[LoopVectorize] improve IR fast-math-flags propagation in reductions

This is another step (see D95452) towards correcting fast-math-flags
bugs in vector reductions.

There are multiple bugs visible in the test diffs, and this is still
not working as it should. We still use function attributes (rather
than FMF) to drive part of the logic, but we are not checking for
the correct FP function attributes.

Note that FMF may not be propagated optimally on selects (example
in https://llvm.org/PR35607 ). That's why I'm proposing to union the
FMF of a fcmp+select pair and avoid regressions on existing vectorizer
tests.

Differential Revision: https://reviews.llvm.org/D95690

1 files changed, 0 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index 5c66cb0..07dc3ac 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -944,12 +944,6 @@ Value *llvm::createMinMaxOp(IRBuilderBase &Builder, RecurKind RK, Value *Left,
     break;
   }
 
-  // We only match FP sequences that are 'fast', so we can unconditionally
-  // set it on any generated instructions.
-  IRBuilderBase::FastMathFlagGuard FMFG(Builder);
-  FastMathFlags FMF;
-  FMF.setFast();
-  Builder.setFastMathFlags(FMF);
   Value *Cmp = Builder.CreateCmp(Pred, Left, Right, "rdx.minmax.cmp");
   Value *Select = Builder.CreateSelect(Cmp, Left, Right, "rdx.minmax.select");
   return Select;