From ecf23ce5f339bb22800f2a9bc3c156ecc036c1cb Mon Sep 17 00:00:00 2001
From: Yu Yang <yuyang18@baidu.com>
Date: Wed, 26 Jul 2017 16:04:53 +0800
Subject: [PATCH] Update Backward

---
 paddle/framework/CMakeLists.txt |  2 +
 paddle/framework/backward.cc    | 93 +++++++++++++++++++++++++++++++++
 paddle/framework/backward.h     | 31 +++++++++++
 paddle/framework/op_registry.h  |  2 +
 4 files changed, 128 insertions(+)
 create mode 100644 paddle/framework/backward.cc
 create mode 100644 paddle/framework/backward.h

diff --git a/paddle/framework/CMakeLists.txt b/paddle/framework/CMakeLists.txt
index a29a81c994c..26d93336b13 100644
--- a/paddle/framework/CMakeLists.txt
+++ b/paddle/framework/CMakeLists.txt
@@ -31,3 +31,5 @@ add_dependencies(framework_py_proto framework_py_proto_init)
 
 cc_library(net SRCS net.cc DEPS op_registry)
 cc_test(net_op_test SRCS net_op_test.cc DEPS net add_op mul_op sigmoid_op softmax_op fc_op)
+
+cc_library(backward SRCS backward.cc DEPS net)
diff --git a/paddle/framework/backward.cc b/paddle/framework/backward.cc
new file mode 100644
index 00000000000..11690342185
--- /dev/null
+++ b/paddle/framework/backward.cc
@@ -0,0 +1,93 @@
+/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License. */
+
+#include <paddle/framework/backward.h>
+#include <paddle/framework/net.h>
+
+namespace paddle {
+namespace framework {
+
+static bool AllInSet(const std::vector<std::string>& names,
+                     const std::string& suffix,
+                     const std::unordered_set<std::string>& set) {
+  for (auto& name : names) {
+    if (set.find(name + suffix) == set.end()) {
+      return false;
+    }
+  }
+  return true;
+}
+
+static std::vector<int> InSetIdx(const std::vector<std::string>& names,
+                                 const std::string& suffix,
+                                 const std::unordered_set<std::string>& set) {
+  std::vector<int> ret_val;
+  ret_val.reserve(names.size());
+  for (size_t i = 0; i < names.size(); ++i) {
+    if (set.find(names[i] + suffix) != set.end()) {
+      ret_val.push_back(i);
+    }
+  }
+  return ret_val;
+}
+
+static std::shared_ptr<OperatorBase> EmptyOp() {
+  auto net_op = std::make_shared<NetOp>();
+  net_op->CompleteAddOp();
+  return net_op;
+}
+
+static std::shared_ptr<OperatorBase> BackwardImpl(
+    const OperatorBase& forwardOp,
+    std::unordered_set<std::string>& no_grad_names, int& uniq_id) {
+  if (AllInSet(forwardOp.inputs_, OperatorBase::GRAD_VAR_SUFFIX(),
+               no_grad_names)) {
+    return EmptyOp();
+  }
+
+  if (AllInSet(forwardOp.outputs_, OperatorBase::GRAD_VAR_SUFFIX(),
+               no_grad_names)) {
+    for (auto& name : forwardOp.inputs_) {
+      // Mark all input is not need
+      no_grad_names.insert(name + OperatorBase::GRAD_VAR_SUFFIX());
+    }
+    return EmptyOp();
+  }
+
+  auto* net = new NetOp();
+
+  if (forwardOp.IsNetOp()) {
+    //! TODO(dzh)
+  } else {
+    //! TODO(fjy)
+  }
+
+  net->CompleteAddOp();
+  return std::shared_ptr<OperatorBase>(net);
+}
+
+extern std::shared_ptr<OperatorBase> Backward(
+    const std::shared_ptr<OperatorBase>& forwardOp,
+    const std::unordered_set<std::string>& no_grad_vars) {
+  std::unordered_set<std::string> no_grad_names;
+  no_grad_names.reserve(no_grad_vars.size());
+
+  for (auto& name : no_grad_vars) {
+    no_grad_names.insert(name + OperatorBase::GRAD_VAR_SUFFIX());
+  }
+  int uid = 0;
+  return BackwardImpl(*forwardOp, no_grad_names, uid);
+}
+}  // namespace framework
+}  // namespace paddle
diff --git a/paddle/framework/backward.h b/paddle/framework/backward.h
new file mode 100644
index 00000000000..e835ef63511
--- /dev/null
+++ b/paddle/framework/backward.h
@@ -0,0 +1,31 @@
+/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License. */
+
+#pragma once
+#include <unordered_set>
+#include "operator.h"
+namespace paddle {
+namespace framework {
+
+/**
+ * @brief
+ * @param forwardOp
+ * @param no_grad_vars ignored input name of forward
+ * @return
+ */
+extern std::shared_ptr<OperatorBase> Backward(
+    const std::shared_ptr<OperatorBase>& forwardOp,
+    const std::unordered_set<std::string>& no_grad_vars);
+}  // namespace framework
+}  // namespace paddle
diff --git a/paddle/framework/op_registry.h b/paddle/framework/op_registry.h
index f16deae028d..5bcd7ac9279 100644
--- a/paddle/framework/op_registry.h
+++ b/paddle/framework/op_registry.h
@@ -302,6 +302,8 @@ class OpRegistry {
 
   static std::shared_ptr<OperatorBase> CreateGradOp(
       std::shared_ptr<OperatorBase> op) {
+    PADDLE_ENFORCE(!op->IsNetOp(),
+                   "Use framework::Backward to get backward ops");
     GradOpBuilder builder(op.get());
     std::shared_ptr<OperatorBase> grad_op(builder.Build());
     grad_op->Init();
-- 
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