroot (x) /* ??? lossage here ??? */ + uid_t x; +@{ + return x == 0; +@} +@end example + +Suppose the type @code{uid_t} happens to be @code{short}. ISO C does +not allow this example, because subword arguments in old-style +non-prototype definitions are promoted. Therefore in this example the +function definition's argument is really an @code{int}, which does not +match the prototype argument type of @code{short}. + +This restriction of ISO C makes it hard to write code that is portable +to traditional C compilers, because the programmer does not know +whether the @code{uid_t} type is @code{short}, @code{int}, or +@code{long}. Therefore, in cases like these GNU C allows a prototype +to override a later old-style definition. More precisely, in GNU C, a +function prototype argument type overrides the argument type specified +by a later old-style definition if the former type is the same as the +latter type before promotion. Thus in GNU C the above example is +equivalent to the following: + +@example +int isroot (uid_t); + +int +isroot (uid_t x) +@{ + return x == 0; +@} +@end example + +@noindent +GNU C++ does not support old-style function definitions, so this +extension is irrelevant. + +@node C++ Comments +@section C++ Style Comments +@cindex // +@cindex C++ comments +@cindex comments, C++ style + +In GNU C, you may use C++ style comments, which start with @samp{//} and +continue until the end of the line. Many other C implementations allow +such comments, and they are likely to be in a future C standard. +However, C++ style comments are not recognized if you specify +@w{@option{-ansi}}, a @option{-std} option specifying a version of ISO C +before C99, or @w{@option{-traditional}}, since they are incompatible +with traditional constructs like @code{dividend//*comment*/divisor}. + +@node Dollar Signs +@section Dollar Signs in Identifier Names +@cindex $ +@cindex dollar signs in identifier names +@cindex identifier names, dollar signs in + +In GNU C, you may normally use dollar signs in identifier names. +This is because many traditional C implementations allow such identifiers. +However, dollar signs in identifiers are not supported on a few target +machines, typically because the target assembler does not allow them. + +@node Character Escapes +@section The Character @key{ESC} in Constants + +You can use the sequence @samp{\e} in a string or character constant to +stand for the ASCII character @key{ESC}. + +@node Alignment +@section Inquiring on Alignment of Types or Variables +@cindex alignment +@cindex type alignment +@cindex variable alignment + +The keyword @code{__alignof__} allows you to inquire about how an object +is aligned, or the minimum alignment usually required by a type. Its +syntax is just like @code{sizeof}. + +For example, if the target machine requires a @code{double} value to be +aligned on an 8-byte boundary, then @code{__alignof__ (double)} is 8. +This is true on many RISC machines. On more traditional machine +designs, @code{__alignof__ (double)} is 4 or even 2. + +Some machines never actually require alignment; they allow reference to any +data type even at an odd addresses. For these machines, @code{__alignof__} +reports the @emph{recommended} alignment of a type. + +If the operand of @code{__alignof__} is an lvalue rather than a type, +its value is the required alignment for its type, taking into account +any minimum alignment specified with GCC's @code{__attribute__} +extension (@pxref{Variable Attributes}). For example, after this +declaration: + +@example +struct foo @{ int x; char y; @} foo1; +@end example + +@noindent +the value of @code{__alignof__ (foo1.y)} is 1, even though its actual +alignment is probably 2 or 4, the same as @code{__alignof__ (int)}. + +It is an error to ask for the alignment of an incomplete type. + +@node Variable Attributes +@section Specifying Attributes of Variables +@cindex attribute of variables +@cindex variable attributes + +The keyword @code{__attribute__} allows you to specify special +attributes of variables or structure fields. This keyword is followed +by an attribute specification inside double parentheses. Ten +attributes are currently defined for variables: @code{aligned}, +@code{mode}, @code{nocommon}, @code{packed}, @code{section}, +@code{transparent_union}, @code{unused}, @code{deprecated}, +@code{vector_size}, and @code{weak}. Some other attributes are defined +for variables on particular target systems. Other attributes are +available for functions (@pxref{Function Attributes}) and for types +(@pxref{Type Attributes}). Other front ends might define more +attributes (@pxref{C++ Extensions,,Extensions to the C++ Language}). + +You may also specify attributes with @samp{__} preceding and following +each keyword. This allows you to use them in header files without +being concerned about a possible macro of the same name. For example, +you may use @code{__aligned__} instead of @code{aligned}. + +@xref{Attribute Syntax}, for details of the exact syntax for using +attributes. + +@table @code +@cindex @code{aligned} attribute +@item aligned (@var{alignment}) +This attribute specifies a minimum alignment for the variable or +structure field, measured in bytes. For example, the declaration: + +@smallexample +int x __attribute__ ((aligned (16))) = 0; +@end smallexample + +@noindent +causes the compiler to allocate the global variable @code{x} on a +16-byte boundary. On a 68040, this could be used in conjunction with +an @code{asm} expression to access the @code{move16} instruction which +requires 16-byte aligned operands. + +You can also specify the alignment of structure fields. For example, to +create a double-word aligned @code{int} pair, you could write: + +@smallexample +struct foo @{ int x[2] __attribute__ ((aligned (8))); @}; +@end smallexample + +@noindent +This is an alternative to creating a union with a @code{double} member +that forces the union to be double-word aligned. + +It is not possible to specify the alignment of functions; the alignment +of functions is determined by the machine's requirements and cannot be +changed. You cannot specify alignment for a typedef name because such a +name is just an alias, not a distinct type. + +As in the preceding examples, you can explicitly specify the alignment +(in bytes) that you wish the compiler to use for a given variable or +structure field. Alternatively, you can leave out the alignment factor +and just ask the compiler to align a variable or field to the maximum +useful alignment for the target machine you are compiling for. For +example, you could write: + +@smallexample +short array[3] __attribute__ ((aligned)); +@end smallexample + +Whenever you leave out the alignment factor in an @code{aligned} attribute +specification, the compiler automatically sets the alignment for the declared +variable or field to the largest alignment which is ever used for any data +type on the target machine you are compiling for. Doing this can often make +copy operations more efficient, because the compiler can use whatever +instructions copy the biggest chunks of memory when performing copies to +or from the variables or fields that you have aligned this way. + +The @code{aligned} attribute can only increase the alignment; but you +can decrease it by specifying @code{packed} as well. See below. + +Note that the effectiveness of @code{aligned} attributes may be limited +by inherent limitations in your linker. On many systems, the linker is +only able to arrange for variables to be aligned up to a certain maximum +alignment. (For some linkers, the maximum supported alignment may +be very very small.) If your linker is only able to align variables +up to a maximum of 8 byte alignment, then specifying @code{aligned(16)} +in an @code{__attribute__} will still only provide you with 8 byte +alignment. See your linker documentation for further information. + +@item mode (@var{mode}) +@cindex @code{mode} attribute +This attribute specifies the data type for the declaration---whichever +type corresponds to the mode @var{mode}. This in effect lets you +request an integer or floating point type according to its width. + +You may also specify a mode of @samp{byte} or @samp{__byte__} to +indicate the mode corresponding to a one-byte integer, @samp{word} or +@samp{__word__} for the mode of a one-word integer, and @samp{pointer} +or @samp{__pointer__} for the mode used to represent pointers. + +@item nocommon +@cindex @code{nocommon} attribute +@opindex fno-common +This attribute specifies requests GCC not to place a variable +``common'' but instead to allocate space for it directly. If you +specify the @option{-fno-common} flag, GCC will do this for all +variables. + +Specifying the @code{nocommon} attribute for a variable provides an +initialization of zeros. A variable may only be initialized in one +source file. + +@item packed +@cindex @code{packed} attribute +The @code{packed} attribute specifies that a variable or structure field +should have the smallest possible alignment---one byte for a variable, +and one bit for a field, unless you specify a larger value with the +@code{aligned} attribute. + +Here is a structure in which the field @code{x} is packed, so that it +immediately follows @code{a}: + +@example +struct foo +@{ + char a; + int x[2] __attribute__ ((packed)); +@}; +@end example + +@item section ("@var{section-name}") +@cindex @code{section} variable attribute +Normally, the compiler places the objects it generates in sections like +@code{data} and @code{bss}. Sometimes, however, you need additional sections, +or you need certain particular variables to appear in special sections, +for example to map to special hardware. The @code{section} +attribute specifies that a variable (or function) lives in a particular +section. For example, this small program uses several specific section names: + +@smallexample +struct duart a __attribute__ ((section ("DUART_A"))) = @{ 0 @}; +struct duart b __attribute__ ((section ("DUART_B"))) = @{ 0 @}; +char stack[10000] __attribute__ ((section ("STACK"))) = @{ 0 @}; +int init_data __attribute__ ((section ("INITDATA"))) = 0; + +main() +@{ + /* Initialize stack pointer */ + init_sp (stack + sizeof (stack)); + + /* Initialize initialized data */ + memcpy (&init_data, &data, &edata - &data); + + /* Turn on the serial ports */ + init_duart (&a); + init_duart (&b); +@} +@end smallexample + +@noindent +Use the @code{section} attribute with an @emph{initialized} definition +of a @emph{global} variable, as shown in the example. GCC issues +a warning and otherwise ignores the @code{section} attribute in +uninitialized variable declarations. + +You may only use the @code{section} attribute with a fully initialized +global definition because of the way linkers work. The linker requires +each object be defined once, with the exception that uninitialized +variables tentatively go in the @code{common} (or @code{bss}) section +and can be multiply ``defined''. You can force a variable to be +initialized with the @option{-fno-common} flag or the @code{nocommon} +attribute. + +Some file formats do not support arbitrary sections so the @code{section} +attribute is not available on all platforms. +If you need to map the entire contents of a module to a particular +section, consider using the facilities of the linker instead. + +@item shared +@cindex @code{shared} variable attribute +On Windows NT, in addition to putting variable definitions in a named +section, the section can also be shared among all running copies of an +executable or DLL@. For example, this small program defines shared data +by putting it in a named section @code{shared} and marking the section +shareable: + +@smallexample +int foo __attribute__((section ("shared"), shared)) = 0; + +int +main() +@{ + /* Read and write foo. All running + copies see the same value. */ + return 0; +@} +@end smallexample + +@noindent +You may only use the @code{shared} attribute along with @code{section} +attribute with a fully initialized global definition because of the way +linkers work. See @code{section} attribute for more information. + +The @code{shared} attribute is only available on Windows NT@. + +@item transparent_union +This attribute, attached to a function parameter which is a union, means +that the corresponding argument may have the type of any union member, +but the argument is passed as if its type were that of the first union +member. For more details see @xref{Type Attributes}. You can also use +this attribute on a @code{typedef} for a union data type; then it +applies to all function parameters with that type. + +@item unused +This attribute, attached to a variable, means that the variable is meant +to be possibly unused. GCC will not produce a warning for this +variable. + +@item deprecated +The @code{deprecated} attribute results in a warning if the variable +is used anywhere in the source file. This is useful when identifying +variables that are expected to be removed in a future version of a +program. The warning also includes the location of the declaration +of the deprecated variable, to enable users to easily find further +information about why the variable is deprecated, or what they should +do instead. Note that the warnings only occurs for uses: + +@smallexample +extern int old_var __attribute__ ((deprecated)); +extern int old_var; +int new_fn () @{ return old_var; @} +@end smallexample + +results in a warning on line 3 but not line 2. + +The @code{deprecated} attribute can also be used for functions and +types (@pxref{Function Attributes}, @pxref{Type Attributes}.) + +@item vector_size (@var{bytes}) +This attribute specifies the vector size for the variable, measured in +bytes. For example, the declaration: + +@smallexample +int foo __attribute__ ((vector_size (16))); +@end smallexample + +@noindent +causes the compiler to set the mode for @code{foo}, to be 16 bytes, +divided into @code{int} sized units. Assuming a 32-bit int (a vector of +4 units of 4 bytes), the corresponding mode of @code{foo} will be V4SI@. + +This attribute is only applicable to integral and float scalars, +although arrays, pointers, and function return values are allowed in +conjunction with this construct. + +Aggregates with this attribute are invalid, even if they are of the same +size as a corresponding scalar. For example, the declaration: + +@smallexample +struct S @{ int a; @}; +struct S __attribute__ ((vector_size (16))) foo; +@end smallexample + +@noindent +is invalid even if the size of the structure is the same as the size of +the @code{int}. + +@item weak +The @code{weak} attribute is described in @xref{Function Attributes}. + +@item model (@var{model-name}) +@cindex variable addressability on the M32R/D +Use this attribute on the M32R/D to set the addressability of an object. +The identifier @var{model-name} is one of @code{small}, @code{medium}, +or @code{large}, representing each of the code models. + +Small model objects live in the lower 16MB of memory (so that their +addresses can be loaded with the @code{ld24} instruction). + +Medium and large model objects may live anywhere in the 32-bit address space +(the compiler will generate @code{seth/add3} instructions to load their +addresses). + +@end table + +To specify multiple attributes, separate them by commas within the +double parentheses: for example, @samp{__attribute__ ((aligned (16), +packed))}. + +@node Type Attributes +@section Specifying Attributes of Types +@cindex attribute of types +@cindex type attributes + +The keyword @code{__attribute__} allows you to specify special +attributes of @code{struct} and @code{union} types when you define such +types. This keyword is followed by an attribute specification inside +double parentheses. Five attributes are currently defined for types: +@code{aligned}, @code{packed}, @code{transparent_union}, @code{unused}, +and @code{deprecated}. Other attributes are defined for functions +(@pxref{Function Attributes}) and for variables (@pxref{Variable Attributes}). + +You may also specify any one of these attributes with @samp{__} +preceding and following its keyword. This allows you to use these +attributes in header files without being concerned about a possible +macro of the same name. For example, you may use @code{__aligned__} +instead of @code{aligned}. + +You may specify the @code{aligned} and @code{transparent_union} +attributes either in a @code{typedef} declaration or just past the +closing curly brace of a complete enum, struct or union type +@emph{definition} and the @code{packed} attribute only past the closing +brace of a definition. + +You may also specify attributes between the enum, struct or union +tag and the name of the type rather than after the closing brace. + +@xref{Attribute Syntax}, for details of the exact syntax for using +attributes. + +@table @code +@cindex @code{aligned} attribute +@item aligned (@var{alignment}) +This attribute specifies a minimum alignment (in bytes) for variables +of the specified type. For example, the declarations: + +@smallexample +struct S @{ short f[3]; @} __attribute__ ((aligned (8))); +typedef int more_aligned_int __attribute__ ((aligned (8))); +@end smallexample + +@noindent +force the compiler to insure (as far as it can) that each variable whose +type is @code{struct S} or @code{more_aligned_int} will be allocated and +aligned @emph{at least} on a 8-byte boundary. On a Sparc, having all +variables of type @code{struct S} aligned to 8-byte boundaries allows +the compiler to use the @code{ldd} and @code{std} (doubleword load and +store) instructions when copying one variable of type @code{struct S} to +another, thus improving run-time efficiency. + +Note that the alignment of any given @code{struct} or @code{union} type +is required by the ISO C standard to be at least a perfect multiple of +the lowest common multiple of the alignments of all of the members of +the @code{struct} or @code{union} in question. This means that you @emph{can} +effectively adjust the alignment of a @code{struct} or @code{union} +type by attaching an @code{aligned} attribute to any one of the members +of such a type, but the notation illustrated in the example above is a +more obvious, intuitive, and readable way to request the compiler to +adjust the alignment of an entire @code{struct} or @code{union} type. + +As in the preceding example, you can explicitly specify the alignment +(in bytes) that you wish the compiler to use for a given @code{struct} +or @code{union} type. Alternatively, you can leave out the alignment factor +and just ask the compiler to align a type to the maximum +useful alignment for the target machine you are compiling for. For +example, you could write: + +@smallexample +struct S @{ short f[3]; @} __attribute__ ((aligned)); +@end smallexample + +Whenever you leave out the alignment factor in an @code{aligned} +attribute specification, the compiler automatically sets the alignment +for the type to the largest alignment which is ever used for any data +type on the target machine you are compiling for. Doing this can often +make copy operations more efficient, because the compiler can use +whatever instructions copy the biggest chunks of memory when performing +copies to or from the variables which have types that you have aligned +this way. + +In the example above, if the size of each @code{short} is 2 bytes, then +the size of the entire @code{struct S} type is 6 bytes. The smallest +power of two which is greater than or equal to that is 8, so the +compiler sets the alignment for the entire @code{struct S} type to 8 +bytes. + +Note that although you can ask the compiler to select a time-efficient +alignment for a given type and then declare only individual stand-alone +objects of that type, the compiler's ability to select a time-efficient +alignment is primarily useful only when you plan to create arrays of +variables having the relevant (efficiently aligned) type. If you +declare or use arrays of variables of an efficiently-aligned type, then +it is likely that your program will also be doing pointer arithmetic (or +subscripting, which amounts to the same thing) on pointers to the +relevant type, and the code that the compiler generates for these +pointer arithmetic operations will often be more efficient for +efficiently-aligned types than for other types. + +The @code{aligned} attribute can only increase the alignment; but you +can decrease it by specifying @code{packed} as well. See below. + +Note that the effectiveness of @code{aligned} attributes may be limited +by inherent limitations in your linker. On many systems, the linker is +only able to arrange for variables to be aligned up to a certain maximum +alignment. (For some linkers, the maximum supported alignment may +be very very small.) If your linker is only able to align variables +up to a maximum of 8 byte alignment, then specifying @code{aligned(16)} +in an @code{__attribute__} will still only provide you with 8 byte +alignment. See your linker documentation for further information. + +@item packed +This attribute, attached to an @code{enum}, @code{struct}, or +@code{union} type definition, specified that the minimum required memory +be used to represent the type. + +@opindex fshort-enums +Specifying this attribute for @code{struct} and @code{union} types is +equivalent to specifying the @code{packed} attribute on each of the +structure or union members. Specifying the @option{-fshort-enums} +flag on the line is equivalent to specifying the @code{packed} +attribute on all @code{enum} definitions. + +You may only specify this attribute after a closing curly brace on an +@code{enum} definition, not in a @code{typedef} declaration, unless that +declaration also contains the definition of the @code{enum}. + +@item transparent_union +This attribute, attached to a @code{union} type definition, indicates +that any function parameter having that union type causes calls to that +function to be treated in a special way. + +First, the argument corresponding to a transparent union type can be of +any type in the union; no cast is required. Also, if the union contains +a pointer type, the corresponding argument can be a null pointer +constant or a void pointer expression; and if the union contains a void +pointer type, the corresponding argument can be any pointer expression. +If the union member type is a pointer, qualifiers like @code{const} on +the referenced type must be respected, just as with normal pointer +conversions. + +Second, the argument is passed to the function using the calling +conventions of first member of the transparent union, not the calling +conventions of the union itself. All members of the union must have the +same machine representation; this is necessary for this argument passing +to work properly. + +Transparent unions are designed for library functions that have multiple +interfaces for compatibility reasons. For example, suppose the +@code{wait} function must accept either a value of type @code{int *} to +comply with Posix, or a value of type @code{union wait *} to comply with +the 4.1BSD interface. If @code{wait}'s parameter were @code{void *}, +@code{wait} would accept both kinds of arguments, but it would also +accept any other pointer type and this would make argument type checking +less useful. Instead, @code{} might define the interface +as follows: + +@smallexample +typedef union + @{ + int *__ip; + union wait *__up; + @} wait_status_ptr_t __attribute__ ((__transparent_union__)); + +pid_t wait (wait_status_ptr_t); +@end smallexample + +This interface allows either @code{int *} or @code{union wait *} +arguments to be passed, using the @code{int *} calling convention. +The program can call @code{wait} with arguments of either type: + +@example +int w1 () @{ int w; return wait (&w); @} +int w2 () @{ union wait w; return wait (&w); @} +@end example + +With this interface, @code{wait}'s implementation might look like this: + +@example +pid_t wait (wait_status_ptr_t p) +@{ + return waitpid (-1, p.__ip, 0); +@} +@end example + +@item unused +When attached to a type (including a @code{union} or a @code{struct}), +this attribute means that variables of that type are meant to appear +possibly unused. GCC will not produce a warning for any variables of +that type, even if the variable appears to do nothing. This is often +the case with lock or thread classes, which are usually defined and then +not referenced, but contain constructors and destructors that have +nontrivial bookkeeping functions. + +@item deprecated +The @code{deprecated} attribute results in a warning if the type +is used anywhere in the source file. This is useful when identifying +types that are expected to be removed in a future version of a program. +If possible, the warning also includes the location of the declaration +of the deprecated type, to enable users to easily find further +information about why the type is deprecated, or what they should do +instead. Note that the warnings only occur for uses and then only +if the type is being applied to an identifier that itself is not being +declared as deprecated. + +@smallexample +typedef int T1 __attribute__ ((deprecated)); +T1 x; +typedef T1 T2; +T2 y; +typedef T1 T3 __attribute__ ((deprecated)); +T3 z __attribute__ ((deprecated)); +@end smallexample + +results in a warning on line 2 and 3 but not lines 4, 5, or 6. No +warning is issued for line 4 because T2 is not explicitly +deprecated. Line 5 has no warning because T3 is explicitly +deprecated. Similarly for line 6. + +The @code{deprecated} attribute can also be used for functions and +variables (@pxref{Function Attributes}, @pxref{Variable Attributes}.) + +@end table + +To specify multiple attributes, separate them by commas within the +double parentheses: for example, @samp{__attribute__ ((aligned (16), +packed))}. + +@node Inline +@section An Inline Function is As Fast As a Macro +@cindex inline functions +@cindex integrating function code +@cindex open coding +@cindex macros, inline alternative + +By declaring a function @code{inline}, you can direct GCC to +integrate that function's code into the code for its callers. This +makes execution faster by eliminating the function-call overhead; in +addition, if any of the actual argument values are constant, their known +values may permit simplifications at compile time so that not all of the +inline function's code needs to be included. The effect on code size is +less predictable; object code may be larger or smaller with function +inlining, depending on the particular case. Inlining of functions is an +optimization and it really ``works'' only in optimizing compilation. If +you don't use @option{-O}, no function is really inline. + +Inline functions are included in the ISO C99 standard, but there are +currently substantial differences between what GCC implements and what +the ISO C99 standard requires. + +To declare a function inline, use the @code{inline} keyword in its +declaration, like this: + +@example +inline int +inc (int *a) +@{ + (*a)++; +@} +@end example + +(If you are writing a header file to be included in ISO C programs, write +@code{__inline__} instead of @code{inline}. @xref{Alternate Keywords}.) +You can also make all ``simple enough'' functions inline with the option +@option{-finline-functions}. + +@opindex Winline +Note that certain usages in a function definition can make it unsuitable +for inline substitution. Among these usages are: use of varargs, use of +alloca, use of variable sized data types (@pxref{Variable Length}), +use of computed goto (@pxref{Labels as Values}), use of nonlocal goto, +and nested functions (@pxref{Nested Functions}). Using @option{-Winline} +will warn when a function marked @code{inline} could not be substituted, +and will give the reason for the failure. + +Note that in C and Objective-C, unlike C++, the @code{inline} keyword +does not affect the linkage of the function. + +@cindex automatic @code{inline} for C++ member fns +@cindex @code{inline} automatic for C++ member fns +@cindex member fns, automatically @code{inline} +@cindex C++ member fns, automatically @code{inline} +@opindex fno-default-inline +GCC automatically inlines member functions defined within the class +body of C++ programs even if they are not explicitly declared +@code{inline}. (You can override this with @option{-fno-default-inline}; +@pxref{C++ Dialect Options,,Options Controlling C++ Dialect}.) + +@cindex inline functions, omission of +@opindex fkeep-inline-functions +When a function is both inline and @code{static}, if all calls to the +function are integrated into the caller, and the function's address is +never used, then the function's own assembler code is never referenced. +In this case, GCC does not actually output assembler code for the +function, unless you specify the option @option{-fkeep-inline-functions}. +Some calls cannot be integrated for various reasons (in particular, +calls that precede the function's definition cannot be integrated, and +neither can recursive calls within the definition). If there is a +nonintegrated call, then the function is compiled to assembler code as +usual. The function must also be compiled as usual if the program +refers to its address, because that can't be inlined. + +@cindex non-static inline function +When an inline function is not @code{static}, then the compiler must assume +that there may be calls from other source files; since a global symbol can +be defined only once in any program, the function must not be defined in +the other source files, so the calls therein cannot be integrated. +Therefore, a non-@code{static} inline function is always compiled on its +own in the usual fashion. + +If you specify both @code{inline} and @code{extern} in the function +definition, then the definition is used only for inlining. In no case +is the function compiled on its own, not even if you refer to its +address explicitly. Such an address becomes an external reference, as +if you had only declared the function, and had not defined it. + +This combination of @code{inline} and @code{extern} has almost the +effect of a macro. The way to use it is to put a function definition in +a header file with these keywords, and put another copy of the +definition (lacking @code{inline} and @code{extern}) in a library file. +The definition in the header file will cause most calls to the function +to be inlined. If any uses of the function remain, they will refer to +the single copy in the library. + +For future compatibility with when GCC implements ISO C99 semantics for +inline functions, it is best to use @code{static inline} only. (The +existing semantics will remain available when @option{-std=gnu89} is +specified, but eventually the default will be @option{-std=gnu99} and +that will implement the C99 semantics, though it does not do so yet.) + +GCC does not inline any functions when not optimizing. It is not +clear whether it is better to inline or not, in this case, but we found +that a correct implementation when not optimizing was difficult. So we +did the easy thing, and turned it off. + +@node Extended Asm +@section Assembler Instructions with C Expression Operands +@cindex extended @code{asm} +@cindex @code{asm} expressions +@cindex assembler instructions +@cindex registers + +In an assembler instruction using @code{asm}, you can specify the +operands of the instruction using C expressions. This means you need not +guess which registers or memory locations will contain the data you want +to use. + +You must specify an assembler instruction template much like what +appears in a machine description, plus an operand constraint string for +each operand. + +For example, here is how to use the 68881's @code{fsinx} instruction: + +@example +asm ("fsinx %1,%0" : "=f" (result) : "f" (angle)); +@end example + +@noindent +Here @code{angle} is the C expression for the input operand while +@code{result} is that of the output operand. Each has @samp{"f"} as its +operand constraint, saying that a floating point register is required. +The @samp{=} in @samp{=f} indicates that the operand is an output; all +output operands' constraints must use @samp{=}. The constraints use the +same language used in the machine description (@pxref{Constraints}). + +Each operand is described by an operand-constraint string followed by +the C expression in parentheses. A colon separates the assembler +template from the first output operand and another separates the last +output operand from the first input, if any. Commas separate the +operands within each group. The total number of operands is currently +limited to 30; this limitation may be lifted in some future version of +GCC. + +If there are no output operands but there are input operands, you must +place two consecutive colons surrounding the place where the output +operands would go. + +As of GCC version 3.1, it is also possible to specify input and output +operands using symbolic names which can be referenced within the +assembler code. These names are specified inside square brackets +preceding the constraint string, and can be referenced inside the +assembler code using @code{%[@var{name}]} instead of a percentage sign +followed by the operand number. Using named operands the above example +could look like: + +@example +asm ("fsinx %[angle],%[output]" + : [output] "=f" (result) + : [angle] "f" (angle)); +@end example + +@noindent +Note that the symbolic operand names have no relation whatsoever to +other C identifiers. You may use any name you like, even those of +existing C symbols, but must ensure that no two operands within the same +assembler construct use the same symbolic name. + +Output operand expressions must be lvalues; the compiler can check this. +The input operands need not be lvalues. The compiler cannot check +whether the operands have data types that are reasonable for the +instruction being executed. It does not parse the assembler instruction +template and does not know what it means or even whether it is valid +assembler input. The extended @code{asm} feature is most often used for +machine instructions the compiler itself does not know exist. If +the output expression cannot be directly addressed (for example, it is a +bit-field), your constraint must allow a register. In that case, GCC +will use the register as the output of the @code{asm}, and then store +that register into the output. + +The ordinary output operands must be write-only; GCC will assume that +the values in these operands before the instruction are dead and need +not be generated. Extended asm supports input-output or read-write +operands. Use the constraint character @samp{+} to indicate such an +operand and list it with the output operands. + +When the constraints for the read-write operand (or the operand in which +only some of the bits are to be changed) allows a register, you may, as +an alternative, logically split its function into two separate operands, +one input operand and one write-only output operand. The connection +between them is expressed by constraints which say they need to be in +the same location when the instruction executes. You can use the same C +expression for both operands, or different expressions. For example, +here we write the (fictitious) @samp{combine} instruction with +@code{bar} as its read-only source operand and @code{foo} as its +read-write destination: + +@example +asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar)); +@end example + +@noindent +The constraint @samp{"0"} for operand 1 says that it must occupy the +same location as operand 0. A number in constraint is allowed only in +an input operand and it must refer to an output operand. + +Only a number in the constraint can guarantee that one operand will be in +the same place as another. The mere fact that @code{foo} is the value +of both operands is not enough to guarantee that they will be in the +same place in the generated assembler code. The following would not +work reliably: + +@example +asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar)); +@end example + +Various optimizations or reloading could cause operands 0 and 1 to be in +different registers; GCC knows no reason not to do so. For example, the +compiler might find a copy of the value of @code{foo} in one register and +use it for operand 1, but generate the output operand 0 in a different +register (copying it afterward to @code{foo}'s own address). Of course, +since the register for operand 1 is not even mentioned in the assembler +code, the result will not work, but GCC can't tell that. + +As of GCC version 3.1, one may write @code{[@var{name}]} instead of +the operand number for a matching constraint. For example: + +@example +asm ("cmoveq %1,%2,%[result]" + : [result] "=r"(result) + : "r" (test), "r"(new), "[result]"(old)); +@end example + +Some instructions clobber specific hard registers. To describe this, +write a third colon after the input operands, followed by the names of +the clobbered hard registers (given as strings). Here is a realistic +example for the VAX: + +@example +asm volatile ("movc3 %0,%1,%2" + : /* no outputs */ + : "g" (from), "g" (to), "g" (count) + : "r0", "r1", "r2", "r3", "r4", "r5"); +@end example + +You may not write a clobber description in a way that overlaps with an +input or output operand. For example, you may not have an operand +describing a register class with one member if you mention that register +in the clobber list. There is no way for you to specify that an input +operand is modified without also specifying it as an output +operand. Note that if all the output operands you specify are for this +purpose (and hence unused), you will then also need to specify +@code{volatile} for the @code{asm} construct, as described below, to +prevent GCC from deleting the @code{asm} statement as unused. + +If you refer to a particular hardware register from the assembler code, +you will probably have to list the register after the third colon to +tell the compiler the register's value is modified. In some assemblers, +the register names begin with @samp{%}; to produce one @samp{%} in the +assembler code, you must write @samp{%%} in the input. + +If your assembler instruction can alter the condition code register, add +@samp{cc} to the list of clobbered registers. GCC on some machines +represents the condition codes as a specific hardware register; +@samp{cc} serves to name this register. On other machines, the +condition code is handled differently, and specifying @samp{cc} has no +effect. But it is valid no matter what the machine. + +If your assembler instruction modifies memory in an unpredictable +fashion, add @samp{memory} to the list of clobbered registers. This +will cause GCC to not keep memory values cached in registers across +the assembler instruction. You will also want to add the +@code{volatile} keyword if the memory affected is not listed in the +inputs or outputs of the @code{asm}, as the @samp{memory} clobber does +not count as a side-effect of the @code{asm}. + +You can put multiple assembler instructions together in a single +@code{asm} template, separated by the characters normally used in assembly +code for the system. A combination that works in most places is a newline +to break the line, plus a tab character to move to the instruction field +(written as @samp{\n\t}). Sometimes semicolons can be used, if the +assembler allows semicolons as a line-breaking character. Note that some +assembler dialects use semicolons to start a comment. +The input operands are guaranteed not to use any of the clobbered +registers, and neither will the output operands' addresses, so you can +read and write the clobbered registers as many times as you like. Here +is an example of multiple instructions in a template; it assumes the +subroutine @code{_foo} accepts arguments in registers 9 and 10: + +@example +asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo" + : /* no outputs */ + : "g" (from), "g" (to) + : "r9", "r10"); +@end example + +Unless an output operand has the @samp{&} constraint modifier, GCC +may allocate it in the same register as an unrelated input operand, on +the assumption the inputs are consumed before the outputs are produced. +This assumption may be false if the assembler code actually consists of +more than one instruction. In such a case, use @samp{&} for each output +operand that may not overlap an input. @xref{Modifiers}. + +If you want to test the condition code produced by an assembler +instruction, you must include a branch and a label in the @code{asm} +construct, as follows: + +@example +asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:" + : "g" (result) + : "g" (input)); +@end example + +@noindent +This assumes your assembler supports local labels, as the GNU assembler +and most Unix assemblers do. + +Speaking of labels, jumps from one @code{asm} to another are not +supported. The compiler's optimizers do not know about these jumps, and +therefore they cannot take account of them when deciding how to +optimize. + +@cindex macros containing @code{asm} +Usually the most convenient way to use these @code{asm} instructions is to +encapsulate them in macros that look like functions. For example, + +@example +#define sin(x) \ +(@{ double __value, __arg = (x); \ + asm ("fsinx %1,%0": "=f" (__value): "f" (__arg)); \ + __value; @}) +@end example + +@noindent +Here the variable @code{__arg} is used to make sure that the instruction +operates on a proper @code{double} value, and to accept only those +arguments @code{x} which can convert automatically to a @code{double}. + +Another way to make sure the instruction operates on the correct data +type is to use a cast in the @code{asm}. This is different from using a +variable @code{__arg} in that it converts more different types. For +example, if the desired type were @code{int}, casting the argument to +@code{int} would accept a pointer with no complaint, while assigning the +argument to an @code{int} variable named @code{__arg} would warn about +using a pointer unless the caller explicitly casts it. + +If an @code{asm} has output operands, GCC assumes for optimization +purposes the instruction has no side effects except to change the output +operands. This does not mean instructions with a side effect cannot be +used, but you must be careful, because the compiler may eliminate them +if the output operands aren't used, or move them out of loops, or +replace two with one if they constitute a common subexpression. Also, +if your instruction does have a side effect on a variable that otherwise +appears not to change, the old value of the variable may be reused later +if it happens to be found in a register. + +You can prevent an @code{asm} instruction from being deleted, moved +significantly, or combined, by writing the keyword @code{volatile} after +the @code{asm}. For example: + +@example +#define get_and_set_priority(new) \ +(@{ int __old; \ + asm volatile ("get_and_set_priority %0, %1" \ + : "=g" (__old) : "g" (new)); \ + __old; @}) +@end example + +@noindent +If you write an @code{asm} instruction with no outputs, GCC will know +the instruction has side-effects and will not delete the instruction or +move it outside of loops. + +The @code{volatile} keyword indicates that the instruction has +important side-effects. GCC will not delete a volatile @code{asm} if +it is reachable. (The instruction can still be deleted if GCC can +prove that control-flow will never reach the location of the +instruction.) In addition, GCC will not reschedule instructions +across a volatile @code{asm} instruction. For example: + +@example +*(volatile int *)addr = foo; +asm volatile ("eieio" : : ); +@end example + +@noindent +Assume @code{addr} contains the address of a memory mapped device +register. The PowerPC @code{eieio} instruction (Enforce In-order +Execution of I/O) tells the CPU to make sure that the store to that +device register happens before it issues any other I/O@. + +Note that even a volatile @code{asm} instruction can be moved in ways +that appear insignificant to the compiler, such as across jump +instructions. You can't expect a sequence of volatile @code{asm} +instructions to remain perfectly consecutive. If you want consecutive +output, use a single @code{asm}. Also, GCC will perform some +optimizations across a volatile @code{asm} instruction; GCC does not +``forget everything'' when it encounters a volatile @code{asm} +instruction the way some other compilers do. + +An @code{asm} instruction without any operands or clobbers (an ``old +style'' @code{asm}) will be treated identically to a volatile +@code{asm} instruction. + +It is a natural idea to look for a way to give access to the condition +code left by the assembler instruction. However, when we attempted to +implement this, we found no way to make it work reliably. The problem +is that output operands might need reloading, which would result in +additional following ``store'' instructions. On most machines, these +instructions would alter the condition code before there was time to +test it. This problem doesn't arise for ordinary ``test'' and +``compare'' instructions because they don't have any output operands. + +For reasons similar to those described above, it is not possible to give +an assembler instruction access to the condition code left by previous +instructions. + +If you are writing a header file that should be includable in ISO C +programs, write @code{__asm__} instead of @code{asm}. @xref{Alternate +Keywords}. + +@subsection i386 floating point asm operands + +There are several rules on the usage of stack-like regs in +asm_operands insns. These rules apply only to the operands that are +stack-like regs: + +@enumerate +@item +Given a set of input regs that die in an asm_operands, it is +necessary to know which are implicitly popped by the asm, and +which must be explicitly popped by gcc. + +An input reg that is implicitly popped by the asm must be +explicitly clobbered, unless it is constrained to match an +output operand. + +@item +For any input reg that is implicitly popped by an asm, it is +necessary to know how to adjust the stack to compensate for the pop. +If any non-popped input is closer to the top of the reg-stack than +the implicitly popped reg, it would not be possible to know what the +stack looked like---it's not clear how the rest of the stack ``slides +up''. + +All implicitly popped input regs must be closer to the top of +the reg-stack than any input that is not implicitly popped. + +It is possible that if an input dies in an insn, reload might +use the input reg for an output reload. Consider this example: + +@example +asm ("foo" : "=t" (a) : "f" (b)); +@end example + +This asm says that input B is not popped by the asm, and that +the asm pushes a result onto the reg-stack, i.e., the stack is one +deeper after the asm than it was before. But, it is possible that +reload will think that it can use the same reg for both the input and +the output, if input B dies in this insn. + +If any input operand uses the @code{f} constraint, all output reg +constraints must use the @code{&} earlyclobber. + +The asm above would be written as + +@example +asm ("foo" : "=&t" (a) : "f" (b)); +@end example + +@item +Some operands need to be in particular places on the stack. All +output operands fall in this category---there is no other way to +know which regs the outputs appear in unless the user indicates +this in the constraints. + +Output operands must specifically indicate which reg an output +appears in after an asm. @code{=f} is not allowed: the operand +constraints must select a class with a single reg. + +@item +Output operands may not be ``inserted'' between existing stack regs. +Since no 387 opcode uses a read/write operand, all output operands +are dead before the asm_operands, and are pushed by the asm_operands. +It makes no sense to push anywhere but the top of the reg-stack. + +Output operands must start at the top of the reg-stack: output +operands may not ``skip'' a reg. + +@item +Some asm statements may need extra stack space for internal +calculations. This can be guaranteed by clobbering stack registers +unrelated to the inputs and outputs. + +@end enumerate + +Here are a couple of reasonable asms to want to write. This asm +takes one input, which is internally popped, and produces two outputs. + +@example +asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp)); +@end example + +This asm takes two inputs, which are popped by the @code{fyl2xp1} opcode, +and replaces them with one output. The user must code the @code{st(1)} +clobber for reg-stack.c to know that @code{fyl2xp1} pops both inputs. + +@example +asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)"); +@end example + +@include md.texi + +@node Asm Labels +@section Controlling Names Used in Assembler Code +@cindex assembler names for identifiers +@cindex names used in assembler code +@cindex identifiers, names in assembler code + +You can specify the name to be used in the assembler code for a C +function or variable by writing the @code{asm} (or @code{__asm__}) +keyword after the declarator as follows: + +@example +int foo asm ("myfoo") = 2; +@end example + +@noindent +This specifies that the name to be used for the variable @code{foo} in +the assembler code should be @samp{myfoo} rather than the usual +@samp{_foo}. + +On systems where an underscore is normally prepended to the name of a C +function or variable, this feature allows you to define names for the +linker that do not start with an underscore. + +It does not make sense to use this feature with a non-static local +variable since such variables do not have assembler names. If you are +trying to put the variable in a particular register, see @ref{Explicit +Reg Vars}. GCC presently accepts such code with a warning, but will +probably be changed to issue an error, rather than a warning, in the +future. + +You cannot use @code{asm} in this way in a function @emph{definition}; but +you can get the same effect by writing a declaration for the function +before its definition and putting @code{asm} there, like this: + +@example +extern func () asm ("FUNC"); + +func (x, y) + int x, y; +@dots{} +@end example + +It is up to you to make sure that the assembler names you choose do not +conflict with any other assembler symbols. Also, you must not use a +register name; that would produce completely invalid assembler code. GCC +does not as yet have the ability to store static variables in registers. +Perhaps that will be added. + +@node Explicit Reg Vars +@section Variables in Specified Registers +@cindex explicit register variables +@cindex variables in specified registers +@cindex specified registers +@cindex registers, global allocation + +GNU C allows you to put a few global variables into specified hardware +registers. You can also specify the register in which an ordinary +register variable should be allocated. + +@itemize @bullet +@item +Global register variables reserve registers throughout the program. +This may be useful in programs such as programming language +interpreters which have a couple of global variables that are accessed +very often. + +@item +Local register variables in specific registers do not reserve the +registers. The compiler's data flow analysis is capable of determining +where the specified registers contain live values, and where they are +available for other uses. Stores into local register variables may be deleted +when they appear to be dead according to dataflow analysis. References +to local register variables may be deleted or moved or simplified. + +These local variables are sometimes convenient for use with the extended +@code{asm} feature (@pxref{Extended Asm}), if you want to write one +output of the assembler instruction directly into a particular register. +(This will work provided the register you specify fits the constraints +specified for that operand in the @code{asm}.) +@end itemize + +@menu +* Global Reg Vars:: +* Local Reg Vars:: +@end menu + +@node Global Reg Vars +@subsection Defining Global Register Variables +@cindex global register variables +@cindex registers, global variables in + +You can define a global register variable in GNU C like this: + +@example +register int *foo asm ("a5"); +@end example + +@noindent +Here @code{a5} is the name of the register which should be used. Choose a +register which is normally saved and restored by function calls on your +machine, so that library routines will not clobber it. + +Naturally the register name is cpu-dependent, so you would need to +conditionalize your program according to cpu type. The register +@code{a5} would be a good choice on a 68000 for a variable of pointer +type. On machines with register windows, be sure to choose a ``global'' +register that is not affected magically by the function call mechanism. + +In addition, operating systems on one type of cpu may differ in how they +name the registers; then you would need additional conditionals. For +example, some 68000 operating systems call this register @code{%a5}. + +Eventually there may be a way of asking the compiler to choose a register +automatically, but first we need to figure out how it should choose and +how to enable you to guide the choice. No solution is evident. + +Defining a global register variable in a certain register reserves that +register entirely for this use, at least within the current compilation. +The register will not be allocated for any other purpose in the functions +in the current compilation. The register will not be saved and restored by +these functions. Stores into this register are never deleted even if they +would appear to be dead, but references may be deleted or moved or +simplified. + +It is not safe to access the global register variables from signal +handlers, or from more than one thread of control, because the system +library routines may temporarily use the register for other things (unless +you recompile them specially for the task at hand). + +@cindex @code{qsort}, and global register variables +It is not safe for one function that uses a global register variable to +call another such function @code{foo} by way of a third function +@code{lose} that was compiled without knowledge of this variable (i.e.@: in a +different source file in which the variable wasn't declared). This is +because @code{lose} might save the register and put some other value there. +For example, you can't expect a global register variable to be available in +the comparison-function that you pass to @code{qsort}, since @code{qsort} +might have put something else in that register. (If you are prepared to +recompile @code{qsort} with the same global register variable, you can +solve this problem.) + +If you want to recompile @code{qsort} or other source files which do not +actually use your global register variable, so that they will not use that +register for any other purpose, then it suffices to specify the compiler +option @option{-ffixed-@var{reg}}. You need not actually add a global +register declaration to their source code. + +A function which can alter the value of a global register variable cannot +safely be called from a function compiled without this variable, because it +could clobber the value the caller expects to find there on return. +Therefore, the function which is the entry point into the part of the +program that uses the global register variable must explicitly save and +restore the value which belongs to its caller. + +@cindex register variable after @code{longjmp} +@cindex global register after @code{longjmp} +@cindex value after @code{longjmp} +@findex longjmp +@findex setjmp +On most machines, @code{longjmp} will restore to each global register +variable the value it had at the time of the @code{setjmp}. On some +machines, however, @code{longjmp} will not change the value of global +register variables. To be portable, the function that called @code{setjmp} +should make other arrangements to save the values of the global register +variables, and to restore them in a @code{longjmp}. This way, the same +thing will happen regardless of what @code{longjmp} does. + +All global register variable declarations must precede all function +definitions. If such a declaration could appear after function +definitions, the declaration would be too late to prevent the register from +being used for other purposes in the preceding functions. + +Global register variables may not have initial values, because an +executable file has no means to supply initial contents for a register. + +On the Sparc, there are reports that g3 @dots{} g7 are suitable +registers, but certain library functions, such as @code{getwd}, as well +as the subroutines for division and remainder, modify g3 and g4. g1 and +g2 are local temporaries. + +On the 68000, a2 @dots{} a5 should be suitable, as should d2 @dots{} d7. +Of course, it will not do to use more than a few of those. + +@node Local Reg Vars +@subsection Specifying Registers for Local Variables +@cindex local variables, specifying registers +@cindex specifying registers for local variables +@cindex registers for local variables + +You can define a local register variable with a specified register +like this: + +@example +register int *foo asm ("a5"); +@end example + +@noindent +Here @code{a5} is the name of the register which should be used. Note +that this is the same syntax used for defining global register +variables, but for a local variable it would appear within a function. + +Naturally the register name is cpu-dependent, but this is not a +problem, since specific registers are most often useful with explicit +assembler instructions (@pxref{Extended Asm}). Both of these things +generally require that you conditionalize your program according to +cpu type. + +In addition, operating systems on one type of cpu may differ in how they +name the registers; then you would need additional conditionals. For +example, some 68000 operating systems call this register @code{%a5}. + +Defining such a register variable does not reserve the register; it +remains available for other uses in places where flow control determines +the variable's value is not live. However, these registers are made +unavailable for use in the reload pass; excessive use of this feature +leaves the compiler too few available registers to compile certain +functions. + +This option does not guarantee that GCC will generate code that has +this variable in the register you specify at all times. You may not +code an explicit reference to this register in an @code{asm} statement +and assume it will always refer to this variable. + +Stores into local register variables may be deleted when they appear to be dead +according to dataflow analysis. References to local register variables may +be deleted or moved or simplified. + +@node Alternate Keywords +@section Alternate Keywords +@cindex alternate keywords +@cindex keywords, alternate + +The option @option{-traditional} disables certain keywords; +@option{-ansi} and the various @option{-std} options disable certain +others. This causes trouble when you want to use GNU C extensions, or +ISO C features, in a general-purpose header file that should be usable +by all programs, including ISO C programs and traditional ones. The +keywords @code{asm}, @code{typeof} and @code{inline} cannot be used +since they won't work in a program compiled with @option{-ansi} +(although @code{inline} can be used in a program compiled with +@option{-std=c99}), while the keywords @code{const}, @code{volatile}, +@code{signed}, @code{typeof} and @code{inline} won't work in a program +compiled with @option{-traditional}. The ISO C99 keyword +@code{restrict} is only available when @option{-std=gnu99} (which will +eventually be the default) or @option{-std=c99} (or the equivalent +@option{-std=iso9899:1999}) is used. + +The way to solve these problems is to put @samp{__} at the beginning and +end of each problematical keyword. For example, use @code{__asm__} +instead of @code{asm}, @code{__const__} instead of @code{const}, and +@code{__inline__} instead of @code{inline}. + +Other C compilers won't accept these alternative keywords; if you want to +compile with another compiler, you can define the alternate keywords as +macros to replace them with the customary keywords. It looks like this: + +@example +#ifndef __GNUC__ +#define __asm__ asm +#endif +@end example + +@findex __extension__ +@opindex pedantic +@option{-pedantic} and other options cause warnings for many GNU C extensions. +You can +prevent such warnings within one expression by writing +@code{__extension__} before the expression. @code{__extension__} has no +effect aside from this. + +@node Incomplete Enums +@section Incomplete @code{enum} Types + +You can define an @code{enum} tag without specifying its possible values. +This results in an incomplete type, much like what you get if you write +@code{struct foo} without describing the elements. A later declaration +which does specify the possible values completes the type. + +You can't allocate variables or storage using the type while it is +incomplete. However, you can work with pointers to that type. + +This extension may not be very useful, but it makes the handling of +@code{enum} more consistent with the way @code{struct} and @code{union} +are handled. + +This extension is not supported by GNU C++. + +@node Function Names +@section Function Names as Strings +@cindex @code{__FUNCTION__} identifier +@cindex @code{__PRETTY_FUNCTION__} identifier +@cindex @code{__func__} identifier + +GCC predefines two magic identifiers to hold the name of the current +function. The identifier @code{__FUNCTION__} holds the name of the function +as it appears in the source. The identifier @code{__PRETTY_FUNCTION__} +holds the name of the function pretty printed in a language specific +fashion. + +These names are always the same in a C function, but in a C++ function +they may be different. For example, this program: + +@smallexample +extern "C" @{ +extern int printf (char *, ...); +@} + +class a @{ + public: + sub (int i) + @{ + printf ("__FUNCTION__ = %s\n", __FUNCTION__); + printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__); + @} +@}; + +int +main (void) +@{ + a ax; + ax.sub (0); + return 0; +@} +@end smallexample + +@noindent +gives this output: + +@smallexample +__FUNCTION__ = sub +__PRETTY_FUNCTION__ = int a::sub (int) +@end smallexample + +The compiler automagically replaces the identifiers with a string +literal containing the appropriate name. Thus, they are neither +preprocessor macros, like @code{__FILE__} and @code{__LINE__}, nor +variables. This means that they catenate with other string literals, and +that they can be used to initialize char arrays. For example + +@smallexample +char here[] = "Function " __FUNCTION__ " in " __FILE__; +@end smallexample + +On the other hand, @samp{#ifdef __FUNCTION__} does not have any special +meaning inside a function, since the preprocessor does not do anything +special with the identifier @code{__FUNCTION__}. + +Note that these semantics are deprecated, and that GCC 3.2 will handle +@code{__FUNCTION__} and @code{__PRETTY_FUNCTION__} the same way as +@code{__func__}. @code{__func__} is defined by the ISO standard C99: + +@display +The identifier @code{__func__} is implicitly declared by the translator +as if, immediately following the opening brace of each function +definition, the declaration + +@smallexample +static const char __func__[] = "function-name"; +@end smallexample + +appeared, where function-name is the name of the lexically-enclosing +function. This name is the unadorned name of the function. +@end display + +By this definition, @code{__func__} is a variable, not a string literal. +In particular, @code{__func__} does not catenate with other string +literals. + +In @code{C++}, @code{__FUNCTION__} and @code{__PRETTY_FUNCTION__} are +variables, declared in the same way as @code{__func__}. + +@node Return Address +@section Getting the Return or Frame Address of a Function + +These functions may be used to get information about the callers of a +function. + +@deftypefn {Built-in Function} {void *} __builtin_return_address (unsigned int @var{level}) +This function returns the return address of the current function, or of +one of its callers. The @var{level} argument is number of frames to +scan up the call stack. A value of @code{0} yields the return address +of the current function, a value of @code{1} yields the return address +of the caller of the current function, and so forth. + +The @var{level} argument must be a constant integer. + +On some machines it may be impossible to determine the return address of +any function other than the current one; in such cases, or when the top +of the stack has been reached, this function will return @code{0} or a +random value. In addition, @code{__builtin_frame_address} may be used +to determine if the top of the stack has been reached. + +This function should only be used with a nonzero argument for debugging +purposes. +@end deftypefn + +@deftypefn {Built-in Function} {void *} __builtin_frame_address (unsigned int @var{level}) +This function is similar to @code{__builtin_return_address}, but it +returns the address of the function frame rather than the return address +of the function. Calling @code{__builtin_frame_address} with a value of +@code{0} yields the frame address of the current function, a value of +@code{1} yields the frame address of the caller of the current function, +and so forth. + +The frame is the area on the stack which holds local variables and saved +registers. The frame address is normally the address of the first word +pushed on to the stack by the function. However, the exact definition +depends upon the processor and the calling convention. If the processor +has a dedicated frame pointer register, and the function has a frame, +then @code{__builtin_frame_address} will return the value of the frame +pointer register. + +On some machines it may be impossible to determine the frame address of +any function other than the current one; in such cases, or when the top +of the stack has been reached, this function will return @code{0} if +the first frame pointer is properly initialized by the startup code. + +This function should only be used with a nonzero argument for debugging +purposes. +@end deftypefn + +@node Vector Extensions +@section Using vector instructions through built-in functions + +On some targets, the instruction set contains SIMD vector instructions that +operate on multiple values contained in one large register at the same time. +For example, on the i386 the MMX, 3Dnow! and SSE extensions can be used +this way. + +The first step in using these extensions is to provide the necessary data +types. This should be done using an appropriate @code{typedef}: + +@example +typedef int v4si __attribute__ ((mode(V4SI))); +@end example + +The base type @code{int} is effectively ignored by the compiler, the +actual properties of the new type @code{v4si} are defined by the +@code{__attribute__}. It defines the machine mode to be used; for vector +types these have the form @code{V@var{n}@var{B}}; @var{n} should be the +number of elements in the vector, and @var{B} should be the base mode of the +individual elements. The following can be used as base modes: + +@table @code +@item QI +An integer that is as wide as the smallest addressable unit, usually 8 bits. +@item HI +An integer, twice as wide as a QI mode integer, usually 16 bits. +@item SI +An integer, four times as wide as a QI mode integer, usually 32 bits. +@item DI +An integer, eight times as wide as a QI mode integer, usually 64 bits. +@item SF +A floating point value, as wide as a SI mode integer, usually 32 bits. +@item DF +A floating point value, as wide as a DI mode integer, usually 64 bits. +@end table + +Not all base types or combinations are always valid; which modes can be used +is determined by the target machine. For example, if targetting the i386 MMX +extensions, only @code{V8QI}, @code{V4HI} and @code{V2SI} are allowed modes. + +There are no @code{V1xx} vector modes - they would be identical to the +corresponding base mode. + +There is no distinction between signed and unsigned vector modes. This +distinction is made by the operations that perform on the vectors, not +by the data type. + +The types defined in this manner are somewhat special, they cannot be +used with most normal C operations (i.e., a vector addition can @emph{not} +be represented by a normal addition of two vector type variables). You +can declare only variables and use them in function calls and returns, as +well as in assignments and some casts. It is possible to cast from one +vector type to another, provided they are of the same size (in fact, you +can also cast vectors to and from other datatypes of the same size). + +A port that supports vector operations provides a set of built-in functions +that can be used to operate on vectors. For example, a function to add two +vectors and multiply the result by a third could look like this: + +@example +v4si f (v4si a, v4si b, v4si c) +@{ + v4si tmp = __builtin_addv4si (a, b); + return __builtin_mulv4si (tmp, c); +@} + +@end example + +@node Other Builtins +@section Other built-in functions provided by GCC +@cindex built-in functions +@findex __builtin_isgreater +@findex __builtin_isgreaterequal +@findex __builtin_isless +@findex __builtin_islessequal +@findex __builtin_islessgreater +@findex __builtin_isunordered +@findex abort +@findex abs +@findex alloca +@findex bcmp +@findex bzero +@findex cimag +@findex cimagf +@findex cimagl +@findex conj +@findex conjf +@findex conjl +@findex cos +@findex cosf +@findex cosl +@findex creal +@findex crealf +@findex creall +@findex exit +@findex _exit +@findex _Exit +@findex fabs +@findex fabsf +@findex fabsl +@findex ffs +@findex fprintf +@findex fprintf_unlocked +@findex fputs +@findex fputs_unlocked +@findex imaxabs +@findex index +@findex labs +@findex llabs +@findex memcmp +@findex memcpy +@findex memset +@findex printf +@findex printf_unlocked +@findex rindex +@findex sin +@findex sinf +@findex sinl +@findex sqrt +@findex sqrtf +@findex sqrtl +@findex strcat +@findex strchr +@findex strcmp +@findex strcpy +@findex strcspn +@findex strlen +@findex strncat +@findex strncmp +@findex strncpy +@findex strpbrk +@findex strrchr +@findex strspn +@findex strstr + +GCC provides a large number of built-in functions other than the ones +mentioned above. Some of these are for internal use in the processing +of exceptions or variable-length argument lists and will not be +documented here because they may change from time to time; we do not +recommend general use of these functions. + +The remaining functions are provided for optimization purposes. + +@opindex fno-builtin +GCC includes built-in versions of many of the functions in the standard +C library. The versions prefixed with @code{__builtin_} will always be +treated as having the same meaning as the C library function even if you +specify the @option{-fno-builtin} option. (@pxref{C Dialect Options}) +Many of these functions are only optimized in certain cases; if they are +not optimized in a particular case, a call to the library function will +be emitted. + +@opindex ansi +@opindex std +The functions @code{abort}, @code{exit}, @code{_Exit} and @code{_exit} +are recognized and presumed not to return, but otherwise are not built +in. @code{_exit} is not recognized in strict ISO C mode (@option{-ansi}, +@option{-std=c89} or @option{-std=c99}). @code{_Exit} is not recognized in +strict C89 mode (@option{-ansi} or @option{-std=c89}). + +Outside strict ISO C mode, the functions @code{alloca}, @code{bcmp}, +@code{bzero}, @code{index}, @code{rindex}, @code{ffs}, @code{fputs_unlocked}, +@code{printf_unlocked} and @code{fprintf_unlocked} may be handled as +built-in functions. All these functions have corresponding versions +prefixed with @code{__builtin_}, which may be used even in strict C89 +mode. + +The ISO C99 functions @code{conj}, @code{conjf}, @code{conjl}, +@code{creal}, @code{crealf}, @code{creall}, @code{cimag}, @code{cimagf}, +@code{cimagl}, @code{llabs} and @code{imaxabs} are handled as built-in +functions except in strict ISO C89 mode. There are also built-in +versions of the ISO C99 functions @code{cosf}, @code{cosl}, +@code{fabsf}, @code{fabsl}, @code{sinf}, @code{sinl}, @code{sqrtf}, and +@code{sqrtl}, that are recognized in any mode since ISO C89 reserves +these names for the purpose to which ISO C99 puts them. All these +functions have corresponding versions prefixed with @code{__builtin_}. + +The ISO C89 functions @code{abs}, @code{cos}, @code{fabs}, +@code{fprintf}, @code{fputs}, @code{labs}, @code{memcmp}, @code{memcpy}, +@code{memset}, @code{printf}, @code{sin}, @code{sqrt}, @code{strcat}, +@code{strchr}, @code{strcmp}, @code{strcpy}, @code{strcspn}, +@code{strlen}, @code{strncat}, @code{strncmp}, @code{strncpy}, +@code{strpbrk}, @code{strrchr}, @code{strspn}, and @code{strstr} are all +recognized as built-in functions unless @option{-fno-builtin} is +specified (or @option{-fno-builtin-@var{function}} is specified for an +individual function). All of these functions have corresponding +versions prefixed with @code{__builtin_}. + +GCC provides built-in versions of the ISO C99 floating point comparison +macros that avoid raising exceptions for unordered operands. They have +the same names as the standard macros ( @code{isgreater}, +@code{isgreaterequal}, @code{isless}, @code{islessequal}, +@code{islessgreater}, and @code{isunordered}) , with @code{__builtin_} +prefixed. We intend for a library implementor to be able to simply +@code{#define} each standard macro to its built-in equivalent. + +@deftypefn {Built-in Function} int __builtin_types_compatible_p (@var{type1}, @var{type2}) + +You can use the built-in function @code{__builtin_types_compatible_p} to +determine whether two types are the same. + +This built-in function returns 1 if the unqualified versions of the +types @var{type1} and @var{type2} (which are types, not expressions) are +compatible, 0 otherwise. The result of this built-in function can be +used in integer constant expressions. + +This built-in function ignores top level qualifiers (e.g., @code{const}, +@code{volatile}). For example, @code{int} is equivalent to @code{const +int}. + +The type @code{int[]} and @code{int[5]} are compatible. On the other +hand, @code{int} and @code{char *} are not compatible, even if the size +of their types, on the particular architecture are the same. Also, the +amount of pointer indirection is taken into account when determining +similarity. Consequently, @code{short *} is not similar to +@code{short **}. Furthermore, two types that are typedefed are +considered compatible if their underlying types are compatible. + +An @code{enum} type is considered to be compatible with another +@code{enum} type. For example, @code{enum @{foo, bar@}} is similar to +@code{enum @{hot, dog@}}. + +You would typically use this function in code whose execution varies +depending on the arguments' types. For example: + +@smallexample +#define foo(x) \ + (@{ \ + typeof (x) tmp; \ + if (__builtin_types_compatible_p (typeof (x), long double)) \ + tmp = foo_long_double (tmp); \ + else if (__builtin_types_compatible_p (typeof (x), double)) \ + tmp = foo_double (tmp); \ + else if (__builtin_types_compatible_p (typeof (x), float)) \ + tmp = foo_float (tmp); \ + else \ + abort (); \ + tmp; \ + @}) +@end smallexample + +@emph{Note:} This construct is only available for C. + +@end deftypefn + +@deftypefn {Built-in Function} @var{type} __builtin_choose_expr (@var{const_exp}, @var{exp1}, @var{exp2}) + +You can use the built-in function @code{__builtin_choose_expr} to +evaluate code depending on the value of a constant expression. This +built-in function returns @var{exp1} if @var{const_exp}, which is a +constant expression that must be able to be determined at compile time, +is nonzero. Otherwise it returns 0. + +This built-in function is analogous to the @samp{? :} operator in C, +except that the expression returned has its type unaltered by promotion +rules. Also, the built-in function does not evaluate the expression +that was not chosen. For example, if @var{const_exp} evaluates to true, +@var{exp2} is not evaluated even if it has side-effects. + +This built-in function can return an lvalue if the chosen argument is an +lvalue. + +If @var{exp1} is returned, the return type is the same as @var{exp1}'s +type. Similarly, if @var{exp2} is returned, its return type is the same +as @var{exp2}. + +Example: + +@smallexample +#define foo(x) \ + __builtin_choose_expr (__builtin_types_compatible_p (typeof (x), double), \ + foo_double (x), \ + __builtin_choose_expr (__builtin_types_compatible_p (typeof (x), float), \ + foo_float (x), \ + /* @r{The void expression results in a compile-time error} \ + @r{when assigning the result to something.} */ \ + (void)0)) +@end smallexample + +@emph{Note:} This construct is only available for C. Furthermore, the +unused expression (@var{exp1} or @var{exp2} depending on the value of +@var{const_exp}) may still generate syntax errors. This may change in +future revisions. + +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_constant_p (@var{exp}) +You can use the built-in function @code{__builtin_constant_p} to +determine if a value is known to be constant at compile-time and hence +that GCC can perform constant-folding on expressions involving that +value. The argument of the function is the value to test. The function +returns the integer 1 if the argument is known to be a compile-time +constant and 0 if it is not known to be a compile-time constant. A +return of 0 does not indicate that the value is @emph{not} a constant, +but merely that GCC cannot prove it is a constant with the specified +value of the @option{-O} option. + +You would typically use this function in an embedded application where +memory was a critical resource. If you have some complex calculation, +you may want it to be folded if it involves constants, but need to call +a function if it does not. For example: + +@smallexample +#define Scale_Value(X) \ + (__builtin_constant_p (X) \ + ? ((X) * SCALE + OFFSET) : Scale (X)) +@end smallexample + +You may use this built-in function in either a macro or an inline +function. However, if you use it in an inlined function and pass an +argument of the function as the argument to the built-in, GCC will +never return 1 when you call the inline function with a string constant +or compound literal (@pxref{Compound Literals}) and will not return 1 +when you pass a constant numeric value to the inline function unless you +specify the @option{-O} option. + +You may also use @code{__builtin_constant_p} in initializers for static +data. For instance, you can write + +@smallexample +static const int table[] = @{ + __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1, + /* ... */ +@}; +@end smallexample + +@noindent +This is an acceptable initializer even if @var{EXPRESSION} is not a +constant expression. GCC must be more conservative about evaluating the +built-in in this case, because it has no opportunity to perform +optimization. + +Previous versions of GCC did not accept this built-in in data +initializers. The earliest version where it is completely safe is +3.0.1. +@end deftypefn + +@deftypefn {Built-in Function} long __builtin_expect (long @var{exp}, long @var{c}) +@opindex fprofile-arcs +You may use @code{__builtin_expect} to provide the compiler with +branch prediction information. In general, you should prefer to +use actual profile feedback for this (@option{-fprofile-arcs}), as +programmers are notoriously bad at predicting how their programs +actually perform. However, there are applications in which this +data is hard to collect. + +The return value is the value of @var{exp}, which should be an +integral expression. The value of @var{c} must be a compile-time +constant. The semantics of the built-in are that it is expected +that @var{exp} == @var{c}. For example: + +@smallexample +if (__builtin_expect (x, 0)) + foo (); +@end smallexample + +@noindent +would indicate that we do not expect to call @code{foo}, since +we expect @code{x} to be zero. Since you are limited to integral +expressions for @var{exp}, you should use constructions such as + +@smallexample +if (__builtin_expect (ptr != NULL, 1)) + error (); +@end smallexample + +@noindent +when testing pointer or floating-point values. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_prefetch (const void *@var{addr}, ...) +This function is used to minimize cache-miss latency by moving data into +a cache before it is accessed. +You can insert calls to @code{__builtin_prefetch} into code for which +you know addresses of data in memory that is likely to be accessed soon. +If the target supports them, data prefetch instructions will be generated. +If the prefetch is done early enough before the access then the data will +be in the cache by the time it is accessed. + +The value of @var{addr} is the address of the memory to prefetch. +There are two optional arguments, @var{rw} and @var{locality}. +The value of @var{rw} is a compile-time constant one or zero; one +means that the prefetch is preparing for a write to the memory address +and zero, the default, means that the prefetch is preparing for a read. +The value @var{locality} must be a compile-time constant integer between +zero and three. A value of zero means that the data has no temporal +locality, so it need not be left in the cache after the access. A value +of three means that the data has a high degree of temporal locality and +should be left in all levels of cache possible. Values of one and two +mean, respectively, a low or moderate degree of temporal locality. The +default is three. + +@smallexample +for (i = 0; i < n; i++) + @{ + a[i] = a[i] + b[i]; + __builtin_prefetch (&a[i+j], 1, 1); + __builtin_prefetch (&b[i+j], 0, 1); + /* ... */ + @} +@end smallexample + +Data prefetch does not generate faults if @var{addr} is invalid, but +the address expression itself must be valid. For example, a prefetch +of @code{p->next} will not fault if @code{p->next} is not a valid +address, but evaluation will fault if @code{p} is not a valid address. + +If the target does not support data prefetch, the address expression +is evaluated if it includes side effects but no other code is generated +and GCC does not issue a warning. +@end deftypefn + +@node Target Builtins +@section Built-in Functions Specific to Particular Target Machines + +On some target machines, GCC supports many built-in functions specific +to those machines. Generally these generate calls to specific machine +instructions, but allow the compiler to schedule those calls. + +@menu +* X86 Built-in Functions:: +* PowerPC AltiVec Built-in Functions:: +@end menu + +@node X86 Built-in Functions +@subsection X86 Built-in Functions + +These built-in functions are available for the i386 and x86-64 family +of computers, depending on the command-line switches used. + +The following machine modes are available for use with MMX built-in functions +(@pxref{Vector Extensions}): @code{V2SI} for a vector of two 32-bit integers, +@code{V4HI} for a vector of four 16-bit integers, and @code{V8QI} for a +vector of eight 8-bit integers. Some of the built-in functions operate on +MMX registers as a whole 64-bit entity, these use @code{DI} as their mode. + +If 3Dnow extensions are enabled, @code{V2SF} is used as a mode for a vector +of two 32-bit floating point values. + +If SSE extensions are enabled, @code{V4SF} is used for a vector of four 32-bit +floating point values. Some instructions use a vector of four 32-bit +integers, these use @code{V4SI}. Finally, some instructions operate on an +entire vector register, interpreting it as a 128-bit integer, these use mode +@code{TI}. + +The following built-in functions are made available by @option{-mmmx}. +All of them generate the machine instruction that is part of the name. + +@example +v8qi __builtin_ia32_paddb (v8qi, v8qi) +v4hi __builtin_ia32_paddw (v4hi, v4hi) +v2si __builtin_ia32_paddd (v2si, v2si) +v8qi __builtin_ia32_psubb (v8qi, v8qi) +v4hi __builtin_ia32_psubw (v4hi, v4hi) +v2si __builtin_ia32_psubd (v2si, v2si) +v8qi __builtin_ia32_paddsb (v8qi, v8qi) +v4hi __builtin_ia32_paddsw (v4hi, v4hi) +v8qi __builtin_ia32_psubsb (v8qi, v8qi) +v4hi __builtin_ia32_psubsw (v4hi, v4hi) +v8qi __builtin_ia32_paddusb (v8qi, v8qi) +v4hi __builtin_ia32_paddusw (v4hi, v4hi) +v8qi __builtin_ia32_psubusb (v8qi, v8qi) +v4hi __builtin_ia32_psubusw (v4hi, v4hi) +v4hi __builtin_ia32_pmullw (v4hi, v4hi) +v4hi __builtin_ia32_pmulhw (v4hi, v4hi) +di __builtin_ia32_pand (di, di) +di __builtin_ia32_pandn (di,di) +di __builtin_ia32_por (di, di) +di __builtin_ia32_pxor (di, di) +v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi) +v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi) +v2si __builtin_ia32_pcmpeqd (v2si, v2si) +v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi) +v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi) +v2si __builtin_ia32_pcmpgtd (v2si, v2si) +v8qi __builtin_ia32_punpckhbw (v8qi, v8qi) +v4hi __builtin_ia32_punpckhwd (v4hi, v4hi) +v2si __builtin_ia32_punpckhdq (v2si, v2si) +v8qi __builtin_ia32_punpcklbw (v8qi, v8qi) +v4hi __builtin_ia32_punpcklwd (v4hi, v4hi) +v2si __builtin_ia32_punpckldq (v2si, v2si) +v8qi __builtin_ia32_packsswb (v4hi, v4hi) +v4hi __builtin_ia32_packssdw (v2si, v2si) +v8qi __builtin_ia32_packuswb (v4hi, v4hi) +@end example + +The following built-in functions are made available either with +@option{-msse}, or with a combination of @option{-m3dnow} and +@option{-march=athlon}. All of them generate the machine +instruction that is part of the name. + +@example +v4hi __builtin_ia32_pmulhuw (v4hi, v4hi) +v8qi __builtin_ia32_pavgb (v8qi, v8qi) +v4hi __builtin_ia32_pavgw (v4hi, v4hi) +v4hi __builtin_ia32_psadbw (v8qi, v8qi) +v8qi __builtin_ia32_pmaxub (v8qi, v8qi) +v4hi __builtin_ia32_pmaxsw (v4hi, v4hi) +v8qi __builtin_ia32_pminub (v8qi, v8qi) +v4hi __builtin_ia32_pminsw (v4hi, v4hi) +int __builtin_ia32_pextrw (v4hi, int) +v4hi __builtin_ia32_pinsrw (v4hi, int, int) +int __builtin_ia32_pmovmskb (v8qi) +void __builtin_ia32_maskmovq (v8qi, v8qi, char *) +void __builtin_ia32_movntq (di *, di) +void __builtin_ia32_sfence (void) +@end example + +The following built-in functions are available when @option{-msse} is used. +All of them generate the machine instruction that is part of the name. + +@example +int __builtin_ia32_comieq (v4sf, v4sf) +int __builtin_ia32_comineq (v4sf, v4sf) +int __builtin_ia32_comilt (v4sf, v4sf) +int __builtin_ia32_comile (v4sf, v4sf) +int __builtin_ia32_comigt (v4sf, v4sf) +int __builtin_ia32_comige (v4sf, v4sf) +int __builtin_ia32_ucomieq (v4sf, v4sf) +int __builtin_ia32_ucomineq (v4sf, v4sf) +int __builtin_ia32_ucomilt (v4sf, v4sf) +int __builtin_ia32_ucomile (v4sf, v4sf) +int __builtin_ia32_ucomigt (v4sf, v4sf) +int __builtin_ia32_ucomige (v4sf, v4sf) +v4sf __builtin_ia32_addps (v4sf, v4sf) +v4sf __builtin_ia32_subps (v4sf, v4sf) +v4sf __builtin_ia32_mulps (v4sf, v4sf) +v4sf __builtin_ia32_divps (v4sf, v4sf) +v4sf __builtin_ia32_addss (v4sf, v4sf) +v4sf __builtin_ia32_subss (v4sf, v4sf) +v4sf __builtin_ia32_mulss (v4sf, v4sf) +v4sf __builtin_ia32_divss (v4sf, v4sf) +v4si __builtin_ia32_cmpeqps (v4sf, v4sf) +v4si __builtin_ia32_cmpltps (v4sf, v4sf) +v4si __builtin_ia32_cmpleps (v4sf, v4sf) +v4si __builtin_ia32_cmpgtps (v4sf, v4sf) +v4si __builtin_ia32_cmpgeps (v4sf, v4sf) +v4si __builtin_ia32_cmpunordps (v4sf, v4sf) +v4si __builtin_ia32_cmpneqps (v4sf, v4sf) +v4si __builtin_ia32_cmpnltps (v4sf, v4sf) +v4si __builtin_ia32_cmpnleps (v4sf, v4sf) +v4si __builtin_ia32_cmpngtps (v4sf, v4sf) +v4si __builtin_ia32_cmpngeps (v4sf, v4sf) +v4si __builtin_ia32_cmpordps (v4sf, v4sf) +v4si __builtin_ia32_cmpeqss (v4sf, v4sf) +v4si __builtin_ia32_cmpltss (v4sf, v4sf) +v4si __builtin_ia32_cmpless (v4sf, v4sf) +v4si __builtin_ia32_cmpgtss (v4sf, v4sf) +v4si __builtin_ia32_cmpgess (v4sf, v4sf) +v4si __builtin_ia32_cmpunordss (v4sf, v4sf) +v4si __builtin_ia32_cmpneqss (v4sf, v4sf) +v4si __builtin_ia32_cmpnlts (v4sf, v4sf) +v4si __builtin_ia32_cmpnless (v4sf, v4sf) +v4si __builtin_ia32_cmpngtss (v4sf, v4sf) +v4si __builtin_ia32_cmpngess (v4sf, v4sf) +v4si __builtin_ia32_cmpordss (v4sf, v4sf) +v4sf __builtin_ia32_maxps (v4sf, v4sf) +v4sf __builtin_ia32_maxss (v4sf, v4sf) +v4sf __builtin_ia32_minps (v4sf, v4sf) +v4sf __builtin_ia32_minss (v4sf, v4sf) +v4sf __builtin_ia32_andps (v4sf, v4sf) +v4sf __builtin_ia32_andnps (v4sf, v4sf) +v4sf __builtin_ia32_orps (v4sf, v4sf) +v4sf __builtin_ia32_xorps (v4sf, v4sf) +v4sf __builtin_ia32_movss (v4sf, v4sf) +v4sf __builtin_ia32_movhlps (v4sf, v4sf) +v4sf __builtin_ia32_movlhps (v4sf, v4sf) +v4sf __builtin_ia32_unpckhps (v4sf, v4sf) +v4sf __builtin_ia32_unpcklps (v4sf, v4sf) +v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si) +v4sf __builtin_ia32_cvtsi2ss (v4sf, int) +v2si __builtin_ia32_cvtps2pi (v4sf) +int __builtin_ia32_cvtss2si (v4sf) +v2si __builtin_ia32_cvttps2pi (v4sf) +int __builtin_ia32_cvttss2si (v4sf) +v4sf __builtin_ia32_rcpps (v4sf) +v4sf __builtin_ia32_rsqrtps (v4sf) +v4sf __builtin_ia32_sqrtps (v4sf) +v4sf __builtin_ia32_rcpss (v4sf) +v4sf __builtin_ia32_rsqrtss (v4sf) +v4sf __builtin_ia32_sqrtss (v4sf) +v4sf __builtin_ia32_shufps (v4sf, v4sf, int) +void __builtin_ia32_movntps (float *, v4sf) +int __builtin_ia32_movmskps (v4sf) +@end example + +The following built-in functions are available when @option{-msse} is used. + +@table @code +@item v4sf __builtin_ia32_loadaps (float *) +Generates the @code{movaps} machine instruction as a load from memory. +@item void __builtin_ia32_storeaps (float *, v4sf) +Generates the @code{movaps} machine instruction as a store to memory. +@item v4sf __builtin_ia32_loadups (float *) +Generates the @code{movups} machine instruction as a load from memory. +@item void __builtin_ia32_storeups (float *, v4sf) +Generates the @code{movups} machine instruction as a store to memory. +@item v4sf __builtin_ia32_loadsss (float *) +Generates the @code{movss} machine instruction as a load from memory. +@item void __builtin_ia32_storess (float *, v4sf) +Generates the @code{movss} machine instruction as a store to memory. +@item v4sf __builtin_ia32_loadhps (v4sf, v2si *) +Generates the @code{movhps} machine instruction as a load from memory. +@item v4sf __builtin_ia32_loadlps (v4sf, v2si *) +Generates the @code{movlps} machine instruction as a load from memory +@item void __builtin_ia32_storehps (v4sf, v2si *) +Generates the @code{movhps} machine instruction as a store to memory. +@item void __builtin_ia32_storelps (v4sf, v2si *) +Generates the @code{movlps} machine instruction as a store to memory. +@end table + +The following built-in functions are available when @option{-m3dnow} is used. +All of them generate the machine instruction that is part of the name. + +@example +void __builtin_ia32_femms (void) +v8qi __builtin_ia32_pavgusb (v8qi, v8qi) +v2si __builtin_ia32_pf2id (v2sf) +v2sf __builtin_ia32_pfacc (v2sf, v2sf) +v2sf __builtin_ia32_pfadd (v2sf, v2sf) +v2si __builtin_ia32_pfcmpeq (v2sf, v2sf) +v2si __builtin_ia32_pfcmpge (v2sf, v2sf) +v2si __builtin_ia32_pfcmpgt (v2sf, v2sf) +v2sf __builtin_ia32_pfmax (v2sf, v2sf) +v2sf __builtin_ia32_pfmin (v2sf, v2sf) +v2sf __builtin_ia32_pfmul (v2sf, v2sf) +v2sf __builtin_ia32_pfrcp (v2sf) +v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf) +v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf) +v2sf __builtin_ia32_pfrsqrt (v2sf) +v2sf __builtin_ia32_pfrsqrtit1 (v2sf, v2sf) +v2sf __builtin_ia32_pfsub (v2sf, v2sf) +v2sf __builtin_ia32_pfsubr (v2sf, v2sf) +v2sf __builtin_ia32_pi2fd (v2si) +v4hi __builtin_ia32_pmulhrw (v4hi, v4hi) +@end example + +The following built-in functions are available when both @option{-m3dnow} +and @option{-march=athlon} are used. All of them generate the machine +instruction that is part of the name. + +@example +v2si __builtin_ia32_pf2iw (v2sf) +v2sf __builtin_ia32_pfnacc (v2sf, v2sf) +v2sf __builtin_ia32_pfpnacc (v2sf, v2sf) +v2sf __builtin_ia32_pi2fw (v2si) +v2sf __builtin_ia32_pswapdsf (v2sf) +v2si __builtin_ia32_pswapdsi (v2si) +@end example + +@node PowerPC AltiVec Built-in Functions +@subsection PowerPC AltiVec Built-in Functions + +These built-in functions are available for the PowerPC family +of computers, depending on the command-line switches used. + +The following machine modes are available for use with AltiVec built-in +functions (@pxref{Vector Extensions}): @code{V4SI} for a vector of four +32-bit integers, @code{V4SF} for a vector of four 32-bit floating point +numbers, @code{V8HI} for a vector of eight 16-bit integers, and +@code{V16QI} for a vector of sixteen 8-bit integers. + +The following functions are made available by including +@code{} and using @option{-maltivec} and +@option{-mabi=altivec}. The functions implement the functionality +described in Motorola's AltiVec Programming Interface Manual. + +@smallexample +vector signed char vec_abs (vector signed char, vector signed char); +vector signed short vec_abs (vector signed short, vector signed short); +vector signed int vec_abs (vector signed int, vector signed int); +vector signed float vec_abs (vector signed float, vector signed float); + +vector signed char vec_abss (vector signed char, vector signed char); +vector signed short vec_abss (vector signed short, vector signed short); + +vector signed char vec_add (vector signed char, vector signed char); +vector unsigned char vec_add (vector signed char, vector unsigned char); + +vector unsigned char vec_add (vector unsigned char, vector signed char); + +vector unsigned char vec_add (vector unsigned char, vector unsigned char); +vector signed short vec_add (vector signed short, vector signed short); +vector unsigned short vec_add (vector signed short, vector unsigned short); +vector unsigned short vec_add (vector unsigned short, vector signed short); +vector unsigned short vec_add (vector unsigned short, vector unsigned short); +vector signed int vec_add (vector signed int, vector signed int); +vector unsigned int vec_add (vector signed int, vector unsigned int); +vector unsigned int vec_add (vector unsigned int, vector signed int); +vector unsigned int vec_add (vector unsigned int, vector unsigned int); +vector float vec_add (vector float, vector float); + +vector unsigned int vec_addc (vector unsigned int, vector unsigned int); + +vector unsigned char vec_adds (vector signed char, vector unsigned char); +vector unsigned char vec_adds (vector unsigned char, vector signed char); +vector unsigned char vec_adds (vector unsigned char, vector unsigned char); +vector signed char vec_adds (vector signed char, vector signed char); +vector unsigned short vec_adds (vector signed short, vector unsigned short); +vector unsigned short vec_adds (vector unsigned short, vector signed short); +vector unsigned short vec_adds (vector unsigned short, vector unsigned short); +vector signed short vec_adds (vector signed short, vector signed short); + +vector unsigned int vec_adds (vector signed int, vector unsigned int); +vector unsigned int vec_adds (vector unsigned int, vector signed int); +vector unsigned int vec_adds (vector unsigned int, vector unsigned int); + +vector signed int vec_adds (vector signed int, vector signed int); + +vector float vec_and (vector float, vector float); +vector float vec_and (vector float, vector signed int); +vector float vec_and (vector signed int, vector float); +vector signed int vec_and (vector signed int, vector signed int); +vector unsigned int vec_and (vector signed int, vector unsigned int); +vector unsigned int vec_and (vector unsigned int, vector signed int); +vector unsigned int vec_and (vector unsigned int, vector unsigned int); +vector signed short vec_and (vector signed short, vector signed short); +vector unsigned short vec_and (vector signed short, vector unsigned short); +vector unsigned short vec_and (vector unsigned short, vector signed short); +vector unsigned short vec_and (vector unsigned short, vector unsigned short); +vector signed char vec_and (vector signed char, vector signed char); +vector unsigned char vec_and (vector signed char, vector unsigned char); + +vector unsigned char vec_and (vector unsigned char, vector signed char); + +vector unsigned char vec_and (vector unsigned char, vector unsigned char); + +vector float vec_andc (vector float, vector float); +vector float vec_andc (vector float, vector signed int); +vector float vec_andc (vector signed int, vector float); +vector signed int vec_andc (vector signed int, vector signed int); +vector unsigned int vec_andc (vector signed int, vector unsigned int); +vector unsigned int vec_andc (vector unsigned int, vector signed int); +vector unsigned int vec_andc (vector unsigned int, vector unsigned int); + +vector signed short vec_andc (vector signed short, vector signed short); + +vector unsigned short vec_andc (vector signed short, vector unsigned short); +vector unsigned short vec_andc (vector unsigned short, vector signed short); +vector unsigned short vec_andc (vector unsigned short, vector unsigned short); +vector signed char vec_andc (vector signed char, vector signed char); +vector unsigned char vec_andc (vector signed char, vector unsigned char); +vector unsigned char vec_andc (vector unsigned char, vector signed char); +vector unsigned char vec_andc (vector unsigned char, vector unsigned char); + +vector unsigned char vec_avg (vector unsigned char, vector unsigned char); +vector signed char vec_avg (vector signed char, vector signed char); +vector unsigned short vec_avg (vector unsigned short, vector unsigned short); +vector signed short vec_avg (vector signed short, vector signed short); +vector unsigned int vec_avg (vector unsigned int, vector unsigned int); +vector signed int vec_avg (vector signed int, vector signed int); + +vector float vec_ceil (vector float); + +vector signed int vec_cmpb (vector float, vector float); + +vector signed char vec_cmpeq (vector signed char, vector signed char); +vector signed char vec_cmpeq (vector unsigned char, vector unsigned char); +vector signed short vec_cmpeq (vector signed short, vector signed short); +vector signed short vec_cmpeq (vector unsigned short, vector unsigned short); +vector signed int vec_cmpeq (vector signed int, vector signed int); +vector signed int vec_cmpeq (vector unsigned int, vector unsigned int); +vector signed int vec_cmpeq (vector float, vector float); + +vector signed int vec_cmpge (vector float, vector float); + +vector signed char vec_cmpgt (vector unsigned char, vector unsigned char); +vector signed char vec_cmpgt (vector signed char, vector signed char); +vector signed short vec_cmpgt (vector unsigned short, vector unsigned short); +vector signed short vec_cmpgt (vector signed short, vector signed short); +vector signed int vec_cmpgt (vector unsigned int, vector unsigned int); +vector signed int vec_cmpgt (vector signed int, vector signed int); +vector signed int vec_cmpgt (vector float, vector float); + +vector signed int vec_cmple (vector float, vector float); + +vector signed char vec_cmplt (vector unsigned char, vector unsigned char); +vector signed char vec_cmplt (vector signed char, vector signed char); +vector signed short vec_cmplt (vector unsigned short, vector unsigned short); +vector signed short vec_cmplt (vector signed short, vector signed short); +vector signed int vec_cmplt (vector unsigned int, vector unsigned int); +vector signed int vec_cmplt (vector signed int, vector signed int); +vector signed int vec_cmplt (vector float, vector float); + +vector float vec_ctf (vector unsigned int, const char); +vector float vec_ctf (vector signed int, const char); + +vector signed int vec_cts (vector float, const char); + +vector unsigned int vec_ctu (vector float, const char); + +void vec_dss (const char); + +void vec_dssall (void); + +void vec_dst (void *, int, const char); + +void vec_dstst (void *, int, const char); + +void vec_dststt (void *, int, const char); + +void vec_dstt (void *, int, const char); + +vector float vec_expte (vector float, vector float); + +vector float vec_floor (vector float, vector float); + +vector float vec_ld (int, vector float *); +vector float vec_ld (int, float *): +vector signed int vec_ld (int, int *); +vector signed int vec_ld (int, vector signed int *); +vector unsigned int vec_ld (int, vector unsigned int *); +vector unsigned int vec_ld (int, unsigned int *); +vector signed short vec_ld (int, short *, vector signed short *); +vector unsigned short vec_ld (int, unsigned short *, vector unsigned short *); +vector signed char vec_ld (int, signed char *); +vector signed char vec_ld (int, vector signed char *); +vector unsigned char vec_ld (int, unsigned char *); +vector unsigned char vec_ld (int, vector unsigned char *); + +vector signed char vec_lde (int, signed char *); +vector unsigned char vec_lde (int, unsigned char *); +vector signed short vec_lde (int, short *); +vector unsigned short vec_lde (int, unsigned short *); +vector float vec_lde (int, float *); +vector signed int vec_lde (int, int *); +vector unsigned int vec_lde (int, unsigned int *); + +void float vec_ldl (int, float *); +void float vec_ldl (int, vector float *); +void signed int vec_ldl (int, vector signed int *); +void signed int vec_ldl (int, int *); +void unsigned int vec_ldl (int, unsigned int *); +void unsigned int vec_ldl (int, vector unsigned int *); +void signed short vec_ldl (int, vector signed short *); +void signed short vec_ldl (int, short *); +void unsigned short vec_ldl (int, vector unsigned short *); +void unsigned short vec_ldl (int, unsigned short *); +void signed char vec_ldl (int, vector signed char *); +void signed char vec_ldl (int, signed char *); +void unsigned char vec_ldl (int, vector unsigned char *); +void unsigned char vec_ldl (int, unsigned char *); + +vector float vec_loge (vector float); + +vector unsigned char vec_lvsl (int, void *, int *); + +vector unsigned char vec_lvsr (int, void *, int *); + +vector float vec_madd (vector float, vector float, vector float); + +vector signed short vec_madds (vector signed short, vector signed short, vector signed short); + +vector unsigned char vec_max (vector signed char, vector unsigned char); + +vector unsigned char vec_max (vector unsigned char, vector signed char); + +vector unsigned char vec_max (vector unsigned char, vector unsigned char); +vector signed char vec_max (vector signed char, vector signed char); +vector unsigned short vec_max (vector signed short, vector unsigned short); +vector unsigned short vec_max (vector unsigned short, vector signed short); +vector unsigned short vec_max (vector unsigned short, vector unsigned short); +vector signed short vec_max (vector signed short, vector signed short); +vector unsigned int vec_max (vector signed int, vector unsigned int); +vector unsigned int vec_max (vector unsigned int, vector signed int); +vector unsigned int vec_max (vector unsigned int, vector unsigned int); +vector signed int vec_max (vector signed int, vector signed int); +vector float vec_max (vector float, vector float); + +vector signed char vec_mergeh (vector signed char, vector signed char); +vector unsigned char vec_mergeh (vector unsigned char, vector unsigned char); +vector signed short vec_mergeh (vector signed short, vector signed short); +vector unsigned short vec_mergeh (vector unsigned short, vector unsigned short); +vector float vec_mergeh (vector float, vector float); +vector signed int vec_mergeh (vector signed int, vector signed int); +vector unsigned int vec_mergeh (vector unsigned int, vector unsigned int); + +vector signed char vec_mergel (vector signed char, vector signed char); +vector unsigned char vec_mergel (vector unsigned char, vector unsigned char); +vector signed short vec_mergel (vector signed short, vector signed short); +vector unsigned short vec_mergel (vector unsigned short, vector unsigned short); +vector float vec_mergel (vector float, vector float); +vector signed int vec_mergel (vector signed int, vector signed int); +vector unsigned int vec_mergel (vector unsigned int, vector unsigned int); + +vector unsigned short vec_mfvscr (void); + +vector unsigned char vec_min (vector signed char, vector unsigned char); + +vector unsigned char vec_min (vector unsigned char, vector signed char); + +vector unsigned char vec_min (vector unsigned char, vector unsigned char); +vector signed char vec_min (vector signed char, vector signed char); +vector unsigned short vec_min (vector signed short, vector unsigned short); +vector unsigned short vec_min (vector unsigned short, vector signed short); +vector unsigned short vec_min (vector unsigned short, vector unsigned short); +vector signed short vec_min (vector signed short, vector signed short); +vector unsigned int vec_min (vector signed int, vector unsigned int); +vector unsigned int vec_min (vector unsigned int, vector signed int); +vector unsigned int vec_min (vector unsigned int, vector unsigned int); +vector signed int vec_min (vector signed int, vector signed int); +vector float vec_min (vector float, vector float); + +vector signed short vec_mladd (vector signed short, vector signed short, vector signed short); +vector signed short vec_mladd (vector signed short, vector unsigned short, vector unsigned short); +vector signed short vec_mladd (vector unsigned short, vector signed short, vector signed short); +vector unsigned short vec_mladd (vector unsigned short, vector unsigned short, vector unsigned short); + +vector signed short vec_mradds (vector signed short, vector signed short, vector signed short); + +vector unsigned int vec_msum (vector unsigned char, vector unsigned char, vector unsigned int); +vector signed int vec_msum (vector signed char, vector unsigned char, vector signed int); +vector unsigned int vec_msum (vector unsigned short, vector unsigned short, vector unsigned int); +vector signed int vec_msum (vector signed short, vector signed short, vector signed int); + +vector unsigned int vec_msums (vector unsigned short, vector unsigned short, vector unsigned int); +vector signed int vec_msums (vector signed short, vector signed short, vector signed int); + +void vec_mtvscr (vector signed int); +void vec_mtvscr (vector unsigned int); +void vec_mtvscr (vector signed short); +void vec_mtvscr (vector unsigned short); +void vec_mtvscr (vector signed char); +void vec_mtvscr (vector unsigned char); + +vector unsigned short vec_mule (vector unsigned char, vector unsigned char); +vector signed short vec_mule (vector signed char, vector signed char); +vector unsigned int vec_mule (vector unsigned short, vector unsigned short); +vector signed int vec_mule (vector signed short, vector signed short); + +vector unsigned short vec_mulo (vector unsigned char, vector unsigned char); +vector signed short vec_mulo (vector signed char, vector signed char); +vector unsigned int vec_mulo (vector unsigned short, vector unsigned short); +vector signed int vec_mulo (vector signed short, vector signed short); + +vector float vec_nmsub (vector float, vector float, vector float); + +vector float vec_nor (vector float, vector float); +vector signed int vec_nor (vector signed int, vector signed int); +vector unsigned int vec_nor (vector unsigned int, vector unsigned int); +vector signed short vec_nor (vector signed short, vector signed short); +vector unsigned short vec_nor (vector unsigned short, vector unsigned short); +vector signed char vec_nor (vector signed char, vector signed char); +vector unsigned char vec_nor (vector unsigned char, vector unsigned char); + +vector float vec_or (vector float, vector float); +vector float vec_or (vector float, vector signed int); +vector float vec_or (vector signed int, vector float); +vector signed int vec_or (vector signed int, vector signed int); +vector unsigned int vec_or (vector signed int, vector unsigned int); +vector unsigned int vec_or (vector unsigned int, vector signed int); +vector unsigned int vec_or (vector unsigned int, vector unsigned int); +vector signed short vec_or (vector signed short, vector signed short); +vector unsigned short vec_or (vector signed short, vector unsigned short); +vector unsigned short vec_or (vector unsigned short, vector signed short); +vector unsigned short vec_or (vector unsigned short, vector unsigned short); +vector signed char vec_or (vector signed char, vector signed char); +vector unsigned char vec_or (vector signed char, vector unsigned char); +vector unsigned char vec_or (vector unsigned char, vector signed char); +vector unsigned char vec_or (vector unsigned char, vector unsigned char); + +vector signed char vec_pack (vector signed short, vector signed short); +vector unsigned char vec_pack (vector unsigned short, vector unsigned short); +vector signed short vec_pack (vector signed int, vector signed int); +vector unsigned short vec_pack (vector unsigned int, vector unsigned int); + +vector signed short vec_packpx (vector unsigned int, vector unsigned int); + +vector unsigned char vec_packs (vector unsigned short, vector unsigned short); +vector signed char vec_packs (vector signed short, vector signed short); + +vector unsigned short vec_packs (vector unsigned int, vector unsigned int); +vector signed short vec_packs (vector signed int, vector signed int); + +vector unsigned char vec_packsu (vector unsigned short, vector unsigned short); +vector unsigned char vec_packsu (vector signed short, vector signed short); +vector unsigned short vec_packsu (vector unsigned int, vector unsigned int); +vector unsigned short vec_packsu (vector signed int, vector signed int); + +vector float vec_perm (vector float, vector float, vector unsigned char); +vector signed int vec_perm (vector signed int, vector signed int, vector unsigned char); +vector unsigned int vec_perm (vector unsigned int, vector unsigned int, vector unsigned char); +vector signed short vec_perm (vector signed short, vector signed short, vector unsigned char); +vector unsigned short vec_perm (vector unsigned short, vector unsigned short, vector unsigned char); +vector signed char vec_perm (vector signed char, vector signed char, vector unsigned char); +vector unsigned char vec_perm (vector unsigned char, vector unsigned char, vector unsigned char); + +vector float vec_re (vector float); + +vector signed char vec_rl (vector signed char, vector unsigned char); +vector unsigned char vec_rl (vector unsigned char, vector unsigned char); +vector signed short vec_rl (vector signed short, vector unsigned short); + +vector unsigned short vec_rl (vector unsigned short, vector unsigned short); +vector signed int vec_rl (vector signed int, vector unsigned int); +vector unsigned int vec_rl (vector unsigned int, vector unsigned int); + +vector float vec_round (vector float); + +vector float vec_rsqrte (vector float); + +vector float vec_sel (vector float, vector float, vector signed int); +vector float vec_sel (vector float, vector float, vector unsigned int); +vector signed int vec_sel (vector signed int, vector signed int, vector signed int); +vector signed int vec_sel (vector signed int, vector signed int, vector unsigned int); +vector unsigned int vec_sel (vector unsigned int, vector unsigned int, vector signed int); +vector unsigned int vec_sel (vector unsigned int, vector unsigned int, vector unsigned int); +vector signed short vec_sel (vector signed short, vector signed short, vector signed short); +vector signed short vec_sel (vector signed short, vector signed short, vector unsigned short); +vector unsigned short vec_sel (vector unsigned short, vector unsigned short, vector signed short); +vector unsigned short vec_sel (vector unsigned short, vector unsigned short, vector unsigned short); +vector signed char vec_sel (vector signed char, vector signed char, vector signed char); +vector signed char vec_sel (vector signed char, vector signed char, vector unsigned char); +vector unsigned char vec_sel (vector unsigned char, vector unsigned char, vector signed char); +vector unsigned char vec_sel (vector unsigned char, vector unsigned char, vector unsigned char); + +vector signed char vec_sl (vector signed char, vector unsigned char); +vector unsigned char vec_sl (vector unsigned char, vector unsigned char); +vector signed short vec_sl (vector signed short, vector unsigned short); + +vector unsigned short vec_sl (vector unsigned short, vector unsigned short); +vector signed int vec_sl (vector signed int, vector unsigned int); +vector unsigned int vec_sl (vector unsigned int, vector unsigned int); + +vector float vec_sld (vector float, vector float, const char); +vector signed int vec_sld (vector signed int, vector signed int, const char); +vector unsigned int vec_sld (vector unsigned int, vector unsigned int, const char); +vector signed short vec_sld (vector signed short, vector signed short, const char); +vector unsigned short vec_sld (vector unsigned short, vector unsigned short, const char); +vector signed char vec_sld (vector signed char, vector signed char, const char); +vector unsigned char vec_sld (vector unsigned char, vector unsigned char, const char); + +vector signed int vec_sll (vector signed int, vector unsigned int); +vector signed int vec_sll (vector signed int, vector unsigned short); +vector signed int vec_sll (vector signed int, vector unsigned char); +vector unsigned int vec_sll (vector unsigned int, vector unsigned int); +vector unsigned int vec_sll (vector unsigned int, vector unsigned short); +vector unsigned int vec_sll (vector unsigned int, vector unsigned char); + +vector signed short vec_sll (vector signed short, vector unsigned int); +vector signed short vec_sll (vector signed short, vector unsigned short); +vector signed short vec_sll (vector signed short, vector unsigned char); + +vector unsigned short vec_sll (vector unsigned short, vector unsigned int); +vector unsigned short vec_sll (vector unsigned short, vector unsigned short); +vector unsigned short vec_sll (vector unsigned short, vector unsigned char); +vector signed char vec_sll (vector signed char, vector unsigned int); +vector signed char vec_sll (vector signed char, vector unsigned short); +vector signed char vec_sll (vector signed char, vector unsigned char); +vector unsigned char vec_sll (vector unsigned char, vector unsigned int); +vector unsigned char vec_sll (vector unsigned char, vector unsigned short); +vector unsigned char vec_sll (vector unsigned char, vector unsigned char); + +vector float vec_slo (vector float, vector signed char); +vector float vec_slo (vector float, vector unsigned char); +vector signed int vec_slo (vector signed int, vector signed char); +vector signed int vec_slo (vector signed int, vector unsigned char); +vector unsigned int vec_slo (vector unsigned int, vector signed char); +vector unsigned int vec_slo (vector unsigned int, vector unsigned char); + +vector signed short vec_slo (vector signed short, vector signed char); +vector signed short vec_slo (vector signed short, vector unsigned char); + +vector unsigned short vec_slo (vector unsigned short, vector signed char); +vector unsigned short vec_slo (vector unsigned short, vector unsigned char); +vector signed char vec_slo (vector signed char, vector signed char); +vector signed char vec_slo (vector signed char, vector unsigned char); +vector unsigned char vec_slo (vector unsigned char, vector signed char); + +vector unsigned char vec_slo (vector unsigned char, vector unsigned char); + +vector signed char vec_splat (vector signed char, const char); +vector unsigned char vec_splat (vector unsigned char, const char); +vector signed short vec_splat (vector signed short, const char); +vector unsigned short vec_splat (vector unsigned short, const char); +vector float vec_splat (vector float, const char); +vector signed int vec_splat (vector signed int, const char); +vector unsigned int vec_splat (vector unsigned int, const char); + +vector signed char vec_splat_s8 (const char); + +vector signed short vec_splat_s16 (const char); + +vector signed int vec_splat_s32 (const char); + +vector unsigned char vec_splat_u8 (const char); + +vector unsigned short vec_splat_u16 (const char); + +vector unsigned int vec_splat_u32 (const char); + +vector signed char vec_sr (vector signed char, vector unsigned char); +vector unsigned char vec_sr (vector unsigned char, vector unsigned char); +vector signed short vec_sr (vector signed short, vector unsigned short); + +vector unsigned short vec_sr (vector unsigned short, vector unsigned short); +vector signed int vec_sr (vector signed int, vector unsigned int); +vector unsigned int vec_sr (vector unsigned int, vector unsigned int); + +vector signed char vec_sra (vector signed char, vector unsigned char); +vector unsigned char vec_sra (vector unsigned char, vector unsigned char); +vector signed short vec_sra (vector signed short, vector unsigned short); +vector unsigned short vec_sra (vector unsigned short, vector unsigned short); +vector signed int vec_sra (vector signed int, vector unsigned int); +vector unsigned int vec_sra (vector unsigned int, vector unsigned int); + +vector signed int vec_srl (vector signed int, vector unsigned int); +vector signed int vec_srl (vector signed int, vector unsigned short); +vector signed int vec_srl (vector signed int, vector unsigned char); +vector unsigned int vec_srl (vector unsigned int, vector unsigned int); +vector unsigned int vec_srl (vector unsigned int, vector unsigned short); +vector unsigned int vec_srl (vector unsigned int, vector unsigned char); + +vector signed short vec_srl (vector signed short, vector unsigned int); +vector signed short vec_srl (vector signed short, vector unsigned short); +vector signed short vec_srl (vector signed short, vector unsigned char); + +vector unsigned short vec_srl (vector unsigned short, vector unsigned int); +vector unsigned short vec_srl (vector unsigned short, vector unsigned short); +vector unsigned short vec_srl (vector unsigned short, vector unsigned char); +vector signed char vec_srl (vector signed char, vector unsigned int); +vector signed char vec_srl (vector signed char, vector unsigned short); +vector signed char vec_srl (vector signed char, vector unsigned char); +vector unsigned char vec_srl (vector unsigned char, vector unsigned int); +vector unsigned char vec_srl (vector unsigned char, vector unsigned short); +vector unsigned char vec_srl (vector unsigned char, vector unsigned char); + +vector float vec_sro (vector float, vector signed char); +vector float vec_sro (vector float, vector unsigned char); +vector signed int vec_sro (vector signed int, vector signed char); +vector signed int vec_sro (vector signed int, vector unsigned char); +vector unsigned int vec_sro (vector unsigned int, vector signed char); +vector unsigned int vec_sro (vector unsigned int, vector unsigned char); + +vector signed short vec_sro (vector signed short, vector signed char); +vector signed short vec_sro (vector signed short, vector unsigned char); + +vector unsigned short vec_sro (vector unsigned short, vector signed char); +vector unsigned short vec_sro (vector unsigned short, vector unsigned char); +vector signed char vec_sro (vector signed char, vector signed char); +vector signed char vec_sro (vector signed char, vector unsigned char); +vector unsigned char vec_sro (vector unsigned char, vector signed char); + +vector unsigned char vec_sro (vector unsigned char, vector unsigned char); + +void vec_st (vector float, int, float *); +void vec_st (vector float, int, vector float *); +void vec_st (vector signed int, int, int *); +void vec_st (vector signed int, int, unsigned int *); +void vec_st (vector unsigned int, int, unsigned int *); +void vec_st (vector unsigned int, int, vector unsigned int *); +void vec_st (vector signed short, int, short *); +void vec_st (vector signed short, int, vector unsigned short *); +void vec_st (vector signed short, int, vector signed short *); +void vec_st (vector unsigned short, int, unsigned short *); +void vec_st (vector unsigned short, int, vector unsigned short *); +void vec_st (vector signed char, int, signed char *); +void vec_st (vector signed char, int, unsigned char *); +void vec_st (vector signed char, int, vector signed char *); +void vec_st (vector unsigned char, int, unsigned char *); +void vec_st (vector unsigned char, int, vector unsigned char *); + +void vec_ste (vector signed char, int, unsigned char *); +void vec_ste (vector signed char, int, signed char *); +void vec_ste (vector unsigned char, int, unsigned char *); +void vec_ste (vector signed short, int, short *); +void vec_ste (vector signed short, int, unsigned short *); +void vec_ste (vector unsigned short, int, void *); +void vec_ste (vector signed int, int, unsigned int *); +void vec_ste (vector signed int, int, int *); +void vec_ste (vector unsigned int, int, unsigned int *); +void vec_ste (vector float, int, float *); + +void vec_stl (vector float, int, vector float *); +void vec_stl (vector float, int, float *); +void vec_stl (vector signed int, int, vector signed int *); +void vec_stl (vector signed int, int, int *); +void vec_stl (vector signed int, int, unsigned int *); +void vec_stl (vector unsigned int, int, vector unsigned int *); +void vec_stl (vector unsigned int, int, unsigned int *); +void vec_stl (vector signed short, int, short *); +void vec_stl (vector signed short, int, unsigned short *); +void vec_stl (vector signed short, int, vector signed short *); +void vec_stl (vector unsigned short, int, unsigned short *); +void vec_stl (vector unsigned short, int, vector signed short *); +void vec_stl (vector signed char, int, signed char *); +void vec_stl (vector signed char, int, unsigned char *); +void vec_stl (vector signed char, int, vector signed char *); +void vec_stl (vector unsigned char, int, unsigned char *); +void vec_stl (vector unsigned char, int, vector unsigned char *); + +vector signed char vec_sub (vector signed char, vector signed char); +vector unsigned char vec_sub (vector signed char, vector unsigned char); + +vector unsigned char vec_sub (vector unsigned char, vector signed char); + +vector unsigned char vec_sub (vector unsigned char, vector unsigned char); +vector signed short vec_sub (vector signed short, vector signed short); +vector unsigned short vec_sub (vector signed short, vector unsigned short); +vector unsigned short vec_sub (vector unsigned short, vector signed short); +vector unsigned short vec_sub (vector unsigned short, vector unsigned short); +vector signed int vec_sub (vector signed int, vector signed int); +vector unsigned int vec_sub (vector signed int, vector unsigned int); +vector unsigned int vec_sub (vector unsigned int, vector signed int); +vector unsigned int vec_sub (vector unsigned int, vector unsigned int); +vector float vec_sub (vector float, vector float); + +vector unsigned int vec_subc (vector unsigned int, vector unsigned int); + +vector unsigned char vec_subs (vector signed char, vector unsigned char); +vector unsigned char vec_subs (vector unsigned char, vector signed char); +vector unsigned char vec_subs (vector unsigned char, vector unsigned char); +vector signed char vec_subs (vector signed char, vector signed char); +vector unsigned short vec_subs (vector signed short, vector unsigned short); +vector unsigned short vec_subs (vector unsigned short, vector signed short); +vector unsigned short vec_subs (vector unsigned short, vector unsigned short); +vector signed short vec_subs (vector signed short, vector signed short); + +vector unsigned int vec_subs (vector signed int, vector unsigned int); +vector unsigned int vec_subs (vector unsigned int, vector signed int); +vector unsigned int vec_subs (vector unsigned int, vector unsigned int); + +vector signed int vec_subs (vector signed int, vector signed int); + +vector unsigned int vec_sum4s (vector unsigned char, vector unsigned int); +vector signed int vec_sum4s (vector signed char, vector signed int); +vector signed int vec_sum4s (vector signed short, vector signed int); + +vector signed int vec_sum2s (vector signed int, vector signed int); + +vector signed int vec_sums (vector signed int, vector signed int); + +vector float vec_trunc (vector float); + +vector signed short vec_unpackh (vector signed char); +vector unsigned int vec_unpackh (vector signed short); +vector signed int vec_unpackh (vector signed short); + +vector signed short vec_unpackl (vector signed char); +vector unsigned int vec_unpackl (vector signed short); +vector signed int vec_unpackl (vector signed short); + +vector float vec_xor (vector float, vector float); +vector float vec_xor (vector float, vector signed int); +vector float vec_xor (vector signed int, vector float); +vector signed int vec_xor (vector signed int, vector signed int); +vector unsigned int vec_xor (vector signed int, vector unsigned int); +vector unsigned int vec_xor (vector unsigned int, vector signed int); +vector unsigned int vec_xor (vector unsigned int, vector unsigned int); +vector signed short vec_xor (vector signed short, vector signed short); +vector unsigned short vec_xor (vector signed short, vector unsigned short); +vector unsigned short vec_xor (vector unsigned short, vector signed short); +vector unsigned short vec_xor (vector unsigned short, vector unsigned short); +vector signed char vec_xor (vector signed char, vector signed char); +vector unsigned char vec_xor (vector signed char, vector unsigned char); + +vector unsigned char vec_xor (vector unsigned char, vector signed char); + +vector unsigned char vec_xor (vector unsigned char, vector unsigned char); + +vector signed int vec_all_eq (vector signed char, vector unsigned char); + +vector signed int vec_all_eq (vector signed char, vector signed char); +vector signed int vec_all_eq (vector unsigned char, vector signed char); + +vector signed int vec_all_eq (vector unsigned char, vector unsigned char); +vector signed int vec_all_eq (vector signed short, vector unsigned short); +vector signed int vec_all_eq (vector signed short, vector signed short); + +vector signed int vec_all_eq (vector unsigned short, vector signed short); +vector signed int vec_all_eq (vector unsigned short, vector unsigned short); +vector signed int vec_all_eq (vector signed int, vector unsigned int); +vector signed int vec_all_eq (vector signed int, vector signed int); +vector signed int vec_all_eq (vector unsigned int, vector signed int); +vector signed int vec_all_eq (vector unsigned int, vector unsigned int); + +vector signed int vec_all_eq (vector float, vector float); + +vector signed int vec_all_ge (vector signed char, vector unsigned char); + +vector signed int vec_all_ge (vector unsigned char, vector signed char); + +vector signed int vec_all_ge (vector unsigned char, vector unsigned char); +vector signed int vec_all_ge (vector signed char, vector signed char); +vector signed int vec_all_ge (vector signed short, vector unsigned short); +vector signed int vec_all_ge (vector unsigned short, vector signed short); +vector signed int vec_all_ge (vector unsigned short, vector unsigned short); +vector signed int vec_all_ge (vector signed short, vector signed short); + +vector signed int vec_all_ge (vector signed int, vector unsigned int); +vector signed int vec_all_ge (vector unsigned int, vector signed int); +vector signed int vec_all_ge (vector unsigned int, vector unsigned int); + +vector signed int vec_all_ge (vector signed int, vector signed int); +vector signed int vec_all_ge (vector float, vector float); + +vector signed int vec_all_gt (vector signed char, vector unsigned char); + +vector signed int vec_all_gt (vector unsigned char, vector signed char); + +vector signed int vec_all_gt (vector unsigned char, vector unsigned char); +vector signed int vec_all_gt (vector signed char, vector signed char); +vector signed int vec_all_gt (vector signed short, vector unsigned short); +vector signed int vec_all_gt (vector unsigned short, vector signed short); +vector signed int vec_all_gt (vector unsigned short, vector unsigned short); +vector signed int vec_all_gt (vector signed short, vector signed short); + +vector signed int vec_all_gt (vector signed int, vector unsigned int); +vector signed int vec_all_gt (vector unsigned int, vector signed int); +vector signed int vec_all_gt (vector unsigned int, vector unsigned int); + +vector signed int vec_all_gt (vector signed int, vector signed int); +vector signed int vec_all_gt (vector float, vector float); + +vector signed int vec_all_in (vector float, vector float); + +vector signed int vec_all_le (vector signed char, vector unsigned char); + +vector signed int vec_all_le (vector unsigned char, vector signed char); + +vector signed int vec_all_le (vector unsigned char, vector unsigned char); +vector signed int vec_all_le (vector signed char, vector signed char); +vector signed int vec_all_le (vector signed short, vector unsigned short); +vector signed int vec_all_le (vector unsigned short, vector signed short); +vector signed int vec_all_le (vector unsigned short, vector unsigned short); +vector signed int vec_all_le (vector signed short, vector signed short); + +vector signed int vec_all_le (vector signed int, vector unsigned int); +vector signed int vec_all_le (vector unsigned int, vector signed int); +vector signed int vec_all_le (vector unsigned int, vector unsigned int); + +vector signed int vec_all_le (vector signed int, vector signed int); +vector signed int vec_all_le (vector float, vector float); + +vector signed int vec_all_lt (vector signed char, vector unsigned char); + +vector signed int vec_all_lt (vector unsigned char, vector signed char); + +vector signed int vec_all_lt (vector unsigned char, vector unsigned char); +vector signed int vec_all_lt (vector signed char, vector signed char); +vector signed int vec_all_lt (vector signed short, vector unsigned short); +vector signed int vec_all_lt (vector unsigned short, vector signed short); +vector signed int vec_all_lt (vector unsigned short, vector unsigned short); +vector signed int vec_all_lt (vector signed short, vector signed short); + +vector signed int vec_all_lt (vector signed int, vector unsigned int); +vector signed int vec_all_lt (vector unsigned int, vector signed int); +vector signed int vec_all_lt (vector unsigned int, vector unsigned int); + +vector signed int vec_all_lt (vector signed int, vector signed int); +vector signed int vec_all_lt (vector float, vector float); + +vector signed int vec_all_nan (vector float); + +vector signed int vec_all_ne (vector signed char, vector unsigned char); + +vector signed int vec_all_ne (vector signed char, vector signed char); +vector signed int vec_all_ne (vector unsigned char, vector signed char); + +vector signed int vec_all_ne (vector unsigned char, vector unsigned char); +vector signed int vec_all_ne (vector signed short, vector unsigned short); +vector signed int vec_all_ne (vector signed short, vector signed short); + +vector signed int vec_all_ne (vector unsigned short, vector signed short); +vector signed int vec_all_ne (vector unsigned short, vector unsigned short); +vector signed int vec_all_ne (vector signed int, vector unsigned int); +vector signed int vec_all_ne (vector signed int, vector signed int); +vector signed int vec_all_ne (vector unsigned int, vector signed int); +vector signed int vec_all_ne (vector unsigned int, vector unsigned int); + +vector signed int vec_all_ne (vector float, vector float); + +vector signed int vec_all_nge (vector float, vector float); + +vector signed int vec_all_ngt (vector float, vector float); + +vector signed int vec_all_nle (vector float, vector float); + +vector signed int vec_all_nlt (vector float, vector float); + +vector signed int vec_all_numeric (vector float); + +vector signed int vec_any_eq (vector signed char, vector unsigned char); + +vector signed int vec_any_eq (vector signed char, vector signed char); +vector signed int vec_any_eq (vector unsigned char, vector signed char); + +vector signed int vec_any_eq (vector unsigned char, vector unsigned char); +vector signed int vec_any_eq (vector signed short, vector unsigned short); +vector signed int vec_any_eq (vector signed short, vector signed short); + +vector signed int vec_any_eq (vector unsigned short, vector signed short); +vector signed int vec_any_eq (vector unsigned short, vector unsigned short); +vector signed int vec_any_eq (vector signed int, vector unsigned int); +vector signed int vec_any_eq (vector signed int, vector signed int); +vector signed int vec_any_eq (vector unsigned int, vector signed int); +vector signed int vec_any_eq (vector unsigned int, vector unsigned int); + +vector signed int vec_any_eq (vector float, vector float); + +vector signed int vec_any_ge (vector signed char, vector unsigned char); + +vector signed int vec_any_ge (vector unsigned char, vector signed char); + +vector signed int vec_any_ge (vector unsigned char, vector unsigned char); +vector signed int vec_any_ge (vector signed char, vector signed char); +vector signed int vec_any_ge (vector signed short, vector unsigned short); +vector signed int vec_any_ge (vector unsigned short, vector signed short); +vector signed int vec_any_ge (vector unsigned short, vector unsigned short); +vector signed int vec_any_ge (vector signed short, vector signed short); + +vector signed int vec_any_ge (vector signed int, vector unsigned int); +vector signed int vec_any_ge (vector unsigned int, vector signed int); +vector signed int vec_any_ge (vector unsigned int, vector unsigned int); + +vector signed int vec_any_ge (vector signed int, vector signed int); +vector signed int vec_any_ge (vector float, vector float); + +vector signed int vec_any_gt (vector signed char, vector unsigned char); + +vector signed int vec_any_gt (vector unsigned char, vector signed char); + +vector signed int vec_any_gt (vector unsigned char, vector unsigned char); +vector signed int vec_any_gt (vector signed char, vector signed char); +vector signed int vec_any_gt (vector signed short, vector unsigned short); +vector signed int vec_any_gt (vector unsigned short, vector signed short); +vector signed int vec_any_gt (vector unsigned short, vector unsigned short); +vector signed int vec_any_gt (vector signed short, vector signed short); + +vector signed int vec_any_gt (vector signed int, vector unsigned int); +vector signed int vec_any_gt (vector unsigned int, vector signed int); +vector signed int vec_any_gt (vector unsigned int, vector unsigned int); + +vector signed int vec_any_gt (vector signed int, vector signed int); +vector signed int vec_any_gt (vector float, vector float); + +vector signed int vec_any_le (vector signed char, vector unsigned char); + +vector signed int vec_any_le (vector unsigned char, vector signed char); + +vector signed int vec_any_le (vector unsigned char, vector unsigned char); +vector signed int vec_any_le (vector signed char, vector signed char); +vector signed int vec_any_le (vector signed short, vector unsigned short); +vector signed int vec_any_le (vector unsigned short, vector signed short); +vector signed int vec_any_le (vector unsigned short, vector unsigned short); +vector signed int vec_any_le (vector signed short, vector signed short); + +vector signed int vec_any_le (vector signed int, vector unsigned int); +vector signed int vec_any_le (vector unsigned int, vector signed int); +vector signed int vec_any_le (vector unsigned int, vector unsigned int); + +vector signed int vec_any_le (vector signed int, vector signed int); +vector signed int vec_any_le (vector float, vector float); + +vector signed int vec_any_lt (vector signed char, vector unsigned char); + +vector signed int vec_any_lt (vector unsigned char, vector signed char); + +vector signed int vec_any_lt (vector unsigned char, vector unsigned char); +vector signed int vec_any_lt (vector signed char, vector signed char); +vector signed int vec_any_lt (vector signed short, vector unsigned short); +vector signed int vec_any_lt (vector unsigned short, vector signed short); +vector signed int vec_any_lt (vector unsigned short, vector unsigned short); +vector signed int vec_any_lt (vector signed short, vector signed short); + +vector signed int vec_any_lt (vector signed int, vector unsigned int); +vector signed int vec_any_lt (vector unsigned int, vector signed int); +vector signed int vec_any_lt (vector unsigned int, vector unsigned int); + +vector signed int vec_any_lt (vector signed int, vector signed int); +vector signed int vec_any_lt (vector float, vector float); + +vector signed int vec_any_nan (vector float); + +vector signed int vec_any_ne (vector signed char, vector unsigned char); + +vector signed int vec_any_ne (vector signed char, vector signed char); +vector signed int vec_any_ne (vector unsigned char, vector signed char); + +vector signed int vec_any_ne (vector unsigned char, vector unsigned char); +vector signed int vec_any_ne (vector signed short, vector unsigned short); +vector signed int vec_any_ne (vector signed short, vector signed short); + +vector signed int vec_any_ne (vector unsigned short, vector signed short); +vector signed int vec_any_ne (vector unsigned short, vector unsigned short); +vector signed int vec_any_ne (vector signed int, vector unsigned int); +vector signed int vec_any_ne (vector signed int, vector signed int); +vector signed int vec_any_ne (vector unsigned int, vector signed int); +vector signed int vec_any_ne (vector unsigned int, vector unsigned int); + +vector signed int vec_any_ne (vector float, vector float); + +vector signed int vec_any_nge (vector float, vector float); + +vector signed int vec_any_ngt (vector float, vector float); + +vector signed int vec_any_nle (vector float, vector float); + +vector signed int vec_any_nlt (vector float, vector float); + +vector signed int vec_any_numeric (vector float); + +vector signed int vec_any_out (vector float, vector float); +@end smallexample + +@node Pragmas +@section Pragmas Accepted by GCC +@cindex pragmas +@cindex #pragma + +GCC supports several types of pragmas, primarily in order to compile +code originally written for other compilers. Note that in general +we do not recommend the use of pragmas; @xref{Function Attributes}, +for further explanation. + +@menu +* ARM Pragmas:: +* Darwin Pragmas:: +@end menu + +@node ARM Pragmas +@subsection ARM Pragmas + +The ARM target defines pragmas for controlling the default addition of +@code{long_call} and @code{short_call} attributes to functions. +@xref{Function Attributes}, for information about the effects of these +attributes. + +@table @code +@item long_calls +@cindex pragma, long_calls +Set all subsequent functions to have the @code{long_call} attribute. + +@item no_long_calls +@cindex pragma, no_long_calls +Set all subsequent functions to have the @code{short_call} attribute. + +@item long_calls_off +@cindex pragma, long_calls_off +Do not affect the @code{long_call} or @code{short_call} attributes of +subsequent functions. +@end table + +@c Describe c4x pragmas here. +@c Describe h8300 pragmas here. +@c Describe i370 pragmas here. +@c Describe i960 pragmas here. +@c Describe sh pragmas here. +@c Describe v850 pragmas here. + +@node Darwin Pragmas +@subsection Darwin Pragmas + +The following pragmas are available for all architectures running the +Darwin operating system. These are useful for compatibility with other +MacOS compilers. + +@table @code +@item mark @var{tokens}@dots{} +@cindex pragma, mark +This pragma is accepted, but has no effect. + +@item options align=@var{alignment} +@cindex pragma, options align +This pragma sets the alignment of fields in structures. The values of +@var{alignment} may be @code{mac68k}, to emulate m68k alignment, or +@code{power}, to emulate PowerPC alignment. Uses of this pragma nest +properly; to restore the previous setting, use @code{reset} for the +@var{alignment}. + +@item segment @var{tokens}@dots{} +@cindex pragma, segment +This pragma is accepted, but has no effect. + +@item unused (@var{var} [, @var{var}]@dots{}) +@cindex pragma, unused +This pragma declares variables to be possibly unused. GCC will not +produce warnings for the listed variables. The effect is similar to +that of the @code{unused} attribute, except that this pragma may appear +anywhere within the variables' scopes. +@end table + +@node Unnamed Fields +@section Unnamed struct/union fields within structs/unions. +@cindex struct +@cindex union + +For compatibility with other compilers, GCC allows you to define +a structure or union that contains, as fields, structures and unions +without names. For example: + +@example +struct @{ + int a; + union @{ + int b; + float c; + @}; + int d; +@} foo; +@end example + +In this example, the user would be able to access members of the unnamed +union with code like @samp{foo.b}. Note that only unnamed structs and +unions are allowed, you may not have, for example, an unnamed +@code{int}. + +You must never create such structures that cause ambiguous field definitions. +For example, this structure: + +@example +struct @{ + int a; + struct @{ + int a; + @}; +@} foo; +@end example + +It is ambiguous which @code{a} is being referred to with @samp{foo.a}. +Such constructs are not supported and must be avoided. In the future, +such constructs may be detected and treated as compilation errors. + +@node C++ Extensions +@chapter Extensions to the C++ Language +@cindex extensions, C++ language +@cindex C++ language extensions + +The GNU compiler provides these extensions to the C++ language (and you +can also use most of the C language extensions in your C++ programs). If you +want to write code that checks whether these features are available, you can +test for the GNU compiler the same way as for C programs: check for a +predefined macro @code{__GNUC__}. You can also use @code{__GNUG__} to +test specifically for GNU C++ (@pxref{Standard Predefined,,Standard +Predefined Macros,cpp.info,The C Preprocessor}). + +@menu +* Min and Max:: C++ Minimum and maximum operators. +* Volatiles:: What constitutes an access to a volatile object. +* Restricted Pointers:: C99 restricted pointers and references. +* Vague Linkage:: Where G++ puts inlines, vtables and such. +* C++ Interface:: You can use a single C++ header file for both + declarations and definitions. +* Template Instantiation:: Methods for ensuring that exactly one copy of + each needed template instantiation is emitted. +* Bound member functions:: You can extract a function pointer to the + method denoted by a @samp{->*} or @samp{.*} expression. +* C++ Attributes:: Variable, function, and type attributes for C++ only. +* Java Exceptions:: Tweaking exception handling to work with Java. +* Deprecated Features:: Things might disappear from g++. +* Backwards Compatibility:: Compatibilities with earlier definitions of C++. +@end menu + +@node Min and Max +@section Minimum and Maximum Operators in C++ + +It is very convenient to have operators which return the ``minimum'' or the +``maximum'' of two arguments. In GNU C++ (but not in GNU C), + +@table @code +@item @var{a} ? @var{b} +@findex >? +@cindex maximum operator +is the @dfn{maximum}, returning the larger of the numeric values @var{a} +and @var{b}. +@end table + +These operations are not primitive in ordinary C++, since you can +use a macro to return the minimum of two things in C++, as in the +following example. + +@example +#define MIN(X,Y) ((X) < (Y) ? : (X) : (Y)) +@end example + +@noindent +You might then use @w{@samp{int min = MIN (i, j);}} to set @var{min} to +the minimum value of variables @var{i} and @var{j}. + +However, side effects in @code{X} or @code{Y} may cause unintended +behavior. For example, @code{MIN (i++, j++)} will fail, incrementing +the smaller counter twice. A GNU C extension allows you to write safe +macros that avoid this kind of problem (@pxref{Naming Types,,Naming an +Expression's Type}). However, writing @code{MIN} and @code{MAX} as +macros also forces you to use function-call notation for a +fundamental arithmetic operation. Using GNU C++ extensions, you can +write @w{@samp{int min = i ?} are built into the compiler, they properly +handle expressions with side-effects; @w{@samp{int min = i++ (*ptr1)}. + +When using a reference to volatile, G++ does not treat equivalent +expressions as accesses to volatiles, but instead issues a warning that +no volatile is accessed. The rationale for this is that otherwise it +becomes difficult to determine where volatile access occur, and not +possible to ignore the return value from functions returning volatile +references. Again, if you wish to force a read, cast the reference to +an rvalue. + +@node Restricted Pointers +@section Restricting Pointer Aliasing +@cindex restricted pointers +@cindex restricted references +@cindex restricted this pointer + +As with gcc, g++ understands the C99 feature of restricted pointers, +specified with the @code{__restrict__}, or @code{__restrict} type +qualifier. Because you cannot compile C++ by specifying the @option{-std=c99} +language flag, @code{restrict} is not a keyword in C++. + +In addition to allowing restricted pointers, you can specify restricted +references, which indicate that the reference is not aliased in the local +context. + +@example +void fn (int *__restrict__ rptr, int &__restrict__ rref) +@{ + @dots{} +@} +@end example + +@noindent +In the body of @code{fn}, @var{rptr} points to an unaliased integer and +@var{rref} refers to a (different) unaliased integer. + +You may also specify whether a member function's @var{this} pointer is +unaliased by using @code{__restrict__} as a member function qualifier. + +@example +void T::fn () __restrict__ +@{ + @dots{} +@} +@end example + +@noindent +Within the body of @code{T::fn}, @var{this} will have the effective +definition @code{T *__restrict__ const this}. Notice that the +interpretation of a @code{__restrict__} member function qualifier is +different to that of @code{const} or @code{volatile} qualifier, in that it +is applied to the pointer rather than the object. This is consistent with +other compilers which implement restricted pointers. + +As with all outermost parameter qualifiers, @code{__restrict__} is +ignored in function definition matching. This means you only need to +specify @code{__restrict__} in a function definition, rather than +in a function prototype as well. + +@node Vague Linkage +@section Vague Linkage +@cindex vague linkage + +There are several constructs in C++ which require space in the object +file but are not clearly tied to a single translation unit. We say that +these constructs have ``vague linkage''. Typically such constructs are +emitted wherever they are needed, though sometimes we can be more +clever. + +@table @asis +@item Inline Functions +Inline functions are typically defined in a header file which can be +included in many different compilations. Hopefully they can usually be +inlined, but sometimes an out-of-line copy is necessary, if the address +of the function is taken or if inlining fails. In general, we emit an +out-of-line copy in all translation units where one is needed. As an +exception, we only emit inline virtual functions with the vtable, since +it will always require a copy. + +Local static variables and string constants used in an inline function +are also considered to have vague linkage, since they must be shared +between all inlined and out-of-line instances of the function. + +@item VTables +@cindex vtable +C++ virtual functions are implemented in most compilers using a lookup +table, known as a vtable. The vtable contains pointers to the virtual +functions provided by a class, and each object of the class contains a +pointer to its vtable (or vtables, in some multiple-inheritance +situations). If the class declares any non-inline, non-pure virtual +functions, the first one is chosen as the ``key method'' for the class, +and the vtable is only emitted in the translation unit where the key +method is defined. + +@emph{Note:} If the chosen key method is later defined as inline, the +vtable will still be emitted in every translation unit which defines it. +Make sure that any inline virtuals are declared inline in the class +body, even if they are not defined there. + +@item type_info objects +@cindex type_info +@cindex RTTI +C++ requires information about types to be written out in order to +implement @samp{dynamic_cast}, @samp{typeid} and exception handling. +For polymorphic classes (classes with virtual functions), the type_info +object is written out along with the vtable so that @samp{dynamic_cast} +can determine the dynamic type of a class object at runtime. For all +other types, we write out the type_info object when it is used: when +applying @samp{typeid} to an expression, throwing an object, or +referring to a type in a catch clause or exception specification. + +@item Template Instantiations +Most everything in this section also applies to template instantiations, +but there are other options as well. +@xref{Template Instantiation,,Where's the Template?}. + +@end table + +When used with GNU ld version 2.8 or later on an ELF system such as +Linux/GNU or Solaris 2, or on Microsoft Windows, duplicate copies of +these constructs will be discarded at link time. This is known as +COMDAT support. + +On targets that don't support COMDAT, but do support weak symbols, GCC +will use them. This way one copy will override all the others, but +the unused copies will still take up space in the executable. + +For targets which do not support either COMDAT or weak symbols, +most entities with vague linkage will be emitted as local symbols to +avoid duplicate definition errors from the linker. This will not happen +for local statics in inlines, however, as having multiple copies will +almost certainly break things. + +@xref{C++ Interface,,Declarations and Definitions in One Header}, for +another way to control placement of these constructs. + +@node C++ Interface +@section Declarations and Definitions in One Header + +@cindex interface and implementation headers, C++ +@cindex C++ interface and implementation headers +C++ object definitions can be quite complex. In principle, your source +code will need two kinds of things for each object that you use across +more than one source file. First, you need an @dfn{interface} +specification, describing its structure with type declarations and +function prototypes. Second, you need the @dfn{implementation} itself. +It can be tedious to maintain a separate interface description in a +header file, in parallel to the actual implementation. It is also +dangerous, since separate interface and implementation definitions may +not remain parallel. + +@cindex pragmas, interface and implementation +With GNU C++, you can use a single header file for both purposes. + +@quotation +@emph{Warning:} The mechanism to specify this is in transition. For the +nonce, you must use one of two @code{#pragma} commands; in a future +release of GNU C++, an alternative mechanism will make these +@code{#pragma} commands unnecessary. +@end quotation + +The header file contains the full definitions, but is marked with +@samp{#pragma interface} in the source code. This allows the compiler +to use the header file only as an interface specification when ordinary +source files incorporate it with @code{#include}. In the single source +file where the full implementation belongs, you can use either a naming +convention or @samp{#pragma implementation} to indicate this alternate +use of the header file. + +@table @code +@item #pragma interface +@itemx #pragma interface "@var{subdir}/@var{objects}.h" +@kindex #pragma interface +Use this directive in @emph{header files} that define object classes, to save +space in most of the object files that use those classes. Normally, +local copies of certain information (backup copies of inline member +functions, debugging information, and the internal tables that implement +virtual functions) must be kept in each object file that includes class +definitions. You can use this pragma to avoid such duplication. When a +header file containing @samp{#pragma interface} is included in a +compilation, this auxiliary information will not be generated (unless +the main input source file itself uses @samp{#pragma implementation}). +Instead, the object files will contain references to be resolved at link +time. + +The second form of this directive is useful for the case where you have +multiple headers with the same name in different directories. If you +use this form, you must specify the same string to @samp{#pragma +implementation}. + +@item #pragma implementation +@itemx #pragma implementation "@var{objects}.h" +@kindex #pragma implementation +Use this pragma in a @emph{main input file}, when you want full output from +included header files to be generated (and made globally visible). The +included header file, in turn, should use @samp{#pragma interface}. +Backup copies of inline member functions, debugging information, and the +internal tables used to implement virtual functions are all generated in +implementation files. + +@cindex implied @code{#pragma implementation} +@cindex @code{#pragma implementation}, implied +@cindex naming convention, implementation headers +If you use @samp{#pragma implementation} with no argument, it applies to +an include file with the same basename@footnote{A file's @dfn{basename} +was the name stripped of all leading path information and of trailing +suffixes, such as @samp{.h} or @samp{.C} or @samp{.cc}.} as your source +file. For example, in @file{allclass.cc}, giving just +@samp{#pragma implementation} +by itself is equivalent to @samp{#pragma implementation "allclass.h"}. + +In versions of GNU C++ prior to 2.6.0 @file{allclass.h} was treated as +an implementation file whenever you would include it from +@file{allclass.cc} even if you never specified @samp{#pragma +implementation}. This was deemed to be more trouble than it was worth, +however, and disabled. + +If you use an explicit @samp{#pragma implementation}, it must appear in +your source file @emph{before} you include the affected header files. + +Use the string argument if you want a single implementation file to +include code from multiple header files. (You must also use +@samp{#include} to include the header file; @samp{#pragma +implementation} only specifies how to use the file---it doesn't actually +include it.) + +There is no way to split up the contents of a single header file into +multiple implementation files. +@end table + +@cindex inlining and C++ pragmas +@cindex C++ pragmas, effect on inlining +@cindex pragmas in C++, effect on inlining +@samp{#pragma implementation} and @samp{#pragma interface} also have an +effect on function inlining. + +If you define a class in a header file marked with @samp{#pragma +interface}, the effect on a function defined in that class is similar to +an explicit @code{extern} declaration---the compiler emits no code at +all to define an independent version of the function. Its definition +is used only for inlining with its callers. + +@opindex fno-implement-inlines +Conversely, when you include the same header file in a main source file +that declares it as @samp{#pragma implementation}, the compiler emits +code for the function itself; this defines a version of the function +that can be found via pointers (or by callers compiled without +inlining). If all calls to the function can be inlined, you can avoid +emitting the function by compiling with @option{-fno-implement-inlines}. +If any calls were not inlined, you will get linker errors. + +@node Template Instantiation +@section Where's the Template? + +@cindex template instantiation + +C++ templates are the first language feature to require more +intelligence from the environment than one usually finds on a UNIX +system. Somehow the compiler and linker have to make sure that each +template instance occurs exactly once in the executable if it is needed, +and not at all otherwise. There are two basic approaches to this +problem, which I will refer to as the Borland model and the Cfront model. + +@table @asis +@item Borland model +Borland C++ solved the template instantiation problem by adding the code +equivalent of common blocks to their linker; the compiler emits template +instances in each translation unit that uses them, and the linker +collapses them together. The advantage of this model is that the linker +only has to consider the object files themselves; there is no external +complexity to worry about. This disadvantage is that compilation time +is increased because the template code is being compiled repeatedly. +Code written for this model tends to include definitions of all +templates in the header file, since they must be seen to be +instantiated. + +@item Cfront model +The AT&T C++ translator, Cfront, solved the template instantiation +problem by creating the notion of a template repository, an +automatically maintained place where template instances are stored. A +more modern version of the repository works as follows: As individual +object files are built, the compiler places any template definitions and +instantiations encountered in the repository. At link time, the link +wrapper adds in the objects in the repository and compiles any needed +instances that were not previously emitted. The advantages of this +model are more optimal compilation speed and the ability to use the +system linker; to implement the Borland model a compiler vendor also +needs to replace the linker. The disadvantages are vastly increased +complexity, and thus potential for error; for some code this can be +just as transparent, but in practice it can been very difficult to build +multiple programs in one directory and one program in multiple +directories. Code written for this model tends to separate definitions +of non-inline member templates into a separate file, which should be +compiled separately. +@end table + +When used with GNU ld version 2.8 or later on an ELF system such as +Linux/GNU or Solaris 2, or on Microsoft Windows, g++ supports the +Borland model. On other systems, g++ implements neither automatic +model. + +A future version of g++ will support a hybrid model whereby the compiler +will emit any instantiations for which the template definition is +included in the compile, and store template definitions and +instantiation context information into the object file for the rest. +The link wrapper will extract that information as necessary and invoke +the compiler to produce the remaining instantiations. The linker will +then combine duplicate instantiations. + +In the mean time, you have the following options for dealing with +template instantiations: + +@enumerate +@item +@opindex frepo +Compile your template-using code with @option{-frepo}. The compiler will +generate files with the extension @samp{.rpo} listing all of the +template instantiations used in the corresponding object files which +could be instantiated there; the link wrapper, @samp{collect2}, will +then update the @samp{.rpo} files to tell the compiler where to place +those instantiations and rebuild any affected object files. The +link-time overhead is negligible after the first pass, as the compiler +will continue to place the instantiations in the same files. + +This is your best option for application code written for the Borland +model, as it will just work. Code written for the Cfront model will +need to be modified so that the template definitions are available at +one or more points of instantiation; usually this is as simple as adding +@code{#include } to the end of each template header. + +For library code, if you want the library to provide all of the template +instantiations it needs, just try to link all of its object files +together; the link will fail, but cause the instantiations to be +generated as a side effect. Be warned, however, that this may cause +conflicts if multiple libraries try to provide the same instantiations. +For greater control, use explicit instantiation as described in the next +option. + +@item +@opindex fno-implicit-templates +Compile your code with @option{-fno-implicit-templates} to disable the +implicit generation of template instances, and explicitly instantiate +all the ones you use. This approach requires more knowledge of exactly +which instances you need than do the others, but it's less +mysterious and allows greater control. You can scatter the explicit +instantiations throughout your program, perhaps putting them in the +translation units where the instances are used or the translation units +that define the templates themselves; you can put all of the explicit +instantiations you need into one big file; or you can create small files +like + +@example +#include "Foo.h" +#include "Foo.cc" + +template class Foo; +template ostream& operator << + (ostream&, const Foo&); +@end example + +for each of the instances you need, and create a template instantiation +library from those. + +If you are using Cfront-model code, you can probably get away with not +using @option{-fno-implicit-templates} when compiling files that don't +@samp{#include} the member template definitions. + +If you use one big file to do the instantiations, you may want to +compile it without @option{-fno-implicit-templates} so you get all of the +instances required by your explicit instantiations (but not by any +other files) without having to specify them as well. + +g++ has extended the template instantiation syntax outlined in the +Working Paper to allow forward declaration of explicit instantiations +(with @code{extern}), instantiation of the compiler support data for a +template class (i.e.@: the vtable) without instantiating any of its +members (with @code{inline}), and instantiation of only the static data +members of a template class, without the support data or member +functions (with (@code{static}): + +@example +extern template int max (int, int); +inline template class Foo; +static template class Foo; +@end example + +@item +Do nothing. Pretend g++ does implement automatic instantiation +management. Code written for the Borland model will work fine, but +each translation unit will contain instances of each of the templates it +uses. In a large program, this can lead to an unacceptable amount of code +duplication. + +@item +@opindex fexternal-templates +Add @samp{#pragma interface} to all files containing template +definitions. For each of these files, add @samp{#pragma implementation +"@var{filename}"} to the top of some @samp{.C} file which +@samp{#include}s it. Then compile everything with +@option{-fexternal-templates}. The templates will then only be expanded +in the translation unit which implements them (i.e.@: has a @samp{#pragma +implementation} line for the file where they live); all other files will +use external references. If you're lucky, everything should work +properly. If you get undefined symbol errors, you need to make sure +that each template instance which is used in the program is used in the +file which implements that template. If you don't have any use for a +particular instance in that file, you can just instantiate it +explicitly, using the syntax from the latest C++ working paper: + +@example +template class A; +template ostream& operator << (ostream&, const A&); +@end example + +This strategy will work with code written for either model. If you are +using code written for the Cfront model, the file containing a class +template and the file containing its member templates should be +implemented in the same translation unit. + +@item +@opindex falt-external-templates +A slight variation on this approach is to use the flag +@option{-falt-external-templates} instead. This flag causes template +instances to be emitted in the translation unit that implements the +header where they are first instantiated, rather than the one which +implements the file where the templates are defined. This header must +be the same in all translation units, or things are likely to break. + +@xref{C++ Interface,,Declarations and Definitions in One Header}, for +more discussion of these pragmas. +@end enumerate + +@node Bound member functions +@section Extracting the function pointer from a bound pointer to member function + +@cindex pmf +@cindex pointer to member function +@cindex bound pointer to member function + +In C++, pointer to member functions (PMFs) are implemented using a wide +pointer of sorts to handle all the possible call mechanisms; the PMF +needs to store information about how to adjust the @samp{this} pointer, +and if the function pointed to is virtual, where to find the vtable, and +where in the vtable to look for the member function. If you are using +PMFs in an inner loop, you should really reconsider that decision. If +that is not an option, you can extract the pointer to the function that +would be called for a given object/PMF pair and call it directly inside +the inner loop, to save a bit of time. + +Note that you will still be paying the penalty for the call through a +function pointer; on most modern architectures, such a call defeats the +branch prediction features of the CPU@. This is also true of normal +virtual function calls. + +The syntax for this extension is + +@example +extern A a; +extern int (A::*fp)(); +typedef int (*fptr)(A *); + +fptr p = (fptr)(a.*fp); +@end example + +For PMF constants (i.e.@: expressions of the form @samp{&Klasse::Member}), +no object is needed to obtain the address of the function. They can be +converted to function pointers directly: + +@example +fptr p1 = (fptr)(&A::foo); +@end example + +@opindex Wno-pmf-conversions +You must specify @option{-Wno-pmf-conversions} to use this extension. + +@node C++ Attributes +@section C++-Specific Variable, Function, and Type Attributes + +Some attributes only make sense for C++ programs. + +@table @code +@item init_priority (@var{priority}) +@cindex init_priority attribute + + +In Standard C++, objects defined at namespace scope are guaranteed to be +initialized in an order in strict accordance with that of their definitions +@emph{in a given translation unit}. No guarantee is made for initializations +across translation units. However, GNU C++ allows users to control the +order of initialization of objects defined at namespace scope with the +@code{init_priority} attribute by specifying a relative @var{priority}, +a constant integral expression currently bounded between 101 and 65535 +inclusive. Lower numbers indicate a higher priority. + +In the following example, @code{A} would normally be created before +@code{B}, but the @code{init_priority} attribute has reversed that order: + +@example +Some_Class A __attribute__ ((init_priority (2000))); +Some_Class B __attribute__ ((init_priority (543))); +@end example + +@noindent +Note that the particular values of @var{priority} do not matter; only their +relative ordering. + +@item java_interface +@cindex java_interface attribute + +This type attribute informs C++ that the class is a Java interface. It may +only be applied to classes declared within an @code{extern "Java"} block. +Calls to methods declared in this interface will be dispatched using GCJ's +interface table mechanism, instead of regular virtual table dispatch. + +@end table + +@node Java Exceptions +@section Java Exceptions + +The Java language uses a slightly different exception handling model +from C++. Normally, GNU C++ will automatically detect when you are +writing C++ code that uses Java exceptions, and handle them +appropriately. However, if C++ code only needs to execute destructors +when Java exceptions are thrown through it, GCC will guess incorrectly. +Sample problematic code is: + +@example + struct S @{ ~S(); @}; + extern void bar(); // is written in Java, and may throw exceptions + void foo() + @{ + S s; + bar(); + @} +@end example + +@noindent +The usual effect of an incorrect guess is a link failure, complaining of +a missing routine called @samp{__gxx_personality_v0}. + +You can inform the compiler that Java exceptions are to be used in a +translation unit, irrespective of what it might think, by writing +@samp{@w{#pragma GCC java_exceptions}} at the head of the file. This +@samp{#pragma} must appear before any functions that throw or catch +exceptions, or run destructors when exceptions are thrown through them. + +You cannot mix Java and C++ exceptions in the same translation unit. It +is believed to be safe to throw a C++ exception from one file through +another file compiled for the Java exception model, or vice versa, but +there may be bugs in this area. + +@node Deprecated Features +@section Deprecated Features + +In the past, the GNU C++ compiler was extended to experiment with new +features, at a time when the C++ language was still evolving. Now that +the C++ standard is complete, some of those features are superseded by +superior alternatives. Using the old features might cause a warning in +some cases that the feature will be dropped in the future. In other +cases, the feature might be gone already. + +While the list below is not exhaustive, it documents some of the options +that are now deprecated: + +@table @code +@item -fexternal-templates +@itemx -falt-external-templates +These are two of the many ways for g++ to implement template +instantiation. @xref{Template Instantiation}. The C++ standard clearly +defines how template definitions have to be organized across +implementation units. g++ has an implicit instantiation mechanism that +should work just fine for standard-conforming code. + +@item -fstrict-prototype +@itemx -fno-strict-prototype +Previously it was possible to use an empty prototype parameter list to +indicate an unspecified number of parameters (like C), rather than no +parameters, as C++ demands. This feature has been removed, except where +it is required for backwards compatibility @xref{Backwards Compatibility}. +@end table + +The named return value extension has been deprecated, and is now +removed from g++. + +The use of initializer lists with new expressions has been deprecated, +and is now removed from g++. + +Floating and complex non-type template parameters have been deprecated, +and are now removed from g++. + +The implicit typename extension has been deprecated and will be removed +from g++ at some point. In some cases g++ determines that a dependant +type such as @code{TPL::X} is a type without needing a +@code{typename} keyword, contrary to the standard. + +@node Backwards Compatibility +@section Backwards Compatibility +@cindex Backwards Compatibility +@cindex ARM [Annotated C++ Reference Manual] + +Now that there is a definitive ISO standard C++, G++ has a specification +to adhere to. The C++ language evolved over time, and features that +used to be acceptable in previous drafts of the standard, such as the ARM +[Annotated C++ Reference Manual], are no longer accepted. In order to allow +compilation of C++ written to such drafts, G++ contains some backwards +compatibilities. @emph{All such backwards compatibility features are +liable to disappear in future versions of G++.} They should be considered +deprecated @xref{Deprecated Features}. + +@table @code +@item For scope +If a variable is declared at for scope, it used to remain in scope until +the end of the scope which contained the for statement (rather than just +within the for scope). G++ retains this, but issues a warning, if such a +variable is accessed outside the for scope. + +@item Implicit C language +Old C system header files did not contain an @code{extern "C" @{@dots{}@}} +scope to set the language. On such systems, all header files are +implicitly scoped inside a C language scope. Also, an empty prototype +@code{()} will be treated as an unspecified number of arguments, rather +than no arguments, as C++ demands. +@end table diff --git a/contrib/gcc/doc/fragments.texi b/contrib/gcc/doc/fragments.texi new file mode 100644 index 000000000000..f9ef3d22b82f --- /dev/null +++ b/contrib/gcc/doc/fragments.texi @@ -0,0 +1,190 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Fragments +@chapter Makefile Fragments +@cindex makefile fragment + +When you configure GCC using the @file{configure} script, it will +construct the file @file{Makefile} from the template file +@file{Makefile.in}. When it does this, it can incorporate makefile +fragments from the @file{config} directory. These are used to set +Makefile parameters that are not amenable to being calculated by +autoconf. The list of fragments to incorporate is set by +@file{config.gcc}; @xref{System Config}. + +Fragments are named either @file{t-@var{target}} or @file{x-@var{host}}, +depending on whether they are relevant to configuring GCC to produce +code for a particular target, or to configuring GCC to run on a +particular host. Here @var{target} and @var{host} are mnemonics +which usually have some relationship to the canonical system name, but +no formal connection. + +If these files do not exist, it means nothing needs to be added for a +given target or host. Most targets need a few @file{t-@var{target}} +fragments, but needing @file{x-@var{host}} fragments is rare. + +@menu +* Target Fragment:: Writing @file{t-@var{target}} files. +* Host Fragment:: Writing @file{x-@var{host}} files. +@end menu + +@node Target Fragment +@section Target Makefile Fragments +@cindex target makefile fragment +@cindex @file{t-@var{target}} + +Target makefile fragments can set these Makefile variables. + +@table @code +@findex LIBGCC2_CFLAGS +@item LIBGCC2_CFLAGS +Compiler flags to use when compiling @file{libgcc2.c}. + +@findex LIB2FUNCS_EXTRA +@item LIB2FUNCS_EXTRA +A list of source file names to be compiled or assembled and inserted +into @file{libgcc.a}. + +@findex Floating Point Emulation +@item Floating Point Emulation +To have GCC include software floating point libraries in @file{libgcc.a} +define @code{FPBIT} and @code{DPBIT} along with a few rules as follows: +@smallexample +# We want fine grained libraries, so use the new code +# to build the floating point emulation libraries. +FPBIT = fp-bit.c +DPBIT = dp-bit.c + + +fp-bit.c: $(srcdir)/config/fp-bit.c + echo '#define FLOAT' > fp-bit.c + cat $(srcdir)/config/fp-bit.c >> fp-bit.c + +dp-bit.c: $(srcdir)/config/fp-bit.c + cat $(srcdir)/config/fp-bit.c > dp-bit.c +@end smallexample + +You may need to provide additional #defines at the beginning of @file{fp-bit.c} +and @file{dp-bit.c} to control target endianness and other options. + + +@findex CRTSTUFF_T_CFLAGS +@item CRTSTUFF_T_CFLAGS +Special flags used when compiling @file{crtstuff.c}. +@xref{Initialization}. + +@findex CRTSTUFF_T_CFLAGS_S +@item CRTSTUFF_T_CFLAGS_S +Special flags used when compiling @file{crtstuff.c} for shared +linking. Used if you use @file{crtbeginS.o} and @file{crtendS.o} +in @code{EXTRA-PARTS}. +@xref{Initialization}. + +@findex MULTILIB_OPTIONS +@item MULTILIB_OPTIONS +For some targets, invoking GCC in different ways produces objects +that can not be linked together. For example, for some targets GCC +produces both big and little endian code. For these targets, you must +arrange for multiple versions of @file{libgcc.a} to be compiled, one for +each set of incompatible options. When GCC invokes the linker, it +arranges to link in the right version of @file{libgcc.a}, based on +the command line options used. + +The @code{MULTILIB_OPTIONS} macro lists the set of options for which +special versions of @file{libgcc.a} must be built. Write options that +are mutually incompatible side by side, separated by a slash. Write +options that may be used together separated by a space. The build +procedure will build all combinations of compatible options. + +For example, if you set @code{MULTILIB_OPTIONS} to @samp{m68000/m68020 +msoft-float}, @file{Makefile} will build special versions of +@file{libgcc.a} using the following sets of options: @option{-m68000}, +@option{-m68020}, @option{-msoft-float}, @samp{-m68000 -msoft-float}, and +@samp{-m68020 -msoft-float}. + +@findex MULTILIB_DIRNAMES +@item MULTILIB_DIRNAMES +If @code{MULTILIB_OPTIONS} is used, this variable specifies the +directory names that should be used to hold the various libraries. +Write one element in @code{MULTILIB_DIRNAMES} for each element in +@code{MULTILIB_OPTIONS}. If @code{MULTILIB_DIRNAMES} is not used, the +default value will be @code{MULTILIB_OPTIONS}, with all slashes treated +as spaces. + +For example, if @code{MULTILIB_OPTIONS} is set to @samp{m68000/m68020 +msoft-float}, then the default value of @code{MULTILIB_DIRNAMES} is +@samp{m68000 m68020 msoft-float}. You may specify a different value if +you desire a different set of directory names. + +@findex MULTILIB_MATCHES +@item MULTILIB_MATCHES +Sometimes the same option may be written in two different ways. If an +option is listed in @code{MULTILIB_OPTIONS}, GCC needs to know about +any synonyms. In that case, set @code{MULTILIB_MATCHES} to a list of +items of the form @samp{option=option} to describe all relevant +synonyms. For example, @samp{m68000=mc68000 m68020=mc68020}. + +@findex MULTILIB_EXCEPTIONS +@item MULTILIB_EXCEPTIONS +Sometimes when there are multiple sets of @code{MULTILIB_OPTIONS} being +specified, there are combinations that should not be built. In that +case, set @code{MULTILIB_EXCEPTIONS} to be all of the switch exceptions +in shell case syntax that should not be built. + +For example, in the PowerPC embedded ABI support, it is not desirable +to build libraries compiled with the @option{-mcall-aix} option +and either of the @option{-fleading-underscore} or @option{-mlittle} options +at the same time. Therefore @code{MULTILIB_EXCEPTIONS} is set to +@smallexample +*mcall-aix/*fleading-underscore* *mlittle/*mcall-aix* +@end smallexample + +@findex MULTILIB_EXTRA_OPTS +@item MULTILIB_EXTRA_OPTS +Sometimes it is desirable that when building multiple versions of +@file{libgcc.a} certain options should always be passed on to the +compiler. In that case, set @code{MULTILIB_EXTRA_OPTS} to be the list +of options to be used for all builds. +@end table + +@node Host Fragment +@section Host Makefile Fragments +@cindex host makefile fragment +@cindex @file{x-@var{host}} + +The use of @file{x-@var{host}} fragments is discouraged. You should do +so only if there is no other mechanism to get the behavior desired. +Host fragments should never forcibly override variables set by the +configure script, as they may have been adjusted by the user. + +Variables provided for host fragments to set include: + +@table @code + +@item X_CFLAGS +@itemx X_CPPFLAGS +These are extra flags to pass to the C compiler and preprocessor, +respectively. They are used both when building GCC, and when compiling +things with the just-built GCC. + +@item XCFLAGS +These are extra flags to use when building the compiler. They are not +used when compiling @file{libgcc.a}. However, they @emph{are} used when +recompiling the compiler with itself in later stages of a bootstrap. + +@item BOOT_LDFLAGS +Flags to be passed to the linker when recompiling the compiler with +itself in later stages of a bootstrap. You might need to use this if, +for instance, one of the front ends needs more text space than the +linker provides by default. + +@item EXTRA_PROGRAMS +A list of additional programs required to use the compiler on this host, +which should be compiled with GCC and installed alongside the front +ends. If you set this variable, you must also provide rules to build +the extra programs. + +@end table diff --git a/contrib/gcc/doc/frontends.texi b/contrib/gcc/doc/frontends.texi new file mode 100644 index 000000000000..ffaa9aa6fe8f --- /dev/null +++ b/contrib/gcc/doc/frontends.texi @@ -0,0 +1,70 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node G++ and GCC +@chapter Compile C, C++, Objective-C, Ada, CHILL, Fortran, or Java + +@cindex Objective-C +@cindex Fortran +@cindex Java +@cindex CHILL +@cindex Ada +Several versions of the compiler (C, C++, Objective-C, Ada, CHILL, +Fortran, and Java) are integrated; this is why we use the name +``GNU Compiler Collection''. GCC can compile programs written in any of these +languages. The Ada, CHILL, Fortran, and Java compilers are described in +separate manuals. + +@cindex GCC +``GCC'' is a common shorthand term for the GNU Compiler Collection. This is both +the most general name for the compiler, and the name used when the +emphasis is on compiling C programs (as the abbreviation formerly +stood for ``GNU C Compiler''). + +@cindex C++ +@cindex G++ +When referring to C++ compilation, it is usual to call the compiler +``G++''. Since there is only one compiler, it is also accurate to call +it ``GCC'' no matter what the language context; however, the term +``G++'' is more useful when the emphasis is on compiling C++ programs. + +@cindex Ada +@cindex GNAT +Similarly, when we talk about Ada compilation, we usually call the +compiler ``GNAT'', for the same reasons. + +We use the name ``GCC'' to refer to the compilation system as a +whole, and more specifically to the language-independent part of the +compiler. For example, we refer to the optimization options as +affecting the behavior of ``GCC'' or sometimes just ``the compiler''. + +Front ends for other languages, such as Mercury and Pascal exist but +have not yet been integrated into GCC@. These front ends, like that for C++, +are built in subdirectories of GCC and link to it. The result is an +integrated compiler that can compile programs written in C, C++, +Objective-C, or any of the languages for which you have installed front +ends. + +In this manual, we only discuss the options for the C, Objective-C, and +C++ compilers and those of the GCC core. Consult the documentation +of the other front ends for the options to use when compiling programs +written in other languages. + +@cindex compiler compared to C++ preprocessor +@cindex intermediate C version, nonexistent +@cindex C intermediate output, nonexistent +G++ is a @emph{compiler}, not merely a preprocessor. G++ builds object +code directly from your C++ program source. There is no intermediate C +version of the program. (By contrast, for example, some other +implementations use a program that generates a C program from your C++ +source.) Avoiding an intermediate C representation of the program means +that you get better object code, and better debugging information. The +GNU debugger, GDB, works with this information in the object code to +give you comprehensive C++ source-level editing capabilities +(@pxref{C,,C and C++,gdb.info, Debugging with GDB}). + +@c FIXME! Someone who knows something about Objective-C ought to put in +@c a paragraph or two about it here, and move the index entry down when +@c there is more to point to than the general mention in the 1st par. diff --git a/contrib/gcc/doc/gcc.texi b/contrib/gcc/doc/gcc.texi new file mode 100644 index 000000000000..d8579e7aa3e8 --- /dev/null +++ b/contrib/gcc/doc/gcc.texi @@ -0,0 +1,234 @@ +\input texinfo @c -*-texinfo-*- +@c %**start of header +@setfilename gcc.info +@c INTERNALS is used by md.texi to determine whether to include the +@c whole of that file, in the internals manual, or only the part +@c dealing with constraints, in the user manual. +@clear INTERNALS + +@c NOTE: checks/things to do: +@c +@c -have bob do a search in all seven files for "mew" (ideally --mew, +@c but i may have forgotten the occasional "--"..). +@c Just checked... all have `--'! Bob 22Jul96 +@c Use this to search: grep -n '\-\-mew' *.texi +@c -item/itemx, text after all (sub/sub)section titles, etc.. +@c -consider putting the lists of options on pp 17--> etc in columns or +@c some such. +@c -overfulls. do a search for "mew" in the files, and you will see +@c overfulls that i noted but could not deal with. +@c -have to add text: beginning of chapter 8 + +@c +@c anything else? --mew 10feb93 + +@include gcc-common.texi + +@settitle Using the GNU Compiler Collection (GCC) + +@c Create a separate index for command line options. +@defcodeindex op +@c Merge the standard indexes into a single one. +@syncodeindex fn cp +@syncodeindex vr cp +@syncodeindex ky cp +@syncodeindex pg cp +@syncodeindex tp cp + +@c %**end of header + +@c Use with @@smallbook. + +@c Cause even numbered pages to be printed on the left hand side of +@c the page and odd numbered pages to be printed on the right hand +@c side of the page. Using this, you can print on both sides of a +@c sheet of paper and have the text on the same part of the sheet. + +@c The text on right hand pages is pushed towards the right hand +@c margin and the text on left hand pages is pushed toward the left +@c hand margin. +@c (To provide the reverse effect, set bindingoffset to -0.75in.) + +@c @tex +@c \global\bindingoffset=0.75in +@c \global\normaloffset =0.75in +@c @end tex + +@c Change the font used for @def... commands, since the default +@c proportional one used is bad for names starting __. +@tex +\global\setfont\defbf\ttbshape{10}{\magstep1} +@end tex + +@macro copyrightnotice +Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +1999, 2000, 2001, 2002 Free Software Foundation, Inc. +@end macro +@ifnottex +@dircategory Programming +@direntry +* gcc: (gcc). The GNU Compiler Collection. +@end direntry +This file documents the use of the GNU compilers. +@sp 1 +Published by the Free Software Foundation@* +59 Temple Place - Suite 330@* +Boston, MA 02111-1307 USA +@sp 1 +@copyrightnotice{} +@sp 1 +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'' and ``Funding +Free Software'', the Front-Cover texts being (a) (see below), and with +the Back-Cover Texts being (b) (see below). A copy of the license is +included in the section entitled ``GNU Free Documentation License''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end ifnottex + +@setchapternewpage odd +@titlepage +@center @titlefont{Using the GNU Compiler Collection} +@sp 2 +@center Richard M. Stallman +@sp 3 +@center Last updated 7 January 2002 +@sp 1 + +@center for GCC @value{version-GCC} +@page +@vskip 0pt plus 1filll +@copyrightnotice{} +@sp 2 +For GCC Version @value{version-GCC}@* +@sp 1 +Published by the Free Software Foundation @* +59 Temple Place---Suite 330@* +Boston, MA 02111-1307, USA@* +Last printed April, 1998.@* +Printed copies are available for $50 each.@* +@c Update this ISBN when printing a new edition. +@ifset FSFPRINT +ISBN 1-882114-37-X +@end ifset +@sp 1 +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'', the Front-Cover +texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end titlepage +@summarycontents +@contents +@page + +@node Top, G++ and GCC,, (DIR) +@top Introduction +@cindex introduction + +This manual documents how to use the GNU compilers, +as well as their features and incompatibilities, and how to report +bugs. It corresponds to GCC version @value{version-GCC}. +The internals of the GNU compilers, including how to port them to new +targets and some information about how to write front ends for new +languages, are documented in a separate manual. @xref{Top,, +Introduction, gccint, GNU Compiler Collection (GCC) Internals}. + +@menu +* G++ and GCC:: You can compile C or C++ programs. +* Standards:: Language standards supported by GCC. +* Invoking GCC:: Command options supported by @samp{gcc}. +* C Implementation:: How GCC implements the ISO C specification. +* C Extensions:: GNU extensions to the C language family. +* C++ Extensions:: GNU extensions to the C++ language. +* Objective-C:: GNU Objective-C runtime features. +* Gcov:: gcov: a GCC test coverage program. +* Trouble:: If you have trouble using GCC. +* Bugs:: How, why and where to report bugs. +* Service:: How to find suppliers of support for GCC. +* Contributing:: How to contribute to testing and developing GCC. +* VMS:: Using GCC on VMS. + +* Funding:: How to help assure funding for free software. +* GNU Project:: The GNU Project and GNU/Linux. + +* Copying:: GNU General Public License says + how you can copy and share GCC. +* GNU Free Documentation License:: How you can copy and share this manual. +* Contributors:: People who have contributed to GCC. + +* Option Index:: Index to command line options. +* Index:: Index of concepts and symbol names. +@end menu + +@include frontends.texi +@include standards.texi +@include invoke.texi +@include extend.texi +@include objc.texi +@include gcov.texi +@include trouble.texi +@include bugreport.texi +@include service.texi +@include contribute.texi +@include vms.texi + +@include funding.texi +@include gnu.texi +@include gpl.texi + +@c --------------------------------------------------------------------- +@c GFDL +@c --------------------------------------------------------------------- + +@include fdl.texi + +@include contrib.texi + +@c --------------------------------------------------------------------- +@c Indexes +@c --------------------------------------------------------------------- + +@node Option Index +@unnumbered Option Index + +GCC's command line options are indexed here without any initial @samp{-} +or @samp{--}. Where an option has both positive and negative forms +(such as @option{-f@var{option}} and @option{-fno-@var{option}}), +relevant entries in the manual are indexed under the most appropriate +form; it may sometimes be useful to look up both forms. + +@printindex op + +@node Index +@unnumbered Index + +@printindex cp + +@c --------------------------------------------------------------------- +@c Epilogue +@c --------------------------------------------------------------------- + +@bye diff --git a/contrib/gcc/doc/gccint.texi b/contrib/gcc/doc/gccint.texi new file mode 100644 index 000000000000..82a7d317a40b --- /dev/null +++ b/contrib/gcc/doc/gccint.texi @@ -0,0 +1,236 @@ +\input texinfo @c -*-texinfo-*- +@c %**start of header +@setfilename gccint.info +@c INTERNALS is used by md.texi to determine whether to include the +@c whole of that file, in the internals manual, or only the part +@c dealing with constraints, in the user manual. +@set INTERNALS + +@c See miscellaneous notes in gcc.texi on checks/things to do. + +@include gcc-common.texi + +@settitle GNU Compiler Collection (GCC) Internals + +@c Create a separate index for command line options. +@defcodeindex op +@c Merge the standard indexes into a single one. +@syncodeindex fn cp +@syncodeindex vr cp +@syncodeindex ky cp +@syncodeindex pg cp +@syncodeindex tp cp + +@c %**end of header + +@c Use with @@smallbook. + +@c Cause even numbered pages to be printed on the left hand side of +@c the page and odd numbered pages to be printed on the right hand +@c side of the page. Using this, you can print on both sides of a +@c sheet of paper and have the text on the same part of the sheet. + +@c The text on right hand pages is pushed towards the right hand +@c margin and the text on left hand pages is pushed toward the left +@c hand margin. +@c (To provide the reverse effect, set bindingoffset to -0.75in.) + +@c @tex +@c \global\bindingoffset=0.75in +@c \global\normaloffset =0.75in +@c @end tex + +@c Change the font used for @def... commands, since the default +@c proportional one used is bad for names starting __. +@tex +\global\setfont\defbf\ttbshape{10}{\magstep1} +@end tex + +@macro copyrightnotice +Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +1999, 2000, 2001, 2002 Free Software Foundation, Inc. +@end macro +@ifnottex +@dircategory Programming +@direntry +* gccint: (gccint). Internals of the GNU Compiler Collection. +@end direntry +This file documents the internals of the GNU compilers. +@sp 1 +Published by the Free Software Foundation@* +59 Temple Place - Suite 330@* +Boston, MA 02111-1307 USA +@sp 1 +@copyrightnotice{} +@sp 1 +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'' and ``Funding +Free Software'', the Front-Cover texts being (a) (see below), and with +the Back-Cover Texts being (b) (see below). A copy of the license is +included in the section entitled ``GNU Free Documentation License''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end ifnottex + +@setchapternewpage odd +@titlepage +@center @titlefont{GNU Compiler Collection Internals} +@sp 2 +@center Richard M. Stallman +@sp 3 +@center Last updated 10 January 2002 +@sp 1 + +@center for GCC @value{version-GCC} +@page +@vskip 0pt plus 1filll +@copyrightnotice{} +@sp 2 +For GCC Version @value{version-GCC}@* +@sp 1 +Published by the Free Software Foundation @* +59 Temple Place---Suite 330@* +Boston, MA 02111-1307, USA@* +Last printed April, 1998.@* +Printed copies are available for $50 each.@* +@c Update this ISBN when printing a new edition. +@ifset FSFPRINT +ISBN 1-882114-37-X +@end ifset +@sp 1 +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'', the Front-Cover +texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end titlepage +@summarycontents +@contents +@page + +@node Top, Contributing,, (DIR) +@top Introduction +@cindex introduction + +This manual documents the internals of the GNU compilers, including +how to port them to new targets and some information about how to +write front ends for new languages. It corresponds to GCC version +@value{version-GCC}. The use of the GNU compilers is documented in a +separate manual. @xref{Top,, Introduction, gcc, Using the GNU +Compiler Collection (GCC)}. + +This manual is mainly a reference manual rather than a tutorial. It +discusses how to contribute to GCC (@pxref{Contributing}), the +characteristics of the machines supported by GCC as hosts and targets +(@pxref{Portability}), how GCC relates to the ABIs on such systems +(@pxref{Interface}), and the characteristics of the languages for +which GCC front ends are written (@pxref{Languages}). It then +describes the GCC source tree structure and build system, some of the +interfaces to GCC front ends, and how support for a target system is +implemented in GCC@. + +Additional tutorial information is linked to from +@uref{http://gcc.gnu.org/readings.html}. + +@menu +* Contributing:: How to contribute to testing and developing GCC. +* Portability:: Goals of GCC's portability features. +* Interface:: Function-call interface of GCC output. +* Languages:: Languages for which GCC front ends are written. +* Source Tree:: GCC source tree structure and build system. +* Passes:: Order of passes, what they do, and what each file is for. +* Trees:: The source representation used by the C and C++ front ends. +* RTL:: The intermediate representation that most passes work on. +* Machine Desc:: How to write machine description instruction patterns. +* Target Macros:: How to write the machine description C macros and functions. +* Host Config:: Writing the @file{xm-@var{machine}.h} file. +* Fragments:: Writing the @file{t-@var{target}} and @file{x-@var{host}} files. +* Collect2:: How @code{collect2} works; how it finds @code{ld}. +* Header Dirs:: Understanding the standard header file directories. + +* Funding:: How to help assure funding for free software. +* GNU Project:: The GNU Project and GNU/Linux. + +* Copying:: GNU General Public License says + how you can copy and share GCC. +* GNU Free Documentation License:: How you can copy and share this manual. +* Contributors:: People who have contributed to GCC. + +* Option Index:: Index to command line options. +* Index:: Index of concepts and symbol names. +@end menu + +@include contribute.texi +@include portability.texi +@include interface.texi +@include languages.texi +@include sourcebuild.texi +@include passes.texi +@include c-tree.texi +@include rtl.texi +@include md.texi +@include tm.texi +@include hostconfig.texi +@include fragments.texi +@include collect2.texi +@include headerdirs.texi + +@include funding.texi +@include gnu.texi +@include gpl.texi + +@c --------------------------------------------------------------------- +@c GFDL +@c --------------------------------------------------------------------- + +@include fdl.texi + +@include contrib.texi + +@c --------------------------------------------------------------------- +@c Indexes +@c --------------------------------------------------------------------- + +@node Option Index +@unnumbered Option Index + +GCC's command line options are indexed here without any initial @samp{-} +or @samp{--}. Where an option has both positive and negative forms +(such as @option{-f@var{option}} and @option{-fno-@var{option}}), +relevant entries in the manual are indexed under the most appropriate +form; it may sometimes be useful to look up both forms. + +@printindex op + +@node Index +@unnumbered Index + +@printindex cp + +@c --------------------------------------------------------------------- +@c Epilogue +@c --------------------------------------------------------------------- + +@bye diff --git a/contrib/gcc/doc/gcov.texi b/contrib/gcc/doc/gcov.texi new file mode 100644 index 000000000000..86b64e0e8e55 --- /dev/null +++ b/contrib/gcc/doc/gcov.texi @@ -0,0 +1,406 @@ +@c Copyright (C) 1996, 1997, 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@ignore +@c man begin COPYRIGHT +Copyright @copyright{} 1996, 1997, 1999, 2000, 2001 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'' and ``Funding +Free Software'', the Front-Cover texts being (a) (see below), and with +the Back-Cover Texts being (b) (see below). A copy of the license is +included in the gfdl(7) man page. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@c Set file name and title for the man page. +@setfilename gcov +@settitle coverage testing tool +@end ignore + +@node Gcov +@chapter @command{gcov}: a Test Coverage Program + +@command{gcov} is a tool you can use in conjunction with GCC to +test code coverage in your programs. + +@menu +* Gcov Intro:: Introduction to gcov. +* Invoking Gcov:: How to use gcov. +* Gcov and Optimization:: Using gcov with GCC optimization. +* Gcov Data Files:: The files used by gcov. +@end menu + +@node Gcov Intro +@section Introduction to @command{gcov} +@c man begin DESCRIPTION + +@command{gcov} is a test coverage program. Use it in concert with GCC +to analyze your programs to help create more efficient, faster +running code. You can use @command{gcov} as a profiling tool to help +discover where your optimization efforts will best affect your code. You +can also use @command{gcov} along with the other profiling tool, +@command{gprof}, to assess which parts of your code use the greatest amount +of computing time. + +Profiling tools help you analyze your code's performance. Using a +profiler such as @command{gcov} or @command{gprof}, you can find out some +basic performance statistics, such as: + +@itemize @bullet +@item +how often each line of code executes + +@item +what lines of code are actually executed + +@item +how much computing time each section of code uses +@end itemize + +Once you know these things about how your code works when compiled, you +can look at each module to see which modules should be optimized. +@command{gcov} helps you determine where to work on optimization. + +Software developers also use coverage testing in concert with +testsuites, to make sure software is actually good enough for a release. +Testsuites can verify that a program works as expected; a coverage +program tests to see how much of the program is exercised by the +testsuite. Developers can then determine what kinds of test cases need +to be added to the testsuites to create both better testing and a better +final product. + +You should compile your code without optimization if you plan to use +@command{gcov} because the optimization, by combining some lines of code +into one function, may not give you as much information as you need to +look for `hot spots' where the code is using a great deal of computer +time. Likewise, because @command{gcov} accumulates statistics by line (at +the lowest resolution), it works best with a programming style that +places only one statement on each line. If you use complicated macros +that expand to loops or to other control structures, the statistics are +less helpful---they only report on the line where the macro call +appears. If your complex macros behave like functions, you can replace +them with inline functions to solve this problem. + +@command{gcov} creates a logfile called @file{@var{sourcefile}.gcov} which +indicates how many times each line of a source file @file{@var{sourcefile}.c} +has executed. You can use these logfiles along with @command{gprof} to aid +in fine-tuning the performance of your programs. @command{gprof} gives +timing information you can use along with the information you get from +@command{gcov}. + +@command{gcov} works only on code compiled with GCC@. It is not +compatible with any other profiling or test coverage mechanism. + +@c man end + +@node Invoking Gcov +@section Invoking gcov + +@smallexample +gcov @r{[}@var{options}@r{]} @var{sourcefile} +@end smallexample + +@command{gcov} accepts the following options: + +@ignore +@c man begin SYNOPSIS +gcov [@option{-v}|@option{--version}] [@option{-h}|@option{--help}] + [@option{-b}|@option{--branch-probabilities}] [@option{-c}|@option{--branch-counts}] + [@option{-n}|@option{--no-output}] [@option{-l}|@option{--long-file-names}] + [@option{-f}|@option{--function-summaries}] + [@option{-o}|@option{--object-directory} @var{directory}] @var{sourcefile} +@c man end +@c man begin SEEALSO +gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry for @file{gcc}. +@c man end +@end ignore + +@c man begin OPTIONS +@table @gcctabopt +@item -h +@itemx --help +Display help about using @command{gcov} (on the standard output), and +exit without doing any further processing. + +@item -v +@itemx --version +Display the @command{gcov} version number (on the standard output), +and exit without doing any further processing. + +@item -b +@itemx --branch-probabilities +Write branch frequencies to the output file, and write branch summary +info to the standard output. This option allows you to see how often +each branch in your program was taken. + +@item -c +@itemx --branch-counts +Write branch frequencies as the number of branches taken, rather than +the percentage of branches taken. + +@item -n +@itemx --no-output +Do not create the @command{gcov} output file. + +@item -l +@itemx --long-file-names +Create long file names for included source files. For example, if the +header file @file{x.h} contains code, and was included in the file +@file{a.c}, then running @command{gcov} on the file @file{a.c} will produce +an output file called @file{a.c.x.h.gcov} instead of @file{x.h.gcov}. +This can be useful if @file{x.h} is included in multiple source files. + +@item -f +@itemx --function-summaries +Output summaries for each function in addition to the file level summary. + +@item -o @var{directory} +@itemx --object-directory @var{directory} +The directory where the object files live. Gcov will search for @file{.bb}, +@file{.bbg}, and @file{.da} files in this directory. +@end table + +@need 3000 +When using @command{gcov}, you must first compile your program with two +special GCC options: @samp{-fprofile-arcs -ftest-coverage}. +This tells the compiler to generate additional information needed by +gcov (basically a flow graph of the program) and also includes +additional code in the object files for generating the extra profiling +information needed by gcov. These additional files are placed in the +directory where the source code is located. + +Running the program will cause profile output to be generated. For each +source file compiled with @option{-fprofile-arcs}, an accompanying @file{.da} +file will be placed in the source directory. + +Running @command{gcov} with your program's source file names as arguments +will now produce a listing of the code along with frequency of execution +for each line. For example, if your program is called @file{tmp.c}, this +is what you see when you use the basic @command{gcov} facility: + +@smallexample +$ gcc -fprofile-arcs -ftest-coverage tmp.c +$ a.out +$ gcov tmp.c + 87.50% of 8 source lines executed in file tmp.c +Creating tmp.c.gcov. +@end smallexample + +The file @file{tmp.c.gcov} contains output from @command{gcov}. +Here is a sample: + +@smallexample + main() + @{ + 1 int i, total; + + 1 total = 0; + + 11 for (i = 0; i < 10; i++) + 10 total += i; + + 1 if (total != 45) + ###### printf ("Failure\n"); + else + 1 printf ("Success\n"); + 1 @} +@end smallexample + +@need 450 +When you use the @option{-b} option, your output looks like this: + +@smallexample +$ gcov -b tmp.c + 87.50% of 8 source lines executed in file tmp.c + 80.00% of 5 branches executed in file tmp.c + 80.00% of 5 branches taken at least once in file tmp.c + 50.00% of 2 calls executed in file tmp.c +Creating tmp.c.gcov. +@end smallexample + +Here is a sample of a resulting @file{tmp.c.gcov} file: + +@smallexample + main() + @{ + 1 int i, total; + + 1 total = 0; + + 11 for (i = 0; i < 10; i++) +branch 0 taken = 91% +branch 1 taken = 100% +branch 2 taken = 100% + 10 total += i; + + 1 if (total != 45) +branch 0 taken = 100% + ###### printf ("Failure\n"); +call 0 never executed +branch 1 never executed + else + 1 printf ("Success\n"); +call 0 returns = 100% + 1 @} +@end smallexample + +For each basic block, a line is printed after the last line of the basic +block describing the branch or call that ends the basic block. There can +be multiple branches and calls listed for a single source line if there +are multiple basic blocks that end on that line. In this case, the +branches and calls are each given a number. There is no simple way to map +these branches and calls back to source constructs. In general, though, +the lowest numbered branch or call will correspond to the leftmost construct +on the source line. + +For a branch, if it was executed at least once, then a percentage +indicating the number of times the branch was taken divided by the +number of times the branch was executed will be printed. Otherwise, the +message ``never executed'' is printed. + +For a call, if it was executed at least once, then a percentage +indicating the number of times the call returned divided by the number +of times the call was executed will be printed. This will usually be +100%, but may be less for functions call @code{exit} or @code{longjmp}, +and thus may not return every time they are called. + +The execution counts are cumulative. If the example program were +executed again without removing the @file{.da} file, the count for the +number of times each line in the source was executed would be added to +the results of the previous run(s). This is potentially useful in +several ways. For example, it could be used to accumulate data over a +number of program runs as part of a test verification suite, or to +provide more accurate long-term information over a large number of +program runs. + +The data in the @file{.da} files is saved immediately before the program +exits. For each source file compiled with @option{-fprofile-arcs}, the profiling +code first attempts to read in an existing @file{.da} file; if the file +doesn't match the executable (differing number of basic block counts) it +will ignore the contents of the file. It then adds in the new execution +counts and finally writes the data to the file. + +@node Gcov and Optimization +@section Using @command{gcov} with GCC Optimization + +If you plan to use @command{gcov} to help optimize your code, you must +first compile your program with two special GCC options: +@samp{-fprofile-arcs -ftest-coverage}. Aside from that, you can use any +other GCC options; but if you want to prove that every single line +in your program was executed, you should not compile with optimization +at the same time. On some machines the optimizer can eliminate some +simple code lines by combining them with other lines. For example, code +like this: + +@smallexample +if (a != b) + c = 1; +else + c = 0; +@end smallexample + +@noindent +can be compiled into one instruction on some machines. In this case, +there is no way for @command{gcov} to calculate separate execution counts +for each line because there isn't separate code for each line. Hence +the @command{gcov} output looks like this if you compiled the program with +optimization: + +@smallexample + 100 if (a != b) + 100 c = 1; + 100 else + 100 c = 0; +@end smallexample + +The output shows that this block of code, combined by optimization, +executed 100 times. In one sense this result is correct, because there +was only one instruction representing all four of these lines. However, +the output does not indicate how many times the result was 0 and how +many times the result was 1. +@c man end + +@node Gcov Data Files +@section Brief description of @command{gcov} data files + +@command{gcov} uses three files for doing profiling. The names of these +files are derived from the original @emph{source} file by substituting +the file suffix with either @file{.bb}, @file{.bbg}, or @file{.da}. All +of these files are placed in the same directory as the source file, and +contain data stored in a platform-independent method. + +The @file{.bb} and @file{.bbg} files are generated when the source file +is compiled with the GCC @option{-ftest-coverage} option. The +@file{.bb} file contains a list of source files (including headers), +functions within those files, and line numbers corresponding to each +basic block in the source file. + +The @file{.bb} file format consists of several lists of 4-byte integers +which correspond to the line numbers of each basic block in the +file. Each list is terminated by a line number of 0. A line number of @minus{}1 +is used to designate that the source file name (padded to a 4-byte +boundary and followed by another @minus{}1) follows. In addition, a line number +of @minus{}2 is used to designate that the name of a function (also padded to a +4-byte boundary and followed by a @minus{}2) follows. + +The @file{.bbg} file is used to reconstruct the program flow graph for +the source file. It contains a list of the program flow arcs (possible +branches taken from one basic block to another) for each function which, +in combination with the @file{.bb} file, enables gcov to reconstruct the +program flow. + +In the @file{.bbg} file, the format is: +@smallexample + number of basic blocks for function #0 (4-byte number) + total number of arcs for function #0 (4-byte number) + count of arcs in basic block #0 (4-byte number) + destination basic block of arc #0 (4-byte number) + flag bits (4-byte number) + destination basic block of arc #1 (4-byte number) + flag bits (4-byte number) + @dots{} + destination basic block of arc #N (4-byte number) + flag bits (4-byte number) + count of arcs in basic block #1 (4-byte number) + destination basic block of arc #0 (4-byte number) + flag bits (4-byte number) + @dots{} +@end smallexample + +A @minus{}1 (stored as a 4-byte number) is used to separate each function's +list of basic blocks, and to verify that the file has been read +correctly. + +The @file{.da} file is generated when a program containing object files +built with the GCC @option{-fprofile-arcs} option is executed. A +separate @file{.da} file is created for each source file compiled with +this option, and the name of the @file{.da} file is stored as an +absolute pathname in the resulting object file. This path name is +derived from the source file name by substituting a @file{.da} suffix. + +The format of the @file{.da} file is fairly simple. The first 8-byte +number is the number of counts in the file, followed by the counts +(stored as 8-byte numbers). Each count corresponds to the number of +times each arc in the program is executed. The counts are cumulative; +each time the program is executed, it attempts to combine the existing +@file{.da} files with the new counts for this invocation of the +program. It ignores the contents of any @file{.da} files whose number of +arcs doesn't correspond to the current program, and merely overwrites +them instead. + +All three of these files use the functions in @file{gcov-io.h} to store +integers; the functions in this header provide a machine-independent +mechanism for storing and retrieving data from a stream. + diff --git a/contrib/gcc/doc/gnu.texi b/contrib/gcc/doc/gnu.texi new file mode 100644 index 000000000000..641fe307253a --- /dev/null +++ b/contrib/gcc/doc/gnu.texi @@ -0,0 +1,20 @@ +@c Copyright (C) 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node GNU Project +@unnumbered The GNU Project and GNU/Linux + +The GNU Project was launched in 1984 to develop a complete Unix-like +operating system which is free software: the GNU system. (GNU is a +recursive acronym for ``GNU's Not Unix''; it is pronounced +``guh-NEW''@.) Variants of the GNU operating system, which use the +kernel Linux, are now widely used; though these systems are often +referred to as ``Linux'', they are more accurately called GNU/Linux +systems. + +For more information, see: +@smallexample +@uref{http://www.gnu.org/} +@uref{http://www.gnu.org/gnu/linux-and-gnu.html} +@end smallexample diff --git a/contrib/gcc/doc/headerdirs.texi b/contrib/gcc/doc/headerdirs.texi new file mode 100644 index 000000000000..17db57f05601 --- /dev/null +++ b/contrib/gcc/doc/headerdirs.texi @@ -0,0 +1,33 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Header Dirs +@chapter Standard Header File Directories + +@code{GCC_INCLUDE_DIR} means the same thing for native and cross. It is +where GNU CC stores its private include files, and also where GNU CC +stores the fixed include files. A cross compiled GNU CC runs +@code{fixincludes} on the header files in @file{$(tooldir)/include}. +(If the cross compilation header files need to be fixed, they must be +installed before GNU CC is built. If the cross compilation header files +are already suitable for ISO C and GNU CC, nothing special need be +done). + +@code{GPLUSPLUS_INCLUDE_DIR} means the same thing for native and cross. It +is where @code{g++} looks first for header files. The C++ library +installs only target independent header files in that directory. + +@code{LOCAL_INCLUDE_DIR} is used only by native compilers. GNU CC +doesn't install anything there. It is normally +@file{/usr/local/include}. This is where local additions to a packaged +system should place header files. + +@code{CROSS_INCLUDE_DIR} is used only by cross compilers. GNU CC +doesn't install anything there. + +@code{TOOL_INCLUDE_DIR} is used for both native and cross compilers. It +is the place for other packages to install header files that GNU CC will +use. For a cross-compiler, this is the equivalent of +@file{/usr/include}. When you build a cross-compiler, +@code{fixincludes} processes any header files in this directory. diff --git a/contrib/gcc/doc/hostconfig.texi b/contrib/gcc/doc/hostconfig.texi new file mode 100644 index 000000000000..33c0a3bb28bb --- /dev/null +++ b/contrib/gcc/doc/hostconfig.texi @@ -0,0 +1,130 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001, 2002 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Host Config +@chapter Host Configuration Headers +@cindex configuration file +@cindex @file{xm-@var{machine}.h} + +Host configuration headers contain macro definitions that describe the +machine and system on which the compiler is running. They are usually +unnecessary. Most of the things GCC needs to know about the host +system can be deduced by the @command{configure} script. + +If your host does need a special configuration header, it should be +named @file{xm-@var{machine}.h}, where @var{machine} is a short mnemonic +for the machine. Here are some macros which this header can define. + +@ftable @code +@item VMS +Define this macro if the host system is VMS@. + +@item FATAL_EXIT_CODE +A C expression for the status code to be returned when the compiler +exits after serious errors. The default is the system-provided macro +@samp{EXIT_FAILURE}, or @samp{1} if the system doesn't define that +macro. Define this macro only if these defaults are incorrect. + +@item SUCCESS_EXIT_CODE +A C expression for the status code to be returned when the compiler +exits without serious errors. (Warnings are not serious errors.) The +default is the system-provided macro @samp{EXIT_SUCCESS}, or @samp{0} if +the system doesn't define that macro. Define this macro only if these +defaults are incorrect. + +@item USE_C_ALLOCA +Define this macro if GCC should use the C implementation of @code{alloca} +provided by @file{libiberty.a}. This only affects how some parts of the +compiler itself allocate memory. It does not change code generation. + +When GCC is built with a compiler other than itself, the C @code{alloca} +is always used. This is because most other implementations have serious +bugs. You should define this macro only on a system where no +stack-based @code{alloca} can possibly work. For instance, if a system +has a small limit on the size of the stack, GCC's builtin @code{alloca} +will not work reliably. + +@item HAVE_DOS_BASED_FILE_SYSTEM +Define this macro if the host file system obeys the semantics defined by +MS-DOS instead of Unix. DOS file systems are case insensitive, file +specifications may begin with a drive letter, and both forward slash and +backslash (@samp{/} and @samp{\}) are directory separators. If you +define this macro, you probably need to define the next three macros too. + +@item PATH_SEPARATOR +If defined, this macro should expand to a character constant specifying +the separator for elements of search paths. The default value is a +colon (@samp{:}). DOS-based systems usually use semicolon (@samp{;}). + +@item DIR_SEPARATOR +@itemx DIR_SEPARATOR_2 +If defined, these macros expand to character constants specifying +separators for directory names within a file specification. They are +used somewhat inconsistently throughout the compiler. If your system +behaves like Unix (only forward slash separates pathnames), define +neither of them. If your system behaves like DOS (both forward and +backward slash can be used), define @code{DIR_SEPARATOR} to @samp{/} +and @code{DIR_SEPARATOR_2} to @samp{\}. + +@item HOST_OBJECT_SUFFIX +Define this macro to be a C string representing the suffix for object +files on your host machine. If you do not define this macro, GCC will +use @samp{.o} as the suffix for object files. + +@item HOST_EXECUTABLE_SUFFIX +Define this macro to be a C string representing the suffix for +executable files on your host machine. If you do not define this macro, +GCC will use the null string as the suffix for executable files. + +@item HOST_BIT_BUCKET +A pathname defined by the host operating system, which can be opened as +a file and written to, but all the information written is discarded. +This is commonly known as a @dfn{bit bucket} or @dfn{null device}. If +you do not define this macro, GCC will use @samp{/dev/null} as the bit +bucket. If the host does not support a bit bucket, define this macro to +an invalid filename. + +@item COLLECT2_HOST_INITIALIZATION +If defined, a C statement (sans semicolon) that performs host-dependent +initialization when @code{collect2} is being initialized. + +@item GCC_DRIVER_HOST_INITIALIZATION +If defined, a C statement (sans semicolon) that performs host-dependent +initialization when a compilation driver is being initialized. + +@item UPDATE_PATH_HOST_CANONICALIZE (@var{path}) +If defined, a C statement (sans semicolon) that performs host-dependent +canonicalization when a path used in a compilation driver or +preprocessor is canonicalized. @var{path} is a malloc-ed path to be +canonicalized. If the C statement does canonicalize @var{path} into a +different buffer, the old path should be freed and the new buffer should +have been allocated with malloc. + +@item DUMPFILE_FORMAT +Define this macro to be a C string representing the format to use for +constructing the index part of debugging dump file names. The resultant +string must fit in fifteen bytes. The full filename will be the +concatenation of: the prefix of the assembler file name, the string +resulting from applying this format to an index number, and a string +unique to each dump file kind, e.g. @samp{rtl}. + +If you do not define this macro, GCC will use @samp{.%02d.}. You should +define this macro if using the default will create an invalid file name. + +@item SMALL_ARG_MAX +Define this macro if the host system has a small limit on the total +size of an argument vector. This causes the driver to take more care +not to pass unnecessary arguments to subprocesses. +@end ftable + +In addition, if @command{configure} generates an incorrect definition of +any of the macros in @file{auto-host.h}, you can override that +definition in a host configuration header. If you need to do this, +first see if it is possible to fix @command{configure}. + +If you need to define only a few of these macros, and they have simple +definitions, consider using the @code{xm_defines} variable in your +@file{config.gcc} entry instead of creating a host configuration header. +@xref{System Config}. diff --git a/contrib/gcc/doc/include/fdl.texi b/contrib/gcc/doc/include/fdl.texi new file mode 100644 index 000000000000..1f3d8b6521d7 --- /dev/null +++ b/contrib/gcc/doc/include/fdl.texi @@ -0,0 +1,434 @@ +@ignore +@c Set file name and title for man page. +@setfilename gfdl +@settitle GNU Free Documentation License +@c man begin SEEALSO +gpl(7), fsf-funding(7). +@c man end +@c man begin COPYRIGHT +Copyright @copyright{} 2000 Free Software Foundation, Inc. +59 Temple Place, Suite 330, Boston, MA 02111-1307, USA + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@c man end +@end ignore +@c Special handling for inclusion in the install manual. +@ifset gfdlhtml +@ifnothtml +@comment node-name, next, previous, up +@node GNU Free Documentation License, Concept Index, Old, Top +@end ifnothtml +@html +

