REF_DROP         2246 lj_opt_fold.c    return REF_DROP;
REF_DROP          114 lj_opt_loop.c      if (lref == rref || rref == REF_DROP) {  /* Invariants are redundant. */
REF_DROP          348 lj_opt_loop.c  	} else if (ref != REF_DROP && irr->o == IR_CONV &&