Vendor import of clang 3.0 final release:vendor/clang/clang-r145349

http://llvm.org/svn/llvm-project/cfe/tags/RELEASE_30/final@145349

37 files changed, 1113 insertions, 882 deletions

diff --git a/bindings/python/clang/cindex.py b/bindings/python/clang/cindex.py
index 35c423d7d898..7cc9ddaf7646 100644
--- a/bindings/python/clang/cindex.py
+++ b/bindings/python/clang/cindex.py
@@ -815,7 +815,7 @@ class Cursor(Structure):
     The Cursor class represents a reference to an element within the AST. It
     acts as a kind of iterator.
     """
-    _fields_ = [("_kind_id", c_int), ("data", c_void_p * 3)]
+    _fields_ = [("_kind_id", c_int), ("xdata", c_int), ("data", c_void_p * 3)]
 
     def __eq__(self, other):
         return Cursor_eq(self, other)
@@ -1019,7 +1019,7 @@ TypeKind.OBJCINTERFACE = TypeKind(108)
 TypeKind.OBJCOBJECTPOINTER = TypeKind(109)
 TypeKind.FUNCTIONNOPROTO = TypeKind(110)
 TypeKind.FUNCTIONPROTO = TypeKind(111)
-
+TypeKind.CONSTANTARRAY = TypeKind(112)
 
 class Type(Structure):
     """
diff --git a/bindings/python/tests/cindex/test_type.py b/bindings/python/tests/cindex/test_type.py
index cd27a4cbb98d..35c7bbbfa2fa 100644
--- a/bindings/python/tests/cindex/test_type.py
+++ b/bindings/python/tests/cindex/test_type.py
@@ -74,3 +74,22 @@ def test_a_struct():
 
     else:
         assert False, "Didn't find teststruct??"
+
+
+constarrayInput="""
+struct teststruct {
+  void *A[2];
+};
+"""
+def testConstantArray():
+    index = Index.create()
+    tu = index.parse('t.c', unsaved_files = [('t.c',constarrayInput)])
+
+    for n in tu.cursor.get_children():
+        if n.spelling == 'teststruct':
+            fields = list(n.get_children())
+            assert fields[0].spelling == 'A'
+            assert fields[0].type.kind == TypeKind.CONSTANTARRAY
+            break
+    else:
+        assert False, "Didn't find teststruct??"
diff --git a/include/clang/Basic/Builtins.def b/include/clang/Basic/Builtins.def
index e5690c123393..e06e05b1aa17 100644
--- a/include/clang/Basic/Builtins.def
+++ b/include/clang/Basic/Builtins.def
@@ -672,16 +672,16 @@ LIBBUILTIN(rindex, "c*cC*i",      "f",     "strings.h", ALL_LANGUAGES)
 LIBBUILTIN(bzero, "vv*z",         "f",     "strings.h", ALL_LANGUAGES)
 // POSIX unistd.h
 LIBBUILTIN(_exit, "vi",           "fr",    "unistd.h", ALL_LANGUAGES)
-LIBBUILTIN(vfork, "iJ",           "fj",    "unistd.h", ALL_LANGUAGES)
+LIBBUILTIN(vfork, "i",            "fj",    "unistd.h", ALL_LANGUAGES)
 // POSIX setjmp.h
 
 // In some systems setjmp is a macro that expands to _setjmp. We undefine
 // it here to avoid having two identical LIBBUILTIN entries.
 #undef setjmp
 LIBBUILTIN(_setjmp, "iJ",         "fj",   "setjmp.h", ALL_LANGUAGES)
-LIBBUILTIN(__sigsetjmp, "iJ",     "fj",   "setjmp.h", ALL_LANGUAGES)
+LIBBUILTIN(__sigsetjmp, "iJi",    "fj",   "setjmp.h", ALL_LANGUAGES)
 LIBBUILTIN(setjmp, "iJ",          "fj",   "setjmp.h", ALL_LANGUAGES)
-LIBBUILTIN(sigsetjmp, "iJ",       "fj",   "setjmp.h", ALL_LANGUAGES)
+LIBBUILTIN(sigsetjmp, "iJi",      "fj",   "setjmp.h", ALL_LANGUAGES)
 LIBBUILTIN(setjmp_syscall, "iJ",  "fj",   "setjmp.h", ALL_LANGUAGES)
 LIBBUILTIN(savectx, "iJ",         "fj",   "setjmp.h", ALL_LANGUAGES)
 LIBBUILTIN(qsetjmp, "iJ",         "fj",   "setjmp.h", ALL_LANGUAGES)
diff --git a/include/clang/Driver/CC1Options.td b/include/clang/Driver/CC1Options.td
index 4473d46e2b32..b9d835be8faa 100644
--- a/include/clang/Driver/CC1Options.td
+++ b/include/clang/Driver/CC1Options.td
@@ -642,6 +642,17 @@ def isystem : JoinedOrSeparate<"-isystem">, MetaVarName<"<directory>">,
 def iwithsysroot : JoinedOrSeparate<"-iwithsysroot">,MetaVarName<"<directory>">,
   HelpText<"Add directory to SYSTEM include search path, "
            "absolute paths are relative to -isysroot">;
+def internal_isystem : JoinedOrSeparate<"-internal-isystem">,
+  MetaVarName<"<directory>">,
+  HelpText<"Add directory to the internal system include search path; these "
+           "are assumed to not be user-provided and are used to model system "
+           "and standard headers' paths.">;
+def internal_externc_isystem : JoinedOrSeparate<"-internal-externc-isystem">,
+  MetaVarName<"<directory>">,
+  HelpText<"Add directory to the internal system include search path with "
+           "implicit extern \"C\" semantics; these are assumed to not be "
+           "user-provided and are used to model system and standard headers' "
+           "paths.">;
 def iprefix : JoinedOrSeparate<"-iprefix">, MetaVarName<"<prefix>">,
   HelpText<"Set the -iwithprefix/-iwithprefixbefore prefix">;
 def iwithprefix : JoinedOrSeparate<"-iwithprefix">, MetaVarName<"<dir>">,
diff --git a/include/clang/Driver/ToolChain.h b/include/clang/Driver/ToolChain.h
index a5d51ca9d7c9..2e6218a23145 100644
--- a/include/clang/Driver/ToolChain.h
+++ b/include/clang/Driver/ToolChain.h
@@ -195,15 +195,21 @@ public:
   /// FIXME: this really belongs on some sort of DeploymentTarget abstraction
   virtual bool hasBlocksRuntime() const { return true; }
 
+  /// \brief Add the clang cc1 arguments for system include paths.
+  ///
+  /// This routine is responsible for adding the necessary cc1 arguments to
+  /// include headers from standard system header directories.
+  virtual void AddClangSystemIncludeArgs(const ArgList &DriverArgs,
+                                         ArgStringList &CC1Args) const;
+
   // GetCXXStdlibType - Determine the C++ standard library type to use with the
   // given compilation arguments.
   virtual CXXStdlibType GetCXXStdlibType(const ArgList &Args) const;
 
   /// AddClangCXXStdlibIncludeArgs - Add the clang -cc1 level arguments to set
   /// the include paths to use for the given C++ standard library type.
-  virtual void AddClangCXXStdlibIncludeArgs(const ArgList &Args,
-                                            ArgStringList &CmdArgs,
-                                            bool ObjCXXAutoRefCount) const;
+  virtual void AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
+                                            ArgStringList &CC1Args) const;
 
   /// AddCXXStdlibLibArgs - Add the system specific linker arguments to use
   /// for the given C++ standard library type.
diff --git a/include/clang/Frontend/HeaderSearchOptions.h b/include/clang/Frontend/HeaderSearchOptions.h
index 92790e99d890..687f439fe1ff 100644
--- a/include/clang/Frontend/HeaderSearchOptions.h
+++ b/include/clang/Frontend/HeaderSearchOptions.h
@@ -49,10 +49,24 @@ public:
     /// path.
     unsigned IgnoreSysRoot : 1;
 
+    /// \brief True if this entry is an internal search path.
+    ///
+    /// This typically indicates that users didn't directly provide it, but
+    /// instead it was provided by a compatibility layer for a particular
+    /// system. This isn't redundant with IsUserSupplied (even though perhaps
+    /// it should be) because that is false for user provided '-iwithprefix'
+    /// header search entries.
+    unsigned IsInternal : 1;
+
+    /// \brief True if this entry's headers should be wrapped in extern "C".
+    unsigned ImplicitExternC : 1;
+
     Entry(StringRef path, frontend::IncludeDirGroup group,
-          bool isUserSupplied, bool isFramework, bool ignoreSysRoot)
+          bool isUserSupplied, bool isFramework, bool ignoreSysRoot,
+          bool isInternal, bool implicitExternC)
       : Path(path), Group(group), IsUserSupplied(isUserSupplied),
-        IsFramework(isFramework), IgnoreSysRoot(ignoreSysRoot) {}
+        IsFramework(isFramework), IgnoreSysRoot(ignoreSysRoot),
+        IsInternal(isInternal), ImplicitExternC(implicitExternC) {}
   };
 
   /// If non-empty, the directory to use as a "virtual system root" for include
@@ -98,9 +112,10 @@ public:
 
   /// AddPath - Add the \arg Path path to the specified \arg Group list.
   void AddPath(StringRef Path, frontend::IncludeDirGroup Group,
-               bool IsUserSupplied, bool IsFramework, bool IgnoreSysRoot) {
+               bool IsUserSupplied, bool IsFramework, bool IgnoreSysRoot,
+               bool IsInternal = false, bool ImplicitExternC = false) {
     UserEntries.push_back(Entry(Path, Group, IsUserSupplied, IsFramework,
-                                IgnoreSysRoot));
+                                IgnoreSysRoot, IsInternal, ImplicitExternC));
   }
 };
 
diff --git a/lib/Basic/Version.cpp b/lib/Basic/Version.cpp
index 4705eda02e28..83678c5901ba 100644
--- a/lib/Basic/Version.cpp
+++ b/lib/Basic/Version.cpp
@@ -32,7 +32,7 @@ std::string getClangRepositoryPath() {
 
   // If the SVN_REPOSITORY is empty, try to use the SVN keyword. This helps us
   // pick up a tag in an SVN export, for example.
-  static StringRef SVNRepository("$URL: http://llvm.org/svn/llvm-project/cfe/branches/release_30/lib/Basic/Version.cpp $");
+  static StringRef SVNRepository("$URL: http://llvm.org/svn/llvm-project/cfe/tags/RELEASE_30/final/lib/Basic/Version.cpp $");
   if (URL.empty()) {
     URL = SVNRepository.slice(SVNRepository.find(':'),
                               SVNRepository.find("/lib/Basic"));
diff --git a/lib/CodeGen/CGObjCGNU.cpp b/lib/CodeGen/CGObjCGNU.cpp
index d3da649fbbf3..688e9924be50 100644
--- a/lib/CodeGen/CGObjCGNU.cpp
+++ b/lib/CodeGen/CGObjCGNU.cpp
@@ -538,11 +538,12 @@ protected:
                                  llvm::Value *cmd,
                                  llvm::MDNode *node) {
     CGBuilderTy &Builder = CGF.Builder;
-    llvm::Value *imp = Builder.CreateCall2(MsgLookupFn, 
-            EnforceType(Builder, Receiver, IdTy),
-            EnforceType(Builder, cmd, SelectorTy));
-    cast<llvm::CallInst>(imp)->setMetadata(msgSendMDKind, node);
-    return imp;
+    llvm::Value *args[] = {
+      EnforceType(Builder, Receiver, IdTy),
+      EnforceType(Builder, cmd, SelectorTy) };
+    llvm::CallSite imp = CGF.EmitCallOrInvoke(MsgLookupFn, args);
+    imp->setMetadata(msgSendMDKind, node);
+    return imp.getInstruction();
   }
   virtual llvm::Value *LookupIMPSuper(CodeGenFunction &CGF,
                                       llvm::Value *ObjCSuper,
@@ -597,16 +598,17 @@ class CGObjCGNUstep : public CGObjCGNU {
       // The lookup function is guaranteed not to capture the receiver pointer.
       LookupFn->setDoesNotCapture(1);
 
-      llvm::CallInst *slot =
-          Builder.CreateCall3(LookupFn,
-              EnforceType(Builder, ReceiverPtr, PtrToIdTy),
-              EnforceType(Builder, cmd, SelectorTy),
-              EnforceType(Builder, self, IdTy));
-      slot->setOnlyReadsMemory();
+      llvm::Value *args[] = {
+        EnforceType(Builder, ReceiverPtr, PtrToIdTy),
+        EnforceType(Builder, cmd, SelectorTy),
+        EnforceType(Builder, self, IdTy) };
+      llvm::CallSite slot = CGF.EmitCallOrInvoke(LookupFn, args);
+      slot.setOnlyReadsMemory();
       slot->setMetadata(msgSendMDKind, node);
 
       // Load the imp from the slot
-      llvm::Value *imp = Builder.CreateLoad(Builder.CreateStructGEP(slot, 4));
+      llvm::Value *imp =
+        Builder.CreateLoad(Builder.CreateStructGEP(slot.getInstruction(), 4));
 
       // The lookup function may have changed the receiver, so make sure we use
       // the new one.
@@ -1361,8 +1363,8 @@ llvm::Constant *CGObjCGNU::GenerateClassStructure(
       LongTy,                 // abi_version
       IvarOffsets->getType(), // ivar_offsets
       Properties->getType(),  // properties
-      Int64Ty,                // strong_pointers
-      Int64Ty,                // weak_pointers
+      IntPtrTy,               // strong_pointers
+      IntPtrTy,               // weak_pointers
       NULL);
   llvm::Constant *Zero = llvm::ConstantInt::get(LongTy, 0);
   // Fill in the structure
@@ -1723,12 +1725,14 @@ void CGObjCGNU::GenerateProtocolHolderCategory(void) {
 /// bitfield / with the 63rd bit set will be 1<<64.
 llvm::Constant *CGObjCGNU::MakeBitField(llvm::SmallVectorImpl<bool> &bits) {
   int bitCount = bits.size();
-  if (bitCount < 64) {
+  int ptrBits =
+        (TheModule.getPointerSize() == llvm::Module::Pointer32) ? 32 : 64;
+  if (bitCount < ptrBits) {
     uint64_t val = 1;
     for (int i=0 ; i<bitCount ; ++i) {
       if (bits[i]) val |= 1ULL<<(i+1);
     }
-    return llvm::ConstantInt::get(Int64Ty, val);
+    return llvm::ConstantInt::get(IntPtrTy, val);
   }
   llvm::SmallVector<llvm::Constant*, 8> values;
   int v=0;
@@ -1748,8 +1752,6 @@ llvm::Constant *CGObjCGNU::MakeBitField(llvm::SmallVectorImpl<bool> &bits) {
   llvm::Constant *GS = MakeGlobal(llvm::StructType::get(Int32Ty, arrayTy,
         NULL), fields);
   llvm::Constant *ptr = llvm::ConstantExpr::getPtrToInt(GS, IntPtrTy);
-  if (IntPtrTy != Int64Ty)
-    ptr = llvm::ConstantExpr::getZExt(ptr, Int64Ty);
   return ptr;
 }
 
