[arch-general] Enforcing CFLAGS in PKGBUILDs

[Ray Rashif]

On 5 August 2011 16:54, Jan de Groot <jan at jgc.homeip.net> 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.
> 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.

Good that you bring this up - I was totally unaware of this correlation.


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