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 <rsbul...@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
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