@@ -2073,12 +2075,12 @@ void CGObjCGNU::GenerateClass(const ObjCImplementationDecl *OID) {
       }
       ++ivarIndex;
   }
-  llvm::Constant *Zero64 = llvm::ConstantInt::get(Int64Ty, 0);
+  llvm::Constant *ZeroPtr = llvm::ConstantInt::get(IntPtrTy, 0);
   //Generate metaclass for class methods
   llvm::Constant *MetaClassStruct = GenerateClassStructure(NULLPtr,
       NULLPtr, 0x12L, ClassName.c_str(), 0, Zeros[0], GenerateIvarList(
         empty, empty, empty), ClassMethodList, NULLPtr,
-      NULLPtr, NULLPtr, Zero64, Zero64, true);
+      NULLPtr, NULLPtr, ZeroPtr, ZeroPtr, true);
 
   // Generate the class structure
   llvm::Constant *ClassStruct =
diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 924ec8448e86..275045cff84c 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -29,6 +29,7 @@
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/Mangle.h"
 #include "clang/AST/RecordLayout.h"
+#include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
@@ -858,6 +859,59 @@ void CodeGenModule::EmitGlobal(GlobalDecl GD) {
   }
 }
 
+namespace {
+  struct FunctionIsDirectlyRecursive :
+    public RecursiveASTVisitor<FunctionIsDirectlyRecursive> {
+    const StringRef Name;
+    bool Result;
+    FunctionIsDirectlyRecursive(const FunctionDecl *F) :
+      Name(F->getName()), Result(false) {
+    }
+    typedef RecursiveASTVisitor<FunctionIsDirectlyRecursive> Base;
+
+    bool TraverseCallExpr(CallExpr *E) {
+      const Decl *D = E->getCalleeDecl();
+      if (!D)
+        return true;
+      AsmLabelAttr *Attr = D->getAttr<AsmLabelAttr>();
+      if (!Attr)
+        return true;
+      if (Name == Attr->getLabel()) {
+        Result = true;
+        return false;
+      }
+      return true;
+    }
+  };
+}
+
+// isTriviallyRecursiveViaAsm - Check if this function calls another
+// decl that, because of the asm attribute, ends up pointing to itself.
+bool
+CodeGenModule::isTriviallyRecursiveViaAsm(const FunctionDecl *F) {
+  if (getCXXABI().getMangleContext().shouldMangleDeclName(F))
+    return false;
+
+  FunctionIsDirectlyRecursive Walker(F);
+  Walker.TraverseFunctionDecl(const_cast<FunctionDecl*>(F));
+  return Walker.Result;
+}
+
+bool
+CodeGenModule::shouldEmitFunction(const FunctionDecl *F) {
+  if (getFunctionLinkage(F) != llvm::Function::AvailableExternallyLinkage)
+    return true;
+  if (CodeGenOpts.OptimizationLevel == 0 &&
+      !F->hasAttr<AlwaysInlineAttr>())
+    return false;
+  // PR9614. Avoid cases where the source code is lying to us. An available
+  // externally function should have an equivalent function somewhere else,
+  // but a function that calls itself is clearly not equivalent to the real
+  // implementation.
+  // This happens in glibc's btowc and in some configure checks.
+  return !isTriviallyRecursiveViaAsm(F);
+}
+
 void CodeGenModule::EmitGlobalDefinition(GlobalDecl GD) {
   const ValueDecl *D = cast<ValueDecl>(GD.getDecl());
 
@@ -868,10 +922,7 @@ void CodeGenModule::EmitGlobalDefinition(GlobalDecl GD) {
   if (const FunctionDecl *Function = dyn_cast<FunctionDecl>(D)) {
     // At -O0, don't generate IR for functions with available_externally 
     // linkage.
-    if (CodeGenOpts.OptimizationLevel == 0 && 
-        !Function->hasAttr<AlwaysInlineAttr>() &&
-        getFunctionLinkage(Function) 
-                                  == llvm::Function::AvailableExternallyLinkage)
+    if (!shouldEmitFunction(Function))
       return;
 
     if (const CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(D)) {
diff --git a/lib/CodeGen/CodeGenModule.h b/lib/CodeGen/CodeGenModule.h
index 8e38a8999013..dbc6a87bd19b 100644
--- a/lib/CodeGen/CodeGenModule.h
+++ b/lib/CodeGen/CodeGenModule.h
@@ -324,6 +324,8 @@ class CodeGenModule : public CodeGenTypeCache {
   void createOpenCLRuntime();
   void createCUDARuntime();
 
+  bool isTriviallyRecursiveViaAsm(const FunctionDecl *F);
+  bool shouldEmitFunction(const FunctionDecl *F);
   llvm::LLVMContext &VMContext;
 
   /// @name Cache for Blocks Runtime Globals
diff --git a/lib/Driver/CMakeLists.txt b/lib/Driver/CMakeLists.txt
index ee7ded94d4db..ac63a2dfbb4e 100644
--- a/lib/Driver/CMakeLists.txt
+++ b/lib/Driver/CMakeLists.txt
@@ -21,5 +21,13 @@ add_clang_library(clangDriver
   Types.cpp
   )
 
+IF(MSVC)
+  get_target_property(NON_ANSI_COMPILE_FLAGS clangDriver COMPILE_FLAGS)
+  string(REPLACE /Za
+    "" NON_ANSI_COMPILE_FLAGS
+    ${NON_ANSI_COMPILE_FLAGS})
+  set_target_properties(clangDriver PROPERTIES COMPILE_FLAGS ${NON_ANSI_COMPILE_FLAGS})
+ENDIF(MSVC)
+
 add_dependencies(clangDriver ClangAttrList ClangDiagnosticDriver
                  ClangDriverOptions ClangCC1Options ClangCC1AsOptions)
diff --git a/lib/Driver/ToolChain.cpp b/lib/Driver/ToolChain.cpp
index d09ab16814a0..9453848ec00d 100644
--- a/lib/Driver/ToolChain.cpp
+++ b/lib/Driver/ToolChain.cpp
@@ -211,6 +211,11 @@ std::string ToolChain::ComputeEffectiveClangTriple(const ArgList &Args,
   return ComputeLLVMTriple(Args, InputType);
 }
 
+void ToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
+                                          ArgStringList &CC1Args) const {
+  // Each toolchain should provide the appropriate include flags.
+}
+
 ToolChain::CXXStdlibType ToolChain::GetCXXStdlibType(const ArgList &Args) const{
   if (Arg *A = Args.getLastArg(options::OPT_stdlib_EQ)) {
     StringRef Value = A->getValue(Args);
@@ -225,24 +230,18 @@ ToolChain::CXXStdlibType ToolChain::GetCXXStdlibType(const ArgList &Args) const{
   return ToolChain::CST_Libstdcxx;
 }
 
-void ToolChain::AddClangCXXStdlibIncludeArgs(const ArgList &Args,
-                                             ArgStringList &CmdArgs,
-                                             bool ObjCXXAutoRefCount) const {
-  CXXStdlibType Type = GetCXXStdlibType(Args);
-
-  // Header search paths are handled by the mass of goop in InitHeaderSearch.
-
-  switch (Type) {
-  case ToolChain::CST_Libcxx:
-    if (ObjCXXAutoRefCount)
-      CmdArgs.push_back("-fobjc-arc-cxxlib=libc++");
-    break;
-
-  case ToolChain::CST_Libstdcxx:
-    if (ObjCXXAutoRefCount)
-      CmdArgs.push_back("-fobjc-arc-cxxlib=libstdc++");
-    break;
-  }
+void ToolChain::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
+                                             ArgStringList &CC1Args) const {
+  // Header search paths should be handled by each of the subclasses.
+  // Historically, they have not been, and instead have been handled inside of
+  // the CC1-layer frontend. As the logic is hoisted out, this generic function
+  // will slowly stop being called.
+  //
+  // While it is being called, replicate a bit of a hack to propagate the
+  // '-stdlib=' flag down to CC1 so that it can in turn customize the C++
+  // header search paths with it. Once all systems are overriding this
+  // function, the CC1 flag and this line can be removed.
+  DriverArgs.AddAllArgs(CC1Args, options::OPT_stdlib_EQ);
 }
 
 void ToolChain::AddCXXStdlibLibArgs(const ArgList &Args,
diff --git a/lib/Driver/ToolChains.cpp b/lib/Driver/ToolChains.cpp
index 825a83d8b8d8..eb730e53cac3 100644
--- a/lib/Driver/ToolChains.cpp
+++ b/lib/Driver/ToolChains.cpp
@@ -40,10 +40,51 @@
 
 #include "llvm/Config/config.h" // for CXX_INCLUDE_ROOT
 
+// Include the necessary headers to interface with the Windows registry and
+// environment.
+#ifdef _MSC_VER
+  #define WIN32_LEAN_AND_MEAN 1
+  #include <Windows.h>
+  #undef min
+  #undef max
+#endif
+
 using namespace clang::driver;
 using namespace clang::driver::toolchains;
 using namespace clang;
 
+/// \brief Utility function to add a system include directory to CC1 arguments.
+static void addSystemInclude(const ArgList &DriverArgs, ArgStringList &CC1Args,
+                             const Twine &Path) {
+  CC1Args.push_back("-internal-isystem");
+  CC1Args.push_back(DriverArgs.MakeArgString(Path));
+}
+
+/// \brief Utility function to add a system include directory with extern "C"
+/// semantics to CC1 arguments.
+///
+/// Note that this should be used rarely, and only for directories that
+/// historically and for legacy reasons are treated as having implicit extern
+/// "C" semantics. These semantics are *ignored* by and large today, but its
+/// important to preserve the preprocessor changes resulting from the
+/// classification.
+static void addExternCSystemInclude(const ArgList &DriverArgs,
+                                    ArgStringList &CC1Args, const Twine &Path) {
+  CC1Args.push_back("-internal-externc-isystem");
+  CC1Args.push_back(DriverArgs.MakeArgString(Path));
+}
+
+/// \brief Utility function to add a list of system include directories to CC1.
+static void addSystemIncludes(const ArgList &DriverArgs,
+                              ArgStringList &CC1Args,
+                              ArrayRef<StringRef> Paths) {
+  for (ArrayRef<StringRef>::iterator I = Paths.begin(), E = Paths.end();
+       I != E; ++I) {
+    CC1Args.push_back("-internal-isystem");
+    CC1Args.push_back(DriverArgs.MakeArgString(*I));
+  }
+}
+
 /// Darwin - Darwin tool chain for i386 and x86_64.
 
 Darwin::Darwin(const HostInfo &Host, const llvm::Triple& Triple)
@@ -1385,19 +1426,6 @@ static bool IsUbuntu(enum LinuxDistro Distro) {
          Distro == UbuntuNatty  || Distro == UbuntuOneiric;
 }
 
-// FIXME: This should be deleted. We should assume a multilib environment, and
-// fallback gracefully if any parts of it are absent.
-static bool HasMultilib(llvm::Triple::ArchType Arch, enum LinuxDistro Distro) {
-  if (Arch == llvm::Triple::x86_64) {
-    bool Exists;
-    if (Distro == Exherbo &&
-        (llvm::sys::fs::exists("/usr/lib32/libc.so", Exists) || !Exists))
-      return false;
-  }
-
-  return true;
-}
-
 static LinuxDistro DetectLinuxDistro(llvm::Triple::ArchType Arch) {
   llvm::OwningPtr<llvm::MemoryBuffer> File;
   if (!llvm::MemoryBuffer::getFile("/etc/lsb-release", File)) {
@@ -1482,280 +1510,293 @@ static LinuxDistro DetectLinuxDistro(llvm::Triple::ArchType Arch) {
   return UnknownDistro;
 }
 
-/// \brief Trivial helper function to simplify code checking path existence.
-static bool PathExists(StringRef Path) {
-  bool Exists;
-  if (!llvm::sys::fs::exists(Path, Exists))
-    return Exists;
-  return false;
-}
-
-namespace {
-/// \brief This is a class to find a viable GCC installation for Clang to use.
+/// \brief Parse a GCCVersion object out of a string of text.
 ///
-/// This class tries to find a GCC installation on the system, and report
-/// information about it. It starts from the host information provided to the
-/// Driver, and has logic for fuzzing that where appropriate.
-class GCCInstallationDetector {
-  /// \brief Struct to store and manipulate GCC versions.
-  ///
-  /// We rely on assumptions about the form and structure of GCC version
-  /// numbers: they consist of at most three '.'-separated components, and each
-  /// component is a non-negative integer.
-  struct GCCVersion {
-    unsigned Major, Minor, Patch;
-
-    static GCCVersion Parse(StringRef VersionText) {
-      const GCCVersion BadVersion = {0, 0, 0};
-      std::pair<StringRef, StringRef> First = VersionText.split('.');
-      std::pair<StringRef, StringRef> Second = First.second.split('.');
-
-      GCCVersion GoodVersion = {0, 0, 0};
-      if (First.first.getAsInteger(10, GoodVersion.Major))
-        return BadVersion;
-      if (Second.first.getAsInteger(10, GoodVersion.Minor))
+/// This is the primary means of forming GCCVersion objects.
+/*static*/ Linux::GCCVersion Linux::GCCVersion::Parse(StringRef VersionText) {
+  const GCCVersion BadVersion = { VersionText.str(), -1, -1, -1, "" };
+  std::pair<StringRef, StringRef> First = VersionText.split('.');
+  std::pair<StringRef, StringRef> Second = First.second.split('.');
+
+  GCCVersion GoodVersion = { VersionText.str(), -1, -1, -1, "" };
+  if (First.first.getAsInteger(10, GoodVersion.Major) ||
+      GoodVersion.Major < 0)
+    return BadVersion;
+  if (Second.first.getAsInteger(10, GoodVersion.Minor) ||
+      GoodVersion.Minor < 0)
+    return BadVersion;
+
+  // First look for a number prefix and parse that if present. Otherwise just
+  // stash the entire patch string in the suffix, and leave the number
+  // unspecified. This covers versions strings such as:
+  //   4.4
+  //   4.4.0
+  //   4.4.x
+  //   4.4.2-rc4
+  //   4.4.x-patched
+  // And retains any patch number it finds.
+  StringRef PatchText = GoodVersion.PatchSuffix = Second.second.str();
+  if (!PatchText.empty()) {
+    if (unsigned EndNumber = PatchText.find_first_not_of("0123456789")) {
+      // Try to parse the number and any suffix.
+      if (PatchText.slice(0, EndNumber).getAsInteger(10, GoodVersion.Patch) ||
+          GoodVersion.Patch < 0)
         return BadVersion;
-      // We accept a number, or a string for the patch version, in case there
-      // is a strang suffix, or other mangling: '4.1.x', '4.1.2-rc3'. When it
-      // isn't a number, we just use '0' as the number but accept it.
-      if (Second.first.getAsInteger(10, GoodVersion.Patch))
-        GoodVersion.Patch = 0;
-      return GoodVersion;
+      GoodVersion.PatchSuffix = PatchText.substr(EndNumber).str();
     }
+  }
 
