http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51798
--- Comment #16 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-26 20:39:40 UTC --- Apologies for my phrasing. What I meant is that it's not a matter of consistency. Localising all uses of __sync_bool_compare_and_swap by adding an unnecessary additional layer of indirection in atomicity.h would not have been appropriate. GCC already abstracts the required CAS operation with __sync_bool_compare_and_swap, so that is used directly when needed. One of the main reasons for the wrappers in atomicity.h is to fall back to non-atomic ops in non-threaded code, rather than just to localize the use of intrinisics. Having a fall back for non-threaded code isn't necessary for the places where __sync_bool_compare_and_swap is used in shared_ptr and parallel mode. Our shared_ptr has a partial specialization for the non-threaded case, which doesn't use CAS, and using parallel mode in non-threaded code doesn't make sense. So __sync_bool_compare_and_swap is used directly. "It's own atomicity.h" doesn't include a CAS operation, and I see no benefit to adding CAS to that file.
