Re: [gentoo-user] gcc 4.2 and Core 2 Duo

[Daniel Pielmeier]

Andrew Gaydenko schrieb:
> I have noticed, the official portage tree has included gcc 4.2. Now for
> Core 2 Duo CPU (amd64 Gentoo arch) I use in make.conf file:
>
> CFLAGS="-O2 -march=nocona -pipe"
>
> gcc' changelog has this note:
>
> --------------------
> ...
> IA-32/x86-64
>
>     * -mtune=generic can now be used to generate code running well on common x86 chips.
>       This includes AMD Athlon, AMD Opteron, Intel Pentium-M, Intel Pentium 4 and Intel
>       Core 2.
>     * -mtune=native and -march=native will produce code optimized for the host
>       architecture as detected using the cpuid instruction.
> ...
> --------------------
>
> The question is: must I replace '-march=nocona' with '-mtune=native and -march=native'?

Here you will find additional information http://tinyurl.com/2b6spk.
It is stated there that you can use either -march=cpu-type or
-mtune=cpu-type and that -march=cpu-type implies -mtune=cpu-type.

I think you can also use the nocona option for the cpu-type until gcc
4.3 is out which brings you -march=core2, see here http://tinyurl.com/ottvh.

Using mtune or march depends on where you want to use your compiled
software, if you only want to use it only on your own machine
-march=native is probably the best option and if you want to use it on
other machines too, you should choose -mtune=native. If you don't know
at all the weather the cpu is IA32 AMD64 or EM64T you should use
-mtune=generic.

Maybe someone could explain it better, but this is what i understand!

Regards,

Daniel
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