//    (except for constant) are explicitly passed in.
// 2. no side effect: Every operation inside whileOp can be safely
//    remove when it is useEmpty().
// 3. no call func inside while.
bool ReduceWhileOperands(TFL::WhileOp while_op) {
  std::vector<uint64_t> explicitly_consumed_ids;
  Block &cond = while_op.getCond().front();
  Block &body = while_op.getBody().front();

  auto n = while_op.getNumOperands();