[InstCombine] allow fdiv with constant dividend folds with less than full -ffast-math

It's possible that we could allow this either 'arcp' or 'reassoc' alone, but this
should be conservatively better than what we have right now. GCC allows this with
only -freciprocal-math.

The last test is changed to show a case that is expected to fold, but we need D43398.

llvm-svn: 325533

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 17ca01d4aa9..9df0d4673b8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1316,10 +1316,11 @@ static Instruction *foldFDivConstantDivisor(BinaryOperator &FDiv) {
   return BinaryOperator::CreateFMul(FDiv.getOperand(0), RecipCFP);
 }
 
-/// Try to strength-reduce C / X expressions where X includes another constant.
+/// Try to reassociate C / X expressions where X includes another constant.
 static Instruction *foldFDivConstantDividend(BinaryOperator &I) {
   Constant *C1;
-  if (!I.isFast() || !match(I.getOperand(0), m_Constant(C1)))
+  if (!I.hasAllowReassoc() || !I.hasAllowReciprocal() ||
+      !match(I.getOperand(0), m_Constant(C1)))
     return nullptr;
 
   Value *X;