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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/Intrinsics.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);

};

/// 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);

};

/// 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