Driver: Link crtfastmath.o if it's available and -ffast-math is specified.

crtfastmath.o contains routines to set the floating point flags to a faster,
unsafe mode. Linking it in speeds up code dealing with denormals significantly
(PR14024).

For now this is only enabled on linux where I can test it and crtfastmath.o is
widely available. We may want to provide a similar file with compiler-rt
eventually and/or enable it on other platforms too.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@165240 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 0 deletions

diff --git a/lib/Driver/ToolChain.cpp b/lib/Driver/ToolChain.cpp
index 6bcea58b9e..16c5ae6d9d 100644
--- a/lib/Driver/ToolChain.cpp
+++ b/lib/Driver/ToolChain.cpp
@@ -14,6 +14,7 @@
 #include "clang/Driver/ArgList.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
+#include "clang/Driver/Option.h"
 #include "clang/Driver/Options.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -281,3 +282,24 @@ void ToolChain::AddCCKextLibArgs(const ArgList &Args,
                                  ArgStringList &CmdArgs) const {
   CmdArgs.push_back("-lcc_kext");
 }
+
+bool ToolChain::AddFastMathRuntimeIfAvailable(const ArgList &Args,
+                                              ArgStringList &CmdArgs) const {
+  // Check if -ffast-math or -funsafe-math is enabled.
+  Arg *A = Args.getLastArg(options::OPT_ffast_math,
+                           options::OPT_fno_fast_math,
+                           options::OPT_funsafe_math_optimizations,
+                           options::OPT_fno_unsafe_math_optimizations);
+
+  if (!A || A->getOption().getID() == options::OPT_fno_fast_math ||
+      A->getOption().getID() == options::OPT_fno_unsafe_math_optimizations)
+    return false;
+
+  // If crtfastmath.o exists add it to the arguments.
+  std::string Path = GetFilePath("crtfastmath.o");
+  if (Path == "crtfastmath.o") // Not found.
+    return false;
+
+  CmdArgs.push_back(Args.MakeArgString(Path));
+  return true;
+}