[VPlan] Infer result type for ComptueReductionResult in ::execute (NFC).

Remove explicit use of underlying instruction to get type.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -647,15 +647,14 @@ Value *VPInstruction::generate(VPTransformState &State) {
     // FIXME: The cross-recipe dependency on VPReductionPHIRecipe is temporary
     // and will be removed by breaking up the recipe further.
     auto *PhiR = cast<VPReductionPHIRecipe>(getOperand(0));
-    auto *OrigPhi = cast<PHINode>(PhiR->getUnderlyingValue());
     // Get its reduction variable descriptor.
     const RecurrenceDescriptor &RdxDesc = PhiR->getRecurrenceDescriptor();
 
     RecurKind RK = RdxDesc.getRecurrenceKind();
     assert(!RecurrenceDescriptor::isFindLastIVRecurrenceKind(RK) &&
            "should be handled by ComputeFindLastIVResult");
 
-    Type *PhiTy = OrigPhi->getType();
+    Type *ResultTy = State.TypeAnalysis.inferScalarType(this);
     // The recipe's operands are the reduction phi, followed by one operand for
     // each part of the reduction.
     unsigned UF = getNumOperands() - 1;
@@ -671,7 +670,7 @@ Value *VPInstruction::generate(VPTransformState &State) {
     // then extend the loop exit value to enable InstCombine to evaluate the
     // entire expression in the smaller type.
     // TODO: Handle this in truncateToMinBW.
-    if (State.VF.isVector() && PhiTy != RdxDesc.getRecurrenceType()) {
+    if (State.VF.isVector() && ResultTy != RdxDesc.getRecurrenceType()) {
       Type *RdxVecTy = VectorType::get(RdxDesc.getRecurrenceType(), State.VF);
       for (unsigned Part = 0; Part < UF; ++Part)
         RdxParts[Part] = Builder.CreateTrunc(RdxParts[Part], RdxVecTy);
@@ -703,10 +702,10 @@ Value *VPInstruction::generate(VPTransformState &State) {
 
       // If the reduction can be performed in a smaller type, we need to extend
       // the reduction to the wider type before we branch to the original loop.
-      if (PhiTy != RdxDesc.getRecurrenceType())
+      if (ResultTy != RdxDesc.getRecurrenceType())
         ReducedPartRdx = RdxDesc.isSigned()
-                             ? Builder.CreateSExt(ReducedPartRdx, PhiTy)
-                             : Builder.CreateZExt(ReducedPartRdx, PhiTy);
+                             ? Builder.CreateSExt(ReducedPartRdx, ResultTy)
+                             : Builder.CreateZExt(ReducedPartRdx, ResultTy);
     }
 
     return ReducedPartRdx;