On 25 April 2018 at 12:27, Игорь Сотниченко wrote: > 3. When I have replaced O2 with keys from O1 and O2 ( > https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html), then there is no > difference in results, but there is a calculation speed degradation > compared to O2. You can't just replace -O2 with the individual flags, you need to use one of the -Ox options or there is NO OPTIMIZATION AT ALL. I repeat, if you don't use one of the -Ox options NO OPTIMIZATION HAPPENS. See https://gcc.gnu.org/wiki/FAQ#optimization-options
