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      1 //== CallGraph.cpp - AST-based 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 //
     10 //  This file defines the AST-based CallGraph.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 #include "clang/Analysis/CallGraph.h"
     14 #include "clang/AST/ASTContext.h"
     15 #include "clang/AST/Decl.h"
     16 #include "clang/AST/StmtVisitor.h"
     17 #include "llvm/ADT/PostOrderIterator.h"
     18 #include "llvm/ADT/Statistic.h"
     19 #include "llvm/Support/GraphWriter.h"
     20 
     21 using namespace clang;
     22 
     23 #define DEBUG_TYPE "CallGraph"
     24 
     25 STATISTIC(NumObjCCallEdges, "Number of Objective-C method call edges");
     26 STATISTIC(NumBlockCallEdges, "Number of block call edges");
     27 
     28 namespace {
     29 /// A helper class, which walks the AST and locates all the call sites in the
     30 /// given function body.
     31 class CGBuilder : public StmtVisitor<CGBuilder> {
     32   CallGraph *G;
     33   CallGraphNode *CallerNode;
     34 
     35 public:
     36   CGBuilder(CallGraph *g, CallGraphNode *N)
     37     : G(g), CallerNode(N) {}
     38 
     39   void VisitStmt(Stmt *S) { VisitChildren(S); }
     40 
     41   Decl *getDeclFromCall(CallExpr *CE) {
     42     if (FunctionDecl *CalleeDecl = CE->getDirectCallee())
     43       return CalleeDecl;
     44 
     45     // Simple detection of a call through a block.
     46     Expr *CEE = CE->getCallee()->IgnoreParenImpCasts();
     47     if (BlockExpr *Block = dyn_cast<BlockExpr>(CEE)) {
     48       NumBlockCallEdges++;
     49       return Block->getBlockDecl();
     50     }
     51 
     52     return nullptr;
     53   }
     54 
     55   void addCalledDecl(Decl *D) {
     56     if (G->includeInGraph(D)) {
     57       CallGraphNode *CalleeNode = G->getOrInsertNode(D);
     58       CallerNode->addCallee(CalleeNode, G);
     59     }
     60   }
     61 
     62   void VisitCallExpr(CallExpr *CE) {
     63     if (Decl *D = getDeclFromCall(CE))
     64       addCalledDecl(D);
     65   }
     66 
     67   // Adds may-call edges for the ObjC message sends.
     68   void VisitObjCMessageExpr(ObjCMessageExpr *ME) {
     69     if (ObjCInterfaceDecl *IDecl = ME->getReceiverInterface()) {
     70       Selector Sel = ME->getSelector();
     71 
     72       // Find the callee definition within the same translation unit.
     73       Decl *D = nullptr;
     74       if (ME->isInstanceMessage())
     75         D = IDecl->lookupPrivateMethod(Sel);
     76       else
     77         D = IDecl->lookupPrivateClassMethod(Sel);
     78       if (D) {
     79         addCalledDecl(D);
     80         NumObjCCallEdges++;
     81       }
     82     }
     83   }
     84 
     85   void VisitChildren(Stmt *S) {
     86     for (Stmt *SubStmt : S->children())
     87       if (SubStmt)
     88         this->Visit(SubStmt);
     89   }
     90 };
     91 
     92 } // end anonymous namespace
     93 
     94 void CallGraph::addNodesForBlocks(DeclContext *D) {
     95   if (BlockDecl *BD = dyn_cast<BlockDecl>(D))
     96     addNodeForDecl(BD, true);
     97 
     98   for (auto *I : D->decls())
     99     if (auto *DC = dyn_cast<DeclContext>(I))
    100       addNodesForBlocks(DC);
    101 }
    102 
    103 CallGraph::CallGraph() {
    104   Root = getOrInsertNode(nullptr);
    105 }
    106 
    107 CallGraph::~CallGraph() {
    108   llvm::DeleteContainerSeconds(FunctionMap);
    109 }
    110 
    111 bool CallGraph::includeInGraph(const Decl *D) {
    112   assert(D);
    113   if (!D->hasBody())
    114     return false;
    115 
    116   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
    117     // We skip function template definitions, as their semantics is
    118     // only determined when they are instantiated.
