anijain2305 commented on a change in pull request #4922: [Relay][pass] call graph for relay URL: https://github.com/apache/incubator-tvm/pull/4922#discussion_r384183704
########## File path: src/relay/pass/call_graph.cc ########## @@ -0,0 +1,339 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you 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. + */ + +/*! + * \file tvm/relay/pass/call_graph.cc + * \brief Implementation of APIs to handle the call graph of a Relay module. + */ + +#include "call_graph.h" + +#include <tvm/relay/expr_functor.h> +#include <tvm/runtime/object.h> +#include <algorithm> +#include <memory> +#include <sstream> +#include <unordered_set> +#include <vector> + +namespace tvm { +namespace relay { + +CallGraph::CallGraph(IRModule module) { + auto n = make_object<CallGraphNode>(); + n->module = std::move(module); + auto gvar_funcs = n->module->functions; + for (const auto& it : gvar_funcs) { + if (const auto* fn = it.second.as<FunctionNode>()) { + auto func = GetRef<Function>(fn); + // Add the global function to gradually build up the call graph. + n->AddToCallGraph(it.first, func); + } + } + data_ = std::move(n); +} + +void CallGraphNode::AddToCallGraph(const GlobalVar& gv, const Function& func) { + CHECK(func.defined() && gv.defined()); + // Add the current global function as an entry to the call grpah. + CallGraphEntry* cg_node = LookupGlobalVar(gv); + + // Only GlobalVar nodes need to be handled in a function. It indicates that + // the global function of a callee is called by the function that is being + // processed. An edge will be added from the current global function, cg_node, + // to the node that contains the found callee GlobalVarNode. + // + // This is the major overhead for constructing a call graph because the + // post-order visitor will visit each AST node of the current function to + // figure out the dependencies between functions. + PostOrderVisit(func, [&](const Expr& expr) { + if (const GlobalVarNode* gvn = expr.as<GlobalVarNode>()) { + auto callee = GetRef<GlobalVar>(gvn); + cg_node->AddCalledGlobal(LookupGlobalVar(callee)); + } + }); +} + +const CallGraphEntry* CallGraphNode::operator[](const GlobalVar& gv) const { + const_iterator cit = call_graph_.find(gv); + CHECK(cit != call_graph_.end()) + << "GlobalVar " << gv->name_hint << " not found in the call graph!"; + return cit->second.get(); +} + +CallGraphEntry* CallGraphNode::operator[](const GlobalVar& gv) { + const_iterator cit = call_graph_.find(gv); + CHECK(cit != call_graph_.end()) + << "GlobalVar " << gv->name_hint << " not found in the call graph!"; + return cit->second.get(); +} + +// Query the existence of a GlobalVar in the call graph. It creates an entry if +// there is no such a node available. +CallGraphEntry* CallGraphNode::LookupGlobalVar(const GlobalVar& gv) { + CHECK(gv.defined()); + + // This inserts an element to the call graph if it is not there yet. + auto& call_graph_node = call_graph_[gv]; + if (call_graph_node) return call_graph_node.get(); + + CHECK(module->ContainGlobalVar(gv->name_hint)) + << "GlobalVar " << gv->name_hint << " not found in the current ir module"; + + // Create the node for the inserted entry. + call_graph_node = std::unique_ptr<CallGraphEntry>(new CallGraphEntry(gv)); + return call_graph_node.get(); +} + +void CallGraphNode::Print(std::ostream& os) const { + // Print the call graph in the topological order. + std::vector<CallGraphEntry*> nodes = TopologicalOrder(); + for (const auto* cgn : nodes) { + cgn->Print(os); + } +} + +GlobalVar CallGraphNode::RemoveGlobalVarFromModule(CallGraphEntry* cg_node, + bool update_call_graph) { + CHECK(cg_node->empty() || (cg_node->IsRecursive() && cg_node->size() == 1)) + << "Cannot remove global var " << cg_node->GetNameHint() + << " from call graph, because it still calls " + << cg_node->size() << " other global functions"; + + if (update_call_graph) { + // Update the call graph by removing all edges that point to the node + // `cg_node`. + for (auto& it : *this) { + it.second->RemoveAllCallTo(cg_node); + } + } + GlobalVar gv = cg_node->GetGlobalVar(); + call_graph_.erase(gv); + // Update the IR module. + module->Remove(gv); + return gv; +} + +std::vector<CallGraphEntry*> CallGraphNode::GetEntryGlobals() const { + std::vector<CallGraphEntry*> ret; + // An entry function in Relay is a function that never called by other + // functions or only called by itself. + for (const auto& it : *this) { + if (it.second->GetRefCount() == 0 || it.second->IsRecursiveEntry()) { + ret.push_back(it.second.get()); + } + } + return ret; +} + +std::vector<CallGraphEntry*> CallGraphNode::TopologicalOrder() const { + std::vector<CallGraphEntry*> ret; + // Collect all entry nodes. + std::vector<CallGraphEntry*> entries = GetEntryGlobals(); + CallGraphEntry::CallGraphEntrySet visited; + + for (const auto& it : entries) { + // Keep tracking the nodes that have been visited. + auto topo = it->TopologicalOrder(&visited); + // Preprend the collected items. The intermeidate nodes that are shared by + // multiple entries are guaranteed to be collected when visiting the + // previous entries. Therefore, topological order remains. + ret.insert(ret.begin(), topo.begin(), topo.end()); + } + + // Find out the missing global functions if there are any to help debugging. + if (ret.size() != module->functions.size()) { + for (auto it : module->functions) { + if (visited.find((*this)[it.first]) == visited.end()) { + LOG(WARNING) << "Missing global:" << it.first->name_hint + << " with # refs = " << (*this)[it.first]->GetRefCount(); + } + } + LOG(FATAL) << "Expected " << module->functions.size() + << " globals, but received " + << ret.size(); + } + + return ret; +} + +// A BSF traverser is used to collect the nodes in a CallGraphEntry. The nodes +// that are visited by previous CallGraphEntry entries can be memoized. This +// helps us to make sure no entry will be visited multiple times when collecting +// the nodes for an entir call graph. 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