build_cinn_pass.cc

/* Copyright (c) 2021 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 "paddle/fluid/framework/paddle2cinn/build_cinn_pass.h"

#include <algorithm>
#include <iterator>
#include <memory>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

#include "cinn/frontend/op_mapper_registry.h"
#include "cinn/frontend/op_mappers/use_op_mappers.h"
#include "paddle/fluid/framework/ir/graph.h"
#include "paddle/fluid/framework/ir/node.h"
#include "paddle/fluid/framework/ir/subgraph_detector.h"
#include "paddle/fluid/framework/paddle2cinn/cinn_compiler.h"

namespace paddle {
namespace framework {
namespace paddle2cinn {

using framework::ir::Graph;
using framework::ir::Node;

using GraphNodeVec = std::vector<Node*>;
using GraphNodeSet = std::unordered_set<Node*>;

// Deal with subgraph's feed input var node:
// create a new input var node and it's feed op node
void AddFeedOpAndVar(const std::unordered_set<Node*>& feed_vars,
                     const GraphNodeSet& cluster,
                     const std::unordered_map<Node*, Node*>& old_op2new_op,
                     Graph* graph) {
  for (auto* old_var : feed_vars) {
    // create feed op
    OpDesc desc;
    desc.SetType("feed");
    desc.SetOutput("Out", {old_var->Name()});
    auto op = graph->CreateOpNode(&desc);

    // create new feed var node (SSAGraph)
    auto var = graph->CreateVarNode(old_var->Var());

    // link feed op and feed var
    op->outputs = {var};
    var->inputs = {op};

    // link feed var to cluster op
    for (auto* old_op : old_var->outputs) {
      if (cluster.count(old_op)) {
        var->outputs.emplace_back(old_op2new_op.at(old_op));
        old_op2new_op.at(old_op)->inputs.emplace_back(var);
      }
      // Do not need relink old op or old var here, they will be
      // fixed in RemoveLinkFromCluster, here we just deal with
      // new subgraph's node.
    }
  }
}

// Deal with subgraph's parameter var node:
// create a new input var node, it's data will get by scope,
// so it don't need feed op
void AddParamVar(const std::unordered_set<Node*>& param_vars,
                 const GraphNodeSet& cluster,
                 const std::unordered_map<Node*, Node*>& old_op2new_op,
                 Graph* graph) {
  for (auto* old_var : param_vars) {
    auto var = graph->CreateVarNode(old_var->Var());

    for (auto* old_op : old_var->outputs) {
      if (cluster.count(old_op)) {
        var->outputs.emplace_back(old_op2new_op.at(old_op));
        old_op2new_op.at(old_op)->inputs.emplace_back(var);
      }
    }
  }
}

// Deal with subgraph's outputs var node:
// create a new output var node and it's fetch op
void AddOutputVar(const std::unordered_set<Node*>& output_vars,
                  const GraphNodeSet& cluster,
                  const std::unordered_map<Node*, Node*>& old_op2new_op,
                  Graph* graph) {
  for (auto* old_var : output_vars) {
    auto var = graph->CreateVarNode(old_var->Var());

    for (auto* old_op : old_var->inputs) {
      if (cluster.count(old_op)) {
        var->inputs.emplace_back(old_op2new_op.at(old_op));
        old_op2new_op.at(old_op)->outputs.emplace_back(var);
      }
    }
  }
}

// Create new subgraph with and op nodes are cluster nodes, and all
// var node are from internal nodes
std::unique_ptr<Graph> CreateNewSubGraph(const GraphNodeSet& cluster,
                                         const GraphNodeSet& cluster_internals,
                                         const GraphNodeSet& cluster_inputs) {
  // Graph's constructor must has one parameter, and in our code,
  // the ProgramDesc is useless, so here we pass a temporary object.
  auto subgraph = std::make_unique<Graph>(framework::ProgramDesc());

  std::unordered_map<Node*, Node*> old_op2new_op;
  for (auto* op : cluster) {
    auto sub_node = subgraph->CreateOpNode(op->Op());
    old_op2new_op[op] = sub_node;
  }

  std::unordered_map<Node*, Node*> old_var2new_var;
  for (auto* var : cluster_internals) {
    auto sub_node = subgraph->CreateVarNode(var->Var());
    old_var2new_var[var] = sub_node;
  }

