title: When can't a compiler use RVO or NRVO?
body: <p>Move semantics can be useful when the compiler cannot use <a href="http://en.wikipedia.org/wiki/Return_value_optimization" rel="nofollow">RVO</a> and <a href="http://www.efnetcpp.org/wiki/Return_value_optimization#Named_RVO" rel="nofollow">NRVO</a>. But in which case can't the compiler use these features?</p>