Installing GCC: GNU Free Documentation License

+@end html +@ifnothtml +@unnumbered GNU Free Documentation License +@end ifnothtml +@end ifset +@c man begin DESCRIPTION +@ifclear gfdlhtml +@node GNU Free Documentation License +@unnumbered GNU Free Documentation License +@end ifclear + +@cindex FDL, GNU Free Documentation License +@center Version 1.1, March 2000 + +@display +Copyright @copyright{} 2000 Free Software Foundation, Inc. +59 Temple Place, Suite 330, Boston, MA 02111-1307, USA + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@end display + +@enumerate 0 +@item +PREAMBLE + +The purpose of this License is to make a manual, textbook, or other +written document @dfn{free} in the sense of freedom: to assure everyone +the effective freedom to copy and redistribute it, with or without +modifying it, either commercially or noncommercially. Secondarily, +this License preserves for the author and publisher a way to get +credit for their work, while not being considered responsible for +modifications made by others. + +This License is a kind of ``copyleft'', which means that derivative +works of the document must themselves be free in the same sense. It +complements the GNU General Public License, which is a copyleft +license designed for free software. + +We have designed this License in order to use it for manuals for free +software, because free software needs free documentation: a free +program should come with manuals providing the same freedoms that the +software does. But this License is not limited to software manuals; +it can be used for any textual work, regardless of subject matter or +whether it is published as a printed book. 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To do this, add their titles to the +list of Invariant Sections in the Modified Version's license notice. +These titles must be distinct from any other section titles. + +You may add a section entitled ``Endorsements'', provided it contains +nothing but endorsements of your Modified Version by various +parties---for example, statements of peer review or that the text has +been approved by an organization as the authoritative definition of a +standard. + +You may add a passage of up to five words as a Front-Cover Text, and a +passage of up to 25 words as a Back-Cover Text, to the end of the list +of Cover Texts in the Modified Version. Only one passage of +Front-Cover Text and one of Back-Cover Text may be added by (or +through arrangements made by) any one entity. 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Such a compilation is called an ``aggregate'', and this +License does not apply to the other self-contained works thus compiled +with the Document, on account of their being thus compiled, if they +are not themselves derivative works of the Document. + +If the Cover Text requirement of section 3 is applicable to these +copies of the Document, then if the Document is less than one quarter +of the entire aggregate, the Document's Cover Texts may be placed on +covers that surround only the Document within the aggregate. +Otherwise they must appear on covers around the whole aggregate. + +@item +TRANSLATION + +Translation is considered a kind of modification, so you may +distribute translations of the Document under the terms of section 4. +Replacing Invariant Sections with translations requires special +permission from their copyright holders, but you may include +translations of some or all Invariant Sections in addition to the +original versions of these Invariant Sections. You may include a +translation of this License provided that you also include the +original English version of this License. In case of a disagreement +between the translation and the original English version of this +License, the original English version will prevail. + +@item +TERMINATION + +You may not copy, modify, sublicense, or distribute the Document except +as expressly provided for under this License. Any other attempt to +copy, modify, sublicense or distribute the Document is void, and will +automatically terminate your rights under this License. However, +parties who have received copies, or rights, from you under this +License will not have their licenses terminated so long as such +parties remain in full compliance. + +@item +FUTURE REVISIONS OF THIS LICENSE + +The Free Software Foundation may publish new, revised versions +of the GNU Free Documentation License from time to time. Such new +versions will be similar in spirit to the present version, but may +differ in detail to address new problems or concerns. See +@uref{http://www.gnu.org/copyleft/}. + +Each version of the License is given a distinguishing version number. +If the Document specifies that a particular numbered version of this +License ``or any later version'' applies to it, you have the option of +following the terms and conditions either of that specified version or +of any later version that has been published (not as a draft) by the +Free Software Foundation. If the Document does not specify a version +number of this License, you may choose any version ever published (not +as a draft) by the Free Software Foundation. +@end enumerate + +@page +@unnumberedsec ADDENDUM: How to use this License for your documents + +To use this License in a document you have written, include a copy of +the License in the document and put the following copyright and +license notices just after the title page: + +@smallexample +@group + Copyright (C) @var{year} @var{your name}. + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.1 + or any later version published by the Free Software Foundation; + with the Invariant Sections being @var{list their titles}, with the + Front-Cover Texts being @var{list}, and with the Back-Cover Texts being @var{list}. + A copy of the license is included in the section entitled ``GNU + Free Documentation License''. +@end group +@end smallexample + +If you have no Invariant Sections, write ``with no Invariant Sections'' +instead of saying which ones are invariant. If you have no +Front-Cover Texts, write ``no Front-Cover Texts'' instead of +``Front-Cover Texts being @var{list}''; likewise for Back-Cover Texts. + +If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of +free software license, such as the GNU General Public License, +to permit their use in free software. + +@c Local Variables: +@c ispell-local-pdict: "ispell-dict" +@c End: + +@c man end diff --git a/contrib/gcc/doc/include/funding.texi b/contrib/gcc/doc/include/funding.texi new file mode 100644 index 000000000000..d1583fabc0d8 --- /dev/null +++ b/contrib/gcc/doc/include/funding.texi @@ -0,0 +1,60 @@ +@ignore +@c Set file name and title for man page. +@setfilename fsf-funding +@settitle Funding Free Software +@c man begin SEEALSO +gpl(7), gfdl(7). +@c man end +@end ignore +@node Funding +@c man begin DESCRIPTION +@unnumbered Funding Free Software + +If you want to have more free software a few years from now, it makes +sense for you to help encourage people to contribute funds for its +development. The most effective approach known is to encourage +commercial redistributors to donate. + +Users of free software systems can boost the pace of development by +encouraging for-a-fee distributors to donate part of their selling price +to free software developers---the Free Software Foundation, and others. + +The way to convince distributors to do this is to demand it and expect +it from them. So when you compare distributors, judge them partly by +how much they give to free software development. Show distributors +they must compete to be the one who gives the most. + +To make this approach work, you must insist on numbers that you can +compare, such as, ``We will donate ten dollars to the Frobnitz project +for each disk sold.'' Don't be satisfied with a vague promise, such as +``A portion of the profits are donated,'' since it doesn't give a basis +for comparison. + +Even a precise fraction ``of the profits from this disk'' is not very +meaningful, since creative accounting and unrelated business decisions +can greatly alter what fraction of the sales price counts as profit. +If the price you pay is $50, ten percent of the profit is probably +less than a dollar; it might be a few cents, or nothing at all. + +Some redistributors do development work themselves. This is useful too; +but to keep everyone honest, you need to inquire how much they do, and +what kind. Some kinds of development make much more long-term +difference than others. For example, maintaining a separate version of +a program contributes very little; maintaining the standard version of a +program for the whole community contributes much. Easy new ports +contribute little, since someone else would surely do them; difficult +ports such as adding a new CPU to the GNU Compiler Collection contribute more; +major new features or packages contribute the most. + +By establishing the idea that supporting further development is ``the +proper thing to do'' when distributing free software for a fee, we can +assure a steady flow of resources into making more free software. +@c man end + +@display +@c man begin COPYRIGHT +Copyright @copyright{} 1994 Free Software Foundation, Inc. +Verbatim copying and redistribution of this section is permitted +without royalty; alteration is not permitted. +@c man end +@end display diff --git a/contrib/gcc/doc/include/gcc-common.texi b/contrib/gcc/doc/include/gcc-common.texi new file mode 100644 index 000000000000..947dde19f71a --- /dev/null +++ b/contrib/gcc/doc/include/gcc-common.texi @@ -0,0 +1,36 @@ +@c Copyright (C) 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@c Common values used in the GCC manuals: + +@set version-GCC 3.1 + +@c Common macros to support generating man pages: + +@macro gcctabopt{body} +@code{\body\} +@end macro +@macro gccoptlist{body} +@smallexample +\body\ +@end smallexample +@end macro +@c Makeinfo handles the above macro OK, TeX needs manual line breaks; +@c they get lost at some point in handling the macro. But if @macro is +@c used here rather than @alias, it produces double line breaks. +@iftex +@alias gol = * +@end iftex +@ifnottex +@macro gol +@end macro +@end ifnottex + +@c For FSF printing, define FSFPRINT. Also update the ISBNs and last +@c printing dates in gcc.texi and gccint.texi. +@c @set FSFPRINT +@ifset FSFPRINT +@smallbook +@finalout +@end ifset diff --git a/contrib/gcc/doc/include/gpl.texi b/contrib/gcc/doc/include/gpl.texi new file mode 100644 index 000000000000..4304b724e0d0 --- /dev/null +++ b/contrib/gcc/doc/include/gpl.texi @@ -0,0 +1,409 @@ +@ignore +@c Set file name and title for man page. +@setfilename gpl +@settitle GNU General Public License +@c man begin SEEALSO +gfdl(7), fsf-funding(7). +@c man end +@c man begin COPYRIGHT +Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. +59 Temple Place - Suite 330, Boston, MA 02111-1307, USA + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@c man end +@end ignore +@node Copying +@c man begin DESCRIPTION +@unnumbered GNU GENERAL PUBLIC LICENSE +@center Version 2, June 1991 + +@display +Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. +59 Temple Place - Suite 330, Boston, MA 02111-1307, USA + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@end display + +@unnumberedsec Preamble + + The licenses for most software are designed to take away your +freedom to share and change it. By contrast, the GNU General Public +License is intended to guarantee your freedom to share and change free +software---to make sure the software is free for all its users. This +General Public License applies to most of the Free Software +Foundation's software and to any other program whose authors commit to +using it. (Some other Free Software Foundation software is covered by +the GNU Library General Public License instead.) You can apply it to +your programs, too. + + When we speak of free software, we are referring to freedom, not +price. Our General Public Licenses are designed to make sure that you +have the freedom to distribute copies of free software (and charge for +this service if you wish), that you receive source code or can get it +if you want it, that you can change the software or use pieces of it +in new free programs; and that you know you can do these things. + + To protect your rights, we need to make restrictions that forbid +anyone to deny you these rights or to ask you to surrender the rights. +These restrictions translate to certain responsibilities for you if you +distribute copies of the software, or if you modify it. + + For example, if you distribute copies of such a program, whether +gratis or for a fee, you must give the recipients all the rights that +you have. You must make sure that they, too, receive or can get the +source code. And you must show them these terms so they know their +rights. + + We protect your rights with two steps: (1) copyright the software, and +(2) offer you this license which gives you legal permission to copy, +distribute and/or modify the software. + + Also, for each author's protection and ours, we want to make certain +that everyone understands that there is no warranty for this free +software. If the software is modified by someone else and passed on, we +want its recipients to know that what they have is not the original, so +that any problems introduced by others will not reflect on the original +authors' reputations. + + Finally, any free program is threatened constantly by software +patents. We wish to avoid the danger that redistributors of a free +program will individually obtain patent licenses, in effect making the +program proprietary. To prevent this, we have made it clear that any +patent must be licensed for everyone's free use or not licensed at all. + + The precise terms and conditions for copying, distribution and +modification follow. + +@iftex +@unnumberedsec TERMS AND CONDITIONS FOR COPYING,@*DISTRIBUTION AND MODIFICATION +@end iftex +@ifnottex +@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION +@end ifnottex + +@enumerate 0 +@item +This License applies to any program or other work which contains +a notice placed by the copyright holder saying it may be distributed +under the terms of this General Public License. The ``Program'', below, +refers to any such program or work, and a ``work based on the Program'' +means either the Program or any derivative work under copyright law: +that is to say, a work containing the Program or a portion of it, +either verbatim or with modifications and/or translated into another +language. (Hereinafter, translation is included without limitation in +the term ``modification''.) Each licensee is addressed as ``you''. + +Activities other than copying, distribution and modification are not +covered by this License; they are outside its scope. The act of +running the Program is not restricted, and the output from the Program +is covered only if its contents constitute a work based on the +Program (independent of having been made by running the Program). +Whether that is true depends on what the Program does. + +@item +You may copy and distribute verbatim copies of the Program's +source code as you receive it, in any medium, provided that you +conspicuously and appropriately publish on each copy an appropriate +copyright notice and disclaimer of warranty; keep intact all the +notices that refer to this License and to the absence of any warranty; +and give any other recipients of the Program a copy of this License +along with the Program. + +You may charge a fee for the physical act of transferring a copy, and +you may at your option offer warranty protection in exchange for a fee. + +@item +You may modify your copy or copies of the Program or any portion +of it, thus forming a work based on the Program, and copy and +distribute such modifications or work under the terms of Section 1 +above, provided that you also meet all of these conditions: + +@enumerate a +@item +You must cause the modified files to carry prominent notices +stating that you changed the files and the date of any change. + +@item +You must cause any work that you distribute or publish, that in +whole or in part contains or is derived from the Program or any +part thereof, to be licensed as a whole at no charge to all third +parties under the terms of this License. + +@item +If the modified program normally reads commands interactively +when run, you must cause it, when started running for such +interactive use in the most ordinary way, to print or display an +announcement including an appropriate copyright notice and a +notice that there is no warranty (or else, saying that you provide +a warranty) and that users may redistribute the program under +these conditions, and telling the user how to view a copy of this +License. (Exception: if the Program itself is interactive but +does not normally print such an announcement, your work based on +the Program is not required to print an announcement.) +@end enumerate + +These requirements apply to the modified work as a whole. If +identifiable sections of that work are not derived from the Program, +and can be reasonably considered independent and separate works in +themselves, then this License, and its terms, do not apply to those +sections when you distribute them as separate works. But when you +distribute the same sections as part of a whole which is a work based +on the Program, the distribution of the whole must be on the terms of +this License, whose permissions for other licensees extend to the +entire whole, and thus to each and every part regardless of who wrote it. + +Thus, it is not the intent of this section to claim rights or contest +your rights to work written entirely by you; rather, the intent is to +exercise the right to control the distribution of derivative or +collective works based on the Program. + +In addition, mere aggregation of another work not based on the Program +with the Program (or with a work based on the Program) on a volume of +a storage or distribution medium does not bring the other work under +the scope of this License. + +@item +You may copy and distribute the Program (or a work based on it, +under Section 2) in object code or executable form under the terms of +Sections 1 and 2 above provided that you also do one of the following: + +@enumerate a +@item +Accompany it with the complete corresponding machine-readable +source code, which must be distributed under the terms of Sections +1 and 2 above on a medium customarily used for software interchange; or, + +@item +Accompany it with a written offer, valid for at least three +years, to give any third party, for a charge no more than your +cost of physically performing source distribution, a complete +machine-readable copy of the corresponding source code, to be +distributed under the terms of Sections 1 and 2 above on a medium +customarily used for software interchange; or, + +@item +Accompany it with the information you received as to the offer +to distribute corresponding source code. (This alternative is +allowed only for noncommercial distribution and only if you +received the program in object code or executable form with such +an offer, in accord with Subsection b above.) +@end enumerate + +The source code for a work means the preferred form of the work for +making modifications to it. For an executable work, complete source +code means all the source code for all modules it contains, plus any +associated interface definition files, plus the scripts used to +control compilation and installation of the executable. However, as a +special exception, the source code distributed need not include +anything that is normally distributed (in either source or binary +form) with the major components (compiler, kernel, and so on) of the +operating system on which the executable runs, unless that component +itself accompanies the executable. + +If distribution of executable or object code is made by offering +access to copy from a designated place, then offering equivalent +access to copy the source code from the same place counts as +distribution of the source code, even though third parties are not +compelled to copy the source along with the object code. + +@item +You may not copy, modify, sublicense, or distribute the Program +except as expressly provided under this License. Any attempt +otherwise to copy, modify, sublicense or distribute the Program is +void, and will automatically terminate your rights under this License. +However, parties who have received copies, or rights, from you under +this License will not have their licenses terminated so long as such +parties remain in full compliance. + +@item +You are not required to accept this License, since you have not +signed it. However, nothing else grants you permission to modify or +distribute the Program or its derivative works. These actions are +prohibited by law if you do not accept this License. Therefore, by +modifying or distributing the Program (or any work based on the +Program), you indicate your acceptance of this License to do so, and +all its terms and conditions for copying, distributing or modifying +the Program or works based on it. + +@item +Each time you redistribute the Program (or any work based on the +Program), the recipient automatically receives a license from the +original licensor to copy, distribute or modify the Program subject to +these terms and conditions. You may not impose any further +restrictions on the recipients' exercise of the rights granted herein. +You are not responsible for enforcing compliance by third parties to +this License. + +@item +If, as a consequence of a court judgment or allegation of patent +infringement or for any other reason (not limited to patent issues), +conditions are imposed on you (whether by court order, agreement or +otherwise) that contradict the conditions of this License, they do not +excuse you from the conditions of this License. If you cannot +distribute so as to satisfy simultaneously your obligations under this +License and any other pertinent obligations, then as a consequence you +may not distribute the Program at all. For example, if a patent +license would not permit royalty-free redistribution of the Program by +all those who receive copies directly or indirectly through you, then +the only way you could satisfy both it and this License would be to +refrain entirely from distribution of the Program. + +If any portion of this section is held invalid or unenforceable under +any particular circumstance, the balance of the section is intended to +apply and the section as a whole is intended to apply in other +circumstances. + +It is not the purpose of this section to induce you to infringe any +patents or other property right claims or to contest validity of any +such claims; this section has the sole purpose of protecting the +integrity of the free software distribution system, which is +implemented by public license practices. Many people have made +generous contributions to the wide range of software distributed +through that system in reliance on consistent application of that +system; it is up to the author/donor to decide if he or she is willing +to distribute software through any other system and a licensee cannot +impose that choice. + +This section is intended to make thoroughly clear what is believed to +be a consequence of the rest of this License. + +@item +If the distribution and/or use of the Program is restricted in +certain countries either by patents or by copyrighted interfaces, the +original copyright holder who places the Program under this License +may add an explicit geographical distribution limitation excluding +those countries, so that distribution is permitted only in or among +countries not thus excluded. In such case, this License incorporates +the limitation as if written in the body of this License. + +@item +The Free Software Foundation may publish revised and/or new versions +of the General Public License from time to time. Such new versions will +be similar in spirit to the present version, but may differ in detail to +address new problems or concerns. + +Each version is given a distinguishing version number. If the Program +specifies a version number of this License which applies to it and ``any +later version'', you have the option of following the terms and conditions +either of that version or of any later version published by the Free +Software Foundation. If the Program does not specify a version number of +this License, you may choose any version ever published by the Free Software +Foundation. + +@item +If you wish to incorporate parts of the Program into other free +programs whose distribution conditions are different, write to the author +to ask for permission. For software which is copyrighted by the Free +Software Foundation, write to the Free Software Foundation; we sometimes +make exceptions for this. Our decision will be guided by the two goals +of preserving the free status of all derivatives of our free software and +of promoting the sharing and reuse of software generally. + +@iftex +@heading NO WARRANTY +@end iftex +@ifnottex +@center NO WARRANTY +@end ifnottex + +@item +BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY +FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN +OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES +PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED +OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF +MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS +TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE +PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, +REPAIR OR CORRECTION. + +@item +IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING +WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR +REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, +INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING +OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED +TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY +YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER +PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE +POSSIBILITY OF SUCH DAMAGES. +@end enumerate + +@iftex +@heading END OF TERMS AND CONDITIONS +@end iftex +@ifnottex +@center END OF TERMS AND CONDITIONS +@end ifnottex + +@page +@unnumberedsec How to Apply These Terms to Your New Programs + + If you develop a new program, and you want it to be of the greatest +possible use to the public, the best way to achieve this is to make it +free software which everyone can redistribute and change under these terms. + + To do so, attach the following notices to the program. It is safest +to attach them to the start of each source file to most effectively +convey the exclusion of warranty; and each file should have at least +the ``copyright'' line and a pointer to where the full notice is found. + +@smallexample +@var{one line to give the program's name and a brief idea of what it does.} +Copyright (C) @var{year} @var{name of author} + +This program is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 2 of the License, or +(at your option) any later version. + +This program is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +GNU General Public License for more details. + +You should have received a copy of the GNU General Public License +along with this program; if not, write to the Free Software +Foundation, Inc., 59 Temple Place - Suite 330, +Boston, MA 02111-1307, USA. +@end smallexample + +Also add information on how to contact you by electronic and paper mail. + +If the program is interactive, make it output a short notice like this +when it starts in an interactive mode: + +@smallexample +Gnomovision version 69, Copyright (C) @var{year} @var{name of author} +Gnomovision comes with ABSOLUTELY NO WARRANTY; for details +type `show w'. +This is free software, and you are welcome to redistribute it +under certain conditions; type `show c' for details. +@end smallexample + +The hypothetical commands @samp{show w} and @samp{show c} should show +the appropriate parts of the General Public License. Of course, the +commands you use may be called something other than @samp{show w} and +@samp{show c}; they could even be mouse-clicks or menu items---whatever +suits your program. + +You should also get your employer (if you work as a programmer) or your +school, if any, to sign a ``copyright disclaimer'' for the program, if +necessary. Here is a sample; alter the names: + +@smallexample +Yoyodyne, Inc., hereby disclaims all copyright interest in the program +`Gnomovision' (which makes passes at compilers) written by James Hacker. + +@var{signature of Ty Coon}, 1 April 1989 +Ty Coon, President of Vice +@end smallexample + +This General Public License does not permit incorporating your program into +proprietary programs. If your program is a subroutine library, you may +consider it more useful to permit linking proprietary applications with the +library. If this is what you want to do, use the GNU Library General +Public License instead of this License. +@c man end diff --git a/contrib/gcc/doc/install-old.texi b/contrib/gcc/doc/install-old.texi new file mode 100644 index 000000000000..9ce98968f91a --- /dev/null +++ b/contrib/gcc/doc/install-old.texi @@ -0,0 +1,725 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file install.texi. + +@ifnothtml +@comment node-name, next, previous, up +@node Old, GNU Free Documentation License, Specific, Top +@end ifnothtml +@html +

Old installation documentation

+@end html +@ifnothtml +@chapter Old installation documentation +@end ifnothtml + +Note most of this information is out of date and superseded by the +previous chapters of this manual. It is provided for historical +reference only, because of a lack of volunteers to merge it into the +main manual. + +@ifnothtml +@menu +* Configurations:: Configurations Supported by GNU CC. +* Cross-Compiler:: Building and installing a cross-compiler. +* VMS Install:: See below for installation on VMS. +@end menu +@end ifnothtml + +Here is the procedure for installing GNU CC on a GNU or Unix system. +See @ref{VMS Install}, for VMS systems. + +@enumerate +@item +If you have chosen a configuration for GNU CC which requires other GNU +tools (such as GAS or the GNU linker) instead of the standard system +tools, install the required tools in the build directory under the names +@file{as}, @file{ld} or whatever is appropriate. This will enable the +compiler to find the proper tools for compilation of the program +@file{enquire}. + +Alternatively, you can do subsequent compilation using a value of the +@code{PATH} environment variable such that the necessary GNU tools come +before the standard system tools. + +@item +Specify the host, build and target machine configurations. You do this +when you run the @file{configure} script. + +The @dfn{build} machine is the system which you are using, the +@dfn{host} machine is the system where you want to run the resulting +compiler (normally the build machine), and the @dfn{target} machine is +the system for which you want the compiler to generate code. + +If you are building a compiler to produce code for the machine it runs +on (a native compiler), you normally do not need to specify any operands +to @file{configure}; it will try to guess the type of machine you are on +and use that as the build, host and target machines. So you don't need +to specify a configuration when building a native compiler unless +@file{configure} cannot figure out what your configuration is or guesses +wrong. + +In those cases, specify the build machine's @dfn{configuration name} +with the @option{--host} option; the host and target will default to be +the same as the host machine. (If you are building a cross-compiler, +see @ref{Cross-Compiler}.) + +Here is an example: + +@smallexample +./configure --host=sparc-sun-sunos4.1 +@end smallexample + +A configuration name may be canonical or it may be more or less +abbreviated. + +A canonical configuration name has three parts, separated by dashes. +It looks like this: @samp{@var{cpu}-@var{company}-@var{system}}. +(The three parts may themselves contain dashes; @file{configure} +can figure out which dashes serve which purpose.) For example, +@samp{m68k-sun-sunos4.1} specifies a Sun 3. + +You can also replace parts of the configuration by nicknames or aliases. +For example, @samp{sun3} stands for @samp{m68k-sun}, so +@samp{sun3-sunos4.1} is another way to specify a Sun 3. + +You can specify a version number after any of the system types, and some +of the CPU types. In most cases, the version is irrelevant, and will be +ignored. So you might as well specify the version if you know it. + +See @ref{Configurations}, for a list of supported configuration names and +notes on many of the configurations. You should check the notes in that +section before proceeding any further with the installation of GNU CC@. + +@end enumerate + +@ifnothtml +@node Configurations, Cross-Compiler, , Old +@section Configurations Supported by GNU CC +@end ifnothtml +@html +

@anchor{Configurations}Configurations Supported by GNU CC

+@end html +@cindex configurations supported by GNU CC + +Here are the possible CPU types: + +@quotation +@c gmicro, fx80, spur and tahoe omitted since they don't work. +1750a, a29k, alpha, arm, avr, c@var{n}, clipper, dsp16xx, elxsi, fr30, h8300, +hppa1.0, hppa1.1, i370, i386, i486, i586, i686, i786, i860, i960, m32r, +m68000, m68k, m6811, m6812, m88k, mcore, mips, mipsel, mips64, mips64el, +mn10200, mn10300, ns32k, pdp11, powerpc, powerpcle, romp, rs6000, sh, sparc, +sparclite, sparc64, v850, vax, we32k. +@end quotation + +Here are the recognized company names. As you can see, customary +abbreviations are used rather than the longer official names. + +@c What should be done about merlin, tek*, dolphin? +@quotation +acorn, alliant, altos, apollo, apple, att, bull, +cbm, convergent, convex, crds, dec, dg, dolphin, +elxsi, encore, harris, hitachi, hp, ibm, intergraph, isi, +mips, motorola, ncr, next, ns, omron, plexus, +sequent, sgi, sony, sun, tti, unicom, wrs. +@end quotation + +The company name is meaningful only to disambiguate when the rest of +the information supplied is insufficient. You can omit it, writing +just @samp{@var{cpu}-@var{system}}, if it is not needed. For example, +@samp{vax-ultrix4.2} is equivalent to @samp{vax-dec-ultrix4.2}. + +Here is a list of system types: + +@quotation +386bsd, aix, acis, amigaos, aos, aout, aux, bosx, bsd, clix, coff, ctix, cxux, +dgux, dynix, ebmon, ecoff, elf, esix, freebsd, hms, genix, gnu, linux, +linux-gnu, hiux, hpux, iris, irix, isc, luna, lynxos, mach, minix, msdos, mvs, +netbsd, newsos, nindy, ns, osf, osfrose, ptx, riscix, riscos, rtu, sco, sim, +solaris, sunos, sym, sysv, udi, ultrix, unicos, uniplus, unos, vms, vsta, +vxworks, winnt, xenix. +@end quotation + +@noindent +You can omit the system type; then @file{configure} guesses the +operating system from the CPU and company. + +You can add a version number to the system type; this may or may not +make a difference. For example, you can write @samp{bsd4.3} or +@samp{bsd4.4} to distinguish versions of BSD@. In practice, the version +number is most needed for @samp{sysv3} and @samp{sysv4}, which are often +treated differently. + +@samp{linux-gnu} is the canonical name for the GNU/Linux target; however +GNU CC will also accept @samp{linux}. The version of the kernel in use is +not relevant on these systems. A suffix such as @samp{libc1} or @samp{aout} +distinguishes major versions of the C library; all of the suffixed versions +are obsolete. + +If you specify an impossible combination such as @samp{i860-dg-vms}, +then you may get an error message from @file{configure}, or it may +ignore part of the information and do the best it can with the rest. +@file{configure} always prints the canonical name for the alternative +that it used. GNU CC does not support all possible alternatives. + +Often a particular model of machine has a name. Many machine names are +recognized as aliases for CPU/company combinations. Thus, the machine +name @samp{sun3}, mentioned above, is an alias for @samp{m68k-sun}. +Sometimes we accept a company name as a machine name, when the name is +popularly used for a particular machine. Here is a table of the known +machine names: + +@quotation +3300, 3b1, 3b@var{n}, 7300, altos3068, altos, +apollo68, att-7300, balance, +convex-c@var{n}, crds, decstation-3100, +decstation, delta, encore, +fx2800, gmicro, hp7@var{nn}, hp8@var{nn}, +hp9k2@var{nn}, hp9k3@var{nn}, hp9k7@var{nn}, +hp9k8@var{nn}, iris4d, iris, isi68, +m3230, magnum, merlin, miniframe, +mmax, news-3600, news800, news, next, +pbd, pc532, pmax, powerpc, powerpcle, ps2, risc-news, +rtpc, sun2, sun386i, sun386, sun3, +sun4, symmetry, tower-32, tower. +@end quotation + +@noindent +Remember that a machine name specifies both the cpu type and the company +name. +If you want to install your own homemade configuration files, you can +use @samp{local} as the company name to access them. If you use +configuration @samp{@var{cpu}-local}, the configuration name +without the cpu prefix +is used to form the configuration file names. + +Thus, if you specify @samp{m68k-local}, configuration uses +files @file{m68k.md}, @file{local.h}, @file{m68k.c}, +@file{xm-local.h}, @file{t-local}, and @file{x-local}, all in the +directory @file{config/m68k}. + +Here is a list of configurations that have special treatment or special +things you must know: + +@table @samp +@item vax-dec-vms +See @ref{VMS Install}, for details on how to install GNU CC on VMS@. +@end table + +@ifnothtml +@node Cross-Compiler, VMS Install, Configurations, Old +@section Building and Installing a Cross-Compiler +@end ifnothtml +@html +

@anchor{Cross-Compiler}Building and Installing a Cross-Compiler

+@end html +@cindex cross-compiler, installation + +GNU CC can function as a cross-compiler for many machines, but not all. + +@itemize @bullet +@item +Cross-compilers for the Mips as target using the Mips assembler +currently do not work, because the auxiliary programs +@file{mips-tdump.c} and @file{mips-tfile.c} can't be compiled on +anything but a Mips. It does work to cross compile for a Mips +if you use the GNU assembler and linker. + +@item +Cross-compilers between machines with different floating point formats +have not all been made to work. GNU CC now has a floating point +emulator with which these can work, but each target machine description +needs to be updated to take advantage of it. + +@item +Cross-compilation between machines of different word sizes is +somewhat problematic and sometimes does not work. +@end itemize + +Since GNU CC generates assembler code, you probably need a +cross-assembler that GNU CC can run, in order to produce object files. +If you want to link on other than the target machine, you need a +cross-linker as well. You also need header files and libraries suitable +for the target machine that you can install on the host machine. + +@ifnothtml +@menu +* Steps of Cross:: Using a cross-compiler involves several steps + that may be carried out on different machines. +* Configure Cross:: Configuring a cross-compiler. +* Tools and Libraries:: Where to put the linker and assembler, and the C library. +* Cross Headers:: Finding and installing header files + for a cross-compiler. +* Build Cross:: Actually compiling the cross-compiler. +@end menu +@end ifnothtml + +@ifnothtml +@node Steps of Cross, Configure Cross, , Cross-Compiler +@subsection Steps of Cross-Compilation +@end ifnothtml +@html +

Steps of Cross-Compilation

+@end html + +To compile and run a program using a cross-compiler involves several +steps: + +@itemize @bullet +@item +Run the cross-compiler on the host machine to produce assembler files +for the target machine. This requires header files for the target +machine. + +@item +Assemble the files produced by the cross-compiler. You can do this +either with an assembler on the target machine, or with a +cross-assembler on the host machine. + +@item +Link those files to make an executable. You can do this either with a +linker on the target machine, or with a cross-linker on the host +machine. Whichever machine you use, you need libraries and certain +startup files (typically @file{crt@dots{}.o}) for the target machine. +@end itemize + +It is most convenient to do all of these steps on the same host machine, +since then you can do it all with a single invocation of GNU CC@. This +requires a suitable cross-assembler and cross-linker. For some targets, +the GNU assembler and linker are available. + +@ifnothtml +@node Configure Cross, Tools and Libraries, Steps of Cross, Cross-Compiler +@subsection Configuring a Cross-Compiler +@end ifnothtml +@html +

Configuring a Cross-Compiler

+@end html + +To build GNU CC as a cross-compiler, you start out by running +@file{configure}. Use the @option{--target=@var{target}} to specify the +target type. If @file{configure} was unable to correctly identify the +system you are running on, also specify the @option{--build=@var{build}} +option. For example, here is how to configure for a cross-compiler that +produces code for an HP 68030 system running BSD on a system that +@file{configure} can correctly identify: + +@smallexample +./configure --target=m68k-hp-bsd4.3 +@end smallexample + +@ifnothtml +@node Tools and Libraries, Cross Headers, Configure Cross, Cross-Compiler +@subsection Tools and Libraries for a Cross-Compiler +@end ifnothtml +@html +

Tools and Libraries for a Cross-Compiler

+@end html + +If you have a cross-assembler and cross-linker available, you should +install them now. Put them in the directory +@file{/usr/local/@var{target}/bin}. Here is a table of the tools +you should put in this directory: + +@table @file +@item as +This should be the cross-assembler. + +@item ld +This should be the cross-linker. + +@item ar +This should be the cross-archiver: a program which can manipulate +archive files (linker libraries) in the target machine's format. + +@item ranlib +This should be a program to construct a symbol table in an archive file. +@end table + +The installation of GNU CC will find these programs in that directory, +and copy or link them to the proper place to for the cross-compiler to +find them when run later. + +The easiest way to provide these files is to build the Binutils package +and GAS@. Configure them with the same @option{--host} and @option{--target} +options that you use for configuring GNU CC, then build and install +them. They install their executables automatically into the proper +directory. Alas, they do not support all the targets that GNU CC +supports. + +If you want to install libraries to use with the cross-compiler, such as +a standard C library, put them in the directory +@file{/usr/local/@var{target}/lib}; installation of GNU CC copies +all the files in that subdirectory into the proper place for GNU CC to +find them and link with them. Here's an example of copying some +libraries from a target machine: + +@example +ftp @var{target-machine} +lcd /usr/local/@var{target}/lib +cd /lib +get libc.a +cd /usr/lib +get libg.a +get libm.a +quit +@end example + +@noindent +The precise set of libraries you'll need, and their locations on +the target machine, vary depending on its operating system. + +@cindex start files +Many targets require ``start files'' such as @file{crt0.o} and +@file{crtn.o} which are linked into each executable; these too should be +placed in @file{/usr/local/@var{target}/lib}. There may be several +alternatives for @file{crt0.o}, for use with profiling or other +compilation options. Check your target's definition of +@code{STARTFILE_SPEC} to find out what start files it uses. +Here's an example of copying these files from a target machine: + +@example +ftp @var{target-machine} +lcd /usr/local/@var{target}/lib +prompt +cd /lib +mget *crt*.o +cd /usr/lib +mget *crt*.o +quit +@end example + +@ifnothtml +@node Cross Headers, Build Cross, Tools and Libraries, Cross-Compiler +@subsection Cross-Compilers and Header Files +@end ifnothtml +@html +

Cross-Compilers and Header Files

+@end html + +If you are cross-compiling a standalone program or a program for an +embedded system, then you may not need any header files except the few +that are part of GNU CC (and those of your program). However, if you +intend to link your program with a standard C library such as +@file{libc.a}, then you probably need to compile with the header files +that go with the library you use. + +The GNU C compiler does not come with these files, because (1) they are +system-specific, and (2) they belong in a C library, not in a compiler. + +If the GNU C library supports your target machine, then you can get the +header files from there (assuming you actually use the GNU library when +you link your program). + +If your target machine comes with a C compiler, it probably comes with +suitable header files also. If you make these files accessible from the host +machine, the cross-compiler can use them also. + +Otherwise, you're on your own in finding header files to use when +cross-compiling. + +When you have found suitable header files, you should put them in the +directory @file{/usr/local/@var{target}/include}, before building the +cross compiler. Then installation will run fixincludes properly and +install the corrected versions of the header files where the compiler +will use them. + +Provide the header files before you build the cross-compiler, because +the build stage actually runs the cross-compiler to produce parts of +@file{libgcc.a}. (These are the parts that @emph{can} be compiled with +GNU CC@.) Some of them need suitable header files. + +Here's an example showing how to copy the header files from a target +machine. On the target machine, do this: + +@example +(cd /usr/include; tar cf - .) > tarfile +@end example + +Then, on the host machine, do this: + +@example +ftp @var{target-machine} +lcd /usr/local/@var{target}/include +get tarfile +quit +tar xf tarfile +@end example + +@ifnothtml +@node Build Cross, , Cross Headers, Cross-Compiler +@subsection Actually Building the Cross-Compiler +@end ifnothtml +@html +

Actually Building the Cross-Compiler

+@end html + +Now you can proceed just as for compiling a single-machine compiler +through the step of building stage 1. + +If your target is exotic, you may need to provide the header file +@file{float.h}.One way to do this is to compile @file{enquire} and run +it on your target machine. The job of @file{enquire} is to run on the +target machine and figure out by experiment the nature of its floating +point representation. @file{enquire} records its findings in the header +file @file{float.h}. If you can't produce this file by running +@file{enquire} on the target machine, then you will need to come up with +a suitable @file{float.h} in some other way (or else, avoid using it in +your programs). + +Do not try to build stage 2 for a cross-compiler. It doesn't work to +rebuild GNU CC as a cross-compiler using the cross-compiler, because +that would produce a program that runs on the target machine, not on the +host. For example, if you compile a 386-to-68030 cross-compiler with +itself, the result will not be right either for the 386 (because it was +compiled into 68030 code) or for the 68030 (because it was configured +for a 386 as the host). If you want to compile GNU CC into 68030 code, +whether you compile it on a 68030 or with a cross-compiler on a 386, you +must specify a 68030 as the host when you configure it. + +To install the cross-compiler, use @samp{make install}, as usual. + +@ifnothtml +@node VMS Install, , Cross-Compiler, Old +@section Installing GNU CC on VMS +@end ifnothtml +@html +

@anchor{VMS Install}Installing GNU CC on VMS

+@end html +@cindex VMS installation +@cindex installing GNU CC on VMS + +The VMS version of GNU CC is distributed in a backup saveset containing +both source code and precompiled binaries. + +To install the @file{gcc} command so you can use the compiler easily, in +the same manner as you use the VMS C compiler, you must install the VMS CLD +file for GNU CC as follows: + +@enumerate +@item +Define the VMS logical names @samp{GNU_CC} and @samp{GNU_CC_INCLUDE} +to point to the directories where the GNU CC executables +(@file{gcc-cpp.exe}, @file{gcc-cc1.exe}, etc.) and the C include files are +kept respectively. This should be done with the commands: + +@smallexample +$ assign /system /translation=concealed - + disk:[gcc.] gnu_cc +$ assign /system /translation=concealed - + disk:[gcc.include.] gnu_cc_include +@end smallexample + +@noindent +with the appropriate disk and directory names. These commands can be +placed in your system startup file so they will be executed whenever +the machine is rebooted. You may, if you choose, do this via the +@file{GCC_INSTALL.COM} script in the @file{[GCC]} directory. + +@item +Install the @file{GCC} command with the command line: + +@smallexample +$ set command /table=sys$common:[syslib]dcltables - + /output=sys$common:[syslib]dcltables gnu_cc:[000000]gcc +$ install replace sys$common:[syslib]dcltables +@end smallexample + +@item +To install the help file, do the following: + +@smallexample +$ library/help sys$library:helplib.hlb gcc.hlp +@end smallexample + +@noindent +Now you can invoke the compiler with a command like @samp{gcc /verbose +file.c}, which is equivalent to the command @samp{gcc -v -c file.c} in +Unix. +@end enumerate + +If you wish to use GNU C++ you must first install GNU CC, and then +perform the following steps: + +@enumerate +@item +Define the VMS logical name @samp{GNU_GXX_INCLUDE} to point to the +directory where the preprocessor will search for the C++ header files. +This can be done with the command: + +@smallexample +$ assign /system /translation=concealed - + disk:[gcc.gxx_include.] gnu_gxx_include +@end smallexample + +@noindent +with the appropriate disk and directory name. If you are going to be +using a C++ runtime library, this is where its install procedure will install +its header files. + +@item +Obtain the file @file{gcc-cc1plus.exe}, and place this in the same +directory that @file{gcc-cc1.exe} is kept. + +The GNU C++ compiler can be invoked with a command like @samp{gcc /plus +/verbose file.cc}, which is equivalent to the command @samp{g++ -v -c +file.cc} in Unix. +@end enumerate + +We try to put corresponding binaries and sources on the VMS distribution +tape. But sometimes the binaries will be from an older version than the +sources, because we don't always have time to update them. (Use the +@samp{/version} option to determine the version number of the binaries and +compare it with the source file @file{version.c} to tell whether this is +so.) In this case, you should use the binaries you get to recompile the +sources. If you must recompile, here is how: + +@enumerate +@item +Execute the command procedure @file{vmsconfig.com} to set up the files +@file{tm.h}, @file{config.h}, @file{aux-output.c}, and @file{md.}, and +to create files @file{tconfig.h} and @file{hconfig.h}. This procedure +also creates several linker option files used by @file{make-cc1.com} and +a data file used by @file{make-l2.com}. + +@smallexample +$ @@vmsconfig.com +@end smallexample + +@item +Setup the logical names and command tables as defined above. In +addition, define the VMS logical name @samp{GNU_BISON} to point at the +to the directories where the Bison executable is kept. This should be +done with the command: + +@smallexample +$ assign /system /translation=concealed - + disk:[bison.] gnu_bison +@end smallexample + +You may, if you choose, use the @file{INSTALL_BISON.COM} script in the +@file{[BISON]} directory. + +@item +Install the @samp{BISON} command with the command line: + +@smallexample +$ set command /table=sys$common:[syslib]dcltables - + /output=sys$common:[syslib]dcltables - + gnu_bison:[000000]bison +$ install replace sys$common:[syslib]dcltables +@end smallexample + +@item +Type @samp{@@make-gcc} to recompile everything, or submit the file +@file{make-gcc.com} to a batch queue. If you wish to build the GNU C++ +compiler as well as the GNU CC compiler, you must first edit +@file{make-gcc.com} and follow the instructions that appear in the +comments. + +@item +In order to use GCC, you need a library of functions which GCC compiled code +will call to perform certain tasks, and these functions are defined in the +file @file{libgcc2.c}. To compile this you should use the command procedure +@file{make-l2.com}, which will generate the library @file{libgcc2.olb}. +@file{libgcc2.olb} should be built using the compiler built from +the same distribution that @file{libgcc2.c} came from, and +@file{make-gcc.com} will automatically do all of this for you. + +To install the library, use the following commands: + +@smallexample +$ library gnu_cc:[000000]gcclib/delete=(new,eprintf) +$ library gnu_cc:[000000]gcclib/delete=L_* +$ library libgcc2/extract=*/output=libgcc2.obj +$ library gnu_cc:[000000]gcclib libgcc2.obj +@end smallexample + +The first command simply removes old modules that will be replaced with +modules from @file{libgcc2} under different module names. The modules +@code{new} and @code{eprintf} may not actually be present in your +@file{gcclib.olb}---if the VMS librarian complains about those modules +not being present, simply ignore the message and continue on with the +next command. The second command removes the modules that came from the +previous version of the library @file{libgcc2.c}. + +Whenever you update the compiler on your system, you should also update the +library with the above procedure. + +@item +You may wish to build GCC in such a way that no files are written to the +directory where the source files reside. An example would be the when +the source files are on a read-only disk. In these cases, execute the +following DCL commands (substituting your actual path names): + +@smallexample +$ assign dua0:[gcc.build_dir.]/translation=concealed, - + dua1:[gcc.source_dir.]/translation=concealed gcc_build +$ set default gcc_build:[000000] +@end smallexample + +@noindent +where the directory @file{dua1:[gcc.source_dir]} contains the source +code, and the directory @file{dua0:[gcc.build_dir]} is meant to contain +all of the generated object files and executables. Once you have done +this, you can proceed building GCC as described above. (Keep in mind +that @file{gcc_build} is a rooted logical name, and thus the device +names in each element of the search list must be an actual physical +device name rather than another rooted logical name). + +@item +@strong{If you are building GNU CC with a previous version of GNU CC, +you also should check to see that you have the newest version of the +assembler}. In particular, GNU CC version 2 treats global constant +variables slightly differently from GNU CC version 1, and GAS version +1.38.1 does not have the patches required to work with GCC version 2. +If you use GAS 1.38.1, then @code{extern const} variables will not have +the read-only bit set, and the linker will generate warning messages +about mismatched psect attributes for these variables. These warning +messages are merely a nuisance, and can safely be ignored. + +@item +If you want to build GNU CC with the VAX C compiler, you will need to +make minor changes in @file{make-cccp.com} and @file{make-cc1.com} +to choose alternate definitions of @code{CC}, @code{CFLAGS}, and +@code{LIBS}. See comments in those files. However, you must +also have a working version of the GNU assembler (GNU as, aka GAS) as +it is used as the back end for GNU CC to produce binary object modules +and is not included in the GNU CC sources. GAS is also needed to +compile @file{libgcc2} in order to build @file{gcclib} (see above); +@file{make-l2.com} expects to be able to find it operational in +@file{gnu_cc:[000000]gnu-as.exe}. + +To use GNU CC on VMS, you need the VMS driver programs +@file{gcc.exe}, @file{gcc.com}, and @file{gcc.cld}. They are +distributed with the VMS binaries (@file{gcc-vms}) rather than the +GNU CC sources. GAS is also included in @file{gcc-vms}, as is Bison. + +Once you have successfully built GNU CC with VAX C, you should use the +resulting compiler to rebuild itself. Before doing this, be sure to +restore the @code{CC}, @code{CFLAGS}, and @code{LIBS} definitions in +@file{make-cccp.com} and @file{make-cc1.com}. The second generation +compiler will be able to take advantage of many optimizations that must +be suppressed when building with other compilers. +@end enumerate + +Under previous versions of GNU CC, the generated code would occasionally +give strange results when linked with the sharable @file{VAXCRTL} library. +Now this should work. + +Even with this version, however, GNU CC itself should not be linked with +the sharable @file{VAXCRTL}. The version of @code{qsort} in +@file{VAXCRTL} has a bug (known to be present in VMS versions V4.6 +through V5.5) which causes the compiler to fail. + +The executables are generated by @file{make-cc1.com} and +@file{make-cccp.com} use the object library version of @file{VAXCRTL} in +order to make use of the @code{qsort} routine in @file{gcclib.olb}. If +you wish to link the compiler executables with the shareable image +version of @file{VAXCRTL}, you should edit the file @file{tm.h} (created +by @file{vmsconfig.com}) to define the macro @code{QSORT_WORKAROUND}. + +@code{QSORT_WORKAROUND} is always defined when GNU CC is compiled with +VAX C, to avoid a problem in case @file{gcclib.olb} is not yet +available. diff --git a/contrib/gcc/doc/install.texi b/contrib/gcc/doc/install.texi new file mode 100644 index 000000000000..6913d03d088c --- /dev/null +++ b/contrib/gcc/doc/install.texi @@ -0,0 +1,3823 @@ +\input texinfo.tex @c -*-texinfo-*- +@c @ifnothtml +@c %**start of header +@setfilename install.info +@settitle Installing GCC +@setchapternewpage odd +@c %**end of header +@c @end ifnothtml + +@c Specify title for specific html page +@ifset indexhtml +@settitle Installing GCC +@end ifset +@ifset specifichtml +@settitle Host/Target specific installation notes for GCC +@end ifset +@ifset downloadhtml +@settitle Downloading GCC +@end ifset +@ifset configurehtml +@settitle Installing GCC: Configuration +@end ifset +@ifset buildhtml +@settitle Installing GCC: Building +@end ifset +@ifset testhtml +@settitle Installing GCC: Testing +@end ifset +@ifset finalinstallhtml +@settitle Installing GCC: Final installation +@end ifset +@ifset binarieshtml +@settitle Installing GCC: Binaries +@end ifset +@ifset oldhtml +@settitle Installing GCC: Old documentation +@end ifset +@ifset gfdlhtml +@settitle Installing GCC: GNU Free Documentation License +@end ifset + +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001, 2002 Free Software Foundation, Inc. +@c *** Converted to texinfo by Dean Wakerley, dean@wakerley.com + +@c Include everything if we're not making html +@ifnothtml +@set indexhtml +@set specifichtml +@set downloadhtml +@set configurehtml +@set buildhtml +@set testhtml +@set finalinstallhtml +@set binarieshtml +@set oldhtml +@set gfdlhtml +@end ifnothtml + +@c Part 2 Summary Description and Copyright +@macro copyrightnotice +Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +1999, 2000, 2001, 2002 Free Software Foundation, Inc. +@sp 1 +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with no +Invariant Sections, the Front-Cover texts being (a) (see below), and +with the Back-Cover Texts being (b) (see below). A copy of the +license is included in the section entitled ``@uref{./gfdl.html,,GNU +Free Documentation License}''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end macro +@ifinfo +@copyrightnotice{} +@end ifinfo + +@c Part 3 Titlepage and Copyright +@titlepage +@sp 10 +@comment The title is printed in a large font. +@center @titlefont{Installing GCC} + +@c The following two commands start the copyright page. +@page +@vskip 0pt plus 1filll +@copyrightnotice{} +@end titlepage + +@c Part 4 Top node and Master Menu +@ifinfo +@node Top, , , (dir) +@comment node-name, next, Previous, up + +@menu +* Installing GCC:: This document describes the generic installation + procedure for GCC as well as detailing some target + specific installation instructions. + +* Specific:: Host/target specific installation notes for GCC. +* Binaries:: Where to get pre-compiled binaries. + +* Old:: Old installation documentation. + +* GNU Free Documentation License:: How you can copy and share this manual. +* Concept Index:: This index has two entries. +@end menu +@end ifinfo + +@c Part 5 The Body of the Document +@c ***Installing GCC********************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Installing GCC, Binaries, , Top +@end ifnothtml +@ifset indexhtml +@html +

Installing GCC

+@end html +@ifnothtml +@chapter Installing GCC +@end ifnothtml + +The latest version of this document is always available at +@uref{http://gcc.gnu.org/install/,,http://gcc.gnu.org/install/}. + +This document describes the generic installation procedure for GCC as well +as detailing some target specific installation instructions. + +GCC includes several components that previously were separate distributions +with their own installation instructions. This document supersedes all +package specific installation instructions. + +@emph{Before} starting the build/install procedure please check the +@ifnothtml +@ref{Specific, host/target specific installation notes}. +@end ifnothtml +@ifhtml +@uref{specific.html,,host/target specific installation notes}. +@end ifhtml +We recommend you browse the entire generic installation instructions before +you proceed. + +Lists of successful builds for released versions of GCC are +available at our web pages for +@uref{http://gcc.gnu.org/gcc-3.0/buildstat.html,,3.0} +and +@uref{http://gcc.gnu.org/gcc-2.95/buildstat.html,,2.95}. +These lists are updated as new information becomes available. + +The installation procedure itself is broken into five steps. + +@ifinfo +@menu +* Downloading the source:: +* Configuration:: +* Building:: +* Testing:: (optional) +* Final install:: +@end menu +@end ifinfo +@ifhtml +@enumerate +@item +@uref{download.html,,Downloading the source} +@item +@uref{configure.html,,Configuration} +@item +@uref{build.html,,Building} +@item +@uref{test.html,,Testing} (optional) +@item +@uref{finalinstall.html,,Final install} +@end enumerate +@end ifhtml + +Please note that GCC does not support @samp{make uninstall} and probably +won't do so in the near future as this would open a can of worms. Instead, +we suggest that you install GCC into a directory of its own and simply +remove that directory when you do not need that specific version of GCC +any longer, and, if shared libraries are installed there as well, no +more binaries exist that use them. + +@ifhtml +There are also some @uref{old.html,,old installation instructions}, +which are mostly obsolete but still contain some information which has +not yet been merged into the main part of this manual. +@end ifhtml + +@html +
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} + +@copyrightnotice{} +@end ifhtml +@end ifset + +@c ***Downloading the source************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Downloading the source, Configuration, , Installing GCC +@end ifnothtml +@ifset downloadhtml +@html +

Downloading GCC

+@end html +@ifnothtml +@chapter Downloading GCC +@end ifnothtml +@cindex Downloading GCC +@cindex Downloading the Source + +GCC is distributed via @uref{http://gcc.gnu.org/cvs.html,,CVS} and FTP +tarballs compressed with @command{gzip} or +@command{bzip2}. It is possible to download a full distribution or specific +components. + +Please refer to our @uref{http://gcc.gnu.org/releases.html,,releases web page} +for information on how to obtain GCC@. + +The full distribution includes the C, C++, Objective-C, Fortran, Java, +and CHILL compilers. The full distribution also includes runtime libraries +for C++, Objective-C, Fortran, Java and CHILL. (GCC 3.0 does not +include CHILL.) In GCC 3.0 and later versions, GNU compiler testsuites +are also included in the full distribution. + +If you choose to download specific components, you must download the core +GCC distribution plus any language specific distributions you wish to +use. The core distribution includes the C language front end as well as the +shared components. Each language has a tarball which includes the language +front end as well as the language runtime (when appropriate). + +Unpack the core distribution as well as any language specific +distributions in the same directory. + +If you also intend to build binutils (either to upgrade an existing +installation or for use in place of the corresponding tools of your +OS), unpack the binutils distribution either in the same directory or +a separate one. In the latter case, add symbolic links to any +components of the binutils you intend to build alongside the compiler +(@file{bfd}, @file{binutils}, @file{gas}, @file{gprof}, @file{ld}, +@file{opcodes}, @dots{}) to the directory containing the GCC sources. + +@html +
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Configuration*********************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Configuration, Building, Downloading the source, Installing GCC +@end ifnothtml +@ifset configurehtml +@html +

Installing GCC: Configuration

+@end html +@ifnothtml +@chapter Installing GCC: Configuration +@end ifnothtml +@cindex Configuration +@cindex Installing GCC: Configuration + +Like most GNU software, GCC must be configured before it can be built. +This document describes the recommended configuration procedure +for both native and cross targets. + +We use @var{srcdir} to refer to the toplevel source directory for +GCC; we use @var{objdir} to refer to the toplevel build/object directory. + +If you obtained the sources via CVS, @var{srcdir} must refer to the top +@file{gcc} directory, the one where the @file{MAINTAINERS} can be found, +and not its @file{gcc} subdirectory, otherwise the build will fail. + +First, we @strong{highly} recommend that GCC be built into a +separate directory than the sources which does @strong{not} reside +within the source tree. This is how we generally build GCC; building +where @var{srcdir} == @var{objdir} should still work, but doesn't +get extensive testing; building where @var{objdir} is a subdirectory +of @var{srcdir} is unsupported. + +If you have previously built GCC in the same directory for a +different target machine, do @samp{make distclean} to delete all files +that might be invalid. One of the files this deletes is +@file{Makefile}; if @samp{make distclean} complains that @file{Makefile} +does not exist, it probably means that the directory is already suitably +clean. However, with the recommended method of building in a separate +@var{objdir}, you should simply use a different @var{objdir} for each +target. + +Second, when configuring a native system, either @command{cc} or +@command{gcc} must be in your path or you must set @env{CC} in +your environment before running configure. Otherwise the configuration +scripts may fail. + +Note that the bootstrap compiler and the resulting GCC must be link +compatible, else the bootstrap will fail with linker errors about +incompatible object file formats. Several multilibed targets are +affected by this requirement, see +@ifnothtml +@ref{Specific, host/target specific installation notes}. +@end ifnothtml +@ifhtml +@uref{specific.html,,host/target specific installation notes}. +@end ifhtml + +To configure GCC: + +@example + % mkdir @var{objdir} + % cd @var{objdir} + % @var{srcdir}/configure [@var{options}] [@var{target}] +@end example + + +@heading Target specification +@itemize @bullet +@item +GCC has code to correctly determine the correct value for @var{target} +for nearly all native systems. Therefore, we highly recommend you not +provide a configure target when configuring a native compiler. + +@item +@var{target} must be specified as @option{--target=@var{target}} +when configuring a cross compiler; examples of valid targets would be +i960-rtems, m68k-coff, sh-elf, etc. + +@item +Specifying just @var{target} instead of @option{--target=@var{target}} +implies that the host defaults to @var{target}. +@end itemize + + +@heading Options specification + +Use @var{options} to override several configure time options for +GCC@. A list of supported @var{options} follows; @command{configure +--help} may list other options, but those not listed below may not +work and should not normally be used. + +@table @code +@item --prefix=@var{dirname} +Specify the toplevel installation +directory. This is the recommended way to install the tools into a directory +other than the default. The toplevel installation directory defaults to +@file{/usr/local}. + +We @strong{highly} recommend against @var{dirname} being the same or a +subdirectory of @var{objdir} or vice versa. + +These additional options control where certain parts of the distribution +are installed. Normally you should not need to use these options. +@table @code + +@item --exec-prefix=@var{dirname} +Specify the toplevel installation directory for architecture-dependent +files. The default is @file{@var{prefix}}. + +@item --bindir=@var{dirname} +Specify the installation directory for the executables called by users +(such as @command{gcc} and @command{g++}). The default is +@file{@var{exec-prefix}/bin}. + +@item --libdir=@var{dirname} +Specify the installation directory for object code libraries and +internal parts of GCC@. The default is @file{@var{exec-prefix}/lib}. + +@item --with-slibdir=@var{dirname} +Specify the installation directory for the shared libgcc library. The +default is @file{@var{libdir}}. + +@item --infodir=@var{dirname} +Specify the installation directory for documentation in info format. +The default is @file{@var{prefix}/info}. + +@item --mandir=@var{dirname} +Specify the installation directory for manual pages. The default is +@file{@var{prefix}/man}. (Note that the manual pages are only extracts from +the full GCC manuals, which are provided in Texinfo format. The +@command{g77} manpage is unmaintained and may be out of date; the others +are derived by an automatic conversion process from parts of the full +manual.) + +@item --with-gxx-include-dir=@var{dirname} +Specify +the installation directory for G++ header files. The default is +@file{@var{prefix}/include/g++-v3}. + +@end table + +@item --program-prefix=@var{prefix} +GCC supports some transformations of the names of its programs when +installing them. This option prepends @var{prefix} to the names of +programs to install in @var{bindir} (see above). For example, specifying +@option{--program-prefix=foo-} would result in @samp{gcc} +being installed as @file{/usr/local/bin/foo-gcc}. + +@item --program-suffix=@var{suffix} +Appends @var{suffix} to the names of programs to install in @var{bindir} +(see above). For example, specifying @option{--program-suffix=-3.1} +would result in @samp{gcc} being installed as +@file{/usr/local/bin/gcc-3.1}. + +@item --program-transform-name=@var{pattern} +Applies the @samp{sed} script @var{pattern} to be applied to the names +of programs to install in @var{bindir} (see above). @var{pattern} has to +consist of one or more basic @samp{sed} editing commands, separated by +semicolons. For example, if you want the @samp{gcc} program name to be +transformed to the installed program @file{/usr/local/bin/myowngcc} and +the @samp{g++} program name to be transformed to +@file{/usr/local/bin/gspecial++} without changing other program names, +you could use the pattern +@option{--program-transform-name='s/^gcc$/myowngcc/; s/^g++$/gspecial++/'} +to achieve this effect. + +All three options can be combined and used together, resulting in more +complex conversion patterns. As a basic rule, @var{prefix} (and +@var{suffix}) are prepended (appended) before further transformations +can happen with a special transformation script @var{pattern}. + +As currently implemented, this options only take effect for native +builds; cross compiler binaries' names are not transformed even when a +transformation is explicitly asked for by one of this options. + +For native builds, some of the installed programs are also installed +with the target alias in front of their name, as in +@samp{i686-pc-linux-gnu-gcc}. All of the above transformations happen +before the target alias is prepended to the name - so, specifying +@option{--program-prefix=foo-} and @option{program-suffix=-3.1}, the +resulting binary would be installed as +@file{/usr/local/bin/i686-pc-linux-gnu-foo-gcc-3.1}. + +As a last shortcoming, none of the installed CHILL and Ada programs are +transformed yet, which will be fixed in some time. + +@item --with-local-prefix=@var{dirname} +Specify the +installation directory for local include files. The default is +@file{/usr/local}. Specify this option if you want the compiler to +search directory @file{@var{dirname}/include} for locally installed +header files @emph{instead} of @file{/usr/local/include}. + +You should specify @option{--with-local-prefix} @strong{only} if your +site has a different convention (not @file{/usr/local}) for where to put +site-specific files. + +The default value for @option{--with-local-prefix} is @file{/usr/local} +regardless of the value of @option{--prefix}. Specifying +@option{--prefix} has no effect on which directory GCC searches for +local header files. This may seem counterintuitive, but actually it is +logical. + +The purpose of @option{--prefix} is to specify where to @emph{install +GCC}. The local header files in @file{/usr/local/include}---if you put +any in that directory---are not part of GCC@. They are part of other +programs---perhaps many others. (GCC installs its own header files in +another directory which is based on the @option{--prefix} value.) + +@strong{Do not} specify @file{/usr} as the @option{--with-local-prefix}! +The directory you use for @option{--with-local-prefix} @strong{must not} +contain any of the system's standard header files. If it did contain +them, certain programs would be miscompiled (including GNU Emacs, on +certain targets), because this would override and nullify the header +file corrections made by the @code{fixincludes} script. + +Indications are that people who use this option use it based on mistaken +ideas of what it is for. People use it as if it specified where to +install part of GCC@. Perhaps they make this assumption because +installing GCC creates the directory. + +@item --enable-shared[=@var{package}[,@dots{}]] +Build shared versions of libraries, if shared libraries are supported on +the target platform. Unlike GCC 2.95.x and earlier, shared libraries +are enabled by default on all platforms that support shared libraries, +except for @samp{libobjc} which is built as a static library only by +default. + +If a list of packages is given as an argument, build shared libraries +only for the listed packages. For other packages, only static libraries +will be built. Package names currently recognized in the GCC tree are +@samp{libgcc} (also known as @samp{gcc}), @samp{libstdc++} (not +@samp{libstdc++-v3}), @samp{libffi}, @samp{zlib}, @samp{boehm-gc} and +@samp{libjava}. Note that @samp{libobjc} does not recognize itself by +any name, so, if you list package names in @option{--enable-shared}, +you will only get static Objective-C libraries. @samp{libf2c} and +@samp{libiberty} do not support shared libraries at all. + +Use @option{--disable-shared} to build only static libraries. Note that +@option{--disable-shared} does not accept a list of package names as +argument, only @option{--enable-shared} does. + +@item @anchor{with-gnu-as}--with-gnu-as +Specify that the compiler should assume that the +assembler it finds is the GNU assembler. However, this does not modify +the rules to find an assembler and will result in confusion if found +assembler is not actually the GNU assembler. (Confusion will also +result if the compiler finds the GNU assembler but has not been +configured with @option{--with-gnu-as}.) If you have more than one +assembler installed on your system, you may want to use this option in +connection with @option{--with-as=@var{pathname}}. + +The systems where it makes a difference whether you use the GNU assembler are +@samp{hppa1.0-@var{any}-@var{any}}, @samp{hppa1.1-@var{any}-@var{any}}, +@samp{i386-@var{any}-sysv}, @samp{i386-@var{any}-isc}, +@samp{i860-@var{any}-bsd}, @samp{m68k-bull-sysv}, +@samp{m68k-hp-hpux}, @samp{m68k-sony-bsd}, +@samp{m68k-altos-sysv}, @samp{m68000-hp-hpux}, +@samp{m68000-att-sysv}, @samp{@var{any}-lynx-lynxos}, +and @samp{mips-@var{any}}. +On any other system, @option{--with-gnu-as} has no effect. + +On the systems listed above (except for the HP-PA, for ISC on the +386, and for @samp{mips-sgi-irix5.*}), if you use the GNU assembler, +you should also use the GNU linker (and specify @option{--with-gnu-ld}). + +@item --with-as=@var{pathname} +Specify that the +compiler should use the assembler pointed to by @var{pathname}, rather +than the one found by the standard rules to find an assembler, which +are: +@itemize @bullet +@item +Check the +@file{@var{exec_prefix}/lib/gcc-lib/@var{target}/@var{version}} +directory, where @var{exec_prefix} defaults to @var{prefix} which +defaults to @file{/usr/local} unless overridden by the +@option{--prefix=@var{pathname}} switch described above. @var{target} is the +target system triple, such as @samp{sparc-sun-solaris2.7}, and +@var{version} denotes the GCC version, such as 3.0. +@item +Check operating system specific directories (e.g.@: @file{/usr/ccs/bin} on +Sun Solaris 2). +@end itemize +Note that these rules do not check for the value of @env{PATH}. You may +want to use @option{--with-as} if no assembler is installed in the +directories listed above, or if you have multiple assemblers installed +and want to choose one that is not found by the above rules. + +@item @anchor{with-gnu-ld}--with-gnu-ld +Same as @uref{#with-gnu-as,,@option{--with-gnu-as}} +but for linker. + + +@item --with-ld=@var{pathname} +Same as +@option{--with-as}, but for the linker. + +@item --with-stabs +Specify that stabs debugging +information should be used instead of whatever format the host normally +uses. Normally GCC uses the same debug format as the host system. + +On MIPS based systems and on Alphas, you must specify whether you want +GCC to create the normal ECOFF debugging format, or to use BSD-style +stabs passed through the ECOFF symbol table. The normal ECOFF debug +format cannot fully handle languages other than C@. BSD stabs format can +handle other languages, but it only works with the GNU debugger GDB@. + +Normally, GCC uses the ECOFF debugging format by default; if you +prefer BSD stabs, specify @option{--with-stabs} when you configure GCC@. + +No matter which default you choose when you configure GCC, the user +can use the @option{-gcoff} and @option{-gstabs+} options to specify explicitly +the debug format for a particular compilation. + +@option{--with-stabs} is meaningful on the ISC system on the 386, also, if +@option{--with-gas} is used. It selects use of stabs debugging +information embedded in COFF output. This kind of debugging information +supports C++ well; ordinary COFF debugging information does not. + +@option{--with-stabs} is also meaningful on 386 systems running SVR4. It +selects use of stabs debugging information embedded in ELF output. The +C++ compiler currently (2.6.0) does not support the DWARF debugging +information normally used on 386 SVR4 platforms; stabs provide a +workable alternative. This requires gas and gdb, as the normal SVR4 +tools can not generate or interpret stabs. + +@item --disable-multilib +Specify that multiple target +libraries to support different target variants, calling +conventions, etc should not be built. The default is to build a +predefined set of them. + +Some targets provide finer-grained control over which multilibs are built +(e.g., @option{--disable-softfloat}): +@table @code + +@item arc-*-elf* +biendian. + +@item arm-*-* +fpu, 26bit, underscore, interwork, biendian, nofmult. + +@item m68*-*-* +softfloat, m68881, m68000, m68020. + +@item mips*-*-* +single-float, biendian, softfloat. + +@item powerpc*-*-*, rs6000*-*-* +aix64, pthread, softfloat, powercpu, powerpccpu, powerpcos, biendian, +sysv, aix. + +@end table + +@item --enable-threads +Specify that the target +supports threads. This affects the Objective-C compiler and runtime +library, and exception handling for other languages like C++ and Java. +On some systems, this is the default. + +In general, the best (and, in many cases, the only known) threading +model available will be configured for use. Beware that on some +systems, gcc has not been taught what threading models are generally +available for the system. In this case, @option{--enable-threads} is an +alias for @option{--enable-threads=single}. + +@item --disable-threads +Specify that threading support should be disabled for the system. +This is an alias for @option{--enable-threads=single}. + +@item --enable-threads=@var{lib} +Specify that +@var{lib} is the thread support library. This affects the Objective-C +compiler and runtime library, and exception handling for other languages +like C++ and Java. The possibilities for @var{lib} are: + +@table @code +@item aix +AIX thread support. +@item dce +DCE thread support. +@item mach +Generic MACH thread support, known to work on NeXTSTEP@. (Please note +that the file needed to support this configuration, @file{gthr-mach.h}, is +missing and thus this setting will cause a known bootstrap failure.) +@item no +This is an alias for @samp{single}. +@item posix +Generic POSIX thread support. +@item pthreads +Same as @samp{posix} on arm*-*-linux*, *-*-chorusos* and *-*-freebsd* +only. A future release of gcc might remove this alias or extend it +to all platforms. +@item rtems +RTEMS thread support. +@item single +Disable thread support, should work for all platforms. +@item solaris +Sun Solaris 2 thread support. +@item vxworks +VxWorks thread support. +@item win32 +Microsoft Win32 API thread support. +@end table + +@item --with-cpu=@var{cpu} +Specify which cpu variant the +compiler should generate code for by default. This is currently +only supported on the some ports, specifically arm, powerpc, and +SPARC@. If configure does not recognize the model name (e.g.@: arm700, +603e, or ultrasparc) you provide, please check the configure script +for a complete list of supported models. + +@item --enable-altivec +Specify that the target supports AltiVec vector enhancements. This +option will adjust the ABI for AltiVec enhancements, as well as generate +AltiVec code when appropriate. This option is only available for +PowerPC systems. + +@item --enable-target-optspace +Specify that target +libraries should be optimized for code space instead of code speed. +This is the default for the m32r platform. + +@item --disable-cpp +Specify that a user visible @command{cpp} program should not be installed. + +@item --with-cpp-install-dir=@var{dirname} +Specify that the user visible @command{cpp} program should be installed +in @file{@var{prefix}/@var{dirname}/cpp}, in addition to @var{bindir}. + +@item --enable-maintainer-mode +The build rules that +regenerate the GCC master message catalog @file{gcc.pot} are normally +disabled. This is because it can only be rebuilt if the complete source +tree is present. If you have changed the sources and want to rebuild the +catalog, configuring with @option{--enable-maintainer-mode} will enable +this. Note that you need a recent version of the @code{gettext} tools +to do so. + +@item --enable-version-specific-runtime-libs +Specify +that runtime libraries should be installed in the compiler specific +subdirectory (@file{@var{libsubdir}}) rather than the usual places. In +addition, @samp{libstdc++}'s include files will be installed in +@file{@var{libsubdir}/include/g++} unless you overruled it by using +@option{--with-gxx-include-dir=@var{dirname}}. Using this option is +particularly useful if you intend to use several versions of GCC in +parallel. This is currently supported by @samp{libf2c} and +@samp{libstdc++}, and is the default for @samp{libobjc} which cannot be +changed in this case. + +@item --enable-languages=@var{lang1},@var{lang2},@dots{} +Specify that only a particular subset of compilers and +their runtime libraries should be built. For a list of valid values for +@var{langN} you can issue the following command in the +@file{gcc} directory of your GCC source tree:@* +@example +grep language= */config-lang.in +@end example +Currently, you can use any of the following: +@code{ada}, @code{c}, @code{c++}, @code{f77}, @code{java}, @code{objc}. +@code{CHILL} is not currently maintained, and will almost +certainly fail to compile. Building the Ada compiler has special +requirements, see below.@* +If you do not pass this flag, all languages available in the @file{gcc} +sub-tree will be configured. Re-defining @code{LANGUAGES} when calling +@samp{make bootstrap} @strong{does not} work anymore, as those +language sub-directories might not have been configured! + +@item --disable-libgcj +Specify that the run-time libraries +used by GCJ should not be built. This is useful in case you intend +to use GCJ with some other run-time, or you're going to install it +separately, or it just happens not to build on your particular +machine. In general, if the Java front end is enabled, the GCJ +libraries will be enabled too, unless they're known to not work on +the target platform. If GCJ is enabled but @samp{libgcj} isn't built, you +may need to port it; in this case, before modifying the top-level +@file{configure.in} so that @samp{libgcj} is enabled by default on this platform, +you may use @option{--enable-libgcj} to override the default. + +@item --with-dwarf2 +Specify that the compiler should +use DWARF 2 debugging information as the default. + +@item --enable-win32-registry +@itemx --enable-win32-registry=@var{key} +@itemx --disable-win32-registry +The @option{--enable-win32-registry} option enables Windows-hosted GCC +to look up installations paths in the registry using the following key: + +@smallexample +@code{HKEY_LOCAL_MACHINE\SOFTWARE\Free Software Foundation\@var{key}} +@end smallexample + +@var{key} defaults to GCC version number, and can be overridden by the +@option{--enable-win32-registry=@var{key}} option. Vendors and distributors +who use custom installers are encouraged to provide a different key, +perhaps one comprised of vendor name and GCC version number, to +avoid conflict with existing installations. This feature is enabled +by default, and can be disabled by @option{--disable-win32-registry} +option. This option has no effect on the other hosts. + +@item --nfp +Specify that the machine does not have a floating point unit. This +option only applies to @samp{m68k-sun-sunos@var{n}} and +@samp{m68k-isi-bsd}. On any other system, @option{--nfp} has no effect. + +@item --enable-checking +@itemx --enable-checking=@var{list} +When you specify this option, the compiler is built to perform checking +of tree node types when referencing fields of that node, and some other +internal consistency checks. This does not change the generated code, +but adds error checking within the compiler. This will slow down the +compiler and may only work properly if you are building the compiler +with GCC@. This is on by default when building from CVS or snapshots, +but off for releases. More control over the checks may be had by +specifying @var{list}; the categories of checks available are +@samp{misc}, @samp{tree}, @samp{gc}, @samp{rtl} and @samp{gcac}. The +default when @var{list} is not specified is @samp{misc,tree,gc}; the +checks @samp{rtl} and @samp{gcac} are very expensive. + +@item --enable-nls +@itemx --disable-nls +The @option{--enable-nls} option enables Native Language Support (NLS), +which lets GCC output diagnostics in languages other than American +English. Native Language Support is enabled by default if not doing a +canadian cross build. The @option{--disable-nls} option disables NLS@. + +@item --with-included-gettext +If NLS is enabled, the @option{--with-included-gettext} option causes the build +procedure to prefer its copy of GNU @command{gettext}. + +@item --with-catgets +If NLS is enabled, and if the host lacks @code{gettext} but has the +inferior @code{catgets} interface, the GCC build procedure normally +ignores @code{catgets} and instead uses GCC's copy of the GNU +@code{gettext} library. The @option{--with-catgets} option causes the +build procedure to use the host's @code{catgets} in this situation. + +@item --with-system-zlib +Use installed zlib rather than that included with GCC@. This option +only applies if the Java front end is being built. +@end table + +Some options which only apply to building cross compilers: +@table @code +@item --with-headers=@var{dir} +Specifies a directory +which has target include files. +@emph{This options is required} when building a cross +compiler, if @file{@var{prefix}/@var{target}/sys-include} doesn't pre-exist. +These include files will be copied into the @file{gcc} install directory. +Fixincludes will be run on these files to make them compatible with +GCC. +@item --with-libs=``@var{dir1} @var{dir2} @dots{} @var{dirN}'' +Specifies a list of directories which contain the target runtime +libraries. These libraries will be copied into the @file{gcc} install +directory. +@item --with-newlib +Specifies that @samp{newlib} is +being used as the target C library. This causes @code{__eprintf} to be +omitted from @file{libgcc.a} on the assumption that it will be provided by +@samp{newlib}. +@end table + +Note that each @option{--enable} option has a corresponding +@option{--disable} option and that each @option{--with} option has a +corresponding @option{--without} option. + +@html +
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Building**************************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Building, Testing, Configuration, Installing GCC +@end ifnothtml +@ifset buildhtml +@html +

Installing GCC: Building

+@end html +@ifnothtml +@chapter Building +@end ifnothtml +@cindex Installing GCC: Building + +Now that GCC is configured, you are ready to build the compiler and +runtime libraries. + +We @strong{highly} recommend that GCC be built using GNU make; +other versions may work, then again they might not. +GNU make is required for compiling GNAT, the Ada compiler. + +(For example, many broken versions of make will fail if you use the +recommended setup where @var{objdir} is different from @var{srcdir}. +Other broken versions may recompile parts of the compiler when +installing the compiler.) + +Some commands executed when making the compiler may fail (return a +nonzero status) and be ignored by @code{make}. These failures, which +are often due to files that were not found, are expected, and can safely +be ignored. + +It is normal to have compiler warnings when compiling certain files. +Unless you are a GCC developer, you can generally ignore these warnings +unless they cause compilation to fail. + +On certain old systems, defining certain environment variables such as +@env{CC} can interfere with the functioning of @command{make}. + +If you encounter seemingly strange errors when trying to build the +compiler in a directory other than the source directory, it could be +because you have previously configured the compiler in the source +directory. Make sure you have done all the necessary preparations. + +If you build GCC on a BSD system using a directory stored in an old System +V file system, problems may occur in running @code{fixincludes} if the +System V file system doesn't support symbolic links. These problems +result in a failure to fix the declaration of @code{size_t} in +@file{sys/types.h}. If you find that @code{size_t} is a signed type and +that type mismatches occur, this could be the cause. + +The solution is not to use such a directory for building GCC@. + +When building from CVS or snapshots, or if you modify parser sources, +you need the Bison parser generator installed. Any version 1.25 or +later should work; older versions may also work. If you do not modify +parser sources, releases contain the Bison-generated files and you do +not need Bison installed to build them. + +When building from CVS or snapshots, or if you modify Texinfo +documentation, you need version 4.0 or later of Texinfo installed if you +want Info documentation to be regenerated. Releases contain Info +documentation pre-built for the unmodified documentation in the release. + +@section Building a native compiler + +For a native build issue the command @samp{make bootstrap}. This +will build the entire GCC system, which includes the following steps: + +@itemize @bullet +@item +Build host tools necessary to build the compiler such as texinfo, bison, +gperf. + +@item +Build target tools for use by the compiler such as binutils (bfd, +binutils, gas, gprof, ld, and opcodes) +if they have been individually linked +or moved into the top level GCC source tree before configuring. + +@item +Perform a 3-stage bootstrap of the compiler. + +@item +Perform a comparison test of the stage2 and stage3 compilers. + +@item +Build runtime libraries using the stage3 compiler from the previous step. + +@end itemize + +If you are short on disk space you might consider @samp{make +bootstrap-lean} instead. This is identical to @samp{make +bootstrap} except that object files from the stage1 and +stage2 of the 3-stage bootstrap of the compiler are deleted as +soon as they are no longer needed. + + +If you want to save additional space during the bootstrap and in +the final installation as well, you can build the compiler binaries +without debugging information with @samp{make CFLAGS='-O' LIBCFLAGS='-g +-O2' LIBCXXFLAGS='-g -O2 -fno-implicit-templates' bootstrap}. This will save +roughly 40% of disk space both for the bootstrap and the final installation. +(Libraries will still contain debugging information.) + +If you wish to use non-default GCC flags when compiling the stage2 and +stage3 compilers, set @code{BOOT_CFLAGS} on the command line when doing +@samp{make bootstrap}. Non-default optimization flags are less well +tested here than the default of @samp{-g -O2}, but should still work. +In a few cases, you may find that you need to specify special flags such +as @option{-msoft-float} here to complete the bootstrap; or, if the +native compiler miscompiles the stage1 compiler, you may need to work +around this, by choosing @code{BOOT_CFLAGS} to avoid the parts of the +stage1 compiler that were miscompiled, or by using @samp{make +bootstrap4} to increase the number of stages of bootstrap. + +If you used the flag @option{--enable-languages=@dots{}} to restrict +the compilers to be built, only those you've actually enabled will be +built. This will of course only build those runtime libraries, for +which the particular compiler has been built. Please note, +that re-defining @env{LANGUAGES} when calling @samp{make bootstrap} +@strong{does not} work anymore! + +If the comparison of stage2 and stage3 fails, this normally indicates +that the stage2 compiler has compiled GCC incorrectly, and is therefore +a potentially serious bug which you should investigate and report. (On +a few systems, meaningful comparison of object files is impossible; they +always appear ``different''. If you encounter this problem, you will +need to disable comparison in the @file{Makefile}.) + +@section Building a cross compiler + +We recommend reading the +@uref{http://www.objsw.com/CrossGCC/,,crossgcc FAQ} +for information about building cross compilers. + +When building a cross compiler, it is not generally possible to do a +3-stage bootstrap of the compiler. This makes for an interesting problem +as parts of GCC can only be built with GCC@. + +To build a cross compiler, we first recommend building and installing a +native compiler. You can then use the native GCC compiler to build the +cross compiler. The installed native compiler needs to be GCC version +2.95 or later. + +Assuming you have already installed a native copy of GCC and configured +your cross compiler, issue the command @command{make}, which performs the +following steps: + +@itemize @bullet +@item +Build host tools necessary to build the compiler such as texinfo, bison, +gperf. + +@item +Build target tools for use by the compiler such as binutils (bfd, +binutils, gas, gprof, ld, and opcodes) +if they have been individually linked or moved into the top level GCC source +tree before configuring. + +@item +Build the compiler (single stage only). + +@item +Build runtime libraries using the compiler from the previous step. +@end itemize + +Note that if an error occurs in any step the make process will exit. + +@section Building in parallel + +If you have a multiprocessor system you can use @samp{make bootstrap +MAKE="make -j 2" -j 2} or just @samp{make -j 2 bootstrap} +for GNU Make 3.79 and above instead of just @samp{make bootstrap} +when building GCC@. You can use a bigger number instead of two if +you like. In most cases, it won't help to use a number bigger than +the number of processors in your machine. + +@section Building the Ada compiler + +In order to build GNAT, the Ada compiler, you need a working GNAT +compiler, since the Ada front end is written in Ada (with some +GNAT-specific extensions), and GNU make. + +However, you do not need a full installation of GNAT, just the GNAT +binary @file{gnat1}, a copy of @file{gnatbind}, and a compiler driver +which can deal with Ada input (by invoking the @file{gnat1} binary). +You can specify this compiler driver by setting the @env{ADAC} +environment variable at the configure step. @command{configure} can +detect the driver automatically if it has got a common name such as +@command{gcc} or @command{gnatgcc}. Of course, you still need a working +C compiler (the compiler driver can be different or not). + +Additional build tools (such as @command{gnatmake}) or a working GNAT +run-time library installation are usually @emph{not} required. However, +if you want to boostrap the compiler using a minimal version of GNAT, +you have to issue the following commands before invoking @samp{make +boostrap} (this assumes that you start with an unmodified and consistent +source distribution): + +@example + cd @var{srcdir}/gcc/ada + touch treeprs.ads [es]info.h nmake.ad[bs] +@end example + +At the moment, the GNAT library and several tools for GNAT are not built +by @samp{make bootstrap}. You have to invoke +@samp{make gnatlib_and_tools} in the @file{@var{objdir}/gcc} +subdirectory before proceeding with the next steps. + +For example, you can build a native Ada compiler by issuing the +following commands (assuming @command{make} is GNU make): + +@example + cd @var{objdir} + @var{srcdir}/configure --enable-languages=c,ada + cd @var{srcdir}/gcc/ada + touch treeprs.ads [es]info.h nmake.ad[bs] + cd @var{objdir} + make bootstrap + cd gcc + make gnatlib_and_tools + cd .. +@end example + +Currently, when compiling the Ada front end, you cannot use the parallel +build feature described in the previous section. + +@html +
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Testing***************************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Testing, Final install, Building, Installing GCC +@end ifnothtml +@ifset testhtml +@html +

Installing GCC: Testing

+@end html +@ifnothtml +@chapter Installing GCC: Testing +@end ifnothtml +@cindex Testing +@cindex Installing GCC: Testing +@cindex Testsuite + +Before you install GCC, you might wish to run the testsuite. This +step is optional and may require you to download additional software. + +First, you must have @uref{download.html,,downloaded the testsuites}. +The full distribution contains testsuites; only if you downloaded the +``core'' compiler plus any front ends, you do not have the testsuites. + +Second, you must have a @uref{http://www.gnu.org/software/dejagnu/,,current version of DejaGnu} installed; +dejagnu 1.3 is not sufficient. + +Now you may need specific preparations: + +@itemize @bullet + +@item +The following environment variables may need to be set appropriately, as in +the following example (which assumes that DejaGnu has been installed +under @file{/usr/local}): + +@example + TCL_LIBRARY = /usr/local/share/tcl8.0 + DEJAGNULIBS = /usr/local/share/dejagnu +@end example + +On systems such as Cygwin, these paths are required to be actual +paths, not mounts or links; presumably this is due to some lack of +portability in the DejaGnu code. + +If the directories where @command{runtest} and @command{expect} were +installed are in the @env{PATH}, it should not be necessary to set these +environment variables. + +@end itemize + +Finally, you can run the testsuite (which may take a long time): +@example + cd @var{objdir}; make -k check +@end example + +The testing process will try to test as many components in the GCC +distribution as possible, including the C, C++, Objective-C and Fortran +compilers as well as the C++ and Java runtime libraries. + +@section How can I run the test suite on selected tests? + +As a first possibility to cut down the number of tests that are run it is +possible to use @samp{make check-gcc} or @samp{make check-g++} +in the @file{gcc} subdirectory of the object directory. To further cut down the +tests the following is possible: + +@example + make check-gcc RUNTESTFLAGS="execute.exp @var{other-options}" +@end example + +This will run all @command{gcc} execute tests in the testsuite. + +@example + make check-g++ RUNTESTFLAGS="old-deja.exp=9805* @var{other-options}" +@end example + +This will run the @command{g++} ``old-deja'' tests in the testsuite where the filename +matches @samp{9805*}. + +The @file{*.exp} files are located in the testsuite directories of the GCC +source, the most important ones being @file{compile.exp}, +@file{execute.exp}, @file{dg.exp} and @file{old-deja.exp}. +To get a list of the possible @file{*.exp} files, pipe the +output of @samp{make check} into a file and look at the +@samp{Running @dots{} .exp} lines. + +@section How to interpret test results + +After the testsuite has run you'll find various @file{*.sum} and @file{*.log} +files in the testsuite subdirectories. The @file{*.log} files contain a +detailed log of the compiler invocations and the corresponding +results, the @file{*.sum} files summarize the results. These summaries list +all the tests that have been run with a corresponding status code: + +@itemize @bullet +@item +PASS: the test passed as expected +@item +XPASS: the test unexpectedly passed +@item +FAIL: the test unexpectedly failed +@item +XFAIL: the test failed as expected +@item +UNSUPPORTED: the test is not supported on this platform +@item +ERROR: the testsuite detected an error +@item +WARNING: the testsuite detected a possible problem +@end itemize + +It is normal for some tests to report unexpected failures. At the +current time our testing harness does not allow fine grained control +over whether or not a test is expected to fail. We expect to fix this +problem in future releases. + + +@section Submitting test results + +If you want to report the results to the GCC project, use the +@file{contrib/test_summary} shell script. Start it in the @var{objdir} with + +@example + @var{srcdir}/contrib/test_summary -p your_commentary.txt \ + -m gcc-testresults@@gcc.gnu.org |sh +@end example + +This script uses the @command{Mail} program to send the results, so +make sure it is in your @env{PATH}. The file @file{your_commentary.txt} is +prepended to the testsuite summary and should contain any special +remarks you have on your results or your build environment. Please +do not edit the testsuite result block or the subject line, as these +messages are automatically parsed and presented at the +@uref{http://gcc.gnu.org/testresults/,,GCC testresults} web +page. Here you can also gather information on how specific tests +behave on different platforms and compare them with your results. A +few failing testcases are possible even on released versions and you +should look here first if you think your results are unreasonable. + +@html +
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Final install*********************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Final install, , Testing, Installing GCC +@end ifnothtml +@ifset finalinstallhtml +@html +

Installing GCC: Final installation

+@end html +@ifnothtml +@chapter Installing GCC: Final installation +@end ifnothtml + +Now that GCC has been built (and optionally tested), you can install it with +@example +cd @var{objdir}; make install +@end example + +That step completes the installation of GCC; user level binaries can +be found in @file{@var{prefix}/bin} where @var{prefix} is the value you +specified with the @option{--prefix} to configure (or @file{/usr/local} +by default). (If you specified @option{--bindir}, that directory will +be used instead; otherwise, if you specified @option{--exec-prefix}, +@file{@var{exec-prefix}/bin} will be used.) Headers for the C++ and +Java libraries are installed in @file{@var{prefix}/include}; libraries +in @file{@var{libdir}} (normally @file{@var{prefix}/lib}); internal +parts of the compiler in @file{@var{libdir}/gcc-lib}; documentation in +info format in @file{@var{infodir}} (normally @file{@var{prefix}/info}). + +If you built a released version of GCC then if you don't mind, please +quickly review the build status page for +@uref{http://gcc.gnu.org/gcc-3.0/buildstat.html,,3.0} or +@uref{http://gcc.gnu.org/gcc-2.95/buildstat.html,,2.95}. +If your system is not listed for the version of GCC that you built, +send a note to +@email{gcc@@gcc.gnu.org} indicating +that you successfully built and installed GCC. +Include the following information: + +@itemize @bullet +@item +Output from running @file{@var{srcdir}/config.guess}. Do not send us +that file itself, just the one-line output from running it. + +@item +The output of @samp{gcc -v} for your newly installed gcc. +This tells us which version of GCC you built and the options you passed to +configure. + +@item +If the build was for GNU/Linux, also include: +@itemize @bullet +@item +The distribution name and version (e.g., Red Hat 7.1 or Debian 2.2.3); +this information should be available from @file{/etc/issue}. + +@item +The version of the Linux kernel, available from @samp{uname --version} +or @samp{uname -a}. + +@item +The version of glibc you used; for RPM-based systems like Red Hat, +Mandrake, and SuSE type @samp{rpm -q glibc} to get the glibc version, +and on systems like Debian and Progeny use @samp{dpkg -l libc6}. +@end itemize +For other systems, you can include similar information if you think it is +relevant. + +@item +Any other information that you think would be useful to people building +GCC on the same configuration. The new entry in the build status list +will include a link to the archived copy of your message. +@end itemize + +We'd also like to know if the +@ifnothtml +@ref{Specific, host/target specific installation notes} +@end ifnothtml +@ifhtml +@uref{specific.html,,host/target specific installation notes} +@end ifhtml +didn't include your host/target information or if that information is +incomplete or out of date. Send a note to +@email{gcc@@gcc.gnu.org} telling us how the information should be changed. + +If you find a bug, please report it following our +@uref{../bugs.html,,bug reporting guidelines}. + +If you want to print the GCC manuals, do @samp{cd @var{objdir}; make +dvi}. You will need to have @command{texi2dvi} (version at least 4.0) +and @TeX{} installed. This creates a number of @file{.dvi} files in +subdirectories of @file{@var{objdir}}; these may be converted for +printing with programs such as @command{dvips}. You can also +@uref{http://www.gnu.org/order/order.html,,buy printed manuals from the +Free Software Foundation}, though such manuals may not be for the most +recent version of GCC@. + +@html +
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Binaries**************************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Binaries, Specific, Installing GCC, Top +@end ifnothtml +@ifset binarieshtml +@html +

Installing GCC: Binaries

+@end html +@ifnothtml +@chapter Installing GCC: Binaries +@end ifnothtml +@cindex Binaries +@cindex Installing GCC: Binaries + +We are often asked about pre-compiled versions of GCC@. While we cannot +provide these for all platforms, below you'll find links to binaries for +various platforms where creating them by yourself is not easy due to various +reasons. + +Please note that we did not create these binaries, nor do we +support them. If you have any problems installing them, please +contact their makers. + +@itemize +@item +AIX: +@itemize +@item +@uref{http://freeware.bull.net,,Bull's Freeware and Shareware Archive for AIX}; + +@item +@uref{http://aixpdslib.seas.ucla.edu,,UCLA Software Library for AIX}; +@end itemize + +@item +DOS---@uref{http://www.delorie.com/djgpp/,,DJGPP}; + +@item +HP-UX: +@itemize +@item +@uref{http://hpux.cae.wisc.edu/,,HP-UX Porting Center}; + +@item +@uref{ftp://sunsite.informatik.rwth-aachen.de/pub/packages/gcc_hpux/,,Binaries for HP-UX 11.00 at Aachen University of Technology}. +@end itemize + +@item +@uref{http://www.sco.com/skunkware/devtools/index.html#gcc,,SCO +OpenServer/Unixware}; + +@item +Solaris 2 (SPARC, Intel)---@uref{http://www.sunfreeware.com/,,Sunfreeware}; + +@item +SGI---@uref{http://freeware.sgi.com/,,SGI Freeware}; + +@item +Windows 95, 98, and NT: +@itemize +@item +The @uref{http://sources.redhat.com/cygwin/,,Cygwin} project; +@item +@uref{http://www.xraylith.wisc.edu/~khan/software/gnu-win32/,,GNU Win32} +related projects by Mumit Khan. +@end itemize + +@item +@uref{ftp://ftp.thewrittenword.com/packages/free/by-name/,,The +Written Word} offers binaries for Solaris 2.5.1, 2.6, 2.7/SPARC, 2.7/Intel, +IRIX 6.2, 6.5, Digital UNIX 4.0D, HP-UX 10.20, and HP-UX 11.00. + +@item +Hitachi H8/300[HS]---@uref{http://h8300-hms.sourceforge.net/,,GNU +Development Tools for the Hitachi H8/300[HS] Series} + +@end itemize + +In addition to those specific offerings, you can get a binary +distribution CD-ROM from the +@uref{http://www.fsf.org/order/order.html,,Free Software Foundation}. +It contains binaries for a number of platforms, and +includes not only GCC, but other stuff as well. The current CD does +not contain the latest version of GCC, but it should allow +bootstrapping the compiler. An updated version of that disk is in the +works. + +@html +
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Specific**************************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Specific, Old, Binaries, Top +@end ifnothtml +@ifset specifichtml +@html +

Host/target specific installation notes for GCC

+@end html +@ifnothtml +@chapter Host/target specific installation notes for GCC +@end ifnothtml +@cindex Specific +@cindex Specific installation notes +@cindex Target specific installation +@cindex Host specific installation +@cindex Target specific installation notes + +Please read this document carefully @emph{before} installing the +GNU Compiler Collection on your machine. + +Lists of successful builds for released versions of GCC are +available at our web pages for +@uref{http://gcc.gnu.org/gcc-3.0/buildstat.html,,3.0} +and +@uref{http://gcc.gnu.org/gcc-2.95/buildstat.html,,2.95}. +These lists are updated as new information becomes available. + +@ifhtml +@itemize +@item +@uref{#1750a-*-*,,1750a-*-*} +@item +@uref{#a29k,,a29k} +@item +@uref{#a29k-*-bsd,,a29k-*-bsd} +@item +@uref{#alpha*-*-*,,alpha*-*-*} +@item +@uref{#alpha*-dec-osf*,,alpha*-dec-osf*} +@item +@uref{#alphaev5-cray-unicosmk*,,alphaev5-cray-unicosmk*} +@item +@uref{#arc-*-elf,,arc-*-elf} +@item +@uref{#arm-*-aout,,arm-*-aout} +@item +@uref{#arm-*-elf,,arm-*-elf} +@item +@uref{#arm*-*-linux-gnu,,arm*-*-linux-gnu} +@item +@uref{#arm-*-riscix,,arm-*-riscix} +@item +@uref{#avr,,avr} +@item +@uref{#c4x,,c4x} +@item +@uref{#dos,,DOS} +@item +@uref{#dsp16xx,,dsp16xx} +@item +@uref{#elxsi-elxsi-bsd,,elxsi-elxsi-bsd} +@item +@uref{#*-*-freebsd*,,*-*-freebsd*} +@item +@uref{#h8300-hms,,h8300-hms} +@item +@uref{#hppa*-hp-hpux*,,hppa*-hp-hpux*} +@item +@uref{#hppa*-hp-hpux9,,hppa*-hp-hpux9} +@item +@uref{#hppa*-hp-hpux10,,hppa*-hp-hpux10} +@item +@uref{#hppa*-hp-hpux11,,hppa*-hp-hpux11} +@item +@uref{#i370-*-*,,i370-*-*} +@item +@uref{#*-*-linux-gnu,,*-*-linux-gnu} +@item +@uref{#ix86-*-linux*oldld,,i?86-*-linux*oldld} +@item +@uref{#ix86-*-linux*aout,,i?86-*-linux*aout} +@item +@uref{#ix86-*-linux*,,i?86-*-linux*} +@item +@uref{#ix86-*-sco,,i?86-*-sco} +@item +@uref{#ix86-*-sco3.2v4,,i?86-*-sco3.2v4} +@item +@uref{#ix86-*-sco3.2v5*,,i?86-*-sco3.2v5*} +@item +@uref{#ix86-*-udk,,i?86-*-udk} +@item +@uref{#ix86-*-isc,,i?86-*-isc} +@item +@uref{#ix86-*-esix,,i?86-*-esix} +@item +@uref{#ix86-ibm-aix,,i?86-ibm-aix} +@item +@uref{#ix86-sequent-bsd,,i?86-sequent-bsd} +@item +@uref{#ix86-sequent-ptx1*,,i?86-sequent-ptx1*, i?86-sequent-ptx2*} +@item +@uref{#ix86-*-sysv3*,,i?86-*-sysv3*} +@item +@uref{#i860-intel-osf*,,i860-intel-osf*} +@item +@uref{#ia64-*-linux,,ia64-*-linux} +@item +@uref{#*-lynx-lynxos,,*-lynx-lynxos} +@item +@uref{#*-ibm-aix*,,*-ibm-aix*} +@item +@uref{#m32r-*-elf,,m32r-*-elf} +@item +@uref{#m68000-hp-bsd,,m68000-hp-bsd} +@item +@uref{#m6811-elf,,m6811-elf} +@item +@uref{#m6812-elf,,m6812-elf} +@item +@uref{#m68k-altos,,m68k-altos} +@item +@uref{#m68k-apple-aux,,m68k-apple-aux} +@item +@uref{#m68k-att-sysv,,m68k-att-sysv} +@item +@uref{#m68k-bull-sysv,,m68k-bull-sysv} +@item +@uref{#m68k-crds-unox,,m68k-crds-unox} +@item +@uref{#m68k-hp-hpux,,m68k-hp-hpux} +@item +@uref{#m68k-*-nextstep*,,m68k-*-nextstep*} +@item +@uref{#m68k-ncr-*,,m68k-ncr-*} +@item +@uref{#m68k-sun,,m68k-sun} +@item +@uref{#m68k-sun-sunos4.1.1,,m68k-sun-sunos4.1.1} +@item +@uref{#m88k-*-svr3,,m88k-*-svr3} +@item +@uref{#m88k-*-dgux,,m88k-*-dgux} +@item +@uref{#m88k-tektronix-sysv3,,m88k-tektronix-sysv3} +@item +@uref{#mips-*-*,,mips-*-*} +@item +@uref{#mips-dec-*,,mips-dec-*} +@item +@uref{#mips-mips-bsd,,mips-mips-bsd} +@item +@uref{#mips-mips-riscos*,,mips-mips-riscos*} +@item +@uref{#mips-sgi-irix4,,mips-sgi-irix4} +@item +@uref{#mips-sgi-irix5,,mips-sgi-irix5} +@item +@uref{#mips-sgi-irix6,,mips-sgi-irix6} +@item +@uref{#mips-sony-sysv,,mips-sony-sysv} +@item +@uref{#ns32k-encore,,ns32k-encore} +@item +@uref{#ns32k-*-genix,,ns32k-*-genix} +@item +@uref{#ns32k-sequent,,ns32k-sequent} +@item +@uref{#ns32k-utek,,ns32k-utek} +@item +@uref{#powerpc*-*-*,,powerpc*-*-*, powerpc-*-sysv4} +@item +@uref{#powerpc-*-darwin*,,powerpc-*-darwin*} +@item +@uref{#powerpc-*-elf,,powerpc-*-elf, powerpc-*-sysv4} +@item +@uref{#powerpc-*-linux-gnu*,,powerpc-*-linux-gnu*} +@item +@uref{#powerpc-*-netbsd*,,powerpc-*-netbsd*} +@item +@uref{#powerpc-*-eabiaix,,powerpc-*-eabiaix} +@item +@uref{#powerpc-*-eabisim,,powerpc-*-eabisim} +@item +@uref{#powerpc-*-eabi,,powerpc-*-eabi} +@item +@uref{#powerpcle-*-elf,,powerpcle-*-elf, powerpcle-*-sysv4} +@item +@uref{#powerpcle-*-eabisim,,powerpcle-*-eabisim} +@item +@uref{#powerpcle-*-eabi,,powerpcle-*-eabi} +@item +@uref{#powerpcle-*-winnt,,powerpcle-*-winnt, powerpcle-*-pe} +@item +@uref{#romp-*-aos,,romp-*-aos, romp-*-mach} +@item +@uref{#s390-*-linux*} +@item +@uref{#s390x-*-linux*} +@item +@uref{#*-*-solaris2*,,*-*-solaris2*} +@item +@uref{#sparc-sun-solaris2*,,sparc-sun-solaris2*} +@item +@uref{#sparc-sun-solaris2.7,,sparc-sun-solaris2.7} +@item +@uref{#*-*-solaris2.8,,*-*-solaris2.8} +@item +@uref{#sparc-sun-sunos4*,,sparc-sun-sunos4*} +@item +@uref{#sparc-unknown-linux-gnulibc1,,sparc-unknown-linux-gnulibc1} +@item +@uref{#sparc-*-linux*,,sparc-*-linux*} +@item +@uref{#sparc64-*-*,,sparc64-*-*} +@item +@uref{#sparcv9-*-solaris2*,,sparcv9-*-solaris2*} +@item +@uref{#*-*-sysv*,,*-*-sysv*} +@item +@uref{#vax-dec-ultrix,,vax-dec-ultrix} +@item +@uref{#we32k-*-*,,we32k-*-*} +@item +@uref{#xtensa-*-elf,,xtensa-*-elf} +@item +@uref{#xtensa-*-linux*,,xtensa-*-linux*} +@item +@uref{#windows,,Microsoft Windows} +@item +@uref{#os2,,OS/2} +@item +@uref{#older,,Older systems} +@end itemize + +@itemize +@item +@uref{#elf_targets,,all ELF targets} (SVR4, Solaris 2, etc.) +@end itemize +@end ifhtml + + +@html + +
+@end html +@heading @anchor{1750a-*-*}1750a-*-* +MIL-STD-1750A processors. + +The MIL-STD-1750A cross configuration produces output for +@code{as1750}, an assembler/linker available under the GNU General Public +License for the 1750A@. @code{as1750} can be obtained at +@uref{ftp://ftp.fta-berlin.de/pub/crossgcc/1750gals/}. +A similarly licensed simulator for +the 1750A is available from same address. + +You should ignore a fatal error during the building of @samp{libgcc} +(@samp{libgcc} is not yet implemented for the 1750A@.) + +The @code{as1750} assembler requires the file @file{ms1750.inc}, which is +found in the directory @file{gcc/config/1750a}. + +GCC produced the same sections as the Fairchild F9450 C Compiler, +namely: + +@table @code +@item Normal +The program code section. + +@item Static +The read/write (RAM) data section. + +@item Konst +The read-only (ROM) constants section. + +@item Init +Initialization section (code to copy KREL to SREL)@. +@end table + +The smallest addressable unit is 16 bits (@code{BITS_PER_UNIT} is 16). This +means that type @code{char} is represented with a 16-bit word per character. +The 1750A's ``Load/Store Upper/Lower Byte'' instructions are not used by +GCC@. + +@html +

+
+@end html +@heading @anchor{a29k}a29k +AMD Am29k-family processors. These are normally used in embedded +applications. There are no standard Unix configurations. +This configuration +corresponds to AMD's standard calling sequence and binary interface +and is compatible with other 29k tools. + +You may need to make a variant of the file @file{a29k.h} for your +particular configuration. + +@html +

+
+@end html +@heading @anchor{a29k-*-bsd}a29k-*-bsd +AMD Am29050 used in a system running a variant of BSD Unix. + +@html +

+
+@end html +@heading @anchor{alpha*-*-*}alpha*-*-* + +This section contains general configuration information for all +alpha-based platforms using ELF (in particular, ignore this section for +DEC OSF/1, Digital UNIX and Tru64 UNIX)@. In addition to reading this +section, please read all other sections that match your target. + +We require binutils 2.11.2 or newer. +Previous binutils releases had a number of problems with DWARF 2 +debugging information, not the least of which is incorrect linking of +shared libraries. + +@html +

+
+@end html +@heading @anchor{alpha*-dec-osf*}alpha*-dec-osf* +Systems using processors that implement the DEC Alpha architecture and +are running the DEC/Compaq Unix (DEC OSF/1, Digital UNIX, or Compaq +Tru64 UNIX) operating system, for example the DEC Alpha AXP systems. + +In Tru64 UNIX V5.1, Compaq introduced a new assembler that does not +currently (2001-06-13) work with @command{mips-tfile}. As a workaround, +we need to use the old assembler, invoked via the barely documented +@option{-oldas} option. To bootstrap GCC, you either need to use the +Compaq C Compiler: + +@example + % CC=cc @var{srcdir}/configure [@var{options}] [@var{target}] +@end example + +or you can use a copy of GCC 2.95.3 or higher built on Tru64 UNIX V4.0: + +@example + % CC=gcc -Wa,-oldas @var{srcdir}/configure [@var{options}] [@var{target}] +@end example + +As of GNU binutils 2.11.2, neither GNU @command{as} nor GNU @command{ld} +are supported on Tru64 UNIX, so you must not configure GCC with +@option{--with-gnu-as} or @option{--with-gnu-ld}. + +The @option{--enable-threads} options isn't supported yet. A patch is +in preparation for a future release. The Java runtime library has been +reported to work on Tru64 UNIX V4.0F, V5.0, and V5.1, so you may try +@option{--enable-libgcj} and report your results. + +GCC writes a @samp{.verstamp} directive to the assembler output file +unless it is built as a cross-compiler. It gets the version to use from +the system header file @file{/usr/include/stamp.h}. If you install a +new version of DEC Unix, you should rebuild GCC to pick up the new version +stamp. + +Note that since the Alpha is a 64-bit architecture, cross-compilers from +32-bit machines will not generate code as efficient as that generated +when the compiler is running on a 64-bit machine because many +optimizations that depend on being able to represent a word on the +target in an integral value on the host cannot be performed. Building +cross-compilers on the Alpha for 32-bit machines has only been tested in +a few cases and may not work properly. + +@code{make compare} may fail on old versions of DEC Unix unless you add +@option{-save-temps} to @code{CFLAGS}. On these systems, the name of the +assembler input file is stored in the object file, and that makes +comparison fail if it differs between the @code{stage1} and +@code{stage2} compilations. The option @option{-save-temps} forces a +fixed name to be used for the assembler input file, instead of a +randomly chosen name in @file{/tmp}. Do not add @option{-save-temps} +unless the comparisons fail without that option. If you add +@option{-save-temps}, you will have to manually delete the @samp{.i} and +@samp{.s} files after each series of compilations. + +GCC now supports both the native (ECOFF) debugging format used by DBX +and GDB and an encapsulated STABS format for use only with GDB@. See the +discussion of the @option{--with-stabs} option of @file{configure} above +for more information on these formats and how to select them. + +There is a bug in DEC's assembler that produces incorrect line numbers +for ECOFF format when the @samp{.align} directive is used. To work +around this problem, GCC will not emit such alignment directives +while writing ECOFF format debugging information even if optimization is +being performed. Unfortunately, this has the very undesirable +side-effect that code addresses when @option{-O} is specified are +different depending on whether or not @option{-g} is also specified. + +To avoid this behavior, specify @option{-gstabs+} and use GDB instead of +DBX@. DEC is now aware of this problem with the assembler and hopes to +provide a fix shortly. + +@html +

+
+@end html +@heading @anchor{alphaev5-cray-unicosmk*}alphaev5-cray-unicosmk* +Cray T3E systems running Unicos/Mk. + +This port is incomplete and has many known bugs. We hope to improve the +support for this target soon. Currently, only the C front end is supported, +and it is not possible to build parallel applications. Cray modules are not +supported; in particular, Craylibs are assumed to be in +@file{/opt/ctl/craylibs/craylibs}. + +You absolutely @strong{must} use GNU make on this platform. Also, you +need to tell GCC where to find the assembler and the linker. The +simplest way to do so is by providing @option{--with-as} and +@option{--with-ld} to @file{configure}, e.g.@: + +@samp{configure --with-as=/opt/ctl/bin/cam --with-ld=/opt/ctl/bin/cld +--enable-languages=c} + +The comparison test during @samp{make bootstrap} fails on Unicos/Mk +because the assembler inserts timestamps into object files. You should +be able to work around this by doing @samp{make all} after getting this +failure. + +@html +

+
+@end html +@heading @anchor{arc-*-elf}arc-*-elf +Argonaut ARC processor. +This configuration is intended for embedded systems. + +@html +

+
+@end html +@heading @anchor{arm-*-aout}arm-*-aout +Advanced RISC Machines ARM-family processors. These are often used in +embedded applications. There are no standard Unix configurations. +This configuration corresponds to the basic instruction sequences and will +produce @file{a.out} format object modules. + +You may need to make a variant of the file @file{arm.h} for your particular +configuration. + +@html +

+
+@end html +@heading @anchor{arm-*-elf}arm-*-elf +This configuration is intended for embedded systems. + +@html +

+
+@end html +@heading @anchor{arm*-*-linux-gnu}arm*-*-linux-gnu + +We require GNU binutils 2.10 or newer. + +@html +

+
+@end html +@heading @anchor{arm-*-riscix}arm-*-riscix +The ARM2 or ARM3 processor running RISC iX, Acorn's port of BSD Unix. +If you are running a version of RISC iX prior to 1.2 then you must +specify the version number during configuration. Note that the +assembler shipped with RISC iX does not support stabs debugging +information; a new version of the assembler, with stabs support +included, is now available from Acorn and via ftp +@uref{ftp://ftp.acorn.com/pub/riscix/as+xterm.tar.Z}. To enable stabs +debugging, pass @option{--with-gnu-as} to configure. + +You will need to install GNU @command{sed} before you can run configure. + +@html +

+
+@end html +@heading @anchor{avr}avr + +ATMEL AVR-family micro controllers. These are used in embedded +applications. There are no standard Unix configurations. +@ifnothtml +@xref{AVR Options,, AVR Options, gcc, Using and Porting the GNU Compiler +Collection (GCC)}, +@end ifnothtml +@ifhtml +See ``AVR Options'' in the main manual +@end ifhtml +for the list of supported MCU types. + +Use @samp{configure --target=avr --enable-languages="c"} to configure GCC@. + +Further installation notes and other useful information about AVR tools +can also be obtained from: + +@itemize @bullet +@item +@uref{http://home.overta.ru/users/denisc,,http://home.overta.ru/users/denisc} +@item +@uref{http://www.itnet.pl/amelektr/avr,,http://www.itnet.pl/amelektr/avr} +@end itemize + +We @emph{strongly} recommend using binutils 2.11 or newer. + +The following error: +@example + Error: register required +@end example + +indicates that you should upgrade to a newer version of the binutils. + +@html +

+
+@end html +@heading @anchor{c4x}c4x + +Texas Instruments TMS320C3x and TMS320C4x Floating Point Digital Signal +Processors. These are used in embedded applications. There are no +standard Unix configurations. +@ifnothtml +@xref{TMS320C3x/C4x Options,, TMS320C3x/C4x Options, gcc, Using and +Porting the GNU Compiler Collection (GCC)}, +@end ifnothtml +@ifhtml +See ``TMS320C3x/C4x Options'' in the main manual +@end ifhtml +for the list of supported MCU types. + +GCC can be configured as a cross compiler for both the C3x and C4x +architectures on the same system. Use @samp{configure --target=c4x +--enable-languages="c,c++"} to configure. + + +Further installation notes and other useful information about C4x tools +can also be obtained from: + +@itemize @bullet +@item +@uref{http://www.elec.canterbury.ac.nz/c4x/,,http://www.elec.canterbury.ac.nz/c4x/} +@end itemize + +@html +

+
+@end html +@heading @anchor{cris}CRIS + +CRIS is the CPU architecture in Axis Communications ETRAX system-on-a-chip +series. These are used in embedded applications. + +@ifnothtml +@xref{CRIS Options,, CRIS Options, gcc, Using and Porting the GNU Compiler +Collection (GCC)}, +@end ifnothtml +@ifhtml +See ``CRIS Options'' in the main manual +@end ifhtml +for a list of CRIS-specific options. + +There are a few different CRIS targets: +@table @code +@item cris-axis-aout +Old target. Includes a multilib for the @samp{elinux} a.out-based +target. No multilibs for newer architecture variants. +@item cris-axis-elf +Mainly for monolithic embedded systems. Includes a multilib for the +@samp{v10} core used in @samp{ETRAX 100 LX}. +@item cris-axis-linux-gnu +A GNU/Linux port for the CRIS architecture, currently targeting +@samp{ETRAX 100 LX} by default. +@end table + +For @code{cris-axis-aout} and @code{cris-axis-elf} you need binutils 2.11 +or newer. For @code{cris-axis-linux-gnu} you need binutils 2.12 or newer. + +Pre-packaged tools can be obtained from +@uref{ftp://ftp.axis.com/pub/axis/tools/cris/compiler-kit/}. More +information about this platform is available at +@uref{http://developer.axis.com/}. + +@html +

+
+@end html +@heading @anchor{dos}DOS + +Please have a look at our @uref{binaries.html,,binaries page}. + +You cannot install GCC by itself on MSDOS; it will not compile under +any MSDOS compiler except itself. You need to get the complete +compilation package DJGPP, which includes binaries as well as sources, +and includes all the necessary compilation tools and libraries. + +@html +

+
+@end html +@heading @anchor{dsp16xx}dsp16xx +A port to the AT&T DSP1610 family of processors. + +@html +

+
+@end html +@heading @anchor{*-*-freebsd*}*-*-freebsd* + +The version of binutils installed in @file{/usr/bin} is known to work unless +otherwise specified in any per-architecture notes. However, binutils +2.11 is known to improve overall testsuite results. + +For FreeBSD 1, FreeBSD 2 or any mutant a.out versions of FreeBSD 3: All +configuration support and files as shipped with GCC 2.95 are still in +place. FreeBSD 2.2.7 has been known to bootstrap completely; however, +it is unknown which version of binutils was used (it is assumed that it +was the system copy in @file{/usr/bin}) and C++ EH failures were noted. + +For FreeBSD using the ELF file format: DWARF 2 debugging is now the +default for all CPU architectures. It had been the default on +FreeBSD/alpha since its inception. You may use @option{-gstabs} instead +of @option{-g}, if you really want the old debugging format. There are +no known issues with mixing object files and libraries with different +debugging formats. Otherwise, this release of GCC should now match more +of the configuration used in the stock FreeBSD configuration of GCC. In +particular, @option{--enable-threads} is now configured by default. +However, as a general user, do not attempt to replace the system +compiler with this release. Known to bootstrap and check with good +results on FreeBSD 3.0, 3.4, 4.0, 4.2, 4.3 and 5-CURRENT@. + +At this time, @option{--enable-threads} is not compatible with +@option{--enable-libgcj} on FreeBSD@. + +@html +

+
+@end html +@heading @anchor{elxsi-elxsi-bsd}elxsi-elxsi-bsd +The Elxsi's C compiler has known limitations that prevent it from +compiling GCC@. Please contact @email{mrs@@wrs.com} for more details. + +@html +

+
+@end html +@heading @anchor{h8300-hms}h8300-hms +Hitachi H8/300 series of processors. + +Please have a look at our @uref{binaries.html,,binaries page}. + +The calling convention and structure layout has changed in release 2.6. +All code must be recompiled. The calling convention now passes the +first three arguments in function calls in registers. Structures are no +longer a multiple of 2 bytes. + +@html +

+
+@end html +@heading @anchor{hppa*-hp-hpux*}hppa*-hp-hpux* + +We @emph{highly} recommend using gas/binutils 2.8 or newer on all hppa +platforms; you may encounter a variety of problems when using the HP +assembler. + +Specifically, @option{-g} does not work on HP-UX (since that system +uses a peculiar debugging format which GCC does not know about), unless you +use GAS and GDB and configure GCC with the +@uref{./configure.html#with-gnu-as,,@option{--with-gnu-as}} and +@option{--with-as=@dots{}} options. + +If you wish to use pa-risc 2.0 architecture support, you must use either +the HP assembler, gas/binutils 2.11 or a recent +@uref{ftp://sources.redhat.com/pub/binutils/snapshots,,snapshot of gas}. + +More specific information to @samp{hppa*-hp-hpux*} targets follows. + +@html +

+
+@end html +@heading @anchor{hppa*-hp-hpux9}hppa*-hp-hpux9 + +The HP assembler has major problems on this platform. We've tried to work +around the worst of the problems. However, those workarounds may be causing +linker crashes in some circumstances; the workarounds also probably prevent +shared libraries from working. Use the GNU assembler to avoid these problems. + + +The configuration scripts for GCC will also trigger a bug in the hpux9 +shell. To avoid this problem set @env{CONFIG_SHELL} to @file{/bin/ksh} +and @env{SHELL} to @file{/bin/ksh} in your environment. + + +@html +

+
+@end html +@heading @anchor{hppa*-hp-hpux10}hppa*-hp-hpux10 + +For hpux10.20, we @emph{highly} recommend you pick up the latest sed patch +@code{PHCO_19798} from HP@. HP has two sites which provide patches free of +charge: + +@itemize @bullet +@item +@html +US, Canada, Asia-Pacific, and +Latin-America +@end html +@ifnothtml +@uref{http://us-support.external.hp.com,,}US, Canada, Asia-Pacific, and +Latin-America +@end ifnothtml +@item +@uref{http://europe-support.external.hp.com,,Europe} +@end itemize + +The HP assembler on these systems is much better than the hpux9 assembler, +but still has some problems. Most notably the assembler inserts timestamps +into each object file it creates, causing the 3-stage comparison test to fail +during a @samp{make bootstrap}. You should be able to continue by +saying @samp{make all} after getting the failure from @samp{make +bootstrap}. + + +@html +

+
+@end html +@heading @anchor{hppa*-hp-hpux11}hppa*-hp-hpux11 + +GCC 3.0 supports HP-UX 11. You must use GNU binutils 2.11 or above on +this platform. Thread support is not currently implemented for this +platform, so @option{--enable-threads} does not work. +See @uref{http://gcc.gnu.org/ml/gcc-prs/2002-01/msg00551.html} +and @uref{http://gcc.gnu.org/ml/gcc-bugs/2002-01/msg00663.html}. +GCC 2.95.x is not supported under HP-UX 11 and cannot be used to +compile GCC 3.0. Refer to @uref{binaries.html,,binaries} for information +about obtaining precompiled GCC binaries for HP-UX. + +@html +

+
+@end html +@heading @anchor{i370-*-*}i370-*-* +This port is very preliminary and has many known bugs. We hope to +have a higher-quality port for this machine soon. + +@html +

+
+@end html +@heading @anchor{*-*-linux-gnu}*-*-linux-gnu + +If you use glibc 2.2 (or 2.1.9x), GCC 2.95.2 won't install +out-of-the-box. You'll get compile errors while building @samp{libstdc++}. +The patch @uref{glibc-2.2.patch,,glibc-2.2.patch}, that is to be +applied in the GCC source tree, fixes the compatibility problems. + +@html +

+@end html + +@html +

+@end html + +Currently Glibc 2.2.3 (and older releases) and GCC 3.0 are out of sync +since the latest exception handling changes for GCC@. Compiling glibc +with GCC 3.0 will give a binary incompatible glibc and therefore cause +lots of problems and might make your system completly unusable. This +will definitly need fixes in glibc but might also need fixes in GCC@. We +strongly advise to wait for glibc 2.2.4 and to read the release notes of +glibc 2.2.4 whether patches for GCC 3.0 are needed. You can use glibc +2.2.3 with GCC 3.0, just do not try to recompile it. + +@html +

+
+@end html +@heading @anchor{ix86-*-linux*oldld}i?86-*-linux*oldld +Use this configuration to generate @file{a.out} binaries on Linux-based +GNU systems if you do not have gas/binutils version 2.5.2 or later +installed. This is an obsolete configuration. + +@html +

+
+@end html +@heading @anchor{ix86-*-linux*aout}i?86-*-linux*aout +Use this configuration to generate @file{a.out} binaries on Linux-based +GNU systems. This configuration is being superseded. You must use +gas/binutils version 2.5.2 or later. + +@html +

+
+@end html +@heading @anchor{ix86-*-linux*}i?86-*-linux* + +You will need binutils 2.9.1.0.15 or newer for exception handling to work. + +If you receive Signal 11 errors when building on GNU/Linux, then it is +possible you have a hardware problem. Further information on this can be +found on @uref{http://www.bitwizard.nl/sig11/,,www.bitwizard.nl}. + +@html +

+
+@end html +@heading @anchor{ix86-*-sco}i?86-*-sco +Compilation with RCC is recommended. Also, it may be a good idea to +link with GNU malloc instead of the malloc that comes with the system. + +@html +

+
+@end html +@heading @anchor{ix86-*-sco3.2v4}i?86-*-sco3.2v4 +Use this configuration for SCO release 3.2 version 4. + +@html +

+
+@end html +@heading @anchor{ix86-*-sco3.2v5*}i?86-*-sco3.2v5* +Use this for the SCO OpenServer Release 5 family of operating systems. + +Unlike earlier versions of GCC, the ability to generate COFF with this +target is no longer provided. + +Earlier versions of GCC emitted DWARF 1 when generating ELF to allow +the system debugger to be used. That support was too burdensome to +maintain. GCC now emits only DWARF 2 for this target. This means you +may use either the UDK debugger or GDB to debug programs built by this +version of GCC@. + +Use of the @option{-march=pentiumpro} flag can result in +unrecognized opcodes when using the native assembler on OS versions before +5.0.6. (Support for P6 opcodes was added to the native ELF assembler in +that version.) While it's rather rare to see these emitted by GCC yet, +errors of the basic form: + +@example + /usr/tmp/ccaNlqBc.s:22:unknown instruction: fcomip + /usr/tmp/ccaNlqBc.s:50:unknown instruction: fucomip +@end example + +are symptoms of this problem. You may work around this by not +building affected files with that flag, by using the GNU assembler, or +by using the assembler provided with the current version of the OS@. +Users of GNU assembler should see the note below for hazards on doing +so. + +The native SCO assembler that is provided with the OS at no +charge is normally required. If, however, you must be able to use +the GNU assembler (perhaps you're compiling code with asms that +require GAS syntax) you may configure this package using the flags +@uref{./configure.html#with-gnu-as,,@option{--with-gnu-as}}. You must +use a recent version of GNU binutils; versions past 2.9.1 seem to work +well. + +In general, the @option{--with-gnu-as} option isn't as well tested +as the native assembler. + +Look in @file{gcc/config/i386/sco5.h} (search for ``messy'') for +additional OpenServer-specific flags. + +Systems based on OpenServer before 5.0.4 (@samp{uname -X} +will tell you what you're running) require TLS597 from +@uref{ftp://ftp.sco.com/TLS/,,ftp://ftp.sco.com/TLS/} +for C++ constructors and destructors to work right. + +The system linker in (at least) 5.0.4 and 5.0.5 will sometimes +do the wrong thing for a construct that GCC will emit for PIC +code. This can be seen as execution testsuite failures when using +@option{-fPIC} on @file{921215-1.c}, @file{931002-1.c}, @file{nestfunc-1.c}, and @file{gcov-1.c}. +For 5.0.5, an updated linker that will cure this problem is +available. You must install both +@uref{ftp://ftp.sco.com/Supplements/rs505a/,,ftp://ftp.sco.com/Supplements/rs505a/} +and @uref{ftp://ftp.sco.com/SLS/,,OSS499A}. + +The dynamic linker in OpenServer 5.0.5 (earlier versions may show +the same problem) aborts on certain G77-compiled programs. It's particularly +likely to be triggered by building Fortran code with the @option{-fPIC} flag. +Although it's conceivable that the error could be triggered by other +code, only G77-compiled code has been observed to cause this abort. +If you are getting core dumps immediately upon execution of your +G77 program---and especially if it's compiled with @option{-fPIC}---try applying +@uref{sco_osr5_g77.patch,,@file{sco_osr5_g77.patch}} to your @samp{libf2c} and +rebuilding GCC@. +Affected faults, when analyzed in a debugger, will show a stack +backtrace with a fault occurring in @code{rtld()} and the program +running as @file{/usr/lib/ld.so.1}. This problem has been reported to SCO +engineering and will hopefully be addressed in later releases. + + +@html +

+
+@end html +@heading @anchor{ix86-*-udk}i?86-*-udk + +This target emulates the SCO Universal Development Kit and requires that +package be installed. (If it is installed, you will have a +@file{/udk/usr/ccs/bin/cc} file present.) It's very much like the +@samp{i?86-*-unixware7*} target +but is meant to be used when hosting on a system where UDK isn't the +default compiler such as OpenServer 5 or Unixware 2. This target will +generate binaries that will run on OpenServer, Unixware 2, or Unixware 7, +with the same warnings and caveats as the SCO UDK@. + +This target is a little tricky to build because we have to distinguish +it from the native tools (so it gets headers, startups, and libraries +from the right place) while making the tools not think we're actually +building a cross compiler. The easiest way to do this is with a configure +command like this: + +@samp{CC=/udk/usr/ccs/bin/cc @var{/your/path/to}/gcc/configure +--host=i686-pc-udk --target=i686-pc-udk --program-prefix=udk-} + +@emph{You should substitute @samp{i686} in the above command with the appropriate +processor for your host.} + +After the usual @samp{make bootstrap} and +@samp{make install}, you can then access the UDK-targeted GCC +tools by adding @command{udk-} before the commonly known name. For +example, to invoke the C compiler, you would use @command{udk-gcc}. +They will coexist peacefully with any native-target GCC tools you may +have installed. + + +@html +

+
+@end html +@heading @anchor{ix86-*-isc}i?86-*-isc +It may be a good idea to link with GNU malloc instead of the malloc that +comes with the system. + +In ISC version 4.1, @command{sed} core dumps when building +@file{deduced.h}. Use the version of @command{sed} from version 4.0. + +@html +

+
+@end html +@heading @anchor{ix86-*-esix}i?86-*-esix +It may be good idea to link with GNU malloc instead of the malloc that +comes with the system. + +@html +

+
+@end html +@heading @anchor{ix86-ibm-aix}i?86-ibm-aix +You need to use GAS version 2.1 or later, and LD from +GNU binutils version 2.2 or later. + +@html +

+
+@end html +@heading @anchor{ix86-sequent-bsd}i?86-sequent-bsd +Go to the Berkeley universe before compiling. + +@html +

+
+@end html +@heading @anchor{ix86-sequent-ptx1*}i?86-sequent-ptx1*, i?86-sequent-ptx2* +You must install GNU @command{sed} before running @command{configure}. + +@html +

+
+@end html +@heading @anchor{#ix86-*-sysv3*}i?86-*-sysv3* +The @code{fixproto} shell script may trigger a bug in the system shell. +If you encounter this problem, upgrade your operating system or +use @command{bash} (the GNU shell) to run @code{fixproto}. + + +@html +

+
+@end html +@heading @anchor{i860-intel-osf*}i860-intel-osf* +On the Intel Paragon (an i860 machine), if you are using operating +system version 1.0, you will get warnings or errors about redefinition +of @code{va_arg} when you build GCC@. + +If this happens, then you need to link most programs with the library +@file{iclib.a}. You must also modify @file{stdio.h} as follows: before +the lines + +@example +#if defined(__i860__) && !defined(_VA_LIST) +#include +@end example + +@noindent +insert the line + +@example +#if __PGC__ +@end example + +@noindent +and after the lines + +@example +extern int vprintf(const char *, va_list ); +extern int vsprintf(char *, const char *, va_list ); +#endif +@end example + +@noindent +insert the line + +@example +#endif /* __PGC__ */ +@end example + +These problems don't exist in operating system version 1.1. + +@html +

+
+@end html +@heading @anchor{ia64-*-linux}ia64-*-linux +IA-64 processor (also known as IPF, or Itanium Processor Family) +running GNU/Linux. + +The toolchain is not completely finished, so requirements will continue +to change. +GCC 3.0.1 and later require glibc 2.2.4. +GCC 3.0.2 requires binutils from 2001-09-05 or later. +GCC 3.0.1 requires binutils 2.11.1 or later. + +None of the following versions of GCC has an ABI that is compatible +with any of the other versions in this list, with the exception that +Red Hat 2.96 and Trillian 000171 are compatible with each other: +3.0.2, 3.0.1, 3.0, Red Hat 2.96, and Trillian 000717. +This primarily affects C++ programs and programs that create shared libraries. +Because of these ABI incompatibilities, GCC 3.0.2 is not recommended for +user programs on GNU/Linux systems built using earlier compiler releases. +GCC 3.0.2 is recommended for compiling linux, the kernel. +GCC 3.0.2 is believed to be fully ABI compliant, and hence no more major +ABI changes are expected. + +@html +

+
+@end html +@heading @anchor{*-lynx-lynxos}*-lynx-lynxos +LynxOS 2.2 and earlier comes with GCC 1.x already installed as +@file{/bin/gcc}. You should compile with this instead of @file{/bin/cc}. +You can tell GCC to use the GNU assembler and linker, by specifying +@samp{--with-gnu-as --with-gnu-ld} when configuring. These will produce +COFF format object files and executables; otherwise GCC will use the +installed tools, which produce @file{a.out} format executables. + +@html +

+
+ +@end html +@heading @anchor{*-ibm-aix*}*-ibm-aix* + +AIX Make frequently has problems with GCC makefiles. GNU Make 3.76 or +newer is recommended to build on this platform. + +Errors involving @code{alloca} when building GCC generally are due +to an incorrect definition of @code{CC} in the Makefile or mixing files +compiled with the native C compiler and GCC@. During the stage1 phase of +the build, the native AIX compiler @strong{must} be invoked as @command{cc} +(not @command{xlc}). Once @command{configure} has been informed of +@command{xlc}, one needs to use @samp{make distclean} to remove the +configure cache files and ensure that @env{CC} environment variable +does not provide a definition that will confuse @command{configure}. +If this error occurs during stage2 or later, then the problem most likely +is the version of Make (see above). + +The GNU Assembler incorrectly reports that it supports WEAK symbols on +AIX which causes GCC to try to utilize weak symbol functionality which +is not really supported on the platform. The native @command{as} and +@command{ld} still are recommended. The native AIX tools do +interoperate with GCC@. + +Building @file{libstdc++.a} requires a fix for a AIX Assembler bug +APAR IY26685 (AIX 4.3) or APAR IY25528 (AIX 5.1). + +Linking executables and shared libraries may produce warnings of +duplicate symbols. The assembly files generated by GCC for AIX always +have included multiple symbol definitions for certain global variable +and function declarations in the original program. The warnings should +not prevent the linker from producing a correct library or runnable +executable. + +AIX 4.3 utilizes a ``large format'' archive to support both 32-bit and +64-bit object modules. The routines provided in AIX 4.3.0 and AIX 4.3.1 +to parse archive libraries did not handle the new format correctly. +These routines are used by GCC and result in error messages during +linking such as ``not a COFF file''. The version of the routines shipped +with AIX 4.3.1 should work for a 32-bit environment. The @option{-g} +option of the archive command may be used to create archives of 32-bit +objects using the original ``small format''. A correct version of the +routines is shipped with AIX 4.3.2 and above. + +Some versions of the AIX binder (linker) can fail with a relocation +overflow severe error when the @option{-bbigtoc} option is used to link +GCC-produced object files into an executable that overflows the TOC@. A fix +for APAR IX75823 (OVERFLOW DURING LINK WHEN USING GCC AND -BBIGTOC) is +available from IBM Customer Support and from its +@uref{http://techsupport.services.ibm.com/,,techsupport.services.ibm.com} +website as PTF U455193. + +The AIX 4.3.2.1 linker (bos.rte.bind_cmds Level 4.3.2.1) will dump core +with a segmentation fault when invoked by any version of GCC@. A fix for +APAR IX87327 is available from IBM Customer Support and from its +@uref{http://techsupport.services.ibm.com/,,techsupport.services.ibm.com} +website as PTF U461879. This fix is incorporated in AIX 4.3.3 and above. + +The initial assembler shipped with AIX 4.3.0 generates incorrect object +files. A fix for APAR IX74254 (64BIT DISASSEMBLED OUTPUT FROM COMPILER FAILS +TO ASSEMBLE/BIND) is available from IBM Customer Support and from its +@uref{http://techsupport.services.ibm.com/,,techsupport.services.ibm.com} +website as PTF U453956. This fix is incorporated in AIX 4.3.1 and above. + +AIX provides National Language Support (NLS)@. Compilers and assemblers +use NLS to support locale-specific representations of various data +formats including floating-point numbers (e.g., @samp{.} vs @samp{,} for +separating decimal fractions). There have been problems reported where +GCC does not produce the same floating-point formats that the assembler +expects. If one encounters this problem, set the @env{LANG} +environment variable to @samp{C} or @samp{En_US}. + +By default, GCC for AIX 4.1 and above produces code that can be used on +both Power or PowerPC processors. + +A default can be specified with the @option{-mcpu=@var{cpu_type}} +switch and using the configure option @option{--with-cpu-@var{cpu_type}}. + +@html +

+
+@end html +@heading @anchor{m32r-*-elf}m32r-*-elf +Mitsubishi M32R processor. +This configuration is intended for embedded systems. + +@html +

+
+@end html +@heading @anchor{m68000-hp-bsd}m68000-hp-bsd +HP 9000 series 200 running BSD@. Note that the C compiler that comes +with this system cannot compile GCC; contact @email{law@@cygnus.com} +to get binaries of GCC for bootstrapping. + +@html +

+
+@end html +@heading @anchor{m6811-elf}m6811-elf +Motorola 68HC11 family micro controllers. These are used in embedded +applications. There are no standard Unix configurations. + +@html +

+
+@end html +@heading @anchor{m6812-elf}m6812-elf +Motorola 68HC12 family micro controllers. These are used in embedded +applications. There are no standard Unix configurations. + +@html +

+
+@end html +@heading @anchor{m68k-altos}m68k-altos +Altos 3068. You must use the GNU assembler, linker and debugger. +Also, you must fix a kernel bug. + +@html +

+
+@end html +@heading @anchor{m68k-apple-aux}m68k-apple-aux +Apple Macintosh running A/UX@. +You may configure GCC to use either the system assembler and +linker or the GNU assembler and linker. You should use the GNU configuration +if you can, especially if you also want to use G++. You enable +that configuration with the @option{--with-gnu-as} and @option{--with-gnu-ld} +options to @code{configure}. + +Note the C compiler that comes +with this system cannot compile GCC@. You can find binaries of GCC +for bootstrapping on @code{jagubox.gsfc.nasa.gov}. +You will also a patched version of @file{/bin/ld} there that +raises some of the arbitrary limits found in the original. + +@html +

+
+@end html +@heading @anchor{m68k-att-sysv}m68k-att-sysv +AT&T 3b1, a.k.a.@: 7300 PC@. This version of GCC cannot +be compiled with the system C compiler, which is too buggy. +You will need to get a previous version of GCC and use it to +bootstrap. Binaries are available from the OSU-CIS archive, at +@uref{ftp://archive.cis.ohio-state.edu/pub/att7300/}. + +@html +

+
+@end html +@heading @anchor{m68k-bull-sysv}m68k-bull-sysv +Bull DPX/2 series 200 and 300 with BOS-2.00.45 up to BOS-2.01. GCC works +either with native assembler or GNU assembler. You can use +GNU assembler with native COFF generation by providing @option{--with-gnu-as} to +the configure script or use GNU assembler with stabs-in-COFF encapsulation +by providing @samp{--with-gnu-as --stabs}. For any problem with the native +assembler or for availability of the DPX/2 port of GAS, contact +@email{F.Pierresteguy@@frcl.bull.fr}. + +@html +

+
+@end html +@heading @anchor{m68k-crds-unox}m68k-crds-unox +Use @samp{configure unos} for building on Unos. + +The Unos assembler is named @code{casm} instead of @code{as}. For some +strange reason linking @file{/bin/as} to @file{/bin/casm} changes the +behavior, and does not work. So, when installing GCC, you should +install the following script as @file{as} in the subdirectory where +the passes of GCC are installed: + +@example +#!/bin/sh +casm $* +@end example + +The default Unos library is named @file{libunos.a} instead of +@file{libc.a}. To allow GCC to function, either change all +references to @option{-lc} in @file{gcc.c} to @option{-lunos} or link +@file{/lib/libc.a} to @file{/lib/libunos.a}. + +@cindex @code{alloca}, for Unos +When compiling GCC with the standard compiler, to overcome bugs in +the support of @code{alloca}, do not use @option{-O} when making stage 2. +Then use the stage 2 compiler with @option{-O} to make the stage 3 +compiler. This compiler will have the same characteristics as the usual +stage 2 compiler on other systems. Use it to make a stage 4 compiler +and compare that with stage 3 to verify proper compilation. + +(Perhaps simply defining @code{ALLOCA} in @file{x-crds} as described in +the comments there will make the above paragraph superfluous. Please +inform us of whether this works.) + +Unos uses memory segmentation instead of demand paging, so you will need +a lot of memory. 5 Mb is barely enough if no other tasks are running. +If linking @file{cc1} fails, try putting the object files into a library +and linking from that library. + +@html +

+
+@end html +@heading @anchor{m68k-hp-hpux}m68k-hp-hpux +HP 9000 series 300 or 400 running HP-UX@. HP-UX version 8.0 has a bug in +the assembler that prevents compilation of GCC@. This +bug manifests itself during the first stage of compilation, while +building @file{libgcc2.a}: + +@smallexample +_floatdisf +cc1: warning: `-g' option not supported on this version of GCC +cc1: warning: `-g1' option not supported on this version of GCC +./xgcc: Internal compiler error: program as got fatal signal 11 +@end smallexample + +A patched version of the assembler is available as the file +@uref{ftp://altdorf.ai.mit.edu/archive/cph/hpux-8.0-assembler}. If you +have HP software support, the patch can also be obtained directly from +HP, as described in the following note: + +@quotation +This is the patched assembler, to patch SR#1653-010439, where the +assembler aborts on floating point constants. + +The bug is not really in the assembler, but in the shared library +version of the function ``cvtnum(3c)''. The bug on ``cvtnum(3c)'' is +SR#4701-078451. Anyway, the attached assembler uses the archive +library version of ``cvtnum(3c)'' and thus does not exhibit the bug. +@end quotation + +This patch is also known as PHCO_4484. + +In addition, if you wish to use gas, you must use +gas version 2.1 or later, and you must use the GNU linker version 2.1 or +later. Earlier versions of gas relied upon a program which converted the +gas output into the native HP-UX format, but that program has not been +kept up to date. gdb does not understand that native HP-UX format, so +you must use gas if you wish to use gdb. + +On HP-UX version 8.05, but not on 8.07 or more recent versions, the +@code{fixproto} shell script triggers a bug in the system shell. If you +encounter this problem, upgrade your operating system or use BASH (the +GNU shell) to run @code{fixproto}. This bug will cause the fixproto +program to report an error of the form: + +@example +./fixproto: sh internal 1K buffer overflow +@end example + +To fix this, you can also change the first line of the fixproto script +to look like: + +@example +#!/bin/ksh +@end example + + +@html +

+
+@end html +@heading @anchor{m68k-*-nextstep*}m68k-*-nextstep* + +Current GCC versions probably do not work on version 2 of the NeXT +operating system. + +On NeXTStep 3.0, the Objective-C compiler does not work, due, +apparently, to a kernel bug that it happens to trigger. This problem +does not happen on 3.1. + +You absolutely @strong{must} use GNU sed and GNU make on this platform. + + +On NeXTSTEP 3.x where x < 3 the build of GCC will abort during +stage1 with an error message like this: + +@example + _eh + /usr/tmp/ccbbsZ0U.s:987:Unknown pseudo-op: .section + /usr/tmp/ccbbsZ0U.s:987:Rest of line ignored. 1st junk character + valued 95 (_). +@end example + +The reason for this is the fact that NeXT's assembler for these +versions of the operating system does not support the @samp{.section} +pseudo op that's needed for full C++ exception functionality. + +As NeXT's assembler is a derived work from GNU as, a free +replacement that does can be obtained at +@uref{ftp://ftp.next.peak.org:/next-ftp/next/apps/devtools/as.3.3.NIHS.s.tar.gz,,ftp://ftp.next.peak.org:/next-ftp/next/apps/devtools/as.3.3.NIHS.s.tar.gz}. + +If you try to build the integrated C++ & C++ runtime libraries on this system +you will run into trouble with include files. The way to get around this is +to use the following sequence. Note you must have write permission to +the directory @var{prefix} you specified in the configuration process of GCC +for this sequence to work. + +@example + cd bld-gcc + make all-texinfo all-bison all-byacc all-binutils all-gas all-ld + cd gcc + make bootstrap + make install-headers-tar + cd .. + make bootstrap3 +@end example + +@html +

+
+@end html +@heading @anchor{m68k-ncr-*}m68k-ncr-* +On the Tower models 4@var{n}0 and 6@var{n}0, by default a process is not +allowed to have more than one megabyte of memory. GCC cannot compile +itself (or many other programs) with @option{-O} in that much memory. + +To solve this problem, reconfigure the kernel adding the following line +to the configuration file: + +@smallexample +MAXUMEM = 4096 +@end smallexample + + +@html +

+
+@end html +@heading @anchor{m68k-sun}m68k-sun +Sun 3. We do not provide a configuration file to use the Sun FPA by +default, because programs that establish signal handlers for floating +point traps inherently cannot work with the FPA@. + +@html +

+
+@end html +@heading @anchor{m68k-sun-sunos4.1.1}m68k-sun-sunos4.1.1 + +It is reported that you may need the GNU assembler on this platform. + + +@html +

+
+@end html +@heading @anchor{m88k-*-svr3}m88k-*-svr3 +Motorola m88k running the AT&T/Unisoft/Motorola V.3 reference port. +These systems tend to use the Green Hills C, revision 1.8.5, as the +standard C compiler. There are apparently bugs in this compiler that +result in object files differences between stage 2 and stage 3. If this +happens, make the stage 4 compiler and compare it to the stage 3 +compiler. If the stage 3 and stage 4 object files are identical, this +suggests you encountered a problem with the standard C compiler; the +stage 3 and 4 compilers may be usable. + +It is best, however, to use an older version of GCC for bootstrapping +if you have one. + +@html +

+
+@end html +@heading @anchor{m88k-*-dgux}m88k-*-dgux +Motorola m88k running DG/UX@. To build 88open BCS native or cross +compilers on DG/UX, specify the configuration name as +@samp{m88k-*-dguxbcs} and build in the 88open BCS software development +environment. To build ELF native or cross compilers on DG/UX, specify +@samp{m88k-*-dgux} and build in the DG/UX ELF development environment. +You set the software development environment by issuing +@samp{sde-target} command and specifying either @samp{m88kbcs} or +@samp{m88kdguxelf} as the operand. + +If you do not specify a configuration name, @file{configure} guesses the +configuration based on the current software development environment. + +@html +

+
+@end html +@heading @anchor{m88k-tektronix-sysv3}m88k-tektronix-sysv3 +Tektronix XD88 running UTekV 3.2e. Do not turn on +optimization while building stage1 if you bootstrap with +the buggy Green Hills compiler. Also, the bundled LAI +System V NFS is buggy so if you build in an NFS mounted +directory, start from a fresh reboot, or avoid NFS all together. +Otherwise you may have trouble getting clean comparisons +between stages. + +@html +

+
+@end html +@heading @anchor{mips-*-*}mips-*-* +If you use the 1.31 version of the MIPS assembler (such as was shipped +with Ultrix 3.1), you will need to use the @option{-fno-delayed-branch} switch +when optimizing floating point code. Otherwise, the assembler will +complain when the GCC compiler fills a branch delay slot with a +floating point instruction, such as @code{add.d}. + +If on a MIPS system you get an error message saying ``does not have gp +sections for all it's [sic] sectons [sic]'', don't worry about it. This +happens whenever you use GAS with the MIPS linker, but there is not +really anything wrong, and it is okay to use the output file. You can +stop such warnings by installing the GNU linker. + +It would be nice to extend GAS to produce the gp tables, but they are +optional, and there should not be a warning about their absence. + +Users have reported some problems with version 2.0 of the MIPS +compiler tools that were shipped with Ultrix 4.1. Version 2.10 +which came with Ultrix 4.2 seems to work fine. + +Users have also reported some problems with version 2.20 of the +MIPS compiler tools that were shipped with RISC/os 4.x. The earlier +version 2.11 seems to work fine. + +Some versions of the MIPS linker will issue an assertion failure +when linking code that uses @code{alloca} against shared +libraries on RISC-OS 5.0, and DEC's OSF/1 systems. This is a bug +in the linker, that is supposed to be fixed in future revisions. +To protect against this, GCC passes @option{-non_shared} to the +linker unless you pass an explicit @option{-shared} or +@option{-call_shared} switch. + +@heading @anchor{mips-mips-bsd}mips-mips-bsd +MIPS machines running the MIPS operating system in BSD mode. It's +possible that some old versions of the system lack the functions +@code{memcpy}, @code{memmove}, @code{memcmp}, and @code{memset}. If your +system lacks these, you must remove or undo the definition of +@code{TARGET_MEM_FUNCTIONS} in @file{mips-bsd.h}. + +If you use the MIPS C compiler to bootstrap, it may be necessary +to increase its table size for switch statements with the +@option{-Wf,-XNg1500} option. If you use the @option{-O2} +optimization option, you also need to use @option{-Olimit 3000}. +Both of these options are automatically generated in the +@file{Makefile} that the shell script @file{configure} builds. +If you override the @code{CC} make variable and use the MIPS +compilers, you may need to add @option{-Wf,-XNg1500 -Olimit 3000}. + +@html +

+
+@end html +@heading @anchor{mips-dec-*}mips-dec-* +MIPS-based DECstations can support three different personalities: +Ultrix, DEC OSF/1, and OSF/rose. (Alpha-based DECstation products have +a configuration name beginning with @samp{alpha*-dec}.) To configure GCC +for these platforms use the following configurations: + +@table @samp +@item mips-dec-ultrix +Ultrix configuration. + +@item mips-dec-osf1 +DEC's version of OSF/1. + +@item mips-dec-osfrose +Open Software Foundation reference port of OSF/1 which uses the +OSF/rose object file format instead of ECOFF@. Normally, you +would not select this configuration. +@end table + +If you use the MIPS C compiler to bootstrap, it may be necessary +to increase its table size for switch statements with the +@option{-Wf,-XNg1500} option. If you use the @option{-O2} +optimization option, you also need to use @option{-Olimit 3000}. +Both of these options are automatically generated in the +@file{Makefile} that the shell script @file{configure} builds. +If you override the @code{CC} make variable and use the MIPS +compilers, you may need to add @option{-Wf,-XNg1500 -Olimit 3000}. + +@html +

+
+@end html +@heading @anchor{mips-mips-riscos*}mips-mips-riscos* +If you use the MIPS C compiler to bootstrap, it may be necessary +to increase its table size for switch statements with the +@option{-Wf,-XNg1500} option. If you use the @option{-O2} +optimization option, you also need to use @option{-Olimit 3000}. +Both of these options are automatically generated in the +@file{Makefile} that the shell script @file{configure} builds. +If you override the @code{CC} make variable and use the MIPS +compilers, you may need to add @samp{-Wf,-XNg1500 -Olimit 3000}. + +MIPS computers running RISC-OS can support four different +personalities: default, BSD 4.3, System V.3, and System V.4 +(older versions of RISC-OS don't support V.4). To configure GCC +for these platforms use the following configurations: + +@table @samp +@item mips-mips-riscos@var{rev} +Default configuration for RISC-OS, revision @var{rev}. + +@item mips-mips-riscos@var{rev}bsd +BSD 4.3 configuration for RISC-OS, revision @var{rev}. + +@item mips-mips-riscos@var{rev}sysv4 +System V.4 configuration for RISC-OS, revision @var{rev}. + +@html +

+
+@end html +@item mips-mips-riscos@var{rev}sysv +System V.3 configuration for RISC-OS, revision @var{rev}. +@end table + +The revision @code{rev} mentioned above is the revision of +RISC-OS to use. You must reconfigure GCC when going from a +RISC-OS revision 4 to RISC-OS revision 5. This has the effect of +avoiding a linker bug. + +@html +

+
+@end html +@heading @anchor{mips-sgi-irix4}mips-sgi-irix4 + +In order to compile GCC on an SGI running IRIX 4, the ``c.hdr.lib'' +option must be installed from the CD-ROM supplied from Silicon Graphics. +This is found on the 2nd CD in release 4.0.1. + +On IRIX version 4.0.5F, and perhaps on some other versions as well, +there is an assembler bug that reorders instructions incorrectly. To +work around it, specify the target configuration +@samp{mips-sgi-irix4loser}. This configuration inhibits assembler +optimization. + +In a compiler configured with target @samp{mips-sgi-irix4}, you can turn +off assembler optimization by using the @option{-noasmopt} option. This +compiler option passes the option @option{-O0} to the assembler, to +inhibit reordering. + +The @option{-noasmopt} option can be useful for testing whether a problem +is due to erroneous assembler reordering. Even if a problem does not go +away with @option{-noasmopt}, it may still be due to assembler +reordering---perhaps GCC itself was miscompiled as a result. + +You may get the following warning on IRIX 4 platforms, it can be safely +ignored. +@example + warning: foo.o does not have gp tables for all its sections. +@end example + +@html +

+
+@end html +@heading @anchor{mips-sgi-irix5}mips-sgi-irix5 + +This configuration has considerable problems, which will be fixed in a +future release. + +In order to compile GCC on an SGI running IRIX 5, the ``compiler_dev.hdr'' +subsystem must be installed from the IDO CD-ROM supplied by Silicon +Graphics. It is also available for download from +@uref{http://www.sgi.com/developers/devtools/apis/ido.html,,http://www.sgi.com/developers/devtools/apis/ido.html}. + +@code{make compare} may fail on version 5 of IRIX unless you add +@option{-save-temps} to @code{CFLAGS}. On these systems, the name of the +assembler input file is stored in the object file, and that makes +comparison fail if it differs between the @code{stage1} and +@code{stage2} compilations. The option @option{-save-temps} forces a +fixed name to be used for the assembler input file, instead of a +randomly chosen name in @file{/tmp}. Do not add @option{-save-temps} +unless the comparisons fail without that option. If you do you +@option{-save-temps}, you will have to manually delete the @samp{.i} and +@samp{.s} files after each series of compilations. + +If you use the MIPS C compiler to bootstrap, it may be necessary +to increase its table size for switch statements with the +@option{-Wf,-XNg1500} option. If you use the @option{-O2} +optimization option, you also need to use @option{-Olimit 3000}. + +To enable debugging under IRIX 5, you must use GNU @command{as} 2.11.2 +or later, +and use the @option{--with-gnu-as} configure option when configuring GCC. +GNU @command{as} is distributed as part of the binutils package. +When using release 2.11.2, you need to apply a patch +@uref{http://sources.redhat.com/ml/binutils/2001-07/msg00352.html,,http://sources.redhat.com/ml/binutils/2001-07/msg00352.html} +which will be included in the next release of binutils. + +When building GCC, the build process loops rebuilding @command{cc1} over +and over again. This happens on @samp{mips-sgi-irix5.2}, and possibly +other platforms. It has been reported that this is a known bug in the +@command{make} shipped with IRIX 5.2. We recommend you use GNU +@command{make} instead of the vendor supplied @command{make} program; +however, you may have success with @command{smake} on IRIX 5.2 if you do +not have GNU @command{make} available. + +@html +

+
+@end html +@heading @anchor{mips-sgi-irix6}mips-sgi-irix6 + +If you are using IRIX @command{cc} as your bootstrap compiler, you must +ensure that the N32 ABI is in use. To test this, compile a simple C +file with @command{cc} and then run @command{file} on the +resulting object file. The output should look like: + +@example +test.o: ELF N32 MSB @dots{} +@end example + +If you see: + +@example +test.o: ELF 32-bit MSB @dots{} +@end example + +or + +@example +test.o: ELF 64-bit MSB @dots{} +@end example + +then your version of @command{cc} uses the O32 or N64 ABI by default. You +should set the environment variable @env{CC} to @samp{cc -n32} +before configuring GCC@. + +GCC on IRIX 6 is usually built to support both the N32 and N64 ABIs. If +you build GCC on a system that doesn't have the N64 libraries installed, +you need to configure with @option{--disable-multilib} so GCC doesn't +try to use them. Look for @file{/usr/lib64/libc.so.1} to see if you +have the 64-bit libraries installed. + +You must @emph{not} use GNU @command{as} (which isn't built anyway as of +binutils 2.11.2) on IRIX 6 platforms; doing so will only cause problems. + +GCC does not currently support generating O32 ABI binaries in the +@samp{mips-sgi-irix6} configurations. It is possible to create a GCC +with O32 ABI only support by configuring it for the @samp{mips-sgi-irix5} +target and using a patched GNU @command{as} 2.11.2 as documented in the +@uref{#mips-sgi-irix5,,@samp{mips-sgi-irix5}} section above. Using the +native assembler requires patches to GCC which will be included in a +future release. It is +expected that O32 ABI support will be available again in a future release. + +The @option{--enable-threads} option doesn't currently work, a patch is +in preparation for a future release. The @option{--enable-libgcj} +option is disabled by default: IRIX 6 uses a very low default limit +(20480) for the command line length. Although libtool contains a +workaround for this problem, at least the N64 @samp{libgcj} is known not +to build despite this, running into an internal error of the native +@command{ld}. A sure fix is to increase this limit (@samp{ncargs}) to +its maximum of 262144 bytes. If you have root access, you can use the +@command{systune} command to do this. + +GCC does not correctly pass/return structures which are +smaller than 16 bytes and which are not 8 bytes. The problem is very +involved and difficult to fix. It affects a number of other targets also, +but IRIX 6 is affected the most, because it is a 64 bit target, and 4 byte +structures are common. The exact problem is that structures are being padded +at the wrong end, e.g.@: a 4 byte structure is loaded into the lower 4 bytes +of the register when it should be loaded into the upper 4 bytes of the +register. + +GCC is consistent with itself, but not consistent with the SGI C compiler +(and the SGI supplied runtime libraries), so the only failures that can +happen are when there are library functions that take/return such +structures. There are very few such library functions. Currently this +is known to affect @code{inet_ntoa}, @code{inet_lnaof}, +@code{inet_netof}, @code{inet_makeaddr}, and @code{semctl}. Until the +bug is fixed, GCC contains workarounds for the known affected functions. + +See @uref{http://freeware.sgi.com/,,http://freeware.sgi.com/} for more +information about using GCC on IRIX platforms. + +@html +

+
+@end html +@heading @anchor{mips-sony-sysv}mips-sony-sysv +Sony MIPS NEWS@. This works in NEWSOS 5.0.1, but not in 5.0.2 (which +uses ELF instead of COFF)@. Support for 5.0.2 will probably be provided +soon by volunteers. In particular, the linker does not like the +code generated by GCC when shared libraries are linked in. + + +@html +

+
+@end html +@heading @anchor{ns32k-encore}ns32k-encore +Encore ns32000 system. Encore systems are supported only under BSD@. + +@html +

+
+@end html +@heading @anchor{ns32k-*-genix}ns32k-*-genix +National Semiconductor ns32000 system. Genix has bugs in @code{alloca} +and @code{malloc}; you must get the compiled versions of these from GNU +Emacs. + +@html +

+
+@end html +@heading @anchor{ns32k-sequent}ns32k-sequent +Go to the Berkeley universe before compiling. + +@html +

+
+@end html +@heading @anchor{ns32k-utek}ns32k-utek +UTEK ns32000 system (``merlin''). The C compiler that comes with this +system cannot compile GCC; contact @samp{tektronix!reed!mason} to get +binaries of GCC for bootstrapping. + + +@html +

+
+@end html +@heading @anchor{powerpc*-*-*}powerpc-*-* + +You can specify a default version for the @option{-mcpu=@var{cpu_type}} +switch by using the configure option @option{--with-cpu-@var{cpu_type}}. + +@html +

+
+@end html +@heading @anchor{powerpc-*-darwin*}powerpc-*-darwin* +PowerPC running Darwin (Mac OS X kernel). + +GCC 3.0 does not support Darwin, but 3.1 and later releases will work. + +Pre-installed versions of Mac OS X may not include any developer tools, +meaning that you will not be able to build GCC from source. Tool +binaries are available at +@uref{http://www.opensource.apple.com/projects/darwin} (free +registration required). + +Versions of the assembler prior to ``cctools-364'' cannot handle the +4-argument form of rlwinm and related mask-using instructions. Darwin +1.3 (Mac OS X 10.0) uses cctools-353 for instance. To get cctools-364, +check out @file{cctools} with tag @samp{Apple-364}, build it, and +install the assembler as @file{usr/bin/as}. See +@uref{http://www.opensource.apple.com/tools/cvs/docs.html} for details. + +Also, the default stack limit of 512K is too small, and a bootstrap will +typically fail when self-compiling @file{expr.c}. Set the stack to 800K +or more, for instance by doing @samp{limit stack 800}. It's also +convenient to use the GNU preprocessor instead of Apple's during the +first stage of bootstrapping; this is automatic when doing @samp{make +bootstrap}, but to do it from the toplevel objdir you will need to say +@samp{make CC='cc -no-cpp-precomp' bootstrap}. + +Note that the version of GCC shipped by Apple typically includes a +number of extensions not available in a standard GCC release. These +extensions are generally specific to Mac programming. + +@html +

+
+@end html +@heading @anchor{powerpc-*-elf}powerpc-*-elf, powerpc-*-sysv4 +PowerPC system in big endian mode, running System V.4. + +@html +

+
+@end html +@heading @anchor{powerpc-*-linux-gnu*}powerpc-*-linux-gnu* + +You will need +@uref{ftp://ftp.varesearch.com/pub/support/hjl/binutils,,binutils 2.9.4.0.8} +or newer for a working GCC@. It is strongly recommended to recompile binutils +if you initially built it with gcc-2.7.2.x. + +@html +

+
+@end html +@heading @anchor{powerpc-*-netbsd*}powerpc-*-netbsd* +PowerPC system in big endian mode running NetBSD@. To build the +documentation you will need Texinfo version 4.0 (NetBSD 1.5.1 included +Texinfo version 3.12). + +@html +

+
+@end html +@heading @anchor{powerpc-*-eabiaix}powerpc-*-eabiaix +Embedded PowerPC system in big endian mode with @option{-mcall-aix} selected as +the default. + +@html +

+
+@end html +@heading @anchor{powerpc-*-eabisim}powerpc-*-eabisim +Embedded PowerPC system in big endian mode for use in running under the +PSIM simulator. + +@html +

+
+@end html +@heading @anchor{powerpc-*-eabi}powerpc-*-eabi +Embedded PowerPC system in big endian mode. + +@html +

+
+@end html +@heading @anchor{powerpcle-*-elf}powerpcle-*-elf, powerpcle-*-sysv4 +PowerPC system in little endian mode, running System V.4. + +@html +

+
+@end html +@heading @anchor{powerpcle-*-eabisim}powerpcle-*-eabisim +Embedded PowerPC system in little endian mode for use in running under +the PSIM simulator. + +@html +

+
+@end html +@heading @anchor{powerpcle-*-eabi}powerpcle-*-eabi +Embedded PowerPC system in little endian mode. + +@html +

+
+@end html +@heading @anchor{powerpcle-*-winnt}powerpcle-*-winnt, powerpcle-*-pe +PowerPC system in little endian mode running Windows NT@. + +@html +

+
+@end html +@heading @anchor{romp-*-aos}romp-*-aos, romp-*-mach +The only operating systems supported for the IBM RT PC are AOS and +MACH@. GCC does not support AIX running on the RT@. We recommend you +compile GCC with an earlier version of itself; if you compile GCC +with @command{hc}, the Metaware compiler, it will work, but you will get +mismatches between the stage 2 and stage 3 compilers in various files. +These errors are minor differences in some floating-point constants and +can be safely ignored; the stage 3 compiler is correct. + +@html +

+
+@end html +@heading @anchor{s390-*-linux*}s390-*-linux* +S/390 system running Linux for S/390@. + +@html +

+
+@end html +@heading @anchor{s390x-*-linux*}s390x-*-linux* +zSeries system (64 Bit) running Linux for zSeries@. + +@html +

+
+@end html +@c Please use Solaris 2 to refer to all release of Solaris, starting +@c with 2.0 until 2.6, 7, and 8. Solaris 1 was a marketing name for +@c SunOS 4 releases which we don't use to avoid confusion. Solaris +@c alone is too unspecific and must be avoided. +@heading @anchor{*-*-solaris2*}*-*-solaris2* + +Sun does not ship a C compiler with Solaris 2. To bootstrap and install +GCC you first have to install a pre-built compiler, see our +@uref{binaries.html,,binaries page} for details. + +The Solaris 2 @command{/bin/sh} will often fail to configure +@file{libstdc++-v3}, @file{boehm-gc} or +@file{libjava}. If you encounter this problem, set @env{CONFIG_SHELL} to +@command{/bin/ksh} in your environment and run @command{make bootstrap} again. +Another possibility that sometimes helps is to remove +@file{*-*-solaris2*/config.cache}. + +Solaris 2 comes with a number of optional OS packages. Some of these +packages are needed to use GCC fully, namely @code{SUNWarc}, +@code{SUNWbtool}, @code{SUNWesu}, @code{SUNWhea}, @code{SUNWlibm}, +@code{SUNWsprot}, and @code{SUNWtoo}. If you did not install all +optional packages when installing Solaris 2, you will need to verify that +the packages that GCC needs are installed. + +To check whether an optional package is installed, use +the @command{pkginfo} command. To add an optional package, use the +@command{pkgadd} command. For further details, see the Solaris 2 +documentation. + +Trying to use the linker and other tools in +@file{/usr/ucb} to install GCC has been observed to cause trouble. +For example, the linker may hang indefinitely. The fix is to remove +@file{/usr/ucb} from your @env{PATH}. + +All releases of GNU binutils prior to 2.11.2 have known bugs on this +platform. We recommend the use of GNU binutils 2.11.2 or the vendor +tools (Sun @command{as}, Sun @command{ld}). + +Sun bug 4296832 turns up when compiling X11 headers with GCC 2.95 or +newer: @command{g++} will complain that types are missing. These headers assume +that omitting the type means @code{int}; this assumption worked for C89 but +is wrong for C++, and is now wrong for C99 also. + +@command{g++} accepts such (invalid) constructs with the option +@option{-fpermissive}; it +will assume that any missing type is @code{int} (as defined by C89). + +There are patches for Solaris 2.6 (105633-56 or newer for SPARC, +106248-42 or newer for Intel), Solaris 7 (108376-21 or newer for SPARC, +108377-20 for Intel), and Solaris 8 (108652-24 or newer for SPARC, +108653-22 for Intel) that fix this bug. + +@html +

+
+@end html +@heading @anchor{sparc-sun-solaris2*}sparc-sun-solaris2* + +Sun @command{as} 4.x is broken in that it cannot cope with long symbol names. +A typical error message might look similar to the following: + +@samp{/usr/ccs/bin/as: "/var/tmp/ccMsw135.s", line 11041: +error: can't compute value of an expression involving an external symbol.} + +This is Sun bug 4237974. This is fixed with patch 108908-02 for Solaris +2.6 and has been fixed in later (5.x) versions of the assembler, +starting with Solaris 7. + +Starting with Solaris 7, the operating system is capable of executing +64-bit SPARC V9 binaries. GCC 3.1 and later should properly support +this. GCC 3.0 lacks the infrastructure necessary to support this +configuration properly. However, if all you want is code tuned for +the UltraSPARC CPU, you should try the @option{-mtune=ultrasparc} +option instead, which should be safe from those bugs and produce code +that, unlike full 64-bit code, can still run on non-UltraSPARC +machines. + +@html +

+
+@end html +@heading @anchor{sparc-sun-solaris2.7}sparc-sun-solaris2.7 + +Sun patch 107058-01 (1999-01-13) for Solaris 7/SPARC triggers a bug in +the dynamic linker. This problem (Sun bug 4210064) affects GCC 2.8 +and later, including all EGCS releases. Sun formerly recommended +107058-01 for all Solaris 7 users, but around 1999-09-01 it started to +recommend it only for people who use Sun's compilers. + +Here are some workarounds to this problem: +@itemize @bullet +@item +Do not install Sun patch 107058-01 until after Sun releases a +complete patch for bug 4210064. This is the simplest course to take, +unless you must also use Sun's C compiler. Unfortunately 107058-01 +is preinstalled on some new Solaris 7-based hosts, so you may have to +back it out. + +@item +Copy the original, unpatched Solaris 7 +@command{/usr/ccs/bin/as} into +@command{/usr/local/lib/gcc-lib/sparc-sun-solaris2.7/3.0/as}, +adjusting the latter name to fit your local conventions and software +version numbers. + +@item +Install Sun patch 106950-03 (1999-05-25) or later. Nobody with +both 107058-01 and 106950-03 installed has reported the bug with GCC +and Sun's dynamic linker. This last course of action is riskiest, +for two reasons. First, you must install 106950 on all hosts that +run code generated by GCC; it doesn't suffice to install it only on +the hosts that run GCC itself. Second, Sun says that 106950-03 is +only a partial fix for bug 4210064, but Sun doesn't know whether the +partial fix is adequate for GCC@. Revision -08 or later should fix +the bug. The current (as of 2001-09-24) revision is -14, and is included in +the Solaris 7 Recommended Patch Cluster. +@end itemize + + +@html +

+

+@end html +@heading @anchor{*-*-solaris2.8}*-*-solaris2.8 + +The Solaris 8 linker fails to link some @samp{libjava} programs if +previously-installed GCC java libraries already exist in the configured +prefix. For this reason, @samp{libgcj} is disabled by default on Solaris 8. +If you use GNU @command{ld}, or if you don't have a previously-installed @samp{libgcj} in +the same prefix, use @option{--enable-libgcj} to build and install the +Java libraries. + +@html +

+

+@end html +@heading @anchor{sparc-sun-sunos4*}sparc-sun-sunos4* + +A bug in the SunOS 4 linker will cause it to crash when linking +@option{-fPIC} compiled objects (and will therefore not allow you to build +shared libraries). + +To fix this problem you can either use the most recent version of +binutils or get the latest SunOS 4 linker patch (patch ID 100170-10) +from Sun's patch site. + +Sometimes on a Sun 4 you may observe a crash in the program +@command{genflags} or @command{genoutput} while building GCC. This is said to +be due to a bug in @command{sh}. You can probably get around it by running +@command{genflags} or @command{genoutput} manually and then retrying the +@command{make}. + +@html +

+
+@end html +@heading @anchor{sparc-unknown-linux-gnulibc1}sparc-unknown-linux-gnulibc1 + +It has been reported that you might need +@uref{ftp://ftp.yggdrasil.com/private/hjl,,binutils 2.8.1.0.23} +for this platform, too. + + +@html +

+
+@end html +@heading @anchor{sparc-*-linux*}sparc-*-linux* + +GCC versions 3.0 and higher require binutils 2.11.2 and glibc 2.2.4 +or newer on this platform. All earlier binutils and glibc +releases mishandled unaligned relocations on @code{sparc-*-*} targets. + + +@html +

+
+@end html +@heading @anchor{sparc64-*-*}sparc64-*-* + +GCC version 2.95 is not able to compile code correctly for +@code{sparc64} targets. Users of the Linux kernel, at least, +can use the @code{sparc32} program to start up a new shell +invocation with an environment that causes @command{configure} to +recognize (via @samp{uname -a}) the system as @samp{sparc-*-*} instead. + +@html +

+
+@end html +@heading @anchor{sparcv9-*-solaris2*}sparcv9-*-solaris2* + +The following compiler flags must be specified in the configure +step in order to bootstrap this target with the Sun compiler: + +@example + % CC="cc -xildoff -xarch=v9" @var{srcdir}/configure [@var{options}] [@var{target}] +@end example + +@option{-xildoff} turns off the incremental linker, and @option{-xarch=v9} +specifies the v9 architecture to the Sun linker and assembler. + +@html +

+
+@end html +@heading @anchor{#*-*-sysv*}*-*-sysv* +On System V release 3, you may get this error message +while linking: + +@smallexample +ld fatal: failed to write symbol name @var{something} + in strings table for file @var{whatever} +@end smallexample + +This probably indicates that the disk is full or your ulimit won't allow +the file to be as large as it needs to be. + +This problem can also result because the kernel parameter @code{MAXUMEM} +is too small. If so, you must regenerate the kernel and make the value +much larger. The default value is reported to be 1024; a value of 32768 +is said to work. Smaller values may also work. + +On System V, if you get an error like this, + +@example +/usr/local/lib/bison.simple: In function `yyparse': +/usr/local/lib/bison.simple:625: virtual memory exhausted +@end example + +@noindent +that too indicates a problem with disk space, ulimit, or @code{MAXUMEM}. + +On a System V release 4 system, make sure @file{/usr/bin} precedes +@file{/usr/ucb} in @code{PATH}. The @code{cc} command in +@file{/usr/ucb} uses libraries which have bugs. + +@html +

+
+@end html +@heading @anchor{vax-dec-ultrix}vax-dec-ultrix +Don't try compiling with VAX C (@code{vcc}). It produces incorrect code +in some cases (for example, when @code{alloca} is used). + +@html +

+
+@end html +@heading @anchor{we32k-*-*}we32k-*-* +These computers are also known as the 3b2, 3b5, 3b20 and other similar +names. (However, the 3b1 is actually a 68000.) + +Don't use @option{-g} when compiling with the system's compiler. The +system's linker seems to be unable to handle such a large program with +debugging information. + +The system's compiler runs out of capacity when compiling @file{stmt.c} +in GCC@. You can work around this by building @file{cpp} in GCC +first, then use that instead of the system's preprocessor with the +system's C compiler to compile @file{stmt.c}. Here is how: + +@smallexample +mv /lib/cpp /lib/cpp.att +cp cpp /lib/cpp.gnu +echo '/lib/cpp.gnu -traditional $@{1+"$@@"@}' > /lib/cpp +chmod +x /lib/cpp +@end smallexample + +The system's compiler produces bad code for some of the GCC +optimization files. So you must build the stage 2 compiler without +optimization. Then build a stage 3 compiler with optimization. +That executable should work. Here are the necessary commands: + +@smallexample +make LANGUAGES=c CC=stage1/xgcc CFLAGS="-Bstage1/ -g" +make stage2 +make CC=stage2/xgcc CFLAGS="-Bstage2/ -g -O" +@end smallexample + +You may need to raise the ULIMIT setting to build a C++ compiler, +as the file @file{cc1plus} is larger than one megabyte. + +@html +

+
+@end html +@heading @anchor{xtensa-*-elf}xtensa-*-elf + +This target is intended for embedded Xtensa systems using the +@samp{newlib} C library. It uses ELF but does not support shared +objects. Designed-defined instructions specified via the +Tensilica Instruction Extension (TIE) language are only supported +through inline assembly. + +The Xtensa configuration information must be specified prior to +building GCC@. The @file{gcc/config/xtensa/xtensa-config.h} header +file contains the configuration information. If you created your +own Xtensa configuration with the Xtensa Processor Generator, the +downloaded files include a customized copy of this header file, +which you can use to replace the default header file. + +@html +

+
+@end html +@heading @anchor{xtensa-*-linux*}xtensa-*-linux* + +This target is for Xtensa systems running GNU/Linux. It supports ELF +shared objects and the GNU C library (glibc). It also generates +position-independent code (PIC) regardless of whether the +@option{-fpic} or @option{-fPIC} options are used. In other +respects, this target is the same as the +@uref{#xtensa-*-elf,,@samp{xtensa-*-elf}} target. + +@html +

+
+@end html +@heading @anchor{windows}Microsoft Windows (32 bit) + +A port of GCC 2.95.x is included with the +@uref{http://www.cygwin.com/,,Cygwin environment}. + +Current (as of early 2001) snapshots of GCC will build under Cygwin +without modification. + +@html +

+
+@end html +@heading @anchor{os2}OS/2 + +GCC does not currently support OS/2. However, Andrew Zabolotny has been +working on a generic OS/2 port with pgcc. The current code can be found +at @uref{http://www.goof.com/pcg/os2/,,http://www.goof.com/pcg/os2/}. + +An older copy of GCC 2.8.1 is included with the EMX tools available at +@uref{ftp://ftp.leo.org/pub/comp/os/os2/leo/devtools/emx+gcc/,, +ftp://ftp.leo.org/pub/comp/os/os2/leo/devtools/emx+gcc/}. + +@html +

+
+@end html +@heading @anchor{older}Older systems + +GCC contains support files for many older (1980s and early +1990s) Unix variants. For the most part, support for these systems +has not been deliberately removed, but it has not been maintained for +several years and may suffer from bitrot. Support from some systems +has been removed from GCC 3: fx80, ns32-ns-genix, pyramid, tahoe, +gmicro, spur; most of these targets had not been updated since GCC +version 1. + +Support for older systems as targets for cross-compilation is less +problematic than support for them as hosts for GCC; if an enthusiast +wishes to make such a target work again (including resurrecting any +of the targets that never worked with GCC 2, starting from the last +CVS version before they were removed), patches +@uref{../contribute.html,,following the usual requirements} +would be likely to be accepted, since they should not affect the +support for more modern targets. + +Support for old systems as hosts for GCC can cause problems if the +workarounds for compiler, library and operating system bugs affect the +cleanliness or maintainability of the rest of GCC@. In some cases, to +bring GCC up on such a system, if still possible with current GCC, may +require first installing an old version of GCC which did work on that +system, and using it to compile a more recent GCC, to avoid bugs in +the vendor compiler. Old releases of GCC 1 and GCC 2 are available in +the @file{old-releases} directory on the +@uref{../mirrors.html,,GCC mirror sites}. Header bugs may generally +be avoided using @command{fixincludes}, but bugs or deficiencies in +libraries and the operating system may still cause problems. + +For some systems, old versions of GNU binutils may also be useful, +and are available from @file{pub/binutils/old-releases} on +@uref{http://sources.redhat.com/mirrors.html,,sources.redhat.com mirror sites}. + +Some of the information on specific systems above relates to +such older systems, but much of the information +about GCC on such systems (which may no longer be applicable to +current GCC) is to be found in the GCC texinfo manual. + +@html +