-    bool operator<(const GCCVersion &RHS) const {
-      if (Major < RHS.Major) return true;
-      if (Major > RHS.Major) return false;
-      if (Minor < RHS.Minor) return true;
-      if (Minor > RHS.Minor) return false;
-      return Patch < RHS.Patch;
-    }
-    bool operator>(const GCCVersion &RHS) const { return RHS < *this; }
-    bool operator<=(const GCCVersion &RHS) const { return !(*this > RHS); }
-    bool operator>=(const GCCVersion &RHS) const { return !(*this < RHS); }
-  };
+  return GoodVersion;
+}
 
-  bool IsValid;
-  std::string GccTriple;
-
-  // FIXME: These might be better as path objects.
-  std::string GccInstallPath;
-  std::string GccParentLibPath;
-
-  llvm::SmallString<128> CxxIncludeRoot;
-
-public:
-  /// \brief Construct a GCCInstallationDetector from the driver.
-  ///
-  /// This performs all of the autodetection and sets up the various paths.
-  /// Once constructed, a GCCInstallation is esentially immutable.
-  GCCInstallationDetector(const Driver &D)
-    : IsValid(false),
-      GccTriple(D.DefaultHostTriple),
-      CxxIncludeRoot(CXX_INCLUDE_ROOT) {
-    // FIXME: Using CXX_INCLUDE_ROOT is here is a bit of a hack, but
-    // avoids adding yet another option to configure/cmake.
-    // It would probably be cleaner to break it in two variables
-    // CXX_GCC_ROOT with just /foo/bar
-    // CXX_GCC_VER with 4.5.2
-    // Then we would have
-    // CXX_INCLUDE_ROOT = CXX_GCC_ROOT/include/c++/CXX_GCC_VER
-    // and this function would return
-    // CXX_GCC_ROOT/lib/gcc/CXX_INCLUDE_ARCH/CXX_GCC_VER
-    if (CxxIncludeRoot != "") {
-      // This is of the form /foo/bar/include/c++/4.5.2/
-      if (CxxIncludeRoot.back() == '/')
-        llvm::sys::path::remove_filename(CxxIncludeRoot); // remove the /
-      StringRef Version = llvm::sys::path::filename(CxxIncludeRoot);
-      llvm::sys::path::remove_filename(CxxIncludeRoot); // remove the version
-      llvm::sys::path::remove_filename(CxxIncludeRoot); // remove the c++
-      llvm::sys::path::remove_filename(CxxIncludeRoot); // remove the include
-      GccInstallPath = CxxIncludeRoot.str();
-      GccInstallPath.append("/lib/gcc/");
-      GccInstallPath.append(CXX_INCLUDE_ARCH);
-      GccInstallPath.append("/");
-      GccInstallPath.append(Version);
-      GccParentLibPath = GccInstallPath + "/../../..";
-      IsValid = true;
-      return;
-    }
+/// \brief Less-than for GCCVersion, implementing a Strict Weak Ordering.
+bool Linux::GCCVersion::operator<(const GCCVersion &RHS) const {
+  if (Major < RHS.Major) return true; if (Major > RHS.Major) return false;
+  if (Minor < RHS.Minor) return true; if (Minor > RHS.Minor) return false;
 
-    llvm::Triple::ArchType HostArch = llvm::Triple(GccTriple).getArch();
-    // The library directories which may contain GCC installations.
-    SmallVector<StringRef, 4> CandidateLibDirs;
-    // The compatible GCC triples for this particular architecture.
-    SmallVector<StringRef, 10> CandidateTriples;
-    CollectLibDirsAndTriples(HostArch, CandidateLibDirs, CandidateTriples);
-
-    // Always include the default host triple as the final fallback if no
-    // specific triple is detected.
-    CandidateTriples.push_back(D.DefaultHostTriple);
-
-    // Compute the set of prefixes for our search.
-    SmallVector<std::string, 8> Prefixes(D.PrefixDirs.begin(),
-                                         D.PrefixDirs.end());
-    Prefixes.push_back(D.SysRoot);
-    Prefixes.push_back(D.SysRoot + "/usr");
-    Prefixes.push_back(D.InstalledDir + "/..");
-
-    // Loop over the various components which exist and select the best GCC
-    // installation available. GCC installs are ranked by version number.
-    GCCVersion BestVersion = {0, 0, 0};
-    for (unsigned i = 0, ie = Prefixes.size(); i < ie; ++i) {
-      if (!PathExists(Prefixes[i]))
-        continue;
-      for (unsigned j = 0, je = CandidateLibDirs.size(); j < je; ++j) {
-        const std::string LibDir = Prefixes[i] + CandidateLibDirs[j].str();
-        if (!PathExists(LibDir))
-          continue;
-        for (unsigned k = 0, ke = CandidateTriples.size(); k < ke; ++k)
-          ScanLibDirForGCCTriple(LibDir, CandidateTriples[k], BestVersion);
-      }
-    }
+  // Note that we rank versions with *no* patch specified is better than ones
+  // hard-coding a patch version. Thus if the RHS has no patch, it always
+  // wins, and the LHS only wins if it has no patch and the RHS does have
+  // a patch.
+  if (RHS.Patch == -1) return true;   if (Patch == -1) return false;
+  if (Patch < RHS.Patch) return true; if (Patch > RHS.Patch) return false;
+
+  // Finally, between completely tied version numbers, the version with the
+  // suffix loses as we prefer full releases.
+  if (RHS.PatchSuffix.empty()) return true;
+  return false;
+}
+
+/// \brief Construct a GCCInstallationDetector from the driver.
+///
+/// This performs all of the autodetection and sets up the various paths.
+/// Once constructed, a GCCInstallation is esentially immutable.
+Linux::GCCInstallationDetector::GCCInstallationDetector(const Driver &D)
+  : IsValid(false),
+    GccTriple(D.DefaultHostTriple) {
+  // FIXME: Using CXX_INCLUDE_ROOT is here is a bit of a hack, but
+  // avoids adding yet another option to configure/cmake.
+  // It would probably be cleaner to break it in two variables
+  // CXX_GCC_ROOT with just /foo/bar
+  // CXX_GCC_VER with 4.5.2
+  // Then we would have
+  // CXX_INCLUDE_ROOT = CXX_GCC_ROOT/include/c++/CXX_GCC_VER
+  // and this function would return
+  // CXX_GCC_ROOT/lib/gcc/CXX_INCLUDE_ARCH/CXX_GCC_VER
+  llvm::SmallString<128> CxxIncludeRoot(CXX_INCLUDE_ROOT);
+  if (CxxIncludeRoot != "") {
+    // This is of the form /foo/bar/include/c++/4.5.2/
+    if (CxxIncludeRoot.back() == '/')
+      llvm::sys::path::remove_filename(CxxIncludeRoot); // remove the /
+    StringRef Version = llvm::sys::path::filename(CxxIncludeRoot);
+    llvm::sys::path::remove_filename(CxxIncludeRoot); // remove the version
+    llvm::sys::path::remove_filename(CxxIncludeRoot); // remove the c++
+    llvm::sys::path::remove_filename(CxxIncludeRoot); // remove the include
+    GccInstallPath = CxxIncludeRoot.str();
+    GccInstallPath.append("/lib/gcc/");
+    GccInstallPath.append(CXX_INCLUDE_ARCH);
+    GccInstallPath.append("/");
+    GccInstallPath.append(Version);
+    GccParentLibPath = GccInstallPath + "/../../..";
+    IsValid = true;
+    return;
   }
 
-  /// \brief Check whether we detected a valid GCC install.
-  bool isValid() const { return IsValid; }
-
-  /// \brief Get the GCC triple for the detected install.
-  const std::string &getTriple() const { return GccTriple; }
-
-  /// \brief Get the detected GCC installation path.
-  const std::string &getInstallPath() const { return GccInstallPath; }
-
-  /// \brief Get the detected GCC parent lib path.
-  const std::string &getParentLibPath() const { return GccParentLibPath; }
-
-private:
-  static void CollectLibDirsAndTriples(llvm::Triple::ArchType HostArch,
-                                       SmallVectorImpl<StringRef> &LibDirs,
-                                       SmallVectorImpl<StringRef> &Triples) {
-    if (HostArch == llvm::Triple::arm || HostArch == llvm::Triple::thumb) {
-      static const char *const ARMLibDirs[] = { "/lib" };
-      static const char *const ARMTriples[] = { "arm-linux-gnueabi" };
-      LibDirs.append(ARMLibDirs, ARMLibDirs + llvm::array_lengthof(ARMLibDirs));
-      Triples.append(ARMTriples, ARMTriples + llvm::array_lengthof(ARMTriples));
-    } else if (HostArch == llvm::Triple::x86_64) {
-      static const char *const X86_64LibDirs[] = { "/lib64", "/lib" };
-      static const char *const X86_64Triples[] = {
-        "x86_64-linux-gnu",
-        "x86_64-unknown-linux-gnu",
-        "x86_64-pc-linux-gnu",
-        "x86_64-redhat-linux6E",
-        "x86_64-redhat-linux",
-        "x86_64-suse-linux",
-        "x86_64-manbo-linux-gnu",
-        "x86_64-linux-gnu",
-        "x86_64-slackware-linux"
-      };
-      LibDirs.append(X86_64LibDirs,
-                     X86_64LibDirs + llvm::array_lengthof(X86_64LibDirs));
-      Triples.append(X86_64Triples,
-                     X86_64Triples + llvm::array_lengthof(X86_64Triples));
-    } else if (HostArch == llvm::Triple::x86) {
-      static const char *const X86LibDirs[] = { "/lib32", "/lib" };
-      static const char *const X86Triples[] = {
-        "i686-linux-gnu",
-        "i386-linux-gnu",
-        "i686-pc-linux-gnu",
-        "i486-linux-gnu",
-        "i686-redhat-linux",
-        "i386-redhat-linux",
-        "i586-suse-linux",
-        "i486-slackware-linux"
-      };
-      LibDirs.append(X86LibDirs, X86LibDirs + llvm::array_lengthof(X86LibDirs));
-      Triples.append(X86Triples, X86Triples + llvm::array_lengthof(X86Triples));
-    } else if (HostArch == llvm::Triple::ppc) {
-      static const char *const PPCLibDirs[] = { "/lib32", "/lib" };
-      static const char *const PPCTriples[] = {
-        "powerpc-linux-gnu",
-        "powerpc-unknown-linux-gnu"
-      };
-      LibDirs.append(PPCLibDirs, PPCLibDirs + llvm::array_lengthof(PPCLibDirs));
-      Triples.append(PPCTriples, PPCTriples + llvm::array_lengthof(PPCTriples));
-    } else if (HostArch == llvm::Triple::ppc64) {
-      static const char *const PPC64LibDirs[] = { "/lib64", "/lib" };
-      static const char *const PPC64Triples[] = {
-        "powerpc64-unknown-linux-gnu"
-      };
-      LibDirs.append(PPC64LibDirs,
-                     PPC64LibDirs + llvm::array_lengthof(PPC64LibDirs));
-      Triples.append(PPC64Triples,
-                     PPC64Triples + llvm::array_lengthof(PPC64Triples));
+  llvm::Triple::ArchType HostArch = llvm::Triple(GccTriple).getArch();
+  // The library directories which may contain GCC installations.
+  SmallVector<StringRef, 4> CandidateLibDirs;
+  // The compatible GCC triples for this particular architecture.
+  SmallVector<StringRef, 10> CandidateTriples;
+  CollectLibDirsAndTriples(HostArch, CandidateLibDirs, CandidateTriples);
+
+  // Always include the default host triple as the final fallback if no
+  // specific triple is detected.
+  CandidateTriples.push_back(D.DefaultHostTriple);
+
+  // Compute the set of prefixes for our search.
+  SmallVector<std::string, 8> Prefixes(D.PrefixDirs.begin(),
+                                       D.PrefixDirs.end());
+  Prefixes.push_back(D.SysRoot);
+  Prefixes.push_back(D.SysRoot + "/usr");
+  Prefixes.push_back(D.InstalledDir + "/..");
+
+  // Loop over the various components which exist and select the best GCC
+  // installation available. GCC installs are ranked by version number.
+  Version = GCCVersion::Parse("0.0.0");
+  for (unsigned i = 0, ie = Prefixes.size(); i < ie; ++i) {
+    if (!llvm::sys::fs::exists(Prefixes[i]))
+      continue;
+    for (unsigned j = 0, je = CandidateLibDirs.size(); j < je; ++j) {
+      const std::string LibDir = Prefixes[i] + CandidateLibDirs[j].str();
+      if (!llvm::sys::fs::exists(LibDir))
+        continue;
+      for (unsigned k = 0, ke = CandidateTriples.size(); k < ke; ++k)
+        ScanLibDirForGCCTriple(HostArch, LibDir, CandidateTriples[k]);
     }
   }
+}
 
