1 //===- Steensgaard.cpp - Context Insensitive Alias Analysis ---------------===//
3 // This pass uses the data structure graphs to implement a simple context
4 // insensitive alias analysis. It does this by computing the local analysis
5 // graphs for all of the functions, then merging them together into a single big
6 // graph without cloning.
8 //===----------------------------------------------------------------------===//
10 #include "llvm/Analysis/DataStructure.h"
11 #include "llvm/Analysis/DSGraph.h"
12 #include "llvm/Analysis/AliasAnalysis.h"
13 #include "llvm/Module.h"
14 #include "Support/Statistic.h"
17 class Steens : public Pass, public AliasAnalysis {
19 DSGraph *GlobalsGraph; // FIXME: Eliminate globals graph stuff from DNE
21 Steens() : ResultGraph(0), GlobalsGraph(0) {}
24 assert(ResultGraph == 0 && "releaseMemory not called?");
27 //------------------------------------------------
28 // Implement the Pass API
31 // run - Build up the result graph, representing the pointer graph for the
36 virtual void releaseMyMemory() { delete ResultGraph; ResultGraph = 0; }
38 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
39 AliasAnalysis::getAnalysisUsage(AU);
40 AU.setPreservesAll(); // Does not transform code...
41 AU.addRequired<LocalDataStructures>(); // Uses local dsgraph
42 AU.addRequired<AliasAnalysis>(); // Chains to another AA impl...
45 // print - Implement the Pass::print method...
46 void print(std::ostream &O, const Module *M) const {
47 assert(ResultGraph && "Result graph has not yet been computed!");
48 ResultGraph->writeGraphToFile(O, "steensgaards");
51 //------------------------------------------------
52 // Implement the AliasAnalysis API
55 // alias - This is the only method here that does anything interesting...
56 AliasResult alias(const Value *V1, unsigned V1Size,
57 const Value *V2, unsigned V2Size);
60 void ResolveFunctionCall(Function *F, const DSCallSite &Call,
61 DSNodeHandle &RetVal);
64 // Register the pass...
65 RegisterOpt<Steens> X("steens-aa",
66 "Steensgaard's alias analysis (DSGraph based)");
68 // Register as an implementation of AliasAnalysis
69 RegisterAnalysisGroup<AliasAnalysis, Steens> Y;
73 /// ResolveFunctionCall - Resolve the actual arguments of a call to function F
74 /// with the specified call site descriptor. This function links the arguments
75 /// and the return value for the call site context-insensitively.
77 void Steens::ResolveFunctionCall(Function *F, const DSCallSite &Call,
78 DSNodeHandle &RetVal) {
79 assert(ResultGraph != 0 && "Result graph not allocated!");
80 hash_map<Value*, DSNodeHandle> &ValMap = ResultGraph->getScalarMap();
82 // Handle the return value of the function...
83 if (Call.getRetVal().getNode() && RetVal.getNode())
84 RetVal.mergeWith(Call.getRetVal());
86 // Loop over all pointer arguments, resolving them to their provided pointers
87 unsigned PtrArgIdx = 0;
88 for (Function::aiterator AI = F->abegin(), AE = F->aend();
89 AI != AE && PtrArgIdx < Call.getNumPtrArgs(); ++AI) {
90 hash_map<Value*, DSNodeHandle>::iterator I = ValMap.find(AI);
91 if (I != ValMap.end()) // If its a pointer argument...
92 I->second.mergeWith(Call.getPtrArg(PtrArgIdx++));
97 /// run - Build up the result graph, representing the pointer graph for the
100 bool Steens::run(Module &M) {
101 InitializeAliasAnalysis(this);
102 assert(ResultGraph == 0 && "Result graph already allocated!");
103 LocalDataStructures &LDS = getAnalysis<LocalDataStructures>();
105 // Create a new, empty, graph...