+
+@end html +@heading @anchor{elf_targets}all ELF targets (SVR4, Solaris 2, etc.) + +C++ support is significantly better on ELF targets if you use the +@uref{./configure.html#with-gnu-ld,,GNU linker}; duplicate copies of +inlines, vtables and template instantiations will be discarded +automatically. + + +@html +

+
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Old documentation****************************************************** +@ifset oldhtml +@include install-old.texi +@html +

+
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***GFDL******************************************************************** +@ifset gfdlhtml +@include fdl.texi +@html +

+
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c *************************************************************************** +@c Part 6 The End of the Document +@ifinfo +@comment node-name, next, previous, up +@node Concept Index, , GNU Free Documentation License, Top +@end ifinfo + +@ifinfo +@unnumbered Concept Index + +@printindex cp + +@contents +@end ifinfo +@bye diff --git a/contrib/gcc/doc/install.texi2html b/contrib/gcc/doc/install.texi2html new file mode 100755 index 000000000000..3917e2af33e8 --- /dev/null +++ b/contrib/gcc/doc/install.texi2html @@ -0,0 +1,31 @@ +#!/bin/sh +# +# Convert the GCC install documentation from texinfo format to HTML. +# +# $SOURCEDIR and $DESTDIR, resp., refer to the directory containing +# the texinfo source and the directory to put the HTML version in. +# +# (C) 2001 Free Software Foundation +# Originally by Gerald Pfeifer , June 2001. +# +# This script is Free Software, and it can be copied, distributed and +# modified as defined in the GNU General Public License. A copy of +# its license can be downloaded from http://www.gnu.org/copyleft/gpl.html + +SOURCEDIR=${SOURCEDIR-.} +DESTDIR=${DESTDIR-HTML} + +MAKEINFO=${MAKEINFO-makeinfo} + +if [ ! -d $DESTDIR ]; then + mkdir -p $DESTDIR +fi + +for x in index.html specific.html download.html configure.html \ + build.html test.html finalinstall.html binaries.html old.html \ + gfdl.html +do + define=`echo $x | sed -e 's/\.//g'` + echo "define = $define" + $MAKEINFO -I $SOURCEDIR -I $SOURCEDIR/include $SOURCEDIR/install.texi --html --no-split -D$define -o$DESTDIR/$x +done diff --git a/contrib/gcc/doc/interface.texi b/contrib/gcc/doc/interface.texi new file mode 100644 index 000000000000..846de56bd62c --- /dev/null +++ b/contrib/gcc/doc/interface.texi @@ -0,0 +1,102 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Interface +@chapter Interfacing to GCC Output +@cindex interfacing to GCC output +@cindex run-time conventions +@cindex function call conventions +@cindex conventions, run-time + +GCC is normally configured to use the same function calling convention +normally in use on the target system. This is done with the +machine-description macros described (@pxref{Target Macros}). + +@cindex unions, returning +@cindex structures, returning +@cindex returning structures and unions +However, returning of structure and union values is done differently on +some target machines. As a result, functions compiled with PCC +returning such types cannot be called from code compiled with GCC, +and vice versa. This does not cause trouble often because few Unix +library routines return structures or unions. + +GCC code returns structures and unions that are 1, 2, 4 or 8 bytes +long in the same registers used for @code{int} or @code{double} return +values. (GCC typically allocates variables of such types in +registers also.) Structures and unions of other sizes are returned by +storing them into an address passed by the caller (usually in a +register). The machine-description macros @code{STRUCT_VALUE} and +@code{STRUCT_INCOMING_VALUE} tell GCC where to pass this address. + +By contrast, PCC on most target machines returns structures and unions +of any size by copying the data into an area of static storage, and then +returning the address of that storage as if it were a pointer value. +The caller must copy the data from that memory area to the place where +the value is wanted. This is slower than the method used by GCC, and +fails to be reentrant. + +On some target machines, such as RISC machines and the 80386, the +standard system convention is to pass to the subroutine the address of +where to return the value. On these machines, GCC has been +configured to be compatible with the standard compiler, when this method +is used. It may not be compatible for structures of 1, 2, 4 or 8 bytes. + +@cindex argument passing +@cindex passing arguments +GCC uses the system's standard convention for passing arguments. On +some machines, the first few arguments are passed in registers; in +others, all are passed on the stack. It would be possible to use +registers for argument passing on any machine, and this would probably +result in a significant speedup. But the result would be complete +incompatibility with code that follows the standard convention. So this +change is practical only if you are switching to GCC as the sole C +compiler for the system. We may implement register argument passing on +certain machines once we have a complete GNU system so that we can +compile the libraries with GCC@. + +On some machines (particularly the Sparc), certain types of arguments +are passed ``by invisible reference''. This means that the value is +stored in memory, and the address of the memory location is passed to +the subroutine. + +@cindex @code{longjmp} and automatic variables +If you use @code{longjmp}, beware of automatic variables. ISO C says that +automatic variables that are not declared @code{volatile} have undefined +values after a @code{longjmp}. And this is all GCC promises to do, +because it is very difficult to restore register variables correctly, and +one of GCC's features is that it can put variables in registers without +your asking it to. + +If you want a variable to be unaltered by @code{longjmp}, and you don't +want to write @code{volatile} because old C compilers don't accept it, +just take the address of the variable. If a variable's address is ever +taken, even if just to compute it and ignore it, then the variable cannot +go in a register: + +@example +@{ + int careful; + &careful; + @dots{} +@} +@end example + +@cindex arithmetic libraries +@cindex math libraries +@opindex msoft-float +Code compiled with GCC may call certain library routines. Most of +them handle arithmetic for which there are no instructions. This +includes multiply and divide on some machines, and floating point +operations on any machine for which floating point support is disabled +with @option{-msoft-float}. Some standard parts of the C library, such as +@code{bcopy} or @code{memcpy}, are also called automatically. The usual +function call interface is used for calling the library routines. + +Some of these routines can be defined in mostly machine-independent C; +they appear in @file{libgcc2.c}. Others must be hand-written in +assembly language for each processor. Wherever they are defined, they +are compiled into the support library, @file{libgcc.a}, which is +automatically searched when you link programs with GCC@. diff --git a/contrib/gcc/doc/invoke.texi b/contrib/gcc/doc/invoke.texi new file mode 100644 index 000000000000..51db49adb028 --- /dev/null +++ b/contrib/gcc/doc/invoke.texi @@ -0,0 +1,10463 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, +@c 2000, 2001, 2002 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@ignore +@c man begin COPYRIGHT +Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, +1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'' and ``Funding +Free Software'', the Front-Cover texts being (a) (see below), and with +the Back-Cover Texts being (b) (see below). A copy of the license is +included in the gfdl(7) man page. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@c Set file name and title for the man page. +@setfilename gcc +@settitle GNU project C and C++ compiler +@c man begin SYNOPSIS +gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] + [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] + [@option{-W}@var{warn}@dots{}] [@option{-pedantic}] + [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] + [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] + [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] + [@option{-o} @var{outfile}] @var{infile}@dots{} + +Only the most useful options are listed here; see below for the +remainder. @samp{g++} accepts mostly the same options as @samp{gcc}. +@c man end +@c man begin SEEALSO +gpl(7), gfdl(7), fsf-funding(7), +cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) +and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as}, +@file{ld}, @file{binutils} and @file{gdb}. +@c man end +@c man begin BUGS +For instructions on reporting bugs, see +@w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug} +script to report bugs is recommended. +@c man end +@c man begin AUTHOR +See the Info entry for @command{gcc}, or +@w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, +for contributors to GCC@. +@c man end +@end ignore + +@node Invoking GCC +@chapter GCC Command Options +@cindex GCC command options +@cindex command options +@cindex options, GCC command + +@c man begin DESCRIPTION + +When you invoke GCC, it normally does preprocessing, compilation, +assembly and linking. The ``overall options'' allow you to stop this +process at an intermediate stage. For example, the @option{-c} option +says not to run the linker. Then the output consists of object files +output by the assembler. + +Other options are passed on to one stage of processing. Some options +control the preprocessor and others the compiler itself. Yet other +options control the assembler and linker; most of these are not +documented here, since you rarely need to use any of them. + +@cindex C compilation options +Most of the command line options that you can use with GCC are useful +for C programs; when an option is only useful with another language +(usually C++), the explanation says so explicitly. If the description +for a particular option does not mention a source language, you can use +that option with all supported languages. + +@cindex C++ compilation options +@xref{Invoking G++,,Compiling C++ Programs}, for a summary of special +options for compiling C++ programs. + +@cindex grouping options +@cindex options, grouping +The @command{gcc} program accepts options and file names as operands. Many +options have multi-letter names; therefore multiple single-letter options +may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d +-r}}. + +@cindex order of options +@cindex options, order +You can mix options and other arguments. For the most part, the order +you use doesn't matter. Order does matter when you use several options +of the same kind; for example, if you specify @option{-L} more than once, +the directories are searched in the order specified. + +Many options have long names starting with @samp{-f} or with +@samp{-W}---for example, @option{-fforce-mem}, +@option{-fstrength-reduce}, @option{-Wformat} and so on. Most of +these have both positive and negative forms; the negative form of +@option{-ffoo} would be @option{-fno-foo}. This manual documents +only one of these two forms, whichever one is not the default. + +@c man end + +@xref{Option Index}, for an index to GCC's options. + +@menu +* Option Summary:: Brief list of all options, without explanations. +* Overall Options:: Controlling the kind of output: + an executable, object files, assembler files, + or preprocessed source. +* Invoking G++:: Compiling C++ programs. +* C Dialect Options:: Controlling the variant of C language compiled. +* C++ Dialect Options:: Variations on C++. +* Objective-C Dialect Options:: Variations on Objective-C. +* Language Independent Options:: Controlling how diagnostics should be + formatted. +* Warning Options:: How picky should the compiler be? +* Debugging Options:: Symbol tables, measurements, and debugging dumps. +* Optimize Options:: How much optimization? +* Preprocessor Options:: Controlling header files and macro definitions. + Also, getting dependency information for Make. +* Assembler Options:: Passing options to the assembler. +* Link Options:: Specifying libraries and so on. +* Directory Options:: Where to find header files and libraries. + Where to find the compiler executable files. +* Spec Files:: How to pass switches to sub-processes. +* Target Options:: Running a cross-compiler, or an old version of GCC. +* Submodel Options:: Specifying minor hardware or convention variations, + such as 68010 vs 68020. +* Code Gen Options:: Specifying conventions for function calls, data layout + and register usage. +* Environment Variables:: Env vars that affect GCC. +* Running Protoize:: Automatically adding or removing function prototypes. +@end menu + +@c man begin OPTIONS + +@node Option Summary +@section Option Summary + +Here is a summary of all the options, grouped by type. Explanations are +in the following sections. + +@table @emph +@item Overall Options +@xref{Overall Options,,Options Controlling the Kind of Output}. +@gccoptlist{ +-c -S -E -o @var{file} -pipe -pass-exit-codes -x @var{language} @gol +-v --target-help --help} + +@item C Language Options +@xref{C Dialect Options,,Options Controlling C Dialect}. +@gccoptlist{ +-ansi -std=@var{standard} -aux-info @var{filename} @gol +-fno-asm -fno-builtin -fno-builtin-@var{function} @gol +-fhosted -ffreestanding @gol +-trigraphs -traditional -traditional-cpp @gol +-fallow-single-precision -fcond-mismatch @gol +-fsigned-bitfields -fsigned-char @gol +-funsigned-bitfields -funsigned-char @gol +-fwritable-strings -fshort-wchar} + +@item C++ Language Options +@xref{C++ Dialect Options,,Options Controlling C++ Dialect}. +@gccoptlist{ +-fno-access-control -fcheck-new -fconserve-space @gol +-fno-const-strings -fdollars-in-identifiers @gol +-fno-elide-constructors @gol +-fno-enforce-eh-specs -fexternal-templates @gol +-falt-external-templates @gol +-ffor-scope -fno-for-scope -fno-gnu-keywords @gol +-fno-implicit-templates @gol +-fno-implicit-inline-templates @gol +-fno-implement-inlines -fms-extensions @gol +-fno-nonansi-builtins -fno-operator-names @gol +-fno-optional-diags -fpermissive @gol +-frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol +-fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol +-fno-default-inline -Wctor-dtor-privacy @gol +-Wnon-virtual-dtor -Wreorder @gol +-Weffc++ -Wno-deprecated @gol +-Wno-non-template-friend -Wold-style-cast @gol +-Woverloaded-virtual -Wno-pmf-conversions @gol +-Wsign-promo -Wsynth} + +@item Objective-C Language Options +@xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}. +@gccoptlist{ +-fconstant-string-class=@var{class-name} @gol +-fgnu-runtime -fnext-runtime -gen-decls @gol +-Wno-protocol -Wselector} + +@item Language Independent Options +@xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}. +@gccoptlist{ +-fmessage-length=@var{n} @gol +-fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}} + +@item Warning Options +@xref{Warning Options,,Options to Request or Suppress Warnings}. +@gccoptlist{ +-fsyntax-only -pedantic -pedantic-errors @gol +-w -W -Wall -Waggregate-return @gol +-Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol +-Wconversion -Wno-deprecated-declarations @gol +-Wdisabled-optimization -Wdiv-by-zero -Werror @gol +-Wfloat-equal -Wformat -Wformat=2 @gol +-Wformat-nonliteral -Wformat-security @gol +-Wimplicit -Wimplicit-int @gol +-Wimplicit-function-declaration @gol +-Werror-implicit-function-declaration @gol +-Wimport -Winline @gol +-Wlarger-than-@var{len} -Wlong-long @gol +-Wmain -Wmissing-braces -Wmissing-declarations @gol +-Wmissing-format-attribute -Wmissing-noreturn @gol +-Wmultichar -Wno-format-extra-args -Wno-format-y2k @gol +-Wno-import -Wpacked -Wpadded @gol +-Wparentheses -Wpointer-arith -Wredundant-decls @gol +-Wreturn-type -Wsequence-point -Wshadow @gol +-Wsign-compare -Wswitch -Wsystem-headers @gol +-Wtrigraphs -Wundef -Wuninitialized @gol +-Wunknown-pragmas -Wunreachable-code @gol +-Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol +-Wunused-value -Wunused-variable -Wwrite-strings} + +@item C-only Warning Options +@gccoptlist{ +-Wbad-function-cast -Wmissing-prototypes -Wnested-externs @gol +-Wstrict-prototypes -Wtraditional} + +@item Debugging Options +@xref{Debugging Options,,Options for Debugging Your Program or GCC}. +@gccoptlist{ +-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol +-fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol +-fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol +-fdump-tree-original@r{[}-@var{n}@r{]} -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol +-fdump-tree-inlined@r{[}-@var{n}@r{]} @gol +-fmem-report -fpretend-float @gol +-fprofile-arcs -ftest-coverage -ftime-report @gol +-g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol +-ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol +-p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol +-print-multi-directory -print-multi-lib @gol +-print-prog-name=@var{program} -print-search-dirs -Q @gol +-save-temps -time} + +@item Optimization Options +@xref{Optimize Options,,Options that Control Optimization}. +@gccoptlist{ +-falign-functions=@var{n} -falign-jumps=@var{n} @gol +-falign-labels=@var{n} -falign-loops=@var{n} @gol +-fbranch-probabilities -fcaller-saves -fcprop-registers @gol +-fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol +-fdelayed-branch -fdelete-null-pointer-checks @gol +-fexpensive-optimizations -ffast-math -ffloat-store @gol +-fforce-addr -fforce-mem -ffunction-sections @gol +-fgcse -fgcse-lm -fgcse-sm @gol +-finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol +-fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol +-fmove-all-movables -fno-default-inline -fno-defer-pop @gol +-fno-function-cse -fno-guess-branch-probability @gol +-fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol +-funsafe-math-optimizations -fno-trapping-math @gol +-fomit-frame-pointer -foptimize-register-move @gol +-foptimize-sibling-calls -fprefetch-loop-arrays @gol +-freduce-all-givs -fregmove -frename-registers @gol +-frerun-cse-after-loop -frerun-loop-opt @gol +-fschedule-insns -fschedule-insns2 @gol +-fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol +-fstrength-reduce -fstrict-aliasing -fthread-jumps -ftrapv @gol +-funroll-all-loops -funroll-loops @gol +--param @var{name}=@var{value} +-O -O0 -O1 -O2 -O3 -Os} + +@item Preprocessor Options +@xref{Preprocessor Options,,Options Controlling the Preprocessor}. +@gccoptlist{ +-$ -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol +-C -dD -dI -dM -dN @gol +-D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol +-idirafter @var{dir} @gol +-include @var{file} -imacros @var{file} @gol +-iprefix @var{file} -iwithprefix @var{dir} @gol +-iwithprefixbefore @var{dir} -isystem @var{dir} @gol +-M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol +-trigraphs -undef -U@var{macro} -Wp,@var{option}} + +@item Assembler Option +@xref{Assembler Options,,Passing Options to the Assembler}. +@gccoptlist{ +-Wa,@var{option}} + +@item Linker Options +@xref{Link Options,,Options for Linking}. +@gccoptlist{ +@var{object-file-name} -l@var{library} @gol +-nostartfiles -nodefaultlibs -nostdlib @gol +-s -static -static-libgcc -shared -shared-libgcc -symbolic @gol +-Wl,@var{option} -Xlinker @var{option} @gol +-u @var{symbol}} + +@item Directory Options +@xref{Directory Options,,Options for Directory Search}. +@gccoptlist{ +-B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}} + +@item Target Options +@c I wrote this xref this way to avoid overfull hbox. -- rms +@xref{Target Options}. +@gccoptlist{ +-b @var{machine} -V @var{version}} + +@item Machine Dependent Options +@xref{Submodel Options,,Hardware Models and Configurations}. + +@emph{M680x0 Options} +@gccoptlist{ +-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol +-m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol +-mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol +-malign-int -mstrict-align} + +@emph{M68hc1x Options} +@gccoptlist{ +-m6811 -m6812 -m68hc11 -m68hc12 @gol +-mauto-incdec -mshort -msoft-reg-count=@var{count}} + +@emph{VAX Options} +@gccoptlist{ +-mg -mgnu -munix} + +@emph{SPARC Options} +@gccoptlist{ +-mcpu=@var{cpu-type} @gol +-mtune=@var{cpu-type} @gol +-mcmodel=@var{code-model} @gol +-m32 -m64 @gol +-mapp-regs -mbroken-saverestore -mcypress @gol +-mepilogue -mfaster-structs -mflat @gol +-mfpu -mhard-float -mhard-quad-float @gol +-mimpure-text -mlive-g0 -mno-app-regs @gol +-mno-epilogue -mno-faster-structs -mno-flat -mno-fpu @gol +-mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol +-msoft-float -msoft-quad-float -msparclite -mstack-bias @gol +-msupersparc -munaligned-doubles -mv8} + +@emph{Convex Options} +@gccoptlist{ +-mc1 -mc2 -mc32 -mc34 -mc38 @gol +-margcount -mnoargcount @gol +-mlong32 -mlong64 @gol +-mvolatile-cache -mvolatile-nocache} + +@emph{AMD29K Options} +@gccoptlist{ +-m29000 -m29050 -mbw -mnbw -mdw -mndw @gol +-mlarge -mnormal -msmall @gol +-mkernel-registers -mno-reuse-arg-regs @gol +-mno-stack-check -mno-storem-bug @gol +-mreuse-arg-regs -msoft-float -mstack-check @gol +-mstorem-bug -muser-registers} + +@emph{ARM Options} +@gccoptlist{ +-mapcs-frame -mno-apcs-frame @gol +-mapcs-26 -mapcs-32 @gol +-mapcs-stack-check -mno-apcs-stack-check @gol +-mapcs-float -mno-apcs-float @gol +-mapcs-reentrant -mno-apcs-reentrant @gol +-msched-prolog -mno-sched-prolog @gol +-mlittle-endian -mbig-endian -mwords-little-endian @gol +-malignment-traps -mno-alignment-traps @gol +-msoft-float -mhard-float -mfpe @gol +-mthumb-interwork -mno-thumb-interwork @gol +-mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol +-mstructure-size-boundary=@var{n} @gol +-mbsd -mxopen -mno-symrename @gol +-mabort-on-noreturn @gol +-mlong-calls -mno-long-calls @gol +-msingle-pic-base -mno-single-pic-base @gol +-mpic-register=@var{reg} @gol +-mnop-fun-dllimport @gol +-mpoke-function-name @gol +-mthumb -marm @gol +-mtpcs-frame -mtpcs-leaf-frame @gol +-mcaller-super-interworking -mcallee-super-interworking } + +@emph{MN10200 Options} +@gccoptlist{ +-mrelax} + +@emph{MN10300 Options} +@gccoptlist{ +-mmult-bug -mno-mult-bug @gol +-mam33 -mno-am33 @gol +-mno-crt0 -mrelax} + +@emph{M32R/D Options} +@gccoptlist{ +-m32rx -m32r -mcode-model=@var{model-type} -msdata=@var{sdata-type} @gol +-G @var{num}} + +@emph{M88K Options} +@gccoptlist{ +-m88000 -m88100 -m88110 -mbig-pic @gol +-mcheck-zero-division -mhandle-large-shift @gol +-midentify-revision -mno-check-zero-division @gol +-mno-ocs-debug-info -mno-ocs-frame-position @gol +-mno-optimize-arg-area -mno-serialize-volatile @gol +-mno-underscores -mocs-debug-info @gol +-mocs-frame-position -moptimize-arg-area @gol +-mserialize-volatile -mshort-data-@var{num} -msvr3 @gol +-msvr4 -mtrap-large-shift -muse-div-instruction @gol +-mversion-03.00 -mwarn-passed-structs} + +@emph{RS/6000 and PowerPC Options} +@gccoptlist{ +-mcpu=@var{cpu-type} @gol +-mtune=@var{cpu-type} @gol +-mpower -mno-power -mpower2 -mno-power2 @gol +-mpowerpc -mpowerpc64 -mno-powerpc @gol +-maltivec -mno-altivec @gol +-mpowerpc-gpopt -mno-powerpc-gpopt @gol +-mpowerpc-gfxopt -mno-powerpc-gfxopt @gol +-mnew-mnemonics -mold-mnemonics @gol +-mfull-toc -mminimal-toc -mno-fop-in-toc -mno-sum-in-toc @gol +-m64 -m32 -mxl-call -mno-xl-call -mpe @gol +-msoft-float -mhard-float -mmultiple -mno-multiple @gol +-mstring -mno-string -mupdate -mno-update @gol +-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol +-mstrict-align -mno-strict-align -mrelocatable @gol +-mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol +-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol +-mcall-aix -mcall-sysv -mcall-netbsd @gol +-maix-struct-return -msvr4-struct-return +-mabi=altivec @gol +-mprototype -mno-prototype @gol +-msim -mmvme -mads -myellowknife -memb -msdata @gol +-msdata=@var{opt} -mvxworks -G @var{num} -pthread} + +@emph{RT Options} +@gccoptlist{ +-mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol +-mfull-fp-blocks -mhc-struct-return -min-line-mul @gol +-mminimum-fp-blocks -mnohc-struct-return} + +@emph{MIPS Options} +@gccoptlist{ +-mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol +-mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol +-membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol +-mgas -mgp32 -mgp64 @gol +-mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol +-mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol +-mmips-as -mmips-tfile -mno-abicalls @gol +-mno-embedded-data -mno-uninit-const-in-rodata @gol +-mno-embedded-pic -mno-gpopt -mno-long-calls @gol +-mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol +-mrnames -msoft-float @gol +-m4650 -msingle-float -mmad @gol +-mstats -EL -EB -G @var{num} -nocpp @gol +-mabi=32 -mabi=n32 -mabi=64 -mabi=eabi @gol +-mfix7000 -mno-crt0 -mflush-func=@var{func} -mno-flush-func} + +@emph{i386 and x86-64 Options} +@gccoptlist{ +-mcpu=@var{cpu-type} -march=@var{cpu-type} -mfpmath=@var{unit} @gol +-masm=@var{dialect} -mno-fancy-math-387 @gol +-mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol +-mno-wide-multiply -mrtd -malign-double @gol +-mpreferred-stack-boundary=@var{num} @gol +-mmmx -msse -msse2 -msse-math -m3dnow @gol +-mthreads -mno-align-stringops -minline-all-stringops @gol +-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol +-m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol +-mno-red-zone@gol +-m32 -m64} + +@emph{HPPA Options} +@gccoptlist{ +-march=@var{architecture-type} @gol +-mbig-switch -mdisable-fpregs -mdisable-indexing @gol +-mfast-indirect-calls -mgas -mjump-in-delay @gol +-mlong-load-store -mno-big-switch -mno-disable-fpregs @gol +-mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol +-mno-jump-in-delay -mno-long-load-store @gol +-mno-portable-runtime -mno-soft-float @gol +-mno-space-regs -msoft-float -mpa-risc-1-0 @gol +-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol +-mschedule=@var{cpu-type} -mspace-regs} + +@emph{Intel 960 Options} +@gccoptlist{ +-m@var{cpu-type} -masm-compat -mclean-linkage @gol +-mcode-align -mcomplex-addr -mleaf-procedures @gol +-mic-compat -mic2.0-compat -mic3.0-compat @gol +-mintel-asm -mno-clean-linkage -mno-code-align @gol +-mno-complex-addr -mno-leaf-procedures @gol +-mno-old-align -mno-strict-align -mno-tail-call @gol +-mnumerics -mold-align -msoft-float -mstrict-align @gol +-mtail-call} + +@emph{DEC Alpha Options} +@gccoptlist{ +-mno-fp-regs -msoft-float -malpha-as -mgas @gol +-mieee -mieee-with-inexact -mieee-conformant @gol +-mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol +-mtrap-precision=@var{mode} -mbuild-constants @gol +-mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol +-mbwx -mmax -mfix -mcix @gol +-mfloat-vax -mfloat-ieee @gol +-mexplicit-relocs -msmall-data -mlarge-data @gol +-mmemory-latency=@var{time}} + +@emph{DEC Alpha/VMS Options} +@gccoptlist{ +-mvms-return-codes} + +@emph{Clipper Options} +@gccoptlist{ +-mc300 -mc400} + +@emph{H8/300 Options} +@gccoptlist{ +-mrelax -mh -ms -mint32 -malign-300} + +@emph{SH Options} +@gccoptlist{ +-m1 -m2 -m3 -m3e @gol +-m4-nofpu -m4-single-only -m4-single -m4 @gol +-mb -ml -mdalign -mrelax @gol +-mbigtable -mfmovd -mhitachi -mnomacsave @gol +-mieee -misize -mpadstruct -mspace @gol +-mprefergot -musermode} + +@emph{System V Options} +@gccoptlist{ +-Qy -Qn -YP,@var{paths} -Ym,@var{dir}} + +@emph{ARC Options} +@gccoptlist{ +-EB -EL @gol +-mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol +-mdata=@var{data-section} -mrodata=@var{readonly-data-section}} + +@emph{TMS320C3x/C4x Options} +@gccoptlist{ +-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol +-mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol +-mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol +-mparallel-insns -mparallel-mpy -mpreserve-float} + +@emph{V850 Options} +@gccoptlist{ +-mlong-calls -mno-long-calls -mep -mno-ep @gol +-mprolog-function -mno-prolog-function -mspace @gol +-mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol +-mv850 -mbig-switch} + +@emph{NS32K Options} +@gccoptlist{ +-m32032 -m32332 -m32532 -m32081 -m32381 @gol +-mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol +-mregparam -mnoregparam -msb -mnosb @gol +-mbitfield -mnobitfield -mhimem -mnohimem} + +@emph{AVR Options} +@gccoptlist{ +-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol +-mcall-prologues -mno-tablejump -mtiny-stack} + +@emph{MCore Options} +@gccoptlist{ +-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol +-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol +-m4byte-functions -mno-4byte-functions -mcallgraph-data @gol +-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol +-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} + +@emph{MMIX Options} +@gccoptlist{ +-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol +-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol +-melf -mbranch-predict -mno-branch-predict} + +@emph{IA-64 Options} +@gccoptlist{ +-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol +-mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol +-mconstant-gp -mauto-pic -minline-divide-min-latency @gol +-minline-divide-max-throughput -mno-dwarf2-asm @gol +-mfixed-range=@var{register-range}} + +@emph{D30V Options} +@gccoptlist{ +-mextmem -mextmemory -monchip -mno-asm-optimize -masm-optimize @gol +-mbranch-cost=@var{n} -mcond-exec=@var{n}} + +@emph{S/390 and zSeries Options} +@gccoptlist{ +-mhard-float -msoft-float -mbackchain -mno-backchain @gol +-msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol +-m64 -m31 -mdebug -mno-debug} + +@emph{CRIS Options} +@gccoptlist{ +-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol +-mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol +-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol +-mstack-align -mdata-align -mconst-align @gol +-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol +-melf -maout -melinux -mlinux -sim -sim2} + +@emph{PDP-11 Options} +@gccoptlist{ +-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol +-mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol +-mint16 -mno-int32 -mfloat32 -mno-float64 @gol +-mfloat64 -mno-float32 -mabshi -mno-abshi @gol +-mbranch-expensive -mbranch-cheap @gol +-msplit -mno-split -munix-asm -mdec-asm} + +@emph{Xstormy16 Options} +@gccoptlist{ +-msim} + +@emph{Xtensa Options} +@gccoptlist{ +-mbig-endian -mlittle-endian @gol +-mdensity -mno-density @gol +-mmac16 -mno-mac16 @gol +-mmul16 -mno-mul16 @gol +-mmul32 -mno-mul32 @gol +-mnsa -mno-nsa @gol +-mminmax -mno-minmax @gol +-msext -mno-sext @gol +-mbooleans -mno-booleans @gol +-mhard-float -msoft-float @gol +-mfused-madd -mno-fused-madd @gol +-mserialize-volatile -mno-serialize-volatile @gol +-mtext-section-literals -mno-text-section-literals @gol +-mtarget-align -mno-target-align @gol +-mlongcalls -mno-longcalls} + +@item Code Generation Options +@xref{Code Gen Options,,Options for Code Generation Conventions}. +@gccoptlist{ +-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol +-ffixed-@var{reg} -fexceptions @gol +-fnon-call-exceptions -funwind-tables @gol +-fasynchronous-unwind-tables @gol +-finhibit-size-directive -finstrument-functions @gol +-fno-common -fno-ident -fno-gnu-linker @gol +-fpcc-struct-return -fpic -fPIC @gol +-freg-struct-return -fshared-data -fshort-enums @gol +-fshort-double -fvolatile @gol +-fvolatile-global -fvolatile-static @gol +-fverbose-asm -fpack-struct -fstack-check @gol +-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol +-fargument-alias -fargument-noalias @gol +-fargument-noalias-global -fleading-underscore} +@end table + +@menu +* Overall Options:: Controlling the kind of output: + an executable, object files, assembler files, + or preprocessed source. +* C Dialect Options:: Controlling the variant of C language compiled. +* C++ Dialect Options:: Variations on C++. +* Objective-C Dialect Options:: Variations on Objective-C. +* Language Independent Options:: Controlling how diagnostics should be + formatted. +* Warning Options:: How picky should the compiler be? +* Debugging Options:: Symbol tables, measurements, and debugging dumps. +* Optimize Options:: How much optimization? +* Preprocessor Options:: Controlling header files and macro definitions. + Also, getting dependency information for Make. +* Assembler Options:: Passing options to the assembler. +* Link Options:: Specifying libraries and so on. +* Directory Options:: Where to find header files and libraries. + Where to find the compiler executable files. +* Spec Files:: How to pass switches to sub-processes. +* Target Options:: Running a cross-compiler, or an old version of GCC. +@end menu + +@node Overall Options +@section Options Controlling the Kind of Output + +Compilation can involve up to four stages: preprocessing, compilation +proper, assembly and linking, always in that order. The first three +stages apply to an individual source file, and end by producing an +object file; linking combines all the object files (those newly +compiled, and those specified as input) into an executable file. + +@cindex file name suffix +For any given input file, the file name suffix determines what kind of +compilation is done: + +@table @gcctabopt +@item @var{file}.c +C source code which must be preprocessed. + +@item @var{file}.i +C source code which should not be preprocessed. + +@item @var{file}.ii +C++ source code which should not be preprocessed. + +@item @var{file}.m +Objective-C source code. Note that you must link with the library +@file{libobjc.a} to make an Objective-C program work. + +@item @var{file}.mi +Objective-C source code which should not be preprocessed. + +@item @var{file}.h +C header file (not to be compiled or linked). + +@item @var{file}.cc +@itemx @var{file}.cp +@itemx @var{file}.cxx +@itemx @var{file}.cpp +@itemx @var{file}.c++ +@itemx @var{file}.C +C++ source code which must be preprocessed. Note that in @samp{.cxx}, +the last two letters must both be literally @samp{x}. Likewise, +@samp{.C} refers to a literal capital C@. + +@item @var{file}.f +@itemx @var{file}.for +@itemx @var{file}.FOR +Fortran source code which should not be preprocessed. + +@item @var{file}.F +@itemx @var{file}.fpp +@itemx @var{file}.FPP +Fortran source code which must be preprocessed (with the traditional +preprocessor). + +@item @var{file}.r +Fortran source code which must be preprocessed with a RATFOR +preprocessor (not included with GCC)@. + +@xref{Overall Options,,Options Controlling the Kind of Output, g77, +Using and Porting GNU Fortran}, for more details of the handling of +Fortran input files. + +@c FIXME: Descriptions of Java file types. +@c @var{file}.java +@c @var{file}.class +@c @var{file}.zip +@c @var{file}.jar + +@item @var{file}.ads +Ada source code file which contains a library unit declaration (a +declaration of a package, subprogram, or generic, or a generic +instantiation), or a library unit renaming declaration (a package, +generic, or subprogram renaming declaration). Such files are also +called @dfn{specs}. + +@itemx @var{file}.adb +Ada source code file containing a library unit body (a subprogram or +package body). Such files are also called @dfn{bodies}. + +@c GCC also knows about some suffixes for languages not yet included: +@c Pascal: +@c @var{file}.p +@c @var{file}.pas + +@item @var{file}.ch +@itemx @var{file}.chi +CHILL source code (preprocessed with the traditional preprocessor). + +@item @var{file}.s +Assembler code. + +@item @var{file}.S +Assembler code which must be preprocessed. + +@item @var{other} +An object file to be fed straight into linking. +Any file name with no recognized suffix is treated this way. +@end table + +@opindex x +You can specify the input language explicitly with the @option{-x} option: + +@table @gcctabopt +@item -x @var{language} +Specify explicitly the @var{language} for the following input files +(rather than letting the compiler choose a default based on the file +name suffix). This option applies to all following input files until +the next @option{-x} option. Possible values for @var{language} are: +@example +c c-header cpp-output +c++ c++-cpp-output +objective-c objc-cpp-output +assembler assembler-with-cpp +ada +chill +f77 f77-cpp-input ratfor +java +@end example + +@item -x none +Turn off any specification of a language, so that subsequent files are +handled according to their file name suffixes (as they are if @option{-x} +has not been used at all). + +@item -pass-exit-codes +@opindex pass-exit-codes +Normally the @command{gcc} program will exit with the code of 1 if any +phase of the compiler returns a non-success return code. If you specify +@option{-pass-exit-codes}, the @command{gcc} program will instead return with +numerically highest error produced by any phase that returned an error +indication. +@end table + +If you only want some of the stages of compilation, you can use +@option{-x} (or filename suffixes) to tell @command{gcc} where to start, and +one of the options @option{-c}, @option{-S}, or @option{-E} to say where +@command{gcc} is to stop. Note that some combinations (for example, +@samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. + +@table @gcctabopt +@item -c +@opindex c +Compile or assemble the source files, but do not link. The linking +stage simply is not done. The ultimate output is in the form of an +object file for each source file. + +By default, the object file name for a source file is made by replacing +the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. + +Unrecognized input files, not requiring compilation or assembly, are +ignored. + +@item -S +@opindex S +Stop after the stage of compilation proper; do not assemble. The output +is in the form of an assembler code file for each non-assembler input +file specified. + +By default, the assembler file name for a source file is made by +replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. + +Input files that don't require compilation are ignored. + +@item -E +@opindex E +Stop after the preprocessing stage; do not run the compiler proper. The +output is in the form of preprocessed source code, which is sent to the +standard output. + +Input files which don't require preprocessing are ignored. + +@cindex output file option +@item -o @var{file} +@opindex o +Place output in file @var{file}. This applies regardless to whatever +sort of output is being produced, whether it be an executable file, +an object file, an assembler file or preprocessed C code. + +Since only one output file can be specified, it does not make sense to +use @option{-o} when compiling more than one input file, unless you are +producing an executable file as output. + +If @option{-o} is not specified, the default is to put an executable file +in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in +@file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and +all preprocessed C source on standard output. + +@item -v +@opindex v +Print (on standard error output) the commands executed to run the stages +of compilation. Also print the version number of the compiler driver +program and of the preprocessor and the compiler proper. + +@item -pipe +@opindex pipe +Use pipes rather than temporary files for communication between the +various stages of compilation. This fails to work on some systems where +the assembler is unable to read from a pipe; but the GNU assembler has +no trouble. + +@item --help +@opindex help +Print (on the standard output) a description of the command line options +understood by @command{gcc}. If the @option{-v} option is also specified +then @option{--help} will also be passed on to the various processes +invoked by @command{gcc}, so that they can display the command line options +they accept. If the @option{-W} option is also specified then command +line options which have no documentation associated with them will also +be displayed. + +@item --target-help +@opindex target-help +Print (on the standard output) a description of target specific command +line options for each tool. +@end table + +@node Invoking G++ +@section Compiling C++ Programs + +@cindex suffixes for C++ source +@cindex C++ source file suffixes +C++ source files conventionally use one of the suffixes @samp{.C}, +@samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx}; +preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes +files with these names and compiles them as C++ programs even if you +call the compiler the same way as for compiling C programs (usually with +the name @command{gcc}). + +@findex g++ +@findex c++ +However, C++ programs often require class libraries as well as a +compiler that understands the C++ language---and under some +circumstances, you might want to compile programs from standard input, +or otherwise without a suffix that flags them as C++ programs. +@command{g++} is a program that calls GCC with the default language +set to C++, and automatically specifies linking against the C++ +library. On many systems, @command{g++} is also +installed with the name @command{c++}. + +@cindex invoking @command{g++} +When you compile C++ programs, you may specify many of the same +command-line options that you use for compiling programs in any +language; or command-line options meaningful for C and related +languages; or options that are meaningful only for C++ programs. +@xref{C Dialect Options,,Options Controlling C Dialect}, for +explanations of options for languages related to C@. +@xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for +explanations of options that are meaningful only for C++ programs. + +@node C Dialect Options +@section Options Controlling C Dialect +@cindex dialect options +@cindex language dialect options +@cindex options, dialect + +The following options control the dialect of C (or languages derived +from C, such as C++ and Objective-C) that the compiler accepts: + +@table @gcctabopt +@cindex ANSI support +@cindex ISO support +@item -ansi +@opindex ansi +In C mode, support all ISO C89 programs. In C++ mode, +remove GNU extensions that conflict with ISO C++. + +This turns off certain features of GCC that are incompatible with ISO +C89 (when compiling C code), or of standard C++ (when compiling C++ code), +such as the @code{asm} and @code{typeof} keywords, and +predefined macros such as @code{unix} and @code{vax} that identify the +type of system you are using. It also enables the undesirable and +rarely used ISO trigraph feature. For the C compiler, +it disables recognition of C++ style @samp{//} comments as well as +the @code{inline} keyword. + +The alternate keywords @code{__asm__}, @code{__extension__}, +@code{__inline__} and @code{__typeof__} continue to work despite +@option{-ansi}. You would not want to use them in an ISO C program, of +course, but it is useful to put them in header files that might be included +in compilations done with @option{-ansi}. Alternate predefined macros +such as @code{__unix__} and @code{__vax__} are also available, with or +without @option{-ansi}. + +The @option{-ansi} option does not cause non-ISO programs to be +rejected gratuitously. For that, @option{-pedantic} is required in +addition to @option{-ansi}. @xref{Warning Options}. + +The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi} +option is used. Some header files may notice this macro and refrain +from declaring certain functions or defining certain macros that the +ISO standard doesn't call for; this is to avoid interfering with any +programs that might use these names for other things. + +Functions which would normally be built in but do not have semantics +defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in +functions with @option{-ansi} is used. @xref{Other Builtins,,Other +built-in functions provided by GCC}, for details of the functions +affected. + +@item -std= +@opindex std +Determine the language standard. This option is currently only +supported when compiling C@. A value for this option must be provided; +possible values are + +@table @samp +@item c89 +@itemx iso9899:1990 +ISO C89 (same as @option{-ansi}). + +@item iso9899:199409 +ISO C89 as modified in amendment 1. + +@item c99 +@itemx c9x +@itemx iso9899:1999 +@itemx iso9899:199x +ISO C99. Note that this standard is not yet fully supported; see +@w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The +names @samp{c9x} and @samp{iso9899:199x} are deprecated. + +@item gnu89 +Default, ISO C89 plus GNU extensions (including some C99 features). + +@item gnu99 +@item gnu9x +ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC, +this will become the default. The name @samp{gnu9x} is deprecated. + +@end table + +Even when this option is not specified, you can still use some of the +features of newer standards in so far as they do not conflict with +previous C standards. For example, you may use @code{__restrict__} even +when @option{-std=c99} is not specified. + +The @option{-std} options specifying some version of ISO C have the same +effects as @option{-ansi}, except that features that were not in ISO C89 +but are in the specified version (for example, @samp{//} comments and +the @code{inline} keyword in ISO C99) are not disabled. + +@xref{Standards,,Language Standards Supported by GCC}, for details of +these standard versions. + +@item -aux-info @var{filename} +@opindex aux-info +Output to the given filename prototyped declarations for all functions +declared and/or defined in a translation unit, including those in header +files. This option is silently ignored in any language other than C@. + +Besides declarations, the file indicates, in comments, the origin of +each declaration (source file and line), whether the declaration was +implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or +@samp{O} for old, respectively, in the first character after the line +number and the colon), and whether it came from a declaration or a +definition (@samp{C} or @samp{F}, respectively, in the following +character). In the case of function definitions, a K&R-style list of +arguments followed by their declarations is also provided, inside +comments, after the declaration. + +@item -fno-asm +@opindex fno-asm +Do not recognize @code{asm}, @code{inline} or @code{typeof} as a +keyword, so that code can use these words as identifiers. You can use +the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} +instead. @option{-ansi} implies @option{-fno-asm}. + +In C++, this switch only affects the @code{typeof} keyword, since +@code{asm} and @code{inline} are standard keywords. You may want to +use the @option{-fno-gnu-keywords} flag instead, which has the same +effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this +switch only affects the @code{asm} and @code{typeof} keywords, since +@code{inline} is a standard keyword in ISO C99. + +@item -fno-builtin +@itemx -fno-builtin-@var{function} @r{(C and Objective-C only)} +@opindex fno-builtin +@cindex built-in functions +Don't recognize built-in functions that do not begin with +@samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in +functions provided by GCC}, for details of the functions affected, +including those which are not built-in functions when @option{-ansi} or +@option{-std} options for strict ISO C conformance are used because they +do not have an ISO standard meaning. + +GCC normally generates special code to handle certain built-in functions +more efficiently; for instance, calls to @code{alloca} may become single +instructions that adjust the stack directly, and calls to @code{memcpy} +may become inline copy loops. The resulting code is often both smaller +and faster, but since the function calls no longer appear as such, you +cannot set a breakpoint on those calls, nor can you change the behavior +of the functions by linking with a different library. + +In C++, @option{-fno-builtin} is always in effect. The @option{-fbuiltin} +option has no effect. Therefore, in C++, the only way to get the +optimization benefits of built-in functions is to call the function +using the @samp{__builtin_} prefix. The GNU C++ Standard Library uses +built-in functions to implement many functions (like +@code{std::strchr}), so that you automatically get efficient code. + +With the @option{-fno-builtin-@var{function}} option, not available +when compiling C++, only the built-in function @var{function} is +disabled. @var{function} must not begin with @samp{__builtin_}. If a +function is named this is not built-in in this version of GCC, this +option is ignored. There is no corresponding +@option{-fbuiltin-@var{function}} option; if you wish to enable +built-in functions selectively when using @option{-fno-builtin} or +@option{-ffreestanding}, you may define macros such as: + +@smallexample +#define abs(n) __builtin_abs ((n)) +#define strcpy(d, s) __builtin_strcpy ((d), (s)) +@end smallexample + +@item -fhosted +@opindex fhosted +@cindex hosted environment + +Assert that compilation takes place in a hosted environment. This implies +@option{-fbuiltin}. A hosted environment is one in which the +entire standard library is available, and in which @code{main} has a return +type of @code{int}. Examples are nearly everything except a kernel. +This is equivalent to @option{-fno-freestanding}. + +@item -ffreestanding +@opindex ffreestanding +@cindex hosted environment + +Assert that compilation takes place in a freestanding environment. This +implies @option{-fno-builtin}. A freestanding environment +is one in which the standard library may not exist, and program startup may +not necessarily be at @code{main}. The most obvious example is an OS kernel. +This is equivalent to @option{-fno-hosted}. + +@xref{Standards,,Language Standards Supported by GCC}, for details of +freestanding and hosted environments. + +@item -trigraphs +@opindex trigraphs +Support ISO C trigraphs. The @option{-ansi} option (and @option{-std} +options for strict ISO C conformance) implies @option{-trigraphs}. + +@cindex traditional C language +@cindex C language, traditional +@item -traditional +@opindex traditional +Attempt to support some aspects of traditional C compilers. +Specifically: + +@itemize @bullet +@item +All @code{extern} declarations take effect globally even if they +are written inside of a function definition. This includes implicit +declarations of functions. + +@item +The newer keywords @code{typeof}, @code{inline}, @code{signed}, @code{const} +and @code{volatile} are not recognized. (You can still use the +alternative keywords such as @code{__typeof__}, @code{__inline__}, and +so on.) + +@item +Comparisons between pointers and integers are always allowed. + +@item +Integer types @code{unsigned short} and @code{unsigned char} promote +to @code{unsigned int}. + +@item +Out-of-range floating point literals are not an error. + +@item +Certain constructs which ISO regards as a single invalid preprocessing +number, such as @samp{0xe-0xd}, are treated as expressions instead. + +@item +String ``constants'' are not necessarily constant; they are stored in +writable space, and identical looking constants are allocated +separately. (This is the same as the effect of +@option{-fwritable-strings}.) + +@cindex @code{longjmp} and automatic variables +@item +All automatic variables not declared @code{register} are preserved by +@code{longjmp}. Ordinarily, GNU C follows ISO C: automatic variables +not declared @code{volatile} may be clobbered. + +@item +@cindex @samp{\x} +@cindex @samp{\a} +@cindex escape sequences, traditional +The character escape sequences @samp{\x} and @samp{\a} evaluate as the +literal characters @samp{x} and @samp{a} respectively. Without +@w{@option{-traditional}}, @samp{\x} is a prefix for the hexadecimal +representation of a character, and @samp{\a} produces a bell. +@end itemize + +This option is deprecated and may be removed. + +You may wish to use @option{-fno-builtin} as well as @option{-traditional} +if your program uses names that are normally GNU C built-in functions for +other purposes of its own. + +You cannot use @option{-traditional} if you include any header files that +rely on ISO C features. Some vendors are starting to ship systems with +ISO C header files and you cannot use @option{-traditional} on such +systems to compile files that include any system headers. + +The @option{-traditional} option also enables @option{-traditional-cpp}. + +@item -traditional-cpp +@opindex traditional-cpp +Attempt to support some aspects of traditional C preprocessors. +See the GNU CPP manual for details. + +@item -fcond-mismatch +@opindex fcond-mismatch +Allow conditional expressions with mismatched types in the second and +third arguments. The value of such an expression is void. This option +is not supported for C++. + +@item -funsigned-char +@opindex funsigned-char +Let the type @code{char} be unsigned, like @code{unsigned char}. + +Each kind of machine has a default for what @code{char} should +be. It is either like @code{unsigned char} by default or like +@code{signed char} by default. + +Ideally, a portable program should always use @code{signed char} or +@code{unsigned char} when it depends on the signedness of an object. +But many programs have been written to use plain @code{char} and +expect it to be signed, or expect it to be unsigned, depending on the +machines they were written for. This option, and its inverse, let you +make such a program work with the opposite default. + +The type @code{char} is always a distinct type from each of +@code{signed char} or @code{unsigned char}, even though its behavior +is always just like one of those two. + +@item -fsigned-char +@opindex fsigned-char +Let the type @code{char} be signed, like @code{signed char}. + +Note that this is equivalent to @option{-fno-unsigned-char}, which is +the negative form of @option{-funsigned-char}. Likewise, the option +@option{-fno-signed-char} is equivalent to @option{-funsigned-char}. + +@item -fsigned-bitfields +@itemx -funsigned-bitfields +@itemx -fno-signed-bitfields +@itemx -fno-unsigned-bitfields +@opindex fsigned-bitfields +@opindex funsigned-bitfields +@opindex fno-signed-bitfields +@opindex fno-unsigned-bitfields +These options control whether a bit-field is signed or unsigned, when the +declaration does not use either @code{signed} or @code{unsigned}. By +default, such a bit-field is signed, because this is consistent: the +basic integer types such as @code{int} are signed types. + +However, when @option{-traditional} is used, bit-fields are all unsigned +no matter what. + +@item -fwritable-strings +@opindex fwritable-strings +Store string constants in the writable data segment and don't uniquize +them. This is for compatibility with old programs which assume they can +write into string constants. The option @option{-traditional} also has +this effect. + +Writing into string constants is a very bad idea; ``constants'' should +be constant. + +@item -fallow-single-precision +@opindex fallow-single-precision +Do not promote single precision math operations to double precision, +even when compiling with @option{-traditional}. + +Traditional K&R C promotes all floating point operations to double +precision, regardless of the sizes of the operands. On the +architecture for which you are compiling, single precision may be faster +than double precision. If you must use @option{-traditional}, but want +to use single precision operations when the operands are single +precision, use this option. This option has no effect when compiling +with ISO or GNU C conventions (the default). + +@item -fshort-wchar +@opindex fshort-wchar +Override the underlying type for @samp{wchar_t} to be @samp{short +unsigned int} instead of the default for the target. This option is +useful for building programs to run under WINE@. +@end table + +@node C++ Dialect Options +@section Options Controlling C++ Dialect + +@cindex compiler options, C++ +@cindex C++ options, command line +@cindex options, C++ +This section describes the command-line options that are only meaningful +for C++ programs; but you can also use most of the GNU compiler options +regardless of what language your program is in. For example, you +might compile a file @code{firstClass.C} like this: + +@example +g++ -g -frepo -O -c firstClass.C +@end example + +@noindent +In this example, only @option{-frepo} is an option meant +only for C++ programs; you can use the other options with any +language supported by GCC@. + +Here is a list of options that are @emph{only} for compiling C++ programs: + +@table @gcctabopt +@item -fno-access-control +@opindex fno-access-control +Turn off all access checking. This switch is mainly useful for working +around bugs in the access control code. + +@item -fcheck-new +@opindex fcheck-new +Check that the pointer returned by @code{operator new} is non-null +before attempting to modify the storage allocated. The current Working +Paper requires that @code{operator new} never return a null pointer, so +this check is normally unnecessary. + +An alternative to using this option is to specify that your +@code{operator new} does not throw any exceptions; if you declare it +@samp{throw()}, G++ will check the return value. See also @samp{new +(nothrow)}. + +@item -fconserve-space +@opindex fconserve-space +Put uninitialized or runtime-initialized global variables into the +common segment, as C does. This saves space in the executable at the +cost of not diagnosing duplicate definitions. If you compile with this +flag and your program mysteriously crashes after @code{main()} has +completed, you may have an object that is being destroyed twice because +two definitions were merged. + +This option is no longer useful on most targets, now that support has +been added for putting variables into BSS without making them common. + +@item -fno-const-strings +@opindex fno-const-strings +Give string constants type @code{char *} instead of type @code{const +char *}. By default, G++ uses type @code{const char *} as required by +the standard. Even if you use @option{-fno-const-strings}, you cannot +actually modify the value of a string constant, unless you also use +@option{-fwritable-strings}. + +This option might be removed in a future release of G++. For maximum +portability, you should structure your code so that it works with +string constants that have type @code{const char *}. + +@item -fdollars-in-identifiers +@opindex fdollars-in-identifiers +Accept @samp{$} in identifiers. You can also explicitly prohibit use of +@samp{$} with the option @option{-fno-dollars-in-identifiers}. (GNU C allows +@samp{$} by default on most target systems, but there are a few exceptions.) +Traditional C allowed the character @samp{$} to form part of +identifiers. However, ISO C and C++ forbid @samp{$} in identifiers. + +@item -fno-elide-constructors +@opindex fno-elide-constructors +The C++ standard allows an implementation to omit creating a temporary +which is only used to initialize another object of the same type. +Specifying this option disables that optimization, and forces G++ to +call the copy constructor in all cases. + +@item -fno-enforce-eh-specs +@opindex fno-enforce-eh-specs +Don't check for violation of exception specifications at runtime. This +option violates the C++ standard, but may be useful for reducing code +size in production builds, much like defining @samp{NDEBUG}. The compiler +will still optimize based on the exception specifications. + +@item -fexternal-templates +@opindex fexternal-templates + +Cause @samp{#pragma interface} and @samp{implementation} to apply to +template instantiation; template instances are emitted or not according +to the location of the template definition. @xref{Template +Instantiation}, for more information. + +This option is deprecated. + +@item -falt-external-templates +@opindex falt-external-templates +Similar to @option{-fexternal-templates}, but template instances are +emitted or not according to the place where they are first instantiated. +@xref{Template Instantiation}, for more information. + +This option is deprecated. + +@item -ffor-scope +@itemx -fno-for-scope +@opindex ffor-scope +@opindex fno-for-scope +If @option{-ffor-scope} is specified, the scope of variables declared in +a @i{for-init-statement} is limited to the @samp{for} loop itself, +as specified by the C++ standard. +If @option{-fno-for-scope} is specified, the scope of variables declared in +a @i{for-init-statement} extends to the end of the enclosing scope, +as was the case in old versions of G++, and other (traditional) +implementations of C++. + +The default if neither flag is given to follow the standard, +but to allow and give a warning for old-style code that would +otherwise be invalid, or have different behavior. + +@item -fno-gnu-keywords +@opindex fno-gnu-keywords +Do not recognize @code{typeof} as a keyword, so that code can use this +word as an identifier. You can use the keyword @code{__typeof__} instead. +@option{-ansi} implies @option{-fno-gnu-keywords}. + +@item -fno-implicit-templates +@opindex fno-implicit-templates +Never emit code for non-inline templates which are instantiated +implicitly (i.e.@: by use); only emit code for explicit instantiations. +@xref{Template Instantiation}, for more information. + +@item -fno-implicit-inline-templates +@opindex fno-implicit-inline-templates +Don't emit code for implicit instantiations of inline templates, either. +The default is to handle inlines differently so that compiles with and +without optimization will need the same set of explicit instantiations. + +@item -fno-implement-inlines +@opindex fno-implement-inlines +To save space, do not emit out-of-line copies of inline functions +controlled by @samp{#pragma implementation}. This will cause linker +errors if these functions are not inlined everywhere they are called. + +@item -fms-extensions +@opindex fms-extensions +Disable pedantic warnings about constructs used in MFC, such as implicit +int and getting a pointer to member function via non-standard syntax. + +@item -fno-nonansi-builtins +@opindex fno-nonansi-builtins +Disable built-in declarations of functions that are not mandated by +ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, +@code{index}, @code{bzero}, @code{conjf}, and other related functions. + +@item -fno-operator-names +@opindex fno-operator-names +Do not treat the operator name keywords @code{and}, @code{bitand}, +@code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as +synonyms as keywords. + +@item -fno-optional-diags +@opindex fno-optional-diags +Disable diagnostics that the standard says a compiler does not need to +issue. Currently, the only such diagnostic issued by G++ is the one for +a name having multiple meanings within a class. + +@item -fpermissive +@opindex fpermissive +Downgrade messages about nonconformant code from errors to warnings. By +default, G++ effectively sets @option{-pedantic-errors} without +@option{-pedantic}; this option reverses that. This behavior and this +option are superseded by @option{-pedantic}, which works as it does for GNU C@. + +@item -frepo +@opindex frepo +Enable automatic template instantiation at link time. This option also +implies @option{-fno-implicit-templates}. @xref{Template +Instantiation}, for more information. + +@item -fno-rtti +@opindex fno-rtti +Disable generation of information about every class with virtual +functions for use by the C++ runtime type identification features +(@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts +of the language, you can save some space by using this flag. Note that +exception handling uses the same information, but it will generate it as +needed. + +@item -fstats +@opindex fstats +Emit statistics about front-end processing at the end of the compilation. +This information is generally only useful to the G++ development team. + +@item -ftemplate-depth-@var{n} +@opindex ftemplate-depth +Set the maximum instantiation depth for template classes to @var{n}. +A limit on the template instantiation depth is needed to detect +endless recursions during template class instantiation. ANSI/ISO C++ +conforming programs must not rely on a maximum depth greater than 17. + +@item -fuse-cxa-atexit +@opindex fuse-cxa-atexit +Register destructors for objects with static storage duration with the +@code{__cxa_atexit} function rather than the @code{atexit} function. +This option is required for fully standards-compliant handling of static +destructors, but will only work if your C library supports +@code{__cxa_atexit}. + +@item -fvtable-gc +@opindex fvtable-gc +Emit special relocations for vtables and virtual function references +so that the linker can identify unused virtual functions and zero out +vtable slots that refer to them. This is most useful with +@option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to +also discard the functions themselves. + +This optimization requires GNU as and GNU ld. Not all systems support +this option. @option{-Wl,--gc-sections} is ignored without @option{-static}. + +@item -fno-weak +@opindex fno-weak +Do not use weak symbol support, even if it is provided by the linker. +By default, G++ will use weak symbols if they are available. This +option exists only for testing, and should not be used by end-users; +it will result in inferior code and has no benefits. This option may +be removed in a future release of G++. + +@item -nostdinc++ +@opindex nostdinc++ +Do not search for header files in the standard directories specific to +C++, but do still search the other standard directories. (This option +is used when building the C++ library.) +@end table + +In addition, these optimization, warning, and code generation options +have meanings only for C++ programs: + +@table @gcctabopt +@item -fno-default-inline +@opindex fno-default-inline +Do not assume @samp{inline} for functions defined inside a class scope. +@xref{Optimize Options,,Options That Control Optimization}. Note that these +functions will have linkage like inline functions; they just won't be +inlined by default. + +@item -Wctor-dtor-privacy @r{(C++ only)} +@opindex Wctor-dtor-privacy +Warn when a class seems unusable, because all the constructors or +destructors in a class are private and the class has no friends or +public static member functions. + +@item -Wnon-virtual-dtor @r{(C++ only)} +@opindex Wnon-virtual-dtor +Warn when a class declares a non-virtual destructor that should probably +be virtual, because it looks like the class will be used polymorphically. + +@item -Wreorder @r{(C++ only)} +@opindex Wreorder +@cindex reordering, warning +@cindex warning for reordering of member initializers +Warn when the order of member initializers given in the code does not +match the order in which they must be executed. For instance: + +@smallexample +struct A @{ + int i; + int j; + A(): j (0), i (1) @{ @} +@}; +@end smallexample + +Here the compiler will warn that the member initializers for @samp{i} +and @samp{j} will be rearranged to match the declaration order of the +members. +@end table + +The following @option{-W@dots{}} options are not affected by @option{-Wall}. + +@table @gcctabopt +@item -Weffc++ @r{(C++ only)} +@opindex Weffc++ +Warn about violations of various style guidelines from Scott Meyers' +@cite{Effective C++} books. If you use this option, you should be aware +that the standard library headers do not obey all of these guidelines; +you can use @samp{grep -v} to filter out those warnings. + +@item -Wno-deprecated @r{(C++ only)} +@opindex Wno-deprecated +Do not warn about usage of deprecated features. @xref{Deprecated Features}. + +@item -Wno-non-template-friend @r{(C++ only)} +@opindex Wno-non-template-friend +Disable warnings when non-templatized friend functions are declared +within a template. With the advent of explicit template specification +support in G++, if the name of the friend is an unqualified-id (i.e., +@samp{friend foo(int)}), the C++ language specification demands that the +friend declare or define an ordinary, nontemplate function. (Section +14.5.3). Before G++ implemented explicit specification, unqualified-ids +could be interpreted as a particular specialization of a templatized +function. Because this non-conforming behavior is no longer the default +behavior for G++, @option{-Wnon-template-friend} allows the compiler to +check existing code for potential trouble spots, and is on by default. +This new compiler behavior can be turned off with +@option{-Wno-non-template-friend} which keeps the conformant compiler code +but disables the helpful warning. + +@item -Wold-style-cast @r{(C++ only)} +@opindex Wold-style-cast +Warn if an old-style (C-style) cast to a non-void type is used within +a C++ program. The new-style casts (@samp{static_cast}, +@samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to +unintended effects, and much easier to grep for. + +@item -Woverloaded-virtual @r{(C++ only)} +@opindex Woverloaded-virtual +@cindex overloaded virtual fn, warning +@cindex warning for overloaded virtual fn +Warn when a function declaration hides virtual functions from a +base class. For example, in: + +@smallexample +struct A @{ + virtual void f(); +@}; + +struct B: public A @{ + void f(int); +@}; +@end smallexample + +the @code{A} class version of @code{f} is hidden in @code{B}, and code +like this: + +@smallexample +B* b; +b->f(); +@end smallexample + +will fail to compile. + +@item -Wno-pmf-conversions @r{(C++ only)} +@opindex Wno-pmf-conversions +Disable the diagnostic for converting a bound pointer to member function +to a plain pointer. + +@item -Wsign-promo @r{(C++ only)} +@opindex Wsign-promo +Warn when overload resolution chooses a promotion from unsigned or +enumeral type to a signed type over a conversion to an unsigned type of +the same size. Previous versions of G++ would try to preserve +unsignedness, but the standard mandates the current behavior. + +@item -Wsynth @r{(C++ only)} +@opindex Wsynth +@cindex warning for synthesized methods +@cindex synthesized methods, warning +Warn when G++'s synthesis behavior does not match that of cfront. For +instance: + +@smallexample +struct A @{ + operator int (); + A& operator = (int); +@}; + +main () +@{ + A a,b; + a = b; +@} +@end smallexample + +In this example, G++ will synthesize a default @samp{A& operator = +(const A&);}, while cfront will use the user-defined @samp{operator =}. +@end table + +@node Objective-C Dialect Options +@section Options Controlling Objective-C Dialect + +@cindex compiler options, Objective-C +@cindex Objective-C options, command line +@cindex options, Objective-C +This section describes the command-line options that are only meaningful +for Objective-C programs; but you can also use most of the GNU compiler +options regardless of what language your program is in. For example, +you might compile a file @code{some_class.m} like this: + +@example +gcc -g -fgnu-runtime -O -c some_class.m +@end example + +@noindent +In this example, only @option{-fgnu-runtime} is an option meant only for +Objective-C programs; you can use the other options with any language +supported by GCC@. + +Here is a list of options that are @emph{only} for compiling Objective-C +programs: + +@table @gcctabopt +@item -fconstant-string-class=@var{class-name} +@opindex fconstant-string-class +Use @var{class-name} as the name of the class to instantiate for each +literal string specified with the syntax @code{@@"@dots{}"}. The default +class name is @code{NXConstantString}. + +@item -fgnu-runtime +@opindex fgnu-runtime +Generate object code compatible with the standard GNU Objective-C +runtime. This is the default for most types of systems. + +@item -fnext-runtime +@opindex fnext-runtime +Generate output compatible with the NeXT runtime. This is the default +for NeXT-based systems, including Darwin and Mac OS X@. + +@item -gen-decls +@opindex gen-decls +Dump interface declarations for all classes seen in the source file to a +file named @file{@var{sourcename}.decl}. + +@item -Wno-protocol +@opindex Wno-protocol +Do not warn if methods required by a protocol are not implemented +in the class adopting it. + +@item -Wselector +@opindex Wselector +Warn if a selector has multiple methods of different types defined. + +@c not documented because only avail via -Wp +@c @item -print-objc-runtime-info + +@end table + +@node Language Independent Options +@section Options to Control Diagnostic Messages Formatting +@cindex options to control diagnostics formatting +@cindex diagnostic messages +@cindex message formatting + +Traditionally, diagnostic messages have been formatted irrespective of +the output device's aspect (e.g.@: its width, @dots{}). The options described +below can be used to control the diagnostic messages formatting +algorithm, e.g.@: how many characters per line, how often source location +information should be reported. Right now, only the C++ front end can +honor these options. However it is expected, in the near future, that +the remaining front ends would be able to digest them correctly. + +@table @gcctabopt +@item -fmessage-length=@var{n} +@opindex fmessage-length +Try to format error messages so that they fit on lines of about @var{n} +characters. The default is 72 characters for @command{g++} and 0 for the rest of +the front ends supported by GCC@. If @var{n} is zero, then no +line-wrapping will be done; each error message will appear on a single +line. + +@opindex fdiagnostics-show-location +@item -fdiagnostics-show-location=once +Only meaningful in line-wrapping mode. Instructs the diagnostic messages +reporter to emit @emph{once} source location information; that is, in +case the message is too long to fit on a single physical line and has to +be wrapped, the source location won't be emitted (as prefix) again, +over and over, in subsequent continuation lines. This is the default +behavior. + +@item -fdiagnostics-show-location=every-line +Only meaningful in line-wrapping mode. Instructs the diagnostic +messages reporter to emit the same source location information (as +prefix) for physical lines that result from the process of breaking +a message which is too long to fit on a single line. + +@end table + +@node Warning Options +@section Options to Request or Suppress Warnings +@cindex options to control warnings +@cindex warning messages +@cindex messages, warning +@cindex suppressing warnings + +Warnings are diagnostic messages that report constructions which +are not inherently erroneous but which are risky or suggest there +may have been an error. + +You can request many specific warnings with options beginning @samp{-W}, +for example @option{-Wimplicit} to request warnings on implicit +declarations. Each of these specific warning options also has a +negative form beginning @samp{-Wno-} to turn off warnings; +for example, @option{-Wno-implicit}. This manual lists only one of the +two forms, whichever is not the default. + +These options control the amount and kinds of warnings produced by GCC: + +@table @gcctabopt +@cindex syntax checking +@item -fsyntax-only +@opindex fsyntax-only +Check the code for syntax errors, but don't do anything beyond that. + +@item -pedantic +@opindex pedantic +Issue all the warnings demanded by strict ISO C and ISO C++; +reject all programs that use forbidden extensions, and some other +programs that do not follow ISO C and ISO C++. For ISO C, follows the +version of the ISO C standard specified by any @option{-std} option used. + +Valid ISO C and ISO C++ programs should compile properly with or without +this option (though a rare few will require @option{-ansi} or a +@option{-std} option specifying the required version of ISO C)@. However, +without this option, certain GNU extensions and traditional C and C++ +features are supported as well. With this option, they are rejected. + +@option{-pedantic} does not cause warning messages for use of the +alternate keywords whose names begin and end with @samp{__}. Pedantic +warnings are also disabled in the expression that follows +@code{__extension__}. However, only system header files should use +these escape routes; application programs should avoid them. +@xref{Alternate Keywords}. + +Some users try to use @option{-pedantic} to check programs for strict ISO +C conformance. They soon find that it does not do quite what they want: +it finds some non-ISO practices, but not all---only those for which +ISO C @emph{requires} a diagnostic, and some others for which +diagnostics have been added. + +A feature to report any failure to conform to ISO C might be useful in +some instances, but would require considerable additional work and would +be quite different from @option{-pedantic}. We don't have plans to +support such a feature in the near future. + +Where the standard specified with @option{-std} represents a GNU +extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a +corresponding @dfn{base standard}, the version of ISO C on which the GNU +extended dialect is based. Warnings from @option{-pedantic} are given +where they are required by the base standard. (It would not make sense +for such warnings to be given only for features not in the specified GNU +C dialect, since by definition the GNU dialects of C include all +features the compiler supports with the given option, and there would be +nothing to warn about.) + +@item -pedantic-errors +@opindex pedantic-errors +Like @option{-pedantic}, except that errors are produced rather than +warnings. + +@item -w +@opindex w +Inhibit all warning messages. + +@item -Wno-import +@opindex Wno-import +Inhibit warning messages about the use of @samp{#import}. + +@item -Wchar-subscripts +@opindex Wchar-subscripts +Warn if an array subscript has type @code{char}. This is a common cause +of error, as programmers often forget that this type is signed on some +machines. + +@item -Wcomment +@opindex Wcomment +Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} +comment, or whenever a Backslash-Newline appears in a @samp{//} comment. + +@item -Wformat +@opindex Wformat +Check calls to @code{printf} and @code{scanf}, etc., to make sure that +the arguments supplied have types appropriate to the format string +specified, and that the conversions specified in the format string make +sense. This includes standard functions, and others specified by format +attributes (@pxref{Function Attributes}), in the @code{printf}, +@code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, +not in the C standard) families. + +The formats are checked against the format features supported by GNU +libc version 2.2. These include all ISO C89 and C99 features, as well +as features from the Single Unix Specification and some BSD and GNU +extensions. Other library implementations may not support all these +features; GCC does not support warning about features that go beyond a +particular library's limitations. However, if @option{-pedantic} is used +with @option{-Wformat}, warnings will be given about format features not +in the selected standard version (but not for @code{strfmon} formats, +since those are not in any version of the C standard). @xref{C Dialect +Options,,Options Controlling C Dialect}. + +@option{-Wformat} is included in @option{-Wall}. For more control over some +aspects of format checking, the options @option{-Wno-format-y2k}, +@option{-Wno-format-extra-args}, @option{-Wformat-nonliteral}, +@option{-Wformat-security} and @option{-Wformat=2} are available, but are +not included in @option{-Wall}. + +@item -Wno-format-y2k +@opindex Wno-format-y2k +If @option{-Wformat} is specified, do not warn about @code{strftime} +formats which may yield only a two-digit year. + +@item -Wno-format-extra-args +@opindex Wno-format-extra-args +If @option{-Wformat} is specified, do not warn about excess arguments to a +@code{printf} or @code{scanf} format function. The C standard specifies +that such arguments are ignored. + +Where the unused arguments lie between used arguments that are +specified with @samp{$} operand number specifications, normally +warnings are still given, since the implementation could not know what +type to pass to @code{va_arg} to skip the unused arguments. However, +in the case of @code{scanf} formats, this option will suppress the +warning if the unused arguments are all pointers, since the Single +Unix Specification says that such unused arguments are allowed. + +@item -Wformat-nonliteral +@opindex Wformat-nonliteral +If @option{-Wformat} is specified, also warn if the format string is not a +string literal and so cannot be checked, unless the format function +takes its format arguments as a @code{va_list}. + +@item -Wformat-security +@opindex Wformat-security +If @option{-Wformat} is specified, also warn about uses of format +functions that represent possible security problems. At present, this +warns about calls to @code{printf} and @code{scanf} functions where the +format string is not a string literal and there are no format arguments, +as in @code{printf (foo);}. This may be a security hole if the format +string came from untrusted input and contains @samp{%n}. (This is +currently a subset of what @option{-Wformat-nonliteral} warns about, but +in future warnings may be added to @option{-Wformat-security} that are not +included in @option{-Wformat-nonliteral}.) + +@item -Wformat=2 +@opindex Wformat=2 +Enable @option{-Wformat} plus format checks not included in +@option{-Wformat}. Currently equivalent to @samp{-Wformat +-Wformat-nonliteral -Wformat-security}. + +@item -Wimplicit-int +@opindex Wimplicit-int +Warn when a declaration does not specify a type. + +@item -Wimplicit-function-declaration +@itemx -Werror-implicit-function-declaration +@opindex Wimplicit-function-declaration +@opindex Werror-implicit-function-declaration +Give a warning (or error) whenever a function is used before being +declared. + +@item -Wimplicit +@opindex Wimplicit +Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}. + +@item -Wmain +@opindex Wmain +Warn if the type of @samp{main} is suspicious. @samp{main} should be a +function with external linkage, returning int, taking either zero +arguments, two, or three arguments of appropriate types. + +@item -Wmissing-braces +@opindex Wmissing-braces +Warn if an aggregate or union initializer is not fully bracketed. In +the following example, the initializer for @samp{a} is not fully +bracketed, but that for @samp{b} is fully bracketed. + +@smallexample +int a[2][2] = @{ 0, 1, 2, 3 @}; +int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; +@end smallexample + +@item -Wparentheses +@opindex Wparentheses +Warn if parentheses are omitted in certain contexts, such +as when there is an assignment in a context where a truth value +is expected, or when operators are nested whose precedence people +often get confused about. + +Also warn about constructions where there may be confusion to which +@code{if} statement an @code{else} branch belongs. Here is an example of +such a case: + +@smallexample +@group +@{ + if (a) + if (b) + foo (); + else + bar (); +@} +@end group +@end smallexample + +In C, every @code{else} branch belongs to the innermost possible @code{if} +statement, which in this example is @code{if (b)}. This is often not +what the programmer expected, as illustrated in the above example by +indentation the programmer chose. When there is the potential for this +confusion, GCC will issue a warning when this flag is specified. +To eliminate the warning, add explicit braces around the innermost +@code{if} statement so there is no way the @code{else} could belong to +the enclosing @code{if}. The resulting code would look like this: + +@smallexample +@group +@{ + if (a) + @{ + if (b) + foo (); + else + bar (); + @} +@} +@end group +@end smallexample + +@item -Wsequence-point +@opindex Wsequence-point +Warn about code that may have undefined semantics because of violations +of sequence point rules in the C standard. + +The C standard defines the order in which expressions in a C program are +evaluated in terms of @dfn{sequence points}, which represent a partial +ordering between the execution of parts of the program: those executed +before the sequence point, and those executed after it. These occur +after the evaluation of a full expression (one which is not part of a +larger expression), after the evaluation of the first operand of a +@code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a +function is called (but after the evaluation of its arguments and the +expression denoting the called function), and in certain other places. +Other than as expressed by the sequence point rules, the order of +evaluation of subexpressions of an expression is not specified. All +these rules describe only a partial order rather than a total order, +since, for example, if two functions are called within one expression +with no sequence point between them, the order in which the functions +are called is not specified. However, the standards committee have +ruled that function calls do not overlap. + +It is not specified when between sequence points modifications to the +values of objects take effect. Programs whose behavior depends on this +have undefined behavior; the C standard specifies that ``Between the +previous and next sequence point an object shall have its stored value +modified at most once by the evaluation of an expression. Furthermore, +the prior value shall be read only to determine the value to be +stored.''. If a program breaks these rules, the results on any +particular implementation are entirely unpredictable. + +Examples of code with undefined behavior are @code{a = a++;}, @code{a[n] += b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not +diagnosed by this option, and it may give an occasional false positive +result, but in general it has been found fairly effective at detecting +this sort of problem in programs. + +The present implementation of this option only works for C programs. A +future implementation may also work for C++ programs. + +The C standard is worded confusingly, therefore there is some debate +over the precise meaning of the sequence point rules in subtle cases. +Links to discussions of the problem, including proposed formal +definitions, may be found on our readings page, at +@w{@uref{http://gcc.gnu.org/readings.html}}. + +@item -Wreturn-type +@opindex Wreturn-type +Warn whenever a function is defined with a return-type that defaults to +@code{int}. Also warn about any @code{return} statement with no +return-value in a function whose return-type is not @code{void}. + +For C++, a function without return type always produces a diagnostic +message, even when @option{-Wno-return-type} is specified. The only +exceptions are @samp{main} and functions defined in system headers. + +@item -Wswitch +@opindex Wswitch +Warn whenever a @code{switch} statement has an index of enumeral type +and lacks a @code{case} for one or more of the named codes of that +enumeration. (The presence of a @code{default} label prevents this +warning.) @code{case} labels outside the enumeration range also +provoke warnings when this option is used. + +@item -Wtrigraphs +@opindex Wtrigraphs +Warn if any trigraphs are encountered that might change the meaning of +the program (trigraphs within comments are not warned about). + +@item -Wunused-function +@opindex Wunused-function +Warn whenever a static function is declared but not defined or a +non\-inline static function is unused. + +@item -Wunused-label +@opindex Wunused-label +Warn whenever a label is declared but not used. + +To suppress this warning use the @samp{unused} attribute +(@pxref{Variable Attributes}). + +@item -Wunused-parameter +@opindex Wunused-parameter +Warn whenever a function parameter is unused aside from its declaration. + +To suppress this warning use the @samp{unused} attribute +(@pxref{Variable Attributes}). + +@item -Wunused-variable +@opindex Wunused-variable +Warn whenever a local variable or non-constant static variable is unused +aside from its declaration + +To suppress this warning use the @samp{unused} attribute +(@pxref{Variable Attributes}). + +@item -Wunused-value +@opindex Wunused-value +Warn whenever a statement computes a result that is explicitly not used. + +To suppress this warning cast the expression to @samp{void}. + +@item -Wunused +@opindex Wunused +All all the above @option{-Wunused} options combined. + +In order to get a warning about an unused function parameter, you must +either specify @samp{-W -Wunused} or separately specify +@option{-Wunused-parameter}. + +@item -Wuninitialized +@opindex Wuninitialized +Warn if an automatic variable is used without first being initialized or +if a variable may be clobbered by a @code{setjmp} call. + +These warnings are possible only in optimizing compilation, +because they require data flow information that is computed only +when optimizing. If you don't specify @option{-O}, you simply won't +get these warnings. + +These warnings occur only for variables that are candidates for +register allocation. Therefore, they do not occur for a variable that +is declared @code{volatile}, or whose address is taken, or whose size +is other than 1, 2, 4 or 8 bytes. Also, they do not occur for +structures, unions or arrays, even when they are in registers. + +Note that there may be no warning about a variable that is used only +to compute a value that itself is never used, because such +computations may be deleted by data flow analysis before the warnings +are printed. + +These warnings are made optional because GCC is not smart +enough to see all the reasons why the code might be correct +despite appearing to have an error. Here is one example of how +this can happen: + +@smallexample +@group +@{ + int x; + switch (y) + @{ + case 1: x = 1; + break; + case 2: x = 4; + break; + case 3: x = 5; + @} + foo (x); +@} +@end group +@end smallexample + +@noindent +If the value of @code{y} is always 1, 2 or 3, then @code{x} is +always initialized, but GCC doesn't know this. Here is +another common case: + +@smallexample +@{ + int save_y; + if (change_y) save_y = y, y = new_y; + @dots{} + if (change_y) y = save_y; +@} +@end smallexample + +@noindent +This has no bug because @code{save_y} is used only if it is set. + +@cindex @code{longjmp} warnings +This option also warns when a non-volatile automatic variable might be +changed by a call to @code{longjmp}. These warnings as well are possible +only in optimizing compilation. + +The compiler sees only the calls to @code{setjmp}. It cannot know +where @code{longjmp} will be called; in fact, a signal handler could +call it at any point in the code. As a result, you may get a warning +even when there is in fact no problem because @code{longjmp} cannot +in fact be called at the place which would cause a problem. + +Some spurious warnings can be avoided if you declare all the functions +you use that never return as @code{noreturn}. @xref{Function +Attributes}. + +@item -Wreorder @r{(C++ only)} +@opindex Wreorder +@cindex reordering, warning +@cindex warning for reordering of member initializers +Warn when the order of member initializers given in the code does not +match the order in which they must be executed. For instance: + +@item -Wunknown-pragmas +@opindex Wunknown-pragmas +@cindex warning for unknown pragmas +@cindex unknown pragmas, warning +@cindex pragmas, warning of unknown +Warn when a #pragma directive is encountered which is not understood by +GCC@. If this command line option is used, warnings will even be issued +for unknown pragmas in system header files. This is not the case if +the warnings were only enabled by the @option{-Wall} command line option. + +@item -Wall +@opindex Wall +All of the above @samp{-W} options combined. This enables all the +warnings about constructions that some users consider questionable, and +that are easy to avoid (or modify to prevent the warning), even in +conjunction with macros. + +@item -Wdiv-by-zero +@opindex Wno-div-by-zero +@opindex Wdiv-by-zero +Warn about compile-time integer division by zero. This is default. To +inhibit the warning messages, use @option{-Wno-div-by-zero}. Floating +point division by zero is not warned about, as it can be a legitimate +way of obtaining infinities and NaNs. + +@item -Wmultichar +@opindex Wno-multichar +@opindex Wmultichar +Warn if a multicharacter constant (@samp{'FOOF'}) is used. This is +default. To inhibit the warning messages, use @option{-Wno-multichar}. +Usually they indicate a typo in the user's code, as they have +implementation-defined values, and should not be used in portable code. + +@item -Wsystem-headers +@opindex Wsystem-headers +@cindex warnings from system headers +@cindex system headers, warnings from +Print warning messages for constructs found in system header files. +Warnings from system headers are normally suppressed, on the assumption +that they usually do not indicate real problems and would only make the +compiler output harder to read. Using this command line option tells +GCC to emit warnings from system headers as if they occurred in user +code. However, note that using @option{-Wall} in conjunction with this +option will @emph{not} warn about unknown pragmas in system +headers---for that, @option{-Wunknown-pragmas} must also be used. +@end table + +The following @option{-W@dots{}} options are not implied by @option{-Wall}. +Some of them warn about constructions that users generally do not +consider questionable, but which occasionally you might wish to check +for; others warn about constructions that are necessary or hard to avoid +in some cases, and there is no simple way to modify the code to suppress +the warning. + +@table @gcctabopt +@item -W +@opindex W +Print extra warning messages for these events: + +@itemize @bullet +@item +A function can return either with or without a value. (Falling +off the end of the function body is considered returning without +a value.) For example, this function would evoke such a +warning: + +@smallexample +@group +foo (a) +@{ + if (a > 0) + return a; +@} +@end group +@end smallexample + +@item +An expression-statement or the left-hand side of a comma expression +contains no side effects. +To suppress the warning, cast the unused expression to void. +For example, an expression such as @samp{x[i,j]} will cause a warning, +but @samp{x[(void)i,j]} will not. + +@item +An unsigned value is compared against zero with @samp{<} or @samp{<=}. + +@item +A comparison like @samp{x<=y<=z} appears; this is equivalent to +@samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from +that of ordinary mathematical notation. + +@item +Storage-class specifiers like @code{static} are not the first things in +a declaration. According to the C Standard, this usage is obsolescent. + +@item +The return type of a function has a type qualifier such as @code{const}. +Such a type qualifier has no effect, since the value returned by a +function is not an lvalue. (But don't warn about the GNU extension of +@code{volatile void} return types. That extension will be warned about +if @option{-pedantic} is specified.) + +@item +If @option{-Wall} or @option{-Wunused} is also specified, warn about unused +arguments. + +@item +A comparison between signed and unsigned values could produce an +incorrect result when the signed value is converted to unsigned. +(But don't warn if @option{-Wno-sign-compare} is also specified.) + +@item +An aggregate has a partly bracketed initializer. +For example, the following code would evoke such a warning, +because braces are missing around the initializer for @code{x.h}: + +@smallexample +struct s @{ int f, g; @}; +struct t @{ struct s h; int i; @}; +struct t x = @{ 1, 2, 3 @}; +@end smallexample + +@item +An aggregate has an initializer which does not initialize all members. +For example, the following code would cause such a warning, because +@code{x.h} would be implicitly initialized to zero: + +@smallexample +struct s @{ int f, g, h; @}; +struct s x = @{ 3, 4 @}; +@end smallexample +@end itemize + +@item -Wfloat-equal +@opindex Wfloat-equal +Warn if floating point values are used in equality comparisons. + +The idea behind this is that sometimes it is convenient (for the +programmer) to consider floating-point values as approximations to +infinitely precise real numbers. If you are doing this, then you need +to compute (by analysing the code, or in some other way) the maximum or +likely maximum error that the computation introduces, and allow for it +when performing comparisons (and when producing output, but that's a +different problem). In particular, instead of testing for equality, you +would check to see whether the two values have ranges that overlap; and +this is done with the relational operators, so equality comparisons are +probably mistaken. + +@item -Wtraditional @r{(C only)} +@opindex Wtraditional +Warn about certain constructs that behave differently in traditional and +ISO C@. Also warn about ISO C constructs that have no traditional C +equivalent, and/or problematic constructs which should be avoided. + +@itemize @bullet +@item +Macro parameters that appear within string literals in the macro body. +In traditional C macro replacement takes place within string literals, +but does not in ISO C@. + +@item +In traditional C, some preprocessor directives did not exist. +Traditional preprocessors would only consider a line to be a directive +if the @samp{#} appeared in column 1 on the line. Therefore +@option{-Wtraditional} warns about directives that traditional C +understands but would ignore because the @samp{#} does not appear as the +first character on the line. It also suggests you hide directives like +@samp{#pragma} not understood by traditional C by indenting them. Some +traditional implementations would not recognize @samp{#elif}, so it +suggests avoiding it altogether. + +@item +A function-like macro that appears without arguments. + +@item +The unary plus operator. + +@item +The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point +constant suffixes. (Traditional C does support the @samp{L} suffix on integer +constants.) Note, these suffixes appear in macros defined in the system +headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{}. +Use of these macros in user code might normally lead to spurious +warnings, however gcc's integrated preprocessor has enough context to +avoid warning in these cases. + +@item +A function declared external in one block and then used after the end of +the block. + +@item +A @code{switch} statement has an operand of type @code{long}. + +@item +A non-@code{static} function declaration follows a @code{static} one. +This construct is not accepted by some traditional C compilers. + +@item +The ISO type of an integer constant has a different width or +signedness from its traditional type. This warning is only issued if +the base of the constant is ten. I.e.@: hexadecimal or octal values, which +typically represent bit patterns, are not warned about. + +@item +Usage of ISO string concatenation is detected. + +@item +Initialization of automatic aggregates. + +@item +Identifier conflicts with labels. Traditional C lacks a separate +namespace for labels. + +@item +Initialization of unions. If the initializer is zero, the warning is +omitted. This is done under the assumption that the zero initializer in +user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing +initializer warnings and relies on default initialization to zero in the +traditional C case. + +@item +Conversions by prototypes between fixed/floating point values and vice +versa. The absence of these prototypes when compiling with traditional +C would cause serious problems. This is a subset of the possible +conversion warnings, for the full set use @option{-Wconversion}. +@end itemize + +@item -Wundef +@opindex Wundef +Warn if an undefined identifier is evaluated in an @samp{#if} directive. + +@item -Wshadow +@opindex Wshadow +Warn whenever a local variable shadows another local variable, parameter or +global variable or whenever a built-in function is shadowed. + +@item -Wlarger-than-@var{len} +@opindex Wlarger-than +Warn whenever an object of larger than @var{len} bytes is defined. + +@item -Wpointer-arith +@opindex Wpointer-arith +Warn about anything that depends on the ``size of'' a function type or +of @code{void}. GNU C assigns these types a size of 1, for +convenience in calculations with @code{void *} pointers and pointers +to functions. + +@item -Wbad-function-cast @r{(C only)} +@opindex Wbad-function-cast +Warn whenever a function call is cast to a non-matching type. +For example, warn if @code{int malloc()} is cast to @code{anything *}. + +@item -Wcast-qual +@opindex Wcast-qual +Warn whenever a pointer is cast so as to remove a type qualifier from +the target type. For example, warn if a @code{const char *} is cast +to an ordinary @code{char *}. + +@item -Wcast-align +@opindex Wcast-align +Warn whenever a pointer is cast such that the required alignment of the +target is increased. For example, warn if a @code{char *} is cast to +an @code{int *} on machines where integers can only be accessed at +two- or four-byte boundaries. + +@item -Wwrite-strings +@opindex Wwrite-strings +When compiling C, give string constants the type @code{const +char[@var{length}]} so that +copying the address of one into a non-@code{const} @code{char *} +pointer will get a warning; when compiling C++, warn about the +deprecated conversion from string constants to @code{char *}. +These warnings will help you find at +compile time code that can try to write into a string constant, but +only if you have been very careful about using @code{const} in +declarations and prototypes. Otherwise, it will just be a nuisance; +this is why we did not make @option{-Wall} request these warnings. + +@item -Wconversion +@opindex Wconversion +Warn if a prototype causes a type conversion that is different from what +would happen to the same argument in the absence of a prototype. This +includes conversions of fixed point to floating and vice versa, and +conversions changing the width or signedness of a fixed point argument +except when the same as the default promotion. + +Also, warn if a negative integer constant expression is implicitly +converted to an unsigned type. For example, warn about the assignment +@code{x = -1} if @code{x} is unsigned. But do not warn about explicit +casts like @code{(unsigned) -1}. + +@item -Wsign-compare +@opindex Wsign-compare +@cindex warning for comparison of signed and unsigned values +@cindex comparison of signed and unsigned values, warning +@cindex signed and unsigned values, comparison warning +Warn when a comparison between signed and unsigned values could produce +an incorrect result when the signed value is converted to unsigned. +This warning is also enabled by @option{-W}; to get the other warnings +of @option{-W} without this warning, use @samp{-W -Wno-sign-compare}. + +@item -Waggregate-return +@opindex Waggregate-return +Warn if any functions that return structures or unions are defined or +called. (In languages where you can return an array, this also elicits +a warning.) + +@item -Wstrict-prototypes @r{(C only)} +@opindex Wstrict-prototypes +Warn if a function is declared or defined without specifying the +argument types. (An old-style function definition is permitted without +a warning if preceded by a declaration which specifies the argument +types.) + +@item -Wmissing-prototypes @r{(C only)} +@opindex Wmissing-prototypes +Warn if a global function is defined without a previous prototype +declaration. This warning is issued even if the definition itself +provides a prototype. The aim is to detect global functions that fail +to be declared in header files. + +@item -Wmissing-declarations +@opindex Wmissing-declarations +Warn if a global function is defined without a previous declaration. +Do so even if the definition itself provides a prototype. +Use this option to detect global functions that are not declared in +header files. + +@item -Wmissing-noreturn +@opindex Wmissing-noreturn +Warn about functions which might be candidates for attribute @code{noreturn}. +Note these are only possible candidates, not absolute ones. Care should +be taken to manually verify functions actually do not ever return before +adding the @code{noreturn} attribute, otherwise subtle code generation +bugs could be introduced. You will not get a warning for @code{main} in +hosted C environments. + +@item -Wmissing-format-attribute +@opindex Wmissing-format-attribute +@opindex Wformat +If @option{-Wformat} is enabled, also warn about functions which might be +candidates for @code{format} attributes. Note these are only possible +candidates, not absolute ones. GCC will guess that @code{format} +attributes might be appropriate for any function that calls a function +like @code{vprintf} or @code{vscanf}, but this might not always be the +case, and some functions for which @code{format} attributes are +appropriate may not be detected. This option has no effect unless +@option{-Wformat} is enabled (possibly by @option{-Wall}). + +@item -Wno-deprecated-declarations +@opindex Wno-deprecated-declarations +Do not warn about uses of functions, variables, and types marked as +deprecated by using the @code{deprecated} attribute. +(@pxref{Function Attributes}, @pxref{Variable Attributes}, +@pxref{Type Attributes}.) + +@item -Wpacked +@opindex Wpacked +Warn if a structure is given the packed attribute, but the packed +attribute has no effect on the layout or size of the structure. +Such structures may be mis-aligned for little benefit. For +instance, in this code, the variable @code{f.x} in @code{struct bar} +will be misaligned even though @code{struct bar} does not itself +have the packed attribute: + +@smallexample +@group +struct foo @{ + int x; + char a, b, c, d; +@} __attribute__((packed)); +struct bar @{ + char z; + struct foo f; +@}; +@end group +@end smallexample + +@item -Wpadded +@opindex Wpadded +Warn if padding is included in a structure, either to align an element +of the structure or to align the whole structure. Sometimes when this +happens it is possible to rearrange the fields of the structure to +reduce the padding and so make the structure smaller. + +@item -Wredundant-decls +@opindex Wredundant-decls +Warn if anything is declared more than once in the same scope, even in +cases where multiple declaration is valid and changes nothing. + +@item -Wnested-externs @r{(C only)} +@opindex Wnested-externs +Warn if an @code{extern} declaration is encountered within a function. + +@item -Wunreachable-code +@opindex Wunreachable-code +Warn if the compiler detects that code will never be executed. + +This option is intended to warn when the compiler detects that at +least a whole line of source code will never be executed, because +some condition is never satisfied or because it is after a +procedure that never returns. + +It is possible for this option to produce a warning even though there +are circumstances under which part of the affected line can be executed, +so care should be taken when removing apparently-unreachable code. + +For instance, when a function is inlined, a warning may mean that the +line is unreachable in only one inlined copy of the function. + +This option is not made part of @option{-Wall} because in a debugging +version of a program there is often substantial code which checks +correct functioning of the program and is, hopefully, unreachable +because the program does work. Another common use of unreachable +code is to provide behavior which is selectable at compile-time. + +@item -Winline +@opindex Winline +Warn if a function can not be inlined and it was declared as inline. + +@item -Wlong-long +@opindex Wlong-long +@opindex Wno-long-long +Warn if @samp{long long} type is used. This is default. To inhibit +the warning messages, use @option{-Wno-long-long}. Flags +@option{-Wlong-long} and @option{-Wno-long-long} are taken into account +only when @option{-pedantic} flag is used. + +@item -Wdisabled-optimization +@opindex Wdisabled-optimization +Warn if a requested optimization pass is disabled. This warning does +not generally indicate that there is anything wrong with your code; it +merely indicates that GCC's optimizers were unable to handle the code +effectively. Often, the problem is that your code is too big or too +complex; GCC will refuse to optimize programs when the optimization +itself is likely to take inordinate amounts of time. + +@item -Werror +@opindex Werror +Make all warnings into errors. +@end table + +@node Debugging Options +@section Options for Debugging Your Program or GCC +@cindex options, debugging +@cindex debugging information options + +GCC has various special options that are used for debugging +either your program or GCC: + +@table @gcctabopt +@item -g +@opindex g +Produce debugging information in the operating system's native format +(stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging +information. + +On most systems that use stabs format, @option{-g} enables use of extra +debugging information that only GDB can use; this extra information +makes debugging work better in GDB but will probably make other debuggers +crash or +refuse to read the program. If you want to control for certain whether +to generate the extra information, use @option{-gstabs+}, @option{-gstabs}, +@option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1}, +or @option{-gvms} (see below). + +Unlike most other C compilers, GCC allows you to use @option{-g} with +@option{-O}. The shortcuts taken by optimized code may occasionally +produce surprising results: some variables you declared may not exist +at all; flow of control may briefly move where you did not expect it; +some statements may not be executed because they compute constant +results or their values were already at hand; some statements may +execute in different places because they were moved out of loops. + +Nevertheless it proves possible to debug optimized output. This makes +it reasonable to use the optimizer for programs that might have bugs. + +The following options are useful when GCC is generated with the +capability for more than one debugging format. + +@item -ggdb +@opindex ggdb +Produce debugging information for use by GDB@. This means to use the +most expressive format available (DWARF 2, stabs, or the native format +if neither of those are supported), including GDB extensions if at all +possible. + +@item -gstabs +@opindex gstabs +Produce debugging information in stabs format (if that is supported), +without GDB extensions. This is the format used by DBX on most BSD +systems. On MIPS, Alpha and System V Release 4 systems this option +produces stabs debugging output which is not understood by DBX or SDB@. +On System V Release 4 systems this option requires the GNU assembler. + +@item -gstabs+ +@opindex gstabs+ +Produce debugging information in stabs format (if that is supported), +using GNU extensions understood only by the GNU debugger (GDB)@. The +use of these extensions is likely to make other debuggers crash or +refuse to read the program. + +@item -gcoff +@opindex gcoff +Produce debugging information in COFF format (if that is supported). +This is the format used by SDB on most System V systems prior to +System V Release 4. + +@item -gxcoff +@opindex gxcoff +Produce debugging information in XCOFF format (if that is supported). +This is the format used by the DBX debugger on IBM RS/6000 systems. + +@item -gxcoff+ +@opindex gxcoff+ +Produce debugging information in XCOFF format (if that is supported), +using GNU extensions understood only by the GNU debugger (GDB)@. The +use of these extensions is likely to make other debuggers crash or +refuse to read the program, and may cause assemblers other than the GNU +assembler (GAS) to fail with an error. + +@item -gdwarf +@opindex gdwarf +Produce debugging information in DWARF version 1 format (if that is +supported). This is the format used by SDB on most System V Release 4 +systems. + +@item -gdwarf+ +@opindex gdwarf+ +Produce debugging information in DWARF version 1 format (if that is +supported), using GNU extensions understood only by the GNU debugger +(GDB)@. The use of these extensions is likely to make other debuggers +crash or refuse to read the program. + +@item -gdwarf-2 +@opindex gdwarf-2 +Produce debugging information in DWARF version 2 format (if that is +supported). This is the format used by DBX on IRIX 6. + +@item -gvms +@opindex gvms +Produce debugging information in VMS debug format (if that is +supported). This is the format used by DEBUG on VMS systems. + +@item -g@var{level} +@itemx -ggdb@var{level} +@itemx -gstabs@var{level} +@itemx -gcoff@var{level} +@itemx -gxcoff@var{level} +@itemx -gdwarf@var{level} +@itemx -gdwarf-2@var{level} +@itemx -gvms@var{level} +Request debugging information and also use @var{level} to specify how +much information. The default level is 2. + +Level 1 produces minimal information, enough for making backtraces in +parts of the program that you don't plan to debug. This includes +descriptions of functions and external variables, but no information +about local variables and no line numbers. + +Level 3 includes extra information, such as all the macro definitions +present in the program. Some debuggers support macro expansion when +you use @option{-g3}. + +@cindex @code{prof} +@item -p +@opindex p +Generate extra code to write profile information suitable for the +analysis program @code{prof}. You must use this option when compiling +the source files you want data about, and you must also use it when +linking. + +@cindex @code{gprof} +@item -pg +@opindex pg +Generate extra code to write profile information suitable for the +analysis program @code{gprof}. You must use this option when compiling +the source files you want data about, and you must also use it when +linking. + +@cindex @code{tcov} +@item -a +@opindex a +Generate extra code to write profile information for basic blocks, which will +record the number of times each basic block is executed, the basic block start +address, and the function name containing the basic block. If @option{-g} is +used, the line number and filename of the start of the basic block will also be +recorded. If not overridden by the machine description, the default action is +to append to the text file @file{bb.out}. + +This data could be analyzed by a program like @code{tcov}. Note, +however, that the format of the data is not what @code{tcov} expects. +Eventually GNU @code{gprof} should be extended to process this data. + +@item -Q +@opindex Q +Makes the compiler print out each function name as it is compiled, and +print some statistics about each pass when it finishes. + +@item -ftime-report +@opindex ftime-report +Makes the compiler print some statistics about the time consumed by each +pass when it finishes. + +@item -fmem-report +@opindex fmem-report +Makes the compiler print some statistics about permanent memory +allocation when it finishes. + +@item -fprofile-arcs +@opindex fprofile-arcs +Instrument @dfn{arcs} during compilation to generate coverage data +or for profile-directed block ordering. During execution the program +records how many times each branch is executed and how many times it is +taken. When the compiled program exits it saves this data to a file +called @file{@var{sourcename}.da} for each source file. + +For profile-directed block ordering, compile the program with +@option{-fprofile-arcs} plus optimization and code generation options, +generate the arc profile information by running the program on a +selected workload, and then compile the program again with the same +optimization and code generation options plus +@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that +Control Optimization}). + +The other use of @option{-fprofile-arcs} is for use with @code{gcov}, +when it is used with the @option{-ftest-coverage} option. GCC +supports two methods of determining code coverage: the options that +support @code{gcov}, and options @option{-a} and @option{-ax}, which +write information to text files. The options that support @code{gcov} +do not need to instrument every arc in the program, so a program compiled +with them runs faster than a program compiled with @option{-a}, which +adds instrumentation code to every basic block in the program. The +tradeoff: since @code{gcov} does not have execution counts for all +branches, it must start with the execution counts for the instrumented +branches, and then iterate over the program flow graph until the entire +graph has been solved. Hence, @code{gcov} runs a little more slowly than +a program which uses information from @option{-a} and @option{-ax}. + +With @option{-fprofile-arcs}, for each function of your program GCC +creates a program flow graph, then finds a spanning tree for the graph. +Only arcs that are not on the spanning tree have to be instrumented: the +compiler adds code to count the number of times that these arcs are +executed. When an arc is the only exit or only entrance to a block, the +instrumentation code can be added to the block; otherwise, a new basic +block must be created to hold the instrumentation code. + +This option makes it possible to estimate branch probabilities and to +calculate basic block execution counts. In general, basic block +execution counts as provided by @option{-a} do not give enough +information to estimate all branch probabilities. + +@need 2000 +@item -ftest-coverage +@opindex ftest-coverage +Create data files for the @code{gcov} code-coverage utility +(@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}). +The data file names begin with the name of your source file: + +@table @gcctabopt +@item @var{sourcename}.bb +A mapping from basic blocks to line numbers, which @code{gcov} uses to +associate basic block execution counts with line numbers. + +@item @var{sourcename}.bbg +A list of all arcs in the program flow graph. This allows @code{gcov} +to reconstruct the program flow graph, so that it can compute all basic +block and arc execution counts from the information in the +@code{@var{sourcename}.da} file. +@end table + +Use @option{-ftest-coverage} with @option{-fprofile-arcs}; the latter +option adds instrumentation to the program, which then writes +execution counts to another data file: + +@table @gcctabopt +@item @var{sourcename}.da +Runtime arc execution counts, used in conjunction with the arc +information in the file @code{@var{sourcename}.bbg}. +@end table + +Coverage data will map better to the source files if +@option{-ftest-coverage} is used without optimization. + +@item -d@var{letters} +@opindex d +Says to make debugging dumps during compilation at times specified by +@var{letters}. This is used for debugging the compiler. The file names +for most of the dumps are made by appending a pass number and a word to +the source file name (e.g. @file{foo.c.00.rtl} or @file{foo.c.01.sibling}). +Here are the possible letters for use in @var{letters}, and their meanings: + +@table @samp +@item A +@opindex dA +Annotate the assembler output with miscellaneous debugging information. +@item b +@opindex db +Dump after computing branch probabilities, to @file{@var{file}.14.bp}. +@item B +@opindex dB +Dump after block reordering, to @file{@var{file}.29.bbro}. +@item c +@opindex dc +Dump after instruction combination, to the file @file{@var{file}.16.combine}. +@item C +@opindex dC +Dump after the first if conversion, to the file @file{@var{file}.17.ce}. +@item d +@opindex dd +Dump after delayed branch scheduling, to @file{@var{file}.31.dbr}. +@item D +@opindex dD +Dump all macro definitions, at the end of preprocessing, in addition to +normal output. +@item e +@opindex de +Dump after SSA optimizations, to @file{@var{file}.04.ssa} and +@file{@var{file}.07.ussa}. +@item E +@opindex dE +Dump after the second if conversion, to @file{@var{file}.26.ce2}. +@item f +@opindex df +Dump after life analysis, to @file{@var{file}.15.life}. +@item F +@opindex dF +Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.09.addressof}. +@item g +@opindex dg +Dump after global register allocation, to @file{@var{file}.21.greg}. +@item h +@opindex dh +Dump after finalization of EH handling code, to @file{@var{file}.02.eh}. +@item k +@opindex dk +Dump after reg-to-stack conversion, to @file{@var{file}.28.stack}. +@item o +@opindex do +Dump after post-reload optimizations, to @file{@var{file}.22.postreload}. +@item G +@opindex dG +Dump after GCSE, to @file{@var{file}.10.gcse}. +@item i +@opindex di +Dump after sibling call optimizations, to @file{@var{file}.01.sibling}. +@item j +@opindex dj +Dump after the first jump optimization, to @file{@var{file}.03.jump}. +@item k +@opindex dk +Dump after conversion from registers to stack, to @file{@var{file}.32.stack}. +@item l +@opindex dl +Dump after local register allocation, to @file{@var{file}.20.lreg}. +@item L +@opindex dL +Dump after loop optimization, to @file{@var{file}.11.loop}. +@item M +@opindex dM +Dump after performing the machine dependent reorganisation pass, to +@file{@var{file}.30.mach}. +@item n +@opindex dn +Dump after register renumbering, to @file{@var{file}.25.rnreg}. +@item N +@opindex dN +Dump after the register move pass, to @file{@var{file}.18.regmove}. +@item r +@opindex dr +Dump after RTL generation, to @file{@var{file}.00.rtl}. +@item R +@opindex dR +Dump after the second scheduling pass, to @file{@var{file}.27.sched2}. +@item s +@opindex ds +Dump after CSE (including the jump optimization that sometimes follows +CSE), to @file{@var{file}.08.cse}. +@item S +@opindex dS +Dump after the first scheduling pass, to @file{@var{file}.19.sched}. +@item t +@opindex dt +Dump after the second CSE pass (including the jump optimization that +sometimes follows CSE), to @file{@var{file}.12.cse2}. +@item w +@opindex dw +Dump after the second flow pass, to @file{@var{file}.23.flow2}. +@item X +@opindex dX +Dump after SSA dead code elimination, to @file{@var{file}.06.ssadce}. +@item z +@opindex dz +Dump after the peephole pass, to @file{@var{file}.24.peephole2}. +@item a +@opindex da +Produce all the dumps listed above. +@item m +@opindex dm +Print statistics on memory usage, at the end of the run, to +standard error. +@item p +@opindex dp +Annotate the assembler output with a comment indicating which +pattern and alternative was used. The length of each instruction is +also printed. +@item P +@opindex dP +Dump the RTL in the assembler output as a comment before each instruction. +Also turns on @option{-dp} annotation. +@item v +@opindex dv +For each of the other indicated dump files (except for +@file{@var{file}.00.rtl}), dump a representation of the control flow graph +suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}. +@item x +@opindex dx +Just generate RTL for a function instead of compiling it. Usually used +with @samp{r}. +@item y +@opindex dy +Dump debugging information during parsing, to standard error. +@end table + +@item -fdump-unnumbered +@opindex fdump-unnumbered +When doing debugging dumps (see @option{-d} option above), suppress instruction +numbers and line number note output. This makes it more feasible to +use diff on debugging dumps for compiler invocations with different +options, in particular with and without @option{-g}. + +@item -fdump-translation-unit @r{(C and C++ only)} +@itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)} +@opindex fdump-translation-unit +Dump a representation of the tree structure for the entire translation +unit to a file. The file name is made by appending @file{.tu} to the +source file name. If the @samp{-@var{options}} form is used, @var{options} +controls the details of the dump as described for the +@option{-fdump-tree} options. + +@item -fdump-class-hierarchy @r{(C++ only)} +@itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)} +@opindex fdump-class-hierarchy +Dump a representation of each class's hierarchy and virtual function +table layout to a file. The file name is made by appending @file{.class} +to the source file name. If the @samp{-@var{options}} form is used, +@var{options} controls the details of the dump as described for the +@option{-fdump-tree} options. + +@item -fdump-tree-@var{switch} @r{(C++ only)} +@itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)} +@opindex fdump-tree +Control the dumping at various stages of processing the intermediate +language tree to a file. The file name is generated by appending a switch +specific suffix to the source file name. If the @samp{-@var{options}} +form is used, @var{options} is a list of @samp{-} separated options that +control the details of the dump. Not all options are applicable to all +dumps, those which are not meaningful will be ignored. The following +options are available + +@table @samp +@item address +Print the address of each node. Usually this is not meaningful as it +changes according to the environment and source file. Its primary use +is for tying up a dump file with a debug environment. +@item slim +Inhibit dumping of members of a scope or body of a function merely +because that scope has been reached. Only dump such items when they +are directly reachable by some other path. +@item all +Turn on all options. +@end table + +The following tree dumps are possible: +@table @samp +@item original +Dump before any tree based optimization, to @file{@var{file}.original}. +@item optimized +Dump after all tree based optimization, to @file{@var{file}.optimized}. +@item inlined +Dump after function inlining, to @file{@var{file}.inlined}. +@end table + +@item -fpretend-float +@opindex fpretend-float +When running a cross-compiler, pretend that the target machine uses the +same floating point format as the host machine. This causes incorrect +output of the actual floating constants, but the actual instruction +sequence will probably be the same as GCC would make when running on +the target machine. + +@item -save-temps +@opindex save-temps +Store the usual ``temporary'' intermediate files permanently; place them +in the current directory and name them based on the source file. Thus, +compiling @file{foo.c} with @samp{-c -save-temps} would produce files +@file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a +preprocessed @file{foo.i} output file even though the compiler now +normally uses an integrated preprocessor. + +@item -time +@opindex time +Report the CPU time taken by each subprocess in the compilation +sequence. For C source files, this is the compiler proper and assembler +(plus the linker if linking is done). The output looks like this: + +@smallexample +# cc1 0.12 0.01 +# as 0.00 0.01 +@end smallexample + +The first number on each line is the ``user time,'' that is time spent +executing the program itself. The second number is ``system time,'' +time spent executing operating system routines on behalf of the program. +Both numbers are in seconds. + +@item -print-file-name=@var{library} +@opindex print-file-name +Print the full absolute name of the library file @var{library} that +would be used when linking---and don't do anything else. With this +option, GCC does not compile or link anything; it just prints the +file name. + +@item -print-multi-directory +@opindex print-multi-directory +Print the directory name corresponding to the multilib selected by any +other switches present in the command line. This directory is supposed +to exist in @env{GCC_EXEC_PREFIX}. + +@item -print-multi-lib +@opindex print-multi-lib +Print the mapping from multilib directory names to compiler switches +that enable them. The directory name is separated from the switches by +@samp{;}, and each switch starts with an @samp{@@} instead of the +@samp{-}, without spaces between multiple switches. This is supposed to +ease shell-processing. + +@item -print-prog-name=@var{program} +@opindex print-prog-name +Like @option{-print-file-name}, but searches for a program such as @samp{cpp}. + +@item -print-libgcc-file-name +@opindex print-libgcc-file-name +Same as @option{-print-file-name=libgcc.a}. + +This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs} +but you do want to link with @file{libgcc.a}. You can do + +@example +gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` +@end example + +@item -print-search-dirs +@opindex print-search-dirs +Print the name of the configured installation directory and a list of +program and library directories gcc will search---and don't do anything else. + +This is useful when gcc prints the error message +@samp{installation problem, cannot exec cpp0: No such file or directory}. +To resolve this you either need to put @file{cpp0} and the other compiler +components where gcc expects to find them, or you can set the environment +variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. +Don't forget the trailing '/'. +@xref{Environment Variables}. + +@item -dumpmachine +@opindex dumpmachine +Print the compiler's target machine (for example, +@samp{i686-pc-linux-gnu})---and don't do anything else. + +@item -dumpversion +@opindex dumpversion +Print the compiler version (for example, @samp{3.0})---and don't do +anything else. + +@item -dumpspecs +@opindex dumpspecs +Print the compiler's built-in specs---and don't do anything else. (This +is used when GCC itself is being built.) @xref{Spec Files}. +@end table + +@node Optimize Options +@section Options That Control Optimization +@cindex optimize options +@cindex options, optimization + +These options control various sorts of optimizations: + +@table @gcctabopt +@item -O +@itemx -O1 +@opindex O +@opindex O1 +Optimize. Optimizing compilation takes somewhat more time, and a lot +more memory for a large function. + +Without @option{-O}, the compiler's goal is to reduce the cost of +compilation and to make debugging produce the expected results. +Statements are independent: if you stop the program with a breakpoint +between statements, you can then assign a new value to any variable or +change the program counter to any other statement in the function and +get exactly the results you would expect from the source code. + +With @option{-O}, the compiler tries to reduce code size and execution +time, without performing any optimizations that take a great deal of +compilation time. + +@item -O2 +@opindex O2 +Optimize even more. GCC performs nearly all supported optimizations +that do not involve a space-speed tradeoff. The compiler does not +perform loop unrolling or function inlining when you specify @option{-O2}. +As compared to @option{-O}, this option increases both compilation time +and the performance of the generated code. + +@option{-O2} turns on all optional optimizations except for loop unrolling, +function inlining, and register renaming. It also turns on the +@option{-fforce-mem} option on all machines and frame pointer elimination +on machines where doing so does not interfere with debugging. + +Please note the warning under @option{-fgcse} about +invoking @option{-O2} on programs that use computed gotos. + +@item -O3 +@opindex O3 +Optimize yet more. @option{-O3} turns on all optimizations specified by +@option{-O2} and also turns on the @option{-finline-functions} and +@option{-frename-registers} options. + +@item -O0 +@opindex O0 +Do not optimize. + +@item -Os +@opindex Os +Optimize for size. @option{-Os} enables all @option{-O2} optimizations that +do not typically increase code size. It also performs further +optimizations designed to reduce code size. + +If you use multiple @option{-O} options, with or without level numbers, +the last such option is the one that is effective. +@end table + +Options of the form @option{-f@var{flag}} specify machine-independent +flags. Most flags have both positive and negative forms; the negative +form of @option{-ffoo} would be @option{-fno-foo}. In the table below, +only one of the forms is listed---the one which is not the default. +You can figure out the other form by either removing @samp{no-} or +adding it. + +@table @gcctabopt +@item -ffloat-store +@opindex ffloat-store +Do not store floating point variables in registers, and inhibit other +options that might change whether a floating point value is taken from a +register or memory. + +@cindex floating point precision +This option prevents undesirable excess precision on machines such as +the 68000 where the floating registers (of the 68881) keep more +precision than a @code{double} is supposed to have. Similarly for the +x86 architecture. For most programs, the excess precision does only +good, but a few programs rely on the precise definition of IEEE floating +point. Use @option{-ffloat-store} for such programs, after modifying +them to store all pertinent intermediate computations into variables. + +@item -fno-default-inline +@opindex fno-default-inline +Do not make member functions inline by default merely because they are +defined inside the class scope (C++ only). Otherwise, when you specify +@w{@option{-O}}, member functions defined inside class scope are compiled +inline by default; i.e., you don't need to add @samp{inline} in front of +the member function name. + +@item -fno-defer-pop +@opindex fno-defer-pop +Always pop the arguments to each function call as soon as that function +returns. For machines which must pop arguments after a function call, +the compiler normally lets arguments accumulate on the stack for several +function calls and pops them all at once. + +@item -fforce-mem +@opindex fforce-mem +Force memory operands to be copied into registers before doing +arithmetic on them. This produces better code by making all memory +references potential common subexpressions. When they are not common +subexpressions, instruction combination should eliminate the separate +register-load. The @option{-O2} option turns on this option. + +@item -fforce-addr +@opindex fforce-addr +Force memory address constants to be copied into registers before +doing arithmetic on them. This may produce better code just as +@option{-fforce-mem} may. + +@item -fomit-frame-pointer +@opindex fomit-frame-pointer +Don't keep the frame pointer in a register for functions that +don't need one. This avoids the instructions to save, set up and +restore frame pointers; it also makes an extra register available +in many functions. @strong{It also makes debugging impossible on +some machines.} + +On some machines, such as the VAX, this flag has no effect, because +the standard calling sequence automatically handles the frame pointer +and nothing is saved by pretending it doesn't exist. The +machine-description macro @code{FRAME_POINTER_REQUIRED} controls +whether a target machine supports this flag. @xref{Registers,,Register +Usage, gccint, GNU Compiler Collection (GCC) Internals}. + +@item -foptimize-sibling-calls +@opindex foptimize-sibling-calls +Optimize sibling and tail recursive calls. + +@item -ftrapv +@opindex ftrapv +This option generates traps for signed overflow on addition, subtraction, +multiplication operations. + +@item -fno-inline +@opindex fno-inline +Don't pay attention to the @code{inline} keyword. Normally this option +is used to keep the compiler from expanding any functions inline. +Note that if you are not optimizing, no functions can be expanded inline. + +@item -finline-functions +@opindex finline-functions +Integrate all simple functions into their callers. The compiler +heuristically decides which functions are simple enough to be worth +integrating in this way. + +If all calls to a given function are integrated, and the function is +declared @code{static}, then the function is normally not output as +assembler code in its own right. + +@item -finline-limit=@var{n} +@opindex finline-limit +By default, gcc limits the size of functions that can be inlined. This flag +allows the control of this limit for functions that are explicitly marked as +inline (ie marked with the inline keyword or defined within the class +definition in c++). @var{n} is the size of functions that can be inlined in +number of pseudo instructions (not counting parameter handling). The default +value of @var{n} is 600. +Increasing this value can result in more inlined code at +the cost of compilation time and memory consumption. Decreasing usually makes +the compilation faster and less code will be inlined (which presumably +means slower programs). This option is particularly useful for programs that +use inlining heavily such as those based on recursive templates with C++. + +@emph{Note:} pseudo instruction represents, in this particular context, an +abstract measurement of function's size. In no way, it represents a count +of assembly instructions and as such its exact meaning might change from one +release to an another. + +@item -fkeep-inline-functions +@opindex fkeep-inline-functions +Even if all calls to a given function are integrated, and the function +is declared @code{static}, nevertheless output a separate run-time +callable version of the function. This switch does not affect +@code{extern inline} functions. + +@item -fkeep-static-consts +@opindex fkeep-static-consts +Emit variables declared @code{static const} when optimization isn't turned +on, even if the variables aren't referenced. + +GCC enables this option by default. If you want to force the compiler to +check if the variable was referenced, regardless of whether or not +optimization is turned on, use the @option{-fno-keep-static-consts} option. + +@item -fmerge-constants +Attempt to merge identical constants (string constants and floating point +constants) accross compilation units. + +This option is default for optimized compilation if assembler and linker +support it. Use @option{-fno-merge-constants} to inhibit this behavior. + +@item -fmerge-all-constants +Attempt to merge identical constants and identical variables. + +This option implies @option{-fmerge-constants}. In addition to +@option{-fmerge-constants} this considers e.g. even constant initialized +arrays or initialized constant variables with integral or floating point +types. Languages like C or C++ require each non-automatic variable to +have distinct location, so using this option will result in non-conforming +behavior. + +@item -fno-function-cse +@opindex fno-function-cse +Do not put function addresses in registers; make each instruction that +calls a constant function contain the function's address explicitly. + +This option results in less efficient code, but some strange hacks +that alter the assembler output may be confused by the optimizations +performed when this option is not used. + +@item -ffast-math +@opindex ffast-math +Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, and @* +@option{-fno-trapping-math}. + +This option causes the preprocessor macro @code{__FAST_MATH__} to be defined. + +This option should never be turned on by any @option{-O} option since +it can result in incorrect output for programs which depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. + +@item -fno-math-errno +@opindex fno-math-errno +Do not set ERRNO after calling math functions that are executed +with a single instruction, e.g., sqrt. A program that relies on +IEEE exceptions for math error handling may want to use this flag +for speed while maintaining IEEE arithmetic compatibility. + +This option should never be turned on by any @option{-O} option since +it can result in incorrect output for programs which depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. + +The default is @option{-fmath-errno}. + +@item -funsafe-math-optimizations +@opindex funsafe-math-optimizations +Allow optimizations for floating-point arithmetic that (a) assume +that arguments and results are valid and (b) may violate IEEE or +ANSI standards. When used at link-time, it may include libraries +or startup files that change the default FPU control word or other +similar optimizations. + +This option should never be turned on by any @option{-O} option since +it can result in incorrect output for programs which depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. + +The default is @option{-fno-unsafe-math-optimizations}. + +@item -fno-trapping-math +@opindex fno-trapping-math +Compile code assuming that floating-point operations cannot generate +user-visible traps. Setting this option may allow faster code +if one relies on ``non-stop'' IEEE arithmetic, for example. + +This option should never be turned on by any @option{-O} option since +it can result in incorrect output for programs which depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. + +The default is @option{-ftrapping-math}. +@end table + +The following options control specific optimizations. The @option{-O2} +option turns on all of these optimizations except @option{-funroll-loops} +and @option{-funroll-all-loops}. On most machines, the @option{-O} option +turns on the @option{-fthread-jumps} and @option{-fdelayed-branch} options, +but specific machines may handle it differently. + +You can use the following flags in the rare cases when ``fine-tuning'' +of optimizations to be performed is desired. + +Not all of the optimizations performed by GCC have @option{-f} options +to control them. + +@table @gcctabopt +@item -fstrength-reduce +@opindex fstrength-reduce +Perform the optimizations of loop strength reduction and +elimination of iteration variables. + +@item -fthread-jumps +@opindex fthread-jumps +Perform optimizations where we check to see if a jump branches to a +location where another comparison subsumed by the first is found. If +so, the first branch is redirected to either the destination of the +second branch or a point immediately following it, depending on whether +the condition is known to be true or false. + +@item -fcse-follow-jumps +@opindex fcse-follow-jumps +In common subexpression elimination, scan through jump instructions +when the target of the jump is not reached by any other path. For +example, when CSE encounters an @code{if} statement with an +@code{else} clause, CSE will follow the jump when the condition +tested is false. + +@item -fcse-skip-blocks +@opindex fcse-skip-blocks +This is similar to @option{-fcse-follow-jumps}, but causes CSE to +follow jumps which conditionally skip over blocks. When CSE +encounters a simple @code{if} statement with no else clause, +@option{-fcse-skip-blocks} causes CSE to follow the jump around the +body of the @code{if}. + +@item -frerun-cse-after-loop +@opindex frerun-cse-after-loop +Re-run common subexpression elimination after loop optimizations has been +performed. + +@item -frerun-loop-opt +@opindex frerun-loop-opt +Run the loop optimizer twice. + +@item -fgcse +@opindex fgcse +Perform a global common subexpression elimination pass. +This pass also performs global constant and copy propagation. + +@emph{Note:} When compiling a program using computed gotos, a GCC +extension, you may get better runtime performance if you disable +the global common subexpression elmination pass by adding +@option{-fno-gcse} to the command line. + +@item -fgcse-lm +@opindex fgcse-lm +When @option{-fgcse-lm} is enabled, global common subexpression elimination will +attempt to move loads which are only killed by stores into themselves. This +allows a loop containing a load/store sequence to be changed to a load outside +the loop, and a copy/store within the loop. + +@item -fgcse-sm +@opindex fgcse-sm +When @option{-fgcse-sm} is enabled, A store motion pass is run after global common +subexpression elimination. This pass will attempt to move stores out of loops. +When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence +can be changed to a load before the loop and a store after the loop. + +@item -fdelete-null-pointer-checks +@opindex fdelete-null-pointer-checks +Use global dataflow analysis to identify and eliminate useless checks +for null pointers. The compiler assumes that dereferencing a null +pointer would have halted the program. If a pointer is checked after +it has already been dereferenced, it cannot be null. + +In some environments, this assumption is not true, and programs can +safely dereference null pointers. Use +@option{-fno-delete-null-pointer-checks} to disable this optimization +for programs which depend on that behavior. + +@item -fexpensive-optimizations +@opindex fexpensive-optimizations +Perform a number of minor optimizations that are relatively expensive. + +@item -foptimize-register-move +@itemx -fregmove +@opindex foptimize-register-move +@opindex fregmove +Attempt to reassign register numbers in move instructions and as +operands of other simple instructions in order to maximize the amount of +register tying. This is especially helpful on machines with two-operand +instructions. GCC enables this optimization by default with @option{-O2} +or higher. + +Note @option{-fregmove} and @option{-foptimize-register-move} are the same +optimization. + +@item -fdelayed-branch +@opindex fdelayed-branch +If supported for the target machine, attempt to reorder instructions +to exploit instruction slots available after delayed branch +instructions. + +@item -fschedule-insns +@opindex fschedule-insns +If supported for the target machine, attempt to reorder instructions to +eliminate execution stalls due to required data being unavailable. This +helps machines that have slow floating point or memory load instructions +by allowing other instructions to be issued until the result of the load +or floating point instruction is required. + +@item -fschedule-insns2 +@opindex fschedule-insns2 +Similar to @option{-fschedule-insns}, but requests an additional pass of +instruction scheduling after register allocation has been done. This is +especially useful on machines with a relatively small number of +registers and where memory load instructions take more than one cycle. + +@item -ffunction-sections +@itemx -fdata-sections +@opindex ffunction-sections +@opindex fdata-sections +Place each function or data item into its own section in the output +file if the target supports arbitrary sections. The name of the +function or the name of the data item determines the section's name +in the output file. + +Use these options on systems where the linker can perform optimizations +to improve locality of reference in the instruction space. HPPA +processors running HP-UX and Sparc processors running Solaris 2 have +linkers with such optimizations. Other systems using the ELF object format +as well as AIX may have these optimizations in the future. + +Only use these options when there are significant benefits from doing +so. When you specify these options, the assembler and linker will +create larger object and executable files and will also be slower. +You will not be able to use @code{gprof} on all systems if you +specify this option and you may have problems with debugging if +you specify both this option and @option{-g}. + +@item -fcaller-saves +@opindex fcaller-saves +Enable values to be allocated in registers that will be clobbered by +function calls, by emitting extra instructions to save and restore the +registers around such calls. Such allocation is done only when it +seems to result in better code than would otherwise be produced. + +This option is always enabled by default on certain machines, usually +those which have no call-preserved registers to use instead. + +For all machines, optimization level 2 and higher enables this flag by +default. + +@item -funroll-loops +@opindex funroll-loops +Unroll loops whose number of iterations can be determined at compile +time or upon entry to the loop. @option{-funroll-loops} implies both +@option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This +option makes code larger, and may or may not make it run faster. + +@item -funroll-all-loops +@opindex funroll-all-loops +Unroll all loops, even if their number of iterations is uncertain when +the loop is entered. This usually makes programs run more slowly. +@option{-funroll-all-loops} implies the same options as +@option{-funroll-loops}, + +@item -fprefetch-loop-arrays +@opindex fprefetch-loop-arrays +If supported by the target machine, generate instructions to prefetch +memory to improve the performance of loops that access large arrays. + +@item -fmove-all-movables +@opindex fmove-all-movables +Forces all invariant computations in loops to be moved +outside the loop. + +@item -freduce-all-givs +@opindex freduce-all-givs +Forces all general-induction variables in loops to be +strength-reduced. + +@emph{Note:} When compiling programs written in Fortran, +@option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled +by default when you use the optimizer. + +These options may generate better or worse code; results are highly +dependent on the structure of loops within the source code. + +These two options are intended to be removed someday, once +they have helped determine the efficacy of various +approaches to improving loop optimizations. + +Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}}) +know how use of these options affects +the performance of your production code. +We're very interested in code that runs @emph{slower} +when these options are @emph{enabled}. + +@item -fno-peephole +@itemx -fno-peephole2 +@opindex fno-peephole +@opindex fno-peephole2 +Disable any machine-specific peephole optimizations. The difference +between @option{-fno-peephole} and @option{-fno-peephole2} is in how they +are implemented in the compiler; some targets use one, some use the +other, a few use both. + +@item -fbranch-probabilities +@opindex fbranch-probabilities +After running a program compiled with @option{-fprofile-arcs} +(@pxref{Debugging Options,, Options for Debugging Your Program or +@command{gcc}}), you can compile it a second time using +@option{-fbranch-probabilities}, to improve optimizations based on +the number of times each branch was taken. When the program +compiled with @option{-fprofile-arcs} exits it saves arc execution +counts to a file called @file{@var{sourcename}.da} for each source +file The information in this data file is very dependent on the +structure of the generated code, so you must use the same source code +and the same optimization options for both compilations. + +With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT} +note on the first instruction of each basic block, and a +@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. +These can be used to improve optimization. Currently, they are only +used in one place: in @file{reorg.c}, instead of guessing which path a +branch is mostly to take, the @samp{REG_BR_PROB} values are used to +exactly determine which path is taken more often. + +@item -fno-guess-branch-probability +@opindex fno-guess-branch-probability +Do not guess branch probabilities using a randomized model. + +Sometimes gcc will opt to use a randomized model to guess branch +probabilities, when none are available from either profiling feedback +(@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that +different runs of the compiler on the same program may produce different +object code. + +In a hard real-time system, people don't want different runs of the +compiler to produce code that has different behavior; minimizing +non-determinism is of paramount import. This switch allows users to +reduce non-determinism, possibly at the expense of inferior +optimization. + +@item -fstrict-aliasing +@opindex fstrict-aliasing +Allows the compiler to assume the strictest aliasing rules applicable to +the language being compiled. For C (and C++), this activates +optimizations based on the type of expressions. In particular, an +object of one type is assumed never to reside at the same address as an +object of a different type, unless the types are almost the same. For +example, an @code{unsigned int} can alias an @code{int}, but not a +@code{void*} or a @code{double}. A character type may alias any other +type. + +Pay special attention to code like this: +@example +union a_union @{ + int i; + double d; +@}; + +int f() @{ + a_union t; + t.d = 3.0; + return t.i; +@} +@end example +The practice of reading from a different union member than the one most +recently written to (called ``type-punning'') is common. Even with +@option{-fstrict-aliasing}, type-punning is allowed, provided the memory +is accessed through the union type. So, the code above will work as +expected. However, this code might not: +@example +int f() @{ + a_union t; + int* ip; + t.d = 3.0; + ip = &t.i; + return *ip; +@} +@end example + +Every language that wishes to perform language-specific alias analysis +should define a function that computes, given an @code{tree} +node, an alias set for the node. Nodes in different alias sets are not +allowed to alias. For an example, see the C front-end function +@code{c_get_alias_set}. + +@item -falign-functions +@itemx -falign-functions=@var{n} +@opindex falign-functions +Align the start of functions to the next power-of-two greater than +@var{n}, skipping up to @var{n} bytes. For instance, +@option{-falign-functions=32} aligns functions to the next 32-byte +boundary, but @option{-falign-functions=24} would align to the next +32-byte boundary only if this can be done by skipping 23 bytes or less. + +@option{-fno-align-functions} and @option{-falign-functions=1} are +equivalent and mean that functions will not be aligned. + +Some assemblers only support this flag when @var{n} is a power of two; +in that case, it is rounded up. + +If @var{n} is not specified, use a machine-dependent default. + +@item -falign-labels +@itemx -falign-labels=@var{n} +@opindex falign-labels +Align all branch targets to a power-of-two boundary, skipping up to +@var{n} bytes like @option{-falign-functions}. This option can easily +make code slower, because it must insert dummy operations for when the +branch target is reached in the usual flow of the code. + +If @option{-falign-loops} or @option{-falign-jumps} are applicable and +are greater than this value, then their values are used instead. + +If @var{n} is not specified, use a machine-dependent default which is +very likely to be @samp{1}, meaning no alignment. + +@item -falign-loops +@itemx -falign-loops=@var{n} +@opindex falign-loops +Align loops to a power-of-two boundary, skipping up to @var{n} bytes +like @option{-falign-functions}. The hope is that the loop will be +executed many times, which will make up for any execution of the dummy +operations. + +If @var{n} is not specified, use a machine-dependent default. + +@item -falign-jumps +@itemx -falign-jumps=@var{n} +@opindex falign-jumps +Align branch targets to a power-of-two boundary, for branch targets +where the targets can only be reached by jumping, skipping up to @var{n} +bytes like @option{-falign-functions}. In this case, no dummy operations +need be executed. + +If @var{n} is not specified, use a machine-dependent default. + +@item -fssa +@opindex fssa +Perform optimizations in static single assignment form. Each function's +flow graph is translated into SSA form, optimizations are performed, and +the flow graph is translated back from SSA form. Users should not +specify this option, since it is not yet ready for production use. + +@item -fssa-ccp +@opindex fssa-ccp +Perform Sparse Conditional Constant Propagation in SSA form. Requires +@option{-fssa}. Like @option{-fssa}, this is an experimental feature. + +@item -fssa-dce +@opindex fssa-dce +Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}. +Like @option{-fssa}, this is an experimental feature. + +@item -fsingle-precision-constant +@opindex fsingle-precision-constant +Treat floating point constant as single precision constant instead of +implicitly converting it to double precision constant. + +@item -frename-registers +@opindex frename-registers +Attempt to avoid false dependencies in scheduled code by making use +of registers left over after register allocation. This optimization +will most benefit processors with lots of registers. It can, however, +make debugging impossible, since variables will no longer stay in +a ``home register''. + +@item -fno-cprop-registers +@opindex fno-cprop-registers +After register allocation and post-register allocation instruction splitting, +we perform a copy-propagation pass to try to reduce scheduling dependencies +and occasionally eliminate the copy. + +@item --param @var{name}=@var{value} +@opindex param +In some places, GCC uses various constants to control the amount of +optimization that is done. For example, GCC will not inline functions +that contain more that a certain number of instructions. You can +control some of these constants on the command-line using the +@option{--param} option. + +In each case, the @var{value} is an integer. The allowable choices for +@var{name} are given in the following table: + +@table @gcctabopt +@item max-delay-slot-insn-search +The maximum number of instructions to consider when looking for an +instruction to fill a delay slot. If more than this arbitrary number of +instructions is searched, the time savings from filling the delay slot +will be minimal so stop searching. Increasing values mean more +aggressive optimization, making the compile time increase with probably +small improvement in executable run time. + +@item max-delay-slot-live-search +When trying to fill delay slots, the maximum number of instructions to +consider when searching for a block with valid live register +information. Increasing this arbitrarily chosen value means more +aggressive optimization, increasing the compile time. This parameter +should be removed when the delay slot code is rewritten to maintain the +control-flow graph. + +@item max-gcse-memory +The approximate maximum amount of memory that will be allocated in +order to perform the global common subexpression elimination +optimization. If more memory than specified is required, the +optimization will not be done. + +@item max-gcse-passes +The maximum number of passes of GCSE to run. + +@item max-pending-list-length +The maximum number of pending dependencies scheduling will allow +before flushing the current state and starting over. Large functions +with few branches or calls can create excessively large lists which +needlessly consume memory and resources. + +@item max-inline-insns +If an function contains more than this many instructions, it +will not be inlined. This option is precisely equivalent to +@option{-finline-limit}. + +@end table +@end table + +@node Preprocessor Options +@section Options Controlling the Preprocessor +@cindex preprocessor options +@cindex options, preprocessor + +These options control the C preprocessor, which is run on each C source +file before actual compilation. + +If you use the @option{-E} option, nothing is done except preprocessing. +Some of these options make sense only together with @option{-E} because +they cause the preprocessor output to be unsuitable for actual +compilation. + +@table @gcctabopt +@item -include @var{file} +@opindex include +Process @var{file} as input before processing the regular input file. +In effect, the contents of @var{file} are compiled first. Any @option{-D} +and @option{-U} options on the command line are always processed before +@option{-include @var{file}}, regardless of the order in which they are +written. All the @option{-include} and @option{-imacros} options are +processed in the order in which they are written. + +@item -imacros @var{file} +@opindex imacros +Process @var{file} as input, discarding the resulting output, before +processing the regular input file. Because the output generated from +@var{file} is discarded, the only effect of @option{-imacros @var{file}} +is to make the macros defined in @var{file} available for use in the +main input. All the @option{-include} and @option{-imacros} options are +processed in the order in which they are written. + +@item -idirafter @var{dir} +@opindex idirafter +@cindex second include path +Add the directory @var{dir} to the second include path. The directories +on the second include path are searched when a header file is not found +in any of the directories in the main include path (the one that +@option{-I} adds to). + +@item -iprefix @var{prefix} +@opindex iprefix +Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix} +options. + +@item -iwithprefix @var{dir} +@opindex iwithprefix +Add a directory to the second include path. The directory's name is +made by concatenating @var{prefix} and @var{dir}, where @var{prefix} was +specified previously with @option{-iprefix}. If you have not specified a +prefix yet, the directory containing the installed passes of the +compiler is used as the default. + +@item -iwithprefixbefore @var{dir} +@opindex iwithprefixbefore +Add a directory to the main include path. The directory's name is made +by concatenating @var{prefix} and @var{dir}, as in the case of +@option{-iwithprefix}. + +@item -isystem @var{dir} +@opindex isystem +Add a directory to the beginning of the second include path, marking it +as a system directory, so that it gets the same special treatment as +is applied to the standard system directories. + +@item -nostdinc +@opindex nostdinc +Do not search the standard system directories for header files. Only +the directories you have specified with @option{-I} options (and the +current directory, if appropriate) are searched. @xref{Directory +Options}, for information on @option{-I}. + +By using both @option{-nostdinc} and @option{-I-}, you can limit the include-file +search path to only those directories you specify explicitly. + +@item -remap +@opindex remap +When searching for a header file in a directory, remap file names if a +file named @file{header.gcc} exists in that directory. This can be used +to work around limitations of file systems with file name restrictions. +The @file{header.gcc} file should contain a series of lines with two +tokens on each line: the first token is the name to map, and the second +token is the actual name to use. + +@item -undef +@opindex undef +Do not predefine any nonstandard macros. (Including architecture flags). + +@item -E +@opindex E +Run only the C preprocessor. Preprocess all the C source files +specified and output the results to standard output or to the +specified output file. + +@item -C +@opindex C +Tell the preprocessor not to discard comments. Used with the +@option{-E} option. + +@item -P +@opindex P +Tell the preprocessor not to generate @samp{#line} directives. +Used with the @option{-E} option. + +@cindex make +@cindex dependencies, make +@item -M +@opindex M +Instead of outputting the result of preprocessing, output a rule +suitable for @code{make} describing the dependencies of the main source +file. The preprocessor outputs one @code{make} rule containing the +object file name for that source file, a colon, and the names of all the +included files. Unless overridden explicitly, the object file name +consists of the basename of the source file with any suffix replaced with +object file suffix. If there are many included files then the +rule is split into several lines using @samp{\}-newline. + +@option{-M} implies @option{-E}. + +@item -MM +@opindex MM +Like @option{-M}, but mention only the files included with @samp{#include +"@var{file}"}. System header files included with @samp{#include +<@var{file}>} are omitted. + +@item -MD +@opindex MD +Like @option{-M} but the dependency information is written to a file +rather than stdout. @code{gcc} will use the same file name and +directory as the object file, but with the suffix @file{.d} instead. + +This is in addition to compiling the main file as specified---@option{-MD} +does not inhibit ordinary compilation the way @option{-M} does, +unless you also specify @option{-MG}. + +With Mach, you can use the utility @code{md} to merge multiple +dependency files into a single dependency file suitable for using with +the @samp{make} command. + +@item -MMD +@opindex MMD +Like @option{-MD} except mention only user header files, not system +-header files. + +@item -MF @var{file} +@opindex MF +When used with @option{-M} or @option{-MM}, specifies a file to write the +dependencies to. This allows the preprocessor to write the preprocessed +file to stdout normally. If no @option{-MF} switch is given, CPP sends +the rules to stdout and suppresses normal preprocessed output. + +Another way to specify output of a @code{make} rule is by setting +the environment variable @env{DEPENDENCIES_OUTPUT} (@pxref{Environment +Variables}). + +@item -MG +@opindex MG +When used with @option{-M} or @option{-MM}, @option{-MG} says to treat missing +header files as generated files and assume they live in the same +directory as the source file. It suppresses preprocessed output, as a +missing header file is ordinarily an error. + +This feature is used in automatic updating of makefiles. + +@item -MP +@opindex MP +This option instructs CPP to add a phony target for each dependency +other than the main file, causing each to depend on nothing. These +dummy rules work around errors @code{make} gives if you remove header +files without updating the @code{Makefile} to match. + +This is typical output:- + +@smallexample +/tmp/test.o: /tmp/test.c /tmp/test.h + +/tmp/test.h: +@end smallexample + +@item -MQ @var{target} +@item -MT @var{target} +@opindex MQ +@opindex MT +By default CPP uses the main file name, including any path, and appends +the object suffix, normally ``.o'', to it to obtain the name of the +target for dependency generation. With @option{-MT} you can specify a +target yourself, overriding the default one. + +If you want multiple targets, you can specify them as a single argument +to @option{-MT}, or use multiple @option{-MT} options. + +The targets you specify are output in the order they appear on the +command line. @option{-MQ} is identical to @option{-MT}, except that the +target name is quoted for Make, but with @option{-MT} it isn't. For +example, @option{-MT '$(objpfx)foo.o'} gives + +@smallexample +$(objpfx)foo.o: /tmp/foo.c +@end smallexample + +but @option{-MQ '$(objpfx)foo.o'} gives + +@smallexample +$$(objpfx)foo.o: /tmp/foo.c +@end smallexample + +The default target is automatically quoted, as if it were given with +@option{-MQ}. + +@item -H +@opindex H +Print the name of each header file used, in addition to other normal +activities. + +@item -A@var{question}(@var{answer}) +@opindex A +Assert the answer @var{answer} for @var{question}, in case it is tested +with a preprocessing conditional such as @samp{#if +#@var{question}(@var{answer})}. @option{-A-} disables the standard +assertions that normally describe the target machine. + +@item -D@var{macro} +@opindex D +Define macro @var{macro} with the string @samp{1} as its definition. + +@item -D@var{macro}=@var{defn} +Define macro @var{macro} as @var{defn}. All instances of @option{-D} on +the command line are processed before any @option{-U} options. + +Any @option{-D} and @option{-U} options on the command line are processed in +order, and always before @option{-imacros @var{file}}, regardless of the +order in which they are written. + +@item -U@var{macro} +@opindex U +Undefine macro @var{macro}. @option{-U} options are evaluated after all +@option{-D} options, but before any @option{-include} and @option{-imacros} +options. + +Any @option{-D} and @option{-U} options on the command line are processed in +order, and always before @option{-imacros @var{file}}, regardless of the +order in which they are written. + +@item -dM +@opindex dM +Tell the preprocessor to output only a list of the macro definitions +that are in effect at the end of preprocessing. Used with the @option{-E} +option. + +@item -dD +@opindex dD +Tell the preprocessing to pass all macro definitions into the output, in +their proper sequence in the rest of the output. + +@item -dN +@opindex dN +Like @option{-dD} except that the macro arguments and contents are omitted. +Only @samp{#define @var{name}} is included in the output. + +@item -dI +@opindex dI +Output @samp{#include} directives in addition to the result of +preprocessing. + +@item -fpreprocessed +@opindex fpreprocessed +Indicate to the preprocessor that the input file has already been +preprocessed. This suppresses things like macro expansion, trigraph +conversion, escaped newline splicing, and processing of most directives. +The preprocessor still recognizes and removes comments, so that you can +pass a file preprocessed with @option{-C} to the compiler without +problems. In this mode the integrated preprocessor is little more than +a tokenizer for the front ends. + +@option{-fpreprocessed} is implicit if the input file has one of the +extensions @samp{i}, @samp{ii} or @samp{mi}. These are the extensions +that GCC uses for preprocessed files created by @option{-save-temps}. + +@item -trigraphs +@opindex trigraphs +Process ISO standard trigraph sequences. These are three-character +sequences, all starting with @samp{??}, that are defined by ISO C to +stand for single characters. For example, @samp{??/} stands for +@samp{\}, so @samp{'??/n'} is a character constant for a newline. By +default, GCC ignores trigraphs, but in standard-conforming modes it +converts them. See the @option{-std} and @option{-ansi} options. + +The nine trigraph sequences are +@table @samp +@item ??( +@expansion{} @samp{[} + +@item ??) +@expansion{} @samp{]} + +@item ??< +@expansion{} @samp{@{} + +@item ??> +@expansion{} @samp{@}} + +@item ??= +@expansion{} @samp{#} + +@item ??/ +@expansion{} @samp{\} + +@item ??' +@expansion{} @samp{^} + +@item ??! +@expansion{} @samp{|} + +@item ??- +@expansion{} @samp{~} + +@end table + +Trigraph support is not popular, so many compilers do not implement it +properly. Portable code should not rely on trigraphs being either +converted or ignored. + +@item -Wp,@var{option} +@opindex Wp +Pass @var{option} as an option to the preprocessor. If @var{option} +contains commas, it is split into multiple options at the commas. +@end table + +@node Assembler Options +@section Passing Options to the Assembler + +@c prevent bad page break with this line +You can pass options to the assembler. + +@table @gcctabopt +@item -Wa,@var{option} +@opindex Wa +Pass @var{option} as an option to the assembler. If @var{option} +contains commas, it is split into multiple options at the commas. +@end table + +@node Link Options +@section Options for Linking +@cindex link options +@cindex options, linking + +These options come into play when the compiler links object files into +an executable output file. They are meaningless if the compiler is +not doing a link step. + +@table @gcctabopt +@cindex file names +@item @var{object-file-name} +A file name that does not end in a special recognized suffix is +considered to name an object file or library. (Object files are +distinguished from libraries by the linker according to the file +contents.) If linking is done, these object files are used as input +to the linker. + +@item -c +@itemx -S +@itemx -E +@opindex c +@opindex S +@opindex E +If any of these options is used, then the linker is not run, and +object file names should not be used as arguments. @xref{Overall +Options}. + +@cindex Libraries +@item -l@var{library} +@itemx -l @var{library} +@opindex l +Search the library named @var{library} when linking. (The second +alternative with the library as a separate argument is only for +POSIX compliance and is not recommended.) + +It makes a difference where in the command you write this option; the +linker searches and processes libraries and object files in the order they +are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} +after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers +to functions in @samp{z}, those functions may not be loaded. + +The linker searches a standard list of directories for the library, +which is actually a file named @file{lib@var{library}.a}. The linker +then uses this file as if it had been specified precisely by name. + +The directories searched include several standard system directories +plus any that you specify with @option{-L}. + +Normally the files found this way are library files---archive files +whose members are object files. The linker handles an archive file by +scanning through it for members which define symbols that have so far +been referenced but not defined. But if the file that is found is an +ordinary object file, it is linked in the usual fashion. The only +difference between using an @option{-l} option and specifying a file name +is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a} +and searches several directories. + +@item -lobjc +@opindex lobjc +You need this special case of the @option{-l} option in order to +link an Objective-C program. + +@item -nostartfiles +@opindex nostartfiles +Do not use the standard system startup files when linking. +The standard system libraries are used normally, unless @option{-nostdlib} +or @option{-nodefaultlibs} is used. + +@item -nodefaultlibs +@opindex nodefaultlibs +Do not use the standard system libraries when linking. +Only the libraries you specify will be passed to the linker. +The standard startup files are used normally, unless @option{-nostartfiles} +is used. The compiler may generate calls to memcmp, memset, and memcpy +for System V (and ISO C) environments or to bcopy and bzero for +BSD environments. These entries are usually resolved by entries in +libc. These entry points should be supplied through some other +mechanism when this option is specified. + +@item -nostdlib +@opindex nostdlib +Do not use the standard system startup files or libraries when linking. +No startup files and only the libraries you specify will be passed to +the linker. The compiler may generate calls to memcmp, memset, and memcpy +for System V (and ISO C) environments or to bcopy and bzero for +BSD environments. These entries are usually resolved by entries in +libc. These entry points should be supplied through some other +mechanism when this option is specified. + +@cindex @option{-lgcc}, use with @option{-nostdlib} +@cindex @option{-nostdlib} and unresolved references +@cindex unresolved references and @option{-nostdlib} +@cindex @option{-lgcc}, use with @option{-nodefaultlibs} +@cindex @option{-nodefaultlibs} and unresolved references +@cindex unresolved references and @option{-nodefaultlibs} +One of the standard libraries bypassed by @option{-nostdlib} and +@option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines +that GCC uses to overcome shortcomings of particular machines, or special +needs for some languages. +(@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler +Collection (GCC) Internals}, +for more discussion of @file{libgcc.a}.) +In most cases, you need @file{libgcc.a} even when you want to avoid +other standard libraries. In other words, when you specify @option{-nostdlib} +or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well. +This ensures that you have no unresolved references to internal GCC +library subroutines. (For example, @samp{__main}, used to ensure C++ +constructors will be called; @pxref{Collect2,,@code{collect2}, gccint, +GNU Compiler Collection (GCC) Internals}.) + +@item -s +@opindex s +Remove all symbol table and relocation information from the executable. + +@item -static +@opindex static +On systems that support dynamic linking, this prevents linking with the shared +libraries. On other systems, this option has no effect. + +@item -shared +@opindex shared +Produce a shared object which can then be linked with other objects to +form an executable. Not all systems support this option. For predictable +results, you must also specify the same set of options that were used to +generate code (@option{-fpic}, @option{-fPIC}, or model suboptions) +when you specify this option.@footnote{On some systems, @samp{gcc -shared} +needs to build supplementary stub code for constructors to work. On +multi-libbed systems, @samp{gcc -shared} must select the correct support +libraries to link against. Failing to supply the correct flags may lead +to subtle defects. Supplying them in cases where they are not necessary +is innocuous.} + +@item -shared-libgcc +@itemx -static-libgcc +@opindex shared-libgcc +@opindex static-libgcc +On systems that provide @file{libgcc} as a shared library, these options +force the use of either the shared or static version respectively. +If no shared version of @file{libgcc} was built when the compiler was +configured, these options have no effect. + +There are several situations in which an application should use the +shared @file{libgcc} instead of the static version. The most common +of these is when the application wishes to throw and catch exceptions +across different shared libraries. In that case, each of the libraries +as well as the application itself should use the shared @file{libgcc}. + +Therefore, whenever you specify the @option{-shared} option, the GCC +driver automatically adds @option{-shared-libgcc}, unless you explicitly +specify @option{-static-libgcc}. The G++ driver automatically adds +@option{-shared-libgcc} when you build a main executable as well because +for C++ programs that is typically the right thing to do. +(Exception-handling will not work reliably otherwise.) + +However, when linking a main executable written in C, you must +explicitly say @option{-shared-libgcc} if you want to use the shared +@file{libgcc}. + +@item -symbolic +@opindex symbolic +Bind references to global symbols when building a shared object. Warn +about any unresolved references (unless overridden by the link editor +option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support +this option. + +@item -Xlinker @var{option} +@opindex Xlinker +Pass @var{option} as an option to the linker. You can use this to +supply system-specific linker options which GCC does not know how to +recognize. + +If you want to pass an option that takes an argument, you must use +@option{-Xlinker} twice, once for the option and once for the argument. +For example, to pass @option{-assert definitions}, you must write +@samp{-Xlinker -assert -Xlinker definitions}. It does not work to write +@option{-Xlinker "-assert definitions"}, because this passes the entire +string as a single argument, which is not what the linker expects. + +@item -Wl,@var{option} +@opindex Wl +Pass @var{option} as an option to the linker. If @var{option} contains +commas, it is split into multiple options at the commas. + +@item -u @var{symbol} +@opindex u +Pretend the symbol @var{symbol} is undefined, to force linking of +library modules to define it. You can use @option{-u} multiple times with +different symbols to force loading of additional library modules. +@end table + +@node Directory Options +@section Options for Directory Search +@cindex directory options +@cindex options, directory search +@cindex search path + +These options specify directories to search for header files, for +libraries and for parts of the compiler: + +@table @gcctabopt +@item -I@var{dir} +@opindex I +Add the directory @var{dir} to the head of the list of directories to be +searched for header files. This can be used to override a system header +file, substituting your own version, since these directories are +searched before the system header file directories. However, you should +not use this option to add directories that contain vendor-supplied +system header files (use @option{-isystem} for that). If you use more than +one @option{-I} option, the directories are scanned in left-to-right +order; the standard system directories come after. + +If a standard system include directory, or a directory specified with +@option{-isystem}, is also specified with @option{-I}, it will be +searched only in the position requested by @option{-I}. Also, it will +not be considered a system include directory. If that directory really +does contain system headers, there is a good chance that they will +break. For instance, if GCC's installation procedure edited the headers +in @file{/usr/include} to fix bugs, @samp{-I/usr/include} will cause the +original, buggy headers to be found instead of the corrected ones. GCC +will issue a warning when a system include directory is hidden in this +way. + +@item -I- +@opindex I- +Any directories you specify with @option{-I} options before the @option{-I-} +option are searched only for the case of @samp{#include "@var{file}"}; +they are not searched for @samp{#include <@var{file}>}. + +If additional directories are specified with @option{-I} options after +the @option{-I-}, these directories are searched for all @samp{#include} +directives. (Ordinarily @emph{all} @option{-I} directories are used +this way.) + +In addition, the @option{-I-} option inhibits the use of the current +directory (where the current input file came from) as the first search +directory for @samp{#include "@var{file}"}. There is no way to +override this effect of @option{-I-}. With @option{-I.} you can specify +searching the directory which was current when the compiler was +invoked. That is not exactly the same as what the preprocessor does +by default, but it is often satisfactory. + +@option{-I-} does not inhibit the use of the standard system directories +for header files. Thus, @option{-I-} and @option{-nostdinc} are +independent. + +@item -L@var{dir} +@opindex L +Add directory @var{dir} to the list of directories to be searched +for @option{-l}. + +@item -B@var{prefix} +@opindex B +This option specifies where to find the executables, libraries, +include files, and data files of the compiler itself. + +The compiler driver program runs one or more of the subprograms +@file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries +@var{prefix} as a prefix for each program it tries to run, both with and +without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}). + +For each subprogram to be run, the compiler driver first tries the +@option{-B} prefix, if any. If that name is not found, or if @option{-B} +was not specified, the driver tries two standard prefixes, which are +@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of +those results in a file name that is found, the unmodified program +name is searched for using the directories specified in your +@env{PATH} environment variable. + +The compiler will check to see if the path provided by the @option{-B} +refers to a directory, and if necessary it will add a directory +separator character at the end of the path. + +@option{-B} prefixes that effectively specify directory names also apply +to libraries in the linker, because the compiler translates these +options into @option{-L} options for the linker. They also apply to +includes files in the preprocessor, because the compiler translates these +options into @option{-isystem} options for the preprocessor. In this case, +the compiler appends @samp{include} to the prefix. + +The run-time support file @file{libgcc.a} can also be searched for using +the @option{-B} prefix, if needed. If it is not found there, the two +standard prefixes above are tried, and that is all. The file is left +out of the link if it is not found by those means. + +Another way to specify a prefix much like the @option{-B} prefix is to use +the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment +Variables}. + +As a special kludge, if the path provided by @option{-B} is +@file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to +9, then it will be replaced by @file{[dir/]include}. This is to help +with boot-strapping the compiler. + +@item -specs=@var{file} +@opindex specs +Process @var{file} after the compiler reads in the standard @file{specs} +file, in order to override the defaults that the @file{gcc} driver +program uses when determining what switches to pass to @file{cc1}, +@file{cc1plus}, @file{as}, @file{ld}, etc. More than one +@option{-specs=@var{file}} can be specified on the command line, and they +are processed in order, from left to right. +@end table + +@c man end + +@node Spec Files +@section Specifying subprocesses and the switches to pass to them +@cindex Spec Files +@command{gcc} is a driver program. It performs its job by invoking a +sequence of other programs to do the work of compiling, assembling and +linking. GCC interprets its command-line parameters and uses these to +deduce which programs it should invoke, and which command-line options +it ought to place on their command lines. This behavior is controlled +by @dfn{spec strings}. In most cases there is one spec string for each +program that GCC can invoke, but a few programs have multiple spec +strings to control their behavior. The spec strings built into GCC can +be overridden by using the @option{-specs=} command-line switch to specify +a spec file. + +@dfn{Spec files} are plaintext files that are used to construct spec +strings. They consist of a sequence of directives separated by blank +lines. The type of directive is determined by the first non-whitespace +character on the line and it can be one of the following: + +@table @code +@item %@var{command} +Issues a @var{command} to the spec file processor. The commands that can +appear here are: + +@table @code +@item %include <@var{file}> +@cindex %include +Search for @var{file} and insert its text at the current point in the +specs file. + +@item %include_noerr <@var{file}> +@cindex %include_noerr +Just like @samp{%include}, but do not generate an error message if the include +file cannot be found. + +@item %rename @var{old_name} @var{new_name} +@cindex %rename +Rename the spec string @var{old_name} to @var{new_name}. + +@end table + +@item *[@var{spec_name}]: +This tells the compiler to create, override or delete the named spec +string. All lines after this directive up to the next directive or +blank line are considered to be the text for the spec string. If this +results in an empty string then the spec will be deleted. (Or, if the +spec did not exist, then nothing will happened.) Otherwise, if the spec +does not currently exist a new spec will be created. If the spec does +exist then its contents will be overridden by the text of this +directive, unless the first character of that text is the @samp{+} +character, in which case the text will be appended to the spec. + +@item [@var{suffix}]: +Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive +and up to the next directive or blank line are considered to make up the +spec string for the indicated suffix. When the compiler encounters an +input file with the named suffix, it will processes the spec string in +order to work out how to compile that file. For example: + +@smallexample +.ZZ: +z-compile -input %i +@end smallexample + +This says that any input file whose name ends in @samp{.ZZ} should be +passed to the program @samp{z-compile}, which should be invoked with the +command-line switch @option{-input} and with the result of performing the +@samp{%i} substitution. (See below.) + +As an alternative to providing a spec string, the text that follows a +suffix directive can be one of the following: + +@table @code +@item @@@var{language} +This says that the suffix is an alias for a known @var{language}. This is +similar to using the @option{-x} command-line switch to GCC to specify a +language explicitly. For example: + +@smallexample +.ZZ: +@@c++ +@end smallexample + +Says that .ZZ files are, in fact, C++ source files. + +@item #@var{name} +This causes an error messages saying: + +@smallexample +@var{name} compiler not installed on this system. +@end smallexample +@end table + +GCC already has an extensive list of suffixes built into it. +This directive will add an entry to the end of the list of suffixes, but +since the list is searched from the end backwards, it is effectively +possible to override earlier entries using this technique. + +@end table + +GCC has the following spec strings built into it. Spec files can +override these strings or create their own. Note that individual +targets can also add their own spec strings to this list. + +@smallexample +asm Options to pass to the assembler +asm_final Options to pass to the assembler post-processor +cpp Options to pass to the C preprocessor +cc1 Options to pass to the C compiler +cc1plus Options to pass to the C++ compiler +endfile Object files to include at the end of the link +link Options to pass to the linker +lib Libraries to include on the command line to the linker +libgcc Decides which GCC support library to pass to the linker +linker Sets the name of the linker +predefines Defines to be passed to the C preprocessor +signed_char Defines to pass to CPP to say whether @code{char} is signed + by default +startfile Object files to include at the start of the link +@end smallexample + +Here is a small example of a spec file: + +@smallexample +%rename lib old_lib + +*lib: +--start-group -lgcc -lc -leval1 --end-group %(old_lib) +@end smallexample + +This example renames the spec called @samp{lib} to @samp{old_lib} and +then overrides the previous definition of @samp{lib} with a new one. +The new definition adds in some extra command-line options before +including the text of the old definition. + +@dfn{Spec strings} are a list of command-line options to be passed to their +corresponding program. In addition, the spec strings can contain +@samp{%}-prefixed sequences to substitute variable text or to +conditionally insert text into the command line. Using these constructs +it is possible to generate quite complex command lines. + +Here is a table of all defined @samp{%}-sequences for spec +strings. Note that spaces are not generated automatically around the +results of expanding these sequences. Therefore you can concatenate them +together or combine them with constant text in a single argument. + +@table @code +@item %% +Substitute one @samp{%} into the program name or argument. + +@item %i +Substitute the name of the input file being processed. + +@item %b +Substitute the basename of the input file being processed. +This is the substring up to (and not including) the last period +and not including the directory. + +@item %B +This is the same as @samp{%b}, but include the file suffix (text after +the last period). + +@item %d +Marks the argument containing or following the @samp{%d} as a +temporary file name, so that that file will be deleted if GCC exits +successfully. Unlike @samp{%g}, this contributes no text to the +argument. + +@item %g@var{suffix} +Substitute a file name that has suffix @var{suffix} and is chosen +once per compilation, and mark the argument in the same way as +@samp{%d}. To reduce exposure to denial-of-service attacks, the file +name is now chosen in a way that is hard to predict even when previously +chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s} +might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches +the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is +treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} +was simply substituted with a file name chosen once per compilation, +without regard to any appended suffix (which was therefore treated +just like ordinary text), making such attacks more likely to succeed. + +@item %u@var{suffix} +Like @samp{%g}, but generates a new temporary file name even if +@samp{%u@var{suffix}} was already seen. + +@item %U@var{suffix} +Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a +new one if there is no such last file name. In the absence of any +@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share +the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s} +would involve the generation of two distinct file names, one +for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was +simply substituted with a file name chosen for the previous @samp{%u}, +without regard to any appended suffix. + +@item %j@var{SUFFIX} +Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is +writable, and if save-temps is off; otherwise, substitute the name +of a temporary file, just like @samp{%u}. This temporary file is not +meant for communication between processes, but rather as a junk +disposal mechanism. + +@item %.@var{SUFFIX} +Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args +when it is subsequently output with @samp{%*}. @var{SUFFIX} is +terminated by the next space or %. + +@item %w +Marks the argument containing or following the @samp{%w} as the +designated output file of this compilation. This puts the argument +into the sequence of arguments that @samp{%o} will substitute later. + +@item %o +Substitutes the names of all the output files, with spaces +automatically placed around them. You should write spaces +around the @samp{%o} as well or the results are undefined. +@samp{%o} is for use in the specs for running the linker. +Input files whose names have no recognized suffix are not compiled +at all, but they are included among the output files, so they will +be linked. + +@item %O +Substitutes the suffix for object files. Note that this is +handled specially when it immediately follows @samp{%g, %u, or %U}, +because of the need for those to form complete file names. The +handling is such that @samp{%O} is treated exactly as if it had already +been substituted, except that @samp{%g, %u, and %U} do not currently +support additional @var{suffix} characters following @samp{%O} as they would +following, for example, @samp{.o}. + +@item %p +Substitutes the standard macro predefinitions for the +current target machine. Use this when running @code{cpp}. + +@item %P +Like @samp{%p}, but puts @samp{__} before and after the name of each +predefined macro, except for macros that start with @samp{__} or with +@samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO +C@. + +@item %I +Substitute a @option{-iprefix} option made from @env{GCC_EXEC_PREFIX}. + +@item %s +Current argument is the name of a library or startup file of some sort. +Search for that file in a standard list of directories and substitute +the full name found. + +@item %e@var{str} +Print @var{str} as an error message. @var{str} is terminated by a newline. +Use this when inconsistent options are detected. + +@item %| +Output @samp{-} if the input for the current command is coming from a pipe. + +@item %(@var{name}) +Substitute the contents of spec string @var{name} at this point. + +@item %[@var{name}] +Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments. + +@item %x@{@var{option}@} +Accumulate an option for @samp{%X}. + +@item %X +Output the accumulated linker options specified by @option{-Wl} or a @samp{%x} +spec string. + +@item %Y +Output the accumulated assembler options specified by @option{-Wa}. + +@item %Z +Output the accumulated preprocessor options specified by @option{-Wp}. + +@item %v1 +Substitute the major version number of GCC@. +(For version 2.9.5, this is 2.) + +@item %v2 +Substitute the minor version number of GCC@. +(For version 2.9.5, this is 9.) + +@item %v3 +Substitute the patch level number of GCC@. +(For version 2.9.5, this is 5.) + +@item %a +Process the @code{asm} spec. This is used to compute the +switches to be passed to the assembler. + +@item %A +Process the @code{asm_final} spec. This is a spec string for +passing switches to an assembler post-processor, if such a program is +needed. + +@item %l +Process the @code{link} spec. This is the spec for computing the +command line passed to the linker. Typically it will make use of the +@samp{%L %G %S %D and %E} sequences. + +@item %D +Dump out a @option{-L} option for each directory that GCC believes might +contain startup files. If the target supports multilibs then the +current multilib directory will be prepended to each of these paths. + +@item %M +Output the multilib directory with directory separators replaced with +@samp{_}. If multilib directories are not set, or the multilib directory is +@file{.} then this option emits nothing. + +@item %L +Process the @code{lib} spec. This is a spec string for deciding which +libraries should be included on the command line to the linker. + +@item %G +Process the @code{libgcc} spec. This is a spec string for deciding +which GCC support library should be included on the command line to the linker. + +@item %S +Process the @code{startfile} spec. This is a spec for deciding which +object files should be the first ones passed to the linker. Typically +this might be a file named @file{crt0.o}. + +@item %E +Process the @code{endfile} spec. This is a spec string that specifies +the last object files that will be passed to the linker. + +@item %C +Process the @code{cpp} spec. This is used to construct the arguments +to be passed to the C preprocessor. + +@item %c +Process the @code{signed_char} spec. This is intended to be used +to tell cpp whether a char is signed. It typically has the definition: +@smallexample +%@{funsigned-char:-D__CHAR_UNSIGNED__@} +@end smallexample + +@item %1 +Process the @code{cc1} spec. This is used to construct the options to be +passed to the actual C compiler (@samp{cc1}). + +@item %2 +Process the @code{cc1plus} spec. This is used to construct the options to be +passed to the actual C++ compiler (@samp{cc1plus}). + +@item %* +Substitute the variable part of a matched option. See below. +Note that each comma in the substituted string is replaced by +a single space. + +@item %@{@code{S}@} +Substitutes the @code{-S} switch, if that switch was given to GCC@. +If that switch was not specified, this substitutes nothing. Note that +the leading dash is omitted when specifying this option, and it is +automatically inserted if the substitution is performed. Thus the spec +string @samp{%@{foo@}} would match the command-line option @option{-foo} +and would output the command line option @option{-foo}. + +@item %W@{@code{S}@} +Like %@{@code{S}@} but mark last argument supplied within as a file to be +deleted on failure. + +@item %@{@code{S}*@} +Substitutes all the switches specified to GCC whose names start +with @code{-S}, but which also take an argument. This is used for +switches like @option{-o}, @option{-D}, @option{-I}, etc. +GCC considers @option{-o foo} as being +one switch whose names starts with @samp{o}. %@{o*@} would substitute this +text, including the space. Thus two arguments would be generated. + +@item %@{^@code{S}*@} +Like %@{@code{S}*@}, but don't put a blank between a switch and its +argument. Thus %@{^o*@} would only generate one argument, not two. + +@item %@{@code{S}*&@code{T}*@} +Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options +(the order of @code{S} and @code{T} in the spec is not significant). +There can be any number of ampersand-separated variables; for each the +wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}. + +@item %@{<@code{S}@} +Remove all occurrences of @code{-S} from the command line. Note---this +command is position dependent. @samp{%} commands in the spec string +before this option will see @code{-S}, @samp{%} commands in the spec +string after this option will not. + +@item %@{@code{S}*:@code{X}@} +Substitutes @code{X} if one or more switches whose names start with +@code{-S} are specified to GCC@. Note that the tail part of the +@code{-S} option (i.e.@: the part matched by the @samp{*}) will be substituted +for each occurrence of @samp{%*} within @code{X}. + +@item %@{@code{S}:@code{X}@} +Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC@. + +@item %@{!@code{S}:@code{X}@} +Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC@. + +@item %@{|@code{S}:@code{X}@} +Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}. + +@item %@{|!@code{S}:@code{X}@} +Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}. + +@item %@{.@code{S}:@code{X}@} +Substitutes @code{X}, but only if processing a file with suffix @code{S}. + +@item %@{!.@code{S}:@code{X}@} +Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}. + +@item %@{@code{S}|@code{P}:@code{X}@} +Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@. This may be +combined with @samp{!} and @samp{.} sequences as well, although they +have a stronger binding than the @samp{|}. For example a spec string +like this: + +@smallexample +%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} +@end smallexample + +will output the following command-line options from the following input +command-line options: + +@smallexample +fred.c -foo -baz +jim.d -bar -boggle +-d fred.c -foo -baz -boggle +-d jim.d -bar -baz -boggle +@end smallexample + +@end table + +The conditional text @code{X} in a %@{@code{S}:@code{X}@} or +%@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs +or spaces, or even newlines. They are processed as usual, as described +above. + +The @option{-O}, @option{-f}, @option{-m}, and @option{-W} +switches are handled specifically in these +constructs. If another value of @option{-O} or the negated form of a @option{-f}, @option{-m}, or +@option{-W} switch is found later in the command line, the earlier switch +value is ignored, except with @{@code{S}*@} where @code{S} is just one +letter, which passes all matching options. + +The character @samp{|} at the beginning of the predicate text is used to indicate +that a command should be piped to the following command, but only if @option{-pipe} +is specified. + +It is built into GCC which switches take arguments and which do not. +(You might think it would be useful to generalize this to allow each +compiler's spec to say which switches take arguments. But this cannot +be done in a consistent fashion. GCC cannot even decide which input +files have been specified without knowing which switches take arguments, +and it must know which input files to compile in order to tell which +compilers to run). + +GCC also knows implicitly that arguments starting in @option{-l} are to be +treated as compiler output files, and passed to the linker in their +proper position among the other output files. + +@c man begin OPTIONS + +@node Target Options +@section Specifying Target Machine and Compiler Version +@cindex target options +@cindex cross compiling +@cindex specifying machine version +@cindex specifying compiler version and target machine +@cindex compiler version, specifying +@cindex target machine, specifying + +By default, GCC compiles code for the same type of machine that you +are using. However, it can also be installed as a cross-compiler, to +compile for some other type of machine. In fact, several different +configurations of GCC, for different target machines, can be +installed side by side. Then you specify which one to use with the +@option{-b} option. + +In addition, older and newer versions of GCC can be installed side +by side. One of them (probably the newest) will be the default, but +you may sometimes wish to use another. + +@table @gcctabopt +@item -b @var{machine} +@opindex b +The argument @var{machine} specifies the target machine for compilation. +This is useful when you have installed GCC as a cross-compiler. + +The value to use for @var{machine} is the same as was specified as the +machine type when configuring GCC as a cross-compiler. For +example, if a cross-compiler was configured with @samp{configure +i386v}, meaning to compile for an 80386 running System V, then you +would specify @option{-b i386v} to run that cross compiler. + +When you do not specify @option{-b}, it normally means to compile for +the same type of machine that you are using. + +@item -V @var{version} +@opindex V +The argument @var{version} specifies which version of GCC to run. +This is useful when multiple versions are installed. For example, +@var{version} might be @samp{2.0}, meaning to run GCC version 2.0. + +The default version, when you do not specify @option{-V}, is the last +version of GCC that you installed. +@end table + +The @option{-b} and @option{-V} options actually work by controlling part of +the file name used for the executable files and libraries used for +compilation. A given version of GCC, for a given target machine, is +normally kept in the directory @file{/usr/local/lib/gcc-lib/@var{machine}/@var{version}}. + +Thus, sites can customize the effect of @option{-b} or @option{-V} either by +changing the names of these directories or adding alternate names (or +symbolic links). If in directory @file{/usr/local/lib/gcc-lib/} the +file @file{80386} is a link to the file @file{i386v}, then @option{-b +80386} becomes an alias for @option{-b i386v}. + +In one respect, the @option{-b} or @option{-V} do not completely change +to a different compiler: the top-level driver program @command{gcc} +that you originally invoked continues to run and invoke the other +executables (preprocessor, compiler per se, assembler and linker) +that do the real work. However, since no real work is done in the +driver program, it usually does not matter that the driver program +in use is not the one for the specified target. It is common for the +interface to the other executables to change incompatibly between +compiler versions, so unless the version specified is very close to that +of the driver (for example, @option{-V 3.0} with a driver program from GCC +version 3.0.1), use of @option{-V} may not work; for example, using +@option{-V 2.95.2} will not work with a driver program from GCC 3.0. + +The only way that the driver program depends on the target machine is +in the parsing and handling of special machine-specific options. +However, this is controlled by a file which is found, along with the +other executables, in the directory for the specified version and +target machine. As a result, a single installed driver program adapts +to any specified target machine, and sufficiently similar compiler +versions. + +The driver program executable does control one significant thing, +however: the default version and target machine. Therefore, you can +install different instances of the driver program, compiled for +different targets or versions, under different names. + +For example, if the driver for version 2.0 is installed as @command{ogcc} +and that for version 2.1 is installed as @command{gcc}, then the command +@command{gcc} will use version 2.1 by default, while @command{ogcc} will use +2.0 by default. However, you can choose either version with either +command with the @option{-V} option. + +@node Submodel Options +@section Hardware Models and Configurations +@cindex submodel options +@cindex specifying hardware config +@cindex hardware models and configurations, specifying +@cindex machine dependent options + +Earlier we discussed the standard option @option{-b} which chooses among +different installed compilers for completely different target +machines, such as VAX vs.@: 68000 vs.@: 80386. + +In addition, each of these target machine types can have its own +special options, starting with @samp{-m}, to choose among various +hardware models or configurations---for example, 68010 vs 68020, +floating coprocessor or none. A single installed version of the +compiler can compile for any model or configuration, according to the +options specified. + +Some configurations of the compiler also support additional special +options, usually for compatibility with other compilers on the same +platform. + +These options are defined by the macro @code{TARGET_SWITCHES} in the +machine description. The default for the options is also defined by +that macro, which enables you to change the defaults. + +@menu +* M680x0 Options:: +* M68hc1x Options:: +* VAX Options:: +* SPARC Options:: +* Convex Options:: +* AMD29K Options:: +* ARM Options:: +* MN10200 Options:: +* MN10300 Options:: +* M32R/D Options:: +* M88K Options:: +* RS/6000 and PowerPC Options:: +* RT Options:: +* MIPS Options:: +* i386 and x86-64 Options:: +* HPPA Options:: +* Intel 960 Options:: +* DEC Alpha Options:: +* DEC Alpha/VMS Options:: +* Clipper Options:: +* H8/300 Options:: +* SH Options:: +* System V Options:: +* TMS320C3x/C4x Options:: +* V850 Options:: +* ARC Options:: +* NS32K Options:: +* AVR Options:: +* MCore Options:: +* IA-64 Options:: +* D30V Options:: +* S/390 and zSeries Options:: +* CRIS Options:: +* MMIX Options:: +* PDP-11 Options:: +* Xstormy16 Options:: +* Xtensa Options:: +@end menu + +@node M680x0 Options +@subsection M680x0 Options +@cindex M680x0 options + +These are the @samp{-m} options defined for the 68000 series. The default +values for these options depends on which style of 68000 was selected when +the compiler was configured; the defaults for the most common choices are +given below. + +@table @gcctabopt +@item -m68000 +@itemx -mc68000 +@opindex m68000 +@opindex mc68000 +Generate output for a 68000. This is the default +when the compiler is configured for 68000-based systems. + +Use this option for microcontrollers with a 68000 or EC000 core, +including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. + +@item -m68020 +@itemx -mc68020 +@opindex m68020 +@opindex mc68020 +Generate output for a 68020. This is the default +when the compiler is configured for 68020-based systems. + +@item -m68881 +@opindex m68881 +Generate output containing 68881 instructions for floating point. +This is the default for most 68020 systems unless @option{--nfp} was +specified when the compiler was configured. + +@item -m68030 +@opindex m68030 +Generate output for a 68030. This is the default when the compiler is +configured for 68030-based systems. + +@item -m68040 +@opindex m68040 +Generate output for a 68040. This is the default when the compiler is +configured for 68040-based systems. + +This option inhibits the use of 68881/68882 instructions that have to be +emulated by software on the 68040. Use this option if your 68040 does not +have code to emulate those instructions. + +@item -m68060 +@opindex m68060 +Generate output for a 68060. This is the default when the compiler is +configured for 68060-based systems. + +This option inhibits the use of 68020 and 68881/68882 instructions that +have to be emulated by software on the 68060. Use this option if your 68060 +does not have code to emulate those instructions. + +@item -mcpu32 +@opindex mcpu32 +Generate output for a CPU32. This is the default +when the compiler is configured for CPU32-based systems. + +Use this option for microcontrollers with a +CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, +68336, 68340, 68341, 68349 and 68360. + +@item -m5200 +@opindex m5200 +Generate output for a 520X ``coldfire'' family cpu. This is the default +when the compiler is configured for 520X-based systems. + +Use this option for microcontroller with a 5200 core, including +the MCF5202, MCF5203, MCF5204 and MCF5202. + + +@item -m68020-40 +@opindex m68020-40 +Generate output for a 68040, without using any of the new instructions. +This results in code which can run relatively efficiently on either a +68020/68881 or a 68030 or a 68040. The generated code does use the +68881 instructions that are emulated on the 68040. + +@item -m68020-60 +@opindex m68020-60 +Generate output for a 68060, without using any of the new instructions. +This results in code which can run relatively efficiently on either a +68020/68881 or a 68030 or a 68040. The generated code does use the +68881 instructions that are emulated on the 68060. + +@item -mfpa +@opindex mfpa +Generate output containing Sun FPA instructions for floating point. