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

[via llvm-commits]

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@@ -492,12 +498,11 @@ Value *VPInstruction::generatePerPart(VPTransformState &State, unsigned Part) {
     return EVL;
   }
   case VPInstruction::CanonicalIVIncrementForPart: {
+    unsigned Part = getUnrollPartOperand();
     auto *IV = State.get(getOperand(0), VPIteration(0, 0));
-    if (Part == 0)
-      return IV;
-
-    // The canonical IV is incremented by the vectorization factor (num of SIMD
-    // elements) times the unroll part.
+    assert(Part != 0 && "Must have  a part");
----------------
ayalz wrote:

```suggestion
    assert(Part != 0 && "Must have a positive part");
```

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