[FFmpeg-devel] [PATCH] vp9: change order of operations in adapt_prob().

Michael Niedermayer michael at niedermayer.cc
Fri Oct 14 21:29:37 EEST 2016

On Fri, Oct 14, 2016 at 11:09:30AM -0700, James Zern wrote:
> Ronald,
> On Fri, Oct 14, 2016 at 10:01 AM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
> > This is intended to workaround bug "665 Integer Divide Instruction May
> > Cause Unpredictable Behavior" on some early AMD CPUs, which causes a
> > div-by-zero in this codepath, such as reported in Mozilla bug #1293996.
> >
> > Note that this isn't guaranteed to fix the bug, since a compiler is free
> > to reorder instructions that don't depend on each other. However, it
> > appears to fix the bug in Firefox, and a similar patch was applied to
> > libvpx also (see Chrome bug #599899).
> >
> I recently made a few additional changes as this regressed in chrome
> [1][2], but just like this change there's no guarantee it won't occur
> again.

maybe you can use empty "asm volatile(:::"memory")" statments to
prevent unwanted instruction reordering by the compiler
never tried something like this so dunno, also it would be specific
to gcc compatible compilers but should not be architecture specific


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No snowflake in an avalanche ever feels responsible. -- Voltaire
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