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

[Luke Lau via llvm-commits]

================
@@ -3570,7 +3591,7 @@ void VPExpressionRecipe::decompose() {
     LiveInPlaceholders[Idx]->replaceAllUsesWith(Op);
 
   replaceAllUsesWith(ExpressionRecipes.back());
-  ExpressionRecipes.clear();
+  return std::move(ExpressionRecipes);
----------------
lukel97 wrote:

I think there can be duplicate expression recipes, so if we erase them in optimizeMasksToEVL I think it might crash. Probably the easiest fix is to just change decompose to return a new smallvector of recipes that were inserted, i.e. without duplicates

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