[Driver] Make the use of relax relocations a per target option

[phosek]

Summary

The support for relax relocations is dependent on the linker and
different toolchains within the same compiler can be using different
linkers some of which may or may not support relax relocations.

Give toolchains the option to control whether they want to use relax
relocations in addition to the existing (global) build system option.

[mcgrathr]

test case?

[phosek]

Added a test case.

[mcgrathr]

LGTM

cfe/trunk/cmake/caches/Fuchsia-stage2.cmake

 set(CLANG_PLUGIN_SUPPORT OFF CACHE BOOL "")
 
 set(LLVM_ENABLE_LTO ON CACHE BOOL "")
 if(NOT APPLE)
   set(LLVM_ENABLE_LLD ON CACHE BOOL "")
   set(CLANG_DEFAULT_LINKER lld CACHE STRING "")
 endif()
 
-# This is a "Does your linker support it?" option that only applies
-# to x86-64 ELF targets.  All Fuchsia target linkers do support it.
-# For x86-64 Linux, it's supported by LLD and by GNU linkers since
-# binutils 2.27, so one can hope that all Linux hosts in use handle it.
-# Ideally this would be settable as a per-target option.
-set(ENABLE_X86_RELAX_RELOCATIONS ON CACHE BOOL "")
-
 if(APPLE)
   set(LLDB_CODESIGN_IDENTITY "" CACHE STRING "")
 endif()
 
 set(CMAKE_BUILD_TYPE RelWithDebInfo CACHE STRING "")
 set(CMAKE_C_FLAGS_RELWITHDEBINFO "-O3 -gline-tables-only -DNDEBUG" CACHE STRING "")
 set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O3 -gline-tables-only -DNDEBUG" CACHE STRING "")
 

cfe/trunk/include/clang/Driver/ToolChain.h

public:
   /// IsObjCNonFragileABIDefault - Does this tool chain set
   /// -fobjc-nonfragile-abi by default.
   virtual bool IsObjCNonFragileABIDefault() const { return false; }
 
   /// UseObjCMixedDispatchDefault - When using non-legacy dispatch, should the
   /// mixed dispatch method be used?
   virtual bool UseObjCMixedDispatch() const { return false; }
 
+  /// \brief Check whether to enable x86 relax relocations by default.
+  virtual bool useRelaxRelocations() const;
+
   /// GetDefaultStackProtectorLevel - Get the default stack protector level for
   /// this tool chain (0=off, 1=on, 2=strong, 3=all).
   virtual unsigned GetDefaultStackProtectorLevel(bool KernelOrKext) const {
     return 0;
   }
 
   /// GetDefaultLinker - Get the default linker to use.
   virtual const char *getDefaultLinker() const {

cfe/trunk/lib/Driver/ToolChain.cpp

 vfs::FileSystem &ToolChain::getVFS() const { return getDriver().getVFS(); }
 
 bool ToolChain::useIntegratedAs() const {
   return Args.hasFlag(options::OPT_fintegrated_as,
                       options::OPT_fno_integrated_as,
                       IsIntegratedAssemblerDefault());
 }
 
+bool ToolChain::useRelaxRelocations() const {
+  return ENABLE_X86_RELAX_RELOCATIONS;
+}
+
 const SanitizerArgs& ToolChain::getSanitizerArgs() const {
   if (!SanitizerArguments.get())
     SanitizerArguments.reset(new SanitizerArgs(*this, Args));
   return *SanitizerArguments.get();
 }
 
 const XRayArgs& ToolChain::getXRayArgs() const {
   if (!XRayArguments.get())

cfe/trunk/lib/Driver/ToolChains/Clang.cpp

static void CollectArgsForIntegratedAssembler(Compilation &C,
 
   // When passing -I arguments to the assembler we sometimes need to
   // unconditionally take the next argument.  For example, when parsing
   // '-Wa,-I -Wa,foo' we need to accept the -Wa,foo arg after seeing the
   // -Wa,-I arg and when parsing '-Wa,-I,foo' we need to accept the 'foo'
   // arg after parsing the '-I' arg.
   bool TakeNextArg = false;
 
-  bool UseRelaxRelocations = ENABLE_X86_RELAX_RELOCATIONS;
+  bool UseRelaxRelocations = C.getDefaultToolChain().useRelaxRelocations();
   const char *MipsTargetFeature = nullptr;
   for (const Arg *A :
        Args.filtered(options::OPT_Wa_COMMA, options::OPT_Xassembler)) {
     A->claim();
 
     for (StringRef Value : A->getValues()) {
       if (TakeNextArg) {
         CmdArgs.push_back(Value.data());

cfe/trunk/lib/Driver/ToolChains/Fuchsia.h

 class LLVM_LIBRARY_VISIBILITY Fuchsia : public ToolChain {
 public:
   Fuchsia(const Driver &D, const llvm::Triple &Triple,
           const llvm::opt::ArgList &Args);
 
   bool HasNativeLLVMSupport() const override { return true; }
   bool IsIntegratedAssemblerDefault() const override { return true; }
   bool IsMathErrnoDefault() const override { return false; }
+  bool useRelaxRelocations() const override { return true; };
   RuntimeLibType GetDefaultRuntimeLibType() const override {
     return ToolChain::RLT_CompilerRT;
   }
   CXXStdlibType GetDefaultCXXStdlibType() const override {
     return ToolChain::CST_Libcxx;
   }
   bool IsUnwindTablesDefault(const llvm::opt::ArgList &Args) const override {
     return true;

cfe/trunk/test/Driver/fuchsia.c

 // RUN: %clang %s -### -no-canonical-prefixes --target=x86_64-unknown-fuchsia \
 // RUN:     --sysroot=%S/platform 2>&1 \
 // RUN:     | FileCheck -check-prefixes=CHECK,CHECK-X86_64 %s
 // RUN: %clang %s -### -no-canonical-prefixes --target=aarch64-unknown-fuchsia \
 // RUN:     --sysroot=%S/platform 2>&1 \
 // RUN:     | FileCheck -check-prefixes=CHECK,CHECK-AARCH64 %s
 // CHECK: {{.*}}clang{{.*}}" "-cc1"
+// CHECK: "--mrelax-relocations"
 // CHECK: "-munwind-tables"
 // CHECK: "-fuse-init-array"
 // CHECK: "-isysroot" "[[SYSROOT:[^"]+]]"
 // CHECK: "-internal-externc-isystem" "[[SYSROOT]]{{/|\\\\}}include"
 // CHECK: {{.*}}ld.lld{{.*}}" "-z" "rodynamic"
 // CHECK: "--sysroot=[[SYSROOT]]"
 // CHECK: "-pie"
 // CHECK: "--build-id"