llvm-project

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//===- CallGraph.cpp - AST-based Call graph -------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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//  This file defines the AST-based CallGraph.
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//
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//===----------------------------------------------------------------------===//
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#include "clang/Analysis/CallGraph.h"
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#include "clang/AST/Decl.h"
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#include "clang/AST/DeclBase.h"
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#include "clang/AST/DeclObjC.h"
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#include "clang/AST/Expr.h"
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#include "clang/AST/ExprObjC.h"
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#include "clang/AST/Stmt.h"
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#include "clang/AST/StmtVisitor.h"
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#include "clang/Basic/IdentifierTable.h"
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#include "clang/Basic/LLVM.h"
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#include "llvm/ADT/PostOrderIterator.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/DOTGraphTraits.h"
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#include "llvm/Support/GraphWriter.h"
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#include "llvm/Support/raw_ostream.h"
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#include <cassert>
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#include <memory>
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#include <string>
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using namespace clang;
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#define DEBUG_TYPE "CallGraph"
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STATISTIC(NumObjCCallEdges, "Number of Objective-C method call edges");
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STATISTIC(NumBlockCallEdges, "Number of block call edges");
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namespace {
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/// A helper class, which walks the AST and locates all the call sites in the
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/// given function body.
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class CGBuilder : public StmtVisitor<CGBuilder> {
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  CallGraph *G;
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  CallGraphNode *CallerNode;
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public:
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  CGBuilder(CallGraph *g, CallGraphNode *N) : G(g), CallerNode(N) {}
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  void VisitStmt(Stmt *S) { VisitChildren(S); }
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  Decl *getDeclFromCall(CallExpr *CE) {
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    if (FunctionDecl *CalleeDecl = CE->getDirectCallee())
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      return CalleeDecl;
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    // Simple detection of a call through a block.
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    Expr *CEE = CE->getCallee()->IgnoreParenImpCasts();
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    if (BlockExpr *Block = dyn_cast<BlockExpr>(CEE)) {
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      NumBlockCallEdges++;
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      return Block->getBlockDecl();
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    }
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    return nullptr;
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  }
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  void addCalledDecl(Decl *D, Expr *CallExpr) {
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    if (G->includeCalleeInGraph(D)) {
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      CallGraphNode *CalleeNode = G->getOrInsertNode(D);
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      CallerNode->addCallee({CalleeNode, CallExpr});
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    }
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  }
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  void VisitCallExpr(CallExpr *CE) {
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    if (Decl *D = getDeclFromCall(CE))
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      addCalledDecl(D, CE);
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    VisitChildren(CE);
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  }
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  void VisitLambdaExpr(LambdaExpr *LE) {
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    if (FunctionTemplateDecl *FTD = LE->getDependentCallOperator())
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      for (FunctionDecl *FD : FTD->specializations())
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        G->VisitFunctionDecl(FD);
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    else if (CXXMethodDecl *MD = LE->getCallOperator())
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      G->VisitFunctionDecl(MD);
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  }
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  void VisitCXXNewExpr(CXXNewExpr *E) {
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    if (FunctionDecl *FD = E->getOperatorNew())
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      addCalledDecl(FD, E);
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    VisitChildren(E);
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  }
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  void VisitCXXConstructExpr(CXXConstructExpr *E) {
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    CXXConstructorDecl *Ctor = E->getConstructor();
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    if (FunctionDecl *Def = Ctor->getDefinition())
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      addCalledDecl(Def, E);
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    VisitChildren(E);
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  }
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  // Include the evaluation of the default argument.
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  void VisitCXXDefaultArgExpr(CXXDefaultArgExpr *E) {
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    Visit(E->getExpr());
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  }
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  // Include the evaluation of the default initializers in a class.
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  void VisitCXXDefaultInitExpr(CXXDefaultInitExpr *E) {
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    Visit(E->getExpr());
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  }
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  // Adds may-call edges for the ObjC message sends.
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  void VisitObjCMessageExpr(ObjCMessageExpr *ME) {
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    if (ObjCInterfaceDecl *IDecl = ME->getReceiverInterface()) {
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      Selector Sel = ME->getSelector();
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      // Find the callee definition within the same translation unit.
