linktable
linktable(gco2t(o), &g->gray);
linktable(h, &g->weak); /* has to be cleared later */
linktable(h, &g->grayagain); /* no need to clean */
linktable(h, &g->ephemeron); /* have to propagate again */
linktable(h, &g->allweak); /* may have to clean white keys */
linktable(h, &g->grayagain); /* no need to clean */
linktable(h, &g->allweak); /* nothing to traverse now */