[FFmpeg-devel] r9017 breaks WMA decoding on Intel Macs

[Zuxy Meng]

Hi,

2007/5/30, Guillaume POIRIER <poirierg at gmail.com>:
> Hi,
>
> On 5/30/07, Trent Piepho <xyzzy at speakeasy.org> wrote:
> > > On Wed, 30 May 2007, Guillaume POIRIER wrote:
> > > On 5/29/07, Zuxy Meng <zuxy.meng at gmail.com> wrote:
> > > > These warnings comes from the assembler not the compiler about cases
> > > > like 16+(%esi). The FSF as treats this as equivalent to 16+0(esi) ==
> > > > 16(esi) (therefore the assumed 0). If the Apple as treats it
> > > > differently without even a warning then the result is catastrophic...
> > > >
> > > Linux:
> > >  1bd:   0f 28 02                movaps (%edx),%xmm0
> > >  1c0:   0f 28 19                movaps (%ecx),%xmm3
> > >  1c3:   0f 28 62 f0             movaps 0xfffffff0(%edx),%xmm4
> > >  1c7:   0f 28 79 10             movaps 0x10(%ecx),%xmm7
> > >
> > > 000001d7        movaps  (%ebx),%xmm0
> > > 000001da        movaps  (%edi),%xmm3
> > > 000001dd        movaps  0x00(%ebx),%xmm4
> > > 000001e1        movaps  0x00(%edi),%xmm7
> > >
> > > As you can clearly see, that damn OSX manage to loose the offset.
> > > Zuxy, do you know another syntax than the one you suggested, that
> > > wouldn't confuse OSX's assembler?
> >
> > Doesn't my patch fix this?  That would be the alternate syntax that doesn't
> > confuse the assembler.
>
> Yep, your fixed patch does fix the problem (I said that earlier BTW ;-) ).
> Now that we know where the problem comes from, I was just wondering if
> there wasn't a simpler, less-invasive way. (not that your patch is
> unbearably longer, but based on the analysis I made of the
> disassembled code, it leads to more code, so I'd expect your patch to
> be slower (that, off course, would have to be benchmarked).

No it won't. Trent's patch is the correct and optimal way, giving gcc
more freedom in allocating general registers. I should have done this
in my original code but I was a bit too lazy and was concerned if too
many constraints would break gcc 2.95, while the fact is Trent's patch
compiles with gcc 2.95. So there isn't any doubt in the patch itself.

-- 
Zuxy
Beauty is truth,
While truth is beauty.
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