GCSpropagate
g->gcstate = GCSpropagate;
case GCSpropagate: {
lua_assert(g->gcstate == GCSpropagate);
g->gcstate = GCSpropagate; /* skip restart */
lua_assert(g->gcstate == GCSpropagate);
luaC_runtilstate(L, bitmask(GCSpropagate));
luaC_runtilstate(L, bitmask(GCSpropagate));
check_exp(g->gcstate == GCSpropagate || !isgenerational(g), \