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      1 //===- CallGraph.cpp - Build a Module's call graph ------------------------===//
      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 #include "llvm/Analysis/CallGraph.h"
     11 #include "llvm/IR/CallSite.h"
     12 #include "llvm/IR/Instructions.h"
     13 #include "llvm/IR/IntrinsicInst.h"
     14 #include "llvm/IR/Module.h"
     15 #include "llvm/Support/Debug.h"
     16 #include "llvm/Support/raw_ostream.h"
     17 using namespace llvm;
     18 
     19 //===----------------------------------------------------------------------===//
     20 // Implementations of the CallGraph class methods.
     21 //
     22 
     23 CallGraph::CallGraph(Module &M)
     24     : M(M), Root(nullptr), ExternalCallingNode(getOrInsertFunction(nullptr)),
     25       CallsExternalNode(llvm::make_unique<CallGraphNode>(nullptr)) {
     26   // Add every function to the call graph.
     27   for (Function &F : M)
     28     addToCallGraph(&F);
     29 
     30   // If we didn't find a main function, use the external call graph node
     31   if (!Root)
     32     Root = ExternalCallingNode;
     33 }
     34 
     35 CallGraph::CallGraph(CallGraph &&Arg)
     36     : M(Arg.M), FunctionMap(std::move(Arg.FunctionMap)), Root(Arg.Root),
     37       ExternalCallingNode(Arg.ExternalCallingNode),
     38       CallsExternalNode(std::move(Arg.CallsExternalNode)) {
     39   Arg.FunctionMap.clear();
     40   Arg.Root = nullptr;
     41   Arg.ExternalCallingNode = nullptr;
     42 }
     43 
     44 CallGraph::~CallGraph() {
     45   // CallsExternalNode is not in the function map, delete it explicitly.
     46   if (CallsExternalNode)
     47     CallsExternalNode->allReferencesDropped();
     48 
     49 // Reset all node's use counts to zero before deleting them to prevent an
     50 // assertion from firing.
     51 #ifndef NDEBUG
     52   for (auto &I : FunctionMap)
     53     I.second->allReferencesDropped();
     54 #endif
     55 }
     56 
     57 void CallGraph::addToCallGraph(Function *F) {
     58   CallGraphNode *Node = getOrInsertFunction(F);
     59 
     60   // If this function has external linkage, anything could call it.
     61   if (!F->hasLocalLinkage()) {
     62     ExternalCallingNode->addCalledFunction(CallSite(), Node);
     63 
     64     // Found the entry point?
     65     if (F->getName() == "main") {
     66       if (Root) // Found multiple external mains?  Don't pick one.
     67         Root = ExternalCallingNode;
     68       else
     69         Root = Node; // Found a main, keep track of it!
     70     }
     71   }
     72 
     73   // If this function has its address taken, anything could call it.
     74   if (F->hasAddressTaken())
     75     ExternalCallingNode->addCalledFunction(CallSite(), Node);
     76 
     77   // If this function is not defined in this translation unit, it could call
     78   // anything.
     79   if (F->isDeclaration() && !F->isIntrinsic())
     80     Node->addCalledFunction(CallSite(), CallsExternalNode.get());
     81 
     82   // Look for calls by this function.
     83   for (BasicBlock &BB : *F)
     84     for (Instruction &I : BB) {
     85       if (auto CS = CallSite(&I)) {
     86         const Function *Callee = CS.getCalledFunction();
     87         if (!Callee || !Intrinsic::isLeaf(Callee->getIntrinsicID()))
     88           // Indirect calls of intrinsics are not allowed so no need to check.
     89           // We can be more precise here by using TargetArg returned by
     90           // Intrinsic::isLeaf.
     91           Node->addCalledFunction(CS, CallsExternalNode.get());
     92         else if (!Callee->isIntrinsic())
     93           Node->addCalledFunction(CS, getOrInsertFunction(Callee));
     94       }
     95     }
     96 }
     97 
     98 void CallGraph::print(raw_ostream &OS) const {
     99   OS << "CallGraph Root is: ";
    100   if (Function *F = Root->getFunction())
    101     OS << F->getName() << "\n";
    102   else {
    103     OS << "<<null function: 0x" << Root << ">>\n";
    104   }
    105 
    106   // Print in a deterministic order by sorting CallGraphNodes by name.  We do
    107   // this here to avoid slowing down the non-printing fast path.
