__sg_next
(__iter) = __sgt_iter(__sg_next((__iter).sgp), true), 0 : 0)
(__iter) = __sgt_iter(__sg_next((__iter).sgp), false), 0 : 0)
sg = __sg_next(sg);
iter->sg = __sg_next(iter->sg);
iter->sg = __sg_next(iter->sg);
iter.sg = __sg_next(iter.sg);
sg = __sg_next(sg);
iter = __sg_next(iter);
sg = __sg_next(sg);
for (sg = st->sgl; sg; sg = __sg_next(sg)) {