[llvm] [VPlan] Hook IR blocks into VPlan during skeleton creation (NFC) (PR #114292)

[via llvm-commits]

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@@ -1005,16 +1016,23 @@ void VPlan::execute(VPTransformState *State) {
   State->CFG.DTU.applyUpdates(
       {{DominatorTree::Delete, VectorPreHeader, State->CFG.ExitBB}});
 
-  // Replace regular VPBB's for the middle and scalar preheader blocks with
-  // VPIRBasicBlocks wrapping their IR blocks. The IR blocks are created during
-  // skeleton creation, so we can only create the VPIRBasicBlocks now during
-  // VPlan execution rather than earlier during VPlan construction.
+  // Replace regular VPBB's for the vector preheader, middle and scalar
+  // preheader blocks with VPIRBasicBlocks wrapping their IR blocks. The IR
+  // blocks are created during skeleton creation, so we can only create the
+  // VPIRBasicBlocks now during VPlan execution rather than earlier during VPlan
+  // construction.
+  replaceVPBBWithIRVPBB(getVectorPreheader(), VectorPreHeader);
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ayalz wrote:

```suggestion
```
better positioned below along with the other replaceVPBBWithIRVPBB(); in any case better deal with them according to their natural order.

https://github.com/llvm/llvm-project/pull/114292