  std::unordered_set<Node*> need_feed_vars;
  std::unordered_set<Node *> param_vars, output_vars;
  // the subgraph is independently, so here we only need link
  // to the node in new subgraph, and discard the link to
  // out-graph.
  for (auto* op : cluster) {
    for (auto* var : op->inputs) {
      if (cluster_internals.count(var)) {
        old_op2new_op[op]->inputs.emplace_back(old_var2new_var[var]);
      } else if (cluster_inputs.count(var)) {
        if (var->Var()->IsParameter()) {
          // Parameters have been preserved in scope, compared to feed var,
          // param just need add new var and don't need add feed op.
          // The var is used for check whether we need preserve the tensor
          // when transform paddle scope to CINN scope.
          param_vars.insert(var);
        } else {
          // When the var is subgraph input and the var is not parameter,
          // we need add a new feed op to feed the var.
          need_feed_vars.insert(var);
        }
      }
    }
    for (auto* var : op->outputs) {
      if (cluster_internals.count(var)) {
        old_op2new_op[op]->outputs.emplace_back(old_var2new_var[var]);
      } else {
        // Create new output var node to guarantee the independency of
        // subgraph. In other words, the subgraph has no connection with
        // other graph, even the input graph.
        output_vars.insert(var);
      }
    }
  }

  AddFeedOpAndVar(need_feed_vars, cluster, old_op2new_op, subgraph.get());
  AddParamVar(param_vars, cluster, old_op2new_op, subgraph.get());
  AddOutputVar(output_vars, cluster, old_op2new_op, subgraph.get());

  for (auto* var : cluster_internals) {
    for (auto* op : var->inputs) {
      if (cluster.count(op)) {
        old_var2new_var[var]->inputs.emplace_back(old_op2new_op[op]);
      }
    }
    for (auto* op : var->outputs) {
      if (cluster.count(op)) {
        old_var2new_var[var]->outputs.emplace_back(old_op2new_op[op]);
      }
    }
  }

  return subgraph;
}

// This interface is used to classify all variables involved in a cluster into
// three types: inputs, outputs, and internals.
// The input node is some subgraph op's input but not any subgraph op's output.
// The output node is some subgraph op's output and some out-graph op's input.
// Specially, the internal node is a node that only used by subgraph, and
// out-graph should not using this node at all.
// cluster_inputs & cluster_outputs & cluster_internals == NULL
// cluster_outputs | cluster_internals == all graph op's outputs node
void AnalyseClusterVariables(const GraphNodeSet& cluster,
                             GraphNodeSet* cluster_inputs,
                             GraphNodeSet* cluster_outputs,
                             GraphNodeSet* cluster_internals) {
  // collecting all input and output of op
  for (auto* op_node : cluster) {
    for (auto* input_var_node : op_node->inputs) {
      cluster_inputs->insert(input_var_node);
    }
    for (auto* output_var_node : op_node->outputs) {
      cluster_outputs->insert(output_var_node);
    }
  }
  // remove output node from cluster_inputs,
  // and add cluster_internals node
  for (auto* var_node : *cluster_outputs) {
    if (cluster_inputs->count(var_node) > 0) {
      // if a input node also exists in output list, remove
      cluster_inputs->erase(var_node);

      // the internal node is must an output node of sub-graph,
      // but not any input node of out-graph.
      bool is_only_used_internal = true;
      for (auto* next_op_node : var_node->outputs) {
        is_only_used_internal &= (cluster.count(next_op_node) > 0);
      }
      if (is_only_used_internal) {
        cluster_internals->insert(var_node);
      }
    }
  }

  // if a output node also exists in internal list, remove.
  for (auto* var_node : *cluster_internals) {
    cluster_outputs->erase(var_node);
  }
}

Node* AddSpecialOpToGraph(const GraphNodeSet& cluster_inputs,
                          const GraphNodeSet& cluster_outputs,
                          const std::string& compilation_key, Graph* graph) {
  // add special cinn op
  framework::OpDesc special_op_desc;
  special_op_desc.SetType(kCinnLaunchOp);
  std::vector<std::string> input_names;
  std::transform(cluster_inputs.begin(), cluster_inputs.end(),
                 std::back_inserter(input_names),
                 [](Node* n) { return n->Name(); });
  special_op_desc.SetInput("X", input_names);
  std::vector<std::string> output_names;
  std::transform(cluster_outputs.begin(), cluster_outputs.end(),
                 std::back_inserter(output_names),
                 [](Node* n) { return n->Name(); });
  special_op_desc.SetOutput("Out", output_names);
  special_op_desc.SetAttr(kCompilationKey, compilation_key);
  special_op_desc.Flush();
  auto* special_op_node = graph->CreateOpNode(&special_op_desc);
  special_op_node->inputs.assign(cluster_inputs.begin(), cluster_inputs.end());
  special_op_node->outputs.assign(cluster_outputs.begin(),
                                  cluster_outputs.end());
  return special_op_node;
}

void AddLinkToSpecialOp(const GraphNodeSet& cluster_inputs,
                        const GraphNodeSet& cluster_outputs,
                        Node* special_op_node) {
  // add new link from cluster_inputs to special_op_node
  for (auto* var_node : cluster_inputs) {
    var_node->outputs.push_back(special_op_node);
  }

