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) {}
22 ~Steens() { assert(ResultGraph == 0 && "releaseMemory not called?"); }
24 //------------------------------------------------
25 // Implement the Pass API
28 // run - Build up the result graph, representing the pointer graph for the
33 virtual void releaseMemory() { delete ResultGraph; ResultGraph = 0; }
35 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
36 AU.setPreservesAll(); // Does not transform code...
37 AU.addRequired<LocalDataStructures>(); // Uses local dsgraph
38 AU.addRequired<AliasAnalysis>(); // Chains to another AA impl...
41 // print - Implement the Pass::print method...
42 void print(std::ostream &O, const Module *M) const {
43 assert(ResultGraph && "Result graph has not yet been computed!");
44 ResultGraph->writeGraphToFile(O, "steensgaards");
47 //------------------------------------------------
48 // Implement the AliasAnalysis API
51 // alias - This is the only method here that does anything interesting...
52 Result alias(const Value *V1, const Value *V2);
54 /// canCallModify - Not implemented yet: FIXME
56 Result canCallModify(const CallInst &CI, const Value *Ptr) {
60 /// canInvokeModify - Not implemented yet: FIXME
62 Result canInvokeModify(const InvokeInst &I, const Value *Ptr) {
67 void ResolveFunctionCall(Function *F, const DSCallSite &Call,
68 DSNodeHandle &RetVal);
71 // Register the pass...
72 RegisterOpt<Steens> X("steens-aa",
73 "Steensgaard's alias analysis (DSGraph based)");
75 // Register as an implementation of AliasAnalysis
76 RegisterAnalysisGroup<AliasAnalysis, Steens> Y;
80 /// ResolveFunctionCall - Resolve the actual arguments of a call to function F
81 /// with the specified call site descriptor. This function links the arguments
82 /// and the return value for the call site context-insensitively.
84 void Steens::ResolveFunctionCall(Function *F, const DSCallSite &Call,
85 DSNodeHandle &RetVal) {
86 assert(ResultGraph != 0 && "Result graph not allocated!");
87 hash_map<Value*, DSNodeHandle> &ValMap = ResultGraph->getScalarMap();
89 // Handle the return value of the function...
90 if (Call.getRetVal().getNode() && RetVal.getNode())
91 RetVal.mergeWith(Call.getRetVal());
93 // Loop over all pointer arguments, resolving them to their provided pointers
94 unsigned PtrArgIdx = 0;
95 for (Function::aiterator AI = F->abegin(), AE = F->aend();
96 AI != AE && PtrArgIdx < Call.getNumPtrArgs(); ++AI) {
97 hash_map<Value*, DSNodeHandle>::iterator I = ValMap.find(AI);
98 if (I != ValMap.end()) // If its a pointer argument...
99 I->second.mergeWith(Call.getPtrArg(PtrArgIdx++));
104 /// run - Build up the result graph, representing the pointer graph for the
107 bool Steens::run(Module &M) {
108 assert(ResultGraph == 0 && "Result graph already allocated!");
109 LocalDataStructures &LDS = getAnalysis<LocalDataStructures>();
111 // Create a new, empty, graph...
112 ResultGraph = new DSGraph();
113 GlobalsGraph = new DSGraph();
114 ResultGraph->setGlobalsGraph(GlobalsGraph);
115 ResultGraph->setPrintAuxCalls();
117 // RetValMap - Keep track of the return values for all functions that return
120 hash_map<Function*, DSNodeHandle> RetValMap;
122 // Loop over the rest of the module, merging graphs for non-external functions
126 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
127 if (!I->isExternal()) {
128 hash_map<Value*, DSNodeHandle> ValMap;
129 { // Scope to free NodeMap memory ASAP
130 hash_map<const DSNode*, DSNodeHandle> NodeMap;
131 const DSGraph &FDSG = LDS.getDSGraph(*I);
132 DSNodeHandle RetNode = ResultGraph->cloneInto(FDSG, ValMap, NodeMap);
134 // Keep track of the return node of the function's graph if it returns a
137 if (RetNode.getNode())
138 RetValMap[I] = RetNode;
141 // Incorporate the inlined Function's ScalarMap into the global
143 hash_map<Value*, DSNodeHandle> &GVM = ResultGraph->getScalarMap();
144 for (hash_map<Value*, DSNodeHandle>::iterator I = ValMap.begin(),
145 E = ValMap.end(); I != E; ++I)
146 GVM[I->first].mergeWith(I->second);
148 if ((++Count & 1) == 0) // Prune nodes out every other time...
