[flang] Add -ffast-math and -Ofast

clang -cc1 accepts -Ofast. I did not add it to flang -fc1 because this
seems redundant because the compiler driver will always resolve -Ofast
into -O3 -ffast-math (I added a test for this).

-menable-infs is removed from the frontend-forwarding test because if
all of the fast-math component flags are present, these will be resolved
into the fast-math flag. Instead -menable-infs is tested in the
fast-math test.

Specifying -ffast-math to the compiler driver causes linker invocations
to include crtfastmath.o.

RFC: https://discourse.llvm.org/t/rfc-the-meaning-of-ofast/66554

Differential Revision: https://reviews.llvm.org/D138675

1 files changed, 10 insertions, 0 deletions

diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index e5fa38e..33ec6af 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -728,6 +728,16 @@ static bool parseFloatingPointArgs(CompilerInvocation &invoc,
     opts.ReciprocalMath = true;
   }
 
+  if (args.getLastArg(clang::driver::options::OPT_ffast_math)) {
+    opts.NoHonorInfs = true;
+    opts.NoHonorNaNs = true;
+    opts.AssociativeMath = true;
+    opts.ReciprocalMath = true;
+    opts.ApproxFunc = true;
+    opts.NoSignedZeros = true;
+    opts.setFPContractMode(LangOptions::FPM_Fast);
+  }
+
   return true;
 }