Remove redundant option -menable-unsafe-fp-math.

There are currently two options that are used to tell the compiler to perform
unsafe floating-point optimizations:
'-ffast-math' and '-funsafe-math-optimizations'.

'-ffast-math' is enabled by default. It automatically enables the driver option
'-menable-unsafe-fp-math'.
Below is a table illustrating the special operations enabled automatically by
'-ffast-math', '-funsafe-math-optimizations' and '-menable-unsafe-fp-math'
respectively.

Special Operations -ffast-math	-funsafe-math-optimizations -menable-unsafe-fp-math
MathErrno	       0	         1	                    1
FiniteMathOnly         1 	         0                          0
AllowFPReassoc	       1         	 1                          1
NoSignedZero	       1                 1                          1
AllowRecip             1                 1                          1
ApproxFunc             1                 1                          1
RoundingMath	       0                 0                          0
UnsafeFPMath	       1                 0                          1
FPContract	       fast	         on	                    on

'-ffast-math' enables '-fno-math-errno', '-ffinite-math-only',
'-funsafe-math-optimzations' and sets 'FpContract' to 'fast'. The driver option
'-menable-unsafe-fp-math' enables the same special options than
'-funsafe-math-optimizations'. This is redundant.
We propose to remove the driver option '-menable-unsafe-fp-math' and use
instead, the setting of the special operations to set the function attribute
'unsafe-fp-math'. This attribute will be enabled only if those special
operations are enabled and if 'FPContract' is either 'fast' or set to the
default value.

Differential Revision: https://reviews.llvm.org/D135097

1 files changed, 5 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 1df9c6b..146271f 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -1862,7 +1862,11 @@ void CodeGenModule::getDefaultFunctionAttributes(StringRef Name,
       FuncAttrs.addAttribute("no-nans-fp-math", "true");
     if (LangOpts.ApproxFunc)
       FuncAttrs.addAttribute("approx-func-fp-math", "true");
-    if (LangOpts.UnsafeFPMath)
+    if ((LangOpts.FastMath ||
+         !LangOpts.FastMath && LangOpts.AllowFPReassoc && LangOpts.AllowRecip &&
+             !LangOpts.FiniteMathOnly && LangOpts.NoSignedZero &&
+             LangOpts.ApproxFunc) &&
+        LangOpts.getDefaultFPContractMode() != LangOptions::FPModeKind::FPM_Off)
       FuncAttrs.addAttribute("unsafe-fp-math", "true");
     if (CodeGenOpts.SoftFloat)
       FuncAttrs.addAttribute("use-soft-float", "true");