-  void ScanLibDirForGCCTriple(const std::string &LibDir,
-                              StringRef CandidateTriple,
-                              GCCVersion &BestVersion) {
-    // There are various different suffixes involving the triple we
-    // check for. We also record what is necessary to walk from each back
-    // up to the lib directory.
-    const std::string Suffixes[] = {
-      "/gcc/" + CandidateTriple.str(),
-      "/" + CandidateTriple.str() + "/gcc/" + CandidateTriple.str(),
-
-      // Ubuntu has a strange mis-matched pair of triples that this happens to
-      // match.
-      // FIXME: It may be worthwhile to generalize this and look for a second
-      // triple.
-      "/" + CandidateTriple.str() + "/gcc/i686-linux-gnu"
+/*static*/ void Linux::GCCInstallationDetector::CollectLibDirsAndTriples(
+    llvm::Triple::ArchType HostArch, SmallVectorImpl<StringRef> &LibDirs,
+    SmallVectorImpl<StringRef> &Triples) {
+  if (HostArch == llvm::Triple::arm || HostArch == llvm::Triple::thumb) {
+    static const char *const ARMLibDirs[] = { "/lib" };
+    static const char *const ARMTriples[] = { "arm-linux-gnueabi" };
+    LibDirs.append(ARMLibDirs, ARMLibDirs + llvm::array_lengthof(ARMLibDirs));
+    Triples.append(ARMTriples, ARMTriples + llvm::array_lengthof(ARMTriples));
+  } else if (HostArch == llvm::Triple::x86_64) {
+    static const char *const X86_64LibDirs[] = { "/lib64", "/lib" };
+    static const char *const X86_64Triples[] = {
+      "x86_64-linux-gnu",
+      "x86_64-unknown-linux-gnu",
+      "x86_64-pc-linux-gnu",
+      "x86_64-redhat-linux6E",
+      "x86_64-redhat-linux",
+      "x86_64-suse-linux",
+      "x86_64-manbo-linux-gnu",
+      "x86_64-linux-gnu",
+      "x86_64-slackware-linux"
     };
-    const std::string InstallSuffixes[] = {
-      "/../../..",
-      "/../../../..",
-      "/../../../.."
+    LibDirs.append(X86_64LibDirs,
+                   X86_64LibDirs + llvm::array_lengthof(X86_64LibDirs));
+    Triples.append(X86_64Triples,
+                   X86_64Triples + llvm::array_lengthof(X86_64Triples));
+  } else if (HostArch == llvm::Triple::x86) {
+    static const char *const X86LibDirs[] = { "/lib32", "/lib" };
+    static const char *const X86Triples[] = {
+      "i686-linux-gnu",
+      "i686-pc-linux-gnu",
+      "i486-linux-gnu",
+      "i386-linux-gnu",
+      "i686-redhat-linux",
+      "i586-redhat-linux",
+      "i386-redhat-linux",
+      "i586-suse-linux",
+      "i486-slackware-linux"
     };
-    // Only look at the final, weird Ubuntu suffix for i386-linux-gnu.
-    const unsigned NumSuffixes = (llvm::array_lengthof(Suffixes) -
-                                  (CandidateTriple != "i386-linux-gnu"));
-    for (unsigned i = 0; i < NumSuffixes; ++i) {
-      StringRef Suffix = Suffixes[i];
-      llvm::error_code EC;
-      for (llvm::sys::fs::directory_iterator LI(LibDir + Suffix, EC), LE;
-           !EC && LI != LE; LI = LI.increment(EC)) {
-        StringRef VersionText = llvm::sys::path::filename(LI->path());
-        GCCVersion CandidateVersion = GCCVersion::Parse(VersionText);
-        static const GCCVersion MinVersion = { 4, 1, 1 };
-        if (CandidateVersion < MinVersion)
-          continue;
-        if (CandidateVersion <= BestVersion)
-          continue;
-        if (!PathExists(LI->path() + "/crtbegin.o"))
-          continue;
+    LibDirs.append(X86LibDirs, X86LibDirs + llvm::array_lengthof(X86LibDirs));
+    Triples.append(X86Triples, X86Triples + llvm::array_lengthof(X86Triples));
+  } else if (HostArch == llvm::Triple::ppc) {
+    static const char *const PPCLibDirs[] = { "/lib32", "/lib" };
+    static const char *const PPCTriples[] = {
+      "powerpc-linux-gnu",
+      "powerpc-unknown-linux-gnu"
+    };
+    LibDirs.append(PPCLibDirs, PPCLibDirs + llvm::array_lengthof(PPCLibDirs));
+    Triples.append(PPCTriples, PPCTriples + llvm::array_lengthof(PPCTriples));
+  } else if (HostArch == llvm::Triple::ppc64) {
+    static const char *const PPC64LibDirs[] = { "/lib64", "/lib" };
+    static const char *const PPC64Triples[] = {
+      "powerpc64-unknown-linux-gnu"
+    };
+    LibDirs.append(PPC64LibDirs,
+                   PPC64LibDirs + llvm::array_lengthof(PPC64LibDirs));
+    Triples.append(PPC64Triples,
+                   PPC64Triples + llvm::array_lengthof(PPC64Triples));
+  }
+}
 
-        BestVersion = CandidateVersion;
-        GccTriple = CandidateTriple.str();
-        // FIXME: We hack together the directory name here instead of
-        // using LI to ensure stable path separators across Windows and
-        // Linux.
-        GccInstallPath = LibDir + Suffixes[i] + "/" + VersionText.str();
-        GccParentLibPath = GccInstallPath + InstallSuffixes[i];
-        IsValid = true;
-      }
+void Linux::GCCInstallationDetector::ScanLibDirForGCCTriple(
+    llvm::Triple::ArchType HostArch, const std::string &LibDir,
+    StringRef CandidateTriple) {
+  // There are various different suffixes involving the triple we
+  // check for. We also record what is necessary to walk from each back
+  // up to the lib directory.
+  const std::string Suffixes[] = {
+    "/gcc/" + CandidateTriple.str(),
+    "/" + CandidateTriple.str() + "/gcc/" + CandidateTriple.str(),
+
+    // Ubuntu has a strange mis-matched pair of triples that this happens to
+    // match.
+    // FIXME: It may be worthwhile to generalize this and look for a second
+    // triple.
+    "/i386-linux-gnu/gcc/" + CandidateTriple.str()
+  };
+  const std::string InstallSuffixes[] = {
+    "/../../..",
+    "/../../../..",
+    "/../../../.."
+  };
+  // Only look at the final, weird Ubuntu suffix for i386-linux-gnu.
+  const unsigned NumSuffixes = (llvm::array_lengthof(Suffixes) -
+                                (HostArch != llvm::Triple::x86));
+  for (unsigned i = 0; i < NumSuffixes; ++i) {
+    StringRef Suffix = Suffixes[i];
+    llvm::error_code EC;
+    for (llvm::sys::fs::directory_iterator LI(LibDir + Suffix, EC), LE;
+         !EC && LI != LE; LI = LI.increment(EC)) {
+      StringRef VersionText = llvm::sys::path::filename(LI->path());
+      GCCVersion CandidateVersion = GCCVersion::Parse(VersionText);
+      static const GCCVersion MinVersion = { "4.1.1", 4, 1, 1, "" };
+      if (CandidateVersion < MinVersion)
+        continue;
+      if (CandidateVersion <= Version)
+        continue;
+      if (!llvm::sys::fs::exists(LI->path() + "/crtbegin.o"))
+        continue;
+
+      Version = CandidateVersion;
+      GccTriple = CandidateTriple.str();
+      // FIXME: We hack together the directory name here instead of
+      // using LI to ensure stable path separators across Windows and
+      // Linux.
+      GccInstallPath = LibDir + Suffixes[i] + "/" + VersionText.str();
+      GccParentLibPath = GccInstallPath + InstallSuffixes[i];
+      IsValid = true;
     }
   }
-};
 }
 
-static void addPathIfExists(const std::string &Path,
-                            ToolChain::path_list &Paths) {
-  if (PathExists(Path)) Paths.push_back(Path);
+static void addPathIfExists(Twine Path, ToolChain::path_list &Paths) {
+  if (llvm::sys::fs::exists(Path)) Paths.push_back(Path.str());
+}
+
+/// \brief Get our best guess at the multiarch triple for a target.
+///
+/// Debian-based systems are starting to use a multiarch setup where they use
+/// a target-triple directory in the library and header search paths.
+/// Unfortunately, this triple does not align with the vanilla target triple,
+/// so we provide a rough mapping here.
+static std::string getMultiarchTriple(const llvm::Triple TargetTriple,
+                                      StringRef SysRoot) {
+  // For most architectures, just use whatever we have rather than trying to be
+  // clever.
+  switch (TargetTriple.getArch()) {
+  default:
+    return TargetTriple.str();
+
+    // We use the existence of '/lib/<triple>' as a directory to detect some
+    // common linux triples that don't quite match the Clang triple for both
+    // 32-bit and 64-bit targets. This works around annoying discrepancies on
+    // Debian-based systems.
+  case llvm::Triple::x86:
+    if (llvm::sys::fs::exists(SysRoot + "/lib/i686-linux-gnu"))
+      return "i686-linux-gnu";
+    if (llvm::sys::fs::exists(SysRoot + "/lib/i386-linux-gnu"))
+      return "i386-linux-gnu";
+    return TargetTriple.str();
+  case llvm::Triple::x86_64:
+    if (llvm::sys::fs::exists(SysRoot + "/lib/x86_64-linux-gnu"))
+      return "x86_64-linux-gnu";
+    if (llvm::sys::fs::exists(SysRoot + "/lib/x86_64-pc-linux-gnu"))
+      return "x86_64-pc-linux-gnu";
+    if (llvm::sys::fs::exists(SysRoot + "/lib/x86_64-unknown-linux-gnu"))
+      return "x86_64-unknown-linux-gnu";
+    return TargetTriple.str();
+  }
 }
 
 Linux::Linux(const HostInfo &Host, const llvm::Triple &Triple)
-  : Generic_ELF(Host, Triple) {
+  : Generic_ELF(Host, Triple), GCCInstallation(getDriver()) {
   llvm::Triple::ArchType Arch =
     llvm::Triple(getDriver().DefaultHostTriple).getArch();
   const std::string &SysRoot = getDriver().SysRoot;
-  GCCInstallationDetector GCCInstallation(getDriver());
 
   // OpenSuse stores the linker with the compiler, add that to the search
   // path.
   ToolChain::path_list &PPaths = getProgramPaths();
-  PPaths.push_back(GCCInstallation.getParentLibPath() + "/../" +
-                   GCCInstallation.getTriple() + "/bin");
+  PPaths.push_back(Twine(GCCInstallation.getParentLibPath() + "/../" +
+                         GCCInstallation.getTriple() + "/bin").str());
 
   Linker = GetProgramPath("ld");
 
@@ -1804,50 +1845,43 @@ Linux::Linux(const HostInfo &Host, const llvm::Triple &Triple)
   const std::string Suffix64 = Arch == llvm::Triple::x86_64 ? "" : "/64";
   const std::string Suffix = Is32Bits ? Suffix32 : Suffix64;
   const std::string Multilib = Is32Bits ? "lib32" : "lib64";
+  const std::string MultiarchTriple = getMultiarchTriple(Triple, SysRoot);
 
-  // FIXME: Because we add paths only when they exist on the system, I think we
-  // should remove the concept of 'HasMultilib'. It's more likely to break the
-  // behavior than to preserve any useful invariant on the system.
-  if (HasMultilib(Arch, Distro)) {
-    // Add the multilib suffixed paths.
-    if (GCCInstallation.isValid()) {
-      const std::string &LibPath = GCCInstallation.getParentLibPath();
-      const std::string &GccTriple = GCCInstallation.getTriple();
-      // FIXME: This OpenSuse-specific path shouldn't be needed any more, but
-      // I don't want to remove it without finding someone to test.
-      if (IsOpenSuse(Distro) && Is32Bits)
-        Paths.push_back(LibPath + "/../" + GccTriple + "/lib/../lib");
-
-      addPathIfExists(GCCInstallation.getInstallPath() + Suffix, Paths);
-      addPathIfExists(LibPath + "/../" + GccTriple + "/lib/../" + Multilib,
-                      Paths);
-      addPathIfExists(LibPath + "/../" + Multilib, Paths);
-    }
-    addPathIfExists(SysRoot + "/lib/../" + Multilib, Paths);
-    addPathIfExists(SysRoot + "/usr/lib/../" + Multilib, Paths);
-
-    // Try walking via the GCC triple path in case of multiarch GCC
-    // installations with strange symlinks.
-    if (GCCInstallation.isValid())
-      addPathIfExists(SysRoot + "/usr/lib/" + GCCInstallation.getTriple() +
-                      "/../../" + Multilib, Paths);
+  // Add the multilib suffixed paths where they are available.
+  if (GCCInstallation.isValid()) {
+    const std::string &LibPath = GCCInstallation.getParentLibPath();
+    const std::string &GccTriple = GCCInstallation.getTriple();
+    addPathIfExists(GCCInstallation.getInstallPath() + Suffix, Paths);
+    addPathIfExists(LibPath + "/../" + GccTriple + "/lib/../" + Multilib,
+                    Paths);
+    addPathIfExists(LibPath + "/" + MultiarchTriple, Paths);
+    addPathIfExists(LibPath + "/../" + Multilib, Paths);
   }
+  addPathIfExists(SysRoot + "/lib/" + MultiarchTriple, Paths);
+  addPathIfExists(SysRoot + "/lib/../" + Multilib, Paths);
+  addPathIfExists(SysRoot + "/usr/lib/" + MultiarchTriple, Paths);
+  addPathIfExists(SysRoot + "/usr/lib/../" + Multilib, Paths);
+
+  // Try walking via the GCC triple path in case of multiarch GCC
+  // installations with strange symlinks.
+  if (GCCInstallation.isValid())
+    addPathIfExists(SysRoot + "/usr/lib/" + GCCInstallation.getTriple() +
+                    "/../../" + Multilib, Paths);
 
   // Add the non-multilib suffixed paths (if potentially different).
   if (GCCInstallation.isValid()) {
     const std::string &LibPath = GCCInstallation.getParentLibPath();
     const std::string &GccTriple = GCCInstallation.getTriple();
-    if (!Suffix.empty() || !HasMultilib(Arch, Distro))
+    if (!Suffix.empty())
       addPathIfExists(GCCInstallation.getInstallPath(), Paths);
     addPathIfExists(LibPath + "/../" + GccTriple + "/lib", Paths);
+    addPathIfExists(LibPath + "/" + MultiarchTriple, Paths);
     addPathIfExists(LibPath, Paths);
   }
+  addPathIfExists(SysRoot + "/lib/" + MultiarchTriple, Paths);
   addPathIfExists(SysRoot + "/lib", Paths);
+  addPathIfExists(SysRoot + "/usr/lib/" + MultiarchTriple, Paths);
   addPathIfExists(SysRoot + "/usr/lib", Paths);
-
-  // Add a multiarch lib directory whenever it exists and is plausible.
-  if (GCCInstallation.isValid() && Arch == getArch())
-    addPathIfExists(SysRoot + "/usr/lib/" + GCCInstallation.getTriple(), Paths);
 }
 
 bool Linux::HasNativeLLVMSupport() const {
@@ -1885,6 +1919,161 @@ Tool &Linux::SelectTool(const Compilation &C, const JobAction &JA,
   return *T;
 }
 
