<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 - Missed opportunity for BTR instruction"
   href="https://bugs.llvm.org/show_bug.cgi?id=37938">37938</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Missed opportunity for BTR instruction
          </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>Linux
          </td>
        </tr>

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

        <tr>
          <th>Severity</th>
          <td>enhancement
          </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>david.bolvansky@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Hello,

Code:
uint64_t btr_maybe(uint64_t x, unsigned bit) {
    return x & ~(1ULL << bit);
}


Clang -03 gives:
btr_maybe: # @btr_maybe
  mov rax, -2
  mov ecx, esi
  rol rax, cl
  and rax, rdi
  ret


But BTR instruction can be used (and GCC 8+ emits it):
btr_maybe(unsigned long, unsigned int):
  mov rax, rdi
  btr rax, rsi
  ret</pre>
        </div>
      </p>


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