(1) Original pylayer operation:
                (%1, %2) = "pd_op.pylayer" (%0) {
                    () = "cf.tuple_pop" [id:1]
                    (%3, %4) = "dist_op.xxx" [id:2]
                    () = "cf.yield" [id:3] (%3, %4)
                }
            (2) After calling `update_pylayer_output(%4)`, the updated pylayer operation removes the unused output:
                (%1) = "pd_op.pylayer" (%0) {
                    () = "cf.tuple_pop" [id:1]
                    (%3) = "dist_op.xxx" [id:2]
                    () = "cf.yield" [id:3] (%3)
                }