<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/84802>84802</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            atomic_is_always_lock_free provides inconsistent results on Apple
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            compiler-rt
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          ldionne
      </td>
    </tr>
</table>

<pre>
    For a struct of size 16, `atomic_is_always_lock_free` seems to provide inconsistent results based on the address we're passing to the builtin. This seems odd since `is_always_lock_free` should tell us whether *any* instance of that type is lock free, regardless of its address?

```c++
// clang++ x.cpp -std=c++20 -o a.out && ./a.out

#include <iostream>

template <size_t N>
struct Sized { char x[N]; };

template <class T>
void test() {
    std::cout << "sizeof(" << typeid(T).name() << ") = " << sizeof(T) << std::endl;
    std::cout << "__atomic_always_lock_free(" << typeid(T).name() << ") = " << __atomic_always_lock_free(sizeof(T), 0) << std::endl;
    T x;
 std::cout << "__atomic_always_lock_free with ptr(" << typeid(T).name() << ") = " << __atomic_always_lock_free(sizeof(T), &x) << std::endl;
 std::cout << "__atomic_is_lock_free(" << typeid(T).name() << ") = " << __atomic_is_lock_free(sizeof(T), &x) << std::endl;
}

int main() {
    test<Sized<16>>();
}
```

Output:

```
$ clang++ x.cpp -std=c++20 -o a.out && ./a.out
sizeof(5SizedILm16EE) = 16
__atomic_always_lock_free(5SizedILm16EE) = 1
__atomic_always_lock_free with ptr(5SizedILm16EE) = 0
__atomic_is_lock_free(5SizedILm16EE) = 0
```

</pre>
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