1 //===- Steensgaard.cpp - Context Insensitive Alias Analysis ---------------===//
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 pass uses the data structure graphs to implement a simple context
11 // insensitive alias analysis. It does this by computing the local analysis
12 // graphs for all of the functions, then merging them together into a single big
13 // graph without cloning.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Analysis/DataStructure/DataStructure.h"
18 #include "llvm/Analysis/DataStructure/DSGraph.h"
19 #include "llvm/Analysis/AliasAnalysis.h"
20 #include "llvm/Analysis/Passes.h"
21 #include "llvm/Module.h"
22 #include "llvm/Support/Debug.h"
27 class Steens : public ModulePass, public AliasAnalysis {
30 EquivalenceClasses<GlobalValue*> GlobalECs; // Always empty
32 Steens() : ResultGraph(0) {}
35 assert(ResultGraph == 0 && "releaseMemory not called?");
38 //------------------------------------------------
39 // Implement the Pass API
42 // run - Build up the result graph, representing the pointer graph for the
45 bool runOnModule(Module &M);
47 virtual void releaseMyMemory() { delete ResultGraph; ResultGraph = 0; }
49 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
50 AliasAnalysis::getAnalysisUsage(AU);
51 AU.setPreservesAll(); // Does not transform code...
52 AU.addRequired<LocalDataStructures>(); // Uses local dsgraph
55 // print - Implement the Pass::print method...
56 void print(std::ostream &O, const Module *M) const {
57 assert(ResultGraph && "Result graph has not yet been computed!");
58 ResultGraph->writeGraphToFile(O, "steensgaards");
61 //------------------------------------------------
62 // Implement the AliasAnalysis API
65 AliasResult alias(const Value *V1, unsigned V1Size,
66 const Value *V2, unsigned V2Size);
68 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
71 void ResolveFunctionCall(Function *F, const DSCallSite &Call,
72 DSNodeHandle &RetVal);
75 // Register the pass...
76 RegisterOpt<Steens> X("steens-aa",
77 "Steensgaard's alias analysis (DSGraph based)");
79 // Register as an implementation of AliasAnalysis
80 RegisterAnalysisGroup<AliasAnalysis, Steens> Y;
83 ModulePass *llvm::createSteensgaardPass() { return new Steens(); }
85 /// ResolveFunctionCall - Resolve the actual arguments of a call to function F
86 /// with the specified call site descriptor. This function links the arguments
87 /// and the return value for the call site context-insensitively.
89 void Steens::ResolveFunctionCall(Function *F, const DSCallSite &Call,
90 DSNodeHandle &RetVal) {
91 assert(ResultGraph != 0 && "Result graph not allocated!");
92 DSGraph::ScalarMapTy &ValMap = ResultGraph->getScalarMap();
94 // Handle the return value of the function...
95 if (Call.getRetVal().getNode() && RetVal.getNode())
96 RetVal.mergeWith(Call.getRetVal());
98 // Loop over all pointer arguments, resolving them to their provided pointers
99 unsigned PtrArgIdx = 0;
100 for (Function::arg_iterator AI = F->arg_begin(), AE = F->arg_end();
101 AI != AE && PtrArgIdx < Call.getNumPtrArgs(); ++AI) {
102 DSGraph::ScalarMapTy::iterator I = ValMap.find(AI);
103 if (I != ValMap.end()) // If its a pointer argument...
104 I->second.mergeWith(Call.getPtrArg(PtrArgIdx++));
109 /// run - Build up the result graph, representing the pointer graph for the
112 bool Steens::runOnModule(Module &M) {
113 InitializeAliasAnalysis(this);
114 assert(ResultGraph == 0 && "Result graph already allocated!");
115 LocalDataStructures &LDS = getAnalysis<LocalDataStructures>();
117 // Create a new, empty, graph...
118 ResultGraph = new DSGraph(GlobalECs, getTargetData());
119 ResultGraph->spliceFrom(LDS.getGlobalsGraph());
121 // Loop over the rest of the module, merging graphs for non-external functions
124 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
125 if (!I->isExternal())
126 ResultGraph->spliceFrom(LDS.getDSGraph(*I));
128 ResultGraph->removeTriviallyDeadNodes();
130 // FIXME: Must recalculate and use the Incomplete markers!!
132 // Now that we have all of the graphs inlined, we can go about eliminating
135 std::list<DSCallSite> &Calls = ResultGraph->getAuxFunctionCalls();
136 assert(Calls.empty() && "Aux call list is already in use??");
138 // Start with a copy of the original call sites.
