There is also the possibility that if your program has an aliasing bug, the bug may only cause failure at -O2 but not at -O0 or -O1. See http://gcc.gnu.org/bug

There is also the possibility that if your program has an aliasing bug, the bug may only cause failure at -O2 but not at -O0 or -O1. See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35653 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35653, for example.