106 ResultGraph = new DSGraph();
107 GlobalsGraph = new DSGraph();
108 ResultGraph->setGlobalsGraph(GlobalsGraph);
109 ResultGraph->setPrintAuxCalls();
111 // RetValMap - Keep track of the return values for all functions that return
114 hash_map<Function*, DSNodeHandle> RetValMap;
116 // Loop over the rest of the module, merging graphs for non-external functions
120 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
121 if (!I->isExternal()) {
122 hash_map<Value*, DSNodeHandle> ValMap;
123 { // Scope to free NodeMap memory ASAP
124 hash_map<const DSNode*, DSNodeHandle> NodeMap;
125 const DSGraph &FDSG = LDS.getDSGraph(*I);
126 DSNodeHandle RetNode = ResultGraph->cloneInto(FDSG, ValMap, NodeMap);
128 // Keep track of the return node of the function's graph if it returns a
131 if (RetNode.getNode())
132 RetValMap[I] = RetNode;
135 // Incorporate the inlined Function's ScalarMap into the global
137 hash_map<Value*, DSNodeHandle> &GVM = ResultGraph->getScalarMap();
138 for (hash_map<Value*, DSNodeHandle>::iterator I = ValMap.begin(),
139 E = ValMap.end(); I != E; ++I)
140 GVM[I->first].mergeWith(I->second);
142 if ((++Count & 1) == 0) // Prune nodes out every other time...
143 ResultGraph->removeTriviallyDeadNodes();
146 // FIXME: Must recalculate and use the Incomplete markers!!
148 // Now that we have all of the graphs inlined, we can go about eliminating
151 std::vector<DSCallSite> &Calls =
152 ResultGraph->getAuxFunctionCalls();
153 assert(Calls.empty() && "Aux call list is already in use??");
155 // Start with a copy of the original call sites...
156 Calls = ResultGraph->getFunctionCalls();
158 for (unsigned i = 0; i != Calls.size(); ) {
159 DSCallSite &CurCall = Calls[i];
161 // Loop over the called functions, eliminating as many as possible...
162 std::vector<GlobalValue*> CallTargets;
163 if (CurCall.isDirectCall())
164 CallTargets.push_back(CurCall.getCalleeFunc());
166 CallTargets = CurCall.getCalleeNode()->getGlobals();
168 for (unsigned c = 0; c != CallTargets.size(); ) {
169 // If we can eliminate this function call, do so!
170 bool Eliminated = false;
171 if (Function *F = dyn_cast<Function>(CallTargets[c]))
172 if (!F->isExternal()) {
173 ResolveFunctionCall(F, CurCall, RetValMap[F]);
177 CallTargets[c] = CallTargets.back();
178 CallTargets.pop_back();
180 ++c; // Cannot eliminate this call, skip over it...
183 if (CallTargets.empty()) { // Eliminated all calls?
184 CurCall = Calls.back(); // Remove entry
187 ++i; // Skip this call site...
192 // Update the "incomplete" markers on the nodes, ignoring unknownness due to
193 // incoming arguments...
194 ResultGraph->maskIncompleteMarkers();
195 ResultGraph->markIncompleteNodes(DSGraph::IgnoreFormalArgs);
197 // Remove any nodes that are dead after all of the merging we have done...
198 // FIXME: We should be able to disable the globals graph for steens!
199 ResultGraph->removeDeadNodes(DSGraph::KeepUnreachableGlobals);
201 DEBUG(print(std::cerr, &M));
205 // alias - This is the only method here that does anything interesting...
206 AliasAnalysis::AliasResult Steens::alias(const Value *V1, unsigned V1Size,
207 const Value *V2, unsigned V2Size) {
208 // FIXME: HANDLE Size argument!
209 assert(ResultGraph && "Result graph has not been computed yet!");
211 hash_map<Value*, DSNodeHandle> &GSM = ResultGraph->getScalarMap();
213 hash_map<Value*, DSNodeHandle>::iterator I = GSM.find(const_cast<Value*>(V1));
214 if (I != GSM.end() && I->second.getNode()) {
215 DSNodeHandle &V1H = I->second;
216 hash_map<Value*, DSNodeHandle>::iterator J=GSM.find(const_cast<Value*>(V2));
217 if (J != GSM.end() && J->second.getNode()) {
218 DSNodeHandle &V2H = J->second;
219 // If the two pointers point to different data structure graph nodes, they
221 if (V1H.getNode() != V2H.getNode()) // FIXME: Handle incompleteness!
224 // FIXME: If the two pointers point to the same node, and the offsets are
225 // different, and the LinkIndex vector doesn't alias the section, then the
226 // two pointers do not alias. We need access size information for the two
232 // If we cannot determine alias properties based on our graph, fall back on
233 // some other AA implementation.
235 return getAnalysis<AliasAnalysis>().alias(V1, V1Size, V2, V2Size);