[PATCH] Fix an logic error in the clang driver preventing crtfastmath.o from linking when -Ofast is used without -ffast-math

[Zinovy Nis]

Hi doug.gregor, mcrosier,

In gcc using -Ofast forces linking of crtfastmath.o. 
In the current clang crtfastmath.o is only linked when -ffast-math/-funsafe-math-optimizations passed. It can lead to performance issues, when using only -Ofast without explicit -ffast-math (I faced with it).
My patch fixes inconsistency with gcc behaviour and also introduces few tests on it.

http://llvm-reviews.chandlerc.com/D3114

Files:
  include/clang/Driver/ToolChain.h
  lib/Driver/ToolChain.cpp
  test/Driver/linux-ld.c

Index: include/clang/Driver/ToolChain.h
===================================================================
--- include/clang/Driver/ToolChain.h
+++ include/clang/Driver/ToolChain.h
@@ -311,7 +311,7 @@
   /// AddFastMathRuntimeIfAvailable - If a runtime library exists that sets
   /// global flags for unsafe floating point math, add it and return true.
   ///
-  /// This checks for presence of the -ffast-math or -funsafe-math flags.
+  /// This checks for presence of the -Ofast, -ffast-math or -funsafe-math flags.
   virtual bool
   AddFastMathRuntimeIfAvailable(const llvm::opt::ArgList &Args,
                                 llvm::opt::ArgStringList &CmdArgs) const;
Index: lib/Driver/ToolChain.cpp
===================================================================
--- lib/Driver/ToolChain.cpp
+++ lib/Driver/ToolChain.cpp
@@ -341,16 +341,20 @@
 
 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;
-
+  // Do not check for -fno-fast-math or -fno-unsafe-math when -Ofast passed
+  // (to keep the linker options consistent with gcc and clang itself).
+  // TODO: reuse the code from the Tools.cpp::isOptimizationLevelFast()
+  if(!Args.hasFlag(options::OPT_Ofast, options::OPT_O_Group, false)) {
+    // Check if -ffast-math or -funsafe-math.
+    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.
Index: test/Driver/linux-ld.c
===================================================================
--- test/Driver/linux-ld.c
+++ test/Driver/linux-ld.c
@@ -825,7 +825,7 @@
 // CHECK-FSL-PPC64: "{{.*}}{{/|\\\\}}crtbegin.o"
 // CHECK-FSL-PPC64: "-L[[SYSROOT]]/usr/lib64/powerpc64-fsl-linux/4.6.2/../.."
 //
-// Check that crtfastmath.o is linked with -ffast-math.
+// Check that crtfastmath.o is linked with -ffast-math and with -Ofast.
 // RUN: %clang --target=x86_64-unknown-linux -### %s \
 // RUN:        --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s
@@ -835,9 +835,30 @@
 // RUN: %clang --target=x86_64-unknown-linux -### %s -funsafe-math-optimizations\
 // RUN:        --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
+// RUN: %clang --target=x86_64-unknown-linux -### %s -Ofast\
+// RUN:        --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
+// RUN: %clang --target=x86_64-unknown-linux -### %s -Ofast -O3\
+// RUN:        --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s
+// RUN: %clang --target=x86_64-unknown-linux -### %s -O3 -Ofast\
+// RUN:        --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
 // RUN: %clang --target=x86_64-unknown-linux -### %s -ffast-math -fno-fast-math \
 // RUN:        --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s
+// RUN: %clang --target=x86_64-unknown-linux -### %s -Ofast -fno-fast-math \
+// RUN:        --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
+// RUN: %clang --target=x86_64-unknown-linux -### %s -Ofast -fno-unsafe-math-optimizations \
+// RUN:        --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
+// RUN: %clang --target=x86_64-unknown-linux -### %s -fno-fast-math -Ofast  \
+// RUN:        --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
+// RUN: %clang --target=x86_64-unknown-linux -### %s -fno-unsafe-math-optimizations -Ofast \
+// RUN:        --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
 // We don't have crtfastmath.o in the i386 tree, use it to check that file
 // detection works.
 // RUN: %clang --target=i386-unknown-linux -### %s -ffast-math \
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