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

[via llvm-commits]

================
@@ -83,17 +83,19 @@ const SCEV *vputils::getSCEVExprForVPValue(const VPValue *V,
     return SE.getCouldNotCompute();
   }
 
+  if (auto *CanIV = dyn_cast<VPRegionValue>(V)) {
----------------
ayalz wrote:

This assumes every region value V is the canonical IV?

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