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    <head>
      <base href="http://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 --- - Void expression address does not generate an error (C only)"
   href="http://llvm.org/bugs/show_bug.cgi?id=21724">21724</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Void expression address does not generate an error (C only)
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>3.4
          </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>normal
          </td>
        </tr>

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

        <tr>
          <th>Component</th>
          <td>-New Bugs
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>hamsa.bugs@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvmbugs@cs.uiuc.edu
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>This compiles without warnings:

    extern void foo; // 1

    int main()
    {
      &foo; // 2
    }

(1) The validity of the `foo` declaration is questionable. There is no apparent
direct prohibition in the standard to declare (as opposed to define) void
objects, but as one cannot define a `void` object, it is not clear how such a
declaration could refer to a valid object. Apart from that, the declared
identifier cannot be used in any way.

(2) The expression appears to be outright invalid, because of 6.3.22.1/1 (in
C11):

    An lvalue is an expression (with an object type other than void) that 
    potentially designates an object;

Thus `foo` is not an lvalue, nor it is a function designator, so its address
cannot be taken.

To reiterate, all of this applies to the C front-end only.</pre>
        </div>
      </p>
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