[Mesa-dev] Building with -fno-builtin-memcmp for improved performance

Keith Whitwell keithw at vmware.com
Tue Sep 20 07:15:13 PDT 2011

On Tue, 2011-09-20 at 16:02 +0200, Roland Scheidegger wrote:
> Am 20.09.2011 12:35, schrieb Keith Whitwell:
> > On Tue, 2011-09-20 at 10:59 +0200, Fabio wrote:
> >> There was a discussion some months ago about using -fno-builtin-memcmp for 
> >> improving memcmp performance:
> >> http://lists.freedesktop.org/archives/mesa-dev/2011-June/009078.html
> >>
> >> Since then, was it properly addressed in mesa or the flag is still 
> >> recommended? If so, what about adding it in configure.ac?
> > 
> > I've been meaning to follow up on this too.  I don't know the answer,
> > but pinging Roland in case he does.
> I guess it is still recommended.
> Ideally this is really something which should be fixed in gcc - the
> compiler has all the knowledge about fixed alignment and size (if any)
> (and more importantly knows if only a binary answer is needed which
> makes this much easier) and doesn't need to do any function call.
> If you enable that flag and some platform just has the same primitive
> repz cmpsb sequence in the system library it will just get even slower,
> though I guess chances of that happening are slim (with the possible
> exception of windows).
> I think in most cases it won't make much difference, so nobody cared to
> implement that change. It is most likely still a good idea unless gcc
> addressed that in the meantime...

Hmm, it seemed like it made a big difference in the earlier

I should take a look at reducing the size of the struct (as mentioned
before), but surely there's some way to pull in a better memcmp??


More information about the mesa-dev mailing list