add distributed training deps.

Author: panyx0718

paddle/fluid/framework/ir/graph.cc

@@ -61,6 +61,49 @@ Graph::Graph(const ProgramDesc &program) : program_(program) {
       var->inputs.push_back(node);
     }
   }
+
+  std::vector<ir::Node *> send_ops;
+  ir::Node *send_bar = nullptr;
+  std::vector<ir::Node *> recv_ops;
+  ir::Node *fetch_bar = nullptr;
+  for (ir::Node *node : Nodes()) {
+    if (node->Name() == "send") {
+      send_ops.push_back(node);
+    } else if (node->Name() == "send_barrier") {
+      PADDLE_ENFORCE(!send_bar, "only has one send barrier");
+      send_bar = node;
+    } else if (node->Name() == "recv") {
+      recv_ops.push_back(node);
+    } else if (node->Name() == "fetch_barrier") {
+      PADDLE_ENFORCE(!fetch_bar, "only has one fetch barrier");
+      fetch_bar = node;
+    }
+  }
+  if (send_bar) {
+    for (ir::Node *send : send_ops) {
+      ir::Node *dep_var = CreateControlDepVar();
+      send->outputs.push_back(dep_var);
+      dep_var->inputs.push_back(send);
+      send_bar->inputs.push_back(dep_var);
+      dep_var->outputs.push_back(send_bar);
+    }
+    for (ir::Node *recv : recv_ops) {
+      ir::Node *dep_var = CreateControlDepVar();
+      recv->inputs.push_back(dep_var);
+      dep_var->outputs.push_back(recv);
+      send_bar->outputs.push_back(dep_var);
+      dep_var->inputs.push_back(send_bar);
+    }
+  }
+  if (fetch_bar) {
+    for (ir::Node *recv : recv_ops) {
+      ir::Node *dep_var = CreateControlDepVar();
+      recv->outputs.push_back(dep_var);
+      dep_var->inputs.push_back(recv);
+      fetch_bar->inputs.push_back(dep_var);
+      dep_var->outputs.push_back(fetch_bar);
+    }
+  }
   /**
    * We only handle write after read(WAR), since it should not have a write
    * after write in program. If there are write after write operators, we need