// and these uses will be dropped after legalization of each op.
    unsigned idx = 0;
    Block &block = graph_func.getBody().front();
    for (auto iter = block.args_begin(), end_iter = block.args_end();
         iter != end_iter; ++iter) {
      if (!mlir::isa<tfg::ControlType>(iter->getType()))
        iter->replaceAllUsesWith(func.getBody().getArgument(idx++));
    }

  if (only_one_return_value) {
    return_values.resize(1);
  }
  if (extern_values_passthrough)
    return_values.insert(return_values.end(),
                         first_block.args_begin() + num_region_arguments,
                         first_block.args_end());

  // Replace the existing terminator with a return.
  terminator = first_block.getTerminator();
  builder.setInsertionPoint(terminator);