Re: [gentoo-dev] Replacing cpu-feature USE flags

[Brian Harring]

On Fri, Jul 07, 2006 at 02:24:49PM +0200, Martin Schlemmer wrote:
> On Fri, 2006-07-07 at 02:08 +0200, Diego 'Flameeyes' Pettenò wrote:
> > On Friday 07 July 2006 01:54, Ciaran McCreesh wrote:
> > > | No, we never spent years telling them not to use your so-called
> > > | "CFLAGS hacks" that are rather a proper usage of what the compiler
> > > | gives you.
> > > Wrong. We did.
> > Then you were wrong. I could have spent time explaining them when they make
> > sense and why they don't in their usecases. If you did, well, then you really
> > need to know better what you do because you seem to me pretty confused
> > yourself, and I feel pity for you.
> >
>
> Yes, we did.  Were we wrong?  Out of a purest point of view ... maybe.
> The problem was though that earlier gcc's was very bad at generating
> sse/sse2, and sometimes mmx code.
>
> Users being what they are though (ricers should say it all), they
> enabled every flag that sounded like it could make their old box two
> times faster.  This included -msse, -msse2, etc.  Which quite frankly
> produced bad code in many cases.  So we told the users to not add any
> -m* flags, and let gcc do its job with the proper -march.
>
> So yeah, I can see that general use flags for cpu features might become
> more tedious with the many new modules of processors out there, but to
> say handle it by adding -msse, etc to CFLAGS, will surely if not on
> gcc4, but then on gcc3 systems just ask for trouble.
>
> And yes, I know you are saying that that is not exactly what you are
> proposing, but the users will see it as a clear passport to stick all
> those nice sounding flags just right back in, and then it will be too
> late to tell them its not proper thing to do when the bugs start
> flooding in.

Dumb question, but what really blocks them from doing that now for 
x86 (for example)?

Yes, can't enable certain flags for non x86/x86_64 arches, but the con 
you're pointing at exists now for the most part.

~harring