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 //===- CallGraph.h - Build a Module's call graph ----------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 /// \file
 ///
 /// This file provides interfaces used to build and manipulate a call graph,
 /// which is a very useful tool for interprocedural optimization.
 ///
 /// Every function in a module is represented as a node in the call graph.  The
 /// callgraph node keeps track of which functions are called by the function
 /// corresponding to the node.
 ///
 /// A call graph may contain nodes where the function that they correspond to
 /// is null.  These 'external' nodes are used to represent control flow that is
 /// not represented (or analyzable) in the module.  In particular, this
 /// analysis builds one external node such that:
 ///   1. All functions in the module without internal linkage will have edges
 ///      from this external node, indicating that they could be called by
 ///      functions outside of the module.
 ///   2. All functions whose address is used for something more than a direct
 ///      call, for example being stored into a memory location will also have
 ///      an edge from this external node.  Since they may be called by an
 ///      unknown caller later, they must be tracked as such.
 ///
 /// There is a second external node added for calls that leave this module.
 /// Functions have a call edge to the external node iff:
 ///   1. The function is external, reflecting the fact that they could call
 ///      anything without internal linkage or that has its address taken.
 ///   2. The function contains an indirect function call.
 ///
 /// As an extension in the future, there may be multiple nodes with a null
 /// function.  These will be used when we can prove (through pointer analysis)
 /// that an indirect call site can call only a specific set of functions.
 ///
 /// Because of these properties, the CallGraph captures a conservative superset
 /// of all of the caller-callee relationships, which is useful for
 /// transformations.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ANALYSIS_CALLGRAPH_H
 #define LLVM_ANALYSIS_CALLGRAPH_H
 
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Pass.h"
 #include <cassert>
 #include <map>
 #include <memory>
 #include <utility>
 #include <vector>
 
 namespace llvm {
 
 template <class GraphType> struct GraphTraits;
 class CallGraphNode;
 class Function;
 class Module;
 class raw_ostream;
 
 /// The basic data container for the call graph of a \c Module of IR.
 ///
 /// This class exposes both the interface to the call graph for a module of IR.
 ///
 /// The core call graph itself can also be updated to reflect changes to the IR.
 class CallGraph {
   Module &M;
 
   using FunctionMapTy =
       std::map<const Function *, std::unique_ptr<CallGraphNode>>;
 
   /// A map from \c Function* to \c CallGraphNode*.
   FunctionMapTy FunctionMap;
 
   /// This node has edges to all external functions and those internal
   /// functions that have their address taken.
   CallGraphNode *ExternalCallingNode;
 
   /// This node has edges to it from all functions making indirect calls
   /// or calling an external function.
   std::unique_ptr<CallGraphNode> CallsExternalNode;
 
 public:
   explicit CallGraph(Module &M);
   CallGraph(CallGraph &&Arg);
   ~CallGraph();
 
   void print(raw_ostream &OS) const;
   void dump() const;
 
   using iterator = FunctionMapTy::iterator;
   using const_iterator = FunctionMapTy::const_iterator;
 
   /// Returns the module the call graph corresponds to.
   Module &getModule() const { return M; }
 
   bool invalidate(Module &, const PreservedAnalyses &PA,
                   ModuleAnalysisManager::Invalidator &);
 
   inline iterator begin() { return FunctionMap.begin(); }
   inline iterator end() { return FunctionMap.end(); }
   inline const_iterator begin() const { return FunctionMap.begin(); }
   inline const_iterator end() const { return FunctionMap.end(); }
 
   /// Returns the call graph node for the provided function.
   inline const CallGraphNode *operator[](const Function *F) const {
     const_iterator I = FunctionMap.find(F);
     assert(I != FunctionMap.end() && "Function not in callgraph!");
     return I->second.get();
   }
 
   /// Returns the call graph node for the provided function.
   inline CallGraphNode *operator[](const Function *F) {
     const_iterator I = FunctionMap.find(F);
     assert(I != FunctionMap.end() && "Function not in callgraph!");
     return I->second.get();
   }
 
   /// Returns the \c CallGraphNode which is used to represent
   /// undetermined calls into the callgraph.
   CallGraphNode *getExternalCallingNode() const { return ExternalCallingNode; }
 
   CallGraphNode *getCallsExternalNode() const {
     return CallsExternalNode.get();
   }
 
   /// Old node has been deleted, and New is to be used in its place, update the
   /// ExternalCallingNode.
   void ReplaceExternalCallEdge(CallGraphNode *Old, CallGraphNode *New);
 
   //===---------------------------------------------------------------------
   // Functions to keep a call graph up to date with a function that has been
   // modified.
   //
 
