if (!isValid()) throw new IllegalStateException("accessing top or bottom frame");
if (!isValid()) throw new DataflowAnalysisException("accessing top or bottom frame");
	public ValueType popValue() throws DataflowAnalysisException {		if (!isValid()) throw new IllegalStateException("accessing top or bottom frame");		if (slotList.size() == numLocals) throw new DataflowAnalysisException("operand stack empty");		return slotList.remove(slotList.size() - 1);	}