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diff --git a/contrib/gcc/README.NS32K b/contrib/gcc/README.NS32K deleted file mode 100644 index 93c5beaef54a..000000000000 --- a/contrib/gcc/README.NS32K +++ /dev/null @@ -1,130 +0,0 @@ -This file describes the implementation notes of the GNU C Compiler for -the National Semiconductor 32032 chip (and 32000 family). - -The 32032 machine description and configuration file for this compiler -is, for NS32000 family machine, primarily machine independent. -However, since this release still depends on vendor-supplied -assemblers and linkers, the compiler must obey the existing -conventions of the actual machine to which this compiler is targeted. -In this case, the actual machine which this compiler was targeted to -is a Sequent Balance 8000, running DYNIX 2.1. - -The assembler for DYNIX 2.1 (and DYNIX 3.0, alas) does not cope with -the full generality of the addressing mode REGISTER RELATIVE. -Specifically, it generates incorrect code for operands of the -following form: - - sym(rn) - -Where `rn' is one of the general registers. Correct code is generated -for operands of the form - - sym(pn) - -where `pn' is one of the special processor registers (sb, fp, or sp). - -An equivalent operand can be generated by the form - - sym[rn:b] - -although this addressing mode is about twice as slow on the 32032. - -The more efficient addressing mode is controlled by defining the -constant SEQUENT_ADDRESS_BUG to 0. It is currently defined to be 1. - -Another bug in the assembler makes it impossible to compute with -explicit addresses. In order to compute with a symbolic address, it -is necessary to load that address into a register using the "addr" -instruction. For example, it is not possible to say - - cmpd _p,@_x - -Rather one must say - - addr _x,rn - cmpd _p,rn - - -The ns32032 chip has a number of known bugs. Any attempt to make the -compiler unaware of these deficiencies will surely bring disaster. -The current list of know bugs are as follows (list provided by Richard -Stallman): - -1) instructions with two overlapping operands in memory -(unlikely in C code, perhaps impossible). - -2) floating point conversion instructions with constant -operands (these may never happen, but I'm not certain). - -3) operands crossing a page boundary. These can be prevented -by setting the flag in tm.h that requires strict alignment. - -4) Scaled indexing in an insn following an insn that has a read-write -operand in memory. This can be prevented by placing a no-op in -between. I, Michael Tiemann, do not understand what exactly is meant -by `read-write operand in memory'. If this is referring to the special -TOS mode, for example "addd 5,tos" then one need not fear, since this -will never be generated. However, is this includes "addd 5,-4(fp)" -then there is room for disaster. The Sequent compiler does not insert -a no-op for code involving the latter, and I have been informed that -Sequent is aware of this list of bugs, so I must assume that it is not -a problem. - -5) The 32032 cannot shift by 32 bits. It shifts modulo the word size -of the operand. Therefore, for 32-bit operations, 32-bit shifts are -interpreted as zero bit shifts. 32-bit shifts have been removed from -the compiler, but future hackers must be careful not to reintroduce -them. - -6) The ns32032 is a very slow chip; however, some instructions are -still very much slower than one might expect. For example, it is -almost always faster to double a quantity by adding it to itself than -by shifting it by one, even if that quantity is deep in memory. The -MOVM instruction has a 20-cycle setup time, after which it moves data -at about the speed that normal moves would. It is also faster to use -address generation instructions than shift instructions for left -shifts less than 4. I do not claim that I generate optimal code for all -given patterns, but where I did escape from National's "clean -architecture", I did so because the timing specification from the data -book says that I will win if I do. I suppose this is called the -"performance gap". - - -Signed bitfield extraction has not been implemented. It is not -provided by the NS32032, and while it is most certainly possible to do -better than the standard shift-left/shift-right sequence, it is also -quite hairy. Also, since signed bitfields do not yet exist in C, this -omission seems relatively harmless. - - -Zero extractions could be better implemented if it were possible in -GCC to provide sized zero extractions: i.e. a byte zero extraction -would be allowed to yield a byte result. The current implementation -of GCC manifests 68000-ist thinking, where bitfields are extracted -into a register, and automatically sign/zero extended to fill the -register. See comments in ns32k.md around the "extzv" insn for more -details. - - -It should be noted that while the NS32000 family was designed to -provide odd-aligned addressing capability for multi-byte data (also -provided by the 68020, but not by the 68000 or 68010), many machines -do not opt to take advantage of this. For example, on the sequent, -although there is no advantage to long-word aligning word data, shorts -must be int-aligned in structs. This is an example of another -machine-specific machine dependency. - - -Because the ns32032 is has a coherent byte-order/bit-order -architecture, many instructions which would be different for -68000-style machines, fold into the same instruction for the 32032. -The classic case is push effective address, where it does not matter -whether one is pushing a long, word, or byte address. They all will -push the same address. - - -The macro FUNCTION_VALUE_REGNO_P is probably not sufficient, what is -needed is FUNCTION_VALUE_P, which also takes a MODE parameter. In -this way it will be possible to determine more exactly whether a -register is really a function value register, or just one that happens -to look right. |