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      1 //===- CallGraph.h - Build a Module's call graph ----------------*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 /// \file
     10 ///
     11 /// This file provides interfaces used to build and manipulate a call graph,
     12 /// which is a very useful tool for interprocedural optimization.
     13 ///
     14 /// Every function in a module is represented as a node in the call graph.  The
     15 /// callgraph node keeps track of which functions are called by the function
     16 /// corresponding to the node.
     17 ///
     18 /// A call graph may contain nodes where the function that they correspond to
     19 /// is null.  These 'external' nodes are used to represent control flow that is
     20 /// not represented (or analyzable) in the module.  In particular, this
     21 /// analysis builds one external node such that:
     22 ///   1. All functions in the module without internal linkage will have edges
     23 ///      from this external node, indicating that they could be called by
     24 ///      functions outside of the module.
     25 ///   2. All functions whose address is used for something more than a direct
     26 ///      call, for example being stored into a memory location will also have
     27 ///      an edge from this external node.  Since they may be called by an
     28 ///      unknown caller later, they must be tracked as such.
     29 ///
     30 /// There is a second external node added for calls that leave this module.
     31 /// Functions have a call edge to the external node iff:
     32 ///   1. The function is external, reflecting the fact that they could call
     33 ///      anything without internal linkage or that has its address taken.
     34 ///   2. The function contains an indirect function call.
     35 ///
     36 /// As an extension in the future, there may be multiple nodes with a null
     37 /// function.  These will be used when we can prove (through pointer analysis)
     38 /// that an indirect call site can call only a specific set of functions.
     39 ///
     40 /// Because of these properties, the CallGraph captures a conservative superset
     41 /// of all of the caller-callee relationships, which is useful for
     42 /// transformations.
     43 ///
     44 /// The CallGraph class also attempts to figure out what the root of the
     45 /// CallGraph is, which it currently does by looking for a function named
     46 /// 'main'. If no function named 'main' is found, the external node is used as
     47 /// the entry node, reflecting the fact that any function without internal
     48 /// linkage could be called into (which is common for libraries).
     49 ///
     50 //===----------------------------------------------------------------------===//
     51 
     52 #ifndef LLVM_ANALYSIS_CALLGRAPH_H
     53 #define LLVM_ANALYSIS_CALLGRAPH_H
     54 
     55 #include "llvm/ADT/GraphTraits.h"
     56 #include "llvm/ADT/STLExtras.h"
     57 #include "llvm/IR/CallSite.h"
     58 #include "llvm/IR/Function.h"
     59 #include "llvm/IR/Intrinsics.h"
     60 #include "llvm/IR/PassManager.h"
     61 #include "llvm/IR/ValueHandle.h"
     62 #include "llvm/Pass.h"
     63 #include <map>
     64 
     65 namespace llvm {
     66 
     67 class Function;
     68 class Module;
     69 class CallGraphNode;
     70 
     71 /// \brief The basic data container for the call graph of a \c Module of IR.
     72 ///
     73 /// This class exposes both the interface to the call graph for a module of IR.
     74 ///
     75 /// The core call graph itself can also be updated to reflect changes to the IR.
     76 class CallGraph {
     77   Module &M;
     78 
     79   typedef std::map<const Function *, std::unique_ptr<CallGraphNode>>
     80       FunctionMapTy;
     81 
     82   /// \brief A map from \c Function* to \c CallGraphNode*.
     83   FunctionMapTy FunctionMap;
     84 
     85   /// \brief Root is root of the call graph, or the external node if a 'main'
     86   /// function couldn't be found.
     87   CallGraphNode *Root;
     88 
     89   /// \brief This node has edges to all external functions and those internal
     90   /// functions that have their address taken.
     91   CallGraphNode *ExternalCallingNode;
     92 
     93   /// \brief This node has edges to it from all functions making indirect calls
     94   /// or calling an external function.
     95   std::unique_ptr<CallGraphNode> CallsExternalNode;
     96 
     97   /// \brief Replace the function represented by this node by another.
     98   ///
     99   /// This does not rescan the body of the function, so it is suitable when
    100   /// splicing the body of one function to another while also updating all
    101   /// callers from the old function to the new.
    102   void spliceFunction(const Function *From, const Function *To);
    103 
    104   /// \brief Add a function to the call graph, and link the node to all of the
    105   /// functions that it calls.