    119     if (FD->isDependentContext())
    120       return false;
    121 
    122     IdentifierInfo *II = FD->getIdentifier();
    123     if (II && II->getName().startswith("__inline"))
    124       return false;
    125   }
    126 
    127   return true;
    128 }
    129 
    130 void CallGraph::addNodeForDecl(Decl* D, bool IsGlobal) {
    131   assert(D);
    132 
    133   // Allocate a new node, mark it as root, and process it's calls.
    134   CallGraphNode *Node = getOrInsertNode(D);
    135 
    136   // Process all the calls by this function as well.
    137   CGBuilder builder(this, Node);
    138   if (Stmt *Body = D->getBody())
    139     builder.Visit(Body);
    140 }
    141 
    142 CallGraphNode *CallGraph::getNode(const Decl *F) const {
    143   FunctionMapTy::const_iterator I = FunctionMap.find(F);
    144   if (I == FunctionMap.end()) return nullptr;
    145   return I->second;
    146 }
    147 
    148 CallGraphNode *CallGraph::getOrInsertNode(Decl *F) {
    149   if (F && !isa<ObjCMethodDecl>(F))
    150     F = F->getCanonicalDecl();
    151 
    152   CallGraphNode *&Node = FunctionMap[F];
    153   if (Node)
    154     return Node;
    155 
    156   Node = new CallGraphNode(F);
    157   // Make Root node a parent of all functions to make sure all are reachable.
    158   if (F)
    159     Root->addCallee(Node, this);
    160   return Node;
    161 }
    162 
    163 void CallGraph::print(raw_ostream &OS) const {
    164   OS << " --- Call graph Dump --- \n";
    165 
    166   // We are going to print the graph in reverse post order, partially, to make
    167   // sure the output is deterministic.
    168   llvm::ReversePostOrderTraversal<const clang::CallGraph*> RPOT(this);
    169   for (llvm::ReversePostOrderTraversal<const clang::CallGraph*>::rpo_iterator
    170          I = RPOT.begin(), E = RPOT.end(); I != E; ++I) {
    171     const CallGraphNode *N = *I;
    172 
    173     OS << "  Function: ";
    174     if (N == Root)
    175       OS << "< root >";
    176     else
    177       N->print(OS);
    178 
    179     OS << " calls: ";
    180     for (CallGraphNode::const_iterator CI = N->begin(),
    181                                        CE = N->end(); CI != CE; ++CI) {
    182       assert(*CI != Root && "No one can call the root node.");
    183       (*CI)->print(OS);
    184       OS << " ";
    185     }
    186     OS << '\n';
    187   }
    188   OS.flush();
    189 }
    190 
    191 void CallGraph::dump() const {
    192   print(llvm::errs());
    193 }
    194 
    195 void CallGraph::viewGraph() const {
    196   llvm::ViewGraph(this, "CallGraph");
    197 }
    198 
    199 void CallGraphNode::print(raw_ostream &os) const {
    200   if (const NamedDecl *ND = dyn_cast_or_null<NamedDecl>(FD))
    201       return ND->printName(os);
    202   os << "< >";
    203 }
    204 
    205 void CallGraphNode::dump() const {
    206   print(llvm::errs());
    207 }
    208 
    209 namespace llvm {
    210 
    211 template <>
    212 struct DOTGraphTraits<const CallGraph*> : public DefaultDOTGraphTraits {
    213 
    214   DOTGraphTraits (bool isSimple=false) : DefaultDOTGraphTraits(isSimple) {}
    215 
    216   static std::string getNodeLabel(const CallGraphNode *Node,
    217                                   const CallGraph *CG) {
    218     if (CG->getRoot() == Node) {
    219       return "< root >";
    220     }
    221     if (const NamedDecl *ND = dyn_cast_or_null<NamedDecl>(Node->getDecl()))
    222       return ND->getNameAsString();
    223     else
    224       return "< >";
    225   }
    226 
    227 };
    228 }
    229