Refactor ExtTy type inference

Author: SamTebbs33

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -304,8 +304,8 @@ VPPartialReductionRecipe::computeCost(ElementCount VF,
   VPRecipeBase *ExtBR = BinOpR->getOperand(1)->getDefiningRecipe();
 
   auto *PhiType = Ctx.Types.inferScalarType(getOperand(1));
-  auto *ExtTy = ExtAR ? Ctx.Types.inferScalarType(ExtAR->getOperand(0))
-                      : BinOpR->getOperand(0)->getUnderlyingValue()->getType();
+  auto *ExtTy = Ctx.Types.inferScalarType(ExtAR ? ExtAR->getOperand(0)
+                                                : BinOpR->getOperand(0));
 
   auto GetExtendKind = [](VPRecipeBase *R) {
     // The extend could come from outside the plan.