title: Enabling AVX512 support on compilation significantly decreases performance
body: <p>I've got a C/C++ project that uses a static library. The library is built for 'skylake' architecture. The project is a data processing module, i.e. it performs many arithmetic operations, memory copying, searching, comparing, etc.</p>
  <p>The CPU is Xeon Gold 6130T, it supports AVX512. I tried to compile my project with both <code>-march=skylake</code> and <code>-march=skylake-avx512</code> and then link with the library.</p>
  <p>In case of using <code>-march=skylake-avx512</code> the project performance is significantly decreased (by 30% on average) in comparison to the project built with <code>-march=skylake</code>.</p>
  <p>How can this be explained? What could be the reason?</p>
  <p>Info:</p>
  <ul>
  <li>Linux 3.10</li>
  <li>gcc 9.2</li>
  <li>Intel Xeon Gold 6130T</li>
  </ul>