@Override
  public Set<N> predecessors() {
    return Collections.unmodifiableSet(predecessorsMultiset().elementSet());
  }

  private Multiset<N> predecessorsMultiset() {
    Multiset<N> predecessors = getReference(predecessorsReference);
    if (predecessors == null) {
      predecessors = HashMultiset.create(inEdgeMap.values());

  @Override
  public Set<N> predecessors() {
    return Collections.unmodifiableSet(predecessorsMultiset().elementSet());
  }

  private Multiset<N> predecessorsMultiset() {
    Multiset<N> predecessors = getReference(predecessorsReference);
    if (predecessors == null) {
      predecessors = HashMultiset.create(inEdgeMap.values());

  if (!attr) return false;
  return !attr.getValue().empty();
}

// Returns the predecessors of `op` when `op`'s predecessors are wrapped by
// islands.
llvm::SmallVector<Operation*> IslandPredecessors(Operation* op) {
  llvm::SmallVector<Operation*> predecessors;
  for (Value operand : op->getOperands()) {
    if (Operation* pred = operand.getDefiningOp()) {

                      Iterators.transform(
                          graph.predecessors(node).iterator(),
                          (N predecessor) -> EndpointPair.ordered(predecessor, node)),
                      Iterators.transform(
                          // filter out 'node' from successors (already covered by predecessors,
                          // above)

                      Iterators.transform(
                          graph.predecessors(node).iterator(),
                          (N predecessor) -> EndpointPair.ordered(predecessor, node)),
                      Iterators.transform(
                          // filter out 'node' from successors (already covered by predecessors,
                          // above)

	//    and len(b.Preds) is equal to 2.
	// 2. find the common dominator(b0) of the predecessors(pb0, pb1) of block b, and the
	//    dominator(b0) is a If block.
	//    Special case: one of the predecessors(pb0 or pb1) is the dominator(b0).
	// 3. the successors(sb0, sb1) of the dominator need to dominate the predecessors(pb0, pb1)
	//    of block b respectively.
	// 4. replace this boolean Phi based on dominator block.
	//

    if (isDirected()) { // In undirected graphs, the successor and predecessor sets are equal.
      // Since views are returned, we need to copy the predecessors that will be removed.
      // Thus we avoid modifying the underlying view while iterating over it.
      for (N predecessor : ImmutableList.copyOf(connections.predecessors())) {
        // requireNonNull is safe because the node is a predecessor.
        checkState(

    if (isDirected()) { // In undirected graphs, the successor and predecessor sets are equal.
      // Since views are returned, we need to copy the predecessors that will be removed.
      // Thus we avoid modifying the underlying view while iterating over it.
      for (N predecessor : ImmutableList.copyOf(connections.predecessors())) {
        // requireNonNull is safe because the node is a predecessor.
        checkState(

  ElementOrder<N> nodeOrder();

  /**
   * Returns an {@link ElementOrder} that specifies the order of iteration for the elements of
   * {@link #edges()}, {@link #adjacentNodes(Object)}, {@link #predecessors(Object)}, {@link
   * #successors(Object)} and {@link #incidentEdges(Object)}.
   *
   * @since 29.0
   */
  ElementOrder<N> incidentEdgeOrder();

  //
  // Element-level accessors
  //

  /**

  ElementOrder<N> nodeOrder();

  /**
   * Returns an {@link ElementOrder} that specifies the order of iteration for the elements of
   * {@link #edges()}, {@link #adjacentNodes(Object)}, {@link #predecessors(Object)}, {@link
   * #successors(Object)} and {@link #incidentEdges(Object)}.
   *
   * @since 29.0
   */
  ElementOrder<N> incidentEdgeOrder();

  //
  // Element-level accessors
  //

  /**