[llvm] [LV][EVL] Support in-loop reduction using tail folding with EVL. (PR #90184)

[Mel Chen via llvm-commits]

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@@ -1446,23 +1454,39 @@ bool VPlanTransforms::tryAddExplicitVectorLength(VPlan &Plan) {
 
   for (VPValue *HeaderMask : collectAllHeaderMasks(Plan)) {
     for (VPUser *U : collectUsersRecursively(HeaderMask)) {
-      auto *MemR = dyn_cast<VPWidenMemoryRecipe>(U);
-      if (!MemR)
+      VPRecipeBase *NewRecipe = nullptr;
+      auto *CurRecipe = dyn_cast<VPRecipeBase>(U);
+      if (!CurRecipe || CurRecipe->getNumDefinedValues() > 1)
         continue;
-      VPValue *OrigMask = MemR->getMask();
-      assert(OrigMask && "Unmasked widen memory recipe when folding tail");
-      VPValue *NewMask = HeaderMask == OrigMask ? nullptr : OrigMask;
-      if (auto *L = dyn_cast<VPWidenLoadRecipe>(MemR)) {
-        auto *N = new VPWidenLoadEVLRecipe(L, VPEVL, NewMask);
-        N->insertBefore(L);
-        L->replaceAllUsesWith(N);
-        L->eraseFromParent();
-      } else if (auto *S = dyn_cast<VPWidenStoreRecipe>(MemR)) {
-        auto *N = new VPWidenStoreEVLRecipe(S, VPEVL, NewMask);
-        N->insertBefore(S);
-        S->eraseFromParent();
-      } else {
-        llvm_unreachable("unsupported recipe");
+
+      auto GetNewMask = [&](VPValue *OrigMask) -> VPValue * {
+        assert(OrigMask && "Unmasked recipe when folding tail");
+        return HeaderMask == OrigMask ? nullptr : OrigMask;
+      };
+      if (auto *MemR = dyn_cast<VPWidenMemoryRecipe>(CurRecipe)) {
+        VPValue *NewMask = GetNewMask(MemR->getMask());
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Mel-Chen wrote:

I don't quite understand the comment's meaning. Are you referring to [this change](https://github.com/llvm/llvm-project/pull/93854/files#diff-53267225b83e943ceae51c326c9941e323fd7aaf74a08b5e6998d6456f88d1ddR1499)? If so, I think we can just  change this in #93854?

https://github.com/llvm/llvm-project/pull/90184