Scott Alfter salfter at salfter.dyndns.org
Thu Jan 25 09:55:32 PST 2001

On Tue, Jan 23, 2001 at 02:12:58PM -0500, Steve Hayashi wrote:
> If you have a 486, then -march=i486 is best
> If you have a Pentium (the original) then -march=i586 will be optimal
> If you have Pentium Pro or better, use -march=i486

Actually, you should use -march-i686 with P6-core boxen (PPro, PII, P!!!,

> Note: the above may not work if you have a Cyrix or AMD.  Someone else
> will have to comment on that for me.

For AMD K6* processors, use -march=k6 (this is how mine was compiled, as the
server is a K6-2-300 and the diskless workstations hanging off it are a
K6-III-450 (this one has local storage, but WinME lives on it) and a
K6-200).  For the K5, use -march=i586.  For the Athlon/Duron, there's no
specific optimization yet.  I would suspect that either i586 or k6 would be
suitable, though I don't know which of the two would be better. i686
wouldn't be a good choice for any AMD processor as the instruction
scheduling in Intel's P6-core processors is almost completely different from
everything else out there (it's part of why the PPro sucked hard at 16-bit
code; Intel tends to not pay much attention to legacy software in its new
designs, as the P4 has demonstrated again).  Code optimized for the PPro
won't run optimally on AMD-based systems, just as code optimized for the K6
won't run optimally on Intel-based systems.

As for Cyrix processors, you probably want to use -march=i486 with the 6x86,
MediaGX, and maybe the 6x86MX/MII as there are some operations in the
Pentium instruction set that aren't implemented in the 6x86.  You definitely
want -march=i486 with the 5x86 (my firewall uses one of these).  I don't
know enough about Cyrix's (make that VIA's) newest stuff to know which way
you'd want to go with them, as I've never dealt with anything from Cyrix
newer than the 6x86MX.

 / v \
(IIGS(  Scott Alfter (salfter at salfter.dyndns.org)
 \_^_/  http://salfter.dyndns.org
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