http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51798
--- Comment #5 from David Edelsohn <dje at gcc dot gnu.org> 2012-01-24 15:29:44 UTC --- Are you suggesting that the existing atomicity support in libstdc++ should be changed to use ACQ_REL semantics? libstdc++ uses one function to both acquire and release a lock. It adds a positive value (increment) to acquire a lock and a negative value (decrement) to release a lock. POWER appears to be the most flexible and delicate platform with respect to atomic operations and we have been building and testing with my patch for weeks without problem. ACQUIRE, RELEASE, ACQ_REL and SEQ_CST does not make a practical difference in the emitted code on other platforms, so relaxing the semantics would not cause a problem.
