1//===- CallGraph.cpp - AST-based Call graph -------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9//  This file defines the AST-based CallGraph.
10//
11//===----------------------------------------------------------------------===//
12
13#include "clang/Analysis/CallGraph.h"
14#include "clang/AST/Decl.h"
15#include "clang/AST/DeclBase.h"
16#include "clang/AST/DeclObjC.h"
17#include "clang/AST/Expr.h"
18#include "clang/AST/ExprObjC.h"
19#include "clang/AST/Stmt.h"
20#include "clang/AST/StmtVisitor.h"
21#include "clang/Basic/IdentifierTable.h"
22#include "clang/Basic/LLVM.h"
23#include "llvm/ADT/PostOrderIterator.h"
24#include "llvm/ADT/STLExtras.h"
25#include "llvm/ADT/Statistic.h"
26#include "llvm/Support/Casting.h"
27#include "llvm/Support/Compiler.h"
28#include "llvm/Support/DOTGraphTraits.h"
29#include "llvm/Support/GraphWriter.h"
30#include "llvm/Support/raw_ostream.h"
31#include <cassert>
32#include <memory>
33#include <string>
34
35using namespace clang;
36
37#define DEBUG_TYPE "CallGraph"
38
39STATISTIC(NumObjCCallEdges, "Number of Objective-C method call edges");
40STATISTIC(NumBlockCallEdges, "Number of block call edges");
41
42namespace {
43
44/// A helper class, which walks the AST and locates all the call sites in the
45/// given function body.
46class CGBuilder : public StmtVisitor<CGBuilder> {
47  CallGraph *G;
48  CallGraphNode *CallerNode;
49
50public:
51  CGBuilder(CallGraph *g, CallGraphNode *N) : G(g), CallerNode(N) {}
52
53  void VisitStmt(Stmt *S) { VisitChildren(S); }
54
55  Decl *getDeclFromCall(CallExpr *CE) {
56    if (FunctionDecl *CalleeDecl = CE->getDirectCallee())
57      return CalleeDecl;
58
59    // Simple detection of a call through a block.
60    Expr *CEE = CE->getCallee()->IgnoreParenImpCasts();
61    if (BlockExpr *Block = dyn_cast<BlockExpr>(CEE)) {
62      NumBlockCallEdges++;
63      return Block->getBlockDecl();
64    }
65
66    return nullptr;
67  }
68
69  void addCalledDecl(Decl *D) {
70    if (G->includeInGraph(D)) {
71      CallGraphNode *CalleeNode = G->getOrInsertNode(D);
72      CallerNode->addCallee(CalleeNode);
73    }
74  }
75
76  void VisitCallExpr(CallExpr *CE) {
77    if (Decl *D = getDeclFromCall(CE))
78      addCalledDecl(D);
79    VisitChildren(CE);
80  }
81
82  void VisitLambdaExpr(LambdaExpr *LE) {
83    if (FunctionTemplateDecl *FTD = LE->getDependentCallOperator())
84      for (FunctionDecl *FD : FTD->specializations())
85        G->VisitFunctionDecl(FD);
86    else if (CXXMethodDecl *MD = LE->getCallOperator())
87      G->VisitFunctionDecl(MD);
88  }
89
90  void VisitCXXNewExpr(CXXNewExpr *E) {
91    if (FunctionDecl *FD = E->getOperatorNew())
92      addCalledDecl(FD);
93    VisitChildren(E);
94  }
95
96  void VisitCXXConstructExpr(CXXConstructExpr *E) {
97    CXXConstructorDecl *Ctor = E->getConstructor();
98    if (FunctionDecl *Def = Ctor->getDefinition())
99      addCalledDecl(Def);
100    VisitChildren(E);
101  }
102
103  // Include the evaluation of the default argument.
104  void VisitCXXDefaultArgExpr(CXXDefaultArgExpr *E) {
105    Visit(E->getExpr());
106  }
107
108  // Include the evaluation of the default initializers in a class.
109  void VisitCXXDefaultInitExpr(CXXDefaultInitExpr *E) {
110    Visit(E->getExpr());
111  }
112
113  // Adds may-call edges for the ObjC message sends.
114  void VisitObjCMessageExpr(ObjCMessageExpr *ME) {
115    if (ObjCInterfaceDecl *IDecl = ME->getReceiverInterface()) {
116      Selector Sel = ME->getSelector();
117
118      // Find the callee definition within the same translation unit.
