[llvm] [VPlan] Make CanIV part of region. (PR #144803)

[via llvm-commits]

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@@ -4148,13 +4152,8 @@ class VPlan {
 #endif
 
   /// Returns the canonical induction recipe of the vector loop.
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ayalz wrote:

```suggestion
  /// Returns the canonical induction VPValue of the vector loop.
```

https://github.com/llvm/llvm-project/pull/144803