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not available for all m68k +targets. Normally the facilities of the machine's usual C compiler are +used, but this can't be done directly in cross-compilation. You must +make your own arrangements to provide suitable library functions for +cross-compilation. The embedded targets @samp{m68k-*-aout} and +@samp{m68k-*-coff} do provide software floating point support. + +@item -mshort +@opindex mshort +Consider type @code{int} to be 16 bits wide, like @code{short int}. + +@item -mnobitfield +@opindex mnobitfield +Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32} +and @option{-m5200} options imply @w{@option{-mnobitfield}}. + +@item -mbitfield +@opindex mbitfield +Do use the bit-field instructions. The @option{-m68020} option implies +@option{-mbitfield}. This is the default if you use a configuration +designed for a 68020. + +@item -mrtd +@opindex mrtd +Use a different function-calling convention, in which functions +that take a fixed number of arguments return with the @code{rtd} +instruction, which pops their arguments while returning. This +saves one instruction in the caller since there is no need to pop +the arguments there. + +This calling convention is incompatible with the one normally +used on Unix, so you cannot use it if you need to call libraries +compiled with the Unix compiler. + +Also, you must provide function prototypes for all functions that +take variable numbers of arguments (including @code{printf}); +otherwise incorrect code will be generated for calls to those +functions. + +In addition, seriously incorrect code will result if you call a +function with too many arguments. (Normally, extra arguments are +harmlessly ignored.) + +The @code{rtd} instruction is supported by the 68010, 68020, 68030, +68040, 68060 and CPU32 processors, but not by the 68000 or 5200. + +@item -malign-int +@itemx -mno-align-int +@opindex malign-int +@opindex mno-align-int +Control whether GCC aligns @code{int}, @code{long}, @code{long long}, +@code{float}, @code{double}, and @code{long double} variables on a 32-bit +boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}). +Aligning variables on 32-bit boundaries produces code that runs somewhat +faster on processors with 32-bit busses at the expense of more memory. + +@strong{Warning:} if you use the @option{-malign-int} switch, GCC will +align structures containing the above types differently than +most published application binary interface specifications for the m68k. + +@item -mpcrel +@opindex mpcrel +Use the pc-relative addressing mode of the 68000 directly, instead of +using a global offset table. At present, this option implies @option{-fpic}, +allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is +not presently supported with @option{-mpcrel}, though this could be supported for +68020 and higher processors. + +@item -mno-strict-align +@itemx -mstrict-align +@opindex mno-strict-align +@opindex mstrict-align +Do not (do) assume that unaligned memory references will be handled by +the system. + +@end table + +@node M68hc1x Options +@subsection M68hc1x Options +@cindex M68hc1x options + +These are the @samp{-m} options defined for the 68hc11 and 68hc12 +microcontrollers. The default values for these options depends on +which style of microcontroller was selected when the compiler was configured; +the defaults for the most common choices are given below. + +@table @gcctabopt +@item -m6811 +@itemx -m68hc11 +@opindex m6811 +@opindex m68hc11 +Generate output for a 68HC11. This is the default +when the compiler is configured for 68HC11-based systems. + +@item -m6812 +@itemx -m68hc12 +@opindex m6812 +@opindex m68hc12 +Generate output for a 68HC12. This is the default +when the compiler is configured for 68HC12-based systems. + +@item -mauto-incdec +@opindex mauto-incdec +Enable the use of 68HC12 pre and post auto-increment and auto-decrement +addressing modes. + +@item -mshort +@opindex mshort +Consider type @code{int} to be 16 bits wide, like @code{short int}. + +@item -msoft-reg-count=@var{count} +@opindex msoft-reg-count +Specify the number of pseudo-soft registers which are used for the +code generation. The maximum number is 32. Using more pseudo-soft +register may or may not result in better code depending on the program. +The default is 4 for 68HC11 and 2 for 68HC12. + +@end table + +@node VAX Options +@subsection VAX Options +@cindex VAX options + +These @samp{-m} options are defined for the VAX: + +@table @gcctabopt +@item -munix +@opindex munix +Do not output certain jump instructions (@code{aobleq} and so on) +that the Unix assembler for the VAX cannot handle across long +ranges. + +@item -mgnu +@opindex mgnu +Do output those jump instructions, on the assumption that you +will assemble with the GNU assembler. + +@item -mg +@opindex mg +Output code for g-format floating point numbers instead of d-format. +@end table + +@node SPARC Options +@subsection SPARC Options +@cindex SPARC options + +These @samp{-m} switches are supported on the SPARC: + +@table @gcctabopt +@item -mno-app-regs +@itemx -mapp-regs +@opindex mno-app-regs +@opindex mapp-regs +Specify @option{-mapp-regs} to generate output using the global registers +2 through 4, which the SPARC SVR4 ABI reserves for applications. This +is the default. + +To be fully SVR4 ABI compliant at the cost of some performance loss, +specify @option{-mno-app-regs}. You should compile libraries and system +software with this option. + +@item -mfpu +@itemx -mhard-float +@opindex mfpu +@opindex mhard-float +Generate output containing floating point instructions. This is the +default. + +@item -mno-fpu +@itemx -msoft-float +@opindex mno-fpu +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not available for all SPARC +targets. Normally the facilities of the machine's usual C compiler are +used, but this cannot be done directly in cross-compilation. You must make +your own arrangements to provide suitable library functions for +cross-compilation. The embedded targets @samp{sparc-*-aout} and +@samp{sparclite-*-*} do provide software floating point support. + +@option{-msoft-float} changes the calling convention in the output file; +therefore, it is only useful if you compile @emph{all} of a program with +this option. In particular, you need to compile @file{libgcc.a}, the +library that comes with GCC, with @option{-msoft-float} in order for +this to work. + +@item -mhard-quad-float +@opindex mhard-quad-float +Generate output containing quad-word (long double) floating point +instructions. + +@item -msoft-quad-float +@opindex msoft-quad-float +Generate output containing library calls for quad-word (long double) +floating point instructions. The functions called are those specified +in the SPARC ABI@. This is the default. + +As of this writing, there are no sparc implementations that have hardware +support for the quad-word floating point instructions. They all invoke +a trap handler for one of these instructions, and then the trap handler +emulates the effect of the instruction. Because of the trap handler overhead, +this is much slower than calling the ABI library routines. Thus the +@option{-msoft-quad-float} option is the default. + +@item -mno-epilogue +@itemx -mepilogue +@opindex mno-epilogue +@opindex mepilogue +With @option{-mepilogue} (the default), the compiler always emits code for +function exit at the end of each function. Any function exit in +the middle of the function (such as a return statement in C) will +generate a jump to the exit code at the end of the function. + +With @option{-mno-epilogue}, the compiler tries to emit exit code inline +at every function exit. + +@item -mno-flat +@itemx -mflat +@opindex mno-flat +@opindex mflat +With @option{-mflat}, the compiler does not generate save/restore instructions +and will use a ``flat'' or single register window calling convention. +This model uses %i7 as the frame pointer and is compatible with the normal +register window model. Code from either may be intermixed. +The local registers and the input registers (0--5) are still treated as +``call saved'' registers and will be saved on the stack as necessary. + +With @option{-mno-flat} (the default), the compiler emits save/restore +instructions (except for leaf functions) and is the normal mode of operation. + +@item -mno-unaligned-doubles +@itemx -munaligned-doubles +@opindex mno-unaligned-doubles +@opindex munaligned-doubles +Assume that doubles have 8 byte alignment. This is the default. + +With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte +alignment only if they are contained in another type, or if they have an +absolute address. Otherwise, it assumes they have 4 byte alignment. +Specifying this option avoids some rare compatibility problems with code +generated by other compilers. It is not the default because it results +in a performance loss, especially for floating point code. + +@item -mno-faster-structs +@itemx -mfaster-structs +@opindex mno-faster-structs +@opindex mfaster-structs +With @option{-mfaster-structs}, the compiler assumes that structures +should have 8 byte alignment. This enables the use of pairs of +@code{ldd} and @code{std} instructions for copies in structure +assignment, in place of twice as many @code{ld} and @code{st} pairs. +However, the use of this changed alignment directly violates the Sparc +ABI@. Thus, it's intended only for use on targets where the developer +acknowledges that their resulting code will not be directly in line with +the rules of the ABI@. + +@item -mv8 +@itemx -msparclite +@opindex mv8 +@opindex msparclite +These two options select variations on the SPARC architecture. + +By default (unless specifically configured for the Fujitsu SPARClite), +GCC generates code for the v7 variant of the SPARC architecture. + +@option{-mv8} will give you SPARC v8 code. The only difference from v7 +code is that the compiler emits the integer multiply and integer +divide instructions which exist in SPARC v8 but not in SPARC v7. + +@option{-msparclite} will give you SPARClite code. This adds the integer +multiply, integer divide step and scan (@code{ffs}) instructions which +exist in SPARClite but not in SPARC v7. + +These options are deprecated and will be deleted in a future GCC release. +They have been replaced with @option{-mcpu=xxx}. + +@item -mcypress +@itemx -msupersparc +@opindex mcypress +@opindex msupersparc +These two options select the processor for which the code is optimized. + +With @option{-mcypress} (the default), the compiler optimizes code for the +Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series. +This is also appropriate for the older SparcStation 1, 2, IPX etc. + +With @option{-msupersparc} the compiler optimizes code for the SuperSparc cpu, as +used in the SparcStation 10, 1000 and 2000 series. This flag also enables use +of the full SPARC v8 instruction set. + +These options are deprecated and will be deleted in a future GCC release. +They have been replaced with @option{-mcpu=xxx}. + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set the instruction set, register set, and instruction scheduling parameters +for machine type @var{cpu_type}. Supported values for @var{cpu_type} are +@samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite}, +@samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934}, +@samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}. + +Default instruction scheduling parameters are used for values that select +an architecture and not an implementation. These are @samp{v7}, @samp{v8}, +@samp{sparclite}, @samp{sparclet}, @samp{v9}. + +Here is a list of each supported architecture and their supported +implementations. + +@smallexample + v7: cypress + v8: supersparc, hypersparc + sparclite: f930, f934, sparclite86x + sparclet: tsc701 + v9: ultrasparc +@end smallexample + +@item -mtune=@var{cpu_type} +@opindex mtune +Set the instruction scheduling parameters for machine type +@var{cpu_type}, but do not set the instruction set or register set that the +option @option{-mcpu=@var{cpu_type}} would. + +The same values for @option{-mcpu=@var{cpu_type}} can be used for +@option{-mtune=@var{cpu_type}}, but the only useful values are those +that select a particular cpu implementation. Those are @samp{cypress}, +@samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934}, +@samp{sparclite86x}, @samp{tsc701}, and @samp{ultrasparc}. + +@end table + +These @samp{-m} switches are supported in addition to the above +on the SPARCLET processor. + +@table @gcctabopt +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a processor running in little-endian mode. + +@item -mlive-g0 +@opindex mlive-g0 +Treat register @code{%g0} as a normal register. +GCC will continue to clobber it as necessary but will not assume +it always reads as 0. + +@item -mbroken-saverestore +@opindex mbroken-saverestore +Generate code that does not use non-trivial forms of the @code{save} and +@code{restore} instructions. Early versions of the SPARCLET processor do +not correctly handle @code{save} and @code{restore} instructions used with +arguments. They correctly handle them used without arguments. A @code{save} +instruction used without arguments increments the current window pointer +but does not allocate a new stack frame. It is assumed that the window +overflow trap handler will properly handle this case as will interrupt +handlers. +@end table + +These @samp{-m} switches are supported in addition to the above +on SPARC V9 processors in 64-bit environments. + +@table @gcctabopt +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a processor running in little-endian mode. + +@item -m32 +@itemx -m64 +@opindex m32 +@opindex m64 +Generate code for a 32-bit or 64-bit environment. +The 32-bit environment sets int, long and pointer to 32 bits. +The 64-bit environment sets int to 32 bits and long and pointer +to 64 bits. + +@item -mcmodel=medlow +@opindex mcmodel=medlow +Generate code for the Medium/Low code model: the program must be linked +in the low 32 bits of the address space. Pointers are 64 bits. +Programs can be statically or dynamically linked. + +@item -mcmodel=medmid +@opindex mcmodel=medmid +Generate code for the Medium/Middle code model: the program must be linked +in the low 44 bits of the address space, the text segment must be less than +2G bytes, and data segment must be within 2G of the text segment. +Pointers are 64 bits. + +@item -mcmodel=medany +@opindex mcmodel=medany +Generate code for the Medium/Anywhere code model: the program may be linked +anywhere in the address space, the text segment must be less than +2G bytes, and data segment must be within 2G of the text segment. +Pointers are 64 bits. + +@item -mcmodel=embmedany +@opindex mcmodel=embmedany +Generate code for the Medium/Anywhere code model for embedded systems: +assume a 32-bit text and a 32-bit data segment, both starting anywhere +(determined at link time). Register %g4 points to the base of the +data segment. Pointers are still 64 bits. +Programs are statically linked, PIC is not supported. + +@item -mstack-bias +@itemx -mno-stack-bias +@opindex mstack-bias +@opindex mno-stack-bias +With @option{-mstack-bias}, GCC assumes that the stack pointer, and +frame pointer if present, are offset by @minus{}2047 which must be added back +when making stack frame references. +Otherwise, assume no such offset is present. +@end table + +@node Convex Options +@subsection Convex Options +@cindex Convex options + +These @samp{-m} options are defined for Convex: + +@table @gcctabopt +@item -mc1 +@opindex mc1 +Generate output for C1. The code will run on any Convex machine. +The preprocessor symbol @code{__convex__c1__} is defined. + +@item -mc2 +@opindex mc2 +Generate output for C2. Uses instructions not available on C1. +Scheduling and other optimizations are chosen for max performance on C2. +The preprocessor symbol @code{__convex_c2__} is defined. + +@item -mc32 +@opindex mc32 +Generate output for C32xx. Uses instructions not available on C1. +Scheduling and other optimizations are chosen for max performance on C32. +The preprocessor symbol @code{__convex_c32__} is defined. + +@item -mc34 +@opindex mc34 +Generate output for C34xx. Uses instructions not available on C1. +Scheduling and other optimizations are chosen for max performance on C34. +The preprocessor symbol @code{__convex_c34__} is defined. + +@item -mc38 +@opindex mc38 +Generate output for C38xx. Uses instructions not available on C1. +Scheduling and other optimizations are chosen for max performance on C38. +The preprocessor symbol @code{__convex_c38__} is defined. + +@item -margcount +@opindex margcount +Generate code which puts an argument count in the word preceding each +argument list. This is compatible with regular CC, and a few programs +may need the argument count word. GDB and other source-level debuggers +do not need it; this info is in the symbol table. + +@item -mnoargcount +@opindex mnoargcount +Omit the argument count word. This is the default. + +@item -mvolatile-cache +@opindex mvolatile-cache +Allow volatile references to be cached. This is the default. + +@item -mvolatile-nocache +@opindex mvolatile-nocache +Volatile references bypass the data cache, going all the way to memory. +This is only needed for multi-processor code that does not use standard +synchronization instructions. Making non-volatile references to volatile +locations will not necessarily work. + +@item -mlong32 +@opindex mlong32 +Type long is 32 bits, the same as type int. This is the default. + +@item -mlong64 +@opindex mlong64 +Type long is 64 bits, the same as type long long. This option is useless, +because no library support exists for it. +@end table + +@node AMD29K Options +@subsection AMD29K Options +@cindex AMD29K options + +These @samp{-m} options are defined for the AMD Am29000: + +@table @gcctabopt +@item -mdw +@opindex mdw +@cindex DW bit (29k) +Generate code that assumes the @code{DW} bit is set, i.e., that byte and +halfword operations are directly supported by the hardware. This is the +default. + +@item -mndw +@opindex mndw +Generate code that assumes the @code{DW} bit is not set. + +@item -mbw +@opindex mbw +@cindex byte writes (29k) +Generate code that assumes the system supports byte and halfword write +operations. This is the default. + +@item -mnbw +@opindex mnbw +Generate code that assumes the systems does not support byte and +halfword write operations. @option{-mnbw} implies @option{-mndw}. + +@item -msmall +@opindex msmall +@cindex memory model (29k) +Use a small memory model that assumes that all function addresses are +either within a single 256 KB segment or at an absolute address of less +than 256k. This allows the @code{call} instruction to be used instead +of a @code{const}, @code{consth}, @code{calli} sequence. + +@item -mnormal +@opindex mnormal +Use the normal memory model: Generate @code{call} instructions only when +calling functions in the same file and @code{calli} instructions +otherwise. This works if each file occupies less than 256 KB but allows +the entire executable to be larger than 256 KB@. This is the default. + +@item -mlarge +@opindex mlarge +Always use @code{calli} instructions. Specify this option if you expect +a single file to compile into more than 256 KB of code. + +@item -m29050 +@opindex m29050 +@cindex processor selection (29k) +Generate code for the Am29050. + +@item -m29000 +@opindex m29000 +Generate code for the Am29000. This is the default. + +@item -mkernel-registers +@opindex mkernel-registers +@cindex kernel and user registers (29k) +Generate references to registers @code{gr64-gr95} instead of to +registers @code{gr96-gr127}. This option can be used when compiling +kernel code that wants a set of global registers disjoint from that used +by user-mode code. + +Note that when this option is used, register names in @samp{-f} flags +must use the normal, user-mode, names. + +@item -muser-registers +@opindex muser-registers +Use the normal set of global registers, @code{gr96-gr127}. This is the +default. + +@item -mstack-check +@itemx -mno-stack-check +@opindex mstack-check +@opindex mno-stack-check +@cindex stack checks (29k) +Insert (or do not insert) a call to @code{__msp_check} after each stack +adjustment. This is often used for kernel code. + +@item -mstorem-bug +@itemx -mno-storem-bug +@opindex mstorem-bug +@opindex mno-storem-bug +@cindex storem bug (29k) +@option{-mstorem-bug} handles 29k processors which cannot handle the +separation of a mtsrim insn and a storem instruction (most 29000 chips +to date, but not the 29050). + +@item -mno-reuse-arg-regs +@itemx -mreuse-arg-regs +@opindex mno-reuse-arg-regs +@opindex mreuse-arg-regs +@option{-mno-reuse-arg-regs} tells the compiler to only use incoming argument +registers for copying out arguments. This helps detect calling a function +with fewer arguments than it was declared with. + +@item -mno-impure-text +@itemx -mimpure-text +@opindex mno-impure-text +@opindex mimpure-text +@option{-mimpure-text}, used in addition to @option{-shared}, tells the compiler to +not pass @option{-assert pure-text} to the linker when linking a shared object. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not part of GCC@. +Normally the facilities of the machine's usual C compiler are used, but +this can't be done directly in cross-compilation. You must make your +own arrangements to provide suitable library functions for +cross-compilation. + +@item -mno-multm +@opindex mno-multm +Do not generate multm or multmu instructions. This is useful for some embedded +systems which do not have trap handlers for these instructions. +@end table + +@node ARM Options +@subsection ARM Options +@cindex ARM options + +These @samp{-m} options are defined for Advanced RISC Machines (ARM) +architectures: + +@table @gcctabopt +@item -mapcs-frame +@opindex mapcs-frame +Generate a stack frame that is compliant with the ARM Procedure Call +Standard for all functions, even if this is not strictly necessary for +correct execution of the code. Specifying @option{-fomit-frame-pointer} +with this option will cause the stack frames not to be generated for +leaf functions. The default is @option{-mno-apcs-frame}. + +@item -mapcs +@opindex mapcs +This is a synonym for @option{-mapcs-frame}. + +@item -mapcs-26 +@opindex mapcs-26 +Generate code for a processor running with a 26-bit program counter, +and conforming to the function calling standards for the APCS 26-bit +option. This option replaces the @option{-m2} and @option{-m3} options +of previous releases of the compiler. + +@item -mapcs-32 +@opindex mapcs-32 +Generate code for a processor running with a 32-bit program counter, +and conforming to the function calling standards for the APCS 32-bit +option. This option replaces the @option{-m6} option of previous releases +of the compiler. + +@ignore +@c not currently implemented +@item -mapcs-stack-check +@opindex mapcs-stack-check +Generate code to check the amount of stack space available upon entry to +every function (that actually uses some stack space). If there is +insufficient space available then either the function +@samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be +called, depending upon the amount of stack space required. The run time +system is required to provide these functions. The default is +@option{-mno-apcs-stack-check}, since this produces smaller code. + +@c not currently implemented +@item -mapcs-float +@opindex mapcs-float +Pass floating point arguments using the float point registers. This is +one of the variants of the APCS@. This option is recommended if the +target hardware has a floating point unit or if a lot of floating point +arithmetic is going to be performed by the code. The default is +@option{-mno-apcs-float}, since integer only code is slightly increased in +size if @option{-mapcs-float} is used. + +@c not currently implemented +@item -mapcs-reentrant +@opindex mapcs-reentrant +Generate reentrant, position independent code. The default is +@option{-mno-apcs-reentrant}. +@end ignore + +@item -mthumb-interwork +@opindex mthumb-interwork +Generate code which supports calling between the ARM and Thumb +instruction sets. Without this option the two instruction sets cannot +be reliably used inside one program. The default is +@option{-mno-thumb-interwork}, since slightly larger code is generated +when @option{-mthumb-interwork} is specified. + +@item -mno-sched-prolog +@opindex mno-sched-prolog +Prevent the reordering of instructions in the function prolog, or the +merging of those instruction with the instructions in the function's +body. This means that all functions will start with a recognizable set +of instructions (or in fact one of a choice from a small set of +different function prologues), and this information can be used to +locate the start if functions inside an executable piece of code. The +default is @option{-msched-prolog}. + +@item -mhard-float +@opindex mhard-float +Generate output containing floating point instructions. This is the +default. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not available for all ARM +targets. Normally the facilities of the machine's usual C compiler are +used, but this cannot be done directly in cross-compilation. You must make +your own arrangements to provide suitable library functions for +cross-compilation. + +@option{-msoft-float} changes the calling convention in the output file; +therefore, it is only useful if you compile @emph{all} of a program with +this option. In particular, you need to compile @file{libgcc.a}, the +library that comes with GCC, with @option{-msoft-float} in order for +this to work. + +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a processor running in little-endian mode. This is +the default for all standard configurations. + +@item -mbig-endian +@opindex mbig-endian +Generate code for a processor running in big-endian mode; the default is +to compile code for a little-endian processor. + +@item -mwords-little-endian +@opindex mwords-little-endian +This option only applies when generating code for big-endian processors. +Generate code for a little-endian word order but a big-endian byte +order. That is, a byte order of the form @samp{32107654}. Note: this +option should only be used if you require compatibility with code for +big-endian ARM processors generated by versions of the compiler prior to +2.8. + +@item -malignment-traps +@opindex malignment-traps +Generate code that will not trap if the MMU has alignment traps enabled. +On ARM architectures prior to ARMv4, there were no instructions to +access half-word objects stored in memory. However, when reading from +memory a feature of the ARM architecture allows a word load to be used, +even if the address is unaligned, and the processor core will rotate the +data as it is being loaded. This option tells the compiler that such +misaligned accesses will cause a MMU trap and that it should instead +synthesise the access as a series of byte accesses. The compiler can +still use word accesses to load half-word data if it knows that the +address is aligned to a word boundary. + +This option is ignored when compiling for ARM architecture 4 or later, +since these processors have instructions to directly access half-word +objects in memory. + +@item -mno-alignment-traps +@opindex mno-alignment-traps +Generate code that assumes that the MMU will not trap unaligned +accesses. This produces better code when the target instruction set +does not have half-word memory operations (i.e.@: implementations prior to +ARMv4). + +Note that you cannot use this option to access unaligned word objects, +since the processor will only fetch one 32-bit aligned object from +memory. + +The default setting for most targets is @option{-mno-alignment-traps}, since +this produces better code when there are no half-word memory +instructions available. + +@item -mshort-load-bytes +@itemx -mno-short-load-words +@opindex mshort-load-bytes +@opindex mno-short-load-words +These are deprecated aliases for @option{-malignment-traps}. + +@item -mno-short-load-bytes +@itemx -mshort-load-words +@opindex mno-short-load-bytes +@opindex mshort-load-words +This are deprecated aliases for @option{-mno-alignment-traps}. + +@item -mbsd +@opindex mbsd +This option only applies to RISC iX@. Emulate the native BSD-mode +compiler. This is the default if @option{-ansi} is not specified. + +@item -mxopen +@opindex mxopen +This option only applies to RISC iX@. Emulate the native X/Open-mode +compiler. + +@item -mno-symrename +@opindex mno-symrename +This option only applies to RISC iX@. Do not run the assembler +post-processor, @samp{symrename}, after code has been assembled. +Normally it is necessary to modify some of the standard symbols in +preparation for linking with the RISC iX C library; this option +suppresses this pass. The post-processor is never run when the +compiler is built for cross-compilation. + +@item -mcpu=@var{name} +@opindex mcpu +This specifies the name of the target ARM processor. GCC uses this name +to determine what kind of instructions it can emit when generating +assembly code. Permissible names are: @samp{arm2}, @samp{arm250}, +@samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610}, +@samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm}, +@samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700}, +@samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100}, +@samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8}, +@samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100}, +@samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920}, +@samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi}, +@samp{arm1020t}, @samp{xscale}. + +@itemx -mtune=@var{name} +@opindex mtune +This option is very similar to the @option{-mcpu=} option, except that +instead of specifying the actual target processor type, and hence +restricting which instructions can be used, it specifies that GCC should +tune the performance of the code as if the target were of the type +specified in this option, but still choosing the instructions that it +will generate based on the cpu specified by a @option{-mcpu=} option. +For some ARM implementations better performance can be obtained by using +this option. + +@item -march=@var{name} +@opindex march +This specifies the name of the target ARM architecture. GCC uses this +name to determine what kind of instructions it can emit when generating +assembly code. This option can be used in conjunction with or instead +of the @option{-mcpu=} option. Permissible names are: @samp{armv2}, +@samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t}, +@samp{armv5}, @samp{armv5t}, @samp{armv5te}. + +@item -mfpe=@var{number} +@itemx -mfp=@var{number} +@opindex mfpe +@opindex mfp +This specifies the version of the floating point emulation available on +the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym +for @option{-mfpe=}, for compatibility with older versions of GCC@. + +@item -mstructure-size-boundary=@var{n} +@opindex mstructure-size-boundary +The size of all structures and unions will be rounded up to a multiple +of the number of bits set by this option. Permissible values are 8 and +32. The default value varies for different toolchains. For the COFF +targeted toolchain the default value is 8. Specifying the larger number +can produce faster, more efficient code, but can also increase the size +of the program. The two values are potentially incompatible. Code +compiled with one value cannot necessarily expect to work with code or +libraries compiled with the other value, if they exchange information +using structures or unions. + +@item -mabort-on-noreturn +@opindex mabort-on-noreturn +Generate a call to the function @code{abort} at the end of a +@code{noreturn} function. It will be executed if the function tries to +return. + +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Tells the compiler to perform function calls by first loading the +address of the function into a register and then performing a subroutine +call on this register. This switch is needed if the target function +will lie outside of the 64 megabyte addressing range of the offset based +version of subroutine call instruction. + +Even if this switch is enabled, not all function calls will be turned +into long calls. The heuristic is that static functions, functions +which have the @samp{short-call} attribute, functions that are inside +the scope of a @samp{#pragma no_long_calls} directive and functions whose +definitions have already been compiled within the current compilation +unit, will not be turned into long calls. The exception to this rule is +that weak function definitions, functions with the @samp{long-call} +attribute or the @samp{section} attribute, and functions that are within +the scope of a @samp{#pragma long_calls} directive, will always be +turned into long calls. + +This feature is not enabled by default. Specifying +@option{-mno-long-calls} will restore the default behavior, as will +placing the function calls within the scope of a @samp{#pragma +long_calls_off} directive. Note these switches have no effect on how +the compiler generates code to handle function calls via function +pointers. + +@item -mnop-fun-dllimport +@opindex mnop-fun-dllimport +Disable support for the @code{dllimport} attribute. + +@item -msingle-pic-base +@opindex msingle-pic-base +Treat the register used for PIC addressing as read-only, rather than +loading it in the prologue for each function. The run-time system is +responsible for initializing this register with an appropriate value +before execution begins. + +@item -mpic-register=@var{reg} +@opindex mpic-register +Specify the register to be used for PIC addressing. The default is R10 +unless stack-checking is enabled, when R9 is used. + +@item -mpoke-function-name +@opindex mpoke-function-name +Write the name of each function into the text section, directly +preceding the function prologue. The generated code is similar to this: + +@smallexample + t0 + .ascii "arm_poke_function_name", 0 + .align + t1 + .word 0xff000000 + (t1 - t0) + arm_poke_function_name + mov ip, sp + stmfd sp!, @{fp, ip, lr, pc@} + sub fp, ip, #4 +@end smallexample + +When performing a stack backtrace, code can inspect the value of +@code{pc} stored at @code{fp + 0}. If the trace function then looks at +location @code{pc - 12} and the top 8 bits are set, then we know that +there is a function name embedded immediately preceding this location +and has length @code{((pc[-3]) & 0xff000000)}. + +@item -mthumb +@opindex mthumb +Generate code for the 16-bit Thumb instruction set. The default is to +use the 32-bit ARM instruction set. + +@item -mtpcs-frame +@opindex mtpcs-frame +Generate a stack frame that is compliant with the Thumb Procedure Call +Standard for all non-leaf functions. (A leaf function is one that does +not call any other functions.) The default is @option{-mno-tpcs-frame}. + +@item -mtpcs-leaf-frame +@opindex mtpcs-leaf-frame +Generate a stack frame that is compliant with the Thumb Procedure Call +Standard for all leaf functions. (A leaf function is one that does +not call any other functions.) The default is @option{-mno-apcs-leaf-frame}. + +@item -mcallee-super-interworking +@opindex mcallee-super-interworking +Gives all externally visible functions in the file being compiled an ARM +instruction set header which switches to Thumb mode before executing the +rest of the function. This allows these functions to be called from +non-interworking code. + +@item -mcaller-super-interworking +@opindex mcaller-super-interworking +Allows calls via function pointers (including virtual functions) to +execute correctly regardless of whether the target code has been +compiled for interworking or not. There is a small overhead in the cost +of executing a function pointer if this option is enabled. + +@end table + +@node MN10200 Options +@subsection MN10200 Options +@cindex MN10200 options +These @option{-m} options are defined for Matsushita MN10200 architectures: +@table @gcctabopt + +@item -mrelax +@opindex mrelax +Indicate to the linker that it should perform a relaxation optimization pass +to shorten branches, calls and absolute memory addresses. This option only +has an effect when used on the command line for the final link step. + +This option makes symbolic debugging impossible. +@end table + +@node MN10300 Options +@subsection MN10300 Options +@cindex MN10300 options +These @option{-m} options are defined for Matsushita MN10300 architectures: + +@table @gcctabopt +@item -mmult-bug +@opindex mmult-bug +Generate code to avoid bugs in the multiply instructions for the MN10300 +processors. This is the default. + +@item -mno-mult-bug +@opindex mno-mult-bug +Do not generate code to avoid bugs in the multiply instructions for the +MN10300 processors. + +@item -mam33 +@opindex mam33 +Generate code which uses features specific to the AM33 processor. + +@item -mno-am33 +@opindex mno-am33 +Do not generate code which uses features specific to the AM33 processor. This +is the default. + +@item -mno-crt0 +@opindex mno-crt0 +Do not link in the C run-time initialization object file. + +@item -mrelax +@opindex mrelax +Indicate to the linker that it should perform a relaxation optimization pass +to shorten branches, calls and absolute memory addresses. This option only +has an effect when used on the command line for the final link step. + +This option makes symbolic debugging impossible. +@end table + + +@node M32R/D Options +@subsection M32R/D Options +@cindex M32R/D options + +These @option{-m} options are defined for Mitsubishi M32R/D architectures: + +@table @gcctabopt +@item -m32rx +@opindex m32rx +Generate code for the M32R/X@. + +@item -m32r +@opindex m32r +Generate code for the M32R@. This is the default. + +@item -mcode-model=small +@opindex mcode-model=small +Assume all objects live in the lower 16MB of memory (so that their addresses +can be loaded with the @code{ld24} instruction), and assume all subroutines +are reachable with the @code{bl} instruction. +This is the default. + +The addressability of a particular object can be set with the +@code{model} attribute. + +@item -mcode-model=medium +@opindex mcode-model=medium +Assume objects may be anywhere in the 32-bit address space (the compiler +will generate @code{seth/add3} instructions to load their addresses), and +assume all subroutines are reachable with the @code{bl} instruction. + +@item -mcode-model=large +@opindex mcode-model=large +Assume objects may be anywhere in the 32-bit address space (the compiler +will generate @code{seth/add3} instructions to load their addresses), and +assume subroutines may not be reachable with the @code{bl} instruction +(the compiler will generate the much slower @code{seth/add3/jl} +instruction sequence). + +@item -msdata=none +@opindex msdata=none +Disable use of the small data area. Variables will be put into +one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the +@code{section} attribute has been specified). +This is the default. + +The small data area consists of sections @samp{.sdata} and @samp{.sbss}. +Objects may be explicitly put in the small data area with the +@code{section} attribute using one of these sections. + +@item -msdata=sdata +@opindex msdata=sdata +Put small global and static data in the small data area, but do not +generate special code to reference them. + +@item -msdata=use +@opindex msdata=use +Put small global and static data in the small data area, and generate +special instructions to reference them. + +@item -G @var{num} +@opindex G +@cindex smaller data references +Put global and static objects less than or equal to @var{num} bytes +into the small data or bss sections instead of the normal data or bss +sections. The default value of @var{num} is 8. +The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use} +for this option to have any effect. + +All modules should be compiled with the same @option{-G @var{num}} value. +Compiling with different values of @var{num} may or may not work; if it +doesn't the linker will give an error message---incorrect code will not be +generated. + +@end table + +@node M88K Options +@subsection M88K Options +@cindex M88k options + +These @samp{-m} options are defined for Motorola 88k architectures: + +@table @gcctabopt +@item -m88000 +@opindex m88000 +Generate code that works well on both the m88100 and the +m88110. + +@item -m88100 +@opindex m88100 +Generate code that works best for the m88100, but that also +runs on the m88110. + +@item -m88110 +@opindex m88110 +Generate code that works best for the m88110, and may not run +on the m88100. + +@item -mbig-pic +@opindex mbig-pic +Obsolete option to be removed from the next revision. +Use @option{-fPIC}. + +@item -midentify-revision +@opindex midentify-revision +@cindex identifying source, compiler (88k) +Include an @code{ident} directive in the assembler output recording the +source file name, compiler name and version, timestamp, and compilation +flags used. + +@item -mno-underscores +@opindex mno-underscores +@cindex underscores, avoiding (88k) +In assembler output, emit symbol names without adding an underscore +character at the beginning of each name. The default is to use an +underscore as prefix on each name. + +@item -mocs-debug-info +@itemx -mno-ocs-debug-info +@opindex mocs-debug-info +@opindex mno-ocs-debug-info +@cindex OCS (88k) +@cindex debugging, 88k OCS +Include (or omit) additional debugging information (about registers used +in each stack frame) as specified in the 88open Object Compatibility +Standard, ``OCS''@. This extra information allows debugging of code that +has had the frame pointer eliminated. The default for DG/UX, SVr4, and +Delta 88 SVr3.2 is to include this information; other 88k configurations +omit this information by default. + +@item -mocs-frame-position +@opindex mocs-frame-position +@cindex register positions in frame (88k) +When emitting COFF debugging information for automatic variables and +parameters stored on the stack, use the offset from the canonical frame +address, which is the stack pointer (register 31) on entry to the +function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use +@option{-mocs-frame-position}; other 88k configurations have the default +@option{-mno-ocs-frame-position}. + +@item -mno-ocs-frame-position +@opindex mno-ocs-frame-position +@cindex register positions in frame (88k) +When emitting COFF debugging information for automatic variables and +parameters stored on the stack, use the offset from the frame pointer +register (register 30). When this option is in effect, the frame +pointer is not eliminated when debugging information is selected by the +-g switch. + +@item -moptimize-arg-area +@opindex moptimize-arg-area +@cindex arguments in frame (88k) +Save space by reorganizing the stack frame. This option generates code +that does not agree with the 88open specifications, but uses less +memory. + +@itemx -mno-optimize-arg-area +@opindex mno-optimize-arg-area +Do not reorganize the stack frame to save space. This is the default. +The generated conforms to the specification, but uses more memory. + +@item -mshort-data-@var{num} +@opindex mshort-data +@cindex smaller data references (88k) +@cindex r0-relative references (88k) +Generate smaller data references by making them relative to @code{r0}, +which allows loading a value using a single instruction (rather than the +usual two). You control which data references are affected by +specifying @var{num} with this option. For example, if you specify +@option{-mshort-data-512}, then the data references affected are those +involving displacements of less than 512 bytes. +@option{-mshort-data-@var{num}} is not effective for @var{num} greater +than 64k. + +@item -mserialize-volatile +@opindex mserialize-volatile +@itemx -mno-serialize-volatile +@opindex mno-serialize-volatile +@cindex sequential consistency on 88k +Do, or don't, generate code to guarantee sequential consistency +of volatile memory references. By default, consistency is +guaranteed. + +The order of memory references made by the MC88110 processor does +not always match the order of the instructions requesting those +references. In particular, a load instruction may execute before +a preceding store instruction. Such reordering violates +sequential consistency of volatile memory references, when there +are multiple processors. When consistency must be guaranteed, +GCC generates special instructions, as needed, to force +execution in the proper order. + +The MC88100 processor does not reorder memory references and so +always provides sequential consistency. However, by default, GCC +generates the special instructions to guarantee consistency +even when you use @option{-m88100}, so that the code may be run on an +MC88110 processor. If you intend to run your code only on the +MC88100 processor, you may use @option{-mno-serialize-volatile}. + +The extra code generated to guarantee consistency may affect the +performance of your application. If you know that you can safely +forgo this guarantee, you may use @option{-mno-serialize-volatile}. + +@item -msvr4 +@itemx -msvr3 +@opindex msvr4 +@opindex msvr3 +@cindex assembler syntax, 88k +@cindex SVr4 +Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions +related to System V release 4 (SVr4). This controls the following: + +@enumerate +@item +Which variant of the assembler syntax to emit. +@item +@option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak} +that is used on System V release 4. +@item +@option{-msvr4} makes GCC issue additional declaration directives used in +SVr4. +@end enumerate + +@option{-msvr4} is the default for the m88k-motorola-sysv4 and +m88k-dg-dgux m88k configurations. @option{-msvr3} is the default for all +other m88k configurations. + +@item -mversion-03.00 +@opindex mversion-03.00 +This option is obsolete, and is ignored. +@c ??? which asm syntax better for GAS? option there too? + +@item -mno-check-zero-division +@itemx -mcheck-zero-division +@opindex mno-check-zero-division +@opindex mcheck-zero-division +@cindex zero division on 88k +Do, or don't, generate code to guarantee that integer division by +zero will be detected. By default, detection is guaranteed. + +Some models of the MC88100 processor fail to trap upon integer +division by zero under certain conditions. By default, when +compiling code that might be run on such a processor, GCC +generates code that explicitly checks for zero-valued divisors +and traps with exception number 503 when one is detected. Use of +@option{-mno-check-zero-division} suppresses such checking for code +generated to run on an MC88100 processor. + +GCC assumes that the MC88110 processor correctly detects all instances +of integer division by zero. When @option{-m88110} is specified, no +explicit checks for zero-valued divisors are generated, and both +@option{-mcheck-zero-division} and @option{-mno-check-zero-division} are +ignored. + +@item -muse-div-instruction +@opindex muse-div-instruction +@cindex divide instruction, 88k +Use the div instruction for signed integer division on the +MC88100 processor. By default, the div instruction is not used. + +On the MC88100 processor the signed integer division instruction +div) traps to the operating system on a negative operand. The +operating system transparently completes the operation, but at a +large cost in execution time. By default, when compiling code +that might be run on an MC88100 processor, GCC emulates signed +integer division using the unsigned integer division instruction +divu), thereby avoiding the large penalty of a trap to the +operating system. Such emulation has its own, smaller, execution +cost in both time and space. To the extent that your code's +important signed integer division operations are performed on two +nonnegative operands, it may be desirable to use the div +instruction directly. + +On the MC88110 processor the div instruction (also known as the +divs instruction) processes negative operands without trapping to +the operating system. When @option{-m88110} is specified, +@option{-muse-div-instruction} is ignored, and the div instruction is used +for signed integer division. + +Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In +particular, the behavior of such a division with and without +@option{-muse-div-instruction} may differ. + +@item -mtrap-large-shift +@itemx -mhandle-large-shift +@opindex mtrap-large-shift +@opindex mhandle-large-shift +@cindex bit shift overflow (88k) +@cindex large bit shifts (88k) +Include code to detect bit-shifts of more than 31 bits; respectively, +trap such shifts or emit code to handle them properly. By default GCC +makes no special provision for large bit shifts. + +@item -mwarn-passed-structs +@opindex mwarn-passed-structs +@cindex structure passing (88k) +Warn when a function passes a struct as an argument or result. +Structure-passing conventions have changed during the evolution of the C +language, and are often the source of portability problems. By default, +GCC issues no such warning. +@end table + +@c break page here to avoid unsightly interparagraph stretch. +@c -zw, 2001-8-17 +@page + +@node RS/6000 and PowerPC Options +@subsection IBM RS/6000 and PowerPC Options +@cindex RS/6000 and PowerPC Options +@cindex IBM RS/6000 and PowerPC Options + +These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: +@table @gcctabopt +@item -mpower +@itemx -mno-power +@itemx -mpower2 +@itemx -mno-power2 +@itemx -mpowerpc +@itemx -mno-powerpc +@itemx -mpowerpc-gpopt +@itemx -mno-powerpc-gpopt +@itemx -mpowerpc-gfxopt +@itemx -mno-powerpc-gfxopt +@itemx -mpowerpc64 +@itemx -mno-powerpc64 +@opindex mpower +@opindex mno-power +@opindex mpower2 +@opindex mno-power2 +@opindex mpowerpc +@opindex mno-powerpc +@opindex mpowerpc-gpopt +@opindex mno-powerpc-gpopt +@opindex mpowerpc-gfxopt +@opindex mno-powerpc-gfxopt +@opindex mpowerpc64 +@opindex mno-powerpc64 +GCC supports two related instruction set architectures for the +RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those +instructions supported by the @samp{rios} chip set used in the original +RS/6000 systems and the @dfn{PowerPC} instruction set is the +architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and +the IBM 4xx microprocessors. + +Neither architecture is a subset of the other. However there is a +large common subset of instructions supported by both. An MQ +register is included in processors supporting the POWER architecture. + +You use these options to specify which instructions are available on the +processor you are using. The default value of these options is +determined when configuring GCC@. Specifying the +@option{-mcpu=@var{cpu_type}} overrides the specification of these +options. We recommend you use the @option{-mcpu=@var{cpu_type}} option +rather than the options listed above. + +The @option{-mpower} option allows GCC to generate instructions that +are found only in the POWER architecture and to use the MQ register. +Specifying @option{-mpower2} implies @option{-power} and also allows GCC +to generate instructions that are present in the POWER2 architecture but +not the original POWER architecture. + +The @option{-mpowerpc} option allows GCC to generate instructions that +are found only in the 32-bit subset of the PowerPC architecture. +Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows +GCC to use the optional PowerPC architecture instructions in the +General Purpose group, including floating-point square root. Specifying +@option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to +use the optional PowerPC architecture instructions in the Graphics +group, including floating-point select. + +The @option{-mpowerpc64} option allows GCC to generate the additional +64-bit instructions that are found in the full PowerPC64 architecture +and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to +@option{-mno-powerpc64}. + +If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC +will use only the instructions in the common subset of both +architectures plus some special AIX common-mode calls, and will not use +the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc} +permits GCC to use any instruction from either architecture and to +allow use of the MQ register; specify this for the Motorola MPC601. + +@item -mnew-mnemonics +@itemx -mold-mnemonics +@opindex mnew-mnemonics +@opindex mold-mnemonics +Select which mnemonics to use in the generated assembler code. With +@option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for +the PowerPC architecture. With @option{-mold-mnemonics} it uses the +assembler mnemonics defined for the POWER architecture. Instructions +defined in only one architecture have only one mnemonic; GCC uses that +mnemonic irrespective of which of these options is specified. + +GCC defaults to the mnemonics appropriate for the architecture in +use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the +value of these option. Unless you are building a cross-compiler, you +should normally not specify either @option{-mnew-mnemonics} or +@option{-mold-mnemonics}, but should instead accept the default. + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set architecture type, register usage, choice of mnemonics, and +instruction scheduling parameters for machine type @var{cpu_type}. +Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1}, +@samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602}, +@samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620}, +@samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750}, +@samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505}, +@samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}. + +@option{-mcpu=common} selects a completely generic processor. Code +generated under this option will run on any POWER or PowerPC processor. +GCC will use only the instructions in the common subset of both +architectures, and will not use the MQ register. GCC assumes a generic +processor model for scheduling purposes. + +@option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and +@option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit +PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine +types, with an appropriate, generic processor model assumed for +scheduling purposes. + +The other options specify a specific processor. Code generated under +those options will run best on that processor, and may not run at all on +others. + +The @option{-mcpu} options automatically enable or disable other +@option{-m} options as follows: + +@table @samp +@item common +@option{-mno-power}, @option{-mno-powerc} + +@item power +@itemx power2 +@itemx rios1 +@itemx rios2 +@itemx rsc +@option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics} + +@item powerpc +@itemx rs64a +@itemx 602 +@itemx 603 +@itemx 603e +@itemx 604 +@itemx 620 +@itemx 630 +@itemx 740 +@itemx 7400 +@itemx 7450 +@itemx 750 +@itemx 505 +@option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics} + +@item 601 +@option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics} + +@item 403 +@itemx 821 +@itemx 860 +@option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float} +@end table + +@item -mtune=@var{cpu_type} +@opindex mtune +Set the instruction scheduling parameters for machine type +@var{cpu_type}, but do not set the architecture type, register usage, or +choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same +values for @var{cpu_type} are used for @option{-mtune} as for +@option{-mcpu}. If both are specified, the code generated will use the +architecture, registers, and mnemonics set by @option{-mcpu}, but the +scheduling parameters set by @option{-mtune}. + +@item -maltivec +@itemx -mno-altivec +@opindex maltivec +@opindex mno-altivec +These switches enable or disable the use of built-in functions that +allow access to the AltiVec instruction set. You may also need to set +@option{-mabi=altivec} to adjust the current ABI with AltiVec ABI +enhancements. + +@item -mfull-toc +@itemx -mno-fp-in-toc +@itemx -mno-sum-in-toc +@itemx -mminimal-toc +@opindex mfull-toc +@opindex mno-fp-in-toc +@opindex mno-sum-in-toc +@opindex mminimal-toc +Modify generation of the TOC (Table Of Contents), which is created for +every executable file. The @option{-mfull-toc} option is selected by +default. In that case, GCC will allocate at least one TOC entry for +each unique non-automatic variable reference in your program. GCC +will also place floating-point constants in the TOC@. However, only +16,384 entries are available in the TOC@. + +If you receive a linker error message that saying you have overflowed +the available TOC space, you can reduce the amount of TOC space used +with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options. +@option{-mno-fp-in-toc} prevents GCC from putting floating-point +constants in the TOC and @option{-mno-sum-in-toc} forces GCC to +generate code to calculate the sum of an address and a constant at +run-time instead of putting that sum into the TOC@. You may specify one +or both of these options. Each causes GCC to produce very slightly +slower and larger code at the expense of conserving TOC space. + +If you still run out of space in the TOC even when you specify both of +these options, specify @option{-mminimal-toc} instead. This option causes +GCC to make only one TOC entry for every file. When you specify this +option, GCC will produce code that is slower and larger but which +uses extremely little TOC space. You may wish to use this option +only on files that contain less frequently executed code. + +@item -maix64 +@itemx -maix32 +@opindex maix64 +@opindex maix32 +Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit +@code{long} type, and the infrastructure needed to support them. +Specifying @option{-maix64} implies @option{-mpowerpc64} and +@option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and +implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}. + +@item -mxl-call +@itemx -mno-xl-call +@opindex mxl-call +@opindex mno-xl-call +On AIX, pass floating-point arguments to prototyped functions beyond the +register save area (RSA) on the stack in addition to argument FPRs. The +AIX calling convention was extended but not initially documented to +handle an obscure K&R C case of calling a function that takes the +address of its arguments with fewer arguments than declared. AIX XL +compilers access floating point arguments which do not fit in the +RSA from the stack when a subroutine is compiled without +optimization. Because always storing floating-point arguments on the +stack is inefficient and rarely needed, this option is not enabled by +default and only is necessary when calling subroutines compiled by AIX +XL compilers without optimization. + +@item -mpe +@opindex mpe +Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an +application written to use message passing with special startup code to +enable the application to run. The system must have PE installed in the +standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file +must be overridden with the @option{-specs=} option to specify the +appropriate directory location. The Parallel Environment does not +support threads, so the @option{-mpe} option and the @option{-pthread} +option are incompatible. + +@item -msoft-float +@itemx -mhard-float +@opindex msoft-float +@opindex mhard-float +Generate code that does not use (uses) the floating-point register set. +Software floating point emulation is provided if you use the +@option{-msoft-float} option, and pass the option to GCC when linking. + +@item -mmultiple +@itemx -mno-multiple +@opindex mmultiple +@opindex mno-multiple +Generate code that uses (does not use) the load multiple word +instructions and the store multiple word instructions. These +instructions are generated by default on POWER systems, and not +generated on PowerPC systems. Do not use @option{-mmultiple} on little +endian PowerPC systems, since those instructions do not work when the +processor is in little endian mode. The exceptions are PPC740 and +PPC750 which permit the instructions usage in little endian mode. + +@item -mstring +@itemx -mno-string +@opindex mstring +@opindex mno-string +Generate code that uses (does not use) the load string instructions +and the store string word instructions to save multiple registers and +do small block moves. These instructions are generated by default on +POWER systems, and not generated on PowerPC systems. Do not use +@option{-mstring} on little endian PowerPC systems, since those +instructions do not work when the processor is in little endian mode. +The exceptions are PPC740 and PPC750 which permit the instructions +usage in little endian mode. + +@item -mupdate +@itemx -mno-update +@opindex mupdate +@opindex mno-update +Generate code that uses (does not use) the load or store instructions +that update the base register to the address of the calculated memory +location. These instructions are generated by default. If you use +@option{-mno-update}, there is a small window between the time that the +stack pointer is updated and the address of the previous frame is +stored, which means code that walks the stack frame across interrupts or +signals may get corrupted data. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Generate code that uses (does not use) the floating point multiply and +accumulate instructions. These instructions are generated by default if +hardware floating is used. + +@item -mno-bit-align +@itemx -mbit-align +@opindex mno-bit-align +@opindex mbit-align +On System V.4 and embedded PowerPC systems do not (do) force structures +and unions that contain bit-fields to be aligned to the base type of the +bit-field. + +For example, by default a structure containing nothing but 8 +@code{unsigned} bit-fields of length 1 would be aligned to a 4 byte +boundary and have a size of 4 bytes. By using @option{-mno-bit-align}, +the structure would be aligned to a 1 byte boundary and be one byte in +size. + +@item -mno-strict-align +@itemx -mstrict-align +@opindex mno-strict-align +@opindex mstrict-align +On System V.4 and embedded PowerPC systems do not (do) assume that +unaligned memory references will be handled by the system. + +@item -mrelocatable +@itemx -mno-relocatable +@opindex mrelocatable +@opindex mno-relocatable +On embedded PowerPC systems generate code that allows (does not allow) +the program to be relocated to a different address at runtime. If you +use @option{-mrelocatable} on any module, all objects linked together must +be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}. + +@item -mrelocatable-lib +@itemx -mno-relocatable-lib +@opindex mrelocatable-lib +@opindex mno-relocatable-lib +On embedded PowerPC systems generate code that allows (does not allow) +the program to be relocated to a different address at runtime. Modules +compiled with @option{-mrelocatable-lib} can be linked with either modules +compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or +with modules compiled with the @option{-mrelocatable} options. + +@item -mno-toc +@itemx -mtoc +@opindex mno-toc +@opindex mtoc +On System V.4 and embedded PowerPC systems do not (do) assume that +register 2 contains a pointer to a global area pointing to the addresses +used in the program. + +@item -mlittle +@itemx -mlittle-endian +@opindex mlittle +@opindex mlittle-endian +On System V.4 and embedded PowerPC systems compile code for the +processor in little endian mode. The @option{-mlittle-endian} option is +the same as @option{-mlittle}. + +@item -mbig +@itemx -mbig-endian +@opindex mbig +@opindex mbig-endian +On System V.4 and embedded PowerPC systems compile code for the +processor in big endian mode. The @option{-mbig-endian} option is +the same as @option{-mbig}. + +@item -mcall-sysv +@opindex mcall-sysv +On System V.4 and embedded PowerPC systems compile code using calling +conventions that adheres to the March 1995 draft of the System V +Application Binary Interface, PowerPC processor supplement. This is the +default unless you configured GCC using @samp{powerpc-*-eabiaix}. + +@item -mcall-sysv-eabi +@opindex mcall-sysv-eabi +Specify both @option{-mcall-sysv} and @option{-meabi} options. + +@item -mcall-sysv-noeabi +@opindex mcall-sysv-noeabi +Specify both @option{-mcall-sysv} and @option{-mno-eabi} options. + +@item -mcall-aix +@opindex mcall-aix +On System V.4 and embedded PowerPC systems compile code using calling +conventions that are similar to those used on AIX@. This is the +default if you configured GCC using @samp{powerpc-*-eabiaix}. + +@item -mcall-solaris +@opindex mcall-solaris +On System V.4 and embedded PowerPC systems compile code for the Solaris +operating system. + +@item -mcall-linux +@opindex mcall-linux +On System V.4 and embedded PowerPC systems compile code for the +Linux-based GNU system. + +@item -mcall-gnu +@opindex mcall-gnu +On System V.4 and embedded PowerPC systems compile code for the +Hurd-based GNU system. + +@item -mcall-netbsd +@opindex mcall-netbsd +On System V.4 and embedded PowerPC systems compile code for the +NetBSD operating system. + +@item -maix-struct-return +@opindex maix-struct-return +Return all structures in memory (as specified by the AIX ABI)@. + +@item -msvr4-struct-return +@opindex msvr4-struct-return +Return structures smaller than 8 bytes in registers (as specified by the +SVR4 ABI)@. + +@item -mabi=altivec +@opindex mabi=altivec +Extend the current ABI with AltiVec ABI extensions. This does not +change the default ABI, instead it adds the AltiVec ABI extensions to +the current ABI@. + +@item -mprototype +@itemx -mno-prototype +@opindex mprototype +@opindex mno-prototype +On System V.4 and embedded PowerPC systems assume that all calls to +variable argument functions are properly prototyped. Otherwise, the +compiler must insert an instruction before every non prototyped call to +set or clear bit 6 of the condition code register (@var{CR}) to +indicate whether floating point values were passed in the floating point +registers in case the function takes a variable arguments. With +@option{-mprototype}, only calls to prototyped variable argument functions +will set or clear the bit. + +@item -msim +@opindex msim +On embedded PowerPC systems, assume that the startup module is called +@file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and +@file{libc.a}. This is the default for @samp{powerpc-*-eabisim}. +configurations. + +@item -mmvme +@opindex mmvme +On embedded PowerPC systems, assume that the startup module is called +@file{crt0.o} and the standard C libraries are @file{libmvme.a} and +@file{libc.a}. + +@item -mads +@opindex mads +On embedded PowerPC systems, assume that the startup module is called +@file{crt0.o} and the standard C libraries are @file{libads.a} and +@file{libc.a}. + +@item -myellowknife +@opindex myellowknife +On embedded PowerPC systems, assume that the startup module is called +@file{crt0.o} and the standard C libraries are @file{libyk.a} and +@file{libc.a}. + +@item -mvxworks +@opindex mvxworks +On System V.4 and embedded PowerPC systems, specify that you are +compiling for a VxWorks system. + +@item -memb +@opindex memb +On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags +header to indicate that @samp{eabi} extended relocations are used. + +@item -meabi +@itemx -mno-eabi +@opindex meabi +@opindex mno-eabi +On System V.4 and embedded PowerPC systems do (do not) adhere to the +Embedded Applications Binary Interface (eabi) which is a set of +modifications to the System V.4 specifications. Selecting @option{-meabi} +means that the stack is aligned to an 8 byte boundary, a function +@code{__eabi} is called to from @code{main} to set up the eabi +environment, and the @option{-msdata} option can use both @code{r2} and +@code{r13} to point to two separate small data areas. Selecting +@option{-mno-eabi} means that the stack is aligned to a 16 byte boundary, +do not call an initialization function from @code{main}, and the +@option{-msdata} option will only use @code{r13} to point to a single +small data area. The @option{-meabi} option is on by default if you +configured GCC using one of the @samp{powerpc*-*-eabi*} options. + +@item -msdata=eabi +@opindex msdata=eabi +On System V.4 and embedded PowerPC systems, put small initialized +@code{const} global and static data in the @samp{.sdata2} section, which +is pointed to by register @code{r2}. Put small initialized +non-@code{const} global and static data in the @samp{.sdata} section, +which is pointed to by register @code{r13}. Put small uninitialized +global and static data in the @samp{.sbss} section, which is adjacent to +the @samp{.sdata} section. The @option{-msdata=eabi} option is +incompatible with the @option{-mrelocatable} option. The +@option{-msdata=eabi} option also sets the @option{-memb} option. + +@item -msdata=sysv +@opindex msdata=sysv +On System V.4 and embedded PowerPC systems, put small global and static +data in the @samp{.sdata} section, which is pointed to by register +@code{r13}. Put small uninitialized global and static data in the +@samp{.sbss} section, which is adjacent to the @samp{.sdata} section. +The @option{-msdata=sysv} option is incompatible with the +@option{-mrelocatable} option. + +@item -msdata=default +@itemx -msdata +@opindex msdata=default +@opindex msdata +On System V.4 and embedded PowerPC systems, if @option{-meabi} is used, +compile code the same as @option{-msdata=eabi}, otherwise compile code the +same as @option{-msdata=sysv}. + +@item -msdata-data +@opindex msdata-data +On System V.4 and embedded PowerPC systems, put small global and static +data in the @samp{.sdata} section. Put small uninitialized global and +static data in the @samp{.sbss} section. Do not use register @code{r13} +to address small data however. This is the default behavior unless +other @option{-msdata} options are used. + +@item -msdata=none +@itemx -mno-sdata +@opindex msdata=none +@opindex mno-sdata +On embedded PowerPC systems, put all initialized global and static data +in the @samp{.data} section, and all uninitialized data in the +@samp{.bss} section. + +@item -G @var{num} +@opindex G +@cindex smaller data references (PowerPC) +@cindex .sdata/.sdata2 references (PowerPC) +On embedded PowerPC systems, put global and static items less than or +equal to @var{num} bytes into the small data or bss sections instead of +the normal data or bss section. By default, @var{num} is 8. The +@option{-G @var{num}} switch is also passed to the linker. +All modules should be compiled with the same @option{-G @var{num}} value. + +@item -mregnames +@itemx -mno-regnames +@opindex mregnames +@opindex mno-regnames +On System V.4 and embedded PowerPC systems do (do not) emit register +names in the assembly language output using symbolic forms. + +@item -pthread +@opindex pthread +Adds support for multithreading with the @dfn{pthreads} library. +This option sets flags for both the preprocessor and linker. + +@end table + +@node RT Options +@subsection IBM RT Options +@cindex RT options +@cindex IBM RT options + +These @samp{-m} options are defined for the IBM RT PC: + +@table @gcctabopt +@item -min-line-mul +@opindex min-line-mul +Use an in-line code sequence for integer multiplies. This is the +default. + +@item -mcall-lib-mul +@opindex mcall-lib-mul +Call @code{lmul$$} for integer multiples. + +@item -mfull-fp-blocks +@opindex mfull-fp-blocks +Generate full-size floating point data blocks, including the minimum +amount of scratch space recommended by IBM@. This is the default. + +@item -mminimum-fp-blocks +@opindex mminimum-fp-blocks +Do not include extra scratch space in floating point data blocks. This +results in smaller code, but slower execution, since scratch space must +be allocated dynamically. + +@cindex @file{varargs.h} and RT PC +@cindex @file{stdarg.h} and RT PC +@item -mfp-arg-in-fpregs +@opindex mfp-arg-in-fpregs +Use a calling sequence incompatible with the IBM calling convention in +which floating point arguments are passed in floating point registers. +Note that @code{varargs.h} and @code{stdarg.h} will not work with +floating point operands if this option is specified. + +@item -mfp-arg-in-gregs +@opindex mfp-arg-in-gregs +Use the normal calling convention for floating point arguments. This is +the default. + +@item -mhc-struct-return +@opindex mhc-struct-return +Return structures of more than one word in memory, rather than in a +register. This provides compatibility with the MetaWare HighC (hc) +compiler. Use the option @option{-fpcc-struct-return} for compatibility +with the Portable C Compiler (pcc). + +@item -mnohc-struct-return +@opindex mnohc-struct-return +Return some structures of more than one word in registers, when +convenient. This is the default. For compatibility with the +IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the +option @option{-mhc-struct-return}. +@end table + +@node MIPS Options +@subsection MIPS Options +@cindex MIPS options + +These @samp{-m} options are defined for the MIPS family of computers: + +@table @gcctabopt + +@item -march=@var{cpu-type} +@opindex march +Assume the defaults for the machine type @var{cpu-type} when generating +instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000}, +@samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400}, +@samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000}, +and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000}, +@samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as +@samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. + +@item -mtune=@var{cpu-type} +@opindex mtune +Assume the defaults for the machine type @var{cpu-type} when scheduling +instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000}, +@samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400}, +@samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000}, +and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000}, +@samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as +@samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. While picking a specific +@var{cpu-type} will schedule things appropriately for that particular +chip, the compiler will not generate any code that does not meet level 1 +of the MIPS ISA (instruction set architecture) without a @option{-mipsX} +or @option{-mabi} switch being used. + +@item -mcpu=@var{cpu-type} +@opindex mcpu +This is identical to specifying both @option{-march} and @option{-mtune}. + +@item -mips1 +@opindex mips1 +Issue instructions from level 1 of the MIPS ISA@. This is the default. +@samp{r3000} is the default @var{cpu-type} at this ISA level. + +@item -mips2 +@opindex mips2 +Issue instructions from level 2 of the MIPS ISA (branch likely, square +root instructions). @samp{r6000} is the default @var{cpu-type} at this +ISA level. + +@item -mips3 +@opindex mips3 +Issue instructions from level 3 of the MIPS ISA (64-bit instructions). +@samp{r4000} is the default @var{cpu-type} at this ISA level. + +@item -mips4 +@opindex mips4 +Issue instructions from level 4 of the MIPS ISA (conditional move, +prefetch, enhanced FPU instructions). @samp{r8000} is the default +@var{cpu-type} at this ISA level. + +@item -mfp32 +@opindex mfp32 +Assume that 32 32-bit floating point registers are available. This is +the default. + +@item -mfp64 +@opindex mfp64 +Assume that 32 64-bit floating point registers are available. This is +the default when the @option{-mips3} option is used. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Generate code that uses (does not use) the floating point multiply and +accumulate instructions, when they are available. These instructions +are generated by default if they are available, but this may be +undesirable if the extra precision causes problems or on certain chips +in the mode where denormals are rounded to zero where denormals +generated by multiply and accumulate instructions cause exceptions +anyway. + +@item -mgp32 +@opindex mgp32 +Assume that 32 32-bit general purpose registers are available. This is +the default. + +@item -mgp64 +@opindex mgp64 +Assume that 32 64-bit general purpose registers are available. This is +the default when the @option{-mips3} option is used. + +@item -mint64 +@opindex mint64 +Force int and long types to be 64 bits wide. See @option{-mlong32} for an +explanation of the default, and the width of pointers. + +@item -mlong64 +@opindex mlong64 +Force long types to be 64 bits wide. See @option{-mlong32} for an +explanation of the default, and the width of pointers. + +@item -mlong32 +@opindex mlong32 +Force long, int, and pointer types to be 32 bits wide. + +If none of @option{-mlong32}, @option{-mlong64}, or @option{-mint64} are set, +the size of ints, longs, and pointers depends on the ABI and ISA chosen. +For @option{-mabi=32}, and @option{-mabi=n32}, ints and longs are 32 bits +wide. For @option{-mabi=64}, ints are 32 bits, and longs are 64 bits wide. +For @option{-mabi=eabi} and either @option{-mips1} or @option{-mips2}, ints +and longs are 32 bits wide. For @option{-mabi=eabi} and higher ISAs, ints +are 32 bits, and longs are 64 bits wide. The width of pointer types is +the smaller of the width of longs or the width of general purpose +registers (which in turn depends on the ISA)@. + +@item -mabi=32 +@itemx -mabi=o64 +@itemx -mabi=n32 +@itemx -mabi=64 +@itemx -mabi=eabi +@opindex mabi=32 +@opindex mabi=o64 +@opindex mabi=n32 +@opindex mabi=64 +@opindex mabi=eabi +Generate code for the indicated ABI@. The default instruction level is +@option{-mips1} for @samp{32}, @option{-mips3} for @samp{n32}, and +@option{-mips4} otherwise. Conversely, with @option{-mips1} or +@option{-mips2}, the default ABI is @samp{32}; otherwise, the default ABI +is @samp{64}. + +@item -mmips-as +@opindex mmips-as +Generate code for the MIPS assembler, and invoke @file{mips-tfile} to +add normal debug information. This is the default for all +platforms except for the OSF/1 reference platform, using the OSF/rose +object format. If the either of the @option{-gstabs} or @option{-gstabs+} +switches are used, the @file{mips-tfile} program will encapsulate the +stabs within MIPS ECOFF@. + +@item -mgas +@opindex mgas +Generate code for the GNU assembler. This is the default on the OSF/1 +reference platform, using the OSF/rose object format. Also, this is +the default if the configure option @option{--with-gnu-as} is used. + +@item -msplit-addresses +@itemx -mno-split-addresses +@opindex msplit-addresses +@opindex mno-split-addresses +Generate code to load the high and low parts of address constants separately. +This allows GCC to optimize away redundant loads of the high order +bits of addresses. This optimization requires GNU as and GNU ld. +This optimization is enabled by default for some embedded targets where +GNU as and GNU ld are standard. + +@item -mrnames +@itemx -mno-rnames +@opindex mrnames +@opindex mno-rnames +The @option{-mrnames} switch says to output code using the MIPS software +names for the registers, instead of the hardware names (ie, @var{a0} +instead of @var{$4}). The only known assembler that supports this option +is the Algorithmics assembler. + +@item -mgpopt +@itemx -mno-gpopt +@opindex mgpopt +@opindex mno-gpopt +The @option{-mgpopt} switch says to write all of the data declarations +before the instructions in the text section, this allows the MIPS +assembler to generate one word memory references instead of using two +words for short global or static data items. This is on by default if +optimization is selected. + +@item -mstats +@itemx -mno-stats +@opindex mstats +@opindex mno-stats +For each non-inline function processed, the @option{-mstats} switch +causes the compiler to emit one line to the standard error file to +print statistics about the program (number of registers saved, stack +size, etc.). + +@item -mmemcpy +@itemx -mno-memcpy +@opindex mmemcpy +@opindex mno-memcpy +The @option{-mmemcpy} switch makes all block moves call the appropriate +string function (@samp{memcpy} or @samp{bcopy}) instead of possibly +generating inline code. + +@item -mmips-tfile +@itemx -mno-mips-tfile +@opindex mmips-tfile +@opindex mno-mips-tfile +The @option{-mno-mips-tfile} switch causes the compiler not +postprocess the object file with the @file{mips-tfile} program, +after the MIPS assembler has generated it to add debug support. If +@file{mips-tfile} is not run, then no local variables will be +available to the debugger. In addition, @file{stage2} and +@file{stage3} objects will have the temporary file names passed to the +assembler embedded in the object file, which means the objects will +not compare the same. The @option{-mno-mips-tfile} switch should only +be used when there are bugs in the @file{mips-tfile} program that +prevents compilation. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not part of GCC@. +Normally the facilities of the machine's usual C compiler are used, but +this can't be done directly in cross-compilation. You must make your +own arrangements to provide suitable library functions for +cross-compilation. + +@item -mhard-float +@opindex mhard-float +Generate output containing floating point instructions. This is the +default if you use the unmodified sources. + +@item -mabicalls +@itemx -mno-abicalls +@opindex mabicalls +@opindex mno-abicalls +Emit (or do not emit) the pseudo operations @samp{.abicalls}, +@samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for +position independent code. + +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Do all calls with the @samp{JALR} instruction, which requires +loading up a function's address into a register before the call. +You need to use this switch, if you call outside of the current +512 megabyte segment to functions that are not through pointers. + +@item -mhalf-pic +@itemx -mno-half-pic +@opindex mhalf-pic +@opindex mno-half-pic +Put pointers to extern references into the data section and load them +up, rather than put the references in the text section. + +@item -membedded-pic +@itemx -mno-embedded-pic +@opindex membedded-pic +@opindex mno-embedded-pic +Generate PIC code suitable for some embedded systems. All calls are +made using PC relative address, and all data is addressed using the $gp +register. No more than 65536 bytes of global data may be used. This +requires GNU as and GNU ld which do most of the work. This currently +only works on targets which use ECOFF; it does not work with ELF@. + +@item -membedded-data +@itemx -mno-embedded-data +@opindex membedded-data +@opindex mno-embedded-data +Allocate variables to the read-only data section first if possible, then +next in the small data section if possible, otherwise in data. This gives +slightly slower code than the default, but reduces the amount of RAM required +when executing, and thus may be preferred for some embedded systems. + +@item -muninit-const-in-rodata +@itemx -mno-uninit-const-in-rodata +@opindex muninit-const-in-rodata +@opindex mno-uninit-const-in-rodata +When used together with @option{-membedded-data}, it will always store uninitialized +const variables in the read-only data section. + +@item -msingle-float +@itemx -mdouble-float +@opindex msingle-float +@opindex mdouble-float +The @option{-msingle-float} switch tells gcc to assume that the floating +point coprocessor only supports single precision operations, as on the +@samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use +double precision operations. This is the default. + +@item -mmad +@itemx -mno-mad +@opindex mmad +@opindex mno-mad +Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions, +as on the @samp{r4650} chip. + +@item -m4650 +@opindex m4650 +Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now, +@option{-mcpu=r4650}. + +@item -mips16 +@itemx -mno-mips16 +@opindex mips16 +@opindex mno-mips16 +Enable 16-bit instructions. + +@item -mentry +@opindex mentry +Use the entry and exit pseudo ops. This option can only be used with +@option{-mips16}. + +@item -EL +@opindex EL +Compile code for the processor in little endian mode. +The requisite libraries are assumed to exist. + +@item -EB +@opindex EB +Compile code for the processor in big endian mode. +The requisite libraries are assumed to exist. + +@item -G @var{num} +@opindex G +@cindex smaller data references (MIPS) +@cindex gp-relative references (MIPS) +Put global and static items less than or equal to @var{num} bytes into +the small data or bss sections instead of the normal data or bss +section. This allows the assembler to emit one word memory reference +instructions based on the global pointer (@var{gp} or @var{$28}), +instead of the normal two words used. By default, @var{num} is 8 when +the MIPS assembler is used, and 0 when the GNU assembler is used. The +@option{-G @var{num}} switch is also passed to the assembler and linker. +All modules should be compiled with the same @option{-G @var{num}} +value. + +@item -nocpp +@opindex nocpp +Tell the MIPS assembler to not run its preprocessor over user +assembler files (with a @samp{.s} suffix) when assembling them. + +@item -mfix7000 +@opindex mfix7000 +Pass an option to gas which will cause nops to be inserted if +the read of the destination register of an mfhi or mflo instruction +occurs in the following two instructions. + +@item -no-crt0 +@opindex no-crt0 +Do not include the default crt0. + +@item -mflush-func=@var{func} +@itemx -mno-flush-func +@opindex mflush-func +Specifies the function to call to flush the I and D caches, or to not +call any such function. If called, the function must take the same +arguments as the common @code{_flush_func()}, that is, the address of the +memory range for which the cache is being flushed, the size of the +memory range, and the number 3 (to flush both caches). The default +depends on the target gcc was configured for, but commonly is either +@samp{_flush_func} or @samp{__cpu_flush}. +@end table + +These options are defined by the macro +@code{TARGET_SWITCHES} in the machine description. The default for the +options is also defined by that macro, which enables you to change the +defaults. + +@node i386 and x86-64 Options +@subsection Intel 386 and AMD x86-64 Options +@cindex i386 Options +@cindex x86-64 Options +@cindex Intel 386 Options +@cindex AMD x86-64 Options + +These @samp{-m} options are defined for the i386 and x86-64 family of +computers: + +@table @gcctabopt +@item -mcpu=@var{cpu-type} +@opindex mcpu +Tune to @var{cpu-type} everything applicable about the generated code, except +for the ABI and the set of available instructions. The choices for +@var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686}, +@samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2}, +@samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3}, +@samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp} +and @samp{athlon-mp}. + +While picking a specific @var{cpu-type} will schedule things appropriately +for that particular chip, the compiler will not generate any code that +does not run on the i386 without the @option{-march=@var{cpu-type}} option +being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686} +is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the +AMD chips as opposed to the Intel ones. + +@item -march=@var{cpu-type} +@opindex march +Generate instructions for the machine type @var{cpu-type}. The choices +for @var{cpu-type} are the same as for @option{-mcpu}. Moreover, +specifying @option{-march=@var{cpu-type}} implies @option{-mcpu=@var{cpu-type}}. + +@item -m386 +@itemx -m486 +@itemx -mpentium +@itemx -mpentiumpro +@opindex m386 +@opindex m486 +@opindex mpentium +@opindex mpentiumpro +These options are synonyms for @option{-mcpu=i386}, @option{-mcpu=i486}, +@option{-mcpu=pentium}, and @option{-mcpu=pentiumpro} respectively. +These synonyms are deprecated. + +@item -mfpmath=@var{unit} +@opindex march +generate floating point arithmetics for selected unit @var{unit}. the choices +for @var{unit} are: + +@table @samp +@item 387 +Use the standard 387 floating point coprocessor present majority of chips and +emulated otherwise. Code compiled with this option will run almost everywhere. +The temporary results are computed in 80bit precesion instead of precision +specified by the type resulting in slightly different results compared to most +of other chips. See @option{-ffloat-store} for more detailed description. + +This is the default choice for i386 compiler. + +@item sse +Use scalar floating point instructions present in the SSE instruction set. +This instruction set is supported by Pentium3 and newer chips, in the AMD line +by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE +instruction set supports only single precision arithmetics, thus the double and +extended precision arithmetics is still done using 387. Later version, present +only in Pentium4 and the future AMD x86-64 chips supports double precision +arithmetics too. + +For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or +@option{-msse2} switches to enable SSE extensions and make this option +effective. For x86-64 compiler, these extensions are enabled by default. + +The resulting code should be considerably faster in majority of cases and avoid +the numerical instability problems of 387 code, but may break some existing +code that expects temporaries to be 80bit. + +This is the default choice for x86-64 compiler. + +@item sse,387 +Attempt to utilize both instruction sets at once. This effectivly double the +amount of available registers and on chips with separate execution units for +387 and SSE the execution resources too. Use this option with care, as it is +still experimental, because gcc register allocator does not model separate +functional units well resulting in instable performance. +@end table + +@item -masm=@var{dialect} +@opindex masm=@var{dialect} +Output asm instructions using selected @var{dialect}. Supported choices are +@samp{intel} or @samp{att} (the default one). + +@item -mieee-fp +@itemx -mno-ieee-fp +@opindex mieee-fp +@opindex mno-ieee-fp +Control whether or not the compiler uses IEEE floating point +comparisons. These handle correctly the case where the result of a +comparison is unordered. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not part of GCC@. +Normally the facilities of the machine's usual C compiler are used, but +this can't be done directly in cross-compilation. You must make your +own arrangements to provide suitable library functions for +cross-compilation. + +On machines where a function returns floating point results in the 80387 +register stack, some floating point opcodes may be emitted even if +@option{-msoft-float} is used. + +@item -mno-fp-ret-in-387 +@opindex mno-fp-ret-in-387 +Do not use the FPU registers for return values of functions. + +The usual calling convention has functions return values of types +@code{float} and @code{double} in an FPU register, even if there +is no FPU@. The idea is that the operating system should emulate +an FPU@. + +The option @option{-mno-fp-ret-in-387} causes such values to be returned +in ordinary CPU registers instead. + +@item -mno-fancy-math-387 +@opindex mno-fancy-math-387 +Some 387 emulators do not support the @code{sin}, @code{cos} and +@code{sqrt} instructions for the 387. Specify this option to avoid +generating those instructions. This option is the default on FreeBSD@. +As of revision 2.6.1, these instructions are not generated unless you +also use the @option{-funsafe-math-optimizations} switch. + +@item -malign-double +@itemx -mno-align-double +@opindex malign-double +@opindex mno-align-double +Control whether GCC aligns @code{double}, @code{long double}, and +@code{long long} variables on a two word boundary or a one word +boundary. Aligning @code{double} variables on a two word boundary will +produce code that runs somewhat faster on a @samp{Pentium} at the +expense of more memory. + +@item -m128bit-long-double +@opindex m128bit-long-double +Control the size of @code{long double} type. i386 application binary interface +specify the size to be 12 bytes, while modern architectures (Pentium and newer) +prefer @code{long double} aligned to 8 or 16 byte boundary. This is +impossible to reach with 12 byte long doubles in the array accesses. + +@strong{Warning:} if you use the @option{-m128bit-long-double} switch, the +structures and arrays containing @code{long double} will change their size as +well as function calling convention for function taking @code{long double} +will be modified. + +@item -m96bit-long-double +@opindex m96bit-long-double +Set the size of @code{long double} to 96 bits as required by the i386 +application binary interface. This is the default. + +@item -msvr3-shlib +@itemx -mno-svr3-shlib +@opindex msvr3-shlib +@opindex mno-svr3-shlib +Control whether GCC places uninitialized local variables into the +@code{bss} or @code{data} segments. @option{-msvr3-shlib} places them +into @code{bss}. These options are meaningful only on System V Release 3. + +@item -mrtd +@opindex mrtd +Use a different function-calling convention, in which functions that +take a fixed number of arguments return with the @code{ret} @var{num} +instruction, which pops their arguments while returning. This saves one +instruction in the caller since there is no need to pop the arguments +there. + +You can specify that an individual function is called with this calling +sequence with the function attribute @samp{stdcall}. You can also +override the @option{-mrtd} option by using the function attribute +@samp{cdecl}. @xref{Function Attributes}. + +@strong{Warning:} this calling convention is incompatible with the one +normally used on Unix, so you cannot use it if you need to call +libraries compiled with the Unix compiler. + +Also, you must provide function prototypes for all functions that +take variable numbers of arguments (including @code{printf}); +otherwise incorrect code will be generated for calls to those +functions. + +In addition, seriously incorrect code will result if you call a +function with too many arguments. (Normally, extra arguments are +harmlessly ignored.) + +@item -mregparm=@var{num} +@opindex mregparm +Control how many registers are used to pass integer arguments. By +default, no registers are used to pass arguments, and at most 3 +registers can be used. You can control this behavior for a specific +function by using the function attribute @samp{regparm}. +@xref{Function Attributes}. + +@strong{Warning:} if you use this switch, and +@var{num} is nonzero, then you must build all modules with the same +value, including any libraries. This includes the system libraries and +startup modules. + +@item -mpreferred-stack-boundary=@var{num} +@opindex mpreferred-stack-boundary +Attempt to keep the stack boundary aligned to a 2 raised to @var{num} +byte boundary. If @option{-mpreferred-stack-boundary} is not specified, +the default is 4 (16 bytes or 128 bits), except when optimizing for code +size (@option{-Os}), in which case the default is the minimum correct +alignment (4 bytes for x86, and 8 bytes for x86-64). + +On Pentium and PentiumPro, @code{double} and @code{long double} values +should be aligned to an 8 byte boundary (see @option{-malign-double}) or +suffer significant run time performance penalties. On Pentium III, the +Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar +penalties if it is not 16 byte aligned. + +To ensure proper alignment of this values on the stack, the stack boundary +must be as aligned as that required by any value stored on the stack. +Further, every function must be generated such that it keeps the stack +aligned. Thus calling a function compiled with a higher preferred +stack boundary from a function compiled with a lower preferred stack +boundary will most likely misalign the stack. It is recommended that +libraries that use callbacks always use the default setting. + +This extra alignment does consume extra stack space, and generally +increases code size. Code that is sensitive to stack space usage, such +as embedded systems and operating system kernels, may want to reduce the +preferred alignment to @option{-mpreferred-stack-boundary=2}. + +@item -mmmx +@itemx -mno-mmx +@item -msse +@itemx -mno-sse +@item -msse2 +@itemx -mno-sse2 +@item -m3dnow +@itemx -mno-3dnow +@opindex mmmx +@opindex mno-mmx +@opindex msse +@opindex mno-sse +@opindex m3dnow +@opindex mno-3dnow +These switches enable or disable the use of built-in functions that allow +direct access to the MMX, SSE and 3Dnow extensions of the instruction set. + +@xref{X86 Built-in Functions}, for details of the functions enabled +and disabled by these switches. + +@item -mpush-args +@itemx -mno-push-args +@opindex mpush-args +@opindex mno-push-args +Use PUSH operations to store outgoing parameters. This method is shorter +and usually equally fast as method using SUB/MOV operations and is enabled +by default. In some cases disabling it may improve performance because of +improved scheduling and reduced dependencies. + +@item -maccumulate-outgoing-args +@opindex maccumulate-outgoing-args +If enabled, the maximum amount of space required for outgoing arguments will be +computed in the function prologue. This is faster on most modern CPUs +because of reduced dependencies, improved scheduling and reduced stack usage +when preferred stack boundary is not equal to 2. The drawback is a notable +increase in code size. This switch implies @option{-mno-push-args}. + +@item -mthreads +@opindex mthreads +Support thread-safe exception handling on @samp{Mingw32}. Code that relies +on thread-safe exception handling must compile and link all code with the +@option{-mthreads} option. When compiling, @option{-mthreads} defines +@option{-D_MT}; when linking, it links in a special thread helper library +@option{-lmingwthrd} which cleans up per thread exception handling data. + +@item -mno-align-stringops +@opindex mno-align-stringops +Do not align destination of inlined string operations. This switch reduces +code size and improves performance in case the destination is already aligned, +but gcc don't know about it. + +@item -minline-all-stringops +@opindex minline-all-stringops +By default GCC inlines string operations only when destination is known to be +aligned at least to 4 byte boundary. This enables more inlining, increase code +size, but may improve performance of code that depends on fast memcpy, strlen +and memset for short lengths. + +@item -momit-leaf-frame-pointer +@opindex momit-leaf-frame-pointer +Don't keep the frame pointer in a register for leaf functions. This +avoids the instructions to save, set up and restore frame pointers and +makes an extra register available in leaf functions. The option +@option{-fomit-frame-pointer} removes the frame pointer for all functions +which might make debugging harder. +@end table + +These @samp{-m} switches are supported in addition to the above +on AMD x86-64 processors in 64-bit environments. + +@table @gcctabopt +@item -m32 +@itemx -m64 +@opindex m32 +@opindex m64 +Generate code for a 32-bit or 64-bit environment. +The 32-bit environment sets int, long and pointer to 32 bits and +generates code that runs on any i386 system. +The 64-bit environment sets int to 32 bits and long and pointer +to 64 bits and generates code for AMD's x86-64 architecture. + +@item -mno-red-zone +@opindex no-red-zone +Do not use a so called red zone for x86-64 code. The red zone is mandated +by the x86-64 ABI, it is a 128-byte area beyond the location of the +stack pointer that will not be modified by signal or interrupt handlers +and therefore can be used for temporary data without adjusting the stack +pointer. The flag @option{-mno-red-zone} disables this red zone. +@end table + +@node HPPA Options +@subsection HPPA Options +@cindex HPPA Options + +These @samp{-m} options are defined for the HPPA family of computers: + +@table @gcctabopt +@item -march=@var{architecture-type} +@opindex march +Generate code for the specified architecture. The choices for +@var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA +1.1, and @samp{2.0} for PA 2.0 processors. Refer to +@file{/usr/lib/sched.models} on an HP-UX system to determine the proper +architecture option for your machine. Code compiled for lower numbered +architectures will run on higher numbered architectures, but not the +other way around. + +PA 2.0 support currently requires gas snapshot 19990413 or later. The +next release of binutils (current is 2.9.1) will probably contain PA 2.0 +support. + +@item -mpa-risc-1-0 +@itemx -mpa-risc-1-1 +@itemx -mpa-risc-2-0 +@opindex mpa-risc-1-0 +@opindex mpa-risc-1-1 +@opindex mpa-risc-2-0 +Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively. + +@item -mbig-switch +@opindex mbig-switch +Generate code suitable for big switch tables. Use this option only if +the assembler/linker complain about out of range branches within a switch +table. + +@item -mjump-in-delay +@opindex mjump-in-delay +Fill delay slots of function calls with unconditional jump instructions +by modifying the return pointer for the function call to be the target +of the conditional jump. + +@item -mdisable-fpregs +@opindex mdisable-fpregs +Prevent floating point registers from being used in any manner. This is +necessary for compiling kernels which perform lazy context switching of +floating point registers. If you use this option and attempt to perform +floating point operations, the compiler will abort. + +@item -mdisable-indexing +@opindex mdisable-indexing +Prevent the compiler from using indexing address modes. This avoids some +rather obscure problems when compiling MIG generated code under MACH@. + +@item -mno-space-regs +@opindex mno-space-regs +Generate code that assumes the target has no space registers. This allows +GCC to generate faster indirect calls and use unscaled index address modes. + +Such code is suitable for level 0 PA systems and kernels. + +@item -mfast-indirect-calls +@opindex mfast-indirect-calls +Generate code that assumes calls never cross space boundaries. This +allows GCC to emit code which performs faster indirect calls. + +This option will not work in the presence of shared libraries or nested +functions. + +@item -mlong-load-store +@opindex mlong-load-store +Generate 3-instruction load and store sequences as sometimes required by +the HP-UX 10 linker. This is equivalent to the @samp{+k} option to +the HP compilers. + +@item -mportable-runtime +@opindex mportable-runtime +Use the portable calling conventions proposed by HP for ELF systems. + +@item -mgas +@opindex mgas +Enable the use of assembler directives only GAS understands. + +@item -mschedule=@var{cpu-type} +@opindex mschedule +Schedule code according to the constraints for the machine type +@var{cpu-type}. The choices for @var{cpu-type} are @samp{700} +@samp{7100}, @samp{7100LC}, @samp{7200}, and @samp{8000}. Refer to +@file{/usr/lib/sched.models} on an HP-UX system to determine the +proper scheduling option for your machine. + +@item -mlinker-opt +@opindex mlinker-opt +Enable the optimization pass in the HPUX linker. Note this makes symbolic +debugging impossible. It also triggers a bug in the HPUX 8 and HPUX 9 linkers +in which they give bogus error messages when linking some programs. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not available for all HPPA +targets. Normally the facilities of the machine's usual C compiler are +used, but this cannot be done directly in cross-compilation. You must make +your own arrangements to provide suitable library functions for +cross-compilation. The embedded target @samp{hppa1.1-*-pro} +does provide software floating point support. + +@option{-msoft-float} changes the calling convention in the output file; +therefore, it is only useful if you compile @emph{all} of a program with +this option. In particular, you need to compile @file{libgcc.a}, the +library that comes with GCC, with @option{-msoft-float} in order for +this to work. +@end table + +@node Intel 960 Options +@subsection Intel 960 Options + +These @samp{-m} options are defined for the Intel 960 implementations: + +@table @gcctabopt +@item -m@var{cpu-type} +@opindex mka +@opindex mkb +@opindex mmc +@opindex mca +@opindex mcf +@opindex msa +@opindex msb +Assume the defaults for the machine type @var{cpu-type} for some of +the other options, including instruction scheduling, floating point +support, and addressing modes. The choices for @var{cpu-type} are +@samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf}, +@samp{sa}, and @samp{sb}. +The default is +@samp{kb}. + +@item -mnumerics +@itemx -msoft-float +@opindex mnumerics +@opindex msoft-float +The @option{-mnumerics} option indicates that the processor does support +floating-point instructions. The @option{-msoft-float} option indicates +that floating-point support should not be assumed. + +@item -mleaf-procedures +@itemx -mno-leaf-procedures +@opindex mleaf-procedures +@opindex mno-leaf-procedures +Do (or do not) attempt to alter leaf procedures to be callable with the +@code{bal} instruction as well as @code{call}. This will result in more +efficient code for explicit calls when the @code{bal} instruction can be +substituted by the assembler or linker, but less efficient code in other +cases, such as calls via function pointers, or using a linker that doesn't +support this optimization. + +@item -mtail-call +@itemx -mno-tail-call +@opindex mtail-call +@opindex mno-tail-call +Do (or do not) make additional attempts (beyond those of the +machine-independent portions of the compiler) to optimize tail-recursive +calls into branches. You may not want to do this because the detection of +cases where this is not valid is not totally complete. The default is +@option{-mno-tail-call}. + +@item -mcomplex-addr +@itemx -mno-complex-addr +@opindex mcomplex-addr +@opindex mno-complex-addr +Assume (or do not assume) that the use of a complex addressing mode is a +win on this implementation of the i960. Complex addressing modes may not +be worthwhile on the K-series, but they definitely are on the C-series. +The default is currently @option{-mcomplex-addr} for all processors except +the CB and CC@. + +@item -mcode-align +@itemx -mno-code-align +@opindex mcode-align +@opindex mno-code-align +Align code to 8-byte boundaries for faster fetching (or don't bother). +Currently turned on by default for C-series implementations only. + +@ignore +@item -mclean-linkage +@itemx -mno-clean-linkage +@opindex mclean-linkage +@opindex mno-clean-linkage +These options are not fully implemented. +@end ignore + +@item -mic-compat +@itemx -mic2.0-compat +@itemx -mic3.0-compat +@opindex mic-compat +@opindex mic2.0-compat +@opindex mic3.0-compat +Enable compatibility with iC960 v2.0 or v3.0. + +@item -masm-compat +@itemx -mintel-asm +@opindex masm-compat +@opindex mintel-asm +Enable compatibility with the iC960 assembler. + +@item -mstrict-align +@itemx -mno-strict-align +@opindex mstrict-align +@opindex mno-strict-align +Do not permit (do permit) unaligned accesses. + +@item -mold-align +@opindex mold-align +Enable structure-alignment compatibility with Intel's gcc release version +1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}. + +@item -mlong-double-64 +@opindex mlong-double-64 +Implement type @samp{long double} as 64-bit floating point numbers. +Without the option @samp{long double} is implemented by 80-bit +floating point numbers. The only reason we have it because there is +no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it +is only useful for people using soft-float targets. Otherwise, we +should recommend against use of it. + +@end table + +@node DEC Alpha Options +@subsection DEC Alpha Options + +These @samp{-m} options are defined for the DEC Alpha implementations: + +@table @gcctabopt +@item -mno-soft-float +@itemx -msoft-float +@opindex mno-soft-float +@opindex msoft-float +Use (do not use) the hardware floating-point instructions for +floating-point operations. When @option{-msoft-float} is specified, +functions in @file{libgcc.a} will be used to perform floating-point +operations. Unless they are replaced by routines that emulate the +floating-point operations, or compiled in such a way as to call such +emulations routines, these routines will issue floating-point +operations. If you are compiling for an Alpha without floating-point +operations, you must ensure that the library is built so as not to call +them. + +Note that Alpha implementations without floating-point operations are +required to have floating-point registers. + +@item -mfp-reg +@itemx -mno-fp-regs +@opindex mfp-reg +@opindex mno-fp-regs +Generate code that uses (does not use) the floating-point register set. +@option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point +register set is not used, floating point operands are passed in integer +registers as if they were integers and floating-point results are passed +in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence, +so any function with a floating-point argument or return value called by code +compiled with @option{-mno-fp-regs} must also be compiled with that +option. + +A typical use of this option is building a kernel that does not use, +and hence need not save and restore, any floating-point registers. + +@item -mieee +@opindex mieee +The Alpha architecture implements floating-point hardware optimized for +maximum performance. It is mostly compliant with the IEEE floating +point standard. However, for full compliance, software assistance is +required. This option generates code fully IEEE compliant code +@emph{except} that the @var{inexact-flag} is not maintained (see below). +If this option is turned on, the preprocessor macro @code{_IEEE_FP} is +defined during compilation. The resulting code is less efficient but is +able to correctly support denormalized numbers and exceptional IEEE +values such as not-a-number and plus/minus infinity. Other Alpha +compilers call this option @option{-ieee_with_no_inexact}. + +@item -mieee-with-inexact +@opindex mieee-with-inexact +This is like @option{-mieee} except the generated code also maintains +the IEEE @var{inexact-flag}. Turning on this option causes the +generated code to implement fully-compliant IEEE math. In addition to +@code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor +macro. On some Alpha implementations the resulting code may execute +significantly slower than the code generated by default. Since there is +very little code that depends on the @var{inexact-flag}, you should +normally not specify this option. Other Alpha compilers call this +option @option{-ieee_with_inexact}. + +@item -mfp-trap-mode=@var{trap-mode} +@opindex mfp-trap-mode +This option controls what floating-point related traps are enabled. +Other Alpha compilers call this option @option{-fptm @var{trap-mode}}. +The trap mode can be set to one of four values: + +@table @samp +@item n +This is the default (normal) setting. The only traps that are enabled +are the ones that cannot be disabled in software (e.g., division by zero +trap). + +@item u +In addition to the traps enabled by @samp{n}, underflow traps are enabled +as well. + +@item su +Like @samp{su}, but the instructions are marked to be safe for software +completion (see Alpha architecture manual for details). + +@item sui +Like @samp{su}, but inexact traps are enabled as well. +@end table + +@item -mfp-rounding-mode=@var{rounding-mode} +@opindex mfp-rounding-mode +Selects the IEEE rounding mode. Other Alpha compilers call this option +@option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one +of: + +@table @samp +@item n +Normal IEEE rounding mode. Floating point numbers are rounded towards +the nearest machine number or towards the even machine number in case +of a tie. + +@item m +Round towards minus infinity. + +@item c +Chopped rounding mode. Floating point numbers are rounded towards zero. + +@item d +Dynamic rounding mode. A field in the floating point control register +(@var{fpcr}, see Alpha architecture reference manual) controls the +rounding mode in effect. The C library initializes this register for +rounding towards plus infinity. Thus, unless your program modifies the +@var{fpcr}, @samp{d} corresponds to round towards plus infinity. +@end table + +@item -mtrap-precision=@var{trap-precision} +@opindex mtrap-precision +In the Alpha architecture, floating point traps are imprecise. This +means without software assistance it is impossible to recover from a +floating trap and program execution normally needs to be terminated. +GCC can generate code that can assist operating system trap handlers +in determining the exact location that caused a floating point trap. +Depending on the requirements of an application, different levels of +precisions can be selected: + +@table @samp +@item p +Program precision. This option is the default and means a trap handler +can only identify which program caused a floating point exception. + +@item f +Function precision. The trap handler can determine the function that +caused a floating point exception. + +@item i +Instruction precision. The trap handler can determine the exact +instruction that caused a floating point exception. +@end table + +Other Alpha compilers provide the equivalent options called +@option{-scope_safe} and @option{-resumption_safe}. + +@item -mieee-conformant +@opindex mieee-conformant +This option marks the generated code as IEEE conformant. You must not +use this option unless you also specify @option{-mtrap-precision=i} and either +@option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect +is to emit the line @samp{.eflag 48} in the function prologue of the +generated assembly file. Under DEC Unix, this has the effect that +IEEE-conformant math library routines will be linked in. + +@item -mbuild-constants +@opindex mbuild-constants +Normally GCC examines a 32- or 64-bit integer constant to +see if it can construct it from smaller constants in two or three +instructions. If it cannot, it will output the constant as a literal and +generate code to load it from the data segment at runtime. + +Use this option to require GCC to construct @emph{all} integer constants +using code, even if it takes more instructions (the maximum is six). + +You would typically use this option to build a shared library dynamic +loader. Itself a shared library, it must relocate itself in memory +before it can find the variables and constants in its own data segment. + +@item -malpha-as +@itemx -mgas +@opindex malpha-as +@opindex mgas +Select whether to generate code to be assembled by the vendor-supplied +assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}. + +@item -mbwx +@itemx -mno-bwx +@itemx -mcix +@itemx -mno-cix +@itemx -mfix +@itemx -mno-fix +@itemx -mmax +@itemx -mno-max +@opindex mbwx +@opindex mno-bwx +@opindex mcix +@opindex mno-cix +@opindex mfix +@opindex mno-fix +@opindex mmax +@opindex mno-max +Indicate whether GCC should generate code to use the optional BWX, +CIX, FIX and MAX instruction sets. The default is to use the instruction +sets supported by the CPU type specified via @option{-mcpu=} option or that +of the CPU on which GCC was built if none was specified. + +@item -mfloat-vax +@itemx -mfloat-ieee +@opindex mfloat-vax +@opindex mfloat-ieee +Generate code that uses (does not use) VAX F and G floating point +arithmetic instead of IEEE single and double precision. + +@item -mexplicit-relocs +@itemx -mno-explicit-relocs +@opindex mexplicit-relocs +@opindex mno-explicit-relocs +Older Alpha assemblers provided no way to generate symbol relocations +except via assembler macros. Use of these macros does not allow +optimial instruction scheduling. GNU binutils as of version 2.12 +supports a new syntax that allows the compiler to explicitly mark +which relocations should apply to which instructions. This option +is mostly useful for debugging, as GCC detects the capabilities of +the assembler when it is built and sets the default accordingly. + +@item -msmall-data +@itemx -mlarge-data +@opindex msmall-data +@opindex mlarge-data +When @option{-mexplicit-relocs} is in effect, static data is +accessed via @dfn{gp-relative} relocations. When @option{-msmall-data} +is used, objects 8 bytes long or smaller are placed in a @dfn{small data area} +(the @code{.sdata} and @code{.sbss} sections) and are accessed via +16-bit relocations off of the @code{$gp} register. This limits the +size of the small data area to 64KB, but allows the variables to be +directly accessed via a single instruction. + +The default is @option{-mlarge-data}. With this option the data area +is limited to just below 2GB. Programs that require more than 2GB of +data must use @code{malloc} or @code{mmap} to allocate the data in the +heap instead of in the program's data segment. + +When generating code for shared libraries, @option{-fpic} implies +@option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}. + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set the instruction set and instruction scheduling parameters for +machine type @var{cpu_type}. You can specify either the @samp{EV} +style name or the corresponding chip number. GCC supports scheduling +parameters for the EV4, EV5 and EV6 family of processors and will +choose the default values for the instruction set from the processor +you specify. If you do not specify a processor type, GCC will default +to the processor on which the compiler was built. + +Supported values for @var{cpu_type} are + +@table @samp +@item ev4 +@item ev45 +@itemx 21064 +Schedules as an EV4 and has no instruction set extensions. + +@item ev5 +@itemx 21164 +Schedules as an EV5 and has no instruction set extensions. + +@item ev56 +@itemx 21164a +Schedules as an EV5 and supports the BWX extension. + +@item pca56 +@itemx 21164pc +@itemx 21164PC +Schedules as an EV5 and supports the BWX and MAX extensions. + +@item ev6 +@itemx 21264 +Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. + +@item ev67 +@item 21264a +Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. +@end table + +@item -mtune=@var{cpu_type} +@opindex mtune +Set only the instruction scheduling parameters for machine type +@var{cpu_type}. The instruction set is not changed. + +@item -mmemory-latency=@var{time} +@opindex mmemory-latency +Sets the latency the scheduler should assume for typical memory +references as seen by the application. This number is highly +dependent on the memory access patterns used by the application +and the size of the external cache on the machine. + +Valid options for @var{time} are + +@table @samp +@item @var{number} +A decimal number representing clock cycles. + +@item L1 +@itemx L2 +@itemx L3 +@itemx main +The compiler contains estimates of the number of clock cycles for +``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches +(also called Dcache, Scache, and Bcache), as well as to main memory. +Note that L3 is only valid for EV5. + +@end table +@end table + +@node DEC Alpha/VMS Options +@subsection DEC Alpha/VMS Options + +These @samp{-m} options are defined for the DEC Alpha/VMS implementations: + +@table @gcctabopt +@item -mvms-return-codes +@opindex mvms-return-codes +Return VMS condition codes from main. The default is to return POSIX +style condition (e.g.@ error) codes. +@end table + +@node Clipper Options +@subsection Clipper Options + +These @samp{-m} options are defined for the Clipper implementations: + +@table @gcctabopt +@item -mc300 +@opindex mc300 +Produce code for a C300 Clipper processor. This is the default. + +@item -mc400 +@opindex mc400 +Produce code for a C400 Clipper processor, i.e.@: use floating point +registers f8--f15. +@end table + +@node H8/300 Options +@subsection H8/300 Options + +These @samp{-m} options are defined for the H8/300 implementations: + +@table @gcctabopt +@item -mrelax +@opindex mrelax +Shorten some address references at link time, when possible; uses the +linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300, +ld.info, Using ld}, for a fuller description. + +@item -mh +@opindex mh +Generate code for the H8/300H@. + +@item -ms +@opindex ms +Generate code for the H8/S@. + +@item -ms2600 +@opindex ms2600 +Generate code for the H8/S2600. This switch must be used with @option{-ms}. + +@item -mint32 +@opindex mint32 +Make @code{int} data 32 bits by default. + +@item -malign-300 +@opindex malign-300 +On the H8/300H and H8/S, use the same alignment rules as for the H8/300. +The default for the H8/300H and H8/S is to align longs and floats on 4 +byte boundaries. +@option{-malign-300} causes them to be aligned on 2 byte boundaries. +This option has no effect on the H8/300. +@end table + +@node SH Options +@subsection SH Options + +These @samp{-m} options are defined for the SH implementations: + +@table @gcctabopt +@item -m1 +@opindex m1 +Generate code for the SH1. + +@item -m2 +@opindex m2 +Generate code for the SH2. + +@item -m3 +@opindex m3 +Generate code for the SH3. + +@item -m3e +@opindex m3e +Generate code for the SH3e. + +@item -m4-nofpu +@opindex m4-nofpu +Generate code for the SH4 without a floating-point unit. + +@item -m4-single-only +@opindex m4-single-only +Generate code for the SH4 with a floating-point unit that only +supports single-precision arithmetic. + +@item -m4-single +@opindex m4-single +Generate code for the SH4 assuming the floating-point unit is in +single-precision mode by default. + +@item -m4 +@opindex m4 +Generate code for the SH4. + +@item -mb +@opindex mb +Compile code for the processor in big endian mode. + +@item -ml +@opindex ml +Compile code for the processor in little endian mode. + +@item -mdalign +@opindex mdalign +Align doubles at 64-bit boundaries. Note that this changes the calling +conventions, and thus some functions from the standard C library will +not work unless you recompile it first with @option{-mdalign}. + +@item -mrelax +@opindex mrelax +Shorten some address references at link time, when possible; uses the +linker option @option{-relax}. + +@item -mbigtable +@opindex mbigtable +Use 32-bit offsets in @code{switch} tables. The default is to use +16-bit offsets. + +@item -mfmovd +@opindex mfmovd +Enable the use of the instruction @code{fmovd}. + +@item -mhitachi +@opindex mhitachi +Comply with the calling conventions defined by Hitachi. + +@item -mnomacsave +@opindex mnomacsave +Mark the @code{MAC} register as call-clobbered, even if +@option{-mhitachi} is given. + +@item -mieee +@opindex mieee +Increase IEEE-compliance of floating-point code. + +@item -misize +@opindex misize +Dump instruction size and location in the assembly code. + +@item -mpadstruct +@opindex mpadstruct +This option is deprecated. It pads structures to multiple of 4 bytes, +which is incompatible with the SH ABI@. + +@item -mspace +@opindex mspace +Optimize for space instead of speed. Implied by @option{-Os}. + +@item -mprefergot +@opindex mprefergot +When generating position-independent code, emit function calls using +the Global Offset Table instead of the Procedure Linkage Table. + +@item -musermode +@opindex musermode +Generate a library function call to invalidate instruction cache +entries, after fixing up a trampoline. This library function call +doesn't assume it can write to the whole memory address space. This +is the default when the target is @code{sh-*-linux*}. +@end table + +@node System V Options +@subsection Options for System V + +These additional options are available on System V Release 4 for +compatibility with other compilers on those systems: + +@table @gcctabopt +@item -G +@opindex G +Create a shared object. +It is recommended that @option{-symbolic} or @option{-shared} be used instead. + +@item -Qy +@opindex Qy +Identify the versions of each tool used by the compiler, in a +@code{.ident} assembler directive in the output. + +@item -Qn +@opindex Qn +Refrain from adding @code{.ident} directives to the output file (this is +the default). + +@item -YP,@var{dirs} +@opindex YP +Search the directories @var{dirs}, and no others, for libraries +specified with @option{-l}. + +@item -Ym,@var{dir} +@opindex Ym +Look in the directory @var{dir} to find the M4 preprocessor. +The assembler uses this option. +@c This is supposed to go with a -Yd for predefined M4 macro files, but +@c the generic assembler that comes with Solaris takes just -Ym. +@end table + +@node TMS320C3x/C4x Options +@subsection TMS320C3x/C4x Options +@cindex TMS320C3x/C4x Options + +These @samp{-m} options are defined for TMS320C3x/C4x implementations: + +@table @gcctabopt + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set the instruction set, register set, and instruction scheduling +parameters for machine type @var{cpu_type}. Supported values for +@var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and +@samp{c44}. The default is @samp{c40} to generate code for the +TMS320C40. + +@item -mbig-memory +@item -mbig +@itemx -msmall-memory +@itemx -msmall +@opindex mbig-memory +@opindex mbig +@opindex msmall-memory +@opindex msmall +Generates code for the big or small memory model. The small memory +model assumed that all data fits into one 64K word page. At run-time +the data page (DP) register must be set to point to the 64K page +containing the .bss and .data program sections. The big memory model is +the default and requires reloading of the DP register for every direct +memory access. + +@item -mbk +@itemx -mno-bk +@opindex mbk +@opindex mno-bk +Allow (disallow) allocation of general integer operands into the block +count register BK@. + +@item -mdb +@itemx -mno-db +@opindex mdb +@opindex mno-db +Enable (disable) generation of code using decrement and branch, +DBcond(D), instructions. This is enabled by default for the C4x. To be +on the safe side, this is disabled for the C3x, since the maximum +iteration count on the C3x is @math{2^23 + 1} (but who iterates loops more than +@math{2^23} times on the C3x?). Note that GCC will try to reverse a loop so +that it can utilise the decrement and branch instruction, but will give +up if there is more than one memory reference in the loop. Thus a loop +where the loop counter is decremented can generate slightly more +efficient code, in cases where the RPTB instruction cannot be utilised. + +@item -mdp-isr-reload +@itemx -mparanoid +@opindex mdp-isr-reload +@opindex mparanoid +Force the DP register to be saved on entry to an interrupt service +routine (ISR), reloaded to point to the data section, and restored on +exit from the ISR@. This should not be required unless someone has +violated the small memory model by modifying the DP register, say within +an object library. + +@item -mmpyi +@itemx -mno-mpyi +@opindex mmpyi +@opindex mno-mpyi +For the C3x use the 24-bit MPYI instruction for integer multiplies +instead of a library call to guarantee 32-bit results. Note that if one +of the operands is a constant, then the multiplication will be performed +using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x, +then squaring operations are performed inline instead of a library call. + +@item -mfast-fix +@itemx -mno-fast-fix +@opindex mfast-fix +@opindex mno-fast-fix +The C3x/C4x FIX instruction to convert a floating point value to an +integer value chooses the nearest integer less than or equal to the +floating point value rather than to the nearest integer. Thus if the +floating point number is negative, the result will be incorrectly +truncated an additional code is necessary to detect and correct this +case. This option can be used to disable generation of the additional +code required to correct the result. + +@item -mrptb +@itemx -mno-rptb +@opindex mrptb +@opindex mno-rptb +Enable (disable) generation of repeat block sequences using the RPTB +instruction for zero overhead looping. The RPTB construct is only used +for innermost loops that do not call functions or jump across the loop +boundaries. There is no advantage having nested RPTB loops due to the +overhead required to save and restore the RC, RS, and RE registers. +This is enabled by default with @option{-O2}. + +@item -mrpts=@var{count} +@itemx -mno-rpts +@opindex mrpts +@opindex mno-rpts +Enable (disable) the use of the single instruction repeat instruction +RPTS@. If a repeat block contains a single instruction, and the loop +count can be guaranteed to be less than the value @var{count}, GCC will +emit a RPTS instruction instead of a RPTB@. If no value is specified, +then a RPTS will be emitted even if the loop count cannot be determined +at compile time. Note that the repeated instruction following RPTS does +not have to be reloaded from memory each iteration, thus freeing up the +CPU buses for operands. However, since interrupts are blocked by this +instruction, it is disabled by default. + +@item -mloop-unsigned +@itemx -mno-loop-unsigned +@opindex mloop-unsigned +@opindex mno-loop-unsigned +The maximum iteration count when using RPTS and RPTB (and DB on the C40) +is @math{2^31 + 1} since these instructions test if the iteration count is +negative to terminate the loop. If the iteration count is unsigned +there is a possibility than the @math{2^31 + 1} maximum iteration count may be +exceeded. This switch allows an unsigned iteration count. + +@item -mti +@opindex mti +Try to emit an assembler syntax that the TI assembler (asm30) is happy +with. This also enforces compatibility with the API employed by the TI +C3x C compiler. For example, long doubles are passed as structures +rather than in floating point registers. + +@item -mregparm +@itemx -mmemparm +@opindex mregparm +@opindex mmemparm +Generate code that uses registers (stack) for passing arguments to functions. +By default, arguments are passed in registers where possible rather +than by pushing arguments on to the stack. + +@item -mparallel-insns +@itemx -mno-parallel-insns +@opindex mparallel-insns +@opindex mno-parallel-insns +Allow the generation of parallel instructions. This is enabled by +default with @option{-O2}. + +@item -mparallel-mpy +@itemx -mno-parallel-mpy +@opindex mparallel-mpy +@opindex mno-parallel-mpy +Allow the generation of MPY||ADD and MPY||SUB parallel instructions, +provided @option{-mparallel-insns} is also specified. These instructions have +tight register constraints which can pessimize the code generation +of large functions. + +@end table + +@node V850 Options +@subsection V850 Options +@cindex V850 Options + +These @samp{-m} options are defined for V850 implementations: + +@table @gcctabopt +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Treat all calls as being far away (near). If calls are assumed to be +far away, the compiler will always load the functions address up into a +register, and call indirect through the pointer. + +@item -mno-ep +@itemx -mep +@opindex mno-ep +@opindex mep +Do not optimize (do optimize) basic blocks that use the same index +pointer 4 or more times to copy pointer into the @code{ep} register, and +use the shorter @code{sld} and @code{sst} instructions. The @option{-mep} +option is on by default if you optimize. + +@item -mno-prolog-function +@itemx -mprolog-function +@opindex mno-prolog-function +@opindex mprolog-function +Do not use (do use) external functions to save and restore registers at +the prolog and epilog of a function. The external functions are slower, +but use less code space if more than one function saves the same number +of registers. The @option{-mprolog-function} option is on by default if +you optimize. + +@item -mspace +@opindex mspace +Try to make the code as small as possible. At present, this just turns +on the @option{-mep} and @option{-mprolog-function} options. + +@item -mtda=@var{n} +@opindex mtda +Put static or global variables whose size is @var{n} bytes or less into +the tiny data area that register @code{ep} points to. The tiny data +area can hold up to 256 bytes in total (128 bytes for byte references). + +@item -msda=@var{n} +@opindex msda +Put static or global variables whose size is @var{n} bytes or less into +the small data area that register @code{gp} points to. The small data +area can hold up to 64 kilobytes. + +@item -mzda=@var{n} +@opindex mzda +Put static or global variables whose size is @var{n} bytes or less into +the first 32 kilobytes of memory. + +@item -mv850 +@opindex mv850 +Specify that the target processor is the V850. + +@item -mbig-switch +@opindex mbig-switch +Generate code suitable for big switch tables. Use this option only if +the assembler/linker complain about out of range branches within a switch +table. +@end table + +@node ARC Options +@subsection ARC Options +@cindex ARC Options + +These options are defined for ARC implementations: + +@table @gcctabopt +@item -EL +@opindex EL +Compile code for little endian mode. This is the default. + +@item -EB +@opindex EB +Compile code for big endian mode. + +@item -mmangle-cpu +@opindex mmangle-cpu +Prepend the name of the cpu to all public symbol names. +In multiple-processor systems, there are many ARC variants with different +instruction and register set characteristics. This flag prevents code +compiled for one cpu to be linked with code compiled for another. +No facility exists for handling variants that are ``almost identical''. +This is an all or nothing option. + +@item -mcpu=@var{cpu} +@opindex mcpu +Compile code for ARC variant @var{cpu}. +Which variants are supported depend on the configuration. +All variants support @option{-mcpu=base}, this is the default. + +@item -mtext=@var{text-section} +@itemx -mdata=@var{data-section} +@itemx -mrodata=@var{readonly-data-section} +@opindex mtext +@opindex mdata +@opindex mrodata +Put functions, data, and readonly data in @var{text-section}, +@var{data-section}, and @var{readonly-data-section} respectively +by default. This can be overridden with the @code{section} attribute. +@xref{Variable Attributes}. + +@end table + +@node NS32K Options +@subsection NS32K Options +@cindex NS32K options + +These are the @samp{-m} options defined for the 32000 series. The default +values for these options depends on which style of 32000 was selected when +the compiler was configured; the defaults for the most common choices are +given below. + +@table @gcctabopt +@item -m32032 +@itemx -m32032 +@opindex m32032 +@opindex m32032 +Generate output for a 32032. This is the default +when the compiler is configured for 32032 and 32016 based systems. + +@item -m32332 +@itemx -m32332 +@opindex m32332 +@opindex m32332 +Generate output for a 32332. This is the default +when the compiler is configured for 32332-based systems. + +@item -m32532 +@itemx -m32532 +@opindex m32532 +@opindex m32532 +Generate output for a 32532. This is the default +when the compiler is configured for 32532-based systems. + +@item -m32081 +@opindex m32081 +Generate output containing 32081 instructions for floating point. +This is the default for all systems. + +@item -m32381 +@opindex m32381 +Generate output containing 32381 instructions for floating point. This +also implies @option{-m32081}. The 32381 is only compatible with the 32332 +and 32532 cpus. This is the default for the pc532-netbsd configuration. + +@item -mmulti-add +@opindex mmulti-add +Try and generate multiply-add floating point instructions @code{polyF} +and @code{dotF}. This option is only available if the @option{-m32381} +option is in effect. Using these instructions requires changes to +register allocation which generally has a negative impact on +performance. This option should only be enabled when compiling code +particularly likely to make heavy use of multiply-add instructions. + +@item -mnomulti-add +@opindex mnomulti-add +Do not try and generate multiply-add floating point instructions +@code{polyF} and @code{dotF}. This is the default on all platforms. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries may not be available. + +@item -mnobitfield +@opindex mnobitfield +Do not use the bit-field instructions. On some machines it is faster to +use shifting and masking operations. This is the default for the pc532. + +@item -mbitfield +@opindex mbitfield +Do use the bit-field instructions. This is the default for all platforms +except the pc532. + +@item -mrtd +@opindex mrtd +Use a different function-calling convention, in which functions +that take a fixed number of arguments return pop their +arguments on return with the @code{ret} instruction. + +This calling convention is incompatible with the one normally +used on Unix, so you cannot use it if you need to call libraries +compiled with the Unix compiler. + +Also, you must provide function prototypes for all functions that +take variable numbers of arguments (including @code{printf}); +otherwise incorrect code will be generated for calls to those +functions. + +In addition, seriously incorrect code will result if you call a +function with too many arguments. (Normally, extra arguments are +harmlessly ignored.) + +This option takes its name from the 680x0 @code{rtd} instruction. + + +@item -mregparam +@opindex mregparam +Use a different function-calling convention where the first two arguments +are passed in registers. + +This calling convention is incompatible with the one normally +used on Unix, so you cannot use it if you need to call libraries +compiled with the Unix compiler. + +@item -mnoregparam +@opindex mnoregparam +Do not pass any arguments in registers. This is the default for all +targets. + +@item -msb +@opindex msb +It is OK to use the sb as an index register which is always loaded with +zero. This is the default for the pc532-netbsd target. + +@item -mnosb +@opindex mnosb +The sb register is not available for use or has not been initialized to +zero by the run time system. This is the default for all targets except +the pc532-netbsd. It is also implied whenever @option{-mhimem} or +@option{-fpic} is set. + +@item -mhimem +@opindex mhimem +Many ns32000 series addressing modes use displacements of up to 512MB@. +If an address is above 512MB then displacements from zero can not be used. +This option causes code to be generated which can be loaded above 512MB@. +This may be useful for operating systems or ROM code. + +@item -mnohimem +@opindex mnohimem +Assume code will be loaded in the first 512MB of virtual address space. +This is the default for all platforms. + + +@end table + +@node AVR Options +@subsection AVR Options +@cindex AVR Options + +These options are defined for AVR implementations: + +@table @gcctabopt +@item -mmcu=@var{mcu} +@opindex mmcu +Specify ATMEL AVR instruction set or MCU type. + +Instruction set avr1 is for the minimal AVR core, not supported by the C +compiler, only for assembler programs (MCU types: at90s1200, attiny10, +attiny11, attiny12, attiny15, attiny28). + +Instruction set avr2 (default) is for the classic AVR core with up to +8K program memory space (MCU types: at90s2313, at90s2323, attiny22, +at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515, +at90c8534, at90s8535). + +Instruction set avr3 is for the classic AVR core with up to 128K program +memory space (MCU types: atmega103, atmega603, at43usb320, at76c711). + +Instruction set avr4 is for the enhanced AVR core with up to 8K program +memory space (MCU types: atmega8, atmega83, atmega85). + +Instruction set avr5 is for the enhanced AVR core with up to 128K program +memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323, +atmega64, atmega128, at43usb355, at94k). + +@item -msize +@opindex msize +Output instruction sizes to the asm file. + +@item -minit-stack=@var{N} +@opindex minit-stack +Specify the initial stack address, which may be a symbol or numeric value, +@samp{__stack} is the default. + +@item -mno-interrupts +@opindex mno-interrupts +Generated code is not compatible with hardware interrupts. +Code size will be smaller. + +@item -mcall-prologues +@opindex mcall-prologues +Functions prologues/epilogues expanded as call to appropriate +subroutines. Code size will be smaller. + +@item -mno-tablejump +@opindex mno-tablejump +Do not generate tablejump insns which sometimes increase code size. + +@item -mtiny-stack +@opindex mtiny-stack +Change only the low 8 bits of the stack pointer. +@end table + +@node MCore Options +@subsection MCore Options +@cindex MCore options + +These are the @samp{-m} options defined for the Motorola M*Core +processors. + +@table @gcctabopt + +@item -mhardlit +@itemx -mhardlit +@itemx -mno-hardlit +@opindex mhardlit +@opindex mhardlit +@opindex mno-hardlit +Inline constants into the code stream if it can be done in two +instructions or less. + +@item -mdiv +@itemx -mdiv +@itemx -mno-div +@opindex mdiv +@opindex mdiv +@opindex mno-div +Use the divide instruction. (Enabled by default). + +@item -mrelax-immediate +@itemx -mrelax-immediate +@itemx -mno-relax-immediate +@opindex mrelax-immediate +@opindex mrelax-immediate +@opindex mno-relax-immediate +Allow arbitrary sized immediates in bit operations. + +@item -mwide-bitfields +@itemx -mwide-bitfields +@itemx -mno-wide-bitfields +@opindex mwide-bitfields +@opindex mwide-bitfields +@opindex mno-wide-bitfields +Always treat bit-fields as int-sized. + +@item -m4byte-functions +@itemx -m4byte-functions +@itemx -mno-4byte-functions +@opindex m4byte-functions +@opindex m4byte-functions +@opindex mno-4byte-functions +Force all functions to be aligned to a four byte boundary. + +@item -mcallgraph-data +@itemx -mcallgraph-data +@itemx -mno-callgraph-data +@opindex mcallgraph-data +@opindex mcallgraph-data +@opindex mno-callgraph-data +Emit callgraph information. + +@item -mslow-bytes +@itemx -mslow-bytes +@itemx -mno-slow-bytes +@opindex mslow-bytes +@opindex mslow-bytes +@opindex mno-slow-bytes +Prefer word access when reading byte quantities. + +@item -mlittle-endian +@itemx -mlittle-endian +@itemx -mbig-endian +@opindex mlittle-endian +@opindex mlittle-endian +@opindex mbig-endian +Generate code for a little endian target. + +@item -m210 +@itemx -m210 +@itemx -m340 +@opindex m210 +@opindex m210 +@opindex m340 +Generate code for the 210 processor. +@end table + +@node IA-64 Options +@subsection IA-64 Options +@cindex IA-64 Options + +These are the @samp{-m} options defined for the Intel IA-64 architecture. + +@table @gcctabopt +@item -mbig-endian +@opindex mbig-endian +Generate code for a big endian target. This is the default for HPUX@. + +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a little endian target. This is the default for AIX5 +and Linux. + +@item -mgnu-as +@itemx -mno-gnu-as +@opindex mgnu-as +@opindex mno-gnu-as +Generate (or don't) code for the GNU assembler. This is the default. +@c Also, this is the default if the configure option @option{--with-gnu-as} +@c is used. + +@item -mgnu-ld +@itemx -mno-gnu-ld +@opindex mgnu-ld +@opindex mno-gnu-ld +Generate (or don't) code for the GNU linker. This is the default. +@c Also, this is the default if the configure option @option{--with-gnu-ld} +@c is used. + +@item -mno-pic +@opindex mno-pic +Generate code that does not use a global pointer register. The result +is not position independent code, and violates the IA-64 ABI@. + +@item -mvolatile-asm-stop +@itemx -mno-volatile-asm-stop +@opindex mvolatile-asm-stop +@opindex mno-volatile-asm-stop +Generate (or don't) a stop bit immediately before and after volatile asm +statements. + +@item -mb-step +@opindex mb-step +Generate code that works around Itanium B step errata. + +@item -mregister-names +@itemx -mno-register-names +@opindex mregister-names +@opindex mno-register-names +Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for +the stacked registers. This may make assembler output more readable. + +@item -mno-sdata +@itemx -msdata +@opindex mno-sdata +@opindex msdata +Disable (or enable) optimizations that use the small data section. This may +be useful for working around optimizer bugs. + +@item -mconstant-gp +@opindex mconstant-gp +Generate code that uses a single constant global pointer value. This is +useful when compiling kernel code. + +@item -mauto-pic +@opindex mauto-pic +Generate code that is self-relocatable. This implies @option{-mconstant-gp}. +This is useful when compiling firmware code. + +@item -minline-divide-min-latency +@opindex minline-divide-min-latency +Generate code for inline divides using the minimum latency algorithm. + +@item -minline-divide-max-throughput +@opindex minline-divide-max-throughput +Generate code for inline divides using the maximum throughput algorithm. + +@item -mno-dwarf2-asm +@itemx -mdwarf2-asm +@opindex mno-dwarf2-asm +@opindex mdwarf2-asm +Don't (or do) generate assembler code for the DWARF2 line number debugging +info. This may be useful when not using the GNU assembler. + +@item -mfixed-range=@var{register-range} +@opindex mfixed-range +Generate code treating the given register range as fixed registers. +A fixed register is one that the register allocator can not use. This is +useful when compiling kernel code. A register range is specified as +two registers separated by a dash. Multiple register ranges can be +specified separated by a comma. +@end table + +@node D30V Options +@subsection D30V Options +@cindex D30V Options + +These @samp{-m} options are defined for D30V implementations: + +@table @gcctabopt +@item -mextmem +@opindex mextmem +Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings}, +@samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external +memory, which starts at location @code{0x80000000}. + +@item -mextmemory +@opindex mextmemory +Same as the @option{-mextmem} switch. + +@item -monchip +@opindex monchip +Link the @samp{.text} section into onchip text memory, which starts at +location @code{0x0}. Also link @samp{.data}, @samp{.bss}, +@samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections +into onchip data memory, which starts at location @code{0x20000000}. + +@item -mno-asm-optimize +@itemx -masm-optimize +@opindex mno-asm-optimize +@opindex masm-optimize +Disable (enable) passing @option{-O} to the assembler when optimizing. +The assembler uses the @option{-O} option to automatically parallelize +adjacent short instructions where possible. + +@item -mbranch-cost=@var{n} +@opindex mbranch-cost +Increase the internal costs of branches to @var{n}. Higher costs means +that the compiler will issue more instructions to avoid doing a branch. +The default is 2. + +@item -mcond-exec=@var{n} +@opindex mcond-exec +Specify the maximum number of conditionally executed instructions that +replace a branch. The default is 4. +@end table + +@node S/390 and zSeries Options +@subsection S/390 and zSeries Options +@cindex S/390 and zSeries Options + +These are the @samp{-m} options defined for the S/390 and zSeries architecture. + +@table @gcctabopt +@item -mhard-float +@itemx -msoft-float +@opindex mhard-float +@opindex msoft-float +Use (do not use) the hardware floating-point instructions and registers +for floating-point operations. When @option{-msoft-float} is specified, +functions in @file{libgcc.a} will be used to perform floating-point +operations. When @option{-mhard-float} is specified, the compiler +generates IEEE floating-point instructions. This is the default. + +@item -mbackchain +@itemx -mno-backchain +@opindex mbackchain +@opindex mno-backchain +Generate (or do not generate) code which maintains an explicit +backchain within the stack frame that points to the caller's frame. +This is currently needed to allow debugging. The default is to +generate the backchain. + +@item -msmall-exec +@itemx -mno-small-exec +@opindex msmall-exec +@opindex mno-small-exec +Generate (or do not generate) code using the @code{bras} instruction +to do subroutine calls. +This only works reliably if the total executable size does not +exceed 64k. The default is to use the @code{basr} instruction instead, +which does not have this limitation. + +@item -m64 +@itemx -m31 +@opindex m64 +@opindex m31 +When @option{-m31} is specified, generate code compliant to the +Linux for S/390 ABI@. When @option{-m64} is specified, generate +code compliant to the Linux for zSeries ABI@. This allows GCC in +particular to generate 64-bit instructions. For the @samp{s390} +targets, the default is @option{-m31}, while the @samp{s390x} +targets default to @option{-m64}. + +@item -mmvcle +@itemx -mno-mvcle +@opindex mmvcle +@opindex mno-mvcle +Generate (or do not generate) code using the @code{mvcle} instruction +to perform block moves. When @option{-mno-mvcle} is specifed, +use a @code{mvc} loop instead. This is the default. + +@item -mdebug +@itemx -mno-debug +@opindex mdebug +@opindex mno-debug +Print (or do not print) additional debug information when compiling. +The default is to not print debug information. + +@end table + +@node CRIS Options +@subsection CRIS Options +@cindex CRIS Options + +These options are defined specifically for the CRIS ports. + +@table @gcctabopt +@item -march=@var{architecture-type} +@itemx -mcpu=@var{architecture-type} +@opindex march +@opindex mcpu +Generate code for the specified architecture. The choices for +@var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for +respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX. +Default is @samp{v0} except for cris-axis-linux-gnu, where the default is +@samp{v10}. + +@item -mtune=@var{architecture-type} +@opindex mtune +Tune to @var{architecture-type} everything applicable about the generated +code, except for the ABI and the set of available instructions. The +choices for @var{architecture-type} are the same as for +@option{-march=@var{architecture-type}}. + +@item -mmax-stack-frame=@var{n} +@opindex mmax-stack-frame +Warn when the stack frame of a function exceeds @var{n} bytes. + +@item -melinux-stacksize=@var{n} +@opindex melinux-stacksize +Only available with the @samp{cris-axis-aout} target. Arranges for +indications in the program to the kernel loader that the stack of the +program should be set to @var{n} bytes. + +@item -metrax4 +@itemx -metrax100 +@opindex metrax4 +@opindex metrax100 +The options @option{-metrax4} and @option{-metrax100} are synonyms for +@option{-march=v3} and @option{-march=v8} respectively. + +@item -mpdebug +@opindex mpdebug +Enable CRIS-specific verbose debug-related information in the assembly +code. This option also has the effect to turn off the @samp{#NO_APP} +formatted-code indicator to the assembler at the beginning of the +assembly file. + +@item -mcc-init +@opindex mcc-init +Do not use condition-code results from previous instruction; always emit +compare and test instructions before use of condition codes. + +@item -mno-side-effects +@opindex mno-side-effects +Do not emit instructions with side-effects in addressing modes other than +post-increment. + +@item -mstack-align +@itemx -mno-stack-align +@itemx -mdata-align +@itemx -mno-data-align +@itemx -mconst-align +@itemx -mno-const-align +@opindex mstack-align +@opindex mno-stack-align +@opindex mdata-align +@opindex mno-data-align +@opindex mconst-align +@opindex mno-const-align +These options (no-options) arranges (eliminate arrangements) for the +stack-frame, individual data and constants to be aligned for the maximum +single data access size for the chosen CPU model. The default is to +arrange for 32-bit alignment. ABI details such as structure layout are +not affected by these options. + +@item -m32-bit +@itemx -m16-bit +@itemx -m8-bit +@opindex m32-bit +@opindex m16-bit +@opindex m8-bit +Similar to the stack- data- and const-align options above, these options +arrange for stack-frame, writable data and constants to all be 32-bit, +16-bit or 8-bit aligned. The default is 32-bit alignment. + +@item -mno-prologue-epilogue +@itemx -mprologue-epilogue +@opindex mno-prologue-epilogue +@opindex mprologue-epilogue +With @option{-mno-prologue-epilogue}, the normal function prologue and +epilogue that sets up the stack-frame are omitted and no return +instructions or return sequences are generated in the code. Use this +option only together with visual inspection of the compiled code: no +warnings or errors are generated when call-saved registers must be saved, +or storage for local variable needs to be allocated. + +@item -mno-gotplt +@itemx -mgotplt +@opindex mno-gotplt +@opindex mgotplt +With @option{-fpic} and @option{-fPIC}, don't generate (do generate) +instruction sequences that load addresses for functions from the PLT part +of the GOT rather than (traditional on other architectures) calls to the +PLT. The default is @option{-mgotplt}. + +@item -maout +@opindex maout +Legacy no-op option only recognized with the cris-axis-aout target. + +@item -melf +@opindex melf +Legacy no-op option only recognized with the cris-axis-elf and +cris-axis-linux-gnu targets. + +@item -melinux +@opindex melinux +Only recognized with the cris-axis-aout target, where it selects a +GNU/linux-like multilib, include files and instruction set for +@option{-march=v8}. + +@item -mlinux +@opindex mlinux +Legacy no-op option only recognized with the cris-axis-linux-gnu target. + +@item -sim +@opindex sim +This option, recognized for the cris-axis-aout and cris-axis-elf arranges +to link with input-output functions from a simulator library. Code, +initialized data and zero-initialized data are allocated consecutively. + +@item -sim2 +@opindex sim2 +Like @option{-sim}, but pass linker options to locate initialized data at +0x40000000 and zero-initialized data at 0x80000000. +@end table + +@node MMIX Options +@subsection MMIX Options +@cindex MMIX Options + +These options are defined for the MMIX: + +@table @gcctabopt +@item -mlibfuncs +@itemx -mno-libfuncs +@opindex mlibfuncs +@opindex mno-libfuncs +Specify that intrinsic library functions are being compiled, passing all +values in registers, no matter the size. + +@item -mepsilon +@itemx -mno-epsilon +@opindex mepsilon +@opindex mno-epsilon +Generate floating-point comparison instructions that compare with respect +to the @code{rE} epsilon register. + +@item -mabi=mmixware +@itemx -mabi=gnu +@opindex mabi-mmixware +@opindex mabi=gnu +Generate code that passes function parameters and return values that (in +the called function) are seen as registers @code{$0} and up, as opposed to +the GNU ABI which uses global registers @code{$231} and up. + +@item -mzero-extend +@itemx -mno-zero-extend +@opindex mzero-extend +@opindex mno-zero-extend +When reading data from memory in sizes shorter than 64 bits, use (do not +use) zero-extending load instructions by default, rather than +sign-extending ones. + +@item -mknuthdiv +@itemx -mno-knuthdiv +@opindex mknuthdiv +@opindex mno-knuthdiv +Make the result of a division yielding a remainder have the same sign as +the divisor. With the default, @option{-mno-knuthdiv}, the sign of the +remainder follows the sign of the dividend. Both methods are +arithmetically valid, the latter being almost exclusively used. + +@item -mtoplevel-symbols +@itemx -mno-toplevel-symbols +@opindex mtoplevel-symbols +@opindex mno-toplevel-symbols +Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly +code can be used with the @code{PREFIX} assembly directive. + +@item -melf +@opindex melf +Generate an executable in the ELF format, rather than the default +@samp{mmo} format used by the @command{mmix} simulator. + +@item -mbranch-predict +@itemx -mno-branch-predict +@opindex mbranch-predict +@opindex mno-branch-predict +Use (do not use) the probable-branch instructions, when static branch +prediction indicates a probable branch. +@end table + +@node PDP-11 Options +@subsection PDP-11 Options +@cindex PDP-11 Options + +These options are defined for the PDP-11: + +@table @gcctabopt +@item -mfpu +@opindex mfpu +Use hardware FPP floating point. This is the default. (FIS floating +point on the PDP-11/40 is not supported.) + +@item -msoft-float +@opindex msoft-float +Do not use hardware floating point. + +@item -mac0 +@opindex mac0 +Return floating-point results in ac0 (fr0 in Unix assembler syntax). + +@item -mno-ac0 +@opindex mno-ac0 +Return floating-point results in memory. This is the default. + +@item -m40 +@opindex m40 +Generate code for a PDP-11/40. + +@item -m45 +@opindex m45 +Generate code for a PDP-11/45. This is the default. + +@item -m10 +@opindex m10 +Generate code for a PDP-11/10. + +@item -mbcopy-builtin +@opindex bcopy-builtin +Use inline @code{movstrhi} patterns for copying memory. This is the +default. + +@item -mbcopy +@opindex mbcopy +Do not use inline @code{movstrhi} patterns for copying memory. + +@item -mint16 +@itemx -mno-int32 +@opindex mint16 +@opindex mno-int32 +Use 16-bit @code{int}. This is the default. + +@item -mint32 +@itemx -mno-int16 +@opindex mint32 +@opindex mno-int16 +Use 32-bit @code{int}. + +@item -mfloat64 +@itemx -mno-float32 +@opindex mfloat64 +@opindex mno-float32 +Use 64-bit @code{float}. This is the default. + +@item -mfloat32 +@item -mno-float64 +@opindex mfloat32 +@opindex mno-float64 +Use 32-bit @code{float}. + +@item -mabshi +@opindex mabshi +Use @code{abshi2} pattern. This is the default. + +@item -mno-abshi +@opindex mno-abshi +Do not use @code{abshi2} pattern. + +@item -mbranch-expensive +@opindex mbranch-expensive +Pretend that branches are expensive. This is for experimenting with +code generation only. + +@item -mbranch-cheap +@opindex mbranch-cheap +Do not pretend that branches are expensive. This is the default. + +@item -msplit +@opindex msplit +Generate code for a system with split I&D. + +@item -mno-split +@opindex mno-split +Generate code for a system without split I&D. This is the default. + +@item -munix-asm +@opindex munix-asm +Use Unix assembler syntax. This is the default when configured for +@samp{pdp11-*-bsd}. + +@item -mdec-asm +@opindex mdec-asm +Use DEC assembler syntax. This is the default when configured for any +PDP-11 target other than @samp{pdp11-*-bsd}. +@end table + +@node Xstormy16 Options +@subsection Xstormy16 Options +@cindex Xstormy16 Options + +These options are defined for Xstormy16: + +@table @gcctabopt +@item -msim +@opindex msim +Choose startup files and linker script suitable for the simulator. +@end table + +@node Xtensa Options +@subsection Xtensa Options +@cindex Xtensa Options + +The Xtensa architecture is designed to support many different +configurations. The compiler's default options can be set to match a +particular Xtensa configuration by copying a configuration file into the +GCC sources when building GCC@. The options below may be used to +override the default options. + +@table @gcctabopt +@item -mbig-endian +@itemx -mlittle-endian +@opindex mbig-endian +@opindex mlittle-endian +Specify big-endian or little-endian byte ordering for the target Xtensa +processor. + +@item -mdensity +@itemx -mno-density +@opindex mdensity +@opindex mno-density +Enable or disable use of the optional Xtensa code density instructions. + +@item -mmac16 +@itemx -mno-mac16 +@opindex mmac16 +@opindex mno-mac16 +Enable or disable use of the Xtensa MAC16 option. When enabled, GCC +will generate MAC16 instructions from standard C code, with the +limitation that it will use neither the MR register file nor any +instruction that operates on the MR registers. When this option is +disabled, GCC will translate 16-bit multiply/accumulate operations to a +combination of core instructions and library calls, depending on whether +any other multiplier options are enabled. + +@item -mmul16 +@itemx -mno-mul16 +@opindex mmul16 +@opindex mno-mul16 +Enable or disable use of the 16-bit integer multiplier option. When +enabled, the compiler will generate 16-bit multiply instructions for +multiplications of 16 bits or smaller in standard C code. When this +option is disabled, the compiler will either use 32-bit multiply or +MAC16 instructions if they are available or generate library calls to +perform the multiply operations using shifts and adds. + +@item -mmul32 +@itemx -mno-mul32 +@opindex mmul32 +@opindex mno-mul32 +Enable or disable use of the 32-bit integer multiplier option. When +enabled, the compiler will generate 32-bit multiply instructions for +multiplications of 32 bits or smaller in standard C code. When this +option is disabled, the compiler will generate library calls to perform +the multiply operations using either shifts and adds or 16-bit multiply +instructions if they are available. + +@item -mnsa +@itemx -mno-nsa +@opindex mnsa +@opindex mno-nsa +Enable or disable use of the optional normalization shift amount +(@code{NSA}) instructions to implement the built-in @code{ffs} function. + +@item -mminmax +@itemx -mno-minmax +@opindex mminmax +@opindex mno-minmax +Enable or disable use of the optional minimum and maximum value +instructions. + +@item -msext +@itemx -mno-sext +@opindex msext +@opindex mno-sext +Enable or disable use of the optional sign extend (@code{SEXT}) +instruction. + +@item -mbooleans +@itemx -mno-booleans +@opindex mbooleans +@opindex mno-booleans +Enable or disable support for the boolean register file used by Xtensa +coprocessors. This is not typically useful by itself but may be +required for other options that make use of the boolean registers (e.g., +the floating-point option). + +@item -mhard-float +@itemx -msoft-float +@opindex mhard-float +@opindex msoft-float +Enable or disable use of the floating-point option. When enabled, GCC +generates floating-point instructions for 32-bit @code{float} +operations. When this option is disabled, GCC generates library calls +to emulate 32-bit floating-point operations using integer instructions. +Regardless of this option, 64-bit @code{double} operations are always +emulated with calls to library functions. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Enable or disable use of fused multiply/add and multiply/subtract +instructions in the floating-point option. This has no effect if the +floating-point option is not also enabled. Disabling fused multiply/add +and multiply/subtract instructions forces the compiler to use separate +instructions for the multiply and add/subtract operations. This may be +desirable in some cases where strict IEEE 754-compliant results are +required: the fused multiply add/subtract instructions do not round the +intermediate result, thereby producing results with @emph{more} bits of +precision than specified by the IEEE standard. Disabling fused multiply +add/subtract instructions also ensures that the program output is not +sensitive to the compiler's ability to combine multiply and add/subtract +operations. + +@item -mserialize-volatile +@itemx -mno-serialize-volatile +@opindex mserialize-volatile +@opindex mno-serialize-volatile +When this option is enabled, GCC inserts @code{MEMW} instructions before +@code{volatile} memory references to guarantee sequential consistency. +The default is @option{-mserialize-volatile}. Use +@option{-mno-serialize-volatile} to omit the @code{MEMW} instructions. + +@item -mtext-section-literals +@itemx -mno-text-section-literals +@opindex mtext-section-literals +@opindex mno-text-section-literals +Control the treatment of literal pools. The default is +@option{-mno-text-section-literals}, which places literals in a separate +section in the output file. This allows the literal pool to be placed +in a data RAM/ROM, and it also allows the linker to combine literal +pools from separate object files to remove redundant literals and +improve code size. With @option{-mtext-section-literals}, the literals +are interspersed in the text section in order to keep them as close as +possible to their references. This may be necessary for large assembly +files. + +@item -mtarget-align +@itemx -mno-target-align +@opindex mtarget-align +@opindex mno-target-align +When this option is enabled, GCC instructs the assembler to +automatically align instructions to reduce branch penalties at the +expense of some code density. The assembler attempts to widen density +instructions to align branch targets and the instructions following call +instructions. If there are not enough preceding safe density +instructions to align a target, no widening will be performed. The +default is @option{-mtarget-align}. These options do not affect the +treatment of auto-aligned instructions like @code{LOOP}, which the +assembler will always align, either by widening density instructions or +by inserting no-op instructions. + +@item -mlongcalls +@itemx -mno-longcalls +@opindex mlongcalls +@opindex mno-longcalls +When this option is enabled, GCC instructs the assembler to translate +direct calls to indirect calls unless it can determine that the target +of a direct call is in the range allowed by the call instruction. This +translation typically occurs for calls to functions in other source +files. Specifically, the assembler translates a direct @code{CALL} +instruction into an @code{L32R} followed by a @code{CALLX} instruction. +The default is @option{-mno-longcalls}. This option should be used in +programs where the call target can potentially be out of range. This +option is implemented in the assembler, not the compiler, so the +assembly code generated by GCC will still show direct call +instructions---look at the disassembled object code to see the actual +instructions. Note that the assembler will use an indirect call for +every cross-file call, not just those that really will be out of range. +@end table + +@node Code Gen Options +@section Options for Code Generation Conventions +@cindex code generation conventions +@cindex options, code generation +@cindex run-time options + +These machine-independent options control the interface conventions +used in code generation. + +Most of them have both positive and negative forms; the negative form +of @option{-ffoo} would be @option{-fno-foo}. In the table below, only +one of the forms is listed---the one which is not the default. You +can figure out the other form by either removing @samp{no-} or adding +it. + +@table @gcctabopt +@item -fexceptions +@opindex fexceptions +Enable exception handling. Generates extra code needed to propagate +exceptions. For some targets, this implies GCC will generate frame +unwind information for all functions, which can produce significant data +size overhead, although it does not affect execution. If you do not +specify this option, GCC will enable it by default for languages like +C++ which normally require exception handling, and disable it for +languages like C that do not normally require it. However, you may need +to enable this option when compiling C code that needs to interoperate +properly with exception handlers written in C++. You may also wish to +disable this option if you are compiling older C++ programs that don't +use exception handling. + +@item -fnon-call-exceptions +@opindex fnon-call-exceptions +Generate code that allows trapping instructions to throw exceptions. +Note that this requires platform-specific runtime support that does +not exist everywhere. Moreover, it only allows @emph{trapping} +instructions to throw exceptions, i.e.@: memory references or floating +point instructions. It does not allow exceptions to be thrown from +arbitrary signal handlers such as @code{SIGALRM}. + +@item -funwind-tables +@opindex funwind-tables +Similar to @option{-fexceptions}, except that it will just generate any needed +static data, but will not affect the generated code in any other way. +You will normally not enable this option; instead, a language processor +that needs this handling would enable it on your behalf. + +@item -fasynchronous-unwind-tables +@opindex funwind-tables +Generate unwind table in dwarf2 format, if supported by target machine. The +table is exact at each instruction boundary, so it can be used for stack +unwinding from asynchronous events (such as debugger or garbage collector). + +@item -fpcc-struct-return +@opindex fpcc-struct-return +Return ``short'' @code{struct} and @code{union} values in memory like +longer ones, rather than in registers. This convention is less +efficient, but it has the advantage of allowing intercallability between +GCC-compiled files and files compiled with other compilers. + +The precise convention for returning structures in memory depends +on the target configuration macros. + +Short structures and unions are those whose size and alignment match +that of some integer type. + +@item -freg-struct-return +@opindex freg-struct-return +Return @code{struct} and @code{union} values in registers when possible. +This is more efficient for small structures than +@option{-fpcc-struct-return}. + +If you specify neither @option{-fpcc-struct-return} nor +@option{-freg-struct-return}, GCC defaults to whichever convention is +standard for the target. If there is no standard convention, GCC +defaults to @option{-fpcc-struct-return}, except on targets where GCC is +the principal compiler. In those cases, we can choose the standard, and +we chose the more efficient register return alternative. + +@item -fshort-enums +@opindex fshort-enums +Allocate to an @code{enum} type only as many bytes as it needs for the +declared range of possible values. Specifically, the @code{enum} type +will be equivalent to the smallest integer type which has enough room. + +@item -fshort-double +@opindex fshort-double +Use the same size for @code{double} as for @code{float}. + +@item -fshared-data +@opindex fshared-data +Requests that the data and non-@code{const} variables of this +compilation be shared data rather than private data. The distinction +makes sense only on certain operating systems, where shared data is +shared between processes running the same program, while private data +exists in one copy per process. + +@item -fno-common +@opindex fno-common +In C, allocate even uninitialized global variables in the data section of the +object file, rather than generating them as common blocks. This has the +effect that if the same variable is declared (without @code{extern}) in +two different compilations, you will get an error when you link them. +The only reason this might be useful is if you wish to verify that the +program will work on other systems which always work this way. + +@item -fno-ident +@opindex fno-ident +Ignore the @samp{#ident} directive. + +@item -fno-gnu-linker +@opindex fno-gnu-linker +Do not output global initializations (such as C++ constructors and +destructors) in the form used by the GNU linker (on systems where the GNU +linker is the standard method of handling them). Use this option when +you want to use a non-GNU linker, which also requires using the +@command{collect2} program to make sure the system linker includes +constructors and destructors. (@command{collect2} is included in the GCC +distribution.) For systems which @emph{must} use @command{collect2}, the +compiler driver @command{gcc} is configured to do this automatically. + +@item -finhibit-size-directive +@opindex finhibit-size-directive +Don't output a @code{.size} assembler directive, or anything else that +would cause trouble if the function is split in the middle, and the +two halves are placed at locations far apart in memory. This option is +used when compiling @file{crtstuff.c}; you should not need to use it +for anything else. + +@item -fverbose-asm +@opindex fverbose-asm +Put extra commentary information in the generated assembly code to +make it more readable. This option is generally only of use to those +who actually need to read the generated assembly code (perhaps while +debugging the compiler itself). + +@option{-fno-verbose-asm}, the default, causes the +extra information to be omitted and is useful when comparing two assembler +files. + +@item -fvolatile +@opindex fvolatile +Consider all memory references through pointers to be volatile. + +@item -fvolatile-global +@opindex fvolatile-global +Consider all memory references to extern and global data items to +be volatile. GCC does not consider static data items to be volatile +because of this switch. + +@item -fvolatile-static +@opindex fvolatile-static +Consider all memory references to static data to be volatile. + +@item -fpic +@opindex fpic +@cindex global offset table +@cindex PIC +Generate position-independent code (PIC) suitable for use in a shared +library, if supported for the target machine. Such code accesses all +constant addresses through a global offset table (GOT)@. The dynamic +loader resolves the GOT entries when the program starts (the dynamic +loader is not part of GCC; it is part of the operating system). If +the GOT size for the linked executable exceeds a machine-specific +maximum size, you get an error message from the linker indicating that +@option{-fpic} does not work; in that case, recompile with @option{-fPIC} +instead. (These maximums are 16k on the m88k, 8k on the Sparc, and 32k +on the m68k and RS/6000. The 386 has no such limit.) + +Position-independent code requires special support, and therefore works +only on certain machines. For the 386, GCC supports PIC for System V +but not for the Sun 386i. Code generated for the IBM RS/6000 is always +position-independent. + +@item -fPIC +@opindex fPIC +If supported for the target machine, emit position-independent code, +suitable for dynamic linking and avoiding any limit on the size of the +global offset table. This option makes a difference on the m68k, m88k, +and the Sparc. + +Position-independent code requires special support, and therefore works +only on certain machines. + +@item -ffixed-@var{reg} +@opindex ffixed +Treat the register named @var{reg} as a fixed register; generated code +should never refer to it (except perhaps as a stack pointer, frame +pointer or in some other fixed role). + +@var{reg} must be the name of a register. The register names accepted +are machine-specific and are defined in the @code{REGISTER_NAMES} +macro in the machine description macro file. + +This flag does not have a negative form, because it specifies a +three-way choice. + +@item -fcall-used-@var{reg} +@opindex fcall-used +Treat the register named @var{reg} as an allocable register that is +clobbered by function calls. It may be allocated for temporaries or +variables that do not live across a call. Functions compiled this way +will not save and restore the register @var{reg}. + +It is an error to used this flag with the frame pointer or stack pointer. +Use of this flag for other registers that have fixed pervasive roles in +the machine's execution model will produce disastrous results. + +This flag does not have a negative form, because it specifies a +three-way choice. + +@item -fcall-saved-@var{reg} +@opindex fcall-saved +Treat the register named @var{reg} as an allocable register saved by +functions. It may be allocated even for temporaries or variables that +live across a call. Functions compiled this way will save and restore +the register @var{reg} if they use it. + +It is an error to used this flag with the frame pointer or stack pointer. +Use of this flag for other registers that have fixed pervasive roles in +the machine's execution model will produce disastrous results. + +A different sort of disaster will result from the use of this flag for +a register in which function values may be returned. + +This flag does not have a negative form, because it specifies a +three-way choice. + +@item -fpack-struct +@opindex fpack-struct +Pack all structure members together without holes. Usually you would +not want to use this option, since it makes the code suboptimal, and +the offsets of structure members won't agree with system libraries. + +@item -finstrument-functions +@opindex finstrument-functions +Generate instrumentation calls for entry and exit to functions. Just +after function entry and just before function exit, the following +profiling functions will be called with the address of the current +function and its call site. (On some platforms, +@code{__builtin_return_address} does not work beyond the current +function, so the call site information may not be available to the +profiling functions otherwise.) + +@example +void __cyg_profile_func_enter (void *this_fn, + void *call_site); +void __cyg_profile_func_exit (void *this_fn, + void *call_site); +@end example + +The first argument is the address of the start of the current function, +which may be looked up exactly in the symbol table. + +This instrumentation is also done for functions expanded inline in other +functions. The profiling calls will indicate where, conceptually, the +inline function is entered and exited. This means that addressable +versions of such functions must be available. If all your uses of a +function are expanded inline, this may mean an additional expansion of +code size. If you use @samp{extern inline} in your C code, an +addressable version of such functions must be provided. (This is +normally the case anyways, but if you get lucky and the optimizer always +expands the functions inline, you might have gotten away without +providing static copies.) + +A function may be given the attribute @code{no_instrument_function}, in +which case this instrumentation will not be done. This can be used, for +example, for the profiling functions listed above, high-priority +interrupt routines, and any functions from which the profiling functions +cannot safely be called (perhaps signal handlers, if the profiling +routines generate output or allocate memory). + +@item -fstack-check +@opindex fstack-check +Generate code to verify that you do not go beyond the boundary of the +stack. You should specify this flag if you are running in an +environment with multiple threads, but only rarely need to specify it in +a single-threaded environment since stack overflow is automatically +detected on nearly all systems if there is only one stack. + +Note that this switch does not actually cause checking to be done; the +operating system must do that. The switch causes generation of code +to ensure that the operating system sees the stack being extended. + +@item -fstack-limit-register=@var{reg} +@itemx -fstack-limit-symbol=@var{sym} +@itemx -fno-stack-limit +@opindex fstack-limit-register +@opindex fstack-limit-symbol +@opindex fno-stack-limit +Generate code to ensure that the stack does not grow beyond a certain value, +either the value of a register or the address of a symbol. If the stack +would grow beyond the value, a signal is raised. For most targets, +the signal is raised before the stack overruns the boundary, so +it is possible to catch the signal without taking special precautions. + +For instance, if the stack starts at absolute address @samp{0x80000000} +and grows downwards, you can use the flags +@option{-fstack-limit-symbol=__stack_limit} and +@option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit +of 128KB@. Note that this may only work with the GNU linker. + +@cindex aliasing of parameters +@cindex parameters, aliased +@item -fargument-alias +@itemx -fargument-noalias +@itemx -fargument-noalias-global +@opindex fargument-alias +@opindex fargument-noalias +@opindex fargument-noalias-global +Specify the possible relationships among parameters and between +parameters and global data. + +@option{-fargument-alias} specifies that arguments (parameters) may +alias each other and may alias global storage.@* +@option{-fargument-noalias} specifies that arguments do not alias +each other, but may alias global storage.@* +@option{-fargument-noalias-global} specifies that arguments do not +alias each other and do not alias global storage. + +Each language will automatically use whatever option is required by +the language standard. You should not need to use these options yourself. + +@item -fleading-underscore +@opindex fleading-underscore +This option and its counterpart, @option{-fno-leading-underscore}, forcibly +change the way C symbols are represented in the object file. One use +is to help link with legacy assembly code. + +Be warned that you should know what you are doing when invoking this +option, and that not all targets provide complete support for it. +@end table + +@c man end + +@node Environment Variables +@section Environment Variables Affecting GCC +@cindex environment variables + +@c man begin ENVIRONMENT + +This section describes several environment variables that affect how GCC +operates. Some of them work by specifying directories or prefixes to use +when searching for various kinds of files. Some are used to specify other +aspects of the compilation environment. + +Note that you can also specify places to search using options such as +@option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These +take precedence over places specified using environment variables, which +in turn take precedence over those specified by the configuration of GCC@. +@xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint, +GNU Compiler Collection (GCC) Internals}. + +@table @env +@item LANG +@itemx LC_CTYPE +@c @itemx LC_COLLATE +@itemx LC_MESSAGES +@c @itemx LC_MONETARY +@c @itemx LC_NUMERIC +@c @itemx LC_TIME +@itemx LC_ALL +@findex LANG +@findex LC_CTYPE +@c @findex LC_COLLATE +@findex LC_MESSAGES +@c @findex LC_MONETARY +@c @findex LC_NUMERIC +@c @findex LC_TIME +@findex LC_ALL +@cindex locale +These environment variables control the way that GCC uses +localization information that allow GCC to work with different +national conventions. GCC inspects the locale categories +@env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do +so. These locale categories can be set to any value supported by your +installation. A typical value is @samp{en_UK} for English in the United +Kingdom. + +The @env{LC_CTYPE} environment variable specifies character +classification. GCC uses it to determine the character boundaries in +a string; this is needed for some multibyte encodings that contain quote +and escape characters that would otherwise be interpreted as a string +end or escape. + +The @env{LC_MESSAGES} environment variable specifies the language to +use in diagnostic messages. + +If the @env{LC_ALL} environment variable is set, it overrides the value +of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE} +and @env{LC_MESSAGES} default to the value of the @env{LANG} +environment variable. If none of these variables are set, GCC +defaults to traditional C English behavior. + +@item TMPDIR +@findex TMPDIR +If @env{TMPDIR} is set, it specifies the directory to use for temporary +files. GCC uses temporary files to hold the output of one stage of +compilation which is to be used as input to the next stage: for example, +the output of the preprocessor, which is the input to the compiler +proper. + +@item GCC_EXEC_PREFIX +@findex GCC_EXEC_PREFIX +If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the +names of the subprograms executed by the compiler. No slash is added +when this prefix is combined with the name of a subprogram, but you can +specify a prefix that ends with a slash if you wish. + +If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out +an appropriate prefix to use based on the pathname it was invoked with. + +If GCC cannot find the subprogram using the specified prefix, it +tries looking in the usual places for the subprogram. + +The default value of @env{GCC_EXEC_PREFIX} is +@file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value +of @code{prefix} when you ran the @file{configure} script. + +Other prefixes specified with @option{-B} take precedence over this prefix. + +This prefix is also used for finding files such as @file{crt0.o} that are +used for linking. + +In addition, the prefix is used in an unusual way in finding the +directories to search for header files. For each of the standard +directories whose name normally begins with @samp{/usr/local/lib/gcc-lib} +(more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries +replacing that beginning with the specified prefix to produce an +alternate directory name. Thus, with @option{-Bfoo/}, GCC will search +@file{foo/bar} where it would normally search @file{/usr/local/lib/bar}. +These alternate directories are searched first; the standard directories +come next. + +@item COMPILER_PATH +@findex COMPILER_PATH +The value of @env{COMPILER_PATH} is a colon-separated list of +directories, much like @env{PATH}. GCC tries the directories thus +specified when searching for subprograms, if it can't find the +subprograms using @env{GCC_EXEC_PREFIX}. + +@item LIBRARY_PATH +@findex LIBRARY_PATH +The value of @env{LIBRARY_PATH} is a colon-separated list of +directories, much like @env{PATH}. When configured as a native compiler, +GCC tries the directories thus specified when searching for special +linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking +using GCC also uses these directories when searching for ordinary +libraries for the @option{-l} option (but directories specified with +@option{-L} come first). + +@item C_INCLUDE_PATH +@itemx CPLUS_INCLUDE_PATH +@itemx OBJC_INCLUDE_PATH +@findex C_INCLUDE_PATH +@findex CPLUS_INCLUDE_PATH +@findex OBJC_INCLUDE_PATH +@c @itemx OBJCPLUS_INCLUDE_PATH +These environment variables pertain to particular languages. Each +variable's value is a colon-separated list of directories, much like +@env{PATH}. When GCC searches for header files, it tries the +directories listed in the variable for the language you are using, after +the directories specified with @option{-I} but before the standard header +file directories. + +@item DEPENDENCIES_OUTPUT +@findex DEPENDENCIES_OUTPUT +@cindex dependencies for make as output +If this variable is set, its value specifies how to output dependencies +for Make based on the header files processed by the compiler. This +output looks much like the output from the @option{-M} option +(@pxref{Preprocessor Options}), but it goes to a separate file, and is +in addition to the usual results of compilation. + +The value of @env{DEPENDENCIES_OUTPUT} can be just a file name, in +which case the Make rules are written to that file, guessing the target +name from the source file name. Or the value can have the form +@samp{@var{file} @var{target}}, in which case the rules are written to +file @var{file} using @var{target} as the target name. + +@item LANG +@findex LANG +@cindex locale definition +This variable is used to pass locale information to the compiler. One way in +which this information is used is to determine the character set to be used +when character literals, string literals and comments are parsed in C and C++. +When the compiler is configured to allow multibyte characters, +the following values for @env{LANG} are recognized: + +@table @samp +@item C-JIS +Recognize JIS characters. +@item C-SJIS +Recognize SJIS characters. +@item C-EUCJP +Recognize EUCJP characters. +@end table + +If @env{LANG} is not defined, or if it has some other value, then the +compiler will use mblen and mbtowc as defined by the default locale to +recognize and translate multibyte characters. +@end table + +@c man end + +@node Running Protoize +@section Running Protoize + +The program @code{protoize} is an optional part of GCC@. You can use +it to add prototypes to a program, thus converting the program to ISO +C in one respect. The companion program @code{unprotoize} does the +reverse: it removes argument types from any prototypes that are found. + +When you run these programs, you must specify a set of source files as +command line arguments. The conversion programs start out by compiling +these files to see what functions they define. The information gathered +about a file @var{foo} is saved in a file named @file{@var{foo}.X}. + +After scanning comes actual conversion. The specified files are all +eligible to be converted; any files they include (whether sources or +just headers) are eligible as well. + +But not all the eligible files are converted. By default, +@code{protoize} and @code{unprotoize} convert only source and header +files in the current directory. You can specify additional directories +whose files should be converted with the @option{-d @var{directory}} +option. You can also specify particular files to exclude with the +@option{-x @var{file}} option. A file is converted if it is eligible, its +directory name matches one of the specified directory names, and its +name within the directory has not been excluded. + +Basic conversion with @code{protoize} consists of rewriting most +function definitions and function declarations to specify the types of +the arguments. The only ones not rewritten are those for varargs +functions. + +@code{protoize} optionally inserts prototype declarations at the +beginning of the source file, to make them available for any calls that +precede the function's definition. Or it can insert prototype +declarations with block scope in the blocks where undeclared functions +are called. + +Basic conversion with @code{unprotoize} consists of rewriting most +function declarations to remove any argument types, and rewriting +function definitions to the old-style pre-ISO form. + +Both conversion programs print a warning for any function declaration or +definition that they can't convert. You can suppress these warnings +with @option{-q}. + +The output from @code{protoize} or @code{unprotoize} replaces the +original source file. The original file is renamed to a name ending +with @samp{.save} (for DOS, the saved filename ends in @samp{.sav} +without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav} +for DOS) file already exists, then the source file is simply discarded. + +@code{protoize} and @code{unprotoize} both depend on GCC itself to +scan the program and collect information about the functions it uses. +So neither of these programs will work until GCC is installed. + +Here is a table of the options you can use with @code{protoize} and +@code{unprotoize}. Each option works with both programs unless +otherwise stated. + +@table @code +@item -B @var{directory} +Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the +usual directory (normally @file{/usr/local/lib}). This file contains +prototype information about standard system functions. This option +applies only to @code{protoize}. + +@item -c @var{compilation-options} +Use @var{compilation-options} as the options when running @code{gcc} to +produce the @samp{.X} files. The special option @option{-aux-info} is +always passed in addition, to tell @code{gcc} to write a @samp{.X} file. + +Note that the compilation options must be given as a single argument to +@code{protoize} or @code{unprotoize}. If you want to specify several +@code{gcc} options, you must quote the entire set of compilation options +to make them a single word in the shell. + +There are certain @code{gcc} arguments that you cannot use, because they +would produce the wrong kind of output. These include @option{-g}, +@option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in +the @var{compilation-options}, they are ignored. + +@item -C +Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file +systems) instead of @samp{.c}. This is convenient if you are converting +a C program to C++. This option applies only to @code{protoize}. + +@item -g +Add explicit global declarations. This means inserting explicit +declarations at the beginning of each source file for each function +that is called in the file and was not declared. These declarations +precede the first function definition that contains a call to an +undeclared function. This option applies only to @code{protoize}. + +@item -i @var{string} +Indent old-style parameter declarations with the string @var{string}. +This option applies only to @code{protoize}. + +@code{unprotoize} converts prototyped function definitions to old-style +function definitions, where the arguments are declared between the +argument list and the initial @samp{@{}. By default, @code{unprotoize} +uses five spaces as the indentation. If you want to indent with just +one space instead, use @option{-i " "}. + +@item -k +Keep the @samp{.X} files. Normally, they are deleted after conversion +is finished. + +@item -l +Add explicit local declarations. @code{protoize} with @option{-l} inserts +a prototype declaration for each function in each block which calls the +function without any declaration. This option applies only to +@code{protoize}. + +@item -n +Make no real changes. This mode just prints information about the conversions +that would have been done without @option{-n}. + +@item -N +Make no @samp{.save} files. The original files are simply deleted. +Use this option with caution. + +@item -p @var{program} +Use the program @var{program} as the compiler. Normally, the name +@file{gcc} is used. + +@item -q +Work quietly. Most warnings are suppressed. + +@item -v +Print the version number, just like @option{-v} for @code{gcc}. +@end table + +If you need special compiler options to compile one of your program's +source files, then you should generate that file's @samp{.X} file +specially, by running @code{gcc} on that source file with the +appropriate options and the option @option{-aux-info}. Then run +@code{protoize} on the entire set of files. @code{protoize} will use +the existing @samp{.X} file because it is newer than the source file. +For example: + +@example +gcc -Dfoo=bar file1.c -aux-info file1.X +protoize *.c +@end example + +@noindent +You need to include the special files along with the rest in the +@code{protoize} command, even though their @samp{.X} files already +exist, because otherwise they won't get converted. + +@xref{Protoize Caveats}, for more information on how to use +@code{protoize} successfully. diff --git a/contrib/gcc/doc/languages.texi b/contrib/gcc/doc/languages.texi new file mode 100644 index 000000000000..514cb08ecced --- /dev/null +++ b/contrib/gcc/doc/languages.texi @@ -0,0 +1,36 @@ +@c Copyright (C) 2002 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Languages +@chapter Language Front Ends in GCC + +The interface to front ends for languages in GCC, and in particular +the @code{tree} structure (@pxref{Trees}), was initially designed for +C, and many aspects of it are still somewhat biased towards C and +C-like languages. It is, however, reasonably well suited to other +procedural languages, and front ends for many such languages have been +written for GCC@. + +Writing a compiler as a front end for GCC, rather than compiling +directly to assembler or generating C code which is then compiled by +GCC, has several advantages: + +@itemize @bullet +@item GCC front ends benefit from the support for many different +target machines already present in GCC@. +@item GCC front ends benefit from all the optimizations in GCC@. Some +of these, such as alias analysis, may work better when GCC is +compiling directly from source code then when it is compiling from +generated C code. +@item Better debugging information is generated when compiling +directly from source code than when going via intermediate generated C +code. +@end itemize + +Because of the advantages of writing a compiler as a GCC front end, +GCC front ends have also been created for languages very different +from those for which GCC was designed, such as the declarative +logic/functional language Mercury. For these reasons, it may also be +useful to implement compilers created for specialized purposes (for +example, as part of a research project) as GCC front ends. diff --git a/contrib/gcc/doc/makefile.texi b/contrib/gcc/doc/makefile.texi new file mode 100644 index 000000000000..69d621ba66c6 --- /dev/null +++ b/contrib/gcc/doc/makefile.texi @@ -0,0 +1,102 @@ +@c Copyright (C) 2001, 2002 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Makefile +@subsection Makefile Targets +@cindex makefile targets +@cindex targets, makefile + +@table @code +@item all +This is the default target. Depending on what your build/host/target +configuration is, it coordinates all the things that need to be built. + +@item doc +Produce info-formatted documentation. Also, @code{make dvi} is +available for DVI-formatted documentation, and @code{make +generated-manpages} to generate man pages. + +@item mostlyclean +Delete the files made while building the compiler. + +@item clean +That, and all the other files built by @code{make all}. + +@item distclean +That, and all the files created by @code{configure}. + +@item extraclean +That, and any temporary or intermediate files, like emacs backup files. + +@item maintainer-clean +Distclean plus any file that can be generated from other files. Note +that additional tools may be required beyond what is normally needed to +build gcc. + +@item install +Installs gcc. + +@item uninstall +Deletes installed files. + +@item check +Run the testsuite. This creates a @file{testsuite} subdirectory that +has various @file{.sum} and @file{.log} files containing the results of +the testing. You can run subsets with, for example, @code{make check-gcc}. +You can specify specific tests by setting RUNTESTFLAGS to be the name +of the @file{.exp} file, optionally followed by (for some tests) an equals +and a file wildcard, like: + +@example +make check-gcc RUNTESTFLAGS="execute.exp=19980413-*" +@end example + +Note that running the testsuite may require additional tools be +installed, such as TCL or dejagnu. + +@item bootstrap +Builds gcc three times---once with the native compiler, once with the +native-built compiler it just built, and once with the compiler it built +the second time. In theory, the last two should produce the same +results, which @code{make compare} can check. Each step of this process +is called a ``stage'', and the results of each stage @var{N} +(@var{N} = 1@dots{}3) are copied to a subdirectory @file{stage@var{N}/}. + +@item bootstrap-lean +Like @code{bootstrap}, except that the various stages are removed once +they're no longer needed. This saves disk space. + +@item bubblestrap +Once bootstrapped, this incrementally rebuilds each of the three stages, +one at a time. It does this by ``bubbling'' the stages up from their +subdirectories, rebuilding them, and copying them back to their +subdirectories. This will allow you to, for example, quickly rebuild a +bootstrapped compiler after changing the sources, without having to do a +full bootstrap. + +@item quickstrap +Rebuilds the most recently built stage. Since each stage requires +special invocation, using this target means you don't have to keep track +of which stage you're on or what invocation that stage needs. + +@item cleanstrap +Removed everything (@code{make clean}) and rebuilds (@code{make bootstrap}). + +@item stage@var{N} (@var{N} = 1@dots{}4) +For each stage, moves the appropriate files to the @file{stage@var{N}} +subdirectory. + +@item unstage@var{N} (@var{N} = 1@dots{}4) +Undoes the corresponding @code{stage@var{N}}. + +@item restage@var{N} (@var{N} = 1@dots{}4) +Undoes the corresponding @code{stage@var{N}} and rebuilds it with the +appropriate flags. + +@item compare +Compares the results of stages 2 and 3. This ensures that the compiler +is running properly, since it should produce the same object files +regardless of how it itself was compiled. + +@end table diff --git a/contrib/gcc/doc/md.texi b/contrib/gcc/doc/md.texi new file mode 100644 index 000000000000..ca59a6c69e01 --- /dev/null +++ b/contrib/gcc/doc/md.texi @@ -0,0 +1,5303 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1996, 1998, 1999, 2000, 2001, 2002 +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@ifset INTERNALS +@node Machine Desc +@chapter Machine Descriptions +@cindex machine descriptions + +A machine description has two parts: a file of instruction patterns +(@file{.md} file) and a C header file of macro definitions. + +The @file{.md} file for a target machine contains a pattern for each +instruction that the target machine supports (or at least each instruction +that is worth telling the compiler about). It may also contain comments. +A semicolon causes the rest of the line to be a comment, unless the semicolon +is inside a quoted string. + +See the next chapter for information on the C header file. + +@menu +* Overview:: How the machine description is used. +* Patterns:: How to write instruction patterns. +* Example:: An explained example of a @code{define_insn} pattern. +* RTL Template:: The RTL template defines what insns match a pattern. +* Output Template:: The output template says how to make assembler code + from such an insn. +* Output Statement:: For more generality, write C code to output + the assembler code. +* Constraints:: When not all operands are general operands. +* Standard Names:: Names mark patterns to use for code generation. +* Pattern Ordering:: When the order of patterns makes a difference. +* Dependent Patterns:: Having one pattern may make you need another. +* Jump Patterns:: Special considerations for patterns for jump insns. +* Looping Patterns:: How to define patterns for special looping insns. +* Insn Canonicalizations::Canonicalization of Instructions +* Expander Definitions::Generating a sequence of several RTL insns + for a standard operation. +* Insn Splitting:: Splitting Instructions into Multiple Instructions. +* Including Patterns:: Including Patterns in Machine Descriptions. +* Peephole Definitions::Defining machine-specific peephole optimizations. +* Insn Attributes:: Specifying the value of attributes for generated insns. +* Conditional Execution::Generating @code{define_insn} patterns for + predication. +* Constant Definitions::Defining symbolic constants that can be used in the + md file. +@end menu + +@node Overview +@section Overview of How the Machine Description is Used + +There are three main conversions that happen in the compiler: + +@enumerate + +@item +The front end reads the source code and builds a parse tree. + +@item +The parse tree is used to generate an RTL insn list based on named +instruction patterns. + +@item +The insn list is matched against the RTL templates to produce assembler +code. + +@end enumerate + +For the generate pass, only the names of the insns matter, from either a +named @code{define_insn} or a @code{define_expand}. The compiler will +choose the pattern with the right name and apply the operands according +to the documentation later in this chapter, without regard for the RTL +template or operand constraints. Note that the names the compiler looks +for are hard-coded in the compiler---it will ignore unnamed patterns and +patterns with names it doesn't know about, but if you don't provide a +named pattern it needs, it will abort. + +If a @code{define_insn} is used, the template given is inserted into the +insn list. If a @code{define_expand} is used, one of three things +happens, based on the condition logic. The condition logic may manually +create new insns for the insn list, say via @code{emit_insn()}, and +invoke @code{DONE}. For certain named patterns, it may invoke @code{FAIL} to tell the +compiler to use an alternate way of performing that task. If it invokes +neither @code{DONE} nor @code{FAIL}, the template given in the pattern +is inserted, as if the @code{define_expand} were a @code{define_insn}. + +Once the insn list is generated, various optimization passes convert, +replace, and rearrange the insns in the insn list. This is where the +@code{define_split} and @code{define_peephole} patterns get used, for +example. + +Finally, the insn list's RTL is matched up with the RTL templates in the +@code{define_insn} patterns, and those patterns are used to emit the +final assembly code. For this purpose, each named @code{define_insn} +acts like it's unnamed, since the names are ignored. + +@node Patterns +@section Everything about Instruction Patterns +@cindex patterns +@cindex instruction patterns + +@findex define_insn +Each instruction pattern contains an incomplete RTL expression, with pieces +to be filled in later, operand constraints that restrict how the pieces can +be filled in, and an output pattern or C code to generate the assembler +output, all wrapped up in a @code{define_insn} expression. + +A @code{define_insn} is an RTL expression containing four or five operands: + +@enumerate +@item +An optional name. The presence of a name indicate that this instruction +pattern can perform a certain standard job for the RTL-generation +pass of the compiler. This pass knows certain names and will use +the instruction patterns with those names, if the names are defined +in the machine description. + +The absence of a name is indicated by writing an empty string +where the name should go. Nameless instruction patterns are never +used for generating RTL code, but they may permit several simpler insns +to be combined later on. + +Names that are not thus known and used in RTL-generation have no +effect; they are equivalent to no name at all. + +For the purpose of debugging the compiler, you may also specify a +name beginning with the @samp{*} character. Such a name is used only +for identifying the instruction in RTL dumps; it is entirely equivalent +to having a nameless pattern for all other purposes. + +@item +The @dfn{RTL template} (@pxref{RTL Template}) is a vector of incomplete +RTL expressions which show what the instruction should look like. It is +incomplete because it may contain @code{match_operand}, +@code{match_operator}, and @code{match_dup} expressions that stand for +operands of the instruction. + +If the vector has only one element, that element is the template for the +instruction pattern. If the vector has multiple elements, then the +instruction pattern is a @code{parallel} expression containing the +elements described. + +@item +@cindex pattern conditions +@cindex conditions, in patterns +A condition. This is a string which contains a C expression that is +the final test to decide whether an insn body matches this pattern. + +@cindex named patterns and conditions +For a named pattern, the condition (if present) may not depend on +the data in the insn being matched, but only the target-machine-type +flags. The compiler needs to test these conditions during +initialization in order to learn exactly which named instructions are +available in a particular run. + +@findex operands +For nameless patterns, the condition is applied only when matching an +individual insn, and only after the insn has matched the pattern's +recognition template. The insn's operands may be found in the vector +@code{operands}. + +@item +The @dfn{output template}: a string that says how to output matching +insns as assembler code. @samp{%} in this string specifies where +to substitute the value of an operand. @xref{Output Template}. + +When simple substitution isn't general enough, you can specify a piece +of C code to compute the output. @xref{Output Statement}. + +@item +Optionally, a vector containing the values of attributes for insns matching +this pattern. @xref{Insn Attributes}. +@end enumerate + +@node Example +@section Example of @code{define_insn} +@cindex @code{define_insn} example + +Here is an actual example of an instruction pattern, for the 68000/68020. + +@example +(define_insn "tstsi" + [(set (cc0) + (match_operand:SI 0 "general_operand" "rm"))] + "" + "* +@{ + if (TARGET_68020 || ! ADDRESS_REG_P (operands[0])) + return \"tstl %0\"; + return \"cmpl #0,%0\"; +@}") +@end example + +@noindent +This can also be written using braced strings: + +@example +(define_insn "tstsi" + [(set (cc0) + (match_operand:SI 0 "general_operand" "rm"))] + "" +@{ + if (TARGET_68020 || ! ADDRESS_REG_P (operands[0])) + return "tstl %0"; + return "cmpl #0,%0"; +@}) +@end example + +This is an instruction that sets the condition codes based on the value of +a general operand. It has no condition, so any insn whose RTL description +has the form shown may be handled according to this pattern. The name +@samp{tstsi} means ``test a @code{SImode} value'' and tells the RTL generation +pass that, when it is necessary to test such a value, an insn to do so +can be constructed using this pattern. + +The output control string is a piece of C code which chooses which +output template to return based on the kind of operand and the specific +type of CPU for which code is being generated. + +@samp{"rm"} is an operand constraint. Its meaning is explained below. + +@node RTL Template +@section RTL Template +@cindex RTL insn template +@cindex generating insns +@cindex insns, generating +@cindex recognizing insns +@cindex insns, recognizing + +The RTL template is used to define which insns match the particular pattern +and how to find their operands. For named patterns, the RTL template also +says how to construct an insn from specified operands. + +Construction involves substituting specified operands into a copy of the +template. Matching involves determining the values that serve as the +operands in the insn being matched. Both of these activities are +controlled by special expression types that direct matching and +substitution of the operands. + +@table @code +@findex match_operand +@item (match_operand:@var{m} @var{n} @var{predicate} @var{constraint}) +This expression is a placeholder for operand number @var{n} of +the insn. When constructing an insn, operand number @var{n} +will be substituted at this point. When matching an insn, whatever +appears at this position in the insn will be taken as operand +number @var{n}; but it must satisfy @var{predicate} or this instruction +pattern will not match at all. + +Operand numbers must be chosen consecutively counting from zero in +each instruction pattern. There may be only one @code{match_operand} +expression in the pattern for each operand number. Usually operands +are numbered in the order of appearance in @code{match_operand} +expressions. In the case of a @code{define_expand}, any operand numbers +used only in @code{match_dup} expressions have higher values than all +other operand numbers. + +@var{predicate} is a string that is the name of a C function that accepts two +arguments, an expression and a machine mode. During matching, the +function will be called with the putative operand as the expression and +@var{m} as the mode argument (if @var{m} is not specified, +@code{VOIDmode} will be used, which normally causes @var{predicate} to accept +any mode). If it returns zero, this instruction pattern fails to match. +@var{predicate} may be an empty string; then it means no test is to be done +on the operand, so anything which occurs in this position is valid. + +Most of the time, @var{predicate} will reject modes other than @var{m}---but +not always. For example, the predicate @code{address_operand} uses +@var{m} as the mode of memory ref that the address should be valid for. +Many predicates accept @code{const_int} nodes even though their mode is +@code{VOIDmode}. + +@var{constraint} controls reloading and the choice of the best register +class to use for a value, as explained later (@pxref{Constraints}). + +People are often unclear on the difference between the constraint and the +predicate. The predicate helps decide whether a given insn matches the +pattern. The constraint plays no role in this decision; instead, it +controls various decisions in the case of an insn which does match. + +@findex general_operand +On CISC machines, the most common @var{predicate} is +@code{"general_operand"}. This function checks that the putative +operand is either a constant, a register or a memory reference, and that +it is valid for mode @var{m}. + +@findex register_operand +For an operand that must be a register, @var{predicate} should be +@code{"register_operand"}. Using @code{"general_operand"} would be +valid, since the reload pass would copy any non-register operands +through registers, but this would make GCC do extra work, it would +prevent invariant operands (such as constant) from being removed from +loops, and it would prevent the register allocator from doing the best +possible job. On RISC machines, it is usually most efficient to allow +@var{predicate} to accept only objects that the constraints allow. + +@findex immediate_operand +For an operand that must be a constant, you must be sure to either use +@code{"immediate_operand"} for @var{predicate}, or make the instruction +pattern's extra condition require a constant, or both. You cannot +expect the constraints to do this work! If the constraints allow only +constants, but the predicate allows something else, the compiler will +crash when that case arises. + +@findex match_scratch +@item (match_scratch:@var{m} @var{n} @var{constraint}) +This expression is also a placeholder for operand number @var{n} +and indicates that operand must be a @code{scratch} or @code{reg} +expression. + +When matching patterns, this is equivalent to + +@smallexample +(match_operand:@var{m} @var{n} "scratch_operand" @var{pred}) +@end smallexample + +but, when generating RTL, it produces a (@code{scratch}:@var{m}) +expression. + +If the last few expressions in a @code{parallel} are @code{clobber} +expressions whose operands are either a hard register or +@code{match_scratch}, the combiner can add or delete them when +necessary. @xref{Side Effects}. + +@findex match_dup +@item (match_dup @var{n}) +This expression is also a placeholder for operand number @var{n}. +It is used when the operand needs to appear more than once in the +insn. + +In construction, @code{match_dup} acts just like @code{match_operand}: +the operand is substituted into the insn being constructed. But in +matching, @code{match_dup} behaves differently. It assumes that operand +number @var{n} has already been determined by a @code{match_operand} +appearing earlier in the recognition template, and it matches only an +identical-looking expression. + +Note that @code{match_dup} should not be used to tell the compiler that +a particular register is being used for two operands (example: +@code{add} that adds one register to another; the second register is +both an input operand and the output operand). Use a matching +constraint (@pxref{Simple Constraints}) for those. @code{match_dup} is for the cases where one +operand is used in two places in the template, such as an instruction +that computes both a quotient and a remainder, where the opcode takes +two input operands but the RTL template has to refer to each of those +twice; once for the quotient pattern and once for the remainder pattern. + +@findex match_operator +@item (match_operator:@var{m} @var{n} @var{predicate} [@var{operands}@dots{}]) +This pattern is a kind of placeholder for a variable RTL expression +code. + +When constructing an insn, it stands for an RTL expression whose +expression code is taken from that of operand @var{n}, and whose +operands are constructed from the patterns @var{operands}. + +When matching an expression, it matches an expression if the function +@var{predicate} returns nonzero on that expression @emph{and} the +patterns @var{operands} match the operands of the expression. + +Suppose that the function @code{commutative_operator} is defined as +follows, to match any expression whose operator is one of the +commutative arithmetic operators of RTL and whose mode is @var{mode}: + +@smallexample +int +commutative_operator (x, mode) + rtx x; + enum machine_mode mode; +@{ + enum rtx_code code = GET_CODE (x); + if (GET_MODE (x) != mode) + return 0; + return (GET_RTX_CLASS (code) == 'c' + || code == EQ || code == NE); +@} +@end smallexample + +Then the following pattern will match any RTL expression consisting +of a commutative operator applied to two general operands: + +@smallexample +(match_operator:SI 3 "commutative_operator" + [(match_operand:SI 1 "general_operand" "g") + (match_operand:SI 2 "general_operand" "g")]) +@end smallexample + +Here the vector @code{[@var{operands}@dots{}]} contains two patterns +because the expressions to be matched all contain two operands. + +When this pattern does match, the two operands of the commutative +operator are recorded as operands 1 and 2 of the insn. (This is done +by the two instances of @code{match_operand}.) Operand 3 of the insn +will be the entire commutative expression: use @code{GET_CODE +(operands[3])} to see which commutative operator was used. + +The machine mode @var{m} of @code{match_operator} works like that of +@code{match_operand}: it is passed as the second argument to the +predicate function, and that function is solely responsible for +deciding whether the expression to be matched ``has'' that mode. + +When constructing an insn, argument 3 of the gen-function will specify +the operation (i.e.