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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 (Function::iterator BB = F->begin(), BBE = F->end(); BB != BBE; ++BB)
     84     for (BasicBlock::iterator II = BB->begin(), IE = BB->end(); II != IE;
     85          ++II) {
     86       CallSite CS(cast<Value>(II));
     87       if (CS) {
     88         const Function *Callee = CS.getCalledFunction();
     89         if (!Callee || !Intrinsic::isLeaf(Callee->getIntrinsicID()))
     90           // Indirect calls of intrinsics are not allowed so no need to check.
     91           // We can be more precise here by using TargetArg returned by
     92           // Intrinsic::isLeaf.
     93           Node->addCalledFunction(CS, CallsExternalNode.get());
     94         else if (!Callee->isIntrinsic())
     95           Node->addCalledFunction(CS, getOrInsertFunction(Callee));
     96       }
     97     }
     98 }
     99 
    100 void CallGraph::print(raw_ostream &OS) const {
    101   OS << "CallGraph Root is: ";
    102   if (Function *F = Root->getFunction())
    103     OS << F->getName() << "\n";
    104   else {
    105     OS << "<<null function: 0x" << Root << ">>\n";
    106   }
    107 
    108   // Print in a deterministic order by sorting CallGraphNodes by name.  We do
    109   // this here to avoid slowing down the non-printing fast path.
    110 
    111   SmallVector<CallGraphNode *, 16> Nodes;
    112   Nodes.reserve(FunctionMap.size());
    113 
    114   for (auto I = begin(), E = end(); I != E; ++I)
    115     Nodes.push_back(I->second.get());
    116 
    117   std::sort(Nodes.begin(), Nodes.end(),
    118             [](CallGraphNode *LHS, CallGraphNode *RHS) {
    119     if (Function *LF = LHS->getFunction())
    120       if (Function *RF = RHS->getFunction())
    121         return LF->getName() < RF->getName();
    122 
    123     return RHS->getFunction() != nullptr;
    124   });
    125 
    126   for (CallGraphNode *CN : Nodes)
    127     CN->print(OS);
    128 }
    129 
    130 LLVM_DUMP_METHOD
    131 void CallGraph::dump() const { print(dbgs()); }
    132 
    133 // removeFunctionFromModule - Unlink the function from this module, returning
    134 // it.  Because this removes the function from the module, the call graph node
    135 // is destroyed.  This is only valid if the function does not call any other
    136 // functions (ie, there are no edges in it's CGN).  The easiest way to do this
    137 // is to dropAllReferences before calling this.
    138 //
    139 Function *CallGraph::removeFunctionFromModule(CallGraphNode *CGN) {
    140   assert(CGN->empty() && "Cannot remove function from call "
    141          "graph if it references other functions!");
    142   Function *F = CGN->getFunction(); // Get the function for the call graph node
    143   FunctionMap.erase(F);             // Remove the call graph node from the map
    144 
    145   M.getFunctionList().remove(F);
    146   return F;
    147 }
    148 
    149 /// spliceFunction - Replace the function represented by this node by another.
    150 /// This does not rescan the body of the function, so it is suitable when
    151 /// splicing the body of the old function to the new while also updating all
    152 /// callers from old to new.
    153 ///
    154 void CallGraph::spliceFunction(const Function *From, const Function *To) {
    155   assert(FunctionMap.count(From) && "No CallGraphNode for function!");
    156   assert(!FunctionMap.count(To) &&
    157          "Pointing CallGraphNode at a function that already exists");
    158   FunctionMapTy::iterator I = FunctionMap.find(From);
    159   I->second->F = const_cast<Function*>(To);
    160   FunctionMap[To] = std::move(I->second);
    161   FunctionMap.erase(I);
    162 }
    163 
    164 // getOrInsertFunction - This method is identical to calling operator[], but
    165 // it will insert a new CallGraphNode for the specified function if one does
    166 // not already exist.
    167 CallGraphNode *CallGraph::getOrInsertFunction(const Function *F) {
    168   auto &CGN = FunctionMap[F];
    169   if (CGN)
    170     return CGN.get();
    171 
    172   assert((!F || F->getParent() == &M) && "Function not in current module!");
    173   CGN = llvm::make_unique<CallGraphNode>(const_cast<Function *>(F));
    174   return CGN.get();
    175 }
    176 
    177 //===----------------------------------------------------------------------===//
    178 // Implementations of the CallGraphNode class methods.
