[FFmpeg-devel] [PATCH v2] SH4 mpegaudio decoder optimizations

[Reimar Döffinger]

On Wed, Dec 15, 2010 at 01:26:20AM +0100, Guennadi Liakhovetski wrote:
> > > +    : [hi] "+r" (u.u32[1]),                          \
> > > +      [lo] "+r" (u.u32[0]),                          \
> > > +      [wp] "+r" (wp),                                \
> > > +      [pp] "+r" (pp)                                 \
> > 
> > Do all compilers/compiler versions that are in use support
> > named asm arguments?
> 
> Do you know any ones, used for SH, where this is not supported? I don't.
> 
> > I also think as a paranoia measure these should be +&r
> > (but I admit I never understood that so 100%).
> 
> hm, don't remember seeing this - early clobber input-output? Does it make 
> sense at all? Early clobber tells the compiler, that it cannot reuse an 
> input register for this output parameter, and this is anyway the case, if 
> it is also an input, isn't it?

You have also an input-only operand. If the compiler knows it to have
the same value as one of the in-out ones it could reuse the in-out register
for it. And I think that would break for your code since the input-only
operand is used even after the in-out ones were modified...