docs: public ValueType getStackValue(int loc) throws DataflowAnalysisException {
          if (!isValid()) {
              throw new DataflowAnalysisException("Accessing TOP or BOTTOM frame!");
          }
          int stackDepth = getStackDepth();
          if (loc >= stackDepth) {
              throw new DataflowAnalysisException("not enough values on stack: access=" + loc + ", avail=" + stackDepth);
          }
          if (loc < 0) {
              throw new DataflowAnalysisException("can't get position " + loc + " of stack");
          }
          int pos = slotList.size() - (loc + 1);
          return slotList.get(pos);
      }