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

[Sam Tebbs via llvm-commits]

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@@ -3013,10 +3014,16 @@ class VPExpressionRecipe : public VPSingleDefRecipe {
                            {Ext0, Ext1, Mul, Red}) {}
 
   ~VPExpressionRecipe() override {
-    for (auto *R : reverse(ExpressionRecipes))
-      delete R;
-    for (VPValue *T : LiveInPlaceholders)
-      delete T;
+    SmallSet<VPSingleDefRecipe *, 4> ExpressionRecipesSeen;
+    for (auto *R : reverse(ExpressionRecipes)) {
+      if (ExpressionRecipesSeen.insert(R).second)
+        delete R;
+    }
+    SmallSet<VPValue *, 4> PlaceholdersSeen;
+    for (VPValue *T : LiveInPlaceholders) {
+      if (PlaceholdersSeen.insert(T).second)
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SamTebbs33 wrote:

Currently I'm caching the placeholder for each operand so that duplicate operands share the same placeholder, so we do need to care about duplicates here to avoid deleting placeholders that have already been deleted. But I've changed it so that the same operands don't share a placeholder.

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