O flags

[Segher Boessenkool]

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