Re: gcc, march and sse

["Jim Capozzoli" <saltmiser%gmail.com@localhost>]

On Wed, Dec 3, 2008 at 10:26 AM, Joel Carnat <joel%carnat.net@localhost> wrote:
> Hello,
>
> I read that Slackware Linux compiles most of its packages with
> "-march=i486 -mtune=i686". As far as I understood gcc's manpage, this
> means "keep code compatible with 486 CPU but allow the use pentiumpro
> special features", right ?
>
> Still from the man page, MMX is supported since "pentium2 (or pentium-mmx
> only)", SSE since "pentium3", SSE2 since "pentium-m", SSE3 since
> "prescott".
>
> I tweaked my mk.conf to compile pkgsrc (on a domU) using "-O2 -march=486
> -mtune=686" but I'm now wondering if any on those compiled programs will
> use MMX or SSE when running on my laptop or intel-based servers (intel
> core2duo).
>
> Then second question, in case the previous thought is correct, if I use
> "-march=i486 -mtune=nocona", is there a way to see which instruction the
> program uses ? For example, if I compile xorg/firefox/mplayer and then run
> it in a special manner, can I see that the core2duo uses MMX/SSE*
> instruction while the C3 only use MMX instruction (from the same binary) ?
>
> TIA,
>    Jo
>
>
>
Well, there's this script or something that can figure out the ideal
flags for you so you don't have to worry about it.

http://pkgsrc.se/devel/cpuflags

On my pentium3 machine it has everything building with MMX
instruction, and everything seems to be working nicely.

Hope this helps.

-- 
Jim Capozzoli
D6499626857801B6065013E3645A6B75