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

[Mel Chen 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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Mel-Chen wrote:

That’s possible, but the reason I’m not doing it for now is that, in case some reverse operations can't be eliminated, we might want to convert reverse accesses into strided accesses with a stride of -1. Keeping the Reverse field could make it easier to identify the target recipes that need conversion. Also, reverse masks generally can not do permutation elimination, I think. So that’s why I haven’t done it this way.

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