[llvm] [VPlan] Refactor VPlan creation, add transform introducing region (NFC). (PR #128419)

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@@ -3589,6 +3574,8 @@ class VPlan {
     TripCount = NewTripCount;
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ayalz wrote:

Above error message that "TripCount always must be set" needs to be updated.

https://github.com/llvm/llvm-project/pull/128419