[llvm] [VPlan] Add VPPhiAccessors to provide interface for phi recipes (NFC) (PR #129388)

[via llvm-commits]

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@@ -3694,25 +3720,10 @@ void VPReductionPHIRecipe::print(raw_ostream &O, const Twine &Indent,
 }
 #endif
 
-VPBasicBlock *VPWidenPHIRecipe::getIncomingBlock(unsigned I) {
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ayalz wrote:

Better keep delegating the implementation of `getIncomingBlock(Idx)` to recipes that inherit from `VPPhiAccessors`?

https://github.com/llvm/llvm-project/pull/129388