libsanitizer mege from upstream r169371

[Jakub Jelinek]

On Wed, Dec 05, 2012 at 04:53:44PM +0400, Dmitry Vyukov wrote:
> On Wed, Dec 5, 2012 at 4:42 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> > On Wed, Dec 05, 2012 at 03:13:20PM +0400, Dmitry Vyukov wrote:
> >> I hope I addressed all your comments in this revision.
> >> I've fixed nand atomic operation, made atomic operations atomic again
> >> and added visibility attribute to interface functions.
> >
> > Mostly, still, __sync_lock_test_and_set isn't full barrier unlike most other
> > __sync_* builtins, so either you'd need to use __atomic_exchange_n if
> > available (you can e.g. guard it with #ifdef __ATOMIC_SEQ_CST), or
> > if not available also use __sync_synchronize ().
> 
> 
> __atomic_xxx are available since gcc 4.7 and we use gcc 4.4 on some
> bots. I do not want to clutter the code with macros too much.

Well, one option would be just a single #ifdef somewhere,
#ifndef __ATOMIC_SEQ_CST
#define __ATOMIC_RELEASE 0
...
#define __atomic_...(...) __sync_...(...)
...
#endif
i.e. implement __atomic_* as macros using __sync_* if not available,
then just use __atomic_* in the code everywhere.

	Jakub