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

[via llvm-commits]

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@@ -1948,6 +1968,12 @@ class VPWidenIntOrFpInductionRecipe : public VPHeaderPHIRecipe {
   VPValue *getVFValue() { return getOperand(2); }
   const VPValue *getVFValue() const { return getOperand(2); }
 
+  VPValue *getSplatVFValue() {
+    // If the recipe has been unrolled (4 operands), return the VPValue for the
+    // induction increment.
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ayalz wrote:

```suggestion
    // induction increment, otherwise return null.
```

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