[llvm-branch-commits] [llvm] [LoopVectorizer] Bundle partial reductions inside VPMulAccumulateReductionRecipe (PR #136173)

[Sander de Smalen via llvm-branch-commits]

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@@ -2432,12 +2437,40 @@ static void tryToCreateAbstractReductionRecipe(VPReductionRecipe *Red,
   Red->replaceAllUsesWith(AbstractR);
 }
 
+/// This function tries to create an abstract recipe from a partial reduction to
+/// hide its mul and extends from cost estimation.
+static void
+tryToCreateAbstractPartialReductionRecipe(VPPartialReductionRecipe *PRed) {
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sdesmalen-arm wrote:

The way I read the code is that at the point of getting to this point in the code, it has recognised a reduction so there is a `VP[Partial]ReductionRecipe`. It then tries to analyse whether that recipe can be transformed into a `VPMulAccumulateReductionRecipe`. For `VPReductionRecipe` it will clamp the range to all the VFs that can be turned into a `VPMulAccumulateReductionRecipe`, but for `VPPartialReductionRecipe` it doesn't do that. I don't see why for partial reductions we'd do something different.

In fact, why wouldn't the `tryToMatchAndCreateMulAccumulateReduction` code be sufficient here? Now that you've made `VPPartialReductionRecipe` a subclass of `VPReductionRecipe`, I'd expect that code to function roughly the same.

https://github.com/llvm/llvm-project/pull/136173