[llvm] [VPlan] Remove original loop if dead after vectorization. (PR #155497)

[Ramkumar Ramachandra via llvm-commits]

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@@ -977,24 +977,26 @@ void VPlan::execute(VPTransformState *State) {
     // logic generic during VPlan execution.
     State->CFG.DTU.applyUpdates(
         {{DominatorTree::Delete, ScalarPh, ScalarPh->getSingleSuccessor()}});
-  } else {
+  }
+  ReversePostOrderTraversal<VPBlockShallowTraversalWrapper<VPBlockBase *>> RPOT(
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artagnon wrote:

Hm, not sure if I'm correct, but I think a shallow RPOT traversal can be replaced by vp_post_order_shallow? Not sure if we're gaining anything by reversing a shallow post-order traversal?

https://github.com/llvm/llvm-project/pull/155497