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

[Luke Lau via llvm-commits]

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@@ -2858,25 +2858,43 @@ static VPRecipeBase *optimizeMaskToEVL(VPValue *HeaderMask,
     return new VPWidenLoadEVLRecipe(cast<VPWidenLoadRecipe>(CurRecipe), Addr,
                                     EVL, Mask);
 
-  if (match(&CurRecipe,
+  VPValue *ReversedVal;
+  if (match(&CurRecipe, m_Reverse(m_VPValue(ReversedVal))) &&
+      match(ReversedVal,
             m_MaskedLoad(m_VPValue(EndPtr), m_RemoveMask(HeaderMask, Mask))) &&
       match(EndPtr, m_VecEndPtr(m_VPValue(Addr), m_Specific(&Plan->getVF()))) &&
-      cast<VPWidenLoadRecipe>(CurRecipe).isReverse())
-    return new VPWidenLoadEVLRecipe(cast<VPWidenLoadRecipe>(CurRecipe),
-                                    AdjustEndPtr(EndPtr), EVL, Mask);
+      cast<VPWidenLoadRecipe>(ReversedVal)->isReverse()) {
+    auto *LoadR = new VPWidenLoadEVLRecipe(
+        *cast<VPWidenLoadRecipe>(ReversedVal), AdjustEndPtr(EndPtr), EVL, Mask);
+    LoadR->insertBefore(&CurRecipe);
+    return new VPWidenIntrinsicRecipe(
+        Intrinsic::experimental_vp_reverse, {LoadR, Plan->getTrue(), &EVL},
+        TypeInfo.inferScalarType(LoadR), {}, {}, DL);
+  }
 
   if (match(&CurRecipe, m_MaskedStore(m_VPValue(Addr), m_VPValue(),
                                       m_RemoveMask(HeaderMask, Mask))) &&
       !cast<VPWidenStoreRecipe>(CurRecipe).isReverse())
     return new VPWidenStoreEVLRecipe(cast<VPWidenStoreRecipe>(CurRecipe), Addr,
                                      EVL, Mask);
 
-  if (match(&CurRecipe, m_MaskedStore(m_VPValue(EndPtr), m_VPValue(),
+  VPValue *StoredVal;
+  if (match(&CurRecipe, m_MaskedStore(m_VPValue(EndPtr), m_VPValue(StoredVal),
----------------
lukel97 wrote:

Can this just match the reverse in the same line so you don't need the separate match on line 2886

```suggestion
  if (match(&CurRecipe, m_MaskedStore(m_VPValue(EndPtr), m_Reverse(m_VPValue(ReversedVal)),
```

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