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

[Michael Niedermayer]

On Fri, Oct 14, 2016 at 08:29:37PM +0200, Michael Niedermayer wrote:
> 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

thinking again, why dont you write the function in asm for x86 ?
this would take the compiler out of the equation

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The educated differ from the uneducated as much as the living from the
dead. -- Aristotle 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20161014/7eab33f4/attachment.sig>