g++-5.1.1 warns about unused variable only when optimization flag is used
问题 In a large project, I've been getting some compiler warnings from g++-5.1.1 only when building the release version (which uses optimization flags) but not while building the debug version (which disables most compiler optimization). I've narrowed down the problem to a minimal example listed below with commands to reproduce the problem. The problem does not occur if I use g++-4.8.4. Is this a bug in g++-5.1.1? Or, is this code doing something that is legitimately wrong and warrants that