// Stack to keep track of region based control flow op nesting and current
  // op to visit.
  SmallVector<OpVisitorState, 4> ops_to_visit{
      {/*region_idx=*/std::nullopt, init_token, &func_body.front()}};

  while (!ops_to_visit.empty()) {
    OpVisitorState op_to_visit = ops_to_visit.pop_back_val();
    Operation* curr_op = op_to_visit.op;

    Value token = op_to_visit.token;