code: public void add(final AbstractInsnNode insn) {
          ++size;
          if (last == null) {
              first = insn;
              last = insn;
          } else {
              last.next = insn;
              insn.prev = last;
          }
          last = insn;
          cache = null;
          insn.index = 0; // insn now belongs to an InsnList
      }
docs: Adds the given instruction to the end of this list.
  
  @param insn
  an instruction, <i>which must not belong to any
  {@link InsnList}</i>.