"Dr. David Kirkby" <david.kirkby@xxxxxxxxxx> writes: > How safe is it to distribute code for others to build, where you have > selected -O3 for them? I'm a bit concerned that might be a bit > aggressive to use as a default, given it will potentially be compiled > by different gcc versions on different platforms. The -O3 optoin should be safe for correct code. An important difference between -O2/-O3 and -O1 is that -O2 and -O3 enable strict aliasing and strict overflow. Those options provide better optimization for correct code, but are far more likely to cause unexpected code generation for incorrect code. See the -fstrict-aliasing and -fstrict-overflow options. > I believe -O2 might be a more sensible default, but would welcome the > opinions of others on the matter. The main difference between -O3 and -O2 is that -O3 enables more speculative optimizations. These should not miscompile your code, but they may cause your program to run more slowly. Ian
