<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/94879>94879</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libcxx] Trying to use `atomic_ref<const T>` and `atomic_ref<volatile T>` fails with a compilation error
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            libc++
      </td>
    </tr>

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

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

<pre>
    The following code fails to compile, complaining that it cannot pass a `const T*` or `volatile T*` to the relevant intrinsic.

```c++
int i = 0;
std::atomic_ref<const int> cref(i);
int val = cref.load(); // error
cref.wait(); // error

volatile int vi = 0;
std::atomic_ref<volatile int> vref(v);
val = vref.load(); // error
vref.exchange(val); // error
vref.compare_exchange_weak(val, 0); // error
vref.compare_exchange_strong(val, 0); // error
vref.wait(0); // error
```

See  https://godbolt.org/z/TbjYdd3Kx

The problem is that the local variable `__ret` used to receive the result of a load has type `_Tp*`, whereas it really needs to have type `remove_cv_t<_Tp>*`.

e.g. you can fix the `atomic_ref::load()` method by applying the following change:
```diff
   _LIBCPP_HIDE_FROM_ABI _Tp load(memory_order __order = memory_order::seq_cst) const noexcept
 _LIBCPP_CHECK_LOAD_MEMORY_ORDER(__order) {
 _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
         __order == memory_order::relaxed || __order == memory_order::consume || __order == memory_order::acquire ||
             __order == memory_order::seq_cst,
         "atomic_ref: memory order argument to atomic load operation is invalid");
     alignas(_Tp) byte __mem[sizeof(_Tp)];
-    auto* __ret = reinterpret_cast<_Tp*>(__mem);
+ auto* __ret = reinterpret_cast<remove_cv_t<_Tp>*>(__mem);
 __atomic_load(__ptr_, __ret, std::__to_gcc_order(__order));
     return *__ret;
   }
```
</pre>
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