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 // getNodeFor - Return the node for the specified function or create one if it
51 // does not already exist.
53 CallGraphNode *CallGraph::getNodeFor(Function *F) {
54 CallGraphNode *&CGN = FunctionMap[F];
57 assert((!F || F->getParent() == Mod) && "Function not in current module!");
58 return CGN = new CallGraphNode(F);
61 // addToCallGraph - Add a function to the call graph, and link the node to all
62 // of the functions that it calls.
64 void CallGraph::addToCallGraph(Function *M) {
65 CallGraphNode *Node = getNodeFor(M);
67 // If this function has external linkage,
68 if (!M->hasInternalLinkage()) {
69 ExternalNode->addCalledFunction(Node);
71 // Found the entry point?
72 if (M->getName() == "main") {
74 Root = ExternalNode; // Found multiple external mains? Don't pick one.
76 Root = Node; // Found a main, keep track of it!
78 } else if (M->isExternal()) { // Not defined in this xlation unit?
79 Node->addCalledFunction(ExternalNode); // It could call anything...
82 // Loop over all of the users of the function... looking for callers...
84 for (Value::use_iterator I = M->use_begin(), E = M->use_end(); I != E; ++I) {
86 if (CallInst *CI = dyn_cast<CallInst>(U))
87 getNodeFor(CI->getParent()->getParent())->addCalledFunction(Node);
88 else if (InvokeInst *II = dyn_cast<InvokeInst>(U))
89 getNodeFor(II->getParent()->getParent())->addCalledFunction(Node);
90 else // Can't classify the user!
91 ExternalNode->addCalledFunction(Node);
94 // Look for an indirect function call...
95 for (Function::iterator BB = M->begin(), BBE = M->end(); BB != BBE; ++BB)
96 for (BasicBlock::iterator II = BB->begin(), IE = BB->end(); II != IE; ++II){
99 if (CallInst *CI = dyn_cast<CallInst>(&I)) {
100 if (CI->getCalledFunction() == 0)
101 Node->addCalledFunction(ExternalNode);
102 } else if (InvokeInst *II = dyn_cast<InvokeInst>(&I)) {
103 if (II->getCalledFunction() == 0)
104 Node->addCalledFunction(ExternalNode);
109 bool CallGraph::run(Module &M) {
113 ExternalNode = getNodeFor(0);
116 // Add every function to the call graph...
117 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
120 // If we didn't find a main function, use the external call graph node
121 if (Root == 0) Root = ExternalNode;
126 void CallGraph::destroy() {
127 for (FunctionMapTy::iterator I = FunctionMap.begin(), E = FunctionMap.end();
133 static void WriteToOutput(const CallGraphNode *CGN, std::ostream &o) {
134 if (CGN->getFunction())
135 o << "Call graph node for function: '"
136 << CGN->getFunction()->getName() <<"'\n";
138 o << "Call graph node null function:\n";
140 for (unsigned i = 0; i < CGN->size(); ++i)
141 if ((*CGN)[i]->getFunction())
142 o << " Calls function '" << (*CGN)[i]->getFunction()->getName() << "'\n";
144 o << " Calls external node\n";
148 void CallGraph::print(std::ostream &o, const Module *M) const {
149 o << "CallGraph Root is:\n" << getRoot();
151 for (CallGraph::const_iterator I = begin(), E = end(); I != E; ++I)
152 WriteToOutput(I->second, o);
156 //===----------------------------------------------------------------------===//
157 // Implementations of public modification methods
160 // Functions to keep a call graph up to date with a function that has been
163 void CallGraph::addFunctionToModule(Function *Meth) {
164 assert(0 && "not implemented");
168 // removeFunctionFromModule - Unlink the function from this module, returning
169 // it. Because this removes the function from the module, the call graph node
170 // is destroyed. This is only valid if the function does not call any other
171 // functions (ie, there are no edges in it's CGN). The easiest way to do this
172 // is to dropAllReferences before calling this.
174 Function *CallGraph::removeFunctionFromModule(CallGraphNode *CGN) {
175 assert(CGN->CalledFunctions.empty() && "Cannot remove function from call "
176 "graph if it references other functions!");
177 Function *M = CGN->getFunction(); // Get the function for the call graph node
178 delete CGN; // Delete the call graph node for this func
179 FunctionMap.erase(M); // Remove the call graph node from the map
181 Mod->getFunctionList().remove(M);