Add helper function in GradOpDescMakerBase. Make it easier to use.

doc/design/register_grad_op.md

@@ -33,22 +33,45 @@ The mapping relationship between an operator and its gradient operators is a fun
 
 ```cpp
 // (OpDesc) --> vector<OpDesc>
-using GradOpDescMaker = std::function<std::vector<OpDesc>(const OpDesc&)>;
+std::function<std::vector<OpDescBind>(const OpDescBind&)>;
 ```
 
-The function take a `OpDesc` of the forward operator and return one or many gradient operator descriptions.
+The function takes an `OpDescBind` of the forward operator and returns one or many gradient operator descriptions. `OpDescBind` is a C++ wrapper for protobuf message `OpDesc` to manipulate `OpDesc` fast.
 
 The `GradOpDescMaker` will be registered in `OpInfo`, to replace `grad_op_type_` field. The `OpInfo` should be
 
 ```cpp
 struct OpInfo {
-  GradOpDescMaker grad_op_maker_;
+  std::function<std::vector<OpDescBind>(const OpDescBind&)>  grad_op_maker_;
   ...
 };
 ```
 
 The `grad_op_maker_ ` is `nullptr` if the operator does not have associated gradient operators.
 
+We propose a base class called `GradOpDescMakerBase` to let operator developers generate `Gradient Operators` easily. The public interface of that class is
+
+```cpp
+class GradOpDescMakerBase {
+public:
+  GradOpDescMakerBase(const OpDescBind& );
+  virtual std::vector<OpDescBind> operator()()const = 0;
+};
+```
+
+We can convert `GradOpDescMakerBase` to `std::function<std::vector<OpDescBind>(const OpDescBind&)>` by
+
+```cpp
+using GradOpMaker = ...;
+std::function<std::vector<OpDescBind>(const OpDescBind&)> func;
+func = [] (const OpDescBind& fwd_op) {
+  GradOpMaker maker(fwd_op);
+  return maker();
+};
+```
+
+We can write many helper functions since the `GradOpDescMakerBase` is a class now. The basic helper functions get the variables of `Input`, `Output`, `InputGradient` and `OutputGradient` in the forwarding operator.
+
 We should chagne register macros at the same time. In the current solution, there is no difference between forwarding operators and backward operators. So `REGISTER_OP` just register one operator. If the `REGISTER_OPERATOR ` contains `OpProtoAndCheckerMaker` and `GradOpDescMaker`, we just list them in the same macro. It can be done by a macro contains `__VA_ARGS__`.
 
 The user interface should be

paddle/framework/details/op_registry.h

@@ -14,6 +14,7 @@
 
 #pragma once
 
+#include "paddle/framework/grad_op_desc_maker.h"
 #include "paddle/framework/op_info.h"
 #include "paddle/framework/op_proto_maker.h"
 #include "paddle/framework/operator.h"
@@ -96,7 +97,10 @@ struct OpInfoFiller<T, kOpProtoAndCheckerMaker> {
 template <typename T>
 struct OpInfoFiller<T, kGradOpDescMaker> {
   void operator()(const char* op_type, OpInfo* info) const {
-    info->grad_op_maker_ = new T();
+    info->grad_op_maker_ = [](const OpDescBind& fwd_op) {
+      T maker(fwd_op);
+      return maker();
+    };
   }
 };
 }  // namespace details

paddle/framework/grad_op_desc_maker.h

@@ -0,0 +1,120 @@
+/* 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 "paddle/framework/op_desc.h"
+#include "paddle/framework/operator.h"
+
+namespace paddle {
+namespace framework {
+
+class GradOpDescMakerBase {
+ public:
+  explicit GradOpDescMakerBase(const OpDescBind& fwd_op) : fwd_op_(fwd_op) {}
+
+  virtual ~GradOpDescMakerBase() = default;
+  virtual std::vector<OpDescBind> operator()() const = 0;
+
+ protected:
+  static std::vector<std::string> ToGradNames(
+      const std::vector<std::string>& var_names) {
+    std::vector<std::string> ret_val;
+    ret_val.reserve(var_names.size());
+    std::transform(var_names.begin(), var_names.end(),
+                   std::back_inserter(ret_val), GradVarName);
+    return ret_val;
+  }
+
+  std::vector<std::string> InputGrad(const std::string& name) const {
+    return ToGradNames(fwd_op_.Input(name));
+  }
+
+  std::vector<std::string> OutputGrad(const std::string& name) const {
+    return ToGradNames(fwd_op_.Output(name));
+  }
+
+  std::vector<std::string> InputNames() const {
+    return this->fwd_op_.InputNames();
+  }
+
+  std::vector<std::string> OutputNames() const {
+    return this->fwd_op_.OutputNames();
+  }
+
+  std::vector<std::string> Input(const std::string& name) const {
+    return fwd_op_.Input(name);
+  }
+
+  std::vector<std::string> Output(const std::string& name) const {
+    return fwd_op_.Output(name);
+  }
+
+  const std::unordered_map<std::string, Attribute>& Attrs() const {
+    return fwd_op_.GetAttrMap();
+  }
+
+  const Attribute& GetAttr(const std::string& name) const {
+    auto& map = fwd_op_.GetAttrMap();
+    auto it = map.find(name);
+    PADDLE_ENFORCE(it != map.end(), "Cannot find attribute %s", name);
+    return it->second;
+  }
+
+  std::string ForwardOpType() const { return this->fwd_op_.Type(); }
+
+ private:
+  const OpDescBind& fwd_op_;
+};
+
+class SingleGradOpDescMaker : public GradOpDescMakerBase {
+ public:
+  using GradOpDescMakerBase::GradOpDescMakerBase;
+
+  std::vector<OpDescBind> operator()() const { return {this->Apply()}; }
+
+ protected:
+  virtual OpDescBind Apply() const = 0;
+};
+
+class DefaultGradOpDescMaker : public SingleGradOpDescMaker {
+ public:
+  using SingleGradOpDescMaker::SingleGradOpDescMaker;
+
+ protected:
+  virtual OpDescBind Apply() const {
+    OpDescBind grad;
+    grad.SetType(this->GradOpType());
+
+    for (auto& input_param : this->InputNames()) {
+      grad.SetInput(input_param, this->Input(input_param));
+      grad.SetOutput(GradVarName(input_param), this->InputGrad(input_param));
+    }
+
+    for (auto& output_param : this->OutputNames()) {
+      grad.SetInput(output_param, this->Output(output_param));
+      grad.SetInput(GradVarName(output_param), this->OutputGrad(output_param));
+    }
+
+    grad.SetAttrMap(this->Attrs());
+
+    return grad;
+  }
+
+  virtual std::string GradOpType() const {
+    return this->ForwardOpType() + "_grad";
+  }
+};
+
+}  // namespace framework
+}  // namespace paddle