    106   void addToCallGraph(Function *F);
    107 
    108 public:
    109   explicit CallGraph(Module &M);
    110   CallGraph(CallGraph &&Arg);
    111   ~CallGraph();
    112 
    113   void print(raw_ostream &OS) const;
    114   void dump() const;
    115 
    116   typedef FunctionMapTy::iterator iterator;
    117   typedef FunctionMapTy::const_iterator const_iterator;
    118 
    119   /// \brief Returns the module the call graph corresponds to.
    120   Module &getModule() const { return M; }
    121 
    122   inline iterator begin() { return FunctionMap.begin(); }
    123   inline iterator end() { return FunctionMap.end(); }
    124   inline const_iterator begin() const { return FunctionMap.begin(); }
    125   inline const_iterator end() const { return FunctionMap.end(); }
    126 
    127   /// \brief Returns the call graph node for the provided function.
    128   inline const CallGraphNode *operator[](const Function *F) const {
    129     const_iterator I = FunctionMap.find(F);
    130     assert(I != FunctionMap.end() && "Function not in callgraph!");
    131     return I->second.get();
    132   }
    133 
    134   /// \brief Returns the call graph node for the provided function.
    135   inline CallGraphNode *operator[](const Function *F) {
    136     const_iterator I = FunctionMap.find(F);
    137     assert(I != FunctionMap.end() && "Function not in callgraph!");
    138     return I->second.get();
    139   }
    140 
    141   /// \brief Returns the \c CallGraphNode which is used to represent
    142   /// undetermined calls into the callgraph.
    143   CallGraphNode *getExternalCallingNode() const { return ExternalCallingNode; }
    144 
    145   CallGraphNode *getCallsExternalNode() const {
    146     return CallsExternalNode.get();
    147   }
    148 
    149   //===---------------------------------------------------------------------
    150   // Functions to keep a call graph up to date with a function that has been
    151   // modified.
    152   //
    153 
    154   /// \brief Unlink the function from this module, returning it.
    155   ///
    156   /// Because this removes the function from the module, the call graph node is
    157   /// destroyed.  This is only valid if the function does not call any other
    158   /// functions (ie, there are no edges in it's CGN).  The easiest way to do
    159   /// this is to dropAllReferences before calling this.
    160   Function *removeFunctionFromModule(CallGraphNode *CGN);
    161 
    162   /// \brief Similar to operator[], but this will insert a new CallGraphNode for
    163   /// \c F if one does not already exist.
    164   CallGraphNode *getOrInsertFunction(const Function *F);
    165 };
    166 
    167 /// \brief A node in the call graph for a module.
    168 ///
    169 /// Typically represents a function in the call graph. There are also special
    170 /// "null" nodes used to represent theoretical entries in the call graph.
    171 class CallGraphNode {
    172 public:
    173   /// \brief A pair of the calling instruction (a call or invoke)
    174   /// and the call graph node being called.
    175   typedef std::pair<WeakVH, CallGraphNode *> CallRecord;
    176 
    177 public:
    178   typedef std::vector<CallRecord> CalledFunctionsVector;
    179 
    180   /// \brief Creates a node for the specified function.
    181   inline CallGraphNode(Function *F) : F(F), NumReferences(0) {}
    182 
    183   ~CallGraphNode() {
    184     assert(NumReferences == 0 && "Node deleted while references remain");
    185   }
    186 
    187   typedef std::vector<CallRecord>::iterator iterator;
    188   typedef std::vector<CallRecord>::const_iterator const_iterator;
    189 
    190   /// \brief Returns the function that this call graph node represents.
    191   Function *getFunction() const { return F; }
    192 
    193   inline iterator begin() { return CalledFunctions.begin(); }
    194   inline iterator end() { return CalledFunctions.end(); }
    195   inline const_iterator begin() const { return CalledFunctions.begin(); }
    196   inline const_iterator end() const { return CalledFunctions.end(); }
    197   inline bool empty() const { return CalledFunctions.empty(); }
    198   inline unsigned size() const { return (unsigned)CalledFunctions.size(); }
    199 
    200   /// \brief Returns the number of other CallGraphNodes in this CallGraph that
    201   /// reference this node in their callee list.
