grad_op_desc_maker.h

/* 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 <string>
#include <unordered_set>
#include <vector>
#include "paddle/framework/op_desc.h"
#include "paddle/framework/operator.h"

namespace paddle {
namespace framework {

/*
  This functor class is responsible for creating the gradient ops for the given
  operator fwd_op. After it is called (through operator()), the pairs of
  (gradient variable, corresponding input variable of fwd_op) will be added to
  grad_to_var. If an input variable of fwd_op is contained in no_grad_set, its
  gradient varialbe will be ignored or kEmptyVarName depending on the template
  argument DropEmptyIG in the derived classes.
 */
class GradOpDescMakerBase {
 public:
  explicit GradOpDescMakerBase(
      const OpDesc& fwd_op, const std::unordered_set<std::string>& no_grad_set,
      std::unordered_map<std::string, std::string>* grad_to_var,
      const std::vector<BlockDesc*>& grad_block = std::vector<BlockDesc*>())
      : fwd_op_(fwd_op),
        no_grad_set_(no_grad_set),
        grad_to_var_(grad_to_var),
        grad_block_(grad_block) {}

  virtual ~GradOpDescMakerBase() = default;
  virtual std::vector<std::unique_ptr<OpDesc>> operator()() const = 0;

 protected:
  std::vector<std::string> InputGrad(const std::string& name,
                                     bool drop_empty_grad = true) const {
    std::vector<std::string> ret_val;
    auto var_names = this->Input(name);
    ret_val.reserve(var_names.size());
    std::transform(var_names.begin(), var_names.end(),
                   std::back_inserter(ret_val),
                   [this](const std::string& fwd_var_name) -> std::string {
                     auto g_name = GradVarName(fwd_var_name);
                     if (no_grad_set_.count(g_name)) {
                       return kEmptyVarName;
                     } else {
                       (*this->grad_to_var_)[g_name] = fwd_var_name;
                       return g_name;
                     }
                   });
    if (!drop_empty_grad) {
      return ret_val;
    }
    PADDLE_ENFORCE_LE(var_names.size(), 1UL,
                      "BUG from operator developer:"
                      " for input argument with a list of variables, "
                      " drop_empty_grad is not allowed because it makes"
                      " the correspondence bewteen a variable and its gradient"
                      " ambiguous. Use REGISTER_OP_EX to register the op"
                      " or call InputGrad(?,false) in GradOpDescMaker."
                      " Op type %s",
                      fwd_op_.Type());

    std::vector<std::string> dropped_ret_val;
    dropped_ret_val.reserve(ret_val.size());
    std::copy_if(ret_val.begin(), ret_val.end(),
                 std::back_inserter(dropped_ret_val),
                 [](const std::string& str) { return str != kEmptyVarName; });
    return dropped_ret_val;
  }

  std::vector<std::string> OutputGrad(const std::string& name) const {
    std::vector<std::string> ret_val;
    auto onames = this->Output(name);
    ret_val.reserve(onames.size());
    std::transform(onames.begin(), onames.end(), std::back_inserter(ret_val),
                   GradVarName);
    return ret_val;
  }

  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 OpDesc& fwd_op_;
  const std::unordered_set<std::string>& no_grad_set_;
  std::unordered_map<std::string, std::string>* grad_to_var_;

 protected:
  std::vector<BlockDesc*> grad_block_;
};

class SingleGradOpDescMaker : public GradOpDescMakerBase {
 public:
  using GradOpDescMakerBase::GradOpDescMakerBase;

  std::vector<std::unique_ptr<OpDesc>> operator()() const {
    std::vector<std::unique_ptr<OpDesc>> retv;
    retv.emplace_back(this->Apply());
    return retv;
  }

 protected:
  virtual std::unique_ptr<OpDesc> Apply() const = 0;
};

template <bool DropEmptyIG = true>
class DefaultGradOpDescMaker : public SingleGradOpDescMaker {
 public:
  using SingleGradOpDescMaker::SingleGradOpDescMaker;

 protected:
  virtual std::unique_ptr<OpDesc> Apply() const {
    auto* grad = new OpDesc();
    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, DropEmptyIG));
    }

    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 std::unique_ptr<OpDesc>(grad);
  }

  virtual std::string GradOpType() const {
    return this->ForwardOpType() + "_grad";
  }
};

class EmptyGradOpMaker : public GradOpDescMakerBase {
 public:
  using GradOpDescMakerBase::GradOpDescMakerBase;
  std::vector<std::unique_ptr<OpDesc>> operator()() const override {
    return {};
  }
};

}  // namespace framework
}  // namespace paddle