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

[Sam Tebbs via llvm-commits]

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@@ -2801,21 +2800,36 @@ 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.
+
+  // This map caches the temporary placeholders so duplicates aren't created in
+  // the case that recipes share operands.
+  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());
+      if (OperandPlaceholders.find(Op) == OperandPlaceholders.end())
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SamTebbs33 wrote:

Done, but I've made a variable for the placeholder so we don't have to call `back()`.

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