1 //===- CallGraph.cpp - Build a Module's call graph ------------------------===//
3 // This interface is used to build and manipulate a call graph, which is a very
4 // useful tool for interprocedural optimization.
6 // Every function in a module is represented as a node in the call graph. The
7 // callgraph node keeps track of which functions the are called by the function
8 // corresponding to the node.
10 // A call graph will contain nodes where the function that they correspond to is
11 // null. This 'external' node is used to represent control flow that is not
12 // represented (or analyzable) in the module. As such, the external node will
13 // have edges to functions with the following properties:
14 // 1. All functions in the module without internal linkage, since they could
15 // be called by functions outside of the our analysis capability.
16 // 2. All functions whose address is used for something more than a direct
17 // call, for example being stored into a memory location. Since they may
18 // be called by an unknown caller later, they must be tracked as such.
20 // Similarly, functions have a call edge to the external node iff:
21 // 1. The function is external, reflecting the fact that they could call
22 // anything without internal linkage or that has its address taken.
23 // 2. The function contains an indirect function call.
25 // As an extension in the future, there may be multiple nodes with a null
26 // function. These will be used when we can prove (through pointer analysis)
27 // that an indirect call site can call only a specific set of functions.
29 // Because of these properties, the CallGraph captures a conservative superset
30 // of all of the caller-callee relationships, which is useful for
33 // The CallGraph class also attempts to figure out what the root of the
34 // CallGraph is, which is currently does by looking for a function named 'main'.
35 // If no function named 'main' is found, the external node is used as the entry
36 // node, reflecting the fact that any function without internal linkage could
37 // be called into (which is common for libraries).
39 //===----------------------------------------------------------------------===//
41 #include "llvm/Analysis/CallGraph.h"
42 #include "llvm/Module.h"
43 #include "llvm/iOther.h"
44 #include "llvm/iTerminators.h"
45 #include "Support/STLExtras.h"
48 static RegisterAnalysis<CallGraph> X("callgraph", "Call Graph Construction");
50 AnalysisID CallGraph::ID(AnalysisID::create<CallGraph>());
52 // getNodeFor - Return the node for the specified function or create one if it
53 // does not already exist.
55 CallGraphNode *CallGraph::getNodeFor(Function *F) {
56 CallGraphNode *&CGN = FunctionMap[F];
59 assert((!F || F->getParent() == Mod) && "Function not in current module!");
60 return CGN = new CallGraphNode(F);
63 // addToCallGraph - Add a function to the call graph, and link the node to all
64 // of the functions that it calls.
66 void CallGraph::addToCallGraph(Function *M) {
67 CallGraphNode *Node = getNodeFor(M);
69 // If this function has external linkage,
70 if (!M->hasInternalLinkage()) {
71 ExternalNode->addCalledFunction(Node);
73 // Found the entry point?
74 if (M->getName() == "main") {
76 Root = ExternalNode; // Found multiple external mains? Don't pick one.
78 Root = Node; // Found a main, keep track of it!
80 } else if (M->isExternal()) { // Not defined in this xlation unit?
81 Node->addCalledFunction(ExternalNode); // It could call anything...
84 // Loop over all of the users of the function... looking for callers...
86 for (Value::use_iterator I = M->use_begin(), E = M->use_end(); I != E; ++I) {
88 if (CallInst *CI = dyn_cast<CallInst>(U))
89 getNodeFor(CI->getParent()->getParent())->addCalledFunction(Node);
90 else if (InvokeInst *II = dyn_cast<InvokeInst>(U))
91 getNodeFor(II->getParent()->getParent())->addCalledFunction(Node);
92 else // Can't classify the user!
93 ExternalNode->addCalledFunction(Node);
96 // Look for an indirect function call...
97 for (Function::iterator BB = M->begin(), BBE = M->end(); BB != BBE; ++BB)
98 for (BasicBlock::iterator II = BB->begin(), IE = BB->end(); II != IE; ++II){
101 if (CallInst *CI = dyn_cast<CallInst>(&I)) {
102 if (CI->getCalledFunction() == 0)
103 Node->addCalledFunction(ExternalNode);
104 } else if (InvokeInst *II = dyn_cast<InvokeInst>(&I)) {
105 if (II->getCalledFunction() == 0)
106 Node->addCalledFunction(ExternalNode);
111 bool CallGraph::run(Module &M) {
115 ExternalNode = getNodeFor(0);
118 // Add every function to the call graph...
119 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
122 // If we didn't find a main function, use the external call graph node
123 if (Root == 0) Root = ExternalNode;
128 void CallGraph::destroy() {
129 for (FunctionMapTy::iterator I = FunctionMap.begin(), E = FunctionMap.end();
136 void WriteToOutput(const CallGraphNode *CGN, std::ostream &o) {
137 if (CGN->getFunction())
138 o << "Call graph node for function: '"
139 << CGN->getFunction()->getName() <<"'\n";
141 o << "Call graph node null function:\n";
143 for (unsigned i = 0; i < CGN->size(); ++i)
144 if ((*CGN)[i]->getFunction())
145 o << " Calls function '" << (*CGN)[i]->getFunction()->getName() << "'\n";
147 o << " Calls external node\n";
151 void WriteToOutput(const CallGraph &CG, std::ostream &o) {
152 o << "CallGraph Root is:\n" << CG.getRoot();
154 for (CallGraph::const_iterator I = CG.begin(), E = CG.end(); I != E; ++I)
159 //===----------------------------------------------------------------------===//
160 // Implementations of public modification methods
163 // Functions to keep a call graph up to date with a function that has been
166 void CallGraph::addFunctionToModule(Function *Meth) {
167 assert(0 && "not implemented");
171 // removeFunctionFromModule - Unlink the function from this module, returning
172 // it. Because this removes the function from the module, the call graph node
173 // is destroyed. This is only valid if the function does not call any other
174 // functions (ie, there are no edges in it's CGN). The easiest way to do this
175 // is to dropAllReferences before calling this.
177 Function *CallGraph::removeFunctionFromModule(CallGraphNode *CGN) {
178 assert(CGN->CalledFunctions.empty() && "Cannot remove function from call "
179 "graph if it references other functions!");
180 Function *M = CGN->getFunction(); // Get the function for the call graph node
181 delete CGN; // Delete the call graph node for this func
182 FunctionMap.erase(M); // Remove the call graph node from the map
184 Mod->getFunctionList().remove(M);