return UNCHANGED;
return DefUseEffect.UNCHANGED;
  private static byte checkcast(OPT_AbstractRegisterPool regpool, OPT_Instruction s) {    OPT_Operand ref = TypeCheck.getRef(s);    if (ref.isNullConstant()) {      Empty.mutate(s, NOP);      return REDUCED;    } else if (ref.isConstant()) {      s.operator = CHECKCAST_NOTNULL;      return checkcastNotNull(s);    } else {      VM_TypeReference lhsType = TypeCheck.getType(s).getTypeRef();      VM_TypeReference rhsType = ref.getType();      byte ans = OPT_ClassLoaderProxy.includesType(lhsType, rhsType);      if (ans == OPT_Constants.YES) {        Empty.mutate(s, NOP);        return REDUCED;      } else {        // NOTE: OPT_Constants.NO can't help us because (T)null always succeeds        return UNCHANGED;      }    }  }