Re: MMX instruction and gcc

["Andrew Pinski" <pinskia at gmail dot com>]

On 15 Mar 2007 08:12:21 -0700, Ian Lance Taylor <iant@google.com> wrote:
> Galloth <lordgalloth@gmail.com> writes:
>
> > I want ask, if there is posibilities that gcc will be automaticaly
> > generates MMX instruction? I tried -mtune, -march  -mmmx. But gcc stil
> > generates code without MMX instruction. On net I found only
> > information about inline assembler function or citation from man page.
> > I tried to compile program for adding two arrays of 24 chars.
>
> This question is appropriate for the mailing list
> gcc-help@gcc.gnu.org, not for gcc@gcc.gnu.org.  Please take any
> follow-ups to gcc-help.  Thanks.

Actually this one I think belongs still here because ...

> In some cases gcc may be able to automatically generate MMX
> instructions if you use the -ftree-vectorize option.

This is not true right now.  GCC is not able to automatically use the
MMX instructions at all, this is already filed as PR 22076 and others.
There was a patch posted as an RFC to fix this but it caused
regression on x86_64 and the person who submitted has not updated it
yet for the mainline.

Thanks,
Andrew Pinski