[llvm] [LV] NFCI: Create VPExpressions in transformToPartialReductions. (PR #182863)

[Sander de Smalen via llvm-commits]

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@@ -6130,6 +6148,12 @@ static void transformToPartialReduction(const VPPartialReductionChain &Chain,
     ExitValue->replaceAllUsesWith(PartialRed);
   WidenRecipe->replaceAllUsesWith(PartialRed);
 
+  // For cost-model purposes, see if we can fold this into a VPExpression.
+  if (VPExpressionRecipe *E = createPartialReductionExpression(PartialRed)) {
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sdesmalen-arm wrote:

It theoretically could if the BinOp was not a Mul/FMul, but at the moment `getPartialReductionCost` would return an invalid cost for that. If we always want partial reductions to be represented by a VPExpression, then we should limit `matchExtendedReductionOperand` to always limit to Mul/FMul.

https://github.com/llvm/llvm-project/pull/182863