[VPlan] Replace reverse RPOT with PO traversal (NFC) (#151757)

Author: artagnon

llvm/lib/Transforms/Vectorize/VPlanCFG.h

@@ -230,6 +230,13 @@ vp_post_order_shallow(VPBlockBase *G) {
   return post_order(VPBlockShallowTraversalWrapper<VPBlockBase *>(G));
 }
 
+/// Returns an iterator range to traverse the graph starting at \p G in
+/// post order while traversing through region blocks.
+inline iterator_range<po_iterator<VPBlockDeepTraversalWrapper<VPBlockBase *>>>
+vp_post_order_deep(VPBlockBase *G) {
+  return post_order(VPBlockDeepTraversalWrapper<VPBlockBase *>(G));
+}
+
 /// Returns an iterator range to traverse the graph starting at \p G in
 /// depth-first order while traversing through region blocks.
 inline iterator_range<df_iterator<VPBlockDeepTraversalWrapper<VPBlockBase *>>>

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -545,10 +545,8 @@ static bool isDeadRecipe(VPRecipeBase &R) {
 }
 
 void VPlanTransforms::removeDeadRecipes(VPlan &Plan) {
-  ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<VPBlockBase *>> RPOT(
-      Plan.getEntry());
-
-  for (VPBasicBlock *VPBB : reverse(VPBlockUtils::blocksOnly<VPBasicBlock>(RPOT))) {
+  for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
+           vp_post_order_deep(Plan.getEntry()))) {
     // The recipes in the block are processed in reverse order, to catch chains
     // of dead recipes.
     for (VPRecipeBase &R : make_early_inc_range(reverse(*VPBB))) {