[llvm] [VPlan] Introduce VPScalarPHIRecipe, use for can & EVL IV codegen (NFC). (PR #114305)

[via llvm-commits]

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@@ -7722,6 +7722,7 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   BestVPlan.prepareToExecute(ILV.getTripCount(),
                              ILV.getOrCreateVectorTripCount(nullptr),
                              CanonicalIVStartValue, State);
+  VPlanTransforms::prepareToExecute(BestVPlan);
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ayalz wrote:

Better rename this VPlan2VPlan conversion pass, say, `convertToConcreteRecipes()`, and place it above, following VPlanTransforms::optimizeForVFAndUF(), rather than here, in the midst of `State`-dependent code generation? (BestVPlan.prepareToExecute() actually starts to generate code.)

https://github.com/llvm/llvm-project/pull/114305