    108 
    109   SmallVector<CallGraphNode *, 16> Nodes;
    110   Nodes.reserve(FunctionMap.size());
    111 
    112   for (const auto &I : *this)
    113     Nodes.push_back(I.second.get());
    114 
    115   std::sort(Nodes.begin(), Nodes.end(),
    116             [](CallGraphNode *LHS, CallGraphNode *RHS) {
    117     if (Function *LF = LHS->getFunction())
    118       if (Function *RF = RHS->getFunction())
    119         return LF->getName() < RF->getName();
    120 
    121     return RHS->getFunction() != nullptr;
    122   });
    123 
    124   for (CallGraphNode *CN : Nodes)
    125     CN->print(OS);
    126 }
    127 
    128 LLVM_DUMP_METHOD
    129 void CallGraph::dump() const { print(dbgs()); }
    130 
    131 // removeFunctionFromModule - Unlink the function from this module, returning
    132 // it.  Because this removes the function from the module, the call graph node
    133 // is destroyed.  This is only valid if the function does not call any other
    134 // functions (ie, there are no edges in it's CGN).  The easiest way to do this
    135 // is to dropAllReferences before calling this.
    136 //
    137 Function *CallGraph::removeFunctionFromModule(CallGraphNode *CGN) {
    138   assert(CGN->empty() && "Cannot remove function from call "
    139          "graph if it references other functions!");
    140   Function *F = CGN->getFunction(); // Get the function for the call graph node
    141   FunctionMap.erase(F);             // Remove the call graph node from the map
    142 
    143   M.getFunctionList().remove(F);
    144   return F;
    145 }
    146 
    147 /// spliceFunction - Replace the function represented by this node by another.
    148 /// This does not rescan the body of the function, so it is suitable when
    149 /// splicing the body of the old function to the new while also updating all
    150 /// callers from old to new.
    151 ///
    152 void CallGraph::spliceFunction(const Function *From, const Function *To) {
    153   assert(FunctionMap.count(From) && "No CallGraphNode for function!");
    154   assert(!FunctionMap.count(To) &&
    155          "Pointing CallGraphNode at a function that already exists");
    156   FunctionMapTy::iterator I = FunctionMap.find(From);
    157   I->second->F = const_cast<Function*>(To);
    158   FunctionMap[To] = std::move(I->second);
    159   FunctionMap.erase(I);
    160 }
    161 
    162 // getOrInsertFunction - This method is identical to calling operator[], but
    163 // it will insert a new CallGraphNode for the specified function if one does
    164 // not already exist.
    165 CallGraphNode *CallGraph::getOrInsertFunction(const Function *F) {
    166   auto &CGN = FunctionMap[F];
    167   if (CGN)
    168     return CGN.get();
    169 
    170   assert((!F || F->getParent() == &M) && "Function not in current module!");
    171   CGN = llvm::make_unique<CallGraphNode>(const_cast<Function *>(F));
    172   return CGN.get();
    173 }
    174 
    175 //===----------------------------------------------------------------------===//
    176 // Implementations of the CallGraphNode class methods.
    177 //
    178 
    179 void CallGraphNode::print(raw_ostream &OS) const {
    180   if (Function *F = getFunction())
    181     OS << "Call graph node for function: '" << F->getName() << "'";
    182   else
    183     OS << "Call graph node <<null function>>";
    184 
    185   OS << "<<" << this << ">>  #uses=" << getNumReferences() << '\n';
    186 
    187   for (const auto &I : *this) {
    188     OS << "  CS<" << I.first << "> calls ";
    189     if (Function *FI = I.second->getFunction())
    190       OS << "function '" << FI->getName() <<"'\n";
    191     else
    192       OS << "external node\n";
    193   }
    194   OS << '\n';
    195 }
    196 
    197 LLVM_DUMP_METHOD
    198 void CallGraphNode::dump() const { print(dbgs()); }
    199 
    200 /// removeCallEdgeFor - This method removes the edge in the node for the
    201 /// specified call site.  Note that this method takes linear time, so it
    202 /// should be used sparingly.
    203 void CallGraphNode::removeCallEdgeFor(CallSite CS) {
    204   for (CalledFunctionsVector::iterator I = CalledFunctions.begin(); ; ++I) {
    205     assert(I != CalledFunctions.end() && "Cannot find callsite to remove!");
    206     if (I->first == CS.getInstruction()) {
    207       I->second->DropRef();
    208       *I = CalledFunctions.back();
    209       CalledFunctions.pop_back();
    210       return;
    211     }
    212   }
    213 }
    214 
    215 // removeAnyCallEdgeTo - This method removes any call edges from this node to
    216 // the specified callee function.  This takes more time to execute than
    217 // removeCallEdgeTo, so it should not be used unless necessary.
    218 void CallGraphNode::removeAnyCallEdgeTo(CallGraphNode *Callee) {
    219   for (unsigned i = 0, e = CalledFunctions.size(); i != e; ++i)
    220     if (CalledFunctions[i].second == Callee) {
    221       Callee->DropRef();
    222       CalledFunctions[i] = CalledFunctions.back();
    223       CalledFunctions.pop_back();
    224       --i; --e;
    225     }
    226 }
    227 
    228 /// removeOneAbstractEdgeTo - Remove one edge associated with a null callsite
    229 /// from this node to the specified callee function.