    202   unsigned getNumReferences() const { return NumReferences; }
    203 
    204   /// \brief Returns the i'th called function.
    205   CallGraphNode *operator[](unsigned i) const {
    206     assert(i < CalledFunctions.size() && "Invalid index");
    207     return CalledFunctions[i].second;
    208   }
    209 
    210   /// \brief Print out this call graph node.
    211   void dump() const;
    212   void print(raw_ostream &OS) const;
    213 
    214   //===---------------------------------------------------------------------
    215   // Methods to keep a call graph up to date with a function that has been
    216   // modified
    217   //
    218 
    219   /// \brief Removes all edges from this CallGraphNode to any functions it
    220   /// calls.
    221   void removeAllCalledFunctions() {
    222     while (!CalledFunctions.empty()) {
    223       CalledFunctions.back().second->DropRef();
    224       CalledFunctions.pop_back();
    225     }
    226   }
    227 
    228   /// \brief Moves all the callee information from N to this node.
    229   void stealCalledFunctionsFrom(CallGraphNode *N) {
    230     assert(CalledFunctions.empty() &&
    231            "Cannot steal callsite information if I already have some");
    232     std::swap(CalledFunctions, N->CalledFunctions);
    233   }
    234 
    235   /// \brief Adds a function to the list of functions called by this one.
    236   void addCalledFunction(CallSite CS, CallGraphNode *M) {
    237     assert(!CS.getInstruction() || !CS.getCalledFunction() ||
    238            !CS.getCalledFunction()->isIntrinsic() ||
    239            !Intrinsic::isLeaf(CS.getCalledFunction()->getIntrinsicID()));
    240     CalledFunctions.emplace_back(CS.getInstruction(), M);
    241     M->AddRef();
    242   }
    243 
    244   void removeCallEdge(iterator I) {
    245     I->second->DropRef();
    246     *I = CalledFunctions.back();
    247     CalledFunctions.pop_back();
    248   }
    249 
    250   /// \brief Removes the edge in the node for the specified call site.
    251   ///
    252   /// Note that this method takes linear time, so it should be used sparingly.
    253   void removeCallEdgeFor(CallSite CS);
    254 
    255   /// \brief Removes all call edges from this node to the specified callee
    256   /// function.
    257   ///
    258   /// This takes more time to execute than removeCallEdgeTo, so it should not
    259   /// be used unless necessary.
    260   void removeAnyCallEdgeTo(CallGraphNode *Callee);
    261 
    262   /// \brief Removes one edge associated with a null callsite from this node to
    263   /// the specified callee function.
    264   void removeOneAbstractEdgeTo(CallGraphNode *Callee);
    265 
    266   /// \brief Replaces the edge in the node for the specified call site with a
    267   /// new one.
    268   ///
    269   /// Note that this method takes linear time, so it should be used sparingly.
    270   void replaceCallEdge(CallSite CS, CallSite NewCS, CallGraphNode *NewNode);
    271 
    272 private:
    273   friend class CallGraph;
    274 
    275   AssertingVH<Function> F;
    276 
    277   std::vector<CallRecord> CalledFunctions;
    278 
    279   /// \brief The number of times that this CallGraphNode occurs in the
    280   /// CalledFunctions array of this or other CallGraphNodes.
    281   unsigned NumReferences;
    282 
    283   CallGraphNode(const CallGraphNode &) = delete;
    284   void operator=(const CallGraphNode &) = delete;
    285 
    286   void DropRef() { --NumReferences; }
    287   void AddRef() { ++NumReferences; }
    288 
    289   /// \brief A special function that should only be used by the CallGraph class.
    290   void allReferencesDropped() { NumReferences = 0; }
    291 };
    292 
    293 /// \brief An analysis pass to compute the \c CallGraph for a \c Module.
    294 ///
    295 /// This class implements the concept of an analysis pass used by the \c
    296 /// ModuleAnalysisManager to run an analysis over a module and cache the
    297 /// resulting data.
    298 class CallGraphAnalysis : public AnalysisInfoMixin<CallGraphAnalysis> {
    299   friend AnalysisInfoMixin<CallGraphAnalysis>;
    300   static char PassID;
    301 
    302 public:
    303   /// \brief A formulaic typedef to inform clients of the result type.
    304   typedef CallGraph Result;
    305 
    306   /// \brief Compute the \c CallGraph for the module \c M.
