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

[Florian Hahn via llvm-commits]

================
@@ -3559,18 +3580,23 @@ VPExpressionRecipe::VPExpressionRecipe(
       R->replaceUsesOfWith(LiveIn, Tmp);
 }
 
-void VPExpressionRecipe::decompose() {
-  for (auto *R : ExpressionRecipes)
+SmallVector<VPSingleDefRecipe *> VPExpressionRecipe::decompose() {
+  SmallVector<VPSingleDefRecipe *> InsertedRecipes;
+  for (auto *R : ExpressionRecipes) {
     // Since the list could contain duplicates, make sure the recipe hasn't
     // already been inserted.
-    if (!R->getParent())
+    if (!R->getParent()) {
       R->insertBefore(this);
+      InsertedRecipes.push_back(R);
----------------
fhahn wrote:

I am not sure this will work correctly as-is. If we have duplicates, then we will have to incorrect number of recieps when constructing the EVL VPExpressionRecipe.

e.g. something like 

```
    %e = sext i8 %l to i32
    %mul = mul i32 %e, %e
    %add = add i32 %sum, %mul
```

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