@: the expression code) for the expression to be +made. It should be an RTL expression, whose expression code is copied +into a new expression whose operands are arguments 1 and 2 of the +gen-function. The subexpressions of argument 3 are not used; +only its expression code matters. + +When @code{match_operator} is used in a pattern for matching an insn, +it usually best if the operand number of the @code{match_operator} +is higher than that of the actual operands of the insn. This improves +register allocation because the register allocator often looks at +operands 1 and 2 of insns to see if it can do register tying. + +There is no way to specify constraints in @code{match_operator}. The +operand of the insn which corresponds to the @code{match_operator} +never has any constraints because it is never reloaded as a whole. +However, if parts of its @var{operands} are matched by +@code{match_operand} patterns, those parts may have constraints of +their own. + +@findex match_op_dup +@item (match_op_dup:@var{m} @var{n}[@var{operands}@dots{}]) +Like @code{match_dup}, except that it applies to operators instead of +operands. When constructing an insn, operand number @var{n} will be +substituted at this point. But in matching, @code{match_op_dup} behaves +differently. It assumes that operand number @var{n} has already been +determined by a @code{match_operator} appearing earlier in the +recognition template, and it matches only an identical-looking +expression. + +@findex match_parallel +@item (match_parallel @var{n} @var{predicate} [@var{subpat}@dots{}]) +This pattern is a placeholder for an insn that consists of a +@code{parallel} expression with a variable number of elements. This +expression should only appear at the top level of an insn pattern. + +When constructing an insn, operand number @var{n} will be substituted at +this point. When matching an insn, it matches if the body of the insn +is a @code{parallel} expression with at least as many elements as the +vector of @var{subpat} expressions in the @code{match_parallel}, if each +@var{subpat} matches the corresponding element of the @code{parallel}, +@emph{and} the function @var{predicate} returns nonzero on the +@code{parallel} that is the body of the insn. It is the responsibility +of the predicate to validate elements of the @code{parallel} beyond +those listed in the @code{match_parallel}. + +A typical use of @code{match_parallel} is to match load and store +multiple expressions, which can contain a variable number of elements +in a @code{parallel}. For example, + +@smallexample +(define_insn "" + [(match_parallel 0 "load_multiple_operation" + [(set (match_operand:SI 1 "gpc_reg_operand" "=r") + (match_operand:SI 2 "memory_operand" "m")) + (use (reg:SI 179)) + (clobber (reg:SI 179))])] + "" + "loadm 0,0,%1,%2") +@end smallexample + +This example comes from @file{a29k.md}. The function +@code{load_multiple_operation} is defined in @file{a29k.c} and checks +that subsequent elements in the @code{parallel} are the same as the +@code{set} in the pattern, except that they are referencing subsequent +registers and memory locations. + +An insn that matches this pattern might look like: + +@smallexample +(parallel + [(set (reg:SI 20) (mem:SI (reg:SI 100))) + (use (reg:SI 179)) + (clobber (reg:SI 179)) + (set (reg:SI 21) + (mem:SI (plus:SI (reg:SI 100) + (const_int 4)))) + (set (reg:SI 22) + (mem:SI (plus:SI (reg:SI 100) + (const_int 8))))]) +@end smallexample + +@findex match_par_dup +@item (match_par_dup @var{n} [@var{subpat}@dots{}]) +Like @code{match_op_dup}, but for @code{match_parallel} instead of +@code{match_operator}. + +@findex match_insn +@item (match_insn @var{predicate}) +Match a complete insn. Unlike the other @code{match_*} recognizers, +@code{match_insn} does not take an operand number. + +The machine mode @var{m} of @code{match_insn} works like that of +@code{match_operand}: it is passed as the second argument to the +predicate function, and that function is solely responsible for +deciding whether the expression to be matched ``has'' that mode. + +@findex match_insn2 +@item (match_insn2 @var{n} @var{predicate}) +Match a complete insn. + +The machine mode @var{m} of @code{match_insn2} works like that of +@code{match_operand}: it is passed as the second argument to the +predicate function, and that function is solely responsible for +deciding whether the expression to be matched ``has'' that mode. + +@end table + +@node Output Template +@section Output Templates and Operand Substitution +@cindex output templates +@cindex operand substitution + +@cindex @samp{%} in template +@cindex percent sign +The @dfn{output template} is a string which specifies how to output the +assembler code for an instruction pattern. Most of the template is a +fixed string which is output literally. The character @samp{%} is used +to specify where to substitute an operand; it can also be used to +identify places where different variants of the assembler require +different syntax. + +In the simplest case, a @samp{%} followed by a digit @var{n} says to output +operand @var{n} at that point in the string. + +@samp{%} followed by a letter and a digit says to output an operand in an +alternate fashion. Four letters have standard, built-in meanings described +below. The machine description macro @code{PRINT_OPERAND} can define +additional letters with nonstandard meanings. + +@samp{%c@var{digit}} can be used to substitute an operand that is a +constant value without the syntax that normally indicates an immediate +operand. + +@samp{%n@var{digit}} is like @samp{%c@var{digit}} except that the value of +the constant is negated before printing. + +@samp{%a@var{digit}} can be used to substitute an operand as if it were a +memory reference, with the actual operand treated as the address. This may +be useful when outputting a ``load address'' instruction, because often the +assembler syntax for such an instruction requires you to write the operand +as if it were a memory reference. + +@samp{%l@var{digit}} is used to substitute a @code{label_ref} into a jump +instruction. + +@samp{%=} outputs a number which is unique to each instruction in the +entire compilation. This is useful for making local labels to be +referred to more than once in a single template that generates multiple +assembler instructions. + +@samp{%} followed by a punctuation character specifies a substitution that +does not use an operand. Only one case is standard: @samp{%%} outputs a +@samp{%} into the assembler code. Other nonstandard cases can be +defined in the @code{PRINT_OPERAND} macro. You must also define +which punctuation characters are valid with the +@code{PRINT_OPERAND_PUNCT_VALID_P} macro. + +@cindex \ +@cindex backslash +The template may generate multiple assembler instructions. Write the text +for the instructions, with @samp{\;} between them. + +@cindex matching operands +When the RTL contains two operands which are required by constraint to match +each other, the output template must refer only to the lower-numbered operand. +Matching operands are not always identical, and the rest of the compiler +arranges to put the proper RTL expression for printing into the lower-numbered +operand. + +One use of nonstandard letters or punctuation following @samp{%} is to +distinguish between different assembler languages for the same machine; for +example, Motorola syntax versus MIT syntax for the 68000. Motorola syntax +requires periods in most opcode names, while MIT syntax does not. For +example, the opcode @samp{movel} in MIT syntax is @samp{move.l} in Motorola +syntax. The same file of patterns is used for both kinds of output syntax, +but the character sequence @samp{%.} is used in each place where Motorola +syntax wants a period. The @code{PRINT_OPERAND} macro for Motorola syntax +defines the sequence to output a period; the macro for MIT syntax defines +it to do nothing. + +@cindex @code{#} in template +As a special case, a template consisting of the single character @code{#} +instructs the compiler to first split the insn, and then output the +resulting instructions separately. This helps eliminate redundancy in the +output templates. If you have a @code{define_insn} that needs to emit +multiple assembler instructions, and there is an matching @code{define_split} +already defined, then you can simply use @code{#} as the output template +instead of writing an output template that emits the multiple assembler +instructions. + +If the macro @code{ASSEMBLER_DIALECT} is defined, you can use construct +of the form @samp{@{option0|option1|option2@}} in the templates. These +describe multiple variants of assembler language syntax. +@xref{Instruction Output}. + +@node Output Statement +@section C Statements for Assembler Output +@cindex output statements +@cindex C statements for assembler output +@cindex generating assembler output + +Often a single fixed template string cannot produce correct and efficient +assembler code for all the cases that are recognized by a single +instruction pattern. For example, the opcodes may depend on the kinds of +operands; or some unfortunate combinations of operands may require extra +machine instructions. + +If the output control string starts with a @samp{@@}, then it is actually +a series of templates, each on a separate line. (Blank lines and +leading spaces and tabs are ignored.) The templates correspond to the +pattern's constraint alternatives (@pxref{Multi-Alternative}). For example, +if a target machine has a two-address add instruction @samp{addr} to add +into a register and another @samp{addm} to add a register to memory, you +might write this pattern: + +@smallexample +(define_insn "addsi3" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (plus:SI (match_operand:SI 1 "general_operand" "0,0") + (match_operand:SI 2 "general_operand" "g,r")))] + "" + "@@ + addr %2,%0 + addm %2,%0") +@end smallexample + +@cindex @code{*} in template +@cindex asterisk in template +If the output control string starts with a @samp{*}, then it is not an +output template but rather a piece of C program that should compute a +template. It should execute a @code{return} statement to return the +template-string you want. Most such templates use C string literals, which +require doublequote characters to delimit them. To include these +doublequote characters in the string, prefix each one with @samp{\}. + +If the output control string is written as a brace block instead of a +double-quoted string, it is automatically assumed to be C code. In that +case, it is not necessary to put in a leading asterisk, or to escape the +doublequotes surrounding C string literals. + +The operands may be found in the array @code{operands}, whose C data type +is @code{rtx []}. + +It is very common to select different ways of generating assembler code +based on whether an immediate operand is within a certain range. Be +careful when doing this, because the result of @code{INTVAL} is an +integer on the host machine. If the host machine has more bits in an +@code{int} than the target machine has in the mode in which the constant +will be used, then some of the bits you get from @code{INTVAL} will be +superfluous. For proper results, you must carefully disregard the +values of those bits. + +@findex output_asm_insn +It is possible to output an assembler instruction and then go on to output +or compute more of them, using the subroutine @code{output_asm_insn}. This +receives two arguments: a template-string and a vector of operands. The +vector may be @code{operands}, or it may be another array of @code{rtx} +that you declare locally and initialize yourself. + +@findex which_alternative +When an insn pattern has multiple alternatives in its constraints, often +the appearance of the assembler code is determined mostly by which alternative +was matched. When this is so, the C code can test the variable +@code{which_alternative}, which is the ordinal number of the alternative +that was actually satisfied (0 for the first, 1 for the second alternative, +etc.). + +For example, suppose there are two opcodes for storing zero, @samp{clrreg} +for registers and @samp{clrmem} for memory locations. Here is how +a pattern could use @code{which_alternative} to choose between them: + +@smallexample +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (const_int 0))] + "" + @{ + return (which_alternative == 0 + ? "clrreg %0" : "clrmem %0"); + @}) +@end smallexample + +The example above, where the assembler code to generate was +@emph{solely} determined by the alternative, could also have been specified +as follows, having the output control string start with a @samp{@@}: + +@smallexample +@group +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (const_int 0))] + "" + "@@ + clrreg %0 + clrmem %0") +@end group +@end smallexample +@end ifset + +@c Most of this node appears by itself (in a different place) even +@c when the INTERNALS flag is clear. Passages that require the internals +@c manual's context are conditionalized to appear only in the internals manual. +@ifset INTERNALS +@node Constraints +@section Operand Constraints +@cindex operand constraints +@cindex constraints + +Each @code{match_operand} in an instruction pattern can specify a +constraint for the type of operands allowed. +@end ifset +@ifclear INTERNALS +@node Constraints +@section Constraints for @code{asm} Operands +@cindex operand constraints, @code{asm} +@cindex constraints, @code{asm} +@cindex @code{asm} constraints + +Here are specific details on what constraint letters you can use with +@code{asm} operands. +@end ifclear +Constraints can say whether +an operand may be in a register, and which kinds of register; whether the +operand can be a memory reference, and which kinds of address; whether the +operand may be an immediate constant, and which possible values it may +have. Constraints can also require two operands to match. + +@ifset INTERNALS +@menu +* Simple Constraints:: Basic use of constraints. +* Multi-Alternative:: When an insn has two alternative constraint-patterns. +* Class Preferences:: Constraints guide which hard register to put things in. +* Modifiers:: More precise control over effects of constraints. +* Machine Constraints:: Existing constraints for some particular machines. +@end menu +@end ifset + +@ifclear INTERNALS +@menu +* Simple Constraints:: Basic use of constraints. +* Multi-Alternative:: When an insn has two alternative constraint-patterns. +* Modifiers:: More precise control over effects of constraints. +* Machine Constraints:: Special constraints for some particular machines. +@end menu +@end ifclear + +@node Simple Constraints +@subsection Simple Constraints +@cindex simple constraints + +The simplest kind of constraint is a string full of letters, each of +which describes one kind of operand that is permitted. Here are +the letters that are allowed: + +@table @asis +@item whitespace +Whitespace characters are ignored and can be inserted at any position +except the first. This enables each alternative for different operands to +be visually aligned in the machine description even if they have different +number of constraints and modifiers. + +@cindex @samp{m} in constraint +@cindex memory references in constraints +@item @samp{m} +A memory operand is allowed, with any kind of address that the machine +supports in general. + +@cindex offsettable address +@cindex @samp{o} in constraint +@item @samp{o} +A memory operand is allowed, but only if the address is +@dfn{offsettable}. This means that adding a small integer (actually, +the width in bytes of the operand, as determined by its machine mode) +may be added to the address and the result is also a valid memory +address. + +@cindex autoincrement/decrement addressing +For example, an address which is constant is offsettable; so is an +address that is the sum of a register and a constant (as long as a +slightly larger constant is also within the range of address-offsets +supported by the machine); but an autoincrement or autodecrement +address is not offsettable. More complicated indirect/indexed +addresses may or may not be offsettable depending on the other +addressing modes that the machine supports. + +Note that in an output operand which can be matched by another +operand, the constraint letter @samp{o} is valid only when accompanied +by both @samp{<} (if the target machine has predecrement addressing) +and @samp{>} (if the target machine has preincrement addressing). + +@cindex @samp{V} in constraint +@item @samp{V} +A memory operand that is not offsettable. In other words, anything that +would fit the @samp{m} constraint but not the @samp{o} constraint. + +@cindex @samp{<} in constraint +@item @samp{<} +A memory operand with autodecrement addressing (either predecrement or +postdecrement) is allowed. + +@cindex @samp{>} in constraint +@item @samp{>} +A memory operand with autoincrement addressing (either preincrement or +postincrement) is allowed. + +@cindex @samp{r} in constraint +@cindex registers in constraints +@item @samp{r} +A register operand is allowed provided that it is in a general +register. + +@cindex constants in constraints +@cindex @samp{i} in constraint +@item @samp{i} +An immediate integer operand (one with constant value) is allowed. +This includes symbolic constants whose values will be known only at +assembly time. + +@cindex @samp{n} in constraint +@item @samp{n} +An immediate integer operand with a known numeric value is allowed. +Many systems cannot support assembly-time constants for operands less +than a word wide. Constraints for these operands should use @samp{n} +rather than @samp{i}. + +@cindex @samp{I} in constraint +@item @samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P} +Other letters in the range @samp{I} through @samp{P} may be defined in +a machine-dependent fashion to permit immediate integer operands with +explicit integer values in specified ranges. For example, on the +68000, @samp{I} is defined to stand for the range of values 1 to 8. +This is the range permitted as a shift count in the shift +instructions. + +@cindex @samp{E} in constraint +@item @samp{E} +An immediate floating operand (expression code @code{const_double}) is +allowed, but only if the target floating point format is the same as +that of the host machine (on which the compiler is running). + +@cindex @samp{F} in constraint +@item @samp{F} +An immediate floating operand (expression code @code{const_double}) is +allowed. + +@cindex @samp{G} in constraint +@cindex @samp{H} in constraint +@item @samp{G}, @samp{H} +@samp{G} and @samp{H} may be defined in a machine-dependent fashion to +permit immediate floating operands in particular ranges of values. + +@cindex @samp{s} in constraint +@item @samp{s} +An immediate integer operand whose value is not an explicit integer is +allowed. + +This might appear strange; if an insn allows a constant operand with a +value not known at compile time, it certainly must allow any known +value. So why use @samp{s} instead of @samp{i}? Sometimes it allows +better code to be generated. + +For example, on the 68000 in a fullword instruction it is possible to +use an immediate operand; but if the immediate value is between @minus{}128 +and 127, better code results from loading the value into a register and +using the register. This is because the load into the register can be +done with a @samp{moveq} instruction. We arrange for this to happen +by defining the letter @samp{K} to mean ``any integer outside the +range @minus{}128 to 127'', and then specifying @samp{Ks} in the operand +constraints. + +@cindex @samp{g} in constraint +@item @samp{g} +Any register, memory or immediate integer operand is allowed, except for +registers that are not general registers. + +@cindex @samp{X} in constraint +@item @samp{X} +@ifset INTERNALS +Any operand whatsoever is allowed, even if it does not satisfy +@code{general_operand}. This is normally used in the constraint of +a @code{match_scratch} when certain alternatives will not actually +require a scratch register. +@end ifset +@ifclear INTERNALS +Any operand whatsoever is allowed. +@end ifclear + +@cindex @samp{0} in constraint +@cindex digits in constraint +@item @samp{0}, @samp{1}, @samp{2}, @dots{} @samp{9} +An operand that matches the specified operand number is allowed. If a +digit is used together with letters within the same alternative, the +digit should come last. + +This number is allowed to be more than a single digit. If multiple +digits are encountered consecutavely, they are interpreted as a single +decimal integer. There is scant chance for ambiguity, since to-date +it has never been desirable that @samp{10} be interpreted as matching +either operand 1 @emph{or} operand 0. Should this be desired, one +can use multiple alternatives instead. + +@cindex matching constraint +@cindex constraint, matching +This is called a @dfn{matching constraint} and what it really means is +that the assembler has only a single operand that fills two roles +@ifset INTERNALS +considered separate in the RTL insn. For example, an add insn has two +input operands and one output operand in the RTL, but on most CISC +@end ifset +@ifclear INTERNALS +which @code{asm} distinguishes. For example, an add instruction uses +two input operands and an output operand, but on most CISC +@end ifclear +machines an add instruction really has only two operands, one of them an +input-output operand: + +@smallexample +addl #35,r12 +@end smallexample + +Matching constraints are used in these circumstances. +More precisely, the two operands that match must include one input-only +operand and one output-only operand. Moreover, the digit must be a +smaller number than the number of the operand that uses it in the +constraint. + +@ifset INTERNALS +For operands to match in a particular case usually means that they +are identical-looking RTL expressions. But in a few special cases +specific kinds of dissimilarity are allowed. For example, @code{*x} +as an input operand will match @code{*x++} as an output operand. +For proper results in such cases, the output template should always +use the output-operand's number when printing the operand. +@end ifset + +@cindex load address instruction +@cindex push address instruction +@cindex address constraints +@cindex @samp{p} in constraint +@item @samp{p} +An operand that is a valid memory address is allowed. This is +for ``load address'' and ``push address'' instructions. + +@findex address_operand +@samp{p} in the constraint must be accompanied by @code{address_operand} +as the predicate in the @code{match_operand}. This predicate interprets +the mode specified in the @code{match_operand} as the mode of the memory +reference for which the address would be valid. + +@cindex other register constraints +@cindex extensible constraints +@item @var{other-letters} +Other letters can be defined in machine-dependent fashion to stand for +particular classes of registers or other arbitrary operand types. +@samp{d}, @samp{a} and @samp{f} are defined on the 68000/68020 to stand +for data, address and floating point registers. + +@ifset INTERNALS +The machine description macro @code{REG_CLASS_FROM_LETTER} has first +cut at the otherwise unused letters. If it evaluates to @code{NO_REGS}, +then @code{EXTRA_CONSTRAINT} is evaluated. + +A typical use for @code{EXTRA_CONSTRANT} would be to distinguish certain +types of memory references that affect other insn operands. +@end ifset +@end table + +@ifset INTERNALS +In order to have valid assembler code, each operand must satisfy +its constraint. But a failure to do so does not prevent the pattern +from applying to an insn. Instead, it directs the compiler to modify +the code so that the constraint will be satisfied. Usually this is +done by copying an operand into a register. + +Contrast, therefore, the two instruction patterns that follow: + +@smallexample +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r") + (plus:SI (match_dup 0) + (match_operand:SI 1 "general_operand" "r")))] + "" + "@dots{}") +@end smallexample + +@noindent +which has two operands, one of which must appear in two places, and + +@smallexample +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r") + (plus:SI (match_operand:SI 1 "general_operand" "0") + (match_operand:SI 2 "general_operand" "r")))] + "" + "@dots{}") +@end smallexample + +@noindent +which has three operands, two of which are required by a constraint to be +identical. If we are considering an insn of the form + +@smallexample +(insn @var{n} @var{prev} @var{next} + (set (reg:SI 3) + (plus:SI (reg:SI 6) (reg:SI 109))) + @dots{}) +@end smallexample + +@noindent +the first pattern would not apply at all, because this insn does not +contain two identical subexpressions in the right place. The pattern would +say, ``That does not look like an add instruction; try other patterns.'' +The second pattern would say, ``Yes, that's an add instruction, but there +is something wrong with it.'' It would direct the reload pass of the +compiler to generate additional insns to make the constraint true. The +results might look like this: + +@smallexample +(insn @var{n2} @var{prev} @var{n} + (set (reg:SI 3) (reg:SI 6)) + @dots{}) + +(insn @var{n} @var{n2} @var{next} + (set (reg:SI 3) + (plus:SI (reg:SI 3) (reg:SI 109))) + @dots{}) +@end smallexample + +It is up to you to make sure that each operand, in each pattern, has +constraints that can handle any RTL expression that could be present for +that operand. (When multiple alternatives are in use, each pattern must, +for each possible combination of operand expressions, have at least one +alternative which can handle that combination of operands.) The +constraints don't need to @emph{allow} any possible operand---when this is +the case, they do not constrain---but they must at least point the way to +reloading any possible operand so that it will fit. + +@itemize @bullet +@item +If the constraint accepts whatever operands the predicate permits, +there is no problem: reloading is never necessary for this operand. + +For example, an operand whose constraints permit everything except +registers is safe provided its predicate rejects registers. + +An operand whose predicate accepts only constant values is safe +provided its constraints include the letter @samp{i}. If any possible +constant value is accepted, then nothing less than @samp{i} will do; +if the predicate is more selective, then the constraints may also be +more selective. + +@item +Any operand expression can be reloaded by copying it into a register. +So if an operand's constraints allow some kind of register, it is +certain to be safe. It need not permit all classes of registers; the +compiler knows how to copy a register into another register of the +proper class in order to make an instruction valid. + +@cindex nonoffsettable memory reference +@cindex memory reference, nonoffsettable +@item +A nonoffsettable memory reference can be reloaded by copying the +address into a register. So if the constraint uses the letter +@samp{o}, all memory references are taken care of. + +@item +A constant operand can be reloaded by allocating space in memory to +hold it as preinitialized data. Then the memory reference can be used +in place of the constant. So if the constraint uses the letters +@samp{o} or @samp{m}, constant operands are not a problem. + +@item +If the constraint permits a constant and a pseudo register used in an insn +was not allocated to a hard register and is equivalent to a constant, +the register will be replaced with the constant. If the predicate does +not permit a constant and the insn is re-recognized for some reason, the +compiler will crash. Thus the predicate must always recognize any +objects allowed by the constraint. +@end itemize + +If the operand's predicate can recognize registers, but the constraint does +not permit them, it can make the compiler crash. When this operand happens +to be a register, the reload pass will be stymied, because it does not know +how to copy a register temporarily into memory. + +If the predicate accepts a unary operator, the constraint applies to the +operand. For example, the MIPS processor at ISA level 3 supports an +instruction which adds two registers in @code{SImode} to produce a +@code{DImode} result, but only if the registers are correctly sign +extended. This predicate for the input operands accepts a +@code{sign_extend} of an @code{SImode} register. Write the constraint +to indicate the type of register that is required for the operand of the +@code{sign_extend}. +@end ifset + +@node Multi-Alternative +@subsection Multiple Alternative Constraints +@cindex multiple alternative constraints + +Sometimes a single instruction has multiple alternative sets of possible +operands. For example, on the 68000, a logical-or instruction can combine +register or an immediate value into memory, or it can combine any kind of +operand into a register; but it cannot combine one memory location into +another. + +These constraints are represented as multiple alternatives. An alternative +can be described by a series of letters for each operand. The overall +constraint for an operand is made from the letters for this operand +from the first alternative, a comma, the letters for this operand from +the second alternative, a comma, and so on until the last alternative. +@ifset INTERNALS +Here is how it is done for fullword logical-or on the 68000: + +@smallexample +(define_insn "iorsi3" + [(set (match_operand:SI 0 "general_operand" "=m,d") + (ior:SI (match_operand:SI 1 "general_operand" "%0,0") + (match_operand:SI 2 "general_operand" "dKs,dmKs")))] + @dots{}) +@end smallexample + +The first alternative has @samp{m} (memory) for operand 0, @samp{0} for +operand 1 (meaning it must match operand 0), and @samp{dKs} for operand +2. The second alternative has @samp{d} (data register) for operand 0, +@samp{0} for operand 1, and @samp{dmKs} for operand 2. The @samp{=} and +@samp{%} in the constraints apply to all the alternatives; their +meaning is explained in the next section (@pxref{Class Preferences}). +@end ifset + +@c FIXME Is this ? and ! stuff of use in asm()? If not, hide unless INTERNAL +If all the operands fit any one alternative, the instruction is valid. +Otherwise, for each alternative, the compiler counts how many instructions +must be added to copy the operands so that that alternative applies. +The alternative requiring the least copying is chosen. If two alternatives +need the same amount of copying, the one that comes first is chosen. +These choices can be altered with the @samp{?} and @samp{!} characters: + +@table @code +@cindex @samp{?} in constraint +@cindex question mark +@item ? +Disparage slightly the alternative that the @samp{?} appears in, +as a choice when no alternative applies exactly. The compiler regards +this alternative as one unit more costly for each @samp{?} that appears +in it. + +@cindex @samp{!} in constraint +@cindex exclamation point +@item ! +Disparage severely the alternative that the @samp{!} appears in. +This alternative can still be used if it fits without reloading, +but if reloading is needed, some other alternative will be used. +@end table + +@ifset INTERNALS +When an insn pattern has multiple alternatives in its constraints, often +the appearance of the assembler code is determined mostly by which +alternative was matched. When this is so, the C code for writing the +assembler code can use the variable @code{which_alternative}, which is +the ordinal number of the alternative that was actually satisfied (0 for +the first, 1 for the second alternative, etc.). @xref{Output Statement}. +@end ifset + +@ifset INTERNALS +@node Class Preferences +@subsection Register Class Preferences +@cindex class preference constraints +@cindex register class preference constraints + +@cindex voting between constraint alternatives +The operand constraints have another function: they enable the compiler +to decide which kind of hardware register a pseudo register is best +allocated to. The compiler examines the constraints that apply to the +insns that use the pseudo register, looking for the machine-dependent +letters such as @samp{d} and @samp{a} that specify classes of registers. +The pseudo register is put in whichever class gets the most ``votes''. +The constraint letters @samp{g} and @samp{r} also vote: they vote in +favor of a general register. The machine description says which registers +are considered general. + +Of course, on some machines all registers are equivalent, and no register +classes are defined. Then none of this complexity is relevant. +@end ifset + +@node Modifiers +@subsection Constraint Modifier Characters +@cindex modifiers in constraints +@cindex constraint modifier characters + +@c prevent bad page break with this line +Here are constraint modifier characters. + +@table @samp +@cindex @samp{=} in constraint +@item = +Means that this operand is write-only for this instruction: the previous +value is discarded and replaced by output data. + +@cindex @samp{+} in constraint +@item + +Means that this operand is both read and written by the instruction. + +When the compiler fixes up the operands to satisfy the constraints, +it needs to know which operands are inputs to the instruction and +which are outputs from it. @samp{=} identifies an output; @samp{+} +identifies an operand that is both input and output; all other operands +are assumed to be input only. + +If you specify @samp{=} or @samp{+} in a constraint, you put it in the +first character of the constraint string. + +@cindex @samp{&} in constraint +@cindex earlyclobber operand +@item & +Means (in a particular alternative) that this operand is an +@dfn{earlyclobber} operand, which is modified before the instruction is +finished using the input operands. Therefore, this operand may not lie +in a register that is used as an input operand or as part of any memory +address. + +@samp{&} applies only to the alternative in which it is written. In +constraints with multiple alternatives, sometimes one alternative +requires @samp{&} while others do not. See, for example, the +@samp{movdf} insn of the 68000. + +An input operand can be tied to an earlyclobber operand if its only +use as an input occurs before the early result is written. Adding +alternatives of this form often allows GCC to produce better code +when only some of the inputs can be affected by the earlyclobber. +See, for example, the @samp{mulsi3} insn of the ARM@. + +@samp{&} does not obviate the need to write @samp{=}. + +@cindex @samp{%} in constraint +@item % +Declares the instruction to be commutative for this operand and the +following operand. This means that the compiler may interchange the +two operands if that is the cheapest way to make all operands fit the +constraints. +@ifset INTERNALS +This is often used in patterns for addition instructions +that really have only two operands: the result must go in one of the +arguments. Here for example, is how the 68000 halfword-add +instruction is defined: + +@smallexample +(define_insn "addhi3" + [(set (match_operand:HI 0 "general_operand" "=m,r") + (plus:HI (match_operand:HI 1 "general_operand" "%0,0") + (match_operand:HI 2 "general_operand" "di,g")))] + @dots{}) +@end smallexample +@end ifset + +@cindex @samp{#} in constraint +@item # +Says that all following characters, up to the next comma, are to be +ignored as a constraint. They are significant only for choosing +register preferences. + +@cindex @samp{*} in constraint +@item * +Says that the following character should be ignored when choosing +register preferences. @samp{*} has no effect on the meaning of the +constraint as a constraint, and no effect on reloading. + +@ifset INTERNALS +Here is an example: the 68000 has an instruction to sign-extend a +halfword in a data register, and can also sign-extend a value by +copying it into an address register. While either kind of register is +acceptable, the constraints on an address-register destination are +less strict, so it is best if register allocation makes an address +register its goal. Therefore, @samp{*} is used so that the @samp{d} +constraint letter (for data register) is ignored when computing +register preferences. + +@smallexample +(define_insn "extendhisi2" + [(set (match_operand:SI 0 "general_operand" "=*d,a") + (sign_extend:SI + (match_operand:HI 1 "general_operand" "0,g")))] + @dots{}) +@end smallexample +@end ifset +@end table + +@node Machine Constraints +@subsection Constraints for Particular Machines +@cindex machine specific constraints +@cindex constraints, machine specific + +Whenever possible, you should use the general-purpose constraint letters +in @code{asm} arguments, since they will convey meaning more readily to +people reading your code. Failing that, use the constraint letters +that usually have very similar meanings across architectures. The most +commonly used constraints are @samp{m} and @samp{r} (for memory and +general-purpose registers respectively; @pxref{Simple Constraints}), and +@samp{I}, usually the letter indicating the most common +immediate-constant format. + +For each machine architecture, the +@file{config/@var{machine}/@var{machine}.h} file defines additional +constraints. These constraints are used by the compiler itself for +instruction generation, as well as for @code{asm} statements; therefore, +some of the constraints are not particularly interesting for @code{asm}. +The constraints are defined through these macros: + +@table @code +@item REG_CLASS_FROM_LETTER +Register class constraints (usually lower case). + +@item CONST_OK_FOR_LETTER_P +Immediate constant constraints, for non-floating point constants of +word size or smaller precision (usually upper case). + +@item CONST_DOUBLE_OK_FOR_LETTER_P +Immediate constant constraints, for all floating point constants and for +constants of greater than word size precision (usually upper case). + +@item EXTRA_CONSTRAINT +Special cases of registers or memory. This macro is not required, and +is only defined for some machines. +@end table + +Inspecting these macro definitions in the compiler source for your +machine is the best way to be certain you have the right constraints. +However, here is a summary of the machine-dependent constraints +available on some particular machines. + +@table @emph +@item ARM family---@file{arm.h} +@table @code +@item f +Floating-point register + +@item F +One of the floating-point constants 0.0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 +or 10.0 + +@item G +Floating-point constant that would satisfy the constraint @samp{F} if it +were negated + +@item I +Integer that is valid as an immediate operand in a data processing +instruction. That is, an integer in the range 0 to 255 rotated by a +multiple of 2 + +@item J +Integer in the range @minus{}4095 to 4095 + +@item K +Integer that satisfies constraint @samp{I} when inverted (ones complement) + +@item L +Integer that satisfies constraint @samp{I} when negated (twos complement) + +@item M +Integer in the range 0 to 32 + +@item Q +A memory reference where the exact address is in a single register +(`@samp{m}' is preferable for @code{asm} statements) + +@item R +An item in the constant pool + +@item S +A symbol in the text segment of the current file +@end table + +@item AMD 29000 family---@file{a29k.h} +@table @code +@item l +Local register 0 + +@item b +Byte Pointer (@samp{BP}) register + +@item q +@samp{Q} register + +@item h +Special purpose register + +@item A +First accumulator register + +@item a +Other accumulator register + +@item f +Floating point register + +@item I +Constant greater than 0, less than 0x100 + +@item J +Constant greater than 0, less than 0x10000 + +@item K +Constant whose high 24 bits are on (1) + +@item L +16-bit constant whose high 8 bits are on (1) + +@item M +32-bit constant whose high 16 bits are on (1) + +@item N +32-bit negative constant that fits in 8 bits + +@item O +The constant 0x80000000 or, on the 29050, any 32-bit constant +whose low 16 bits are 0. + +@item P +16-bit negative constant that fits in 8 bits + +@item G +@itemx H +A floating point constant (in @code{asm} statements, use the machine +independent @samp{E} or @samp{F} instead) +@end table + +@item AVR family---@file{avr.h} +@table @code +@item l +Registers from r0 to r15 + +@item a +Registers from r16 to r23 + +@item d +Registers from r16 to r31 + +@item w +Registers from r24 to r31. These registers can be used in @samp{adiw} command + +@item e +Pointer register (r26--r31) + +@item b +Base pointer register (r28--r31) + +@item q +Stack pointer register (SPH:SPL) + +@item t +Temporary register r0 + +@item x +Register pair X (r27:r26) + +@item y +Register pair Y (r29:r28) + +@item z +Register pair Z (r31:r30) + +@item I +Constant greater than @minus{}1, less than 64 + +@item J +Constant greater than @minus{}64, less than 1 + +@item K +Constant integer 2 + +@item L +Constant integer 0 + +@item M +Constant that fits in 8 bits + +@item N +Constant integer @minus{}1 + +@item O +Constant integer 8, 16, or 24 + +@item P +Constant integer 1 + +@item G +A floating point constant 0.0 +@end table + +@item IBM RS6000---@file{rs6000.h} +@table @code +@item b +Address base register + +@item f +Floating point register + +@item h +@samp{MQ}, @samp{CTR}, or @samp{LINK} register + +@item q +@samp{MQ} register + +@item c +@samp{CTR} register + +@item l +@samp{LINK} register + +@item x +@samp{CR} register (condition register) number 0 + +@item y +@samp{CR} register (condition register) + +@item z +@samp{FPMEM} stack memory for FPR-GPR transfers + +@item I +Signed 16-bit constant + +@item J +Unsigned 16-bit constant shifted left 16 bits (use @samp{L} instead for +@code{SImode} constants) + +@item K +Unsigned 16-bit constant + +@item L +Signed 16-bit constant shifted left 16 bits + +@item M +Constant larger than 31 + +@item N +Exact power of 2 + +@item O +Zero + +@item P +Constant whose negation is a signed 16-bit constant + +@item G +Floating point constant that can be loaded into a register with one +instruction per word + +@item Q +Memory operand that is an offset from a register (@samp{m} is preferable +for @code{asm} statements) + +@item R +AIX TOC entry + +@item S +Constant suitable as a 64-bit mask operand + +@item T +Constant suitable as a 32-bit mask operand + +@item U +System V Release 4 small data area reference +@end table + +@item Intel 386---@file{i386.h} +@table @code +@item q +@samp{a}, @code{b}, @code{c}, or @code{d} register for the i386. +For x86-64 it is equivalent to @samp{r} class. (for 8-bit instructions that +do not use upper halves) + +@item Q +@samp{a}, @code{b}, @code{c}, or @code{d} register. (for 8-bit instructions, +that do use upper halves) + +@item R +Legacy register---equivalent to @code{r} class in i386 mode. +(for non-8-bit registers used together with 8-bit upper halves in a single +instruction) + +@item A +Specifies the @samp{a} or @samp{d} registers. This is primarily useful +for 64-bit integer values (when in 32-bit mode) intended to be returned +with the @samp{d} register holding the most significant bits and the +@samp{a} register holding the least significant bits. + +@item f +Floating point register + +@item t +First (top of stack) floating point register + +@item u +Second floating point register + +@item a +@samp{a} register + +@item b +@samp{b} register + +@item c +@samp{c} register + +@item d +@samp{d} register + +@item D +@samp{di} register + +@item S +@samp{si} register + +@item x +@samp{xmm} SSE register + +@item y +MMX register + +@item I +Constant in range 0 to 31 (for 32-bit shifts) + +@item J +Constant in range 0 to 63 (for 64-bit shifts) + +@item K +@samp{0xff} + +@item L +@samp{0xffff} + +@item M +0, 1, 2, or 3 (shifts for @code{lea} instruction) + +@item N +Constant in range 0 to 255 (for @code{out} instruction) + +@item Z +Constant in range 0 to @code{0xffffffff} or symbolic reference known to fit specified range. +(for using immediates in zero extending 32-bit to 64-bit x86-64 instructions) + +@item e +Constant in range @minus{}2147483648 to 2147483647 or symbolic reference known to fit specified range. +(for using immediates in 64-bit x86-64 instructions) + +@item G +Standard 80387 floating point constant +@end table + +@item Intel 960---@file{i960.h} +@table @code +@item f +Floating point register (@code{fp0} to @code{fp3}) + +@item l +Local register (@code{r0} to @code{r15}) + +@item b +Global register (@code{g0} to @code{g15}) + +@item d +Any local or global register + +@item I +Integers from 0 to 31 + +@item J +0 + +@item K +Integers from @minus{}31 to 0 + +@item G +Floating point 0 + +@item H +Floating point 1 +@end table + +@item MIPS---@file{mips.h} +@table @code +@item d +General-purpose integer register + +@item f +Floating-point register (if available) + +@item h +@samp{Hi} register + +@item l +@samp{Lo} register + +@item x +@samp{Hi} or @samp{Lo} register + +@item y +General-purpose integer register + +@item z +Floating-point status register + +@item I +Signed 16-bit constant (for arithmetic instructions) + +@item J +Zero + +@item K +Zero-extended 16-bit constant (for logic instructions) + +@item L +Constant with low 16 bits zero (can be loaded with @code{lui}) + +@item M +32-bit constant which requires two instructions to load (a constant +which is not @samp{I}, @samp{K}, or @samp{L}) + +@item N +Negative 16-bit constant + +@item O +Exact power of two + +@item P +Positive 16-bit constant + +@item G +Floating point zero + +@item Q +Memory reference that can be loaded with more than one instruction +(@samp{m} is preferable for @code{asm} statements) + +@item R +Memory reference that can be loaded with one instruction +(@samp{m} is preferable for @code{asm} statements) + +@item S +Memory reference in external OSF/rose PIC format +(@samp{m} is preferable for @code{asm} statements) +@end table + +@item Motorola 680x0---@file{m68k.h} +@table @code +@item a +Address register + +@item d +Data register + +@item f +68881 floating-point register, if available + +@item x +Sun FPA (floating-point) register, if available + +@item y +First 16 Sun FPA registers, if available + +@item I +Integer in the range 1 to 8 + +@item J +16-bit signed number + +@item K +Signed number whose magnitude is greater than 0x80 + +@item L +Integer in the range @minus{}8 to @minus{}1 + +@item M +Signed number whose magnitude is greater than 0x100 + +@item G +Floating point constant that is not a 68881 constant + +@item H +Floating point constant that can be used by Sun FPA +@end table + +@item Motorola 68HC11 & 68HC12 families---@file{m68hc11.h} +@table @code +@item a +Register 'a' + +@item b +Register 'b' + +@item d +Register 'd' + +@item q +An 8-bit register + +@item t +Temporary soft register _.tmp + +@item u +A soft register _.d1 to _.d31 + +@item w +Stack pointer register + +@item x +Register 'x' + +@item y +Register 'y' + +@item z +Pseudo register 'z' (replaced by 'x' or 'y' at the end) + +@item A +An address register: x, y or z + +@item B +An address register: x or y + +@item D +Register pair (x:d) to form a 32-bit value + +@item L +Constants in the range @minus{}65536 to 65535 + +@item M +Constants whose 16-bit low part is zero + +@item N +Constant integer 1 or @minus{}1 + +@item O +Constant integer 16 + +@item P +Constants in the range @minus{}8 to 2 + +@end table + +@need 1000 +@item SPARC---@file{sparc.h} +@table @code +@item f +Floating-point register that can hold 32- or 64-bit values. + +@item e +Floating-point register that can hold 64- or 128-bit values. + +@item I +Signed 13-bit constant + +@item J +Zero + +@item K +32-bit constant with the low 12 bits clear (a constant that can be +loaded with the @code{sethi} instruction) + +@item G +Floating-point zero + +@item H +Signed 13-bit constant, sign-extended to 32 or 64 bits + +@item Q +Floating-point constant whose integral representation can +be moved into an integer register using a single sethi +instruction + +@item R +Floating-point constant whose integral representation can +be moved into an integer register using a single mov +instruction + +@item S +Floating-point constant whose integral representation can +be moved into an integer register using a high/lo_sum +instruction sequence + +@item T +Memory address aligned to an 8-byte boundary + +@item U +Even register + +@end table + +@item TMS320C3x/C4x---@file{c4x.h} +@table @code +@item a +Auxiliary (address) register (ar0-ar7) + +@item b +Stack pointer register (sp) + +@item c +Standard (32-bit) precision integer register + +@item f +Extended (40-bit) precision register (r0-r11) + +@item k +Block count register (bk) + +@item q +Extended (40-bit) precision low register (r0-r7) + +@item t +Extended (40-bit) precision register (r0-r1) + +@item u +Extended (40-bit) precision register (r2-r3) + +@item v +Repeat count register (rc) + +@item x +Index register (ir0-ir1) + +@item y +Status (condition code) register (st) + +@item z +Data page register (dp) + +@item G +Floating-point zero + +@item H +Immediate 16-bit floating-point constant + +@item I +Signed 16-bit constant + +@item J +Signed 8-bit constant + +@item K +Signed 5-bit constant + +@item L +Unsigned 16-bit constant + +@item M +Unsigned 8-bit constant + +@item N +Ones complement of unsigned 16-bit constant + +@item O +High 16-bit constant (32-bit constant with 16 LSBs zero) + +@item Q +Indirect memory reference with signed 8-bit or index register displacement + +@item R +Indirect memory reference with unsigned 5-bit displacement + +@item S +Indirect memory reference with 1 bit or index register displacement + +@item T +Direct memory reference + +@item U +Symbolic address + +@end table + +@item S/390 and zSeries---@file{s390.h} +@table @code +@item a +Address register (general purpose register except r0) + +@item d +Data register (arbitrary general purpose register) + +@item f +Floating-point register + +@item I +Unsigned 8-bit constant (0--255) + +@item J +Unsigned 12-bit constant (0--4095) + +@item K +Signed 16-bit constant (@minus{}32768--32767) + +@item L +Unsigned 16-bit constant (0--65535) + +@item Q +Memory reference without index register + +@item S +Symbolic constant suitable for use with the @code{larl} instruction + +@end table + +@item Xstormy16---@file{stormy16.h} +@table @code +@item a +Register r0. + +@item b +Register r1. + +@item c +Register r2. + +@item d +Register r8. + +@item e +Registers r0 through r7. + +@item t +Registers r0 and r1. + +@item y +The carry register. + +@item z +Registers r8 and r9. + +@item I +A constant between 0 and 3 inclusive. + +@item J +A constant that has exactly one bit set. + +@item K +A constant that has exactly one bit clear. + +@item L +A constant between 0 and 255 inclusive. + +@item M +A constant between @minus{}255 and 0 inclusive. + +@item N +A constant between @minus{}3 and 0 inclusive. + +@item O +A constant between 1 and 4 inclusive. + +@item P +A constant between @minus{}4 and @minus{}1 inclusive. + +@item Q +A memory reference that is a stack push. + +@item R +A memory reference that is a stack pop. + +@item S +A memory reference that refers to an constant address of known value. + +@item T +The register indicated by Rx (not implemented yet). + +@item U +A constant that is not between 2 and 15 inclusive. + +@end table + +@item Xtensa---@file{xtensa.h} +@table @code +@item a +General-purpose 32-bit register + +@item b +One-bit boolean register + +@item A +MAC16 40-bit accumulator register + +@item I +Signed 12-bit integer constant, for use in MOVI instructions + +@item J +Signed 8-bit integer constant, for use in ADDI instructions + +@item K +Integer constant valid for BccI instructions + +@item L +Unsigned constant valid for BccUI instructions + +@end table + +@end table + +@ifset INTERNALS +@node Standard Names +@section Standard Pattern Names For Generation +@cindex standard pattern names +@cindex pattern names +@cindex names, pattern + +Here is a table of the instruction names that are meaningful in the RTL +generation pass of the compiler. Giving one of these names to an +instruction pattern tells the RTL generation pass that it can use the +pattern to accomplish a certain task. + +@table @asis +@cindex @code{mov@var{m}} instruction pattern +@item @samp{mov@var{m}} +Here @var{m} stands for a two-letter machine mode name, in lower case. +This instruction pattern moves data with that machine mode from operand +1 to operand 0. For example, @samp{movsi} moves full-word data. + +If operand 0 is a @code{subreg} with mode @var{m} of a register whose +own mode is wider than @var{m}, the effect of this instruction is +to store the specified value in the part of the register that corresponds +to mode @var{m}. Bits outside of @var{m}, but which are within the +same target word as the @code{subreg} are undefined. Bits which are +outside the target word are left unchanged. + +This class of patterns is special in several ways. First of all, each +of these names up to and including full word size @emph{must} be defined, +because there is no other way to copy a datum from one place to another. +If there are patterns accepting operands in larger modes, +@samp{mov@var{m}} must be defined for integer modes of those sizes. + +Second, these patterns are not used solely in the RTL generation pass. +Even the reload pass can generate move insns to copy values from stack +slots into temporary registers. When it does so, one of the operands is +a hard register and the other is an operand that can need to be reloaded +into a register. + +@findex force_reg +Therefore, when given such a pair of operands, the pattern must generate +RTL which needs no reloading and needs no temporary registers---no +registers other than the operands. For example, if you support the +pattern with a @code{define_expand}, then in such a case the +@code{define_expand} mustn't call @code{force_reg} or any other such +function which might generate new pseudo registers. + +This requirement exists even for subword modes on a RISC machine where +fetching those modes from memory normally requires several insns and +some temporary registers. + +@findex change_address +During reload a memory reference with an invalid address may be passed +as an operand. Such an address will be replaced with a valid address +later in the reload pass. In this case, nothing may be done with the +address except to use it as it stands. If it is copied, it will not be +replaced with a valid address. No attempt should be made to make such +an address into a valid address and no routine (such as +@code{change_address}) that will do so may be called. Note that +@code{general_operand} will fail when applied to such an address. + +@findex reload_in_progress +The global variable @code{reload_in_progress} (which must be explicitly +declared if required) can be used to determine whether such special +handling is required. + +The variety of operands that have reloads depends on the rest of the +machine description, but typically on a RISC machine these can only be +pseudo registers that did not get hard registers, while on other +machines explicit memory references will get optional reloads. + +If a scratch register is required to move an object to or from memory, +it can be allocated using @code{gen_reg_rtx} prior to life analysis. + +If there are cases which need scratch registers during or after reload, +you must define @code{SECONDARY_INPUT_RELOAD_CLASS} and/or +@code{SECONDARY_OUTPUT_RELOAD_CLASS} to detect them, and provide +patterns @samp{reload_in@var{m}} or @samp{reload_out@var{m}} to handle +them. @xref{Register Classes}. + +@findex no_new_pseudos +The global variable @code{no_new_pseudos} can be used to determine if it +is unsafe to create new pseudo registers. If this variable is nonzero, then +it is unsafe to call @code{gen_reg_rtx} to allocate a new pseudo. + +The constraints on a @samp{mov@var{m}} must permit moving any hard +register to any other hard register provided that +@code{HARD_REGNO_MODE_OK} permits mode @var{m} in both registers and +@code{REGISTER_MOVE_COST} applied to their classes returns a value of 2. + +It is obligatory to support floating point @samp{mov@var{m}} +instructions into and out of any registers that can hold fixed point +values, because unions and structures (which have modes @code{SImode} or +@code{DImode}) can be in those registers and they may have floating +point members. + +There may also be a need to support fixed point @samp{mov@var{m}} +instructions in and out of floating point registers. Unfortunately, I +have forgotten why this was so, and I don't know whether it is still +true. If @code{HARD_REGNO_MODE_OK} rejects fixed point values in +floating point registers, then the constraints of the fixed point +@samp{mov@var{m}} instructions must be designed to avoid ever trying to +reload into a floating point register. + +@cindex @code{reload_in} instruction pattern +@cindex @code{reload_out} instruction pattern +@item @samp{reload_in@var{m}} +@itemx @samp{reload_out@var{m}} +Like @samp{mov@var{m}}, but used when a scratch register is required to +move between operand 0 and operand 1. Operand 2 describes the scratch +register. See the discussion of the @code{SECONDARY_RELOAD_CLASS} +macro in @pxref{Register Classes}. + +There are special restrictions on the form of the @code{match_operand}s +used in these patterns. First, only the predicate for the reload +operand is examined, i.e., @code{reload_in} examines operand 1, but not +the predicates for operand 0 or 2. Second, there may be only one +alternative in the constraints. Third, only a single register class +letter may be used for the constraint; subsequent constraint letters +are ignored. As a special exception, an empty constraint string +matches the @code{ALL_REGS} register class. This may relieve ports +of the burden of defining an @code{ALL_REGS} constraint letter just +for these patterns. + +@cindex @code{movstrict@var{m}} instruction pattern +@item @samp{movstrict@var{m}} +Like @samp{mov@var{m}} except that if operand 0 is a @code{subreg} +with mode @var{m} of a register whose natural mode is wider, +the @samp{movstrict@var{m}} instruction is guaranteed not to alter +any of the register except the part which belongs to mode @var{m}. + +@cindex @code{load_multiple} instruction pattern +@item @samp{load_multiple} +Load several consecutive memory locations into consecutive registers. +Operand 0 is the first of the consecutive registers, operand 1 +is the first memory location, and operand 2 is a constant: the +number of consecutive registers. + +Define this only if the target machine really has such an instruction; +do not define this if the most efficient way of loading consecutive +registers from memory is to do them one at a time. + +On some machines, there are restrictions as to which consecutive +registers can be stored into memory, such as particular starting or +ending register numbers or only a range of valid counts. For those +machines, use a @code{define_expand} (@pxref{Expander Definitions}) +and make the pattern fail if the restrictions are not met. + +Write the generated insn as a @code{parallel} with elements being a +@code{set} of one register from the appropriate memory location (you may +also need @code{use} or @code{clobber} elements). Use a +@code{match_parallel} (@pxref{RTL Template}) to recognize the insn. See +@file{a29k.md} and @file{rs6000.md} for examples of the use of this insn +pattern. + +@cindex @samp{store_multiple} instruction pattern +@item @samp{store_multiple} +Similar to @samp{load_multiple}, but store several consecutive registers +into consecutive memory locations. Operand 0 is the first of the +consecutive memory locations, operand 1 is the first register, and +operand 2 is a constant: the number of consecutive registers. + +@cindex @code{push@var{m}} instruction pattern +@item @samp{push@var{m}} +Output an push instruction. Operand 0 is value to push. Used only when +@code{PUSH_ROUNDING} is defined. For historical reason, this pattern may be +missing and in such case an @code{mov} expander is used instead, with a +@code{MEM} expression forming the push operation. The @code{mov} expander +method is deprecated. + +@cindex @code{add@var{m}3} instruction pattern +@item @samp{add@var{m}3} +Add operand 2 and operand 1, storing the result in operand 0. All operands +must have mode @var{m}. This can be used even on two-address machines, by +means of constraints requiring operands 1 and 0 to be the same location. + +@cindex @code{sub@var{m}3} instruction pattern +@cindex @code{mul@var{m}3} instruction pattern +@cindex @code{div@var{m}3} instruction pattern +@cindex @code{udiv@var{m}3} instruction pattern +@cindex @code{mod@var{m}3} instruction pattern +@cindex @code{umod@var{m}3} instruction pattern +@cindex @code{smin@var{m}3} instruction pattern +@cindex @code{smax@var{m}3} instruction pattern +@cindex @code{umin@var{m}3} instruction pattern +@cindex @code{umax@var{m}3} instruction pattern +@cindex @code{and@var{m}3} instruction pattern +@cindex @code{ior@var{m}3} instruction pattern +@cindex @code{xor@var{m}3} instruction pattern +@item @samp{sub@var{m}3}, @samp{mul@var{m}3} +@itemx @samp{div@var{m}3}, @samp{udiv@var{m}3}, @samp{mod@var{m}3}, @samp{umod@var{m}3} +@itemx @samp{smin@var{m}3}, @samp{smax@var{m}3}, @samp{umin@var{m}3}, @samp{umax@var{m}3} +@itemx @samp{and@var{m}3}, @samp{ior@var{m}3}, @samp{xor@var{m}3} +Similar, for other arithmetic operations. +@cindex @code{min@var{m}3} instruction pattern +@cindex @code{max@var{m}3} instruction pattern +@itemx @samp{min@var{m}3}, @samp{max@var{m}3} +Floating point min and max operations. If both operands are zeros, +or if either operand is NaN, then it is unspecified which of the two +operands is returned as the result. + + +@cindex @code{mulhisi3} instruction pattern +@item @samp{mulhisi3} +Multiply operands 1 and 2, which have mode @code{HImode}, and store +a @code{SImode} product in operand 0. + +@cindex @code{mulqihi3} instruction pattern +@cindex @code{mulsidi3} instruction pattern +@item @samp{mulqihi3}, @samp{mulsidi3} +Similar widening-multiplication instructions of other widths. + +@cindex @code{umulqihi3} instruction pattern +@cindex @code{umulhisi3} instruction pattern +@cindex @code{umulsidi3} instruction pattern +@item @samp{umulqihi3}, @samp{umulhisi3}, @samp{umulsidi3} +Similar widening-multiplication instructions that do unsigned +multiplication. + +@cindex @code{smul@var{m}3_highpart} instruction pattern +@item @samp{smul@var{m}3_highpart} +Perform a signed multiplication of operands 1 and 2, which have mode +@var{m}, and store the most significant half of the product in operand 0. +The least significant half of the product is discarded. + +@cindex @code{umul@var{m}3_highpart} instruction pattern +@item @samp{umul@var{m}3_highpart} +Similar, but the multiplication is unsigned. + +@cindex @code{divmod@var{m}4} instruction pattern +@item @samp{divmod@var{m}4} +Signed division that produces both a quotient and a remainder. +Operand 1 is divided by operand 2 to produce a quotient stored +in operand 0 and a remainder stored in operand 3. + +For machines with an instruction that produces both a quotient and a +remainder, provide a pattern for @samp{divmod@var{m}4} but do not +provide patterns for @samp{div@var{m}3} and @samp{mod@var{m}3}. This +allows optimization in the relatively common case when both the quotient +and remainder are computed. + +If an instruction that just produces a quotient or just a remainder +exists and is more efficient than the instruction that produces both, +write the output routine of @samp{divmod@var{m}4} to call +@code{find_reg_note} and look for a @code{REG_UNUSED} note on the +quotient or remainder and generate the appropriate instruction. + +@cindex @code{udivmod@var{m}4} instruction pattern +@item @samp{udivmod@var{m}4} +Similar, but does unsigned division. + +@cindex @code{ashl@var{m}3} instruction pattern +@item @samp{ashl@var{m}3} +Arithmetic-shift operand 1 left by a number of bits specified by operand +2, and store the result in operand 0. Here @var{m} is the mode of +operand 0 and operand 1; operand 2's mode is specified by the +instruction pattern, and the compiler will convert the operand to that +mode before generating the instruction. + +@cindex @code{ashr@var{m}3} instruction pattern +@cindex @code{lshr@var{m}3} instruction pattern +@cindex @code{rotl@var{m}3} instruction pattern +@cindex @code{rotr@var{m}3} instruction pattern +@item @samp{ashr@var{m}3}, @samp{lshr@var{m}3}, @samp{rotl@var{m}3}, @samp{rotr@var{m}3} +Other shift and rotate instructions, analogous to the +@code{ashl@var{m}3} instructions. + +@cindex @code{neg@var{m}2} instruction pattern +@item @samp{neg@var{m}2} +Negate operand 1 and store the result in operand 0. + +@cindex @code{abs@var{m}2} instruction pattern +@item @samp{abs@var{m}2} +Store the absolute value of operand 1 into operand 0. + +@cindex @code{sqrt@var{m}2} instruction pattern +@item @samp{sqrt@var{m}2} +Store the square root of operand 1 into operand 0. + +The @code{sqrt} built-in function of C always uses the mode which +corresponds to the C data type @code{double}. + +@cindex @code{ffs@var{m}2} instruction pattern +@item @samp{ffs@var{m}2} +Store into operand 0 one plus the index of the least significant 1-bit +of operand 1. If operand 1 is zero, store zero. @var{m} is the mode +of operand 0; operand 1's mode is specified by the instruction +pattern, and the compiler will convert the operand to that mode before +generating the instruction. + +The @code{ffs} built-in function of C always uses the mode which +corresponds to the C data type @code{int}. + +@cindex @code{one_cmpl@var{m}2} instruction pattern +@item @samp{one_cmpl@var{m}2} +Store the bitwise-complement of operand 1 into operand 0. + +@cindex @code{cmp@var{m}} instruction pattern +@item @samp{cmp@var{m}} +Compare operand 0 and operand 1, and set the condition codes. +The RTL pattern should look like this: + +@smallexample +(set (cc0) (compare (match_operand:@var{m} 0 @dots{}) + (match_operand:@var{m} 1 @dots{}))) +@end smallexample + +@cindex @code{tst@var{m}} instruction pattern +@item @samp{tst@var{m}} +Compare operand 0 against zero, and set the condition codes. +The RTL pattern should look like this: + +@smallexample +(set (cc0) (match_operand:@var{m} 0 @dots{})) +@end smallexample + +@samp{tst@var{m}} patterns should not be defined for machines that do +not use @code{(cc0)}. Doing so would confuse the optimizer since it +would no longer be clear which @code{set} operations were comparisons. +The @samp{cmp@var{m}} patterns should be used instead. + +@cindex @code{movstr@var{m}} instruction pattern +@item @samp{movstr@var{m}} +Block move instruction. The addresses of the destination and source +strings are the first two operands, and both are in mode @code{Pmode}. + +The number of bytes to move is the third operand, in mode @var{m}. +Usually, you specify @code{word_mode} for @var{m}. However, if you can +generate better code knowing the range of valid lengths is smaller than +those representable in a full word, you should provide a pattern with a +mode corresponding to the range of values you can handle efficiently +(e.g., @code{QImode} for values in the range 0--127; note we avoid numbers +that appear negative) and also a pattern with @code{word_mode}. + +The fourth operand is the known shared alignment of the source and +destination, in the form of a @code{const_int} rtx. Thus, if the +compiler knows that both source and destination are word-aligned, +it may provide the value 4 for this operand. + +Descriptions of multiple @code{movstr@var{m}} patterns can only be +beneficial if the patterns for smaller modes have fewer restrictions +on their first, second and fourth operands. Note that the mode @var{m} +in @code{movstr@var{m}} does not impose any restriction on the mode of +individually moved data units in the block. + +These patterns need not give special consideration to the possibility +that the source and destination strings might overlap. + +@cindex @code{clrstr@var{m}} instruction pattern +@item @samp{clrstr@var{m}} +Block clear instruction. The addresses of the destination string is the +first operand, in mode @code{Pmode}. The number of bytes to clear is +the second operand, in mode @var{m}. See @samp{movstr@var{m}} for +a discussion of the choice of mode. + +The third operand is the known alignment of the destination, in the form +of a @code{const_int} rtx. Thus, if the compiler knows that the +destination is word-aligned, it may provide the value 4 for this +operand. + +The use for multiple @code{clrstr@var{m}} is as for @code{movstr@var{m}}. + +@cindex @code{cmpstr@var{m}} instruction pattern +@item @samp{cmpstr@var{m}} +Block compare instruction, with five operands. Operand 0 is the output; +it has mode @var{m}. The remaining four operands are like the operands +of @samp{movstr@var{m}}. The two memory blocks specified are compared +byte by byte in lexicographic order. The effect of the instruction is +to store a value in operand 0 whose sign indicates the result of the +comparison. + +@cindex @code{strlen@var{m}} instruction pattern +@item @samp{strlen@var{m}} +Compute the length of a string, with three operands. +Operand 0 is the result (of mode @var{m}), operand 1 is +a @code{mem} referring to the first character of the string, +operand 2 is the character to search for (normally zero), +and operand 3 is a constant describing the known alignment +of the beginning of the string. + +@cindex @code{float@var{mn}2} instruction pattern +@item @samp{float@var{m}@var{n}2} +Convert signed integer operand 1 (valid for fixed point mode @var{m}) to +floating point mode @var{n} and store in operand 0 (which has mode +@var{n}). + +@cindex @code{floatuns@var{mn}2} instruction pattern +@item @samp{floatuns@var{m}@var{n}2} +Convert unsigned integer operand 1 (valid for fixed point mode @var{m}) +to floating point mode @var{n} and store in operand 0 (which has mode +@var{n}). + +@cindex @code{fix@var{mn}2} instruction pattern +@item @samp{fix@var{m}@var{n}2} +Convert operand 1 (valid for floating point mode @var{m}) to fixed +point mode @var{n} as a signed number and store in operand 0 (which +has mode @var{n}). This instruction's result is defined only when +the value of operand 1 is an integer. + +@cindex @code{fixuns@var{mn}2} instruction pattern +@item @samp{fixuns@var{m}@var{n}2} +Convert operand 1 (valid for floating point mode @var{m}) to fixed +point mode @var{n} as an unsigned number and store in operand 0 (which +has mode @var{n}). This instruction's result is defined only when the +value of operand 1 is an integer. + +@cindex @code{ftrunc@var{m}2} instruction pattern +@item @samp{ftrunc@var{m}2} +Convert operand 1 (valid for floating point mode @var{m}) to an +integer value, still represented in floating point mode @var{m}, and +store it in operand 0 (valid for floating point mode @var{m}). + +@cindex @code{fix_trunc@var{mn}2} instruction pattern +@item @samp{fix_trunc@var{m}@var{n}2} +Like @samp{fix@var{m}@var{n}2} but works for any floating point value +of mode @var{m} by converting the value to an integer. + +@cindex @code{fixuns_trunc@var{mn}2} instruction pattern +@item @samp{fixuns_trunc@var{m}@var{n}2} +Like @samp{fixuns@var{m}@var{n}2} but works for any floating point +value of mode @var{m} by converting the value to an integer. + +@cindex @code{trunc@var{mn}2} instruction pattern +@item @samp{trunc@var{m}@var{n}2} +Truncate operand 1 (valid for mode @var{m}) to mode @var{n} and +store in operand 0 (which has mode @var{n}). Both modes must be fixed +point or both floating point. + +@cindex @code{extend@var{mn}2} instruction pattern +@item @samp{extend@var{m}@var{n}2} +Sign-extend operand 1 (valid for mode @var{m}) to mode @var{n} and +store in operand 0 (which has mode @var{n}). Both modes must be fixed +point or both floating point. + +@cindex @code{zero_extend@var{mn}2} instruction pattern +@item @samp{zero_extend@var{m}@var{n}2} +Zero-extend operand 1 (valid for mode @var{m}) to mode @var{n} and +store in operand 0 (which has mode @var{n}). Both modes must be fixed +point. + +@cindex @code{extv} instruction pattern +@item @samp{extv} +Extract a bit-field from operand 1 (a register or memory operand), where +operand 2 specifies the width in bits and operand 3 the starting bit, +and store it in operand 0. Operand 0 must have mode @code{word_mode}. +Operand 1 may have mode @code{byte_mode} or @code{word_mode}; often +@code{word_mode} is allowed only for registers. Operands 2 and 3 must +be valid for @code{word_mode}. + +The RTL generation pass generates this instruction only with constants +for operands 2 and 3. + +The bit-field value is sign-extended to a full word integer +before it is stored in operand 0. + +@cindex @code{extzv} instruction pattern +@item @samp{extzv} +Like @samp{extv} except that the bit-field value is zero-extended. + +@cindex @code{insv} instruction pattern +@item @samp{insv} +Store operand 3 (which must be valid for @code{word_mode}) into a +bit-field in operand 0, where operand 1 specifies the width in bits and +operand 2 the starting bit. Operand 0 may have mode @code{byte_mode} or +@code{word_mode}; often @code{word_mode} is allowed only for registers. +Operands 1 and 2 must be valid for @code{word_mode}. + +The RTL generation pass generates this instruction only with constants +for operands 1 and 2. + +@cindex @code{mov@var{mode}cc} instruction pattern +@item @samp{mov@var{mode}cc} +Conditionally move operand 2 or operand 3 into operand 0 according to the +comparison in operand 1. If the comparison is true, operand 2 is moved +into operand 0, otherwise operand 3 is moved. + +The mode of the operands being compared need not be the same as the operands +being moved. Some machines, sparc64 for example, have instructions that +conditionally move an integer value based on the floating point condition +codes and vice versa. + +If the machine does not have conditional move instructions, do not +define these patterns. + +@cindex @code{s@var{cond}} instruction pattern +@item @samp{s@var{cond}} +Store zero or nonzero in the operand according to the condition codes. +Value stored is nonzero iff the condition @var{cond} is true. +@var{cond} is the name of a comparison operation expression code, such +as @code{eq}, @code{lt} or @code{leu}. + +You specify the mode that the operand must have when you write the +@code{match_operand} expression. The compiler automatically sees +which mode you have used and supplies an operand of that mode. + +The value stored for a true condition must have 1 as its low bit, or +else must be negative. Otherwise the instruction is not suitable and +you should omit it from the machine description. You describe to the +compiler exactly which value is stored by defining the macro +@code{STORE_FLAG_VALUE} (@pxref{Misc}). If a description cannot be +found that can be used for all the @samp{s@var{cond}} patterns, you +should omit those operations from the machine description. + +These operations may fail, but should do so only in relatively +uncommon cases; if they would fail for common cases involving +integer comparisons, it is best to omit these patterns. + +If these operations are omitted, the compiler will usually generate code +that copies the constant one to the target and branches around an +assignment of zero to the target. If this code is more efficient than +the potential instructions used for the @samp{s@var{cond}} pattern +followed by those required to convert the result into a 1 or a zero in +@code{SImode}, you should omit the @samp{s@var{cond}} operations from +the machine description. + +@cindex @code{b@var{cond}} instruction pattern +@item @samp{b@var{cond}} +Conditional branch instruction. Operand 0 is a @code{label_ref} that +refers to the label to jump to. Jump if the condition codes meet +condition @var{cond}. + +Some machines do not follow the model assumed here where a comparison +instruction is followed by a conditional branch instruction. In that +case, the @samp{cmp@var{m}} (and @samp{tst@var{m}}) patterns should +simply store the operands away and generate all the required insns in a +@code{define_expand} (@pxref{Expander Definitions}) for the conditional +branch operations. All calls to expand @samp{b@var{cond}} patterns are +immediately preceded by calls to expand either a @samp{cmp@var{m}} +pattern or a @samp{tst@var{m}} pattern. + +Machines that use a pseudo register for the condition code value, or +where the mode used for the comparison depends on the condition being +tested, should also use the above mechanism. @xref{Jump Patterns}. + +The above discussion also applies to the @samp{mov@var{mode}cc} and +@samp{s@var{cond}} patterns. + +@cindex @code{jump} instruction pattern +@item @samp{jump} +A jump inside a function; an unconditional branch. Operand 0 is the +@code{label_ref} of the label to jump to. This pattern name is mandatory +on all machines. + +@cindex @code{call} instruction pattern +@item @samp{call} +Subroutine call instruction returning no value. Operand 0 is the +function to call; operand 1 is the number of bytes of arguments pushed +as a @code{const_int}; operand 2 is the number of registers used as +operands. + +On most machines, operand 2 is not actually stored into the RTL +pattern. It is supplied for the sake of some RISC machines which need +to put this information into the assembler code; they can put it in +the RTL instead of operand 1. + +Operand 0 should be a @code{mem} RTX whose address is the address of the +function. Note, however, that this address can be a @code{symbol_ref} +expression even if it would not be a legitimate memory address on the +target machine. If it is also not a valid argument for a call +instruction, the pattern for this operation should be a +@code{define_expand} (@pxref{Expander Definitions}) that places the +address into a register and uses that register in the call instruction. + +@cindex @code{call_value} instruction pattern +@item @samp{call_value} +Subroutine call instruction returning a value. Operand 0 is the hard +register in which the value is returned. There are three more +operands, the same as the three operands of the @samp{call} +instruction (but with numbers increased by one). + +Subroutines that return @code{BLKmode} objects use the @samp{call} +insn. + +@cindex @code{call_pop} instruction pattern +@cindex @code{call_value_pop} instruction pattern +@item @samp{call_pop}, @samp{call_value_pop} +Similar to @samp{call} and @samp{call_value}, except used if defined and +if @code{RETURN_POPS_ARGS} is nonzero. They should emit a @code{parallel} +that contains both the function call and a @code{set} to indicate the +adjustment made to the frame pointer. + +For machines where @code{RETURN_POPS_ARGS} can be nonzero, the use of these +patterns increases the number of functions for which the frame pointer +can be eliminated, if desired. + +@cindex @code{untyped_call} instruction pattern +@item @samp{untyped_call} +Subroutine call instruction returning a value of any type. Operand 0 is +the function to call; operand 1 is a memory location where the result of +calling the function is to be stored; operand 2 is a @code{parallel} +expression where each element is a @code{set} expression that indicates +the saving of a function return value into the result block. + +This instruction pattern should be defined to support +@code{__builtin_apply} on machines where special instructions are needed +to call a subroutine with arbitrary arguments or to save the value +returned. This instruction pattern is required on machines that have +multiple registers that can hold a return value +(i.e.@: @code{FUNCTION_VALUE_REGNO_P} is true for more than one register). + +@cindex @code{return} instruction pattern +@item @samp{return} +Subroutine return instruction. This instruction pattern name should be +defined only if a single instruction can do all the work of returning +from a function. + +Like the @samp{mov@var{m}} patterns, this pattern is also used after the +RTL generation phase. In this case it is to support machines where +multiple instructions are usually needed to return from a function, but +some class of functions only requires one instruction to implement a +return. Normally, the applicable functions are those which do not need +to save any registers or allocate stack space. + +@findex reload_completed +@findex leaf_function_p +For such machines, the condition specified in this pattern should only +be true when @code{reload_completed} is nonzero and the function's +epilogue would only be a single instruction. For machines with register +windows, the routine @code{leaf_function_p} may be used to determine if +a register window push is required. + +Machines that have conditional return instructions should define patterns +such as + +@smallexample +(define_insn "" + [(set (pc) + (if_then_else (match_operator + 0 "comparison_operator" + [(cc0) (const_int 0)]) + (return) + (pc)))] + "@var{condition}" + "@dots{}") +@end smallexample + +where @var{condition} would normally be the same condition specified on the +named @samp{return} pattern. + +@cindex @code{untyped_return} instruction pattern +@item @samp{untyped_return} +Untyped subroutine return instruction. This instruction pattern should +be defined to support @code{__builtin_return} on machines where special +instructions are needed to return a value of any type. + +Operand 0 is a memory location where the result of calling a function +with @code{__builtin_apply} is stored; operand 1 is a @code{parallel} +expression where each element is a @code{set} expression that indicates +the restoring of a function return value from the result block. + +@cindex @code{nop} instruction pattern +@item @samp{nop} +No-op instruction. This instruction pattern name should always be defined +to output a no-op in assembler code. @code{(const_int 0)} will do as an +RTL pattern. + +@cindex @code{indirect_jump} instruction pattern +@item @samp{indirect_jump} +An instruction to jump to an address which is operand zero. +This pattern name is mandatory on all machines. + +@cindex @code{casesi} instruction pattern +@item @samp{casesi} +Instruction to jump through a dispatch table, including bounds checking. +This instruction takes five operands: + +@enumerate +@item +The index to dispatch on, which has mode @code{SImode}. + +@item +The lower bound for indices in the table, an integer constant. + +@item +The total range of indices in the table---the largest index +minus the smallest one (both inclusive). + +@item +A label that precedes the table itself. + +@item +A label to jump to if the index has a value outside the bounds. +(If the machine-description macro @code{CASE_DROPS_THROUGH} is defined, +then an out-of-bounds index drops through to the code following +the jump table instead of jumping to this label. In that case, +this label is not actually used by the @samp{casesi} instruction, +but it is always provided as an operand.) +@end enumerate + +The table is a @code{addr_vec} or @code{addr_diff_vec} inside of a +@code{jump_insn}. The number of elements in the table is one plus the +difference between the upper bound and the lower bound. + +@cindex @code{tablejump} instruction pattern +@item @samp{tablejump} +Instruction to jump to a variable address. This is a low-level +capability which can be used to implement a dispatch table when there +is no @samp{casesi} pattern. + +This pattern requires two operands: the address or offset, and a label +which should immediately precede the jump table. If the macro +@code{CASE_VECTOR_PC_RELATIVE} evaluates to a nonzero value then the first +operand is an offset which counts from the address of the table; otherwise, +it is an absolute address to jump to. In either case, the first operand has +mode @code{Pmode}. + +The @samp{tablejump} insn is always the last insn before the jump +table it uses. Its assembler code normally has no need to use the +second operand, but you should incorporate it in the RTL pattern so +that the jump optimizer will not delete the table as unreachable code. + + +@cindex @code{decrement_and_branch_until_zero} instruction pattern +@item @samp{decrement_and_branch_until_zero} +Conditional branch instruction that decrements a register and +jumps if the register is nonzero. Operand 0 is the register to +decrement and test; operand 1 is the label to jump to if the +register is nonzero. @xref{Looping Patterns}. + +This optional instruction pattern is only used by the combiner, +typically for loops reversed by the loop optimizer when strength +reduction is enabled. + +@cindex @code{doloop_end} instruction pattern +@item @samp{doloop_end} +Conditional branch instruction that decrements a register and jumps if +the register is nonzero. This instruction takes five operands: Operand +0 is the register to decrement and test; operand 1 is the number of loop +iterations as a @code{const_int} or @code{const0_rtx} if this cannot be +determined until run-time; operand 2 is the actual or estimated maximum +number of iterations as a @code{const_int}; operand 3 is the number of +enclosed loops as a @code{const_int} (an innermost loop has a value of +1); operand 4 is the label to jump to if the register is nonzero. +@xref{Looping Patterns}. + +This optional instruction pattern should be defined for machines with +low-overhead looping instructions as the loop optimizer will try to +modify suitable loops to utilize it. If nested low-overhead looping is +not supported, use a @code{define_expand} (@pxref{Expander Definitions}) +and make the pattern fail if operand 3 is not @code{const1_rtx}. +Similarly, if the actual or estimated maximum number of iterations is +too large for this instruction, make it fail. + +@cindex @code{doloop_begin} instruction pattern +@item @samp{doloop_begin} +Companion instruction to @code{doloop_end} required for machines that +need to perform some initialization, such as loading special registers +used by a low-overhead looping instruction. If initialization insns do +not always need to be emitted, use a @code{define_expand} +(@pxref{Expander Definitions}) and make it fail. + + +@cindex @code{canonicalize_funcptr_for_compare} instruction pattern +@item @samp{canonicalize_funcptr_for_compare} +Canonicalize the function pointer in operand 1 and store the result +into operand 0. + +Operand 0 is always a @code{reg} and has mode @code{Pmode}; operand 1 +may be a @code{reg}, @code{mem}, @code{symbol_ref}, @code{const_int}, etc +and also has mode @code{Pmode}. + +Canonicalization of a function pointer usually involves computing +the address of the function which would be called if the function +pointer were used in an indirect call. + +Only define this pattern if function pointers on the target machine +can have different values but still call the same function when +used in an indirect call. + +@cindex @code{save_stack_block} instruction pattern +@cindex @code{save_stack_function} instruction pattern +@cindex @code{save_stack_nonlocal} instruction pattern +@cindex @code{restore_stack_block} instruction pattern +@cindex @code{restore_stack_function} instruction pattern +@cindex @code{restore_stack_nonlocal} instruction pattern +@item @samp{save_stack_block} +@itemx @samp{save_stack_function} +@itemx @samp{save_stack_nonlocal} +@itemx @samp{restore_stack_block} +@itemx @samp{restore_stack_function} +@itemx @samp{restore_stack_nonlocal} +Most machines save and restore the stack pointer by copying it to or +from an object of mode @code{Pmode}. Do not define these patterns on +such machines. + +Some machines require special handling for stack pointer saves and +restores. On those machines, define the patterns corresponding to the +non-standard cases by using a @code{define_expand} (@pxref{Expander +Definitions}) that produces the required insns. The three types of +saves and restores are: + +@enumerate +@item +@samp{save_stack_block} saves the stack pointer at the start of a block +that allocates a variable-sized object, and @samp{restore_stack_block} +restores the stack pointer when the block is exited. + +@item +@samp{save_stack_function} and @samp{restore_stack_function} do a +similar job for the outermost block of a function and are used when the +function allocates variable-sized objects or calls @code{alloca}. Only +the epilogue uses the restored stack pointer, allowing a simpler save or +restore sequence on some machines. + +@item +@samp{save_stack_nonlocal} is used in functions that contain labels +branched to by nested functions. It saves the stack pointer in such a +way that the inner function can use @samp{restore_stack_nonlocal} to +restore the stack pointer. The compiler generates code to restore the +frame and argument pointer registers, but some machines require saving +and restoring additional data such as register window information or +stack backchains. Place insns in these patterns to save and restore any +such required data. +@end enumerate + +When saving the stack pointer, operand 0 is the save area and operand 1 +is the stack pointer. The mode used to allocate the save area defaults +to @code{Pmode} but you can override that choice by defining the +@code{STACK_SAVEAREA_MODE} macro (@pxref{Storage Layout}). You must +specify an integral mode, or @code{VOIDmode} if no save area is needed +for a particular type of save (either because no save is needed or +because a machine-specific save area can be used). Operand 0 is the +stack pointer and operand 1 is the save area for restore operations. If +@samp{save_stack_block} is defined, operand 0 must not be +@code{VOIDmode} since these saves can be arbitrarily nested. + +A save area is a @code{mem} that is at a constant offset from +@code{virtual_stack_vars_rtx} when the stack pointer is saved for use by +nonlocal gotos and a @code{reg} in the other two cases. + +@cindex @code{allocate_stack} instruction pattern +@item @samp{allocate_stack} +Subtract (or add if @code{STACK_GROWS_DOWNWARD} is undefined) operand 1 from +the stack pointer to create space for dynamically allocated data. + +Store the resultant pointer to this space into operand 0. If you +are allocating space from the main stack, do this by emitting a +move insn to copy @code{virtual_stack_dynamic_rtx} to operand 0. +If you are allocating the space elsewhere, generate code to copy the +location of the space to operand 0. In the latter case, you must +ensure this space gets freed when the corresponding space on the main +stack is free. + +Do not define this pattern if all that must be done is the subtraction. +Some machines require other operations such as stack probes or +maintaining the back chain. Define this pattern to emit those +operations in addition to updating the stack pointer. + +@cindex @code{probe} instruction pattern +@item @samp{probe} +Some machines require instructions to be executed after space is +allocated from the stack, for example to generate a reference at +the bottom of the stack. + +If you need to emit instructions before the stack has been adjusted, +put them into the @samp{allocate_stack} pattern. Otherwise, define +this pattern to emit the required instructions. + +No operands are provided. + +@cindex @code{check_stack} instruction pattern +@item @samp{check_stack} +If stack checking cannot be done on your system by probing the stack with +a load or store instruction (@pxref{Stack Checking}), define this pattern +to perform the needed check and signaling an error if the stack +has overflowed. The single operand is the location in the stack furthest +from the current stack pointer that you need to validate. Normally, +on machines where this pattern is needed, you would obtain the stack +limit from a global or thread-specific variable or register. + +@cindex @code{nonlocal_goto} instruction pattern +@item @samp{nonlocal_goto} +Emit code to generate a non-local goto, e.g., a jump from one function +to a label in an outer function. This pattern has four arguments, +each representing a value to be used in the jump. The first +argument is to be loaded into the frame pointer, the second is +the address to branch to (code to dispatch to the actual label), +the third is the address of a location where the stack is saved, +and the last is the address of the label, to be placed in the +location for the incoming static chain. + +On most machines you need not define this pattern, since GCC will +already generate the correct code, which is to load the frame pointer +and static chain, restore the stack (using the +@samp{restore_stack_nonlocal} pattern, if defined), and jump indirectly +to the dispatcher. You need only define this pattern if this code will +not work on your machine. + +@cindex @code{nonlocal_goto_receiver} instruction pattern +@item @samp{nonlocal_goto_receiver} +This pattern, if defined, contains code needed at the target of a +nonlocal goto after the code already generated by GCC@. You will not +normally need to define this pattern. A typical reason why you might +need this pattern is if some value, such as a pointer to a global table, +must be restored when the frame pointer is restored. Note that a nonlocal +goto only occurs within a unit-of-translation, so a global table pointer +that is shared by all functions of a given module need not be restored. +There are no arguments. + +@cindex @code{exception_receiver} instruction pattern +@item @samp{exception_receiver} +This pattern, if defined, contains code needed at the site of an +exception handler that isn't needed at the site of a nonlocal goto. You +will not normally need to define this pattern. A typical reason why you +might need this pattern is if some value, such as a pointer to a global +table, must be restored after control flow is branched to the handler of +an exception. There are no arguments. + +@cindex @code{builtin_setjmp_setup} instruction pattern +@item @samp{builtin_setjmp_setup} +This pattern, if defined, contains additional code needed to initialize +the @code{jmp_buf}. You will not normally need to define this pattern. +A typical reason why you might need this pattern is if some value, such +as a pointer to a global table, must be restored. Though it is +preferred that the pointer value be recalculated if possible (given the +address of a label for instance). The single argument is a pointer to +the @code{jmp_buf}. Note that the buffer is five words long and that +the first three are normally used by the generic mechanism. + +@cindex @code{builtin_setjmp_receiver} instruction pattern +@item @samp{builtin_setjmp_receiver} +This pattern, if defined, contains code needed at the site of an +built-in setjmp that isn't needed at the site of a nonlocal goto. You +will not normally need to define this pattern. A typical reason why you +might need this pattern is if some value, such as a pointer to a global +table, must be restored. It takes one argument, which is the label +to which builtin_longjmp transfered control; this pattern may be emitted +at a small offset from that label. + +@cindex @code{builtin_longjmp} instruction pattern +@item @samp{builtin_longjmp} +This pattern, if defined, performs the entire action of the longjmp. +You will not normally need to define this pattern unless you also define +@code{builtin_setjmp_setup}. The single argument is a pointer to the +@code{jmp_buf}. + +@cindex @code{eh_return} instruction pattern +@item @samp{eh_return} +This pattern, if defined, affects the way @code{__builtin_eh_return}, +and thence the call frame exception handling library routines, are +built. It is intended to handle non-trivial actions needed along +the abnormal return path. + +The pattern takes two arguments. The first is an offset to be applied +to the stack pointer. It will have been copied to some appropriate +location (typically @code{EH_RETURN_STACKADJ_RTX}) which will survive +until after reload to when the normal epilogue is generated. +The second argument is the address of the exception handler to which +the function should return. This will normally need to copied by the +pattern to some special register or memory location. + +This pattern only needs to be defined if call frame exception handling +is to be used, and simple moves involving @code{EH_RETURN_STACKADJ_RTX} +and @code{EH_RETURN_HANDLER_RTX} are not sufficient. + +@cindex @code{prologue} instruction pattern +@anchor{prologue instruction pattern} +@item @samp{prologue} +This pattern, if defined, emits RTL for entry to a function. The function +entry is responsible for setting up the stack frame, initializing the frame +pointer register, saving callee saved registers, etc. + +Using a prologue pattern is generally preferred over defining +@code{TARGET_ASM_FUNCTION_PROLOGUE} to emit assembly code for the prologue. + +The @code{prologue} pattern is particularly useful for targets which perform +instruction scheduling. + +@cindex @code{epilogue} instruction pattern +@anchor{epilogue instruction pattern} +@item @samp{epilogue} +This pattern emits RTL for exit from a function. The function +exit is responsible for deallocating the stack frame, restoring callee saved +registers and emitting the return instruction. + +Using an epilogue pattern is generally preferred over defining +@code{TARGET_ASM_FUNCTION_EPILOGUE} to emit assembly code for the epilogue. + +The @code{epilogue} pattern is particularly useful for targets which perform +instruction scheduling or which have delay slots for their return instruction. + +@cindex @code{sibcall_epilogue} instruction pattern +@item @samp{sibcall_epilogue} +This pattern, if defined, emits RTL for exit from a function without the final +branch back to the calling function. This pattern will be emitted before any +sibling call (aka tail call) sites. + +The @code{sibcall_epilogue} pattern must not clobber any arguments used for +parameter passing or any stack slots for arguments passed to the current +function. + +@cindex @code{trap} instruction pattern +@item @samp{trap} +This pattern, if defined, signals an error, typically by causing some +kind of signal to be raised. Among other places, it is used by the Java +front end to signal `invalid array index' exceptions. + +@cindex @code{conditional_trap} instruction pattern +@item @samp{conditional_trap} +Conditional trap instruction. Operand 0 is a piece of RTL which +performs a comparison. Operand 1 is the trap code, an integer. + +A typical @code{conditional_trap} pattern looks like + +@smallexample +(define_insn "conditional_trap" + [(trap_if (match_operator 0 "trap_operator" + [(cc0) (const_int 0)]) + (match_operand 1 "const_int_operand" "i"))] + "" + "@dots{}") +@end smallexample + +@cindex @code{prefetch} instruction pattern +@item @samp{prefetch} + +This pattern, if defined, emits code for a non-faulting data prefetch +instruction. Operand 0 is the address of the memory to prefetch. Operand 1 +is a constant 1 if the prefetch is preparing for a write to the memory +address, or a constant 0 otherwise. Operand 2 is the expected degree of +temporal locality of the data and is a value between 0 and 3, inclusive; 0 +means that the data has no temporal locality, so it need not be left in the +cache after the access; 3 means that the data has a high degree of temporal +locality and should be left in all levels of cache possible; 1 and 2 mean, +respectively, a low or moderate degree of temporal locality. + +Targets that do not support write prefetches or locality hints can ignore +the values of operands 1 and 2. + +@cindex @code{cycle_display} instruction pattern +@item @samp{cycle_display} + +This pattern, if present, will be emitted by the instruction scheduler at +the beginning of each new clock cycle. This can be used for annotating the +assembler output with cycle counts. Operand 0 is a @code{const_int} that +holds the clock cycle. + +@end table + +@node Pattern Ordering +@section When the Order of Patterns Matters +@cindex Pattern Ordering +@cindex Ordering of Patterns + +Sometimes an insn can match more than one instruction pattern. Then the +pattern that appears first in the machine description is the one used. +Therefore, more specific patterns (patterns that will match fewer things) +and faster instructions (those that will produce better code when they +do match) should usually go first in the description. + +In some cases the effect of ordering the patterns can be used to hide +a pattern when it is not valid. For example, the 68000 has an +instruction for converting a fullword to floating point and another +for converting a byte to floating point. An instruction converting +an integer to floating point could match either one. We put the +pattern to convert the fullword first to make sure that one will +be used rather than the other. (Otherwise a large integer might +be generated as a single-byte immediate quantity, which would not work.) +Instead of using this pattern ordering it would be possible to make the +pattern for convert-a-byte smart enough to deal properly with any +constant value. + +@node Dependent Patterns +@section Interdependence of Patterns +@cindex Dependent Patterns +@cindex Interdependence of Patterns + +Every machine description must have a named pattern for each of the +conditional branch names @samp{b@var{cond}}. The recognition template +must always have the form + +@example +(set (pc) + (if_then_else (@var{cond} (cc0) (const_int 0)) + (label_ref (match_operand 0 "" "")) + (pc))) +@end example + +@noindent +In addition, every machine description must have an anonymous pattern +for each of the possible reverse-conditional branches. Their templates +look like + +@example +(set (pc) + (if_then_else (@var{cond} (cc0) (const_int 0)) + (pc) + (label_ref (match_operand 0 "" "")))) +@end example + +@noindent +They are necessary because jump optimization can turn direct-conditional +branches into reverse-conditional branches. + +It is often convenient to use the @code{match_operator} construct to +reduce the number of patterns that must be specified for branches. For +example, + +@example +(define_insn "" + [(set (pc) + (if_then_else (match_operator 0 "comparison_operator" + [(cc0) (const_int 0)]) + (pc) + (label_ref (match_operand 1 "" ""))))] + "@var{condition}" + "@dots{}") +@end example + +In some cases machines support instructions identical except for the +machine mode of one or more operands. For example, there may be +``sign-extend halfword'' and ``sign-extend byte'' instructions whose +patterns are + +@example +(set (match_operand:SI 0 @dots{}) + (extend:SI (match_operand:HI 1 @dots{}))) + +(set (match_operand:SI 0 @dots{}) + (extend:SI (match_operand:QI 1 @dots{}))) +@end example + +@noindent +Constant integers do not specify a machine mode, so an instruction to +extend a constant value could match either pattern. The pattern it +actually will match is the one that appears first in the file. For correct +results, this must be the one for the widest possible mode (@code{HImode}, +here). If the pattern matches the @code{QImode} instruction, the results +will be incorrect if the constant value does not actually fit that mode. + +Such instructions to extend constants are rarely generated because they are +optimized away, but they do occasionally happen in nonoptimized +compilations. + +If a constraint in a pattern allows a constant, the reload pass may +replace a register with a constant permitted by the constraint in some +cases. Similarly for memory references. Because of this substitution, +you should not provide separate patterns for increment and decrement +instructions. Instead, they should be generated from the same pattern +that supports register-register add insns by examining the operands and +generating the appropriate machine instruction. + +@node Jump Patterns +@section Defining Jump Instruction Patterns +@cindex jump instruction patterns +@cindex defining jump instruction patterns + +For most machines, GCC assumes that the machine has a condition code. +A comparison insn sets the condition code, recording the results of both +signed and unsigned comparison of the given operands. A separate branch +insn tests the condition code and branches or not according its value. +The branch insns come in distinct signed and unsigned flavors. Many +common machines, such as the VAX, the 68000 and the 32000, work this +way. + +Some machines have distinct signed and unsigned compare instructions, and +only one set of conditional branch instructions. The easiest way to handle +these machines is to treat them just like the others until the final stage +where assembly code is written. At this time, when outputting code for the +compare instruction, peek ahead at the following branch using +@code{next_cc0_user (insn)}. (The variable @code{insn} refers to the insn +being output, in the output-writing code in an instruction pattern.) If +the RTL says that is an unsigned branch, output an unsigned compare; +otherwise output a signed compare. When the branch itself is output, you +can treat signed and unsigned branches identically. + +The reason you can do this is that GCC always generates a pair of +consecutive RTL insns, possibly separated by @code{note} insns, one to +set the condition code and one to test it, and keeps the pair inviolate +until the end. + +To go with this technique, you must define the machine-description macro +@code{NOTICE_UPDATE_CC} to do @code{CC_STATUS_INIT}; in other words, no +compare instruction is superfluous. + +Some machines have compare-and-branch instructions and no condition code. +A similar technique works for them. When it is time to ``output'' a +compare instruction, record its operands in two static variables. When +outputting the branch-on-condition-code instruction that follows, actually +output a compare-and-branch instruction that uses the remembered operands. + +It also works to define patterns for compare-and-branch instructions. +In optimizing compilation, the pair of compare and branch instructions +will be combined according to these patterns. But this does not happen +if optimization is not requested. So you must use one of the solutions +above in addition to any special patterns you define. + +In many RISC machines, most instructions do not affect the condition +code and there may not even be a separate condition code register. On +these machines, the restriction that the definition and use of the +condition code be adjacent insns is not necessary and can prevent +important optimizations. For example, on the IBM RS/6000, there is a +delay for taken branches unless the condition code register is set three +instructions earlier than the conditional branch. The instruction +scheduler cannot perform this optimization if it is not permitted to +separate the definition and use of the condition code register. + +On these machines, do not use @code{(cc0)}, but instead use a register +to represent the condition code. If there is a specific condition code +register in the machine, use a hard register. If the condition code or +comparison result can be placed in any general register, or if there are +multiple condition registers, use a pseudo register. + +@findex prev_cc0_setter +@findex next_cc0_user +On some machines, the type of branch instruction generated may depend on +the way the condition code was produced; for example, on the 68k and +Sparc, setting the condition code directly from an add or subtract +instruction does not clear the overflow bit the way that a test +instruction does, so a different branch instruction must be used for +some conditional branches. For machines that use @code{(cc0)}, the set +and use of the condition code must be adjacent (separated only by +@code{note} insns) allowing flags in @code{cc_status} to be used. +(@xref{Condition Code}.) Also, the comparison and branch insns can be +located from each other by using the functions @code{prev_cc0_setter} +and @code{next_cc0_user}. + +However, this is not true on machines that do not use @code{(cc0)}. On +those machines, no assumptions can be made about the adjacency of the +compare and branch insns and the above methods cannot be used. Instead, +we use the machine mode of the condition code register to record +different formats of the condition code register. + +Registers used to store the condition code value should have a mode that +is in class @code{MODE_CC}. Normally, it will be @code{CCmode}. If +additional modes are required (as for the add example mentioned above in +the Sparc), define the macro @code{EXTRA_CC_MODES} to list the +additional modes required (@pxref{Condition Code}). Also define +@code{SELECT_CC_MODE} to choose a mode given an operand of a compare. + +If it is known during RTL generation that a different mode will be +required (for example, if the machine has separate compare instructions +for signed and unsigned quantities, like most IBM processors), they can +be specified at that time. + +If the cases that require different modes would be made by instruction +combination, the macro @code{SELECT_CC_MODE} determines which machine +mode should be used for the comparison result. The patterns should be +written using that mode. To support the case of the add on the Sparc +discussed above, we have the pattern + +@smallexample +(define_insn "" + [(set (reg:CC_NOOV 0) + (compare:CC_NOOV + (plus:SI (match_operand:SI 0 "register_operand" "%r") + (match_operand:SI 1 "arith_operand" "rI")) + (const_int 0)))] + "" + "@dots{}") +@end smallexample + +The @code{SELECT_CC_MODE} macro on the Sparc returns @code{CC_NOOVmode} +for comparisons whose argument is a @code{plus}. + +@node Looping Patterns +@section Defining Looping Instruction Patterns +@cindex looping instruction patterns +@cindex defining looping instruction patterns + +Some machines have special jump instructions that can be utilised to +make loops more efficient. A common example is the 68000 @samp{dbra} +instruction which performs a decrement of a register and a branch if the +result was greater than zero. Other machines, in particular digital +signal processors (DSPs), have special block repeat instructions to +provide low-overhead loop support. For example, the TI TMS320C3x/C4x +DSPs have a block repeat instruction that loads special registers to +mark the top and end of a loop and to count the number of loop +iterations. This avoids the need for fetching and executing a +@samp{dbra}-like instruction and avoids pipeline stalls associated with +the jump. + +GCC has three special named patterns to support low overhead looping. +They are @samp{decrement_and_branch_until_zero}, @samp{doloop_begin}, +and @samp{doloop_end}. The first pattern, +@samp{decrement_and_branch_until_zero}, is not emitted during RTL +generation but may be emitted during the instruction combination phase. +This requires the assistance of the loop optimizer, using information +collected during strength reduction, to reverse a loop to count down to +zero. Some targets also require the loop optimizer to add a +@code{REG_NONNEG} note to indicate that the iteration count is always +positive. This is needed if the target performs a signed loop +termination test. For example, the 68000 uses a pattern similar to the +following for its @code{dbra} instruction: + +@smallexample +@group +(define_insn "decrement_and_branch_until_zero" + [(set (pc) + (if_then_else + (ge (plus:SI (match_operand:SI 0 "general_operand" "+d*am") + (const_int -1)) + (const_int 0)) + (label_ref (match_operand 1 "" "")) + (pc))) + (set (match_dup 0) + (plus:SI (match_dup 0) + (const_int -1)))] + "find_reg_note (insn, REG_NONNEG, 0)" + "@dots{}") +@end group +@end smallexample + +Note that since the insn is both a jump insn and has an output, it must +deal with its own reloads, hence the `m' constraints. Also note that +since this insn is generated by the instruction combination phase +combining two sequential insns together into an implicit parallel insn, +the iteration counter needs to be biased by the same amount as the +decrement operation, in this case @minus{}1. Note that the following similar +pattern will not be matched by the combiner. + +@smallexample +@group +(define_insn "decrement_and_branch_until_zero" + [(set (pc) + (if_then_else + (ge (match_operand:SI 0 "general_operand" "+d*am") + (const_int 1)) + (label_ref (match_operand 1 "" "")) + (pc))) + (set (match_dup 0) + (plus:SI (match_dup 0) + (const_int -1)))] + "find_reg_note (insn, REG_NONNEG, 0)" + "@dots{}") +@end group +@end smallexample + +The other two special looping patterns, @samp{doloop_begin} and +@samp{doloop_end}, are emitted by the loop optimizer for certain +well-behaved loops with a finite number of loop iterations using +information collected during strength reduction. + +The @samp{doloop_end} pattern describes the actual looping instruction +(or the implicit looping operation) and the @samp{doloop_begin} pattern +is an optional companion pattern that can be used for initialization +needed for some low-overhead looping instructions. + +Note that some machines require the actual looping instruction to be +emitted at the top of the loop (e.g., the TMS320C3x/C4x DSPs). Emitting +the true RTL for a looping instruction at the top of the loop can cause +problems with flow analysis. So instead, a dummy @code{doloop} insn is +emitted at the end of the loop. The machine dependent reorg pass checks +for the presence of this @code{doloop} insn and then searches back to +the top of the loop, where it inserts the true looping insn (provided +there are no instructions in the loop which would cause problems). Any +additional labels can be emitted at this point. In addition, if the +desired special iteration counter register was not allocated, this +machine dependent reorg pass could emit a traditional compare and jump +instruction pair. + +The essential difference between the +@samp{decrement_and_branch_until_zero} and the @samp{doloop_end} +patterns is that the loop optimizer allocates an additional pseudo +register for the latter as an iteration counter. This pseudo register +cannot be used within the loop (i.e., general induction variables cannot +be derived from it), however, in many cases the loop induction variable +may become redundant and removed by the flow pass. + + +@node Insn Canonicalizations +@section Canonicalization of Instructions +@cindex canonicalization of instructions +@cindex insn canonicalization + +There are often cases where multiple RTL expressions could represent an +operation performed by a single machine instruction. This situation is +most commonly encountered with logical, branch, and multiply-accumulate +instructions. In such cases, the compiler attempts to convert these +multiple RTL expressions into a single canonical form to reduce the +number of insn patterns required. + +In addition to algebraic simplifications, following canonicalizations +are performed: + +@itemize @bullet +@item +For commutative and comparison operators, a constant is always made the +second operand. If a machine only supports a constant as the second +operand, only patterns that match a constant in the second operand need +be supplied. + +@cindex @code{neg}, canonicalization of +@cindex @code{not}, canonicalization of +@cindex @code{mult}, canonicalization of +@cindex @code{plus}, canonicalization of +@cindex @code{minus}, canonicalization of +For these operators, if only one operand is a @code{neg}, @code{not}, +@code{mult}, @code{plus}, or @code{minus} expression, it will be the +first operand. + +@cindex @code{compare}, canonicalization of +@item +For the @code{compare} operator, a constant is always the second operand +on machines where @code{cc0} is used (@pxref{Jump Patterns}). On other +machines, there are rare cases where the compiler might want to construct +a @code{compare} with a constant as the first operand. However, these +cases are not common enough for it to be worthwhile to provide a pattern +matching a constant as the first operand unless the machine actually has +such an instruction. + +An operand of @code{neg}, @code{not}, @code{mult}, @code{plus}, or +@code{minus} is made the first operand under the same conditions as +above. + +@item +@code{(minus @var{x} (const_int @var{n}))} is converted to +@code{(plus @var{x} (const_int @var{-n}))}. + +@item +Within address computations (i.e., inside @code{mem}), a left shift is +converted into the appropriate multiplication by a power of two. + +@cindex @code{ior}, canonicalization of +@cindex @code{and}, canonicalization of +@cindex De Morgan's law +@item +De`Morgan's Law is used to move bitwise negation inside a bitwise +logical-and or logical-or operation. If this results in only one +operand being a @code{not} expression, it will be the first one. + +A machine that has an instruction that performs a bitwise logical-and of one +operand with the bitwise negation of the other should specify the pattern +for that instruction as + +@example +(define_insn "" + [(set (match_operand:@var{m} 0 @dots{}) + (and:@var{m} (not:@var{m} (match_operand:@var{m} 1 @dots{})) + (match_operand:@var{m} 2 @dots{})))] + "@dots{}" + "@dots{}") +@end example + +@noindent +Similarly, a pattern for a ``NAND'' instruction should be written + +@example +(define_insn "" + [(set (match_operand:@var{m} 0 @dots{}) + (ior:@var{m} (not:@var{m} (match_operand:@var{m} 1 @dots{})) + (not:@var{m} (match_operand:@var{m} 2 @dots{}))))] + "@dots{}" + "@dots{}") +@end example + +In both cases, it is not necessary to include patterns for the many +logically equivalent RTL expressions. + +@cindex @code{xor}, canonicalization of +@item +The only possible RTL expressions involving both bitwise exclusive-or +and bitwise negation are @code{(xor:@var{m} @var{x} @var{y})} +and @code{(not:@var{m} (xor:@var{m} @var{x} @var{y}))}. + +@item +The sum of three items, one of which is a constant, will only appear in +the form + +@example +(plus:@var{m} (plus:@var{m} @var{x} @var{y}) @var{constant}) +@end example + +@item +On machines that do not use @code{cc0}, +@code{(compare @var{x} (const_int 0))} will be converted to +@var{x}. + +@cindex @code{zero_extract}, canonicalization of +@cindex @code{sign_extract}, canonicalization of +@item +Equality comparisons of a group of bits (usually a single bit) with zero +will be written using @code{zero_extract} rather than the equivalent +@code{and} or @code{sign_extract} operations. + +@end itemize + +@node Expander Definitions +@section Defining RTL Sequences for Code Generation +@cindex expander definitions +@cindex code generation RTL sequences +@cindex defining RTL sequences for code generation + +On some target machines, some standard pattern names for RTL generation +cannot be handled with single insn, but a sequence of RTL insns can +represent them. For these target machines, you can write a +@code{define_expand} to specify how to generate the sequence of RTL@. + +@findex define_expand +A @code{define_expand} is an RTL expression that looks almost like a +@code{define_insn}; but, unlike the latter, a @code{define_expand} is used +only for RTL generation and it can produce more than one RTL insn. + +A @code{define_expand} RTX has four operands: + +@itemize @bullet +@item +The name. Each @code{define_expand} must have a name, since the only +use for it is to refer to it by name. + +@item +The RTL template. This is a vector of RTL expressions representing +a sequence of separate instructions. Unlike @code{define_insn}, there +is no implicit surrounding @code{PARALLEL}. + +@item +The condition, a string containing a C expression. This expression is +used to express how the availability of this pattern depends on +subclasses of target machine, selected by command-line options when GCC +is run. This is just like the condition of a @code{define_insn} that +has a standard name. Therefore, the condition (if present) may not +depend on the data in the insn being matched, but only the +target-machine-type flags. The compiler needs to test these conditions +during initialization in order to learn exactly which named instructions +are available in a particular run. + +@item +The preparation statements, a string containing zero or more C +statements which are to be executed before RTL code is generated from +the RTL template. + +Usually these statements prepare temporary registers for use as +internal operands in the RTL template, but they can also generate RTL +insns directly by calling routines such as @code{emit_insn}, etc. +Any such insns precede the ones that come from the RTL template. +@end itemize + +Every RTL insn emitted by a @code{define_expand} must match some +@code{define_insn} in the machine description. Otherwise, the compiler +will crash when trying to generate code for the insn or trying to optimize +it. + +The RTL template, in addition to controlling generation of RTL insns, +also describes the operands that need to be specified when this pattern +is used. In particular, it gives a predicate for each operand. + +A true operand, which needs to be specified in order to generate RTL from +the pattern, should be described with a @code{match_operand} in its first +occurrence in the RTL template. This enters information on the operand's +predicate into the tables that record such things. GCC uses the +information to preload the operand into a register if that is required for +valid RTL code. If the operand is referred to more than once, subsequent +references should use @code{match_dup}. + +The RTL template may also refer to internal ``operands'' which are +temporary registers or labels used only within the sequence made by the +@code{define_expand}. Internal operands are substituted into the RTL +template with @code{match_dup}, never with @code{match_operand}. The +values of the internal operands are not passed in as arguments by the +compiler when it requests use of this pattern. Instead, they are computed +within the pattern, in the preparation statements. These statements +compute the values and store them into the appropriate elements of +@code{operands} so that @code{match_dup} can find them. + +There are two special macros defined for use in the preparation statements: +@code{DONE} and @code{FAIL}. Use them with a following semicolon, +as a statement. + +@table @code + +@findex DONE +@item DONE +Use the @code{DONE} macro to end RTL generation for the pattern. The +only RTL insns resulting from the pattern on this occasion will be +those already emitted by explicit calls to @code{emit_insn} within the +preparation statements; the RTL template will not be generated. + +@findex FAIL +@item FAIL +Make the pattern fail on this occasion. When a pattern fails, it means +that the pattern was not truly available. The calling routines in the +compiler will try other strategies for code generation using other patterns. + +Failure is currently supported only for binary (addition, multiplication, +shifting, etc.) and bit-field (@code{extv}, @code{extzv}, and @code{insv}) +operations. +@end table + +If the preparation falls through (invokes neither @code{DONE} nor +@code{FAIL}), then the @code{define_expand} acts like a +@code{define_insn} in that the RTL template is used to generate the +insn. + +The RTL template is not used for matching, only for generating the +initial insn list. If the preparation statement always invokes +@code{DONE} or @code{FAIL}, the RTL template may be reduced to a simple +list of operands, such as this example: + +@smallexample +@group +(define_expand "addsi3" + [(match_operand:SI 0 "register_operand" "") + (match_operand:SI 1 "register_operand" "") + (match_operand:SI 2 "register_operand" "")] +@end group +@group + "" + " +@{ + handle_add (operands[0], operands[1], operands[2]); + DONE; +@}") +@end group +@end smallexample + +Here is an example, the definition of left-shift for the SPUR chip: + +@smallexample +@group +(define_expand "ashlsi3" + [(set (match_operand:SI 0 "register_operand" "") + (ashift:SI +@end group +@group + (match_operand:SI 1 "register_operand" "") + (match_operand:SI 2 "nonmemory_operand" "")))] + "" + " +@end group +@end smallexample + +@smallexample +@group +@{ + if (GET_CODE (operands[2]) != CONST_INT + || (unsigned) INTVAL (operands[2]) > 3) + FAIL; +@}") +@end group +@end smallexample + +@noindent +This example uses @code{define_expand} so that it can generate an RTL insn +for shifting when the shift-count is in the supported range of 0 to 3 but +fail in other cases where machine insns aren't available. When it fails, +the compiler tries another strategy using different patterns (such as, a +library call). + +If the compiler were able to handle nontrivial condition-strings in +patterns with names, then it would be possible to use a +@code{define_insn} in that case. Here is another case (zero-extension +on the 68000) which makes more use of the power of @code{define_expand}: + +@smallexample +(define_expand "zero_extendhisi2" + [(set (match_operand:SI 0 "general_operand" "") + (const_int 0)) + (set (strict_low_part + (subreg:HI + (match_dup 0) + 0)) + (match_operand:HI 1 "general_operand" ""))] + "" + "operands[1] = make_safe_from (operands[1], operands[0]);") +@end smallexample + +@noindent +@findex make_safe_from +Here two RTL insns are generated, one to clear the entire output operand +and the other to copy the input operand into its low half. This sequence +is incorrect if the input operand refers to [the old value of] the output +operand, so the preparation statement makes sure this isn't so. The +function @code{make_safe_from} copies the @code{operands[1]} into a +temporary register if it refers to @code{operands[0]}. It does this +by emitting another RTL insn. + +Finally, a third example shows the use of an internal operand. +Zero-extension on the SPUR chip is done by @code{and}-ing the result +against a halfword mask. But this mask cannot be represented by a +@code{const_int} because the constant value is too large to be legitimate +on this machine. So it must be copied into a register with +@code{force_reg} and then the register used in the @code{and}. + +@smallexample +(define_expand "zero_extendhisi2" + [(set (match_operand:SI 0 "register_operand" "") + (and:SI (subreg:SI + (match_operand:HI 1 "register_operand" "") + 0) + (match_dup 2)))] + "" + "operands[2] + = force_reg (SImode, GEN_INT (65535)); ") +@end smallexample + +@strong{Note:} If the @code{define_expand} is used to serve a +standard binary or unary arithmetic operation or a bit-field operation, +then the last insn it generates must not be a @code{code_label}, +@code{barrier} or @code{note}. It must be an @code{insn}, +@code{jump_insn} or @code{call_insn}. If you don't need a real insn +at the end, emit an insn to copy the result of the operation into +itself. Such an insn will generate no code, but it can avoid problems +in the compiler. + +@node Insn Splitting +@section Defining How to Split Instructions +@cindex insn splitting +@cindex instruction splitting +@cindex splitting instructions + +There are two cases where you should specify how to split a pattern into +multiple insns. On machines that have instructions requiring delay +slots (@pxref{Delay Slots}) or that have instructions whose output is +not available for multiple cycles (@pxref{Function Units}), the compiler +phases that optimize these cases need to be able to move insns into +one-instruction delay slots. However, some insns may generate more than one +machine instruction. These insns cannot be placed into a delay slot. + +Often you can rewrite the single insn as a list of individual insns, +each corresponding to one machine instruction. The disadvantage of +doing so is that it will cause the compilation to be slower and require +more space. If the resulting insns are too complex, it may also +suppress some optimizations. The compiler splits the insn if there is a +reason to believe that it might improve instruction or delay slot +scheduling. + +The insn combiner phase also splits putative insns. If three insns are +merged into one insn with a complex expression that cannot be matched by +some @code{define_insn} pattern, the combiner phase attempts to split +the complex pattern into two insns that are recognized. Usually it can +break the complex pattern into two patterns by splitting out some +subexpression. However, in some other cases, such as performing an +addition of a large constant in two insns on a RISC machine, the way to +split the addition into two insns is machine-dependent. + +@findex define_split +The @code{define_split} definition tells the compiler how to split a +complex insn into several simpler insns. It looks like this: + +@smallexample +(define_split + [@var{insn-pattern}] + "@var{condition}" + [@var{new-insn-pattern-1} + @var{new-insn-pattern-2} + @dots{}] + "@var{preparation-statements}") +@end smallexample + +@var{insn-pattern} is a pattern that needs to be split and +@var{condition} is the final condition to be tested, as in a +@code{define_insn}. When an insn matching @var{insn-pattern} and +satisfying @var{condition} is found, it is replaced in the insn list +with the insns given by @var{new-insn-pattern-1}, +@var{new-insn-pattern-2}, etc. + +The @var{preparation-statements} are similar to those statements that +are specified for @code{define_expand} (@pxref{Expander Definitions}) +and are executed before the new RTL is generated to prepare for the +generated code or emit some insns whose pattern is not fixed. Unlike +those in @code{define_expand}, however, these statements must not +generate any new pseudo-registers. Once reload has completed, they also +must not allocate any space in the stack frame. + +Patterns are matched against @var{insn-pattern} in two different +circumstances. If an insn needs to be split for delay slot scheduling +or insn scheduling, the insn is already known to be valid, which means +that it must have been matched by some @code{define_insn} and, if +@code{reload_completed} is nonzero, is known to satisfy the constraints +of that @code{define_insn}. In that case, the new insn patterns must +also be insns that are matched by some @code{define_insn} and, if +@code{reload_completed} is nonzero, must also satisfy the constraints +of those definitions. + +As an example of this usage of @code{define_split}, consider the following +example from @file{a29k.md}, which splits a @code{sign_extend} from +@code{HImode} to @code{SImode} into a pair of shift insns: + +@smallexample +(define_split + [(set (match_operand:SI 0 "gen_reg_operand" "") + (sign_extend:SI (match_operand:HI 1 "gen_reg_operand" "")))] + "" + [(set (match_dup 0) + (ashift:SI (match_dup 1) + (const_int 16))) + (set (match_dup 0) + (ashiftrt:SI (match_dup 0) + (const_int 16)))] + " +@{ operands[1] = gen_lowpart (SImode, operands[1]); @}") +@end smallexample + +When the combiner phase tries to split an insn pattern, it is always the +case that the pattern is @emph{not} matched by any @code{define_insn}. +The combiner pass first tries to split a single @code{set} expression +and then the same @code{set} expression inside a @code{parallel}, but +followed by a @code{clobber} of a pseudo-reg to use as a scratch +register. In these cases, the combiner expects exactly two new insn +patterns to be generated. It will verify that these patterns match some +@code{define_insn} definitions, so you need not do this test in the +@code{define_split} (of course, there is no point in writing a +@code{define_split} that will never produce insns that match). + +Here is an example of this use of @code{define_split}, taken from +@file{rs6000.md}: + +@smallexample +(define_split + [(set (match_operand:SI 0 "gen_reg_operand" "") + (plus:SI (match_operand:SI 1 "gen_reg_operand" "") + (match_operand:SI 2 "non_add_cint_operand" "")))] + "" + [(set (match_dup 0) (plus:SI (match_dup 1) (match_dup 3))) + (set (match_dup 0) (plus:SI (match_dup 0) (match_dup 4)))] +" +@{ + int low = INTVAL (operands[2]) & 0xffff; + int high = (unsigned) INTVAL (operands[2]) >> 16; + + if (low & 0x8000) + high++, low |= 0xffff0000; + + operands[3] = GEN_INT (high << 16); + operands[4] = GEN_INT (low); +@}") +@end smallexample + +Here the predicate @code{non_add_cint_operand} matches any +@code{const_int} that is @emph{not} a valid operand of a single add +insn. The add with the smaller displacement is written so that it +can be substituted into the address of a subsequent operation. + +An example that uses a scratch register, from the same file, generates +an equality comparison of a register and a large constant: + +@smallexample +(define_split + [(set (match_operand:CC 0 "cc_reg_operand" "") + (compare:CC (match_operand:SI 1 "gen_reg_operand" "") + (match_operand:SI 2 "non_short_cint_operand" ""))) + (clobber (match_operand:SI 3 "gen_reg_operand" ""))] + "find_single_use (operands[0], insn, 0) + && (GET_CODE (*find_single_use (operands[0], insn, 0)) == EQ + || GET_CODE (*find_single_use (operands[0], insn, 0)) == NE)" + [(set (match_dup 3) (xor:SI (match_dup 1) (match_dup 4))) + (set (match_dup 0) (compare:CC (match_dup 3) (match_dup 5)))] + " +@{ + /* Get the constant we are comparing against, C, and see what it + looks like sign-extended to 16 bits. Then see what constant + could be XOR'ed with C to get the sign-extended value. */ + + int c = INTVAL (operands[2]); + int sextc = (c << 16) >> 16; + int xorv = c ^ sextc; + + operands[4] = GEN_INT (xorv); + operands[5] = GEN_INT (sextc); +@}") +@end smallexample + +To avoid confusion, don't write a single @code{define_split} that +accepts some insns that match some @code{define_insn} as well as some +insns that don't. Instead, write two separate @code{define_split} +definitions, one for the insns that are valid and one for the insns that +are not valid. + +The splitter is allowed to split jump instructions into sequence of +jumps or create new jumps in while splitting non-jump instructions. As +the central flowgraph and branch prediction information needs to be updated, +several restriction apply. + +Splitting of jump instruction into sequence that over by another jump +instruction is always valid, as compiler expect identical behavior of new +jump. When new sequence contains multiple jump instructions or new labels, +more assistance is needed. Splitter is required to create only unconditional +jumps, or simple conditional jump instructions. Additionally it must attach a +@code{REG_BR_PROB} note to each conditional jump. An global variable +@code{split_branch_probability} hold the probability of original branch in case +it was an simple conditional jump, @minus{}1 otherwise. To simplify +recomputing of edge frequencies, new sequence is required to have only +forward jumps to the newly created labels. + +@findex define_insn_and_split +For the common case where the pattern of a define_split exactly matches the +pattern of a define_insn, use @code{define_insn_and_split}. It looks like +this: + +@smallexample +(define_insn_and_split + [@var{insn-pattern}] + "@var{condition}" + "@var{output-template}" + "@var{split-condition}" + [@var{new-insn-pattern-1} + @var{new-insn-pattern-2} + @dots{}] + "@var{preparation-statements}" + [@var{insn-attributes}]) + +@end smallexample + +@var{insn-pattern}, @var{condition}, @var{output-template}, and +@var{insn-attributes} are used as in @code{define_insn}. The +@var{new-insn-pattern} vector and the @var{preparation-statements} are used as +in a @code{define_split}. The @var{split-condition} is also used as in +@code{define_split}, with the additional behavior that if the condition starts +with @samp{&&}, the condition used for the split will be the constructed as a +logical ``and'' of the split condition with the insn condition. For example, +from i386.md: + +@smallexample +(define_insn_and_split "zero_extendhisi2_and" + [(set (match_operand:SI 0 "register_operand" "=r") + (zero_extend:SI (match_operand:HI 1 "register_operand" "0"))) + (clobber (reg:CC 17))] + "TARGET_ZERO_EXTEND_WITH_AND && !optimize_size" + "#" + "&& reload_completed" + [(parallel [(set (match_dup 0) + (and:SI (match_dup 0) (const_int 65535))) + (clobber (reg:CC 17))])] + "" + [(set_attr "type" "alu1")]) + +@end smallexample + +In this case, the actual split condition will be +@samp{TARGET_ZERO_EXTEND_WITH_AND && !optimize_size && reload_completed}. + +The @code{define_insn_and_split} construction provides exactly the same +functionality as two separate @code{define_insn} and @code{define_split} +patterns. It exists for compactness, and as a maintenance tool to prevent +having to ensure the two patterns' templates match. + +@node Including Patterns +@section Including Patterns in Machine Descriptions. +@cindex insn includes + +@findex include +The @code{include} pattern tells the compiler tools where to +look for patterns that are in files other than in the file +@file{.md}. This is used only at build time and there is no preprocessing allowed. + +It looks like: + +@smallexample + +(include + @var{pathname}) +@end smallexample + +For example: + +@smallexample + +(include "filestuff") + +@end smallexample + +Where @var{pathname} is a string that specifies the the location of the file, +specifies the include file to be in @file{gcc/config/target/filestuff}. The +directory @file{gcc/config/target} is regarded as the default directory. + + +Machine descriptions may be split up into smaller more manageable subsections +and placed into subdirectories. + +By specifying: + +@smallexample + +(include "BOGUS/filestuff") + +@end smallexample + +the include file is specified to be in @file{gcc/config/@var{target}/BOGUS/filestuff}. + +Specifying an absolute path for the include file such as; +@smallexample + +(include "/u2/BOGUS/filestuff") + +@end smallexample +is permitted but is not encouraged. + +@subsection RTL Generation Tool Options for Directory Search +@cindex directory options .md +@cindex options, directory search +@cindex search options + +The @option{-I@var{dir}} option specifies directories to search for machine descriptions. +For example: + +@smallexample + +genrecog -I/p1/abc/proc1 -I/p2/abcd/pro2 target.md + +@end smallexample + + +Add the directory @var{dir} to the head of the list of directories to be +searched for header files. This can be used to override a system machine definition +file, substituting your own version, since these directories are +searched before the default machine description file directories. If you use more than +one @option{-I} option, the directories are scanned in left-to-right +order; the standard default directory come after. + + +@node Peephole Definitions +@section Machine-Specific Peephole Optimizers +@cindex peephole optimizer definitions +@cindex defining peephole optimizers + +In addition to instruction patterns the @file{md} file may contain +definitions of machine-specific peephole optimizations. + +The combiner does not notice certain peephole optimizations when the data +flow in the program does not suggest that it should try them. For example, +sometimes two consecutive insns related in purpose can be combined even +though the second one does not appear to use a register computed in the +first one. A machine-specific peephole optimizer can detect such +opportunities. + +There are two forms of peephole definitions that may be used. The +original @code{define_peephole} is run at assembly output time to +match insns and substitute assembly text. Use of @code{define_peephole} +is deprecated. + +A newer @code{define_peephole2} matches insns and substitutes new +insns. The @code{peephole2} pass is run after register allocation +but before scheduling, which may result in much better code for +targets that do scheduling. + +@menu +* define_peephole:: RTL to Text Peephole Optimizers +* define_peephole2:: RTL to RTL Peephole Optimizers +@end menu + +@node define_peephole +@subsection RTL to Text Peephole Optimizers +@findex define_peephole + +@need 1000 +A definition looks like this: + +@smallexample +(define_peephole + [@var{insn-pattern-1} + @var{insn-pattern-2} + @dots{}] + "@var{condition}" + "@var{template}" + "@var{optional-insn-attributes}") +@end smallexample + +@noindent +The last string operand may be omitted if you are not using any +machine-specific information in this machine description. If present, +it must obey the same rules as in a @code{define_insn}. + +In this skeleton, @var{insn-pattern-1} and so on are patterns to match +consecutive insns. The optimization applies to a sequence of insns when +@var{insn-pattern-1} matches the first one, @var{insn-pattern-2} matches +the next, and so on. + +Each of the insns matched by a peephole must also match a +@code{define_insn}. Peepholes are checked only at the last stage just +before code generation, and only optionally. Therefore, any insn which +would match a peephole but no @code{define_insn} will cause a crash in code +generation in an unoptimized compilation, or at various optimization +stages. + +The operands of the insns are matched with @code{match_operands}, +@code{match_operator}, and @code{match_dup}, as usual. What is not +usual is that the operand numbers apply to all the insn patterns in the +definition. So, you can check for identical operands in two insns by +using @code{match_operand} in one insn and @code{match_dup} in the +other. + +The operand constraints used in @code{match_operand} patterns do not have +any direct effect on the applicability of the peephole, but they will +be validated afterward, so make sure your constraints are general enough +to apply whenever the peephole matches. If the peephole matches +but the constraints are not satisfied, the compiler will crash. + +It is safe to omit constraints in all the operands of the peephole; or +you can write constraints which serve as a double-check on the criteria +previously tested. + +Once a sequence of insns matches the patterns, the @var{condition} is +checked. This is a C expression which makes the final decision whether to +perform the optimization (we do so if the expression is nonzero). If +@var{condition} is omitted (in other words, the string is empty) then the +optimization is applied to every sequence of insns that matches the +patterns. + +The defined peephole optimizations are applied after register allocation +is complete. Therefore, the peephole definition can check which +operands have ended up in which kinds of registers, just by looking at +the operands. + +@findex prev_active_insn +The way to refer to the operands in @var{condition} is to write +@code{operands[@var{i}]} for operand number @var{i} (as matched by +@code{(match_operand @var{i} @dots{})}). Use the variable @code{insn} +to refer to the last of the insns being matched; use +@code{prev_active_insn} to find the preceding insns. + +@findex dead_or_set_p +When optimizing computations with intermediate results, you can use +@var{condition} to match only when the intermediate results are not used +elsewhere. Use the C expression @code{dead_or_set_p (@var{insn}, +@var{op})}, where @var{insn} is the insn in which you expect the value +to be used for the last time (from the value of @code{insn}, together +with use of @code{prev_nonnote_insn}), and @var{op} is the intermediate +value (from @code{operands[@var{i}]}). + +Applying the optimization means replacing the sequence of insns with one +new insn. The @var{template} controls ultimate output of assembler code +for this combined insn. It works exactly like the template of a +@code{define_insn}. Operand numbers in this template are the same ones +used in matching the original sequence of insns. + +The result of a defined peephole optimizer does not need to match any of +the insn patterns in the machine description; it does not even have an +opportunity to match them. The peephole optimizer definition itself serves +as the insn pattern to control how the insn is output. + +Defined peephole optimizers are run as assembler code is being output, +so the insns they produce are never combined or rearranged in any way. + +Here is an example, taken from the 68000 machine description: + +@smallexample +(define_peephole + [(set (reg:SI 15) (plus:SI (reg:SI 15) (const_int 4))) + (set (match_operand:DF 0 "register_operand" "=f") + (match_operand:DF 1 "register_operand" "ad"))] + "FP_REG_P (operands[0]) && ! FP_REG_P (operands[1])" +@{ + rtx xoperands[2]; + xoperands[1] = gen_rtx (REG, SImode, REGNO (operands[1]) + 1); +#ifdef MOTOROLA + output_asm_insn ("move.l %1,(sp)", xoperands); + output_asm_insn ("move.l %1,-(sp)", operands); + return "fmove.d (sp)+,%0"; +#else + output_asm_insn ("movel %1,sp@@", xoperands); + output_asm_insn ("movel %1,sp@@-", operands); + return "fmoved sp@@+,%0"; +#endif +@}) +@end smallexample + +@need 1000 +The effect of this optimization is to change + +@smallexample +@group +jbsr _foobar +addql #4,sp +movel d1,sp@@- +movel d0,sp@@- +fmoved sp@@+,fp0 +@end group +@end smallexample + +@noindent +into + +@smallexample +@group +jbsr _foobar +movel d1,sp@@ +movel d0,sp@@- +fmoved sp@@+,fp0 +@end group +@end smallexample + +@ignore +@findex CC_REVERSED +If a peephole matches a sequence including one or more jump insns, you must +take account of the flags such as @code{CC_REVERSED} which specify that the +condition codes are represented in an unusual manner. The compiler +automatically alters any ordinary conditional jumps which occur in such +situations, but the compiler cannot alter jumps which have been replaced by +peephole optimizations. So it is up to you to alter the assembler code +that the peephole produces. Supply C code to write the assembler output, +and in this C code check the condition code status flags and change the +assembler code as appropriate. +@end ignore + +@var{insn-pattern-1} and so on look @emph{almost} like the second +operand of @code{define_insn}. There is one important difference: the +second operand of @code{define_insn} consists of one or more RTX's +enclosed in square brackets. Usually, there is only one: then the same +action can be written as an element of a @code{define_peephole}. But +when there are multiple actions in a @code{define_insn}, they are +implicitly enclosed in a @code{parallel}. Then you must explicitly +write the @code{parallel}, and the square brackets within it, in the +@code{define_peephole}. Thus, if an insn pattern looks like this, + +@smallexample +(define_insn "divmodsi4" + [(set (match_operand:SI 0 "general_operand" "=d") + (div:SI (match_operand:SI 1 "general_operand" "0") + (match_operand:SI 2 "general_operand" "dmsK"))) + (set (match_operand:SI 3 "general_operand" "=d") + (mod:SI (match_dup 1) (match_dup 2)))] + "TARGET_68020" + "divsl%.l %2,%3:%0") +@end smallexample + +@noindent +then the way to mention this insn in a peephole is as follows: + +@smallexample +(define_peephole + [@dots{} + (parallel + [(set (match_operand:SI 0 "general_operand" "=d") + (div:SI (match_operand:SI 1 "general_operand" "0") + (match_operand:SI 2 "general_operand" "dmsK"))) + (set (match_operand:SI 3 "general_operand" "=d") + (mod:SI (match_dup 1) (match_dup 2)))]) + @dots{}] + @dots{}) +@end smallexample + +@node define_peephole2 +@subsection RTL to RTL Peephole Optimizers +@findex define_peephole2 + +The @code{define_peephole2} definition tells the compiler how to +substitute one sequence of instructions for another sequence, +what additional scratch registers may be needed and what their +lifetimes must be. + +@smallexample +(define_peephole2 + [@var{insn-pattern-1} + @var{insn-pattern-2} + @dots{}] + "@var{condition}" + [@var{new-insn-pattern-1} + @var{new-insn-pattern-2} + @dots{}] + "@var{preparation-statements}") +@end smallexample + +The definition is almost identical to @code{define_split} +(@pxref{Insn Splitting}) except that the pattern to match is not a +single instruction, but a sequence of instructions. + +It is possible to request additional scratch registers for use in the +output template. If appropriate registers are not free, the pattern +will simply not match. + +@findex match_scratch +@findex match_dup +Scratch registers are requested with a @code{match_scratch} pattern at +the top level of the input pattern. The allocated register (initially) will +be dead at the point requested within the original sequence. If the scratch +is used at more than a single point, a @code{match_dup} pattern at the +top level of the input pattern marks the last position in the input sequence +at which the register must be available. + +Here is an example from the IA-32 machine description: + +@smallexample +(define_peephole2 + [(match_scratch:SI 2 "r") + (parallel [(set (match_operand:SI 0 "register_operand" "") + (match_operator:SI 3 "arith_or_logical_operator" + [(match_dup 0) + (match_operand:SI 1 "memory_operand" "")])) + (clobber (reg:CC 17))])] + "! optimize_size && ! TARGET_READ_MODIFY" + [(set (match_dup 2) (match_dup 1)) + (parallel [(set (match_dup 0) + (match_op_dup 3 [(match_dup 0) (match_dup 2)])) + (clobber (reg:CC 17))])] + "") +@end smallexample + +@noindent +This pattern tries to split a load from its use in the hopes that we'll be +able to schedule around the memory load latency. It allocates a single +@code{SImode} register of class @code{GENERAL_REGS} (@code{"r"}) that needs +to be live only at the point just before the arithmetic. + +A real example requiring extended scratch lifetimes is harder to come by, +so here's a silly made-up example: + +@smallexample +(define_peephole2 + [(match_scratch:SI 4 "r") + (set (match_operand:SI 0 "" "") (match_operand:SI 1 "" "")) + (set (match_operand:SI 2 "" "") (match_dup 1)) + (match_dup 4) + (set (match_operand:SI 3 "" "") (match_dup 1))] + "/* @r{determine 1 does not overlap 0 and 2} */" + [(set (match_dup 4) (match_dup 1)) + (set (match_dup 0) (match_dup 4)) + (set (match_dup 2) (match_dup 4))] + (set (match_dup 3) (match_dup 4))] + "") +@end smallexample + +@noindent +If we had not added the @code{(match_dup 4)} in the middle of the input +sequence, it might have been the case that the register we chose at the +beginning of the sequence is killed by the first or second @code{set}. + +@node Insn Attributes +@section Instruction Attributes +@cindex insn attributes +@cindex instruction attributes + +In addition to describing the instruction supported by the target machine, +the @file{md} file also defines a group of @dfn{attributes} and a set of +values for each. Every generated insn is assigned a value for each attribute. +One possible attribute would be the effect that the insn has on the machine's +condition code. This attribute can then be used by @code{NOTICE_UPDATE_CC} +to track the condition codes. + +@menu +* Defining Attributes:: Specifying attributes and their values. +* Expressions:: Valid expressions for attribute values. +* Tagging Insns:: Assigning attribute values to insns. +* Attr Example:: An example of assigning attributes. +* Insn Lengths:: Computing the length of insns. +* Constant Attributes:: Defining attributes that are constant. +* Delay Slots:: Defining delay slots required for a machine. +* Function Units:: Specifying information for insn scheduling. +@end menu + +@node Defining Attributes +@subsection Defining Attributes and their Values +@cindex defining attributes and their values +@cindex attributes, defining + +@findex define_attr +The @code{define_attr} expression is used to define each attribute required +by the target machine. It looks like: + +@smallexample +(define_attr @var{name} @var{list-of-values} @var{default}) +@end smallexample + +@var{name} is a string specifying the name of the attribute being defined. + +@var{list-of-values} is either a string that specifies a comma-separated +list of values that can be assigned to the attribute, or a null string to +indicate that the attribute takes numeric values. + +@var{default} is an attribute expression that gives the value of this +attribute for insns that match patterns whose definition does not include +an explicit value for this attribute. @xref{Attr Example}, for more +information on the handling of defaults. @xref{Constant Attributes}, +for information on attributes that do not depend on any particular insn. + +@findex insn-attr.h +For each defined attribute, a number of definitions are written to the +@file{insn-attr.h} file. For cases where an explicit set of values is +specified for an attribute, the following are defined: + +@itemize @bullet +@item +A @samp{#define} is written for the symbol @samp{HAVE_ATTR_@var{name}}. + +@item +An enumeral class is defined for @samp{attr_@var{name}} with +elements of the form @samp{@var{upper-name}_@var{upper-value}} where +the attribute name and value are first converted to upper case. + +@item +A function @samp{get_attr_@var{name}} is defined that is passed an insn and +returns the attribute value for that insn. +@end itemize + +For example, if the following is present in the @file{md} file: + +@smallexample +(define_attr "type" "branch,fp,load,store,arith" @dots{}) +@end smallexample + +@noindent +the following lines will be written to the file @file{insn-attr.h}. + +@smallexample +#define HAVE_ATTR_type +enum attr_type @{TYPE_BRANCH, TYPE_FP, TYPE_LOAD, + TYPE_STORE, TYPE_ARITH@}; +extern enum attr_type get_attr_type (); +@end smallexample + +If the attribute takes numeric values, no @code{enum} type will be +defined and the function to obtain the attribute's value will return +@code{int}. + +@node Expressions +@subsection Attribute Expressions +@cindex attribute expressions + +RTL expressions used to define attributes use the codes described above +plus a few specific to attribute definitions, to be discussed below. +Attribute value expressions must have one of the following forms: + +@table @code +@cindex @code{const_int} and attributes +@item (const_int @var{i}) +The integer @var{i} specifies the value of a numeric attribute. @var{i} +must be non-negative. + +The value of a numeric attribute can be specified either with a +@code{const_int}, or as an integer represented as a string in +@code{const_string}, @code{eq_attr} (see below), @code{attr}, +@code{symbol_ref}, simple arithmetic expressions, and @code{set_attr} +overrides on specific instructions (@pxref{Tagging Insns}). + +@cindex @code{const_string} and attributes +@item (const_string @var{value}) +The string @var{value} specifies a constant attribute value. +If @var{value} is specified as @samp{"*"}, it means that the default value of +the attribute is to be used for the insn containing this expression. +@samp{"*"} obviously cannot be used in the @var{default} expression +of a @code{define_attr}. + +If the attribute whose value is being specified is numeric, @var{value} +must be a string containing a non-negative integer (normally +@code{const_int} would be used in this case). Otherwise, it must +contain one of the valid values for the attribute. + +@cindex @code{if_then_else} and attributes +@item (if_then_else @var{test} @var{true-value} @var{false-value}) +@var{test} specifies an attribute test, whose format is defined below. +The value of this expression is @var{true-value} if @var{test} is true, +otherwise it is @var{false-value}. + +@cindex @code{cond} and attributes +@item (cond [@var{test1} @var{value1} @dots{}] @var{default}) +The first operand of this expression is a vector containing an even +number of expressions and consisting of pairs of @var{test} and @var{value} +expressions. The value of the @code{cond} expression is that of the +@var{value} corresponding to the first true @var{test} expression. If +none of the @var{test} expressions are true, the value of the @code{cond} +expression is that of the @var{default} expression. +@end table + +@var{test} expressions can have one of the following forms: + +@table @code +@cindex @code{const_int} and attribute tests +@item (const_int @var{i}) +This test is true if @var{i} is nonzero and false otherwise. + +@cindex @code{not} and attributes +@cindex @code{ior} and attributes +@cindex @code{and} and attributes +@item (not @var{test}) +@itemx (ior @var{test1} @var{test2}) +@itemx (and @var{test1} @var{test2}) +These tests are true if the indicated logical function is true. + +@cindex @code{match_operand} and attributes +@item (match_operand:@var{m} @var{n} @var{pred} @var{constraints}) +This test is true if operand @var{n} of the insn whose attribute value +is being determined has mode @var{m} (this part of the test is ignored +if @var{m} is @code{VOIDmode}) and the function specified by the string +@var{pred} returns a nonzero value when passed operand @var{n} and mode +@var{m} (this part of the test is ignored if @var{pred} is the null +string). + +The @var{constraints} operand is ignored and should be the null string. + +@cindex @code{le} and attributes +@cindex @code{leu} and attributes +@cindex @code{lt} and attributes +@cindex @code{gt} and attributes +@cindex @code{gtu} and attributes +@cindex @code{ge} and attributes +@cindex @code{geu} and attributes +@cindex @code{ne} and attributes +@cindex @code{eq} and attributes +@cindex @code{plus} and attributes +@cindex @code{minus} and attributes +@cindex @code{mult} and attributes +@cindex @code{div} and attributes +@cindex @code{mod} and attributes +@cindex @code{abs} and attributes +@cindex @code{neg} and attributes +@cindex @code{ashift} and attributes +@cindex @code{lshiftrt} and attributes +@cindex @code{ashiftrt} and attributes +@item (le @var{arith1} @var{arith2}) +@itemx (leu @var{arith1} @var{arith2}) +@itemx (lt @var{arith1} @var{arith2}) +@itemx (ltu @var{arith1} @var{arith2}) +@itemx (gt @var{arith1} @var{arith2}) +@itemx (gtu @var{arith1} @var{arith2}) +@itemx (ge @var{arith1} @var{arith2}) +@itemx (geu @var{arith1} @var{arith2}) +@itemx (ne @var{arith1} @var{arith2}) +@itemx (eq @var{arith1} @var{arith2}) +These tests are true if the indicated comparison of the two arithmetic +expressions is true. Arithmetic expressions are formed with +@code{plus}, @code{minus}, @code{mult}, @code{div}, @code{mod}, +@code{abs}, @code{neg}, @code{and}, @code{ior}, @code{xor}, @code{not}, +@code{ashift}, @code{lshiftrt}, and @code{ashiftrt} expressions. + +@findex get_attr +@code{const_int} and @code{symbol_ref} are always valid terms (@pxref{Insn +Lengths},for additional forms). @code{symbol_ref} is a string +denoting a C expression that yields an @code{int} when evaluated by the +@samp{get_attr_@dots{}} routine. It should normally be a global +variable. + +@findex eq_attr +@item (eq_attr @var{name} @var{value}) +@var{name} is a string specifying the name of an attribute. + +@var{value} is a string that is either a valid value for attribute +@var{name}, a comma-separated list of values, or @samp{!} followed by a +value or list. If @var{value} does not begin with a @samp{!}, this +test is true if the value of the @var{name} attribute of the current +insn is in the list specified by @var{value}. If @var{value} begins +with a @samp{!}, this test is true if the attribute's value is +@emph{not} in the specified list. + +For example, + +@smallexample +(eq_attr "type" "load,store") +@end smallexample + +@noindent +is equivalent to + +@smallexample +(ior (eq_attr "type" "load") (eq_attr "type" "store")) +@end smallexample + +If @var{name} specifies an attribute of @samp{alternative}, it refers to the +value of the compiler variable @code{which_alternative} +(@pxref{Output Statement}) and the values must be small integers. For +example, + +@smallexample +(eq_attr "alternative" "2,3") +@end smallexample + +@noindent +is equivalent to + +@smallexample +(ior (eq (symbol_ref "which_alternative") (const_int 2)) + (eq (symbol_ref "which_alternative") (const_int 3))) +@end smallexample + +Note that, for most attributes, an @code{eq_attr} test is simplified in cases +where the value of the attribute being tested is known for all insns matching +a particular pattern. This is by far the most common case. + +@findex attr_flag +@item (attr_flag @var{name}) +The value of an @code{attr_flag} expression is true if the flag +specified by @var{name} is true for the @code{insn} currently being +scheduled. + +@var{name} is a string specifying one of a fixed set of flags to test. +Test the flags @code{forward} and @code{backward} to determine the +direction of a conditional branch. Test the flags @code{very_likely}, +@code{likely}, @code{very_unlikely}, and @code{unlikely} to determine +if a conditional branch is expected to be taken. + +If the @code{very_likely} flag is true, then the @code{likely} flag is also +true. Likewise for the @code{very_unlikely} and @code{unlikely} flags. + +This example describes a conditional branch delay slot which +can be nullified for forward branches that are taken (annul-true) or +for backward branches which are not taken (annul-false). + +@smallexample +(define_delay (eq_attr "type" "cbranch") + [(eq_attr "in_branch_delay" "true") + (and (eq_attr "in_branch_delay" "true") + (attr_flag "forward")) + (and (eq_attr "in_branch_delay" "true") + (attr_flag "backward"))]) +@end smallexample + +The @code{forward} and @code{backward} flags are false if the current +@code{insn} being scheduled is not a conditional branch. + +The @code{very_likely} and @code{likely} flags are true if the +@code{insn} being scheduled is not a conditional branch. +The @code{very_unlikely} and @code{unlikely} flags are false if the +@code{insn} being scheduled is not a conditional branch. + +@code{attr_flag} is only used during delay slot scheduling and has no +meaning to other passes of the compiler. + +@findex attr +@item (attr @var{name}) +The value of another attribute is returned. This is most useful +for numeric attributes, as @code{eq_attr} and @code{attr_flag} +produce more efficient code for non-numeric attributes. +@end table + +@node Tagging Insns +@subsection Assigning Attribute Values to Insns +@cindex tagging insns +@cindex assigning attribute values to insns + +The value assigned to an attribute of an insn is primarily determined by +which pattern is matched by that insn (or which @code{define_peephole} +generated it). Every @code{define_insn} and @code{define_peephole} can +have an optional last argument to specify the values of attributes for +matching insns. The value of any attribute not specified in a particular +insn is set to the default value for that attribute, as specified in its +@code{define_attr}. Extensive use of default values for attributes +permits the specification of the values for only one or two attributes +in the definition of most insn patterns, as seen in the example in the +next section. + +The optional last argument of @code{define_insn} and +@code{define_peephole} is a vector of expressions, each of which defines +the value for a single attribute. The most general way of assigning an +attribute's value is to use a @code{set} expression whose first operand is an +@code{attr} expression giving the name of the attribute being set. The +second operand of the @code{set} is an attribute expression +(@pxref{Expressions}) giving the value of the attribute. + +When the attribute value depends on the @samp{alternative} attribute +(i.e., which is the applicable alternative in the constraint of the +insn), the @code{set_attr_alternative} expression can be used. It +allows the specification of a vector of attribute expressions, one for +each alternative. + +@findex set_attr +When the generality of arbitrary attribute expressions is not required, +the simpler @code{set_attr} expression can be used, which allows +specifying a string giving either a single attribute value or a list +of attribute values, one for each alternative. + +The form of each of the above specifications is shown below. In each case, +@var{name} is a string specifying the attribute to be set. + +@table @code +@item (set_attr @var{name} @var{value-string}) +@var{value-string} is either a string giving the desired attribute value, +or a string containing a comma-separated list giving the values for +succeeding alternatives. The number of elements must match the number +of alternatives in the constraint of the insn pattern. + +Note that it may be useful to specify @samp{*} for some alternative, in +which case the attribute will assume its default value for insns matching +that alternative. + +@findex set_attr_alternative +@item (set_attr_alternative @var{name} [@var{value1} @var{value2} @dots{}]) +Depending on the alternative of the insn, the value will be one of the +specified values. This is a shorthand for using a @code{cond} with +tests on the @samp{alternative} attribute. + +@findex attr +@item (set (attr @var{name}) @var{value}) +The first operand of this @code{set} must be the special RTL expression +@code{attr}, whose sole operand is a string giving the name of the +attribute being set. @var{value} is the value of the attribute. +@end table + +The following shows three different ways of representing the same +attribute value specification: + +@smallexample +(set_attr "type" "load,store,arith") + +(set_attr_alternative "type" + [(const_string "load") (const_string "store") + (const_string "arith")]) + +(set (attr "type") + (cond [(eq_attr "alternative" "1") (const_string "load") + (eq_attr "alternative" "2") (const_string "store")] + (const_string "arith"))) +@end smallexample + +@need 1000 +@findex define_asm_attributes +The @code{define_asm_attributes} expression provides a mechanism to +specify the attributes assigned to insns produced from an @code{asm} +statement. It has the form: + +@smallexample +(define_asm_attributes [@var{attr-sets}]) +@end smallexample + +@noindent +where @var{attr-sets} is specified the same as for both the +@code{define_insn} and the @code{define_peephole} expressions. + +These values will typically be the ``worst case'' attribute values. For +example, they might indicate that the condition code will be clobbered. + +A specification for a @code{length} attribute is handled specially. The +way to compute the length of an @code{asm} insn is to multiply the +length specified in the expression @code{define_asm_attributes} by the +number of machine instructions specified in the @code{asm} statement, +determined by counting the number of semicolons and newlines in the +string. Therefore, the value of the @code{length} attribute specified +in a @code{define_asm_attributes} should be the maximum possible length +of a single machine instruction. + +@node Attr Example +@subsection Example of Attribute Specifications +@cindex attribute specifications example +@cindex attribute specifications + +The judicious use of defaulting is important in the efficient use of +insn attributes. Typically, insns are divided into @dfn{types} and an +attribute, customarily called @code{type}, is used to represent this +value. This attribute is normally used only to define the default value +for other attributes. An example will clarify this usage. + +Assume we have a RISC machine with a condition code and in which only +full-word operations are performed in registers. Let us assume that we +can divide all insns into loads, stores, (integer) arithmetic +operations, floating point operations, and branches. + +Here we will concern ourselves with determining the effect of an insn on +the condition code and will limit ourselves to the following possible +effects: The condition code can be set unpredictably (clobbered), not +be changed, be set to agree with the results of the operation, or only +changed if the item previously set into the condition code has been +modified. + +Here is part of a sample @file{md} file for such a machine: + +@smallexample +(define_attr "type" "load,store,arith,fp,branch" (const_string "arith")) + +(define_attr "cc" "clobber,unchanged,set,change0" + (cond [(eq_attr "type" "load") + (const_string "change0") + (eq_attr "type" "store,branch") + (const_string "unchanged") + (eq_attr "type" "arith") + (if_then_else (match_operand:SI 0 "" "") + (const_string "set") + (const_string "clobber"))] + (const_string "clobber"))) + +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,r,m") + (match_operand:SI 1 "general_operand" "r,m,r"))] + "" + "@@ + move %0,%1 + load %0,%1 + store %0,%1" + [(set_attr "type" "arith,load,store")]) +@end smallexample + +Note that we assume in the above example that arithmetic operations +performed on quantities smaller than a machine word clobber the condition +code since they will set the condition code to a value corresponding to the +full-word result. + +@node Insn Lengths +@subsection Computing the Length of an Insn +@cindex insn lengths, computing +@cindex computing the length of an insn + +For many machines, multiple types of branch instructions are provided, each +for different length branch displacements. In most cases, the assembler +will choose the correct instruction to use. However, when the assembler +cannot do so, GCC can when a special attribute, the @samp{length} +attribute, is defined. This attribute must be defined to have numeric +values by specifying a null string in its @code{define_attr}. + +In the case of the @samp{length} attribute, two additional forms of +arithmetic terms are allowed in test expressions: + +@table @code +@cindex @code{match_dup} and attributes +@item (match_dup @var{n}) +This refers to the address of operand @var{n} of the current insn, which +must be a @code{label_ref}. + +@cindex @code{pc} and attributes +@item (pc) +This refers to the address of the @emph{current} insn. It might have +been more consistent with other usage to make this the address of the +@emph{next} insn but this would be confusing because the length of the +current insn is to be computed. +@end table + +@cindex @code{addr_vec}, length of +@cindex @code{addr_diff_vec}, length of +For normal insns, the length will be determined by value of the +@samp{length} attribute. In the case of @code{addr_vec} and +@code{addr_diff_vec} insn patterns, the length is computed as +the number of vectors multiplied by the size of each vector. + +Lengths are measured in addressable storage units (bytes). + +The following macros can be used to refine the length computation: + +@table @code +@findex FIRST_INSN_ADDRESS +@item FIRST_INSN_ADDRESS +When the @code{length} insn attribute is used, this macro specifies the +value to be assigned to the address of the first insn in a function. If +not specified, 0 is used. + +@findex ADJUST_INSN_LENGTH +@item ADJUST_INSN_LENGTH (@var{insn}, @var{length}) +If defined, modifies the length assigned to instruction @var{insn} as a +function of the context in which it is used. @var{length} is an lvalue +that contains the initially computed length of the insn and should be +updated with the correct length of the insn. + +This macro will normally not be required. A case in which it is +required is the ROMP@. On this machine, the size of an @code{addr_vec} +insn must be increased by two to compensate for the fact that alignment +may be required. +@end table + +@findex get_attr_length +The routine that returns @code{get_attr_length} (the value of the +@code{length} attribute) can be used by the output routine to +determine the form of the branch instruction to be written, as the +example below illustrates. + +As an example of the specification of variable-length branches, consider +the IBM 360. If we adopt the convention that a register will be set to +the starting address of a function, we can jump to labels within 4k of +the start using a four-byte instruction. Otherwise, we need a six-byte +sequence to load the address from memory and then branch to it. + +On such a machine, a pattern for a branch instruction might be specified +as follows: + +@smallexample +(define_insn "jump" + [(set (pc) + (label_ref (match_operand 0 "" "")))] + "" +@{ + return (get_attr_length (insn) == 4 + ? "b %l0" : "l r15,=a(%l0); br r15"); +@} + [(set (attr "length") + (if_then_else (lt (match_dup 0) (const_int 4096)) + (const_int 4) + (const_int 6)))]) +@end smallexample + +@node Constant Attributes +@subsection Constant Attributes +@cindex constant attributes + +A special form of @code{define_attr}, where the expression for the +default value is a @code{const} expression, indicates an attribute that +is constant for a given run of the compiler. Constant attributes may be +used to specify which variety of processor is used. For example, + +@smallexample +(define_attr "cpu" "m88100,m88110,m88000" + (const + (cond [(symbol_ref "TARGET_88100") (const_string "m88100") + (symbol_ref "TARGET_88110") (const_string "m88110")] + (const_string "m88000")))) + +(define_attr "memory" "fast,slow" + (const + (if_then_else (symbol_ref "TARGET_FAST_MEM") + (const_string "fast") + (const_string "slow")))) +@end smallexample + +The routine generated for constant attributes has no parameters as it +does not depend on any particular insn. RTL expressions used to define +the value of a constant attribute may use the @code{symbol_ref} form, +but may not use either the @code{match_operand} form or @code{eq_attr} +forms involving insn attributes. + +@node Delay Slots +@subsection Delay Slot Scheduling +@cindex delay slots, defining + +The insn attribute mechanism can be used to specify the requirements for +delay slots, if any, on a target machine. An instruction is said to +require a @dfn{delay slot} if some instructions that are physically +after the instruction are executed as if they were located before it. +Classic examples are branch and call instructions, which often execute +the following instruction before the branch or call is performed. + +On some machines, conditional branch instructions can optionally +@dfn{annul} instructions in the delay slot. This means that the +instruction will not be executed for certain branch outcomes. Both +instructions that annul if the branch is true and instructions that +annul if the branch is false are supported. + +Delay slot scheduling differs from instruction scheduling in that +determining whether an instruction needs a delay slot is dependent only +on the type of instruction being generated, not on data flow between the +instructions. See the next section for a discussion of data-dependent +instruction scheduling. + +@findex define_delay +The requirement of an insn needing one or more delay slots is indicated +via the @code{define_delay} expression. It has the following form: + +@smallexample +(define_delay @var{test} + [@var{delay-1} @var{annul-true-1} @var{annul-false-1} + @var{delay-2} @var{annul-true-2} @var{annul-false-2} + @dots{}]) +@end smallexample + +@var{test} is an attribute test that indicates whether this +@code{define_delay} applies to a particular insn. If so, the number of +required delay slots is determined by the length of the vector specified +as the second argument. An insn placed in delay slot @var{n} must +satisfy attribute test @var{delay-n}. @var{annul-true-n} is an +attribute test that specifies which insns may be annulled if the branch +is true. Similarly, @var{annul-false-n} specifies which insns in the +delay slot may be annulled if the branch is false. If annulling is not +supported for that delay slot, @code{(nil)} should be coded. + +For example, in the common case where branch and call insns require +a single delay slot, which may contain any insn other than a branch or +call, the following would be placed in the @file{md} file: + +@smallexample +(define_delay (eq_attr "type" "branch,call") + [(eq_attr "type" "!branch,call") (nil) (nil)]) +@end smallexample + +Multiple @code{define_delay} expressions may be specified. In this +case, each such expression specifies different delay slot requirements +and there must be no insn for which tests in two @code{define_delay} +expressions are both true. + +For example, if we have a machine that requires one delay slot for branches +but two for calls, no delay slot can contain a branch or call insn, +and any valid insn in the delay slot for the branch can be annulled if the +branch is true, we might represent this as follows: + +@smallexample +(define_delay (eq_attr "type" "branch") + [(eq_attr "type" "!branch,call") + (eq_attr "type" "!branch,call") + (nil)]) + +(define_delay (eq_attr "type" "call") + [(eq_attr "type" "!branch,call") (nil) (nil) + (eq_attr "type" "!branch,call") (nil) (nil)]) +@end smallexample +@c the above is *still* too long. --mew 4feb93 + +@node Function Units +@subsection Specifying Function Units +@cindex function units, for scheduling + +On most RISC machines, there are instructions whose results are not +available for a specific number of cycles. Common cases are instructions +that load data from memory. On many machines, a pipeline stall will result +if the data is referenced too soon after the load instruction. + +In addition, many newer microprocessors have multiple function units, usually +one for integer and one for floating point, and often will incur pipeline +stalls when a result that is needed is not yet ready. + +The descriptions in this section allow the specification of how much +time must elapse between the execution of an instruction and the time +when its result is used. It also allows specification of when the +execution of an instruction will delay execution of similar instructions +due to function unit conflicts. + +For the purposes of the specifications in this section, a machine is +divided into @dfn{function units}, each of which execute a specific +class of instructions in first-in-first-out order. Function units that +accept one instruction each cycle and allow a result to be used in the +succeeding instruction (usually via forwarding) need not be specified. +Classic RISC microprocessors will normally have a single function unit, +which we can call @samp{memory}. The newer ``superscalar'' processors +will often have function units for floating point operations, usually at +least a floating point adder and multiplier. + +@findex define_function_unit +Each usage of a function units by a class of insns is specified with a +@code{define_function_unit} expression, which looks like this: + +@smallexample +(define_function_unit @var{name} @var{multiplicity} @var{simultaneity} + @var{test} @var{ready-delay} @var{issue-delay} + [@var{conflict-list}]) +@end smallexample + +@var{name} is a string giving the name of the function unit. + +@var{multiplicity} is an integer specifying the number of identical +units in the processor. If more than one unit is specified, they will +be scheduled independently. Only truly independent units should be +counted; a pipelined unit should be specified as a single unit. (The +only common example of a machine that has multiple function units for a +single instruction class that are truly independent and not pipelined +are the two multiply and two increment units of the CDC 6600.) + +@var{simultaneity} specifies the maximum number of insns that can be +executing in each instance of the function unit simultaneously or zero +if the unit is pipelined and has no limit. + +All @code{define_function_unit} definitions referring to function unit +@var{name} must have the same name and values for @var{multiplicity} and +@var{simultaneity}. + +@var{test} is an attribute test that selects the insns we are describing +in this definition. Note that an insn may use more than one function +unit and a function unit may be specified in more than one +@code{define_function_unit}. + +@var{ready-delay} is an integer that specifies the number of cycles +after which the result of the instruction can be used without +introducing any stalls. + +@var{issue-delay} is an integer that specifies the number of cycles +after the instruction matching the @var{test} expression begins using +this unit until a subsequent instruction can begin. A cost of @var{N} +indicates an @var{N-1} cycle delay. A subsequent instruction may also +be delayed if an earlier instruction has a longer @var{ready-delay} +value. This blocking effect is computed using the @var{simultaneity}, +@var{ready-delay}, @var{issue-delay}, and @var{conflict-list} terms. +For a normal non-pipelined function unit, @var{simultaneity} is one, the +unit is taken to block for the @var{ready-delay} cycles of the executing +insn, and smaller values of @var{issue-delay} are ignored. + +@var{conflict-list} is an optional list giving detailed conflict costs +for this unit. If specified, it is a list of condition test expressions +to be applied to insns chosen to execute in @var{name} following the +particular insn matching @var{test} that is already executing in +@var{name}. For each insn in the list, @var{issue-delay} specifies the +conflict cost; for insns not in the list, the cost is zero. If not +specified, @var{conflict-list} defaults to all instructions that use the +function unit. + +Typical uses of this vector are where a floating point function unit can +pipeline either single- or double-precision operations, but not both, or +where a memory unit can pipeline loads, but not stores, etc. + +As an example, consider a classic RISC machine where the result of a +load instruction is not available for two cycles (a single ``delay'' +instruction is required) and where only one load instruction can be executed +simultaneously. This would be specified as: + +@smallexample +(define_function_unit "memory" 1 1 (eq_attr "type" "load") 2 0) +@end smallexample + +For the case of a floating point function unit that can pipeline either +single or double precision, but not both, the following could be specified: + +@smallexample +(define_function_unit + "fp" 1 0 (eq_attr "type" "sp_fp") 4 4 [(eq_attr "type" "dp_fp")]) +(define_function_unit + "fp" 1 0 (eq_attr "type" "dp_fp") 4 4 [(eq_attr "type" "sp_fp")]) +@end smallexample + +@strong{Note:} The scheduler attempts to avoid function unit conflicts +and uses all the specifications in the @code{define_function_unit} +expression. It has recently come to our attention that these +specifications may not allow modeling of some of the newer +``superscalar'' processors that have insns using multiple pipelined +units. These insns will cause a potential conflict for the second unit +used during their execution and there is no way of representing that +conflict. We welcome any examples of how function unit conflicts work +in such processors and suggestions for their representation. + +@node Conditional Execution +@section Conditional Execution +@cindex conditional execution +@cindex predication + +A number of architectures provide for some form of conditional +execution, or predication. The hallmark of this feature is the +ability to nullify most of the instructions in the instruction set. +When the instruction set is large and not entirely symmetric, it +can be quite tedious to describe these forms directly in the +@file{.md} file. An alternative is the @code{define_cond_exec} template. + +@findex define_cond_exec +@smallexample +(define_cond_exec + [@var{predicate-pattern}] + "@var{condition}" + "@var{output-template}") +@end smallexample + +@var{predicate-pattern} is the condition that must be true for the +insn to be executed at runtime and should match a relational operator. +One can use @code{match_operator} to match several relational operators +at once. Any @code{match_operand} operands must have no more than one +alternative. + +@var{condition} is a C expression that must be true for the generated +pattern to match. + +@findex current_insn_predicate +@var{output-template} is a string similar to the @code{define_insn} +output template (@pxref{Output Template}), except that the @samp{*} +and @samp{@@} special cases do not apply. This is only useful if the +assembly text for the predicate is a simple prefix to the main insn. +In order to handle the general case, there is a global variable +@code{current_insn_predicate} that will contain the entire predicate +if the current insn is predicated, and will otherwise be @code{NULL}. + +When @code{define_cond_exec} is used, an implicit reference to +the @code{predicable} instruction attribute is made. +@xref{Insn Attributes}. This attribute must be boolean (i.e.@: have +exactly two elements in its @var{list-of-values}). Further, it must +not be used with complex expressions. That is, the default and all +uses in the insns must be a simple constant, not dependent on the +alternative or anything else. + +For each @code{define_insn} for which the @code{predicable} +attribute is true, a new @code{define_insn} pattern will be +generated that matches a predicated version of the instruction. +For example, + +@smallexample +(define_insn "addsi" + [(set (match_operand:SI 0 "register_operand" "r") + (plus:SI (match_operand:SI 1 "register_operand" "r") + (match_operand:SI 2 "register_operand" "r")))] + "@var{test1}" + "add %2,%1,%0") + +(define_cond_exec + [(ne (match_operand:CC 0 "register_operand" "c") + (const_int 0))] + "@var{test2}" + "(%0)") +@end smallexample + +@noindent +generates a new pattern + +@smallexample +(define_insn "" + [(cond_exec + (ne (match_operand:CC 3 "register_operand" "c") (const_int 0)) + (set (match_operand:SI 0 "register_operand" "r") + (plus:SI (match_operand:SI 1 "register_operand" "r") + (match_operand:SI 2 "register_operand" "r"))))] + "(@var{test2}) && (@var{test1})" + "(%3) add %2,%1,%0") +@end smallexample + +@node Constant Definitions +@section Constant Definitions +@cindex constant definitions +@findex define_constants + +Using literal constants inside instruction patterns reduces legibility and +can be a maintenance problem. + +To overcome this problem, you may use the @code{define_constants} +expression. It contains a vector of name-value pairs. From that +point on, wherever any of the names appears in the MD file, it is as +if the corresponding value had been written instead. You may use +@code{define_constants} multiple times; each appearance adds more +constants to the table. It is an error to redefine a constant with +a different value. + +To come back to the a29k load multiple example, instead of + +@smallexample +(define_insn "" + [(match_parallel 0 "load_multiple_operation" + [(set (match_operand:SI 1 "gpc_reg_operand" "=r") + (match_operand:SI 2 "memory_operand" "m")) + (use (reg:SI 179)) + (clobber (reg:SI 179))])] + "" + "loadm 0,0,%1,%2") +@end smallexample + +You could write: + +@smallexample +(define_constants [ + (R_BP 177) + (R_FC 178) + (R_CR 179) + (R_Q 180) +]) + +(define_insn "" + [(match_parallel 0 "load_multiple_operation" + [(set (match_operand:SI 1 "gpc_reg_operand" "=r") + (match_operand:SI 2 "memory_operand" "m")) + (use (reg:SI R_CR)) + (clobber (reg:SI R_CR))])] + "" + "loadm 0,0,%1,%2") +@end smallexample + +The constants that are defined with a define_constant are also output +in the insn-codes.h header file as #defines. +@end ifset diff --git a/contrib/gcc/doc/objc.texi b/contrib/gcc/doc/objc.texi new file mode 100644 index 000000000000..d3fd775e2c0c --- /dev/null +++ b/contrib/gcc/doc/objc.texi @@ -0,0 +1,458 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Objective-C +@comment node-name, next, previous, up + +@chapter GNU Objective-C runtime features + +This document is meant to describe some of the GNU Objective-C runtime +features. It is not intended to teach you Objective-C, there are several +resources on the Internet that present the language. Questions and +comments about this document to Ovidiu Predescu +@email{ovidiu@@cup.hp.com}. + +@menu +* Executing code before main:: +* Type encoding:: +* Garbage Collection:: +* Constant string objects:: +* compatibility_alias:: +@end menu + +@node Executing code before main, Type encoding, Objective-C, Objective-C +@section @code{+load}: Executing code before main + + +The GNU Objective-C runtime provides a way that allows you to execute +code before the execution of the program enters the @code{main} +function. The code is executed on a per-class and a per-category basis, +through a special class method @code{+load}. + +This facility is very useful if you want to initialize global variables +which can be accessed by the program directly, without sending a message +to the class first. The usual way to initialize global variables, in the +@code{+initialize} method, might not be useful because +@code{+initialize} is only called when the first message is sent to a +class object, which in some cases could be too late. + +Suppose for example you have a @code{FileStream} class that declares +@code{Stdin}, @code{Stdout} and @code{Stderr} as global variables, like +below: + +@example + +FileStream *Stdin = nil; +FileStream *Stdout = nil; +FileStream *Stderr = nil; + +@@implementation FileStream + ++ (void)initialize +@{ + Stdin = [[FileStream new] initWithFd:0]; + Stdout = [[FileStream new] initWithFd:1]; + Stderr = [[FileStream new] initWithFd:2]; +@} + +/* Other methods here */ +@@end + +@end example + +In this example, the initialization of @code{Stdin}, @code{Stdout} and +@code{Stderr} in @code{+initialize} occurs too late. The programmer can +send a message to one of these objects before the variables are actually +initialized, thus sending messages to the @code{nil} object. The +@code{+initialize} method which actually initializes the global +variables is not invoked until the first message is sent to the class +object. The solution would require these variables to be initialized +just before entering @code{main}. + +The correct solution of the above problem is to use the @code{+load} +method instead of @code{+initialize}: + +@example + +@@implementation FileStream + ++ (void)load +@{ + Stdin = [[FileStream new] initWithFd:0]; + Stdout = [[FileStream new] initWithFd:1]; + Stderr = [[FileStream new] initWithFd:2]; +@} + +/* Other methods here */ +@@end + +@end example + +The @code{+load} is a method that is not overridden by categories. If a +class and a category of it both implement @code{+load}, both methods are +invoked. This allows some additional initializations to be performed in +a category. + +This mechanism is not intended to be a replacement for @code{+initialize}. +You should be aware of its limitations when you decide to use it +instead of @code{+initialize}. + +@menu +* What you can and what you cannot do in +load:: +@end menu + + +@node What you can and what you cannot do in +load, , Executing code before main, Executing code before main +@subsection What you can and what you cannot do in @code{+load} + +The @code{+load} implementation in the GNU runtime guarantees you the following +things: + +@itemize @bullet + +@item +you can write whatever C code you like; + +@item +you can send messages to Objective-C constant strings (@code{@@"this is a +constant string"}); + +@item +you can allocate and send messages to objects whose class is implemented +in the same file; + +@item +the @code{+load} implementation of all super classes of a class are executed before the @code{+load} of that class is executed; + +@item +the @code{+load} implementation of a class is executed before the +@code{+load} implementation of any category. + +@end itemize + +In particular, the following things, even if they can work in a +particular case, are not guaranteed: + +@itemize @bullet + +@item +allocation of or sending messages to arbitrary objects; + +@item +allocation of or sending messages to objects whose classes have a +category implemented in the same file; + +@end itemize + +You should make no assumptions about receiving @code{+load} in sibling +classes when you write @code{+load} of a class. The order in which +sibling classes receive @code{+load} is not guaranteed. + +The order in which @code{+load} and @code{+initialize} are called could +be problematic if this matters. If you don't allocate objects inside +@code{+load}, it is guaranteed that @code{+load} is called before +@code{+initialize}. If you create an object inside @code{+load} the +@code{+initialize} method of object's class is invoked even if +@code{+load} was not invoked. Note if you explicitly call @code{+load} +on a class, @code{+initialize} will be called first. To avoid possible +problems try to implement only one of these methods. + +The @code{+load} method is also invoked when a bundle is dynamically +loaded into your running program. This happens automatically without any +intervening operation from you. When you write bundles and you need to +write @code{+load} you can safely create and send messages to objects whose +classes already exist in the running program. The same restrictions as +above apply to classes defined in bundle. + + + +@node Type encoding, Garbage Collection, Executing code before main, Objective-C +@section Type encoding + +The Objective-C compiler generates type encodings for all the +types. These type encodings are used at runtime to find out information +about selectors and methods and about objects and classes. + +The types are encoded in the following way: + +@c @sp 1 + +@multitable @columnfractions .25 .75 +@item @code{char} +@tab @code{c} +@item @code{unsigned char} +@tab @code{C} +@item @code{short} +@tab @code{s} +@item @code{unsigned short} +@tab @code{S} +@item @code{int} +@tab @code{i} +@item @code{unsigned int} +@tab @code{I} +@item @code{long} +@tab @code{l} +@item @code{unsigned long} +@tab @code{L} +@item @code{long long} +@tab @code{q} +@item @code{unsigned long long} +@tab @code{Q} +@item @code{float} +@tab @code{f} +@item @code{double} +@tab @code{d} +@item @code{void} +@tab @code{v} +@item @code{id} +@tab @code{@@} +@item @code{Class} +@tab @code{#} +@item @code{SEL} +@tab @code{:} +@item @code{char*} +@tab @code{*} +@item unknown type +@tab @code{?} +@item bit-fields +@tab @code{b} followed by the starting position of the bit-field, the type of the bit-field and the size of the bit-field (the bit-fields encoding was changed from the NeXT's compiler encoding, see below) +@end multitable + +@c @sp 1 + +The encoding of bit-fields has changed to allow bit-fields to be properly +handled by the runtime functions that compute sizes and alignments of +types that contain bit-fields. The previous encoding contained only the +size of the bit-field. Using only this information it is not possible to +reliably compute the size occupied by the bit-field. This is very +important in the presence of the Boehm's garbage collector because the +objects are allocated using the typed memory facility available in this +collector. The typed memory allocation requires information about where +the pointers are located inside the object. + +The position in the bit-field is the position, counting in bits, of the +bit closest to the beginning of the structure. + +The non-atomic types are encoded as follows: + +@c @sp 1 + +@multitable @columnfractions .2 .8 +@item pointers +@tab @samp{^} followed by the pointed type. +@item arrays +@tab @samp{[} followed by the number of elements in the array followed by the type of the elements followed by @samp{]} +@item structures +@tab @samp{@{} followed by the name of the structure (or @samp{?} if the structure is unnamed), the @samp{=} sign, the type of the members and by @samp{@}} +@item unions +@tab @samp{(} followed by the name of the structure (or @samp{?} if the union is unnamed), the @samp{=} sign, the type of the members followed by @samp{)} +@end multitable + +Here are some types and their encodings, as they are generated by the +compiler on an i386 machine: + +@sp 1 + +@multitable @columnfractions .25 .75 +@item Objective-C type +@tab Compiler encoding +@item +@example +int a[10]; +@end example +@tab @code{[10i]} +@item +@example +struct @{ + int i; + float f[3]; + int a:3; + int b:2; + char c; +@} +@end example +@tab @code{@{?=i[3f]b128i3b131i2c@}} +@end multitable + +@sp 1 + +In addition to the types the compiler also encodes the type +specifiers. The table below describes the encoding of the current +Objective-C type specifiers: + +@sp 1 + +@multitable @columnfractions .25 .75 +@item Specifier +@tab Encoding +@item @code{const} +@tab @code{r} +@item @code{in} +@tab @code{n} +@item @code{inout} +@tab @code{N} +@item @code{out} +@tab @code{o} +@item @code{bycopy} +@tab @code{O} +@item @code{oneway} +@tab @code{V} +@end multitable + +@sp 1 + +The type specifiers are encoded just before the type. Unlike types +however, the type specifiers are only encoded when they appear in method +argument types. + + +@node Garbage Collection, Constant string objects, Type encoding, Objective-C +@section Garbage Collection + +Support for a new memory management policy has been added by using a +powerful conservative garbage collector, known as the +Boehm-Demers-Weiser conservative garbage collector. It is available from +@w{@uref{http://www.hpl.hp.com/personal/Hans_Boehm/gc/}}. + +To enable the support for it you have to configure the compiler using an +additional argument, @w{@option{--enable-objc-gc}}. You need to have +garbage collector installed before building the compiler. This will +build an additional runtime library which has several enhancements to +support the garbage collector. The new library has a new name, +@file{libobjc_gc.a} to not conflict with the non-garbage-collected +library. + +When the garbage collector is used, the objects are allocated using the +so-called typed memory allocation mechanism available in the +Boehm-Demers-Weiser collector. This mode requires precise information on +where pointers are located inside objects. This information is computed +once per class, immediately after the class has been initialized. + +There is a new runtime function @code{class_ivar_set_gcinvisible()} +which can be used to declare a so-called @dfn{weak pointer} +reference. Such a pointer is basically hidden for the garbage collector; +this can be useful in certain situations, especially when you want to +keep track of the allocated objects, yet allow them to be +collected. This kind of pointers can only be members of objects, you +cannot declare a global pointer as a weak reference. Every type which is +a pointer type can be declared a weak pointer, including @code{id}, +@code{Class} and @code{SEL}. + +Here is an example of how to use this feature. Suppose you want to +implement a class whose instances hold a weak pointer reference; the +following class does this: + +@example + +@@interface WeakPointer : Object +@{ + const void* weakPointer; +@} + +- initWithPointer:(const void*)p; +- (const void*)weakPointer; +@@end + + +@@implementation WeakPointer + ++ (void)initialize +@{ + class_ivar_set_gcinvisible (self, "weakPointer", YES); +@} + +- initWithPointer:(const void*)p +@{ + weakPointer = p; + return self; +@} + +- (const void*)weakPointer +@{ + return weakPointer; +@} + +@@end + +@end example + +Weak pointers are supported through a new type character specifier +represented by the @samp{!