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

[Sam Tebbs via llvm-commits]

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@@ -2797,25 +2796,42 @@ VPExpressionRecipe::VPExpressionRecipe(
       R->removeFromParent();
   }
 
+  // Keep track of how many instances of each recipe occur in the recipe list
+  SmallMapVector<VPSingleDefRecipe *, unsigned, 4> ExpressionRecipeCounts;
+  for (auto *R : ExpressionRecipes) {
+    auto *F = ExpressionRecipeCounts.find(R);
+    if (F == ExpressionRecipeCounts.end())
+      ExpressionRecipeCounts.insert(std::make_pair(R, 1));
+    else
+      F->second++;
+  }
+
   // Internalize all external operands to the expression recipes. To do so,
   // 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.
   for (auto *R : ExpressionRecipes) {
+    auto *F = ExpressionRecipeCounts.find(R);
+    F->second--;
     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());
+      auto *Tmp = new VPValue();
+      LiveInPlaceholders.push_back(Tmp);
+      // Only modify this recipe's operands if it's the last time it occurs in
+      // the recipe list
+      if (F->second == 0)
+        R->setOperand(Idx, Tmp);
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SamTebbs33 wrote:

That's nice. It also means we don't have to keep track of the recipe counts. Done.

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