paddle/framework/op_desc.cc

@@ -31,15 +31,6 @@ const std::vector<std::string> &OpDescBind::Input(
   return it->second;
 }
 
-std::vector<std::string> OpDescBind::InputNames() const {
-  std::vector<std::string> retv;
-  retv.reserve(this->inputs_.size());
-  for (auto &ipt : this->inputs_) {
-    retv.push_back(ipt.first);
-  }
-  return retv;
-}
-
 void OpDescBind::SetInput(const std::string &param_name,
                           const std::vector<std::string> &args) {
   need_update_ = true;
@@ -54,15 +45,6 @@ const std::vector<std::string> &OpDescBind::Output(
   return it->second;
 }
 
-std::vector<std::string> OpDescBind::OutputNames() const {
-  std::vector<std::string> retv;
-  retv.reserve(this->outputs_.size());
-  for (auto &ipt : this->outputs_) {
-    retv.push_back(ipt.first);
-  }
-  return retv;
-}
-
 void OpDescBind::SetOutput(const std::string &param_name,
                            const std::vector<std::string> &args) {
   need_update_ = true;

paddle/framework/op_desc.h

@@ -35,15 +35,11 @@ class OpDescBind {
 
   const std::vector<std::string> &Input(const std::string &name) const;
 
-  std::vector<std::string> InputNames() const;
-
   void SetInput(const std::string &param_name,
                 const std::vector<std::string> &args);
 
   const std::vector<std::string> &Output(const std::string &name) const;
 
-  std::vector<std::string> OutputNames() const;
-
   void SetOutput(const std::string &param_name,
                  const std::vector<std::string> &args);
 
@@ -61,17 +57,30 @@ class OpDescBind {
 
   void SetBlockAttr(const std::string &name, BlockDescBind &block);
 
-  // Only be used in C++
-  void SetAttrMap(const AttributeMap &attr_map);
-
   Attribute GetAttr(const std::string &name) const;
 
   int GetBlockAttr(const std::string &name) const;
 
   // Only be used in C++
   const AttributeMap &GetAttrMap() const;
 
+  // Only be used in C++
+  void SetAttrMap(const AttributeMap &attr_map);
+
+  std::vector<std::string> InputNames() const { return MapKeys(inputs_); }
+  std::vector<std::string> OutputNames() const { return MapKeys(outputs_); }
+
  private:
+  template <typename MapType>
+  static std::vector<typename MapType::key_type> MapKeys(const MapType &map) {
+    std::vector<typename MapType::key_type> ret_val;
+    ret_val.reserve(map.size());
+    std::transform(
+        map.begin(), map.end(), ret_val.begin(),
+        [](const typename MapType::value_type &pair) { return pair.first; });
+    return ret_val;
+  }
+
   void Sync();
 
   OpDesc op_desc_;

paddle/framework/op_info.h

@@ -25,16 +25,10 @@
 namespace paddle {
 namespace framework {
 
-class GradOpDescMakerBase {
- public:
-  virtual ~GradOpDescMakerBase() = default;
-  virtual std::vector<OpDescBind> operator()(const OpDescBind&) const = 0;
-};
-
 struct OpInfo {
   OpCreator creator_;
   std::string grad_op_type_;
-  GradOpDescMakerBase* grad_op_maker_{nullptr};
+  std::function<std::vector<OpDescBind>(const OpDescBind&)> grad_op_maker_;
   OpProto* proto_{nullptr};
   OpAttrChecker* checker_{nullptr};