<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/57364>57364</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Usage of std::atomic_flag::test() added in C++20 compiles successfully with --std=c++17
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

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

<pre>
    Usage of the std::atomic_flag::test() method added in C++20 should fail to compile with --std=c++17. Instead, it compiles successfully,

I'm not an expert here, but I think the [code](https://github.com/llvm/llvm-project/blob/main/libcxx/include/atomic#L2393) needs to check the _LIBCPP_STD_VER value.

CC @ogiroux who added this functionality in https://reviews.llvm.org/D68480
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJyVU0uPmzAQ_jXmMgoCGwg5cNgkjRRpD6u-rpHBA7g1OMJ2Hv--A-l2W2krtdLIHnusme8h11bdqy9Odgi2Bd8jOK-YeKKQ3g66ObVGdo8Lj84zXjK-gQF9bxVIpVCBHmHH-JaCJ-B6G4yCVmoD3kJjh7M2CFfte1itlub75vE6XcdwHJ1HqRjfgfavrx240DToXBuMuVONJXuWPD3WI-PrAUbrQY6AtzNOHnqccG5RBw9HYqHH7wsXlm8bq5Dle8Lde392MxN-oOgIUKhjmkgHYy6v2-o82W_YENFDbWxN2yD1OBd13dxulOixMYGa8sNDIcbFMxcbMesyIiq38O6xeWA4PR-3u5eX06fP-9PXDx_hIk3A-HdGux2wLLGdnmy4wbW3P3UlHg7aMDZe21Ea7e-z1H_SmPCi8eriGXpsp46u9kWZlUmEVVoUaZaVRVlEqhJqIzYy8tobfDP8n8x-x-V3jfqLyVGYTPXf4mvnAjpK8rUosqivMpG0iWhzlXJVpqptMJMySTPebjblusbIyBqNq8hzxvmIV1haUE72R7riCedJyfN0LVJexFLmUmUSRSkSyVVODiA5bX4pGU3VAqkOnaOi0c6_yRxJ53RHbi_jqL8M9CGmapDdhDjWRnofLfOrBf8Pqw0VDQ">