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8 years ago
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/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License. */
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#include "paddle/framework/backward.h"
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#include <list>
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#include "paddle/framework/net.h"
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#include "paddle/framework/op_registry.h"
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namespace paddle {
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namespace framework {
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static bool AllInSet(const std::vector<std::string>& names,
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const std::string& suffix,
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const std::unordered_set<std::string>& set) {
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for (auto& name : names) {
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if (set.find(name + suffix) == set.end()) {
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return false;
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}
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}
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return true;
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}
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static std::shared_ptr<OperatorBase> NOP() {
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auto net_op = std::make_shared<NetOp>();
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net_op->type_ = "@NOP@";
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net_op->CompleteAddOp();
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return net_op;
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}
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// Get backward operator from a forward operator, recursively implementation.
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//
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// no_grad_names the gradient variable names without gradient calculating.
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//
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// uniq_id is a unique index used inside recursively calling BackwardRecursive.
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// use `uid = uniq_id++;` to get the unique index, and pass `uniq_id` through
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// recursive calling.
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//
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// returns The backward operator. For simple situation, it is a simple
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// operator. For complex situation, it is a NetOp.
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//
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// See Backward.h for details
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static std::shared_ptr<OperatorBase> BackwardRecursive(
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const OperatorBase& forwardOp,
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std::unordered_set<std::string>& no_grad_names, size_t& uniq_id);
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std::shared_ptr<OperatorBase> BackwardRecursive(
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const OperatorBase& forwardOp,
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std::unordered_set<std::string>& no_grad_names, size_t& uniq_id) {
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// If all input gradients of forwarding operator do not need to calculate,
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// just return an NOP. Not return null ptr because NOP does not take
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// too much time for calculation, but it is useful for simplifying logic.
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if (AllInSet(forwardOp.inputs_, OperatorBase::GRAD_VAR_SUFFIX(),
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no_grad_names)) {
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return NOP();
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}
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// All output gradients of forwarding operator do not need to calculate. Then
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// all input gradients cannot be computed at all, and we put them into
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// `no_grad_names` set. Return an NOP.
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if (AllInSet(forwardOp.outputs_, OperatorBase::GRAD_VAR_SUFFIX(),
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no_grad_names)) {
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for (auto& name : forwardOp.inputs_) {
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// Mark all input is not need
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no_grad_names.insert(name + OperatorBase::GRAD_VAR_SUFFIX());
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}
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return NOP();
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}
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// Returned gradient network
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auto net = std::make_shared<NetOp>();
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if (forwardOp.IsNetOp()) {
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// Because forwardOp is a net op, it can static_cast.
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auto& forwardNet = static_cast<const NetOp&>(forwardOp);
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// Map from output gradient variable name to operator's indices in backward
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// net. That operator generates that variable.
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std::unordered_map<std::string, std::vector<size_t>> dup_output_ops;
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size_t local_op_id = 0;
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// reversely travel forwardNet
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for (auto it = forwardNet.ops_.rbegin(); it != forwardNet.ops_.rend();
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++it, ++local_op_id) {
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auto fwd = *it;
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auto bwd = BackwardRecursive(*fwd, no_grad_names, uniq_id);
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net->AddOp(bwd);
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for (auto& out : bwd->outputs_) {
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dup_output_ops[out].emplace_back(local_op_id);
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}
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}
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// Get unique ID for this method.
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auto uid = uniq_id++;
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// TODO(dzh): more comment
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using Pos = std::pair<size_t, std::shared_ptr<OperatorBase>>;
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std::list<Pos> insert_position;
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for (auto& dup_output_op : dup_output_ops) {
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const std::string& name = dup_output_op.first;
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auto& dup_op = dup_output_op.second;
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if (dup_op.size() == 1) continue;
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std::vector<std::string> dup_outputs;
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for (size_t i = 0; i < dup_op.size(); ++i) {
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auto op_offset = dup_op[i];
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dup_outputs.push_back(name + "@RENAME@" + std::to_string(uid) + "@" +
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std::to_string(i));
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net->ops_[op_offset]->Rename(name, dup_outputs.back());
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}
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insert_position.push_back(
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{dup_op.back(),
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OpRegistry::CreateOp(
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"add", {dup_outputs}, {name},
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{{"input_format",
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std::vector<int>{0, static_cast<int>(dup_outputs.size())}}})});
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}
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insert_position.sort(
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[](const Pos& l, const Pos& r) { return l.first > r.first; });
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for (auto& pos : insert_position) {
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net->InsertOp(pos.first + 1, pos.second);
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}
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} else {
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std::shared_ptr<OperatorBase> grad_op = OpRegistry::CreateGradOp(forwardOp);
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for (std::string& grad_input : grad_op->inputs_) {
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if (no_grad_names.count(grad_input)) {
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std::string prefix = grad_input.substr(
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0, grad_input.size() - OperatorBase::GRAD_VAR_SUFFIX().size());
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grad_input = prefix + OperatorBase::ZERO_VAR_SUFFIX();
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// If part of input gradient of that operator is not calculated, fill
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// zero variables to that input gradient.
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net->AddOp(OpRegistry::CreateOp("fill_zeros_like", {prefix},
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{grad_input}, {}));
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}
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}
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for (std::string& grad_output : grad_op->outputs_) {
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if (no_grad_names.count(grad_output)) {
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grad_output = OperatorBase::EMPTY_VAR_NAME();
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}
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}
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if (net->ops_.empty()) { // Current no aux op is added to network
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return grad_op;
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}
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net->AddOp(grad_op);
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}
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net->type_ = "@GENERATED_BACKWARD@";
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net->CompleteAddOp();
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return net;
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}
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// See header for comments
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std::shared_ptr<OperatorBase> Backward(
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const OperatorBase& forwardOp,
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const std::unordered_set<std::string>& no_grad_vars) {
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std::unordered_set<std::string> no_grad_names;
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no_grad_names.reserve(no_grad_vars.size());
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for (auto& name : no_grad_vars) {
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no_grad_names.insert(name + OperatorBase::GRAD_VAR_SUFFIX());
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}
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size_t uid = 0;
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return BackwardRecursive(forwardOp, no_grad_names, uid);
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}
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} // namespace framework
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} // namespace paddle
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@ -0,0 +1,27 @@
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/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License. */
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#pragma once
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#include <unordered_set>
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#include "operator.h"
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namespace paddle {
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namespace framework {
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// Create the backward operator from a forward operator.
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// TODO(yuyang18): Add more API reference comment.
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extern std::shared_ptr<OperatorBase> Backward(
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const OperatorBase& forwardOp,
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const std::unordered_set<std::string>& no_grad_vars);
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} // namespace framework
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} // namespace paddle
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