[llvm] [VPlan] Add VPRegionBlock::getCanonicalIVType (NFC). (PR #164127)

[via llvm-commits]

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@@ -69,8 +69,7 @@ class UnrollState {
                                 VPBasicBlock::iterator InsertPtForPhi);
 
   VPValue *getConstantVPV(unsigned Part) {
-    Type *CanIVIntTy =
-        Plan.getVectorLoopRegion()->getCanonicalIV()->getScalarType();
+    Type *CanIVIntTy = Plan.getVectorLoopRegion()->getCanonicalIVType();
     return Plan.getOrAddLiveIn(ConstantInt::get(CanIVIntTy, Part));
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ayalz wrote:

Independent: perhaps useful to have a shortcut such as
```suggestion
    return Plan.getConstantInt(CanIVIntTy, Part);
```
which will expand to getOrAddLiveIn(ConstantInt::get(T, V)).

https://github.com/llvm/llvm-project/pull/164127