+void Linux::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
+                                      ArgStringList &CC1Args) const {
+  const Driver &D = getDriver();
+
+  if (DriverArgs.hasArg(options::OPT_nostdinc))
+    return;
+
+  if (!DriverArgs.hasArg(options::OPT_nostdlibinc))
+    addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/usr/local/include");
+
+  if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
+    llvm::sys::Path P(D.ResourceDir);
+    P.appendComponent("include");
+    addSystemInclude(DriverArgs, CC1Args, P.str());
+  }
+
+  if (DriverArgs.hasArg(options::OPT_nostdlibinc))
+    return;
+
+  // Check for configure-time C include directories.
+  StringRef CIncludeDirs(C_INCLUDE_DIRS);
+  if (CIncludeDirs != "") {
+    SmallVector<StringRef, 5> dirs;
+    CIncludeDirs.split(dirs, ":");
+    for (SmallVectorImpl<StringRef>::iterator I = dirs.begin(), E = dirs.end();
+         I != E; ++I) {
+      StringRef Prefix = llvm::sys::path::is_absolute(*I) ? D.SysRoot : "";
+      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + *I);
+    }
+    return;
+  }
+
+  // Lacking those, try to detect the correct set of system includes for the
+  // target triple.
+
+  // Implement generic Debian multiarch support.
+  const StringRef X86_64MultiarchIncludeDirs[] = {
+    "/usr/include/x86_64-linux-gnu",
+
+    // FIXME: These are older forms of multiarch. It's not clear that they're
+    // in use in any released version of Debian, so we should consider
+    // removing them.
+    "/usr/include/i686-linux-gnu/64",
+    "/usr/include/i486-linux-gnu/64"
+  };
+  const StringRef X86MultiarchIncludeDirs[] = {
+    "/usr/include/i386-linux-gnu",
+
+    // FIXME: These are older forms of multiarch. It's not clear that they're
+    // in use in any released version of Debian, so we should consider
+    // removing them.
+    "/usr/include/x86_64-linux-gnu/32",
+    "/usr/include/i686-linux-gnu",
+    "/usr/include/i486-linux-gnu"
+  };
+  const StringRef ARMMultiarchIncludeDirs[] = {
+    "/usr/include/arm-linux-gnueabi"
+  };
+  ArrayRef<StringRef> MultiarchIncludeDirs;
+  if (getTriple().getArch() == llvm::Triple::x86_64) {
+    MultiarchIncludeDirs = X86_64MultiarchIncludeDirs;
+  } else if (getTriple().getArch() == llvm::Triple::x86) {
+    MultiarchIncludeDirs = X86MultiarchIncludeDirs;
+  } else if (getTriple().getArch() == llvm::Triple::arm) {
+    MultiarchIncludeDirs = ARMMultiarchIncludeDirs;
+  }
+  for (ArrayRef<StringRef>::iterator I = MultiarchIncludeDirs.begin(),
+                                     E = MultiarchIncludeDirs.end();
+       I != E; ++I) {
+    if (llvm::sys::fs::exists(*I)) {
+      addExternCSystemInclude(DriverArgs, CC1Args, D.SysRoot + *I);
+      break;
+    }
+  }
+
+  if (getTriple().getOS() == llvm::Triple::RTEMS)
+    return;
+
+  addExternCSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/usr/include");
+}
+
+static bool addLibStdCXXIncludePaths(Twine Base, Twine TargetArchDir,
+                                     const ArgList &DriverArgs,
+                                     ArgStringList &CC1Args) {
+  if (!llvm::sys::fs::exists(Base))
+    return false;
+  addSystemInclude(DriverArgs, CC1Args, Base);
+  addSystemInclude(DriverArgs, CC1Args, Base + "/" + TargetArchDir);
+  addSystemInclude(DriverArgs, CC1Args, Base + "/backward");
+  return true;
+}
+
+void Linux::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
+                                         ArgStringList &CC1Args) const {
+  if (DriverArgs.hasArg(options::OPT_nostdlibinc) ||
+      DriverArgs.hasArg(options::OPT_nostdincxx))
+    return;
+
+  // Check if libc++ has been enabled and provide its include paths if so.
+  if (GetCXXStdlibType(DriverArgs) == ToolChain::CST_Libcxx) {
+    // libc++ is always installed at a fixed path on Linux currently.
+    addSystemInclude(DriverArgs, CC1Args,
+                     getDriver().SysRoot + "/usr/include/c++/v1");
+    return;
+  }
+
+  const llvm::Triple &TargetTriple = getTriple();
+  const llvm::Triple::ArchType TargetArch = TargetTriple.getArch();
+  bool IsTarget64Bit = (TargetArch == llvm::Triple::x86_64 ||
+                        TargetArch == llvm::Triple::ppc64);
+
+  StringRef CxxIncludeRoot(CXX_INCLUDE_ROOT);
+  if (!CxxIncludeRoot.empty()) {
+    StringRef CxxIncludeArch(CXX_INCLUDE_ARCH);
+    if (CxxIncludeArch.empty())
+      CxxIncludeArch = TargetTriple.str();
+
+    addLibStdCXXIncludePaths(
+      CxxIncludeRoot,
+      CxxIncludeArch + (IsTarget64Bit ? CXX_INCLUDE_64BIT_DIR
+                                      : CXX_INCLUDE_32BIT_DIR),
+      DriverArgs, CC1Args);
+    return;
+  }
+
+  // Check if the target architecture specific dirs need a suffix. Note that we
+  // only support the suffix-based bi-arch-like header scheme for host/target
+  // mismatches of just bit width.
+  llvm::Triple::ArchType HostArch =
+    llvm::Triple(getDriver().DefaultHostTriple).getArch();
+  StringRef Suffix;
+  if ((HostArch == llvm::Triple::x86 && TargetArch == llvm::Triple::x86_64) ||
+      (HostArch == llvm::Triple::ppc && TargetArch == llvm::Triple::ppc64))
+    Suffix = "/64";
+  if ((HostArch == llvm::Triple::x86_64 && TargetArch == llvm::Triple::x86) ||
+      (HostArch == llvm::Triple::ppc64 && TargetArch == llvm::Triple::ppc))
+    Suffix = "/32";
+
+  // By default, look for the C++ headers in an include directory adjacent to
+  // the lib directory of the GCC installation. Note that this is expect to be
+  // equivalent to '/usr/include/c++/X.Y' in almost all cases.
+  StringRef LibDir = GCCInstallation.getParentLibPath();
+  StringRef InstallDir = GCCInstallation.getInstallPath();
+  StringRef Version = GCCInstallation.getVersion();
+  if (!addLibStdCXXIncludePaths(LibDir + "/../include/c++/" + Version,
+                                GCCInstallation.getTriple() + Suffix,
+                                DriverArgs, CC1Args)) {
+    // Gentoo is weird and places its headers inside the GCC install, so if the
+    // first attempt to find the headers fails, try this pattern.
+    addLibStdCXXIncludePaths(InstallDir + "/include/g++-v4",
+                             GCCInstallation.getTriple() + Suffix,
+                             DriverArgs, CC1Args);
+  }
+}
+
 /// DragonFly - DragonFly tool chain which can call as(1) and ld(1) directly.
 
 DragonFly::DragonFly(const HostInfo &Host, const llvm::Triple& Triple)
@@ -1986,3 +2175,258 @@ const char *Windows::GetForcedPicModel() const {
     return "pic";
   return 0;
 }
+
+// FIXME: This probably should goto to some platform utils place.
+#ifdef _MSC_VER
+
+/// \brief Read registry string.
+/// This also supports a means to look for high-versioned keys by use
+/// of a $VERSION placeholder in the key path.
+/// $VERSION in the key path is a placeholder for the version number,
+/// causing the highest value path to be searched for and used.
+/// I.e. "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\VisualStudio\\$VERSION".
+/// There can be additional characters in the component.  Only the numberic
+/// characters are compared.
+static bool getSystemRegistryString(const char *keyPath, const char *valueName,
+                                    char *value, size_t maxLength) {
+  HKEY hRootKey = NULL;
+  HKEY hKey = NULL;
+  const char* subKey = NULL;
+  DWORD valueType;
+  DWORD valueSize = maxLength - 1;
+  long lResult;
+  bool returnValue = false;
+
+  if (strncmp(keyPath, "HKEY_CLASSES_ROOT\\", 18) == 0) {
+    hRootKey = HKEY_CLASSES_ROOT;
+    subKey = keyPath + 18;
+  } else if (strncmp(keyPath, "HKEY_USERS\\", 11) == 0) {
+    hRootKey = HKEY_USERS;
+    subKey = keyPath + 11;
+  } else if (strncmp(keyPath, "HKEY_LOCAL_MACHINE\\", 19) == 0) {
+    hRootKey = HKEY_LOCAL_MACHINE;
+    subKey = keyPath + 19;
+  } else if (strncmp(keyPath, "HKEY_CURRENT_USER\\", 18) == 0) {
+    hRootKey = HKEY_CURRENT_USER;
+    subKey = keyPath + 18;
+  } else {
+    return false;
+  }
+
+  const char *placeHolder = strstr(subKey, "$VERSION");
+  char bestName[256];
+  bestName[0] = '\0';
+  // If we have a $VERSION placeholder, do the highest-version search.
+  if (placeHolder) {
+    const char *keyEnd = placeHolder - 1;
+    const char *nextKey = placeHolder;
+    // Find end of previous key.
+    while ((keyEnd > subKey) && (*keyEnd != '\\'))
+      keyEnd--;
+    // Find end of key containing $VERSION.
+    while (*nextKey && (*nextKey != '\\'))
+      nextKey++;
+    size_t partialKeyLength = keyEnd - subKey;
+    char partialKey[256];
+    if (partialKeyLength > sizeof(partialKey))
+      partialKeyLength = sizeof(partialKey);
+    strncpy(partialKey, subKey, partialKeyLength);
+    partialKey[partialKeyLength] = '\0';
+    HKEY hTopKey = NULL;
+    lResult = RegOpenKeyEx(hRootKey, partialKey, 0, KEY_READ, &hTopKey);
+    if (lResult == ERROR_SUCCESS) {
+      char keyName[256];
+      int bestIndex = -1;
+      double bestValue = 0.0;
+      DWORD index, size = sizeof(keyName) - 1;
+      for (index = 0; RegEnumKeyEx(hTopKey, index, keyName, &size, NULL,
+          NULL, NULL, NULL) == ERROR_SUCCESS; index++) {
+        const char *sp = keyName;
+        while (*sp && !isdigit(*sp))
+          sp++;
+        if (!*sp)
+          continue;
+        const char *ep = sp + 1;
+        while (*ep && (isdigit(*ep) || (*ep == '.')))
+          ep++;
+        char numBuf[32];
+        strncpy(numBuf, sp, sizeof(numBuf) - 1);
+        numBuf[sizeof(numBuf) - 1] = '\0';
+        double value = strtod(numBuf, NULL);
+        if (value > bestValue) {
+          bestIndex = (int)index;
+          bestValue = value;
+          strcpy(bestName, keyName);
+        }
+        size = sizeof(keyName) - 1;
+      }
+      // If we found the highest versioned key, open the key and get the value.
+      if (bestIndex != -1) {
+        // Append rest of key.
+        strncat(bestName, nextKey, sizeof(bestName) - 1);
+        bestName[sizeof(bestName) - 1] = '\0';
+        // Open the chosen key path remainder.
+        lResult = RegOpenKeyEx(hTopKey, bestName, 0, KEY_READ, &hKey);
+        if (lResult == ERROR_SUCCESS) {
+          lResult = RegQueryValueEx(hKey, valueName, NULL, &valueType,
+            (LPBYTE)value, &valueSize);
+          if (lResult == ERROR_SUCCESS)
+            returnValue = true;
+          RegCloseKey(hKey);
+        }
+      }
+      RegCloseKey(hTopKey);
+    }
+  } else {
+    lResult = RegOpenKeyEx(hRootKey, subKey, 0, KEY_READ, &hKey);
+    if (lResult == ERROR_SUCCESS) {
+      lResult = RegQueryValueEx(hKey, valueName, NULL, &valueType,
+        (LPBYTE)value, &valueSize);
+      if (lResult == ERROR_SUCCESS)
+        returnValue = true;
+      RegCloseKey(hKey);
+    }
+  }
+  return returnValue;
+}
+
+/// \brief Get Windows SDK installation directory.
+static bool getWindowsSDKDir(std::string &path) {
+  char windowsSDKInstallDir[256];
+  // Try the Windows registry.
+  bool hasSDKDir = getSystemRegistryString(
+   "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Microsoft SDKs\\Windows\\$VERSION",
+                                           "InstallationFolder",
+                                           windowsSDKInstallDir,
+                                           sizeof(windowsSDKInstallDir) - 1);
+    // If we have both vc80 and vc90, pick version we were compiled with.
+  if (hasSDKDir && windowsSDKInstallDir[0]) {
+    path = windowsSDKInstallDir;
+    return true;
+  }
+  return false;
+}
+
+  // Get Visual Studio installation directory.
+static bool getVisualStudioDir(std::string &path) {
+  // First check the environment variables that vsvars32.bat sets.
+  const char* vcinstalldir = getenv("VCINSTALLDIR");
+  if (vcinstalldir) {
+    char *p = const_cast<char *>(strstr(vcinstalldir, "\\VC"));
+    if (p)
+      *p = '\0';
+    path = vcinstalldir;
+    return true;
+  }
+
+  char vsIDEInstallDir[256];
+  char vsExpressIDEInstallDir[256];
+  // Then try the windows registry.
+  bool hasVCDir = getSystemRegistryString(
+    "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\VisualStudio\\$VERSION",
+    "InstallDir", vsIDEInstallDir, sizeof(vsIDEInstallDir) - 1);
+  bool hasVCExpressDir = getSystemRegistryString(
+    "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\VCExpress\\$VERSION",
+    "InstallDir", vsExpressIDEInstallDir, sizeof(vsExpressIDEInstallDir) - 1);
+    // If we have both vc80 and vc90, pick version we were compiled with.
+  if (hasVCDir && vsIDEInstallDir[0]) {
+    char *p = (char*)strstr(vsIDEInstallDir, "\\Common7\\IDE");
+    if (p)
+      *p = '\0';
+    path = vsIDEInstallDir;
+    return true;
+  }
+
+  if (hasVCExpressDir && vsExpressIDEInstallDir[0]) {
+    char *p = (char*)strstr(vsExpressIDEInstallDir, "\\Common7\\IDE");
+    if (p)
+      *p = '\0';
+    path = vsExpressIDEInstallDir;
+    return true;
+  }
+
+  // Try the environment.
+  const char *vs100comntools = getenv("VS100COMNTOOLS");
+  const char *vs90comntools = getenv("VS90COMNTOOLS");
+  const char *vs80comntools = getenv("VS80COMNTOOLS");
+  const char *vscomntools = NULL;
+
+  // Try to find the version that we were compiled with
+  if(false) {}
+  #if (_MSC_VER >= 1600)  // VC100
+  else if(vs100comntools) {
+    vscomntools = vs100comntools;
+  }
+  #elif (_MSC_VER == 1500) // VC80
+  else if(vs90comntools) {
+    vscomntools = vs90comntools;
+  }
+  #elif (_MSC_VER == 1400) // VC80
+  else if(vs80comntools) {
+    vscomntools = vs80comntools;
+  }
+  #endif
+  // Otherwise find any version we can
+  else if (vs100comntools)
+    vscomntools = vs100comntools;
+  else if (vs90comntools)
+    vscomntools = vs90comntools;
+  else if (vs80comntools)
+    vscomntools = vs80comntools;
+
+  if (vscomntools && *vscomntools) {
+    const char *p = strstr(vscomntools, "\\Common7\\Tools");
+    path = p ? std::string(vscomntools, p) : vscomntools;
+    return true;
+  }
+  return false;
+}
+
+#endif // _MSC_VER
+
+void Windows::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
+                                        ArgStringList &CC1Args) const {
+  if (DriverArgs.hasArg(options::OPT_nostdinc))
+    return;
+
+  if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
+    llvm::sys::Path P(getDriver().ResourceDir);
+    P.appendComponent("include");
+    addSystemInclude(DriverArgs, CC1Args, P.str());
+  }
+
+  if (DriverArgs.hasArg(options::OPT_nostdlibinc))
+    return;
+
+  std::string VSDir;
+  std::string WindowsSDKDir;
+
+#ifdef _MSC_VER
+  // When built with access to the proper Windows APIs, try to actually find
+  // the correct include paths first.
+  if (getVisualStudioDir(VSDir)) {
+    addSystemInclude(DriverArgs, CC1Args, VSDir + "\\VC\\include");
+    if (getWindowsSDKDir(WindowsSDKDir))
+      addSystemInclude(DriverArgs, CC1Args, WindowsSDKDir + "\\include");
+    else
+      addSystemInclude(DriverArgs, CC1Args,
+                       VSDir + "\\VC\\PlatformSDK\\Include");
+    return;
+  }
+#endif // _MSC_VER
+
+  // As a fallback, select default install paths.
+  const StringRef Paths[] = {
+    "C:/Program Files/Microsoft Visual Studio 10.0/VC/include",
+    "C:/Program Files/Microsoft Visual Studio 9.0/VC/include",
+    "C:/Program Files/Microsoft Visual Studio 9.0/VC/PlatformSDK/Include",
+    "C:/Program Files/Microsoft Visual Studio 8/VC/include",
+    "C:/Program Files/Microsoft Visual Studio 8/VC/PlatformSDK/Include"
+  };
+  addSystemIncludes(DriverArgs, CC1Args, Paths);
+}
+
+void Windows::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
+                                           ArgStringList &CC1Args) const {
+  // FIXME: There should probably be logic here to find libc++ on Windows.
+}
diff --git a/lib/Driver/ToolChains.h b/lib/Driver/ToolChains.h
index dfcb253acd88..0e4d67c5d149 100644
--- a/lib/Driver/ToolChains.h
+++ b/lib/Driver/ToolChains.h
@@ -372,6 +372,86 @@ public:
 };
 
