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

[via llvm-commits]

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@@ -821,6 +821,10 @@ void VPlan::prepareToExecute(Value *TripCountV, Value *VectorTripCountV,
   // FIXME: Model VF * UF computation completely in VPlan.
   VFxUF.setUnderlyingValue(
       createStepForVF(Builder, TripCountV->getType(), State.VF, State.UF));
+  if (VF.getNumUsers() > 0) {
+    VF.setUnderlyingValue(
+        createStepForVF(Builder, TripCountV->getType(), State.VF, 1));
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ayalz wrote:

```suggestion
        getRuntimeVF(Builder, TripCountV->getType(), State.VF));
```

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