[opensource-dev] (CTS-315) march choice for 64bit builds

[leliel]

On Sat, Oct 23, 2010 at 3:08 AM, Altair Sythos <sythos at gmail.com> wrote:
> On Sat, 23 Oct 2010 03:08:26 +0200
> Boroondas Gupte <sllists at boroon.dasgupta.ch> wrote:
>
>>  Because SSE2 is now required anyway, -march=pentium4 is now passed
>> for building lindenlab/mesh-development. Of course, this doesn't work
>> for 64bit builds. (See CTS-315
>> <https://jira.secondlife.com/browse/CTS-315>.) What should march be
>> set to for 64bit buids, if anything?
>
> pentium4 don't support 64bit, but "nocona" yes

nocona also enables sse3 which would cut out many k8 cpus.

> the other (imho better) way to select right march/mtune is use
> "generic" and declare *all* parameters, sort of:

This is the proper fix imho.

> for 32bit:
> gcc -march=generic -mtune=generic -m32 -mmmx -msse -msse2
> -mfpmath=both <etc.etc.>
>
> for 64bit:
> gcc -march=generic -mtune=generic -m64 -mmmx -msse -msse2
> -mfpmath=both <etc.etc.>

Should use -mfpmath=sse, gcc isn't very good at doing both x87 and sse
fp math at the same time.