[llvm] [VPlan] Make canonical IV part of the region (PR #156262)

[via llvm-commits]

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@@ -3981,23 +3933,35 @@ class LLVM_ABI_FOR_TEST VPRegionBlock : public VPBlockBase {
   /// VPRegionBlock.
   VPBlockBase *Exiting;
 
-  /// An indicator whether this region is to generate multiple replicated
-  /// instances of output IR corresponding to its VPBlockBases.
-  bool IsReplicator;
+  /// Canonical IV of the loop region. If CanIV is nullptr, the region is a
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ayalz wrote:

```suggestion
  /// Holds the Canonical IV of the loop region along with additional information. If CanIV is nullptr, the region is a
```

https://github.com/llvm/llvm-project/pull/156262