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    <head>
      <base href="https://llvm.org/bugs/" />
    </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 --- - Volatile stores of undef values are deleted"
   href="https://llvm.org/bugs/show_bug.cgi?id=27309">27309</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Volatile stores of undef values are deleted
          </td>
        </tr>

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

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

        <tr>
          <th>Hardware</th>
          <td>All
          </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>Scalar Optimizations
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>koriakin@0x04.net
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>All stores of undef values are deleted at the moment - including volatile
stores:

define void @f(i32 *%p) {
  store volatile i32 undef, i32 *%p;
  ret void;
}

Compiles to:

f: retq

In theory, the pointer could point to a hardware device where the store has
some side-effects like increasing a queue pointer.  A driver that wants to
write dummy data could reasonably store an undef and need it to be actually
performed.

Bug found when browsing idly through the code, I don't actually have a
real-world case for it.</pre>
        </div>
      </p>
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      <ul>
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