[clang] [LifetimeSafety] Avoid adding already present items in sets/maps (PR #159582)

[Jan Voung via cfe-commits]

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@@ -910,6 +910,8 @@ template <typename T>
 static llvm::ImmutableSet<T> join(llvm::ImmutableSet<T> A,
                                   llvm::ImmutableSet<T> B,
                                   typename llvm::ImmutableSet<T>::Factory &F) {
+  if (A == B)
+    return A;
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jvoung wrote:

would the `add()` on line 918 also possibly do more allocation than desired (and cost more than checking if contains first), if `E` was already in `A` ?

https://github.com/llvm/llvm-project/pull/159582