[llvm] [LV] Use VPReductionRecipe for partial reductions (PR #144908)

[Sander de Smalen via llvm-commits]

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@@ -2598,6 +2554,16 @@ VPExtendedReductionRecipe::computeCost(ElementCount VF,
 InstructionCost
 VPMulAccumulateReductionRecipe::computeCost(ElementCount VF,
                                             VPCostContext &Ctx) const {
+  if (isPartialReduction())
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sdesmalen-arm wrote:

Should `VPExtendedReductionRecipe::computeCost` also be updated?

https://github.com/llvm/llvm-project/pull/144908