https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65467
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> --- From the original discussions on why this is disabled: _Atomic support is currently disabled for Objective-C and OpenMP. For both (but mainly OpenMP), the relevant parser code needs checking to determine where convert_lvalue_to_rvalue calls need inserting to ensure that accesses to atomic variables involve atomic loads. For Objective-C, there are also various special cases of compound assignment that need special handling for atomics just as standard C compound assignment is handled differently for atomics, as well as some TYPE_MAIN_VARIANT calls to check for correctness for atomics; see the comment on the relevant sorry () call for details. OpenMP should also have TYPE_MAIN_VARIANT uses checked as well as a use of TYPE_QUALS_NO_ADDR_SPACE for a diagnostic in c_parser_omp_declare_reduction (where the diagnostic refers to a particular list of qualifiers). So it looks like there is more than even what Jakub listed. Also patches are welcome to handle OpenMP and _Atomic better.
