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

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.

Differential Revision: https://reviews.llvm.org/D39831

llvm-svn: 318816

clang/cmake/caches/Fuchsia-stage2.cmake

@@ -18,13 +18,6 @@ if(NOT APPLE)
   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()

clang/include/clang/Driver/ToolChain.h

@@ -316,6 +316,9 @@ public:
   /// 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 {

clang/lib/Driver/ToolChain.cpp

@@ -90,6 +90,10 @@ bool ToolChain::useIntegratedAs() const {
                       IsIntegratedAssemblerDefault());
 }
 
+bool ToolChain::useRelaxRelocations() const {
+  return ENABLE_X86_RELAX_RELOCATIONS;
+}
+
 const SanitizerArgs& ToolChain::getSanitizerArgs() const {
   if (!SanitizerArguments.get())
     SanitizerArguments.reset(new SanitizerArgs(*this, Args));

clang/lib/Driver/ToolChains/Clang.cpp

@@ -1869,7 +1869,7 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
   // 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)) {

clang/lib/Driver/ToolChains/Fuchsia.h

@@ -43,6 +43,7 @@ public:
   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;
   }

clang/test/Driver/fuchsia.c

@@ -5,6 +5,7 @@
 // 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:[^"]+]]"