Address comments on PR

Involves adding an extra if statement and changing a comment.

Author: JamesChesterman

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8918,8 +8918,8 @@ VPRecipeBuilder::tryToCreatePartialReduction(Instruction *Reduction,
       isa<VPPartialReductionRecipe>(BinOpRecipe))
     std::swap(BinOp, Accumulator);
 
-  VPValue *Mask = getBlockInMask(Reduction->getParent());
-  if (Mask) {
+  if (CM.blockNeedsPredicationForAnyReason(Reduction->getParent())) {
+    VPValue *Mask = getBlockInMask(Reduction->getParent());
     VPValue *Zero =
         Plan.getOrAddLiveIn(ConstantInt::get(Reduction->getType(), 0));
     BinOp = Builder.createSelect(Mask, BinOp, Zero, Reduction->getDebugLoc());

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -2104,8 +2104,7 @@ class VPReductionPHIRecipe : public VPHeaderPHIRecipe,
 /// A recipe for forming partial reductions. In the loop, an accumulator and
 /// vector operand are added together and passed to the next iteration as the
 /// next accumulator. After the loop body, the accumulator is reduced to a
-/// scalar value. If the mask operand is not nullptr then it is applied to the
-/// vector operand on each iteration.
+/// scalar value.
 class VPPartialReductionRecipe : public VPSingleDefRecipe {
   unsigned Opcode;