[llvm] [LV] Support EVL for partial reduction and VPExpressionRecipe. (PR #205741)

[Luke Lau via llvm-commits]

================
@@ -237,6 +237,29 @@ static VPRecipeBase *optimizeMaskToEVL(VPValue *HeaderMask,
                                            Mask ? Mask : Plan->getTrue(), &EVL},
                                           IntrR->getScalarType(), {}, {}, DL);
 
+  // Transforms the VPReductionRecipe inside the VPExpressionRecipe.
+  if (auto *Expr = dyn_cast<VPExpressionRecipe>(&CurRecipe))
+    if (match(Expr->getOperand(Expr->getNumOperands() - 1),
+              m_RemoveMask(HeaderMask, Mask))) {
+      // Decompose first and construct with EVL recipes later.
+      SmallVector<VPSingleDefRecipe *> ExpressionRecipes(Expr->decompose());
+
+      // Convert recipes to EVL recipes.
+      for (auto [Idx, ExprR] : enumerate(ExpressionRecipes))
+        if (auto *EVLR = cast_if_present<VPSingleDefRecipe>(
+                optimizeMaskToEVL(HeaderMask, *ExprR, EVL))) {
+          EVLR->insertBefore(ExprR);
+          ExprR->replaceAllUsesWith(EVLR);
+          ExprR->eraseFromParent();
+          ExpressionRecipes[Idx] = EVLR;
+        }
+
+      auto *NewExpr =
+          new VPExpressionRecipe(Expr->getExpressionType(), ExpressionRecipes);
+      ExpressionRecipes[ExpressionRecipes.size() - 1]->replaceAllUsesWith(
----------------
lukel97 wrote:

```suggestion
      ExpressionRecipes.back()->replaceAllUsesWith(
```

https://github.com/llvm/llvm-project/pull/205741