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

[via llvm-commits]

================
@@ -1330,6 +1332,9 @@ class VPInstruction : public VPRecipeWithIRFlags {
   /// Returns true if this VPInstruction produces a scalar value from a vector,
   /// e.g. by performing a reduction or extracting a lane.
   bool isVectorToScalar() const;
+
+  /// Return the interleave count from the VPInstruction's last argument.
----------------
ayalz wrote:

```suggestion
  /// Return the interleave count from VPInstruction's last operand.
```
Is this the interleave Count, which should better be a property of (the enclosing) loop region than an operand of VPInstruction, or a specific interleave Part?

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