Only shallow traverse vector loop region

Author: lukel97

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -1028,9 +1028,8 @@ void VPlanTransforms::simplifyRecipes(VPlan &Plan, Type &CanonicalIVTy) {
 /// to make sure the masks are simplified.
 static void simplifyBlends(VPlan &Plan) {
   using namespace llvm::VPlanPatternMatch;
-  ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<VPBlockBase *>> RPOT(
-      Plan.getEntry());
-  for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(RPOT)) {
+  for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
+           vp_depth_first_shallow(Plan.getVectorLoopRegion()->getEntry()))) {
     for (VPRecipeBase &R : make_early_inc_range(*VPBB)) {
       auto *Blend = dyn_cast<VPBlendRecipe>(&R);
       if (!Blend)