} character. The +@code{class_ivar_set_gcinvisible()} function adds or removes this +specifier to the string type description of the instance variable named +as argument. + +@c ========================================================================= +@node Constant string objects +@section Constant string objects + +GNU Objective-C provides constant string objects that are generated +directly by the compiler. You declare a constant string object by +prefixing a C constant string with the character @samp{@@}: + +@example + id myString = @@"this is a constant string object"; +@end example + +The constant string objects are usually instances of the +@code{NXConstantString} class which is provided by the GNU Objective-C +runtime. To get the definition of this class you must include the +@file{objc/NXConstStr.h} header file. + +User defined libraries may want to implement their own constant string +class. To be able to support them, the GNU Objective-C compiler provides +a new command line options @option{-fconstant-string-class=@var{class-name}}. +The provided class should adhere to a strict structure, the same +as @code{NXConstantString}'s structure: + +@example + +@@interface NXConstantString : Object +@{ + char *c_string; + unsigned int len; +@} +@@end + +@end example + +User class libraries may choose to inherit the customized constant +string class from a different class than @code{Object}. There is no +requirement in the methods the constant string class has to implement. + +When a file is compiled with the @option{-fconstant-string-class} option, +all the constant string objects will be instances of the class specified +as argument to this option. It is possible to have multiple compilation +units referring to different constant string classes, neither the +compiler nor the linker impose any restrictions in doing this. + +@c ========================================================================= +@node compatibility_alias +@section compatibility_alias + +This is a feature of the Objective-C compiler rather than of the +runtime, anyway since it is documented nowhere and its existence was +forgotten, we are documenting it here. + +The keyword @code{@@compatibility_alias} allows you to define a class name +as equivalent to another class name. For example: + +@example +@@compatibility_alias WOApplication GSWApplication; +@end example + +tells the compiler that each time it encounters @code{WOApplication} as +a class name, it should replace it with @code{GSWApplication} (that is, +@code{WOApplication} is just an alias for @code{GSWApplication}). + +There are some constraints on how this can be used--- + +@itemize @bullet + +@item @code{WOApplication} (the alias) must not be an existing class; + +@item @code{GSWApplication} (the real class) must be an existing class. + +@end itemize diff --git a/contrib/gcc/doc/passes.texi b/contrib/gcc/doc/passes.texi new file mode 100644 index 000000000000..f248056a9416 --- /dev/null +++ b/contrib/gcc/doc/passes.texi @@ -0,0 +1,659 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Passes +@chapter Passes and Files of the Compiler +@cindex passes and files of the compiler +@cindex files and passes of the compiler +@cindex compiler passes and files + +@cindex top level of compiler +The overall control structure of the compiler is in @file{toplev.c}. This +file is responsible for initialization, decoding arguments, opening and +closing files, and sequencing the passes. + +@cindex parsing pass +The parsing pass is invoked only once, to parse the entire input. A +high level tree representation is then generated from the input, +one function at a time. This tree code is then transformed into RTL +intermediate code, and processed. The files involved in transforming +the trees into RTL are @file{expr.c}, @file{expmed.c}, and +@file{stmt.c}. +@c Note, the above files aren't strictly the only files involved. It's +@c all over the place (function.c, final.c,etc). However, those are +@c the files that are supposed to be directly involved, and have +@c their purpose listed as such, so i've only listed them. +The order of trees that are processed, is not +necessarily the same order they are generated from +the input, due to deferred inlining, and other considerations. + +@findex rest_of_compilation +@findex rest_of_decl_compilation +Each time the parsing pass reads a complete function definition or +top-level declaration, it calls either the function +@code{rest_of_compilation}, or the function +@code{rest_of_decl_compilation} in @file{toplev.c}, which are +responsible for all further processing necessary, ending with output of +the assembler language. All other compiler passes run, in sequence, +within @code{rest_of_compilation}. When that function returns from +compiling a function definition, the storage used for that function +definition's compilation is entirely freed, unless it is an inline +function, or was deferred for some reason (this can occur in +templates, for example). +(@pxref{Inline,,An Inline Function is As Fast As a Macro,gcc,Using the +GNU Compiler Collection (GCC)}). + +Here is a list of all the passes of the compiler and their source files. +Also included is a description of where debugging dumps can be requested +with @option{-d} options. + +@itemize @bullet +@item +Parsing. This pass reads the entire text of a function definition, +constructing a high level tree representation. (Because of the semantic +analysis that takes place during this pass, it does more than is +formally considered to be parsing.) + +The tree representation does not entirely follow C syntax, because it is +intended to support other languages as well. + +Language-specific data type analysis is also done in this pass, and every +tree node that represents an expression has a data type attached. +Variables are represented as declaration nodes. + +The language-independent source files for parsing are +@file{tree.c}, @file{fold-const.c}, and @file{stor-layout.c}. +There are also header files @file{tree.h} and @file{tree.def} +which define the format of the tree representation. + +C preprocessing, for language front ends, that want or require it, is +performed by cpplib, which is covered in separate documentation. In +particular, the internals are covered in @xref{Top, ,Cpplib internals, +cppinternals, Cpplib Internals}. + +@c Avoiding overfull is tricky here. +The source files to parse C are +@file{c-convert.c}, +@file{c-decl.c}, +@file{c-errors.c}, +@file{c-lang.c}, +@file{c-objc-common.c}, +@file{c-parse.in}, +@file{c-aux-info.c}, +and +@file{c-typeck.c}, +along with a header file +@file{c-tree.h} +and some files shared with Objective-C and C++. + +The source files for parsing C++ are in @file{cp/}. +They are @file{parse.y}, +@file{class.c}, +@file{cvt.c}, @file{decl.c}, @file{decl2.c}, +@file{except.c}, +@file{expr.c}, @file{init.c}, @file{lex.c}, +@file{method.c}, @file{ptree.c}, +@file{search.c}, @file{spew.c}, +@file{semantics.c}, @file{tree.c}, +@file{typeck2.c}, and +@file{typeck.c}, along with header files @file{cp-tree.def}, +@file{cp-tree.h}, and @file{decl.h}. + +The special source files for parsing Objective-C are in @file{objc/}. +They are @file{objc-act.c}, @file{objc-tree.def}, and @file{objc-act.h}. +Certain C-specific files are used for this as well. + +The files +@file{c-common.c}, +@file{c-common.def}, +@file{c-format.c}, +@file{c-pragma.c}, +@file{c-semantics.c}, +and +@file{c-lex.c}, +along with header files +@file{c-common.h}, +@file{c-dump.h}, +@file{c-lex.h}, +and +@file{c-pragma.h}, +are also used for all of the above languages. + + +@cindex Tree optimization +@item +Tree optimization. This is the optimization of the tree +representation, before converting into RTL code. + +@cindex inline on trees, automatic +Currently, the main optimization performed here is tree-based +inlining. +This is implemented in @file{tree-inline.c} and used by both C and C++. +Note that tree based inlining turns off rtx based inlining (since it's more +powerful, it would be a waste of time to do rtx based inlining in +addition). + +@cindex constant folding +@cindex arithmetic simplifications +@cindex simplifications, arithmetic +Constant folding and some arithmetic simplifications are also done +during this pass, on the tree representation. +The routines that perform these tasks are located in @file{fold-const.c}. + +@cindex RTL generation +@item +RTL generation. This is the conversion of syntax tree into RTL code. + +@cindex target-parameter-dependent code +This is where the bulk of target-parameter-dependent code is found, +since often it is necessary for strategies to apply only when certain +standard kinds of instructions are available. The purpose of named +instruction patterns is to provide this information to the RTL +generation pass. + +@cindex tail recursion optimization +Optimization is done in this pass for @code{if}-conditions that are +comparisons, boolean operations or conditional expressions. Tail +recursion is detected at this time also. Decisions are made about how +best to arrange loops and how to output @code{switch} statements. + +@c Avoiding overfull is tricky here. +The source files for RTL generation include +@file{stmt.c}, +@file{calls.c}, +@file{expr.c}, +@file{explow.c}, +@file{expmed.c}, +@file{function.c}, +@file{optabs.c} +and @file{emit-rtl.c}. +Also, the file +@file{insn-emit.c}, generated from the machine description by the +program @code{genemit}, is used in this pass. The header file +@file{expr.h} is used for communication within this pass. + +@findex genflags +@findex gencodes +The header files @file{insn-flags.h} and @file{insn-codes.h}, +generated from the machine description by the programs @code{genflags} +and @code{gencodes}, tell this pass which standard names are available +for use and which patterns correspond to them. + +Aside from debugging information output, none of the following passes +refers to the tree structure representation of the function (only +part of which is saved). + +@cindex inline on rtx, automatic +The decision of whether the function can and should be expanded inline +in its subsequent callers is made at the end of rtl generation. The +function must meet certain criteria, currently related to the size of +the function and the types and number of parameters it has. Note that +this function may contain loops, recursive calls to itself +(tail-recursive functions can be inlined!), gotos, in short, all +constructs supported by GCC@. The file @file{integrate.c} contains +the code to save a function's rtl for later inlining and to inline that +rtl when the function is called. The header file @file{integrate.h} +is also used for this purpose. + +@opindex dr +The option @option{-dr} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.rtl} to +the input file name. + +@c Should the exception handling pass be talked about here? + +@cindex sibling call optimization +@item +Sibiling call optimization. This pass performs tail recursion +elimination, and tail and sibling call optimizations. The purpose of +these optimizations is to reduce the overhead of function calls, +whenever possible. + +The source file of this pass is @file{sibcall.c} + +@opindex di +The option @option{-di} causes a debugging dump of the RTL code after +this pass is run. This dump file's name is made by appending +@samp{.sibling} to the input file name. + +@cindex jump optimization +@cindex unreachable code +@cindex dead code +@item +Jump optimization. This pass simplifies jumps to the following +instruction, jumps across jumps, and jumps to jumps. It deletes +unreferenced labels and unreachable code, except that unreachable code +that contains a loop is not recognized as unreachable in this pass. +(Such loops are deleted later in the basic block analysis.) It also +converts some code originally written with jumps into sequences of +instructions that directly set values from the results of comparisons, +if the machine has such instructions. + +Jump optimization is performed two or three times. The first time is +immediately following RTL generation. The second time is after CSE, +but only if CSE says repeated jump optimization is needed. The +last time is right before the final pass. That time, cross-jumping +and deletion of no-op move instructions are done together with the +optimizations described above. + +The source file of this pass is @file{jump.c}. + +@opindex dj +The option @option{-dj} causes a debugging dump of the RTL code after +this pass is run for the first time. This dump file's name is made by +appending @samp{.jump} to the input file name. + + +@cindex register use analysis +@item +Register scan. This pass finds the first and last use of each +register, as a guide for common subexpression elimination. Its source +is in @file{regclass.c}. + +@cindex jump threading +@item +@opindex fthread-jumps +Jump threading. This pass detects a condition jump that branches to an +identical or inverse test. Such jumps can be @samp{threaded} through +the second conditional test. The source code for this pass is in +@file{jump.c}. This optimization is only performed if +@option{-fthread-jumps} is enabled. + +@cindex SSA optimizations +@cindex Single Static Assignment optimizations +@opindex fssa +@item +Static Single Assignment (SSA) based optimization passes. The +SSA conversion passes (to/from) are turned on by the @option{-fssa} +option (it is also done automatically if you enable an SSA optimization pass). +These passes utilize a form called Static Single Assignment. In SSA form, +each variable (pseudo register) is only set once, giving you def-use +and use-def chains for free, and enabling a lot more optimization +passes to be run in linear time. +Conversion to and from SSA form is handled by functions in +@file{ssa.c}. + +@opindex de +The option @option{-de} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.ssa} to +the input file name. +@itemize @bullet +@cindex SSA Conditional Constant Propagation +@cindex Conditional Constant Propagation, SSA based +@cindex conditional constant propagation +@opindex fssa-ccp +@item +SSA Conditional Constant Propagation. Turned on by the @option{-fssa-ccp} +SSA Aggressive Dead Code Elimination. Turned on by the @option{-fssa-dce} +option. This pass performs conditional constant propagation to simplify +instructions including conditional branches. This pass is more aggressive +than the constant propgation done by the CSE and GCSE pases, but operates +in linear time. + +@opindex dW +The option @option{-dW} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.ssaccp} to +the input file name. + +@cindex SSA DCE +@cindex DCE, SSA based +@cindex dead code elimination +@opindex fssa-dce +@item +SSA Aggressive Dead Code Elimination. Turned on by the @option{-fssa-dce} +option. This pass performs elimination of code considered unnecessary because +it has no externally visible effects on the program. It operates in +linear time. + +@opindex dX +The option @option{-dX} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.ssadce} to +the input file name. +@end itemize + +@cindex common subexpression elimination +@cindex constant propagation +@item +Common subexpression elimination. This pass also does constant +propagation. Its source files are @file{cse.c}, and @file{cselib.c}. +If constant propagation causes conditional jumps to become +unconditional or to become no-ops, jump optimization is run again when +CSE is finished. + +@opindex ds +The option @option{-ds} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.cse} to +the input file name. + +@cindex global common subexpression elimination +@cindex constant propagation +@cindex copy propagation +@item +Global common subexpression elimination. This pass performs two +different types of GCSE depending on whether you are optimizing for +size or not (LCM based GCSE tends to increase code size for a gain in +speed, while Morel-Renvoise based GCSE does not). +When optimizing for size, GCSE is done using Morel-Renvoise Partial +Redundancy Elimination, with the exception that it does not try to move +invariants out of loops---that is left to the loop optimization pass. +If MR PRE GCSE is done, code hoisting (aka unification) is also done, as +well as load motion. +If you are optimizing for speed, LCM (lazy code motion) based GCSE is +done. LCM is based on the work of Knoop, Ruthing, and Steffen. LCM +based GCSE also does loop invariant code motion. We also perform load +and store motion when optimizing for speed. +Regardless of which type of GCSE is used, the GCSE pass also performs +global constant and copy propagation. + +The source file for this pass is @file{gcse.c}, and the LCM routines +are in @file{lcm.c}. + +@opindex dG +The option @option{-dG} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.gcse} to +the input file name. + +@cindex loop optimization +@cindex code motion +@cindex strength-reduction +@item +Loop optimization. This pass moves constant expressions out of loops, +and optionally does strength-reduction and loop unrolling as well. +Its source files are @file{loop.c} and @file{unroll.c}, plus the header +@file{loop.h} used for communication between them. Loop unrolling uses +some functions in @file{integrate.c} and the header @file{integrate.h}. +Loop dependency analysis routines are contained in @file{dependence.c}. + +@opindex dL +The option @option{-dL} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.loop} to +the input file name. + +@item +@opindex frerun-cse-after-loop +If @option{-frerun-cse-after-loop} was enabled, a second common +subexpression elimination pass is performed after the loop optimization +pass. Jump threading is also done again at this time if it was specified. + +@opindex dt +The option @option{-dt} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.cse2} to +the input file name. + +@cindex data flow analysis +@cindex analysis, data flow +@cindex basic blocks +@item +Data flow analysis (@file{flow.c}). This pass divides the program +into basic blocks (and in the process deletes unreachable loops); then +it computes which pseudo-registers are live at each point in the +program, and makes the first instruction that uses a value point at +the instruction that computed the value. + +@cindex autoincrement/decrement analysis +This pass also deletes computations whose results are never used, and +combines memory references with add or subtract instructions to make +autoincrement or autodecrement addressing. + +@opindex df +The option @option{-df} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.flow} to +the input file name. If stupid register allocation is in use, this +dump file reflects the full results of such allocation. + +@cindex instruction combination +@item +Instruction combination (@file{combine.c}). This pass attempts to +combine groups of two or three instructions that are related by data +flow into single instructions. It combines the RTL expressions for +the instructions by substitution, simplifies the result using algebra, +and then attempts to match the result against the machine description. + +@opindex dc +The option @option{-dc} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.combine} +to the input file name. + +@cindex if conversion +@item +If-conversion is a transformation that transforms control dependencies +into data dependencies (IE it transforms conditional code into a +single control stream). +It is implemented in the file @file{ifcvt.c}. + +@opindex dE +The option @option{-dE} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.ce} to +the input file name. + +@cindex register movement +@item +Register movement (@file{regmove.c}). This pass looks for cases where +matching constraints would force an instruction to need a reload, and +this reload would be a register-to-register move. It then attempts +to change the registers used by the instruction to avoid the move +instruction. + +@opindex dN +The option @option{-dN} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.regmove} +to the input file name. + +@cindex instruction scheduling +@cindex scheduling, instruction +@item +Instruction scheduling (@file{sched.c}). This pass looks for +instructions whose output will not be available by the time that it is +used in subsequent instructions. (Memory loads and floating point +instructions often have this behavior on RISC machines). It re-orders +instructions within a basic block to try to separate the definition and +use of items that otherwise would cause pipeline stalls. + +Instruction scheduling is performed twice. The first time is immediately +after instruction combination and the second is immediately after reload. + +@opindex dS +The option @option{-dS} causes a debugging dump of the RTL code after this +pass is run for the first time. The dump file's name is made by +appending @samp{.sched} to the input file name. + +@cindex register class preference pass +@item +Register class preferencing. The RTL code is scanned to find out +which register class is best for each pseudo register. The source +file is @file{regclass.c}. + +@cindex register allocation +@cindex local register allocation +@item +Local register allocation (@file{local-alloc.c}). This pass allocates +hard registers to pseudo registers that are used only within one basic +block. Because the basic block is linear, it can use fast and +powerful techniques to do a very good job. + +@opindex dl +The option @option{-dl} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.lreg} to +the input file name. + +@cindex global register allocation +@item +Global register allocation (@file{global.c}). This pass +allocates hard registers for the remaining pseudo registers (those +whose life spans are not contained in one basic block). + +@cindex reloading +@item +Reloading. This pass renumbers pseudo registers with the hardware +registers numbers they were allocated. Pseudo registers that did not +get hard registers are replaced with stack slots. Then it finds +instructions that are invalid because a value has failed to end up in +a register, or has ended up in a register of the wrong kind. It fixes +up these instructions by reloading the problematical values +temporarily into registers. Additional instructions are generated to +do the copying. + +The reload pass also optionally eliminates the frame pointer and inserts +instructions to save and restore call-clobbered registers around calls. + +Source files are @file{reload.c} and @file{reload1.c}, plus the header +@file{reload.h} used for communication between them. + +@opindex dg +The option @option{-dg} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.greg} to +the input file name. + +@cindex instruction scheduling +@cindex scheduling, instruction +@item +Instruction scheduling is repeated here to try to avoid pipeline stalls +due to memory loads generated for spilled pseudo registers. + +@opindex dR +The option @option{-dR} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.sched2} +to the input file name. + +@cindex basic block reordering +@cindex reordering, block +@item +Basic block reordering. This pass implements profile guided code +positioning. If profile information is not available, various types of +static analysis are performed to make the predictions normally coming +from the profile feedback (IE execution frequency, branch probability, +etc). It is implemented in the file @file{bb-reorder.c}, and the +various prediction routines are in @file{predict.c}. + +@opindex dB +The option @option{-dB} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.bbro} to +the input file name. + +@cindex cross-jumping +@cindex no-op move instructions +@item +Jump optimization is repeated, this time including cross-jumping +and deletion of no-op move instructions. + +@opindex dJ +The option @option{-dJ} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.jump2} +to the input file name. + +@cindex delayed branch scheduling +@cindex scheduling, delayed branch +@item +Delayed branch scheduling. This optional pass attempts to find +instructions that can go into the delay slots of other instructions, +usually jumps and calls. The source file name is @file{reorg.c}. + +@opindex dd +The option @option{-dd} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.dbr} +to the input file name. + +@cindex branch shortening +@item +Branch shortening. On many RISC machines, branch instructions have a +limited range. Thus, longer sequences of instructions must be used for +long branches. In this pass, the compiler figures out what how far each +instruction will be from each other instruction, and therefore whether +the usual instructions, or the longer sequences, must be used for each +branch. + +@cindex register-to-stack conversion +@item +Conversion from usage of some hard registers to usage of a register +stack may be done at this point. Currently, this is supported only +for the floating-point registers of the Intel 80387 coprocessor. The +source file name is @file{reg-stack.c}. + +@opindex dk +The options @option{-dk} causes a debugging dump of the RTL code after +this pass. This dump file's name is made by appending @samp{.stack} +to the input file name. + +@cindex final pass +@cindex peephole optimization +@item +Final. This pass outputs the assembler code for the function. It is +also responsible for identifying spurious test and compare +instructions. Machine-specific peephole optimizations are performed +at the same time. The function entry and exit sequences are generated +directly as assembler code in this pass; they never exist as RTL@. + +The source files are @file{final.c} plus @file{insn-output.c}; the +latter is generated automatically from the machine description by the +tool @file{genoutput}. The header file @file{conditions.h} is used +for communication between these files. + +@cindex debugging information generation +@item +Debugging information output. This is run after final because it must +output the stack slot offsets for pseudo registers that did not get +hard registers. Source files are @file{dbxout.c} for DBX symbol table +format, @file{sdbout.c} for SDB symbol table format, @file{dwarfout.c} +for DWARF symbol table format, files @file{dwarf2out.c} and +@file{dwarf2asm.c} for DWARF2 symbol table format, and @file{vmsdbgout.c} +for VMS debug symbol table format. +@end itemize + +Some additional files are used by all or many passes: + +@itemize @bullet +@item +Every pass uses @file{machmode.def} and @file{machmode.h} which define +the machine modes. + +@item +Several passes use @file{real.h}, which defines the default +representation of floating point constants and how to operate on them. + +@item +All the passes that work with RTL use the header files @file{rtl.h} +and @file{rtl.def}, and subroutines in file @file{rtl.c}. The tools +@code{gen*} also use these files to read and work with the machine +description RTL@. + +@item +All the tools that read the machine description use support routines +found in @file{gensupport.c}, @file{errors.c}, and @file{read-rtl.c}. + +@findex genconfig +@item +Several passes refer to the header file @file{insn-config.h} which +contains a few parameters (C macro definitions) generated +automatically from the machine description RTL by the tool +@code{genconfig}. + +@cindex instruction recognizer +@item +Several passes use the instruction recognizer, which consists of +@file{recog.c} and @file{recog.h}, plus the files @file{insn-recog.c} +and @file{insn-extract.c} that are generated automatically from the +machine description by the tools @file{genrecog} and +@file{genextract}. + +@item +Several passes use the header files @file{regs.h} which defines the +information recorded about pseudo register usage, and @file{basic-block.h} +which defines the information recorded about basic blocks. + +@item +@file{hard-reg-set.h} defines the type @code{HARD_REG_SET}, a bit-vector +with a bit for each hard register, and some macros to manipulate it. +This type is just @code{int} if the machine has few enough hard registers; +otherwise it is an array of @code{int} and some of the macros expand +into loops. + +@item +Several passes use instruction attributes. A definition of the +attributes defined for a particular machine is in file +@file{insn-attr.h}, which is generated from the machine description by +the program @file{genattr}. The file @file{insn-attrtab.c} contains +subroutines to obtain the attribute values for insns. It is generated +from the machine description by the program @file{genattrtab}. +@end itemize diff --git a/contrib/gcc/doc/portability.texi b/contrib/gcc/doc/portability.texi new file mode 100644 index 000000000000..c3d8e3913d77 --- /dev/null +++ b/contrib/gcc/doc/portability.texi @@ -0,0 +1,38 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Portability +@chapter GCC and Portability +@cindex portability +@cindex GCC and portability + +The main goal of GCC was to make a good, fast compiler for machines in +the class that the GNU system aims to run on: 32-bit machines that address +8-bit bytes and have several general registers. Elegance, theoretical +power and simplicity are only secondary. + +GCC gets most of the information about the target machine from a machine +description which gives an algebraic formula for each of the machine's +instructions. This is a very clean way to describe the target. But when +the compiler needs information that is difficult to express in this +fashion, I have not hesitated to define an ad-hoc parameter to the machine +description. The purpose of portability is to reduce the total work needed +on the compiler; it was not of interest for its own sake. + +@cindex endianness +@cindex autoincrement addressing, availability +@findex abort +GCC does not contain machine dependent code, but it does contain code +that depends on machine parameters such as endianness (whether the most +significant byte has the highest or lowest address of the bytes in a word) +and the availability of autoincrement addressing. In the RTL-generation +pass, it is often necessary to have multiple strategies for generating code +for a particular kind of syntax tree, strategies that are usable for different +combinations of parameters. Often I have not tried to address all possible +cases, but only the common ones or only the ones that I have encountered. +As a result, a new target may require additional strategies. You will know +if this happens because the compiler will call @code{abort}. Fortunately, +the new strategies can be added in a machine-independent fashion, and will +affect only the target machines that need them. diff --git a/contrib/gcc/doc/rtl.texi b/contrib/gcc/doc/rtl.texi new file mode 100644 index 000000000000..5b614090b284 --- /dev/null +++ b/contrib/gcc/doc/rtl.texi @@ -0,0 +1,3401 @@ +@c Copyright (C) 1988, 1989, 1992, 1994, 1997, 1998, 1999, 2000, 2001, 2002 +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node RTL +@chapter RTL Representation +@cindex RTL representation +@cindex representation of RTL +@cindex Register Transfer Language (RTL) + +Most of the work of the compiler is done on an intermediate representation +called register transfer language. In this language, the instructions to be +output are described, pretty much one by one, in an algebraic form that +describes what the instruction does. + +RTL is inspired by Lisp lists. It has both an internal form, made up of +structures that point at other structures, and a textual form that is used +in the machine description and in printed debugging dumps. The textual +form uses nested parentheses to indicate the pointers in the internal form. + +@menu +* RTL Objects:: Expressions vs vectors vs strings vs integers. +* RTL Classes:: Categories of RTL expression objects, and their structure. +* Accessors:: Macros to access expression operands or vector elts. +* Flags:: Other flags in an RTL expression. +* Machine Modes:: Describing the size and format of a datum. +* Constants:: Expressions with constant values. +* Regs and Memory:: Expressions representing register contents or memory. +* Arithmetic:: Expressions representing arithmetic on other expressions. +* Comparisons:: Expressions representing comparison of expressions. +* Bit-Fields:: Expressions representing bit-fields in memory or reg. +* Vector Operations:: Expressions involving vector datatypes. +* Conversions:: Extending, truncating, floating or fixing. +* RTL Declarations:: Declaring volatility, constancy, etc. +* Side Effects:: Expressions for storing in registers, etc. +* Incdec:: Embedded side-effects for autoincrement addressing. +* Assembler:: Representing @code{asm} with operands. +* Insns:: Expression types for entire insns. +* Calls:: RTL representation of function call insns. +* Sharing:: Some expressions are unique; others *must* be copied. +* Reading RTL:: Reading textual RTL from a file. +@end menu + +@node RTL Objects +@section RTL Object Types +@cindex RTL object types + +@cindex RTL integers +@cindex RTL strings +@cindex RTL vectors +@cindex RTL expression +@cindex RTX (See RTL) +RTL uses five kinds of objects: expressions, integers, wide integers, +strings and vectors. Expressions are the most important ones. An RTL +expression (``RTX'', for short) is a C structure, but it is usually +referred to with a pointer; a type that is given the typedef name +@code{rtx}. + +An integer is simply an @code{int}; their written form uses decimal +digits. A wide integer is an integral object whose type is +@code{HOST_WIDE_INT}; their written form uses decimal digits. + +A string is a sequence of characters. In core it is represented as a +@code{char *} in usual C fashion, and it is written in C syntax as well. +However, strings in RTL may never be null. If you write an empty string in +a machine description, it is represented in core as a null pointer rather +than as a pointer to a null character. In certain contexts, these null +pointers instead of strings are valid. Within RTL code, strings are most +commonly found inside @code{symbol_ref} expressions, but they appear in +other contexts in the RTL expressions that make up machine descriptions. + +In a machine description, strings are normally written with double +quotes, as you would in C. However, strings in machine descriptions may +extend over many lines, which is invalid C, and adjacent string +constants are not concatenated as they are in C. Any string constant +may be surrounded with a single set of parentheses. Sometimes this +makes the machine description easier to read. + +There is also a special syntax for strings, which can be useful when C +code is embedded in a machine description. Wherever a string can +appear, it is also valid to write a C-style brace block. The entire +brace block, including the outermost pair of braces, is considered to be +the string constant. Double quote characters inside the braces are not +special. Therefore, if you write string constants in the C code, you +need not escape each quote character with a backslash. + +A vector contains an arbitrary number of pointers to expressions. The +number of elements in the vector is explicitly present in the vector. +The written form of a vector consists of square brackets +(@samp{[@dots{}]}) surrounding the elements, in sequence and with +whitespace separating them. Vectors of length zero are not created; +null pointers are used instead. + +@cindex expression codes +@cindex codes, RTL expression +@findex GET_CODE +@findex PUT_CODE +Expressions are classified by @dfn{expression codes} (also called RTX +codes). The expression code is a name defined in @file{rtl.def}, which is +also (in upper case) a C enumeration constant. The possible expression +codes and their meanings are machine-independent. The code of an RTX can +be extracted with the macro @code{GET_CODE (@var{x})} and altered with +@code{PUT_CODE (@var{x}, @var{newcode})}. + +The expression code determines how many operands the expression contains, +and what kinds of objects they are. In RTL, unlike Lisp, you cannot tell +by looking at an operand what kind of object it is. Instead, you must know +from its context---from the expression code of the containing expression. +For example, in an expression of code @code{subreg}, the first operand is +to be regarded as an expression and the second operand as an integer. In +an expression of code @code{plus}, there are two operands, both of which +are to be regarded as expressions. In a @code{symbol_ref} expression, +there is one operand, which is to be regarded as a string. + +Expressions are written as parentheses containing the name of the +expression type, its flags and machine mode if any, and then the operands +of the expression (separated by spaces). + +Expression code names in the @samp{md} file are written in lower case, +but when they appear in C code they are written in upper case. In this +manual, they are shown as follows: @code{const_int}. + +@cindex (nil) +@cindex nil +In a few contexts a null pointer is valid where an expression is normally +wanted. The written form of this is @code{(nil)}. + +@node RTL Classes +@section RTL Classes and Formats +@cindex RTL classes +@cindex classes of RTX codes +@cindex RTX codes, classes of +@findex GET_RTX_CLASS + +The various expression codes are divided into several @dfn{classes}, +which are represented by single characters. You can determine the class +of an RTX code with the macro @code{GET_RTX_CLASS (@var{code})}. +Currently, @file{rtx.def} defines these classes: + +@table @code +@item o +An RTX code that represents an actual object, such as a register +(@code{REG}) or a memory location (@code{MEM}, @code{SYMBOL_REF}). +Constants and basic transforms on objects (@code{ADDRESSOF}, +@code{HIGH}, @code{LO_SUM}) are also included. Note that @code{SUBREG} +and @code{STRICT_LOW_PART} are not in this class, but in class @code{x}. + +@item < +An RTX code for a comparison, such as @code{NE} or @code{LT}. + +@item 1 +An RTX code for a unary arithmetic operation, such as @code{NEG}, +@code{NOT}, or @code{ABS}. This category also includes value extension +(sign or zero) and conversions between integer and floating point. + +@item c +An RTX code for a commutative binary operation, such as @code{PLUS} or +@code{AND}. @code{NE} and @code{EQ} are comparisons, so they have class +@code{<}. + +@item 2 +An RTX code for a non-commutative binary operation, such as @code{MINUS}, +@code{DIV}, or @code{ASHIFTRT}. + +@item b +An RTX code for a bit-field operation. Currently only +@code{ZERO_EXTRACT} and @code{SIGN_EXTRACT}. These have three inputs +and are lvalues (so they can be used for insertion as well). +@xref{Bit-Fields}. + +@item 3 +An RTX code for other three input operations. Currently only +@code{IF_THEN_ELSE}. + +@item i +An RTX code for an entire instruction: @code{INSN}, @code{JUMP_INSN}, and +@code{CALL_INSN}. @xref{Insns}. + +@item m +An RTX code for something that matches in insns, such as +@code{MATCH_DUP}. These only occur in machine descriptions. + +@item a +An RTX code for an auto-increment addressing mode, such as +@code{POST_INC}. + +@item x +All other RTX codes. This category includes the remaining codes used +only in machine descriptions (@code{DEFINE_*}, etc.). It also includes +all the codes describing side effects (@code{SET}, @code{USE}, +@code{CLOBBER}, etc.) and the non-insns that may appear on an insn +chain, such as @code{NOTE}, @code{BARRIER}, and @code{CODE_LABEL}. +@end table + +@cindex RTL format +For each expression code, @file{rtl.def} specifies the number of +contained objects and their kinds using a sequence of characters +called the @dfn{format} of the expression code. For example, +the format of @code{subreg} is @samp{ei}. + +@cindex RTL format characters +These are the most commonly used format characters: + +@table @code +@item e +An expression (actually a pointer to an expression). + +@item i +An integer. + +@item w +A wide integer. + +@item s +A string. + +@item E +A vector of expressions. +@end table + +A few other format characters are used occasionally: + +@table @code +@item u +@samp{u} is equivalent to @samp{e} except that it is printed differently +in debugging dumps. It is used for pointers to insns. + +@item n +@samp{n} is equivalent to @samp{i} except that it is printed differently +in debugging dumps. It is used for the line number or code number of a +@code{note} insn. + +@item S +@samp{S} indicates a string which is optional. In the RTL objects in +core, @samp{S} is equivalent to @samp{s}, but when the object is read, +from an @samp{md} file, the string value of this operand may be omitted. +An omitted string is taken to be the null string. + +@item V +@samp{V} indicates a vector which is optional. In the RTL objects in +core, @samp{V} is equivalent to @samp{E}, but when the object is read +from an @samp{md} file, the vector value of this operand may be omitted. +An omitted vector is effectively the same as a vector of no elements. + +@item 0 +@samp{0} means a slot whose contents do not fit any normal category. +@samp{0} slots are not printed at all in dumps, and are often used in +special ways by small parts of the compiler. +@end table + +There are macros to get the number of operands and the format +of an expression code: + +@table @code +@findex GET_RTX_LENGTH +@item GET_RTX_LENGTH (@var{code}) +Number of operands of an RTX of code @var{code}. + +@findex GET_RTX_FORMAT +@item GET_RTX_FORMAT (@var{code}) +The format of an RTX of code @var{code}, as a C string. +@end table + +Some classes of RTX codes always have the same format. For example, it +is safe to assume that all comparison operations have format @code{ee}. + +@table @code +@item 1 +All codes of this class have format @code{e}. + +@item < +@itemx c +@itemx 2 +All codes of these classes have format @code{ee}. + +@item b +@itemx 3 +All codes of these classes have format @code{eee}. + +@item i +All codes of this class have formats that begin with @code{iuueiee}. +@xref{Insns}. Note that not all RTL objects linked onto an insn chain +are of class @code{i}. + +@item o +@itemx m +@itemx x +You can make no assumptions about the format of these codes. +@end table + +@node Accessors +@section Access to Operands +@cindex accessors +@cindex access to operands +@cindex operand access + +@findex XEXP +@findex XINT +@findex XWINT +@findex XSTR +Operands of expressions are accessed using the macros @code{XEXP}, +@code{XINT}, @code{XWINT} and @code{XSTR}. Each of these macros takes +two arguments: an expression-pointer (RTX) and an operand number +(counting from zero). Thus, + +@example +XEXP (@var{x}, 2) +@end example + +@noindent +accesses operand 2 of expression @var{x}, as an expression. + +@example +XINT (@var{x}, 2) +@end example + +@noindent +accesses the same operand as an integer. @code{XSTR}, used in the same +fashion, would access it as a string. + +Any operand can be accessed as an integer, as an expression or as a string. +You must choose the correct method of access for the kind of value actually +stored in the operand. You would do this based on the expression code of +the containing expression. That is also how you would know how many +operands there are. + +For example, if @var{x} is a @code{subreg} expression, you know that it has +two operands which can be correctly accessed as @code{XEXP (@var{x}, 0)} +and @code{XINT (@var{x}, 1)}. If you did @code{XINT (@var{x}, 0)}, you +would get the address of the expression operand but cast as an integer; +that might occasionally be useful, but it would be cleaner to write +@code{(int) XEXP (@var{x}, 0)}. @code{XEXP (@var{x}, 1)} would also +compile without error, and would return the second, integer operand cast as +an expression pointer, which would probably result in a crash when +accessed. Nothing stops you from writing @code{XEXP (@var{x}, 28)} either, +but this will access memory past the end of the expression with +unpredictable results. + +Access to operands which are vectors is more complicated. You can use the +macro @code{XVEC} to get the vector-pointer itself, or the macros +@code{XVECEXP} and @code{XVECLEN} to access the elements and length of a +vector. + +@table @code +@findex XVEC +@item XVEC (@var{exp}, @var{idx}) +Access the vector-pointer which is operand number @var{idx} in @var{exp}. + +@findex XVECLEN +@item XVECLEN (@var{exp}, @var{idx}) +Access the length (number of elements) in the vector which is +in operand number @var{idx} in @var{exp}. This value is an @code{int}. + +@findex XVECEXP +@item XVECEXP (@var{exp}, @var{idx}, @var{eltnum}) +Access element number @var{eltnum} in the vector which is +in operand number @var{idx} in @var{exp}. This value is an RTX@. + +It is up to you to make sure that @var{eltnum} is not negative +and is less than @code{XVECLEN (@var{exp}, @var{idx})}. +@end table + +All the macros defined in this section expand into lvalues and therefore +can be used to assign the operands, lengths and vector elements as well as +to access them. + +@node Flags +@section Flags in an RTL Expression +@cindex flags in RTL expression + +RTL expressions contain several flags (one-bit bit-fields) +that are used in certain types of expression. Most often they +are accessed with the following macros, which expand into lvalues: + +@table @code +@findex CONSTANT_POOL_ADDRESS_P +@cindex @code{symbol_ref} and @samp{/u} +@cindex @code{unchanging}, in @code{symbol_ref} +@item CONSTANT_POOL_ADDRESS_P (@var{x}) +Nonzero in a @code{symbol_ref} if it refers to part of the current +function's constant pool. For most targets these addresses are in a +@code{.rodata} section entirely separate from the function, but for +some targets the addresses are close to the beginning of the function. +In either case GCC assumes these addresses can be addressed directly, +perhaps with the help of base registers. +Stored in the @code{unchanging} field and printed as @samp{/u}. + +@findex CONST_OR_PURE_CALL_P +@cindex @code{call_insn} and @samp{/u} +@cindex @code{unchanging}, in @code{call_insn} +@item CONST_OR_PURE_CALL_P (@var{x}) +In a @code{call_insn}, @code{note}, or an @code{expr_list} for notes, +indicates that the insn represents a call to a const or pure function. +Stored in the @code{unchanging} field and printed as @samp{/u}. + +@findex INSN_ANNULLED_BRANCH_P +@cindex @code{insn} and @samp{/u} +@cindex @code{unchanging}, in @code{insn} +@item INSN_ANNULLED_BRANCH_P (@var{x}) +In an @code{insn} in the delay slot of a branch insn, indicates that an +annulling branch should be used. See the discussion under +@code{sequence} below. Stored in the @code{unchanging} field and printed +as @samp{/u}. + +@findex INSN_DEAD_CODE_P +@cindex @code{insn} and @samp{/s} +@cindex @code{in_struct}, in @code{insn} +@item INSN_DEAD_CODE_P (@var{x}) +In an @code{insn} during the dead-code elimination pass, nonzero if the +insn is dead. +Stored in the @code{in_struct} field and printed as @samp{/s}. + +@findex INSN_DELETED_P +@cindex @code{insn} and @samp{/v} +@cindex @code{volatil}, in @code{insn} +@item INSN_DELETED_P (@var{x}) +In an @code{insn}, nonzero if the insn has been deleted. Stored in the +@code{volatil} field and printed as @samp{/v}. + +@findex INSN_FROM_TARGET_P +@cindex @code{insn} and @samp{/s} +@cindex @code{in_struct}, in @code{insn} +@item INSN_FROM_TARGET_P (@var{x}) +In an @code{insn} in a delay slot of a branch, indicates that the insn +is from the target of the branch. If the branch insn has +@code{INSN_ANNULLED_BRANCH_P} set, this insn will only be executed if +the branch is taken. For annulled branches with +@code{INSN_FROM_TARGET_P} clear, the insn will be executed only if the +branch is not taken. When @code{INSN_ANNULLED_BRANCH_P} is not set, +this insn will always be executed. Stored in the @code{in_struct} +field and printed as @samp{/s}. + +@findex LABEL_OUTSIDE_LOOP_P +@cindex @code{label_ref} and @samp{/s} +@cindex @code{in_struct}, in @code{label_ref} +@item LABEL_OUTSIDE_LOOP_P (@var{x}) +In @code{label_ref} expressions, nonzero if this is a reference to a +label that is outside the innermost loop containing the reference to the +label. Stored in the @code{in_struct} field and printed as @samp{/s}. + +@findex LABEL_PRESERVE_P +@cindex @code{code_label} and @samp{/i} +@cindex @code{in_struct}, in @code{code_label} +@item LABEL_PRESERVE_P (@var{x}) +In a @code{code_label}, indicates that the label is referenced by +code or data not visible to the RTL of a given function. +Labels referenced by a non-local goto will have this bit set. Stored +in the @code{in_struct} field and printed as @samp{/s}. + +@findex LABEL_REF_NONLOCAL_P +@cindex @code{label_ref} and @samp{/v} +@cindex @code{volatil}, in @code{label_ref} +@item LABEL_REF_NONLOCAL_P (@var{x}) +In @code{label_ref} and @code{reg_label} expressions, nonzero if this is +a reference to a non-local label. +Stored in the @code{volatil} field and printed as @samp{/v}. + +@findex LINK_COST_FREE +@cindex @code{insn_list} and @samp{/c} +@cindex @code{call}, in @code{insn_list} +@item LINK_COST_FREE (@var{x}) +In the @code{LOG_LINKS} @code{insn_list} during scheduling, nonzero when +the cost of executing an instruction through the link is zero, i.e., the +link makes the cost free. Stored in the @code{call} field and printed +as @samp{/c}. + +@findex LINK_COST_ZERO +@cindex @code{insn_list} and @samp{/j} +@cindex @code{jump}, in @code{insn_list} +@item LINK_COST_ZERO (@var{x}) +In the @code{LOG_LINKS} @code{insn_list} during scheduling, nonzero when +the cost of executing an instruction through the link varies and is +unchanged, i.e., the link has zero additional cost. +Stored in the @code{jump} field and printed as @samp{/j}. + +@findex MEM_IN_STRUCT_P +@cindex @code{mem} and @samp{/s} +@cindex @code{in_struct}, in @code{mem} +@item MEM_IN_STRUCT_P (@var{x}) +In @code{mem} expressions, nonzero for reference to an entire structure, +union or array, or to a component of one. Zero for references to a +scalar variable or through a pointer to a scalar. If both this flag and +@code{MEM_SCALAR_P} are clear, then we don't know whether this @code{mem} +is in a structure or not. Both flags should never be simultaneously set. +Stored in the @code{in_struct} field and printed as @samp{/s}. + +@findex MEM_KEEP_ALIAS_SET_P +@cindex @code{mem} and @samp{/j} +@cindex @code{jump}, in @code{mem} +@item MEM_KEEP_ALIAS_SET_P (@var{x}) +In @code{mem} expressions, 1 if we should keep the alias set for this +mem unchanged when we access a component. Set to 1, for example, when we +are already in a non-addressable component of an aggregate. +Stored in the @code{jump} field and printed as @samp{/j}. + +@findex MEM_SCALAR_P +@cindex @code{mem} and @samp{/f} +@cindex @code{frame_related}, in @code{mem} +@item MEM_SCALAR_P (@var{x}) +In @code{mem} expressions, nonzero for reference to a scalar known not +to be a member of a structure, union, or array. Zero for such +references and for indirections through pointers, even pointers pointing +to scalar types. If both this flag and @code{MEM_STRUCT_P} are clear, then we +don't know whether this @code{mem} is in a structure or not. Both flags should +never be simultaneously set. +Stored in the @code{frame_related} field and printed as @samp{/f}. + +@findex MEM_VOLATILE_P +@cindex @code{mem} and @samp{/v} +@cindex @code{volatil}, in @code{mem} +@item MEM_VOLATILE_P (@var{x}) +In @code{mem} and @code{asm_operands} expressions, nonzero for volatile +memory references. +Stored in the @code{volatil} field and printed as @samp{/v}. + +@findex REG_FUNCTION_VALUE_P +@cindex @code{reg} and @samp{/i} +@cindex @code{integrated}, in @code{reg} +@item REG_FUNCTION_VALUE_P (@var{x}) +Nonzero in a @code{reg} if it is the place in which this function's +value is going to be returned. (This happens only in a hard +register.) Stored in the @code{integrated} field and printed as +@samp{/i}. + +@findex REG_LOOP_TEST_P +@cindex @code{reg} and @samp{/s} +@cindex @code{in_struct}, in @code{reg} +@item REG_LOOP_TEST_P (@var{x}) +In @code{reg} expressions, nonzero if this register's entire life is +contained in the exit test code for some loop. Stored in the +@code{in_struct} field and printed as @samp{/s}. + +@findex REG_POINTER +@cindex @code{reg} and @samp{/f} +@cindex @code{frame_related}, in @code{reg} +@item REG_POINTER (@var{x}) +Nonzero in a @code{reg} if the register holds a pointer. Stored in the +@code{frame_related} field and printed as @samp{/f}. + +@findex REG_USERVAR_P +@cindex @code{reg} and @samp{/v} +@cindex @code{volatil}, in @code{reg} +@item REG_USERVAR_P (@var{x}) +In a @code{reg}, nonzero if it corresponds to a variable present in +the user's source code. Zero for temporaries generated internally by +the compiler. Stored in the @code{volatil} field and printed as +@samp{/v}. + +The same hard register may be used also for collecting the values of +functions called by this one, but @code{REG_FUNCTION_VALUE_P} is zero +in this kind of use. + +@findex RTX_FRAME_RELATED_P +@cindex @code{insn} and @samp{/f} +@cindex @code{frame_related}, in @code{insn} +@item RTX_FRAME_RELATED_P (@var{x}) +Nonzero in an @code{insn} or @code{set} which is part of a function prologue +and sets the stack pointer, sets the frame pointer, or saves a register. +This flag should also be set on an instruction that sets up a temporary +register to use in place of the frame pointer. +Stored in the @code{frame_related} field and printed as @samp{/f}. + +In particular, on RISC targets where there are limits on the sizes of +immediate constants, it is sometimes impossible to reach the register +save area directly from the stack pointer. In that case, a temporary +register is used that is near enough to the register save area, and the +Canonical Frame Address, i.e., DWARF2's logical frame pointer, register +must (temporarily) be changed to be this temporary register. So, the +instruction that sets this temporary register must be marked as +@code{RTX_FRAME_RELATED_P}. + +If the marked instruction is overly complex (defined in terms of what +@code{dwarf2out_frame_debug_expr} can handle), you will also have to +create a @code{REG_FRAME_RELATED_EXPR} note and attach it to the +instruction. This note should contain a simple expression of the +computation performed by this instruction, i.e., one that +@code{dwarf2out_frame_debug_expr} can handle. + +This flag is required for exception handling support on targets with RTL +prologues. + +@findex RTX_INTEGRATED_P +@cindex @code{insn} and @samp{/i} +@cindex @code{integrated}, in @code{insn} +@item RTX_INTEGRATED_P (@var{x}) +Nonzero in an @code{insn}, @code{insn_list}, or @code{const} if it +resulted from an in-line function call. +Stored in the @code{integrated} field and printed as @samp{/i}. + +@findex RTX_UNCHANGING_P +@cindex @code{reg} and @samp{/u} +@cindex @code{mem} and @samp{/u} +@cindex @code{unchanging}, in @code{reg} and @code{mem} +@item RTX_UNCHANGING_P (@var{x}) +Nonzero in a @code{reg} or @code{mem} if the memory is set at most once, +anywhere. This does not mean that it is function invariant. +Stored in the @code{unchanging} field and printed as @samp{/u}. + +@findex SCHED_GROUP_P +@cindex @code{insn} and @samp{/i} +@cindex @code{in_struct}, in @code{insn} +@item SCHED_GROUP_P (@var{x}) +During instruction scheduling, in an @code{insn}, indicates that the +previous insn must be scheduled together with this insn. This is used to +ensure that certain groups of instructions will not be split up by the +instruction scheduling pass, for example, @code{use} insns before +a @code{call_insn} may not be separated from the @code{call_insn}. +Stored in the @code{in_struct} field and printed as @samp{/s}. + +@findex SET_IS_RETURN_P +@cindex @code{insn} and @samp{/j} +@cindex @code{jump}, in @code{insn} +@item SET_IS_RETURN_P (@var{x}) +For a @code{set}, nonzero if it is for a return. +Stored in the @code{jump} field and printed as @samp{/j}. + +@findex SIBLING_CALL_P +@cindex @code{call_insn} and @samp{/j} +@cindex @code{jump}, in @code{call_insn} +@item SIBLING_CALL_P (@var{x}) +For a @code{call_insn}, nonzero if the insn is a sibling call. +Stored in the @code{jump} field and printed as @samp{/j}. + +@findex STRING_POOL_ADDRESS_P +@cindex @code{symbol_ref} and @samp{/f} +@cindex @code{frame_related}, in @code{symbol_ref} +@item STRING_POOL_ADDRESS_P (@var{x}) +For a @code{symbol_ref} expression, nonzero if it addresses this function's +string constant pool. +Stored in the @code{frame_related} field and printed as @samp{/f}. + +@findex SUBREG_PROMOTED_UNSIGNED_P +@cindex @code{subreg} and @samp{/u} +@cindex @code{unchanging}, in @code{subreg} +@item SUBREG_PROMOTED_UNSIGNED_P (@var{x}) +Nonzero in a @code{subreg} that has @code{SUBREG_PROMOTED_VAR_P} nonzero +if the object being referenced is kept zero-extended and zero if it +is kept sign-extended. Stored in the @code{unchanging} field and +printed as @samp{/u}. + +@findex SUBREG_PROMOTED_VAR_P +@cindex @code{subreg} and @samp{/s} +@cindex @code{in_struct}, in @code{subreg} +@item SUBREG_PROMOTED_VAR_P (@var{x}) +Nonzero in a @code{subreg} if it was made when accessing an object that +was promoted to a wider mode in accord with the @code{PROMOTED_MODE} machine +description macro (@pxref{Storage Layout}). In this case, the mode of +the @code{subreg} is the declared mode of the object and the mode of +@code{SUBREG_REG} is the mode of the register that holds the object. +Promoted variables are always either sign- or zero-extended to the wider +mode on every assignment. Stored in the @code{in_struct} field and +printed as @samp{/s}. + +@findex SYMBOL_REF_FLAG +@cindex @code{symbol_ref} and @samp{/v} +@cindex @code{volatil}, in @code{symbol_ref} +@item SYMBOL_REF_FLAG (@var{x}) +In a @code{symbol_ref}, this is used as a flag for machine-specific purposes. +Stored in the @code{volatil} field and printed as @samp{/v}. + +@findex SYMBOL_REF_USED +@cindex @code{used}, in @code{symbol_ref} +@item SYMBOL_REF_USED (@var{x}) +In a @code{symbol_ref}, indicates that @var{x} has been used. This is +normally only used to ensure that @var{x} is only declared external +once. Stored in the @code{used} field. + +@findex SYMBOL_REF_WEAK +@cindex @code{symbol_ref} and @samp{/i} +@cindex @code{integrated}, in @code{symbol_ref} +@item SYMBOL_REF_WEAK (@var{x}) +In a @code{symbol_ref}, indicates that @var{x} has been declared weak. +Stored in the @code{integrated} field and printed as @samp{/i}. +@end table + +These are the fields to which the above macros refer: + +@table @code +@findex call +@cindex @samp{/c} in RTL dump +@item call +In the @code{LOG_LINKS} of an @code{insn_list} during scheduling, 1 means that +the cost of executing an instruction through the link is zero. + +In an RTL dump, this flag is represented as @samp{/c}. + +@findex frame_related +@cindex @samp{/f} in RTL dump +@item frame_related +In an @code{insn} or @code{set} expression, 1 means that it is part of +a function prologue and sets the stack pointer, sets the frame pointer, +saves a register, or sets up a temporary register to use in place of the +frame pointer. + +In @code{reg} expressions, 1 means that the register holds a pointer. + +In @code{symbol_ref} expressions, 1 means that the reference addresses +this function's string constant pool. + +In @code{mem} expressions, 1 means that the reference is to a scalar. + +In an RTL dump, this flag is represented as @samp{/f}. + +@findex in_struct +@cindex @samp{/s} in RTL dump +@item in_struct +In @code{mem} expressions, it is 1 if the memory datum referred to is +all or part of a structure or array; 0 if it is (or might be) a scalar +variable. A reference through a C pointer has 0 because the pointer +might point to a scalar variable. This information allows the compiler +to determine something about possible cases of aliasing. + +In @code{reg} expressions, it is 1 if the register has its entire life +contained within the test expression of some loop. + +In @code{subreg} expressions, 1 means that the @code{subreg} is accessing +an object that has had its mode promoted from a wider mode. + +In @code{label_ref} expressions, 1 means that the referenced label is +outside the innermost loop containing the insn in which the @code{label_ref} +was found. + +In @code{code_label} expressions, it is 1 if the label may never be deleted. +This is used for labels which are the target of non-local gotos. Such a +label that would have been deleted is replaced with a @code{note} of type +@code{NOTE_INSN_DELETED_LABEL}. + +In an @code{insn} during dead-code elimination, 1 means that the insn is +dead code. + +In an @code{insn} during reorg for an insn in the delay slot of a branch, +1 means that this insn is from the target of the branch. + +In an @code{insn} during instruction scheduling, 1 means that this insn +must be scheduled as part of a group together with the previous insn. + +In an RTL dump, this flag is represented as @samp{/s}. + +@findex integrated +@cindex @samp{/i} in RTL dump +@item integrated +In an @code{insn}, @code{insn_list}, or @code{const}, 1 means the RTL was +produced by procedure integration. + +In @code{reg} expressions, 1 means the register contains +the value to be returned by the current function. On +machines that pass parameters in registers, the same register number +may be used for parameters as well, but this flag is not set on such +uses. + +In @code{symbol_ref} expressions, 1 means the referenced symbol is weak. + +In an RTL dump, this flag is represented as @samp{/i}. + +@findex jump +@cindex @samp{/j} in RTL dump +@item jump +In a @code{mem} expression, 1 means we should keep the alias set for this +mem unchanged when we access a component. + +In a @code{set}, 1 means it is for a return. + +In a @code{call_insn}, 1 means it is a sibling call. + +In the @code{LOG_LINKS} of an @code{insn_list} during scheduling, 1 means the +cost of executing an instruction through the link varies and is unchanging. + +In an RTL dump, this flag is represented as @samp{/j}. + +@findex unchanging +@cindex @samp{/u} in RTL dump +@item unchanging +In @code{reg} and @code{mem} expressions, 1 means +that the value of the expression never changes. + +In @code{subreg} expressions, it is 1 if the @code{subreg} references an +unsigned object whose mode has been promoted to a wider mode. + +In an @code{insn}, 1 means that this is an annulling branch. + +In a @code{symbol_ref} expression, 1 means that this symbol addresses +something in the per-function constant pool. + +In a @code{call_insn}, @code{note}, or an @code{expr_list} of notes, +1 means that this instruction is a call to a const or pure function. + +In an RTL dump, this flag is represented as @samp{/u}. + +@findex used +@item used +This flag is used directly (without an access macro) at the end of RTL +generation for a function, to count the number of times an expression +appears in insns. Expressions that appear more than once are copied, +according to the rules for shared structure (@pxref{Sharing}). + +For a @code{reg}, it is used directly (without an access macro) by the +leaf register renumbering code to ensure that each register is only +renumbered once. + +In a @code{symbol_ref}, it indicates that an external declaration for +the symbol has already been written. + +@findex volatil +@cindex @samp{/v} in RTL dump +@item volatil +@cindex volatile memory references +In a @code{mem} or @code{asm_operands} expression, it is 1 if the memory +reference is volatile. Volatile memory references may not be deleted, +reordered or combined. + +In a @code{symbol_ref} expression, it is used for machine-specific +purposes. + +In a @code{reg} expression, it is 1 if the value is a user-level variable. +0 indicates an internal compiler temporary. + +In an @code{insn}, 1 means the insn has been deleted. + +In @code{label_ref} and @code{reg_label} expressions, 1 means a reference +to a non-local label. + +In an RTL dump, this flag is represented as @samp{/v}. +@end table + +@node Machine Modes +@section Machine Modes +@cindex machine modes + +@findex enum machine_mode +A machine mode describes a size of data object and the representation used +for it. In the C code, machine modes are represented by an enumeration +type, @code{enum machine_mode}, defined in @file{machmode.def}. Each RTL +expression has room for a machine mode and so do certain kinds of tree +expressions (declarations and types, to be precise). + +In debugging dumps and machine descriptions, the machine mode of an RTL +expression is written after the expression code with a colon to separate +them. The letters @samp{mode} which appear at the end of each machine mode +name are omitted. For example, @code{(reg:SI 38)} is a @code{reg} +expression with machine mode @code{SImode}. If the mode is +@code{VOIDmode}, it is not written at all. + +Here is a table of machine modes. The term ``byte'' below refers to an +object of @code{BITS_PER_UNIT} bits (@pxref{Storage Layout}). + +@table @code +@findex BImode +@item BImode +``Bit'' mode represents a single bit, for predicate registers. + +@findex QImode +@item QImode +``Quarter-Integer'' mode represents a single byte treated as an integer. + +@findex HImode +@item HImode +``Half-Integer'' mode represents a two-byte integer. + +@findex PSImode +@item PSImode +``Partial Single Integer'' mode represents an integer which occupies +four bytes but which doesn't really use all four. On some machines, +this is the right mode to use for pointers. + +@findex SImode +@item SImode +``Single Integer'' mode represents a four-byte integer. + +@findex PDImode +@item PDImode +``Partial Double Integer'' mode represents an integer which occupies +eight bytes but which doesn't really use all eight. On some machines, +this is the right mode to use for certain pointers. + +@findex DImode +@item DImode +``Double Integer'' mode represents an eight-byte integer. + +@findex TImode +@item TImode +``Tetra Integer'' (?) mode represents a sixteen-byte integer. + +@findex OImode +@item OImode +``Octa Integer'' (?) mode represents a thirty-two-byte integer. + +@findex QFmode +@item QFmode +``Quarter-Floating'' mode represents a quarter-precision (single byte) +floating point number. + +@findex HFmode +@item HFmode +``Half-Floating'' mode represents a half-precision (two byte) floating +point number. + +@findex TQFmode +@item TQFmode +``Three-Quarter-Floating'' (?) mode represents a three-quarter-precision +(three byte) floating point number. + +@findex SFmode +@item SFmode +``Single Floating'' mode represents a four byte floating point number. +In the common case, of a processor with IEEE arithmetic and 8-bit bytes, +this is a single-precision IEEE floating point number; it can also be +used for double-precision (on processors with 16-bit bytes) and +single-precision VAX and IBM types. + +@findex DFmode +@item DFmode +``Double Floating'' mode represents an eight byte floating point number. +In the common case, of a processor with IEEE arithmetic and 8-bit bytes, +this is a double-precision IEEE floating point number. + +@findex XFmode +@item XFmode +``Extended Floating'' mode represents a twelve byte floating point +number. This mode is used for IEEE extended floating point. On some +systems not all bits within these bytes will actually be used. + +@findex TFmode +@item TFmode +``Tetra Floating'' mode represents a sixteen byte floating point number. +This gets used for both the 96-bit extended IEEE floating-point types +padded to 128 bits, and true 128-bit extended IEEE floating-point types. + +@findex CCmode +@item CCmode +``Condition Code'' mode represents the value of a condition code, which +is a machine-specific set of bits used to represent the result of a +comparison operation. Other machine-specific modes may also be used for +the condition code. These modes are not used on machines that use +@code{cc0} (see @pxref{Condition Code}). + +@findex BLKmode +@item BLKmode +``Block'' mode represents values that are aggregates to which none of +the other modes apply. In RTL, only memory references can have this mode, +and only if they appear in string-move or vector instructions. On machines +which have no such instructions, @code{BLKmode} will not appear in RTL@. + +@findex VOIDmode +@item VOIDmode +Void mode means the absence of a mode or an unspecified mode. +For example, RTL expressions of code @code{const_int} have mode +@code{VOIDmode} because they can be taken to have whatever mode the context +requires. In debugging dumps of RTL, @code{VOIDmode} is expressed by +the absence of any mode. + +@findex QCmode +@findex HCmode +@findex SCmode +@findex DCmode +@findex XCmode +@findex TCmode +@item QCmode, HCmode, SCmode, DCmode, XCmode, TCmode +These modes stand for a complex number represented as a pair of floating +point values. The floating point values are in @code{QFmode}, +@code{HFmode}, @code{SFmode}, @code{DFmode}, @code{XFmode}, and +@code{TFmode}, respectively. + +@findex CQImode +@findex CHImode +@findex CSImode +@findex CDImode +@findex CTImode +@findex COImode +@item CQImode, CHImode, CSImode, CDImode, CTImode, COImode +These modes stand for a complex number represented as a pair of integer +values. The integer values are in @code{QImode}, @code{HImode}, +@code{SImode}, @code{DImode}, @code{TImode}, and @code{OImode}, +respectively. +@end table + +The machine description defines @code{Pmode} as a C macro which expands +into the machine mode used for addresses. Normally this is the mode +whose size is @code{BITS_PER_WORD}, @code{SImode} on 32-bit machines. + +The only modes which a machine description @i{must} support are +@code{QImode}, and the modes corresponding to @code{BITS_PER_WORD}, +@code{FLOAT_TYPE_SIZE} and @code{DOUBLE_TYPE_SIZE}. +The compiler will attempt to use @code{DImode} for 8-byte structures and +unions, but this can be prevented by overriding the definition of +@code{MAX_FIXED_MODE_SIZE}. Alternatively, you can have the compiler +use @code{TImode} for 16-byte structures and unions. Likewise, you can +arrange for the C type @code{short int} to avoid using @code{HImode}. + +@cindex mode classes +Very few explicit references to machine modes remain in the compiler and +these few references will soon be removed. Instead, the machine modes +are divided into mode classes. These are represented by the enumeration +type @code{enum mode_class} defined in @file{machmode.h}. The possible +mode classes are: + +@table @code +@findex MODE_INT +@item MODE_INT +Integer modes. By default these are @code{BImode}, @code{QImode}, +@code{HImode}, @code{SImode}, @code{DImode}, @code{TImode}, and +@code{OImode}. + +@findex MODE_PARTIAL_INT +@item MODE_PARTIAL_INT +The ``partial integer'' modes, @code{PQImode}, @code{PHImode}, +@code{PSImode} and @code{PDImode}. + +@findex MODE_FLOAT +@item MODE_FLOAT +Floating point modes. By default these are @code{QFmode}, +@code{HFmode}, @code{TQFmode}, @code{SFmode}, @code{DFmode}, +@code{XFmode} and @code{TFmode}. + +@findex MODE_COMPLEX_INT +@item MODE_COMPLEX_INT +Complex integer modes. (These are not currently implemented). + +@findex MODE_COMPLEX_FLOAT +@item MODE_COMPLEX_FLOAT +Complex floating point modes. By default these are @code{QCmode}, +@code{HCmode}, @code{SCmode}, @code{DCmode}, @code{XCmode}, and +@code{TCmode}. + +@findex MODE_FUNCTION +@item MODE_FUNCTION +Algol or Pascal function variables including a static chain. +(These are not currently implemented). + +@findex MODE_CC +@item MODE_CC +Modes representing condition code values. These are @code{CCmode} plus +any modes listed in the @code{EXTRA_CC_MODES} macro. @xref{Jump Patterns}, +also see @ref{Condition Code}. + +@findex MODE_RANDOM +@item MODE_RANDOM +This is a catchall mode class for modes which don't fit into the above +classes. Currently @code{VOIDmode} and @code{BLKmode} are in +@code{MODE_RANDOM}. +@end table + +Here are some C macros that relate to machine modes: + +@table @code +@findex GET_MODE +@item GET_MODE (@var{x}) +Returns the machine mode of the RTX @var{x}. + +@findex PUT_MODE +@item PUT_MODE (@var{x}, @var{newmode}) +Alters the machine mode of the RTX @var{x} to be @var{newmode}. + +@findex NUM_MACHINE_MODES +@item NUM_MACHINE_MODES +Stands for the number of machine modes available on the target +machine. This is one greater than the largest numeric value of any +machine mode. + +@findex GET_MODE_NAME +@item GET_MODE_NAME (@var{m}) +Returns the name of mode @var{m} as a string. + +@findex GET_MODE_CLASS +@item GET_MODE_CLASS (@var{m}) +Returns the mode class of mode @var{m}. + +@findex GET_MODE_WIDER_MODE +@item GET_MODE_WIDER_MODE (@var{m}) +Returns the next wider natural mode. For example, the expression +@code{GET_MODE_WIDER_MODE (QImode)} returns @code{HImode}. + +@findex GET_MODE_SIZE +@item GET_MODE_SIZE (@var{m}) +Returns the size in bytes of a datum of mode @var{m}. + +@findex GET_MODE_BITSIZE +@item GET_MODE_BITSIZE (@var{m}) +Returns the size in bits of a datum of mode @var{m}. + +@findex GET_MODE_MASK +@item GET_MODE_MASK (@var{m}) +Returns a bitmask containing 1 for all bits in a word that fit within +mode @var{m}. This macro can only be used for modes whose bitsize is +less than or equal to @code{HOST_BITS_PER_INT}. + +@findex GET_MODE_ALIGNMENT +@item GET_MODE_ALIGNMENT (@var{m}) +Return the required alignment, in bits, for an object of mode @var{m}. + +@findex GET_MODE_UNIT_SIZE +@item GET_MODE_UNIT_SIZE (@var{m}) +Returns the size in bytes of the subunits of a datum of mode @var{m}. +This is the same as @code{GET_MODE_SIZE} except in the case of complex +modes. For them, the unit size is the size of the real or imaginary +part. + +@findex GET_MODE_NUNITS +@item GET_MODE_NUNITS (@var{m}) +Returns the number of units contained in a mode, i.e., +@code{GET_MODE_SIZE} divided by @code{GET_MODE_UNIT_SIZE}. + +@findex GET_CLASS_NARROWEST_MODE +@item GET_CLASS_NARROWEST_MODE (@var{c}) +Returns the narrowest mode in mode class @var{c}. +@end table + +@findex byte_mode +@findex word_mode +The global variables @code{byte_mode} and @code{word_mode} contain modes +whose classes are @code{MODE_INT} and whose bitsizes are either +@code{BITS_PER_UNIT} or @code{BITS_PER_WORD}, respectively. On 32-bit +machines, these are @code{QImode} and @code{SImode}, respectively. + +@node Constants +@section Constant Expression Types +@cindex RTL constants +@cindex RTL constant expression types + +The simplest RTL expressions are those that represent constant values. + +@table @code +@findex const_int +@item (const_int @var{i}) +This type of expression represents the integer value @var{i}. @var{i} +is customarily accessed with the macro @code{INTVAL} as in +@code{INTVAL (@var{exp})}, which is equivalent to @code{XWINT (@var{exp}, 0)}. + +@findex const0_rtx +@findex const1_rtx +@findex const2_rtx +@findex constm1_rtx +There is only one expression object for the integer value zero; it is +the value of the variable @code{const0_rtx}. Likewise, the only +expression for integer value one is found in @code{const1_rtx}, the only +expression for integer value two is found in @code{const2_rtx}, and the +only expression for integer value negative one is found in +@code{constm1_rtx}. Any attempt to create an expression of code +@code{const_int} and value zero, one, two or negative one will return +@code{const0_rtx}, @code{const1_rtx}, @code{const2_rtx} or +@code{constm1_rtx} as appropriate. + +@findex const_true_rtx +Similarly, there is only one object for the integer whose value is +@code{STORE_FLAG_VALUE}. It is found in @code{const_true_rtx}. If +@code{STORE_FLAG_VALUE} is one, @code{const_true_rtx} and +@code{const1_rtx} will point to the same object. If +@code{STORE_FLAG_VALUE} is @minus{}1, @code{const_true_rtx} and +@code{constm1_rtx} will point to the same object. + +@findex const_double +@item (const_double:@var{m} @var{addr} @var{i0} @var{i1} @dots{}) +Represents either a floating-point constant of mode @var{m} or an +integer constant too large to fit into @code{HOST_BITS_PER_WIDE_INT} +bits but small enough to fit within twice that number of bits (GCC +does not provide a mechanism to represent even larger constants). In +the latter case, @var{m} will be @code{VOIDmode}. + +@findex CONST_DOUBLE_MEM +@findex CONST_DOUBLE_CHAIN +@var{addr} is used to contain the @code{mem} expression that corresponds +to the location in memory that at which the constant can be found. If +it has not been allocated a memory location, but is on the chain of all +@code{const_double} expressions in this compilation (maintained using an +undisplayed field), @var{addr} contains @code{const0_rtx}. If it is not +on the chain, @var{addr} contains @code{cc0_rtx}. @var{addr} is +customarily accessed with the macro @code{CONST_DOUBLE_MEM} and the +chain field via @code{CONST_DOUBLE_CHAIN}. + +@findex CONST_DOUBLE_LOW +If @var{m} is @code{VOIDmode}, the bits of the value are stored in +@var{i0} and @var{i1}. @var{i0} is customarily accessed with the macro +@code{CONST_DOUBLE_LOW} and @var{i1} with @code{CONST_DOUBLE_HIGH}. + +If the constant is floating point (regardless of its precision), then +the number of integers used to store the value depends on the size of +@code{REAL_VALUE_TYPE} (@pxref{Cross-compilation}). The integers +represent a floating point number, but not precisely in the target +machine's or host machine's floating point format. To convert them to +the precise bit pattern used by the target machine, use the macro +@code{REAL_VALUE_TO_TARGET_DOUBLE} and friends (@pxref{Data Output}). + +@findex CONST0_RTX +@findex CONST1_RTX +@findex CONST2_RTX +The macro @code{CONST0_RTX (@var{mode})} refers to an expression with +value 0 in mode @var{mode}. If mode @var{mode} is of mode class +@code{MODE_INT}, it returns @code{const0_rtx}. Otherwise, it returns a +@code{CONST_DOUBLE} expression in mode @var{mode}. Similarly, the macro +@code{CONST1_RTX (@var{mode})} refers to an expression with value 1 in +mode @var{mode} and similarly for @code{CONST2_RTX}. + +@findex const_string +@item (const_string @var{str}) +Represents a constant string with value @var{str}. Currently this is +used only for insn attributes (@pxref{Insn Attributes}) since constant +strings in C are placed in memory. + +@findex symbol_ref +@item (symbol_ref:@var{mode} @var{symbol}) +Represents the value of an assembler label for data. @var{symbol} is +a string that describes the name of the assembler label. If it starts +with a @samp{*}, the label is the rest of @var{symbol} not including +the @samp{*}. Otherwise, the label is @var{symbol}, usually prefixed +with @samp{_}. + +The @code{symbol_ref} contains a mode, which is usually @code{Pmode}. +Usually that is the only mode for which a symbol is directly valid. + +@findex label_ref +@item (label_ref @var{label}) +Represents the value of an assembler label for code. It contains one +operand, an expression, which must be a @code{code_label} or a @code{note} +of type @code{NOTE_INSN_DELETED_LABEL} that appears in the instruction +sequence to identify the place where the label should go. + +The reason for using a distinct expression type for code label +references is so that jump optimization can distinguish them. + +@item (const:@var{m} @var{exp}) +Represents a constant that is the result of an assembly-time +arithmetic computation. The operand, @var{exp}, is an expression that +contains only constants (@code{const_int}, @code{symbol_ref} and +@code{label_ref} expressions) combined with @code{plus} and +@code{minus}. However, not all combinations are valid, since the +assembler cannot do arbitrary arithmetic on relocatable symbols. + +@var{m} should be @code{Pmode}. + +@findex high +@item (high:@var{m} @var{exp}) +Represents the high-order bits of @var{exp}, usually a +@code{symbol_ref}. The number of bits is machine-dependent and is +normally the number of bits specified in an instruction that initializes +the high order bits of a register. It is used with @code{lo_sum} to +represent the typical two-instruction sequence used in RISC machines to +reference a global memory location. + +@var{m} should be @code{Pmode}. +@end table + +@node Regs and Memory +@section Registers and Memory +@cindex RTL register expressions +@cindex RTL memory expressions + +Here are the RTL expression types for describing access to machine +registers and to main memory. + +@table @code +@findex reg +@cindex hard registers +@cindex pseudo registers +@item (reg:@var{m} @var{n}) +For small values of the integer @var{n} (those that are less than +@code{FIRST_PSEUDO_REGISTER}), this stands for a reference to machine +register number @var{n}: a @dfn{hard register}. For larger values of +@var{n}, it stands for a temporary value or @dfn{pseudo register}. +The compiler's strategy is to generate code assuming an unlimited +number of such pseudo registers, and later convert them into hard +registers or into memory references. + +@var{m} is the machine mode of the reference. It is necessary because +machines can generally refer to each register in more than one mode. +For example, a register may contain a full word but there may be +instructions to refer to it as a half word or as a single byte, as +well as instructions to refer to it as a floating point number of +various precisions. + +Even for a register that the machine can access in only one mode, +the mode must always be specified. + +The symbol @code{FIRST_PSEUDO_REGISTER} is defined by the machine +description, since the number of hard registers on the machine is an +invariant characteristic of the machine. Note, however, that not +all of the machine registers must be general registers. All the +machine registers that can be used for storage of data are given +hard register numbers, even those that can be used only in certain +instructions or can hold only certain types of data. + +A hard register may be accessed in various modes throughout one +function, but each pseudo register is given a natural mode +and is accessed only in that mode. When it is necessary to describe +an access to a pseudo register using a nonnatural mode, a @code{subreg} +expression is used. + +A @code{reg} expression with a machine mode that specifies more than +one word of data may actually stand for several consecutive registers. +If in addition the register number specifies a hardware register, then +it actually represents several consecutive hardware registers starting +with the specified one. + +Each pseudo register number used in a function's RTL code is +represented by a unique @code{reg} expression. + +@findex FIRST_VIRTUAL_REGISTER +@findex LAST_VIRTUAL_REGISTER +Some pseudo register numbers, those within the range of +@code{FIRST_VIRTUAL_REGISTER} to @code{LAST_VIRTUAL_REGISTER} only +appear during the RTL generation phase and are eliminated before the +optimization phases. These represent locations in the stack frame that +cannot be determined until RTL generation for the function has been +completed. The following virtual register numbers are defined: + +@table @code +@findex VIRTUAL_INCOMING_ARGS_REGNUM +@item VIRTUAL_INCOMING_ARGS_REGNUM +This points to the first word of the incoming arguments passed on the +stack. Normally these arguments are placed there by the caller, but the +callee may have pushed some arguments that were previously passed in +registers. + +@cindex @code{FIRST_PARM_OFFSET} and virtual registers +@cindex @code{ARG_POINTER_REGNUM} and virtual registers +When RTL generation is complete, this virtual register is replaced +by the sum of the register given by @code{ARG_POINTER_REGNUM} and the +value of @code{FIRST_PARM_OFFSET}. + +@findex VIRTUAL_STACK_VARS_REGNUM +@cindex @code{FRAME_GROWS_DOWNWARD} and virtual registers +@item VIRTUAL_STACK_VARS_REGNUM +If @code{FRAME_GROWS_DOWNWARD} is defined, this points to immediately +above the first variable on the stack. Otherwise, it points to the +first variable on the stack. + +@cindex @code{STARTING_FRAME_OFFSET} and virtual registers +@cindex @code{FRAME_POINTER_REGNUM} and virtual registers +@code{VIRTUAL_STACK_VARS_REGNUM} is replaced with the sum of the +register given by @code{FRAME_POINTER_REGNUM} and the value +@code{STARTING_FRAME_OFFSET}. + +@findex VIRTUAL_STACK_DYNAMIC_REGNUM +@item VIRTUAL_STACK_DYNAMIC_REGNUM +This points to the location of dynamically allocated memory on the stack +immediately after the stack pointer has been adjusted by the amount of +memory desired. + +@cindex @code{STACK_DYNAMIC_OFFSET} and virtual registers +@cindex @code{STACK_POINTER_REGNUM} and virtual registers +This virtual register is replaced by the sum of the register given by +@code{STACK_POINTER_REGNUM} and the value @code{STACK_DYNAMIC_OFFSET}. + +@findex VIRTUAL_OUTGOING_ARGS_REGNUM +@item VIRTUAL_OUTGOING_ARGS_REGNUM +This points to the location in the stack at which outgoing arguments +should be written when the stack is pre-pushed (arguments pushed using +push insns should always use @code{STACK_POINTER_REGNUM}). + +@cindex @code{STACK_POINTER_OFFSET} and virtual registers +This virtual register is replaced by the sum of the register given by +@code{STACK_POINTER_REGNUM} and the value @code{STACK_POINTER_OFFSET}. +@end table + +@findex subreg +@item (subreg:@var{m} @var{reg} @var{bytenum}) +@code{subreg} expressions are used to refer to a register in a machine +mode other than its natural one, or to refer to one register of +a multi-part @code{reg} that actually refers to several registers. + +Each pseudo-register has a natural mode. If it is necessary to +operate on it in a different mode---for example, to perform a fullword +move instruction on a pseudo-register that contains a single +byte---the pseudo-register must be enclosed in a @code{subreg}. In +such a case, @var{bytenum} is zero. + +Usually @var{m} is at least as narrow as the mode of @var{reg}, in which +case it is restricting consideration to only the bits of @var{reg} that +are in @var{m}. + +Sometimes @var{m} is wider than the mode of @var{reg}. These +@code{subreg} expressions are often called @dfn{paradoxical}. They are +used in cases where we want to refer to an object in a wider mode but do +not care what value the additional bits have. The reload pass ensures +that paradoxical references are only made to hard registers. + +The other use of @code{subreg} is to extract the individual registers of +a multi-register value. Machine modes such as @code{DImode} and +@code{TImode} can indicate values longer than a word, values which +usually require two or more consecutive registers. To access one of the +registers, use a @code{subreg} with mode @code{SImode} and a +@var{bytenum} offset that says which register. + +Storing in a non-paradoxical @code{subreg} has undefined results for +bits belonging to the same word as the @code{subreg}. This laxity makes +it easier to generate efficient code for such instructions. To +represent an instruction that preserves all the bits outside of those in +the @code{subreg}, use @code{strict_low_part} around the @code{subreg}. + +@cindex @code{WORDS_BIG_ENDIAN}, effect on @code{subreg} +The compilation parameter @code{WORDS_BIG_ENDIAN}, if set to 1, says +that byte number zero is part of the most significant word; otherwise, +it is part of the least significant word. + +@cindex @code{BYTES_BIG_ENDIAN}, effect on @code{subreg} +The compilation parameter @code{BYTES_BIG_ENDIAN}, if set to 1, says +that byte number zero is the most significant byte within a word; +otherwise, it is the least significant byte within a word. + +@cindex @code{FLOAT_WORDS_BIG_ENDIAN}, (lack of) effect on @code{subreg} +On a few targets, @code{FLOAT_WORDS_BIG_ENDIAN} disagrees with +@code{WORDS_BIG_ENDIAN}. +However, most parts of the compiler treat floating point values as if +they had the same endianness as integer values. This works because +they handle them solely as a collection of integer values, with no +particular numerical value. Only real.c and the runtime libraries +care about @code{FLOAT_WORDS_BIG_ENDIAN}. + +@cindex combiner pass +@cindex reload pass +@cindex @code{subreg}, special reload handling +Between the combiner pass and the reload pass, it is possible to have a +paradoxical @code{subreg} which contains a @code{mem} instead of a +@code{reg} as its first operand. After the reload pass, it is also +possible to have a non-paradoxical @code{subreg} which contains a +@code{mem}; this usually occurs when the @code{mem} is a stack slot +which replaced a pseudo register. + +Note that it is not valid to access a @code{DFmode} value in @code{SFmode} +using a @code{subreg}. On some machines the most significant part of a +@code{DFmode} value does not have the same format as a single-precision +floating value. + +It is also not valid to access a single word of a multi-word value in a +hard register when less registers can hold the value than would be +expected from its size. For example, some 32-bit machines have +floating-point registers that can hold an entire @code{DFmode} value. +If register 10 were such a register @code{(subreg:SI (reg:DF 10) 1)} +would be invalid because there is no way to convert that reference to +a single machine register. The reload pass prevents @code{subreg} +expressions such as these from being formed. + +@findex SUBREG_REG +@findex SUBREG_BYTE +The first operand of a @code{subreg} expression is customarily accessed +with the @code{SUBREG_REG} macro and the second operand is customarily +accessed with the @code{SUBREG_BYTE} macro. + +@findex scratch +@cindex scratch operands +@item (scratch:@var{m}) +This represents a scratch register that will be required for the +execution of a single instruction and not used subsequently. It is +converted into a @code{reg} by either the local register allocator or +the reload pass. + +@code{scratch} is usually present inside a @code{clobber} operation +(@pxref{Side Effects}). + +@findex cc0 +@cindex condition code register +@item (cc0) +This refers to the machine's condition code register. It has no +operands and may not have a machine mode. There are two ways to use it: + +@itemize @bullet +@item +To stand for a complete set of condition code flags. This is best on +most machines, where each comparison sets the entire series of flags. + +With this technique, @code{(cc0)} may be validly used in only two +contexts: as the destination of an assignment (in test and compare +instructions) and in comparison operators comparing against zero +(@code{const_int} with value zero; that is to say, @code{const0_rtx}). + +@item +To stand for a single flag that is the result of a single condition. +This is useful on machines that have only a single flag bit, and in +which comparison instructions must specify the condition to test. + +With this technique, @code{(cc0)} may be validly used in only two +contexts: as the destination of an assignment (in test and compare +instructions) where the source is a comparison operator, and as the +first operand of @code{if_then_else} (in a conditional branch). +@end itemize + +@findex cc0_rtx +There is only one expression object of code @code{cc0}; it is the +value of the variable @code{cc0_rtx}. Any attempt to create an +expression of code @code{cc0} will return @code{cc0_rtx}. + +Instructions can set the condition code implicitly. On many machines, +nearly all instructions set the condition code based on the value that +they compute or store. It is not necessary to record these actions +explicitly in the RTL because the machine description includes a +prescription for recognizing the instructions that do so (by means of +the macro @code{NOTICE_UPDATE_CC}). @xref{Condition Code}. Only +instructions whose sole purpose is to set the condition code, and +instructions that use the condition code, need mention @code{(cc0)}. + +On some machines, the condition code register is given a register number +and a @code{reg} is used instead of @code{(cc0)}. This is usually the +preferable approach if only a small subset of instructions modify the +condition code. Other machines store condition codes in general +registers; in such cases a pseudo register should be used. + +Some machines, such as the Sparc and RS/6000, have two sets of +arithmetic instructions, one that sets and one that does not set the +condition code. This is best handled by normally generating the +instruction that does not set the condition code, and making a pattern +that both performs the arithmetic and sets the condition code register +(which would not be @code{(cc0)} in this case). For examples, search +for @samp{addcc} and @samp{andcc} in @file{sparc.md}. + +@findex pc +@item (pc) +@cindex program counter +This represents the machine's program counter. It has no operands and +may not have a machine mode. @code{(pc)} may be validly used only in +certain specific contexts in jump instructions. + +@findex pc_rtx +There is only one expression object of code @code{pc}; it is the value +of the variable @code{pc_rtx}. Any attempt to create an expression of +code @code{pc} will return @code{pc_rtx}. + +All instructions that do not jump alter the program counter implicitly +by incrementing it, but there is no need to mention this in the RTL@. + +@findex mem +@item (mem:@var{m} @var{addr} @var{alias}) +This RTX represents a reference to main memory at an address +represented by the expression @var{addr}. @var{m} specifies how large +a unit of memory is accessed. @var{alias} specifies an alias set for the +reference. In general two items are in different alias sets if they cannot +reference the same memory address. + +@findex addressof +@item (addressof:@var{m} @var{reg}) +This RTX represents a request for the address of register @var{reg}. Its mode +is always @code{Pmode}. If there are any @code{addressof} +expressions left in the function after CSE, @var{reg} is forced into the +stack and the @code{addressof} expression is replaced with a @code{plus} +expression for the address of its stack slot. +@end table + +@node Arithmetic +@section RTL Expressions for Arithmetic +@cindex arithmetic, in RTL +@cindex math, in RTL +@cindex RTL expressions for arithmetic + +Unless otherwise specified, all the operands of arithmetic expressions +must be valid for mode @var{m}. An operand is valid for mode @var{m} +if it has mode @var{m}, or if it is a @code{const_int} or +@code{const_double} and @var{m} is a mode of class @code{MODE_INT}. + +For commutative binary operations, constants should be placed in the +second operand. + +@table @code +@findex plus +@cindex RTL addition +@cindex RTL sum +@item (plus:@var{m} @var{x} @var{y}) +Represents the sum of the values represented by @var{x} and @var{y} +carried out in machine mode @var{m}. + +@findex lo_sum +@item (lo_sum:@var{m} @var{x} @var{y}) +Like @code{plus}, except that it represents that sum of @var{x} and the +low-order bits of @var{y}. The number of low order bits is +machine-dependent but is normally the number of bits in a @code{Pmode} +item minus the number of bits set by the @code{high} code +(@pxref{Constants}). + +@var{m} should be @code{Pmode}. + +@findex minus +@cindex RTL subtraction +@cindex RTL difference +@item (minus:@var{m} @var{x} @var{y}) +Like @code{plus} but represents subtraction. + +@findex ss_plus +@cindex RTL addition with signed saturation +@item (ss_plus:@var{m} @var{x} @var{y}) + +Like @code{plus}, but using signed saturation in case of an overflow. + +@findex us_plus +@cindex RTL addition with unsigned saturation +@item (us_plus:@var{m} @var{x} @var{y}) + +Like @code{plus}, but using unsigned saturation in case of an overflow. + +@findex ss_minus +@cindex RTL addition with signed saturation +@item (ss_minus:@var{m} @var{x} @var{y}) + +Like @code{minus}, but using signed saturation in case of an overflow. + +@findex us_minus +@cindex RTL addition with unsigned saturation +@item (us_minus:@var{m} @var{x} @var{y}) + +Like @code{minus}, but using unsigned saturation in case of an overflow. + +@findex compare +@cindex RTL comparison +@item (compare:@var{m} @var{x} @var{y}) +Represents the result of subtracting @var{y} from @var{x} for purposes +of comparison. The result is computed without overflow, as if with +infinite precision. + +Of course, machines can't really subtract with infinite precision. +However, they can pretend to do so when only the sign of the result will +be used, which is the case when the result is stored in the condition +code. And that is the @emph{only} way this kind of expression may +validly be used: as a value to be stored in the condition codes, either +@code{(cc0)} or a register. @xref{Comparisons}. + +The mode @var{m} is not related to the modes of @var{x} and @var{y}, but +instead is the mode of the condition code value. If @code{(cc0)} is +used, it is @code{VOIDmode}. Otherwise it is some mode in class +@code{MODE_CC}, often @code{CCmode}. @xref{Condition Code}. If @var{m} +is @code{VOIDmode} or @code{CCmode}, the operation returns sufficient +information (in an unspecified format) so that any comparison operator +can be applied to the result of the @code{COMPARE} operation. For other +modes in class @code{MODE_CC}, the operation only returns a subset of +this information. + +Normally, @var{x} and @var{y} must have the same mode. Otherwise, +@code{compare} is valid only if the mode of @var{x} is in class +@code{MODE_INT} and @var{y} is a @code{const_int} or +@code{const_double} with mode @code{VOIDmode}. The mode of @var{x} +determines what mode the comparison is to be done in; thus it must not +be @code{VOIDmode}. + +If one of the operands is a constant, it should be placed in the +second operand and the comparison code adjusted as appropriate. + +A @code{compare} specifying two @code{VOIDmode} constants is not valid +since there is no way to know in what mode the comparison is to be +performed; the comparison must either be folded during the compilation +or the first operand must be loaded into a register while its mode is +still known. + +@findex neg +@item (neg:@var{m} @var{x}) +Represents the negation (subtraction from zero) of the value represented +by @var{x}, carried out in mode @var{m}. + +@findex mult +@cindex multiplication +@cindex product +@item (mult:@var{m} @var{x} @var{y}) +Represents the signed product of the values represented by @var{x} and +@var{y} carried out in machine mode @var{m}. + +Some machines support a multiplication that generates a product wider +than the operands. Write the pattern for this as + +@example +(mult:@var{m} (sign_extend:@var{m} @var{x}) (sign_extend:@var{m} @var{y})) +@end example + +where @var{m} is wider than the modes of @var{x} and @var{y}, which need +not be the same. + +For unsigned widening multiplication, use the same idiom, but with +@code{zero_extend} instead of @code{sign_extend}. + +@findex div +@cindex division +@cindex signed division +@cindex quotient +@item (div:@var{m} @var{x} @var{y}) +Represents the quotient in signed division of @var{x} by @var{y}, +carried out in machine mode @var{m}. If @var{m} is a floating point +mode, it represents the exact quotient; otherwise, the integerized +quotient. + +Some machines have division instructions in which the operands and +quotient widths are not all the same; you should represent +such instructions using @code{truncate} and @code{sign_extend} as in, + +@example +(truncate:@var{m1} (div:@var{m2} @var{x} (sign_extend:@var{m2} @var{y}))) +@end example + +@findex udiv +@cindex unsigned division +@cindex division +@item (udiv:@var{m} @var{x} @var{y}) +Like @code{div} but represents unsigned division. + +@findex mod +@findex umod +@cindex remainder +@cindex division +@item (mod:@var{m} @var{x} @var{y}) +@itemx (umod:@var{m} @var{x} @var{y}) +Like @code{div} and @code{udiv} but represent the remainder instead of +the quotient. + +@findex smin +@findex smax +@cindex signed minimum +@cindex signed maximum +@item (smin:@var{m} @var{x} @var{y}) +@itemx (smax:@var{m} @var{x} @var{y}) +Represents the smaller (for @code{smin}) or larger (for @code{smax}) of +@var{x} and @var{y}, interpreted as signed integers in mode @var{m}. + +@findex umin +@findex umax +@cindex unsigned minimum and maximum +@item (umin:@var{m} @var{x} @var{y}) +@itemx (umax:@var{m} @var{x} @var{y}) +Like @code{smin} and @code{smax}, but the values are interpreted as unsigned +integers. + +@findex not +@cindex complement, bitwise +@cindex bitwise complement +@item (not:@var{m} @var{x}) +Represents the bitwise complement of the value represented by @var{x}, +carried out in mode @var{m}, which must be a fixed-point machine mode. + +@findex and +@cindex logical-and, bitwise +@cindex bitwise logical-and +@item (and:@var{m} @var{x} @var{y}) +Represents the bitwise logical-and of the values represented by +@var{x} and @var{y}, carried out in machine mode @var{m}, which must be +a fixed-point machine mode. + +@findex ior +@cindex inclusive-or, bitwise +@cindex bitwise inclusive-or +@item (ior:@var{m} @var{x} @var{y}) +Represents the bitwise inclusive-or of the values represented by @var{x} +and @var{y}, carried out in machine mode @var{m}, which must be a +fixed-point mode. + +@findex xor +@cindex exclusive-or, bitwise +@cindex bitwise exclusive-or +@item (xor:@var{m} @var{x} @var{y}) +Represents the bitwise exclusive-or of the values represented by @var{x} +and @var{y}, carried out in machine mode @var{m}, which must be a +fixed-point mode. + +@findex ashift +@cindex left shift +@cindex shift +@cindex arithmetic shift +@item (ashift:@var{m} @var{x} @var{c}) +Represents the result of arithmetically shifting @var{x} left by @var{c} +places. @var{x} have mode @var{m}, a fixed-point machine mode. @var{c} +be a fixed-point mode or be a constant with mode @code{VOIDmode}; which +mode is determined by the mode called for in the machine description +entry for the left-shift instruction. For example, on the VAX, the mode +of @var{c} is @code{QImode} regardless of @var{m}. + +@findex lshiftrt +@cindex right shift +@findex ashiftrt +@item (lshiftrt:@var{m} @var{x} @var{c}) +@itemx (ashiftrt:@var{m} @var{x} @var{c}) +Like @code{ashift} but for right shift. Unlike the case for left shift, +these two operations are distinct. + +@findex rotate +@cindex rotate +@cindex left rotate +@findex rotatert +@cindex right rotate +@item (rotate:@var{m} @var{x} @var{c}) +@itemx (rotatert:@var{m} @var{x} @var{c}) +Similar but represent left and right rotate. If @var{c} is a constant, +use @code{rotate}. + +@findex abs +@cindex absolute value +@item (abs:@var{m} @var{x}) +Represents the absolute value of @var{x}, computed in mode @var{m}. + +@findex sqrt +@cindex square root +@item (sqrt:@var{m} @var{x}) +Represents the square root of @var{x}, computed in mode @var{m}. +Most often @var{m} will be a floating point mode. + +@findex ffs +@item (ffs:@var{m} @var{x}) +Represents one plus the index of the least significant 1-bit in +@var{x}, represented as an integer of mode @var{m}. (The value is +zero if @var{x} is zero.) The mode of @var{x} need not be @var{m}; +depending on the target machine, various mode combinations may be +valid. +@end table + +@node Comparisons +@section Comparison Operations +@cindex RTL comparison operations + +Comparison operators test a relation on two operands and are considered +to represent a machine-dependent nonzero value described by, but not +necessarily equal to, @code{STORE_FLAG_VALUE} (@pxref{Misc}) +if the relation holds, or zero if it does not. The mode of the +comparison operation is independent of the mode of the data being +compared. If the comparison operation is being tested (e.g., the first +operand of an @code{if_then_else}), the mode must be @code{VOIDmode}. +If the comparison operation is producing data to be stored in some +variable, the mode must be in class @code{MODE_INT}. All comparison +operations producing data must use the same mode, which is +machine-specific. + +@cindex condition codes +There are two ways that comparison operations may be used. The +comparison operators may be used to compare the condition codes +@code{(cc0)} against zero, as in @code{(eq (cc0) (const_int 0))}. Such +a construct actually refers to the result of the preceding instruction +in which the condition codes were set. The instruction setting the +condition code must be adjacent to the instruction using the condition +code; only @code{note} insns may separate them. + +Alternatively, a comparison operation may directly compare two data +objects. The mode of the comparison is determined by the operands; they +must both be valid for a common machine mode. A comparison with both +operands constant would be invalid as the machine mode could not be +deduced from it, but such a comparison should never exist in RTL due to +constant folding. + +In the example above, if @code{(cc0)} were last set to +@code{(compare @var{x} @var{y})}, the comparison operation is +identical to @code{(eq @var{x} @var{y})}. Usually only one style +of comparisons is supported on a particular machine, but the combine +pass will try to merge the operations to produce the @code{eq} shown +in case it exists in the context of the particular insn involved. + +Inequality comparisons come in two flavors, signed and unsigned. Thus, +there are distinct expression codes @code{gt} and @code{gtu} for signed and +unsigned greater-than. These can produce different results for the same +pair of integer values: for example, 1 is signed greater-than @minus{}1 but not +unsigned greater-than, because @minus{}1 when regarded as unsigned is actually +@code{0xffffffff} which is greater than 1. + +The signed comparisons are also used for floating point values. Floating +point comparisons are distinguished by the machine modes of the operands. + +@table @code +@findex eq +@cindex equal +@item (eq:@var{m} @var{x} @var{y}) +@code{STORE_FLAG_VALUE} if the values represented by @var{x} and @var{y} +are equal, otherwise 0. + +@findex ne +@cindex not equal +@item (ne:@var{m} @var{x} @var{y}) +@code{STORE_FLAG_VALUE} if the values represented by @var{x} and @var{y} +are not equal, otherwise 0. + +@findex gt +@cindex greater than +@item (gt:@var{m} @var{x} @var{y}) +@code{STORE_FLAG_VALUE} if the @var{x} is greater than @var{y}. If they +are fixed-point, the comparison is done in a signed sense. + +@findex gtu +@cindex greater than +@cindex unsigned greater than +@item (gtu:@var{m} @var{x} @var{y}) +Like @code{gt} but does unsigned comparison, on fixed-point numbers only. + +@findex lt +@cindex less than +@findex ltu +@cindex unsigned less than +@item (lt:@var{m} @var{x} @var{y}) +@itemx (ltu:@var{m} @var{x} @var{y}) +Like @code{gt} and @code{gtu} but test for ``less than''. + +@findex ge +@cindex greater than +@findex geu +@cindex unsigned greater than +@item (ge:@var{m} @var{x} @var{y}) +@itemx (geu:@var{m} @var{x} @var{y}) +Like @code{gt} and @code{gtu} but test for ``greater than or equal''. + +@findex le +@cindex less than or equal +@findex leu +@cindex unsigned less than +@item (le:@var{m} @var{x} @var{y}) +@itemx (leu:@var{m} @var{x} @var{y}) +Like @code{gt} and @code{gtu} but test for ``less than or equal''. + +@findex if_then_else +@item (if_then_else @var{cond} @var{then} @var{else}) +This is not a comparison operation but is listed here because it is +always used in conjunction with a comparison operation. To be +precise, @var{cond} is a comparison expression. This expression +represents a choice, according to @var{cond}, between the value +represented by @var{then} and the one represented by @var{else}. + +On most machines, @code{if_then_else} expressions are valid only +to express conditional jumps. + +@findex cond +@item (cond [@var{test1} @var{value1} @var{test2} @var{value2} @dots{}] @var{default}) +Similar to @code{if_then_else}, but more general. Each of @var{test1}, +@var{test2}, @dots{} is performed in turn. The result of this expression is +the @var{value} corresponding to the first nonzero test, or @var{default} if +none of the tests are nonzero expressions. + +This is currently not valid for instruction patterns and is supported only +for insn attributes. @xref{Insn Attributes}. +@end table + +@node Bit-Fields +@section Bit-Fields +@cindex bit-fields + +Special expression codes exist to represent bit-field instructions. +These types of expressions are lvalues in RTL; they may appear +on the left side of an assignment, indicating insertion of a value +into the specified bit-field. + +@table @code +@findex sign_extract +@cindex @code{BITS_BIG_ENDIAN}, effect on @code{sign_extract} +@item (sign_extract:@var{m} @var{loc} @var{size} @var{pos}) +This represents a reference to a sign-extended bit-field contained or +starting in @var{loc} (a memory or register reference). The bit-field +is @var{size} bits wide and starts at bit @var{pos}. The compilation +option @code{BITS_BIG_ENDIAN} says which end of the memory unit +@var{pos} counts from. + +If @var{loc} is in memory, its mode must be a single-byte integer mode. +If @var{loc} is in a register, the mode to use is specified by the +operand of the @code{insv} or @code{extv} pattern +(@pxref{Standard Names}) and is usually a full-word integer mode, +which is the default if none is specified. + +The mode of @var{pos} is machine-specific and is also specified +in the @code{insv} or @code{extv} pattern. + +The mode @var{m} is the same as the mode that would be used for +@var{loc} if it were a register. + +@findex zero_extract +@item (zero_extract:@var{m} @var{loc} @var{size} @var{pos}) +Like @code{sign_extract} but refers to an unsigned or zero-extended +bit-field. The same sequence of bits are extracted, but they +are filled to an entire word with zeros instead of by sign-extension. +@end table + +@node Vector Operations +@section Vector Operations +@cindex vector operations + +All normal RTL expressions can be used with vector modes; they are +interpreted as operating on each part of the vector independently. +Additionally, there are a few new expressions to describe specific vector +operations. + +@table @code +@findex vec_merge +@item (vec_merge:@var{m} @var{vec1} @var{vec2} @var{items}) +This describes a merge operation between two vectors. The result is a vector +of mode @var{m}; its elements are selected from either @var{vec1} or +@var{vec2}. Which elements are selected is described by @var{items}, which +is a bit mask represented by a @code{const_int}; a zero bit indicates the +corresponding element in the result vector is taken from @var{vec2} while +a set bit indicates it is taken from @var{vec1}. + +@findex vec_select +@item (vec_select:@var{m} @var{vec1} @var{selection}) +This describes an operation that selects parts of a vector. @var{vec1} is +the source vector, @var{selection} is a @code{parallel} that contains a +@code{const_int} for each of the subparts of the result vector, giving the +number of the source subpart that should be stored into it. + +@findex vec_concat +@item (vec_concat:@var{m} @var{vec1} @var{vec2}) +Describes a vector concat operation. The result is a concatenation of the +vectors @var{vec1} and @var{vec2}; its length is the sum of the lengths of +the two inputs. + +@findex vec_const +@item (vec_const:@var{m} @var{subparts}) +This describes a constant vector. @var{subparts} is a @code{parallel} that +contains a constant for each of the subparts of the vector. + +@findex vec_duplicate +@item (vec_duplicate:@var{m} @var{vec}) +This operation converts a small vector into a larger one by duplicating the +input values. The output vector mode must have the same submodes as the +input vector mode, and the number of output parts must be an integer multiple +of the number of input parts. + +@end table + +@node Conversions +@section Conversions +@cindex conversions +@cindex machine mode conversions + +All conversions between machine modes must be represented by +explicit conversion operations. For example, an expression +which is the sum of a byte and a full word cannot be written as +@code{(plus:SI (reg:QI 34) (reg:SI 80))} because the @code{plus} +operation requires two operands of the same machine mode. +Therefore, the byte-sized operand is enclosed in a conversion +operation, as in + +@example +(plus:SI (sign_extend:SI (reg:QI 34)) (reg:SI 80)) +@end example + +The conversion operation is not a mere placeholder, because there +may be more than one way of converting from a given starting mode +to the desired final mode. The conversion operation code says how +to do it. + +For all conversion operations, @var{x} must not be @code{VOIDmode} +because the mode in which to do the conversion would not be known. +The conversion must either be done at compile-time or @var{x} +must be placed into a register. + +@table @code +@findex sign_extend +@item (sign_extend:@var{m} @var{x}) +Represents the result of sign-extending the value @var{x} +to machine mode @var{m}. @var{m} must be a fixed-point mode +and @var{x} a fixed-point value of a mode narrower than @var{m}. + +@findex zero_extend +@item (zero_extend:@var{m} @var{x}) +Represents the result of zero-extending the value @var{x} +to machine mode @var{m}. @var{m} must be a fixed-point mode +and @var{x} a fixed-point value of a mode narrower than @var{m}. + +@findex float_extend +@item (float_extend:@var{m} @var{x}) +Represents the result of extending the value @var{x} +to machine mode @var{m}. @var{m} must be a floating point mode +and @var{x} a floating point value of a mode narrower than @var{m}. + +@findex truncate +@item (truncate:@var{m} @var{x}) +Represents the result of truncating the value @var{x} +to machine mode @var{m}. @var{m} must be a fixed-point mode +and @var{x} a fixed-point value of a mode wider than @var{m}. + +@findex ss_truncate +@item (ss_truncate:@var{m} @var{x}) +Represents the result of truncating the value @var{x} +to machine mode @var{m}, using signed saturation in the case of +overflow. Both @var{m} and the mode of @var{x} must be fixed-point +modes. + +@findex us_truncate +@item (us_truncate:@var{m} @var{x}) +Represents the result of truncating the value @var{x} +to machine mode @var{m}, using unsigned saturation in the case of +overflow. Both @var{m} and the mode of @var{x} must be fixed-point +modes. + +@findex float_truncate +@item (float_truncate:@var{m} @var{x}) +Represents the result of truncating the value @var{x} +to machine mode @var{m}. @var{m} must be a floating point mode +and @var{x} a floating point value of a mode wider than @var{m}. + +@findex float +@item (float:@var{m} @var{x}) +Represents the result of converting fixed point value @var{x}, +regarded as signed, to floating point mode @var{m}. + +@findex unsigned_float +@item (unsigned_float:@var{m} @var{x}) +Represents the result of converting fixed point value @var{x}, +regarded as unsigned, to floating point mode @var{m}. + +@findex fix +@item (fix:@var{m} @var{x}) +When @var{m} is a fixed point mode, represents the result of +converting floating point value @var{x} to mode @var{m}, regarded as +signed. How rounding is done is not specified, so this operation may +be used validly in compiling C code only for integer-valued operands. + +@findex unsigned_fix +@item (unsigned_fix:@var{m} @var{x}) +Represents the result of converting floating point value @var{x} to +fixed point mode @var{m}, regarded as unsigned. How rounding is done +is not specified. + +@findex fix +@item (fix:@var{m} @var{x}) +When @var{m} is a floating point mode, represents the result of +converting floating point value @var{x} (valid for mode @var{m}) to an +integer, still represented in floating point mode @var{m}, by rounding +towards zero. +@end table + +@node RTL Declarations +@section Declarations +@cindex RTL declarations +@cindex declarations, RTL + +Declaration expression codes do not represent arithmetic operations +but rather state assertions about their operands. + +@table @code +@findex strict_low_part +@cindex @code{subreg}, in @code{strict_low_part} +@item (strict_low_part (subreg:@var{m} (reg:@var{n} @var{r}) 0)) +This expression code is used in only one context: as the destination operand of a +@code{set} expression. In addition, the operand of this expression +must be a non-paradoxical @code{subreg} expression. + +The presence of @code{strict_low_part} says that the part of the +register which is meaningful in mode @var{n}, but is not part of +mode @var{m}, is not to be altered. Normally, an assignment to such +a subreg is allowed to have undefined effects on the rest of the +register when @var{m} is less than a word. +@end table + +@node Side Effects +@section Side Effect Expressions +@cindex RTL side effect expressions + +The expression codes described so far represent values, not actions. +But machine instructions never produce values; they are meaningful +only for their side effects on the state of the machine. Special +expression codes are used to represent side effects. + +The body of an instruction is always one of these side effect codes; +the codes described above, which represent values, appear only as +the operands of these. + +@table @code +@findex set +@item (set @var{lval} @var{x}) +Represents the action of storing the value of @var{x} into the place +represented by @var{lval}. @var{lval} must be an expression +representing a place that can be stored in: @code{reg} (or @code{subreg} +or @code{strict_low_part}), @code{mem}, @code{pc}, @code{parallel}, or +@code{cc0}. + +If @var{lval} is a @code{reg}, @code{subreg} or @code{mem}, it has a +machine mode; then @var{x} must be valid for that mode. + +If @var{lval} is a @code{reg} whose machine mode is less than the full +width of the register, then it means that the part of the register +specified by the machine mode is given the specified value and the +rest of the register receives an undefined value. Likewise, if +@var{lval} is a @code{subreg} whose machine mode is narrower than +the mode of the register, the rest of the register can be changed in +an undefined way. + +If @var{lval} is a @code{strict_low_part} of a @code{subreg}, then the +part of the register specified by the machine mode of the +@code{subreg} is given the value @var{x} and the rest of the register +is not changed. + +If @var{lval} is @code{(cc0)}, it has no machine mode, and @var{x} may +be either a @code{compare} expression or a value that may have any mode. +The latter case represents a ``test'' instruction. The expression +@code{(set (cc0) (reg:@var{m} @var{n}))} is equivalent to +@code{(set (cc0) (compare (reg:@var{m} @var{n}) (const_int 0)))}. +Use the former expression to save space during the compilation. + +If @var{lval} is a @code{parallel}, it is used to represent the case of +a function returning a structure in multiple registers. Each element +of the @code{parallel} is an @code{expr_list} whose first operand is a +@code{reg} and whose second operand is a @code{const_int} representing the +offset (in bytes) into the structure at which the data in that register +corresponds. The first element may be null to indicate that the structure +is also passed partly in memory. + +@cindex jump instructions and @code{set} +@cindex @code{if_then_else} usage +If @var{lval} is @code{(pc)}, we have a jump instruction, and the +possibilities for @var{x} are very limited. It may be a +@code{label_ref} expression (unconditional jump). It may be an +@code{if_then_else} (conditional jump), in which case either the +second or the third operand must be @code{(pc)} (for the case which +does not jump) and the other of the two must be a @code{label_ref} +(for the case which does jump). @var{x} may also be a @code{mem} or +@code{(plus:SI (pc) @var{y})}, where @var{y} may be a @code{reg} or a +@code{mem}; these unusual patterns are used to represent jumps through +branch tables. + +If @var{lval} is neither @code{(cc0)} nor @code{(pc)}, the mode of +@var{lval} must not be @code{VOIDmode} and the mode of @var{x} must be +valid for the mode of @var{lval}. + +@findex SET_DEST +@findex SET_SRC +@var{lval} is customarily accessed with the @code{SET_DEST} macro and +@var{x} with the @code{SET_SRC} macro. + +@findex return +@item (return) +As the sole expression in a pattern, represents a return from the +current function, on machines where this can be done with one +instruction, such as VAXen. On machines where a multi-instruction +``epilogue'' must be executed in order to return from the function, +returning is done by jumping to a label which precedes the epilogue, and +the @code{return} expression code is never used. + +Inside an @code{if_then_else} expression, represents the value to be +placed in @code{pc} to return to the caller. + +Note that an insn pattern of @code{(return)} is logically equivalent to +@code{(set (pc) (return))}, but the latter form is never used. + +@findex call +@item (call @var{function} @var{nargs}) +Represents a function call. @var{function} is a @code{mem} expression +whose address is the address of the function to be called. +@var{nargs} is an expression which can be used for two purposes: on +some machines it represents the number of bytes of stack argument; on +others, it represents the number of argument registers. + +Each machine has a standard machine mode which @var{function} must +have. The machine description defines macro @code{FUNCTION_MODE} to +expand into the requisite mode name. The purpose of this mode is to +specify what kind of addressing is allowed, on machines where the +allowed kinds of addressing depend on the machine mode being +addressed. + +@findex clobber +@item (clobber @var{x}) +Represents the storing or possible storing of an unpredictable, +undescribed value into @var{x}, which must be a @code{reg}, +@code{scratch}, @code{parallel} or @code{mem} expression. + +One place this is used is in string instructions that store standard +values into particular hard registers. It may not be worth the +trouble to describe the values that are stored, but it is essential to +inform the compiler that the registers will be altered, lest it +attempt to keep data in them across the string instruction. + +If @var{x} is @code{(mem:BLK (const_int 0))}, it means that all memory +locations must be presumed clobbered. If @var{x} is a @code{parallel}, +it has the same meaning as a @code{parallel} in a @code{set} expression. + +Note that the machine description classifies certain hard registers as +``call-clobbered''. All function call instructions are assumed by +default to clobber these registers, so there is no need to use +@code{clobber} expressions to indicate this fact. Also, each function +call is assumed to have the potential to alter any memory location, +unless the function is declared @code{const}. + +If the last group of expressions in a @code{parallel} are each a +@code{clobber} expression whose arguments are @code{reg} or +@code{match_scratch} (@pxref{RTL Template}) expressions, the combiner +phase can add the appropriate @code{clobber} expressions to an insn it +has constructed when doing so will cause a pattern to be matched. + +This feature can be used, for example, on a machine that whose multiply +and add instructions don't use an MQ register but which has an +add-accumulate instruction that does clobber the MQ register. Similarly, +a combined instruction might require a temporary register while the +constituent instructions might not. + +When a @code{clobber} expression for a register appears inside a +@code{parallel} with other side effects, the register allocator +guarantees that the register is unoccupied both before and after that +insn. However, the reload phase may allocate a register used for one of +the inputs unless the @samp{&} constraint is specified for the selected +alternative (@pxref{Modifiers}). You can clobber either a specific hard +register, a pseudo register, or a @code{scratch} expression; in the +latter two cases, GCC will allocate a hard register that is available +there for use as a temporary. + +For instructions that require a temporary register, you should use +@code{scratch} instead of a pseudo-register because this will allow the +combiner phase to add the @code{clobber} when required. You do this by +coding (@code{clobber} (@code{match_scratch} @dots{})). If you do +clobber a pseudo register, use one which appears nowhere else---generate +a new one each time. Otherwise, you may confuse CSE@. + +There is one other known use for clobbering a pseudo register in a +@code{parallel}: when one of the input operands of the insn is also +clobbered by the insn. In this case, using the same pseudo register in +the clobber and elsewhere in the insn produces the expected results. + +@findex use +@item (use @var{x}) +Represents the use of the value of @var{x}. It indicates that the +value in @var{x} at this point in the program is needed, even though +it may not be apparent why this is so. Therefore, the compiler will +not attempt to delete previous instructions whose only effect is to +store a value in @var{x}. @var{x} must be a @code{reg} expression. + +In some situations, it may be tempting to add a @code{use} of a +register in a @code{parallel} to describe a situation where the value +of a special register will modify the behavior of the instruction. +An hypothetical example might be a pattern for an addition that can +either wrap around or use saturating addition depending on the value +of a special control register: + +@example +(parallel [(set (reg:SI 2) (unspec:SI [(reg:SI 3) + (reg:SI 4)] 0)) + (use (reg:SI 1))]) +@end example + +@noindent + +This will not work, several of the optimizers only look at expressions +locally; it is very likely that if you have multiple insns with +identical inputs to the @code{unspec}, they will be optimized away even +if register 1 changes in between. + +This means that @code{use} can @emph{only} be used to describe +that the register is live. You should think twice before adding +@code{use} statements, more often you will want to use @code{unspec} +instead. The @code{use} RTX is most commonly useful to describe that +a fixed register is implicitly used in an insn. It is also safe to use +in patterns where the compiler knows for other reasons that the result +of the whole pattern is variable, such as @samp{movstr@var{m}} or +@samp{call} patterns. + +During the reload phase, an insn that has a @code{use} as pattern +can carry a reg_equal note. These @code{use} insns will be deleted +before the reload phase exits. + +During the delayed branch scheduling phase, @var{x} may be an insn. +This indicates that @var{x} previously was located at this place in the +code and its data dependencies need to be taken into account. These +@code{use} insns will be deleted before the delayed branch scheduling +phase exits. + +@findex parallel +@item (parallel [@var{x0} @var{x1} @dots{}]) +Represents several side effects performed in parallel. The square +brackets stand for a vector; the operand of @code{parallel} is a +vector of expressions. @var{x0}, @var{x1} and so on are individual +side effect expressions---expressions of code @code{set}, @code{call}, +@code{return}, @code{clobber} or @code{use}. + +``In parallel'' means that first all the values used in the individual +side-effects are computed, and second all the actual side-effects are +performed. For example, + +@example +(parallel [(set (reg:SI 1) (mem:SI (reg:SI 1))) + (set (mem:SI (reg:SI 1)) (reg:SI 1))]) +@end example + +@noindent +says unambiguously that the values of hard register 1 and the memory +location addressed by it are interchanged. In both places where +@code{(reg:SI 1)} appears as a memory address it refers to the value +in register 1 @emph{before} the execution of the insn. + +It follows that it is @emph{incorrect} to use @code{parallel} and +expect the result of one @code{set} to be available for the next one. +For example, people sometimes attempt to represent a jump-if-zero +instruction this way: + +@example +(parallel [(set (cc0) (reg:SI 34)) + (set (pc) (if_then_else + (eq (cc0) (const_int 0)) + (label_ref @dots{}) + (pc)))]) +@end example + +@noindent +But this is incorrect, because it says that the jump condition depends +on the condition code value @emph{before} this instruction, not on the +new value that is set by this instruction. + +@cindex peephole optimization, RTL representation +Peephole optimization, which takes place together with final assembly +code output, can produce insns whose patterns consist of a @code{parallel} +whose elements are the operands needed to output the resulting +assembler code---often @code{reg}, @code{mem} or constant expressions. +This would not be well-formed RTL at any other stage in compilation, +but it is ok then because no further optimization remains to be done. +However, the definition of the macro @code{NOTICE_UPDATE_CC}, if +any, must deal with such insns if you define any peephole optimizations. + +@findex cond_exec +@item (cond_exec [@var{cond} @var{expr}]) +Represents a conditionally executed expression. The @var{expr} is +executed only if the @var{cond} is nonzero. The @var{cond} expression +must not have side-effects, but the @var{expr} may very well have +side-effects. + +@findex sequence +@item (sequence [@var{insns} @dots{}]) +Represents a sequence of insns. Each of the @var{insns} that appears +in the vector is suitable for appearing in the chain of insns, so it +must be an @code{insn}, @code{jump_insn}, @code{call_insn}, +@code{code_label}, @code{barrier} or @code{note}. + +A @code{sequence} RTX is never placed in an actual insn during RTL +generation. It represents the sequence of insns that result from a +@code{define_expand} @emph{before} those insns are passed to +@code{emit_insn} to insert them in the chain of insns. When actually +inserted, the individual sub-insns are separated out and the +@code{sequence} is forgotten. + +After delay-slot scheduling is completed, an insn and all the insns that +reside in its delay slots are grouped together into a @code{sequence}. +The insn requiring the delay slot is the first insn in the vector; +subsequent insns are to be placed in the delay slot. + +@code{INSN_ANNULLED_BRANCH_P} is set on an insn in a delay slot to +indicate that a branch insn should be used that will conditionally annul +the effect of the insns in the delay slots. In such a case, +@code{INSN_FROM_TARGET_P} indicates that the insn is from the target of +the branch and should be executed only if the branch is taken; otherwise +the insn should be executed only if the branch is not taken. +@xref{Delay Slots}. +@end table + +These expression codes appear in place of a side effect, as the body of +an insn, though strictly speaking they do not always describe side +effects as such: + +@table @code +@findex asm_input +@item (asm_input @var{s}) +Represents literal assembler code as described by the string @var{s}. + +@findex unspec +@findex unspec_volatile +@item (unspec [@var{operands} @dots{}] @var{index}) +@itemx (unspec_volatile [@var{operands} @dots{}] @var{index}) +Represents a machine-specific operation on @var{operands}. @var{index} +selects between multiple machine-specific operations. +@code{unspec_volatile} is used for volatile operations and operations +that may trap; @code{unspec} is used for other operations. + +These codes may appear inside a @code{pattern} of an +insn, inside a @code{parallel}, or inside an expression. + +@findex addr_vec +@item (addr_vec:@var{m} [@var{lr0} @var{lr1} @dots{}]) +Represents a table of jump addresses. The vector elements @var{lr0}, +etc., are @code{label_ref} expressions. The mode @var{m} specifies +how much space is given to each address; normally @var{m} would be +@code{Pmode}. + +@findex addr_diff_vec +@item (addr_diff_vec:@var{m} @var{base} [@var{lr0} @var{lr1} @dots{}] @var{min} @var{max} @var{flags}) +Represents a table of jump addresses expressed as offsets from +@var{base}. The vector elements @var{lr0}, etc., are @code{label_ref} +expressions and so is @var{base}. The mode @var{m} specifies how much +space is given to each address-difference. @var{min} and @var{max} +are set up by branch shortening and hold a label with a minimum and a +maximum address, respectively. @var{flags} indicates the relative +position of @var{base}, @var{min} and @var{max} to the containing insn +and of @var{min} and @var{max} to @var{base}. See rtl.def for details. + +@findex prefetch +@item (prefetch:@var{m} @var{addr} @var{rw} @var{locality}) +Represents prefetch of memory at address @var{addr}. +Operand @var{rw} is 1 if the prefetch is for data to be written, 0 otherwise; +targets that do not support write prefetches should treat this as a normal +prefetch. +Operand @var{locality} specifies the amount of temporal locality; 0 if there +is none or 1, 2, or 3 for increasing levels of temporal locality; +targets that do not support locality hints should ignore this. + +This insn is used to minimize cache-miss latency by moving data into a +cache before it is accessed. It should use only non-faulting data prefetch +instructions. +@end table + +@node Incdec +@section Embedded Side-Effects on Addresses +@cindex RTL preincrement +@cindex RTL postincrement +@cindex RTL predecrement +@cindex RTL postdecrement + +Six special side-effect expression codes appear as memory addresses. + +@table @code +@findex pre_dec +@item (pre_dec:@var{m} @var{x}) +Represents the side effect of decrementing @var{x} by a standard +amount and represents also the value that @var{x} has after being +decremented. @var{x} must be a @code{reg} or @code{mem}, but most +machines allow only a @code{reg}. @var{m} must be the machine mode +for pointers on the machine in use. The amount @var{x} is decremented +by is the length in bytes of the machine mode of the containing memory +reference of which this expression serves as the address. Here is an +example of its use: + +@example +(mem:DF (pre_dec:SI (reg:SI 39))) +@end example + +@noindent +This says to decrement pseudo register 39 by the length of a @code{DFmode} +value and use the result to address a @code{DFmode} value. + +@findex pre_inc +@item (pre_inc:@var{m} @var{x}) +Similar, but specifies incrementing @var{x} instead of decrementing it. + +@findex post_dec +@item (post_dec:@var{m} @var{x}) +Represents the same side effect as @code{pre_dec} but a different +value. The value represented here is the value @var{x} has @i{before} +being decremented. + +@findex post_inc +@item (post_inc:@var{m} @var{x}) +Similar, but specifies incrementing @var{x} instead of decrementing it. + +@findex post_modify +@item (post_modify:@var{m} @var{x} @var{y}) + +Represents the side effect of setting @var{x} to @var{y} and +represents @var{x} before @var{x} is modified. @var{x} must be a +@code{reg} or @code{mem}, but most machines allow only a @code{reg}. +@var{m} must be the machine mode for pointers on the machine in use. +The amount @var{x} is decremented by is the length in bytes of the +machine mode of the containing memory reference of which this expression +serves as the address. Note that this is not currently implemented. + +The expression @var{y} must be one of three forms: +@table @code +@code{(plus:@var{m} @var{x} @var{z})}, +@code{(minus:@var{m} @var{x} @var{z})}, or +@code{(plus:@var{m} @var{x} @var{i})}, +@end table +where @var{z} is an index register and @var{i} is a constant. + +Here is an example of its use: + +@example +(mem:SF (post_modify:SI (reg:SI 42) (plus (reg:SI 42) + (reg:SI 48)))) +@end example + +This says to modify pseudo register 42 by adding the contents of pseudo +register 48 to it, after the use of what ever 42 points to. + +@findex post_modify +@item (pre_modify:@var{m} @var{x} @var{expr}) +Similar except side effects happen before the use. +@end table + +These embedded side effect expressions must be used with care. Instruction +patterns may not use them. Until the @samp{flow} pass of the compiler, +they may occur only to represent pushes onto the stack. The @samp{flow} +pass finds cases where registers are incremented or decremented in one +instruction and used as an address shortly before or after; these cases are +then transformed to use pre- or post-increment or -decrement. + +If a register used as the operand of these expressions is used in +another address in an insn, the original value of the register is used. +Uses of the register outside of an address are not permitted within the +same insn as a use in an embedded side effect expression because such +insns behave differently on different machines and hence must be treated +as ambiguous and disallowed. + +An instruction that can be represented with an embedded side effect +could also be represented using @code{parallel} containing an additional +@code{set} to describe how the address register is altered. This is not +done because machines that allow these operations at all typically +allow them wherever a memory address is called for. Describing them as +additional parallel stores would require doubling the number of entries +in the machine description. + +@node Assembler +@section Assembler Instructions as Expressions +@cindex assembler instructions in RTL + +@cindex @code{asm_operands}, usage +The RTX code @code{asm_operands} represents a value produced by a +user-specified assembler instruction. It is used to represent +an @code{asm} statement with arguments. An @code{asm} statement with +a single output operand, like this: + +@smallexample +asm ("foo %1,%2,%0" : "=a" (outputvar) : "g" (x + y), "di" (*z)); +@end smallexample + +@noindent +is represented using a single @code{asm_operands} RTX which represents +the value that is stored in @code{outputvar}: + +@smallexample +(set @var{rtx-for-outputvar} + (asm_operands "foo %1,%2,%0" "a" 0 + [@var{rtx-for-addition-result} @var{rtx-for-*z}] + [(asm_input:@var{m1} "g") + (asm_input:@var{m2} "di")])) +@end smallexample + +@noindent +Here the operands of the @code{asm_operands} RTX are the assembler +template string, the output-operand's constraint, the index-number of the +output operand among the output operands specified, a vector of input +operand RTX's, and a vector of input-operand modes and constraints. The +mode @var{m1} is the mode of the sum @code{x+y}; @var{m2} is that of +@code{*z}. + +When an @code{asm} statement has multiple output values, its insn has +several such @code{set} RTX's inside of a @code{parallel}. Each @code{set} +contains a @code{asm_operands}; all of these share the same assembler +template and vectors, but each contains the constraint for the respective +output operand. They are also distinguished by the output-operand index +number, which is 0, 1, @dots{} for successive output operands. + +@node Insns +@section Insns +@cindex insns + +The RTL representation of the code for a function is a doubly-linked +chain of objects called @dfn{insns}. Insns are expressions with +special codes that are used for no other purpose. Some insns are +actual instructions; others represent dispatch tables for @code{switch} +statements; others represent labels to jump to or various sorts of +declarative information. + +In addition to its own specific data, each insn must have a unique +id-number that distinguishes it from all other insns in the current +function (after delayed branch scheduling, copies of an insn with the +same id-number may be present in multiple places in a function, but +these copies will always be identical and will only appear inside a +@code{sequence}), and chain pointers to the preceding and following +insns. These three fields occupy the same position in every insn, +independent of the expression code of the insn. They could be accessed +with @code{XEXP} and @code{XINT}, but instead three special macros are +always used: + +@table @code +@findex INSN_UID +@item INSN_UID (@var{i}) +Accesses the unique id of insn @var{i}. + +@findex PREV_INSN +@item PREV_INSN (@var{i}) +Accesses the chain pointer to the insn preceding @var{i}. +If @var{i} is the first insn, this is a null pointer. + +@findex NEXT_INSN +@item NEXT_INSN (@var{i}) +Accesses the chain pointer to the insn following @var{i}. +If @var{i} is the last insn, this is a null pointer. +@end table + +@findex get_insns +@findex get_last_insn +The first insn in the chain is obtained by calling @code{get_insns}; the +last insn is the result of calling @code{get_last_insn}. Within the +chain delimited by these insns, the @code{NEXT_INSN} and +@code{PREV_INSN} pointers must always correspond: if @var{insn} is not +the first insn, + +@example +NEXT_INSN (PREV_INSN (@var{insn})) == @var{insn} +@end example + +@noindent +is always true and if @var{insn} is not the last insn, + +@example +PREV_INSN (NEXT_INSN (@var{insn})) == @var{insn} +@end example + +@noindent +is always true. + +After delay slot scheduling, some of the insns in the chain might be +@code{sequence} expressions, which contain a vector of insns. The value +of @code{NEXT_INSN} in all but the last of these insns is the next insn +in the vector; the value of @code{NEXT_INSN} of the last insn in the vector +is the same as the value of @code{NEXT_INSN} for the @code{sequence} in +which it is contained. Similar rules apply for @code{PREV_INSN}. + +This means that the above invariants are not necessarily true for insns +inside @code{sequence} expressions. Specifically, if @var{insn} is the +first insn in a @code{sequence}, @code{NEXT_INSN (PREV_INSN (@var{insn}))} +is the insn containing the @code{sequence} expression, as is the value +of @code{PREV_INSN (NEXT_INSN (@var{insn}))} if @var{insn} is the last +insn in the @code{sequence} expression. You can use these expressions +to find the containing @code{sequence} expression. + +Every insn has one of the following six expression codes: + +@table @code +@findex insn +@item insn +The expression code @code{insn} is used for instructions that do not jump +and do not do function calls. @code{sequence} expressions are always +contained in insns with code @code{insn} even if one of those insns +should jump or do function calls. + +Insns with code @code{insn} have four additional fields beyond the three +mandatory ones listed above. These four are described in a table below. + +@findex jump_insn +@item jump_insn +The expression code @code{jump_insn} is used for instructions that may +jump (or, more generally, may contain @code{label_ref} expressions). If +there is an instruction to return from the current function, it is +recorded as a @code{jump_insn}. + +@findex JUMP_LABEL +@code{jump_insn} insns have the same extra fields as @code{insn} insns, +accessed in the same way and in addition contain a field +@code{JUMP_LABEL} which is defined once jump optimization has completed. + +For simple conditional and unconditional jumps, this field contains +the @code{code_label} to which this insn will (possibly conditionally) +branch. In a more complex jump, @code{JUMP_LABEL} records one of the +labels that the insn refers to; the only way to find the others is to +scan the entire body of the insn. In an @code{addr_vec}, +@code{JUMP_LABEL} is @code{NULL_RTX}. + +Return insns count as jumps, but since they do not refer to any +labels, their @code{JUMP_LABEL} is @code{NULL_RTX}. + +@findex call_insn +@item call_insn +The expression code @code{call_insn} is used for instructions that may do +function calls. It is important to distinguish these instructions because +they imply that certain registers and memory locations may be altered +unpredictably. + +@findex CALL_INSN_FUNCTION_USAGE +@code{call_insn} insns have the same extra fields as @code{insn} insns, +accessed in the same way and in addition contain a field +@code{CALL_INSN_FUNCTION_USAGE}, which contains a list (chain of +@code{expr_list} expressions) containing @code{use} and @code{clobber} +expressions that denote hard registers and @code{MEM}s used or +clobbered by the called function. + +A @code{MEM} generally points to a stack slots in which arguments passed +to the libcall by reference (@pxref{Register Arguments, +FUNCTION_ARG_PASS_BY_REFERENCE}) are stored. If the argument is +caller-copied (@pxref{Register Arguments, FUNCTION_ARG_CALLEE_COPIES}), +the stack slot will be mentioned in @code{CLOBBER} and @code{USE} +entries; if it's callee-copied, only a @code{USE} will appear, and the +@code{MEM} may point to addresses that are not stack slots. These +@code{MEM}s are used only in libcalls, because, unlike regular function +calls, @code{CONST_CALL}s (which libcalls generally are, @pxref{Flags, +CONST_CALL_P}) aren't assumed to read and write all memory, so flow +would consider the stores dead and remove them. Note that, since a +libcall must never return values in memory (@pxref{Aggregate Return, +RETURN_IN_MEMORY}), there will never be a @code{CLOBBER} for a memory +address holding a return value. + +@code{CLOBBER}ed registers in this list augment registers specified in +@code{CALL_USED_REGISTERS} (@pxref{Register Basics}). + +@findex code_label +@findex CODE_LABEL_NUMBER +@item code_label +A @code{code_label} insn represents a label that a jump insn can jump +to. It contains two special fields of data in addition to the three +standard ones. @code{CODE_LABEL_NUMBER} is used to hold the @dfn{label +number}, a number that identifies this label uniquely among all the +labels in the compilation (not just in the current function). +Ultimately, the label is represented in the assembler output as an +assembler label, usually of the form @samp{L@var{n}} where @var{n} is +the label number. + +When a @code{code_label} appears in an RTL expression, it normally +appears within a @code{label_ref} which represents the address of +the label, as a number. + +Besides as a @code{code_label}, a label can also be represented as a +@code{note} of type @code{NOTE_INSN_DELETED_LABEL}. + +@findex LABEL_NUSES +The field @code{LABEL_NUSES} is only defined once the jump optimization +phase is completed and contains the number of times this label is +referenced in the current function. + +@findex LABEL_ALTERNATE_NAME +The field @code{LABEL_ALTERNATE_NAME} is used to associate a name with +a @code{code_label}. If this field is defined, the alternate name will +be emitted instead of an internally generated label name. + +@findex barrier +@item barrier +Barriers are placed in the instruction stream when control cannot flow +past them. They are placed after unconditional jump instructions to +indicate that the jumps are unconditional and after calls to +@code{volatile} functions, which do not return (e.g., @code{exit}). +They contain no information beyond the three standard fields. + +@findex note +@findex NOTE_LINE_NUMBER +@findex NOTE_SOURCE_FILE +@item note +@code{note} insns are used to represent additional debugging and +declarative information. They contain two nonstandard fields, an +integer which is accessed with the macro @code{NOTE_LINE_NUMBER} and a +string accessed with @code{NOTE_SOURCE_FILE}. + +If @code{NOTE_LINE_NUMBER} is positive, the note represents the +position of a source line and @code{NOTE_SOURCE_FILE} is the source file name +that the line came from. These notes control generation of line +number data in the assembler output. + +Otherwise, @code{NOTE_LINE_NUMBER} is not really a line number but a +code with one of the following values (and @code{NOTE_SOURCE_FILE} +must contain a null pointer): + +@table @code +@findex NOTE_INSN_DELETED +@item NOTE_INSN_DELETED +Such a note is completely ignorable. Some passes of the compiler +delete insns by altering them into notes of this kind. + +@findex NOTE_INSN_DELETED_LABEL +@item NOTE_INSN_DELETED_LABEL +This marks what used to be a @code{code_label}, but was not used for other +purposes than taking its address and was transformed to mark that no +code jumps to it. + +@findex NOTE_INSN_BLOCK_BEG +@findex NOTE_INSN_BLOCK_END +@item NOTE_INSN_BLOCK_BEG +@itemx NOTE_INSN_BLOCK_END +These types of notes indicate the position of the beginning and end +of a level of scoping of variable names. They control the output +of debugging information. + +@findex NOTE_INSN_EH_REGION_BEG +@findex NOTE_INSN_EH_REGION_END +@item NOTE_INSN_EH_REGION_BEG +@itemx NOTE_INSN_EH_REGION_END +These types of notes indicate the position of the beginning and end of a +level of scoping for exception handling. @code{NOTE_BLOCK_NUMBER} +identifies which @code{CODE_LABEL} or @code{note} of type +@code{NOTE_INSN_DELETED_LABEL} is associated with the given region. + +@findex NOTE_INSN_LOOP_BEG +@findex NOTE_INSN_LOOP_END +@item NOTE_INSN_LOOP_BEG +@itemx NOTE_INSN_LOOP_END +These types of notes indicate the position of the beginning and end +of a @code{while} or @code{for} loop. They enable the loop optimizer +to find loops quickly. + +@findex NOTE_INSN_LOOP_CONT +@item NOTE_INSN_LOOP_CONT +Appears at the place in a loop that @code{continue} statements jump to. + +@findex NOTE_INSN_LOOP_VTOP +@item NOTE_INSN_LOOP_VTOP +This note indicates the place in a loop where the exit test begins for +those loops in which the exit test has been duplicated. This position +becomes another virtual start of the loop when considering loop +invariants. + +@findex NOTE_INSN_FUNCTION_END +@item NOTE_INSN_FUNCTION_END +Appears near the end of the function body, just before the label that +@code{return} statements jump to (on machine where a single instruction +does not suffice for returning). This note may be deleted by jump +optimization. + +@findex NOTE_INSN_SETJMP +@item NOTE_INSN_SETJMP +Appears following each call to @code{setjmp} or a related function. +@end table + +These codes are printed symbolically when they appear in debugging dumps. +@end table + +@cindex @code{TImode}, in @code{insn} +@cindex @code{HImode}, in @code{insn} +@cindex @code{QImode}, in @code{insn} +The machine mode of an insn is normally @code{VOIDmode}, but some +phases use the mode for various purposes. + +The common subexpression elimination pass sets the mode of an insn to +@code{QImode} when it is the first insn in a block that has already +been processed. + +The second Haifa scheduling pass, for targets that can multiple issue, +sets the mode of an insn to @code{TImode} when it is believed that the +instruction begins an issue group. That is, when the instruction +cannot issue simultaneously with the previous. This may be relied on +by later passes, in particular machine-dependent reorg. + +Here is a table of the extra fields of @code{insn}, @code{jump_insn} +and @code{call_insn} insns: + +@table @code +@findex PATTERN +@item PATTERN (@var{i}) +An expression for the side effect performed by this insn. This must be +one of the following codes: @code{set}, @code{call}, @code{use}, +@code{clobber}, @code{return}, @code{asm_input}, @code{asm_output}, +@code{addr_vec}, @code{addr_diff_vec}, @code{trap_if}, @code{unspec}, +@code{unspec_volatile}, @code{parallel}, @code{cond_exec}, or @code{sequence}. If it is a @code{parallel}, +each element of the @code{parallel} must be one these codes, except that +@code{parallel} expressions cannot be nested and @code{addr_vec} and +@code{addr_diff_vec} are not permitted inside a @code{parallel} expression. + +@findex INSN_CODE +@item INSN_CODE (@var{i}) +An integer that says which pattern in the machine description matches +this insn, or @minus{}1 if the matching has not yet been attempted. + +Such matching is never attempted and this field remains @minus{}1 on an insn +whose pattern consists of a single @code{use}, @code{clobber}, +@code{asm_input}, @code{addr_vec} or @code{addr_diff_vec} expression. + +@findex asm_noperands +Matching is also never attempted on insns that result from an @code{asm} +statement. These contain at least one @code{asm_operands} expression. +The function @code{asm_noperands} returns a non-negative value for +such insns. + +In the debugging output, this field is printed as a number followed by +a symbolic representation that locates the pattern in the @file{md} +file as some small positive or negative offset from a named pattern. + +@findex LOG_LINKS +@item LOG_LINKS (@var{i}) +A list (chain of @code{insn_list} expressions) giving information about +dependencies between instructions within a basic block. Neither a jump +nor a label may come between the related insns. + +@findex REG_NOTES +@item REG_NOTES (@var{i}) +A list (chain of @code{expr_list} and @code{insn_list} expressions) +giving miscellaneous information about the insn. It is often +information pertaining to the registers used in this insn. +@end table + +The @code{LOG_LINKS} field of an insn is a chain of @code{insn_list} +expressions. Each of these has two operands: the first is an insn, +and the second is another @code{insn_list} expression (the next one in +the chain). The last @code{insn_list} in the chain has a null pointer +as second operand. The significant thing about the chain is which +insns appear in it (as first operands of @code{insn_list} +expressions). Their order is not significant. + +This list is originally set up by the flow analysis pass; it is a null +pointer until then. Flow only adds links for those data dependencies +which can be used for instruction combination. For each insn, the flow +analysis pass adds a link to insns which store into registers values +that are used for the first time in this insn. The instruction +scheduling pass adds extra links so that every dependence will be +represented. Links represent data dependencies, antidependencies and +output dependencies; the machine mode of the link distinguishes these +three types: antidependencies have mode @code{REG_DEP_ANTI}, output +dependencies have mode @code{REG_DEP_OUTPUT}, and data dependencies have +mode @code{VOIDmode}. + +The @code{REG_NOTES} field of an insn is a chain similar to the +@code{LOG_LINKS} field but it includes @code{expr_list} expressions in +addition to @code{insn_list} expressions. There are several kinds of +register notes, which are distinguished by the machine mode, which in a +register note is really understood as being an @code{enum reg_note}. +The first operand @var{op} of the note is data whose meaning depends on +the kind of note. + +@findex REG_NOTE_KIND +@findex PUT_REG_NOTE_KIND +The macro @code{REG_NOTE_KIND (@var{x})} returns the kind of +register note. Its counterpart, the macro @code{PUT_REG_NOTE_KIND +(@var{x}, @var{newkind})} sets the register note type of @var{x} to be +@var{newkind}. + +Register notes are of three classes: They may say something about an +input to an insn, they may say something about an output of an insn, or +they may create a linkage between two insns. There are also a set +of values that are only used in @code{LOG_LINKS}. + +These register notes annotate inputs to an insn: + +@table @code +@findex REG_DEAD +@item REG_DEAD +The value in @var{op} dies in this insn; that is to say, altering the +value immediately after this insn would not affect the future behavior +of the program. + +It does not follow that the register @var{op} has no useful value after +this insn since @var{op} is not necessarily modified by this insn. +Rather, no subsequent instruction uses the contents of @var{op}. + +@findex REG_UNUSED +@item REG_UNUSED +The register @var{op} being set by this insn will not be used in a +subsequent insn. This differs from a @code{REG_DEAD} note, which +indicates that the value in an input will not be used subsequently. +These two notes are independent; both may be present for the same +register. + +@findex REG_INC +@item REG_INC +The register @var{op} is incremented (or decremented; at this level +there is no distinction) by an embedded side effect inside this insn. +This means it appears in a @code{post_inc}, @code{pre_inc}, +@code{post_dec} or @code{pre_dec} expression. + +@findex REG_NONNEG +@item REG_NONNEG +The register @var{op} is known to have a nonnegative value when this +insn is reached. This is used so that decrement and branch until zero +instructions, such as the m68k dbra, can be matched. + +The @code{REG_NONNEG} note is added to insns only if the machine +description has a @samp{decrement_and_branch_until_zero} pattern. + +@findex REG_NO_CONFLICT +@item REG_NO_CONFLICT +This insn does not cause a conflict between @var{op} and the item +being set by this insn even though it might appear that it does. +In other words, if the destination register and @var{op} could +otherwise be assigned the same register, this insn does not +prevent that assignment. + +Insns with this note are usually part of a block that begins with a +@code{clobber} insn specifying a multi-word pseudo register (which will +be the output of the block), a group of insns that each set one word of +the value and have the @code{REG_NO_CONFLICT} note attached, and a final +insn that copies the output to itself with an attached @code{REG_EQUAL} +note giving the expression being computed. This block is encapsulated +with @code{REG_LIBCALL} and @code{REG_RETVAL} notes on the first and +last insns, respectively. + +@findex REG_LABEL +@item REG_LABEL +This insn uses @var{op}, a @code{code_label} or a @code{note} of type +@code{NOTE_INSN_DELETED_LABEL}, but is not a +@code{jump_insn}, or it is a @code{jump_insn} that required the label to +be held in a register. The presence of this note allows jump +optimization to be aware that @var{op} is, in fact, being used, and flow +optimization to build an accurate flow graph. +@end table + +The following notes describe attributes of outputs of an insn: + +@table @code +@findex REG_EQUIV +@findex REG_EQUAL +@item REG_EQUIV +@itemx REG_EQUAL +This note is only valid on an insn that sets only one register and +indicates that that register will be equal to @var{op} at run time; the +scope of this equivalence differs between the two types of notes. The +value which the insn explicitly copies into the register may look +different from @var{op}, but they will be equal at run time. If the +output of the single @code{set} is a @code{strict_low_part} expression, +the note refers to the register that is contained in @code{SUBREG_REG} +of the @code{subreg} expression. + +For @code{REG_EQUIV}, the register is equivalent to @var{op} throughout +the entire function, and could validly be replaced in all its +occurrences by @var{op}. (``Validly'' here refers to the data flow of +the program; simple replacement may make some insns invalid.) For +example, when a constant is loaded into a register that is never +assigned any other value, this kind of note is used. + +When a parameter is copied into a pseudo-register at entry to a function, +a note of this kind records that the register is equivalent to the stack +slot where the parameter was passed. Although in this case the register +may be set by other insns, it is still valid to replace the register +by the stack slot throughout the function. + +A @code{REG_EQUIV} note is also used on an instruction which copies a +register parameter into a pseudo-register at entry to a function, if +there is a stack slot where that parameter could be stored. Although +other insns may set the pseudo-register, it is valid for the compiler to +replace the pseudo-register by stack slot throughout the function, +provided the compiler ensures that the stack slot is properly +initialized by making the replacement in the initial copy instruction as +well. This is used on machines for which the calling convention +allocates stack space for register parameters. See +@code{REG_PARM_STACK_SPACE} in @ref{Stack Arguments}. + +In the case of @code{REG_EQUAL}, the register that is set by this insn +will be equal to @var{op} at run time at the end of this insn but not +necessarily elsewhere in the function. In this case, @var{op} +is typically an arithmetic expression. For example, when a sequence of +insns such as a library call is used to perform an arithmetic operation, +this kind of note is attached to the insn that produces or copies the +final value. + +These two notes are used in different ways by the compiler passes. +@code{REG_EQUAL} is used by passes prior to register allocation (such as +common subexpression elimination and loop optimization) to tell them how +to think of that value. @code{REG_EQUIV} notes are used by register +allocation to indicate that there is an available substitute expression +(either a constant or a @code{mem} expression for the location of a +parameter on the stack) that may be used in place of a register if +insufficient registers are available. + +Except for stack homes for parameters, which are indicated by a +@code{REG_EQUIV} note and are not useful to the early optimization +passes and pseudo registers that are equivalent to a memory location +throughout their entire life, which is not detected until later in +the compilation, all equivalences are initially indicated by an attached +@code{REG_EQUAL} note. In the early stages of register allocation, a +@code{REG_EQUAL} note is changed into a @code{REG_EQUIV} note if +@var{op} is a constant and the insn represents the only set of its +destination register. + +Thus, compiler passes prior to register allocation need only check for +@code{REG_EQUAL} notes and passes subsequent to register allocation +need only check for @code{REG_EQUIV} notes. + +@findex REG_WAS_0 +@item REG_WAS_0 +The single output of this insn contained zero before this insn. +@var{op} is the insn that set it to zero. You can rely on this note if +it is present and @var{op} has not been deleted or turned into a @code{note}; +its absence implies nothing. +@end table + +These notes describe linkages between insns. They occur in pairs: one +insn has one of a pair of notes that points to a second insn, which has +the inverse note pointing back to the first insn. + +@table @code +@findex REG_RETVAL +@item REG_RETVAL +This insn copies the value of a multi-insn sequence (for example, a +library call), and @var{op} is the first insn of the sequence (for a +library call, the first insn that was generated to set up the arguments +for the library call). + +Loop optimization uses this note to treat such a sequence as a single +operation for code motion purposes and flow analysis uses this note to +delete such sequences whose results are dead. + +A @code{REG_EQUAL} note will also usually be attached to this insn to +provide the expression being computed by the sequence. + +These notes will be deleted after reload, since they are no longer +accurate or useful. + +@findex REG_LIBCALL +@item REG_LIBCALL +This is the inverse of @code{REG_RETVAL}: it is placed on the first +insn of a multi-insn sequence, and it points to the last one. + +These notes are deleted after reload, since they are no longer useful or +accurate. + +@findex REG_CC_SETTER +@findex REG_CC_USER +@item REG_CC_SETTER +@itemx REG_CC_USER +On machines that use @code{cc0}, the insns which set and use @code{cc0} +set and use @code{cc0} are adjacent. However, when branch delay slot +filling is done, this may no longer be true. In this case a +@code{REG_CC_USER} note will be placed on the insn setting @code{cc0} to +point to the insn using @code{cc0} and a @code{REG_CC_SETTER} note will +be placed on the insn using @code{cc0} to point to the insn setting +@code{cc0}. +@end table + +These values are only used in the @code{LOG_LINKS} field, and indicate +the type of dependency that each link represents. Links which indicate +a data dependence (a read after write dependence) do not use any code, +they simply have mode @code{VOIDmode}, and are printed without any +descriptive text. + +@table @code +@findex REG_DEP_ANTI +@item REG_DEP_ANTI +This indicates an anti dependence (a write after read dependence). + +@findex REG_DEP_OUTPUT +@item REG_DEP_OUTPUT +This indicates an output dependence (a write after write dependence). +@end table + +These notes describe information gathered from gcov profile data. They +are stored in the @code{REG_NOTES} field of an insn as an +@code{expr_list}. + +@table @code +@findex REG_EXEC_COUNT +@item REG_EXEC_COUNT +This is used to indicate the number of times a basic block was executed +according to the profile data. The note is attached to the first insn in +the basic block. + +@findex REG_BR_PROB +@item REG_BR_PROB +This is used to specify the ratio of branches to non-branches of a +branch insn according to the profile data. The value is stored as a +value between 0 and REG_BR_PROB_BASE; larger values indicate a higher +probability that the branch will be taken. + +@findex REG_BR_PRED +@item REG_BR_PRED +These notes are found in JUMP insns after delayed branch scheduling +has taken place. They indicate both the direction and the likelihood +of the JUMP@. The format is a bitmask of ATTR_FLAG_* values. + +@findex REG_FRAME_RELATED_EXPR +@item REG_FRAME_RELATED_EXPR +This is used on an RTX_FRAME_RELATED_P insn wherein the attached expression +is used in place of the actual insn pattern. This is done in cases where +the pattern is either complex or misleading. +@end table + +For convenience, the machine mode in an @code{insn_list} or +@code{expr_list} is printed using these symbolic codes in debugging dumps. + +@findex insn_list +@findex expr_list +The only difference between the expression codes @code{insn_list} and +@code{expr_list} is that the first operand of an @code{insn_list} is +assumed to be an insn and is printed in debugging dumps as the insn's +unique id; the first operand of an @code{expr_list} is printed in the +ordinary way as an expression. + +@node Calls +@section RTL Representation of Function-Call Insns +@cindex calling functions in RTL +@cindex RTL function-call insns +@cindex function-call insns + +Insns that call subroutines have the RTL expression code @code{call_insn}. +These insns must satisfy special rules, and their bodies must use a special +RTL expression code, @code{call}. + +@cindex @code{call} usage +A @code{call} expression has two operands, as follows: + +@example +(call (mem:@var{fm} @var{addr}) @var{nbytes}) +@end example + +@noindent +Here @var{nbytes} is an operand that represents the number of bytes of +argument data being passed to the subroutine, @var{fm} is a machine mode +(which must equal as the definition of the @code{FUNCTION_MODE} macro in +the machine description) and @var{addr} represents the address of the +subroutine. + +For a subroutine that returns no value, the @code{call} expression as +shown above is the entire body of the insn, except that the insn might +also contain @code{use} or @code{clobber} expressions. + +@cindex @code{BLKmode}, and function return values +For a subroutine that returns a value whose mode is not @code{BLKmode}, +the value is returned in a hard register. If this register's number is +@var{r}, then the body of the call insn looks like this: + +@example +(set (reg:@var{m} @var{r}) + (call (mem:@var{fm} @var{addr}) @var{nbytes})) +@end example + +@noindent +This RTL expression makes it clear (to the optimizer passes) that the +appropriate register receives a useful value in this insn. + +When a subroutine returns a @code{BLKmode} value, it is handled by +passing to the subroutine the address of a place to store the value. +So the call insn itself does not ``return'' any value, and it has the +same RTL form as a call that returns nothing. + +On some machines, the call instruction itself clobbers some register, +for example to contain the return address. @code{call_insn} insns +on these machines should have a body which is a @code{parallel} +that contains both the @code{call} expression and @code{clobber} +expressions that indicate which registers are destroyed. Similarly, +if the call instruction requires some register other than the stack +pointer that is not explicitly mentioned it its RTL, a @code{use} +subexpression should mention that register. + +Functions that are called are assumed to modify all registers listed in +the configuration macro @code{CALL_USED_REGISTERS} (@pxref{Register +Basics}) and, with the exception of @code{const} functions and library +calls, to modify all of memory. + +Insns containing just @code{use} expressions directly precede the +@code{call_insn} insn to indicate which registers contain inputs to the +function. Similarly, if registers other than those in +@code{CALL_USED_REGISTERS} are clobbered by the called function, insns +containing a single @code{clobber} follow immediately after the call to +indicate which registers. + +@node Sharing +@section Structure Sharing Assumptions +@cindex sharing of RTL components +@cindex RTL structure sharing assumptions + +The compiler assumes that certain kinds of RTL expressions are unique; +there do not exist two distinct objects representing the same value. +In other cases, it makes an opposite assumption: that no RTL expression +object of a certain kind appears in more than one place in the +containing structure. + +These assumptions refer to a single function; except for the RTL +objects that describe global variables and external functions, +and a few standard objects such as small integer constants, +no RTL objects are common to two functions. + +@itemize @bullet +@cindex @code{reg}, RTL sharing +@item +Each pseudo-register has only a single @code{reg} object to represent it, +and therefore only a single machine mode. + +@cindex symbolic label +@cindex @code{symbol_ref}, RTL sharing +@item +For any symbolic label, there is only one @code{symbol_ref} object +referring to it. + +@cindex @code{const_int}, RTL sharing +@item +All @code{const_int} expressions with equal values are shared. + +@cindex @code{pc}, RTL sharing +@item +There is only one @code{pc} expression. + +@cindex @code{cc0}, RTL sharing +@item +There is only one @code{cc0} expression. + +@cindex @code{const_double}, RTL sharing +@item +There is only one @code{const_double} expression with value 0 for +each floating point mode. Likewise for values 1 and 2. + +@cindex @code{label_ref}, RTL sharing +@cindex @code{scratch}, RTL sharing +@item +No @code{label_ref} or @code{scratch} appears in more than one place in +the RTL structure; in other words, it is safe to do a tree-walk of all +the insns in the function and assume that each time a @code{label_ref} +or @code{scratch} is seen it is distinct from all others that are seen. + +@cindex @code{mem}, RTL sharing +@item +Only one @code{mem} object is normally created for each static +variable or stack slot, so these objects are frequently shared in all +the places they appear. However, separate but equal objects for these +variables are occasionally made. + +@cindex @code{asm_operands}, RTL sharing +@item +When a single @code{asm} statement has multiple output operands, a +distinct @code{asm_operands} expression is made for each output operand. +However, these all share the vector which contains the sequence of input +operands. This sharing is used later on to test whether two +@code{asm_operands} expressions come from the same statement, so all +optimizations must carefully preserve the sharing if they copy the +vector at all. + +@item +No RTL object appears in more than one place in the RTL structure +except as described above. Many passes of the compiler rely on this +by assuming that they can modify RTL objects in place without unwanted +side-effects on other insns. + +@findex unshare_all_rtl +@item +During initial RTL generation, shared structure is freely introduced. +After all the RTL for a function has been generated, all shared +structure is copied by @code{unshare_all_rtl} in @file{emit-rtl.c}, +after which the above rules are guaranteed to be followed. + +@findex copy_rtx_if_shared +@item +During the combiner pass, shared structure within an insn can exist +temporarily. However, the shared structure is copied before the +combiner is finished with the insn. This is done by calling +@code{copy_rtx_if_shared}, which is a subroutine of +@code{unshare_all_rtl}. +@end itemize + +@node Reading RTL +@section Reading RTL + +To read an RTL object from a file, call @code{read_rtx}. It takes one +argument, a stdio stream, and returns a single RTL object. This routine +is defined in @file{read-rtl.c}. It is not available in the compiler +itself, only the various programs that generate the compiler back end +from the machine description. + +People frequently have the idea of using RTL stored as text in a file as +an interface between a language front end and the bulk of GCC@. This +idea is not feasible. + +GCC was designed to use RTL internally only. Correct RTL for a given +program is very dependent on the particular target machine. And the RTL +does not contain all the information about the program. + +The proper way to interface GCC to a new language front end is with +the ``tree'' data structure, described in the files @file{tree.h} and +@file{tree.def}. The documentation for this structure (@pxref{Trees}) +is incomplete. diff --git a/contrib/gcc/doc/service.texi b/contrib/gcc/doc/service.texi new file mode 100644 index 000000000000..863774483c81 --- /dev/null +++ b/contrib/gcc/doc/service.texi @@ -0,0 +1,30 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Service +@chapter How To Get Help with GCC + +If you need help installing, using or changing GCC, there are two +ways to find it: + +@itemize @bullet +@item +Send a message to a suitable network mailing list. First try +@email{gcc-help@@gcc.gnu.org} (for help installing or using GCC), and if +that brings no response, try @email{gcc@@gcc.gnu.org}. For help +changing GCC, ask @email{gcc@@gcc.gnu.org}. If you think you have found +a bug in GCC, please report it following the instructions at +@pxref{Bug Reporting}. + +@item +Look in the service directory for someone who might help you for a fee. +The service directory is found at +@uref{http://www.gnu.org/prep/service.html}. +@end itemize + +@c For further information, see +@c @uref{http://gcc.gnu.org/cgi-bin/fom.cgi?file=12}. +@c FIXME: this URL may be too volatile, this FAQ entry needs to move to +@c the regular web pages before we can uncomment the reference. diff --git a/contrib/gcc/doc/sourcebuild.texi b/contrib/gcc/doc/sourcebuild.texi new file mode 100644 index 000000000000..670d501d9e5e --- /dev/null +++ b/contrib/gcc/doc/sourcebuild.texi @@ -0,0 +1,875 @@ +@c Copyright (C) 2002 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Source Tree +@chapter Source Tree Structure and Build System + +This chapter describes the structure of the GCC source tree, and how +GCC is built. The user documentation for building and installing GCC +is in a separate manual (@uref{http://gcc.gnu.org/install/}), with +which it is presumed that you are familiar. + +@menu +* Configure Terms:: Configuration terminology and history. +* Top Level:: The top level source directory. +* gcc Directory:: The @file{gcc} subdirectory. +* Test Suites:: The GCC test suites. +@end menu + +@include configterms.texi + +@node Top Level +@section Top Level Source Directory + +The top level source directory in a GCC distribution contains several +files and directories that are shared with other software +distributions such as that of GNU Binutils. It also contains several +subdirectories that contain parts of GCC and its runtime libraries: + +@table @file +@item boehm-gc +The Boehm conservative garbage collector, used as part of the Java +runtime library. + +@item contrib +Contributed scripts that may be found useful in conjunction with GCC@. +One of these, @file{contrib/texi2pod.pl}, is used to generate man +pages from Texinfo manuals as part of the GCC build process. + +@item fastjar +An implementation of the @command{jar} command, used with the Java +front end. + +@item gcc +The main sources of GCC itself (except for runtime libraries), +including optimizers, support for different target architectures, +language front ends, and test suites. @xref{gcc Directory, , The +@file{gcc} Subdirectory}, for details. + +@item include +Headers for the @code{libiberty} library. + +@item libchill +The CHILL runtime library. + +@item libf2c +The Fortran runtime library. + +@item libffi +The @code{libffi} library, used as part of the Java runtime library. + +@item libiberty +The @code{libibery} library, used for portability and for some +generally useful data structures and algorithms. @xref{Top, , +Introduction, libiberty, @sc{gnu} libiberty}, for more information +about this library. + +@item libjava +The Java runtime library. + +@item libobjc +The Objective-C runtime library. + +@item libstdc++-v3 +The C++ runtime library. + +@item maintainer-scripts +Scripts used by the @code{gccadmin} account on @code{gcc.gnu.org}. + +@item zlib +The @code{zlib} compression library, used by the Java front end and as +part of the Java runtime library. +@end table + +The build system in the top level directory, including how recursion +into subdirectories works and how building runtime libraries for +multilibs is handled, is documented in a separate manual, included +with GNU Binutils. @xref{Top, , GNU configure and build system, +configure, The GNU configure and build system}, for details. + +@node gcc Directory +@section The @file{gcc} Subdirectory + +The @file{gcc} directory contains many files that are part of the C +sources of GCC, other files used as part of the configuration and +build process, and subdirectories including documentation and a +test suite. The files that are sources of GCC are documented in a +separate chapter. @xref{Passes, , Passes and Files of the Compiler}. + +@menu +* Subdirectories:: Subdirectories of @file{gcc}. +* Configuration:: The configuration process, and the files it uses. +* Build:: The build system in the @file{gcc} directory. +* Makefile:: Targets in @file{gcc/Makefile}. +* Library Files:: Library source files and headers under @file{gcc/}. +* Headers:: Headers installed by GCC. +* Documentation:: Building documentation in GCC. +* Front End:: Anatomy of a language front end. +* Back End:: Anatomy of a target back end. +@end menu + +@node Subdirectories +@subsection Subdirectories of @file{gcc} + +The @file{gcc} directory contains the following subdirectories: + +@table @file +@item @var{language} +Subdirectories for various languages. Directories containing a file +@file{config-lang.in} are language subdirectories. The contents of +the subdirectories @file{cp} (for C++) and @file{objc} (for +Objective-C) are documented in this manual (@pxref{Passes, , Passes +and Files of the Compiler}); those for other languages are not. +@xref{Front End, , Anatomy of a Language Front End}, for details of +the files in these directories. + +@item config +Configuration files for supported architectures and operating +systems. @xref{Back End, , Anatomy of a Target Back End}, for +details of the files in thie directory. + +@item doc +Texinfo documentation for GCC, together with automatically generated +man pages and support for converting the installation manual to +HTML@. @xref{Documentation}. + +@item fixinc +The support for fixing system headers to work with GCC@. See +@file{fixinc/README} for more information. The headers fixed by this +mechanism are installed in @file{@var{libsubdir}/include}. Along with +those headers, @file{README-fixinc} is also installed, as +@file{@var{libsubdir}/include/README}. + +@item ginclude +System headers installed by GCC, mainly those required by the C +standard of freestanding implementations. @xref{Headers, , Headers +Installed by GCC}, for details of when these and other headers are +installed. + +@item intl +GNU @code{libintl}, from GNU @code{gettext}, for systems which do not +include it in libc. Properly, this directory should be at top level, +parallel to the @file{gcc} directory. + +@item po +Message catalogs with translations of messages produced by GCC into +various languages, @file{@var{language}.po}. This directory also +contains @file{gcc.pot}, the template for these message catalogues, +@file{exgettext}, a wrapper around @command{gettext} to extract the +messages from the GCC sources and create @file{gcc.pot}, which is run +by @command{make gcc.pot}, and @file{EXCLUDES}, a list of files from +which messages should not be extracted. + +@item testsuite +The GCC test suites (except for those for runtime libraries). +@xref{Test Suites}. +@end table + +@node Configuration +@subsection Configuration in the @file{gcc} Directory + +The @file{gcc} directory is configured with an Autoconf-generated +script @file{configure}. The @file{configure} script is generated +from @file{configure.in} and @file{aclocal.m4}. From the files +@file{configure.in} and @file{acconfig.h}, Autoheader generates the +file @file{config.in}. The file @file{cstamp-h.in} is used as a +timestamp. + +@menu +* Config Fragments:: Scripts used by @file{configure}. +* System Config:: The @file{config.gcc} file. +* Configuration Files:: Files created by running @file{configure}. +@end menu + +@node Config Fragments +@subsubsection Scripts Used by @file{configure} + +@file{configure} uses some other scripts to help in its work: + +@itemize @bullet +@item The standard GNU @file{config.sub} and @file{config.guess} +files, kept in the top level directory, are used. FIXME: when is the +@file{config.guess} file in the @file{gcc} directory (that just calls +the top level one) used? + +@item The file @file{config.gcc} is used to handle configuration +specific to the particular build, host or target machine. (In +general, this should only be used for features that cannot reasonably +be tested in Autoconf feature tests.) @xref{System Config, , The +@file{config.gcc} File}, for details of the contents of this file. + +@item Each language subdirectory has a file +@file{@var{language}/config-lang.in} that is used for +front-end-specific configuration. @xref{Front End Config, , The Front +End @file{config-lang.in} File}, for details of this file. + +@item A helper script @file{configure.frag} is used as part of +creating the output of @file{configure}. +@end itemize + +@node System Config +@subsubsection The @file{config.gcc} File + +FIXME: document the contents of this file, and what variables should +be set to control build, host and target configuration. + +@include configfiles.texi + +@node Build +@subsection Build System in the @file{gcc} Directory + +FIXME: describe the build system, including what is built in what +stages. Also list the various source files that are used in the build +process but aren't source files of GCC itself and so aren't documented +below (@pxref{Passes}). + +@include makefile.texi + +@node Library Files +@subsection Library Source Files and Headers under the @file{gcc} Directory + +FIXME: list here, with explanation, all the C source files and headers +under the @file{gcc} directory that aren't built into the GCC +executable but rather are part of runtime libraries and object files, +such as @file{crtstuff.c} and @file{unwind-dw2.c}. @xref{Headers, , +Headers Installed by GCC}, for more information about the +@file{ginclude} directory. + +@node Headers +@subsection Headers Installed by GCC + +In general, GCC expects the system C library to provide most of the +headers to be used with it. However, GCC will fix those headers if +necessary to make them work with GCC, and will install some headers +required of freestanding implementations. These headers are installed +in @file{@var{libsubdir}/include}. Headers for non-C runtime +libraries are also installed by GCC; these are not documented here. +(FIXME: document them somewhere.) + +Several of the headers GCC installs are in the @file{ginclude} +directory. These headers, @file{iso646.h}, +@file{stdarg.h}, @file{stdbool.h}, @file{stddef.h} and +@file{varargs.h}, are installed in @file{@var{libsubdir}/include}, +unless the target Makefile fragment (@pxref{Target Fragment}) +overrides this by setting @code{USER_H}. + +In addition to these headers and those generated by fixing system +headers to work with GCC, some other headers may also be installed in +@file{@var{libsubdir}/include}. @file{config.gcc} may set +@code{extra_headers}; this specifies additional headers under +@file{config} to be installed on some systems. GCC normally installs +a @code{} file; these are kept as +@file{config/float-@var{format}.h}, where @var{format} is specified by +a @code{float_format} setting in @file{config.gcc}, and a setting +@samp{float_format=none} disables installation of this header. GCC +also installs its own version of @code{}; this is generated +from @file{glimits.h}, together with @file{limitx.h} and +@file{limity.h} if the system also has its own version of +@code{}. (GCC provides its own header because it is +required of ISO C freestanding implementations, but needs to include +the system header from its own header as well because other standards +such as POSIX specify additional values to be defined in +@code{}.) The system's @code{} header is used via +@file{@var{libsubdir}/include/syslimits.h}, which is copied from +@file{gsyslimits.h} if it does not need fixing to work with GCC; if it +needs fixing, @file{syslimits.h} is the fixed copy. + +@node Documentation +@subsection Building Documentation + +The main GCC documentation is in the form of manuals in Texinfo +format. These are installed in Info format, and DVI versions may be +generated by @command{make dvi}. In addition, some man pages are +generated from the Texinfo manuals, there are some other text files +with miscellaneous documentation, and runtime libraries have their own +documentation outside the @file{gcc} directory. FIXME: document the +documentation for runtime libraries somewhere. + +@menu +* Texinfo Manuals:: GCC manuals in Texinfo format. +* Man Page Generation:: Generating man pages from Texinfo manuals. +* Miscellaneous Docs:: Miscellaneous text files with documentation. +@end menu + +@node Texinfo Manuals +@subsubsection Texinfo Manuals + +The manuals for GCC as a whole, and the C and C++ front ends, are in +files @file{doc/*.texi}. Other front ends have their own manuals in +files @file{@var{language}/*.texi}. Common files +@file{doc/include/*.texi} are provided which may be included in +multiple manuals; the following files are in @file{doc/include}: + +@table @file +@item fdl.texi +The GNU Free Documentation License. +@item funding.texi +The section ``Funding Free Software''. +@item gcc-common.texi +Common definitions for manuals. +@item gpl.texi +The GNU General Public License. +@item texinfo.tex +A copy of @file{texinfo.tex} known to work with the GCC manuals. +@end table + +DVI formatted manuals are generated by @command{make dvi}, which uses +@command{texi2dvi} (via the Makefile macro @code{$(TEXI2DVI)}). Info +manuals are generated by @command{make info} (which is run as part of +a bootstrap); this generates the manuals in the source directory, +using @command{makeinfo} via the Makefile macro @code{$(MAKEINFO)}, +and they are included in release distributions. + +Manuals are also provided on the GCC web site, in both HTML and +PostScript forms. This is done via the script +@file{maintainer-scripts/update_web_docs}. Each manual to be +provided online must be listed in the definition of @code{MANUALS} in +that file; a file @file{@var{name}.texi} must only appear once in the +source tree, and the output manual must have the same name as the +source file. (However, other Texinfo files, included in manuals but +not themselves the root files of manuals, may have names that appear +more than once in the source tree.) The manual file +@file{@var{name}.texi} should only include other files in its own +directory or in @file{doc/include}. HTML manuals will be generated by +@command{makeinfo --html} and PostScript manuals by @command{texi2dvi} +and @command{dvips}. All Texinfo files that are parts of manuals must +be checked into CVS, even if they are generated files, for the +generation of online manuals to work. + +The installation manual, @file{doc/install.texi}, is also provided on +the GCC web site. The HTML version is generated by the script +@file{doc/install.texi2html}. + +@node Man Page Generation +@subsubsection Man Page Generation + +Because of user demand, in addition to full Texinfo manuals, man pages +are provided which contain extracts from those manuals. These man +pages are generated from the Texinfo manuals using +@file{contrib/texi2pod.pl} and @command{pod2man}. (The man page for +@command{g++}, @file{cp/g++.1}, just contains a @samp{.so} reference +to @file{gcc.1}, but all the other man pages are generated from +Texinfo manuals.) + +Because many systems may not have the necessary tools installed to +generate the man pages, they are only generated if the +@file{configure} script detects that recent enough tools are +installed, and the Makefiles allow generating man pages to fail +without aborting the build. Man pages are also included in release +distributions. They are generated in the source directory. + +Magic comments in Texinfo files starting @samp{@@c man} control what +parts of a Texinfo file go into a man page. Only a subset of Texinfo +is supported by @file{texi2pod.pl}, and it may be necessary to add +support for more Texinfo features to this script when generating new +man pages. To improve the man page output, some special Texinfo +macros are provided in @file{doc/include/gcc-common.texi} which +@file{texi2pod.pl} understands: + +@table @code +@item @@gcctabopt +Use in the form @samp{@@table @@gcctabopt} for tables of options, +where for printed output the effect of @samp{@@code} is better than +that of @samp{@@option} but for man page output a different effect is +wanted. +@item @@gccoptlist +Use for summary lists of options in manuals. +@item @@gol +Use at the end of each line inside @samp{@@gccoptlist}. This is +necessary to avoid problems with differences in how the +@samp{@@gccoptlist} macro is handled by different Texinfo formatters. +@end table + +FIXME: describe the @file{texi2pod.pl} input language and magic +comments in more detail. + +@node Miscellaneous Docs +@subsubsection Miscellaneous Documentation + +In addition to the formal documentation that is installed by GCC, +there are several other text files with miscellaneous documentation: + +@table @file +@item ABOUT-GCC-NLS +Notes on GCC's Native Language Support. FIXME: this should be part of +this manual rather than a separate file. +@item ABOUT-NLS +Notes on the Free Translation Project. +@item COPYING +The GNU General Public License. +@item COPYING.LIB +The GNU Lesser General Public License. +@item *ChangeLog* +@itemx */ChangeLog* +Change log files for various parts of GCC@. +@item LANGUAGES +Details of a few changes to the GCC front-end interface. FIXME: the +information in this file should be part of general documentation of +the front-end interface in this manual. +@item ONEWS +Information about new features in old versions of GCC@. (For recent +versions, the information is on the GCC web site.) +@item README.Portability +Information about portability issues when writing code in GCC@. FIXME: +why isn't this part of this manual or of the GCC Coding Conventions? +@item SERVICE +A pointer to the GNU Service Directory. +@end table + +FIXME: document such files in subdirectories, at least @file{config}, +@file{cp}, @file{objc}, @file{testsuite}. + +@node Front End +@subsection Anatomy of a Language Front End + +A front end for a language in GCC has the following parts: + +@itemize @bullet +@item +A directory @file{@var{language}} under @file{gcc} containing source +files for that front end. @xref{Front End Directory, , The Front End +@file{@var{language}} Directory}, for details. +@item +A mention of the language in the list of supported languages in +@file{gcc/doc/install.texi}. +@item +Details of contributors to that front end in +@file{gcc/doc/contrib.texi}. If the details are in that front end's +own manual then there should be a link to that manual's list in +@file{contrib.texi}. +@item +Information about support for that language in +@file{gcc/doc/frontends.texi}. +@item +Information about standards for that language, and the front end's +support for them, in @file{gcc/doc/standards.texi}. This may be a +link to such information in the front end's own manual. +@item +Details of source file suffixes for that language and @option{-x +@var{lang}} options supported, in @file{gcc/doc/invoke.texi}. +@item +Entries in @code{default_compilers} in @file{gcc.c} for source file +suffixes for that language. +@item +Preferably test suites, which may be under @file{gcc/testsuite} or +runtime library directories. FIXME: document somewhere how to write +test suite harnesses. +@item +Probably a runtime library for the language, outside the @file{gcc} +directory. FIXME: document this further. +@item +Details of the directories of any runtime libraries in +@file{gcc/doc/sourcebuild.texi}. +@end itemize + +If the front end is added to the official GCC CVS repository, the +following are also necessary: + +@itemize @bullet +@item +At least one GNATS category for bugs in that front end and runtime +libraries. This category needs to be mentioned in +@file{gcc/gccbug.in}, and in @file{gnats.html} on the GCC web site, as +well as being added to the GNATS database. +@item +Normally, one or more maintainers of that front end listed in +@file{MAINTAINERS}. +@item +Mentions on the GCC web site in @file{index.html} and +@file{frontends.html}, with any relevant links on +@file{readings.html}. (Front ends that are not an official part of +GCC may also be listed on @file{frontends.html}, with relevant links.) +@item +A news item on @file{index.html}, and possibly an announcement on the +@email{gcc-announce@@gcc.gnu.org} mailing list. +@item +The front end's manuals should be mentioned in +@file{maintainer-scripts/update_web_docs} (@pxref{Texinfo Manuals}) +and the online manuals should be linked to from +@file{onlinedocs/index.html}. +@item +Any old releases or CVS repositories of the front end, before its +inclusion in GCC, should be made available on the GCC FTP site +@uref{ftp://gcc.gnu.org/pub/gcc/old-releases/}. +@item +The release and snapshot script @file{maintainer-scripts/gcc_release} +should be updated to generate appropriate tarballs for this front end. +@item +If this front end includes its own version files that include the +current date, @file{maintainer-scripts/update_version} should be +updated accordingly. +@item +@file{CVSROOT/modules} in the GCC CVS repository should be updated. +@end itemize + +@menu +* Front End Directory:: The front end @file{@var{language}} directory. +* Front End Config:: The front end @file{config-lang.in} file. +@end menu + +@node Front End Directory +@subsubsection The Front End @file{@var{language}} Directory + +A front end @file{@var{language}} directory contains the source files +of that front end (but not of any runtime libraries, which should be +outside the @file{gcc} directory). This includes documentation, and +possibly some subsidiary programs build alongside the front end. +Certain files are special and other parts of the compiler depend on +their names: + +@table @file +@item config-lang.in +This file is required in all language subdirectories. @xref{Front End +Config, , The Front End @file{config-lang.in} File}, for details of +its contents +@item Make-lang.in +This file is required in all language subdirectories. It contains +targets @code{@var{lang}.@var{hook}} (where @code{@var{lang}} is the +setting of @code{language} in @file{config-lang.in}) for the following +values of @code{@var{hook}}, and any other Makefile rules required to +build those targets (which may if necessary use other Makefiles +specified in @code{outputs} in @file{config-lang.in}, although this is +deprecated). + +@table @code +@item all.build +@itemx all.cross +@itemx start.encap +@itemx rest.encap +FIXME: exactly what goes in each of these targets? +@item info +Build info documentation for the front end, in the source directory. +This target is only called by @command{make bootstrap} if a suitable +version of @command{makeinfo} is available, so does not need to check +for this, and should fail if an error occurs. +@item dvi +Build DVI documentation for the front end, in the build directory. +This should be done using @code{$(TEXI2DVI)}, with appropriate +@option{-I} arguments pointing to directories of included files. +@item generated-manpages +Build generated man pages for the front end from Texinfo manuals +(@pxref{Man Page Generation}), in the source directory. This target +is only called if the necessary tools are available, but should ignore +errors so as not to stop the build if errors occur; man pages are +optional and the tools involved may be installed in a broken way. +@item install-normal +FIXME: what is this target for? +@item install-common +Install everything that is part of the front end, apart from the +compiler executables listed in @code{compilers} in +@file{config-lang.in} that are installed in @file{@var{libsubdir}} by +the main @file{Makefile}. +@item install-info +Install info documentation for the front end, if it is present in the +source directory. (It may not be present if a suitable version of +@command{makeinfo} was not installed.) This target should run the +command @command{install-info} to update the info directory, but +should ignore errors when running that command. +@item install-man +Install man pages for the front end. This target should ignore +errors. +@item uninstall +Uninstall files installed by installing the compiler. This is +currently documented not to be supported, so the hook need not do +anything. +@item mostlyclean +@itemx clean +@itemx distclean +@itemx extraclean +@itemx maintainer-clean +Except for @code{extraclean}, the language parts of the standard GNU +@samp{*clean} targets. @xref{Standard Targets, , Standard Targets for +Users, standards, GNU Coding Standards}, for details of the standard +targets. @code{extraclean} does @code{distclean} and also deletes +anything likely to be found in the source directory that shouldn't be +in the distribution. For GCC, @code{maintainer-clean} should delete +all generated files in the source directory that are not checked into +CVS, but should not delete anything checked into CVS@. +@item stage1 +@itemx stage2 +@itemx stage3 +@itemx stage4 +Move to the stage directory files not included in @code{stagestuff} in +@file{config-lang.in} or otherwise moved by the main @file{Makefile}. +@end table + +@item lang-options.h +This file provides entries for @code{documented_lang_options} in +@file{toplev.c} describing command-line options the front end accepts +for @option{--help} output. +@item lang-specs.h +This file provides entries for @code{default_compilers} in +@file{gcc.c} which override the default of giving an error that a +compiler for that language is not installed. +@item @var{language}-tree.def +This file, which need not exist, defines any language-specific tree +codes. +@end table + +@node Front End Config +@subsubsection The Front End @file{config-lang.in} File + +Each language subdirectory contains a @file{config-lang.in} file. +This file is a shell script that may define some variables describing +the language: + +@table @code +@item language +This definition must be present, and gives the name of the language +for some purposes such as arguments to @option{--enable-languages}. +@item lang_requires +If defined, this variable lists (space-separated) language front ends +other than C that this front end requires to be enabled (with the +names given being their @code{language} settings). For example, the +Java front end depends on the C++ front end, so sets +@samp{lang_requires=c++}. +@item target_libs +If defined, this variable lists (space-separated) targets in the top +level @file{Makefile} to build the runtime libraries for this +language, such as @code{target-libobjc}. +@item lang_dirs +If defined, this variable lists (space-separated) top level +directories (parallel to @file{gcc}), apart from the runtime libraries, +that should not be configured if this front end is not built. +@item build_by_default +If defined to @samp{no}, this language front end is not built unless +enabled in a @option{--enable-languages} argument. Otherwise, front +ends are built by default, subject to any special logic in +@file{configure.in} (as is present to disable the Ada front end if the +Ada compiler is not already installed). +@item boot_language +If defined to @samp{yes}, this front end is built in stage 1 of the +bootstrap. This is only relevant to front ends written in their own +languages. +@item compilers +If defined, a space-separated list of compiler executables that should +be installed in @file{@var{libsubdir}}. The names here will each end +with @samp{\$(exeext)}. +@item stagestuff +If defined, a space-separated list of files that should be moved to +the @file{stage@var{n}} directories in each stage of bootstrap. +@item outputs +If defined, a space-separated list of files that should be generated +by @file{configure} substituting values in them. This mechanism can +be used to create a file @file{@var{language}/Makefile} from +@file{@var{language}/Makefile.in}, but this is deprecated, building +everything from the single @file{gcc/Makefile} is preferred. +@end table + +@node Back End +@subsection Anatomy of a Target Back End + +A back end for a target architecture in GCC has the following parts: + +@itemize @bullet +@item +A directory @file{@var{machine}} under @file{gcc/config}, containing a +machine description @file{@var{machine}.md} file (@pxref{Machine Desc, +, Machine Descriptions}), header files @file{@var{machine}.h} and +@file{@var{machine}-protos.h} and a source file @file{@var{machine}.c} +(@pxref{Target Macros, , Target Description Macros and Functions}), +possibly a target Makefile fragment @file{t-@var{machine}} +(@pxref{Target Fragment, , The Target Makefile Fragment}), and maybe +some other files. The names of these files may be changed from the +defaults given by explicit specifications in @file{config.gcc}. +@item +Entries in @file{config.gcc} (@pxref{System Config, , The +@file{config.gcc} File}) for the systems with this target +architecture. +@item +Documentation in @file{gcc/doc/invoke.texi} for any command-line +options supported by this target (@pxref{Run-time Target, , Run-time +Target Specification}). This means both entries in the summary table +of options and details of the individual options. +@item +Documentation in @file{gcc/doc/extend.texi} for any target-specific +attributes supported (@pxref{Target Attributes, , Defining +target-specific uses of @code{__attribute__}}), including where the +same attribute is already supported on some targets, which are +enumerated in the manual. +@item +Documentation in @file{gcc/doc/extend.texi} for any target-specific +pragmas supported. +@item +Documentation in @file{gcc/doc/extend.texi} of any target-specific +built-in functions supported. +@item +Documentation in @file{gcc/doc/md.texi} of any target-specific +constraint letters (@pxref{Machine Constraints, , Constraints for +Particular Machines}). +@item +A note in @file{gcc/doc/contrib.texi} under the person or people who +contributed the target support. +@item +Entries in @file{gcc/doc/install.texi} for all target triplets +supported with this target architecture, giving details of any special +notes about installation for this target, or saying that there are no +special notes if there are none. +@item +Possibly other support outside the @file{gcc} directory for runtime +libraries. FIXME: reference docs for this. The libstdc++ porting +manual needs to be installed as info for this to work, or to be a +chapter of this manual. +@end itemize + +If the back end is added to the official GCC CVS repository, the +following are also necessary: + +@itemize @bullet +@item +An entry for the target architecture in @file{readings.html} on the +GCC web site, with any relevant links. +@item +A news item about the contribution of support for that target +architecture, in @file{index.html} on the GCC web site. +@item +Normally, one or more maintainers of that target listed in +@file{MAINTAINERS}. Some existing architectures may be unmaintained, +but it would be unusual to add support for a target that does not have +a maintainer when support is added. +@end itemize + +@node Test Suites +@section Test Suites + +GCC contains several test suites to help maintain compiler quality. +Most of the runtime libraries and language front ends in GCC have test +suites. Currently only the C language test suites are documented +here; FIXME: document the others. + +@menu +* Test Idioms:: Idioms used in test suite code. +* C Tests:: The C language test suites. +@end menu + +@node Test Idioms +@subsection Idioms Used in Test Suite Code + +In the @file{gcc.c-torture} test suites, test cases are commonly named +after the date on which they were added. This allows people to tell +at a glance whether a test failure is because of a recently found bug +that has not yet been fixed, or whether it may be a regression. In +other test suites, more descriptive names are used. In general C test +cases have a trailing @file{-@var{n}.c}, starting with @file{-1.c}, in +case other test cases with similar names are added later. + +Test cases should use @code{abort ()} to indicate failure and +@code{exit (0)} for success; on some targets these may be redefined to +indicate failure and success in other ways. + +In the @file{gcc.dg} test suite, it is often necessary to test that an +error is indeed a hard error and not just a warning---for example, +where it is a constraint violation in the C standard, which must +become an error with @option{-pedantic-errors}. The following idiom, +where the first line shown is line @var{line} of the file and the line +that generates the error, is used for this: + +@smallexample +/* @{ dg-bogus "warning" "warning in place of error" @} */ +/* @{ dg-error "@var{regexp}" "@var{message}" @{ target *-*-* @} @var{line} @} */ +@end smallexample + +It may be necessary to check that an expression is an integer constant +expression and has a certain value. To check that @code{@var{E}} has +value @code{@var{V}}, an idiom similar to the following is used: + +@smallexample +char x[((E) == (V) ? 1 : -1)]; +@end smallexample + +In @file{gcc.dg} tests, @code{__typeof__} is sometimes used to make +assertions about the types of expressions. See, for example, +@file{gcc.dg/c99-condexpr-1.c}. The more subtle uses depend on the +exact rules for the types of conditional expressions in the C +standard; see, for example, @file{gcc.dg/c99-intconst-1.c}. + +It is useful to be able to test that optimizations are being made +properly. This cannot be done in all cases, but it can be done where +the optimization will lead to code being optimized away (for example, +where flow analysis or alias analysis should show that certain code +cannot be called) or to functions not being called because they have +been expanded as built-in functions. Such tests go in +@file{gcc.c-torture/execute}. Where code should be optimized away, a +call to a nonexistent function such as @code{link_failure ()} may be +inserted; a definition + +@smallexample +#ifndef __OPTIMIZE__ +void +link_failure (void) +@{ + abort (); +@} +#endif +@end smallexample + +@noindent +will also be needed so that linking still succeeds when the test is +run without optimization. When all calls to a built-in function +should have been optimized and no calls to the non-built-in version of +the function should remain, that function may be defined as +@code{static} to call @code{abort ()} (although redeclaring a function +as static may not work on all targets). + +FIXME: discuss non-C test suites here. + +@node C Tests +@subsection C Language Test Suites + +GCC contains the following C language test suites, in the +@file{gcc/testsuite} directory: + +@table @file +@item gcc.c-torture/compat +FIXME: describe this. + +This directory should probably not be used for new tests. +@item gcc.c-torture/compile +This test suite contains test cases that should compile, but do not +need to link or run. These test cases are compiled with several +different combinations of optimization options. All warnings are +disabled for these test cases, so this directory is not suitable if +you wish to test for the presence or absence of compiler warnings. +While special options can be set, and tests disabled on specific +platforms, by the use of @file{.x} files, mostly these test cases +should not contain platform dependencies. FIXME: discuss how defines +such as @code{NO_LABEL_VALUES} and @code{STACK_SIZE} are used. +@item gcc.c-torture/execute +This test suite contains test cases that should compile, link and run; +otherwise the same comments as for @file{gcc.c-torture/compile} apply. +@item gcc.c-torture/unsorted +FIXME: describe this. + +This directory should probably not be used for new tests. +@item gcc.dg +This test suite contains tests using the more modern @samp{dg} harness. +Magic comments determine whether the file is preprocessed, compiled, +linked or run. In these tests, error and warning message texts are +compared against expected texts or regular expressions given in +comments. These tests are run with the options @samp{-ansi -pedantic} +unless other options are given in the test. Except as noted below they +are not run with multiple optimization options. +@item gcc.dg/cpp +This subdirectory contains tests of the preprocessor. +@item gcc.dg/debug +This subdirectory contains tests for debug formats. Tests in this +subdirectory are run for each debug format that the compiler supports. +@item gcc.dg/format +This subdirectory contains tests of the @option{-Wformat} format +checking. Tests in this directory are run with and without +@option{-DWIDE}. +@item gcc.dg/noncompile +This subdirectory contains tests of code that should not compile and +does not need any special compilation options. They are run with +multiple optimization options, since sometimes invalid code crashes +the compiler with optimization. +@item gcc.dg/special +FIXME: describe this. +@item gcc.c-torture/misc-tests +FIXME: describe this, when it should be used for new tests and when it +shouldn't. +@end table + +FIXME: merge in @file{testsuite/README.gcc} and discuss the format of +test cases and magic comments more. diff --git a/contrib/gcc/doc/standards.texi b/contrib/gcc/doc/standards.texi new file mode 100644 index 000000000000..5d5ed0c9a9b3 --- /dev/null +++ b/contrib/gcc/doc/standards.texi @@ -0,0 +1,178 @@ +@c Copyright (C) 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Standards +@chapter Language Standards Supported by GCC +@cindex C standard +@cindex C standards +@cindex ANSI C standard +@cindex ANSI C +@cindex ANSI C89 +@cindex C89 +@cindex ANSI X3.159-1989 +@cindex X3.159-1989 +@cindex ISO C standard +@cindex ISO C +@cindex ISO C89 +@cindex ISO C90 +@cindex ISO/IEC 9899 +@cindex ISO 9899 +@cindex C90 +@cindex ISO C94 +@cindex C94 +@cindex ISO C95 +@cindex C95 +@cindex ISO C99 +@cindex C99 +@cindex ISO C9X +@cindex C9X +@cindex Technical Corrigenda +@cindex TC1 +@cindex Technical Corrigendum 1 +@cindex TC2 +@cindex Technical Corrigendum 2 +@cindex AMD1 +@cindex freestanding implementation +@cindex freestanding environment +@cindex hosted implementation +@cindex hosted environment +@findex __STDC_HOSTED__ + +For each language compiled by GCC for which there is a standard, GCC +attempts to follow one or more versions of that standard, possibly +with some exceptions, and possibly with some extensions. + +GCC supports three versions of the C standard, although support for +the most recent version is not yet complete. + +@opindex std +@opindex ansi +@opindex pedantic +@opindex pedantic-errors +The original ANSI C standard (X3.159-1989) was ratified in 1989 and +published in 1990. This standard was ratified as an ISO standard +(ISO/IEC 9899:1990) later in 1990. There were no technical +differences between these publications, although the sections of the +ANSI standard were renumbered and became clauses in the ISO standard. +This standard, in both its forms, is commonly known as @dfn{C89}, or +occasionally as @dfn{C90}, from the dates of ratification. The ANSI +standard, but not the ISO standard, also came with a Rationale +document. To select this standard in GCC, use one of the options +@option{-ansi}, @option{-std=c89} or @option{-std=iso9899:1990}; to obtain +all the diagnostics required by the standard, you should also specify +@option{-pedantic} (or @option{-pedantic-errors} if you want them to be +errors rather than warnings). @xref{C Dialect Options,,Options +Controlling C Dialect}. + +Errors in the 1990 ISO C standard were corrected in two Technical +Corrigenda published in 1994 and 1996. GCC does not support the +uncorrected version. + +An amendment to the 1990 standard was published in 1995. This +amendment added digraphs and @code{__STDC_VERSION__} to the language, +but otherwise concerned the library. This amendment is commonly known +as @dfn{AMD1}; the amended standard is sometimes known as @dfn{C94} or +@dfn{C95}. To select this standard in GCC, use the option +@option{-std=iso9899:199409} (with, as for other standard versions, +@option{-pedantic} to receive all required diagnostics). + +A new edition of the ISO C standard was published in 1999 as ISO/IEC +9899:1999, and is commonly known as @dfn{C99}. GCC has incomplete +support for this standard version; see +@uref{http://gcc.gnu.org/c99status.html} for details. To select this +standard, use @option{-std=c99} or @option{-std=iso9899:1999}. (While in +development, drafts of this standard version were referred to as +@dfn{C9X}.) + +Errors in the 1999 ISO C standard were corrected in a Technical +Corrigendum published in 2001. GCC does not support the uncorrected +version. + +@opindex traditional +GCC also has some limited support for traditional (pre-ISO) C with the +@option{-traditional} option. This support may be of use for compiling +some very old programs that have not been updated to ISO C, but should +not be used for new programs. It will not work with some modern C +libraries such as the GNU C library. + +By default, GCC provides some extensions to the C language that on +rare occasions conflict with the C standard. @xref{C +Extensions,,Extensions to the C Language Family}. Use of the +@option{-std} options listed above will disable these extensions where +they conflict with the C standard version selected. You may also +select an extended version of the C language explicitly with +@option{-std=gnu89} (for C89 with GNU extensions) or @option{-std=gnu99} +(for C99 with GNU extensions). The default, if no C language dialect +options are given, is @option{-std=gnu89}; this will change to +@option{-std=gnu99} in some future release when the C99 support is +complete. Some features that are part of the C99 standard are +accepted as extensions in C89 mode. + +The ISO C standard defines (in clause 4) two classes of conforming +implementation. A @dfn{conforming hosted implementation} supports the +whole standard including all the library facilities; a @dfn{conforming +freestanding implementation} is only required to provide certain +library facilities: those in @code{}, @code{}, +@code{}, and @code{}; since AMD1, also those in +@code{}; and in C99, also those in @code{} and +@code{}. In addition, complex types, added in C99, are not +required for freestanding implementations. The standard also defines +two environments for programs, a @dfn{freestanding environment}, +required of all implementations and which may not have library +facilities beyond those required of freestanding implementations, +where the handling of program startup and termination are +implementation-defined, and a @dfn{hosted environment}, which is not +required, in which all the library facilities are provided and startup +is through a function @code{int main (void)} or @code{int main (int, +char *[])}. An OS kernel would be a freestanding environment; a +program using the facilities of an operating system would normally be +in a hosted implementation. + +@opindex ffreestanding +GCC aims towards being usable as a conforming freestanding +implementation, or as the compiler for a conforming hosted +implementation. By default, it will act as the compiler for a hosted +implementation, defining @code{__STDC_HOSTED__} as @code{1} and +presuming that when the names of ISO C functions are used, they have +the semantics defined in the standard. To make it act as a conforming +freestanding implementation for a freestanding environment, use the +option @option{-ffreestanding}; it will then define +@code{__STDC_HOSTED__} to @code{0} and not make assumptions about the +meanings of function names from the standard library. To build an OS +kernel, you may well still need to make your own arrangements for +linking and startup. @xref{C Dialect Options,,Options Controlling C +Dialect}. + +GCC does not provide the library facilities required only of hosted +implementations, nor yet all the facilities required by C99 of +freestanding implementations; to use the facilities of a hosted +environment, you will need to find them elsewhere (for example, in the +GNU C library). @xref{Standard Libraries,,Standard Libraries}. + +For references to Technical Corrigenda, Rationale documents and +information concerning the history of C that is available online, see +@uref{http://gcc.gnu.org/readings.html} + +@c FIXME: details of C++ standard. + +There is no formal written standard for Objective-C@. The most +authoritative manual is ``Object-Oriented Programming and the +Objective-C Language'', available at a number of web sites; +@uref{http://developer.apple.com/techpubs/macosx/Cocoa/ObjectiveC/} has a +recent version, while @uref{http://www.toodarkpark.org/computers/objc/} +is an older example. @uref{http://www.gnustep.org} includes useful +information as well. + +@xref{Top, GNAT Reference Manual, About This Guide, gnat_rm, +GNAT Reference Manual}, for information on standard +conformance and compatibility of the Ada compiler. + +@xref{References,,Language Definition References, chill, GNU Chill}, +for details of the CHILL standard. + +@xref{Language,,The GNU Fortran Language, g77, Using and Porting GNU +Fortran}, for details of the Fortran language supported by GCC@. + +@xref{Compatibility,,Compatibility with the Java Platform, gcj, GNU gcj}, +for details of compatibility between @code{gcj} and the Java Platform. diff --git a/contrib/gcc/doc/tm.texi b/contrib/gcc/doc/tm.texi new file mode 100644 index 000000000000..e9797bfd53f7 --- /dev/null +++ b/contrib/gcc/doc/tm.texi @@ -0,0 +1,8614 @@ +@c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,2002 +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Target Macros +@chapter Target Description Macros and Functions +@cindex machine description macros +@cindex target description macros +@cindex macros, target description +@cindex @file{tm.h} macros + +In addition to the file @file{@var{machine}.md}, a machine description +includes a C header file conventionally given the name +@file{@var{machine}.h} and a C source file named @file{@var{machine}.c}. +The header file defines numerous macros that convey the information +about the target machine that does not fit into the scheme of the +@file{.md} file. The file @file{tm.h} should be a link to +@file{@var{machine}.h}. The header file @file{config.h} includes +@file{tm.h} and most compiler source files include @file{config.h}. The +source file defines a variable @code{targetm}, which is a structure +containing pointers to functions and data relating to the target +machine. @file{@var{machine}.c} should also contain their definitions, +if they are not defined elsewhere in GCC, and other functions called +through the macros defined in the @file{.h} file. + +@menu +* Target Structure:: The @code{targetm} variable. +* Driver:: Controlling how the driver runs the compilation passes. +* Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}. +* Per-Function Data:: Defining data structures for per-function information. +* Storage Layout:: Defining sizes and alignments of data. +* Type Layout:: Defining sizes and properties of basic user data types. +* Escape Sequences:: Defining the value of target character escape sequences +* Registers:: Naming and describing the hardware registers. +* Register Classes:: Defining the classes of hardware registers. +* Stack and Calling:: Defining which way the stack grows and by how much. +* Varargs:: Defining the varargs macros. +* Trampolines:: Code set up at run time to enter a nested function. +* Library Calls:: Controlling how library routines are implicitly called. +* Addressing Modes:: Defining addressing modes valid for memory operands. +* Condition Code:: Defining how insns update the condition code. +* Costs:: Defining relative costs of different operations. +* Scheduling:: Adjusting the behavior of the instruction scheduler. +* Sections:: Dividing storage into text, data, and other sections. +* PIC:: Macros for position independent code. +* Assembler Format:: Defining how to write insns and pseudo-ops to output. +* Debugging Info:: Defining the format of debugging output. +* Cross-compilation:: Handling floating point for cross-compilers. +* Mode Switching:: Insertion of mode-switching instructions. +* Target Attributes:: Defining target-specific uses of @code{__attribute__}. +* Misc:: Everything else. +@end menu + +@node Target Structure +@section The Global @code{targetm} Variable +@cindex target hooks +@cindex target functions + +@deftypevar {struct gcc_target} targetm +The target @file{.c} file must define the global @code{targetm} variable +which contains pointers to functions and data relating to the target +machine. The variable is declared in @file{target.h}; +@file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is +used to initialize the variable, and macros for the default initializers +for elements of the structure. The @file{.c} file should override those +macros for which the default definition is inappropriate. For example: +@smallexample +#include "target.h" +#include "target-def.h" + +/* @r{Initialize the GCC target structure.