On Sun, May 24, 2015 at 08:15:46PM +0200, Robert Mijakovic wrote: > I took optimizations enabled by O[1..3] and tried to enable them all at > once without calling > O flag levels. I have found out that improvements I got by using all > flags used by the > particular O flag level are not even close to what I would get by > explicitly using O flag levels. That is a frequently asked question: http://gcc.gnu.org/wiki/FAQ#optimization-options Segher