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"
26 class Steens : public ModulePass, public AliasAnalysis {
28 DSGraph *GlobalsGraph; // FIXME: Eliminate globals graph stuff from DNE
30 EquivalenceClasses<GlobalValue*> GlobalECs; // Always empty
32 Steens() : ResultGraph(0), GlobalsGraph(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 // alias - This is the only method here that does anything interesting...
66 AliasResult alias(const Value *V1, unsigned V1Size,
67 const Value *V2, unsigned V2Size);
70 void ResolveFunctionCall(Function *F, const DSCallSite &Call,
71 DSNodeHandle &RetVal);
74 // Register the pass...
75 RegisterOpt<Steens> X("steens-aa",
76 "Steensgaard's alias analysis (DSGraph based)");
78 // Register as an implementation of AliasAnalysis
79 RegisterAnalysisGroup<AliasAnalysis, Steens> Y;
82 ModulePass *llvm::createSteensgaardPass() { return new Steens(); }
84 /// ResolveFunctionCall - Resolve the actual arguments of a call to function F
85 /// with the specified call site descriptor. This function links the arguments
86 /// and the return value for the call site context-insensitively.
88 void Steens::ResolveFunctionCall(Function *F, const DSCallSite &Call,
89 DSNodeHandle &RetVal) {
90 assert(ResultGraph != 0 && "Result graph not allocated!");
91 DSGraph::ScalarMapTy &ValMap = ResultGraph->getScalarMap();
93 // Handle the return value of the function...
94 if (Call.getRetVal().getNode() && RetVal.getNode())
95 RetVal.mergeWith(Call.getRetVal());
97 // Loop over all pointer arguments, resolving them to their provided pointers
98 unsigned PtrArgIdx = 0;
99 for (Function::arg_iterator AI = F->arg_begin(), AE = F->arg_end();
100 AI != AE && PtrArgIdx < Call.getNumPtrArgs(); ++AI) {
101 DSGraph::ScalarMapTy::iterator I = ValMap.find(AI);
102 if (I != ValMap.end()) // If its a pointer argument...
103 I->second.mergeWith(Call.getPtrArg(PtrArgIdx++));
108 /// run - Build up the result graph, representing the pointer graph for the
111 bool Steens::runOnModule(Module &M) {
112 InitializeAliasAnalysis(this);
113 assert(ResultGraph == 0 && "Result graph already allocated!");
114 LocalDataStructures &LDS = getAnalysis<LocalDataStructures>();
116 // Create a new, empty, graph...
117 ResultGraph = new DSGraph(GlobalECs, getTargetData());
118 GlobalsGraph = new DSGraph(GlobalECs, getTargetData());
119 ResultGraph->setGlobalsGraph(GlobalsGraph);
120 ResultGraph->setPrintAuxCalls();
122 // RetValMap - Keep track of the return values for all functions that return
125 DSGraph::ReturnNodesTy RetValMap;
127 // Loop over the rest of the module, merging graphs for non-external functions
130 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
131 if (!I->isExternal()) {
132 DSGraph::NodeMapTy NodeMap;
133 ResultGraph->cloneInto(LDS.getDSGraph(*I), RetValMap, NodeMap, 0);
136 ResultGraph->removeTriviallyDeadNodes();
138 // FIXME: Must recalculate and use the Incomplete markers!!
140 // Now that we have all of the graphs inlined, we can go about eliminating
143 std::list<DSCallSite> &Calls = ResultGraph->getAuxFunctionCalls();
144 assert(Calls.empty() && "Aux call list is already in use??");
146 // Start with a copy of the original call sites.
147 Calls = ResultGraph->getFunctionCalls();
149 for (std::list<DSCallSite>::iterator CI = Calls.begin(), E = Calls.end();
151 DSCallSite &CurCall = *CI++;
153 // Loop over the called functions, eliminating as many as possible...
154 std::vector<Function*> CallTargets;
155 if (CurCall.isDirectCall())
156 CallTargets.push_back(CurCall.getCalleeFunc());
158 CurCall.getCalleeNode()->addFullFunctionList(CallTargets);
160 for (unsigned c = 0; c != CallTargets.size(); ) {
161 // If we can eliminate this function call, do so!
162 Function *F = CallTargets[c];
163 if (!F->isExternal()) {
164 ResolveFunctionCall(F, CurCall, RetValMap[F]);
165 CallTargets[c] = CallTargets.back();
166 CallTargets.pop_back();
168 ++c; // Cannot eliminate this call, skip over it...
171 if (CallTargets.empty()) { // Eliminated all calls?
172 std::list<DSCallSite>::iterator I = CI;
173 Calls.erase(--I); // Remove entry
179 // Update the "incomplete" markers on the nodes, ignoring unknownness due to
180 // incoming arguments...
181 ResultGraph->maskIncompleteMarkers();
182 ResultGraph->markIncompleteNodes(DSGraph::IgnoreFormalArgs);
184 // Remove any nodes that are dead after all of the merging we have done...
185 // FIXME: We should be able to disable the globals graph for steens!
186 ResultGraph->removeDeadNodes(DSGraph::KeepUnreachableGlobals);
188 DEBUG(print(std::cerr, &M));
192 // alias - This is the only method here that does anything interesting...
193 AliasAnalysis::AliasResult Steens::alias(const Value *V1, unsigned V1Size,
194 const Value *V2, unsigned V2Size) {
195 // FIXME: HANDLE Size argument!
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 if (I != GSM.end() && I->second.getNode()) {
202 DSNodeHandle &V1H = I->second;
203 DSGraph::ScalarMapTy::iterator J=GSM.find(const_cast<Value*>(V2));
204 if (J != GSM.end() && J->second.getNode()) {
205 DSNodeHandle &V2H = J->second;
206 // If the two pointers point to different data structure graph nodes, they
208 if (V1H.getNode() != V2H.getNode()) // FIXME: Handle incompleteness!
211 // FIXME: If the two pointers point to the same node, and the offsets are
212 // different, and the LinkIndex vector doesn't alias the section, then the
213 // two pointers do not alias. We need access size information for the two
219 // If we cannot determine alias properties based on our graph, fall back on
220 // some other AA implementation.
222 return AliasAnalysis::alias(V1, V1Size, V2, V2Size);