   /// Unlink the function from this module, returning it.
   ///
   /// Because this removes the function from the module, the call graph node is
   /// destroyed.  This is only valid if the function does not call any other
   /// functions (ie, there are no edges in it's CGN).  The easiest way to do
   /// this is to dropAllReferences before calling this.
   Function *removeFunctionFromModule(CallGraphNode *CGN);
 
   /// Similar to operator[], but this will insert a new CallGraphNode for
   /// \c F if one does not already exist.
   CallGraphNode *getOrInsertFunction(const Function *F);
 
   /// Populate \p CGN based on the calls inside the associated function.
   void populateCallGraphNode(CallGraphNode *CGN);
 
   /// Add a function to the call graph, and link the node to all of the
   /// functions that it calls.
   void addToCallGraph(Function *F);
 };
 
 /// A node in the call graph for a module.
 ///
 /// Typically represents a function in the call graph. There are also special
 /// "null" nodes used to represent theoretical entries in the call graph.
 class CallGraphNode {
 public:
   /// A pair of the calling instruction (a call or invoke)
   /// and the call graph node being called.
   /// Call graph node may have two types of call records which represent an edge
   /// in the call graph - reference or a call edge. Reference edges are not
   /// associated with any call instruction and are created with the first field
   /// set to `None`, while real call edges have instruction address in this
   /// field. Therefore, all real call edges are expected to have a value in the
   /// first field and it is not supposed to be `nullptr`.
   /// Reference edges, for example, are used for connecting broker function
   /// caller to the callback function for callback call sites.
   using CallRecord = std::pair<std::optional<WeakTrackingVH>, CallGraphNode *>;
 
 public:
   using CalledFunctionsVector = std::vector<CallRecord>;
 
   /// Creates a node for the specified function.
   inline CallGraphNode(CallGraph *CG, Function *F) : CG(CG), F(F) {}
 
   CallGraphNode(const CallGraphNode &) = delete;
   CallGraphNode &operator=(const CallGraphNode &) = delete;
 
   ~CallGraphNode() {
     assert(NumReferences == 0 && "Node deleted while references remain");
   }
 
   using iterator = std::vector<CallRecord>::iterator;
   using const_iterator = std::vector<CallRecord>::const_iterator;
 
   /// Returns the function that this call graph node represents.
   Function *getFunction() const { return F; }
 
   inline iterator begin() { return CalledFunctions.begin(); }
   inline iterator end() { return CalledFunctions.end(); }
   inline const_iterator begin() const { return CalledFunctions.begin(); }
   inline const_iterator end() const { return CalledFunctions.end(); }
   inline bool empty() const { return CalledFunctions.empty(); }
   inline unsigned size() const { return (unsigned)CalledFunctions.size(); }
 
   /// Returns the number of other CallGraphNodes in this CallGraph that
   /// reference this node in their callee list.
   unsigned getNumReferences() const { return NumReferences; }
 
   /// Returns the i'th called function.
   CallGraphNode *operator[](unsigned i) const {
     assert(i < CalledFunctions.size() && "Invalid index");
     return CalledFunctions[i].second;
   }
 
   /// Print out this call graph node.
   void dump() const;
   void print(raw_ostream &OS) const;
 
   //===---------------------------------------------------------------------
   // Methods to keep a call graph up to date with a function that has been
   // modified
   //
 
   /// Removes all edges from this CallGraphNode to any functions it
   /// calls.
   void removeAllCalledFunctions() {
     while (!CalledFunctions.empty()) {
       CalledFunctions.back().second->DropRef();
       CalledFunctions.pop_back();
     }
   }
 
   /// Moves all the callee information from N to this node.
   void stealCalledFunctionsFrom(CallGraphNode *N) {
     assert(CalledFunctions.empty() &&
            "Cannot steal callsite information if I already have some");
     std::swap(CalledFunctions, N->CalledFunctions);
   }
 
   /// Adds a function to the list of functions called by this one.
   void addCalledFunction(CallBase *Call, CallGraphNode *M) {
     CalledFunctions.emplace_back(Call ? std::optional<WeakTrackingVH>(Call)
                                       : std::optional<WeakTrackingVH>(),
                                  M);
     M->AddRef();
   }
 
   void removeCallEdge(iterator I) {
     I->second->DropRef();
     *I = CalledFunctions.back();
     CalledFunctions.pop_back();
   }
 
   /// Removes the edge in the node for the specified call site.
   ///
   /// Note that this method takes linear time, so it should be used sparingly.
   void removeCallEdgeFor(CallBase &Call);
 
   /// Removes all call edges from this node to the specified callee
   /// function.
   ///
   /// This takes more time to execute than removeCallEdgeTo, so it should not
   /// be used unless necessary.
   void removeAnyCallEdgeTo(CallGraphNode *Callee);
 
