}

void collect_input_defining_islands(IslandOp op, std::vector<IslandOp>& ops) {
  Operation* wrapped_op = &op.GetBody().front();
  for (Value operand : wrapped_op->getOperands()) {
    IslandOp wrapper = dyn_cast_or_null<IslandOp>(operand.getDefiningOp());
    if (!wrapper || !wrapper.WrapsSingleOp()) continue;
    ops.push_back(wrapper);
  }
}

void collect_output_users_islands(IslandOp op, std::vector<IslandOp>& ops) {

  // Construct a new island from the given root.
  explicit MergedIsland(IslandOp root) : insert_point(root) {
    islands.push_back(root);
  }

  // The insertion point anchor of the merged island, or where the merged island
  // will be inserted when created.
  Operation* const insert_point;

  // The set of islands that are to be merged together.
  SmallVector<IslandOp> islands;
};

// (from YieldOps first operand) is forwarded to the IslandOp single data result
// users.
struct DropEmptyIslandNoOperandOneDataResult
    : public OpRewritePattern<IslandOp> {
  using OpRewritePattern<IslandOp>::OpRewritePattern;

  LogicalResult matchAndRewrite(IslandOp op,
                                PatternRewriter &rewriter) const override {

                           ShapedType const_type) {
  IslandOp while_wrapper = while_op->getParentOfType<IslandOp>();
  assert(while_wrapper && "While op is expected to be wrapped in a IslandOp");

  // Get the dummy constant.
  OpBuilder builder(while_wrapper);
  auto loc = NameLoc::get(
      builder.getStringAttr("chain_control_outputs@" + while_op.getBody()));
  IslandOp const_wrapper = GetDummyConstant(builder, const_type, loc);

    cloned_fetch_op.erase();
  };

  return llvm::to_vector(cloned_fetch_op.getFetches());
}

// Creates a new `IslandOp` that wraps a `TF::NoOp`. The `IslandOp` has control
// dependencies to the values provided.
IslandOp CreateNoOpWithControlDependencies(
    const Location loc, GraphOp main_graph_op,
    const ArrayRef<Value> control_dependencies) {

  cloned_fetch_op.erase();

  return control_fetch;
}

// Creates a new `IdentityOp` wrapped by an `IslandOp`. The identity op returns
// the `main_file_prefix_arg` and has control dependencies to `control_inputs`.
IslandOp CreateFilePrefixIdentityOp(const BlockArgument main_file_prefix_arg,
                                    const ArrayRef<Value> control_inputs,

    return ops_have_same_device(sink.GetSource(), sink);
  }

  return llvm::isa<tf_executor::EnterOp, tf_executor::ExitOp,
                   tf_executor::IslandOp, tf_executor::MergeOp,
                   tf_executor::SwitchOp>(op);
}

// Assigns all data results to a specified device.
void PopulateDeviceForOpResults(
    Operation& op, llvm::StringRef device,

    // Update the control type from tf_type.control to tf_executor.control.
    new_types.back() = rewriter.getType<tf_executor::ControlType>();

    // Control operand is attached on tf_executor::IslandOp.
    llvm::SmallVector<Value> island_control_operands;
    llvm::SmallVector<Value> inner_op_operands;

    for (Value value : operands) {
      // Because of the property of graph region, the control operands may

    if (auto graph = dyn_cast<tf_executor::GraphOp>(op)) {
      value = graph.GetFetch().getOperand(res_index);
    } else if (auto island = dyn_cast<tf_executor::IslandOp>(op)) {
      // Control output is generated by the IslandOp, not the yield in
      // in the Island body.
      if (value == island.getControl()) break;
      value = island.GetYield().getOperand(res_index);

  }
};

// Finds first inner op if `op` is a tf_executor.island. Otherwise `op` is
// returned.
Operation* GetIslandInnerOpOrSelf(mlir::Operation* op) {
  auto island = llvm::dyn_cast<mlir::tf_executor::IslandOp>(op);
  if (island) return &island.GetBody().front();
  return op;
}

// Stateful helper class to export a function into a Graph.
class Exporter {
 public: