[llvm] [VPlan] Impl VPlan-based pattern match for ExtendedRed and MulAccRed (NFCI) (PR #113903)

[Florian Hahn via llvm-commits]

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@@ -9419,9 +9389,81 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
       if (CM.blockNeedsPredicationForAnyReason(BB))
         CondOp = RecipeBuilder.getBlockInMask(BB);
 
-      VPReductionRecipe *RedRecipe =
-          new VPReductionRecipe(RdxDesc, CurrentLinkI, PreviousLink, VecOp,
-                                CondOp, CM.useOrderedReductions(RdxDesc));
+      auto TryToMatchMulAcc = [&]() -> VPReductionRecipe * {
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fhahn wrote:

adjustRecipesForReductions is already quite big, probably better to move this out to a separate function to avoid It getting even bigger + document what it is doing.

https://github.com/llvm/llvm-project/pull/113903