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

[Mel Chen via llvm-commits]

================
@@ -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) {
----------------
Mel-Chen wrote:

I was initially worried this might affect interleaved accesses, but I was overthinking it. So far, generating the reverse directly in tryToWidenMemory seems fine.
9d6136b7a21a91fe5c479b9071c113b7802f062f

> This way would mean we could also remove the Reverse field from VPWidenMemoryRecipe
>
We can't remove the Reverse field from VPWidenMemoryRecipe. We still need the reverse mask if it's a reverse access. I also don’t plan to separate the reverse mask either, as I think it would not bring  benefit.

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