@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()) {

      // expected-remark@above {{Predecessors: {6}}}
      // expected-remark@above {{Successors: {8}}}
      tf_executor.yield %read3 : tensor<32xf32>
      // expected-remark@above {{ID: 8}}
      // expected-remark@above {{Predecessors: {4,5,7}}}
    }
    tf_executor.fetch %island#0 : tensor<32xf32>
    // expected-remark@above {{ID: 10}}
    // expected-remark@above {{Predecessors: {9}}}
  }

        }
        assertThat(
                graph.predecessors(node).contains(adjacentNode)
                    || graph.successors(node).contains(adjacentNode))
            .isTrue();
      }

      for (N predecessor : sanityCheckSet(graph.predecessors(node))) {
        assertThat(graph.successors(predecessor)).contains(node);
        assertThat(graph.hasEdgeConnecting(predecessor, node)).isTrue();

    const auto predecessors =
        side_effect_analysis.DirectControlPredecessors(&sub_op);
    // Get the controls from the predecessors.
    llvm::SmallVector<Value, 4> predecessor_controls;
    predecessor_controls.reserve(predecessors.size());
    for (auto predecessor : predecessors) {
      predecessor_controls.push_back(new_control_for_sub_ops[predecessor]);
    }

    assume().that(graphIsMutable()).isTrue();

    addNode(N2);
    Set<Integer> predecessors = graph.predecessors(N2);
    UnsupportedOperationException e =
        assertThrows(UnsupportedOperationException.class, () -> predecessors.add(N1));
    putEdge(N1, N2);
    assertThat(graph.predecessors(N2)).containsExactlyElementsIn(predecessors);
  }

  @Override
  @Test
  public void successors_checkReturnedSetMutability() {

                      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.
	//