[llvm] [LV] Keep duplicate recipes in VPExpressionRecipe (PR #156976)

[Florian Hahn via llvm-commits]

================
@@ -2801,21 +2800,31 @@ VPExpressionRecipe::VPExpressionRecipe(
   // create new temporary VPValues for all operands defined by a recipe outside
   // the expression. The original operands are added as operands of the
   // VPExpressionRecipe itself.
+
+  SmallMapVector<VPValue *, VPValue *, 4> OperandPlaceholders;
   for (auto *R : ExpressionRecipes) {
     for (const auto &[Idx, Op] : enumerate(R->operands())) {
       auto *Def = Op->getDefiningRecipe();
       if (Def && ExpressionRecipesAsSetOfUsers.contains(Def))
         continue;
       addOperand(Op);
-      LiveInPlaceholders.push_back(new VPValue());
-      R->setOperand(Idx, LiveInPlaceholders.back());
+      VPValue *Tmp = new VPValue();
+      OperandPlaceholders[Op] = Tmp;
+      LiveInPlaceholders.push_back(Tmp);
     }
   }
+
+  for (auto *R : ExpressionRecipes)
----------------
fhahn wrote:

doing replace-uses-with will update all uses of the external operand with the first temporary value we created for it, leaving the other tmp values created for the same external operand unused

https://github.com/llvm/llvm-project/pull/156976