   /// Removes one edge associated with a null callsite from this node to
   /// the specified callee function.
   void removeOneAbstractEdgeTo(CallGraphNode *Callee);
 
   /// Replaces the edge in the node for the specified call site with a
   /// new one.
   ///
   /// Note that this method takes linear time, so it should be used sparingly.
   void replaceCallEdge(CallBase &Call, CallBase &NewCall,
                        CallGraphNode *NewNode);
 
 private:
   friend class CallGraph;
 
   CallGraph *CG;
   Function *F;
 
   std::vector<CallRecord> CalledFunctions;
 
   /// The number of times that this CallGraphNode occurs in the
   /// CalledFunctions array of this or other CallGraphNodes.
   unsigned NumReferences = 0;
 
   void DropRef() { --NumReferences; }
   void AddRef() { ++NumReferences; }
 
   /// A special function that should only be used by the CallGraph class.
   void allReferencesDropped() { NumReferences = 0; }
 };
 
 /// An analysis pass to compute the \c CallGraph for a \c Module.
 ///
 /// This class implements the concept of an analysis pass used by the \c
 /// ModuleAnalysisManager to run an analysis over a module and cache the
 /// resulting data.
 class CallGraphAnalysis : public AnalysisInfoMixin<CallGraphAnalysis> {
   friend AnalysisInfoMixin<CallGraphAnalysis>;
 
   static AnalysisKey Key;
 
 public:
   /// A formulaic type to inform clients of the result type.
   using Result = CallGraph;
 
   /// Compute the \c CallGraph for the module \c M.
   ///
   /// The real work here is done in the \c CallGraph constructor.
   CallGraph run(Module &M, ModuleAnalysisManager &) { return CallGraph(M); }
 };
 
 /// Printer pass for the \c CallGraphAnalysis results.
 class CallGraphPrinterPass : public PassInfoMixin<CallGraphPrinterPass> {
   raw_ostream &OS;
 
 public:
   explicit CallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
 
   PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
 
   static bool isRequired() { return true; }
 };
 
 /// Printer pass for the summarized \c CallGraphAnalysis results.
 class CallGraphSCCsPrinterPass
     : public PassInfoMixin<CallGraphSCCsPrinterPass> {
   raw_ostream &OS;
 
 public:
   explicit CallGraphSCCsPrinterPass(raw_ostream &OS) : OS(OS) {}
 
   PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
 
   static bool isRequired() { return true; }
 };
 
 /// The \c ModulePass which wraps up a \c CallGraph and the logic to
 /// build it.
 ///
 /// This class exposes both the interface to the call graph container and the
 /// module pass which runs over a module of IR and produces the call graph. The
 /// call graph interface is entirelly a wrapper around a \c CallGraph object
 /// which is stored internally for each module.
 class CallGraphWrapperPass : public ModulePass {
   std::unique_ptr<CallGraph> G;
 
 public:
   static char ID; // Class identification, replacement for typeinfo
 
   CallGraphWrapperPass();
   ~CallGraphWrapperPass() override;
 
   /// The internal \c CallGraph around which the rest of this interface
   /// is wrapped.
   const CallGraph &getCallGraph() const { return *G; }
   CallGraph &getCallGraph() { return *G; }
 
   using iterator = CallGraph::iterator;
   using const_iterator = CallGraph::const_iterator;
 
   /// Returns the module the call graph corresponds to.
   Module &getModule() const { return G->getModule(); }
 
   inline iterator begin() { return G->begin(); }
   inline iterator end() { return G->end(); }
   inline const_iterator begin() const { return G->begin(); }
   inline const_iterator end() const { return G->end(); }
 
   /// Returns the call graph node for the provided function.
   inline const CallGraphNode *operator[](const Function *F) const {
     return (*G)[F];
   }
 
   /// Returns the call graph node for the provided function.
   inline CallGraphNode *operator[](const Function *F) { return (*G)[F]; }
 
   /// Returns the \c CallGraphNode which is used to represent
   /// undetermined calls into the callgraph.
   CallGraphNode *getExternalCallingNode() const {
     return G->getExternalCallingNode();
   }
 
   CallGraphNode *getCallsExternalNode() const {
     return G->getCallsExternalNode();
   }
 
   //===---------------------------------------------------------------------
   // Functions to keep a call graph up to date with a function that has been
   // modified.
   //
 
   /// Unlink the function from this module, returning it.
   ///
   /// Because this removes the function from the module, the call graph node is
   /// destroyed.  This is only valid if the function does not call any other
   /// functions (ie, there are no edges in it's CGN).  The easiest way to do
   /// this is to dropAllReferences before calling this.
   Function *removeFunctionFromModule(CallGraphNode *CGN) {
     return G->removeFunctionFromModule(CGN);
   }
 
