vm_cref_push     1602 vm_eval.c          cref = vm_cref_push(th, under, blockptr, TRUE);
vm_cref_push     1624 vm_eval.c          cref = vm_cref_push(th, refinement, blockptr, TRUE);
vm_cref_push     1634 vm_eval.c          rb_cref_t *cref = vm_cref_push(GET_THREAD(), under, NULL, SPECIAL_CONST_P(self) && !NIL_P(under));