<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 - Failure to optimize double overflow comparison to __builtin_add_overflow"
   href="https://bugs.llvm.org/show_bug.cgi?id=46432">46432</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Failure to optimize double overflow comparison to __builtin_add_overflow
          </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>Scalar Optimizations
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>gabravier@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org
          </td>
        </tr></table>
      <p>
        <div>
        <pre>unsigned foo(unsigned a, unsigned b)
{
    unsigned sum = a + b;
    if (sum < a)
        abort();
    if (sum < b)
        abort();
    return sum;
}

This can be optimized to remove one of the two checks, or to this :

unsigned foo(unsigned a, unsigned b)
{
    unsigned sum;
    if (__builtin_add_overflow(a, b, &sum))
        abort();
    else
        return sum;
}

This transformation is done by GCC, but not by LLVM.</pre>
        </div>
      </p>


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