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

[via llvm-commits]

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@@ -3665,6 +3690,29 @@ inline bool isUniformAfterVectorization(VPValue *VPV) {
     return VPI->isVectorToScalar();
   return false;
 }
+
+/// Checks if \p C is uniform across all VFs and UFs. It is considered as such
+/// if it is either defined outside the vector region or its operand is known to
+/// be uniform across all VFs and UFs (e.g. VPDerivedIV or VPCanonicalIVPHI).
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ayalz wrote:

```suggestion
/// if it is either loop invariant (defined outside the vector region) or ... its operand is known to
/// be uniform across all VFs and UFs (e.g. VPDerivedIV or VPCanonicalIVPHI).
```

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