[Ffmpeg-devel] H264 decoding problem

Uoti Urpala uoti.urpala
Thu Oct 12 23:10:33 CEST 2006

On Thu, 2006-10-12 at 19:58 +0200, Michael Niedermayer wrote:
> ill bet gcc ignored some of the asm constraints, at least thats what it
> does most of the time when it misscompiles some asm

I tried compiling it with current gcc svn. Using either asm version in
cabac.h fails with -O3. -O2 or C version works.

Adding "memory" to the clobber list of the asm makes it work. I can see
how it could in principle be miscompiled if the compiler doesn't know
that for example c->range can change during the asm (as it's also
accessed from other C functions in cabac.h that call get_cabac), but on
x86 there should be no free registers where the compiler could keep
anything so it shouldn't matter. Haven't yet confirmed whether this is
the real reason for the failure.

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