[llvm] Reapply "[VPlan] Remove legacy costing inside VPBlendRecipe::computeCost (#171846)" (PR #172261)

[Luke Lau via llvm-commits]

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@@ -2551,11 +2551,6 @@ void VPVectorPointerRecipe::printRecipe(raw_ostream &O, const Twine &Indent,
 
 InstructionCost VPBlendRecipe::computeCost(ElementCount VF,
                                            VPCostContext &Ctx) const {
-  // Handle cases where only the first lane is used the same way as the legacy
-  // cost model.
-  if (vputils::onlyFirstLaneUsed(this))
-    return Ctx.TTI.getCFInstrCost(Instruction::PHI, Ctx.CostKind);
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lukel97 wrote:

Oh right, I see now a VPInstruction::Select emits a scalar select if onlyFirstLaneUsed is true. Updated in e7fb48b0609fb6f751f1c895bb84a266aab1c81a

https://github.com/llvm/llvm-project/pull/172261