Merge branch 'feature/backward' of https://github.com/reyoung/Paddle into feature/backward

paddle/framework/backward.cc

@@ -49,9 +49,11 @@ static std::shared_ptr<OperatorBase> EmptyOp() {
   return net_op;
 }
 
-static std::shared_ptr<OperatorBase> BackwardImpl(
-    const OperatorBase& forwardOp,
-    std::unordered_set<std::string>& no_grad_names, int& uniq_id) {
+static void DeDuplicate(NetOp* net, std::unordered_se)
+
+    static std::shared_ptr<OperatorBase> BackwardImpl(
+        const OperatorBase& forwardOp,
+        std::unordered_set<std::string>& no_grad_names, unsigned& uniq_id) {
   if (AllInSet(forwardOp.inputs_, OperatorBase::GRAD_VAR_SUFFIX(),
                no_grad_names)) {
     return EmptyOp();
@@ -70,6 +72,39 @@ static std::shared_ptr<OperatorBase> BackwardImpl(
 
   if (forwardOp.IsNetOp()) {
     //! TODO(dzh)
+    std::unordered_map<std::string, int> dup_output;
+    std::unordered_map<std::string std::vector<int>> dup_output_ops;
+    const unsigned uniq_id_local = uniq_id;
+    unsigned op_id_offset = 0;
+    for (auto& fwd : forwardOp) {
+      auto bwd = Backward(fwd, no_grad_names);
+      net->AddOp(bwd);
+      for (size_t i = 0; i < bwd.outputs_; ++i) {
+        bwd->outputs_[i] += OperatorBase::EMPTY_VAR_NAME();
+        if (dup_output.find(bwd->inputs_[i]) == dup_output.end()) {
+          dup_output[bwd->inputs_[i]] = 1;
+          dup_output_ops[bwd->inputs_[i]] = std::vector<int>{op_id_offset++};
+        } else {
+          dup_output[bwd->inputs_[i]]++;
+          dup_output_ops[bwd->inputs_[i]].emplace_back(op_id_offset++);
+        }
+      }
+    }
+    for (auto dup : dup_output) {
+      if (dup.second == 1) continue;
+      auto op_ids = dup_output_ops.at(dup.first);
+      for (auto& op_id : op_ids) {
+        auto& op_ptr = net->ops_[op_id];
+        for (size_t i = 0; i < op_ptr->inputs_.size(); ++i) {
+          if (op_ptr->inputs_[i] == dup.first) {
+            // unique the duplicate name
+            op_ptr->inputs_[i] += std::to_string(uniq_id++);
+            // TODO(dzh): need a generic add op here
+          }
+        }
+      }
+    }
+
   } else {
     //! TODO(fjy)
     std::shared_ptr<OperatorBase> grad_op = OpRegistry::CreateGradOp(forwardOp);