[LoopVectorize] Use recurrence kind to determine FMF instead of isa<FPMathOperator>

Replace isa<FPMathOperator>(CurrentLinkI) with
RecurrenceDescriptor::isFloatingPointRecurrenceKind(Kind) to determine
whether to use FastMathFlags. This uses information already available at
the VPlan level instead of inspecting the underlying instruction type.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8759,9 +8759,10 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
       RecurrenceDescriptor RdxDesc = Legal->getRecurrenceDescriptor(
           cast<PHINode>(PhiR->getUnderlyingInstr()));
       // Non-FP RdxDescs will have all fast math flags set, so clear them.
-      FastMathFlags FMFs = isa<FPMathOperator>(CurrentLinkI)
-                               ? RdxDesc.getFastMathFlags()
-                               : FastMathFlags();
+      FastMathFlags FMFs =
+          RecurrenceDescriptor::isFloatingPointRecurrenceKind(Kind)
+              ? RdxDesc.getFastMathFlags()
+              : FastMathFlags();
       auto *RedRecipe = new VPReductionRecipe(
           Kind, FMFs, CurrentLinkI, PreviousLink, VecOp, CondOp,
           PhiR->isOrdered(), CurrentLinkI->getDebugLoc());