https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61333
--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Note, libgomp is optimized for Linux futexes, it has bare support for other targets, so unless somebody steps up and submits and maintains a port for other OSes, those will keep using pthread_* APIs with no particular performance work. So, if you want to do any benchmarking, do it on Linux, not on darwin. Also, benchmarking -O0 code is weird. The benchmark looks prehistoric too, even OpenMP 3.1 has min/max reductions.
