@Override
    public void encode(DecodedInstruction insn, CodeOutput out) {
      out.write(codeUnit(insn.getOpcode(), insn.getA()), insn.getBUnit());
    }
Representation of an instruction format, which knows how to decode into and encode from instances
of {@link DecodedInstruction}.
android/android_framework/dex-maker/src/main/java/com/android/dx/io/instructions/InstructionCodec.java