[rfc] improving 32bit user performance/experience...
john.r.moser at gmail.com
Tue May 19 17:58:40 UTC 2009
Daniel J Blueman wrote:
> All older VIA processors, AMD Geode procs and so on support the full
> i586 instruction set, which including MMX instructions and registers,
> which itself can provide a good win.
Geodes have partial implementation, particularly they only handle a few
PREFETCH instructions IIRC.
>>> (does any of this apply to x86-64, eg -mtune=core2 or k8?)
>> Yes but this becomes a mess. Leave it as is. gcc is good at tuning
>> to general-purpose in an instruction set.
> -mtune is instruction-set invariant. gcc will tune for for i386
> scheduling, ie fewer pipeline stages. It's later processors that have
> had to optimise for short-pipeline-scheduled code, not the converse.
> IA64 would have been crippled if the instruction scheduling wasn't
> right from the outset.
Why the hell would you tune 64-bit instructions for a 32-bit processor?
x86-64 has as much to do with IA-32 (i386, x86, i686, etc) as PPC has
to do with SPARC.
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