} */ + +#undef TARGET_COMP_TYPE_ATTRIBUTES +#define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes + +struct gcc_target targetm = TARGET_INITIALIZER; +@end smallexample +@end deftypevar + +Where a macro should be defined in the @file{.c} file in this manner to +form part of the @code{targetm} structure, it is documented below as a +``Target Hook'' with a prototype. Many macros will change in future +from being defined in the @file{.h} file to being part of the +@code{targetm} structure. + +@node Driver +@section Controlling the Compilation Driver, @file{gcc} +@cindex driver +@cindex controlling the compilation driver + +@c prevent bad page break with this line +You can control the compilation driver. + +@table @code +@findex SWITCH_TAKES_ARG +@item SWITCH_TAKES_ARG (@var{char}) +A C expression which determines whether the option @option{-@var{char}} +takes arguments. The value should be the number of arguments that +option takes--zero, for many options. + +By default, this macro is defined as +@code{DEFAULT_SWITCH_TAKES_ARG}, which handles the standard options +properly. You need not define @code{SWITCH_TAKES_ARG} unless you +wish to add additional options which take arguments. Any redefinition +should call @code{DEFAULT_SWITCH_TAKES_ARG} and then check for +additional options. + +@findex WORD_SWITCH_TAKES_ARG +@item WORD_SWITCH_TAKES_ARG (@var{name}) +A C expression which determines whether the option @option{-@var{name}} +takes arguments. The value should be the number of arguments that +option takes--zero, for many options. This macro rather than +@code{SWITCH_TAKES_ARG} is used for multi-character option names. + +By default, this macro is defined as +@code{DEFAULT_WORD_SWITCH_TAKES_ARG}, which handles the standard options +properly. You need not define @code{WORD_SWITCH_TAKES_ARG} unless you +wish to add additional options which take arguments. Any redefinition +should call @code{DEFAULT_WORD_SWITCH_TAKES_ARG} and then check for +additional options. + +@findex SWITCH_CURTAILS_COMPILATION +@item SWITCH_CURTAILS_COMPILATION (@var{char}) +A C expression which determines whether the option @option{-@var{char}} +stops compilation before the generation of an executable. The value is +boolean, nonzero if the option does stop an executable from being +generated, zero otherwise. + +By default, this macro is defined as +@code{DEFAULT_SWITCH_CURTAILS_COMPILATION}, which handles the standard +options properly. You need not define +@code{SWITCH_CURTAILS_COMPILATION} unless you wish to add additional +options which affect the generation of an executable. Any redefinition +should call @code{DEFAULT_SWITCH_CURTAILS_COMPILATION} and then check +for additional options. + +@findex SWITCHES_NEED_SPACES +@item SWITCHES_NEED_SPACES +A string-valued C expression which enumerates the options for which +the linker needs a space between the option and its argument. + +If this macro is not defined, the default value is @code{""}. + +@findex TARGET_OPTION_TRANSLATE_TABLE +@item TARGET_OPTION_TRANSLATE_TABLE +If defined, a list of pairs of strings, the first of which is a +potential command line target to the @file{gcc} driver program, and the +second of which is a space-separated (tabs and other whitespace are not +supported) list of options with which to replace the first option. The +target defining this list is responsible for assuring that the results +are valid. Replacement options may not be the @code{--opt} style, they +must be the @code{-opt} style. It is the intention of this macro to +provide a mechanism for substitution that affects the multilibs chosen, +such as one option that enables many options, some of which select +multilibs. Example nonsensical definition, where @code{-malt-abi}, +@code{-EB}, and @code{-mspoo} cause different multilibs to be chosen: + +@example +#define TARGET_OPTION_TRANSLATE_TABLE \ +@{ "-fast", "-march=fast-foo -malt-abi -I/usr/fast-foo" @}, \ +@{ "-compat", "-EB -malign=4 -mspoo" @} +@end example + +@findex CPP_SPEC +@item CPP_SPEC +A C string constant that tells the GCC driver program options to +pass to CPP@. It can also specify how to translate options you +give to GCC into options for GCC to pass to the CPP@. + +Do not define this macro if it does not need to do anything. + +@findex CPLUSPLUS_CPP_SPEC +@item CPLUSPLUS_CPP_SPEC +This macro is just like @code{CPP_SPEC}, but is used for C++, rather +than C@. If you do not define this macro, then the value of +@code{CPP_SPEC} (if any) will be used instead. + +@findex NO_BUILTIN_SIZE_TYPE +@item NO_BUILTIN_SIZE_TYPE +If this macro is defined, the preprocessor will not define the built-in macro +@code{__SIZE_TYPE__}. The macro @code{__SIZE_TYPE__} must then be defined +by @code{CPP_SPEC} instead. + +This should be defined if @code{SIZE_TYPE} depends on target dependent flags +which are not accessible to the preprocessor. Otherwise, it should not +be defined. + +@findex NO_BUILTIN_PTRDIFF_TYPE +@item NO_BUILTIN_PTRDIFF_TYPE +If this macro is defined, the preprocessor will not define the built-in macro +@code{__PTRDIFF_TYPE__}. The macro @code{__PTRDIFF_TYPE__} must then be +defined by @code{CPP_SPEC} instead. + +This should be defined if @code{PTRDIFF_TYPE} depends on target dependent flags +which are not accessible to the preprocessor. Otherwise, it should not +be defined. + +@findex NO_BUILTIN_WCHAR_TYPE +@item NO_BUILTIN_WCHAR_TYPE +If this macro is defined, the preprocessor will not define the built-in macro +@code{__WCHAR_TYPE__}. The macro @code{__WCHAR_TYPE__} must then be +defined by @code{CPP_SPEC} instead. + +This should be defined if @code{WCHAR_TYPE} depends on target dependent flags +which are not accessible to the preprocessor. Otherwise, it should not +be defined. + +@findex NO_BUILTIN_WINT_TYPE +@item NO_BUILTIN_WINT_TYPE +If this macro is defined, the preprocessor will not define the built-in macro +@code{__WINT_TYPE__}. The macro @code{__WINT_TYPE__} must then be +defined by @code{CPP_SPEC} instead. + +This should be defined if @code{WINT_TYPE} depends on target dependent flags +which are not accessible to the preprocessor. Otherwise, it should not +be defined. + +@findex SIGNED_CHAR_SPEC +@item SIGNED_CHAR_SPEC +A C string constant that tells the GCC driver program options to +pass to CPP@. By default, this macro is defined to pass the option +@option{-D__CHAR_UNSIGNED__} to CPP if @code{char} will be treated as +@code{unsigned char} by @code{cc1}. + +Do not define this macro unless you need to override the default +definition. + +@findex CC1_SPEC +@item CC1_SPEC +A C string constant that tells the GCC driver program options to +pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language +front ends. +It can also specify how to translate options you give to GCC into options +for GCC to pass to front ends. + +Do not define this macro if it does not need to do anything. + +@findex CC1PLUS_SPEC +@item CC1PLUS_SPEC +A C string constant that tells the GCC driver program options to +pass to @code{cc1plus}. It can also specify how to translate options you +give to GCC into options for GCC to pass to the @code{cc1plus}. + +Do not define this macro if it does not need to do anything. +Note that everything defined in CC1_SPEC is already passed to +@code{cc1plus} so there is no need to duplicate the contents of +CC1_SPEC in CC1PLUS_SPEC@. + +@findex ASM_SPEC +@item ASM_SPEC +A C string constant that tells the GCC driver program options to +pass to the assembler. It can also specify how to translate options +you give to GCC into options for GCC to pass to the assembler. +See the file @file{sun3.h} for an example of this. + +Do not define this macro if it does not need to do anything. + +@findex ASM_FINAL_SPEC +@item ASM_FINAL_SPEC +A C string constant that tells the GCC driver program how to +run any programs which cleanup after the normal assembler. +Normally, this is not needed. See the file @file{mips.h} for +an example of this. + +Do not define this macro if it does not need to do anything. + +@findex LINK_SPEC +@item LINK_SPEC +A C string constant that tells the GCC driver program options to +pass to the linker. It can also specify how to translate options you +give to GCC into options for GCC to pass to the linker. + +Do not define this macro if it does not need to do anything. + +@findex LIB_SPEC +@item LIB_SPEC +Another C string constant used much like @code{LINK_SPEC}. The difference +between the two is that @code{LIB_SPEC} is used at the end of the +command given to the linker. + +If this macro is not defined, a default is provided that +loads the standard C library from the usual place. See @file{gcc.c}. + +@findex LIBGCC_SPEC +@item LIBGCC_SPEC +Another C string constant that tells the GCC driver program +how and when to place a reference to @file{libgcc.a} into the +linker command line. This constant is placed both before and after +the value of @code{LIB_SPEC}. + +If this macro is not defined, the GCC driver provides a default that +passes the string @option{-lgcc} to the linker. + +@findex STARTFILE_SPEC +@item STARTFILE_SPEC +Another C string constant used much like @code{LINK_SPEC}. The +difference between the two is that @code{STARTFILE_SPEC} is used at +the very beginning of the command given to the linker. + +If this macro is not defined, a default is provided that loads the +standard C startup file from the usual place. See @file{gcc.c}. + +@findex ENDFILE_SPEC +@item ENDFILE_SPEC +Another C string constant used much like @code{LINK_SPEC}. The +difference between the two is that @code{ENDFILE_SPEC} is used at +the very end of the command given to the linker. + +Do not define this macro if it does not need to do anything. + +@findex THREAD_MODEL_SPEC +@item THREAD_MODEL_SPEC +GCC @code{-v} will print the thread model GCC was configured to use. +However, this doesn't work on platforms that are multilibbed on thread +models, such as AIX 4.3. On such platforms, define +@code{THREAD_MODEL_SPEC} such that it evaluates to a string without +blanks that names one of the recognized thread models. @code{%*}, the +default value of this macro, will expand to the value of +@code{thread_file} set in @file{config.gcc}. + +@findex EXTRA_SPECS +@item EXTRA_SPECS +Define this macro to provide additional specifications to put in the +@file{specs} file that can be used in various specifications like +@code{CC1_SPEC}. + +The definition should be an initializer for an array of structures, +containing a string constant, that defines the specification name, and a +string constant that provides the specification. + +Do not define this macro if it does not need to do anything. + +@code{EXTRA_SPECS} is useful when an architecture contains several +related targets, which have various @code{@dots{}_SPECS} which are similar +to each other, and the maintainer would like one central place to keep +these definitions. + +For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to +define either @code{_CALL_SYSV} when the System V calling sequence is +used or @code{_CALL_AIX} when the older AIX-based calling sequence is +used. + +The @file{config/rs6000/rs6000.h} target file defines: + +@example +#define EXTRA_SPECS \ + @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @}, + +#define CPP_SYS_DEFAULT "" +@end example + +The @file{config/rs6000/sysv.h} target file defines: +@smallexample +#undef CPP_SPEC +#define CPP_SPEC \ +"%@{posix: -D_POSIX_SOURCE @} \ +%@{mcall-sysv: -D_CALL_SYSV @} %@{mcall-aix: -D_CALL_AIX @} \ +%@{!mcall-sysv: %@{!mcall-aix: %(cpp_sysv_default) @}@} \ +%@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}" + +#undef CPP_SYSV_DEFAULT +#define CPP_SYSV_DEFAULT "-D_CALL_SYSV" +@end smallexample + +while the @file{config/rs6000/eabiaix.h} target file defines +@code{CPP_SYSV_DEFAULT} as: + +@smallexample +#undef CPP_SYSV_DEFAULT +#define CPP_SYSV_DEFAULT "-D_CALL_AIX" +@end smallexample + +@findex LINK_LIBGCC_SPECIAL +@item LINK_LIBGCC_SPECIAL +Define this macro if the driver program should find the library +@file{libgcc.a} itself and should not pass @option{-L} options to the +linker. If you do not define this macro, the driver program will pass +the argument @option{-lgcc} to tell the linker to do the search and will +pass @option{-L} options to it. + +@findex LINK_LIBGCC_SPECIAL_1 +@item LINK_LIBGCC_SPECIAL_1 +Define this macro if the driver program should find the library +@file{libgcc.a}. If you do not define this macro, the driver program will pass +the argument @option{-lgcc} to tell the linker to do the search. +This macro is similar to @code{LINK_LIBGCC_SPECIAL}, except that it does +not affect @option{-L} options. + +@findex LINK_COMMAND_SPEC +@item LINK_COMMAND_SPEC +A C string constant giving the complete command line need to execute the +linker. When you do this, you will need to update your port each time a +change is made to the link command line within @file{gcc.c}. Therefore, +define this macro only if you need to completely redefine the command +line for invoking the linker and there is no other way to accomplish +the effect you need. + +@findex LINK_ELIMINATE_DUPLICATE_LDIRECTORIES +@item LINK_ELIMINATE_DUPLICATE_LDIRECTORIES +A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search +directories from linking commands. Do not give it a nonzero value if +removing duplicate search directories changes the linker's semantics. + +@findex MULTILIB_DEFAULTS +@item MULTILIB_DEFAULTS +Define this macro as a C expression for the initializer of an array of +string to tell the driver program which options are defaults for this +target and thus do not need to be handled specially when using +@code{MULTILIB_OPTIONS}. + +Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in +the target makefile fragment or if none of the options listed in +@code{MULTILIB_OPTIONS} are set by default. +@xref{Target Fragment}. + +@findex RELATIVE_PREFIX_NOT_LINKDIR +@item RELATIVE_PREFIX_NOT_LINKDIR +Define this macro to tell @code{gcc} that it should only translate +a @option{-B} prefix into a @option{-L} linker option if the prefix +indicates an absolute file name. + +@findex STANDARD_EXEC_PREFIX +@item STANDARD_EXEC_PREFIX +Define this macro as a C string constant if you wish to override the +standard choice of @file{/usr/local/lib/gcc-lib/} as the default prefix to +try when searching for the executable files of the compiler. + +@findex MD_EXEC_PREFIX +@item MD_EXEC_PREFIX +If defined, this macro is an additional prefix to try after +@code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched +when the @option{-b} option is used, or the compiler is built as a cross +compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it +to the list of directories used to find the assembler in @file{configure.in}. + +@findex STANDARD_STARTFILE_PREFIX +@item STANDARD_STARTFILE_PREFIX +Define this macro as a C string constant if you wish to override the +standard choice of @file{/usr/local/lib/} as the default prefix to +try when searching for startup files such as @file{crt0.o}. + +@findex MD_STARTFILE_PREFIX +@item MD_STARTFILE_PREFIX +If defined, this macro supplies an additional prefix to try after the +standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the +@option{-b} option is used, or when the compiler is built as a cross +compiler. + +@findex MD_STARTFILE_PREFIX_1 +@item MD_STARTFILE_PREFIX_1 +If defined, this macro supplies yet another prefix to try after the +standard prefixes. It is not searched when the @option{-b} option is +used, or when the compiler is built as a cross compiler. + +@findex INIT_ENVIRONMENT +@item INIT_ENVIRONMENT +Define this macro as a C string constant if you wish to set environment +variables for programs called by the driver, such as the assembler and +loader. The driver passes the value of this macro to @code{putenv} to +initialize the necessary environment variables. + +@findex LOCAL_INCLUDE_DIR +@item LOCAL_INCLUDE_DIR +Define this macro as a C string constant if you wish to override the +standard choice of @file{/usr/local/include} as the default prefix to +try when searching for local header files. @code{LOCAL_INCLUDE_DIR} +comes before @code{SYSTEM_INCLUDE_DIR} in the search order. + +Cross compilers do not search either @file{/usr/local/include} or its +replacement. + +@findex MODIFY_TARGET_NAME +@item MODIFY_TARGET_NAME +Define this macro if you with to define command-line switches that modify the +default target name + +For each switch, you can include a string to be appended to the first +part of the configuration name or a string to be deleted from the +configuration name, if present. The definition should be an initializer +for an array of structures. Each array element should have three +elements: the switch name (a string constant, including the initial +dash), one of the enumeration codes @code{ADD} or @code{DELETE} to +indicate whether the string should be inserted or deleted, and the string +to be inserted or deleted (a string constant). + +For example, on a machine where @samp{64} at the end of the +configuration name denotes a 64-bit target and you want the @option{-32} +and @option{-64} switches to select between 32- and 64-bit targets, you would +code + +@smallexample +#define MODIFY_TARGET_NAME \ + @{ @{ "-32", DELETE, "64"@}, \ + @{"-64", ADD, "64"@}@} +@end smallexample + + +@findex SYSTEM_INCLUDE_DIR +@item SYSTEM_INCLUDE_DIR +Define this macro as a C string constant if you wish to specify a +system-specific directory to search for header files before the standard +directory. @code{SYSTEM_INCLUDE_DIR} comes before +@code{STANDARD_INCLUDE_DIR} in the search order. + +Cross compilers do not use this macro and do not search the directory +specified. + +@findex STANDARD_INCLUDE_DIR +@item STANDARD_INCLUDE_DIR +Define this macro as a C string constant if you wish to override the +standard choice of @file{/usr/include} as the default prefix to +try when searching for header files. + +Cross compilers do not use this macro and do not search either +@file{/usr/include} or its replacement. + +@findex STANDARD_INCLUDE_COMPONENT +@item STANDARD_INCLUDE_COMPONENT +The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}. +See @code{INCLUDE_DEFAULTS}, below, for the description of components. +If you do not define this macro, no component is used. + +@findex INCLUDE_DEFAULTS +@item INCLUDE_DEFAULTS +Define this macro if you wish to override the entire default search path +for include files. For a native compiler, the default search path +usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR}, +@code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and +@code{STANDARD_INCLUDE_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR} +and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile}, +and specify private search areas for GCC@. The directory +@code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs. + +The definition should be an initializer for an array of structures. +Each array element should have four elements: the directory name (a +string constant), the component name (also a string constant), a flag +for C++-only directories, +and a flag showing that the includes in the directory don't need to be +wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of +the array with a null element. + +The component name denotes what GNU package the include file is part of, +if any, in all upper-case letters. For example, it might be @samp{GCC} +or @samp{BINUTILS}. If the package is part of a vendor-supplied +operating system, code the component name as @samp{0}. + +For example, here is the definition used for VAX/VMS: + +@example +#define INCLUDE_DEFAULTS \ +@{ \ + @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \ + @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \ + @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \ + @{ ".", 0, 0, 0@}, \ + @{ 0, 0, 0, 0@} \ +@} +@end example +@end table + +Here is the order of prefixes tried for exec files: + +@enumerate +@item +Any prefixes specified by the user with @option{-B}. + +@item +The environment variable @code{GCC_EXEC_PREFIX}, if any. + +@item +The directories specified by the environment variable @code{COMPILER_PATH}. + +@item +The macro @code{STANDARD_EXEC_PREFIX}. + +@item +@file{/usr/lib/gcc/}. + +@item +The macro @code{MD_EXEC_PREFIX}, if any. +@end enumerate + +Here is the order of prefixes tried for startfiles: + +@enumerate +@item +Any prefixes specified by the user with @option{-B}. + +@item +The environment variable @code{GCC_EXEC_PREFIX}, if any. + +@item +The directories specified by the environment variable @code{LIBRARY_PATH} +(or port-specific name; native only, cross compilers do not use this). + +@item +The macro @code{STANDARD_EXEC_PREFIX}. + +@item +@file{/usr/lib/gcc/}. + +@item +The macro @code{MD_EXEC_PREFIX}, if any. + +@item +The macro @code{MD_STARTFILE_PREFIX}, if any. + +@item +The macro @code{STANDARD_STARTFILE_PREFIX}. + +@item +@file{/lib/}. + +@item +@file{/usr/lib/}. +@end enumerate + +@node Run-time Target +@section Run-time Target Specification +@cindex run-time target specification +@cindex predefined macros +@cindex target specifications + +@c prevent bad page break with this line +Here are run-time target specifications. + +@table @code +@findex CPP_PREDEFINES +@item CPP_PREDEFINES +Define this to be a string constant containing @option{-D} options to +define the predefined macros that identify this machine and system. +These macros will be predefined unless the @option{-ansi} option (or a +@option{-std} option for strict ISO C conformance) is specified. + +In addition, a parallel set of macros are predefined, whose names are +made by appending @samp{__} at the beginning and at the end. These +@samp{__} macros are permitted by the ISO standard, so they are +predefined regardless of whether @option{-ansi} or a @option{-std} option +is specified. + +For example, on the Sun, one can use the following value: + +@smallexample +"-Dmc68000 -Dsun -Dunix" +@end smallexample + +The result is to define the macros @code{__mc68000__}, @code{__sun__} +and @code{__unix__} unconditionally, and the macros @code{mc68000}, +@code{sun} and @code{unix} provided @option{-ansi} is not specified. + +@findex extern int target_flags +@item extern int target_flags; +This declaration should be present. + +@cindex optional hardware or system features +@cindex features, optional, in system conventions +@item TARGET_@dots{} +This series of macros is to allow compiler command arguments to +enable or disable the use of optional features of the target machine. +For example, one machine description serves both the 68000 and +the 68020; a command argument tells the compiler whether it should +use 68020-only instructions or not. This command argument works +by means of a macro @code{TARGET_68020} that tests a bit in +@code{target_flags}. + +Define a macro @code{TARGET_@var{featurename}} for each such option. +Its definition should test a bit in @code{target_flags}. It is +recommended that a helper macro @code{TARGET_MASK_@var{featurename}} +is defined for each bit-value to test, and used in +@code{TARGET_@var{featurename}} and @code{TARGET_SWITCHES}. For +example: + +@smallexample +#define TARGET_MASK_68020 1 +#define TARGET_68020 (target_flags & TARGET_MASK_68020) +@end smallexample + +One place where these macros are used is in the condition-expressions +of instruction patterns. Note how @code{TARGET_68020} appears +frequently in the 68000 machine description file, @file{m68k.md}. +Another place they are used is in the definitions of the other +macros in the @file{@var{machine}.h} file. + +@findex TARGET_SWITCHES +@item TARGET_SWITCHES +This macro defines names of command options to set and clear +bits in @code{target_flags}. Its definition is an initializer +with a subgrouping for each command option. + +Each subgrouping contains a string constant, that defines the option +name, a number, which contains the bits to set in +@code{target_flags}, and a second string which is the description +displayed by @option{--help}. If the number is negative then the bits specified +by the number are cleared instead of being set. If the description +string is present but empty, then no help information will be displayed +for that option, but it will not count as an undocumented option. The +actual option name is made by appending @samp{-m} to the specified name. +Non-empty description strings should be marked with @code{N_(@dots{})} for +@command{xgettext}. In addition to the description for @option{--help}, +more detailed documentation for each option should be added to +@file{invoke.texi}. + +One of the subgroupings should have a null string. The number in +this grouping is the default value for @code{target_flags}. Any +target options act starting with that value. + +Here is an example which defines @option{-m68000} and @option{-m68020} +with opposite meanings, and picks the latter as the default: + +@smallexample +#define TARGET_SWITCHES \ + @{ @{ "68020", TARGET_MASK_68020, "" @}, \ + @{ "68000", -TARGET_MASK_68020, \ + N_("Compile for the 68000") @}, \ + @{ "", TARGET_MASK_68020, "" @}@} +@end smallexample + +@findex TARGET_OPTIONS +@item TARGET_OPTIONS +This macro is similar to @code{TARGET_SWITCHES} but defines names of command +options that have values. Its definition is an initializer with a +subgrouping for each command option. + +Each subgrouping contains a string constant, that defines the fixed part +of the option name, the address of a variable, and a description string +(which should again be marked with @code{N_(@dots{})}). +The variable, type @code{char *}, is set to the variable part of the +given option if the fixed part matches. The actual option name is made +by appending @samp{-m} to the specified name. Again, each option should +also be documented in @file{invoke.texi}. + +Here is an example which defines @option{-mshort-data-@var{number}}. If the +given option is @option{-mshort-data-512}, the variable @code{m88k_short_data} +will be set to the string @code{"512"}. + +@smallexample +extern char *m88k_short_data; +#define TARGET_OPTIONS \ + @{ @{ "short-data-", &m88k_short_data, \ + N_("Specify the size of the short data section") @} @} +@end smallexample + +@findex TARGET_VERSION +@item TARGET_VERSION +This macro is a C statement to print on @code{stderr} a string +describing the particular machine description choice. Every machine +description should define @code{TARGET_VERSION}. For example: + +@smallexample +#ifdef MOTOROLA +#define TARGET_VERSION \ + fprintf (stderr, " (68k, Motorola syntax)"); +#else +#define TARGET_VERSION \ + fprintf (stderr, " (68k, MIT syntax)"); +#endif +@end smallexample + +@findex OVERRIDE_OPTIONS +@item OVERRIDE_OPTIONS +Sometimes certain combinations of command options do not make sense on +a particular target machine. You can define a macro +@code{OVERRIDE_OPTIONS} to take account of this. This macro, if +defined, is executed once just after all the command options have been +parsed. + +Don't use this macro to turn on various extra optimizations for +@option{-O}. That is what @code{OPTIMIZATION_OPTIONS} is for. + +@findex OPTIMIZATION_OPTIONS +@item OPTIMIZATION_OPTIONS (@var{level}, @var{size}) +Some machines may desire to change what optimizations are performed for +various optimization levels. This macro, if defined, is executed once +just after the optimization level is determined and before the remainder +of the command options have been parsed. Values set in this macro are +used as the default values for the other command line options. + +@var{level} is the optimization level specified; 2 if @option{-O2} is +specified, 1 if @option{-O} is specified, and 0 if neither is specified. + +@var{size} is nonzero if @option{-Os} is specified and zero otherwise. + +You should not use this macro to change options that are not +machine-specific. These should uniformly selected by the same +optimization level on all supported machines. Use this macro to enable +machine-specific optimizations. + +@strong{Do not examine @code{write_symbols} in +this macro!} The debugging options are not supposed to alter the +generated code. + +@findex CAN_DEBUG_WITHOUT_FP +@item CAN_DEBUG_WITHOUT_FP +Define this macro if debugging can be performed even without a frame +pointer. If this macro is defined, GCC will turn on the +@option{-fomit-frame-pointer} option whenever @option{-O} is specified. +@end table + +@node Per-Function Data +@section Defining data structures for per-function information. +@cindex per-function data +@cindex data structures + +If the target needs to store information on a per-function basis, GCC +provides a macro and a couple of variables to allow this. Note, just +using statics to store the information is a bad idea, since GCC supports +nested functions, so you can be halfway through encoding one function +when another one comes along. + +GCC defines a data structure called @code{struct function} which +contains all of the data specific to an individual function. This +structure contains a field called @code{machine} whose type is +@code{struct machine_function *}, which can be used by targets to point +to their own specific data. + +If a target needs per-function specific data it should define the type +@code{struct machine_function} and also the macro +@code{INIT_EXPANDERS}. This macro should be used to initialize some or +all of the function pointers @code{init_machine_status}, +@code{free_machine_status} and @code{mark_machine_status}. These +pointers are explained below. + +One typical use of per-function, target specific data is to create an +RTX to hold the register containing the function's return address. This +RTX can then be used to implement the @code{__builtin_return_address} +function, for level 0. + +Note---earlier implementations of GCC used a single data area to hold +all of the per-function information. Thus when processing of a nested +function began the old per-function data had to be pushed onto a +stack, and when the processing was finished, it had to be popped off the +stack. GCC used to provide function pointers called +@code{save_machine_status} and @code{restore_machine_status} to handle +the saving and restoring of the target specific information. Since the +single data area approach is no longer used, these pointers are no +longer supported. + +The macro and function pointers are described below. + +@table @code +@findex INIT_EXPANDERS +@item INIT_EXPANDERS +Macro called to initialize any target specific information. This macro +is called once per function, before generation of any RTL has begun. +The intention of this macro is to allow the initialization of the +function pointers below. + +@findex init_machine_status +@item init_machine_status +This is a @code{void (*)(struct function *)} function pointer. If this +pointer is non-@code{NULL} it will be called once per function, before function +compilation starts, in order to allow the target to perform any target +specific initialization of the @code{struct function} structure. It is +intended that this would be used to initialize the @code{machine} of +that structure. + +@findex free_machine_status +@item free_machine_status +This is a @code{void (*)(struct function *)} function pointer. If this +pointer is non-@code{NULL} it will be called once per function, after the +function has been compiled, in order to allow any memory allocated +during the @code{init_machine_status} function call to be freed. + +@findex mark_machine_status +@item mark_machine_status +This is a @code{void (*)(struct function *)} function pointer. If this +pointer is non-@code{NULL} it will be called once per function in order to mark +any data items in the @code{struct machine_function} structure which +need garbage collection. + +@end table + +@node Storage Layout +@section Storage Layout +@cindex storage layout + +Note that the definitions of the macros in this table which are sizes or +alignments measured in bits do not need to be constant. They can be C +expressions that refer to static variables, such as the @code{target_flags}. +@xref{Run-time Target}. + +@table @code +@findex BITS_BIG_ENDIAN +@item BITS_BIG_ENDIAN +Define this macro to have the value 1 if the most significant bit in a +byte has the lowest number; otherwise define it to have the value zero. +This means that bit-field instructions count from the most significant +bit. If the machine has no bit-field instructions, then this must still +be defined, but it doesn't matter which value it is defined to. This +macro need not be a constant. + +This macro does not affect the way structure fields are packed into +bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}. + +@findex BYTES_BIG_ENDIAN +@item BYTES_BIG_ENDIAN +Define this macro to have the value 1 if the most significant byte in a +word has the lowest number. This macro need not be a constant. + +@findex WORDS_BIG_ENDIAN +@item WORDS_BIG_ENDIAN +Define this macro to have the value 1 if, in a multiword object, the +most significant word has the lowest number. This applies to both +memory locations and registers; GCC fundamentally assumes that the +order of words in memory is the same as the order in registers. This +macro need not be a constant. + +@findex LIBGCC2_WORDS_BIG_ENDIAN +@item LIBGCC2_WORDS_BIG_ENDIAN +Define this macro if @code{WORDS_BIG_ENDIAN} is not constant. This must be a +constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be +used only when compiling @file{libgcc2.c}. Typically the value will be set +based on preprocessor defines. + +@findex FLOAT_WORDS_BIG_ENDIAN +@item FLOAT_WORDS_BIG_ENDIAN +Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or +@code{TFmode} floating point numbers are stored in memory with the word +containing the sign bit at the lowest address; otherwise define it to +have the value 0. This macro need not be a constant. + +You need not define this macro if the ordering is the same as for +multi-word integers. + +@findex BITS_PER_UNIT +@item BITS_PER_UNIT +Define this macro to be the number of bits in an addressable storage +unit (byte); normally 8. + +@findex BITS_PER_WORD +@item BITS_PER_WORD +Number of bits in a word; normally 32. + +@findex MAX_BITS_PER_WORD +@item MAX_BITS_PER_WORD +Maximum number of bits in a word. If this is undefined, the default is +@code{BITS_PER_WORD}. Otherwise, it is the constant value that is the +largest value that @code{BITS_PER_WORD} can have at run-time. + +@findex UNITS_PER_WORD +@item UNITS_PER_WORD +Number of storage units in a word; normally 4. + +@findex MIN_UNITS_PER_WORD +@item MIN_UNITS_PER_WORD +Minimum number of units in a word. If this is undefined, the default is +@code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the +smallest value that @code{UNITS_PER_WORD} can have at run-time. + +@findex POINTER_SIZE +@item POINTER_SIZE +Width of a pointer, in bits. You must specify a value no wider than the +width of @code{Pmode}. If it is not equal to the width of @code{Pmode}, +you must define @code{POINTERS_EXTEND_UNSIGNED}. + +@findex POINTERS_EXTEND_UNSIGNED +@item POINTERS_EXTEND_UNSIGNED +A C expression whose value is greater than zero if pointers that need to be +extended from being @code{POINTER_SIZE} bits wide to @code{Pmode} are to +be zero-extended and zero if they are to be sign-extended. If the value +is less then zero then there must be an "ptr_extend" instruction that +extends a pointer from @code{POINTER_SIZE} to @code{Pmode}. + +You need not define this macro if the @code{POINTER_SIZE} is equal +to the width of @code{Pmode}. + +@findex PROMOTE_MODE +@item PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type}) +A macro to update @var{m} and @var{unsignedp} when an object whose type +is @var{type} and which has the specified mode and signedness is to be +stored in a register. This macro is only called when @var{type} is a +scalar type. + +On most RISC machines, which only have operations that operate on a full +register, define this macro to set @var{m} to @code{word_mode} if +@var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most +cases, only integer modes should be widened because wider-precision +floating-point operations are usually more expensive than their narrower +counterparts. + +For most machines, the macro definition does not change @var{unsignedp}. +However, some machines, have instructions that preferentially handle +either signed or unsigned quantities of certain modes. For example, on +the DEC Alpha, 32-bit loads from memory and 32-bit add instructions +sign-extend the result to 64 bits. On such machines, set +@var{unsignedp} according to which kind of extension is more efficient. + +Do not define this macro if it would never modify @var{m}. + +@findex PROMOTE_FUNCTION_ARGS +@item PROMOTE_FUNCTION_ARGS +Define this macro if the promotion described by @code{PROMOTE_MODE} +should also be done for outgoing function arguments. + +@findex PROMOTE_FUNCTION_RETURN +@item PROMOTE_FUNCTION_RETURN +Define this macro if the promotion described by @code{PROMOTE_MODE} +should also be done for the return value of functions. + +If this macro is defined, @code{FUNCTION_VALUE} must perform the same +promotions done by @code{PROMOTE_MODE}. + +@findex PROMOTE_FOR_CALL_ONLY +@item PROMOTE_FOR_CALL_ONLY +Define this macro if the promotion described by @code{PROMOTE_MODE} +should @emph{only} be performed for outgoing function arguments or +function return values, as specified by @code{PROMOTE_FUNCTION_ARGS} +and @code{PROMOTE_FUNCTION_RETURN}, respectively. + +@findex PARM_BOUNDARY +@item PARM_BOUNDARY +Normal alignment required for function parameters on the stack, in +bits. All stack parameters receive at least this much alignment +regardless of data type. On most machines, this is the same as the +size of an integer. + +@findex STACK_BOUNDARY +@item STACK_BOUNDARY +Define this macro to the minimum alignment enforced by hardware for the +stack pointer on this machine. The definition is a C expression for the +desired alignment (measured in bits). This value is used as a default +if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines, +this should be the same as @code{PARM_BOUNDARY}. + +@findex PREFERRED_STACK_BOUNDARY +@item PREFERRED_STACK_BOUNDARY +Define this macro if you wish to preserve a certain alignment for the +stack pointer, greater than what the hardware enforces. The definition +is a C expression for the desired alignment (measured in bits). This +macro must evaluate to a value equal to or larger than +@code{STACK_BOUNDARY}. + +@findex FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN +@item FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN +A C expression that evaluates true if @code{PREFERRED_STACK_BOUNDARY} is +not guaranteed by the runtime and we should emit code to align the stack +at the beginning of @code{main}. + +@cindex @code{PUSH_ROUNDING}, interaction with @code{PREFERRED_STACK_BOUNDARY} +If @code{PUSH_ROUNDING} is not defined, the stack will always be aligned +to the specified boundary. If @code{PUSH_ROUNDING} is defined and specifies +a less strict alignment than @code{PREFERRED_STACK_BOUNDARY}, the stack may +be momentarily unaligned while pushing arguments. + +@findex FUNCTION_BOUNDARY +@item FUNCTION_BOUNDARY +Alignment required for a function entry point, in bits. + +@findex BIGGEST_ALIGNMENT +@item BIGGEST_ALIGNMENT +Biggest alignment that any data type can require on this machine, in bits. + +@findex MINIMUM_ATOMIC_ALIGNMENT +@item MINIMUM_ATOMIC_ALIGNMENT +If defined, the smallest alignment, in bits, that can be given to an +object that can be referenced in one operation, without disturbing any +nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger +on machines that don't have byte or half-word store operations. + +@findex BIGGEST_FIELD_ALIGNMENT +@item BIGGEST_FIELD_ALIGNMENT +Biggest alignment that any structure or union field can require on this +machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for +structure and union fields only, unless the field alignment has been set +by the @code{__attribute__ ((aligned (@var{n})))} construct. + +@findex ADJUST_FIELD_ALIGN +@item ADJUST_FIELD_ALIGN (@var{field}, @var{computed}) +An expression for the alignment of a structure field @var{field} if the +alignment computed in the usual way is @var{computed}. GCC uses +this value instead of the value in @code{BIGGEST_ALIGNMENT} or +@code{BIGGEST_FIELD_ALIGNMENT}, if defined. + +@findex MAX_OFILE_ALIGNMENT +@item MAX_OFILE_ALIGNMENT +Biggest alignment supported by the object file format of this machine. +Use this macro to limit the alignment which can be specified using the +@code{__attribute__ ((aligned (@var{n})))} construct. If not defined, +the default value is @code{BIGGEST_ALIGNMENT}. + +@findex DATA_ALIGNMENT +@item DATA_ALIGNMENT (@var{type}, @var{basic-align}) +If defined, a C expression to compute the alignment for a variable in +the static store. @var{type} is the data type, and @var{basic-align} is +the alignment that the object would ordinarily have. The value of this +macro is used instead of that alignment to align the object. + +If this macro is not defined, then @var{basic-align} is used. + +@findex strcpy +One use of this macro is to increase alignment of medium-size data to +make it all fit in fewer cache lines. Another is to cause character +arrays to be word-aligned so that @code{strcpy} calls that copy +constants to character arrays can be done inline. + +@findex CONSTANT_ALIGNMENT +@item CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align}) +If defined, a C expression to compute the alignment given to a constant +that is being placed in memory. @var{constant} is the constant and +@var{basic-align} is the alignment that the object would ordinarily +have. The value of this macro is used instead of that alignment to +align the object. + +If this macro is not defined, then @var{basic-align} is used. + +The typical use of this macro is to increase alignment for string +constants to be word aligned so that @code{strcpy} calls that copy +constants can be done inline. + +@findex LOCAL_ALIGNMENT +@item LOCAL_ALIGNMENT (@var{type}, @var{basic-align}) +If defined, a C expression to compute the alignment for a variable in +the local store. @var{type} is the data type, and @var{basic-align} is +the alignment that the object would ordinarily have. The value of this +macro is used instead of that alignment to align the object. + +If this macro is not defined, then @var{basic-align} is used. + +One use of this macro is to increase alignment of medium-size data to +make it all fit in fewer cache lines. + +@findex EMPTY_FIELD_BOUNDARY +@item EMPTY_FIELD_BOUNDARY +Alignment in bits to be given to a structure bit-field that follows an +empty field such as @code{int : 0;}. + +Note that @code{PCC_BITFIELD_TYPE_MATTERS} also affects the alignment +that results from an empty field. + +@findex STRUCTURE_SIZE_BOUNDARY +@item STRUCTURE_SIZE_BOUNDARY +Number of bits which any structure or union's size must be a multiple of. +Each structure or union's size is rounded up to a multiple of this. + +If you do not define this macro, the default is the same as +@code{BITS_PER_UNIT}. + +@findex STRICT_ALIGNMENT +@item STRICT_ALIGNMENT +Define this macro to be the value 1 if instructions will fail to work +if given data not on the nominal alignment. If instructions will merely +go slower in that case, define this macro as 0. + +@findex PCC_BITFIELD_TYPE_MATTERS +@item PCC_BITFIELD_TYPE_MATTERS +Define this if you wish to imitate the way many other C compilers handle +alignment of bit-fields and the structures that contain them. + +The behavior is that the type written for a bit-field (@code{int}, +@code{short}, or other integer type) imposes an alignment for the +entire structure, as if the structure really did contain an ordinary +field of that type. In addition, the bit-field is placed within the +structure so that it would fit within such a field, not crossing a +boundary for it. + +Thus, on most machines, a bit-field whose type is written as @code{int} +would not cross a four-byte boundary, and would force four-byte +alignment for the whole structure. (The alignment used may not be four +bytes; it is controlled by the other alignment parameters.) + +If the macro is defined, its definition should be a C expression; +a nonzero value for the expression enables this behavior. + +Note that if this macro is not defined, or its value is zero, some +bit-fields may cross more than one alignment boundary. The compiler can +support such references if there are @samp{insv}, @samp{extv}, and +@samp{extzv} insns that can directly reference memory. + +The other known way of making bit-fields work is to define +@code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}. +Then every structure can be accessed with fullwords. + +Unless the machine has bit-field instructions or you define +@code{STRUCTURE_SIZE_BOUNDARY} that way, you must define +@code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value. + +If your aim is to make GCC use the same conventions for laying out +bit-fields as are used by another compiler, here is how to investigate +what the other compiler does. Compile and run this program: + +@example +struct foo1 +@{ + char x; + char :0; + char y; +@}; + +struct foo2 +@{ + char x; + int :0; + char y; +@}; + +main () +@{ + printf ("Size of foo1 is %d\n", + sizeof (struct foo1)); + printf ("Size of foo2 is %d\n", + sizeof (struct foo2)); + exit (0); +@} +@end example + +If this prints 2 and 5, then the compiler's behavior is what you would +get from @code{PCC_BITFIELD_TYPE_MATTERS}. + +@findex BITFIELD_NBYTES_LIMITED +@item BITFIELD_NBYTES_LIMITED +Like PCC_BITFIELD_TYPE_MATTERS except that its effect is limited to +aligning a bit-field within the structure. + +@findex MEMBER_TYPE_FORCES_BLK +@item MEMBER_TYPE_FORCES_BLK (@var{field}) +Return 1 if a structure or array containing @var{field} should be accessed using +@code{BLKMODE}. + +Normally, this is not needed. See the file @file{c4x.h} for an example +of how to use this macro to prevent a structure having a floating point +field from being accessed in an integer mode. + +@findex ROUND_TYPE_SIZE +@item ROUND_TYPE_SIZE (@var{type}, @var{computed}, @var{specified}) +Define this macro as an expression for the overall size of a type +(given by @var{type} as a tree node) when the size computed in the +usual way is @var{computed} and the alignment is @var{specified}. + +The default is to round @var{computed} up to a multiple of @var{specified}. + +@findex ROUND_TYPE_SIZE_UNIT +@item ROUND_TYPE_SIZE_UNIT (@var{type}, @var{computed}, @var{specified}) +Similar to @code{ROUND_TYPE_SIZE}, but sizes and alignments are +specified in units (bytes). If you define @code{ROUND_TYPE_SIZE}, +you must also define this macro and they must be defined consistently +with each other. + +@findex ROUND_TYPE_ALIGN +@item ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified}) +Define this macro as an expression for the alignment of a type (given +by @var{type} as a tree node) if the alignment computed in the usual +way is @var{computed} and the alignment explicitly specified was +@var{specified}. + +The default is to use @var{specified} if it is larger; otherwise, use +the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT} + +@findex MAX_FIXED_MODE_SIZE +@item MAX_FIXED_MODE_SIZE +An integer expression for the size in bits of the largest integer +machine mode that should actually be used. All integer machine modes of +this size or smaller can be used for structures and unions with the +appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE +(DImode)} is assumed. + +@findex VECTOR_MODE_SUPPORTED_P +@item VECTOR_MODE_SUPPORTED_P(@var{mode}) +Define this macro to be nonzero if the port is prepared to handle insns +involving vector mode @var{mode}. At the very least, it must have move +patterns for this mode. + +@findex STACK_SAVEAREA_MODE +@item STACK_SAVEAREA_MODE (@var{save_level}) +If defined, an expression of type @code{enum machine_mode} that +specifies the mode of the save area operand of a +@code{save_stack_@var{level}} named pattern (@pxref{Standard Names}). +@var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or +@code{SAVE_NONLOCAL} and selects which of the three named patterns is +having its mode specified. + +You need not define this macro if it always returns @code{Pmode}. You +would most commonly define this macro if the +@code{save_stack_@var{level}} patterns need to support both a 32- and a +64-bit mode. + +@findex STACK_SIZE_MODE +@item STACK_SIZE_MODE +If defined, an expression of type @code{enum machine_mode} that +specifies the mode of the size increment operand of an +@code{allocate_stack} named pattern (@pxref{Standard Names}). + +You need not define this macro if it always returns @code{word_mode}. +You would most commonly define this macro if the @code{allocate_stack} +pattern needs to support both a 32- and a 64-bit mode. + +@findex CHECK_FLOAT_VALUE +@item CHECK_FLOAT_VALUE (@var{mode}, @var{value}, @var{overflow}) +A C statement to validate the value @var{value} (of type +@code{double}) for mode @var{mode}. This means that you check whether +@var{value} fits within the possible range of values for mode +@var{mode} on this target machine. The mode @var{mode} is always +a mode of class @code{MODE_FLOAT}. @var{overflow} is nonzero if +the value is already known to be out of range. + +If @var{value} is not valid or if @var{overflow} is nonzero, you should +set @var{overflow} to 1 and then assign some valid value to @var{value}. +Allowing an invalid value to go through the compiler can produce +incorrect assembler code which may even cause Unix assemblers to crash. + +This macro need not be defined if there is no work for it to do. + +@findex TARGET_FLOAT_FORMAT +@item TARGET_FLOAT_FORMAT +A code distinguishing the floating point format of the target machine. +There are five defined values: + +@table @code +@findex IEEE_FLOAT_FORMAT +@item IEEE_FLOAT_FORMAT +This code indicates IEEE floating point. It is the default; there is no +need to define this macro when the format is IEEE@. + +@findex VAX_FLOAT_FORMAT +@item VAX_FLOAT_FORMAT +This code indicates the ``D float'' format used on the VAX@. + +@findex IBM_FLOAT_FORMAT +@item IBM_FLOAT_FORMAT +This code indicates the format used on the IBM System/370. + +@findex C4X_FLOAT_FORMAT +@item C4X_FLOAT_FORMAT +This code indicates the format used on the TMS320C3x/C4x. + +@findex UNKNOWN_FLOAT_FORMAT +@item UNKNOWN_FLOAT_FORMAT +This code indicates any other format. +@end table + +The value of this macro is compared with @code{HOST_FLOAT_FORMAT}, which +is defined by the @command{configure} script, to determine whether the +target machine has the same format as the host machine. If any other +formats are actually in use on supported machines, new codes should be +defined for them. + +The ordering of the component words of floating point values stored in +memory is controlled by @code{FLOAT_WORDS_BIG_ENDIAN}. + +@end table + +@node Type Layout +@section Layout of Source Language Data Types + +These macros define the sizes and other characteristics of the standard +basic data types used in programs being compiled. Unlike the macros in +the previous section, these apply to specific features of C and related +languages, rather than to fundamental aspects of storage layout. + +@table @code +@findex INT_TYPE_SIZE +@item INT_TYPE_SIZE +A C expression for the size in bits of the type @code{int} on the +target machine. If you don't define this, the default is one word. + +@findex SHORT_TYPE_SIZE +@item SHORT_TYPE_SIZE +A C expression for the size in bits of the type @code{short} on the +target machine. If you don't define this, the default is half a word. +(If this would be less than one storage unit, it is rounded up to one +unit.) + +@findex LONG_TYPE_SIZE +@item LONG_TYPE_SIZE +A C expression for the size in bits of the type @code{long} on the +target machine. If you don't define this, the default is one word. + +@findex ADA_LONG_TYPE_SIZE +@item ADA_LONG_TYPE_SIZE +On some machines, the size used for the Ada equivalent of the type +@code{long} by a native Ada compiler differs from that used by C. In +that situation, define this macro to be a C expression to be used for +the size of that type. If you don't define this, the default is the +value of @code{LONG_TYPE_SIZE}. + +@findex MAX_LONG_TYPE_SIZE +@item MAX_LONG_TYPE_SIZE +Maximum number for the size in bits of the type @code{long} on the +target machine. If this is undefined, the default is +@code{LONG_TYPE_SIZE}. Otherwise, it is the constant value that is the +largest value that @code{LONG_TYPE_SIZE} can have at run-time. This is +used in @code{cpp}. + +@findex LONG_LONG_TYPE_SIZE +@item LONG_LONG_TYPE_SIZE +A C expression for the size in bits of the type @code{long long} on the +target machine. If you don't define this, the default is two +words. If you want to support GNU Ada on your machine, the value of this +macro must be at least 64. + +@findex CHAR_TYPE_SIZE +@item CHAR_TYPE_SIZE +A C expression for the size in bits of the type @code{char} on the +target machine. If you don't define this, the default is +@code{BITS_PER_UNIT}. + +@findex MAX_CHAR_TYPE_SIZE +@item MAX_CHAR_TYPE_SIZE +Maximum number for the size in bits of the type @code{char} on the +target machine. If this is undefined, the default is +@code{CHAR_TYPE_SIZE}. Otherwise, it is the constant value that is the +largest value that @code{CHAR_TYPE_SIZE} can have at run-time. This is +used in @code{cpp}. + +@findex BOOL_TYPE_SIZE +@item BOOL_TYPE_SIZE +A C expression for the size in bits of the C++ type @code{bool} on the +target machine. If you don't define this, the default is +@code{CHAR_TYPE_SIZE}. + +@findex FLOAT_TYPE_SIZE +@item FLOAT_TYPE_SIZE +A C expression for the size in bits of the type @code{float} on the +target machine. If you don't define this, the default is one word. + +@findex DOUBLE_TYPE_SIZE +@item DOUBLE_TYPE_SIZE +A C expression for the size in bits of the type @code{double} on the +target machine. If you don't define this, the default is two +words. + +@findex LONG_DOUBLE_TYPE_SIZE +@item LONG_DOUBLE_TYPE_SIZE +A C expression for the size in bits of the type @code{long double} on +the target machine. If you don't define this, the default is two +words. + +@findex MAX_LONG_DOUBLE_TYPE_SIZE +Maximum number for the size in bits of the type @code{long double} on the +target machine. If this is undefined, the default is +@code{LONG_DOUBLE_TYPE_SIZE}. Otherwise, it is the constant value that is +the largest value that @code{LONG_DOUBLE_TYPE_SIZE} can have at run-time. +This is used in @code{cpp}. + +@findex INTEL_EXTENDED_IEEE_FORMAT +Define this macro to be 1 if the target machine uses 80-bit floating-point +values with 128-bit size and alignment. This is used in @file{real.c}. + +@findex WIDEST_HARDWARE_FP_SIZE +@item WIDEST_HARDWARE_FP_SIZE +A C expression for the size in bits of the widest floating-point format +supported by the hardware. If you define this macro, you must specify a +value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}. +If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE} +is the default. + +@findex DEFAULT_SIGNED_CHAR +@item DEFAULT_SIGNED_CHAR +An expression whose value is 1 or 0, according to whether the type +@code{char} should be signed or unsigned by default. The user can +always override this default with the options @option{-fsigned-char} +and @option{-funsigned-char}. + +@findex DEFAULT_SHORT_ENUMS +@item DEFAULT_SHORT_ENUMS +A C expression to determine whether to give an @code{enum} type +only as many bytes as it takes to represent the range of possible values +of that type. A nonzero value means to do that; a zero value means all +@code{enum} types should be allocated like @code{int}. + +If you don't define the macro, the default is 0. + +@findex SIZE_TYPE +@item SIZE_TYPE +A C expression for a string describing the name of the data type to use +for size values. The typedef name @code{size_t} is defined using the +contents of the string. + +The string can contain more than one keyword. If so, separate them with +spaces, and write first any length keyword, then @code{unsigned} if +appropriate, and finally @code{int}. The string must exactly match one +of the data type names defined in the function +@code{init_decl_processing} in the file @file{c-decl.c}. You may not +omit @code{int} or change the order---that would cause the compiler to +crash on startup. + +If you don't define this macro, the default is @code{"long unsigned +int"}. + +@findex PTRDIFF_TYPE +@item PTRDIFF_TYPE +A C expression for a string describing the name of the data type to use +for the result of subtracting two pointers. The typedef name +@code{ptrdiff_t} is defined using the contents of the string. See +@code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is @code{"long int"}. + +@findex WCHAR_TYPE +@item WCHAR_TYPE +A C expression for a string describing the name of the data type to use +for wide characters. The typedef name @code{wchar_t} is defined using +the contents of the string. See @code{SIZE_TYPE} above for more +information. + +If you don't define this macro, the default is @code{"int"}. + +@findex WCHAR_TYPE_SIZE +@item WCHAR_TYPE_SIZE +A C expression for the size in bits of the data type for wide +characters. This is used in @code{cpp}, which cannot make use of +@code{WCHAR_TYPE}. + +@findex MAX_WCHAR_TYPE_SIZE +@item MAX_WCHAR_TYPE_SIZE +Maximum number for the size in bits of the data type for wide +characters. If this is undefined, the default is +@code{WCHAR_TYPE_SIZE}. Otherwise, it is the constant value that is the +largest value that @code{WCHAR_TYPE_SIZE} can have at run-time. This is +used in @code{cpp}. + +@findex GCOV_TYPE_SIZE +@item GCOV_TYPE_SIZE +A C expression for the size in bits of the type used for gcov counters on the +target machine. If you don't define this, the default is one +@code{LONG_TYPE_SIZE} in case it is greater or equal to 64-bit and +@code{LONG_LONG_TYPE_SIZE} otherwise. You may want to re-define the type to +ensure atomicity for counters in multithreaded programs. + +@findex WINT_TYPE +@item WINT_TYPE +A C expression for a string describing the name of the data type to +use for wide characters passed to @code{printf} and returned from +@code{getwc}. The typedef name @code{wint_t} is defined using the +contents of the string. See @code{SIZE_TYPE} above for more +information. + +If you don't define this macro, the default is @code{"unsigned int"}. + +@findex INTMAX_TYPE +@item INTMAX_TYPE +A C expression for a string describing the name of the data type that +can represent any value of any standard or extended signed integer type. +The typedef name @code{intmax_t} is defined using the contents of the +string. See @code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is the first of +@code{"int"}, @code{"long int"}, or @code{"long long int"} that has as +much precision as @code{long long int}. + +@findex UINTMAX_TYPE +@item UINTMAX_TYPE +A C expression for a string describing the name of the data type that +can represent any value of any standard or extended unsigned integer +type. The typedef name @code{uintmax_t} is defined using the contents +of the string. See @code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is the first of +@code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long +unsigned int"} that has as much precision as @code{long long unsigned +int}. + +@findex TARGET_PTRMEMFUNC_VBIT_LOCATION +@item TARGET_PTRMEMFUNC_VBIT_LOCATION +The C++ compiler represents a pointer-to-member-function with a struct +that looks like: + +@example + struct @{ + union @{ + void (*fn)(); + ptrdiff_t vtable_index; + @}; + ptrdiff_t delta; + @}; +@end example + +@noindent +The C++ compiler must use one bit to indicate whether the function that +will be called through a pointer-to-member-function is virtual. +Normally, we assume that the low-order bit of a function pointer must +always be zero. Then, by ensuring that the vtable_index is odd, we can +distinguish which variant of the union is in use. But, on some +platforms function pointers can be odd, and so this doesn't work. In +that case, we use the low-order bit of the @code{delta} field, and shift +the remainder of the @code{delta} field to the left. + +GCC will automatically make the right selection about where to store +this bit using the @code{FUNCTION_BOUNDARY} setting for your platform. +However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY} +set such that functions always start at even addresses, but the lowest +bit of pointers to functions indicate whether the function at that +address is in ARM or Thumb mode. If this is the case of your +architecture, you should define this macro to +@code{ptrmemfunc_vbit_in_delta}. + +In general, you should not have to define this macro. On architectures +in which function addresses are always even, according to +@code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to +@code{ptrmemfunc_vbit_in_pfn}. + +@findex TARGET_VTABLE_USES_DESCRIPTORS +@item TARGET_VTABLE_USES_DESCRIPTORS +Normally, the C++ compiler uses function pointers in vtables. This +macro allows the target to change to use ``function descriptors'' +instead. Function descriptors are found on targets for whom a +function pointer is actually a small data structure. Normally the +data structure consists of the actual code address plus a data +pointer to which the function's data is relative. + +If vtables are used, the value of this macro should be the number +of words that the function descriptor occupies. +@end table + +@node Escape Sequences +@section Target Character Escape Sequences +@cindex escape sequences + +By default, GCC assumes that the C character escape sequences take on +their ASCII values for the target. If this is not correct, you must +explicitly define all of the macros below. + +@table @code +@findex TARGET_BELL +@item TARGET_BELL +A C constant expression for the integer value for escape sequence +@samp{\a}. + +@findex TARGET_ESC +@item TARGET_ESC +A C constant expression for the integer value of the target escape +character. As an extension, GCC evaluates the escape sequences +@samp{\e} and @samp{\E} to this. + +@findex TARGET_TAB +@findex TARGET_BS +@findex TARGET_NEWLINE +@item TARGET_BS +@itemx TARGET_TAB +@itemx TARGET_NEWLINE +C constant expressions for the integer values for escape sequences +@samp{\b}, @samp{\t} and @samp{\n}. + +@findex TARGET_VT +@findex TARGET_FF +@findex TARGET_CR +@item TARGET_VT +@itemx TARGET_FF +@itemx TARGET_CR +C constant expressions for the integer values for escape sequences +@samp{\v}, @samp{\f} and @samp{\r}. +@end table + +@node Registers +@section Register Usage +@cindex register usage + +This section explains how to describe what registers the target machine +has, and how (in general) they can be used. + +The description of which registers a specific instruction can use is +done with register classes; see @ref{Register Classes}. For information +on using registers to access a stack frame, see @ref{Frame Registers}. +For passing values in registers, see @ref{Register Arguments}. +For returning values in registers, see @ref{Scalar Return}. + +@menu +* Register Basics:: Number and kinds of registers. +* Allocation Order:: Order in which registers are allocated. +* Values in Registers:: What kinds of values each reg can hold. +* Leaf Functions:: Renumbering registers for leaf functions. +* Stack Registers:: Handling a register stack such as 80387. +@end menu + +@node Register Basics +@subsection Basic Characteristics of Registers + +@c prevent bad page break with this line +Registers have various characteristics. + +@table @code +@findex FIRST_PSEUDO_REGISTER +@item FIRST_PSEUDO_REGISTER +Number of hardware registers known to the compiler. They receive +numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first +pseudo register's number really is assigned the number +@code{FIRST_PSEUDO_REGISTER}. + +@item FIXED_REGISTERS +@findex FIXED_REGISTERS +@cindex fixed register +An initializer that says which registers are used for fixed purposes +all throughout the compiled code and are therefore not available for +general allocation. These would include the stack pointer, the frame +pointer (except on machines where that can be used as a general +register when no frame pointer is needed), the program counter on +machines where that is considered one of the addressable registers, +and any other numbered register with a standard use. + +This information is expressed as a sequence of numbers, separated by +commas and surrounded by braces. The @var{n}th number is 1 if +register @var{n} is fixed, 0 otherwise. + +The table initialized from this macro, and the table initialized by +the following one, may be overridden at run time either automatically, +by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by +the user with the command options @option{-ffixed-@var{reg}}, +@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}. + +@findex CALL_USED_REGISTERS +@item CALL_USED_REGISTERS +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +Like @code{FIXED_REGISTERS} but has 1 for each register that is +clobbered (in general) by function calls as well as for fixed +registers. This macro therefore identifies the registers that are not +available for general allocation of values that must live across +function calls. + +If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler +automatically saves it on function entry and restores it on function +exit, if the register is used within the function. + +@findex CALL_REALLY_USED_REGISTERS +@item CALL_REALLY_USED_REGISTERS +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +Like @code{CALL_USED_REGISTERS} except this macro doesn't require +that the entire set of @code{FIXED_REGISTERS} be included. +(@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}). +This macro is optional. If not specified, it defaults to the value +of @code{CALL_USED_REGISTERS}. + +@findex HARD_REGNO_CALL_PART_CLOBBERED +@item HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode}) +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +A C expression that is nonzero if it is not permissible to store a +value of mode @var{mode} in hard register number @var{regno} across a +call without some part of it being clobbered. For most machines this +macro need not be defined. It is only required for machines that do not +preserve the entire contents of a register across a call. + +@findex CONDITIONAL_REGISTER_USAGE +@findex fixed_regs +@findex call_used_regs +@item CONDITIONAL_REGISTER_USAGE +Zero or more C statements that may conditionally modify five variables +@code{fixed_regs}, @code{call_used_regs}, @code{global_regs}, +@code{reg_names}, and @code{reg_class_contents}, to take into account +any dependence of these register sets on target flags. The first three +of these are of type @code{char []} (interpreted as Boolean vectors). +@code{global_regs} is a @code{const char *[]}, and +@code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is +called, @code{fixed_regs}, @code{call_used_regs}, +@code{reg_class_contents}, and @code{reg_names} have been initialized +from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS}, +@code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively. +@code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}}, +@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}} +command options have been applied. + +You need not define this macro if it has no work to do. + +@cindex disabling certain registers +@cindex controlling register usage +If the usage of an entire class of registers depends on the target +flags, you may indicate this to GCC by using this macro to modify +@code{fixed_regs} and @code{call_used_regs} to 1 for each of the +registers in the classes which should not be used by GCC@. Also define +the macro @code{REG_CLASS_FROM_LETTER} to return @code{NO_REGS} if it +is called with a letter for a class that shouldn't be used. + +(However, if this class is not included in @code{GENERAL_REGS} and all +of the insn patterns whose constraints permit this class are +controlled by target switches, then GCC will automatically avoid using +these registers when the target switches are opposed to them.) + +@findex NON_SAVING_SETJMP +@item NON_SAVING_SETJMP +If this macro is defined and has a nonzero value, it means that +@code{setjmp} and related functions fail to save the registers, or that +@code{longjmp} fails to restore them. To compensate, the compiler +avoids putting variables in registers in functions that use +@code{setjmp}. + +@findex INCOMING_REGNO +@item INCOMING_REGNO (@var{out}) +Define this macro if the target machine has register windows. This C +expression returns the register number as seen by the called function +corresponding to the register number @var{out} as seen by the calling +function. Return @var{out} if register number @var{out} is not an +outbound register. + +@findex OUTGOING_REGNO +@item OUTGOING_REGNO (@var{in}) +Define this macro if the target machine has register windows. This C +expression returns the register number as seen by the calling function +corresponding to the register number @var{in} as seen by the called +function. Return @var{in} if register number @var{in} is not an inbound +register. + +@findex LOCAL_REGNO +@item LOCAL_REGNO (@var{regno}) +Define this macro if the target machine has register windows. This C +expression returns true if the register is call-saved but is in the +register window. Unlike most call-saved registers, such registers +need not be explicitly restored on function exit or during non-local +gotos. + +@ignore +@findex PC_REGNUM +@item PC_REGNUM +If the program counter has a register number, define this as that +register number. Otherwise, do not define it. +@end ignore +@end table + +@node Allocation Order +@subsection Order of Allocation of Registers +@cindex order of register allocation +@cindex register allocation order + +@c prevent bad page break with this line +Registers are allocated in order. + +@table @code +@findex REG_ALLOC_ORDER +@item REG_ALLOC_ORDER +If defined, an initializer for a vector of integers, containing the +numbers of hard registers in the order in which GCC should prefer +to use them (from most preferred to least). + +If this macro is not defined, registers are used lowest numbered first +(all else being equal). + +One use of this macro is on machines where the highest numbered +registers must always be saved and the save-multiple-registers +instruction supports only sequences of consecutive registers. On such +machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists +the highest numbered allocable register first. + +@findex ORDER_REGS_FOR_LOCAL_ALLOC +@item ORDER_REGS_FOR_LOCAL_ALLOC +A C statement (sans semicolon) to choose the order in which to allocate +hard registers for pseudo-registers local to a basic block. + +Store the desired register order in the array @code{reg_alloc_order}. +Element 0 should be the register to allocate first; element 1, the next +register; and so on. + +The macro body should not assume anything about the contents of +@code{reg_alloc_order} before execution of the macro. + +On most machines, it is not necessary to define this macro. +@end table + +@node Values in Registers +@subsection How Values Fit in Registers + +This section discusses the macros that describe which kinds of values +(specifically, which machine modes) each register can hold, and how many +consecutive registers are needed for a given mode. + +@table @code +@findex HARD_REGNO_NREGS +@item HARD_REGNO_NREGS (@var{regno}, @var{mode}) +A C expression for the number of consecutive hard registers, starting +at register number @var{regno}, required to hold a value of mode +@var{mode}. + +On a machine where all registers are exactly one word, a suitable +definition of this macro is + +@smallexample +#define HARD_REGNO_NREGS(REGNO, MODE) \ + ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \ + / UNITS_PER_WORD) +@end smallexample + +@findex HARD_REGNO_MODE_OK +@item HARD_REGNO_MODE_OK (@var{regno}, @var{mode}) +A C expression that is nonzero if it is permissible to store a value +of mode @var{mode} in hard register number @var{regno} (or in several +registers starting with that one). For a machine where all registers +are equivalent, a suitable definition is + +@smallexample +#define HARD_REGNO_MODE_OK(REGNO, MODE) 1 +@end smallexample + +You need not include code to check for the numbers of fixed registers, +because the allocation mechanism considers them to be always occupied. + +@cindex register pairs +On some machines, double-precision values must be kept in even/odd +register pairs. You can implement that by defining this macro to reject +odd register numbers for such modes. + +The minimum requirement for a mode to be OK in a register is that the +@samp{mov@var{mode}} instruction pattern support moves between the +register and other hard register in the same class and that moving a +value into the register and back out not alter it. + +Since the same instruction used to move @code{word_mode} will work for +all narrower integer modes, it is not necessary on any machine for +@code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided +you define patterns @samp{movhi}, etc., to take advantage of this. This +is useful because of the interaction between @code{HARD_REGNO_MODE_OK} +and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes +to be tieable. + +Many machines have special registers for floating point arithmetic. +Often people assume that floating point machine modes are allowed only +in floating point registers. This is not true. Any registers that +can hold integers can safely @emph{hold} a floating point machine +mode, whether or not floating arithmetic can be done on it in those +registers. Integer move instructions can be used to move the values. + +On some machines, though, the converse is true: fixed-point machine +modes may not go in floating registers. This is true if the floating +registers normalize any value stored in them, because storing a +non-floating value there would garble it. In this case, +@code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in +floating registers. But if the floating registers do not automatically +normalize, if you can store any bit pattern in one and retrieve it +unchanged without a trap, then any machine mode may go in a floating +register, so you can define this macro to say so. + +The primary significance of special floating registers is rather that +they are the registers acceptable in floating point arithmetic +instructions. However, this is of no concern to +@code{HARD_REGNO_MODE_OK}. You handle it by writing the proper +constraints for those instructions. + +On some machines, the floating registers are especially slow to access, +so that it is better to store a value in a stack frame than in such a +register if floating point arithmetic is not being done. As long as the +floating registers are not in class @code{GENERAL_REGS}, they will not +be used unless some pattern's constraint asks for one. + +@findex MODES_TIEABLE_P +@item MODES_TIEABLE_P (@var{mode1}, @var{mode2}) +A C expression that is nonzero if a value of mode +@var{mode1} is accessible in mode @var{mode2} without copying. + +If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and +@code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for +any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})} +should be nonzero. If they differ for any @var{r}, you should define +this macro to return zero unless some other mechanism ensures the +accessibility of the value in a narrower mode. + +You should define this macro to return nonzero in as many cases as +possible since doing so will allow GCC to perform better register +allocation. + +@findex AVOID_CCMODE_COPIES +@item AVOID_CCMODE_COPIES +Define this macro if the compiler should avoid copies to/from @code{CCmode} +registers. You should only define this macro if support for copying to/from +@code{CCmode} is incomplete. +@end table + +@node Leaf Functions +@subsection Handling Leaf Functions + +@cindex leaf functions +@cindex functions, leaf +On some machines, a leaf function (i.e., one which makes no calls) can run +more efficiently if it does not make its own register window. Often this +means it is required to receive its arguments in the registers where they +are passed by the caller, instead of the registers where they would +normally arrive. + +The special treatment for leaf functions generally applies only when +other conditions are met; for example, often they may use only those +registers for its own variables and temporaries. We use the term ``leaf +function'' to mean a function that is suitable for this special +handling, so that functions with no calls are not necessarily ``leaf +functions''. + +GCC assigns register numbers before it knows whether the function is +suitable for leaf function treatment. So it needs to renumber the +registers in order to output a leaf function. The following macros +accomplish this. + +@table @code +@findex LEAF_REGISTERS +@item LEAF_REGISTERS +Name of a char vector, indexed by hard register number, which +contains 1 for a register that is allowable in a candidate for leaf +function treatment. + +If leaf function treatment involves renumbering the registers, then the +registers marked here should be the ones before renumbering---those that +GCC would ordinarily allocate. The registers which will actually be +used in the assembler code, after renumbering, should not be marked with 1 +in this vector. + +Define this macro only if the target machine offers a way to optimize +the treatment of leaf functions. + +@findex LEAF_REG_REMAP +@item LEAF_REG_REMAP (@var{regno}) +A C expression whose value is the register number to which @var{regno} +should be renumbered, when a function is treated as a leaf function. + +If @var{regno} is a register number which should not appear in a leaf +function before renumbering, then the expression should yield @minus{}1, which +will cause the compiler to abort. + +Define this macro only if the target machine offers a way to optimize the +treatment of leaf functions, and registers need to be renumbered to do +this. +@end table + +@findex current_function_is_leaf +@findex current_function_uses_only_leaf_regs +@code{TARGET_ASM_FUNCTION_PROLOGUE} and +@code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions +specially. They can test the C variable @code{current_function_is_leaf} +which is nonzero for leaf functions. @code{current_function_is_leaf} is +set prior to local register allocation and is valid for the remaining +compiler passes. They can also test the C variable +@code{current_function_uses_only_leaf_regs} which is nonzero for leaf +functions which only use leaf registers. +@code{current_function_uses_only_leaf_regs} is valid after reload and is +only useful if @code{LEAF_REGISTERS} is defined. +@c changed this to fix overfull. ALSO: why the "it" at the beginning +@c of the next paragraph?! --mew 2feb93 + +@node Stack Registers +@subsection Registers That Form a Stack + +There are special features to handle computers where some of the +``registers'' form a stack, as in the 80387 coprocessor for the 80386. +Stack registers are normally written by pushing onto the stack, and are +numbered relative to the top of the stack. + +Currently, GCC can only handle one group of stack-like registers, and +they must be consecutively numbered. + +@table @code +@findex STACK_REGS +@item STACK_REGS +Define this if the machine has any stack-like registers. + +@findex FIRST_STACK_REG +@item FIRST_STACK_REG +The number of the first stack-like register. This one is the top +of the stack. + +@findex LAST_STACK_REG +@item LAST_STACK_REG +The number of the last stack-like register. This one is the bottom of +the stack. +@end table + +@node Register Classes +@section Register Classes +@cindex register class definitions +@cindex class definitions, register + +On many machines, the numbered registers are not all equivalent. +For example, certain registers may not be allowed for indexed addressing; +certain registers may not be allowed in some instructions. These machine +restrictions are described to the compiler using @dfn{register classes}. + +You define a number of register classes, giving each one a name and saying +which of the registers belong to it. Then you can specify register classes +that are allowed as operands to particular instruction patterns. + +@findex ALL_REGS +@findex NO_REGS +In general, each register will belong to several classes. In fact, one +class must be named @code{ALL_REGS} and contain all the registers. Another +class must be named @code{NO_REGS} and contain no registers. Often the +union of two classes will be another class; however, this is not required. + +@findex GENERAL_REGS +One of the classes must be named @code{GENERAL_REGS}. There is nothing +terribly special about the name, but the operand constraint letters +@samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is +the same as @code{ALL_REGS}, just define it as a macro which expands +to @code{ALL_REGS}. + +Order the classes so that if class @var{x} is contained in class @var{y} +then @var{x} has a lower class number than @var{y}. + +The way classes other than @code{GENERAL_REGS} are specified in operand +constraints is through machine-dependent operand constraint letters. +You can define such letters to correspond to various classes, then use +them in operand constraints. + +You should define a class for the union of two classes whenever some +instruction allows both classes. For example, if an instruction allows +either a floating point (coprocessor) register or a general register for a +certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS} +which includes both of them. Otherwise you will get suboptimal code. + +You must also specify certain redundant information about the register +classes: for each class, which classes contain it and which ones are +contained in it; for each pair of classes, the largest class contained +in their union. + +When a value occupying several consecutive registers is expected in a +certain class, all the registers used must belong to that class. +Therefore, register classes cannot be used to enforce a requirement for +a register pair to start with an even-numbered register. The way to +specify this requirement is with @code{HARD_REGNO_MODE_OK}. + +Register classes used for input-operands of bitwise-and or shift +instructions have a special requirement: each such class must have, for +each fixed-point machine mode, a subclass whose registers can transfer that +mode to or from memory. For example, on some machines, the operations for +single-byte values (@code{QImode}) are limited to certain registers. When +this is so, each register class that is used in a bitwise-and or shift +instruction must have a subclass consisting of registers from which +single-byte values can be loaded or stored. This is so that +@code{PREFERRED_RELOAD_CLASS} can always have a possible value to return. + +@table @code +@findex enum reg_class +@item enum reg_class +An enumeral type that must be defined with all the register class names +as enumeral values. @code{NO_REGS} must be first. @code{ALL_REGS} +must be the last register class, followed by one more enumeral value, +@code{LIM_REG_CLASSES}, which is not a register class but rather +tells how many classes there are. + +Each register class has a number, which is the value of casting +the class name to type @code{int}. The number serves as an index +in many of the tables described below. + +@findex N_REG_CLASSES +@item N_REG_CLASSES +The number of distinct register classes, defined as follows: + +@example +#define N_REG_CLASSES (int) LIM_REG_CLASSES +@end example + +@findex REG_CLASS_NAMES +@item REG_CLASS_NAMES +An initializer containing the names of the register classes as C string +constants. These names are used in writing some of the debugging dumps. + +@findex REG_CLASS_CONTENTS +@item REG_CLASS_CONTENTS +An initializer containing the contents of the register classes, as integers +which are bit masks. The @var{n}th integer specifies the contents of class +@var{n}. The way the integer @var{mask} is interpreted is that +register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1. + +When the machine has more than 32 registers, an integer does not suffice. +Then the integers are replaced by sub-initializers, braced groupings containing +several integers. Each sub-initializer must be suitable as an initializer +for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}. +In this situation, the first integer in each sub-initializer corresponds to +registers 0 through 31, the second integer to registers 32 through 63, and +so on. + +@findex REGNO_REG_CLASS +@item REGNO_REG_CLASS (@var{regno}) +A C expression whose value is a register class containing hard register +@var{regno}. In general there is more than one such class; choose a class +which is @dfn{minimal}, meaning that no smaller class also contains the +register. + +@findex BASE_REG_CLASS +@item BASE_REG_CLASS +A macro whose definition is the name of the class to which a valid +base register must belong. A base register is one used in an address +which is the register value plus a displacement. + +@findex MODE_BASE_REG_CLASS +@item MODE_BASE_REG_CLASS (@var{mode}) +This is a variation of the @code{BASE_REG_CLASS} macro which allows +the selection of a base register in a mode depenedent manner. If +@var{mode} is VOIDmode then it should return the same value as +@code{BASE_REG_CLASS}. + +@findex INDEX_REG_CLASS +@item INDEX_REG_CLASS +A macro whose definition is the name of the class to which a valid +index register must belong. An index register is one used in an +address where its value is either multiplied by a scale factor or +added to another register (as well as added to a displacement). + +@findex REG_CLASS_FROM_LETTER +@item REG_CLASS_FROM_LETTER (@var{char}) +A C expression which defines the machine-dependent operand constraint +letters for register classes. If @var{char} is such a letter, the +value should be the register class corresponding to it. Otherwise, +the value should be @code{NO_REGS}. The register letter @samp{r}, +corresponding to class @code{GENERAL_REGS}, will not be passed +to this macro; you do not need to handle it. + +@findex REGNO_OK_FOR_BASE_P +@item REGNO_OK_FOR_BASE_P (@var{num}) +A C expression which is nonzero if register number @var{num} is +suitable for use as a base register in operand addresses. It may be +either a suitable hard register or a pseudo register that has been +allocated such a hard register. + +@findex REGNO_MODE_OK_FOR_BASE_P +@item REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode}) +A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that +that expression may examine the mode of the memory reference in +@var{mode}. You should define this macro if the mode of the memory +reference affects whether a register may be used as a base register. If +you define this macro, the compiler will use it instead of +@code{REGNO_OK_FOR_BASE_P}. + +@findex REGNO_OK_FOR_INDEX_P +@item REGNO_OK_FOR_INDEX_P (@var{num}) +A C expression which is nonzero if register number @var{num} is +suitable for use as an index register in operand addresses. It may be +either a suitable hard register or a pseudo register that has been +allocated such a hard register. + +The difference between an index register and a base register is that +the index register may be scaled. If an address involves the sum of +two registers, neither one of them scaled, then either one may be +labeled the ``base'' and the other the ``index''; but whichever +labeling is used must fit the machine's constraints of which registers +may serve in each capacity. The compiler will try both labelings, +looking for one that is valid, and will reload one or both registers +only if neither labeling works. + +@findex PREFERRED_RELOAD_CLASS +@item PREFERRED_RELOAD_CLASS (@var{x}, @var{class}) +A C expression that places additional restrictions on the register class +to use when it is necessary to copy value @var{x} into a register in class +@var{class}. The value is a register class; perhaps @var{class}, or perhaps +another, smaller class. On many machines, the following definition is +safe: + +@example +#define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS +@end example + +Sometimes returning a more restrictive class makes better code. For +example, on the 68000, when @var{x} is an integer constant that is in range +for a @samp{moveq} instruction, the value of this macro is always +@code{DATA_REGS} as long as @var{class} includes the data registers. +Requiring a data register guarantees that a @samp{moveq} will be used. + +If @var{x} is a @code{const_double}, by returning @code{NO_REGS} +you can force @var{x} into a memory constant. This is useful on +certain machines where immediate floating values cannot be loaded into +certain kinds of registers. + +@findex PREFERRED_OUTPUT_RELOAD_CLASS +@item PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class}) +Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of +input reloads. If you don't define this macro, the default is to use +@var{class}, unchanged. + +@findex LIMIT_RELOAD_CLASS +@item LIMIT_RELOAD_CLASS (@var{mode}, @var{class}) +A C expression that places additional restrictions on the register class +to use when it is necessary to be able to hold a value of mode +@var{mode} in a reload register for which class @var{class} would +ordinarily be used. + +Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when +there are certain modes that simply can't go in certain reload classes. + +The value is a register class; perhaps @var{class}, or perhaps another, +smaller class. + +Don't define this macro unless the target machine has limitations which +require the macro to do something nontrivial. + +@findex SECONDARY_RELOAD_CLASS +@findex SECONDARY_INPUT_RELOAD_CLASS +@findex SECONDARY_OUTPUT_RELOAD_CLASS +@item SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +@itemx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +@itemx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +Many machines have some registers that cannot be copied directly to or +from memory or even from other types of registers. An example is the +@samp{MQ} register, which on most machines, can only be copied to or +from general registers, but not memory. Some machines allow copying all +registers to and from memory, but require a scratch register for stores +to some memory locations (e.g., those with symbolic address on the RT, +and those with certain symbolic address on the Sparc when compiling +PIC)@. In some cases, both an intermediate and a scratch register are +required. + +You should define these macros to indicate to the reload phase that it may +need to allocate at least one register for a reload in addition to the +register to contain the data. Specifically, if copying @var{x} to a +register @var{class} in @var{mode} requires an intermediate register, +you should define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the +largest register class all of whose registers can be used as +intermediate registers or scratch registers. + +If copying a register @var{class} in @var{mode} to @var{x} requires an +intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS} +should be defined to return the largest register class required. If the +requirements for input and output reloads are the same, the macro +@code{SECONDARY_RELOAD_CLASS} should be used instead of defining both +macros identically. + +The values returned by these macros are often @code{GENERAL_REGS}. +Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x} +can be directly copied to or from a register of @var{class} in +@var{mode} without requiring a scratch register. Do not define this +macro if it would always return @code{NO_REGS}. + +If a scratch register is required (either with or without an +intermediate register), you should define patterns for +@samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required +(@pxref{Standard Names}. These patterns, which will normally be +implemented with a @code{define_expand}, should be similar to the +@samp{mov@var{m}} patterns, except that operand 2 is the scratch +register. + +Define constraints for the reload register and scratch register that +contain a single register class. If the original reload register (whose +class is @var{class}) can meet the constraint given in the pattern, the +value returned by these macros is used for the class of the scratch +register. Otherwise, two additional reload registers are required. +Their classes are obtained from the constraints in the insn pattern. + +@var{x} might be a pseudo-register or a @code{subreg} of a +pseudo-register, which could either be in a hard register or in memory. +Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is +in memory and the hard register number if it is in a register. + +These macros should not be used in the case where a particular class of +registers can only be copied to memory and not to another class of +registers. In that case, secondary reload registers are not needed and +would not be helpful. Instead, a stack location must be used to perform +the copy and the @code{mov@var{m}} pattern should use memory as an +intermediate storage. This case often occurs between floating-point and +general registers. + +@findex SECONDARY_MEMORY_NEEDED +@item SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m}) +Certain machines have the property that some registers cannot be copied +to some other registers without using memory. Define this macro on +those machines to be a C expression that is nonzero if objects of mode +@var{m} in registers of @var{class1} can only be copied to registers of +class @var{class2} by storing a register of @var{class1} into memory +and loading that memory location into a register of @var{class2}. + +Do not define this macro if its value would always be zero. + +@findex SECONDARY_MEMORY_NEEDED_RTX +@item SECONDARY_MEMORY_NEEDED_RTX (@var{mode}) +Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler +allocates a stack slot for a memory location needed for register copies. +If this macro is defined, the compiler instead uses the memory location +defined by this macro. + +Do not define this macro if you do not define +@code{SECONDARY_MEMORY_NEEDED}. + +@findex SECONDARY_MEMORY_NEEDED_MODE +@item SECONDARY_MEMORY_NEEDED_MODE (@var{mode}) +When the compiler needs a secondary memory location to copy between two +registers of mode @var{mode}, it normally allocates sufficient memory to +hold a quantity of @code{BITS_PER_WORD} bits and performs the store and +load operations in a mode that many bits wide and whose class is the +same as that of @var{mode}. + +This is right thing to do on most machines because it ensures that all +bits of the register are copied and prevents accesses to the registers +in a narrower mode, which some machines prohibit for floating-point +registers. + +However, this default behavior is not correct on some machines, such as +the DEC Alpha, that store short integers in floating-point registers +differently than in integer registers. On those machines, the default +widening will not work correctly and you must define this macro to +suppress that widening in some cases. See the file @file{alpha.h} for +details. + +Do not define this macro if you do not define +@code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that +is @code{BITS_PER_WORD} bits wide is correct for your machine. + +@findex SMALL_REGISTER_CLASSES +@item SMALL_REGISTER_CLASSES +On some machines, it is risky to let hard registers live across arbitrary +insns. Typically, these machines have instructions that require values +to be in specific registers (like an accumulator), and reload will fail +if the required hard register is used for another purpose across such an +insn. + +Define @code{SMALL_REGISTER_CLASSES} to be an expression with a nonzero +value on these machines. When this macro has a nonzero value, the +compiler will try to minimize the lifetime of hard registers. + +It is always safe to define this macro with a nonzero value, but if you +unnecessarily define it, you will reduce the amount of optimizations +that can be performed in some cases. If you do not define this macro +with a nonzero value when it is required, the compiler will run out of +spill registers and print a fatal error message. For most machines, you +should not define this macro at all. + +@findex CLASS_LIKELY_SPILLED_P +@item CLASS_LIKELY_SPILLED_P (@var{class}) +A C expression whose value is nonzero if pseudos that have been assigned +to registers of class @var{class} would likely be spilled because +registers of @var{class} are needed for spill registers. + +The default value of this macro returns 1 if @var{class} has exactly one +register and zero otherwise. On most machines, this default should be +used. Only define this macro to some other expression if pseudos +allocated by @file{local-alloc.c} end up in memory because their hard +registers were needed for spill registers. If this macro returns nonzero +for those classes, those pseudos will only be allocated by +@file{global.c}, which knows how to reallocate the pseudo to another +register. If there would not be another register available for +reallocation, you should not change the definition of this macro since +the only effect of such a definition would be to slow down register +allocation. + +@findex CLASS_MAX_NREGS +@item CLASS_MAX_NREGS (@var{class}, @var{mode}) +A C expression for the maximum number of consecutive registers +of class @var{class} needed to hold a value of mode @var{mode}. + +This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact, +the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})} +should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno}, +@var{mode})} for all @var{regno} values in the class @var{class}. + +This macro helps control the handling of multiple-word values +in the reload pass. + +@item CLASS_CANNOT_CHANGE_MODE +If defined, a C expression for a class that contains registers for +which the compiler may not change modes arbitrarily. + +@item CLASS_CANNOT_CHANGE_MODE_P(@var{from}, @var{to}) +A C expression that is true if, for a register in +@code{CLASS_CANNOT_CHANGE_MODE}, the requested mode punning is invalid. + +For the example, loading 32-bit integer or floating-point objects into +floating-point registers on the Alpha extends them to 64-bits. +Therefore loading a 64-bit object and then storing it as a 32-bit object +does not store the low-order 32-bits, as would be the case for a normal +register. Therefore, @file{alpha.h} defines @code{CLASS_CANNOT_CHANGE_MODE} +as @code{FLOAT_REGS} and @code{CLASS_CANNOT_CHANGE_MODE_P} restricts +mode changes to same-size modes. + +Compare this to IA-64, which extends floating-point values to 82-bits, +and stores 64-bit integers in a different format than 64-bit doubles. +Therefore @code{CLASS_CANNOT_CHANGE_MODE_P} is always true. +@end table + +Three other special macros describe which operands fit which constraint +letters. + +@table @code +@findex CONST_OK_FOR_LETTER_P +@item CONST_OK_FOR_LETTER_P (@var{value}, @var{c}) +A C expression that defines the machine-dependent operand constraint +letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify +particular ranges of integer values. If @var{c} is one of those +letters, the expression should check that @var{value}, an integer, is in +the appropriate range and return 1 if so, 0 otherwise. If @var{c} is +not one of those letters, the value should be 0 regardless of +@var{value}. + +@findex CONST_DOUBLE_OK_FOR_LETTER_P +@item CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c}) +A C expression that defines the machine-dependent operand constraint +letters that specify particular ranges of @code{const_double} values +(@samp{G} or @samp{H}). + +If @var{c} is one of those letters, the expression should check that +@var{value}, an RTX of code @code{const_double}, is in the appropriate +range and return 1 if so, 0 otherwise. If @var{c} is not one of those +letters, the value should be 0 regardless of @var{value}. + +@code{const_double} is used for all floating-point constants and for +@code{DImode} fixed-point constants. A given letter can accept either +or both kinds of values. It can use @code{GET_MODE} to distinguish +between these kinds. + +@findex EXTRA_CONSTRAINT +@item EXTRA_CONSTRAINT (@var{value}, @var{c}) +A C expression that defines the optional machine-dependent constraint +letters that can be used to segregate specific types of operands, usually +memory references, for the target machine. Any letter that is not +elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} +may be used. Normally this macro will not be defined. + +If it is required for a particular target machine, it should return 1 +if @var{value} corresponds to the operand type represented by the +constraint letter @var{c}. If @var{c} is not defined as an extra +constraint, the value returned should be 0 regardless of @var{value}. + +For example, on the ROMP, load instructions cannot have their output +in r0 if the memory reference contains a symbolic address. Constraint +letter @samp{Q} is defined as representing a memory address that does +@emph{not} contain a symbolic address. An alternative is specified with +a @samp{Q} constraint on the input and @samp{r} on the output. The next +alternative specifies @samp{m} on the input and a register class that +does not include r0 on the output. +@end table + +@node Stack and Calling +@section Stack Layout and Calling Conventions +@cindex calling conventions + +@c prevent bad page break with this line +This describes the stack layout and calling conventions. + +@menu +* Frame Layout:: +* Exception Handling:: +* Stack Checking:: +* Frame Registers:: +* Elimination:: +* Stack Arguments:: +* Register Arguments:: +* Scalar Return:: +* Aggregate Return:: +* Caller Saves:: +* Function Entry:: +* Profiling:: +* Tail Calls:: +@end menu + +@node Frame Layout +@subsection Basic Stack Layout +@cindex stack frame layout +@cindex frame layout + +@c prevent bad page break with this line +Here is the basic stack layout. + +@table @code +@findex STACK_GROWS_DOWNWARD +@item STACK_GROWS_DOWNWARD +Define this macro if pushing a word onto the stack moves the stack +pointer to a smaller address. + +When we say, ``define this macro if @dots{},'' it means that the +compiler checks this macro only with @code{#ifdef} so the precise +definition used does not matter. + +@findex STACK_PUSH_CODE +@item STACK_PUSH_CODE + +This macro defines the operation used when something is pushed +on the stack. In RTL, a push operation will be +@code{(set (mem (STACK_PUSH_CODE (reg sp))) ...)} + +The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC}, +and @code{POST_INC}. Which of these is correct depends on +the stack direction and on whether the stack pointer points +to the last item on the stack or whether it points to the +space for the next item on the stack. + +The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is +defined, which is almost always right, and @code{PRE_INC} otherwise, +which is often wrong. + +@findex FRAME_GROWS_DOWNWARD +@item FRAME_GROWS_DOWNWARD +Define this macro if the addresses of local variable slots are at negative +offsets from the frame pointer. + +@findex ARGS_GROW_DOWNWARD +@item ARGS_GROW_DOWNWARD +Define this macro if successive arguments to a function occupy decreasing +addresses on the stack. + +@findex STARTING_FRAME_OFFSET +@item STARTING_FRAME_OFFSET +Offset from the frame pointer to the first local variable slot to be allocated. + +If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by +subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}. +Otherwise, it is found by adding the length of the first slot to the +value @code{STARTING_FRAME_OFFSET}. +@c i'm not sure if the above is still correct.. had to change it to get +@c rid of an overfull. --mew 2feb93 + +@findex STACK_POINTER_OFFSET +@item STACK_POINTER_OFFSET +Offset from the stack pointer register to the first location at which +outgoing arguments are placed. If not specified, the default value of +zero is used. This is the proper value for most machines. + +If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above +the first location at which outgoing arguments are placed. + +@findex FIRST_PARM_OFFSET +@item FIRST_PARM_OFFSET (@var{fundecl}) +Offset from the argument pointer register to the first argument's +address. On some machines it may depend on the data type of the +function. + +If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above +the first argument's address. + +@findex STACK_DYNAMIC_OFFSET +@item STACK_DYNAMIC_OFFSET (@var{fundecl}) +Offset from the stack pointer register to an item dynamically allocated +on the stack, e.g., by @code{alloca}. + +The default value for this macro is @code{STACK_POINTER_OFFSET} plus the +length of the outgoing arguments. The default is correct for most +machines. See @file{function.c} for details. + +@findex DYNAMIC_CHAIN_ADDRESS +@item DYNAMIC_CHAIN_ADDRESS (@var{frameaddr}) +A C expression whose value is RTL representing the address in a stack +frame where the pointer to the caller's frame is stored. Assume that +@var{frameaddr} is an RTL expression for the address of the stack frame +itself. + +If you don't define this macro, the default is to return the value +of @var{frameaddr}---that is, the stack frame address is also the +address of the stack word that points to the previous frame. + +@findex SETUP_FRAME_ADDRESSES +@item SETUP_FRAME_ADDRESSES +If defined, a C expression that produces the machine-specific code to +setup the stack so that arbitrary frames can be accessed. For example, +on the Sparc, we must flush all of the register windows to the stack +before we can access arbitrary stack frames. You will seldom need to +define this macro. + +@findex BUILTIN_SETJMP_FRAME_VALUE +@item BUILTIN_SETJMP_FRAME_VALUE +If defined, a C expression that contains an rtx that is used to store +the address of the current frame into the built in @code{setjmp} buffer. +The default value, @code{virtual_stack_vars_rtx}, is correct for most +machines. One reason you may need to define this macro is if +@code{hard_frame_pointer_rtx} is the appropriate value on your machine. + +@findex RETURN_ADDR_RTX +@item RETURN_ADDR_RTX (@var{count}, @var{frameaddr}) +A C expression whose value is RTL representing the value of the return +address for the frame @var{count} steps up from the current frame, after +the prologue. @var{frameaddr} is the frame pointer of the @var{count} +frame, or the frame pointer of the @var{count} @minus{} 1 frame if +@code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined. + +The value of the expression must always be the correct address when +@var{count} is zero, but may be @code{NULL_RTX} if there is not way to +determine the return address of other frames. + +@findex RETURN_ADDR_IN_PREVIOUS_FRAME +@item RETURN_ADDR_IN_PREVIOUS_FRAME +Define this if the return address of a particular stack frame is accessed +from the frame pointer of the previous stack frame. + +@findex INCOMING_RETURN_ADDR_RTX +@item INCOMING_RETURN_ADDR_RTX +A C expression whose value is RTL representing the location of the +incoming return address at the beginning of any function, before the +prologue. This RTL is either a @code{REG}, indicating that the return +value is saved in @samp{REG}, or a @code{MEM} representing a location in +the stack. + +You only need to define this macro if you want to support call frame +debugging information like that provided by DWARF 2. + +If this RTL is a @code{REG}, you should also define +@code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}. + +@findex INCOMING_FRAME_SP_OFFSET +@item INCOMING_FRAME_SP_OFFSET +A C expression whose value is an integer giving the offset, in bytes, +from the value of the stack pointer register to the top of the stack +frame at the beginning of any function, before the prologue. The top of +the frame is defined to be the value of the stack pointer in the +previous frame, just before the call instruction. + +You only need to define this macro if you want to support call frame +debugging information like that provided by DWARF 2. + +@findex ARG_POINTER_CFA_OFFSET +@item ARG_POINTER_CFA_OFFSET (@var{fundecl}) +A C expression whose value is an integer giving the offset, in bytes, +from the argument pointer to the canonical frame address (cfa). The +final value should coincide with that calculated by +@code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable +during virtual register instantiation. + +The default value for this macro is @code{FIRST_PARM_OFFSET (fundecl)}, +which is correct for most machines; in general, the arguments are found +immediately before the stack frame. Note that this is not the case on +some targets that save registers into the caller's frame, such as SPARC +and rs6000, and so such targets need to define this macro. + +You only need to define this macro if the default is incorrect, and you +want to support call frame debugging information like that provided by +DWARF 2. + +@findex SMALL_STACK +@item SMALL_STACK +Define this macro if the stack size for the target is very small. This +has the effect of disabling gcc's built-in @samp{alloca}, though +@samp{__builtin_alloca} is not affected. +@end table + +@node Exception Handling +@subsection Exception Handling Support +@cindex exception handling + +@table @code +@findex EH_RETURN_DATA_REGNO +@item EH_RETURN_DATA_REGNO (@var{N}) +A C expression whose value is the @var{N}th register number used for +data by exception handlers, or @code{INVALID_REGNUM} if fewer than +@var{N} registers are usable. + +The exception handling library routines communicate with the exception +handlers via a set of agreed upon registers. Ideally these registers +should be call-clobbered; it is possible to use call-saved registers, +but may negatively impact code size. The target must support at least +2 data registers, but should define 4 if there are enough free registers. + +You must define this macro if you want to support call frame exception +handling like that provided by DWARF 2. + +@findex EH_RETURN_STACKADJ_RTX +@item EH_RETURN_STACKADJ_RTX +A C expression whose value is RTL representing a location in which +to store a stack adjustment to be applied before function return. +This is used to unwind the stack to an exception handler's call frame. +It will be assigned zero on code paths that return normally. + +Typically this is a call-clobbered hard register that is otherwise +untouched by the epilogue, but could also be a stack slot. + +You must define this macro if you want to support call frame exception +handling like that provided by DWARF 2. + +@findex EH_RETURN_HANDLER_RTX +@item EH_RETURN_HANDLER_RTX +A C expression whose value is RTL representing a location in which +to store the address of an exception handler to which we should +return. It will not be assigned on code paths that return normally. + +Typically this is the location in the call frame at which the normal +return address is stored. For targets that return by popping an +address off the stack, this might be a memory address just below +the @emph{target} call frame rather than inside the current call +frame. @code{EH_RETURN_STACKADJ_RTX} will have already been assigned, +so it may be used to calculate the location of the target call frame. + +Some targets have more complex requirements than storing to an +address calculable during initial code generation. In that case +the @code{eh_return} instruction pattern should be used instead. + +If you want to support call frame exception handling, you must +define either this macro or the @code{eh_return} instruction pattern. + +@findex ASM_PREFERRED_EH_DATA_FORMAT +@item ASM_PREFERRED_EH_DATA_FORMAT(@var{code}, @var{global}) +This macro chooses the encoding of pointers embedded in the exception +handling sections. If at all possible, this should be defined such +that the exception handling section will not require dynamic relocations, +and so may be read-only. + +@var{code} is 0 for data, 1 for code labels, 2 for function pointers. +@var{global} is true if the symbol may be affected by dynamic relocations. +The macro should return a combination of the @code{DW_EH_PE_*} defines +as found in @file{dwarf2.h}. + +If this macro is not defined, pointers will not be encoded but +represented directly. + +@findex ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX +@item ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX(@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done}) +This macro allows the target to emit whatever special magic is required +to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}. +Generic code takes care of pc-relative and indirect encodings; this must +be defined if the target uses text-relative or data-relative encodings. + +This is a C statement that branches to @var{done} if the format was +handled. @var{encoding} is the format chosen, @var{size} is the number +of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF} +to be emitted. + +@findex MD_FALLBACK_FRAME_STATE_FOR +@item MD_FALLBACK_FRAME_STATE_FOR(@var{context}, @var{fs}, @var{success}) +This macro allows the target to add cpu and operating system specific +code to the call-frame unwinder for use when there is no unwind data +available. The most common reason to implement this macro is to unwind +through signal frames. + +This macro is called from @code{uw_frame_state_for} in @file{unwind-dw2.c} +and @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context}; +@var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra} +for the address of the code being executed and @code{context->cfa} for +the stack pointer value. If the frame can be decoded, the register save +addresses should be updated in @var{fs} and the macro should branch to +@var{success}. If the frame cannot be decoded, the macro should do +nothing. +@end table + +@node Stack Checking +@subsection Specifying How Stack Checking is Done + +GCC will check that stack references are within the boundaries of +the stack, if the @option{-fstack-check} is specified, in one of three ways: + +@enumerate +@item +If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC +will assume that you have arranged for stack checking to be done at +appropriate places in the configuration files, e.g., in +@code{TARGET_ASM_FUNCTION_PROLOGUE}. GCC will do not other special +processing. + +@item +If @code{STACK_CHECK_BUILTIN} is zero and you defined a named pattern +called @code{check_stack} in your @file{md} file, GCC will call that +pattern with one argument which is the address to compare the stack +value against. You must arrange for this pattern to report an error if +the stack pointer is out of range. + +@item +If neither of the above are true, GCC will generate code to periodically +``probe'' the stack pointer using the values of the macros defined below. +@end enumerate + +Normally, you will use the default values of these macros, so GCC +will use the third approach. + +@table @code +@findex STACK_CHECK_BUILTIN +@item STACK_CHECK_BUILTIN +A nonzero value if stack checking is done by the configuration files in a +machine-dependent manner. You should define this macro if stack checking +is require by the ABI of your machine or if you would like to have to stack +checking in some more efficient way than GCC's portable approach. +The default value of this macro is zero. + +@findex STACK_CHECK_PROBE_INTERVAL +@item STACK_CHECK_PROBE_INTERVAL +An integer representing the interval at which GCC must generate stack +probe instructions. You will normally define this macro to be no larger +than the size of the ``guard pages'' at the end of a stack area. The +default value of 4096 is suitable for most systems. + +@findex STACK_CHECK_PROBE_LOAD +@item STACK_CHECK_PROBE_LOAD +A integer which is nonzero if GCC should perform the stack probe +as a load instruction and zero if GCC should use a store instruction. +The default is zero, which is the most efficient choice on most systems. + +@findex STACK_CHECK_PROTECT +@item STACK_CHECK_PROTECT +The number of bytes of stack needed to recover from a stack overflow, +for languages where such a recovery is supported. The default value of +75 words should be adequate for most machines. + +@findex STACK_CHECK_MAX_FRAME_SIZE +@item STACK_CHECK_MAX_FRAME_SIZE +The maximum size of a stack frame, in bytes. GCC will generate probe +instructions in non-leaf functions to ensure at least this many bytes of +stack are available. If a stack frame is larger than this size, stack +checking will not be reliable and GCC will issue a warning. The +default is chosen so that GCC only generates one instruction on most +systems. You should normally not change the default value of this macro. + +@findex STACK_CHECK_FIXED_FRAME_SIZE +@item STACK_CHECK_FIXED_FRAME_SIZE +GCC uses this value to generate the above warning message. It +represents the amount of fixed frame used by a function, not including +space for any callee-saved registers, temporaries and user variables. +You need only specify an upper bound for this amount and will normally +use the default of four words. + +@findex STACK_CHECK_MAX_VAR_SIZE +@item STACK_CHECK_MAX_VAR_SIZE +The maximum size, in bytes, of an object that GCC will place in the +fixed area of the stack frame when the user specifies +@option{-fstack-check}. +GCC computed the default from the values of the above macros and you will +normally not need to override that default. +@end table + +@need 2000 +@node Frame Registers +@subsection Registers That Address the Stack Frame + +@c prevent bad page break with this line +This discusses registers that address the stack frame. + +@table @code +@findex STACK_POINTER_REGNUM +@item STACK_POINTER_REGNUM +The register number of the stack pointer register, which must also be a +fixed register according to @code{FIXED_REGISTERS}. On most machines, +the hardware determines which register this is. + +@findex FRAME_POINTER_REGNUM +@item FRAME_POINTER_REGNUM +The register number of the frame pointer register, which is used to +access automatic variables in the stack frame. On some machines, the +hardware determines which register this is. On other machines, you can +choose any register you wish for this purpose. + +@findex HARD_FRAME_POINTER_REGNUM +@item HARD_FRAME_POINTER_REGNUM +On some machines the offset between the frame pointer and starting +offset of the automatic variables is not known until after register +allocation has been done (for example, because the saved registers are +between these two locations). On those machines, define +@code{FRAME_POINTER_REGNUM} the number of a special, fixed register to +be used internally until the offset is known, and define +@code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number +used for the frame pointer. + +You should define this macro only in the very rare circumstances when it +is not possible to calculate the offset between the frame pointer and +the automatic variables until after register allocation has been +completed. When this macro is defined, you must also indicate in your +definition of @code{ELIMINABLE_REGS} how to eliminate +@code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM} +or @code{STACK_POINTER_REGNUM}. + +Do not define this macro if it would be the same as +@code{FRAME_POINTER_REGNUM}. + +@findex ARG_POINTER_REGNUM +@item ARG_POINTER_REGNUM +The register number of the arg pointer register, which is used to access +the function's argument list. On some machines, this is the same as the +frame pointer register. On some machines, the hardware determines which +register this is. On other machines, you can choose any register you +wish for this purpose. If this is not the same register as the frame +pointer register, then you must mark it as a fixed register according to +@code{FIXED_REGISTERS}, or arrange to be able to eliminate it +(@pxref{Elimination}). + +@findex RETURN_ADDRESS_POINTER_REGNUM +@item RETURN_ADDRESS_POINTER_REGNUM +The register number of the return address pointer register, which is used to +access the current function's return address from the stack. On some +machines, the return address is not at a fixed offset from the frame +pointer or stack pointer or argument pointer. This register can be defined +to point to the return address on the stack, and then be converted by +@code{ELIMINABLE_REGS} into either the frame pointer or stack pointer. + +Do not define this macro unless there is no other way to get the return +address from the stack. + +@findex STATIC_CHAIN_REGNUM +@findex STATIC_CHAIN_INCOMING_REGNUM +@item STATIC_CHAIN_REGNUM +@itemx STATIC_CHAIN_INCOMING_REGNUM +Register numbers used for passing a function's static chain pointer. If +register windows are used, the register number as seen by the called +function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register +number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If +these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need +not be defined. + +The static chain register need not be a fixed register. + +If the static chain is passed in memory, these macros should not be +defined; instead, the next two macros should be defined. + +@findex STATIC_CHAIN +@findex STATIC_CHAIN_INCOMING +@item STATIC_CHAIN +@itemx STATIC_CHAIN_INCOMING +If the static chain is passed in memory, these macros provide rtx giving +@code{mem} expressions that denote where they are stored. +@code{STATIC_CHAIN} and @code{STATIC_CHAIN_INCOMING} give the locations +as seen by the calling and called functions, respectively. Often the former +will be at an offset from the stack pointer and the latter at an offset from +the frame pointer. + +@findex stack_pointer_rtx +@findex frame_pointer_rtx +@findex arg_pointer_rtx +The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and +@code{arg_pointer_rtx} will have been initialized prior to the use of these +macros and should be used to refer to those items. + +If the static chain is passed in a register, the two previous macros should +be defined instead. + +@findex DWARF_FRAME_REGISTERS +@item DWARF_FRAME_REGISTERS +This macro specifies the maximum number of hard registers that can be +saved in a call frame. This is used to size data structures used in +DWARF2 exception handling. + +Prior to GCC 3.0, this macro was needed in order to establish a stable +exception handling ABI in the face of adding new hard registers for ISA +extensions. In GCC 3.0 and later, the EH ABI is insulated from changes +in the number of hard registers. Nevertheless, this macro can still be +used to reduce the runtime memory requirements of the exception handling +routines, which can be substantial if the ISA contains a lot of +registers that are not call-saved. + +If this macro is not defined, it defaults to +@code{FIRST_PSEUDO_REGISTER}. + +@findex PRE_GCC3_DWARF_FRAME_REGISTERS +@item PRE_GCC3_DWARF_FRAME_REGISTERS + +This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided +for backward compatibility in pre GCC 3.0 compiled code. + +If this macro is not defined, it defaults to +@code{DWARF_FRAME_REGISTERS}. + +@end table + +@node Elimination +@subsection Eliminating Frame Pointer and Arg Pointer + +@c prevent bad page break with this line +This is about eliminating the frame pointer and arg pointer. + +@table @code +@findex FRAME_POINTER_REQUIRED +@item FRAME_POINTER_REQUIRED +A C expression which is nonzero if a function must have and use a frame +pointer. This expression is evaluated in the reload pass. If its value is +nonzero the function will have a frame pointer. + +The expression can in principle examine the current function and decide +according to the facts, but on most machines the constant 0 or the +constant 1 suffices. Use 0 when the machine allows code to be generated +with no frame pointer, and doing so saves some time or space. Use 1 +when there is no possible advantage to avoiding a frame pointer. + +In certain cases, the compiler does not know how to produce valid code +without a frame pointer. The compiler recognizes those cases and +automatically gives the function a frame pointer regardless of what +@code{FRAME_POINTER_REQUIRED} says. You don't need to worry about +them. + +In a function that does not require a frame pointer, the frame pointer +register can be allocated for ordinary usage, unless you mark it as a +fixed register. See @code{FIXED_REGISTERS} for more information. + +@findex INITIAL_FRAME_POINTER_OFFSET +@findex get_frame_size +@item INITIAL_FRAME_POINTER_OFFSET (@var{depth-var}) +A C statement to store in the variable @var{depth-var} the difference +between the frame pointer and the stack pointer values immediately after +the function prologue. The value would be computed from information +such as the result of @code{get_frame_size ()} and the tables of +registers @code{regs_ever_live} and @code{call_used_regs}. + +If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and +need not be defined. Otherwise, it must be defined even if +@code{FRAME_POINTER_REQUIRED} is defined to always be true; in that +case, you may set @var{depth-var} to anything. + +@findex ELIMINABLE_REGS +@item ELIMINABLE_REGS +If defined, this macro specifies a table of register pairs used to +eliminate unneeded registers that point into the stack frame. If it is not +defined, the only elimination attempted by the compiler is to replace +references to the frame pointer with references to the stack pointer. + +The definition of this macro is a list of structure initializations, each +of which specifies an original and replacement register. + +On some machines, the position of the argument pointer is not known until +the compilation is completed. In such a case, a separate hard register +must be used for the argument pointer. This register can be eliminated by +replacing it with either the frame pointer or the argument pointer, +depending on whether or not the frame pointer has been eliminated. + +In this case, you might specify: +@example +#define ELIMINABLE_REGS \ +@{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \ + @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \ + @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@} +@end example + +Note that the elimination of the argument pointer with the stack pointer is +specified first since that is the preferred elimination. + +@findex CAN_ELIMINATE +@item CAN_ELIMINATE (@var{from-reg}, @var{to-reg}) +A C expression that returns nonzero if the compiler is allowed to try +to replace register number @var{from-reg} with register number +@var{to-reg}. This macro need only be defined if @code{ELIMINABLE_REGS} +is defined, and will usually be the constant 1, since most of the cases +preventing register elimination are things that the compiler already +knows about. + +@findex INITIAL_ELIMINATION_OFFSET +@item INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var}) +This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It +specifies the initial difference between the specified pair of +registers. This macro must be defined if @code{ELIMINABLE_REGS} is +defined. +@end table + +@node Stack Arguments +@subsection Passing Function Arguments on the Stack +@cindex arguments on stack +@cindex stack arguments + +The macros in this section control how arguments are passed +on the stack. See the following section for other macros that +control passing certain arguments in registers. + +@table @code +@findex PROMOTE_PROTOTYPES +@item PROMOTE_PROTOTYPES +A C expression whose value is nonzero if an argument declared in +a prototype as an integral type smaller than @code{int} should +actually be passed as an @code{int}. In addition to avoiding +errors in certain cases of mismatch, it also makes for better +code on certain machines. If the macro is not defined in target +header files, it defaults to 0. + +@findex PUSH_ARGS +@item PUSH_ARGS +A C expression. If nonzero, push insns will be used to pass +outgoing arguments. +If the target machine does not have a push instruction, set it to zero. +That directs GCC to use an alternate strategy: to +allocate the entire argument block and then store the arguments into +it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too. +On some machines, the definition + +@findex PUSH_ROUNDING +@item PUSH_ROUNDING (@var{npushed}) +A C expression that is the number of bytes actually pushed onto the +stack when an instruction attempts to push @var{npushed} bytes. + +On some machines, the definition + +@example +#define PUSH_ROUNDING(BYTES) (BYTES) +@end example + +@noindent +will suffice. But on other machines, instructions that appear +to push one byte actually push two bytes in an attempt to maintain +alignment. Then the definition should be + +@example +#define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) +@end example + +@findex ACCUMULATE_OUTGOING_ARGS +@findex current_function_outgoing_args_size +@item ACCUMULATE_OUTGOING_ARGS +A C expression. If nonzero, the maximum amount of space required for outgoing arguments +will be computed and placed into the variable +@code{current_function_outgoing_args_size}. No space will be pushed +onto the stack for each call; instead, the function prologue should +increase the stack frame size by this amount. + +Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS} +is not proper. + +@findex REG_PARM_STACK_SPACE +@item REG_PARM_STACK_SPACE (@var{fndecl}) +Define this macro if functions should assume that stack space has been +allocated for arguments even when their values are passed in +registers. + +The value of this macro is the size, in bytes, of the area reserved for +arguments passed in registers for the function represented by @var{fndecl}, +which can be zero if GCC is calling a library function. + +This space can be allocated by the caller, or be a part of the +machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says +which. +@c above is overfull. not sure what to do. --mew 5feb93 did +@c something, not sure if it looks good. --mew 10feb93 + +@findex MAYBE_REG_PARM_STACK_SPACE +@findex FINAL_REG_PARM_STACK_SPACE +@item MAYBE_REG_PARM_STACK_SPACE +@itemx FINAL_REG_PARM_STACK_SPACE (@var{const_size}, @var{var_size}) +Define these macros in addition to the one above if functions might +allocate stack space for arguments even when their values are passed +in registers. These should be used when the stack space allocated +for arguments in registers is not a simple constant independent of the +function declaration. + +The value of the first macro is the size, in bytes, of the area that +we should initially assume would be reserved for arguments passed in registers. + +The value of the second macro is the actual size, in bytes, of the area +that will be reserved for arguments passed in registers. This takes two +arguments: an integer representing the number of bytes of fixed sized +arguments on the stack, and a tree representing the number of bytes of +variable sized arguments on the stack. + +When these macros are defined, @code{REG_PARM_STACK_SPACE} will only be +called for libcall functions, the current function, or for a function +being called when it is known that such stack space must be allocated. +In each case this value can be easily computed. + +When deciding whether a called function needs such stack space, and how +much space to reserve, GCC uses these two macros instead of +@code{REG_PARM_STACK_SPACE}. + +@findex OUTGOING_REG_PARM_STACK_SPACE +@item OUTGOING_REG_PARM_STACK_SPACE +Define this if it is the responsibility of the caller to allocate the area +reserved for arguments passed in registers. + +If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls +whether the space for these arguments counts in the value of +@code{current_function_outgoing_args_size}. + +@findex STACK_PARMS_IN_REG_PARM_AREA +@item STACK_PARMS_IN_REG_PARM_AREA +Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the +stack parameters don't skip the area specified by it. +@c i changed this, makes more sens and it should have taken care of the +@c overfull.. not as specific, tho. --mew 5feb93 + +Normally, when a parameter is not passed in registers, it is placed on the +stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro +suppresses this behavior and causes the parameter to be passed on the +stack in its natural location. + +@findex RETURN_POPS_ARGS +@item RETURN_POPS_ARGS (@var{fundecl}, @var{funtype}, @var{stack-size}) +A C expression that should indicate the number of bytes of its own +arguments that a function pops on returning, or 0 if the +function pops no arguments and the caller must therefore pop them all +after the function returns. + +@var{fundecl} is a C variable whose value is a tree node that describes +the function in question. Normally it is a node of type +@code{FUNCTION_DECL} that describes the declaration of the function. +From this you can obtain the @code{DECL_ATTRIBUTES} of the function. + +@var{funtype} is a C variable whose value is a tree node that +describes the function in question. Normally it is a node of type +@code{FUNCTION_TYPE} that describes the data type of the function. +From this it is possible to obtain the data types of the value and +arguments (if known). + +When a call to a library function is being considered, @var{fundecl} +will contain an identifier node for the library function. Thus, if +you need to distinguish among various library functions, you can do so +by their names. Note that ``library function'' in this context means +a function used to perform arithmetic, whose name is known specially +in the compiler and was not mentioned in the C code being compiled. + +@var{stack-size} is the number of bytes of arguments passed on the +stack. If a variable number of bytes is passed, it is zero, and +argument popping will always be the responsibility of the calling function. + +On the VAX, all functions always pop their arguments, so the definition +of this macro is @var{stack-size}. On the 68000, using the standard +calling convention, no functions pop their arguments, so the value of +the macro is always 0 in this case. But an alternative calling +convention is available in which functions that take a fixed number of +arguments pop them but other functions (such as @code{printf}) pop +nothing (the caller pops all). When this convention is in use, +@var{funtype} is examined to determine whether a function takes a fixed +number of arguments. +@end table + +@node Register Arguments +@subsection Passing Arguments in Registers +@cindex arguments in registers +@cindex registers arguments + +This section describes the macros which let you control how various +types of arguments are passed in registers or how they are arranged in +the stack. + +@table @code +@findex FUNCTION_ARG +@item FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) +A C expression that controls whether a function argument is passed +in a register, and which register. + +The arguments are @var{cum}, which summarizes all the previous +arguments; @var{mode}, the machine mode of the argument; @var{type}, +the data type of the argument as a tree node or 0 if that is not known +(which happens for C support library functions); and @var{named}, +which is 1 for an ordinary argument and 0 for nameless arguments that +correspond to @samp{@dots{}} in the called function's prototype. +@var{type} can be an incomplete type if a syntax error has previously +occurred. + +The value of the expression is usually either a @code{reg} RTX for the +hard register in which to pass the argument, or zero to pass the +argument on the stack. + +For machines like the VAX and 68000, where normally all arguments are +pushed, zero suffices as a definition. + +The value of the expression can also be a @code{parallel} RTX@. This is +used when an argument is passed in multiple locations. The mode of the +of the @code{parallel} should be the mode of the entire argument. The +@code{parallel} holds any number of @code{expr_list} pairs; each one +describes where part of the argument is passed. In each +@code{expr_list} the first operand must be a @code{reg} RTX for the hard +register in which to pass this part of the argument, and the mode of the +register RTX indicates how large this part of the argument is. The +second operand of the @code{expr_list} is a @code{const_int} which gives +the offset in bytes into the entire argument of where this part starts. +As a special exception the first @code{expr_list} in the @code{parallel} +RTX may have a first operand of zero. This indicates that the entire +argument is also stored on the stack. + +The last time this macro is called, it is called with @code{MODE == +VOIDmode}, and its result is passed to the @code{call} or @code{call_value} +pattern as operands 2 and 3 respectively. + +@cindex @file{stdarg.h} and register arguments +The usual way to make the ISO library @file{stdarg.h} work on a machine +where some arguments are usually passed in registers, is to cause +nameless arguments to be passed on the stack instead. This is done +by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0. + +@cindex @code{MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG} +@cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG} +You may use the macro @code{MUST_PASS_IN_STACK (@var{mode}, @var{type})} +in the definition of this macro to determine if this argument is of a +type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE} +is not defined and @code{FUNCTION_ARG} returns nonzero for such an +argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is +defined, the argument will be computed in the stack and then loaded into +a register. + +@findex MUST_PASS_IN_STACK +@item MUST_PASS_IN_STACK (@var{mode}, @var{type}) +Define as a C expression that evaluates to nonzero if we do not know how +to pass TYPE solely in registers. The file @file{expr.h} defines a +definition that is usually appropriate, refer to @file{expr.h} for additional +documentation. + +@findex FUNCTION_INCOMING_ARG +@item FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) +Define this macro if the target machine has ``register windows'', so +that the register in which a function sees an arguments is not +necessarily the same as the one in which the caller passed the +argument. + +For such machines, @code{FUNCTION_ARG} computes the register in which +the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should +be defined in a similar fashion to tell the function being called +where the arguments will arrive. + +If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG} +serves both purposes. + +@findex FUNCTION_ARG_PARTIAL_NREGS +@item FUNCTION_ARG_PARTIAL_NREGS (@var{cum}, @var{mode}, @var{type}, @var{named}) +A C expression for the number of words, at the beginning of an +argument, that must be put in registers. The value must be zero for +arguments that are passed entirely in registers or that are entirely +pushed on the stack. + +On some machines, certain arguments must be passed partially in +registers and partially in memory. On these machines, typically the +first @var{n} words of arguments are passed in registers, and the rest +on the stack. If a multi-word argument (a @code{double} or a +structure) crosses that boundary, its first few words must be passed +in registers and the rest must be pushed. This macro tells the +compiler when this occurs, and how many of the words should go in +registers. + +@code{FUNCTION_ARG} for these arguments should return the first +register to be used by the caller for this argument; likewise +@code{FUNCTION_INCOMING_ARG}, for the called function. + +@findex FUNCTION_ARG_PASS_BY_REFERENCE +@item FUNCTION_ARG_PASS_BY_REFERENCE (@var{cum}, @var{mode}, @var{type}, @var{named}) +A C expression that indicates when an argument must be passed by reference. +If nonzero for an argument, a copy of that argument is made in memory and a +pointer to the argument is passed instead of the argument itself. +The pointer is passed in whatever way is appropriate for passing a pointer +to that type. + +On machines where @code{REG_PARM_STACK_SPACE} is not defined, a suitable +definition of this macro might be +@smallexample +#define FUNCTION_ARG_PASS_BY_REFERENCE\ +(CUM, MODE, TYPE, NAMED) \ + MUST_PASS_IN_STACK (MODE, TYPE) +@end smallexample +@c this is *still* too long. --mew 5feb93 + +@findex FUNCTION_ARG_CALLEE_COPIES +@item FUNCTION_ARG_CALLEE_COPIES (@var{cum}, @var{mode}, @var{type}, @var{named}) +If defined, a C expression that indicates when it is the called function's +responsibility to make a copy of arguments passed by invisible reference. +Normally, the caller makes a copy and passes the address of the copy to the +routine being called. When @code{FUNCTION_ARG_CALLEE_COPIES} is defined and is +nonzero, the caller does not make a copy. Instead, it passes a pointer to the +``live'' value. The called function must not modify this value. If it can be +determined that the value won't be modified, it need not make a copy; +otherwise a copy must be made. + +@findex FUNCTION_ARG_REG_LITTLE_ENDIAN +@item FUNCTION_ARG_REG_LITTLE_ENDIAN +If defined TRUE on a big-endian system then structure arguments passed +(and returned) in registers are passed in a little-endian manner instead of +the big-endian manner. On the HP-UX IA64 and PA64 platforms structures are +aligned differently then integral values and setting this value to true will +allow for the special handling of structure arguments and return values. + +@findex CUMULATIVE_ARGS +@item CUMULATIVE_ARGS +A C type for declaring a variable that is used as the first argument of +@code{FUNCTION_ARG} and other related values. For some target machines, +the type @code{int} suffices and can hold the number of bytes of +argument so far. + +There is no need to record in @code{CUMULATIVE_ARGS} anything about the +arguments that have been passed on the stack. The compiler has other +variables to keep track of that. For target machines on which all +arguments are passed on the stack, there is no need to store anything in +@code{CUMULATIVE_ARGS}; however, the data structure must exist and +should not be empty, so use @code{int}. + +@findex INIT_CUMULATIVE_ARGS +@item INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{indirect}) +A C statement (sans semicolon) for initializing the variable @var{cum} +for the state at the beginning of the argument list. The variable has +type @code{CUMULATIVE_ARGS}. The value of @var{fntype} is the tree node +for the data type of the function which will receive the args, or 0 +if the args are to a compiler support library function. The value of +@var{indirect} is nonzero when processing an indirect call, for example +a call through a function pointer. The value of @var{indirect} is zero +for a call to an explicitly named function, a library function call, or when +@code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function +being compiled. + +When processing a call to a compiler support library function, +@var{libname} identifies which one. It is a @code{symbol_ref} rtx which +contains the name of the function, as a string. @var{libname} is 0 when +an ordinary C function call is being processed. Thus, each time this +macro is called, either @var{libname} or @var{fntype} is nonzero, but +never both of them at once. + +@findex INIT_CUMULATIVE_LIBCALL_ARGS +@item INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname}) +Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls, +it gets a @code{MODE} argument instead of @var{fntype}, that would be +@code{NULL}. @var{indirect} would always be zero, too. If this macro +is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname, +0)} is used instead. + +@findex INIT_CUMULATIVE_INCOMING_ARGS +@item INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname}) +Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of +finding the arguments for the function being compiled. If this macro is +undefined, @code{INIT_CUMULATIVE_ARGS} is used instead. + +The value passed for @var{libname} is always 0, since library routines +with special calling conventions are never compiled with GCC@. The +argument @var{libname} exists for symmetry with +@code{INIT_CUMULATIVE_ARGS}. +@c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe. +@c --mew 5feb93 i switched the order of the sentences. --mew 10feb93 + +@findex FUNCTION_ARG_ADVANCE +@item FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named}) +A C statement (sans semicolon) to update the summarizer variable +@var{cum} to advance past an argument in the argument list. The +values @var{mode}, @var{type} and @var{named} describe that argument. +Once this is done, the variable @var{cum} is suitable for analyzing +the @emph{following} argument with @code{FUNCTION_ARG}, etc. + +This macro need not do anything if the argument in question was passed +on the stack. The compiler knows how to track the amount of stack space +used for arguments without any special help. + +@findex FUNCTION_ARG_PADDING +@item FUNCTION_ARG_PADDING (@var{mode}, @var{type}) +If defined, a C expression which determines whether, and in which direction, +to pad out an argument with extra space. The value should be of type +@code{enum direction}: either @code{upward} to pad above the argument, +@code{downward} to pad below, or @code{none} to inhibit padding. + +The @emph{amount} of padding is always just enough to reach the next +multiple of @code{FUNCTION_ARG_BOUNDARY}; this macro does not control +it. + +This macro has a default definition which is right for most systems. +For little-endian machines, the default is to pad upward. For +big-endian machines, the default is to pad downward for an argument of +constant size shorter than an @code{int}, and upward otherwise. + +@findex PAD_VARARGS_DOWN +@item PAD_VARARGS_DOWN +If defined, a C expression which determines whether the default +implementation of va_arg will attempt to pad down before reading the +next argument, if that argument is smaller than its aligned space as +controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such +arguments are padded down if @code{BYTES_BIG_ENDIAN} is true. + +@findex FUNCTION_ARG_BOUNDARY +@item FUNCTION_ARG_BOUNDARY (@var{mode}, @var{type}) +If defined, a C expression that gives the alignment boundary, in bits, +of an argument with the specified mode and type. If it is not defined, +@code{PARM_BOUNDARY} is used for all arguments. + +@findex FUNCTION_ARG_REGNO_P +@item FUNCTION_ARG_REGNO_P (@var{regno}) +A C expression that is nonzero if @var{regno} is the number of a hard +register in which function arguments are sometimes passed. This does +@emph{not} include implicit arguments such as the static chain and +the structure-value address. On many machines, no registers can be +used for this purpose since all function arguments are pushed on the +stack. + +@findex LOAD_ARGS_REVERSED +@item LOAD_ARGS_REVERSED +If defined, the order in which arguments are loaded into their +respective argument registers is reversed so that the last +argument is loaded first. This macro only affects arguments +passed in registers. + +@end table + +@node Scalar Return +@subsection How Scalar Function Values Are Returned +@cindex return values in registers +@cindex values, returned by functions +@cindex scalars, returned as values + +This section discusses the macros that control returning scalars as +values---values that can fit in registers. + +@table @code +@findex TRADITIONAL_RETURN_FLOAT +@item TRADITIONAL_RETURN_FLOAT +Define this macro if @option{-traditional} should not cause functions +declared to return @code{float} to convert the value to @code{double}. + +@findex FUNCTION_VALUE +@item FUNCTION_VALUE (@var{valtype}, @var{func}) +A C expression to create an RTX representing the place where a +function returns a value of data type @var{valtype}. @var{valtype} is +a tree node representing a data type. Write @code{TYPE_MODE +(@var{valtype})} to get the machine mode used to represent that type. +On many machines, only the mode is relevant. (Actually, on most +machines, scalar values are returned in the same place regardless of +mode). + +The value of the expression is usually a @code{reg} RTX for the hard +register where the return value is stored. The value can also be a +@code{parallel} RTX, if the return value is in multiple places. See +@code{FUNCTION_ARG} for an explanation of the @code{parallel} form. + +If @code{PROMOTE_FUNCTION_RETURN} is defined, you must apply the same +promotion rules specified in @code{PROMOTE_MODE} if @var{valtype} is a +scalar type. + +If the precise function being called is known, @var{func} is a tree +node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null +pointer. This makes it possible to use a different value-returning +convention for specific functions when all their calls are +known. + +@code{FUNCTION_VALUE} is not used for return vales with aggregate data +types, because these are returned in another way. See +@code{STRUCT_VALUE_REGNUM} and related macros, below. + +@findex FUNCTION_OUTGOING_VALUE +@item FUNCTION_OUTGOING_VALUE (@var{valtype}, @var{func}) +Define this macro if the target machine has ``register windows'' +so that the register in which a function returns its value is not +the same as the one in which the caller sees the value. + +For such machines, @code{FUNCTION_VALUE} computes the register in which +the caller will see the value. @code{FUNCTION_OUTGOING_VALUE} should be +defined in a similar fashion to tell the function where to put the +value. + +If @code{FUNCTION_OUTGOING_VALUE} is not defined, +@code{FUNCTION_VALUE} serves both purposes. + +@code{FUNCTION_OUTGOING_VALUE} is not used for return vales with +aggregate data types, because these are returned in another way. See +@code{STRUCT_VALUE_REGNUM} and related macros, below. + +@findex LIBCALL_VALUE +@item LIBCALL_VALUE (@var{mode}) +A C expression to create an RTX representing the place where a library +function returns a value of mode @var{mode}. If the precise function +being called is known, @var{func} is a tree node +(@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null +pointer. This makes it possible to use a different value-returning +convention for specific functions when all their calls are +known. + +Note that ``library function'' in this context means a compiler +support routine, used to perform arithmetic, whose name is known +specially by the compiler and was not mentioned in the C code being +compiled. + +The definition of @code{LIBRARY_VALUE} need not be concerned aggregate +data types, because none of the library functions returns such types. + +@findex FUNCTION_VALUE_REGNO_P +@item FUNCTION_VALUE_REGNO_P (@var{regno}) +A C expression that is nonzero if @var{regno} is the number of a hard +register in which the values of called function may come back. + +A register whose use for returning values is limited to serving as the +second of a pair (for a value of type @code{double}, say) need not be +recognized by this macro. So for most machines, this definition +suffices: + +@example +#define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) +@end example + +If the machine has register windows, so that the caller and the called +function use different registers for the return value, this macro +should recognize only the caller's register numbers. + +@findex APPLY_RESULT_SIZE +@item APPLY_RESULT_SIZE +Define this macro if @samp{untyped_call} and @samp{untyped_return} +need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for +saving and restoring an arbitrary return value. +@end table + +@node Aggregate Return +@subsection How Large Values Are Returned +@cindex aggregates as return values +@cindex large return values +@cindex returning aggregate values +@cindex structure value address + +When a function value's mode is @code{BLKmode} (and in some other +cases), the value is not returned according to @code{FUNCTION_VALUE} +(@pxref{Scalar Return}). Instead, the caller passes the address of a +block of memory in which the value should be stored. This address +is called the @dfn{structure value address}. + +This section describes how to control returning structure values in +memory. + +@table @code +@findex RETURN_IN_MEMORY +@item RETURN_IN_MEMORY (@var{type}) +A C expression which can inhibit the returning of certain function +values in registers, based on the type of value. A nonzero value says +to return the function value in memory, just as large structures are +always returned. Here @var{type} will be a C expression of type +@code{tree}, representing the data type of the value. + +Note that values of mode @code{BLKmode} must be explicitly handled +by this macro. Also, the option @option{-fpcc-struct-return} +takes effect regardless of this macro. On most systems, it is +possible to leave the macro undefined; this causes a default +definition to be used, whose value is the constant 1 for @code{BLKmode} +values, and 0 otherwise. + +Do not use this macro to indicate that structures and unions should always +be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN} +to indicate this. + +@findex DEFAULT_PCC_STRUCT_RETURN +@item DEFAULT_PCC_STRUCT_RETURN +Define this macro to be 1 if all structure and union return values must be +in memory. Since this results in slower code, this should be defined +only if needed for compatibility with other compilers or with an ABI@. +If you define this macro to be 0, then the conventions used for structure +and union return values are decided by the @code{RETURN_IN_MEMORY} macro. + +If not defined, this defaults to the value 1. + +@findex STRUCT_VALUE_REGNUM +@item STRUCT_VALUE_REGNUM +If the structure value address is passed in a register, then +@code{STRUCT_VALUE_REGNUM} should be the number of that register. + +@findex STRUCT_VALUE +@item STRUCT_VALUE +If the structure value address is not passed in a register, define +@code{STRUCT_VALUE} as an expression returning an RTX for the place +where the address is passed. If it returns 0, the address is passed as +an ``invisible'' first argument. + +@findex STRUCT_VALUE_INCOMING_REGNUM +@item STRUCT_VALUE_INCOMING_REGNUM +On some architectures the place where the structure value address +is found by the called function is not the same place that the +caller put it. This can be due to register windows, or it could +be because the function prologue moves it to a different place. + +If the incoming location of the structure value address is in a +register, define this macro as the register number. + +@findex STRUCT_VALUE_INCOMING +@item STRUCT_VALUE_INCOMING +If the incoming location is not a register, then you should define +@code{STRUCT_VALUE_INCOMING} as an expression for an RTX for where the +called function should find the value. If it should find the value on +the stack, define this to create a @code{mem} which refers to the frame +pointer. A definition of 0 means that the address is passed as an +``invisible'' first argument. + +@findex PCC_STATIC_STRUCT_RETURN +@item PCC_STATIC_STRUCT_RETURN +Define this macro if the usual system convention on the target machine +for returning structures and unions is for the called function to return +the address of a static variable containing the value. + +Do not define this if the usual system convention is for the caller to +pass an address to the subroutine. + +This macro has effect in @option{-fpcc-struct-return} mode, but it does +nothing when you use @option{-freg-struct-return} mode. +@end table + +@node Caller Saves +@subsection Caller-Saves Register Allocation + +If you enable it, GCC can save registers around function calls. This +makes it possible to use call-clobbered registers to hold variables that +must live across calls. + +@table @code +@findex DEFAULT_CALLER_SAVES +@item DEFAULT_CALLER_SAVES +Define this macro if function calls on the target machine do not preserve +any registers; in other words, if @code{CALL_USED_REGISTERS} has 1 +for all registers. When defined, this macro enables @option{-fcaller-saves} +by default for all optimization levels. It has no effect for optimization +levels 2 and higher, where @option{-fcaller-saves} is the default. + +@findex CALLER_SAVE_PROFITABLE +@item CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls}) +A C expression to determine whether it is worthwhile to consider placing +a pseudo-register in a call-clobbered hard register and saving and +restoring it around each function call. The expression should be 1 when +this is worth doing, and 0 otherwise. + +If you don't define this macro, a default is used which is good on most +machines: @code{4 * @var{calls} < @var{refs}}. + +@findex HARD_REGNO_CALLER_SAVE_MODE +@item HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs}) +A C expression specifying which mode is required for saving @var{nregs} +of a pseudo-register in call-clobbered hard register @var{regno}. If +@var{regno} is unsuitable for caller save, @code{VOIDmode} should be +returned. For most machines this macro need not be defined since GCC +will select the smallest suitable mode. +@end table + +@node Function Entry +@subsection Function Entry and Exit +@cindex function entry and exit +@cindex prologue +@cindex epilogue + +This section describes the macros that output function entry +(@dfn{prologue}) and exit (@dfn{epilogue}) code. + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size}) +If defined, a function that outputs the assembler code for entry to a +function. The prologue is responsible for setting up the stack frame, +initializing the frame pointer register, saving registers that must be +saved, and allocating @var{size} additional bytes of storage for the +local variables. @var{size} is an integer. @var{file} is a stdio +stream to which the assembler code should be output. + +The label for the beginning of the function need not be output by this +macro. That has already been done when the macro is run. + +@findex regs_ever_live +To determine which registers to save, the macro can refer to the array +@code{regs_ever_live}: element @var{r} is nonzero if hard register +@var{r} is used anywhere within the function. This implies the function +prologue should save register @var{r}, provided it is not one of the +call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use +@code{regs_ever_live}.) + +On machines that have ``register windows'', the function entry code does +not save on the stack the registers that are in the windows, even if +they are supposed to be preserved by function calls; instead it takes +appropriate steps to ``push'' the register stack, if any non-call-used +registers are used in the function. + +@findex frame_pointer_needed +On machines where functions may or may not have frame-pointers, the +function entry code must vary accordingly; it must set up the frame +pointer if one is wanted, and not otherwise. To determine whether a +frame pointer is in wanted, the macro can refer to the variable +@code{frame_pointer_needed}. The variable's value will be 1 at run +time in a function that needs a frame pointer. @xref{Elimination}. + +The function entry code is responsible for allocating any stack space +required for the function. This stack space consists of the regions +listed below. In most cases, these regions are allocated in the +order listed, with the last listed region closest to the top of the +stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and +the highest address if it is not defined). You can use a different order +for a machine if doing so is more convenient or required for +compatibility reasons. Except in cases where required by standard +or by a debugger, there is no reason why the stack layout used by GCC +need agree with that used by other compilers for a machine. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file}) +If defined, a function that outputs assembler code at the end of a +prologue. This should be used when the function prologue is being +emitted as RTL, and you have some extra assembler that needs to be +emitted. @xref{prologue instruction pattern}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file}) +If defined, a function that outputs assembler code at the start of an +epilogue. This should be used when the function epilogue is being +emitted as RTL, and you have some extra assembler that needs to be +emitted. @xref{epilogue instruction pattern}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size}) +If defined, a function that outputs the assembler code for exit from a +function. The epilogue is responsible for restoring the saved +registers and stack pointer to their values when the function was +called, and returning control to the caller. This macro takes the +same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the +registers to restore are determined from @code{regs_ever_live} and +@code{CALL_USED_REGISTERS} in the same way. + +On some machines, there is a single instruction that does all the work +of returning from the function. On these machines, give that +instruction the name @samp{return} and do not define the macro +@code{TARGET_ASM_FUNCTION_EPILOGUE} at all. + +Do not define a pattern named @samp{return} if you want the +@code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target +switches to control whether return instructions or epilogues are used, +define a @samp{return} pattern with a validity condition that tests the +target switches appropriately. If the @samp{return} pattern's validity +condition is false, epilogues will be used. + +On machines where functions may or may not have frame-pointers, the +function exit code must vary accordingly. Sometimes the code for these +two cases is completely different. To determine whether a frame pointer +is wanted, the macro can refer to the variable +@code{frame_pointer_needed}. The variable's value will be 1 when compiling +a function that needs a frame pointer. + +Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and +@code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially. +The C variable @code{current_function_is_leaf} is nonzero for such a +function. @xref{Leaf Functions}. + +On some machines, some functions pop their arguments on exit while +others leave that for the caller to do. For example, the 68020 when +given @option{-mrtd} pops arguments in functions that take a fixed +number of arguments. + +@findex current_function_pops_args +Your definition of the macro @code{RETURN_POPS_ARGS} decides which +functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE} +needs to know what was decided. The variable that is called +@code{current_function_pops_args} is the number of bytes of its +arguments that a function should pop. @xref{Scalar Return}. +@c what is the "its arguments" in the above sentence referring to, pray +@c tell? --mew 5feb93 +@end deftypefn + +@table @code + +@itemize @bullet +@item +@findex current_function_pretend_args_size +A region of @code{current_function_pretend_args_size} bytes of +uninitialized space just underneath the first argument arriving on the +stack. (This may not be at the very start of the allocated stack region +if the calling sequence has pushed anything else since pushing the stack +arguments. But usually, on such machines, nothing else has been pushed +yet, because the function prologue itself does all the pushing.) This +region is used on machines where an argument may be passed partly in +registers and partly in memory, and, in some cases to support the +features in @code{} and @code{}. + +@item +An area of memory used to save certain registers used by the function. +The size of this area, which may also include space for such things as +the return address and pointers to previous stack frames, is +machine-specific and usually depends on which registers have been used +in the function. Machines with register windows often do not require +a save area. + +@item +A region of at least @var{size} bytes, possibly rounded up to an allocation +boundary, to contain the local variables of the function. On some machines, +this region and the save area may occur in the opposite order, with the +save area closer to the top of the stack. + +@item +@cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames +Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of +@code{current_function_outgoing_args_size} bytes to be used for outgoing +argument lists of the function. @xref{Stack Arguments}. +@end itemize + +Normally, it is necessary for the macros +@code{TARGET_ASM_FUNCTION_PROLOGUE} and +@code{TARGET_ASM_FUNCTION_EPILOGUE} to treat leaf functions specially. +The C variable @code{current_function_is_leaf} is nonzero for such a +function. + +@findex EXIT_IGNORE_STACK +@item EXIT_IGNORE_STACK +Define this macro as a C expression that is nonzero if the return +instruction or the function epilogue ignores the value of the stack +pointer; in other words, if it is safe to delete an instruction to +adjust the stack pointer before a return from the function. + +Note that this macro's value is relevant only for functions for which +frame pointers are maintained. It is never safe to delete a final +stack adjustment in a function that has no frame pointer, and the +compiler knows this regardless of @code{EXIT_IGNORE_STACK}. + +@findex EPILOGUE_USES +@item EPILOGUE_USES (@var{regno}) +Define this macro as a C expression that is nonzero for registers that are +used by the epilogue or the @samp{return} pattern. The stack and frame +pointer registers are already be assumed to be used as needed. + +@findex DELAY_SLOTS_FOR_EPILOGUE +@item DELAY_SLOTS_FOR_EPILOGUE +Define this macro if the function epilogue contains delay slots to which +instructions from the rest of the function can be ``moved''. The +definition should be a C expression whose value is an integer +representing the number of delay slots there. + +@findex ELIGIBLE_FOR_EPILOGUE_DELAY +@item ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n}) +A C expression that returns 1 if @var{insn} can be placed in delay +slot number @var{n} of the epilogue. + +The argument @var{n} is an integer which identifies the delay slot now +being considered (since different slots may have different rules of +eligibility). It is never negative and is always less than the number +of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns). +If you reject a particular insn for a given delay slot, in principle, it +may be reconsidered for a subsequent delay slot. Also, other insns may +(at least in principle) be considered for the so far unfilled delay +slot. + +@findex current_function_epilogue_delay_list +@findex final_scan_insn +The insns accepted to fill the epilogue delay slots are put in an RTL +list made with @code{insn_list} objects, stored in the variable +@code{current_function_epilogue_delay_list}. The insn for the first +delay slot comes first in the list. Your definition of the macro +@code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by +outputting the insns in this list, usually by calling +@code{final_scan_insn}. + +You need not define this macro if you did not define +@code{DELAY_SLOTS_FOR_EPILOGUE}. + +@findex ASM_OUTPUT_MI_THUNK +@item ASM_OUTPUT_MI_THUNK (@var{file}, @var{thunk_fndecl}, @var{delta}, @var{function}) +A C compound statement that outputs the assembler code for a thunk +function, used to implement C++ virtual function calls with multiple +inheritance. The thunk acts as a wrapper around a virtual function, +adjusting the implicit object parameter before handing control off to +the real function. + +First, emit code to add the integer @var{delta} to the location that +contains the incoming first argument. Assume that this argument +contains a pointer, and is the one used to pass the @code{this} pointer +in C++. This is the incoming argument @emph{before} the function prologue, +e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of +all other incoming arguments. + +After the addition, emit code to jump to @var{function}, which is a +@code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does +not touch the return address. Hence returning from @var{FUNCTION} will +return to whoever called the current @samp{thunk}. + +The effect must be as if @var{function} had been called directly with +the adjusted first argument. This macro is responsible for emitting all +of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE} +and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked. + +The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function} +have already been extracted from it.) It might possibly be useful on +some targets, but probably not. + +If you do not define this macro, the target-independent code in the C++ +front end will generate a less efficient heavyweight thunk that calls +@var{function} instead of jumping to it. The generic approach does +not support varargs. +@end table + +@node Profiling +@subsection Generating Code for Profiling +@cindex profiling, code generation + +These macros will help you generate code for profiling. + +@table @code +@findex FUNCTION_PROFILER +@item FUNCTION_PROFILER (@var{file}, @var{labelno}) +A C statement or compound statement to output to @var{file} some +assembler code to call the profiling subroutine @code{mcount}. + +@findex mcount +The details of how @code{mcount} expects to be called are determined by +your operating system environment, not by GCC@. To figure them out, +compile a small program for profiling using the system's installed C +compiler and look at the assembler code that results. + +Older implementations of @code{mcount} expect the address of a counter +variable to be loaded into some register. The name of this variable is +@samp{LP} followed by the number @var{labelno}, so you would generate +the name using @samp{LP%d} in a @code{fprintf}. + +@findex PROFILE_HOOK +@item PROFILE_HOOK +A C statement or compound statement to output to @var{file} some assembly +code to call the profiling subroutine @code{mcount} even the target does +not support profiling. + +@findex NO_PROFILE_COUNTERS +@item NO_PROFILE_COUNTERS +Define this macro if the @code{mcount} subroutine on your system does +not need a counter variable allocated for each function. This is true +for almost all modern implementations. If you define this macro, you +must not use the @var{labelno} argument to @code{FUNCTION_PROFILER}. + +@findex PROFILE_BEFORE_PROLOGUE +@item PROFILE_BEFORE_PROLOGUE +Define this macro if the code for function profiling should come before +the function prologue. Normally, the profiling code comes after. + + +@findex TARGET_ALLOWS_PROFILING_WITHOUT_FRAME_POINTER +@item TARGET_ALLOWS_PROFILING_WITHOUT_FRAME_POINTER +On some targets, it is impossible to use profiling when the frame +pointer has been omitted. For example, on x86 GNU/Linux systems, +the @code{mcount} routine provided by the GNU C Library finds the +address of the routine that called the routine that called @code{mcount} +by looking in the immediate caller's stack frame. If the immediate +caller has no frame pointer, this lookup will fail. + +By default, GCC assumes that the target does allow profiling when the +frame pointer is omitted. This macro should be defined to a C +expression that evaluates to @code{false} if the target does not allow +profiling when the frame pointer is omitted. + +@end table + +@node Tail Calls +@subsection Permitting tail calls +@cindex tail calls + +@table @code +@findex FUNCTION_OK_FOR_SIBCALL +@item FUNCTION_OK_FOR_SIBCALL (@var{decl}) +A C expression that evaluates to true if it is ok to perform a sibling +call to @var{decl} from the current function. + +It is not uncommon for limitations of calling conventions to prevent +tail calls to functions outside the current unit of translation, or +during PIC compilation. Use this macro to enforce these restrictions, +as the @code{sibcall} md pattern can not fail, or fall over to a +``normal'' call. +@end table + +@node Varargs +@section Implementing the Varargs Macros +@cindex varargs implementation + +GCC comes with an implementation of @code{} and +@code{} that work without change on machines that pass arguments +on the stack. Other machines require their own implementations of +varargs, and the two machine independent header files must have +conditionals to include it. + +ISO @code{} differs from traditional @code{} mainly in +the calling convention for @code{va_start}. The traditional +implementation takes just one argument, which is the variable in which +to store the argument pointer. The ISO implementation of +@code{va_start} takes an additional second argument. The user is +supposed to write the last named argument of the function here. + +However, @code{va_start} should not use this argument. The way to find +the end of the named arguments is with the built-in functions described +below. + +@table @code +@findex __builtin_saveregs +@item __builtin_saveregs () +Use this built-in function to save the argument registers in memory so +that the varargs mechanism can access them. Both ISO and traditional +versions of @code{va_start} must use @code{__builtin_saveregs}, unless +you use @code{SETUP_INCOMING_VARARGS} (see below) instead. + +On some machines, @code{__builtin_saveregs} is open-coded under the +control of the macro @code{EXPAND_BUILTIN_SAVEREGS}. On other machines, +it calls a routine written in assembler language, found in +@file{libgcc2.c}. + +Code generated for the call to @code{__builtin_saveregs} appears at the +beginning of the function, as opposed to where the call to +@code{__builtin_saveregs} is written, regardless of what the code is. +This is because the registers must be saved before the function starts +to use them for its own purposes. +@c i rewrote the first sentence above to fix an overfull hbox. --mew +@c 10feb93 + +@findex __builtin_args_info +@item __builtin_args_info (@var{category}) +Use this built-in function to find the first anonymous arguments in +registers. + +In general, a machine may have several categories of registers used for +arguments, each for a particular category of data types. (For example, +on some machines, floating-point registers are used for floating-point +arguments while other arguments are passed in the general registers.) +To make non-varargs functions use the proper calling convention, you +have defined the @code{CUMULATIVE_ARGS} data type to record how many +registers in each category have been used so far + +@code{__builtin_args_info} accesses the same data structure of type +@code{CUMULATIVE_ARGS} after the ordinary argument layout is finished +with it, with @var{category} specifying which word to access. Thus, the +value indicates the first unused register in a given category. + +Normally, you would use @code{__builtin_args_info} in the implementation +of @code{va_start}, accessing each category just once and storing the +value in the @code{va_list} object. This is because @code{va_list} will +have to update the values, and there is no way to alter the +values accessed by @code{__builtin_args_info}. + +@findex __builtin_next_arg +@item __builtin_next_arg (@var{lastarg}) +This is the equivalent of @code{__builtin_args_info}, for stack +arguments. It returns the address of the first anonymous stack +argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it +returns the address of the location above the first anonymous stack +argument. Use it in @code{va_start} to initialize the pointer for +fetching arguments from the stack. Also use it in @code{va_start} to +verify that the second parameter @var{lastarg} is the last named argument +of the current function. + +@findex __builtin_classify_type +@item __builtin_classify_type (@var{object}) +Since each machine has its own conventions for which data types are +passed in which kind of register, your implementation of @code{va_arg} +has to embody these conventions. The easiest way to categorize the +specified data type is to use @code{__builtin_classify_type} together +with @code{sizeof} and @code{__alignof__}. + +@code{__builtin_classify_type} ignores the value of @var{object}, +considering only its data type. It returns an integer describing what +kind of type that is---integer, floating, pointer, structure, and so on. + +The file @file{typeclass.h} defines an enumeration that you can use to +interpret the values of @code{__builtin_classify_type}. +@end table + +These machine description macros help implement varargs: + +@table @code +@findex EXPAND_BUILTIN_SAVEREGS +@item EXPAND_BUILTIN_SAVEREGS () +If defined, is a C expression that produces the machine-specific code +for a call to @code{__builtin_saveregs}. This code will be moved to the +very beginning of the function, before any parameter access are made. +The return value of this function should be an RTX that contains the +value to use as the return of @code{__builtin_saveregs}. + +@findex SETUP_INCOMING_VARARGS +@item SETUP_INCOMING_VARARGS (@var{args_so_far}, @var{mode}, @var{type}, @var{pretend_args_size}, @var{second_time}) +This macro offers an alternative to using @code{__builtin_saveregs} and +defining the macro @code{EXPAND_BUILTIN_SAVEREGS}. Use it to store the +anonymous register arguments into the stack so that all the arguments +appear to have been passed consecutively on the stack. Once this is +done, you can use the standard implementation of varargs that works for +machines that pass all their arguments on the stack. + +The argument @var{args_so_far} is the @code{CUMULATIVE_ARGS} data +structure, containing the values that are obtained after processing the +named arguments. The arguments @var{mode} and @var{type} describe the +last named argument---its machine mode and its data type as a tree node. + +The macro implementation should do two things: first, push onto the +stack all the argument registers @emph{not} used for the named +arguments, and second, store the size of the data thus pushed into the +@code{int}-valued variable whose name is supplied as the argument +@var{pretend_args_size}. The value that you store here will serve as +additional offset for setting up the stack frame. + +Because you must generate code to push the anonymous arguments at +compile time without knowing their data types, +@code{SETUP_INCOMING_VARARGS} is only useful on machines that have just +a single category of argument register and use it uniformly for all data +types. + +If the argument @var{second_time} is nonzero, it means that the +arguments of the function are being analyzed for the second time. This +happens for an inline function, which is not actually compiled until the +end of the source file. The macro @code{SETUP_INCOMING_VARARGS} should +not generate any instructions in this case. + +@findex STRICT_ARGUMENT_NAMING +@item STRICT_ARGUMENT_NAMING +Define this macro to be a nonzero value if the location where a function +argument is passed depends on whether or not it is a named argument. + +This macro controls how the @var{named} argument to @code{FUNCTION_ARG} +is set for varargs and stdarg functions. If this macro returns a +nonzero value, the @var{named} argument is always true for named +arguments, and false for unnamed arguments. If it returns a value of +zero, but @code{SETUP_INCOMING_VARARGS} is defined, then all arguments +are treated as named. Otherwise, all named arguments except the last +are treated as named. + +You need not define this macro if it always returns zero. + +@findex PRETEND_OUTGOING_VARARGS_NAMED +@item PRETEND_OUTGOING_VARARGS_NAMED +If you need to conditionally change ABIs so that one works with +@code{SETUP_INCOMING_VARARGS}, but the other works like neither +@code{SETUP_INCOMING_VARARGS} nor @code{STRICT_ARGUMENT_NAMING} was +defined, then define this macro to return nonzero if +@code{SETUP_INCOMING_VARARGS} is used, zero otherwise. +Otherwise, you should not define this macro. +@end table + +@node Trampolines +@section Trampolines for Nested Functions +@cindex trampolines for nested functions +@cindex nested functions, trampolines for + +A @dfn{trampoline} is a small piece of code that is created at run time +when the address of a nested function is taken. It normally resides on +the stack, in the stack frame of the containing function. These macros +tell GCC how to generate code to allocate and initialize a +trampoline. + +The instructions in the trampoline must do two things: load a constant +address into the static chain register, and jump to the real address of +the nested function. On CISC machines such as the m68k, this requires +two instructions, a move immediate and a jump. Then the two addresses +exist in the trampoline as word-long immediate operands. On RISC +machines, it is often necessary to load each address into a register in +two parts. Then pieces of each address form separate immediate +operands. + +The code generated to initialize the trampoline must store the variable +parts---the static chain value and the function address---into the +immediate operands of the instructions. On a CISC machine, this is +simply a matter of copying each address to a memory reference at the +proper offset from the start of the trampoline. On a RISC machine, it +may be necessary to take out pieces of the address and store them +separately. + +@table @code +@findex TRAMPOLINE_TEMPLATE +@item TRAMPOLINE_TEMPLATE (@var{file}) +A C statement to output, on the stream @var{file}, assembler code for a +block of data that contains the constant parts of a trampoline. This +code should not include a label---the label is taken care of +automatically. + +If you do not define this macro, it means no template is needed +for the target. Do not define this macro on systems where the block move +code to copy the trampoline into place would be larger than the code +to generate it on the spot. + +@findex TRAMPOLINE_SECTION +@item TRAMPOLINE_SECTION +The name of a subroutine to switch to the section in which the +trampoline template is to be placed (@pxref{Sections}). The default is +a value of @samp{readonly_data_section}, which places the trampoline in +the section containing read-only data. + +@findex TRAMPOLINE_SIZE +@item TRAMPOLINE_SIZE +A C expression for the size in bytes of the trampoline, as an integer. + +@findex TRAMPOLINE_ALIGNMENT +@item TRAMPOLINE_ALIGNMENT +Alignment required for trampolines, in bits. + +If you don't define this macro, the value of @code{BIGGEST_ALIGNMENT} +is used for aligning trampolines. + +@findex INITIALIZE_TRAMPOLINE +@item INITIALIZE_TRAMPOLINE (@var{addr}, @var{fnaddr}, @var{static_chain}) +A C statement to initialize the variable parts of a trampoline. +@var{addr} is an RTX for the address of the trampoline; @var{fnaddr} is +an RTX for the address of the nested function; @var{static_chain} is an +RTX for the static chain value that should be passed to the function +when it is called. + +@findex TRAMPOLINE_ADJUST_ADDRESS +@item TRAMPOLINE_ADJUST_ADDRESS (@var{addr}) +A C statement that should perform any machine-specific adjustment in +the address of the trampoline. Its argument contains the address that +was passed to @code{INITIALIZE_TRAMPOLINE}. In case the address to be +used for a function call should be different from the address in which +the template was stored, the different address should be assigned to +@var{addr}. If this macro is not defined, @var{addr} will be used for +function calls. + +@findex ALLOCATE_TRAMPOLINE +@item ALLOCATE_TRAMPOLINE (@var{fp}) +A C expression to allocate run-time space for a trampoline. The +expression value should be an RTX representing a memory reference to the +space for the trampoline. + +@cindex @code{TARGET_ASM_FUNCTION_EPILOGUE} and trampolines +@cindex @code{TARGET_ASM_FUNCTION_PROLOGUE} and trampolines +If this macro is not defined, by default the trampoline is allocated as +a stack slot. This default is right for most machines. The exceptions +are machines where it is impossible to execute instructions in the stack +area. On such machines, you may have to implement a separate stack, +using this macro in conjunction with @code{TARGET_ASM_FUNCTION_PROLOGUE} +and @code{TARGET_ASM_FUNCTION_EPILOGUE}. + +@var{fp} points to a data structure, a @code{struct function}, which +describes the compilation status of the immediate containing function of +the function which the trampoline is for. Normally (when +@code{ALLOCATE_TRAMPOLINE} is not defined), the stack slot for the +trampoline is in the stack frame of this containing function. Other +allocation strategies probably must do something analogous with this +information. +@end table + +Implementing trampolines is difficult on many machines because they have +separate instruction and data caches. Writing into a stack location +fails to clear the memory in the instruction cache, so when the program +jumps to that location, it executes the old contents. + +Here are two possible solutions. One is to clear the relevant parts of +the instruction cache whenever a trampoline is set up. The other is to +make all trampolines identical, by having them jump to a standard +subroutine. The former technique makes trampoline execution faster; the +latter makes initialization faster. + +To clear the instruction cache when a trampoline is initialized, define +the following macros which describe the shape of the cache. + +@table @code +@findex INSN_CACHE_SIZE +@item INSN_CACHE_SIZE +The total size in bytes of the cache. + +@findex INSN_CACHE_LINE_WIDTH +@item INSN_CACHE_LINE_WIDTH +The length in bytes of each cache line. The cache is divided into cache +lines which are disjoint slots, each holding a contiguous chunk of data +fetched from memory. Each time data is brought into the cache, an +entire line is read at once. The data loaded into a cache line is +always aligned on a boundary equal to the line size. + +@findex INSN_CACHE_DEPTH +@item INSN_CACHE_DEPTH +The number of alternative cache lines that can hold any particular memory +location. +@end table + +Alternatively, if the machine has system calls or instructions to clear +the instruction cache directly, you can define the following macro. + +@table @code +@findex CLEAR_INSN_CACHE +@item CLEAR_INSN_CACHE (@var{beg}, @var{end}) +If defined, expands to a C expression clearing the @emph{instruction +cache} in the specified interval. If it is not defined, and the macro +@code{INSN_CACHE_SIZE} is defined, some generic code is generated to clear the +cache. The definition of this macro would typically be a series of +@code{asm} statements. Both @var{beg} and @var{end} are both pointer +expressions. +@end table + +To use a standard subroutine, define the following macro. In addition, +you must make sure that the instructions in a trampoline fill an entire +cache line with identical instructions, or else ensure that the +beginning of the trampoline code is always aligned at the same point in +its cache line. Look in @file{m68k.h} as a guide. + +@table @code +@findex TRANSFER_FROM_TRAMPOLINE +@item TRANSFER_FROM_TRAMPOLINE +Define this macro if trampolines need a special subroutine to do their +work. The macro should expand to a series of @code{asm} statements +which will be compiled with GCC@. They go in a library function named +@code{__transfer_from_trampoline}. + +If you need to avoid executing the ordinary prologue code of a compiled +C function when you jump to the subroutine, you can do so by placing a +special label of your own in the assembler code. Use one @code{asm} +statement to generate an assembler label, and another to make the label +global. Then trampolines can use that label to jump directly to your +special assembler code. +@end table + +@node Library Calls +@section Implicit Calls to Library Routines +@cindex library subroutine names +@cindex @file{libgcc.a} + +@c prevent bad page break with this line +Here is an explanation of implicit calls to library routines. + +@table @code +@findex MULSI3_LIBCALL +@item MULSI3_LIBCALL +A C string constant giving the name of the function to call for +multiplication of one signed full-word by another. If you do not +define this macro, the default name is used, which is @code{__mulsi3}, +a function defined in @file{libgcc.a}. + +@findex DIVSI3_LIBCALL +@item DIVSI3_LIBCALL +A C string constant giving the name of the function to call for +division of one signed full-word by another. If you do not define +this macro, the default name is used, which is @code{__divsi3}, a +function defined in @file{libgcc.a}. + +@findex UDIVSI3_LIBCALL +@item UDIVSI3_LIBCALL +A C string constant giving the name of the function to call for +division of one unsigned full-word by another. If you do not define +this macro, the default name is used, which is @code{__udivsi3}, a +function defined in @file{libgcc.a}. + +@findex MODSI3_LIBCALL +@item MODSI3_LIBCALL +A C string constant giving the name of the function to call for the +remainder in division of one signed full-word by another. If you do +not define this macro, the default name is used, which is +@code{__modsi3}, a function defined in @file{libgcc.a}. + +@findex UMODSI3_LIBCALL +@item UMODSI3_LIBCALL +A C string constant giving the name of the function to call for the +remainder in division of one unsigned full-word by another. If you do +not define this macro, the default name is used, which is +@code{__umodsi3}, a function defined in @file{libgcc.a}. + +@findex MULDI3_LIBCALL +@item MULDI3_LIBCALL +A C string constant giving the name of the function to call for +multiplication of one signed double-word by another. If you do not +define this macro, the default name is used, which is @code{__muldi3}, +a function defined in @file{libgcc.a}. + +@findex DIVDI3_LIBCALL +@item DIVDI3_LIBCALL +A C string constant giving the name of the function to call for +division of one signed double-word by another. If you do not define +this macro, the default name is used, which is @code{__divdi3}, a +function defined in @file{libgcc.a}. + +@findex UDIVDI3_LIBCALL +@item UDIVDI3_LIBCALL +A C string constant giving the name of the function to call for +division of one unsigned full-word by another. If you do not define +this macro, the default name is used, which is @code{__udivdi3}, a +function defined in @file{libgcc.a}. + +@findex MODDI3_LIBCALL +@item MODDI3_LIBCALL +A C string constant giving the name of the function to call for the +remainder in division of one signed double-word by another. If you do +not define this macro, the default name is used, which is +@code{__moddi3}, a function defined in @file{libgcc.a}. + +@findex UMODDI3_LIBCALL +@item UMODDI3_LIBCALL +A C string constant giving the name of the function to call for the +remainder in division of one unsigned full-word by another. If you do +not define this macro, the default name is used, which is +@code{__umoddi3}, a function defined in @file{libgcc.a}. + +@findex INIT_TARGET_OPTABS +@item INIT_TARGET_OPTABS +Define this macro as a C statement that declares additional library +routines renames existing ones. @code{init_optabs} calls this macro after +initializing all the normal library routines. + +@findex FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison}) +@item FLOAT_LIB_COMPARE_RETURNS_BOOL +Define this macro as a C statement that returns nonzero if a call to +the floating point comparison library function will return a boolean +value that indicates the result of the comparison. It should return +zero if one of gcc's own libgcc functions is called. + +Most ports don't need to define this macro. + +@findex TARGET_EDOM +@cindex @code{EDOM}, implicit usage +@item TARGET_EDOM +The value of @code{EDOM} on the target machine, as a C integer constant +expression. If you don't define this macro, GCC does not attempt to +deposit the value of @code{EDOM} into @code{errno} directly. Look in +@file{/usr/include/errno.h} to find the value of @code{EDOM} on your +system. + +If you do not define @code{TARGET_EDOM}, then compiled code reports +domain errors by calling the library function and letting it report the +error. If mathematical functions on your system use @code{matherr} when +there is an error, then you should leave @code{TARGET_EDOM} undefined so +that @code{matherr} is used normally. + +@findex GEN_ERRNO_RTX +@cindex @code{errno}, implicit usage +@item GEN_ERRNO_RTX +Define this macro as a C expression to create an rtl expression that +refers to the global ``variable'' @code{errno}. (On certain systems, +@code{errno} may not actually be a variable.) If you don't define this +macro, a reasonable default is used. + +@findex TARGET_MEM_FUNCTIONS +@cindex @code{bcopy}, implicit usage +@cindex @code{memcpy}, implicit usage +@cindex @code{memmove}, implicit usage +@cindex @code{bzero}, implicit usage +@cindex @code{memset}, implicit usage +@item TARGET_MEM_FUNCTIONS +Define this macro if GCC should generate calls to the ISO C +(and System V) library functions @code{memcpy}, @code{memmove} and +@code{memset} rather than the BSD functions @code{bcopy} and @code{bzero}. + +@findex LIBGCC_NEEDS_DOUBLE +@item LIBGCC_NEEDS_DOUBLE +Define this macro if @code{float} arguments cannot be passed to library +routines (so they must be converted to @code{double}). This macro +affects both how library calls are generated and how the library +routines in @file{libgcc.a} accept their arguments. It is useful on +machines where floating and fixed point arguments are passed +differently, such as the i860. + +@findex NEXT_OBJC_RUNTIME +@item NEXT_OBJC_RUNTIME +Define this macro to generate code for Objective-C message sending using +the calling convention of the NeXT system. This calling convention +involves passing the object, the selector and the method arguments all +at once to the method-lookup library function. + +The default calling convention passes just the object and the selector +to the lookup function, which returns a pointer to the method. +@end table + +@node Addressing Modes +@section Addressing Modes +@cindex addressing modes + +@c prevent bad page break with this line +This is about addressing modes. + +@table @code +@findex HAVE_PRE_INCREMENT +@findex HAVE_PRE_DECREMENT +@findex HAVE_POST_INCREMENT +@findex HAVE_POST_DECREMENT +@item HAVE_PRE_INCREMENT +@itemx HAVE_PRE_DECREMENT +@itemx HAVE_POST_INCREMENT +@itemx HAVE_POST_DECREMENT +A C expression that is nonzero if the machine supports pre-increment, +pre-decrement, post-increment, or post-decrement addressing respectively. + +@findex HAVE_POST_MODIFY_DISP +@findex HAVE_PRE_MODIFY_DISP +@item HAVE_PRE_MODIFY_DISP +@itemx HAVE_POST_MODIFY_DISP +A C expression that is nonzero if the machine supports pre- or +post-address side-effect generation involving constants other than +the size of the memory operand. + +@findex HAVE_POST_MODIFY_REG +@findex HAVE_PRE_MODIFY_REG +@item HAVE_PRE_MODIFY_REG +@itemx HAVE_POST_MODIFY_REG +A C expression that is nonzero if the machine supports pre- or +post-address side-effect generation involving a register displacement. + +@findex CONSTANT_ADDRESS_P +@item CONSTANT_ADDRESS_P (@var{x}) +A C expression that is 1 if the RTX @var{x} is a constant which +is a valid address. On most machines, this can be defined as +@code{CONSTANT_P (@var{x})}, but a few machines are more restrictive +in which constant addresses are supported. + +@findex CONSTANT_P +@code{CONSTANT_P} accepts integer-values expressions whose values are +not explicitly known, such as @code{symbol_ref}, @code{label_ref}, and +@code{high} expressions and @code{const} arithmetic expressions, in +addition to @code{const_int} and @code{const_double} expressions. + +@findex MAX_REGS_PER_ADDRESS +@item MAX_REGS_PER_ADDRESS +A number, the maximum number of registers that can appear in a valid +memory address. Note that it is up to you to specify a value equal to +the maximum number that @code{GO_IF_LEGITIMATE_ADDRESS} would ever +accept. + +@findex GO_IF_LEGITIMATE_ADDRESS +@item GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label}) +A C compound statement with a conditional @code{goto @var{label};} +executed if @var{x} (an RTX) is a legitimate memory address on the +target machine for a memory operand of mode @var{mode}. + +It usually pays to define several simpler macros to serve as +subroutines for this one. Otherwise it may be too complicated to +understand. + +This macro must exist in two variants: a strict variant and a +non-strict one. The strict variant is used in the reload pass. It +must be defined so that any pseudo-register that has not been +allocated a hard register is considered a memory reference. In +contexts where some kind of register is required, a pseudo-register +with no hard register must be rejected. + +The non-strict variant is used in other passes. It must be defined to +accept all pseudo-registers in every context where some kind of +register is required. + +@findex REG_OK_STRICT +Compiler source files that want to use the strict variant of this +macro define the macro @code{REG_OK_STRICT}. You should use an +@code{#ifdef REG_OK_STRICT} conditional to define the strict variant +in that case and the non-strict variant otherwise. + +Subroutines to check for acceptable registers for various purposes (one +for base registers, one for index registers, and so on) are typically +among the subroutines used to define @code{GO_IF_LEGITIMATE_ADDRESS}. +Then only these subroutine macros need have two variants; the higher +levels of macros may be the same whether strict or not. + +Normally, constant addresses which are the sum of a @code{symbol_ref} +and an integer are stored inside a @code{const} RTX to mark them as +constant. Therefore, there is no need to recognize such sums +specifically as legitimate addresses. Normally you would simply +recognize any @code{const} as legitimate. + +Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant +sums that are not marked with @code{const}. It assumes that a naked +@code{plus} indicates indexing. If so, then you @emph{must} reject such +naked constant sums as illegitimate addresses, so that none of them will +be given to @code{PRINT_OPERAND_ADDRESS}. + +@cindex @code{ENCODE_SECTION_INFO} and address validation +On some machines, whether a symbolic address is legitimate depends on +the section that the address refers to. On these machines, define the +macro @code{ENCODE_SECTION_INFO} to store the information into the +@code{symbol_ref}, and then check for it here. When you see a +@code{const}, you will have to look inside it to find the +@code{symbol_ref} in order to determine the section. @xref{Assembler +Format}. + +@findex saveable_obstack +The best way to modify the name string is by adding text to the +beginning, with suitable punctuation to prevent any ambiguity. Allocate +the new name in @code{saveable_obstack}. You will have to modify +@code{ASM_OUTPUT_LABELREF} to remove and decode the added text and +output the name accordingly, and define @code{STRIP_NAME_ENCODING} to +access the original name string. + +You can check the information stored here into the @code{symbol_ref} in +the definitions of the macros @code{GO_IF_LEGITIMATE_ADDRESS} and +@code{PRINT_OPERAND_ADDRESS}. + +@findex REG_OK_FOR_BASE_P +@item REG_OK_FOR_BASE_P (@var{x}) +A C expression that is nonzero if @var{x} (assumed to be a @code{reg} +RTX) is valid for use as a base register. For hard registers, it +should always accept those which the hardware permits and reject the +others. Whether the macro accepts or rejects pseudo registers must be +controlled by @code{REG_OK_STRICT} as described above. This usually +requires two variant definitions, of which @code{REG_OK_STRICT} +controls the one actually used. + +@findex REG_MODE_OK_FOR_BASE_P +@item REG_MODE_OK_FOR_BASE_P (@var{x}, @var{mode}) +A C expression that is just like @code{REG_OK_FOR_BASE_P}, except that +that expression may examine the mode of the memory reference in +@var{mode}. You should define this macro if the mode of the memory +reference affects whether a register may be used as a base register. If +you define this macro, the compiler will use it instead of +@code{REG_OK_FOR_BASE_P}. + +@findex REG_OK_FOR_INDEX_P +@item REG_OK_FOR_INDEX_P (@var{x}) +A C expression that is nonzero if @var{x} (assumed to be a @code{reg} +RTX) is valid for use as an index register. + +The difference between an index register and a base register is that +the index register may be scaled. If an address involves the sum of +two registers, neither one of them scaled, then either one may be +labeled the ``base'' and the other the ``index''; but whichever +labeling is used must fit the machine's constraints of which registers +may serve in each capacity. The compiler will try both labelings, +looking for one that is valid, and will reload one or both registers +only if neither labeling works. + +@findex FIND_BASE_TERM +@item FIND_BASE_TERM (@var{x}) +A C expression to determine the base term of address @var{x}. +This macro is used in only one place: `find_base_term' in alias.c. + +It is always safe for this macro to not be defined. It exists so +that alias analysis can understand machine-dependent addresses. + +The typical use of this macro is to handle addresses containing +a label_ref or symbol_ref within an UNSPEC@. + +@findex LEGITIMIZE_ADDRESS +@item LEGITIMIZE_ADDRESS (@var{x}, @var{oldx}, @var{mode}, @var{win}) +A C compound statement that attempts to replace @var{x} with a valid +memory address for an operand of mode @var{mode}. @var{win} will be a +C statement label elsewhere in the code; the macro definition may use + +@example +GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{win}); +@end example + +@noindent +to avoid further processing if the address has become legitimate. + +@findex break_out_memory_refs +@var{x} will always be the result of a call to @code{break_out_memory_refs}, +and @var{oldx} will be the operand that was given to that function to produce +@var{x}. + +The code generated by this macro should not alter the substructure of +@var{x}. If it transforms @var{x} into a more legitimate form, it +should assign @var{x} (which will always be a C variable) a new value. + +It is not necessary for this macro to come up with a legitimate +address. The compiler has standard ways of doing so in all cases. In +fact, it is safe for this macro to do nothing. But often a +machine-dependent strategy can generate better code. + +@findex LEGITIMIZE_RELOAD_ADDRESS +@item LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win}) +A C compound statement that attempts to replace @var{x}, which is an address +that needs reloading, with a valid memory address for an operand of mode +@var{mode}. @var{win} will be a C statement label elsewhere in the code. +It is not necessary to define this macro, but it might be useful for +performance reasons. + +For example, on the i386, it is sometimes possible to use a single +reload register instead of two by reloading a sum of two pseudo +registers into a register. On the other hand, for number of RISC +processors offsets are limited so that often an intermediate address +needs to be generated in order to address a stack slot. By defining +@code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses +generated for adjacent some stack slots can be made identical, and thus +be shared. + +@emph{Note}: This macro should be used with caution. It is necessary +to know something of how reload works in order to effectively use this, +and it is quite easy to produce macros that build in too much knowledge +of reload internals. + +@emph{Note}: This macro must be able to reload an address created by a +previous invocation of this macro. If it fails to handle such addresses +then the compiler may generate incorrect code or abort. + +@findex push_reload +The macro definition should use @code{push_reload} to indicate parts that +need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually +suitable to be passed unaltered to @code{push_reload}. + +The code generated by this macro must not alter the substructure of +@var{x}. If it transforms @var{x} into a more legitimate form, it +should assign @var{x} (which will always be a C variable) a new value. +This also applies to parts that you change indirectly by calling +@code{push_reload}. + +@findex strict_memory_address_p +The macro definition may use @code{strict_memory_address_p} to test if +the address has become legitimate. + +@findex copy_rtx +If you want to change only a part of @var{x}, one standard way of doing +this is to use @code{copy_rtx}. Note, however, that is unshares only a +single level of rtl. Thus, if the part to be changed is not at the +top level, you'll need to replace first the top level. +It is not necessary for this macro to come up with a legitimate +address; but often a machine-dependent strategy can generate better code. + +@findex GO_IF_MODE_DEPENDENT_ADDRESS +@item GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label}) +A C statement or compound statement with a conditional @code{goto +@var{label};} executed if memory address @var{x} (an RTX) can have +different meanings depending on the machine mode of the memory +reference it is used for or if the address is valid for some modes +but not others. + +Autoincrement and autodecrement addresses typically have mode-dependent +effects because the amount of the increment or decrement is the size +of the operand being addressed. Some machines have other mode-dependent +addresses. Many RISC machines have no mode-dependent addresses. + +You may assume that @var{addr} is a valid address for the machine. + +@findex LEGITIMATE_CONSTANT_P +@item LEGITIMATE_CONSTANT_P (@var{x}) +A C expression that is nonzero if @var{x} is a legitimate constant for +an immediate operand on the target machine. You can assume that +@var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact, +@samp{1} is a suitable definition for this macro on machines where +anything @code{CONSTANT_P} is valid. +@end table + +@node Condition Code +@section Condition Code Status +@cindex condition code status + +@c prevent bad page break with this line +This describes the condition code status. + +@findex cc_status +The file @file{conditions.h} defines a variable @code{cc_status} to +describe how the condition code was computed (in case the interpretation of +the condition code depends on the instruction that it was set by). This +variable contains the RTL expressions on which the condition code is +currently based, and several standard flags. + +Sometimes additional machine-specific flags must be defined in the machine +description header file. It can also add additional machine-specific +information by defining @code{CC_STATUS_MDEP}. + +@table @code +@findex CC_STATUS_MDEP +@item CC_STATUS_MDEP +C code for a data type which is used for declaring the @code{mdep} +component of @code{cc_status}. It defaults to @code{int}. + +This macro is not used on machines that do not use @code{cc0}. + +@findex CC_STATUS_MDEP_INIT +@item CC_STATUS_MDEP_INIT +A C expression to initialize the @code{mdep} field to ``empty''. +The default definition does nothing, since most machines don't use +the field anyway. If you want to use the field, you should probably +define this macro to initialize it. + +This macro is not used on machines that do not use @code{cc0}. + +@findex NOTICE_UPDATE_CC +@item NOTICE_UPDATE_CC (@var{exp}, @var{insn}) +A C compound statement to set the components of @code{cc_status} +appropriately for an insn @var{insn} whose body is @var{exp}. It is +this macro's responsibility to recognize insns that set the condition +code as a byproduct of other activity as well as those that explicitly +set @code{(cc0)}. + +This macro is not used on machines that do not use @code{cc0}. + +If there are insns that do not set the condition code but do alter +other machine registers, this macro must check to see whether they +invalidate the expressions that the condition code is recorded as +reflecting. For example, on the 68000, insns that store in address +registers do not set the condition code, which means that usually +@code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such +insns. But suppose that the previous insn set the condition code +based on location @samp{a4@@(102)} and the current insn stores a new +value in @samp{a4}. Although the condition code is not changed by +this, it will no longer be true that it reflects the contents of +@samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter +@code{cc_status} in this case to say that nothing is known about the +condition code value. + +The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal +with the results of peephole optimization: insns whose patterns are +@code{parallel} RTXs containing various @code{reg}, @code{mem} or +constants which are just the operands. The RTL structure of these +insns is not sufficient to indicate what the insns actually do. What +@code{NOTICE_UPDATE_CC} should do when it sees one is just to run +@code{CC_STATUS_INIT}. + +A possible definition of @code{NOTICE_UPDATE_CC} is to call a function +that looks at an attribute (@pxref{Insn Attributes}) named, for example, +@samp{cc}. This avoids having detailed information about patterns in +two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}. + +@findex EXTRA_CC_MODES +@item EXTRA_CC_MODES +A list of additional modes for condition code values in registers +(@pxref{Jump Patterns}). This macro should expand to a sequence of +calls of the macro @code{CC} separated by white space. @code{CC} takes +two arguments. The first is the enumeration name of the mode, which +should begin with @samp{CC} and end with @samp{mode}. The second is a C +string giving the printable name of the mode; it should be the same as +the first argument, but with the trailing @samp{mode} removed. + +You should only define this macro if additional modes are required. + +A sample definition of @code{EXTRA_CC_MODES} is: +@smallexample +#define EXTRA_CC_MODES \ + CC(CC_NOOVmode, "CC_NOOV") \ + CC(CCFPmode, "CCFP") \ + CC(CCFPEmode, "CCFPE") +@end smallexample + +@findex SELECT_CC_MODE +@item SELECT_CC_MODE (@var{op}, @var{x}, @var{y}) +Returns a mode from class @code{MODE_CC} to be used when comparison +operation code @var{op} is applied to rtx @var{x} and @var{y}. For +example, on the Sparc, @code{SELECT_CC_MODE} is defined as (see +@pxref{Jump Patterns} for a description of the reason for this +definition) + +@smallexample +#define SELECT_CC_MODE(OP,X,Y) \ + (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \ + ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \ + : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \ + || GET_CODE (X) == NEG) \ + ? CC_NOOVmode : CCmode)) +@end smallexample + +You need not define this macro if @code{EXTRA_CC_MODES} is not defined. + +@findex CANONICALIZE_COMPARISON +@item CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1}) +On some machines not all possible comparisons are defined, but you can +convert an invalid comparison into a valid one. For example, the Alpha +does not have a @code{GT} comparison, but you can use an @code{LT} +comparison instead and swap the order of the operands. + +On such machines, define this macro to be a C statement to do any +required conversions. @var{code} is the initial comparison code +and @var{op0} and @var{op1} are the left and right operands of the +comparison, respectively. You should modify @var{code}, @var{op0}, and +@var{op1} as required. + +GCC will not assume that the comparison resulting from this macro is +valid but will see if the resulting insn matches a pattern in the +@file{md} file. + +You need not define this macro if it would never change the comparison +code or operands. + +@findex REVERSIBLE_CC_MODE +@item REVERSIBLE_CC_MODE (@var{mode}) +A C expression whose value is one if it is always safe to reverse a +comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE} +can ever return @var{mode} for a floating-point inequality comparison, +then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero. + +You need not define this macro if it would always returns zero or if the +floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}. +For example, here is the definition used on the Sparc, where floating-point +inequality comparisons are always given @code{CCFPEmode}: + +@smallexample +#define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode) +@end smallexample + +@findex REVERSE_CONDITION (@var{code}, @var{mode}) +A C expression whose value is reversed condition code of the @var{code} for +comparison done in CC_MODE @var{mode}. The macro is used only in case +@code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case +machine has some non-standard way how to reverse certain conditionals. For +instance in case all floating point conditions are non-trapping, compiler may +freely convert unordered compares to ordered one. Then definition may look +like: + +@smallexample +#define REVERSE_CONDITION(CODE, MODE) \ + ((MODE) != CCFPmode ? reverse_condition (CODE) \ + : reverse_condition_maybe_unordered (CODE)) +@end smallexample + +@findex REVERSE_CONDEXEC_PREDICATES_P +@item REVERSE_CONDEXEC_PREDICATES_P (@var{code1}, @var{code2}) +A C expression that returns true if the conditional execution predicate +@var{code1} is the inverse of @var{code2} and vice versa. Define this to +return 0 if the target has conditional execution predicates that cannot be +reversed safely. If no expansion is specified, this macro is defined as +follows: + +@smallexample +#define REVERSE_CONDEXEC_PREDICATES_P (x, y) \ + ((x) == reverse_condition (y)) +@end smallexample + +@end table + +@node Costs +@section Describing Relative Costs of Operations +@cindex costs of instructions +@cindex relative costs +@cindex speed of instructions + +These macros let you describe the relative speed of various operations +on the target machine. + +@table @code +@findex CONST_COSTS +@item CONST_COSTS (@var{x}, @var{code}, @var{outer_code}) +A part of a C @code{switch} statement that describes the relative costs +of constant RTL expressions. It must contain @code{case} labels for +expression codes @code{const_int}, @code{const}, @code{symbol_ref}, +@code{label_ref} and @code{const_double}. Each case must ultimately +reach a @code{return} statement to return the relative cost of the use +of that kind of constant value in an expression. The cost may depend on +the precise value of the constant, which is available for examination in +@var{x}, and the rtx code of the expression in which it is contained, +found in @var{outer_code}. + +@var{code} is the expression code---redundant, since it can be +obtained with @code{GET_CODE (@var{x})}. + +@findex RTX_COSTS +@findex COSTS_N_INSNS +@item RTX_COSTS (@var{x}, @var{code}, @var{outer_code}) +Like @code{CONST_COSTS} but applies to nonconstant RTL expressions. +This can be used, for example, to indicate how costly a multiply +instruction is. In writing this macro, you can use the construct +@code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast +instructions. @var{outer_code} is the code of the expression in which +@var{x} is contained. + +This macro is optional; do not define it if the default cost assumptions +are adequate for the target machine. + +@findex DEFAULT_RTX_COSTS +@item DEFAULT_RTX_COSTS (@var{x}, @var{code}, @var{outer_code}) +This macro, if defined, is called for any case not handled by the +@code{RTX_COSTS} or @code{CONST_COSTS} macros. This eliminates the need +to put case labels into the macro, but the code, or any functions it +calls, must assume that the RTL in @var{x} could be of any type that has +not already been handled. The arguments are the same as for +@code{RTX_COSTS}, and the macro should execute a return statement giving +the cost of any RTL expressions that it can handle. The default cost +calculation is used for any RTL for which this macro does not return a +value. + +This macro is optional; do not define it if the default cost assumptions +are adequate for the target machine. + +@findex ADDRESS_COST +@item ADDRESS_COST (@var{address}) +An expression giving the cost of an addressing mode that contains +@var{address}. If not defined, the cost is computed from +the @var{address} expression and the @code{CONST_COSTS} values. + +For most CISC machines, the default cost is a good approximation of the +true cost of the addressing mode. However, on RISC machines, all +instructions normally have the same length and execution time. Hence +all addresses will have equal costs. + +In cases where more than one form of an address is known, the form with +the lowest cost will be used. If multiple forms have the same, lowest, +cost, the one that is the most complex will be used. + +For example, suppose an address that is equal to the sum of a register +and a constant is used twice in the same basic block. When this macro +is not defined, the address will be computed in a register and memory +references will be indirect through that register. On machines where +the cost of the addressing mode containing the sum is no higher than +that of a simple indirect reference, this will produce an additional +instruction and possibly require an additional register. Proper +specification of this macro eliminates this overhead for such machines. + +Similar use of this macro is made in strength reduction of loops. + +@var{address} need not be valid as an address. In such a case, the cost +is not relevant and can be any value; invalid addresses need not be +assigned a different cost. + +On machines where an address involving more than one register is as +cheap as an address computation involving only one register, defining +@code{ADDRESS_COST} to reflect this can cause two registers to be live +over a region of code where only one would have been if +@code{ADDRESS_COST} were not defined in that manner. This effect should +be considered in the definition of this macro. Equivalent costs should +probably only be given to addresses with different numbers of registers +on machines with lots of registers. + +This macro will normally either not be defined or be defined as a +constant. + +@findex REGISTER_MOVE_COST +@item REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to}) +A C expression for the cost of moving data of mode @var{mode} from a +register in class @var{from} to one in class @var{to}. The classes are +expressed using the enumeration values such as @code{GENERAL_REGS}. A +value of 2 is the default; other values are interpreted relative to +that. + +It is not required that the cost always equal 2 when @var{from} is the +same as @var{to}; on some machines it is expensive to move between +registers if they are not general registers. + +If reload sees an insn consisting of a single @code{set} between two +hard registers, and if @code{REGISTER_MOVE_COST} applied to their +classes returns a value of 2, reload does not check to ensure that the +constraints of the insn are met. Setting a cost of other than 2 will +allow reload to verify that the constraints are met. You should do this +if the @samp{mov@var{m}} pattern's constraints do not allow such copying. + +@findex MEMORY_MOVE_COST +@item MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in}) +A C expression for the cost of moving data of mode @var{mode} between a +register of class @var{class} and memory; @var{in} is zero if the value +is to be written to memory, nonzero if it is to be read in. This cost +is relative to those in @code{REGISTER_MOVE_COST}. If moving between +registers and memory is more expensive than between two registers, you +should define this macro to express the relative cost. + +If you do not define this macro, GCC uses a default cost of 4 plus +the cost of copying via a secondary reload register, if one is +needed. If your machine requires a secondary reload register to copy +between memory and a register of @var{class} but the reload mechanism is +more complex than copying via an intermediate, define this macro to +reflect the actual cost of the move. + +GCC defines the function @code{memory_move_secondary_cost} if +secondary reloads are needed. It computes the costs due to copying via +a secondary register. If your machine copies from memory using a +secondary register in the conventional way but the default base value of +4 is not correct for your machine, define this macro to add some other +value to the result of that function. The arguments to that function +are the same as to this macro. + +@findex BRANCH_COST +@item BRANCH_COST +A C expression for the cost of a branch instruction. A value of 1 is +the default; other values are interpreted relative to that. +@end table + +Here are additional macros which do not specify precise relative costs, +but only that certain actions are more expensive than GCC would +ordinarily expect. + +@table @code +@findex SLOW_BYTE_ACCESS +@item SLOW_BYTE_ACCESS +Define this macro as a C expression which is nonzero if accessing less +than a word of memory (i.e.@: a @code{char} or a @code{short}) is no +faster than accessing a word of memory, i.e., if such access +require more than one instruction or if there is no difference in cost +between byte and (aligned) word loads. + +When this macro is not defined, the compiler will access a field by +finding the smallest containing object; when it is defined, a fullword +load will be used if alignment permits. Unless bytes accesses are +faster than word accesses, using word accesses is preferable since it +may eliminate subsequent memory access if subsequent accesses occur to +other fields in the same word of the structure, but to different bytes. + +@findex SLOW_UNALIGNED_ACCESS +@item SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment}) +Define this macro to be the value 1 if memory accesses described by the +@var{mode} and @var{alignment} parameters have a cost many times greater +than aligned accesses, for example if they are emulated in a trap +handler. + +When this macro is nonzero, the compiler will act as if +@code{STRICT_ALIGNMENT} were nonzero when generating code for block +moves. This can cause significantly more instructions to be produced. +Therefore, do not set this macro nonzero if unaligned accesses only add a +cycle or two to the time for a memory access. + +If the value of this macro is always zero, it need not be defined. If +this macro is defined, it should produce a nonzero value when +@code{STRICT_ALIGNMENT} is nonzero. + +@findex DONT_REDUCE_ADDR +@item DONT_REDUCE_ADDR +Define this macro to inhibit strength reduction of memory addresses. +(On some machines, such strength reduction seems to do harm rather +than good.) + +@findex MOVE_RATIO +@item MOVE_RATIO +The threshold of number of scalar memory-to-memory move insns, @emph{below} +which a sequence of insns should be generated instead of a +string move insn or a library call. Increasing the value will always +make code faster, but eventually incurs high cost in increased code size. + +Note that on machines where the corresponding move insn is a +@code{define_expand} that emits a sequence of insns, this macro counts +the number of such sequences. + +If you don't define this, a reasonable default is used. + +@findex MOVE_BY_PIECES_P +@item MOVE_BY_PIECES_P (@var{size}, @var{alignment}) +A C expression used to determine whether @code{move_by_pieces} will be used to +copy a chunk of memory, or whether some other block move mechanism +will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less +than @code{MOVE_RATIO}. + +@findex MOVE_MAX_PIECES +@item MOVE_MAX_PIECES +A C expression used by @code{move_by_pieces} to determine the largest unit +a load or store used to copy memory is. Defaults to @code{MOVE_MAX}. + +@findex USE_LOAD_POST_INCREMENT +@item USE_LOAD_POST_INCREMENT (@var{mode}) +A C expression used to determine whether a load postincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_INCREMENT}. + +@findex USE_LOAD_POST_DECREMENT +@item USE_LOAD_POST_DECREMENT (@var{mode}) +A C expression used to determine whether a load postdecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_DECREMENT}. + +@findex USE_LOAD_PRE_INCREMENT +@item USE_LOAD_PRE_INCREMENT (@var{mode}) +A C expression used to determine whether a load preincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_INCREMENT}. + +@findex USE_LOAD_PRE_DECREMENT +@item USE_LOAD_PRE_DECREMENT (@var{mode}) +A C expression used to determine whether a load predecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_DECREMENT}. + +@findex USE_STORE_POST_INCREMENT +@item USE_STORE_POST_INCREMENT (@var{mode}) +A C expression used to determine whether a store postincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_INCREMENT}. + +@findex USE_STORE_POST_DECREMENT +@item USE_STORE_POST_DECREMENT (@var{mode}) +A C expression used to determine whether a store postdecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_DECREMENT}. + +@findex USE_STORE_PRE_INCREMENT +@item USE_STORE_PRE_INCREMENT (@var{mode}) +This macro is used to determine whether a store preincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_INCREMENT}. + +@findex USE_STORE_PRE_DECREMENT +@item USE_STORE_PRE_DECREMENT (@var{mode}) +This macro is used to determine whether a store predecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_DECREMENT}. + +@findex NO_FUNCTION_CSE +@item NO_FUNCTION_CSE +Define this macro if it is as good or better to call a constant +function address than to call an address kept in a register. + +@findex NO_RECURSIVE_FUNCTION_CSE +@item NO_RECURSIVE_FUNCTION_CSE +Define this macro if it is as good or better for a function to call +itself with an explicit address than to call an address kept in a +register. +@end table + +@node Scheduling +@section Adjusting the Instruction Scheduler + +The instruction scheduler may need a fair amount of machine-specific +adjustment in order to produce good code. GCC provides several target +hooks for this purpose. It is usually enough to define just a few of +them: try the first ones in this list first. + +@deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void) +This hook returns the maximum number of instructions that can ever issue +at the same time on the target machine. The default is one. This value +must be constant over the entire compilation. If you need it to vary +depending on what the instructions are, you must use +@samp{TARGET_SCHED_VARIABLE_ISSUE}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more}) +This hook is executed by the scheduler after it has scheduled an insn +from the ready list. It should return the number of insns which can +still be issued in the current cycle. Normally this is +@samp{@w{@var{more} - 1}}. You should define this hook if some insns +take more machine resources than others, so that fewer insns can follow +them in the same cycle. @var{file} is either a null pointer, or a stdio +stream to write any debug output to. @var{verbose} is the verbose level +provided by @option{-fsched-verbose-@var{n}}. @var{insn} is the +instruction that was scheduled. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost}) +This function corrects the value of @var{cost} based on the relationship +between @var{insn} and @var{dep_insn} through the dependence @var{link}. +It should return the new value. The default is to make no adjustment to +@var{cost}. This can be used for example to specify to the scheduler +that an output- or anti-dependence does not incur the same cost as a +data-dependence. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority}) +This hook adjusts the integer scheduling priority @var{priority} of +@var{insn}. It should return the new priority. Reduce the priority to +execute @var{insn} earlier, increase the priority to execute @var{insn} +later. Do not define this hook if you do not need to adjust the +scheduling priorities of insns. