title: What does "sibling calls" mean?
body: <p>On GCC manual,</p>
  
  <blockquote>
    <p>-foptimize-sibling-calls</p>
    
    <blockquote>
      <p>Optimize sibling and tail recursive calls.</p>
    </blockquote>
  </blockquote>
  
  <p>I know tail recursive calls, for example</p>
  
  <blockquote>
    <p>int sum(int n) { return n == 1 ? 1 : n + sum(n-1); }</p>
  </blockquote>
  
  <p>However, what does sibling calls mean?</p>