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      Decl *D = nullptr;
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      if (ME->isInstanceMessage())
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        D = IDecl->lookupPrivateMethod(Sel);
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      else
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        D = IDecl->lookupPrivateClassMethod(Sel);
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      if (D) {
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        addCalledDecl(D, ME);
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        NumObjCCallEdges++;
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      }
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    }
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  }
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  void VisitChildren(Stmt *S) {
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    for (Stmt *SubStmt : S->children())
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      if (SubStmt)
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        this->Visit(SubStmt);
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  }
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};
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} // namespace
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void CallGraph::addNodesForBlocks(DeclContext *D) {
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  if (BlockDecl *BD = dyn_cast<BlockDecl>(D))
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    addNodeForDecl(BD, true);
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  for (auto *I : D->decls())
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    if (auto *DC = dyn_cast<DeclContext>(I))
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      addNodesForBlocks(DC);
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}
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CallGraph::CallGraph() {
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  Root = getOrInsertNode(nullptr);
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}
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CallGraph::~CallGraph() = default;
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bool CallGraph::includeInGraph(const Decl *D) {
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  assert(D);
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  if (!D->hasBody())
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    return false;
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  return includeCalleeInGraph(D);
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}
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bool CallGraph::includeCalleeInGraph(const Decl *D) {
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  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
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    // We skip function template definitions, as their semantics is
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    // only determined when they are instantiated.
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    if (FD->isDependentContext())
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      return false;
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    IdentifierInfo *II = FD->getIdentifier();
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    if (II && II->getName().starts_with("__inline"))
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      return false;
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  }
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  return true;
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}
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void CallGraph::addNodeForDecl(Decl* D, bool IsGlobal) {
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  assert(D);
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  // Allocate a new node, mark it as root, and process its calls.
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  CallGraphNode *Node = getOrInsertNode(D);
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  // Process all the calls by this function as well.
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  CGBuilder builder(this, Node);
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  if (Stmt *Body = D->getBody())
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    builder.Visit(Body);
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  // Include C++ constructor member initializers.
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  if (auto constructor = dyn_cast<CXXConstructorDecl>(D)) {
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    for (CXXCtorInitializer *init : constructor->inits()) {
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      builder.Visit(init->getInit());
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    }
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  }
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}
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CallGraphNode *CallGraph::getNode(const Decl *F) const {
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  FunctionMapTy::const_iterator I = FunctionMap.find(F);
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  if (I == FunctionMap.end()) return nullptr;
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  return I->second.get();
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}
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CallGraphNode *CallGraph::getOrInsertNode(Decl *F) {
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  if (F && !isa<ObjCMethodDecl>(F))
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    F = F->getCanonicalDecl();
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  std::unique_ptr<CallGraphNode> &Node = FunctionMap[F];
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  if (Node)
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    return Node.get();
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  Node = std::make_unique<CallGraphNode>(F);
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  // Make Root node a parent of all functions to make sure all are reachable.
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  if (F)
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    Root->addCallee({Node.get(), /*Call=*/nullptr});
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  return Node.get();
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}
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void CallGraph::print(raw_ostream &OS) const {
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  OS << " --- Call graph Dump --- \n";
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  // We are going to print the graph in reverse post order, partially, to make
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  // sure the output is deterministic.
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  llvm::ReversePostOrderTraversal<const CallGraph *> RPOT(this);
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  for (llvm::ReversePostOrderTraversal<const CallGraph *>::rpo_iterator
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         I = RPOT.begin(), E = RPOT.end(); I != E; ++I) {
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    const CallGraphNode *N = *I;
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    OS << "  Function: ";
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    if (N == Root)
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      OS << "< root >";
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    else
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      N->print(OS);
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    OS << " calls: ";
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    for (CallGraphNode::const_iterator CI = N->begin(),
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                                       CE = N->end(); CI != CE; ++CI) {
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      assert(CI->Callee != Root && "No one can call the root node.");
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      CI->Callee->print(OS);
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      OS << " ";
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    }
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    OS << '\n';
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  }
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  OS.flush();
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}
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LLVM_DUMP_METHOD void CallGraph::dump() const {
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  print(llvm::errs());
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}
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void CallGraph::viewGraph() const {
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  llvm::ViewGraph(this, "CallGraph");
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}
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void CallGraphNode::print(raw_ostream &os) const {
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  if (const NamedDecl *ND = dyn_cast_or_null<NamedDecl>(FD))
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      return ND->printQualifiedName(os);
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  os << "< >";
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}
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LLVM_DUMP_METHOD void CallGraphNode::dump() const {
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  print(llvm::errs());
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}
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namespace llvm {
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template <>
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struct DOTGraphTraits<const CallGraph*> : public DefaultDOTGraphTraits {
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  DOTGraphTraits (bool isSimple = false) : DefaultDOTGraphTraits(isSimple) {}
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  static std::string getNodeLabel(const CallGraphNode *Node,
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                                  const CallGraph *CG) {
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    if (CG->getRoot() == Node) {
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      return "< root >";
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    }
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    if (const NamedDecl *ND = dyn_cast_or_null<NamedDecl>(Node->getDecl()))
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      return ND->getNameAsString();
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    else
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      return "< >";
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  }
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};
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} // namespace llvm
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