[llvm] [VPlan] Implement interleaving as VPlan-to-VPlan transform. (PR #95842)

[via llvm-commits]

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@@ -3145,6 +3167,8 @@ class VPlan {
   /// Represents the loop-invariant VF * UF of the vector loop region.
   VPValue VFxUF;
 
+  VPValue VF;
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ayalz wrote:

```suggestion
  /// Represents the loop-invariant VF of the vector loop region.
  VPValue VF;
```
The loop-variant EVL case is currently irrelevant because it currently implies UF=1?

These should move to loop/vector region.

https://github.com/llvm/llvm-project/pull/95842