gco2uv
gco2uv(up)->v = (gco2uv(up)->v - oldstack) + L->stack;
while (*pp != NULL && (p = gco2uv(*pp))->v >= level) {
while (L->openupval != NULL && (uv = gco2uv(L->openupval))->v >= level) {
UpVal *uv = gco2uv(o);
case LUA_TUPVAL: luaF_freeupval(L, gco2uv(o)); break;