139 Calls = ResultGraph->getFunctionCalls();
141 for (std::list<DSCallSite>::iterator CI = Calls.begin(), E = Calls.end();
143 DSCallSite &CurCall = *CI++;
145 // Loop over the called functions, eliminating as many as possible...
146 std::vector<Function*> CallTargets;
147 if (CurCall.isDirectCall())
148 CallTargets.push_back(CurCall.getCalleeFunc());
150 CurCall.getCalleeNode()->addFullFunctionList(CallTargets);
152 for (unsigned c = 0; c != CallTargets.size(); ) {
153 // If we can eliminate this function call, do so!
154 Function *F = CallTargets[c];
155 if (!F->isExternal()) {
156 ResolveFunctionCall(F, CurCall, ResultGraph->getReturnNodes()[F]);
157 CallTargets[c] = CallTargets.back();
158 CallTargets.pop_back();
160 ++c; // Cannot eliminate this call, skip over it...
163 if (CallTargets.empty()) { // Eliminated all calls?
164 std::list<DSCallSite>::iterator I = CI;
165 Calls.erase(--I); // Remove entry
169 // Remove our knowledge of what the return values of the functions are, except
170 // for functions that are externally visible from this module (e.g. main). We
171 // keep these functions so that their arguments are marked incomplete.
172 for (DSGraph::ReturnNodesTy::iterator I =
173 ResultGraph->getReturnNodes().begin(),
174 E = ResultGraph->getReturnNodes().end(); I != E; )
175 if (I->first->hasInternalLinkage())
176 ResultGraph->getReturnNodes().erase(I++);
180 // Update the "incomplete" markers on the nodes, ignoring unknownness due to
181 // incoming arguments...
182 ResultGraph->maskIncompleteMarkers();
183 ResultGraph->markIncompleteNodes(DSGraph::IgnoreGlobals |
184 DSGraph::MarkFormalArgs);
186 // Remove any nodes that are dead after all of the merging we have done...
187 // FIXME: We should be able to disable the globals graph for steens!
188 //ResultGraph->removeDeadNodes(DSGraph::KeepUnreachableGlobals);
190 DEBUG(print(std::cerr, &M));
194 AliasAnalysis::AliasResult Steens::alias(const Value *V1, unsigned V1Size,
195 const Value *V2, unsigned V2Size) {
196 assert(ResultGraph && "Result graph has not been computed yet!");
198 DSGraph::ScalarMapTy &GSM = ResultGraph->getScalarMap();
200 DSGraph::ScalarMapTy::iterator I = GSM.find(const_cast<Value*>(V1));
201 DSGraph::ScalarMapTy::iterator J = GSM.find(const_cast<Value*>(V2));
202 if (I != GSM.end() && !I->second.isNull() &&
203 J != GSM.end() && !J->second.isNull()) {
204 DSNodeHandle &V1H = I->second;
205 DSNodeHandle &V2H = J->second;
207 // If at least one of the nodes is complete, we can say something about
208 // this. If one is complete and the other isn't, then they are obviously
209 // different nodes. If they are both complete, we can't say anything
211 if (I->second.getNode()->isComplete() ||
212 J->second.getNode()->isComplete()) {
213 // If the two pointers point to different data structure graph nodes, they
215 if (V1H.getNode() != V2H.getNode())
218 // See if they point to different offsets... if so, we may be able to
219 // determine that they do not alias...
220 unsigned O1 = I->second.getOffset(), O2 = J->second.getOffset();
222 if (O2 < O1) { // Ensure that O1 <= O2
225 std::swap(V1Size, V2Size);
234 // If we cannot determine alias properties based on our graph, fall back on
235 // some other AA implementation.
237 return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
240 AliasAnalysis::ModRefResult
241 Steens::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
242 AliasAnalysis::ModRefResult Result = ModRef;
244 // Find the node in question.
245 DSGraph::ScalarMapTy &GSM = ResultGraph->getScalarMap();
246 DSGraph::ScalarMapTy::iterator I = GSM.find(P);
248 if (I != GSM.end() && !I->second.isNull()) {
249 DSNode *N = I->second.getNode();
250 if (N->isComplete()) {
251 // If this is a direct call to an external function, and if the pointer
252 // points to a complete node, the external function cannot modify or read
253 // the value (we know it's not passed out of the program!).
254 if (Function *F = CS.getCalledFunction())
258 // Otherwise, if the node is complete, but it is only M or R, return this.
259 // This can be useful for globals that should be marked const but are not.
260 if (!N->isModified())
261 Result = (ModRefResult)(Result & ~Mod);
263 Result = (ModRefResult)(Result & ~Ref);
267 return (ModRefResult)(Result & AliasAnalysis::getModRefInfo(CS, P, Size));