Shawn Haggett wrote:
>
> There's two points that come to mind.
>
> 1) mtune is a request for the compiler to make the code more suited to
> the given processor, but without breaking compatibility. march is
> telling the compiler, do everything you can to make this code fastest
> on this processor.
>
> From the GCC docs for 4.2.3:
> "-mtune=cpu-type: Tune to cpu-type everything applicable about the
> generated code, except for the ABI and the set of available
> instructions."
> "-march=cpu-type: Generate instructions for the machine type cpu-type.
> The choices for cpu-type are the same as for -mtune. Moreover,
> specifying -march=cpu-type implies -mtune=cpu-type."
>
> So mtune shouldn't be using any instructions that are in K-6 that
> weren't in a 386.
>
> 2) I believe x86 hardware never goes backwards. That is, if a new
> feature is added, all future versions of the chip have that feature,
> just with more added. Of course Intel and AMD both have their separate
> additions, but since your staying with AMD, moving to a new processor
> shouldn't break anything (even if you had used march).
>
> Disclaimer: I'm not an expert on hardware architectures or compilers,
> so I might be wrong.
>
> Shawn

Thanks Shawn, that's probably the best answer I'm going to get, I doubt
many of the AMD chip designers hang around here... :)