code: @Override
      public void sawOpcode(int seen) {
          try {
              stack.precomputation(this);
  
              if (OpcodeUtils.isStore(seen) || OpcodeUtils.isLoad(seen)) {
                  int reg = getRegisterOperand();
                  unusedParms.clear(reg);
              } else if (OpcodeUtils.isReturn(seen) && (stack.getStackDepth() > 0)) {
                  OpcodeStack.Item item = stack.getStackItem(0);
                  int reg = item.getRegisterNumber();
                  if (reg >= 0) {
                      unusedParms.clear(reg);
                  }
              }
              if (unusedParms.isEmpty()) {
                  throw new StopOpcodeParsingException();
              }
          } finally {
              stack.sawOpcode(this, seen);
          }
      }
docs: implements the visitor to look for usage of parmeter registers.
  
  @param seen
  the opcode of the currently parsed instruction