http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60484
--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> --- Anyway, this is because finish_options is called for every optimize attribute (handle_optimize_attribute->parse_optimize_attribute->decode_options->finish_options) + one more time for command line options and every time it adds the directory prefix. I guess we should add the directory prefix just once.