    307   ///
    308   /// The real work here is done in the \c CallGraph constructor.
    309   CallGraph run(Module &M, ModuleAnalysisManager &) { return CallGraph(M); }
    310 };
    311 
    312 /// \brief Printer pass for the \c CallGraphAnalysis results.
    313 class CallGraphPrinterPass : public PassInfoMixin<CallGraphPrinterPass> {
    314   raw_ostream &OS;
    315 
    316 public:
    317   explicit CallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
    318   PreservedAnalyses run(Module &M, AnalysisManager<Module> &AM);
    319 };
    320 
    321 /// \brief The \c ModulePass which wraps up a \c CallGraph and the logic to
    322 /// build it.
    323 ///
    324 /// This class exposes both the interface to the call graph container and the
    325 /// module pass which runs over a module of IR and produces the call graph. The
    326 /// call graph interface is entirelly a wrapper around a \c CallGraph object
    327 /// which is stored internally for each module.
    328 class CallGraphWrapperPass : public ModulePass {
    329   std::unique_ptr<CallGraph> G;
    330 
    331 public:
    332   static char ID; // Class identification, replacement for typeinfo
    333 
    334   CallGraphWrapperPass();
    335   ~CallGraphWrapperPass() override;
    336 
    337   /// \brief The internal \c CallGraph around which the rest of this interface
    338   /// is wrapped.
    339   const CallGraph &getCallGraph() const { return *G; }
    340   CallGraph &getCallGraph() { return *G; }
    341 
    342   typedef CallGraph::iterator iterator;
    343   typedef CallGraph::const_iterator const_iterator;
    344 
    345   /// \brief Returns the module the call graph corresponds to.
    346   Module &getModule() const { return G->getModule(); }
    347 
    348   inline iterator begin() { return G->begin(); }
    349   inline iterator end() { return G->end(); }
    350   inline const_iterator begin() const { return G->begin(); }
    351   inline const_iterator end() const { return G->end(); }
    352 
    353   /// \brief Returns the call graph node for the provided function.
    354   inline const CallGraphNode *operator[](const Function *F) const {
    355     return (*G)[F];
    356   }
    357 
    358   /// \brief Returns the call graph node for the provided function.
    359   inline CallGraphNode *operator[](const Function *F) { return (*G)[F]; }
    360 
    361   /// \brief Returns the \c CallGraphNode which is used to represent
    362   /// undetermined calls into the callgraph.
    363   CallGraphNode *getExternalCallingNode() const {
    364     return G->getExternalCallingNode();
    365   }
    366 
    367   CallGraphNode *getCallsExternalNode() const {
    368     return G->getCallsExternalNode();
    369   }
    370 
    371   //===---------------------------------------------------------------------
    372   // Functions to keep a call graph up to date with a function that has been
    373   // modified.
    374   //
    375 
    376   /// \brief Unlink the function from this module, returning it.
    377   ///
    378   /// Because this removes the function from the module, the call graph node is
    379   /// destroyed.  This is only valid if the function does not call any other
    380   /// functions (ie, there are no edges in it's CGN).  The easiest way to do
    381   /// this is to dropAllReferences before calling this.
    382   Function *removeFunctionFromModule(CallGraphNode *CGN) {
    383     return G->removeFunctionFromModule(CGN);
    384   }
    385 
    386   /// \brief Similar to operator[], but this will insert a new CallGraphNode for
    387   /// \c F if one does not already exist.
    388   CallGraphNode *getOrInsertFunction(const Function *F) {
    389     return G->getOrInsertFunction(F);
    390   }
    391 
    392   //===---------------------------------------------------------------------
    393   // Implementation of the ModulePass interface needed here.
    394   //
    395 
    396   void getAnalysisUsage(AnalysisUsage &AU) const override;
    397   bool runOnModule(Module &M) override;
    398   void releaseMemory() override;
    399 
    400   void print(raw_ostream &o, const Module *) const override;
    401   void dump() const;
    402 };
    403 
    404 //===----------------------------------------------------------------------===//
    405 // GraphTraits specializations for call graphs so that they can be treated as
    406 // graphs by the generic graph algorithms.
    407 //
    408 
    409 // Provide graph traits for tranversing call graphs using standard graph
    410 // traversals.
