I can only confirm that -O0 performs some optimization, which can be annoying when single-stepping through the code (cough, cough) using a debugger. Hence gcc

I can only confirm that -O0 performs some optimization, which can be annoying when single-stepping through the code (cough, cough) using a debugger. Hence gcc offers -Og to suppress those optimizations (not sure, whether that in itself causes some debugging info to be added though).