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

[via llvm-commits]

================
@@ -4492,7 +4461,7 @@ class LLVM_ABI_FOR_TEST VPRegionBlock : public VPBlockBase {
 
   /// An indicator whether this region is to generate multiple replicated
   /// instances of output IR corresponding to its VPBlockBases.
-  bool isReplicator() const { return IsReplicator; }
+  bool isReplicator() const { return !CanIVInfo; }
----------------
ayalz wrote:

Note: it could be useful in the future for replicate regions to also provide a Region Value that represents their "canonical" IV, i.e., ranging from 0 to VF*UF with step 1. But that may deserve a distinct "ReplicatingIV[Info]".

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