[llvm] [VPlan] Make CanIV part of region. (PR #144803)

[via llvm-commits]

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@@ -411,13 +411,22 @@ static void createLoopRegion(VPlan &Plan, VPBlockBase *HeaderVPB) {
   // LatchExitVPB, taking care to preserve the original predecessor & successor
   // order of blocks. Set region entry and exiting after both HeaderVPB and
   // LatchVPBB have been disconnected from their predecessors/successors.
-  auto *R = Plan.createVPRegionBlock();
+  VPPhi *ScalarCanIV = nullptr;
+  if (!HeaderVPB->getParent())
+    ScalarCanIV = cast<VPPhi>(&*cast<VPBasicBlock>(HeaderVPB)->begin());
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ayalz wrote:

Some explanation about orphan HeaderVPB case?

https://github.com/llvm/llvm-project/pull/144803