149 ResultGraph->removeTriviallyDeadNodes();
152 // FIXME: Must recalculate and use the Incomplete markers!!
154 // Now that we have all of the graphs inlined, we can go about eliminating
157 std::vector<DSCallSite> &Calls =
158 ResultGraph->getAuxFunctionCalls();
159 assert(Calls.empty() && "Aux call list is already in use??");
161 // Start with a copy of the original call sites...
162 Calls = ResultGraph->getFunctionCalls();
164 for (unsigned i = 0; i != Calls.size(); ) {
165 DSCallSite &CurCall = Calls[i];
167 // Loop over the called functions, eliminating as many as possible...
168 std::vector<GlobalValue*> CallTargets;
169 if (CurCall.isDirectCall())
170 CallTargets.push_back(CurCall.getCalleeFunc());
172 CallTargets = CurCall.getCalleeNode()->getGlobals();
174 for (unsigned c = 0; c != CallTargets.size(); ) {
175 // If we can eliminate this function call, do so!
176 bool Eliminated = false;
177 if (Function *F = dyn_cast<Function>(CallTargets[c]))
178 if (!F->isExternal()) {
179 ResolveFunctionCall(F, CurCall, RetValMap[F]);
183 CallTargets[c] = CallTargets.back();
184 CallTargets.pop_back();
186 ++c; // Cannot eliminate this call, skip over it...
189 if (CallTargets.empty()) { // Eliminated all calls?
190 CurCall = Calls.back(); // Remove entry
193 ++i; // Skip this call site...
196 // Update the "incomplete" markers on the nodes, ignoring unknownness due to
197 // incoming arguments...
198 ResultGraph->maskIncompleteMarkers();
199 ResultGraph->markIncompleteNodes(DSGraph::IgnoreFormalArgs);
201 // Remove any nodes that are dead after all of the merging we have done...
202 // FIXME: We should be able to disable the globals graph for steens!
203 ResultGraph->removeDeadNodes(DSGraph::KeepUnreachableGlobals);
205 DEBUG(print(std::cerr, &M));
209 // alias - This is the only method here that does anything interesting...
210 AliasAnalysis::Result Steens::alias(const Value *V1, const Value *V2) {
211 assert(ResultGraph && "Result graph has not been computed yet!");
213 hash_map<Value*, DSNodeHandle> &GSM = ResultGraph->getScalarMap();
215 hash_map<Value*, DSNodeHandle>::iterator I = GSM.find(const_cast<Value*>(V1));
216 if (I != GSM.end() && I->second.getNode()) {
217 DSNodeHandle &V1H = I->second;
218 hash_map<Value*, DSNodeHandle>::iterator J=GSM.find(const_cast<Value*>(V2));
219 if (J != GSM.end() && J->second.getNode()) {
220 DSNodeHandle &V2H = J->second;
221 // If the two pointers point to different data structure graph nodes, they
223 if (V1H.getNode() != V2H.getNode()) // FIXME: Handle incompleteness!
226 // FIXME: If the two pointers point to the same node, and the offsets are
227 // different, and the LinkIndex vector doesn't alias the section, then the
228 // two pointers do not alias. We need access size information for the two
234 // If we cannot determine alias properties based on our graph, fall back on
235 // some other AA implementation.
237 return getAnalysis<AliasAnalysis>().alias(V1, V2);