The handling of 'funsafe-math-optimizations' doesn't update the 'MathErrno'

flag. But the driver checks for 'fno-math-errno' before passing
'funsafe-math-optimizations' to the FE. In GCC, the option
'funsafe-math-optimizations' doesn't affect the 'fmath-errno' flag.
This patch aligns clang with GCC.

'-ffast-math' sets the FPContract to 'fast'. But 'funsafe-math-optimizations'
the driver doesn't consider the FPContract when handling the option.
Unfortunately there are places in the BE that interpret unsafe math
mode as allowing FMA. This patch makes -ffast-math' and
'funsafe-math-optimizations' behave similarly in regard to the setting of the
FPContract.

Differential Revision: https://reviews.llvm.org/D137578

2 files changed, 15 insertions, 6 deletions

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 0633618..217a277b 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2787,7 +2787,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
   // If one wasn't given by the user, don't pass it here.
   StringRef FPContract;
   StringRef LastSeenFfpContractOption;
-  bool SeenFfastMathOption = false;
+  bool SeenUnsafeMathModeOption = false;
   if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
       !JA.isOffloading(Action::OFK_HIP))
     FPContract = "on";
@@ -3003,6 +3003,8 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       ApproxFunc = true;
       TrappingMath = false;
       FPExceptionBehavior = "";
+      FPContract = "fast";
+      SeenUnsafeMathModeOption = true;
       break;
     case options::OPT_fno_unsafe_math_optimizations:
       AssociativeMath = false;
@@ -3015,6 +3017,13 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       // The target may have opted to flush by default, so force IEEE.
       DenormalFPMath = llvm::DenormalMode::getIEEE();
       DenormalFP32Math = llvm::DenormalMode::getIEEE();
+      if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
+          !JA.isOffloading(Action::OFK_HIP)) {
+        if (LastSeenFfpContractOption != "") {
+          FPContract = LastSeenFfpContractOption;
+        } else if (SeenUnsafeMathModeOption)
+          FPContract = "on";
+      }
       break;
 
     case options::OPT_Ofast:
@@ -3034,7 +3043,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       RoundingFPMath = false;
       // If fast-math is set then set the fp-contract mode to fast.
       FPContract = "fast";
-      SeenFfastMathOption = true;
+      SeenUnsafeMathModeOption = true;
       break;
     case options::OPT_fno_fast_math:
       HonorINFs = true;
@@ -3054,7 +3063,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
           !JA.isOffloading(Action::OFK_HIP)) {
         if (LastSeenFfpContractOption != "") {
           FPContract = LastSeenFfpContractOption;
-        } else if (SeenFfastMathOption)
+        } else if (SeenUnsafeMathModeOption)
           FPContract = "on";
       }
       break;
@@ -3095,8 +3104,8 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
   if (MathErrno)
     CmdArgs.push_back("-fmath-errno");
 
-  if (!MathErrno && AssociativeMath && ReciprocalMath && !SignedZeros &&
-      ApproxFunc && !TrappingMath)
+ if (AssociativeMath && ReciprocalMath && !SignedZeros && ApproxFunc &&
+     !TrappingMath)
     CmdArgs.push_back("-funsafe-math-optimizations");
 
   if (!SignedZeros)
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 088e83b..40d556f 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -3799,7 +3799,7 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
     else
       Opts.LongDoubleSize = 0;
   }
-  if (Opts.FastRelaxedMath)
+  if (Opts.FastRelaxedMath || Opts.CLUnsafeMath)
     Opts.setDefaultFPContractMode(LangOptions::FPM_Fast);
 
   llvm::sort(Opts.ModuleFeatures);