Relax constraints for reduction vectorization

Summary:
Gating vectorizing reductions on *all* fastmath flags seems unnecessary;
`reassoc` should be sufficient.

Reviewers: tvvikram, mkuper, kristof.beyls, sdesmalen, Ayal

Reviewed By: sdesmalen

Subscribers: dcaballe, huntergr, jmolloy, mcrosier, jlebar, bixia, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57728

llvm-svn: 355868

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/ExpandReductions.cpp b/llvm/lib/CodeGen/ExpandReductions.cpp
index f44d89156b6..34858883298 100644
--- a/llvm/lib/CodeGen/ExpandReductions.cpp
+++ b/llvm/lib/CodeGen/ExpandReductions.cpp
@@ -118,9 +118,11 @@ bool expandReductions(Function &F, const TargetTransformInfo *TTI) {
     }
     if (!TTI->shouldExpandReduction(II))
       continue;
+    FastMathFlags FMF =
+        isa<FPMathOperator>(II) ? II->getFastMathFlags() : FastMathFlags{};
     Value *Rdx =
         IsOrdered ? getOrderedReduction(Builder, Acc, Vec, getOpcode(ID), MRK)
-                  : getShuffleReduction(Builder, Vec, getOpcode(ID), MRK);
+                  : getShuffleReduction(Builder, Vec, getOpcode(ID), MRK, FMF);
     II->replaceAllUsesWith(Rdx);
     II->eraseFromParent();
     Changed = true;