Bug#320726: acknowledged by developer (Re: Bug#320726: gcc-4.0: mmx, sse asm need -mmmx, -msse)

[matthieu castet <castet.matthieu@free.fr>]

Hi,

Debian Bug Tracking System wrote:
> > Hi,
> >
> > gcc-4.0 need -mmmx, -msee, ... flags in order to compil optimized
> > assembler. But this break runtime decision of the optimisation according
> > to the cpu capcibility : you can't mix in the same file generic code, and
> > runtime selected code.
> >
> > Attached an example where -mmmx is needed.
>
>
> so where is the bug?  please split the code into two files, or compile
> the code two times depending on a preprocessor define into two object
> files/libraries.
There no bug if you split the code in 2 file as you can compile the 
generic code without -mmmx.

The problem occur when using inline asm code.

The problem is that according gcc manual, with -mmmx, gcc could optimize 
the code with mmx instruction. So with the mmx flag the generic code is 
no more generic and won't work on no-mmx machine :(

I can't find a generic code that use mmx instruction with mmx flag, so I 
can't provide a real example.

IIRC there is a discution about that in gcc ML or bugzilla.

regards,
Matthieu