title: How to hint to GCC that a line should be unreachable at compile time?
body: <p>It's common for compilers to provide a <a href="https://stackoverflow.com/questions/3375697/useful-gcc-flags-for-c/3376483#3376483">switch to warn when code is unreachable</a>. I've also seen macros for some libraries, that provide <a href="http://library.gnome.org/devel/glib/2.24/glib-Testing.html#g-assert-not-reached" rel="noreferrer">assertions for unreachable code</a>.</p>
  
  <p><strong>Is there a hint, such as through a pragma, or builtin that I can pass to GCC (or any other compilers for that matter), that will warn or error during compilation if it's determined that a line expected to be unreachable can actually be reached?</strong></p>
  
  <p>Here's an example:</p>
  
  <pre><code>    if (!conf-&gt;devpath) {
          conf-&gt;devpath = arg;
          return 0;
      } // pass other opts into fuse
      else {
          return 1;
      }
      UNREACHABLE_LINE();
  </code></pre>
  
  <p>The value of this is in detecting, after changes in conditions above the expected unreachable line, that the line is in fact reachable.</p>