<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 loop vectorization with reduction and ptr load/store inside loop"
   href="https://bugs.llvm.org/show_bug.cgi?id=52038">52038</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Missed loop vectorization with reduction and ptr load/store inside loop
          </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>Windows NT
          </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>Loop Optimizer
          </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>void test1(int *p, int *t, int N) {
    for (int i = 0; i != N; i++) *t += p[i];
}

void test2(int *p, int *t, int N) {
    if (N > 1024) // hint, N is not small
        for (int i = 0; i != N; i++) *t += p[i];
}

void test3(int *p, int *t, int N) {
    if (N > 1024) { // hint, N is not small
        int s = 0;
        for (int i = 0; i != N; i++) s += p[i];
        *t += s;
    }
}

test3 is successfully vectorized with LLVM, GCC, ICC. Sadly, only ICC can catch
test1 and test2.

<a href="https://godbolt.org/z/PzoYd4eEK">https://godbolt.org/z/PzoYd4eEK</a></pre>
        </div>
      </p>


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