Hello, > On Sun, 2007-04-22 at 14:44 +0200, Richard Guenther wrote: > > On 4/22/07, Laurent GUERBY <[EMAIL PROTECTED]> wrote: > > > > > but also does not make anyone actually use the options. Nobody reads > > > > > the documention. Of course, this is a bit overstatement, but with a > > > > > few exceptions, people in general do not enable non-default flags. > > > > > > > > I don't think this is fair. > > > > Most people don't read the docs because they don't care about > > > > performance, but most people who develop code that spends a lot of CPU > > > > cycles actually read the docs at least up to loop unrolling. > > > > > > Exactly my experience. > > > > > > Unfortunately there's no useful information on this topic in the GCC > > > manual... > > > > Well, we have too many switches really. So the default is use -O2. If you > > want extra speed, try -O3, or even better use profile feedback. (Not many > > people realize that with profile feedback you get faster code than with > > -O3 and smaller code than with -Os - at least for C++ programs) > > At work we use -O3 since it gives 5% performance gain against -O2. > profile-feedback has many flags
actually, only two that are really important -- -fprofile-generate and -fprofile-use. Zdenek