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock}) +This hook is executed by the scheduler after it has scheduled the ready +list, to allow the machine description to reorder it (for example to +combine two small instructions together on @samp{VLIW} machines). +@var{file} is either a null pointer, or a stdio stream to write any +debug output to. @var{verbose} is the verbose level provided by +@option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready +list of instructions that are ready to be scheduled. @var{n_readyp} is +a pointer to the number of elements in the ready list. The scheduler +reads the ready list in reverse order, starting with +@var{ready}[@var{*n_readyp}-1] and going to @var{ready}[0]. @var{clock} +is the timer tick of the scheduler. You may modify the ready list and +the number of ready insns. The return value is the number of insns that +can issue this cycle; normally this is just @code{issue_rate}. See also +@samp{TARGET_SCHED_REORDER2}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_ready}, @var{clock}) +Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That +function is called whenever the scheduler starts a new cycle. This one +is called once per iteration over a cycle, immediately after +@samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and +return the number of insns to be scheduled in the same cycle. Defining +this hook can be useful if there are frequent situations where +scheduling one insn causes other insns to become ready in the same +cycle. These other insns can then be taken into account properly. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready}) +This hook is executed by the scheduler at the beginning of each block of +instructions that are to be scheduled. @var{file} is either a null +pointer, or a stdio stream to write any debug output to. @var{verbose} +is the verbose level provided by @option{-fsched-verbose-@var{n}}. +@var{max_ready} is the maximum number of insns in the current scheduling +region that can be live at the same time. This can be used to allocate +scratch space if it is needed, e.g. by @samp{TARGET_SCHED_REORDER}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose}) +This hook is executed by the scheduler at the end of each block of +instructions that are to be scheduled. It can be used to perform +cleanup of any actions done by the other scheduling hooks. @var{file} +is either a null pointer, or a stdio stream to write any debug output +to. @var{verbose} is the verbose level provided by +@option{-fsched-verbose-@var{n}}. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_SCHED_CYCLE_DISPLAY (int @var{clock}, rtx @var{last}) +This hook is called in verbose mode only, at the beginning of each pass +over a basic block. It should insert an insn into the chain after +@var{last}, which has no effect, but records the value @var{clock} in +RTL dumps and assembly output. Define this hook only if you need this +level of detail about what the scheduler is doing. +@end deftypefn + +@node Sections +@section Dividing the Output into Sections (Texts, Data, @dots{}) +@c the above section title is WAY too long. maybe cut the part between +@c the (...)? --mew 10feb93 + +An object file is divided into sections containing different types of +data. In the most common case, there are three sections: the @dfn{text +section}, which holds instructions and read-only data; the @dfn{data +section}, which holds initialized writable data; and the @dfn{bss +section}, which holds uninitialized data. Some systems have other kinds +of sections. + +The compiler must tell the assembler when to switch sections. These +macros control what commands to output to tell the assembler this. You +can also define additional sections. + +@table @code +@findex TEXT_SECTION_ASM_OP +@item TEXT_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation that should precede instructions and read-only data. +Normally @code{"\t.text"} is right. + +@findex TEXT_SECTION +@item TEXT_SECTION +A C statement that switches to the default section containing instructions. +Normally this is not needed, as simply defining @code{TEXT_SECTION_ASM_OP} +is enough. The MIPS port uses this to sort all functions after all data +declarations. + +@findex DATA_SECTION_ASM_OP +@item DATA_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation to identify the following data as writable initialized +data. Normally @code{"\t.data"} is right. + +@findex SHARED_SECTION_ASM_OP +@item SHARED_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +shared data. If not defined, @code{DATA_SECTION_ASM_OP} will be used. + +@findex BSS_SECTION_ASM_OP +@item BSS_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +uninitialized global data. If not defined, and neither +@code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined, +uninitialized global data will be output in the data section if +@option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be +used. + +@findex SHARED_BSS_SECTION_ASM_OP +@item SHARED_BSS_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +uninitialized global shared data. If not defined, and +@code{BSS_SECTION_ASM_OP} is, the latter will be used. + +@findex INIT_SECTION_ASM_OP +@item INIT_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +initialization code. If not defined, GCC will assume such a section does +not exist. + +@findex FINI_SECTION_ASM_OP +@item FINI_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +finalization code. If not defined, GCC will assume such a section does +not exist. + +@findex CRT_CALL_STATIC_FUNCTION +@item CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function}) +If defined, an ASM statement that switches to a different section +via @var{section_op}, calls @var{function}, and switches back to +the text section. This is used in @file{crtstuff.c} if +@code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls +to initialization and finalization functions from the init and fini +sections. By default, this macro uses a simple function call. Some +ports need hand-crafted assembly code to avoid dependencies on +registers initialized in the function prologue or to ensure that +constant pools don't end up too far way in the text section. + +@findex FORCE_CODE_SECTION_ALIGN +@item FORCE_CODE_SECTION_ALIGN +If defined, an ASM statement that aligns a code section to some +arbitrary boundary. This is used to force all fragments of the +@code{.init} and @code{.fini} sections to have to same alignment +and thus prevent the linker from having to add any padding. + +@findex EXTRA_SECTIONS +@findex in_text +@findex in_data +@item EXTRA_SECTIONS +A list of names for sections other than the standard two, which are +@code{in_text} and @code{in_data}. You need not define this macro +on a system with no other sections (that GCC needs to use). + +@findex EXTRA_SECTION_FUNCTIONS +@findex text_section +@findex data_section +@item EXTRA_SECTION_FUNCTIONS +One or more functions to be defined in @file{varasm.c}. These +functions should do jobs analogous to those of @code{text_section} and +@code{data_section}, for your additional sections. Do not define this +macro if you do not define @code{EXTRA_SECTIONS}. + +@findex READONLY_DATA_SECTION +@item READONLY_DATA_SECTION +On most machines, read-only variables, constants, and jump tables are +placed in the text section. If this is not the case on your machine, +this macro should be defined to be the name of a function (either +@code{data_section} or a function defined in @code{EXTRA_SECTIONS}) that +switches to the section to be used for read-only items. + +If these items should be placed in the text section, this macro should +not be defined. + +@findex SELECT_SECTION +@item SELECT_SECTION (@var{exp}, @var{reloc}, @var{align}) +A C statement or statements to switch to the appropriate section for +output of @var{exp}. You can assume that @var{exp} is either a +@code{VAR_DECL} node or a constant of some sort. @var{reloc} +indicates whether the initial value of @var{exp} requires link-time +relocations. Bit 1 is set when variable contains local relocations +only, while bit 2 is set for global relocations. +Select the section by calling @code{text_section} or one +of the alternatives for other sections. @var{align} is the constant +alignment in bits. + +Do not define this macro if you put all read-only variables and +constants in the read-only data section (usually the text section). + +@findex SELECT_RTX_SECTION +@item SELECT_RTX_SECTION (@var{mode}, @var{rtx}, @var{align}) +A C statement or statements to switch to the appropriate section for +output of @var{rtx} in mode @var{mode}. You can assume that @var{rtx} +is some kind of constant in RTL@. The argument @var{mode} is redundant +except in the case of a @code{const_int} rtx. Select the section by +calling @code{text_section} or one of the alternatives for other +sections. @var{align} is the constant alignment in bits. + +Do not define this macro if you put all constants in the read-only +data section. + +@findex JUMP_TABLES_IN_TEXT_SECTION +@item JUMP_TABLES_IN_TEXT_SECTION +Define this macro to be an expression with a nonzero value if jump +tables (for @code{tablejump} insns) should be output in the text +section, along with the assembler instructions. Otherwise, the +readonly data section is used. + +This macro is irrelevant if there is no separate readonly data section. + +@findex ENCODE_SECTION_INFO +@item ENCODE_SECTION_INFO (@var{decl}) +Define this macro if references to a symbol or a constant must be +treated differently depending on something about the variable or +function named by the symbol (such as what section it is in). + +The macro definition, if any, is executed under two circumstances. One +is immediately after the rtl for @var{decl} that represents a variable +or a function has been created and stored in @code{DECL_RTL +(@var{decl})}. The value of the rtl will be a @code{mem} whose address +is a @code{symbol_ref}. The other is immediately after the rtl for +@var{decl} that represents a constant has been created and stored in +@code{TREE_CST_RTL (@var{decl})}. The macro is called once for each +distinct constant in a source file. + +@cindex @code{SYMBOL_REF_FLAG}, in @code{ENCODE_SECTION_INFO} +The usual thing for this macro to do is to record a flag in the +@code{symbol_ref} (such as @code{SYMBOL_REF_FLAG}) or to store a +modified name string in the @code{symbol_ref} (if one bit is not enough +information). + +@findex STRIP_NAME_ENCODING +@item STRIP_NAME_ENCODING (@var{var}, @var{sym_name}) +Decode @var{sym_name} and store the real name part in @var{var}, sans +the characters that encode section info. Define this macro if +@code{ENCODE_SECTION_INFO} alters the symbol's name string. + +@findex UNIQUE_SECTION +@item UNIQUE_SECTION (@var{decl}, @var{reloc}) +A C statement to build up a unique section name, expressed as a +@code{STRING_CST} node, and assign it to @samp{DECL_SECTION_NAME (@var{decl})}. +@var{reloc} indicates whether the initial value of @var{exp} requires +link-time relocations. If you do not define this macro, GCC will use +the symbol name prefixed by @samp{.} as the section name. Note - this +macro can now be called for uninitialized data items as well as +initialized data and functions. +@end table + +@node PIC +@section Position Independent Code +@cindex position independent code +@cindex PIC + +This section describes macros that help implement generation of position +independent code. Simply defining these macros is not enough to +generate valid PIC; you must also add support to the macros +@code{GO_IF_LEGITIMATE_ADDRESS} and @code{PRINT_OPERAND_ADDRESS}, as +well as @code{LEGITIMIZE_ADDRESS}. You must modify the definition of +@samp{movsi} to do something appropriate when the source operand +contains a symbolic address. You may also need to alter the handling of +switch statements so that they use relative addresses. +@c i rearranged the order of the macros above to try to force one of +@c them to the next line, to eliminate an overfull hbox. --mew 10feb93 + +@table @code +@findex PIC_OFFSET_TABLE_REGNUM +@item PIC_OFFSET_TABLE_REGNUM +The register number of the register used to address a table of static +data addresses in memory. In some cases this register is defined by a +processor's ``application binary interface'' (ABI)@. When this macro +is defined, RTL is generated for this register once, as with the stack +pointer and frame pointer registers. If this macro is not defined, it +is up to the machine-dependent files to allocate such a register (if +necessary). Note that this register must be fixed when in use (e.g.@: +when @code{flag_pic} is true). + +@findex PIC_OFFSET_TABLE_REG_CALL_CLOBBERED +@item PIC_OFFSET_TABLE_REG_CALL_CLOBBERED +Define this macro if the register defined by +@code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. Do not define +this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined. + +@findex FINALIZE_PIC +@item FINALIZE_PIC +By generating position-independent code, when two different programs (A +and B) share a common library (libC.a), the text of the library can be +shared whether or not the library is linked at the same address for both +programs. In some of these environments, position-independent code +requires not only the use of different addressing modes, but also +special code to enable the use of these addressing modes. + +The @code{FINALIZE_PIC} macro serves as a hook to emit these special +codes once the function is being compiled into assembly code, but not +before. (It is not done before, because in the case of compiling an +inline function, it would lead to multiple PIC prologues being +included in functions which used inline functions and were compiled to +assembly language.) + +@findex LEGITIMATE_PIC_OPERAND_P +@item LEGITIMATE_PIC_OPERAND_P (@var{x}) +A C expression that is nonzero if @var{x} is a legitimate immediate +operand on the target machine when generating position independent code. +You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not +check this. You can also assume @var{flag_pic} is true, so you need not +check it either. You need not define this macro if all constants +(including @code{SYMBOL_REF}) can be immediate operands when generating +position independent code. +@end table + +@node Assembler Format +@section Defining the Output Assembler Language + +This section describes macros whose principal purpose is to describe how +to write instructions in assembler language---rather than what the +instructions do. + +@menu +* File Framework:: Structural information for the assembler file. +* Data Output:: Output of constants (numbers, strings, addresses). +* Uninitialized Data:: Output of uninitialized variables. +* Label Output:: Output and generation of labels. +* Initialization:: General principles of initialization + and termination routines. +* Macros for Initialization:: + Specific macros that control the handling of + initialization and termination routines. +* Instruction Output:: Output of actual instructions. +* Dispatch Tables:: Output of jump tables. +* Exception Region Output:: Output of exception region code. +* Alignment Output:: Pseudo ops for alignment and skipping data. +@end menu + +@node File Framework +@subsection The Overall Framework of an Assembler File +@cindex assembler format +@cindex output of assembler code + +@c prevent bad page break with this line +This describes the overall framework of an assembler file. + +@table @code +@findex ASM_FILE_START +@item ASM_FILE_START (@var{stream}) +A C expression which outputs to the stdio stream @var{stream} +some appropriate text to go at the start of an assembler file. + +Normally this macro is defined to output a line containing +@samp{#NO_APP}, which is a comment that has no effect on most +assemblers but tells the GNU assembler that it can save time by not +checking for certain assembler constructs. + +On systems that use SDB, it is necessary to output certain commands; +see @file{attasm.h}. + +@findex ASM_FILE_END +@item ASM_FILE_END (@var{stream}) +A C expression which outputs to the stdio stream @var{stream} +some appropriate text to go at the end of an assembler file. + +If this macro is not defined, the default is to output nothing +special at the end of the file. Most systems don't require any +definition. + +On systems that use SDB, it is necessary to output certain commands; +see @file{attasm.h}. + +@findex ASM_COMMENT_START +@item ASM_COMMENT_START +A C string constant describing how to begin a comment in the target +assembler language. The compiler assumes that the comment will end at +the end of the line. + +@findex ASM_APP_ON +@item ASM_APP_ON +A C string constant for text to be output before each @code{asm} +statement or group of consecutive ones. Normally this is +@code{"#APP"}, which is a comment that has no effect on most +assemblers but tells the GNU assembler that it must check the lines +that follow for all valid assembler constructs. + +@findex ASM_APP_OFF +@item ASM_APP_OFF +A C string constant for text to be output after each @code{asm} +statement or group of consecutive ones. Normally this is +@code{"#NO_APP"}, which tells the GNU assembler to resume making the +time-saving assumptions that are valid for ordinary compiler output. + +@findex ASM_OUTPUT_SOURCE_FILENAME +@item ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) +A C statement to output COFF information or DWARF debugging information +which indicates that filename @var{name} is the current source file to +the stdio stream @var{stream}. + +This macro need not be defined if the standard form of output +for the file format in use is appropriate. + +@findex OUTPUT_QUOTED_STRING +@item OUTPUT_QUOTED_STRING (@var{stream}, @var{string}) +A C statement to output the string @var{string} to the stdio stream +@var{stream}. If you do not call the function @code{output_quoted_string} +in your config files, GCC will only call it to output filenames to +the assembler source. So you can use it to canonicalize the format +of the filename using this macro. + +@findex ASM_OUTPUT_SOURCE_LINE +@item ASM_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}) +A C statement to output DBX or SDB debugging information before code +for line number @var{line} of the current source file to the +stdio stream @var{stream}. + +This macro need not be defined if the standard form of debugging +information for the debugger in use is appropriate. + +@findex ASM_OUTPUT_IDENT +@item ASM_OUTPUT_IDENT (@var{stream}, @var{string}) +A C statement to output something to the assembler file to handle a +@samp{#ident} directive containing the text @var{string}. If this +macro is not defined, nothing is output for a @samp{#ident} directive. + +@findex OBJC_PROLOGUE +@item OBJC_PROLOGUE +A C statement to output any assembler statements which are required to +precede any Objective-C object definitions or message sending. The +statement is executed only when compiling an Objective-C program. +@end table + +@deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, unsigned int @var{align}) +Output assembly directives to switch to section @var{name}. The section +should have attributes as specified by @var{flags}, which is a bit mask +of the @code{SECTION_*} flags defined in @file{output.h}. If @var{align} +is nonzero, it contains an alignment in bytes to be used for the section, +otherwise some target default should be used. Only targets that must +specify an alignment within the section directive need pay attention to +@var{align} -- we will still use @code{ASM_OUTPUT_ALIGN}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_HAVE_NAMED_SECTIONS +This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}. +@end deftypefn + +@deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc}) +Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION} +based on a variable or function decl, a section name, and whether or not the +declaration's initializer may contain runtime relocations. @var{decl} may be + null, in which case read-write data should be assumed. + +The default version if this function handles choosing code vs data, +read-only vs read-write data, and @code{flag_pic}. You should only +need to override this if your target has special flags that might be +set via @code{__attribute__}. +@end deftypefn + +@need 2000 +@node Data Output +@subsection Output of Data + + +@deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP +These hooks specify assembly directives for creating certain kinds +of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a +byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an +aligned two-byte object, and so on. Any of the hooks may be +@code{NULL}, indicating that no suitable directive is available. + +The compiler will print these strings at the start of a new line, +followed immediately by the object's initial value. In most cases, +the string should contain a tab, a pseudo-op, and then another tab. +@end deftypevr + +@deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p}) +The @code{assemble_integer} function uses this hook to output an +integer object. @var{x} is the object's value, @var{size} is its size +in bytes and @var{aligned_p} indicates whether it is aligned. The +function should return @code{true} if it was able to output the +object. If it returns false, @code{assemble_integer} will try to +split the object into smaller parts. + +The default implementation of this hook will use the +@code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false} +when the relevant string is @code{NULL}. +@end deftypefn + +@table @code +@findex OUTPUT_ADDR_CONST_EXTRA +@item OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail}) +A C statement to recognize @var{rtx} patterns that +@code{output_addr_const} can't deal with, and output assembly code to +@var{stream} corresponding to the pattern @var{x}. This may be used to +allow machine-dependent @code{UNSPEC}s to appear within constants. + +If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must +@code{goto fail}, so that a standard error message is printed. If it +prints an error message itself, by calling, for example, +@code{output_operand_lossage}, it may just complete normally. + +@findex ASM_OUTPUT_ASCII +@item ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len}) +A C statement to output to the stdio stream @var{stream} an assembler +instruction to assemble a string constant containing the @var{len} +bytes at @var{ptr}. @var{ptr} will be a C expression of type +@code{char *} and @var{len} a C expression of type @code{int}. + +If the assembler has a @code{.ascii} pseudo-op as found in the +Berkeley Unix assembler, do not define the macro +@code{ASM_OUTPUT_ASCII}. + +@findex ASM_OUTPUT_FDESC +@item ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n}) +A C statement to output word @var{n} of a function descriptor for +@var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS} +is defined, and is otherwise unused. + +@findex CONSTANT_POOL_BEFORE_FUNCTION +@item CONSTANT_POOL_BEFORE_FUNCTION +You may define this macro as a C expression. You should define the +expression to have a nonzero value if GCC should output the constant +pool for a function before the code for the function, or a zero value if +GCC should output the constant pool after the function. If you do +not define this macro, the usual case, GCC will output the constant +pool before the function. + +@findex ASM_OUTPUT_POOL_PROLOGUE +@item ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size}) +A C statement to output assembler commands to define the start of the +constant pool for a function. @var{funname} is a string giving +the name of the function. Should the return type of the function +be required, it can be obtained via @var{fundecl}. @var{size} +is the size, in bytes, of the constant pool that will be written +immediately after this call. + +If no constant-pool prefix is required, the usual case, this macro need +not be defined. + +@findex ASM_OUTPUT_SPECIAL_POOL_ENTRY +@item ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto}) +A C statement (with or without semicolon) to output a constant in the +constant pool, if it needs special treatment. (This macro need not do +anything for RTL expressions that can be output normally.) + +The argument @var{file} is the standard I/O stream to output the +assembler code on. @var{x} is the RTL expression for the constant to +output, and @var{mode} is the machine mode (in case @var{x} is a +@samp{const_int}). @var{align} is the required alignment for the value +@var{x}; you should output an assembler directive to force this much +alignment. + +The argument @var{labelno} is a number to use in an internal label for +the address of this pool entry. The definition of this macro is +responsible for outputting the label definition at the proper place. +Here is how to do this: + +@example +ASM_OUTPUT_INTERNAL_LABEL (@var{file}, "LC", @var{labelno}); +@end example + +When you output a pool entry specially, you should end with a +@code{goto} to the label @var{jumpto}. This will prevent the same pool +entry from being output a second time in the usual manner. + +You need not define this macro if it would do nothing. + +@findex CONSTANT_AFTER_FUNCTION_P +@item CONSTANT_AFTER_FUNCTION_P (@var{exp}) +Define this macro as a C expression which is nonzero if the constant +@var{exp}, of type @code{tree}, should be output after the code for a +function. The compiler will normally output all constants before the +function; you need not define this macro if this is OK@. + +@findex ASM_OUTPUT_POOL_EPILOGUE +@item ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size}) +A C statement to output assembler commands to at the end of the constant +pool for a function. @var{funname} is a string giving the name of the +function. Should the return type of the function be required, you can +obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the +constant pool that GCC wrote immediately before this call. + +If no constant-pool epilogue is required, the usual case, you need not +define this macro. + +@findex IS_ASM_LOGICAL_LINE_SEPARATOR +@item IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}) +Define this macro as a C expression which is nonzero if @var{C} is +used as a logical line separator by the assembler. + +If you do not define this macro, the default is that only +the character @samp{;} is treated as a logical line separator. +@end table + +@deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN +@deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN +These target hooks are C string constants, describing the syntax in the +assembler for grouping arithmetic expressions. If not overridden, they +default to normal parentheses, which is correct for most assemblers. +@end deftypevr + + These macros are provided by @file{real.h} for writing the definitions +of @code{ASM_OUTPUT_DOUBLE} and the like: + +@table @code +@item REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l}) +@itemx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l}) +@itemx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l}) +@findex REAL_VALUE_TO_TARGET_SINGLE +@findex REAL_VALUE_TO_TARGET_DOUBLE +@findex REAL_VALUE_TO_TARGET_LONG_DOUBLE +These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the target's +floating point representation, and store its bit pattern in the array of +@code{long int} whose address is @var{l}. The number of elements in the +output array is determined by the size of the desired target floating +point data type: 32 bits of it go in each @code{long int} array +element. Each array element holds 32 bits of the result, even if +@code{long int} is wider than 32 bits on the host machine. + +The array element values are designed so that you can print them out +using @code{fprintf} in the order they should appear in the target +machine's memory. + +@item REAL_VALUE_TO_DECIMAL (@var{x}, @var{format}, @var{string}) +@findex REAL_VALUE_TO_DECIMAL +This macro converts @var{x}, of type @code{REAL_VALUE_TYPE}, to a +decimal number and stores it as a string into @var{string}. +You must pass, as @var{string}, the address of a long enough block +of space to hold the result. + +The argument @var{format} is a @code{printf}-specification that serves +as a suggestion for how to format the output string. +@end table + +@node Uninitialized Data +@subsection Output of Uninitialized Variables + +Each of the macros in this section is used to do the whole job of +outputting a single uninitialized variable. + +@table @code +@findex ASM_OUTPUT_COMMON +@item ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a common-label named +@var{name} whose size is @var{size} bytes. The variable @var{rounded} +is the size rounded up to whatever alignment the caller wants. + +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. + +This macro controls how the assembler definitions of uninitialized +common global variables are output. + +@findex ASM_OUTPUT_ALIGNED_COMMON +@item ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a +separate, explicit argument. If you define this macro, it is used in +place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in +handling the required alignment of the variable. The alignment is specified +as the number of bits. + +@findex ASM_OUTPUT_ALIGNED_DECL_COMMON +@item ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the +variable to be output, if there is one, or @code{NULL_TREE} if there +is no corresponding variable. If you define this macro, GCC will use it +in place of both @code{ASM_OUTPUT_COMMON} and +@code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see +the variable's decl in order to chose what to output. + +@findex ASM_OUTPUT_SHARED_COMMON +@item ASM_OUTPUT_SHARED_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) +If defined, it is similar to @code{ASM_OUTPUT_COMMON}, except that it +is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_COMMON} +will be used. + +@findex ASM_OUTPUT_BSS +@item ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of uninitialized global @var{decl} named +@var{name} whose size is @var{size} bytes. The variable @var{rounded} +is the size rounded up to whatever alignment the caller wants. + +Try to use function @code{asm_output_bss} defined in @file{varasm.c} when +defining this macro. If unable, use the expression +@code{assemble_name (@var{stream}, @var{name})} to output the name itself; +before and after that, output the additional assembler syntax for defining +the name, and a newline. + +This macro controls how the assembler definitions of uninitialized global +variables are output. This macro exists to properly support languages like +C++ which do not have @code{common} data. However, this macro currently +is not defined for all targets. If this macro and +@code{ASM_OUTPUT_ALIGNED_BSS} are not defined then @code{ASM_OUTPUT_COMMON} +or @code{ASM_OUTPUT_ALIGNED_COMMON} or +@code{ASM_OUTPUT_ALIGNED_DECL_COMMON} is used. + +@findex ASM_OUTPUT_ALIGNED_BSS +@item ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a +separate, explicit argument. If you define this macro, it is used in +place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in +handling the required alignment of the variable. The alignment is specified +as the number of bits. + +Try to use function @code{asm_output_aligned_bss} defined in file +@file{varasm.c} when defining this macro. + +@findex ASM_OUTPUT_SHARED_BSS +@item ASM_OUTPUT_SHARED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded}) +If defined, it is similar to @code{ASM_OUTPUT_BSS}, except that it +is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_BSS} +will be used. + +@findex ASM_OUTPUT_LOCAL +@item ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a local-common-label named +@var{name} whose size is @var{size} bytes. The variable @var{rounded} +is the size rounded up to whatever alignment the caller wants. + +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. + +This macro controls how the assembler definitions of uninitialized +static variables are output. + +@findex ASM_OUTPUT_ALIGNED_LOCAL +@item ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a +separate, explicit argument. If you define this macro, it is used in +place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in +handling the required alignment of the variable. The alignment is specified +as the number of bits. + +@findex ASM_OUTPUT_ALIGNED_DECL_LOCAL +@item ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the +variable to be output, if there is one, or @code{NULL_TREE} if there +is no corresponding variable. If you define this macro, GCC will use it +in place of both @code{ASM_OUTPUT_DECL} and +@code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see +the variable's decl in order to chose what to output. + +@findex ASM_OUTPUT_SHARED_LOCAL +@item ASM_OUTPUT_SHARED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) +If defined, it is similar to @code{ASM_OUTPUT_LOCAL}, except that it +is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_LOCAL} +will be used. +@end table + +@node Label Output +@subsection Output and Generation of Labels + +@c prevent bad page break with this line +This is about outputting labels. + +@table @code +@findex ASM_OUTPUT_LABEL +@findex assemble_name +@item ASM_OUTPUT_LABEL (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a label named @var{name}. +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. + +@findex ASM_DECLARE_FUNCTION_NAME +@item ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of a +function which is being defined. This macro is responsible for +outputting the label definition (perhaps using +@code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the +@code{FUNCTION_DECL} tree node representing the function. + +If this macro is not defined, then the function name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). + +@findex ASM_DECLARE_FUNCTION_SIZE +@item ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the size of a function +which is being defined. The argument @var{name} is the name of the +function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node +representing the function. + +If this macro is not defined, then the function size is not defined. + +@findex ASM_DECLARE_OBJECT_NAME +@item ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of an +initialized variable which is being defined. This macro must output the +label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument +@var{decl} is the @code{VAR_DECL} tree node representing the variable. + +If this macro is not defined, then the variable name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). + +@findex ASM_DECLARE_REGISTER_GLOBAL +@item ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for claiming a register @var{regno} +for a global variable @var{decl} with name @var{name}. + +If you don't define this macro, that is equivalent to defining it to do +nothing. + +@findex ASM_FINISH_DECLARE_OBJECT +@item ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend}) +A C statement (sans semicolon) to finish up declaring a variable name +once the compiler has processed its initializer fully and thus has had a +chance to determine the size of an array when controlled by an +initializer. This is used on systems where it's necessary to declare +something about the size of the object. + +If you don't define this macro, that is equivalent to defining it to do +nothing. + +@findex ASM_GLOBALIZE_LABEL +@item ASM_GLOBALIZE_LABEL (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} some commands that will make the label @var{name} global; +that is, available for reference from other files. Use the expression +@code{assemble_name (@var{stream}, @var{name})} to output the name +itself; before and after that, output the additional assembler syntax +for making that name global, and a newline. + +@findex ASM_WEAKEN_LABEL +@item ASM_WEAKEN_LABEL +A C statement (sans semicolon) to output to the stdio stream +@var{stream} some commands that will make the label @var{name} weak; +that is, available for reference from other files but only used if +no other definition is available. Use the expression +@code{assemble_name (@var{stream}, @var{name})} to output the name +itself; before and after that, output the additional assembler syntax +for making that name weak, and a newline. + +If you don't define this macro, GCC will not support weak +symbols and you should not define the @code{SUPPORTS_WEAK} macro. + +@findex SUPPORTS_WEAK +@item SUPPORTS_WEAK +A C expression which evaluates to true if the target supports weak symbols. + +If you don't define this macro, @file{defaults.h} provides a default +definition. If @code{ASM_WEAKEN_LABEL} is defined, the default +definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if +you want to control weak symbol support with a compiler flag such as +@option{-melf}. + +@findex MAKE_DECL_ONE_ONLY (@var{decl}) +@item MAKE_DECL_ONE_ONLY +A C statement (sans semicolon) to mark @var{decl} to be emitted as a +public symbol such that extra copies in multiple translation units will +be discarded by the linker. Define this macro if your object file +format provides support for this concept, such as the @samp{COMDAT} +section flags in the Microsoft Windows PE/COFF format, and this support +requires changes to @var{decl}, such as putting it in a separate section. + +@findex SUPPORTS_ONE_ONLY +@item SUPPORTS_ONE_ONLY +A C expression which evaluates to true if the target supports one-only +semantics. + +If you don't define this macro, @file{varasm.c} provides a default +definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default +definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if +you want to control one-only symbol support with a compiler flag, or if +setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to +be emitted as one-only. + +@findex ASM_OUTPUT_EXTERNAL +@item ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name of an external +symbol named @var{name} which is referenced in this compilation but +not defined. The value of @var{decl} is the tree node for the +declaration. + +This macro need not be defined if it does not need to output anything. +The GNU assembler and most Unix assemblers don't require anything. + +@findex ASM_OUTPUT_EXTERNAL_LIBCALL +@item ASM_OUTPUT_EXTERNAL_LIBCALL (@var{stream}, @var{symref}) +A C statement (sans semicolon) to output on @var{stream} an assembler +pseudo-op to declare a library function name external. The name of the +library function is given by @var{symref}, which has type @code{rtx} and +is a @code{symbol_ref}. + +This macro need not be defined if it does not need to output anything. +The GNU assembler and most Unix assemblers don't require anything. + +@findex ASM_OUTPUT_LABELREF +@item ASM_OUTPUT_LABELREF (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a reference in assembler syntax to a label named +@var{name}. This should add @samp{_} to the front of the name, if that +is customary on your operating system, as it is in most Berkeley Unix +systems. This macro is used in @code{assemble_name}. + +@findex ASM_OUTPUT_SYMBOL_REF +@item ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym}) +A C statement (sans semicolon) to output a reference to +@code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name} +will be used to output the name of the symbol. This macro may be used +to modify the way a symbol is referenced depending on information +encoded by @code{ENCODE_SECTION_INFO}. + +@findex ASM_OUTPUT_LABEL_REF +@item ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf}) +A C statement (sans semicolon) to output a reference to @var{buf}, the +result of ASM_GENERATE_INTERNAL_LABEL. If not defined, +@code{assemble_name} will be used to output the name of the symbol. +This macro is not used by @code{output_asm_label}, or the @code{%l} +specifier that calls it; the intention is that this macro should be set +when it is necessary to output a label differently when its address +is being taken. + +@findex ASM_OUTPUT_INTERNAL_LABEL +@item ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{prefix}, @var{num}) +A C statement to output to the stdio stream @var{stream} a label whose +name is made from the string @var{prefix} and the number @var{num}. + +It is absolutely essential that these labels be distinct from the labels +used for user-level functions and variables. Otherwise, certain programs +will have name conflicts with internal labels. + +It is desirable to exclude internal labels from the symbol table of the +object file. Most assemblers have a naming convention for labels that +should be excluded; on many systems, the letter @samp{L} at the +beginning of a label has this effect. You should find out what +convention your system uses, and follow it. + +The usual definition of this macro is as follows: + +@example +fprintf (@var{stream}, "L%s%d:\n", @var{prefix}, @var{num}) +@end example + +@findex ASM_OUTPUT_DEBUG_LABEL +@item ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num}) +A C statement to output to the stdio stream @var{stream} a debug info +label whose name is made from the string @var{prefix} and the number +@var{num}. This is useful for VLIW targets, where debug info labels +may need to be treated differently than branch target labels. On some +systems, branch target labels must be at the beginning of instruction +bundles, but debug info labels can occur in the middle of instruction +bundles. + +If this macro is not defined, then @code{ASM_OUTPUT_INTERNAL_LABEL} will be +used. + +@findex ASM_OUTPUT_ALTERNATE_LABEL_NAME +@item ASM_OUTPUT_ALTERNATE_LABEL_NAME (@var{stream}, @var{string}) +A C statement to output to the stdio stream @var{stream} the string +@var{string}. + +The default definition of this macro is as follows: + +@example +fprintf (@var{stream}, "%s:\n", LABEL_ALTERNATE_NAME (INSN)) +@end example + +@findex ASM_GENERATE_INTERNAL_LABEL +@item ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num}) +A C statement to store into the string @var{string} a label whose name +is made from the string @var{prefix} and the number @var{num}. + +This string, when output subsequently by @code{assemble_name}, should +produce the output that @code{ASM_OUTPUT_INTERNAL_LABEL} would produce +with the same @var{prefix} and @var{num}. + +If the string begins with @samp{*}, then @code{assemble_name} will +output the rest of the string unchanged. It is often convenient for +@code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the +string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets +to output the string, and may change it. (Of course, +@code{ASM_OUTPUT_LABELREF} is also part of your machine description, so +you should know what it does on your machine.) + +@findex ASM_FORMAT_PRIVATE_NAME +@item ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number}) +A C expression to assign to @var{outvar} (which is a variable of type +@code{char *}) a newly allocated string made from the string +@var{name} and the number @var{number}, with some suitable punctuation +added. Use @code{alloca} to get space for the string. + +The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to +produce an assembler label for an internal static variable whose name is +@var{name}. Therefore, the string must be such as to result in valid +assembler code. The argument @var{number} is different each time this +macro is executed; it prevents conflicts between similarly-named +internal static variables in different scopes. + +Ideally this string should not be a valid C identifier, to prevent any +conflict with the user's own symbols. Most assemblers allow periods +or percent signs in assembler symbols; putting at least one of these +between the name and the number will suffice. + +@findex ASM_OUTPUT_DEF +@item ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the symbol @var{name} to have the value @var{value}. + +@findex SET_ASM_OP +If @code{SET_ASM_OP} is defined, a default definition is provided which is +correct for most systems. + +@findex ASM_OUTPUT_DEF_FROM_DECLS +@item ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the symbol whose tree node is @var{decl_of_name} +to have the value of the tree node @var{decl_of_value}. This macro will +be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if +the tree nodes are available. + +@findex ASM_OUTPUT_DEFINE_LABEL_DIFFERENCE_SYMBOL +@item ASM_OUTPUT_DEFINE_LABEL_DIFFERENCE_SYMBOL (@var{stream}, @var{symbol}, @var{high}, @var{low}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the symbol @var{symbol} to have a value equal to +the difference of the two symbols @var{high} and @var{low}, +i.e.@: @var{high} minus @var{low}. GCC guarantees that the symbols @var{high} +and @var{low} are already known by the assembler so that the difference +resolves into a constant. + +@findex SET_ASM_OP +If @code{SET_ASM_OP} is defined, a default definition is provided which is +correct for most systems. + +@findex ASM_OUTPUT_WEAK_ALIAS +@item ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the weak symbol @var{name} to have the value +@var{value}. If @var{value} is @code{NULL}, it defines @var{name} as +an undefined weak symbol. + +Define this macro if the target only supports weak aliases; define +@code{ASM_OUTPUT_DEF} instead if possible. + +@findex OBJC_GEN_METHOD_LABEL +@item OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name}) +Define this macro to override the default assembler names used for +Objective-C methods. + +The default name is a unique method number followed by the name of the +class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of +the category is also included in the assembler name (e.g.@: +@samp{_1_Foo_Bar}). + +These names are safe on most systems, but make debugging difficult since +the method's selector is not present in the name. Therefore, particular +systems define other ways of computing names. + +@var{buf} is an expression of type @code{char *} which gives you a +buffer in which to store the name; its length is as long as +@var{class_name}, @var{cat_name} and @var{sel_name} put together, plus +50 characters extra. + +The argument @var{is_inst} specifies whether the method is an instance +method or a class method; @var{class_name} is the name of the class; +@var{cat_name} is the name of the category (or @code{NULL} if the method is not +in a category); and @var{sel_name} is the name of the selector. + +On systems where the assembler can handle quoted names, you can use this +macro to provide more human-readable names. + +@findex ASM_DECLARE_CLASS_REFERENCE +@item ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} commands to declare that the label @var{name} is an +Objective-C class reference. This is only needed for targets whose +linkers have special support for NeXT-style runtimes. + +@findex ASM_DECLARE_UNRESOLVED_REFERENCE +@item ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} commands to declare that the label @var{name} is an +unresolved Objective-C class reference. This is only needed for targets +whose linkers have special support for NeXT-style runtimes. +@end table + +@node Initialization +@subsection How Initialization Functions Are Handled +@cindex initialization routines +@cindex termination routines +@cindex constructors, output of +@cindex destructors, output of + +The compiled code for certain languages includes @dfn{constructors} +(also called @dfn{initialization routines})---functions to initialize +data in the program when the program is started. These functions need +to be called before the program is ``started''---that is to say, before +@code{main} is called. + +Compiling some languages generates @dfn{destructors} (also called +@dfn{termination routines}) that should be called when the program +terminates. + +To make the initialization and termination functions work, the compiler +must output something in the assembler code to cause those functions to +be called at the appropriate time. When you port the compiler to a new +system, you need to specify how to do this. + +There are two major ways that GCC currently supports the execution of +initialization and termination functions. Each way has two variants. +Much of the structure is common to all four variations. + +@findex __CTOR_LIST__ +@findex __DTOR_LIST__ +The linker must build two lists of these functions---a list of +initialization functions, called @code{__CTOR_LIST__}, and a list of +termination functions, called @code{__DTOR_LIST__}. + +Each list always begins with an ignored function pointer (which may hold +0, @minus{}1, or a count of the function pointers after it, depending on +the environment). This is followed by a series of zero or more function +pointers to constructors (or destructors), followed by a function +pointer containing zero. + +Depending on the operating system and its executable file format, either +@file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup +time and exit time. Constructors are called in reverse order of the +list; destructors in forward order. + +The best way to handle static constructors works only for object file +formats which provide arbitrarily-named sections. A section is set +aside for a list of constructors, and another for a list of destructors. +Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each +object file that defines an initialization function also puts a word in +the constructor section to point to that function. The linker +accumulates all these words into one contiguous @samp{.ctors} section. +Termination functions are handled similarly. + +This method will be chosen as the default by @file{target-def.h} if +@code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not +support arbitrary sections, but does support special designated +constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP} +and @code{DTORS_SECTION_ASM_OP} to achieve the same effect. + +When arbitrary sections are available, there are two variants, depending +upon how the code in @file{crtstuff.c} is called. On systems that +support a @dfn{.init} section which is executed at program startup, +parts of @file{crtstuff.c} are compiled into that section. The +program is linked by the @code{gcc} driver like this: + +@example +ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o +@end example + +The prologue of a function (@code{__init}) appears in the @code{.init} +section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise +for the function @code{__fini} in the @dfn{.fini} section. Normally these +files are provided by the operating system or by the GNU C library, but +are provided by GCC for a few targets. + +The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets) +compiled from @file{crtstuff.c}. They contain, among other things, code +fragments within the @code{.init} and @code{.fini} sections that branch +to routines in the @code{.text} section. The linker will pull all parts +of a section together, which results in a complete @code{__init} function +that invokes the routines we need at startup. + +To use this variant, you must define the @code{INIT_SECTION_ASM_OP} +macro properly. + +If no init section is available, when GCC compiles any function called +@code{main} (or more accurately, any function designated as a program +entry point by the language front end calling @code{expand_main_function}), +it inserts a procedure call to @code{__main} as the first executable code +after the function prologue. The @code{__main} function is defined +in @file{libgcc2.c} and runs the global constructors. + +In file formats that don't support arbitrary sections, there are again +two variants. In the simplest variant, the GNU linker (GNU @code{ld}) +and an `a.out' format must be used. In this case, +@code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs} +entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__}, +and with the address of the void function containing the initialization +code as its value. The GNU linker recognizes this as a request to add +the value to a @dfn{set}; the values are accumulated, and are eventually +placed in the executable as a vector in the format described above, with +a leading (ignored) count and a trailing zero element. +@code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init +section is available, the absence of @code{INIT_SECTION_ASM_OP} causes +the compilation of @code{main} to call @code{__main} as above, starting +the initialization process. + +The last variant uses neither arbitrary sections nor the GNU linker. +This is preferable when you want to do dynamic linking and when using +file formats which the GNU linker does not support, such as `ECOFF'@. In +this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and +termination functions are recognized simply by their names. This requires +an extra program in the linkage step, called @command{collect2}. This program +pretends to be the linker, for use with GCC; it does its job by running +the ordinary linker, but also arranges to include the vectors of +initialization and termination functions. These functions are called +via @code{__main} as described above. In order to use this method, +@code{use_collect2} must be defined in the target in @file{config.gcc}. + +@ifinfo +The following section describes the specific macros that control and +customize the handling of initialization and termination functions. +@end ifinfo + +@node Macros for Initialization +@subsection Macros Controlling Initialization Routines + +Here are the macros that control how the compiler handles initialization +and termination functions: + +@table @code +@findex INIT_SECTION_ASM_OP +@item INIT_SECTION_ASM_OP +If defined, a C string constant, including spacing, for the assembler +operation to identify the following data as initialization code. If not +defined, GCC will assume such a section does not exist. When you are +using special sections for initialization and termination functions, this +macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to +run the initialization functions. + +@item HAS_INIT_SECTION +@findex HAS_INIT_SECTION +If defined, @code{main} will not call @code{__main} as described above. +This macro should be defined for systems that control start-up code +on a symbol-by-symbol basis, such as OSF/1, and should not +be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}. + +@item LD_INIT_SWITCH +@findex LD_INIT_SWITCH +If defined, a C string constant for a switch that tells the linker that +the following symbol is an initialization routine. + +@item LD_FINI_SWITCH +@findex LD_FINI_SWITCH +If defined, a C string constant for a switch that tells the linker that +the following symbol is a finalization routine. + +@item COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func}) +If defined, a C statement that will write a function that can be +automatically called when a shared library is loaded. The function +should call @var{func}, which takes no arguments. If not defined, and +the object format requires an explicit initialization function, then a +function called @code{_GLOBAL__DI} will be generated. + +This function and the following one are used by collect2 when linking a +shared library that needs constructors or destructors, or has DWARF2 +exception tables embedded in the code. + +@item COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func}) +If defined, a C statement that will write a function that can be +automatically called when a shared library is unloaded. The function +should call @var{func}, which takes no arguments. If not defined, and +the object format requires an explicit finalization function, then a +function called @code{_GLOBAL__DD} will be generated. + +@item INVOKE__main +@findex INVOKE__main +If defined, @code{main} will call @code{__main} despite the presence of +@code{INIT_SECTION_ASM_OP}. This macro should be defined for systems +where the init section is not actually run automatically, but is still +useful for collecting the lists of constructors and destructors. + +@item SUPPORTS_INIT_PRIORITY +@findex SUPPORTS_INIT_PRIORITY +If nonzero, the C++ @code{init_priority} attribute is supported and the +compiler should emit instructions to control the order of initialization +of objects. If zero, the compiler will issue an error message upon +encountering an @code{init_priority} attribute. +@end table + +@deftypefn {Target Hook} bool TARGET_HAVE_CTORS_DTORS +This value is true if the target supports some ``native'' method of +collecting constructors and destructors to be run at startup and exit. +It is false if we must use @command{collect2}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority}) +If defined, a function that outputs assembler code to arrange to call +the function referenced by @var{symbol} at initialization time. + +Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking +no arguments and with no return value. If the target supports initialization +priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY}; +otherwise it must be @code{DEFAULT_INIT_PRIORITY}. + +If this macro is not defined by the target, a suitable default will +be chosen if (1) the target supports arbitrary section names, (2) the +target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2} +is not defined. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority}) +This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination +functions rather than initialization functions. +@end deftypefn + +If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine +generated for the generated object file will have static linkage. + +If your system uses @command{collect2} as the means of processing +constructors, then that program normally uses @command{nm} to scan +an object file for constructor functions to be called. + +On certain kinds of systems, you can define these macros to make +@command{collect2} work faster (and, in some cases, make it work at all): + +@table @code +@findex OBJECT_FORMAT_COFF +@item OBJECT_FORMAT_COFF +Define this macro if the system uses COFF (Common Object File Format) +object files, so that @command{collect2} can assume this format and scan +object files directly for dynamic constructor/destructor functions. + +@findex OBJECT_FORMAT_ROSE +@item OBJECT_FORMAT_ROSE +Define this macro if the system uses ROSE format object files, so that +@command{collect2} can assume this format and scan object files directly +for dynamic constructor/destructor functions. + +These macros are effective only in a native compiler; @command{collect2} as +part of a cross compiler always uses @command{nm} for the target machine. + +@findex REAL_NM_FILE_NAME +@item REAL_NM_FILE_NAME +Define this macro as a C string constant containing the file name to use +to execute @command{nm}. The default is to search the path normally for +@command{nm}. + +If your system supports shared libraries and has a program to list the +dynamic dependencies of a given library or executable, you can define +these macros to enable support for running initialization and +termination functions in shared libraries: + +@findex LDD_SUFFIX +@item LDD_SUFFIX +Define this macro to a C string constant containing the name of the program +which lists dynamic dependencies, like @command{"ldd"} under SunOS 4. + +@findex PARSE_LDD_OUTPUT +@item PARSE_LDD_OUTPUT (@var{ptr}) +Define this macro to be C code that extracts filenames from the output +of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable +of type @code{char *} that points to the beginning of a line of output +from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the +code must advance @var{ptr} to the beginning of the filename on that +line. Otherwise, it must set @var{ptr} to @code{NULL}. +@end table + +@node Instruction Output +@subsection Output of Assembler Instructions + +@c prevent bad page break with this line +This describes assembler instruction output. + +@table @code +@findex REGISTER_NAMES +@item REGISTER_NAMES +A C initializer containing the assembler's names for the machine +registers, each one as a C string constant. This is what translates +register numbers in the compiler into assembler language. + +@findex ADDITIONAL_REGISTER_NAMES +@item ADDITIONAL_REGISTER_NAMES +If defined, a C initializer for an array of structures containing a name +and a register number. This macro defines additional names for hard +registers, thus allowing the @code{asm} option in declarations to refer +to registers using alternate names. + +@findex ASM_OUTPUT_OPCODE +@item ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr}) +Define this macro if you are using an unusual assembler that +requires different names for the machine instructions. + +The definition is a C statement or statements which output an +assembler instruction opcode to the stdio stream @var{stream}. The +macro-operand @var{ptr} is a variable of type @code{char *} which +points to the opcode name in its ``internal'' form---the form that is +written in the machine description. The definition should output the +opcode name to @var{stream}, performing any translation you desire, and +increment the variable @var{ptr} to point at the end of the opcode +so that it will not be output twice. + +In fact, your macro definition may process less than the entire opcode +name, or more than the opcode name; but if you want to process text +that includes @samp{%}-sequences to substitute operands, you must take +care of the substitution yourself. Just be sure to increment +@var{ptr} over whatever text should not be output normally. + +@findex recog_data.operand +If you need to look at the operand values, they can be found as the +elements of @code{recog_data.operand}. + +If the macro definition does nothing, the instruction is output +in the usual way. + +@findex FINAL_PRESCAN_INSN +@item FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands}) +If defined, a C statement to be executed just prior to the output of +assembler code for @var{insn}, to modify the extracted operands so +they will be output differently. + +Here the argument @var{opvec} is the vector containing the operands +extracted from @var{insn}, and @var{noperands} is the number of +elements of the vector which contain meaningful data for this insn. +The contents of this vector are what will be used to convert the insn +template into assembler code, so you can change the assembler output +by changing the contents of the vector. + +This macro is useful when various assembler syntaxes share a single +file of instruction patterns; by defining this macro differently, you +can cause a large class of instructions to be output differently (such +as with rearranged operands). Naturally, variations in assembler +syntax affecting individual insn patterns ought to be handled by +writing conditional output routines in those patterns. + +If this macro is not defined, it is equivalent to a null statement. + +@findex FINAL_PRESCAN_LABEL +@item FINAL_PRESCAN_LABEL +If defined, @code{FINAL_PRESCAN_INSN} will be called on each +@code{CODE_LABEL}. In that case, @var{opvec} will be a null pointer and +@var{noperands} will be zero. + +@findex PRINT_OPERAND +@item PRINT_OPERAND (@var{stream}, @var{x}, @var{code}) +A C compound statement to output to stdio stream @var{stream} the +assembler syntax for an instruction operand @var{x}. @var{x} is an +RTL expression. + +@var{code} is a value that can be used to specify one of several ways +of printing the operand. It is used when identical operands must be +printed differently depending on the context. @var{code} comes from +the @samp{%} specification that was used to request printing of the +operand. If the specification was just @samp{%@var{digit}} then +@var{code} is 0; if the specification was @samp{%@var{ltr} +@var{digit}} then @var{code} is the ASCII code for @var{ltr}. + +@findex reg_names +If @var{x} is a register, this macro should print the register's name. +The names can be found in an array @code{reg_names} whose type is +@code{char *[]}. @code{reg_names} is initialized from +@code{REGISTER_NAMES}. + +When the machine description has a specification @samp{%@var{punct}} +(a @samp{%} followed by a punctuation character), this macro is called +with a null pointer for @var{x} and the punctuation character for +@var{code}. + +@findex PRINT_OPERAND_PUNCT_VALID_P +@item PRINT_OPERAND_PUNCT_VALID_P (@var{code}) +A C expression which evaluates to true if @var{code} is a valid +punctuation character for use in the @code{PRINT_OPERAND} macro. If +@code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no +punctuation characters (except for the standard one, @samp{%}) are used +in this way. + +@findex PRINT_OPERAND_ADDRESS +@item PRINT_OPERAND_ADDRESS (@var{stream}, @var{x}) +A C compound statement to output to stdio stream @var{stream} the +assembler syntax for an instruction operand that is a memory reference +whose address is @var{x}. @var{x} is an RTL expression. + +@cindex @code{ENCODE_SECTION_INFO} usage +On some machines, the syntax for a symbolic address depends on the +section that the address refers to. On these machines, define the macro +@code{ENCODE_SECTION_INFO} to store the information into the +@code{symbol_ref}, and then check for it here. @xref{Assembler Format}. + +@findex DBR_OUTPUT_SEQEND +@findex dbr_sequence_length +@item DBR_OUTPUT_SEQEND(@var{file}) +A C statement, to be executed after all slot-filler instructions have +been output. If necessary, call @code{dbr_sequence_length} to +determine the number of slots filled in a sequence (zero if not +currently outputting a sequence), to decide how many no-ops to output, +or whatever. + +Don't define this macro if it has nothing to do, but it is helpful in +reading assembly output if the extent of the delay sequence is made +explicit (e.g.@: with white space). + +@findex final_sequence +Note that output routines for instructions with delay slots must be +prepared to deal with not being output as part of a sequence +(i.e.@: when the scheduling pass is not run, or when no slot fillers could be +found.) The variable @code{final_sequence} is null when not +processing a sequence, otherwise it contains the @code{sequence} rtx +being output. + +@findex REGISTER_PREFIX +@findex LOCAL_LABEL_PREFIX +@findex USER_LABEL_PREFIX +@findex IMMEDIATE_PREFIX +@findex asm_fprintf +@item REGISTER_PREFIX +@itemx LOCAL_LABEL_PREFIX +@itemx USER_LABEL_PREFIX +@itemx IMMEDIATE_PREFIX +If defined, C string expressions to be used for the @samp{%R}, @samp{%L}, +@samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see +@file{final.c}). These are useful when a single @file{md} file must +support multiple assembler formats. In that case, the various @file{tm.h} +files can define these macros differently. + +@item ASM_FPRINTF_EXTENSIONS(@var{file}, @var{argptr}, @var{format}) +@findex ASM_FPRINTF_EXTENSIONS +If defined this macro should expand to a series of @code{case} +statements which will be parsed inside the @code{switch} statement of +the @code{asm_fprintf} function. This allows targets to define extra +printf formats which may useful when generating their assembler +statements. Note that upper case letters are reserved for future +generic extensions to asm_fprintf, and so are not available to target +specific code. The output file is given by the parameter @var{file}. +The varargs input pointer is @var{argptr} and the rest of the format +string, starting the character after the one that is being switched +upon, is pointed to by @var{format}. + +@findex ASSEMBLER_DIALECT +@item ASSEMBLER_DIALECT +If your target supports multiple dialects of assembler language (such as +different opcodes), define this macro as a C expression that gives the +numeric index of the assembler language dialect to use, with zero as the +first variant. + +If this macro is defined, you may use constructs of the form +@smallexample +@samp{@{option0|option1|option2@dots{}@}} +@end smallexample +@noindent +in the output templates of patterns (@pxref{Output Template}) or in the +first argument of @code{asm_fprintf}. This construct outputs +@samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of +@code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters +within these strings retain their usual meaning. If there are fewer +alternatives within the braces than the value of +@code{ASSEMBLER_DIALECT}, the construct outputs nothing. + +If you do not define this macro, the characters @samp{@{}, @samp{|} and +@samp{@}} do not have any special meaning when used in templates or +operands to @code{asm_fprintf}. + +Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX}, +@code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express +the variations in assembler language syntax with that mechanism. Define +@code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax +if the syntax variant are larger and involve such things as different +opcodes or operand order. + +@findex ASM_OUTPUT_REG_PUSH +@item ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno}) +A C expression to output to @var{stream} some assembler code +which will push hard register number @var{regno} onto the stack. +The code need not be optimal, since this macro is used only when +profiling. + +@findex ASM_OUTPUT_REG_POP +@item ASM_OUTPUT_REG_POP (@var{stream}, @var{regno}) +A C expression to output to @var{stream} some assembler code +which will pop hard register number @var{regno} off of the stack. +The code need not be optimal, since this macro is used only when +profiling. +@end table + +@node Dispatch Tables +@subsection Output of Dispatch Tables + +@c prevent bad page break with this line +This concerns dispatch tables. + +@table @code +@cindex dispatch table +@findex ASM_OUTPUT_ADDR_DIFF_ELT +@item ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel}) +A C statement to output to the stdio stream @var{stream} an assembler +pseudo-instruction to generate a difference between two labels. +@var{value} and @var{rel} are the numbers of two internal labels. The +definitions of these labels are output using +@code{ASM_OUTPUT_INTERNAL_LABEL}, and they must be printed in the same +way here. For example, + +@example +fprintf (@var{stream}, "\t.word L%d-L%d\n", + @var{value}, @var{rel}) +@end example + +You must provide this macro on machines where the addresses in a +dispatch table are relative to the table's own address. If defined, GCC +will also use this macro on all machines when producing PIC@. +@var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the +mode and flags can be read. + +@findex ASM_OUTPUT_ADDR_VEC_ELT +@item ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value}) +This macro should be provided on machines where the addresses +in a dispatch table are absolute. + +The definition should be a C statement to output to the stdio stream +@var{stream} an assembler pseudo-instruction to generate a reference to +a label. @var{value} is the number of an internal label whose +definition is output using @code{ASM_OUTPUT_INTERNAL_LABEL}. +For example, + +@example +fprintf (@var{stream}, "\t.word L%d\n", @var{value}) +@end example + +@findex ASM_OUTPUT_CASE_LABEL +@item ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table}) +Define this if the label before a jump-table needs to be output +specially. The first three arguments are the same as for +@code{ASM_OUTPUT_INTERNAL_LABEL}; the fourth argument is the +jump-table which follows (a @code{jump_insn} containing an +@code{addr_vec} or @code{addr_diff_vec}). + +This feature is used on system V to output a @code{swbeg} statement +for the table. + +If this macro is not defined, these labels are output with +@code{ASM_OUTPUT_INTERNAL_LABEL}. + +@findex ASM_OUTPUT_CASE_END +@item ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table}) +Define this if something special must be output at the end of a +jump-table. The definition should be a C statement to be executed +after the assembler code for the table is written. It should write +the appropriate code to stdio stream @var{stream}. The argument +@var{table} is the jump-table insn, and @var{num} is the label-number +of the preceding label. + +If this macro is not defined, nothing special is output at the end of +the jump-table. +@end table + +@node Exception Region Output +@subsection Assembler Commands for Exception Regions + +@c prevent bad page break with this line + +This describes commands marking the start and the end of an exception +region. + +@table @code +@findex EH_FRAME_SECTION_NAME +@item EH_FRAME_SECTION_NAME +If defined, a C string constant for the name of the section containing +exception handling frame unwind information. If not defined, GCC will +provide a default definition if the target supports named sections. +@file{crtstuff.c} uses this macro to switch to the appropriate section. + +You should define this symbol if your target supports DWARF 2 frame +unwind information and the default definition does not work. + +@findex EH_FRAME_IN_DATA_SECTION +@item EH_FRAME_IN_DATA_SECTION +If defined, DWARF 2 frame unwind information will be placed in the +data section even though the target supports named sections. This +might be necessary, for instance, if the system linker does garbage +collection and sections cannot be marked as not to be collected. + +Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is +also defined. + +@findex MASK_RETURN_ADDR +@item MASK_RETURN_ADDR +An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so +that it does not contain any extraneous set bits in it. + +@findex DWARF2_UNWIND_INFO +@item DWARF2_UNWIND_INFO +Define this macro to 0 if your target supports DWARF 2 frame unwind +information, but it does not yet work with exception handling. +Otherwise, if your target supports this information (if it defines +@samp{INCOMING_RETURN_ADDR_RTX} and either @samp{UNALIGNED_INT_ASM_OP} +or @samp{OBJECT_FORMAT_ELF}), GCC will provide a default definition of +1. + +If this macro is defined to 1, the DWARF 2 unwinder will be the default +exception handling mechanism; otherwise, @code{setjmp}/@code{longjmp} will be used by +default. + +If this macro is defined to anything, the DWARF 2 unwinder will be used +instead of inline unwinders and @code{__unwind_function} in the non-@code{setjmp} case. + +@findex DWARF_CIE_DATA_ALIGNMENT +@item DWARF_CIE_DATA_ALIGNMENT +This macro need only be defined if the target might save registers in the +function prologue at an offset to the stack pointer that is not aligned to +@code{UNITS_PER_WORD}. The definition should be the negative minimum +alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive +minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if +the target supports DWARF 2 frame unwind information. + +@end table + +@deftypefn {Target Hook} void TARGET_ASM_EXCEPTION_SECTION () +If defined, a function that switches to the section in which the main +exception table is to be placed (@pxref{Sections}). The default is a +function that switches to a section named @code{.gcc_except_table} on +machines that support named sections via +@code{TARGET_ASM_NAMED_SECTION}, otherwise if @option{-fpic} or +@option{-fPIC} is in effect, the @code{data_section}, otherwise the +@code{readonly_data_section}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_EH_FRAME_SECTION () +If defined, a function that switches to the section in which the DWARF 2 +frame unwind information to be placed (@pxref{Sections}). The default +is a function that outputs a standard GAS section directive, if +@code{EH_FRAME_SECTION_NAME} is defined, or else a data section +directive followed by a synthetic label. +@end deftypefn + +@node Alignment Output +@subsection Assembler Commands for Alignment + +@c prevent bad page break with this line +This describes commands for alignment. + +@table @code +@findex JUMP_ALIGN +@item JUMP_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label}, which is +a common destination of jumps and has no fallthru incoming edge. + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @var{align_jumps} in the target's +@code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's +selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation. + +@findex LABEL_ALIGN_AFTER_BARRIER +@item LABEL_ALIGN_AFTER_BARRIER (@var{label}) +The alignment (log base 2) to put in front of @var{label}, which follows +a @code{BARRIER}. + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. + +@findex LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP +@item LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP +The maximum number of bytes to skip when applying +@code{LABEL_ALIGN_AFTER_BARRIER}. This works only if +@code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. + +@findex LOOP_ALIGN +@item LOOP_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label}, which follows +a @code{NOTE_INSN_LOOP_BEG} note. + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @code{align_loops} in the target's +@code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's +selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation. + +@findex LOOP_ALIGN_MAX_SKIP +@item LOOP_ALIGN_MAX_SKIP +The maximum number of bytes to skip when applying @code{LOOP_ALIGN}. +This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. + +@findex LABEL_ALIGN +@item LABEL_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label}. +If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment, +the maximum of the specified values is used. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @code{align_labels} in the target's +@code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's +selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation. + +@findex LABEL_ALIGN_MAX_SKIP +@item LABEL_ALIGN_MAX_SKIP +The maximum number of bytes to skip when applying @code{LABEL_ALIGN}. +This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. + +@findex ASM_OUTPUT_SKIP +@item ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes}) +A C statement to output to the stdio stream @var{stream} an assembler +instruction to advance the location counter by @var{nbytes} bytes. +Those bytes should be zero when loaded. @var{nbytes} will be a C +expression of type @code{int}. + +@findex ASM_NO_SKIP_IN_TEXT +@item ASM_NO_SKIP_IN_TEXT +Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the +text section because it fails to put zeros in the bytes that are skipped. +This is true on many Unix systems, where the pseudo--op to skip bytes +produces no-op instructions rather than zeros when used in the text +section. + +@findex ASM_OUTPUT_ALIGN +@item ASM_OUTPUT_ALIGN (@var{stream}, @var{power}) +A C statement to output to the stdio stream @var{stream} an assembler +command to advance the location counter to a multiple of 2 to the +@var{power} bytes. @var{power} will be a C expression of type @code{int}. + +@findex ASM_OUTPUT_MAX_SKIP_ALIGN +@item ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip}) +A C statement to output to the stdio stream @var{stream} an assembler +command to advance the location counter to a multiple of 2 to the +@var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to +satisfy the alignment request. @var{power} and @var{max_skip} will be +a C expression of type @code{int}. +@end table + +@need 3000 +@node Debugging Info +@section Controlling Debugging Information Format + +@c prevent bad page break with this line +This describes how to specify debugging information. + +@menu +* All Debuggers:: Macros that affect all debugging formats uniformly. +* DBX Options:: Macros enabling specific options in DBX format. +* DBX Hooks:: Hook macros for varying DBX format. +* File Names and DBX:: Macros controlling output of file names in DBX format. +* SDB and DWARF:: Macros for SDB (COFF) and DWARF formats. +* VMS Debug:: Macros for VMS debug format. +@end menu + +@node All Debuggers +@subsection Macros Affecting All Debugging Formats + +@c prevent bad page break with this line +These macros affect all debugging formats. + +@table @code +@findex DBX_REGISTER_NUMBER +@item DBX_REGISTER_NUMBER (@var{regno}) +A C expression that returns the DBX register number for the compiler +register number @var{regno}. In the default macro provided, the value +of this expression will be @var{regno} itself. But sometimes there are +some registers that the compiler knows about and DBX does not, or vice +versa. In such cases, some register may need to have one number in the +compiler and another for DBX@. + +If two registers have consecutive numbers inside GCC, and they can be +used as a pair to hold a multiword value, then they @emph{must} have +consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}. +Otherwise, debuggers will be unable to access such a pair, because they +expect register pairs to be consecutive in their own numbering scheme. + +If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that +does not preserve register pairs, then what you must do instead is +redefine the actual register numbering scheme. + +@findex DEBUGGER_AUTO_OFFSET +@item DEBUGGER_AUTO_OFFSET (@var{x}) +A C expression that returns the integer offset value for an automatic +variable having address @var{x} (an RTL expression). The default +computation assumes that @var{x} is based on the frame-pointer and +gives the offset from the frame-pointer. This is required for targets +that produce debugging output for DBX or COFF-style debugging output +for SDB and allow the frame-pointer to be eliminated when the +@option{-g} options is used. + +@findex DEBUGGER_ARG_OFFSET +@item DEBUGGER_ARG_OFFSET (@var{offset}, @var{x}) +A C expression that returns the integer offset value for an argument +having address @var{x} (an RTL expression). The nominal offset is +@var{offset}. + +@findex PREFERRED_DEBUGGING_TYPE +@item PREFERRED_DEBUGGING_TYPE +A C expression that returns the type of debugging output GCC should +produce when the user specifies just @option{-g}. Define +this if you have arranged for GCC to support more than one format of +debugging output. Currently, the allowable values are @code{DBX_DEBUG}, +@code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG}, +@code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}. + +When the user specifies @option{-ggdb}, GCC normally also uses the +value of this macro to select the debugging output format, but with two +exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined and +@code{LINKER_DOES_NOT_WORK_WITH_DWARF2} is not defined, GCC uses the +value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is +defined, GCC uses @code{DBX_DEBUG}. + +The value of this macro only affects the default debugging output; the +user can always get a specific type of output by using @option{-gstabs}, +@option{-gcoff}, @option{-gdwarf-1}, @option{-gdwarf-2}, @option{-gxcoff}, +or @option{-gvms}. +@end table + +@node DBX Options +@subsection Specific Options for DBX Output + +@c prevent bad page break with this line +These are specific options for DBX output. + +@table @code +@findex DBX_DEBUGGING_INFO +@item DBX_DEBUGGING_INFO +Define this macro if GCC should produce debugging output for DBX +in response to the @option{-g} option. + +@findex XCOFF_DEBUGGING_INFO +@item XCOFF_DEBUGGING_INFO +Define this macro if GCC should produce XCOFF format debugging output +in response to the @option{-g} option. This is a variant of DBX format. + +@findex DEFAULT_GDB_EXTENSIONS +@item DEFAULT_GDB_EXTENSIONS +Define this macro to control whether GCC should by default generate +GDB's extended version of DBX debugging information (assuming DBX-format +debugging information is enabled at all). If you don't define the +macro, the default is 1: always generate the extended information +if there is any occasion to. + +@findex DEBUG_SYMS_TEXT +@item DEBUG_SYMS_TEXT +Define this macro if all @code{.stabs} commands should be output while +in the text section. + +@findex ASM_STABS_OP +@item ASM_STABS_OP +A C string constant, including spacing, naming the assembler pseudo op to +use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol. +If you don't define this macro, @code{"\t.stabs\t"} is used. This macro +applies only to DBX debugging information format. + +@findex ASM_STABD_OP +@item ASM_STABD_OP +A C string constant, including spacing, naming the assembler pseudo op to +use instead of @code{"\t.stabd\t"} to define a debugging symbol whose +value is the current location. If you don't define this macro, +@code{"\t.stabd\t"} is used. This macro applies only to DBX debugging +information format. + +@findex ASM_STABN_OP +@item ASM_STABN_OP +A C string constant, including spacing, naming the assembler pseudo op to +use instead of @code{"\t.stabn\t"} to define a debugging symbol with no +name. If you don't define this macro, @code{"\t.stabn\t"} is used. This +macro applies only to DBX debugging information format. + +@findex DBX_NO_XREFS +@item DBX_NO_XREFS +Define this macro if DBX on your system does not support the construct +@samp{xs@var{tagname}}. On some systems, this construct is used to +describe a forward reference to a structure named @var{tagname}. +On other systems, this construct is not supported at all. + +@findex DBX_CONTIN_LENGTH +@item DBX_CONTIN_LENGTH +A symbol name in DBX-format debugging information is normally +continued (split into two separate @code{.stabs} directives) when it +exceeds a certain length (by default, 80 characters). On some +operating systems, DBX requires this splitting; on others, splitting +must not be done. You can inhibit splitting by defining this macro +with the value zero. You can override the default splitting-length by +defining this macro as an expression for the length you desire. + +@findex DBX_CONTIN_CHAR +@item DBX_CONTIN_CHAR +Normally continuation is indicated by adding a @samp{\} character to +the end of a @code{.stabs} string when a continuation follows. To use +a different character instead, define this macro as a character +constant for the character you want to use. Do not define this macro +if backslash is correct for your system. + +@findex DBX_STATIC_STAB_DATA_SECTION +@item DBX_STATIC_STAB_DATA_SECTION +Define this macro if it is necessary to go to the data section before +outputting the @samp{.stabs} pseudo-op for a non-global static +variable. + +@findex DBX_TYPE_DECL_STABS_CODE +@item DBX_TYPE_DECL_STABS_CODE +The value to use in the ``code'' field of the @code{.stabs} directive +for a typedef. The default is @code{N_LSYM}. + +@findex DBX_STATIC_CONST_VAR_CODE +@item DBX_STATIC_CONST_VAR_CODE +The value to use in the ``code'' field of the @code{.stabs} directive +for a static variable located in the text section. DBX format does not +provide any ``right'' way to do this. The default is @code{N_FUN}. + +@findex DBX_REGPARM_STABS_CODE +@item DBX_REGPARM_STABS_CODE +The value to use in the ``code'' field of the @code{.stabs} directive +for a parameter passed in registers. DBX format does not provide any +``right'' way to do this. The default is @code{N_RSYM}. + +@findex DBX_REGPARM_STABS_LETTER +@item DBX_REGPARM_STABS_LETTER +The letter to use in DBX symbol data to identify a symbol as a parameter +passed in registers. DBX format does not customarily provide any way to +do this. The default is @code{'P'}. + +@findex DBX_MEMPARM_STABS_LETTER +@item DBX_MEMPARM_STABS_LETTER +The letter to use in DBX symbol data to identify a symbol as a stack +parameter. The default is @code{'p'}. + +@findex DBX_FUNCTION_FIRST +@item DBX_FUNCTION_FIRST +Define this macro if the DBX information for a function and its +arguments should precede the assembler code for the function. Normally, +in DBX format, the debugging information entirely follows the assembler +code. + +@findex DBX_LBRAC_FIRST +@item DBX_LBRAC_FIRST +Define this macro if the @code{N_LBRAC} symbol for a block should +precede the debugging information for variables and functions defined in +that block. Normally, in DBX format, the @code{N_LBRAC} symbol comes +first. + +@findex DBX_BLOCKS_FUNCTION_RELATIVE +@item DBX_BLOCKS_FUNCTION_RELATIVE +Define this macro if the value of a symbol describing the scope of a +block (@code{N_LBRAC} or @code{N_RBRAC}) should be relative to the start +of the enclosing function. Normally, GCC uses an absolute address. + +@findex DBX_USE_BINCL +@item DBX_USE_BINCL +Define this macro if GCC should generate @code{N_BINCL} and +@code{N_EINCL} stabs for included header files, as on Sun systems. This +macro also directs GCC to output a type number as a pair of a file +number and a type number within the file. Normally, GCC does not +generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single +number for a type number. +@end table + +@node DBX Hooks +@subsection Open-Ended Hooks for DBX Format + +@c prevent bad page break with this line +These are hooks for DBX format. + +@table @code +@findex DBX_OUTPUT_LBRAC +@item DBX_OUTPUT_LBRAC (@var{stream}, @var{name}) +Define this macro to say how to output to @var{stream} the debugging +information for the start of a scope level for variable names. The +argument @var{name} is the name of an assembler symbol (for use with +@code{assemble_name}) whose value is the address where the scope begins. + +@findex DBX_OUTPUT_RBRAC +@item DBX_OUTPUT_RBRAC (@var{stream}, @var{name}) +Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level. + +@findex DBX_OUTPUT_ENUM +@item DBX_OUTPUT_ENUM (@var{stream}, @var{type}) +Define this macro if the target machine requires special handling to +output an enumeration type. The definition should be a C statement +(sans semicolon) to output the appropriate information to @var{stream} +for the type @var{type}. + +@findex DBX_OUTPUT_FUNCTION_END +@item DBX_OUTPUT_FUNCTION_END (@var{stream}, @var{function}) +Define this macro if the target machine requires special output at the +end of the debugging information for a function. The definition should +be a C statement (sans semicolon) to output the appropriate information +to @var{stream}. @var{function} is the @code{FUNCTION_DECL} node for +the function. + +@findex DBX_OUTPUT_STANDARD_TYPES +@item DBX_OUTPUT_STANDARD_TYPES (@var{syms}) +Define this macro if you need to control the order of output of the +standard data types at the beginning of compilation. The argument +@var{syms} is a @code{tree} which is a chain of all the predefined +global symbols, including names of data types. + +Normally, DBX output starts with definitions of the types for integers +and characters, followed by all the other predefined types of the +particular language in no particular order. + +On some machines, it is necessary to output different particular types +first. To do this, define @code{DBX_OUTPUT_STANDARD_TYPES} to output +those symbols in the necessary order. Any predefined types that you +don't explicitly output will be output afterward in no particular order. + +Be careful not to define this macro so that it works only for C@. There +are no global variables to access most of the built-in types, because +another language may have another set of types. The way to output a +particular type is to look through @var{syms} to see if you can find it. +Here is an example: + +@smallexample +@{ + tree decl; + for (decl = syms; decl; decl = TREE_CHAIN (decl)) + if (!strcmp (IDENTIFIER_POINTER (DECL_NAME (decl)), + "long int")) + dbxout_symbol (decl); + @dots{} +@} +@end smallexample + +@noindent +This does nothing if the expected type does not exist. + +See the function @code{init_decl_processing} in @file{c-decl.c} to find +the names to use for all the built-in C types. + +Here is another way of finding a particular type: + +@c this is still overfull. --mew 10feb93 +@smallexample +@{ + tree decl; + for (decl = syms; decl; decl = TREE_CHAIN (decl)) + if (TREE_CODE (decl) == TYPE_DECL + && (TREE_CODE (TREE_TYPE (decl)) + == INTEGER_CST) + && TYPE_PRECISION (TREE_TYPE (decl)) == 16 + && TYPE_UNSIGNED (TREE_TYPE (decl))) +@group + /* @r{This must be @code{unsigned short}.} */ + dbxout_symbol (decl); + @dots{} +@} +@end group +@end smallexample + +@findex NO_DBX_FUNCTION_END +@item NO_DBX_FUNCTION_END +Some stabs encapsulation formats (in particular ECOFF), cannot handle the +@code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct. +On those machines, define this macro to turn this feature off without +disturbing the rest of the gdb extensions. + +@end table + +@node File Names and DBX +@subsection File Names in DBX Format + +@c prevent bad page break with this line +This describes file names in DBX format. + +@table @code +@findex DBX_WORKING_DIRECTORY +@item DBX_WORKING_DIRECTORY +Define this if DBX wants to have the current directory recorded in each +object file. + +Note that the working directory is always recorded if GDB extensions are +enabled. + +@findex DBX_OUTPUT_MAIN_SOURCE_FILENAME +@item DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name}) +A C statement to output DBX debugging information to the stdio stream +@var{stream} which indicates that file @var{name} is the main source +file---the file specified as the input file for compilation. +This macro is called only once, at the beginning of compilation. + +This macro need not be defined if the standard form of output +for DBX debugging information is appropriate. + +@findex DBX_OUTPUT_MAIN_SOURCE_DIRECTORY +@item DBX_OUTPUT_MAIN_SOURCE_DIRECTORY (@var{stream}, @var{name}) +A C statement to output DBX debugging information to the stdio stream +@var{stream} which indicates that the current directory during +compilation is named @var{name}. + +This macro need not be defined if the standard form of output +for DBX debugging information is appropriate. + +@findex DBX_OUTPUT_MAIN_SOURCE_FILE_END +@item DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name}) +A C statement to output DBX debugging information at the end of +compilation of the main source file @var{name}. + +If you don't define this macro, nothing special is output at the end +of compilation, which is correct for most machines. + +@findex DBX_OUTPUT_SOURCE_FILENAME +@item DBX_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) +A C statement to output DBX debugging information to the stdio stream +@var{stream} which indicates that file @var{name} is the current source +file. This output is generated each time input shifts to a different +source file as a result of @samp{#include}, the end of an included file, +or a @samp{#line} command. + +This macro need not be defined if the standard form of output +for DBX debugging information is appropriate. +@end table + +@need 2000 +@node SDB and DWARF +@subsection Macros for SDB and DWARF Output + +@c prevent bad page break with this line +Here are macros for SDB and DWARF output. + +@table @code +@findex SDB_DEBUGGING_INFO +@item SDB_DEBUGGING_INFO +Define this macro if GCC should produce COFF-style debugging output +for SDB in response to the @option{-g} option. + +@findex DWARF_DEBUGGING_INFO +@item DWARF_DEBUGGING_INFO +Define this macro if GCC should produce dwarf format debugging output +in response to the @option{-g} option. + +@findex DWARF2_DEBUGGING_INFO +@item DWARF2_DEBUGGING_INFO +Define this macro if GCC should produce dwarf version 2 format +debugging output in response to the @option{-g} option. + +To support optional call frame debugging information, you must also +define @code{INCOMING_RETURN_ADDR_RTX} and either set +@code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the +prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save} +as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't. + +@findex DWARF2_FRAME_INFO +@item DWARF2_FRAME_INFO +Define this macro to a nonzero value if GCC should always output +Dwarf 2 frame information. If @code{DWARF2_UNWIND_INFO} +(@pxref{Exception Region Output} is nonzero, GCC will output this +information not matter how you define @code{DWARF2_FRAME_INFO}. + +@findex LINKER_DOES_NOT_WORK_WITH_DWARF2 +@item LINKER_DOES_NOT_WORK_WITH_DWARF2 +Define this macro if the linker does not work with Dwarf version 2. +Normally, if the user specifies only @option{-ggdb} GCC will use Dwarf +version 2 if available; this macro disables this. See the description +of the @code{PREFERRED_DEBUGGING_TYPE} macro for more details. + +@findex DWARF2_GENERATE_TEXT_SECTION_LABEL +@item DWARF2_GENERATE_TEXT_SECTION_LABEL +By default, the Dwarf 2 debugging information generator will generate a +label to mark the beginning of the text section. If it is better simply +to use the name of the text section itself, rather than an explicit label, +to indicate the beginning of the text section, define this macro to zero. + +@findex DWARF2_ASM_LINE_DEBUG_INFO +@item DWARF2_ASM_LINE_DEBUG_INFO +Define this macro to be a nonzero value if the assembler can generate Dwarf 2 +line debug info sections. This will result in much more compact line number +tables, and hence is desirable if it works. + +@findex PUT_SDB_@dots{} +@item PUT_SDB_@dots{} +Define these macros to override the assembler syntax for the special +SDB assembler directives. See @file{sdbout.c} for a list of these +macros and their arguments. If the standard syntax is used, you need +not define them yourself. + +@findex SDB_DELIM +@item SDB_DELIM +Some assemblers do not support a semicolon as a delimiter, even between +SDB assembler directives. In that case, define this macro to be the +delimiter to use (usually @samp{\n}). It is not necessary to define +a new set of @code{PUT_SDB_@var{op}} macros if this is the only change +required. + +@findex SDB_GENERATE_FAKE +@item SDB_GENERATE_FAKE +Define this macro to override the usual method of constructing a dummy +name for anonymous structure and union types. See @file{sdbout.c} for +more information. + +@findex SDB_ALLOW_UNKNOWN_REFERENCES +@item SDB_ALLOW_UNKNOWN_REFERENCES +Define this macro to allow references to unknown structure, +union, or enumeration tags to be emitted. Standard COFF does not +allow handling of unknown references, MIPS ECOFF has support for +it. + +@findex SDB_ALLOW_FORWARD_REFERENCES +@item SDB_ALLOW_FORWARD_REFERENCES +Define this macro to allow references to structure, union, or +enumeration tags that have not yet been seen to be handled. Some +assemblers choke if forward tags are used, while some require it. +@end table + +@need 2000 +@node VMS Debug +@subsection Macros for VMS Debug Format + +@c prevent bad page break with this line +Here are macros for VMS debug format. + +@table @code +@findex VMS_DEBUGGING_INFO +@item VMS_DEBUGGING_INFO +Define this macro if GCC should produce debugging output for VMS +in response to the @option{-g} option. The default behavior for VMS +is to generate minimal debug info for a traceback in the absence of +@option{-g} unless explicitly overridden with @option{-g0}. This +behavior is controlled by @code{OPTIMIZATION_OPTIONS} and +@code{OVERRIDE_OPTIONS}. +@end table + +@node Cross-compilation +@section Cross Compilation and Floating Point +@cindex cross compilation and floating point +@cindex floating point and cross compilation + +While all modern machines use 2's complement representation for integers, +there are a variety of representations for floating point numbers. This +means that in a cross-compiler the representation of floating point numbers +in the compiled program may be different from that used in the machine +doing the compilation. + +@findex atof +Because different representation systems may offer different amounts of +range and precision, the cross compiler cannot safely use the host +machine's floating point arithmetic. Therefore, floating point constants +must be represented in the target machine's format. This means that the +cross compiler cannot use @code{atof} to parse a floating point constant; +it must have its own special routine to use instead. Also, constant +folding must emulate the target machine's arithmetic (or must not be done +at all). + +The macros in the following table should be defined only if you are cross +compiling between different floating point formats. + +Otherwise, don't define them. Then default definitions will be set up which +use @code{double} as the data type, @code{==} to test for equality, etc. + +You don't need to worry about how many times you use an operand of any +of these macros. The compiler never uses operands which have side effects. + +@table @code +@findex REAL_VALUE_TYPE +@item REAL_VALUE_TYPE +A macro for the C data type to be used to hold a floating point value +in the target machine's format. Typically this would be a +@code{struct} containing an array of @code{int}. + +@findex REAL_VALUES_EQUAL +@item REAL_VALUES_EQUAL (@var{x}, @var{y}) +A macro for a C expression which compares for equality the two values, +@var{x} and @var{y}, both of type @code{REAL_VALUE_TYPE}. + +@findex REAL_VALUES_LESS +@item REAL_VALUES_LESS (@var{x}, @var{y}) +A macro for a C expression which tests whether @var{x} is less than +@var{y}, both values being of type @code{REAL_VALUE_TYPE} and +interpreted as floating point numbers in the target machine's +representation. + +@findex REAL_VALUE_LDEXP +@findex ldexp +@item REAL_VALUE_LDEXP (@var{x}, @var{scale}) +A macro for a C expression which performs the standard library +function @code{ldexp}, but using the target machine's floating point +representation. Both @var{x} and the value of the expression have +type @code{REAL_VALUE_TYPE}. The second argument, @var{scale}, is an +integer. + +@findex REAL_VALUE_FIX +@item REAL_VALUE_FIX (@var{x}) +A macro whose definition is a C expression to convert the target-machine +floating point value @var{x} to a signed integer. @var{x} has type +@code{REAL_VALUE_TYPE}. + +@findex REAL_VALUE_UNSIGNED_FIX +@item REAL_VALUE_UNSIGNED_FIX (@var{x}) +A macro whose definition is a C expression to convert the target-machine +floating point value @var{x} to an unsigned integer. @var{x} has type +@code{REAL_VALUE_TYPE}. + +@findex REAL_VALUE_RNDZINT +@item REAL_VALUE_RNDZINT (@var{x}) +A macro whose definition is a C expression to round the target-machine +floating point value @var{x} towards zero to an integer value (but still +as a floating point number). @var{x} has type @code{REAL_VALUE_TYPE}, +and so does the value. + +@findex REAL_VALUE_UNSIGNED_RNDZINT +@item REAL_VALUE_UNSIGNED_RNDZINT (@var{x}) +A macro whose definition is a C expression to round the target-machine +floating point value @var{x} towards zero to an unsigned integer value +(but still represented as a floating point number). @var{x} has type +@code{REAL_VALUE_TYPE}, and so does the value. + +@findex REAL_VALUE_ATOF +@item REAL_VALUE_ATOF (@var{string}, @var{mode}) +A macro for a C expression which converts @var{string}, an expression of +type @code{char *}, into a floating point number in the target machine's +representation for mode @var{mode}. The value has type +@code{REAL_VALUE_TYPE}. + +@findex REAL_INFINITY +@item REAL_INFINITY +Define this macro if infinity is a possible floating point value, and +therefore division by 0 is legitimate. + +@findex REAL_VALUE_ISINF +@findex isinf +@item REAL_VALUE_ISINF (@var{x}) +A macro for a C expression which determines whether @var{x}, a floating +point value, is infinity. The value has type @code{int}. +By default, this is defined to call @code{isinf}. + +@findex REAL_VALUE_ISNAN +@findex isnan +@item REAL_VALUE_ISNAN (@var{x}) +A macro for a C expression which determines whether @var{x}, a floating +point value, is a ``nan'' (not-a-number). The value has type +@code{int}. By default, this is defined to call @code{isnan}. +@end table + +@cindex constant folding and floating point +Define the following additional macros if you want to make floating +point constant folding work while cross compiling. If you don't +define them, cross compilation is still possible, but constant folding +will not happen for floating point values. + +@table @code +@findex REAL_ARITHMETIC +@item REAL_ARITHMETIC (@var{output}, @var{code}, @var{x}, @var{y}) +A macro for a C statement which calculates an arithmetic operation of +the two floating point values @var{x} and @var{y}, both of type +@code{REAL_VALUE_TYPE} in the target machine's representation, to +produce a result of the same type and representation which is stored +in @var{output} (which will be a variable). + +The operation to be performed is specified by @var{code}, a tree code +which will always be one of the following: @code{PLUS_EXPR}, +@code{MINUS_EXPR}, @code{MULT_EXPR}, @code{RDIV_EXPR}, +@code{MAX_EXPR}, @code{MIN_EXPR}. + +@cindex overflow while constant folding +The expansion of this macro is responsible for checking for overflow. +If overflow happens, the macro expansion should execute the statement +@code{return 0;}, which indicates the inability to perform the +arithmetic operation requested. + +@findex REAL_VALUE_NEGATE +@item REAL_VALUE_NEGATE (@var{x}) +A macro for a C expression which returns the negative of the floating +point value @var{x}. Both @var{x} and the value of the expression +have type @code{REAL_VALUE_TYPE} and are in the target machine's +floating point representation. + +There is no way for this macro to report overflow, since overflow +can't happen in the negation operation. + +@findex REAL_VALUE_TRUNCATE +@item REAL_VALUE_TRUNCATE (@var{mode}, @var{x}) +A macro for a C expression which converts the floating point value +@var{x} to mode @var{mode}. + +Both @var{x} and the value of the expression are in the target machine's +floating point representation and have type @code{REAL_VALUE_TYPE}. +However, the value should have an appropriate bit pattern to be output +properly as a floating constant whose precision accords with mode +@var{mode}. + +There is no way for this macro to report overflow. + +@findex REAL_VALUE_TO_INT +@item REAL_VALUE_TO_INT (@var{low}, @var{high}, @var{x}) +A macro for a C expression which converts a floating point value +@var{x} into a double-precision integer which is then stored into +@var{low} and @var{high}, two variables of type @var{int}. + +@item REAL_VALUE_FROM_INT (@var{x}, @var{low}, @var{high}, @var{mode}) +@findex REAL_VALUE_FROM_INT +A macro for a C expression which converts a double-precision integer +found in @var{low} and @var{high}, two variables of type @var{int}, +into a floating point value which is then stored into @var{x}. +The value is in the target machine's representation for mode @var{mode} +and has the type @code{REAL_VALUE_TYPE}. +@end table + +@node Mode Switching +@section Mode Switching Instructions +@cindex mode switching +The following macros control mode switching optimizations: + +@table @code +@findex OPTIMIZE_MODE_SWITCHING +@item OPTIMIZE_MODE_SWITCHING (@var{entity}) +Define this macro if the port needs extra instructions inserted for mode +switching in an optimizing compilation. + +For an example, the SH4 can perform both single and double precision +floating point operations, but to perform a single precision operation, +the FPSCR PR bit has to be cleared, while for a double precision +operation, this bit has to be set. Changing the PR bit requires a general +purpose register as a scratch register, hence these FPSCR sets have to +be inserted before reload, i.e.@: you can't put this into instruction emitting +or @code{MACHINE_DEPENDENT_REORG}. + +You can have multiple entities that are mode-switched, and select at run time +which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should +return nonzero for any @var{entity} that needs mode-switching. +If you define this macro, you also have to define +@code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED}, +@code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}. +@code{NORMAL_MODE} is optional. + +@findex NUM_MODES_FOR_MODE_SWITCHING +@item NUM_MODES_FOR_MODE_SWITCHING +If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as +initializer for an array of integers. Each initializer element +N refers to an entity that needs mode switching, and specifies the number +of different modes that might need to be set for this entity. +The position of the initializer in the initializer - starting counting at +zero - determines the integer that is used to refer to the mode-switched +entity in question. +In macros that take mode arguments / yield a mode result, modes are +represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode +switch is needed / supplied. + +@findex MODE_NEEDED +@item MODE_NEEDED (@var{entity}, @var{insn}) +@var{entity} is an integer specifying a mode-switched entity. If +@code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to +return an integer value not larger than the corresponding element in +@code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must +be switched into prior to the execution of @var{insn}. + +@findex NORMAL_MODE +@item NORMAL_MODE (@var{entity}) +If this macro is defined, it is evaluated for every @var{entity} that needs +mode switching. It should evaluate to an integer, which is a mode that +@var{entity} is assumed to be switched to at function entry and exit. + +@findex MODE_PRIORITY_TO_MODE +@item MODE_PRIORITY_TO_MODE (@var{entity}, @var{n}) +This macro specifies the order in which modes for @var{entity} are processed. +0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the +lowest. The value of the macro should be an integer designating a mode +for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode} +(@var{entity}, @var{n}) shall be a bijection in 0 @dots{} +@code{num_modes_for_mode_switching[@var{entity}] - 1}. + +@findex EMIT_MODE_SET +@item EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live}) +Generate one or more insns to set @var{entity} to @var{mode}. +@var{hard_reg_live} is the set of hard registers live at the point where +the insn(s) are to be inserted. +@end table + +@node Target Attributes +@section Defining target-specific uses of @code{__attribute__} +@cindex target attributes +@cindex machine attributes +@cindex attributes, target-specific + +Target-specific attributes may be defined for functions, data and types. +These are described using the following target hooks; they also need to +be documented in @file{extend.texi}. + +@deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE +If defined, this target hook points to an array of @samp{struct +attribute_spec} (defined in @file{tree.h}) specifying the machine +specific attributes for this target and some of the restrictions on the +entities to which these attributes are applied and the arguments they +take. +@end deftypevr + +@deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) +If defined, this target hook is a function which returns zero if the attributes on +@var{type1} and @var{type2} are incompatible, one if they are compatible, +and two if they are nearly compatible (which causes a warning to be +generated). If this is not defined, machine-specific attributes are +supposed always to be compatible. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type}) +If defined, this target hook is a function which assigns default attributes to +newly defined @var{type}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) +Define this target hook if the merging of type attributes needs special +handling. If defined, the result is a list of the combined +@code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed +that @code{comptypes} has already been called and returned 1. This +function may call @code{merge_attributes} to handle machine-independent +merging. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl}) +Define this target hook if the merging of decl attributes needs special +handling. If defined, the result is a list of the combined +@code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}. +@var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of +when this is needed are when one attribute overrides another, or when an +attribute is nullified by a subsequent definition. This function may +call @code{merge_attributes} to handle machine-independent merging. + +@findex TARGET_DLLIMPORT_DECL_ATTRIBUTES +If the only target-specific handling you require is @samp{dllimport} for +Windows targets, you should define the macro +@code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. This links in a function +called @code{merge_dllimport_decl_attributes} which can then be defined +as the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. This is done +in @file{i386/cygwin.h} and @file{i386/i386.c}, for example. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr}) +Define this target hook if you want to be able to add attributes to a decl +when it is being created. This is normally useful for back ends which +wish to implement a pragma by using the attributes which correspond to +the pragma's effect. The @var{node} argument is the decl which is being +created. The @var{attr_ptr} argument is a pointer to the attribute list +for this decl. The list itself should not be modified, since it may be +shared with other decls, but attributes may be chained on the head of +the list and @code{*@var{attr_ptr}} modified to point to the new +attributes, or a copy of the list may be made if further changes are +needed. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (tree @var{fndecl}) +@cindex inlining +This target hook returns @code{true} if it is ok to inline @var{fndecl} +into the current function, despite its having target-specific +attributes, @code{false} otherwise. By default, if a function has a +target specific attribute attached to it, it will not be inlined. +@end deftypefn + +@node Misc +@section Miscellaneous Parameters +@cindex parameters, miscellaneous + +@c prevent bad page break with this line +Here are several miscellaneous parameters. + +@table @code +@item PREDICATE_CODES +@findex PREDICATE_CODES +Define this if you have defined special-purpose predicates in the file +@file{@var{machine}.c}. This macro is called within an initializer of an +array of structures. The first field in the structure is the name of a +predicate and the second field is an array of rtl codes. For each +predicate, list all rtl codes that can be in expressions matched by the +predicate. The list should have a trailing comma. Here is an example +of two entries in the list for a typical RISC machine: + +@smallexample +#define PREDICATE_CODES \ + @{"gen_reg_rtx_operand", @{SUBREG, REG@}@}, \ + @{"reg_or_short_cint_operand", @{SUBREG, REG, CONST_INT@}@}, +@end smallexample + +Defining this macro does not affect the generated code (however, +incorrect definitions that omit an rtl code that may be matched by the +predicate can cause the compiler to malfunction). Instead, it allows +the table built by @file{genrecog} to be more compact and efficient, +thus speeding up the compiler. The most important predicates to include +in the list specified by this macro are those used in the most insn +patterns. + +For each predicate function named in @code{PREDICATE_CODES}, a +declaration will be generated in @file{insn-codes.h}. + +@item SPECIAL_MODE_PREDICATES +@findex SPECIAL_MODE_PREDICATES +Define this if you have special predicates that know special things +about modes. Genrecog will warn about certain forms of +@code{match_operand} without a mode; if the operand predicate is +listed in @code{SPECIAL_MODE_PREDICATES}, the warning will be +suppressed. + +Here is an example from the IA-32 port (@code{ext_register_operand} +specially checks for @code{HImode} or @code{SImode} in preparation +for a byte extraction from @code{%ah} etc.). + +@smallexample +#define SPECIAL_MODE_PREDICATES \ + "ext_register_operand", +@end smallexample + +@findex CASE_VECTOR_MODE +@item CASE_VECTOR_MODE +An alias for a machine mode name. This is the machine mode that +elements of a jump-table should have. + +@findex CASE_VECTOR_SHORTEN_MODE +@item CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body}) +Optional: return the preferred mode for an @code{addr_diff_vec} +when the minimum and maximum offset are known. If you define this, +it enables extra code in branch shortening to deal with @code{addr_diff_vec}. +To make this work, you also have to define INSN_ALIGN and +make the alignment for @code{addr_diff_vec} explicit. +The @var{body} argument is provided so that the offset_unsigned and scale +flags can be updated. + +@findex CASE_VECTOR_PC_RELATIVE +@item CASE_VECTOR_PC_RELATIVE +Define this macro to be a C expression to indicate when jump-tables +should contain relative addresses. If jump-tables never contain +relative addresses, then you need not define this macro. + +@findex CASE_DROPS_THROUGH +@item CASE_DROPS_THROUGH +Define this if control falls through a @code{case} insn when the index +value is out of range. This means the specified default-label is +actually ignored by the @code{case} insn proper. + +@findex CASE_VALUES_THRESHOLD +@item CASE_VALUES_THRESHOLD +Define this to be the smallest number of different values for which it +is best to use a jump-table instead of a tree of conditional branches. +The default is four for machines with a @code{casesi} instruction and +five otherwise. This is best for most machines. + +@findex WORD_REGISTER_OPERATIONS +@item WORD_REGISTER_OPERATIONS +Define this macro if operations between registers with integral mode +smaller than a word are always performed on the entire register. +Most RISC machines have this property and most CISC machines do not. + +@findex LOAD_EXTEND_OP +@item LOAD_EXTEND_OP (@var{mode}) +Define this macro to be a C expression indicating when insns that read +memory in @var{mode}, an integral mode narrower than a word, set the +bits outside of @var{mode} to be either the sign-extension or the +zero-extension of the data read. Return @code{SIGN_EXTEND} for values +of @var{mode} for which the +insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and +@code{NIL} for other modes. + +This macro is not called with @var{mode} non-integral or with a width +greater than or equal to @code{BITS_PER_WORD}, so you may return any +value in this case. Do not define this macro if it would always return +@code{NIL}. On machines where this macro is defined, you will normally +define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}. + +@findex SHORT_IMMEDIATES_SIGN_EXTEND +@item SHORT_IMMEDIATES_SIGN_EXTEND +Define this macro if loading short immediate values into registers sign +extends. + +@findex FIXUNS_TRUNC_LIKE_FIX_TRUNC +@item FIXUNS_TRUNC_LIKE_FIX_TRUNC +Define this macro if the same instructions that convert a floating +point number to a signed fixed point number also convert validly to an +unsigned one. + +@findex MOVE_MAX +@item MOVE_MAX +The maximum number of bytes that a single instruction can move quickly +between memory and registers or between two memory locations. + +@findex MAX_MOVE_MAX +@item MAX_MOVE_MAX +The maximum number of bytes that a single instruction can move quickly +between memory and registers or between two memory locations. If this +is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the +constant value that is the largest value that @code{MOVE_MAX} can have +at run-time. + +@findex SHIFT_COUNT_TRUNCATED +@item SHIFT_COUNT_TRUNCATED +A C expression that is nonzero if on this machine the number of bits +actually used for the count of a shift operation is equal to the number +of bits needed to represent the size of the object being shifted. When +this macro is nonzero, the compiler will assume that it is safe to omit +a sign-extend, zero-extend, and certain bitwise `and' instructions that +truncates the count of a shift operation. On machines that have +instructions that act on bit-fields at variable positions, which may +include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED} +also enables deletion of truncations of the values that serve as +arguments to bit-field instructions. + +If both types of instructions truncate the count (for shifts) and +position (for bit-field operations), or if no variable-position bit-field +instructions exist, you should define this macro. + +However, on some machines, such as the 80386 and the 680x0, truncation +only applies to shift operations and not the (real or pretended) +bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on +such machines. Instead, add patterns to the @file{md} file that include +the implied truncation of the shift instructions. + +You need not define this macro if it would always have the value of zero. + +@findex TRULY_NOOP_TRUNCATION +@item TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec}) +A C expression which is nonzero if on this machine it is safe to +``convert'' an integer of @var{inprec} bits to one of @var{outprec} +bits (where @var{outprec} is smaller than @var{inprec}) by merely +operating on it as if it had only @var{outprec} bits. + +On many machines, this expression can be 1. + +@c rearranged this, removed the phrase "it is reported that". this was +@c to fix an overfull hbox. --mew 10feb93 +When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for +modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result. +If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in +such cases may improve things. + +@findex STORE_FLAG_VALUE +@item STORE_FLAG_VALUE +A C expression describing the value returned by a comparison operator +with an integral mode and stored by a store-flag instruction +(@samp{s@var{cond}}) when the condition is true. This description must +apply to @emph{all} the @samp{s@var{cond}} patterns and all the +comparison operators whose results have a @code{MODE_INT} mode. + +A value of 1 or @minus{}1 means that the instruction implementing the +comparison operator returns exactly 1 or @minus{}1 when the comparison is true +and 0 when the comparison is false. Otherwise, the value indicates +which bits of the result are guaranteed to be 1 when the comparison is +true. This value is interpreted in the mode of the comparison +operation, which is given by the mode of the first operand in the +@samp{s@var{cond}} pattern. Either the low bit or the sign bit of +@code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by +the compiler. + +If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will +generate code that depends only on the specified bits. It can also +replace comparison operators with equivalent operations if they cause +the required bits to be set, even if the remaining bits are undefined. +For example, on a machine whose comparison operators return an +@code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as +@samp{0x80000000}, saying that just the sign bit is relevant, the +expression + +@smallexample +(ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0)) +@end smallexample + +@noindent +can be converted to + +@smallexample +(ashift:SI @var{x} (const_int @var{n})) +@end smallexample + +@noindent +where @var{n} is the appropriate shift count to move the bit being +tested into the sign bit. + +There is no way to describe a machine that always sets the low-order bit +for a true value, but does not guarantee the value of any other bits, +but we do not know of any machine that has such an instruction. If you +are trying to port GCC to such a machine, include an instruction to +perform a logical-and of the result with 1 in the pattern for the +comparison operators and let us know at @email{gcc@@gcc.gnu.org}. + +Often, a machine will have multiple instructions that obtain a value +from a comparison (or the condition codes). Here are rules to guide the +choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions +to be used: + +@itemize @bullet +@item +Use the shortest sequence that yields a valid definition for +@code{STORE_FLAG_VALUE}. It is more efficient for the compiler to +``normalize'' the value (convert it to, e.g., 1 or 0) than for the +comparison operators to do so because there may be opportunities to +combine the normalization with other operations. + +@item +For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being +slightly preferred on machines with expensive jumps and 1 preferred on +other machines. + +@item +As a second choice, choose a value of @samp{0x80000001} if instructions +exist that set both the sign and low-order bits but do not define the +others. + +@item +Otherwise, use a value of @samp{0x80000000}. +@end itemize + +Many machines can produce both the value chosen for +@code{STORE_FLAG_VALUE} and its negation in the same number of +instructions. On those machines, you should also define a pattern for +those cases, e.g., one matching + +@smallexample +(set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C}))) +@end smallexample + +Some machines can also perform @code{and} or @code{plus} operations on +condition code values with less instructions than the corresponding +@samp{s@var{cond}} insn followed by @code{and} or @code{plus}. On those +machines, define the appropriate patterns. Use the names @code{incscc} +and @code{decscc}, respectively, for the patterns which perform +@code{plus} or @code{minus} operations on condition code values. See +@file{rs6000.md} for some examples. The GNU Superoptizer can be used to +find such instruction sequences on other machines. + +You need not define @code{STORE_FLAG_VALUE} if the machine has no store-flag +instructions. + +@findex FLOAT_STORE_FLAG_VALUE +@item FLOAT_STORE_FLAG_VALUE (@var{mode}) +A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is +returned when comparison operators with floating-point results are true. +Define this macro on machine that have comparison operations that return +floating-point values. If there are no such operations, do not define +this macro. + +@findex Pmode +@item Pmode +An alias for the machine mode for pointers. On most machines, define +this to be the integer mode corresponding to the width of a hardware +pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines. +On some machines you must define this to be one of the partial integer +modes, such as @code{PSImode}. + +The width of @code{Pmode} must be at least as large as the value of +@code{POINTER_SIZE}. If it is not equal, you must define the macro +@code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended +to @code{Pmode}. + +@findex FUNCTION_MODE +@item FUNCTION_MODE +An alias for the machine mode used for memory references to functions +being called, in @code{call} RTL expressions. On most machines this +should be @code{QImode}. + +@findex INTEGRATE_THRESHOLD +@item INTEGRATE_THRESHOLD (@var{decl}) +A C expression for the maximum number of instructions above which the +function @var{decl} should not be inlined. @var{decl} is a +@code{FUNCTION_DECL} node. + +The default definition of this macro is 64 plus 8 times the number of +arguments that the function accepts. Some people think a larger +threshold should be used on RISC machines. + +@findex STDC_0_IN_SYSTEM_HEADERS +@item STDC_0_IN_SYSTEM_HEADERS +In normal operation, the preprocessor expands @code{__STDC__} to the +constant 1, to signify that GCC conforms to ISO Standard C@. On some +hosts, like Solaris, the system compiler uses a different convention, +where @code{__STDC__} is normally 0, but is 1 if the user specifies +strict conformance to the C Standard. + +Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host +convention when processing system header files, but when processing user +files @code{__STDC__} will always expand to 1. + +@findex SCCS_DIRECTIVE +@item SCCS_DIRECTIVE +Define this if the preprocessor should ignore @code{#sccs} directives +and print no error message. + +@findex NO_IMPLICIT_EXTERN_C +@item NO_IMPLICIT_EXTERN_C +Define this macro if the system header files support C++ as well as C@. +This macro inhibits the usual method of using system header files in +C++, which is to pretend that the file's contents are enclosed in +@samp{extern "C" @{@dots{}@}}. + +@findex HANDLE_PRAGMA +@item HANDLE_PRAGMA (@var{getc}, @var{ungetc}, @var{name}) +This macro is no longer supported. You must use +@code{REGISTER_TARGET_PRAGMAS} instead. + +@findex REGISTER_TARGET_PRAGMAS +@findex #pragma +@findex pragma +@item REGISTER_TARGET_PRAGMAS (@var{pfile}) +Define this macro if you want to implement any target-specific pragmas. +If defined, it is a C expression which makes a series of calls to +@code{cpp_register_pragma} for each pragma, with @var{pfile} passed as +the first argument to to these functions. The macro may also do any +setup required for the pragmas. + +The primary reason to define this macro is to provide compatibility with +other compilers for the same target. In general, we discourage +definition of target-specific pragmas for GCC@. + +If the pragma can be implemented by attributes then you should consider +defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well. + +Preprocessor macros that appear on pragma lines are not expanded. All +@samp{#pragma} directives that do not match any registered pragma are +silently ignored, unless the user specifies @option{-Wunknown-pragmas}. + +@deftypefun void cpp_register_pragma (cpp_reader *@var{pfile}, const char *@var{space}, const char *@var{name}, void (*@var{callback}) (cpp_reader *)) + +Each call to @code{cpp_register_pragma} establishes one pragma. The +@var{callback} routine will be called when the preprocessor encounters a +pragma of the form + +@smallexample +#pragma [@var{space}] @var{name} @dots{} +@end smallexample + +@var{space} is the case-sensitive namespace of the pragma, or +@code{NULL} to put the pragma in the global namespace. The callback +routine receives @var{pfile} as its first argument, which can be passed +on to cpplib's functions if necessary. You can lex tokens after the +@var{name} by calling @code{c_lex}. Tokens that are not read by the +callback will be silently ignored. The end of the line is indicated by +a token of type @code{CPP_EOF}. + +For an example use of this routine, see @file{c4x.h} and the callback +routines defined in @file{c4x-c.c}. + +Note that the use of @code{c_lex} is specific to the C and C++ +compilers. It will not work in the Java or Fortran compilers, or any +other language compilers for that matter. Thus if @code{c_lex} is going +to be called from target-specific code, it must only be done so when +building the C and C++ compilers. This can be done by defining the +variables @code{c_target_objs} and @code{cxx_target_objs} in the +target entry in the @file{config.gcc} file. These variables should name +the target-specific, language-specific object file which contains the +code that uses @code{c_lex}. Note it will also be necessary to add a +rule to the makefile fragment pointed to by @code{tmake_file} that shows +how to build this object file. +@end deftypefun + +@findex HANDLE_SYSV_PRAGMA +@findex #pragma +@findex pragma +@item HANDLE_SYSV_PRAGMA +Define this macro (to a value of 1) if you want the System V style +pragmas @samp{#pragma pack()} and @samp{#pragma weak +[=]} to be supported by gcc. + +The pack pragma specifies the maximum alignment (in bytes) of fields +within a structure, in much the same way as the @samp{__aligned__} and +@samp{__packed__} @code{__attribute__}s do. A pack value of zero resets +the behavior to the default. + +The weak pragma only works if @code{SUPPORTS_WEAK} and +@code{ASM_WEAKEN_LABEL} are defined. If enabled it allows the creation +of specifically named weak labels, optionally with a value. + +@findex HANDLE_PRAGMA_PACK_PUSH_POP +@findex #pragma +@findex pragma +@item HANDLE_PRAGMA_PACK_PUSH_POP +Define this macro (to a value of 1) if you want to support the Win32 +style pragmas @samp{#pragma pack(push,@var{n})} and @samp{#pragma +pack(pop)}. The @samp{pack(push,@var{n})} pragma specifies the maximum alignment +(in bytes) of fields within a structure, in much the same way as the +@samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A +pack value of zero resets the behavior to the default. Successive +invocations of this pragma cause the previous values to be stacked, so +that invocations of @samp{#pragma pack(pop)} will return to the previous +value. + +@findex DOLLARS_IN_IDENTIFIERS +@item DOLLARS_IN_IDENTIFIERS +Define this macro to control use of the character @samp{$} in identifier +names. 0 means @samp{$} is not allowed by default; 1 means it is allowed. +1 is the default; there is no need to define this macro in that case. +This macro controls the compiler proper; it does not affect the preprocessor. + +@findex NO_DOLLAR_IN_LABEL +@item NO_DOLLAR_IN_LABEL +Define this macro if the assembler does not accept the character +@samp{$} in label names. By default constructors and destructors in +G++ have @samp{$} in the identifiers. If this macro is defined, +@samp{.} is used instead. + +@findex NO_DOT_IN_LABEL +@item NO_DOT_IN_LABEL +Define this macro if the assembler does not accept the character +@samp{.} in label names. By default constructors and destructors in G++ +have names that use @samp{.}. If this macro is defined, these names +are rewritten to avoid @samp{.}. + +@findex DEFAULT_MAIN_RETURN +@item DEFAULT_MAIN_RETURN +Define this macro if the target system expects every program's @code{main} +function to return a standard ``success'' value by default (if no other +value is explicitly returned). + +The definition should be a C statement (sans semicolon) to generate the +appropriate rtl instructions. It is used only when compiling the end of +@code{main}. + +@item NEED_ATEXIT +@findex NEED_ATEXIT +Define this if the target system lacks the function @code{atexit} +from the ISO C standard. If this macro is defined, a default definition +will be provided to support C++. If @code{ON_EXIT} is not defined, +a default @code{exit} function will also be provided. + +@item ON_EXIT +@findex ON_EXIT +Define this macro if the target has another way to implement atexit +functionality without replacing @code{exit}. For instance, SunOS 4 has +a similar @code{on_exit} library function. + +The definition should be a functional macro which can be used just like +the @code{atexit} function. + +@item EXIT_BODY +@findex EXIT_BODY +Define this if your @code{exit} function needs to do something +besides calling an external function @code{_cleanup} before +terminating with @code{_exit}. The @code{EXIT_BODY} macro is +only needed if @code{NEED_ATEXIT} is defined and @code{ON_EXIT} is not +defined. + +@findex INSN_SETS_ARE_DELAYED +@item INSN_SETS_ARE_DELAYED (@var{insn}) +Define this macro as a C expression that is nonzero if it is safe for the +delay slot scheduler to place instructions in the delay slot of @var{insn}, +even if they appear to use a resource set or clobbered in @var{insn}. +@var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that +every @code{call_insn} has this behavior. On machines where some @code{insn} +or @code{jump_insn} is really a function call and hence has this behavior, +you should define this macro. + +You need not define this macro if it would always return zero. + +@findex INSN_REFERENCES_ARE_DELAYED +@item INSN_REFERENCES_ARE_DELAYED (@var{insn}) +Define this macro as a C expression that is nonzero if it is safe for the +delay slot scheduler to place instructions in the delay slot of @var{insn}, +even if they appear to set or clobber a resource referenced in @var{insn}. +@var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where +some @code{insn} or @code{jump_insn} is really a function call and its operands +are registers whose use is actually in the subroutine it calls, you should +define this macro. Doing so allows the delay slot scheduler to move +instructions which copy arguments into the argument registers into the delay +slot of @var{insn}. + +You need not define this macro if it would always return zero. + +@findex MACHINE_DEPENDENT_REORG +@item MACHINE_DEPENDENT_REORG (@var{insn}) +In rare cases, correct code generation requires extra machine +dependent processing between the second jump optimization pass and +delayed branch scheduling. On those machines, define this macro as a C +statement to act on the code starting at @var{insn}. + +@findex MULTIPLE_SYMBOL_SPACES +@item MULTIPLE_SYMBOL_SPACES +Define this macro if in some cases global symbols from one translation +unit may not be bound to undefined symbols in another translation unit +without user intervention. For instance, under Microsoft Windows +symbols must be explicitly imported from shared libraries (DLLs). + +@findex MD_ASM_CLOBBERS +@item MD_ASM_CLOBBERS (@var{clobbers}) +A C statement that adds to @var{clobbers} @code{STRING_CST} trees for +any hard regs the port wishes to automatically clobber for all asms. + +@findex MAX_INTEGER_COMPUTATION_MODE +@item MAX_INTEGER_COMPUTATION_MODE +Define this to the largest integer machine mode which can be used for +operations other than load, store and copy operations. + +You need only define this macro if the target holds values larger than +@code{word_mode} in general purpose registers. Most targets should not define +this macro. + +@findex MATH_LIBRARY +@item MATH_LIBRARY +Define this macro as a C string constant for the linker argument to link +in the system math library, or @samp{""} if the target does not have a +separate math library. + +You need only define this macro if the default of @samp{"-lm"} is wrong. + +@findex LIBRARY_PATH_ENV +@item LIBRARY_PATH_ENV +Define this macro as a C string constant for the environment variable that +specifies where the linker should look for libraries. + +You need only define this macro if the default of @samp{"LIBRARY_PATH"} +is wrong. + +@findex TARGET_HAS_F_SETLKW +@item TARGET_HAS_F_SETLKW +Define this macro if the target supports file locking with fcntl / F_SETLKW@. +Note that this functionality is part of POSIX@. +Defining @code{TARGET_HAS_F_SETLKW} will enable the test coverage code +to use file locking when exiting a program, which avoids race conditions +if the program has forked. + +@findex MAX_CONDITIONAL_EXECUTE +@item MAX_CONDITIONAL_EXECUTE + +A C expression for the maximum number of instructions to execute via +conditional execution instructions instead of a branch. A value of +@code{BRANCH_COST}+1 is the default if the machine does not use cc0, and +1 if it does use cc0. + +@findex IFCVT_MODIFY_TESTS +@item IFCVT_MODIFY_TESTS +A C expression to modify the tests in @code{TRUE_EXPR}, and +@code{FALSE_EXPR} for use in converting insns in @code{TEST_BB}, +@code{THEN_BB}, @code{ELSE_BB}, and @code{JOIN_BB} basic blocks to +conditional execution. Set either @code{TRUE_EXPR} or @code{FALSE_EXPR} +to a null pointer if the tests cannot be converted. + +@findex IFCVT_MODIFY_INSN +@item IFCVT_MODIFY_INSN +A C expression to modify the @code{PATTERN} of an @code{INSN} that is to +be converted to conditional execution format. + +@findex IFCVT_MODIFY_FINAL +@item IFCVT_MODIFY_FINAL +A C expression to perform any final machine dependent modifications in +converting code to conditional execution in the basic blocks +@code{TEST_BB}, @code{THEN_BB}, @code{ELSE_BB}, and @code{JOIN_BB}. + +@findex IFCVT_MODIFY_CANCEL +@item IFCVT_MODIFY_CANCEL +A C expression to cancel any machine dependent modifications in +converting code to conditional execution in the basic blocks +@code{TEST_BB}, @code{THEN_BB}, @code{ELSE_BB}, and @code{JOIN_BB}. +@end table + +@deftypefn {Target Hook} void TARGET_INIT_BUILTINS () +Define this hook if you have any machine-specific built-in functions +that need to be defined. It should be a function that performs the +necessary setup. + +Machine specific built-in functions can be useful to expand special machine +instructions that would otherwise not normally be generated because +they have no equivalent in the source language (for example, SIMD vector +instructions or prefetch instructions). + +To create a built-in function, call the function @code{builtin_function} +which is defined by the language front end. You can use any type nodes set +up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2}; +only language front ends that use those two functions will call +@samp{TARGET_INIT_BUILTINS}. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, enum machine_mode @var{mode}, int @var{ignore}) + +Expand a call to a machine specific built-in function that was set up by +@samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the +function call; the result should go to @var{target} if that is +convenient, and have mode @var{mode} if that is convenient. +@var{subtarget} may be used as the target for computing one of +@var{exp}'s operands. @var{ignore} is nonzero if the value is to be +ignored. This function should return the result of the call to the +built-in function. +@end deftypefn + +@table @code +@findex MD_CAN_REDIRECT_BRANCH +@item MD_CAN_REDIRECT_BRANCH(@var{branch1}, @var{branch2}) + +Take a branch insn in @var{branch1} and another in @var{branch2}. +Return true if redirecting @var{branch1} to the destination of +@var{branch2} is possible. + +On some targets, branches may have a limited range. Optimizing the +filling of delay slots can result in branches being redirected, and this +may in turn cause a branch offset to overflow. + +@findex ALLOCATE_INITIAL_VALUE +@item ALLOCATE_INITIAL_VALUE(@var{hard_reg}) + +When the initial value of a hard register has been copied in a pseudo +register, it is often not necessary to actually allocate another register +to this pseudo register, because the original hard register or a stack slot +it has been saved into can be used. @code{ALLOCATE_INITIAL_VALUE}, if +defined, is called at the start of register allocation once for each +hard register that had its initial value copied by using +@code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}. +Possible values are @code{NULL_RTX}, if you don't want +to do any special allocation, a @code{REG} rtx---that would typically be +the hard register itself, if it is known not to be clobbered---or a +@code{MEM}. +If you are returning a @code{MEM}, this is only a hint for the allocator; +it might decide to use another register anyways. +You may use @code{current_function_leaf_function} in the definition of the +macro, functions that use @code{REG_N_SETS}, to determine if the hard +register in question will not be clobbered. + +@findex TARGET_OBJECT_SUFFIX +@item TARGET_OBJECT_SUFFIX +Define this macro to be a C string representing the suffix for object +files on your target machine. If you do not define this macro, GCC will +use @samp{.o} as the suffix for object files. + +@findex TARGET_EXECUTABLE_SUFFIX +@item TARGET_EXECUTABLE_SUFFIX +Define this macro to be a C string representing the suffix to be +automatically added to executable files on your target machine. If you +do not define this macro, GCC will use the null string as the suffix for +executable files. + +@findex COLLECT_EXPORT_LIST +@item COLLECT_EXPORT_LIST +If defined, @code{collect2} will scan the individual object files +specified on its command line and create an export list for the linker. +Define this macro for systems like AIX, where the linker discards +object files that are not referenced from @code{main} and uses export +lists. + +@end table diff --git a/contrib/gcc/doc/trouble.texi b/contrib/gcc/doc/trouble.texi new file mode 100644 index 000000000000..09026fe57f02 --- /dev/null +++ b/contrib/gcc/doc/trouble.texi @@ -0,0 +1,1462 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Trouble +@chapter Known Causes of Trouble with GCC +@cindex bugs, known +@cindex installation trouble +@cindex known causes of trouble + +This section describes known problems that affect users of GCC@. Most +of these are not GCC bugs per se---if they were, we would fix them. +But the result for a user may be like the result of a bug. + +Some of these problems are due to bugs in other software, some are +missing features that are too much work to add, and some are places +where people's opinions differ as to what is best. + +@menu +* Actual Bugs:: Bugs we will fix later. +* Cross-Compiler Problems:: Common problems of cross compiling with GCC. +* Interoperation:: Problems using GCC with other compilers, + and with certain linkers, assemblers and debuggers. +* External Bugs:: Problems compiling certain programs. +* Incompatibilities:: GCC is incompatible with traditional C. +* Fixed Headers:: GCC uses corrected versions of system header files. + This is necessary, but doesn't always work smoothly. +* Standard Libraries:: GCC uses the system C library, which might not be + compliant with the ISO C standard. +* Disappointments:: Regrettable things we can't change, but not quite bugs. +* C++ Misunderstandings:: Common misunderstandings with GNU C++. +* Protoize Caveats:: Things to watch out for when using @code{protoize}. +* Non-bugs:: Things we think are right, but some others disagree. +* Warnings and Errors:: Which problems in your code get warnings, + and which get errors. +@end menu + +@node Actual Bugs +@section Actual Bugs We Haven't Fixed Yet + +@itemize @bullet +@item +The @code{fixincludes} script interacts badly with automounters; if the +directory of system header files is automounted, it tends to be +unmounted while @code{fixincludes} is running. This would seem to be a +bug in the automounter. We don't know any good way to work around it. + +@item +The @code{fixproto} script will sometimes add prototypes for the +@code{sigsetjmp} and @code{siglongjmp} functions that reference the +@code{jmp_buf} type before that type is defined. To work around this, +edit the offending file and place the typedef in front of the +prototypes. + +@item +@opindex pedantic-errors +When @option{-pedantic-errors} is specified, GCC will incorrectly give +an error message when a function name is specified in an expression +involving the comma operator. +@end itemize + +@node Cross-Compiler Problems +@section Cross-Compiler Problems + +You may run into problems with cross compilation on certain machines, +for several reasons. + +@itemize @bullet +@item +Cross compilation can run into trouble for certain machines because +some target machines' assemblers require floating point numbers to be +written as @emph{integer} constants in certain contexts. + +The compiler writes these integer constants by examining the floating +point value as an integer and printing that integer, because this is +simple to write and independent of the details of the floating point +representation. But this does not work if the compiler is running on +a different machine with an incompatible floating point format, or +even a different byte-ordering. + +In addition, correct constant folding of floating point values +requires representing them in the target machine's format. +(The C standard does not quite require this, but in practice +it is the only way to win.) + +It is now possible to overcome these problems by defining macros such +as @code{REAL_VALUE_TYPE}. But doing so is a substantial amount of +work for each target machine. +@xref{Cross-compilation,,Cross Compilation and Floating Point, +gccint, GNU Compiler Collection (GCC) Internals}. + +@item +At present, the program @file{mips-tfile} which adds debug +support to object files on MIPS systems does not work in a cross +compile environment. +@end itemize + +@node Interoperation +@section Interoperation + +This section lists various difficulties encountered in using GCC +together with other compilers or with the assemblers, linkers, +libraries and debuggers on certain systems. + +@itemize @bullet +@item +G++ does not do name mangling in the same way as other C++ +compilers. This means that object files compiled with one compiler +cannot be used with another. + +This effect is intentional, to protect you from more subtle problems. +Compilers differ as to many internal details of C++ implementation, +including: how class instances are laid out, how multiple inheritance is +implemented, and how virtual function calls are handled. If the name +encoding were made the same, your programs would link against libraries +provided from other compilers---but the programs would then crash when +run. Incompatible libraries are then detected at link time, rather than +at run time. + +@item +Older GDB versions sometimes fail to read the output of GCC version +2. If you have trouble, get GDB version 4.4 or later. + +@item +@cindex DBX +DBX rejects some files produced by GCC, though it accepts similar +constructs in output from PCC@. Until someone can supply a coherent +description of what is valid DBX input and what is not, there is +nothing I can do about these problems. You are on your own. + +@item +The GNU assembler (GAS) does not support PIC@. To generate PIC code, you +must use some other assembler, such as @file{/bin/as}. + +@item +On some BSD systems, including some versions of Ultrix, use of profiling +causes static variable destructors (currently used only in C++) not to +be run. + +@ignore +@cindex @code{vfork}, for the Sun-4 +@item +There is a bug in @code{vfork} on the Sun-4 which causes the registers +of the child process to clobber those of the parent. Because of this, +programs that call @code{vfork} are likely to lose when compiled +optimized with GCC when the child code alters registers which contain +C variables in the parent. This affects variables which are live in the +parent across the call to @code{vfork}. + +If you encounter this, you can work around the problem by declaring +variables @code{volatile} in the function that calls @code{vfork}, until +the problem goes away, or by not declaring them @code{register} and not +using @option{-O} for those source files. +@end ignore + +@item +On some SGI systems, when you use @option{-lgl_s} as an option, +it gets translated magically to @samp{-lgl_s -lX11_s -lc_s}. +Naturally, this does not happen when you use GCC@. +You must specify all three options explicitly. + +@item +On a Sparc, GCC aligns all values of type @code{double} on an 8-byte +boundary, and it expects every @code{double} to be so aligned. The Sun +compiler usually gives @code{double} values 8-byte alignment, with one +exception: function arguments of type @code{double} may not be aligned. + +As a result, if a function compiled with Sun CC takes the address of an +argument of type @code{double} and passes this pointer of type +@code{double *} to a function compiled with GCC, dereferencing the +pointer may cause a fatal signal. + +One way to solve this problem is to compile your entire program with GCC@. +Another solution is to modify the function that is compiled with +Sun CC to copy the argument into a local variable; local variables +are always properly aligned. A third solution is to modify the function +that uses the pointer to dereference it via the following function +@code{access_double} instead of directly with @samp{*}: + +@smallexample +inline double +access_double (double *unaligned_ptr) +@{ + union d2i @{ double d; int i[2]; @}; + + union d2i *p = (union d2i *) unaligned_ptr; + union d2i u; + + u.i[0] = p->i[0]; + u.i[1] = p->i[1]; + + return u.d; +@} +@end smallexample + +@noindent +Storing into the pointer can be done likewise with the same union. + +@item +On Solaris, the @code{malloc} function in the @file{libmalloc.a} library +may allocate memory that is only 4 byte aligned. Since GCC on the +Sparc assumes that doubles are 8 byte aligned, this may result in a +fatal signal if doubles are stored in memory allocated by the +@file{libmalloc.a} library. + +The solution is to not use the @file{libmalloc.a} library. Use instead +@code{malloc} and related functions from @file{libc.a}; they do not have +this problem. + +@item +Sun forgot to include a static version of @file{libdl.a} with some +versions of SunOS (mainly 4.1). This results in undefined symbols when +linking static binaries (that is, if you use @option{-static}). If you +see undefined symbols @code{_dlclose}, @code{_dlsym} or @code{_dlopen} +when linking, compile and link against the file +@file{mit/util/misc/dlsym.c} from the MIT version of X windows. + +@item +The 128-bit long double format that the Sparc port supports currently +works by using the architecturally defined quad-word floating point +instructions. Since there is no hardware that supports these +instructions they must be emulated by the operating system. Long +doubles do not work in Sun OS versions 4.0.3 and earlier, because the +kernel emulator uses an obsolete and incompatible format. Long doubles +do not work in Sun OS version 4.1.1 due to a problem in a Sun library. +Long doubles do work on Sun OS versions 4.1.2 and higher, but GCC +does not enable them by default. Long doubles appear to work in Sun OS +5.x (Solaris 2.x). + +@item +On HP-UX version 9.01 on the HP PA, the HP compiler @code{cc} does not +compile GCC correctly. We do not yet know why. However, GCC +compiled on earlier HP-UX versions works properly on HP-UX 9.01 and can +compile itself properly on 9.01. + +@item +On the HP PA machine, ADB sometimes fails to work on functions compiled +with GCC@. Specifically, it fails to work on functions that use +@code{alloca} or variable-size arrays. This is because GCC doesn't +generate HP-UX unwind descriptors for such functions. It may even be +impossible to generate them. + +@item +Debugging (@option{-g}) is not supported on the HP PA machine, unless you use +the preliminary GNU tools. + +@item +Taking the address of a label may generate errors from the HP-UX +PA assembler. GAS for the PA does not have this problem. + +@item +Using floating point parameters for indirect calls to static functions +will not work when using the HP assembler. There simply is no way for GCC +to specify what registers hold arguments for static functions when using +the HP assembler. GAS for the PA does not have this problem. + +@item +In extremely rare cases involving some very large functions you may +receive errors from the HP linker complaining about an out of bounds +unconditional branch offset. This used to occur more often in previous +versions of GCC, but is now exceptionally rare. If you should run +into it, you can work around by making your function smaller. + +@item +GCC compiled code sometimes emits warnings from the HP-UX assembler of +the form: + +@smallexample +(warning) Use of GR3 when + frame >= 8192 may cause conflict. +@end smallexample + +These warnings are harmless and can be safely ignored. + +@item +On the IBM RS/6000, compiling code of the form + +@smallexample +extern int foo; + +@dots{} foo @dots{} + +static int foo; +@end smallexample + +@noindent +will cause the linker to report an undefined symbol @code{foo}. +Although this behavior differs from most other systems, it is not a +bug because redefining an @code{extern} variable as @code{static} +is undefined in ISO C@. + +@item +In extremely rare cases involving some very large functions you may +receive errors from the AIX Assembler complaining about a displacement +that is too large. If you should run into it, you can work around by +making your function smaller. + +@item +The @file{libstdc++.a} library in GCC relies on the SVR4 dynamic +linker semantics which merges global symbols between libraries and +applications, especially necessary for C++ streams functionality. +This is not the default behavior of AIX shared libraries and dynamic +linking. @file{libstdc++.a} is built on AIX with ``runtime-linking'' +enabled so that symbol merging can occur. To utilize this feature, +the application linked with @file{libstdc++.a} must include the +@option{-Wl,-brtl} flag on the link line. G++ cannot impose this +because this option may interfere with the semantics of the user +program and users may not always use @samp{g++} to link his or her +application. Applications are not required to use the +@option{-Wl,-brtl} flag on the link line---the rest of the +@file{libstdc++.a} library which is not dependent on the symbol +merging semantics will continue to function correctly. + +@item +An application can interpose its own definition of functions for +functions invoked by @file{libstdc++.a} with ``runtime-linking'' +enabled on AIX. To accomplish this the application must be linked +with ``runtime-linking'' option and the functions explicitly must be +exported by the application (@option{-Wl,-brtl,-bE:exportfile}). + +@item +AIX on the RS/6000 provides support (NLS) for environments outside of +the United States. Compilers and assemblers use NLS to support +locale-specific representations of various objects including +floating-point numbers (@samp{.} vs @samp{,} for separating decimal +fractions). There have been problems reported where the library linked +with GCC does not produce the same floating-point formats that the +assembler accepts. If you have this problem, set the @env{LANG} +environment variable to @samp{C} or @samp{En_US}. + +@item +@opindex fdollars-in-identifiers +Even if you specify @option{-fdollars-in-identifiers}, +you cannot successfully use @samp{$} in identifiers on the RS/6000 due +to a restriction in the IBM assembler. GAS supports these +identifiers. + +@item +@opindex mno-serialize-volatile +There is an assembler bug in versions of DG/UX prior to 5.4.2.01 that +occurs when the @samp{fldcr} instruction is used. GCC uses +@samp{fldcr} on the 88100 to serialize volatile memory references. Use +the option @option{-mno-serialize-volatile} if your version of the +assembler has this bug. + +@item +On VMS, GAS versions 1.38.1 and earlier may cause spurious warning +messages from the linker. These warning messages complain of mismatched +psect attributes. You can ignore them. + +@item +On NewsOS version 3, if you include both of the files @file{stddef.h} +and @file{sys/types.h}, you get an error because there are two typedefs +of @code{size_t}. You should change @file{sys/types.h} by adding these +lines around the definition of @code{size_t}: + +@smallexample +#ifndef _SIZE_T +#define _SIZE_T +@var{actual-typedef-here} +#endif +@end smallexample + +@cindex Alliant +@item +On the Alliant, the system's own convention for returning structures +and unions is unusual, and is not compatible with GCC no matter +what options are used. + +@cindex RT PC +@cindex IBM RT PC +@item +@opindex mhc-struct-return +On the IBM RT PC, the MetaWare HighC compiler (hc) uses a different +convention for structure and union returning. Use the option +@option{-mhc-struct-return} to tell GCC to use a convention compatible +with it. + +@cindex VAX calling convention +@cindex Ultrix calling convention +@item +@opindex fcall-saved +On Ultrix, the Fortran compiler expects registers 2 through 5 to be saved +by function calls. However, the C compiler uses conventions compatible +with BSD Unix: registers 2 through 5 may be clobbered by function calls. + +GCC uses the same convention as the Ultrix C compiler. You can use +these options to produce code compatible with the Fortran compiler: + +@smallexample +-fcall-saved-r2 -fcall-saved-r3 -fcall-saved-r4 -fcall-saved-r5 +@end smallexample + +@item +On the WE32k, you may find that programs compiled with GCC do not +work with the standard shared C library. You may need to link with +the ordinary C compiler. If you do so, you must specify the following +options: + +@smallexample +-L/usr/local/lib/gcc-lib/we32k-att-sysv/2.8.1 -lgcc -lc_s +@end smallexample + +The first specifies where to find the library @file{libgcc.a} +specified with the @option{-lgcc} option. + +GCC does linking by invoking @command{ld}, just as @command{cc} does, and +there is no reason why it @emph{should} matter which compilation program +you use to invoke @command{ld}. If someone tracks this problem down, +it can probably be fixed easily. + +@item +On the Alpha, you may get assembler errors about invalid syntax as a +result of floating point constants. This is due to a bug in the C +library functions @code{ecvt}, @code{fcvt} and @code{gcvt}. Given valid +floating point numbers, they sometimes print @samp{NaN}. + +@item +On Irix 4.0.5F (and perhaps in some other versions), an assembler bug +sometimes reorders instructions incorrectly when optimization is turned +on. If you think this may be happening to you, try using the GNU +assembler; GAS version 2.1 supports ECOFF on Irix. + +@opindex noasmopt +Or use the @option{-noasmopt} option when you compile GCC with itself, +and then again when you compile your program. (This is a temporary +kludge to turn off assembler optimization on Irix.) If this proves to +be what you need, edit the assembler spec in the file @file{specs} so +that it unconditionally passes @option{-O0} to the assembler, and never +passes @option{-O2} or @option{-O3}. +@end itemize + +@node External Bugs +@section Problems Compiling Certain Programs + +@c prevent bad page break with this line +Certain programs have problems compiling. + +@itemize @bullet +@item +Parse errors may occur compiling X11 on a Decstation running Ultrix 4.2 +because of problems in DEC's versions of the X11 header files +@file{X11/Xlib.h} and @file{X11/Xutil.h}. People recommend adding +@option{-I/usr/include/mit} to use the MIT versions of the header files, +using the @option{-traditional} switch to turn off ISO C, or fixing the +header files by adding this: + +@example +#ifdef __STDC__ +#define NeedFunctionPrototypes 0 +#endif +@end example + +@item +On various 386 Unix systems derived from System V, including SCO, ISC, +and ESIX, you may get error messages about running out of virtual memory +while compiling certain programs. + +You can prevent this problem by linking GCC with the GNU malloc +(which thus replaces the malloc that comes with the system). GNU malloc +is available as a separate package, and also in the file +@file{src/gmalloc.c} in the GNU Emacs 19 distribution. + +If you have installed GNU malloc as a separate library package, use this +option when you relink GCC: + +@example +MALLOC=/usr/local/lib/libgmalloc.a +@end example + +Alternatively, if you have compiled @file{gmalloc.c} from Emacs 19, copy +the object file to @file{gmalloc.o} and use this option when you relink +GCC: + +@example +MALLOC=gmalloc.o +@end example +@end itemize + +@node Incompatibilities +@section Incompatibilities of GCC +@cindex incompatibilities of GCC +@opindex traditional + +There are several noteworthy incompatibilities between GNU C and K&R +(non-ISO) versions of C@. The @option{-traditional} option +eliminates many of these incompatibilities, @emph{but not all}, by +telling GCC to behave like a K&R C compiler. + +@itemize @bullet +@cindex string constants +@cindex read-only strings +@cindex shared strings +@item +GCC normally makes string constants read-only. If several +identical-looking string constants are used, GCC stores only one +copy of the string. + +@cindex @code{mktemp}, and constant strings +One consequence is that you cannot call @code{mktemp} with a string +constant argument. The function @code{mktemp} always alters the +string its argument points to. + +@cindex @code{sscanf}, and constant strings +@cindex @code{fscanf}, and constant strings +@cindex @code{scanf}, and constant strings +Another consequence is that @code{sscanf} does not work on some systems +when passed a string constant as its format control string or input. +This is because @code{sscanf} incorrectly tries to write into the string +constant. Likewise @code{fscanf} and @code{scanf}. + +@opindex fwritable-strings +The best solution to these problems is to change the program to use +@code{char}-array variables with initialization strings for these +purposes instead of string constants. But if this is not possible, +you can use the @option{-fwritable-strings} flag, which directs GCC +to handle string constants the same way most C compilers do. +@option{-traditional} also has this effect, among others. + +@item +@code{-2147483648} is positive. + +This is because 2147483648 cannot fit in the type @code{int}, so +(following the ISO C rules) its data type is @code{unsigned long int}. +Negating this value yields 2147483648 again. + +@item +GCC does not substitute macro arguments when they appear inside of +string constants. For example, the following macro in GCC + +@example +#define foo(a) "a" +@end example + +@noindent +will produce output @code{"a"} regardless of what the argument @var{a} is. + +The @option{-traditional} option directs GCC to handle such cases +(among others) in the old-fashioned (non-ISO) fashion. + +@cindex @code{setjmp} incompatibilities +@cindex @code{longjmp} incompatibilities +@item +When you use @code{setjmp} and @code{longjmp}, the only automatic +variables guaranteed to remain valid are those declared +@code{volatile}. This is a consequence of automatic register +allocation. Consider this function: + +@example +jmp_buf j; + +foo () +@{ + int a, b; + + a = fun1 (); + if (setjmp (j)) + return a; + + a = fun2 (); + /* @r{@code{longjmp (j)} may occur in @code{fun3}.} */ + return a + fun3 (); +@} +@end example + +Here @code{a} may or may not be restored to its first value when the +@code{longjmp} occurs. If @code{a} is allocated in a register, then +its first value is restored; otherwise, it keeps the last value stored +in it. + +@opindex W +If you use the @option{-W} option with the @option{-O} option, you will +get a warning when GCC thinks such a problem might be possible. + +The @option{-traditional} option directs GCC to put variables in +the stack by default, rather than in registers, in functions that +call @code{setjmp}. This results in the behavior found in +traditional C compilers. + +@item +Programs that use preprocessing directives in the middle of macro +arguments do not work with GCC@. For example, a program like this +will not work: + +@example +@group +foobar ( +#define luser + hack) +@end group +@end example + +ISO C does not permit such a construct. It would make sense to support +it when @option{-traditional} is used, but it is too much work to +implement. + +@item +K&R compilers allow comments to cross over an inclusion boundary +(i.e.@: started in an include file and ended in the including file). I think +this would be quite ugly and can't imagine it could be needed. + +@cindex external declaration scope +@cindex scope of external declarations +@cindex declaration scope +@item +Declarations of external variables and functions within a block apply +only to the block containing the declaration. In other words, they +have the same scope as any other declaration in the same place. + +In some other C compilers, a @code{extern} declaration affects all the +rest of the file even if it happens within a block. + +The @option{-traditional} option directs GCC to treat all @code{extern} +declarations as global, like traditional compilers. + +@item +In traditional C, you can combine @code{long}, etc., with a typedef name, +as shown here: + +@example +typedef int foo; +typedef long foo bar; +@end example + +In ISO C, this is not allowed: @code{long} and other type modifiers +require an explicit @code{int}. Because this criterion is expressed +by Bison grammar rules rather than C code, the @option{-traditional} +flag cannot alter it. + +@cindex typedef names as function parameters +@item +PCC allows typedef names to be used as function parameters. The +difficulty described immediately above applies here too. + +@item +When in @option{-traditional} mode, GCC allows the following erroneous +pair of declarations to appear together in a given scope: + +@example +typedef int foo; +typedef foo foo; +@end example + +@item +GCC treats all characters of identifiers as significant, even when in +@option{-traditional} mode. According to K&R-1 (2.2), ``No more than the +first eight characters are significant, although more may be used.''. +Also according to K&R-1 (2.2), ``An identifier is a sequence of letters +and digits; the first character must be a letter. The underscore _ +counts as a letter.'', but GCC also allows dollar signs in identifiers. + +@cindex whitespace +@item +PCC allows whitespace in the middle of compound assignment operators +such as @samp{+=}. GCC, following the ISO standard, does not +allow this. The difficulty described immediately above applies here +too. + +@cindex apostrophes +@cindex ' +@item +GCC complains about unterminated character constants inside of +preprocessing conditionals that fail. Some programs have English +comments enclosed in conditionals that are guaranteed to fail; if these +comments contain apostrophes, GCC will probably report an error. For +example, this code would produce an error: + +@example +#if 0 +You can't expect this to work. +#endif +@end example + +The best solution to such a problem is to put the text into an actual +C comment delimited by @samp{/*@dots{}*/}. However, +@option{-traditional} suppresses these error messages. + +@item +Many user programs contain the declaration @samp{long time ();}. In the +past, the system header files on many systems did not actually declare +@code{time}, so it did not matter what type your program declared it to +return. But in systems with ISO C headers, @code{time} is declared to +return @code{time_t}, and if that is not the same as @code{long}, then +@samp{long time ();} is erroneous. + +The solution is to change your program to use appropriate system headers +(@code{} on systems with ISO C headers) and not to declare +@code{time} if the system header files declare it, or failing that to +use @code{time_t} as the return type of @code{time}. + +@cindex @code{float} as function value type +@item +When compiling functions that return @code{float}, PCC converts it to +a double. GCC actually returns a @code{float}. If you are concerned +with PCC compatibility, you should declare your functions to return +@code{double}; you might as well say what you mean. + +@cindex structures +@cindex unions +@item +When compiling functions that return structures or unions, GCC +output code normally uses a method different from that used on most +versions of Unix. As a result, code compiled with GCC cannot call +a structure-returning function compiled with PCC, and vice versa. + +The method used by GCC is as follows: a structure or union which is +1, 2, 4 or 8 bytes long is returned like a scalar. A structure or union +with any other size is stored into an address supplied by the caller +(usually in a special, fixed register, but on some machines it is passed +on the stack). The machine-description macros @code{STRUCT_VALUE} and +@code{STRUCT_INCOMING_VALUE} tell GCC where to pass this address. + +By contrast, PCC on most target machines returns structures and unions +of any size by copying the data into an area of static storage, and then +returning the address of that storage as if it were a pointer value. +The caller must copy the data from that memory area to the place where +the value is wanted. GCC does not use this method because it is +slower and nonreentrant. + +On some newer machines, PCC uses a reentrant convention for all +structure and union returning. GCC on most of these machines uses a +compatible convention when returning structures and unions in memory, +but still returns small structures and unions in registers. + +@opindex fpcc-struct-return +You can tell GCC to use a compatible convention for all structure and +union returning with the option @option{-fpcc-struct-return}. + +@cindex preprocessing tokens +@cindex preprocessing numbers +@item +GCC complains about program fragments such as @samp{0x74ae-0x4000} +which appear to be two hexadecimal constants separated by the minus +operator. Actually, this string is a single @dfn{preprocessing token}. +Each such token must correspond to one token in C@. Since this does not, +GCC prints an error message. Although it may appear obvious that what +is meant is an operator and two values, the ISO C standard specifically +requires that this be treated as erroneous. + +A @dfn{preprocessing token} is a @dfn{preprocessing number} if it +begins with a digit and is followed by letters, underscores, digits, +periods and @samp{e+}, @samp{e-}, @samp{E+}, @samp{E-}, @samp{p+}, +@samp{p-}, @samp{P+}, or @samp{P-} character sequences. (In strict C89 +mode, the sequences @samp{p+}, @samp{p-}, @samp{P+} and @samp{P-} cannot +appear in preprocessing numbers.) + +To make the above program fragment valid, place whitespace in front of +the minus sign. This whitespace will end the preprocessing number. +@end itemize + +@node Fixed Headers +@section Fixed Header Files + +GCC needs to install corrected versions of some system header files. +This is because most target systems have some header files that won't +work with GCC unless they are changed. Some have bugs, some are +incompatible with ISO C, and some depend on special features of other +compilers. + +Installing GCC automatically creates and installs the fixed header +files, by running a program called @code{fixincludes} (or for certain +targets an alternative such as @code{fixinc.svr4}). Normally, you +don't need to pay attention to this. But there are cases where it +doesn't do the right thing automatically. + +@itemize @bullet +@item +If you update the system's header files, such as by installing a new +system version, the fixed header files of GCC are not automatically +updated. The easiest way to update them is to reinstall GCC@. (If +you want to be clever, look in the makefile and you can find a +shortcut.) + +@item +On some systems, in particular SunOS 4, header file directories contain +machine-specific symbolic links in certain places. This makes it +possible to share most of the header files among hosts running the +same version of SunOS 4 on different machine models. + +The programs that fix the header files do not understand this special +way of using symbolic links; therefore, the directory of fixed header +files is good only for the machine model used to build it. + +In SunOS 4, only programs that look inside the kernel will notice the +difference between machine models. Therefore, for most purposes, you +need not be concerned about this. + +It is possible to make separate sets of fixed header files for the +different machine models, and arrange a structure of symbolic links so +as to use the proper set, but you'll have to do this by hand. + +@item +On Lynxos, GCC by default does not fix the header files. This is +because bugs in the shell cause the @code{fixincludes} script to fail. + +This means you will encounter problems due to bugs in the system header +files. It may be no comfort that they aren't GCC's fault, but it +does mean that there's nothing for us to do about them. +@end itemize + +@node Standard Libraries +@section Standard Libraries + +@opindex Wall +GCC by itself attempts to be a conforming freestanding implementation. +@xref{Standards,,Language Standards Supported by GCC}, for details of +what this means. Beyond the library facilities required of such an +implementation, the rest of the C library is supplied by the vendor of +the operating system. If that C library doesn't conform to the C +standards, then your programs might get warnings (especially when using +@option{-Wall}) that you don't expect. + +For example, the @code{sprintf} function on SunOS 4.1.3 returns +@code{char *} while the C standard says that @code{sprintf} returns an +@code{int}. The @code{fixincludes} program could make the prototype for +this function match the Standard, but that would be wrong, since the +function will still return @code{char *}. + +If you need a Standard compliant library, then you need to find one, as +GCC does not provide one. The GNU C library (called @code{glibc}) +provides ISO C, POSIX, BSD, SystemV and X/Open compatibility for +GNU/Linux and HURD-based GNU systems; no recent version of it supports +other systems, though some very old versions did. Version 2.2 of the +GNU C library includes nearly complete C99 support. You could also ask +your operating system vendor if newer libraries are available. + +@node Disappointments +@section Disappointments and Misunderstandings + +These problems are perhaps regrettable, but we don't know any practical +way around them. + +@itemize @bullet +@item +Certain local variables aren't recognized by debuggers when you compile +with optimization. + +This occurs because sometimes GCC optimizes the variable out of +existence. There is no way to tell the debugger how to compute the +value such a variable ``would have had'', and it is not clear that would +be desirable anyway. So GCC simply does not mention the eliminated +variable when it writes debugging information. + +You have to expect a certain amount of disagreement between the +executable and your source code, when you use optimization. + +@cindex conflicting types +@cindex scope of declaration +@item +Users often think it is a bug when GCC reports an error for code +like this: + +@example +int foo (struct mumble *); + +struct mumble @{ @dots{} @}; + +int foo (struct mumble *x) +@{ @dots{} @} +@end example + +This code really is erroneous, because the scope of @code{struct +mumble} in the prototype is limited to the argument list containing it. +It does not refer to the @code{struct mumble} defined with file scope +immediately below---they are two unrelated types with similar names in +different scopes. + +But in the definition of @code{foo}, the file-scope type is used +because that is available to be inherited. Thus, the definition and +the prototype do not match, and you get an error. + +This behavior may seem silly, but it's what the ISO standard specifies. +It is easy enough for you to make your code work by moving the +definition of @code{struct mumble} above the prototype. It's not worth +being incompatible with ISO C just to avoid an error for the example +shown above. + +@item +Accesses to bit-fields even in volatile objects works by accessing larger +objects, such as a byte or a word. You cannot rely on what size of +object is accessed in order to read or write the bit-field; it may even +vary for a given bit-field according to the precise usage. + +If you care about controlling the amount of memory that is accessed, use +volatile but do not use bit-fields. + +@item +GCC comes with shell scripts to fix certain known problems in system +header files. They install corrected copies of various header files in +a special directory where only GCC will normally look for them. The +scripts adapt to various systems by searching all the system header +files for the problem cases that we know about. + +If new system header files are installed, nothing automatically arranges +to update the corrected header files. You will have to reinstall GCC +to fix the new header files. More specifically, go to the build +directory and delete the files @file{stmp-fixinc} and +@file{stmp-headers}, and the subdirectory @code{include}; then do +@samp{make install} again. + +@item +@cindex floating point precision +On 68000 and x86 systems, for instance, you can get paradoxical results +if you test the precise values of floating point numbers. For example, +you can find that a floating point value which is not a NaN is not equal +to itself. This results from the fact that the floating point registers +hold a few more bits of precision than fit in a @code{double} in memory. +Compiled code moves values between memory and floating point registers +at its convenience, and moving them into memory truncates them. + +@opindex ffloat-store +You can partially avoid this problem by using the @option{-ffloat-store} +option (@pxref{Optimize Options}). + +@item +On the MIPS, variable argument functions using @file{varargs.h} +cannot have a floating point value for the first argument. The +reason for this is that in the absence of a prototype in scope, +if the first argument is a floating point, it is passed in a +floating point register, rather than an integer register. + +If the code is rewritten to use the ISO standard @file{stdarg.h} +method of variable arguments, and the prototype is in scope at +the time of the call, everything will work fine. + +@item +On the H8/300 and H8/300H, variable argument functions must be +implemented using the ISO standard @file{stdarg.h} method of +variable arguments. Furthermore, calls to functions using @file{stdarg.h} +variable arguments must have a prototype for the called function +in scope at the time of the call. + +@item +On AIX and other platforms without weak symbol support, templates +need to be instantiated explicitly and symbols for static members +of templates will not be generated. +@end itemize + +@node C++ Misunderstandings +@section Common Misunderstandings with GNU C++ + +@cindex misunderstandings in C++ +@cindex surprises in C++ +@cindex C++ misunderstandings +C++ is a complex language and an evolving one, and its standard +definition (the ISO C++ standard) was only recently completed. As a +result, your C++ compiler may occasionally surprise you, even when its +behavior is correct. This section discusses some areas that frequently +give rise to questions of this sort. + +@menu +* Static Definitions:: Static member declarations are not definitions +* Temporaries:: Temporaries may vanish before you expect +* Copy Assignment:: Copy Assignment operators copy virtual bases twice +@end menu + +@node Static Definitions +@subsection Declare @emph{and} Define Static Members + +@cindex C++ static data, declaring and defining +@cindex static data in C++, declaring and defining +@cindex declaring static data in C++ +@cindex defining static data in C++ +When a class has static data members, it is not enough to @emph{declare} +the static member; you must also @emph{define} it. For example: + +@example +class Foo +@{ + @dots{} + void method(); + static int bar; +@}; +@end example + +This declaration only establishes that the class @code{Foo} has an +@code{int} named @code{Foo::bar}, and a member function named +@code{Foo::method}. But you still need to define @emph{both} +@code{method} and @code{bar} elsewhere. According to the ISO +standard, you must supply an initializer in one (and only one) source +file, such as: + +@example +int Foo::bar = 0; +@end example + +Other C++ compilers may not correctly implement the standard behavior. +As a result, when you switch to @code{g++} from one of these compilers, +you may discover that a program that appeared to work correctly in fact +does not conform to the standard: @code{g++} reports as undefined +symbols any static data members that lack definitions. + +@node Temporaries +@subsection Temporaries May Vanish Before You Expect + +@cindex temporaries, lifetime of +@cindex portions of temporary objects, pointers to +It is dangerous to use pointers or references to @emph{portions} of a +temporary object. The compiler may very well delete the object before +you expect it to, leaving a pointer to garbage. The most common place +where this problem crops up is in classes like string classes, +especially ones that define a conversion function to type @code{char *} +or @code{const char *}---which is one reason why the standard +@code{string} class requires you to call the @code{c_str} member +function. However, any class that returns a pointer to some internal +structure is potentially subject to this problem. + +For example, a program may use a function @code{strfunc} that returns +@code{string} objects, and another function @code{charfunc} that +operates on pointers to @code{char}: + +@example +string strfunc (); +void charfunc (const char *); + +void +f () +@{ + const char *p = strfunc().c_str(); + @dots{} + charfunc (p); + @dots{} + charfunc (p); +@} +@end example + +@noindent +In this situation, it may seem reasonable to save a pointer to the C +string returned by the @code{c_str} member function and use that rather +than call @code{c_str} repeatedly. However, the temporary string +created by the call to @code{strfunc} is destroyed after @code{p} is +initialized, at which point @code{p} is left pointing to freed memory. + +Code like this may run successfully under some other compilers, +particularly obsolete cfront-based compilers that delete temporaries +along with normal local variables. However, the GNU C++ behavior is +standard-conforming, so if your program depends on late destruction of +temporaries it is not portable. + +The safe way to write such code is to give the temporary a name, which +forces it to remain until the end of the scope of the name. For +example: + +@example +string& tmp = strfunc (); +charfunc (tmp.c_str ()); +@end example + +@node Copy Assignment +@subsection Implicit Copy-Assignment for Virtual Bases + +When a base class is virtual, only one subobject of the base class +belongs to each full object. Also, the constructors and destructors are +invoked only once, and called from the most-derived class. However, such +objects behave unspecified when being assigned. For example: + +@example +struct Base@{ + char *name; + Base(char *n) : name(strdup(n))@{@} + Base& operator= (const Base& other)@{ + free (name); + name = strdup (other.name); + @} +@}; + +struct A:virtual Base@{ + int val; + A():Base("A")@{@} +@}; + +struct B:virtual Base@{ + int bval; + B():Base("B")@{@} +@}; + +struct Derived:public A, public B@{ + Derived():Base("Derived")@{@} +@}; + +void func(Derived &d1, Derived &d2) +@{ + d1 = d2; +@} +@end example + +The C++ standard specifies that @samp{Base::Base} is only called once +when constructing or copy-constructing a Derived object. It is +unspecified whether @samp{Base::operator=} is called more than once when +the implicit copy-assignment for Derived objects is invoked (as it is +inside @samp{func} in the example). + +g++ implements the ``intuitive'' algorithm for copy-assignment: assign all +direct bases, then assign all members. In that algorithm, the virtual +base subobject can be encountered many times. In the example, copying +proceeds in the following order: @samp{val}, @samp{name} (via +@code{strdup}), @samp{bval}, and @samp{name} again. + +If application code relies on copy-assignment, a user-defined +copy-assignment operator removes any uncertainties. With such an +operator, the application can define whether and how the virtual base +subobject is assigned. + +@node Protoize Caveats +@section Caveats of using @command{protoize} + +The conversion programs @command{protoize} and @command{unprotoize} can +sometimes change a source file in a way that won't work unless you +rearrange it. + +@itemize @bullet +@item +@command{protoize} can insert references to a type name or type tag before +the definition, or in a file where they are not defined. + +If this happens, compiler error messages should show you where the new +references are, so fixing the file by hand is straightforward. + +@item +There are some C constructs which @command{protoize} cannot figure out. +For example, it can't determine argument types for declaring a +pointer-to-function variable; this you must do by hand. @command{protoize} +inserts a comment containing @samp{???} each time it finds such a +variable; so you can find all such variables by searching for this +string. ISO C does not require declaring the argument types of +pointer-to-function types. + +@item +Using @command{unprotoize} can easily introduce bugs. If the program +relied on prototypes to bring about conversion of arguments, these +conversions will not take place in the program without prototypes. +One case in which you can be sure @command{unprotoize} is safe is when +you are removing prototypes that were made with @command{protoize}; if +the program worked before without any prototypes, it will work again +without them. + +@opindex Wconversion +You can find all the places where this problem might occur by compiling +the program with the @option{-Wconversion} option. It prints a warning +whenever an argument is converted. + +@item +Both conversion programs can be confused if there are macro calls in and +around the text to be converted. In other words, the standard syntax +for a declaration or definition must not result from expanding a macro. +This problem is inherent in the design of C and cannot be fixed. If +only a few functions have confusing macro calls, you can easily convert +them manually. + +@item +@command{protoize} cannot get the argument types for a function whose +definition was not actually compiled due to preprocessing conditionals. +When this happens, @command{protoize} changes nothing in regard to such +a function. @command{protoize} tries to detect such instances and warn +about them. + +You can generally work around this problem by using @command{protoize} step +by step, each time specifying a different set of @option{-D} options for +compilation, until all of the functions have been converted. There is +no automatic way to verify that you have got them all, however. + +@item +Confusion may result if there is an occasion to convert a function +declaration or definition in a region of source code where there is more +than one formal parameter list present. Thus, attempts to convert code +containing multiple (conditionally compiled) versions of a single +function header (in the same vicinity) may not produce the desired (or +expected) results. + +If you plan on converting source files which contain such code, it is +recommended that you first make sure that each conditionally compiled +region of source code which contains an alternative function header also +contains at least one additional follower token (past the final right +parenthesis of the function header). This should circumvent the +problem. + +@item +@command{unprotoize} can become confused when trying to convert a function +definition or declaration which contains a declaration for a +pointer-to-function formal argument which has the same name as the +function being defined or declared. We recommend you avoid such choices +of formal parameter names. + +@item +You might also want to correct some of the indentation by hand and break +long lines. (The conversion programs don't write lines longer than +eighty characters in any case.) +@end itemize + +@node Non-bugs +@section Certain Changes We Don't Want to Make + +This section lists changes that people frequently request, but which +we do not make because we think GCC is better without them. + +@itemize @bullet +@item +Checking the number and type of arguments to a function which has an +old-fashioned definition and no prototype. + +Such a feature would work only occasionally---only for calls that appear +in the same file as the called function, following the definition. The +only way to check all calls reliably is to add a prototype for the +function. But adding a prototype eliminates the motivation for this +feature. So the feature is not worthwhile. + +@item +Warning about using an expression whose type is signed as a shift count. + +Shift count operands are probably signed more often than unsigned. +Warning about this would cause far more annoyance than good. + +@item +Warning about assigning a signed value to an unsigned variable. + +Such assignments must be very common; warning about them would cause +more annoyance than good. + +@item +Warning when a non-void function value is ignored. + +Coming as I do from a Lisp background, I balk at the idea that there is +something dangerous about discarding a value. There are functions that +return values which some callers may find useful; it makes no sense to +clutter the program with a cast to @code{void} whenever the value isn't +useful. + +@item +@opindex fshort-enums +Making @option{-fshort-enums} the default. + +This would cause storage layout to be incompatible with most other C +compilers. And it doesn't seem very important, given that you can get +the same result in other ways. The case where it matters most is when +the enumeration-valued object is inside a structure, and in that case +you can specify a field width explicitly. + +@item +Making bit-fields unsigned by default on particular machines where ``the +ABI standard'' says to do so. + +The ISO C standard leaves it up to the implementation whether a bit-field +declared plain @code{int} is signed or not. This in effect creates two +alternative dialects of C@. + +@opindex fsigned-bitfields +@opindex funsigned-bitfields +The GNU C compiler supports both dialects; you can specify the signed +dialect with @option{-fsigned-bitfields} and the unsigned dialect with +@option{-funsigned-bitfields}. However, this leaves open the question of +which dialect to use by default. + +Currently, the preferred dialect makes plain bit-fields signed, because +this is simplest. Since @code{int} is the same as @code{signed int} in +every other context, it is cleanest for them to be the same in bit-fields +as well. + +Some computer manufacturers have published Application Binary Interface +standards which specify that plain bit-fields should be unsigned. It is +a mistake, however, to say anything about this issue in an ABI@. This is +because the handling of plain bit-fields distinguishes two dialects of C@. +Both dialects are meaningful on every type of machine. Whether a +particular object file was compiled using signed bit-fields or unsigned +is of no concern to other object files, even if they access the same +bit-fields in the same data structures. + +A given program is written in one or the other of these two dialects. +The program stands a chance to work on most any machine if it is +compiled with the proper dialect. It is unlikely to work at all if +compiled with the wrong dialect. + +Many users appreciate the GNU C compiler because it provides an +environment that is uniform across machines. These users would be +inconvenienced if the compiler treated plain bit-fields differently on +certain machines. + +Occasionally users write programs intended only for a particular machine +type. On these occasions, the users would benefit if the GNU C compiler +were to support by default the same dialect as the other compilers on +that machine. But such applications are rare. And users writing a +program to run on more than one type of machine cannot possibly benefit +from this kind of compatibility. + +This is why GCC does and will treat plain bit-fields in the same +fashion on all types of machines (by default). + +There are some arguments for making bit-fields unsigned by default on all +machines. If, for example, this becomes a universal de facto standard, +it would make sense for GCC to go along with it. This is something +to be considered in the future. + +(Of course, users strongly concerned about portability should indicate +explicitly in each bit-field whether it is signed or not. In this way, +they write programs which have the same meaning in both C dialects.) + +@item +@opindex ansi +@opindex traditional +@opindex std +Undefining @code{__STDC__} when @option{-ansi} is not used. + +Currently, GCC defines @code{__STDC__} as long as you don't use +@option{-traditional}. This provides good results in practice. + +Programmers normally use conditionals on @code{__STDC__} to ask whether +it is safe to use certain features of ISO C, such as function +prototypes or ISO token concatenation. Since plain @command{gcc} supports +all the features of ISO C, the correct answer to these questions is +``yes''. + +Some users try to use @code{__STDC__} to check for the availability of +certain library facilities. This is actually incorrect usage in an ISO +C program, because the ISO C standard says that a conforming +freestanding implementation should define @code{__STDC__} even though it +does not have the library facilities. @samp{gcc -ansi -pedantic} is a +conforming freestanding implementation, and it is therefore required to +define @code{__STDC__}, even though it does not come with an ISO C +library. + +Sometimes people say that defining @code{__STDC__} in a compiler that +does not completely conform to the ISO C standard somehow violates the +standard. This is illogical. The standard is a standard for compilers +that claim to support ISO C, such as @samp{gcc -ansi}---not for other +compilers such as plain @command{gcc}. Whatever the ISO C standard says +is relevant to the design of plain @command{gcc} without @option{-ansi} only +for pragmatic reasons, not as a requirement. + +GCC normally defines @code{__STDC__} to be 1, and in addition +defines @code{__STRICT_ANSI__} if you specify the @option{-ansi} option, +or a @option{-std} option for strict conformance to some version of ISO C@. +On some hosts, system include files use a different convention, where +@code{__STDC__} is normally 0, but is 1 if the user specifies strict +conformance to the C Standard. GCC follows the host convention when +processing system include files, but when processing user files it follows +the usual GNU C convention. + +@item +Undefining @code{__STDC__} in C++. + +Programs written to compile with C++-to-C translators get the +value of @code{__STDC__} that goes with the C compiler that is +subsequently used. These programs must test @code{__STDC__} +to determine what kind of C preprocessor that compiler uses: +whether they should concatenate tokens in the ISO C fashion +or in the traditional fashion. + +These programs work properly with GNU C++ if @code{__STDC__} is defined. +They would not work otherwise. + +In addition, many header files are written to provide prototypes in ISO +C but not in traditional C@. Many of these header files can work without +change in C++ provided @code{__STDC__} is defined. If @code{__STDC__} +is not defined, they will all fail, and will all need to be changed to +test explicitly for C++ as well. + +@item +Deleting ``empty'' loops. + +Historically, GCC has not deleted ``empty'' loops under the +assumption that the most likely reason you would put one in a program is +to have a delay, so deleting them will not make real programs run any +faster. + +However, the rationale here is that optimization of a nonempty loop +cannot produce an empty one, which holds for C but is not always the +case for C++. + +@opindex funroll-loops +Moreover, with @option{-funroll-loops} small ``empty'' loops are already +removed, so the current behavior is both sub-optimal and inconsistent +and will change in the future. + +@item +Making side effects happen in the same order as in some other compiler. + +@cindex side effects, order of evaluation +@cindex order of evaluation, side effects +It is never safe to depend on the order of evaluation of side effects. +For example, a function call like this may very well behave differently +from one compiler to another: + +@example +void func (int, int); + +int i = 2; +func (i++, i++); +@end example + +There is no guarantee (in either the C or the C++ standard language +definitions) that the increments will be evaluated in any particular +order. Either increment might happen first. @code{func} might get the +arguments @samp{2, 3}, or it might get @samp{3, 2}, or even @samp{2, 2}. + +@item +Not allowing structures with volatile fields in registers. + +Strictly speaking, there is no prohibition in the ISO C standard +against allowing structures with volatile fields in registers, but +it does not seem to make any sense and is probably not what you wanted +to do. So the compiler will give an error message in this case. + +@item +Making certain warnings into errors by default. + +Some ISO C testsuites report failure when the compiler does not produce +an error message for a certain program. + +@opindex pedantic-errors +ISO C requires a ``diagnostic'' message for certain kinds of invalid +programs, but a warning is defined by GCC to count as a diagnostic. If +GCC produces a warning but not an error, that is correct ISO C support. +If test suites call this ``failure'', they should be run with the GCC +option @option{-pedantic-errors}, which will turn these warnings into +errors. + +@end itemize + +@node Warnings and Errors +@section Warning Messages and Error Messages + +@cindex error messages +@cindex warnings vs errors +@cindex messages, warning and error +The GNU compiler can produce two kinds of diagnostics: errors and +warnings. Each kind has a different purpose: + +@itemize @w{} +@item +@dfn{Errors} report problems that make it impossible to compile your +program. GCC reports errors with the source file name and line +number where the problem is apparent. + +@item +@dfn{Warnings} report other unusual conditions in your code that +@emph{may} indicate a problem, although compilation can (and does) +proceed. Warning messages also report the source file name and line +number, but include the text @samp{warning:} to distinguish them +from error messages. +@end itemize + +Warnings may indicate danger points where you should check to make sure +that your program really does what you intend; or the use of obsolete +features; or the use of nonstandard features of GNU C or C++. Many +warnings are issued only if you ask for them, with one of the @option{-W} +options (for instance, @option{-Wall} requests a variety of useful +warnings). + +@opindex pedantic +@opindex pedantic-errors +GCC always tries to compile your program if possible; it never +gratuitously rejects a program whose meaning is clear merely because +(for instance) it fails to conform to a standard. In some cases, +however, the C and C++ standards specify that certain extensions are +forbidden, and a diagnostic @emph{must} be issued by a conforming +compiler. The @option{-pedantic} option tells GCC to issue warnings in +such cases; @option{-pedantic-errors} says to make them errors instead. +This does not mean that @emph{all} non-ISO constructs get warnings +or errors. + +@xref{Warning Options,,Options to Request or Suppress Warnings}, for +more detail on these and related command-line options. diff --git a/contrib/gcc/doc/vms.texi b/contrib/gcc/doc/vms.texi new file mode 100644 index 000000000000..5ab266695a84 --- /dev/null +++ b/contrib/gcc/doc/vms.texi @@ -0,0 +1,331 @@ +@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, +@c 1999, 2000, 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node VMS +@chapter Using GCC on VMS + +@c prevent bad page break with this line +Here is how to use GCC on VMS@. + +@menu +* Include Files and VMS:: Where the preprocessor looks for the include files. +* Global Declarations:: How to do globaldef, globalref and globalvalue with + GCC. +* VMS Misc:: Misc information. +@end menu + +@node Include Files and VMS +@section Include Files and VMS + +@cindex include files and VMS +@cindex VMS and include files +@cindex header files and VMS +Due to the differences between the filesystems of Unix and VMS, GCC +attempts to translate file names in @samp{#include} into names that VMS +will understand. The basic strategy is to prepend a prefix to the +specification of the include file, convert the whole filename to a VMS +filename, and then try to open the file. GCC tries various prefixes +one by one until one of them succeeds: + +@enumerate +@item +The first prefix is the @samp{GNU_CC_INCLUDE:} logical name: this is +where GNU C header files are traditionally stored. If you wish to store +header files in non-standard locations, then you can assign the logical +@samp{GNU_CC_INCLUDE} to be a search list, where each element of the +list is suitable for use with a rooted logical. + +@item +The next prefix tried is @samp{SYS$SYSROOT:[SYSLIB.]}. This is where +VAX-C header files are traditionally stored. + +@item +If the include file specification by itself is a valid VMS filename, the +preprocessor then uses this name with no prefix in an attempt to open +the include file. + +@item +If the file specification is not a valid VMS filename (i.e.@: does not +contain a device or a directory specifier, and contains a @samp{/} +character), the preprocessor tries to convert it from Unix syntax to +VMS syntax. + +Conversion works like this: the first directory name becomes a device, +and the rest of the directories are converted into VMS-format directory +names. For example, the name @file{X11/foobar.h} is +translated to @file{X11:[000000]foobar.h} or @file{X11:foobar.h}, +whichever one can be opened. This strategy allows you to assign a +logical name to point to the actual location of the header files. + +@item +If none of these strategies succeeds, the @samp{#include} fails. +@end enumerate + +Include directives of the form: + +@example +#include foobar +@end example + +@noindent +are a common source of incompatibility between VAX-C and GCC@. VAX-C +treats this much like a standard @code{#include } directive. +That is incompatible with the ISO C behavior implemented by GCC: to +expand the name @code{foobar} as a macro. Macro expansion should +eventually yield one of the two standard formats for @code{#include}: + +@example +#include "@var{file}" +#include <@var{file}> +@end example + +If you have this problem, the best solution is to modify the source to +convert the @code{#include} directives to one of the two standard forms. +That will work with either compiler. If you want a quick and dirty fix, +define the file names as macros with the proper expansion, like this: + +@example +#define stdio +@end example + +@noindent +This will work, as long as the name doesn't conflict with anything else +in the program. + +Another source of incompatibility is that VAX-C assumes that: + +@example +#include "foobar" +@end example + +@noindent +is actually asking for the file @file{foobar.h}. GCC does not +make this assumption, and instead takes what you ask for literally; +it tries to read the file @file{foobar}. The best way to avoid this +problem is to always specify the desired file extension in your include +directives. + +GCC for VMS is distributed with a set of include files that is +sufficient to compile most general purpose programs. Even though the +GCC distribution does not contain header files to define constants +and structures for some VMS system-specific functions, there is no +reason why you cannot use GCC with any of these functions. You first +may have to generate or create header files, either by using the public +domain utility @code{UNSDL} (which can be found on a DECUS tape), or by +extracting the relevant modules from one of the system macro libraries, +and using an editor to construct a C header file. + +A @code{#include} file name cannot contain a DECNET node name. The +preprocessor reports an I/O error if you attempt to use a node name, +whether explicitly, or implicitly via a logical name. + +@node Global Declarations +@section Global Declarations and VMS + +@findex GLOBALREF +@findex GLOBALDEF +@findex GLOBALVALUEDEF +@findex GLOBALVALUEREF +GCC does not provide the @code{globalref}, @code{globaldef} and +@code{globalvalue} keywords of VAX-C@. You can get the same effect with +an obscure feature of GAS, the GNU assembler. (This requires GAS +version 1.39 or later.) The following macros allow you to use this +feature in a fairly natural way: + +@smallexample +#ifdef __GNUC__ +#define GLOBALREF(TYPE,NAME) \ + TYPE NAME \ + asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) +#define GLOBALDEF(TYPE,NAME,VALUE) \ + TYPE NAME \ + asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) \ + = VALUE +#define GLOBALVALUEREF(TYPE,NAME) \ + const TYPE NAME[1] \ + asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME) +#define GLOBALVALUEDEF(TYPE,NAME,VALUE) \ + const TYPE NAME[1] \ + asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME) \ + = @{VALUE@} +#else +#define GLOBALREF(TYPE,NAME) \ + globalref TYPE NAME +#define GLOBALDEF(TYPE,NAME,VALUE) \ + globaldef TYPE NAME = VALUE +#define GLOBALVALUEDEF(TYPE,NAME,VALUE) \ + globalvalue TYPE NAME = VALUE +#define GLOBALVALUEREF(TYPE,NAME) \ + globalvalue TYPE NAME +#endif +@end smallexample + +@noindent +(The @code{_$$PsectAttributes_GLOBALSYMBOL} prefix at the start of the +name is removed by the assembler, after it has modified the attributes +of the symbol). These macros are provided in the VMS binaries +distribution in a header file @file{GNU_HACKS.H}. An example of the +usage is: + +@example +GLOBALREF (int, ijk); +GLOBALDEF (int, jkl, 0); +@end example + +The macros @code{GLOBALREF} and @code{GLOBALDEF} cannot be used +straightforwardly for arrays, since there is no way to insert the array +dimension into the declaration at the right place. However, you can +declare an array with these macros if you first define a typedef for the +array type, like this: + +@example +typedef int intvector[10]; +GLOBALREF (intvector, foo); +@end example + +Array and structure initializers will also break the macros; you can +define the initializer to be a macro of its own, or you can expand the +@code{GLOBALDEF} macro by hand. You may find a case where you wish to +use the @code{GLOBALDEF} macro with a large array, but you are not +interested in explicitly initializing each element of the array. In +such cases you can use an initializer like: @code{@{0,@}}, which will +initialize the entire array to @code{0}. + +A shortcoming of this implementation is that a variable declared with +@code{GLOBALVALUEREF} or @code{GLOBALVALUEDEF} is always an array. For +example, the declaration: + +@example +GLOBALVALUEREF(int, ijk); +@end example + +@noindent +declares the variable @code{ijk} as an array of type @code{int [1]}. +This is done because a globalvalue is actually a constant; its ``value'' +is what the linker would normally consider an address. That is not how +an integer value works in C, but it is how an array works. So treating +the symbol as an array name gives consistent results---with the +exception that the value seems to have the wrong type. @strong{Don't +try to access an element of the array.} It doesn't have any elements. +The array ``address'' may not be the address of actual storage. + +The fact that the symbol is an array may lead to warnings where the +variable is used. Insert type casts to avoid the warnings. Here is an +example; it takes advantage of the ISO C feature allowing macros that +expand to use the same name as the macro itself. + +@example +GLOBALVALUEREF (int, ss$_normal); +GLOBALVALUEDEF (int, xyzzy,123); +#ifdef __GNUC__ +#define ss$_normal ((int) ss$_normal) +#define xyzzy ((int) xyzzy) +#endif +@end example + +Don't use @code{globaldef} or @code{globalref} with a variable whose +type is an enumeration type; this is not implemented. Instead, make the +variable an integer, and use a @code{globalvaluedef} for each of the +enumeration values. An example of this would be: + +@example +#ifdef __GNUC__ +GLOBALDEF (int, color, 0); +GLOBALVALUEDEF (int, RED, 0); +GLOBALVALUEDEF (int, BLUE, 1); +GLOBALVALUEDEF (int, GREEN, 3); +#else +enum globaldef color @{RED, BLUE, GREEN = 3@}; +#endif +@end example + +@node VMS Misc +@section Other VMS Issues + +@cindex exit status and VMS +@cindex return value of @code{main} +@cindex @code{main} and the exit status +GCC automatically arranges for @code{main} to return 1 by default if +you fail to specify an explicit return value. This will be interpreted +by VMS as a status code indicating a normal successful completion. +Version 1 of GCC did not provide this default. + +GCC on VMS works only with the GNU assembler, GAS@. You need version +1.37 or later of GAS in order to produce value debugging information for +the VMS debugger. Use the ordinary VMS linker with the object files +produced by GAS@. + +@cindex shared VMS run time system +@cindex @file{VAXCRTL} +Under previous versions of GCC, the generated code would occasionally +give strange results when linked to the sharable @file{VAXCRTL} library. +Now this should work. + +A caveat for use of @code{const} global variables: the @code{const} +modifier must be specified in every external declaration of the variable +in all of the source files that use that variable. Otherwise the linker +will issue warnings about conflicting attributes for the variable. Your +program will still work despite the warnings, but the variable will be +placed in writable storage. + +@cindex name augmentation +@cindex case sensitivity and VMS +@cindex VMS and case sensitivity +Although the VMS linker does distinguish between upper and lower case +letters in global symbols, most VMS compilers convert all such symbols +into upper case and most run-time library routines also have upper case +names. To be able to reliably call such routines, GCC (by means of +the assembler GAS) converts global symbols into upper case like other +VMS compilers. However, since the usual practice in C is to distinguish +case, GCC (via GAS) tries to preserve usual C behavior by augmenting +each name that is not all lower case. This means truncating the name +to at most 23 characters and then adding more characters at the end +which encode the case pattern of those 23. Names which contain at +least one dollar sign are an exception; they are converted directly into +upper case without augmentation. + +Name augmentation yields bad results for programs that use precompiled +libraries (such as Xlib) which were generated by another compiler. You +can use the compiler option @samp{/NOCASE_HACK} to inhibit augmentation; +it makes external C functions and variables case-independent as is usual +on VMS@. Alternatively, you could write all references to the functions +and variables in such libraries using lower case; this will work on VMS, +but is not portable to other systems. The compiler option @samp{/NAMES} +also provides control over global name handling. + +Function and variable names are handled somewhat differently with G++. +The GNU C++ compiler performs @dfn{name mangling} on function +names, which means that it adds information to the function name to +describe the data types of the arguments that the function takes. One +result of this is that the name of a function can become very long. +Since the VMS linker only recognizes the first 31 characters in a name, +special action is taken to ensure that each function and variable has a +unique name that can be represented in 31 characters. + +If the name (plus a name augmentation, if required) is less than 32 +characters in length, then no special action is performed. If the name +is longer than 31 characters, the assembler (GAS) will generate a +hash string based upon the function name, truncate the function name to +23 characters, and append the hash string to the truncated name. If the +@samp{/VERBOSE} compiler option is used, the assembler will print both +the full and truncated names of each symbol that is truncated. + +The @samp{/NOCASE_HACK} compiler option should not be used when you are +compiling programs that use libg++. libg++ has several instances of +objects (i.e. @code{Filebuf} and @code{filebuf}) which become +indistinguishable in a case-insensitive environment. This leads to +cases where you need to inhibit augmentation selectively (if you were +using libg++ and Xlib in the same program, for example). There is no +special feature for doing this, but you can get the result by defining a +macro for each mixed case symbol for which you wish to inhibit +augmentation. The macro should expand into the lower case equivalent of +itself. For example: + +@example +#define StuDlyCapS studlycaps +@end example + +These macro definitions can be placed in a header file to minimize the +number of changes to your source code. -- cgit v1.2.3