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/Constants.h" // Remove when ConstantPointerRefs are gone
50 #include "llvm/Module.h"
51 #include "llvm/iOther.h"
52 #include "llvm/iTerminators.h"
53 #include "llvm/Support/CallSite.h"
54 #include "Support/STLExtras.h"
56 static RegisterAnalysis<CallGraph> X("callgraph", "Call Graph Construction");
58 static const char * const KnownExternalFunctions[] = {
59 // Low-level system calls
68 // Low-level stdc library functions
73 // Standard IO functions
136 // gettext functions used by libstdc++
149 /// ExternalFunctionDoesntCallIntoProgram - This hack is used to indicate to the
150 /// call graph that the specified external function is _KNOWN_ to not call back
151 /// into the program. This is important, because otherwise functions which call
152 /// "printf" for example, end up in a great big SCC that goes from the function
155 static bool ExternalFunctionDoesntCallIntoProgram(const std::string &Name) {
156 static std::vector<std::string> Funcs;
158 // First time this is called?
160 // Add a whole bunch of functions which are often used...
161 Funcs.insert(Funcs.end(), KnownExternalFunctions,
162 KnownExternalFunctions+
163 sizeof(KnownExternalFunctions)/sizeof(KnownExternalFunctions[0]));
164 // Sort the list for efficient access
165 std::sort(Funcs.begin(), Funcs.end());
168 // Binary search for the function name...
169 std::vector<std::string>::iterator I =
170 std::lower_bound(Funcs.begin(), Funcs.end(), Name);
173 return I != Funcs.end() && *I == Name;
178 // getNodeFor - Return the node for the specified function or create one if it
179 // does not already exist.
181 CallGraphNode *CallGraph::getNodeFor(Function *F) {
182 CallGraphNode *&CGN = FunctionMap[F];
185 assert((!F || F->getParent() == Mod) && "Function not in current module!");
186 return CGN = new CallGraphNode(F);
189 static bool isOnlyADirectCall(Function *F, CallSite CS) {
190 if (!CS.getInstruction()) return false;
191 for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); I != E; ++I)
192 if (*I == F) return false;
196 // addToCallGraph - Add a function to the call graph, and link the node to all
197 // of the functions that it calls.
199 void CallGraph::addToCallGraph(Function *F) {
200 CallGraphNode *Node = getNodeFor(F);
202 // If this function has external linkage, anything could call it...
203 if (!F->hasInternalLinkage()) {
204 ExternalNode->addCalledFunction(Node);
206 // Found the entry point?
207 if (F->getName() == "main") {
209 Root = ExternalNode; // Found multiple external mains? Don't pick one.
211 Root = Node; // Found a main, keep track of it!
215 // If this function is not defined in this translation unit, it could call
217 if (F->isExternal() && !F->getIntrinsicID() &&
218 !ExternalFunctionDoesntCallIntoProgram(F->getName()))
219 Node->addCalledFunction(ExternalNode);
221 // Loop over all of the users of the function... looking for callers...
223 bool isUsedExternally = false;
224 for (Value::use_iterator I = F->use_begin(), E = F->use_end(); I != E; ++I) {
225 if (Instruction *Inst = dyn_cast<Instruction>(*I)) {
226 if (isOnlyADirectCall(F, CallSite::get(Inst)))
227 getNodeFor(Inst->getParent()->getParent())->addCalledFunction(Node);
229 isUsedExternally = true;
230 } else if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(*I)) {
231 // THIS IS A DISGUSTING HACK. Brought to you by the power of
232 // ConstantPointerRefs!
233 for (Value::use_iterator I = CPR->use_begin(), E = CPR->use_end();
235 if (Instruction *Inst = dyn_cast<Instruction>(*I)) {
236 if (isOnlyADirectCall(F, CallSite::get(Inst)))
237 getNodeFor(Inst->getParent()->getParent())->addCalledFunction(Node);
239 isUsedExternally = true;
241 isUsedExternally = true;
243 } else { // Can't classify the user!
244 isUsedExternally = true;
247 if (isUsedExternally)
248 ExternalNode->addCalledFunction(Node);
250 // Look for an indirect function call...
251 for (Function::iterator BB = F->begin(), BBE = F->end(); BB != BBE; ++BB)
252 for (BasicBlock::iterator II = BB->begin(), IE = BB->end(); II != IE; ++II){
253 CallSite CS = CallSite::get(II);
254 if (CS.getInstruction() && !CS.getCalledFunction())
255 Node->addCalledFunction(ExternalNode);
259 bool CallGraph::run(Module &M) {
263 ExternalNode = getNodeFor(0);
266 // Add every function to the call graph...
267 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
270 // If we didn't find a main function, use the external call graph node
271 if (Root == 0) Root = ExternalNode;
276 void CallGraph::destroy() {
277 for (FunctionMapTy::iterator I = FunctionMap.begin(), E = FunctionMap.end();
283 static void WriteToOutput(const CallGraphNode *CGN, std::ostream &o) {
284 if (CGN->getFunction())
285 o << "Call graph node for function: '"
286 << CGN->getFunction()->getName() <<"'\n";
288 o << "Call graph node <<null function: 0x" << CGN << ">>:\n";
290 for (unsigned i = 0; i < CGN->size(); ++i)
291 if ((*CGN)[i]->getFunction())
292 o << " Calls function '" << (*CGN)[i]->getFunction()->getName() << "'\n";
294 o << " Calls external node\n";
298 void CallGraph::print(std::ostream &o, const Module *M) const {
299 o << "CallGraph Root is: ";
300 if (getRoot()->getFunction())
301 o << getRoot()->getFunction()->getName() << "\n";
303 o << "<<null function: 0x" << getRoot() << ">>\n";
305 for (CallGraph::const_iterator I = begin(), E = end(); I != E; ++I)
306 WriteToOutput(I->second, o);
310 //===----------------------------------------------------------------------===//
311 // Implementations of public modification methods
314 // Functions to keep a call graph up to date with a function that has been
317 void CallGraph::addFunctionToModule(Function *Meth) {
318 assert(0 && "not implemented");
322 // removeFunctionFromModule - Unlink the function from this module, returning
323 // it. Because this removes the function from the module, the call graph node
324 // is destroyed. This is only valid if the function does not call any other
325 // functions (ie, there are no edges in it's CGN). The easiest way to do this
326 // is to dropAllReferences before calling this.
328 Function *CallGraph::removeFunctionFromModule(CallGraphNode *CGN) {
329 assert(CGN->CalledFunctions.empty() && "Cannot remove function from call "
330 "graph if it references other functions!");
331 Function *F = CGN->getFunction(); // Get the function for the call graph node
332 delete CGN; // Delete the call graph node for this func
333 FunctionMap.erase(F); // Remove the call graph node from the map
335 Mod->getFunctionList().remove(F);
339 void CallGraph::stub() {}