 class LLVM_LIBRARY_VISIBILITY Linux : public Generic_ELF {
+  /// \brief Struct to store and manipulate GCC versions.
+  ///
+  /// We rely on assumptions about the form and structure of GCC version
+  /// numbers: they consist of at most three '.'-separated components, and each
+  /// component is a non-negative integer except for the last component. For
+  /// the last component we are very flexible in order to tolerate release
+  /// candidates or 'x' wildcards.
+  ///
+  /// Note that the ordering established among GCCVersions is based on the
+  /// preferred version string to use. For example we prefer versions without
+  /// a hard-coded patch number to those with a hard coded patch number.
+  ///
+  /// Currently this doesn't provide any logic for textual suffixes to patches
+  /// in the way that (for example) Debian's version format does. If that ever
+  /// becomes necessary, it can be added.
+  struct GCCVersion {
+    /// \brief The unparsed text of the version.
+    std::string Text;
+
+    /// \brief The parsed major, minor, and patch numbers.
+    int Major, Minor, Patch;
+
+    /// \brief Any textual suffix on the patch number.
+    std::string PatchSuffix;
+
+    static GCCVersion Parse(StringRef VersionText);
+    bool operator<(const GCCVersion &RHS) const;
+    bool operator>(const GCCVersion &RHS) const { return RHS < *this; }
+    bool operator<=(const GCCVersion &RHS) const { return !(*this > RHS); }
+    bool operator>=(const GCCVersion &RHS) const { return !(*this < RHS); }
+  };
+
+
+  /// \brief This is a class to find a viable GCC installation for Clang to
+  /// use.
+  ///
+  /// This class tries to find a GCC installation on the system, and report
+  /// information about it. It starts from the host information provided to the
+  /// Driver, and has logic for fuzzing that where appropriate.
+  class GCCInstallationDetector {
+
+    bool IsValid;
+    std::string GccTriple;
+
+    // FIXME: These might be better as path objects.
+    std::string GccInstallPath;
+    std::string GccParentLibPath;
+
+    GCCVersion Version;
+
+  public:
+    GCCInstallationDetector(const Driver &D);
+
+    /// \brief Check whether we detected a valid GCC install.
+    bool isValid() const { return IsValid; }
+
+    /// \brief Get the GCC triple for the detected install.
+    StringRef getTriple() const { return GccTriple; }
+
+    /// \brief Get the detected GCC installation path.
+    StringRef getInstallPath() const { return GccInstallPath; }
+
+    /// \brief Get the detected GCC parent lib path.
+    StringRef getParentLibPath() const { return GccParentLibPath; }
+
+    /// \brief Get the detected GCC version string.
+    StringRef getVersion() const { return Version.Text; }
+
+  private:
+    static void CollectLibDirsAndTriples(llvm::Triple::ArchType HostArch,
+                                         SmallVectorImpl<StringRef> &LibDirs,
+                                         SmallVectorImpl<StringRef> &Triples);
+
+    void ScanLibDirForGCCTriple(llvm::Triple::ArchType HostArch,
+                                const std::string &LibDir,
+                                StringRef CandidateTriple);
+  };
+
+  GCCInstallationDetector GCCInstallation;
+
 public:
   Linux(const HostInfo &Host, const llvm::Triple& Triple);
 
@@ -380,6 +460,11 @@ public:
   virtual Tool &SelectTool(const Compilation &C, const JobAction &JA,
                            const ActionList &Inputs) const;
 
+  virtual void AddClangSystemIncludeArgs(const ArgList &DriverArgs,
+                                         ArgStringList &CC1Args) const;
+  virtual void AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
+                                            ArgStringList &CC1Args) const;
+
   std::string Linker;
   std::vector<std::string> ExtraOpts;
 };
@@ -417,6 +502,12 @@ public:
   virtual bool IsUnwindTablesDefault() const;
   virtual const char *GetDefaultRelocationModel() const;
   virtual const char *GetForcedPicModel() const;
+
+  virtual void AddClangSystemIncludeArgs(const ArgList &DriverArgs,
+                                         ArgStringList &CC1Args) const;
+  virtual void AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
+                                            ArgStringList &CC1Args) const;
+
 };
 
 } // end namespace toolchains
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index 4b4ff25e281f..6151e881930c 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -364,16 +364,6 @@ void Clang::AddPreprocessingOptions(const Driver &D,
   Args.AddAllArgs(CmdArgs, options::OPT_I_Group, options::OPT_F,
                   options::OPT_index_header_map);
 
-  // Add C++ include arguments, if needed.
-  types::ID InputType = Inputs[0].getType();
-  if (types::isCXX(InputType)) {
-    bool ObjCXXAutoRefCount
-      = types::isObjC(InputType) && isObjCAutoRefCount(Args);
-    getToolChain().AddClangCXXStdlibIncludeArgs(Args, CmdArgs,
-                                                ObjCXXAutoRefCount);
-    Args.AddAllArgs(CmdArgs, options::OPT_stdlib_EQ);
-  }
-
   // Add -Wp, and -Xassembler if using the preprocessor.
 
   // FIXME: There is a very unfortunate problem here, some troubled
@@ -428,6 +418,13 @@ void Clang::AddPreprocessingOptions(const Driver &D,
   // OBJCPLUS_INCLUDE_PATH - system includes enabled when compiling ObjC++.
   AddIncludeDirectoryList(Args, CmdArgs, "-objcxx-isystem",
                           ::getenv("OBJCPLUS_INCLUDE_PATH"));
+
+  // Add C++ include arguments, if needed.
+  if (types::isCXX(Inputs[0].getType()))
+    getToolChain().AddClangCXXStdlibIncludeArgs(Args, CmdArgs);
+
+  // Add system include arguments.
+  getToolChain().AddClangSystemIncludeArgs(Args, CmdArgs);
 }
 
 /// getARMTargetCPU - Get the (LLVM) name of the ARM cpu we are targeting.
@@ -1965,6 +1962,16 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (ARC) {
     CmdArgs.push_back("-fobjc-arc");
 
+    // FIXME: It seems like this entire block, and several around it should be
+    // wrapped in isObjC, but for now we just use it here as this is where it
+    // was being used previously.
+    if (types::isCXX(InputType) && types::isObjC(InputType)) {
+      if (getToolChain().GetCXXStdlibType(Args) == ToolChain::CST_Libcxx)
+        CmdArgs.push_back("-fobjc-arc-cxxlib=libc++");
+      else
+        CmdArgs.push_back("-fobjc-arc-cxxlib=libstdc++");
+    }
+
     // Allow the user to enable full exceptions code emission.
     // We define off for Objective-CC, on for Objective-C++.
     if (Args.hasFlag(options::OPT_fobjc_arc_exceptions,
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 1debf3b35318..02b4ec04fd26 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -569,10 +569,18 @@ static void HeaderSearchOptsToArgs(const HeaderSearchOptions &Opts,
         break;
       }
     } else {
-      if (E.Group != frontend::Angled && E.Group != frontend::System)
-        llvm::report_fatal_error("Invalid option set!");
-      Res.push_back(E.Group == frontend::Angled ? "-iwithprefixbefore" :
-                    "-iwithprefix");
+      if (E.IsInternal) {
+        assert(E.Group == frontend::System && "Unexpected header search group");
+        if (E.ImplicitExternC)
+          Res.push_back("-internal-externc-isystem");
+        else
+          Res.push_back("-internal-isystem");
+      } else {
+        if (E.Group != frontend::Angled && E.Group != frontend::System)
+          llvm::report_fatal_error("Invalid option set!");
+        Res.push_back(E.Group == frontend::Angled ? "-iwithprefixbefore" :
+                      "-iwithprefix");
+      }
     }
     Res.push_back(E.Path);
   }
@@ -1462,6 +1470,15 @@ static void ParseHeaderSearchArgs(HeaderSearchOptions &Opts, ArgList &Args) {
        ie = Args.filtered_end(); it != ie; ++it)
     Opts.AddPath((*it)->getValue(Args), frontend::ObjCXXSystem, true, false,
                  true);
+
+  // Add the internal paths from a driver that detects standard include paths.
+  for (arg_iterator I = Args.filtered_begin(OPT_internal_isystem,
+                                            OPT_internal_externc_isystem),
+                    E = Args.filtered_end();
+       I != E; ++I)
+    Opts.AddPath((*I)->getValue(Args), frontend::System,
+                 false, false, /*IgnoreSysRoot=*/true, /*IsInternal=*/true,
+                 (*I)->getOption().matches(OPT_internal_externc_isystem));
 }
 
 void CompilerInvocation::setLangDefaults(LangOptions &Opts, InputKind IK,
diff --git a/lib/Frontend/InitHeaderSearch.cpp b/lib/Frontend/InitHeaderSearch.cpp
index b066e71a9435..051d5634b30f 100644
--- a/lib/Frontend/InitHeaderSearch.cpp
+++ b/lib/Frontend/InitHeaderSearch.cpp
@@ -27,12 +27,9 @@
 #include "llvm/ADT/Triple.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Config/config.h"
-#ifdef _MSC_VER
-  #define WIN32_LEAN_AND_MEAN 1
-  #include <windows.h>
-#endif
 using namespace clang;
 using namespace clang::frontend;
 
@@ -207,219 +204,6 @@ void InitHeaderSearch::AddMinGW64CXXPaths(StringRef Base,
           CXXSystem, true, false, false);
 }
 
