// The CLEANSTACK check is only performed after potential P2SH evaluation,
    // as the non-P2SH evaluation of a P2SH script will obviously not result in
    // a clean stack (the P2SH inputs remain). The same holds for witness
    // evaluation.
    if ((flags & SCRIPT_VERIFY_CLEANSTACK) != 0) {
        // Disallow CLEANSTACK without P2SH, as otherwise a switch
        // CLEANSTACK->P2SH+CLEANSTACK would be possible, which is not a
        // softfork (and P2SH should be one).
        assert((flags & SCRIPT_VERIFY_P2SH) != 0);
        if (stack.size() != 1) {
            return set_error(serror, SCRIPT_ERR_CLEANSTACK);
        }
    }