[LV] Directly add fast-math flags to select recipe (NFC).

Now that VPInstruction can manage fast math flags via
VPRecipeWithIRFlags, use them directly to model the fast-math flags of
the select created for the final reduction value instead of adding them
late.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -3832,9 +3832,6 @@ void InnerLoopVectorizer::fixReduction(VPReductionPHIRecipe *PhiR,
       assert(Sel && "Reduction exit feeds no select");
       State.reset(LoopExitInstDef, Sel, Part);
 
-      if (isa<FPMathOperator>(Sel))
-        Sel->setFastMathFlags(RdxDesc.getFastMathFlags());
-
       // If the target can create a predicated operator for the reduction at no
       // extra cost in the loop (for example a predicated vadd), it can be
       // cheaper for the select to remain in the loop than be sunk out of it,
@@ -9162,12 +9159,19 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
       VPReductionPHIRecipe *PhiR = dyn_cast<VPReductionPHIRecipe>(&R);
       if (!PhiR || PhiR->isInLoop())
         continue;
+      const RecurrenceDescriptor &RdxDesc = PhiR->getRecurrenceDescriptor();
       VPValue *Cond =
           RecipeBuilder.createBlockInMask(OrigLoop->getHeader(), *Plan);
       VPValue *Red = PhiR->getBackedgeValue();
       assert(Red->getDefiningRecipe()->getParent() != LatchVPBB &&
              "reduction recipe must be defined before latch");
-      Builder.createNaryOp(Instruction::Select, {Cond, Red, PhiR});
+      FastMathFlags FMFs = RdxDesc.getFastMathFlags();
+      Type *PhiTy = PhiR->getOperand(0)->getLiveInIRValue()->getType();
+      auto *Select =
+          PhiTy->isFloatingPointTy()
+              ? new VPInstruction(Instruction::Select, {Cond, Red, PhiR}, FMFs)
+              : new VPInstruction(Instruction::Select, {Cond, Red, PhiR});
+      Select->insertBefore(&*Builder.getInsertPoint());
     }
   }
 

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -415,14 +415,15 @@ bool VPInstruction::isFPMathOp() const {
   return Opcode == Instruction::FAdd || Opcode == Instruction::FMul ||
          Opcode == Instruction::FNeg || Opcode == Instruction::FSub ||
          Opcode == Instruction::FDiv || Opcode == Instruction::FRem ||
-         Opcode == Instruction::FCmp;
+         Opcode == Instruction::FCmp || Opcode == Instruction::Select;
 }
 #endif
 
 void VPInstruction::execute(VPTransformState &State) {
   assert(!State.Instance && "VPInstruction executing an Instance");
   IRBuilderBase::FastMathFlagGuard FMFGuard(State.Builder);
-  assert(hasFastMathFlags() == isFPMathOp() &&
+  assert((hasFastMathFlags() == isFPMathOp() ||
+          getOpcode() == Instruction::Select) &&
          "Recipe not a FPMathOp but has fast-math flags?");
   if (hasFastMathFlags())
     State.Builder.setFastMathFlags(getFastMathFlags());