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Re: P4 support question (-> FAQ?)



----- Original Message -----
From: "Jean Francois Martinez" <jfm2@club-internet.fr>
To: "Will Menninger" <william.l.menninger@boeing.com>; <gcc@gcc.gnu.org>
Sent: Thursday, May 24, 2001 10:22 AM
Subject: Re: P4 support question (-> FAQ?)


> On Thursday 24 May 2001 17:51, Will Menninger wrote:
> > Hello,
> >
> > Is there a way to add a question to the gcc FAQ database on the web?
> > Either way, I'd like to see this question added to the platform
specific
> > section (and hopefully answered):  What is the timeline (if any) for
> > supporting Pentium 4 specific instructions (e.g. SSE-2) in gcc?  Is
this
> > being worked on or expected to occur in a specific release of gcc?
> >
> > Please refer me to the appropriate link if this question is answered
> > somewhere in the gcc web pages.
> >
>
> My experince with gcc 2.x is that use of specific instructions brings
only
> minimal sped increases in 99 % of cases, the real speed boost is given by
> using sequences who are optimized for processor.  In other words -march=
> (use of specific instructions) brins very little improvement over -mcpu=
> (optimized for specific cpu but using only 386 instructions).
>
> This could change the day gcc genartes MMX instructions but for now the
> question should be when will gcc be able to optimize for PIV?
>
> JFM
I don't expect any changes in scheduling to make major differences in
performance on P4; gcc already does quite well when P-II optimizations are
selected.  I'm in the middle of a comparison of efficiency of code
sequences generated by various compilers; while SSE code is required in
many situations to make the best of P4, there are situations where gcc
generates P-II compatible code which is faster than that available from
commercial compilers.


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