<html>
    <head>
      <base href="https://bugs.llvm.org/">
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - LLVM too aggressive about using vector ctpop"
   href="https://bugs.llvm.org/show_bug.cgi?id=47825">47825</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>LLVM too aggressive about using vector ctpop
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>libraries
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>Backend: X86
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>dave@znu.io
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, pengfei.wang@intel.com, spatel+llvm@rotateright.com
          </td>
        </tr></table>
      <p>
        <div>
        <pre>The following code generates quite sub-optimal assembly on targets that don't
have a vector population count instruction:

__mmask8 popCountLessThanOrEqualToOne(__m512i value) {
    return _mm512_testn_epi64_mask(value, value - 1);
}

It seems like the generic optimization pass(es) are converting this into a
vector "ctpop" without checking whether the back end has the instruction or
not. Whoops.</pre>
        </div>
      </p>


      <hr>
      <span>You are receiving this mail because:</span>

      <ul>
          <li>You are on the CC list for the bug.</li>
      </ul>
    </body>
</html>