   /// Similar to operator[], but this will insert a new CallGraphNode for
   /// \c F if one does not already exist.
   CallGraphNode *getOrInsertFunction(const Function *F) {
     return G->getOrInsertFunction(F);
   }
 
   //===---------------------------------------------------------------------
   // Implementation of the ModulePass interface needed here.
   //
 
   void getAnalysisUsage(AnalysisUsage &AU) const override;
   bool runOnModule(Module &M) override;
   void releaseMemory() override;
 
   void print(raw_ostream &o, const Module *) const override;
   void dump() const;
 };
 
 //===----------------------------------------------------------------------===//
 // GraphTraits specializations for call graphs so that they can be treated as
 // graphs by the generic graph algorithms.
 //
 
 // Provide graph traits for traversing call graphs using standard graph
 // traversals.
 template <> struct GraphTraits<CallGraphNode *> {
   using NodeRef = CallGraphNode *;
   using CGNPairTy = CallGraphNode::CallRecord;
 
   static NodeRef getEntryNode(CallGraphNode *CGN) { return CGN; }
   static CallGraphNode *CGNGetValue(CGNPairTy P) { return P.second; }
 
   using ChildIteratorType =
       mapped_iterator<CallGraphNode::iterator, decltype(&CGNGetValue)>;
 
   static ChildIteratorType child_begin(NodeRef N) {
     return ChildIteratorType(N->begin(), &CGNGetValue);
   }
 
   static ChildIteratorType child_end(NodeRef N) {
     return ChildIteratorType(N->end(), &CGNGetValue);
   }
 };
 
 template <> struct GraphTraits<const CallGraphNode *> {
   using NodeRef = const CallGraphNode *;
   using CGNPairTy = CallGraphNode::CallRecord;
   using EdgeRef = const CallGraphNode::CallRecord &;
 
   static NodeRef getEntryNode(const CallGraphNode *CGN) { return CGN; }
   static const CallGraphNode *CGNGetValue(CGNPairTy P) { return P.second; }
 
   using ChildIteratorType =
       mapped_iterator<CallGraphNode::const_iterator, decltype(&CGNGetValue)>;
   using ChildEdgeIteratorType = CallGraphNode::const_iterator;
 
   static ChildIteratorType child_begin(NodeRef N) {
     return ChildIteratorType(N->begin(), &CGNGetValue);
   }
 
   static ChildIteratorType child_end(NodeRef N) {
     return ChildIteratorType(N->end(), &CGNGetValue);
   }
 
   static ChildEdgeIteratorType child_edge_begin(NodeRef N) {
     return N->begin();
   }
   static ChildEdgeIteratorType child_edge_end(NodeRef N) { return N->end(); }
 
   static NodeRef edge_dest(EdgeRef E) { return E.second; }
 };
 
 template <>
 struct GraphTraits<CallGraph *> : public GraphTraits<CallGraphNode *> {
   using PairTy =
       std::pair<const Function *const, std::unique_ptr<CallGraphNode>>;
 
   static NodeRef getEntryNode(CallGraph *CGN) {
     return CGN->getExternalCallingNode(); // Start at the external node!
   }
 
   static CallGraphNode *CGGetValuePtr(const PairTy &P) {
     return P.second.get();
   }
 
   // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
   using nodes_iterator =
       mapped_iterator<CallGraph::iterator, decltype(&CGGetValuePtr)>;
 
   static nodes_iterator nodes_begin(CallGraph *CG) {
     return nodes_iterator(CG->begin(), &CGGetValuePtr);
   }
 
   static nodes_iterator nodes_end(CallGraph *CG) {
     return nodes_iterator(CG->end(), &CGGetValuePtr);
   }
 };
 
 template <>
 struct GraphTraits<const CallGraph *> : public GraphTraits<
                                             const CallGraphNode *> {
   using PairTy =
       std::pair<const Function *const, std::unique_ptr<CallGraphNode>>;
 
   static NodeRef getEntryNode(const CallGraph *CGN) {
     return CGN->getExternalCallingNode(); // Start at the external node!
   }
 
   static const CallGraphNode *CGGetValuePtr(const PairTy &P) {
     return P.second.get();
   }
 
   // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
   using nodes_iterator =
       mapped_iterator<CallGraph::const_iterator, decltype(&CGGetValuePtr)>;
 
   static nodes_iterator nodes_begin(const CallGraph *CG) {
     return nodes_iterator(CG->begin(), &CGGetValuePtr);
   }
 
   static nodes_iterator nodes_end(const CallGraph *CG) {
     return nodes_iterator(CG->end(), &CGGetValuePtr);
   }
 };
 
 } // end namespace llvm
 
 #endif // LLVM_ANALYSIS_CALLGRAPH_H

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