[SimplifyLibCalls] don't drop fast-math-flags on trig reflection folds (retry r339608)

Even though this code is below a function called optimizeFloatingPointLibCall(),
we apparently can't guarantee that we're dealing with FPMathOperators, so bail
out immediately if that's not true.

llvm-svn: 339618

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index eda3f059e69..a2e5f8d00f6 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1124,7 +1124,12 @@ Value *LibCallSimplifier::optimizeCAbs(CallInst *CI, IRBuilder<> &B) {
 
 static Value *optimizeTrigReflections(CallInst *Call, LibFunc Func,
                                       IRBuilder<> &B) {
-  // FIXME: This drops FMF.
+  if (!isa<FPMathOperator>(Call))
+    return nullptr;
+  
+  IRBuilder<>::FastMathFlagGuard Guard(B);
+  B.setFastMathFlags(Call->getFastMathFlags());
+  
   // TODO: Add tan() and other calls.
   // TODO: Can this be shared to also handle LLVM intrinsics?
   Value *X;