[Bug libstdc++/51798] [4.7 regression] libstdc++ atomicity performance regression due to __sync_fetch_and_add

[dje at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51798

--- Comment #8 from David Edelsohn <dje at gcc dot gnu.org> 2012-01-25 15:14:29 UTC ---
> At least at this point I'd feel much safer if libstdc++ used just acq_rel
> semantics for the all atomic_fetch_and_add places, instead of somewhere acq and
> somewhere rel semantics.

Can we at least apply the ACQ_REL patch using the new atomic intrinsics?

Unfortunately, without my patch, libstdc++ users of atomicity.h (basic_string,
shared_ptr) do not distinguish between ACQUIRE and RELEASE, so POWER cannot
provide its own atomicity.h with the improved implementation.