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

[Ramkumar Ramachandra via llvm-commits]

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@@ -2339,6 +2355,39 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
       CurVPV->replaceAllUsesWith(EVLRecipe->getVPSingleValue());
     }
     ToErase.push_back(CurRecipe);
+
+    // Convert general reverse operations on loaded values and stored values
+    // into vp.reverse, when the VPVectorEndPointerRecipe adjusting the access
+    // address uses EVL instead of VF.
+    // TODO: Extend conversion along the def-use/use-def chain, as reverse
+    // operations may be eliminated or moved in the future.
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artagnon wrote:

Hm, seems like we may be leaving a footgun here, although I'm not sure how it can be improved?

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