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
72 // Standard IO functions
131 "exp", "sqrt", "cbrt", "hypot",
132 "log", "log10", "pow",
134 "asin", "acos", "atan", "atan2",
143 // gettext functions used by libstdc++
158 /// ExternalFunctionDoesntCallIntoProgram - This hack is used to indicate to the
159 /// call graph that the specified external function is _KNOWN_ to not call back
160 /// into the program. This is important, because otherwise functions which call
161 /// "printf" for example, end up in a great big SCC that goes from the function
164 static bool ExternalFunctionDoesntCallIntoProgram(const std::string &Name) {
165 static std::vector<std::string> Funcs;
167 // First time this is called?
169 // Add a whole bunch of functions which are often used...
170 Funcs.insert(Funcs.end(), KnownExternalFunctions,
171 KnownExternalFunctions+
172 sizeof(KnownExternalFunctions)/sizeof(KnownExternalFunctions[0]));
173 // Sort the list for efficient access
174 std::sort(Funcs.begin(), Funcs.end());
177 if (Name.size() > 7 && !memcmp("__llvm_", Name.c_str(), 7))
180 // Binary search for the function name...
181 std::vector<std::string>::iterator I =
182 std::lower_bound(Funcs.begin(), Funcs.end(), Name);
185 return I != Funcs.end() && *I == Name;
190 // getNodeFor - Return the node for the specified function or create one if it
191 // does not already exist.
193 CallGraphNode *CallGraph::getNodeFor(Function *F) {
194 CallGraphNode *&CGN = FunctionMap[F];
197 assert((!F || F->getParent() == Mod) && "Function not in current module!");
198 return CGN = new CallGraphNode(F);
201 static bool isOnlyADirectCall(Function *F, CallSite CS) {
202 if (!CS.getInstruction()) return false;
203 for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); I != E; ++I)
204 if (*I == F) return false;
208 // addToCallGraph - Add a function to the call graph, and link the node to all
209 // of the functions that it calls.
211 void CallGraph::addToCallGraph(Function *F) {
212 CallGraphNode *Node = getNodeFor(F);
214 // If this function has external linkage, anything could call it...
215 if (!F->hasInternalLinkage()) {
216 ExternalNode->addCalledFunction(Node);
218 // Found the entry point?
219 if (F->getName() == "main") {
221 Root = ExternalNode; // Found multiple external mains? Don't pick one.
223 Root = Node; // Found a main, keep track of it!
227 // If this function is not defined in this translation unit, it could call
229 if (F->isExternal() && !F->getIntrinsicID() &&
230 !ExternalFunctionDoesntCallIntoProgram(F->getName()))
231 Node->addCalledFunction(ExternalNode);
233 // Loop over all of the users of the function... looking for callers...
235 bool isUsedExternally = false;
236 for (Value::use_iterator I = F->use_begin(), E = F->use_end(); I != E; ++I) {
237 if (Instruction *Inst = dyn_cast<Instruction>(*I)) {
238 if (isOnlyADirectCall(F, CallSite::get(Inst)))
239 getNodeFor(Inst->getParent()->getParent())->addCalledFunction(Node);
241 isUsedExternally = true;
242 } else if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(*I)) {
243 // THIS IS A DISGUSTING HACK. Brought to you by the power of
244 // ConstantPointerRefs!
245 for (Value::use_iterator I = CPR->use_begin(), E = CPR->use_end();
247 if (Instruction *Inst = dyn_cast<Instruction>(*I)) {
248 if (isOnlyADirectCall(F, CallSite::get(Inst)))
249 getNodeFor(Inst->getParent()->getParent())->addCalledFunction(Node);
251 isUsedExternally = true;
253 isUsedExternally = true;
255 } else { // Can't classify the user!
256 isUsedExternally = true;
259 if (isUsedExternally)
260 ExternalNode->addCalledFunction(Node);
262 // Look for an indirect function call...
263 for (Function::iterator BB = F->begin(), BBE = F->end(); BB != BBE; ++BB)
264 for (BasicBlock::iterator II = BB->begin(), IE = BB->end(); II != IE; ++II){
265 CallSite CS = CallSite::get(II);
266 if (CS.getInstruction() && !CS.getCalledFunction())
267 Node->addCalledFunction(ExternalNode);
271 bool CallGraph::run(Module &M) {
275 ExternalNode = getNodeFor(0);
278 // Add every function to the call graph...
279 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
282 // If we didn't find a main function, use the external call graph node
283 if (Root == 0) Root = ExternalNode;
288 void CallGraph::destroy() {
289 for (FunctionMapTy::iterator I = FunctionMap.begin(), E = FunctionMap.end();
295 static void WriteToOutput(const CallGraphNode *CGN, std::ostream &o) {
296 if (CGN->getFunction())
297 o << "Call graph node for function: '"
298 << CGN->getFunction()->getName() <<"'\n";
300 o << "Call graph node <<null function: 0x" << CGN << ">>:\n";
302 for (unsigned i = 0; i < CGN->size(); ++i)
303 if ((*CGN)[i]->getFunction())
304 o << " Calls function '" << (*CGN)[i]->getFunction()->getName() << "'\n";
306 o << " Calls external node\n";
310 void CallGraph::print(std::ostream &o, const Module *M) const {
311 o << "CallGraph Root is: ";
312 if (getRoot()->getFunction())
313 o << getRoot()->getFunction()->getName() << "\n";
315 o << "<<null function: 0x" << getRoot() << ">>\n";
317 for (CallGraph::const_iterator I = begin(), E = end(); I != E; ++I)
318 WriteToOutput(I->second, o);
322 //===----------------------------------------------------------------------===//
323 // Implementations of public modification methods
326 // Functions to keep a call graph up to date with a function that has been
329 void CallGraph::addFunctionToModule(Function *Meth) {
330 assert(0 && "not implemented");
334 // removeFunctionFromModule - Unlink the function from this module, returning
335 // it. Because this removes the function from the module, the call graph node
336 // is destroyed. This is only valid if the function does not call any other
337 // functions (ie, there are no edges in it's CGN). The easiest way to do this
338 // is to dropAllReferences before calling this.
340 Function *CallGraph::removeFunctionFromModule(CallGraphNode *CGN) {
341 assert(CGN->CalledFunctions.empty() && "Cannot remove function from call "
342 "graph if it references other functions!");
343 Function *F = CGN->getFunction(); // Get the function for the call graph node
344 delete CGN; // Delete the call graph node for this func
345 FunctionMap.erase(F); // Remove the call graph node from the map
347 Mod->getFunctionList().remove(F);
351 void CallGraph::stub() {}