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

[via llvm-commits]

================
@@ -1556,9 +1600,14 @@ void VPSlotTracker::assignNames(const VPlan &Plan) {
 
   ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<const VPBlockBase *>>
       RPOT(VPBlockDeepTraversalWrapper<const VPBlockBase *>(Plan.getEntry()));
-  for (const VPBasicBlock *VPBB :
-       VPBlockUtils::blocksOnly<const VPBasicBlock>(RPOT))
-    assignNames(VPBB);
+  for (const VPBlockBase *VPB : RPOT) {
+    if (auto *VPBB = dyn_cast<VPBasicBlock>(VPB)) {
+      assignNames(VPBB);
+      continue;
+    }
+    if (auto *CanIV = cast<VPRegionBlock>(VPB)->getCanonicalIV())
----------------
ayalz wrote:

```suggestion
    if (auto *VPBB = dyn_cast<VPBasicBlock>(VPB))
      assignNames(VPBB);
    else if (auto *CanIV = cast<VPRegionBlock>(VPB)->getCanonicalIV())
```

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