graph_pattern_detecter.cc

// Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
//
// 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 <array>
#include <string>
#include <vector>

#include "paddle/fluid/framework/ir/graph_helper.h"
#include "paddle/fluid/framework/ir/graph_pattern_detecter.h"
#include "paddle/fluid/framework/ir/graph_traits.h"
#include "paddle/fluid/platform/enforce.h"

namespace paddle {
namespace framework {
namespace ir {

PDNode* PDPattern::NewNode(PDNode::teller_t&& teller, const std::string& name) {
  nodes_.emplace_back(new PDNode(std::move(teller), name));
  auto* cur = nodes_.back().get();
  return cur;
}

void PDPattern::AddEdge(PDNode* a, PDNode* b) {
  PADDLE_ENFORCE(a);
  PADDLE_ENFORCE(b);
  PADDLE_ENFORCE(a != b, "can't connect to the same nodes.");
  edges_.emplace_back(a, b);
}

void GraphPatternDetecter::operator()(Graph* graph,
                                      GraphPatternDetecter::handle_t handler) {
  if (!MarkPDNodesInGraph(*graph)) return;
  auto subgraphs = DetectPatterns();
  UniquePatterns(&subgraphs);
  RemoveOverlappedMatch(&subgraphs);

  for (auto& g : subgraphs) {
    handler(g, graph);
  }
}

bool GraphPatternDetecter::MarkPDNodesInGraph(const ir::Graph& graph) {
  if (graph.Nodes().empty()) return false;

  for (auto& node : GraphTraits::DFS(graph)) {
    for (const auto& pdnode : pattern_.nodes()) {
      if (pdnode->Tell(&node)) {
        pdnodes2nodes_[pdnode.get()].insert(&node);
      }
    }
  }
  return !pdnodes2nodes_.empty();
}

struct HitGroup {
  std::unordered_map<PDNode*, Node*> roles;

  bool Match(Node* node, PDNode* pat) {
    return !roles.count(pat) || roles.at(pat) == node;
  }

  void Register(Node* node, PDNode* pat) { roles[pat] = node; }
};

// Tell whether Node a links to b.
bool IsNodesLink(Node* a, Node* b) {
  for (auto* node : a->outputs) {
    if (b == node) {
      return true;
    }
  }
  return false;
}

std::vector<GraphPatternDetecter::subgraph_t>
GraphPatternDetecter::DetectPatterns() {
  // Init empty subgraphs.
  std::vector<GraphPatternDetecter::subgraph_t> result;
  std::vector<HitGroup> init_groups;
  PADDLE_ENFORCE(!pattern_.edges().empty(), "At least one edge is needed");
  auto* first_pnode = pattern_.edges().front().first;
  if (!pdnodes2nodes_.count(first_pnode)) return result;
  for (auto* node : pdnodes2nodes_[first_pnode]) {
    HitGroup group;
    group.roles[first_pnode] = node;
    init_groups.emplace_back(group);
  }

  int step = 0;
  std::array<std::vector<HitGroup>, 2> bi_records;
  bi_records[0] = std::move(init_groups);

  // Extend a PDNode to subgraphs by deducing the connection relations defined
  // in edges of PDNodes.
  for (const auto& edge : pattern_.edges()) {
    // Each role has two PDNodes, which indicates two roles.
    // Detect two Nodes that can match these two roles and they are connected.
    auto& pre_groups = bi_records[step % 2];
    auto& cur_groups = bi_records[1 - (step++ % 2)];
    cur_groups.clear();
    // source -> target
    for (Node* source : pdnodes2nodes_[edge.first]) {
      for (Node* target : pdnodes2nodes_[edge.second]) {
        // TODO(Superjomn) add some prune strategies.
        for (const auto& group : pre_groups) {
          HitGroup new_group = group;
          if (IsNodesLink(source, target) &&
              new_group.Match(source, edge.first)) {
            new_group.Register(source, edge.first);
            if (new_group.Match(target, edge.second)) {
              new_group.Register(target, edge.second);
              cur_groups.push_back(new_group);
              // TODO(Superjomn) need to unique
            }
          }
        }
      }
    }
  }

  for (auto& group : bi_records[step % 2]) {
    GraphPatternDetecter::subgraph_t subgraph;
    for (auto& role : group.roles) {
      subgraph.emplace(role.first, role.second);
    }
    result.emplace_back(subgraph);
  }
  return result;
}

void GraphPatternDetecter::UniquePatterns(
    std::vector<GraphPatternDetecter::subgraph_t>* subgraphs) {
  if (subgraphs->empty()) return;
  std::vector<GraphPatternDetecter::subgraph_t> result;

  std::unordered_set<size_t> set;
  for (auto& g : *subgraphs) {
    size_t key = 0;
    for (auto& item : g) {
      key ^= std::hash<void*>{}(item.first);
      key ^= std::hash<void*>{}(item.second);
    }
    if (!set.count(key)) {
      result.emplace_back(g);
      set.insert(key);
    }
  }
  *subgraphs = result;
}

void GraphPatternDetecter::RemoveOverlappedMatch(
    std::vector<subgraph_t>* subgraphs) {
  std::vector<subgraph_t> result;
  std::unordered_set<Node*> node_set;

  for (const auto& subgraph : *subgraphs) {
    bool valid = true;
    for (auto& item : subgraph) {
      if (node_set.count(item.second)) {
        valid = false;
        break;
      }
    }
    if (valid) {
      for (auto& item : subgraph) {
        node_set.insert(item.second);
      }
      result.push_back(subgraph);
    }
  }
  *subgraphs = result;
}

}  // namespace ir
}  // namespace framework
}  // namespace paddle