    411 template <> struct GraphTraits<CallGraphNode *> {
    412   typedef CallGraphNode NodeType;
    413 
    414   typedef CallGraphNode::CallRecord CGNPairTy;
    415   typedef std::pointer_to_unary_function<CGNPairTy, CallGraphNode *>
    416   CGNDerefFun;
    417 
    418   static NodeType *getEntryNode(CallGraphNode *CGN) { return CGN; }
    419 
    420   typedef mapped_iterator<NodeType::iterator, CGNDerefFun> ChildIteratorType;
    421 
    422   static inline ChildIteratorType child_begin(NodeType *N) {
    423     return map_iterator(N->begin(), CGNDerefFun(CGNDeref));
    424   }
    425   static inline ChildIteratorType child_end(NodeType *N) {
    426     return map_iterator(N->end(), CGNDerefFun(CGNDeref));
    427   }
    428 
    429   static CallGraphNode *CGNDeref(CGNPairTy P) { return P.second; }
    430 };
    431 
    432 template <> struct GraphTraits<const CallGraphNode *> {
    433   typedef const CallGraphNode NodeType;
    434 
    435   typedef CallGraphNode::CallRecord CGNPairTy;
    436   typedef std::pointer_to_unary_function<CGNPairTy, const CallGraphNode *>
    437       CGNDerefFun;
    438 
    439   static NodeType *getEntryNode(const CallGraphNode *CGN) { return CGN; }
    440 
    441   typedef mapped_iterator<NodeType::const_iterator, CGNDerefFun>
    442       ChildIteratorType;
    443 
    444   static inline ChildIteratorType child_begin(NodeType *N) {
    445     return map_iterator(N->begin(), CGNDerefFun(CGNDeref));
    446   }
    447   static inline ChildIteratorType child_end(NodeType *N) {
    448     return map_iterator(N->end(), CGNDerefFun(CGNDeref));
    449   }
    450 
    451   static const CallGraphNode *CGNDeref(CGNPairTy P) { return P.second; }
    452 };
    453 
    454 template <>
    455 struct GraphTraits<CallGraph *> : public GraphTraits<CallGraphNode *> {
    456   static NodeType *getEntryNode(CallGraph *CGN) {
    457     return CGN->getExternalCallingNode(); // Start at the external node!
    458   }
    459   typedef std::pair<const Function *const, std::unique_ptr<CallGraphNode>>
    460       PairTy;
    461   typedef std::pointer_to_unary_function<const PairTy &, CallGraphNode &>
    462       DerefFun;
    463 
    464   // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
    465   typedef mapped_iterator<CallGraph::iterator, DerefFun> nodes_iterator;
    466   static nodes_iterator nodes_begin(CallGraph *CG) {
    467     return map_iterator(CG->begin(), DerefFun(CGdereference));
    468   }
    469   static nodes_iterator nodes_end(CallGraph *CG) {
    470     return map_iterator(CG->end(), DerefFun(CGdereference));
    471   }
    472 
    473   static CallGraphNode &CGdereference(const PairTy &P) { return *P.second; }
    474 };
    475 
    476 template <>
    477 struct GraphTraits<const CallGraph *> : public GraphTraits<
    478                                             const CallGraphNode *> {
    479   static NodeType *getEntryNode(const CallGraph *CGN) {
    480     return CGN->getExternalCallingNode(); // Start at the external node!
    481   }
    482   typedef std::pair<const Function *const, std::unique_ptr<CallGraphNode>>
    483       PairTy;
    484   typedef std::pointer_to_unary_function<const PairTy &, const CallGraphNode &>
    485       DerefFun;
    486 
    487   // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
    488   typedef mapped_iterator<CallGraph::const_iterator, DerefFun> nodes_iterator;
    489   static nodes_iterator nodes_begin(const CallGraph *CG) {
    490     return map_iterator(CG->begin(), DerefFun(CGdereference));
    491   }
    492   static nodes_iterator nodes_end(const CallGraph *CG) {
    493     return map_iterator(CG->end(), DerefFun(CGdereference));
    494   }
    495 
    496   static const CallGraphNode &CGdereference(const PairTy &P) {
    497     return *P.second;
    498   }
    499 };
    500 
    501 } // End llvm namespace
    502 
    503 #endif
    504