[VPlan] Collect FMFs for in-loop reduction chain in VPlan. (NFC)

Replace retrieving FMFs for in-loop reduction via underlying instruction
+ legal by collecting the flags during reduction chain traversal in
VPlan.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8665,6 +8665,11 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
         !RecurrenceDescriptor::isFindIVRecurrenceKind(Kind) &&
         "AnyOf and FindIV reductions are not allowed for in-loop reductions");
 
+    bool IsFPRecurrence =
+        RecurrenceDescriptor::isFloatingPointRecurrenceKind(Kind);
+    FastMathFlags FMFs =
+        IsFPRecurrence ? FastMathFlags::getFast() : FastMathFlags();
+
     // Collect the chain of "link" recipes for the reduction starting at PhiR.
     SetVector<VPSingleDefRecipe *> Worklist;
     Worklist.insert(PhiR);
@@ -8705,6 +8710,15 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
         continue;
       }
 
+      if (IsFPRecurrence) {
+        FastMathFlags CurFMF =
+            cast<VPRecipeWithIRFlags>(CurrentLink)->getFastMathFlags();
+        if (match(CurrentLink, m_Select(m_VPValue(), m_VPValue(), m_VPValue())))
+          CurFMF |= cast<VPRecipeWithIRFlags>(CurrentLink->getOperand(0))
+                        ->getFastMathFlags();
+        FMFs &= CurFMF;
+      }
+
       Instruction *CurrentLinkI = CurrentLink->getUnderlyingInstr();
 
       // Index of the first operand which holds a non-mask vector operand.
@@ -8772,13 +8786,6 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
       if (CM.blockNeedsPredicationForAnyReason(CurrentLinkI->getParent()))
         CondOp = RecipeBuilder.getBlockInMask(CurrentLink->getParent());
 
-      // TODO: Retrieve FMFs from recipes directly.
-      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();
       auto *RedRecipe = new VPReductionRecipe(
           Kind, FMFs, CurrentLinkI, PreviousLink, VecOp, CondOp,
           PhiR->isOrdered(), CurrentLinkI->getDebugLoc());