1 //===- CallGraph.cpp - Build a Module's call graph ------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This interface is used to build and manipulate a call graph, which is a very
11 // useful tool for interprocedural optimization.
13 // Every function in a module is represented as a node in the call graph. The
14 // callgraph node keeps track of which functions the are called by the function
15 // corresponding to the node.
17 // A call graph will contain nodes where the function that they correspond to is
18 // null. This 'external' node is used to represent control flow that is not
19 // represented (or analyzable) in the module. As such, the external node will
20 // have edges to functions with the following properties:
21 // 1. All functions in the module without internal linkage, since they could
22 // be called by functions outside of the our analysis capability.
23 // 2. All functions whose address is used for something more than a direct
24 // call, for example being stored into a memory location. Since they may
25 // be called by an unknown caller later, they must be tracked as such.
27 // Similarly, functions have a call edge to the external node iff:
28 // 1. The function is external, reflecting the fact that they could call
29 // anything without internal linkage or that has its address taken.
30 // 2. The function contains an indirect function call.
32 // As an extension in the future, there may be multiple nodes with a null
33 // function. These will be used when we can prove (through pointer analysis)
34 // that an indirect call site can call only a specific set of functions.
36 // Because of these properties, the CallGraph captures a conservative superset
37 // of all of the caller-callee relationships, which is useful for
40 // The CallGraph class also attempts to figure out what the root of the
41 // CallGraph is, which is currently does by looking for a function named 'main'.
42 // If no function named 'main' is found, the external node is used as the entry
43 // node, reflecting the fact that any function without internal linkage could
44 // be called into (which is common for libraries).
46 //===----------------------------------------------------------------------===//
48 #include "llvm/Analysis/CallGraph.h"
49 #include "llvm/Module.h"
50 #include "llvm/iOther.h"
51 #include "llvm/iTerminators.h"
52 #include "Support/STLExtras.h"
55 static RegisterAnalysis<CallGraph> X("callgraph", "Call Graph Construction");
57 // getNodeFor - Return the node for the specified function or create one if it
58 // does not already exist.
60 CallGraphNode *CallGraph::getNodeFor(Function *F) {
61 CallGraphNode *&CGN = FunctionMap[F];
64 assert((!F || F->getParent() == Mod) && "Function not in current module!");
65 return CGN = new CallGraphNode(F);
68 // addToCallGraph - Add a function to the call graph, and link the node to all
69 // of the functions that it calls.
71 void CallGraph::addToCallGraph(Function *F) {
72 CallGraphNode *Node = getNodeFor(F);
74 // If this function has external linkage, anything could call it...
75 if (!F->hasInternalLinkage()) {
76 ExternalNode->addCalledFunction(Node);
78 // Found the entry point?
79 if (F->getName() == "main") {
81 Root = ExternalNode; // Found multiple external mains? Don't pick one.
83 Root = Node; // Found a main, keep track of it!
87 // If this function is not defined in this translation unit, it could call
90 Node->addCalledFunction(ExternalNode);
92 // Loop over all of the users of the function... looking for callers...
94 for (Value::use_iterator I = F->use_begin(), E = F->use_end(); I != E; ++I) {
96 if (CallInst *CI = dyn_cast<CallInst>(U))
97 getNodeFor(CI->getParent()->getParent())->addCalledFunction(Node);
98 else if (InvokeInst *II = dyn_cast<InvokeInst>(U))
99 getNodeFor(II->getParent()->getParent())->addCalledFunction(Node);
100 else // Can't classify the user!
101 ExternalNode->addCalledFunction(Node);
104 // Look for an indirect function call...
105 for (Function::iterator BB = F->begin(), BBE = F->end(); BB != BBE; ++BB)
106 for (BasicBlock::iterator II = BB->begin(), IE = BB->end(); II != IE; ++II){
107 Instruction &I = *II;
109 if (CallInst *CI = dyn_cast<CallInst>(&I)) {
110 if (CI->getCalledFunction() == 0)
111 Node->addCalledFunction(ExternalNode);
112 } else if (InvokeInst *II = dyn_cast<InvokeInst>(&I)) {
113 if (II->getCalledFunction() == 0)
114 Node->addCalledFunction(ExternalNode);
119 bool CallGraph::run(Module &M) {
123 ExternalNode = getNodeFor(0);
126 // Add every function to the call graph...
127 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
130 // If we didn't find a main function, use the external call graph node
131 if (Root == 0) Root = ExternalNode;
136 void CallGraph::destroy() {
137 for (FunctionMapTy::iterator I = FunctionMap.begin(), E = FunctionMap.end();
143 static void WriteToOutput(const CallGraphNode *CGN, std::ostream &o) {
144 if (CGN->getFunction())
145 o << "Call graph node for function: '"
146 << CGN->getFunction()->getName() <<"'\n";
148 o << "Call graph node <<null function: 0x" << CGN << ">>:\n";
150 for (unsigned i = 0; i < CGN->size(); ++i)
151 if ((*CGN)[i]->getFunction())
152 o << " Calls function '" << (*CGN)[i]->getFunction()->getName() << "'\n";
154 o << " Calls external node\n";
158 void CallGraph::print(std::ostream &o, const Module *M) const {
159 o << "CallGraph Root is: ";
160 if (getRoot()->getFunction())
161 o << getRoot()->getFunction()->getName() << "\n";
163 o << "<<null function: 0x" << getRoot() << ">>\n";
165 for (CallGraph::const_iterator I = begin(), E = end(); I != E; ++I)
166 WriteToOutput(I->second, o);
170 //===----------------------------------------------------------------------===//
171 // Implementations of public modification methods
174 // Functions to keep a call graph up to date with a function that has been
177 void CallGraph::addFunctionToModule(Function *Meth) {
178 assert(0 && "not implemented");
182 // removeFunctionFromModule - Unlink the function from this module, returning
183 // it. Because this removes the function from the module, the call graph node
184 // is destroyed. This is only valid if the function does not call any other
185 // functions (ie, there are no edges in it's CGN). The easiest way to do this
186 // is to dropAllReferences before calling this.
188 Function *CallGraph::removeFunctionFromModule(CallGraphNode *CGN) {
189 assert(CGN->CalledFunctions.empty() && "Cannot remove function from call "
190 "graph if it references other functions!");
191 Function *F = CGN->getFunction(); // Get the function for the call graph node
192 delete CGN; // Delete the call graph node for this func
193 FunctionMap.erase(F); // Remove the call graph node from the map
195 Mod->getFunctionList().remove(F);