  // add new link from special_op_node to cluster_outputs
  for (auto* var_node : cluster_outputs) {
    var_node->inputs.push_back(special_op_node);
  }
}

void RemoveLinkFromCluster(const GraphNodeSet& cluster,
                           const GraphNodeSet& cluster_inputs,
                           const GraphNodeSet& cluster_outputs) {
  // remove all nodes in cluster
  auto get_preserved_ops = [&cluster](const GraphNodeVec& ops) {
    GraphNodeVec nodes;
    for (auto* op_node : ops) {
      if (cluster.find(op_node) == cluster.end()) {
        nodes.emplace_back(op_node);
      }
    }
    return nodes;
  };

  // removing useless link from cluster_inputs to cluster
  for (auto* var_node : cluster_inputs) {
    auto preserved_ops = get_preserved_ops(var_node->outputs);
    var_node->outputs.assign(preserved_ops.begin(), preserved_ops.end());
    // According to SSA form, a var node must not be any two op's output,
    // and the cluster_inputs var nodes is defined as an out-graph op's
    // output, so the cluster_inputs var nodes are not any subgraph op's
    // output. Do not reassign input list here.
  }

  // removing useless link from cluster to cluster_outputs
  for (auto* var_node : cluster_outputs) {
    auto preserved_ops = get_preserved_ops(var_node->inputs);
    var_node->inputs.assign(preserved_ops.begin(), preserved_ops.end());

    // Note that cluster_outputs var node maybe some subgraph op's input,
    // here we need remove them.
    preserved_ops = get_preserved_ops(var_node->outputs);
    var_node->outputs.assign(preserved_ops.begin(), preserved_ops.end());
  }
}

// Removing cluster node and internals node from Graph
void RemoveSubGraphFromGraph(const GraphNodeSet& cluster,
                             const GraphNodeSet& cluster_internals,
                             Graph* graph) {
  for (auto* op_node : cluster) {
    graph->RemoveNode(op_node);
  }
  for (auto* var_node : cluster_internals) {
    graph->RemoveNode(var_node);
  }
}

// Replacing Cinn subgraph to a special op node, whose op_type is
// kCinnLaunchOp, and inputs ares cluster_inputs and outputs are
// cluster_outputs.
// Meanwhile, move all links of cluster to the special op.
void ReplaceSubGraphWithSpecialOpNode(const GraphNodeSet& cluster,
                                      const GraphNodeSet& cluster_inputs,
                                      const GraphNodeSet& cluster_outputs,
                                      const GraphNodeSet& cluster_internals,
                                      const std::string& compilation_key,
                                      Graph* graph) {
  // First, add the special op node whose name is "kCinnLaunchOp" into graph
  auto special_op_node = AddSpecialOpToGraph(cluster_inputs, cluster_outputs,
                                             compilation_key, graph);
  // Second, remove all graph's links which are from or to cluster nodes
  RemoveLinkFromCluster(cluster, cluster_inputs, cluster_outputs);
  // Third, add new links from or to the the special op node
  AddLinkToSpecialOp(cluster_inputs, cluster_outputs, special_op_node);
  // Finally, remove the cinn sub graph from graph
  RemoveSubGraphFromGraph(cluster, cluster_internals, graph);
}

// Search all subgraphs which all op node supported by CINN,
// Here we using SubgraphDetector to detecte the subgraph that
// all of op node supported by CINN. We using OpMapperRegistry
// to check whether the op node supported by CINN.
void SearchAllSubgraphs(Graph* graph) {
  auto teller = [](const Node* node) {
    return ::cinn::frontend::OpMapperRegistry::Global()->Find(node->Name()) !=
           nullptr;
  };
  std::vector<GraphNodeVec> clusters =
      framework::ir::SubgraphDetector(graph, teller)();

  auto* cinn_compiler = CinnCompiler::GetInstance();
  for (const auto& node_vec : clusters) {
    // Classify var node to inputs, outputs, and internals.
    GraphNodeSet cluster_set(node_vec.begin(), node_vec.end());

    GraphNodeSet cluster_inputs, cluster_outputs, cluster_internals;
    AnalyseClusterVariables(cluster_set, &cluster_inputs, &cluster_outputs,
                            &cluster_internals);
    // Create a new subgraph according to the found cluster and
    // save it in CinnCompiler
    std::string compilation_key = cinn_compiler->AddGraph(
        CreateNewSubGraph(cluster_set, cluster_internals, cluster_inputs));
    // Replace the found cluster to a new special op node
    ReplaceSubGraphWithSpecialOpNode(cluster_set, cluster_inputs,
                                     cluster_outputs, cluster_internals,
                                     compilation_key, graph);
  }
}

void BuildCinnPass::ApplyImpl(Graph* graph) const { SearchAllSubgraphs(graph); }

}  // namespace paddle2cinn
}  // namespace framework
}  // namespace paddle

REGISTER_PASS(build_cinn_pass, paddle::framework::paddle2cinn::BuildCinnPass);