    230 void CallGraphNode::removeOneAbstractEdgeTo(CallGraphNode *Callee) {
    231   for (CalledFunctionsVector::iterator I = CalledFunctions.begin(); ; ++I) {
    232     assert(I != CalledFunctions.end() && "Cannot find callee to remove!");
    233     CallRecord &CR = *I;
    234     if (CR.second == Callee && CR.first == nullptr) {
    235       Callee->DropRef();
    236       *I = CalledFunctions.back();
    237       CalledFunctions.pop_back();
    238       return;
    239     }
    240   }
    241 }
    242 
    243 /// replaceCallEdge - This method replaces the edge in the node for the
    244 /// specified call site with a new one.  Note that this method takes linear
    245 /// time, so it should be used sparingly.
    246 void CallGraphNode::replaceCallEdge(CallSite CS,
    247                                     CallSite NewCS, CallGraphNode *NewNode){
    248   for (CalledFunctionsVector::iterator I = CalledFunctions.begin(); ; ++I) {
    249     assert(I != CalledFunctions.end() && "Cannot find callsite to remove!");
    250     if (I->first == CS.getInstruction()) {
    251       I->second->DropRef();
    252       I->first = NewCS.getInstruction();
    253       I->second = NewNode;
    254       NewNode->AddRef();
    255       return;
    256     }
    257   }
    258 }
    259 
    260 // Provide an explicit template instantiation for the static ID.
    261 char CallGraphAnalysis::PassID;
    262 
    263 PreservedAnalyses CallGraphPrinterPass::run(Module &M,
    264                                             AnalysisManager<Module> &AM) {
    265   AM.getResult<CallGraphAnalysis>(M).print(OS);
    266   return PreservedAnalyses::all();
    267 }
    268 
    269 //===----------------------------------------------------------------------===//
    270 // Out-of-line definitions of CallGraphAnalysis class members.
    271 //
    272 
    273 //===----------------------------------------------------------------------===//
    274 // Implementations of the CallGraphWrapperPass class methods.
    275 //
    276 
    277 CallGraphWrapperPass::CallGraphWrapperPass() : ModulePass(ID) {
    278   initializeCallGraphWrapperPassPass(*PassRegistry::getPassRegistry());
    279 }
    280 
    281 CallGraphWrapperPass::~CallGraphWrapperPass() {}
    282 
    283 void CallGraphWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
    284   AU.setPreservesAll();
    285 }
    286 
    287 bool CallGraphWrapperPass::runOnModule(Module &M) {
    288   // All the real work is done in the constructor for the CallGraph.
    289   G.reset(new CallGraph(M));
    290   return false;
    291 }
    292 
    293 INITIALIZE_PASS(CallGraphWrapperPass, "basiccg", "CallGraph Construction",
    294                 false, true)
    295 
    296 char CallGraphWrapperPass::ID = 0;
    297 
    298 void CallGraphWrapperPass::releaseMemory() { G.reset(); }
    299 
    300 void CallGraphWrapperPass::print(raw_ostream &OS, const Module *) const {
    301   if (!G) {
    302     OS << "No call graph has been built!\n";
    303     return;
    304   }
    305 
    306   // Just delegate.
    307   G->print(OS);
    308 }
    309 
    310 LLVM_DUMP_METHOD
    311 void CallGraphWrapperPass::dump() const { print(dbgs(), nullptr); }
    312 
    313 namespace {
    314 struct CallGraphPrinterLegacyPass : public ModulePass {
    315   static char ID; // Pass ID, replacement for typeid
    316   CallGraphPrinterLegacyPass() : ModulePass(ID) {
    317     initializeCallGraphPrinterLegacyPassPass(*PassRegistry::getPassRegistry());
    318   }
    319 
    320   void getAnalysisUsage(AnalysisUsage &AU) const override {
    321     AU.setPreservesAll();
    322     AU.addRequiredTransitive<CallGraphWrapperPass>();
    323   }
    324   bool runOnModule(Module &M) override {
    325     getAnalysis<CallGraphWrapperPass>().print(errs(), &M);
    326     return false;
    327   }
    328 };
    329 }
    330 
    331 char CallGraphPrinterLegacyPass::ID = 0;
    332 
    333 INITIALIZE_PASS_BEGIN(CallGraphPrinterLegacyPass, "print-callgraph",
    334                       "Print a call graph", true, true)
    335 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
    336 INITIALIZE_PASS_END(CallGraphPrinterLegacyPass, "print-callgraph",
    337                     "Print a call graph", true, true)
    338