-  // FIXME: This probably should goto to some platform utils place.
-#ifdef _MSC_VER
-
-  // Read registry string.
-  // This also supports a means to look for high-versioned keys by use
-  // of a $VERSION placeholder in the key path.
-  // $VERSION in the key path is a placeholder for the version number,
-  // causing the highest value path to be searched for and used.
-  // I.e. "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\VisualStudio\\$VERSION".
-  // There can be additional characters in the component.  Only the numberic
-  // characters are compared.
-static bool getSystemRegistryString(const char *keyPath, const char *valueName,
-                                    char *value, size_t maxLength) {
-  HKEY hRootKey = NULL;
-  HKEY hKey = NULL;
-  const char* subKey = NULL;
-  DWORD valueType;
-  DWORD valueSize = maxLength - 1;
-  long lResult;
-  bool returnValue = false;
-  
-  if (strncmp(keyPath, "HKEY_CLASSES_ROOT\\", 18) == 0) {
-    hRootKey = HKEY_CLASSES_ROOT;
-    subKey = keyPath + 18;
-  } else if (strncmp(keyPath, "HKEY_USERS\\", 11) == 0) {
-    hRootKey = HKEY_USERS;
-    subKey = keyPath + 11;
-  } else if (strncmp(keyPath, "HKEY_LOCAL_MACHINE\\", 19) == 0) {
-    hRootKey = HKEY_LOCAL_MACHINE;
-    subKey = keyPath + 19;
-  } else if (strncmp(keyPath, "HKEY_CURRENT_USER\\", 18) == 0) {
-    hRootKey = HKEY_CURRENT_USER;
-    subKey = keyPath + 18;
-  }
-  else
-    return false;
-  
-  const char *placeHolder = strstr(subKey, "$VERSION");
-  char bestName[256];
-  bestName[0] = '\0';
-  // If we have a $VERSION placeholder, do the highest-version search.
-  if (placeHolder) {
-    const char *keyEnd = placeHolder - 1;
-    const char *nextKey = placeHolder;
-    // Find end of previous key.
-    while ((keyEnd > subKey) && (*keyEnd != '\\'))
-      keyEnd--;
-    // Find end of key containing $VERSION.
-    while (*nextKey && (*nextKey != '\\'))
-      nextKey++;
-    size_t partialKeyLength = keyEnd - subKey;
-    char partialKey[256];
-    if (partialKeyLength > sizeof(partialKey))
-      partialKeyLength = sizeof(partialKey);
-    strncpy(partialKey, subKey, partialKeyLength);
-    partialKey[partialKeyLength] = '\0';
-    HKEY hTopKey = NULL;
-    lResult = RegOpenKeyEx(hRootKey, partialKey, 0, KEY_READ, &hTopKey);
-    if (lResult == ERROR_SUCCESS) {
-      char keyName[256];
-      int bestIndex = -1;
-      double bestValue = 0.0;
-      DWORD index, size = sizeof(keyName) - 1;
-      for (index = 0; RegEnumKeyEx(hTopKey, index, keyName, &size, NULL,
-          NULL, NULL, NULL) == ERROR_SUCCESS; index++) {
-        const char *sp = keyName;
-        while (*sp && !isdigit(*sp))
-          sp++;
-        if (!*sp)
-          continue;
-        const char *ep = sp + 1;
-        while (*ep && (isdigit(*ep) || (*ep == '.')))
-          ep++;
-        char numBuf[32];
-        strncpy(numBuf, sp, sizeof(numBuf) - 1);
-        numBuf[sizeof(numBuf) - 1] = '\0';
-        double value = strtod(numBuf, NULL);
-        if (value > bestValue) {
-          bestIndex = (int)index;
-          bestValue = value;
-          strcpy(bestName, keyName);
-        }
-        size = sizeof(keyName) - 1;
-      }
-      // If we found the highest versioned key, open the key and get the value.
-      if (bestIndex != -1) {
-        // Append rest of key.
-        strncat(bestName, nextKey, sizeof(bestName) - 1);
-        bestName[sizeof(bestName) - 1] = '\0';
-        // Open the chosen key path remainder.
-        lResult = RegOpenKeyEx(hTopKey, bestName, 0, KEY_READ, &hKey);
-        if (lResult == ERROR_SUCCESS) {
-          lResult = RegQueryValueEx(hKey, valueName, NULL, &valueType,
-            (LPBYTE)value, &valueSize);
-          if (lResult == ERROR_SUCCESS)
-            returnValue = true;
-          RegCloseKey(hKey);
-        }
-      }
-      RegCloseKey(hTopKey);
-    }
-  }
-  else {
-    lResult = RegOpenKeyEx(hRootKey, subKey, 0, KEY_READ, &hKey);
-    if (lResult == ERROR_SUCCESS) {
-      lResult = RegQueryValueEx(hKey, valueName, NULL, &valueType,
-        (LPBYTE)value, &valueSize);
-      if (lResult == ERROR_SUCCESS)
-        returnValue = true;
-      RegCloseKey(hKey);
-    }
-  }
-  return returnValue;
-}
-#else // _MSC_VER
-  // Read registry string.
-static bool getSystemRegistryString(const char*, const char*, char*, size_t) {
-  return(false);
-}
-#endif // _MSC_VER
-
-  // Get Visual Studio installation directory.
-static bool getVisualStudioDir(std::string &path) {
-  // First check the environment variables that vsvars32.bat sets.
-  const char* vcinstalldir = getenv("VCINSTALLDIR");
-  if (vcinstalldir) {
-    char *p = const_cast<char *>(strstr(vcinstalldir, "\\VC"));
-    if (p)
-      *p = '\0';
-    path = vcinstalldir;
-    return true;
-  }
-
-  char vsIDEInstallDir[256];
-  char vsExpressIDEInstallDir[256];
-  // Then try the windows registry.
-  bool hasVCDir = getSystemRegistryString(
-    "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\VisualStudio\\$VERSION",
-    "InstallDir", vsIDEInstallDir, sizeof(vsIDEInstallDir) - 1);
-  bool hasVCExpressDir = getSystemRegistryString(
-    "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\VCExpress\\$VERSION",
-    "InstallDir", vsExpressIDEInstallDir, sizeof(vsExpressIDEInstallDir) - 1);
-    // If we have both vc80 and vc90, pick version we were compiled with.
-  if (hasVCDir && vsIDEInstallDir[0]) {
-    char *p = (char*)strstr(vsIDEInstallDir, "\\Common7\\IDE");
-    if (p)
-      *p = '\0';
-    path = vsIDEInstallDir;
-    return true;
-  }
-  
-  if (hasVCExpressDir && vsExpressIDEInstallDir[0]) {
-    char *p = (char*)strstr(vsExpressIDEInstallDir, "\\Common7\\IDE");
-    if (p)
-      *p = '\0';
-    path = vsExpressIDEInstallDir;
-    return true;
-  }
-
-  // Try the environment.
-  const char *vs100comntools = getenv("VS100COMNTOOLS");
-  const char *vs90comntools = getenv("VS90COMNTOOLS");
-  const char *vs80comntools = getenv("VS80COMNTOOLS");
-  const char *vscomntools = NULL;
-
-  // Try to find the version that we were compiled with
-  if(false) {}
-  #if (_MSC_VER >= 1600)  // VC100
-  else if(vs100comntools) {
-    vscomntools = vs100comntools;
-  }
-  #elif (_MSC_VER == 1500) // VC80
-  else if(vs90comntools) {
-    vscomntools = vs90comntools;
-  }
-  #elif (_MSC_VER == 1400) // VC80
-  else if(vs80comntools) {
-    vscomntools = vs80comntools;
-  }
-  #endif
-  // Otherwise find any version we can
-  else if (vs100comntools)
-    vscomntools = vs100comntools;
-  else if (vs90comntools)
-    vscomntools = vs90comntools;
-  else if (vs80comntools)
-    vscomntools = vs80comntools;
-
-  if (vscomntools && *vscomntools) {
-    const char *p = strstr(vscomntools, "\\Common7\\Tools");
-    path = p ? std::string(vscomntools, p) : vscomntools;
-    return true;
-  }
-  return false;
-}
-
-  // Get Windows SDK installation directory.
-static bool getWindowsSDKDir(std::string &path) {
-  char windowsSDKInstallDir[256];
-  // Try the Windows registry.
-  bool hasSDKDir = getSystemRegistryString(
-   "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Microsoft SDKs\\Windows\\$VERSION",
-                                           "InstallationFolder",
-                                           windowsSDKInstallDir,
-                                           sizeof(windowsSDKInstallDir) - 1);
-    // If we have both vc80 and vc90, pick version we were compiled with.
-  if (hasSDKDir && windowsSDKInstallDir[0]) {
-    path = windowsSDKInstallDir;
-    return(true);
-  }
-  return(false);
-}
-
 void InitHeaderSearch::AddDefaultCIncludePaths(const llvm::Triple &triple,
                                             const HeaderSearchOptions &HSOpts) {
   llvm::Triple::OSType os = triple.getOS();
@@ -464,33 +248,10 @@ void InitHeaderSearch::AddDefaultCIncludePaths(const llvm::Triple &triple,
   }
 
   switch (os) {
-  case llvm::Triple::Win32: {
-    std::string VSDir;
-    std::string WindowsSDKDir;
-    if (getVisualStudioDir(VSDir)) {
-      AddPath(VSDir + "\\VC\\include", System, false, false, false);
-      if (getWindowsSDKDir(WindowsSDKDir))
-        AddPath(WindowsSDKDir + "\\include", System, false, false, false);
-      else
-        AddPath(VSDir + "\\VC\\PlatformSDK\\Include",
-                System, false, false, false);
-    } else {
-      // Default install paths.
-      AddPath("C:/Program Files/Microsoft Visual Studio 10.0/VC/include",
-              System, false, false, false);
-      AddPath("C:/Program Files/Microsoft Visual Studio 9.0/VC/include",
-              System, false, false, false);
-      AddPath(
-        "C:/Program Files/Microsoft Visual Studio 9.0/VC/PlatformSDK/Include",
-        System, false, false, false);
-      AddPath("C:/Program Files/Microsoft Visual Studio 8/VC/include",
-              System, false, false, false);
-      AddPath(
-        "C:/Program Files/Microsoft Visual Studio 8/VC/PlatformSDK/Include",
-        System, false, false, false);
-    }
-    break;
-  }
+  case llvm::Triple::Linux:
+  case llvm::Triple::Win32:
+    llvm_unreachable("Include management is handled in the driver.");
+
   case llvm::Triple::Haiku:
     AddPath("/boot/common/include", System, true, false, false);
     AddPath("/boot/develop/headers/os", System, true, false, false);
@@ -556,19 +317,6 @@ void InitHeaderSearch::AddDefaultCIncludePaths(const llvm::Triple &triple,
     }
     break;
       
-  case llvm::Triple::Linux:
-    // Generic Debian multiarch support:
-    if (triple.getArch() == llvm::Triple::x86_64) {
-      AddPath("/usr/include/x86_64-linux-gnu", System, false, false, false);
-      AddPath("/usr/include/i686-linux-gnu/64", System, false, false, false);
-      AddPath("/usr/include/i486-linux-gnu/64", System, false, false, false);
-    } else if (triple.getArch() == llvm::Triple::x86) {
-      AddPath("/usr/include/x86_64-linux-gnu/32", System, false, false, false);
-      AddPath("/usr/include/i686-linux-gnu", System, false, false, false);
-      AddPath("/usr/include/i486-linux-gnu", System, false, false, false);
-    } else if (triple.getArch() == llvm::Triple::arm) {
-      AddPath("/usr/include/arm-linux-gnueabi", System, false, false, false);
-    }
   default:
     break;
   }
@@ -629,6 +377,10 @@ AddDefaultCPlusPlusIncludePaths(const llvm::Triple &triple, const HeaderSearchOp
   }
 
   switch (os) {
+  case llvm::Triple::Linux:
+  case llvm::Triple::Win32:
+    llvm_unreachable("Include management is handled in the driver.");
+
   case llvm::Triple::Cygwin:
     // Cygwin-1.7
     AddMinGWCPlusPlusIncludePaths("/usr/lib/gcc", "i686-pc-cygwin", "4.3.4");
@@ -656,257 +408,6 @@ AddDefaultCPlusPlusIncludePaths(const llvm::Triple &triple, const HeaderSearchOp
   case llvm::Triple::DragonFly:
     AddPath("/usr/include/c++/4.1", CXXSystem, true, false, false);
     break;
-  case llvm::Triple::Linux:
-    //===------------------------------------------------------------------===//
-    // Debian based distros.
-    // Note: these distros symlink /usr/include/c++/X.Y.Z -> X.Y
-    //===------------------------------------------------------------------===//
-
-    // Ubuntu 11.11 "Oneiric Ocelot" -- gcc-4.6.0
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6",
-                                "x86_64-linux-gnu", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6",
-                                "i686-linux-gnu", "", "64", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6",
-                                "i486-linux-gnu", "", "64", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6",
-                                "arm-linux-gnueabi", "", "", triple);
-
-    // Ubuntu 11.04 "Natty Narwhal" -- gcc-4.5.2
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5",
-                                "x86_64-linux-gnu", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5",
-                                "i686-linux-gnu", "", "64", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5",
-                                "i486-linux-gnu", "", "64", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5",
-                                "arm-linux-gnueabi", "", "", triple);
-
-    // Ubuntu 10.10 "Maverick Meerkat" -- gcc-4.4.5
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4",
-                                "i686-linux-gnu", "", "64", triple);
-    // The rest of 10.10 is the same as previous versions.
-
-    // Ubuntu 10.04 LTS "Lucid Lynx" -- gcc-4.4.3
-    // Ubuntu 9.10 "Karmic Koala"    -- gcc-4.4.1
-    // Debian 6.0 "squeeze"          -- gcc-4.4.2
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4",
-                                "x86_64-linux-gnu", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4",
-                                "i486-linux-gnu", "", "64", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4",
-                                "arm-linux-gnueabi", "", "", triple);
-    // Ubuntu 9.04 "Jaunty Jackalope" -- gcc-4.3.3
-    // Ubuntu 8.10 "Intrepid Ibex"    -- gcc-4.3.2
-    // Debian 5.0 "lenny"             -- gcc-4.3.2
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3",
-                                "x86_64-linux-gnu", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3",
-                                "i486-linux-gnu", "", "64", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3",
-                                "arm-linux-gnueabi", "", "", triple);
-    // Ubuntu 8.04.4 LTS "Hardy Heron"     -- gcc-4.2.4
-    // Ubuntu 8.04.[0-3] LTS "Hardy Heron" -- gcc-4.2.3
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.2",
-                                "x86_64-linux-gnu", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.2",
-                                "i486-linux-gnu", "", "64", triple);
-    // Ubuntu 7.10 "Gutsy Gibbon" -- gcc-4.1.3
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.1",
-                                "x86_64-linux-gnu", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.1",
-                                "i486-linux-gnu", "", "64", triple);
-
-    //===------------------------------------------------------------------===//
-    // Redhat based distros.
-    //===------------------------------------------------------------------===//
-    // Fedora 15 (GCC 4.6.1)
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6.1",
-                                "x86_64-redhat-linux", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6.1",
-                                "i686-redhat-linux", "", "", triple);
-    // Fedora 15 (GCC 4.6.0)
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6.0",
-                                "x86_64-redhat-linux", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6.0",
-                                "i686-redhat-linux", "", "", triple);
-    // Fedora 14
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5.1",
-                                "x86_64-redhat-linux", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5.1",
-                                "i686-redhat-linux", "", "", triple);
-    // RHEL5(gcc44)
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.4",
-                                "x86_64-redhat-linux6E", "32", "", triple);
-    // Fedora 13
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.4",
-                                "x86_64-redhat-linux", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.4",
-                                "i686-redhat-linux","", "", triple);
-    // Fedora 12
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.3",
-                                "x86_64-redhat-linux", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.3",
-                                "i686-redhat-linux","", "", triple);
-    // Fedora 12 (pre-FEB-2010)
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.2",
-                                "x86_64-redhat-linux", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.2",
-                                "i686-redhat-linux","", "", triple);
-    // Fedora 11
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.1",
-                                "x86_64-redhat-linux", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.1",
-                                "i586-redhat-linux","", "", triple);
-    // Fedora 10
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3.2",
-                                "x86_64-redhat-linux", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3.2",
-                                "i386-redhat-linux","", "", triple);
-    // Fedora 9
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3.0",
-                                "x86_64-redhat-linux", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3.0",
-                                "i386-redhat-linux", "", "", triple);
-    // Fedora 8
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.1.2",
-                                "x86_64-redhat-linux", "", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.1.2",
-                                "i386-redhat-linux", "", "", triple);
-      
-    // RHEL 5
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.1.1",
-                                "x86_64-redhat-linux", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.1.1",
-                                "i386-redhat-linux", "", "", triple);
-
-
-    //===------------------------------------------------------------------===//
-
-    // Exherbo (2010-01-25)
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.3",
-                                "x86_64-pc-linux-gnu", "32", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4.3",
-                                "i686-pc-linux-gnu", "", "", triple);
-
-    // openSUSE 11.1 32 bit
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3",
-                                "i586-suse-linux", "", "", triple);
-    // openSUSE 11.1 64 bit
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3",
-                                "x86_64-suse-linux", "32", "", triple);
-    // openSUSE 11.2
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4",
-                                "i586-suse-linux", "", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.4",
-                                "x86_64-suse-linux", "", "", triple);
-
-    // openSUSE 11.4
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5",
-                                "i586-suse-linux", "", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5",
-                                "x86_64-suse-linux", "", "", triple);
-
-    // openSUSE 12.1
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6",
-                                "i586-suse-linux", "", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6",
-                                "x86_64-suse-linux", "", "", triple);
-    // Arch Linux 2008-06-24
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3.1",
-                                "i686-pc-linux-gnu", "", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.3.1",
-                                "x86_64-unknown-linux-gnu", "", "", triple);
-
-    // Arch Linux gcc 4.6
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6.1",
-                                "i686-pc-linux-gnu", "", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6.1",
-                                "x86_64-unknown-linux-gnu", "", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6.0",
-                                "i686-pc-linux-gnu", "", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.6.0",
-                                "x86_64-unknown-linux-gnu", "", "", triple);
-
-    // Slackware gcc 4.5.2 (13.37)
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5.2",
-                                "i486-slackware-linux", "", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5.2",
-                                "x86_64-slackware-linux", "", "", triple);
-    // Slackware gcc 4.5.3 (-current)
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5.3",
-                                "i486-slackware-linux", "", "", triple);
-    AddGnuCPlusPlusIncludePaths("/usr/include/c++/4.5.3",
-                                "x86_64-slackware-linux", "", "", triple);
-
-    // Gentoo x86 gcc 4.5.2
-    AddGnuCPlusPlusIncludePaths(
-      "/usr/lib/gcc/i686-pc-linux-gnu/4.5.2/include/g++-v4",
-      "i686-pc-linux-gnu", "", "", triple);
-    // Gentoo x86 gcc 4.4.5
-    AddGnuCPlusPlusIncludePaths(
-      "/usr/lib/gcc/i686-pc-linux-gnu/4.4.5/include/g++-v4",
-      "i686-pc-linux-gnu", "", "", triple);
-    // Gentoo x86 gcc 4.4.4
-    AddGnuCPlusPlusIncludePaths(
-      "/usr/lib/gcc/i686-pc-linux-gnu/4.4.4/include/g++-v4",
-      "i686-pc-linux-gnu", "", "", triple);
-   // Gentoo x86 2010.0 stable
-    AddGnuCPlusPlusIncludePaths(
-      "/usr/lib/gcc/i686-pc-linux-gnu/4.4.3/include/g++-v4",
-      "i686-pc-linux-gnu", "", "", triple);
-    // Gentoo x86 2009.1 stable
-    AddGnuCPlusPlusIncludePaths(
-      "/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4",
-      "i686-pc-linux-gnu", "", "", triple);
-    // Gentoo x86 2009.0 stable
-    AddGnuCPlusPlusIncludePaths(
-      "/usr/lib/gcc/i686-pc-linux-gnu/4.3.2/include/g++-v4",
-      "i686-pc-linux-gnu", "", "", triple);
-    // Gentoo x86 2008.0 stable
-    AddGnuCPlusPlusIncludePaths(
-      "/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/include/g++-v4",
-      "i686-pc-linux-gnu", "", "", triple);
-    // Gentoo x86 llvm-gcc trunk
-    AddGnuCPlusPlusIncludePaths(
-        "/usr/lib/llvm-gcc-4.2-9999/include/c++/4.2.1",
-        "i686-pc-linux-gnu", "", "", triple);
-
-    // Gentoo amd64 gcc 4.5.2
-    AddGnuCPlusPlusIncludePaths(
-        "/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.2/include/g++-v4",
-        "x86_64-pc-linux-gnu", "32", "", triple);
-    // Gentoo amd64 gcc 4.4.5
-    AddGnuCPlusPlusIncludePaths(
-        "/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.5/include/g++-v4",
-        "x86_64-pc-linux-gnu", "32", "", triple);
-    // Gentoo amd64 gcc 4.4.4
-    AddGnuCPlusPlusIncludePaths(
-        "/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.4/include/g++-v4",
-        "x86_64-pc-linux-gnu", "32", "", triple);
-    // Gentoo amd64 gcc 4.4.3
-    AddGnuCPlusPlusIncludePaths(
-        "/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.3/include/g++-v4",
-        "x86_64-pc-linux-gnu", "32", "", triple);
-    // Gentoo amd64 gcc 4.3.4
-    AddGnuCPlusPlusIncludePaths(
-        "/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include/g++-v4",
-        "x86_64-pc-linux-gnu", "", "", triple);
-    // Gentoo amd64 gcc 4.3.2
-    AddGnuCPlusPlusIncludePaths(
-        "/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.2/include/g++-v4",
-        "x86_64-pc-linux-gnu", "", "", triple);
-    // Gentoo amd64 stable
-    AddGnuCPlusPlusIncludePaths(
-        "/usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/include/g++-v4",
-        "x86_64-pc-linux-gnu", "", "", triple);
-
-    // Gentoo amd64 llvm-gcc trunk
-    AddGnuCPlusPlusIncludePaths(
-        "/usr/lib/llvm-gcc-4.2-9999/include/c++/4.2.1",
-        "x86_64-pc-linux-gnu", "", "", triple);
-
-    break;
   case llvm::Triple::FreeBSD:
     // FreeBSD 8.0
     // FreeBSD 7.3
@@ -942,6 +443,19 @@ AddDefaultCPlusPlusIncludePaths(const llvm::Triple &triple, const HeaderSearchOp
 void InitHeaderSearch::AddDefaultIncludePaths(const LangOptions &Lang,
                                               const llvm::Triple &triple,
                                             const HeaderSearchOptions &HSOpts) {
+  // NB: This code path is going away. All of the logic is moving into the
+  // driver which has the information necessary to do target-specific
+  // selections of default include paths. Each target which moves there will be
+  // exempted from this logic here until we can delete the entire pile of code.
+  switch (triple.getOS()) {
+  default:
+    break; // Everything else continues to use this routine's logic.
+
+  case llvm::Triple::Linux:
+  case llvm::Triple::Win32:
+    return;
+  }
+
   if (Lang.CPlusPlus && HSOpts.UseStandardCXXIncludes &&
       HSOpts.UseStandardSystemIncludes) {
     if (HSOpts.UseLibcxx) {
@@ -1144,8 +658,8 @@ void clang::ApplyHeaderSearchOptions(HeaderSearch &HS,
   // Add the user defined entries.
   for (unsigned i = 0, e = HSOpts.UserEntries.size(); i != e; ++i) {
     const HeaderSearchOptions::Entry &E = HSOpts.UserEntries[i];
-    Init.AddPath(E.Path, E.Group, false, E.IsUserSupplied, E.IsFramework,
-                 E.IgnoreSysRoot);
+    Init.AddPath(E.Path, E.Group, !E.ImplicitExternC, E.IsUserSupplied,
+                 E.IsFramework, E.IgnoreSysRoot);
   }
 
