Method set_opcode

extern/re2/re2/prog.h:117–119

   private:
    void set_opcode(InstOp opcode) {
      out_opcode_ = (out()<<4) | (last()<<3) | opcode;
    }

    void set_last() {
      out_opcode_ = (out()<<4) | (1<<3) | opcode();