[llvm] [VPlan] Extract reverse operation for reverse accesses (PR #146525)

[Luke Lau via llvm-commits]

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@@ -3341,3 +3363,34 @@ void VPlanTransforms::addBranchWeightToMiddleTerminator(
       MDB.createBranchWeights({1, VectorStep - 1}, /*IsExpected=*/false);
   MiddleTerm->addMetadata(LLVMContext::MD_prof, BranchWeights);
 }
+
+void VPlanTransforms::adjustRecipesForReverseAccesses(VPlan &Plan) {
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lukel97 wrote:

I just did a quick scan and it looks like the only places where reverse is set is in `VPRecipeBuilder::tryToWidenMemory`. Instead of introducing another transform, should we just insert the `VPInstruction::Reverse`s there to avoid having to iterate over all the recipes again? 

This way would mean we could also remove the `Reverse` field from `VPWidenMemoryRecipe`

https://github.com/llvm/llvm-project/pull/146525