   Init.AddDefaultIncludePaths(Lang, Triple, HSOpts);
diff --git a/test/Analysis/iterators.cpp b/test/Analysis/iterators.cpp
index 741970aa6c47..1b6340b2af28 100644
--- a/test/Analysis/iterators.cpp
+++ b/test/Analysis/iterators.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -analyze -analyzer-checker=core,experimental.cplusplus.Iterators -verify %s
+// RUN: %clang --analyze -Xclang -analyzer-checker=core,experimental.cplusplus.Iterators -Xclang -verify %s
 // XFAIL: win32
 
 #include <vector>
diff --git a/test/Analysis/security-syntax-checks.m b/test/Analysis/security-syntax-checks.m
index 6fb5b3cf14ef..a04401b531f5 100644
--- a/test/Analysis/security-syntax-checks.m
+++ b/test/Analysis/security-syntax-checks.m
@@ -170,7 +170,7 @@ void test_strcat() {
 //===----------------------------------------------------------------------===
 typedef int __int32_t;
 typedef __int32_t pid_t;
-pid_t vfork(void); //expected-warning{{declaration of built-in function 'vfork' requires inclusion of the header <setjmp.h>}}
+pid_t vfork(void);
 
 void test_vfork() {
   vfork(); //expected-warning{{Call to function 'vfork' is insecure as it can lead to denial of service situations in the parent process.}}
diff --git a/test/CodeGen/pr9614.c b/test/CodeGen/pr9614.c
new file mode 100644
index 000000000000..8c767766832d
--- /dev/null
+++ b/test/CodeGen/pr9614.c
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -emit-llvm %s -O1 -o - | FileCheck %s
+
+extern void foo_alias (void) __asm ("foo");
+inline void foo (void) {
+  return foo_alias ();
+}
+extern void bar_alias (void) __asm ("bar");
+inline __attribute__ ((__always_inline__)) void bar (void) {
+  return bar_alias ();
+}
+void f(void) {
+  foo();
+  bar();
+}
+
+// CHECK: define void @f()
+// CHECK: call void @foo()
+// CHECK-NEXT: call void @bar()
+// CHECK-NEXT: ret void
+
+// CHECK: declare void @foo()
+// CHECK: declare void @bar()
diff --git a/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.6.99/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.6.99/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.6.99/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.6/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.6/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.6/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.7.0/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.7.0/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.7.0/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.7.1/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.7.1/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing1/lib/gcc/i386-unknown-linux/4.7.1/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.6.99/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.6.99/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.6.99/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.6.x/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.6.x/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.6.x/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.7.0/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.7.0/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.7.0/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.7.1/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.7.1/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing2/lib/gcc/i386-unknown-linux/4.7.1/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing3/lib/gcc/i386-unknown-linux/4.7.98/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing3/lib/gcc/i386-unknown-linux/4.7.98/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing3/lib/gcc/i386-unknown-linux/4.7.98/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing4/bin/.keep b/test/Driver/Inputs/gcc_version_parsing4/bin/.keep
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing4/bin/.keep
diff --git a/test/Driver/Inputs/gcc_version_parsing4/lib/gcc/i386-unknown-linux/4.7.98/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing4/lib/gcc/i386-unknown-linux/4.7.98/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing4/lib/gcc/i386-unknown-linux/4.7.98/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing4/lib/gcc/i386-unknown-linux/4.7.99-rc5/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing4/lib/gcc/i386-unknown-linux/4.7.99-rc5/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing4/lib/gcc/i386-unknown-linux/4.7.99-rc5/crtbegin.o
diff --git a/test/Driver/Inputs/gcc_version_parsing4/lib/gcc/i386-unknown-linux/4.7.99/crtbegin.o b/test/Driver/Inputs/gcc_version_parsing4/lib/gcc/i386-unknown-linux/4.7.99/crtbegin.o
new file mode 100644
index 000000000000..e69de29bb2d1
--- /dev/null
+++ b/test/Driver/Inputs/gcc_version_parsing4/lib/gcc/i386-unknown-linux/4.7.99/crtbegin.o
diff --git a/test/Driver/linux-ld.c b/test/Driver/linux-ld.c
index 46fbe7f52dea..456f7add7fe1 100644
--- a/test/Driver/linux-ld.c
+++ b/test/Driver/linux-ld.c
@@ -137,3 +137,11 @@
 // CHECK-GCC-VERSION3: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
 // CHECK-GCC-VERSION3: "{{.*}}/Inputs/gcc_version_parsing3/bin/../lib/gcc/i386-unknown-linux/4.7.99-rc5/crtbegin.o"
 // CHECK-GCC-VERSION3: "-L{{.*}}/Inputs/gcc_version_parsing3/bin/../lib/gcc/i386-unknown-linux/4.7.99-rc5"
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -ccc-host-triple i386-unknown-linux -m32 \
+// RUN:     -ccc-install-dir %S/Inputs/gcc_version_parsing4/bin \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-GCC-VERSION4 %s
+// CHECK-GCC-VERSION4: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
+// CHECK-GCC-VERSION4: "{{.*}}/Inputs/gcc_version_parsing4/bin/../lib/gcc/i386-unknown-linux/4.7.99/crtbegin.o"
+// CHECK-GCC-VERSION4: "-L{{.*}}/Inputs/gcc_version_parsing4/bin/../lib/gcc/i386-unknown-linux/4.7.99"
diff --git a/test/PCH/reloc.c b/test/PCH/reloc.c
index fd78feba6047..5d51eee05db3 100644
--- a/test/PCH/reloc.c
+++ b/test/PCH/reloc.c
@@ -1,6 +1,8 @@
-// RUN: %clang_cc1 -emit-pch -o %t -relocatable-pch -isysroot %S/libroot %S/libroot/usr/include/reloc.h
-// RUN: %clang_cc1 -include-pch %t -isysroot %S/libroot %s -verify
-// RUN: not %clang_cc1 -include-pch %t %s
+// RUN: %clang -ccc-host-triple x86_64-apple-darwin10 --relocatable-pch -o %t \
+// RUN:   -isysroot %S/libroot %S/libroot/usr/include/reloc.h
+// RUN: %clang -ccc-host-triple x86_64-apple-darwin10 -fsyntax-only \
+// RUN:   -include-pch %t -isysroot %S/libroot %s -Xclang -verify
+// RUN: not %clang -ccc-host-triple x86_64-apple-darwin10 -include-pch %t %s
 
 #include <reloc.h>
 
@@ -8,7 +10,5 @@ int x = 2; // expected-error{{redefinition}}
 int y = 5; // expected-error{{redefinition}}
 
 
-
-
 // expected-note{{previous definition}}
 // expected-note{{previous definition}}
diff --git a/test/Preprocessor/header_lookup1.c b/test/Preprocessor/header_lookup1.c
index f52e4fe6ce92..d0909363737c 100644
--- a/test/Preprocessor/header_lookup1.c
+++ b/test/Preprocessor/header_lookup1.c
@@ -1,2 +1,2 @@
-// RUN: %clang -fno-ms-extensions %s -E | grep 'stddef.h.*3.*4'
+// RUN: %clang -fno-ms-extensions %s -E | grep 'stddef.h.*3'
 #include <stddef.h>
diff --git a/test/lit.cfg b/test/lit.cfg
index 8062aa72c1f1..1f4a8452b010 100644
--- a/test/lit.cfg
+++ b/test/lit.cfg
@@ -2,6 +2,9 @@
 
 import os
 import platform
+import re
+import subprocess
+
 
 # Configuration file for the 'lit' test runner.
 
@@ -141,7 +144,23 @@ if lit.useValgrind:
 config.clang = inferClang(config.environment['PATH']).replace('\\', '/')
 if not lit.quiet:
     lit.note('using clang: %r' % config.clang)
-config.substitutions.append( ('%clang_cc1', config.clang + ' -cc1') )
+
+# Note that when substituting %clang_cc1 also fill in the include directory of
+# the builtin headers. Those are part of even a freestanding environment, but
+# Clang relies on the driver to locate them.
+def getClangBuiltinIncludeDir(clang):
+    # FIXME: Rather than just getting the version, we should have clang print
+    # out its resource dir here in an easy to scrape form.
+    cmd = subprocess.Popen([clang, '-print-file-name=include'],
+                           stdout=subprocess.PIPE)
+    if not cmd.stdout:
+      lit.fatal("Couldn't find the include dir for Clang ('%s')" % clang)
+    return cmd.stdout.read().strip()
+
+config.substitutions.append( ('%clang_cc1', '%s -cc1 -internal-isystem %s'
+                              % (config.clang,
+                                 getClangBuiltinIncludeDir(config.clang))) )
+
 config.substitutions.append( ('%clangxx', ' ' + config.clang +
                               ' -ccc-clang-cxx -ccc-cxx '))
 config.substitutions.append( ('%clang', ' ' + config.clang + ' ') )
@@ -175,10 +194,6 @@ if platform.system() not in ['Windows'] or lit.getBashPath() != '':
     config.available_features.add('shell')
 
 # Registered Targets
-import subprocess
-import re
-import os
-
 def getRegisteredTargets(tool):
     set_of_targets = set()