119      Decl *D = nullptr;
120      if (ME->isInstanceMessage())
121        D = IDecl->lookupPrivateMethod(Sel);
122      else
123        D = IDecl->lookupPrivateClassMethod(Sel);
124      if (D) {
125        addCalledDecl(D);
126        NumObjCCallEdges++;
127      }
128    }
129  }
130
131  void VisitChildren(Stmt *S) {
132    for (Stmt *SubStmt : S->children())
133      if (SubStmt)
134        this->Visit(SubStmt);
135  }
136};
137
138} // namespace
139
140void CallGraph::addNodesForBlocks(DeclContext *D) {
141  if (BlockDecl *BD = dyn_cast<BlockDecl>(D))
142    addNodeForDecl(BD, true);
143
144  for (auto *I : D->decls())
145    if (auto *DC = dyn_cast<DeclContext>(I))
146      addNodesForBlocks(DC);
147}
148
149CallGraph::CallGraph() {
150  Root = getOrInsertNode(nullptr);
151}
152
153CallGraph::~CallGraph() = default;
154
155bool CallGraph::includeInGraph(const Decl *D) {
156  assert(D);
157  if (!D->hasBody())
158    return false;
159
160  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
161    // We skip function template definitions, as their semantics is
162    // only determined when they are instantiated.
163    if (FD->isDependentContext())
164      return false;
165
166    IdentifierInfo *II = FD->getIdentifier();
167    if (II && II->getName().startswith("__inline"))
168      return false;
169  }
170
171  return true;
172}
173
174void CallGraph::addNodeForDecl(Decl* D, bool IsGlobal) {
175  assert(D);
176
177  // Allocate a new node, mark it as root, and process its calls.
178  CallGraphNode *Node = getOrInsertNode(D);
179
180  // Process all the calls by this function as well.
181  CGBuilder builder(this, Node);
182  if (Stmt *Body = D->getBody())
183    builder.Visit(Body);
184
185  // Include C++ constructor member initializers.
186  if (auto constructor = dyn_cast<CXXConstructorDecl>(D)) {
187    for (CXXCtorInitializer *init : constructor->inits()) {
188      builder.Visit(init->getInit());
189    }
190  }
191}
192
193CallGraphNode *CallGraph::getNode(const Decl *F) const {
194  FunctionMapTy::const_iterator I = FunctionMap.find(F);
195  if (I == FunctionMap.end()) return nullptr;
196  return I->second.get();
197}
198
199CallGraphNode *CallGraph::getOrInsertNode(Decl *F) {
200  if (F && !isa<ObjCMethodDecl>(F))
201    F = F->getCanonicalDecl();
202
203  std::unique_ptr<CallGraphNode> &Node = FunctionMap[F];
204  if (Node)
205    return Node.get();
206
207  Node = std::make_unique<CallGraphNode>(F);
208  // Make Root node a parent of all functions to make sure all are reachable.
209  if (F)
210    Root->addCallee(Node.get());
211  return Node.get();
212}
213
214void CallGraph::print(raw_ostream &OS) const {
215  OS << " --- Call graph Dump --- \n";
216
217  // We are going to print the graph in reverse post order, partially, to make
218  // sure the output is deterministic.
219  llvm::ReversePostOrderTraversal<const CallGraph *> RPOT(this);
220  for (llvm::ReversePostOrderTraversal<const CallGraph *>::rpo_iterator
221         I = RPOT.begin(), E = RPOT.end(); I != E; ++I) {
222    const CallGraphNode *N = *I;
223
224    OS << "  Function: ";
225    if (N == Root)
226      OS << "< root >";
227    else
228      N->print(OS);
229
230    OS << " calls: ";
231    for (CallGraphNode::const_iterator CI = N->begin(),
232                                       CE = N->end(); CI != CE; ++CI) {
233      assert(*CI != Root && "No one can call the root node.");
234      (*CI)->print(OS);
235      OS << " ";
236    }
237    OS << '\n';
238  }
239  OS.flush();
240}
241
242LLVM_DUMP_METHOD void CallGraph::dump() const {
243  print(llvm::errs());
244}
245
246void CallGraph::viewGraph() const {
247  llvm::ViewGraph(this, "CallGraph");
248}
249
250void CallGraphNode::print(raw_ostream &os) const {
251  if (const NamedDecl *ND = dyn_cast_or_null<NamedDecl>(FD))
252      return ND->printQualifiedName(os);
253  os << "< >";
254}
255
256LLVM_DUMP_METHOD void CallGraphNode::dump() const {
257  print(llvm::errs());
258}
259
260namespace llvm {
261
262template <>
263struct DOTGraphTraits<const CallGraph*> : public DefaultDOTGraphTraits {
264  DOTGraphTraits (bool isSimple = false) : DefaultDOTGraphTraits(isSimple) {}
265
266  static std::string getNodeLabel(const CallGraphNode *Node,
267                                  const CallGraph *CG) {
268    if (CG->getRoot() == Node) {
269      return "< root >";
270    }
271    if (const NamedDecl *ND = dyn_cast_or_null<NamedDecl>(Node->getDecl()))
272      return ND->getNameAsString();
273    else
274      return "< >";
275  }
276};
277
278} // namespace llvm
279