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

[via llvm-commits]

================
@@ -451,12 +451,6 @@ bool VPlanVerifier::verify(const VPlan &Plan) {
     return false;
   }
 
-  if (!isa<VPCanonicalIVPHIRecipe>(&*Entry->begin())) {
-    errs() << "VPlan vector loop header does not start with a "
-              "VPCanonicalIVPHIRecipe\n";
----------------
ayalz wrote:

```suggestion
  if (!Plan.getCanonicalIV()) {
    errs() << "VPlan vector loop lacks a canonical IV\n";
```

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