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

[via llvm-commits]

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@@ -835,6 +840,11 @@ void VPRegionBlock::print(raw_ostream &O, const Twine &Indent,
                           VPSlotTracker &SlotTracker) const {
   O << Indent << (isReplicator() ? "<xVFxUF> " : "<x1> ") << getName() << ": {";
   auto NewIndent = Indent + "  ";
+  if (!isReplicator()) {
+    O << '\n';
+    getCanonicalIV()->print(O, SlotTracker);
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ayalz wrote:

nit: below seems clearer for dumping CanIV, should it also replace isReplicator() above?
```suggestion
  if (auto *CanIV = getCanonicalIV()) {
    O << '\n';
    CanIV->print(O, SlotTracker);
```

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