Function InitGraph2

tensorflow/core/graph/collective_order_test.cc:166–185

Initialize the following graph: a | c1 / \ // c4 id / \ // c2 c3 Here ci denotes a collective node with `instance_key` i. `a` is an input, `id` is identity node.

// Here ci denotes a collective node with `instance_key` i.  `a` is an input,
// `id` is identity node.
std::unique_ptr<Graph> InitGraph2() {
  GraphDefBuilder builder(GraphDefBuilder::kFailImmediately);
  const string dev0 = "/job:localhost/replica:0/task:0/device:CPU:0";
  Node* a = ops::SourceOp("TestParams",
                          builder.opts().WithName("a").WithDevice(dev0));
  Node* c1 = CollectiveReduceNode(&builder, a, "c1", dev0, 1);
  CollectiveReduceNode(&builder, c1, "c4", dev0, 4);
  Node* id = ops::UnaryOp(
      "Identity", c1,
      builder.opts().WithName("id").WithDevice(dev0).WithAttr("T", DT_FLOAT));
  CollectiveReduceNode(&builder, id, "c2", dev0, 2);
  CollectiveReduceNode(&builder, id, "c3", dev0, 3);

  std::unique_ptr<Graph> graph = absl::make_unique<Graph>(OpRegistry::Global());
  Status s = GraphDefBuilderToGraph(builder, graph.get());
  if (!s.ok()) {
    LOG(FATAL) << "Error building graph " << s;
  }
  return graph;
}

// Tests that in the graph created by `InitGraph2`, we add the following control
// edges after calling `OrderCollectives`: c4 -> c3, c3 -> c2.  c4->c2 is