    179 //
    180 
    181 void CallGraphNode::print(raw_ostream &OS) const {
    182   if (Function *F = getFunction())
    183     OS << "Call graph node for function: '" << F->getName() << "'";
    184   else
    185     OS << "Call graph node <<null function>>";
    186 
    187   OS << "<<" << this << ">>  #uses=" << getNumReferences() << '\n';
    188 
    189   for (const_iterator I = begin(), E = end(); I != E; ++I) {
    190     OS << "  CS<" << I->first << "> calls ";
    191     if (Function *FI = I->second->getFunction())
    192       OS << "function '" << FI->getName() <<"'\n";
    193     else
    194       OS << "external node\n";
    195   }
    196   OS << '\n';
    197 }
    198 
    199 LLVM_DUMP_METHOD
    200 void CallGraphNode::dump() const { print(dbgs()); }
    201 
    202 /// removeCallEdgeFor - This method removes the edge in the node for the
    203 /// specified call site.  Note that this method takes linear time, so it
    204 /// should be used sparingly.
    205 void CallGraphNode::removeCallEdgeFor(CallSite CS) {
    206   for (CalledFunctionsVector::iterator I = CalledFunctions.begin(); ; ++I) {
    207     assert(I != CalledFunctions.end() && "Cannot find callsite to remove!");
    208     if (I->first == CS.getInstruction()) {
    209       I->second->DropRef();
    210       *I = CalledFunctions.back();
    211       CalledFunctions.pop_back();
    212       return;
    213     }
    214   }
    215 }
    216 
    217 // removeAnyCallEdgeTo - This method removes any call edges from this node to
    218 // the specified callee function.  This takes more time to execute than
    219 // removeCallEdgeTo, so it should not be used unless necessary.
    220 void CallGraphNode::removeAnyCallEdgeTo(CallGraphNode *Callee) {
    221   for (unsigned i = 0, e = CalledFunctions.size(); i != e; ++i)
    222     if (CalledFunctions[i].second == Callee) {
    223       Callee->DropRef();
    224       CalledFunctions[i] = CalledFunctions.back();
    225       CalledFunctions.pop_back();
    226       --i; --e;
    227     }
    228 }
    229 
    230 /// removeOneAbstractEdgeTo - Remove one edge associated with a null callsite
    231 /// from this node to the specified callee function.
    232 void CallGraphNode::removeOneAbstractEdgeTo(CallGraphNode *Callee) {
    233   for (CalledFunctionsVector::iterator I = CalledFunctions.begin(); ; ++I) {
    234     assert(I != CalledFunctions.end() && "Cannot find callee to remove!");
    235     CallRecord &CR = *I;
    236     if (CR.second == Callee && CR.first == nullptr) {
    237       Callee->DropRef();
    238       *I = CalledFunctions.back();
    239       CalledFunctions.pop_back();
    240       return;
    241     }
    242   }
    243 }
    244 
    245 /// replaceCallEdge - This method replaces the edge in the node for the
    246 /// specified call site with a new one.  Note that this method takes linear
    247 /// time, so it should be used sparingly.
    248 void CallGraphNode::replaceCallEdge(CallSite CS,
    249                                     CallSite NewCS, CallGraphNode *NewNode){
    250   for (CalledFunctionsVector::iterator I = CalledFunctions.begin(); ; ++I) {
    251     assert(I != CalledFunctions.end() && "Cannot find callsite to remove!");
    252     if (I->first == CS.getInstruction()) {
    253       I->second->DropRef();
    254       I->first = NewCS.getInstruction();
    255       I->second = NewNode;
    256       NewNode->AddRef();
    257       return;
    258     }
    259   }
    260 }
    261 
    262 //===----------------------------------------------------------------------===//
    263 // Out-of-line definitions of CallGraphAnalysis class members.
    264 //
    265 
    266 char CallGraphAnalysis::PassID;
    267 
    268 //===----------------------------------------------------------------------===//
    269 // Implementations of the CallGraphWrapperPass class methods.
    270 //
    271 
    272 CallGraphWrapperPass::CallGraphWrapperPass() : ModulePass(ID) {
    273   initializeCallGraphWrapperPassPass(*PassRegistry::getPassRegistry());
    274 }
    275 
    276 CallGraphWrapperPass::~CallGraphWrapperPass() {}
    277 
    278 void CallGraphWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
    279   AU.setPreservesAll();
    280 }
    281 
    282 bool CallGraphWrapperPass::runOnModule(Module &M) {
    283   // All the real work is done in the constructor for the CallGraph.
    284   G.reset(new CallGraph(M));
    285   return false;
    286 }
    287 
    288 INITIALIZE_PASS(CallGraphWrapperPass, "basiccg", "CallGraph Construction",
    289                 false, true)
    290 
    291 char CallGraphWrapperPass::ID = 0;
    292 
    293 void CallGraphWrapperPass::releaseMemory() { G.reset(); }
    294 
    295 void CallGraphWrapperPass::print(raw_ostream &OS, const Module *) const {
    296   if (!G) {
    297     OS << "No call graph has been built!\n";
    298     return;
    299   }
    300 
    301   // Just delegate.
    302   G->print(OS);
    303 }
    304 
    305 LLVM_DUMP_METHOD
    306 void CallGraphWrapperPass::dump() const { print(dbgs(), nullptr); }
    307