Re: Seeking doc on K6 code generation

[Jean Francois Martinez <jfm2 at club-internet dot fr>]

On Sunday  3 June 2001 17:29, Steve Snyder wrote:
> Hello.
>
> I am using the version of GCC that came with RedHat v7.1 and, yes, I know
> that compiler is not an official GCC release.  That said, where can I find
> documentation of the code generation for the K6 (-mcpu=k6 / -march=k6)
> flavor of the x86 architecture?
>
> I am trying to decide whether "-march=i586" or "-march=k6" is most
> appropriate for my K6-2-based machine.  So far I have been unable to find a
> reference describing what code generation is specific to the k6 switches.
>
> Pointers, anyone?
>
> Thanks.

AFAIK there is none (in whatever version of gcc), but you can run benchmarks. 
 I did it (on a K6/2) and I found that compiling with -march=i586 sucks, it 
also sucks on PII, PIIIs.  In fact on everything who is not a true Pentium it 
will be even slower than -mcpu=i386.

I also found that using -march=k6 made no difference resprective to -mcpu=k6 
(and code will run on every x86 box).  It is possible that gcc 2.96 generates 
little K6 specific instructions.  Using -mcpu=k6 will allow code to run on 
non-K6s.

I had surprisingly good results with -mcpu=i686.  In some cases better than 
with -march=k6.   It is probable that this is due to the code generator for 
686 being far more mature than the one for K6 (and possibly due to 
architectural differences between K6/2 and true K6)

			JFM

			JFM