[PATCH] Fix atomic_full_barrier on x86 and x86_64.

[Torvald Riegel]

On Wed, 2014-10-29 at 21:54 +0000, Joseph S. Myers wrote:
> On Wed, 29 Oct 2014, Torvald Riegel wrote:
> 
> > What's the include order on x86, counting down from the most recent
> > supported revision (ie, for an i686 machine, include sysdeps/i386/i686
> > first, then i586 and i486)?
> 
> That depends on the sysdeps Implies file.  For i686, it uses i386/i486 but 
> *not* i386/i586.
> 
> (i586 uses i486, so any files for plain i386 that are overridden for i486, 
> or overridden for both i586 and i686, are dead and can be removed.  It 
> would also be OK to merge i486 into i386 now anything before i486 isn't 
> supported.)

Thanks for the background.

So, mfence seems to have been introduced with SSE2.  Should I try to
test for SSE2 specifically, or rather assume SSE2 support for i786?