-fopenmp use does not cause gcc to automatically link with gomp, this is because Darwin defines its own LINK_COMMAND_SPEC which does not include the following section from the generic version: %{fopenmp:%:include(libgomp.spec)%(link_gomp)}
-- Summary: With -fopenmp, gcc does not link with -lgomp Product: gcc Version: 4.2.0 Status: UNCONFIRMED Keywords: openmp Severity: normal Priority: P3 Component: target AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: pinskia at gcc dot gnu dot org GCC target triplet: *-*-darwin* http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26657