[llvm] [VPlan] First step towards VPlan cost modeling (LegacyCM in CostCtx) (PR #92555)

[via llvm-commits]

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@@ -730,6 +731,81 @@ void VPRegionBlock::execute(VPTransformState *State) {
   State->Instance.reset();
 }
 
+static InstructionCost computeCostForRecipe(VPRecipeBase *R, ElementCount VF,
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ayalz wrote:

A public non-virtual `VPRecipeBase::cost()` or getCost() method can take care of skipping, forcing, or otherwise computing the cost of a recipe. The latter case can invoke a protected virtual `VPRecipeBase::computeCost()` which actually implements cost computations, with CM of underlying Instructions as default. Another naming option: computeCost() and computeCostImpl(). Otherwise the distinction between computeCostForRecipe() and Recipe::computeCost() needs to be explained.

https://github.com/llvm/llvm-project/pull/92555