[arch-general] Enforcing CFLAGS in PKGBUILDs

[Lukas Fleischer]

On Fri, Aug 05, 2011 at 10:54:41AM +0200, Jan de Groot wrote:
> On Fri, 2011-08-05 at 15:23 +0800, Ray Rashif wrote:
> 
> > For eg. some developers like to enforce -O3, so they should first get
> > the system CFLAGS and override it's -O*, if any.
> > 
> > But in general, I agree. We shouldn't enforce anything either unless
> > we're trying to fix something. The ardour PKGBUILD does this [1],
> > maybe it shouldn't, but I assume the -O3 becomes redundant when we
> > pass system CFLAGS to the build as a configuration flag.
> > 
> > [1] http://projects.archlinux.org/svntogit/packages.git/tree/ardour/trunk/PKGBUILD
> 
> Looking at ardour, I see it's also patched to support gcc 4.6. Now let's
> say something about -O3: -O3 optimization can be very bad and the
> results are extremely dependent on the compiler version. Something that
> works optimal with gcc 4.4 and -O3 can break completely with gcc 4.6 and
> -O2.

You should file a bug report if it does. Given the number of PKGBUILDs
that patch optimization levels, I would also say that this is only true
for a minority of cases.

> Just adding -O3 to CFLAGS without knowing which compiler is used is
> plain stupid. Check this blog for example:
> http://glandium.org/blog/?p=1975
> There someone from Mozilla claims they're finally able to build with O3
> +PGO with GCC 4.5. This was at the time we were already doing O2+PGO
> from our PKGBUILD with 4.5 and now 4.6.