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/Debug.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 DSGraph::ScalarMapTy &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 DSGraph::ScalarMapTy::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 DSGraph::ReturnNodesTy 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 DSGraph::ScalarMapTy ValMap;
123 { // Scope to free NodeMap memory ASAP
124 DSGraph::NodeMapTy NodeMap;
125 const DSGraph &FDSG = LDS.getDSGraph(*I);
126 ResultGraph->cloneInto(FDSG, ValMap, RetValMap, NodeMap);
129 // Incorporate the inlined Function's ScalarMap into the global
131 DSGraph::ScalarMapTy &GVM = ResultGraph->getScalarMap();
132 for (DSGraph::ScalarMapTy::iterator I = ValMap.begin(),
133 E = ValMap.end(); I != E; ++I)
134 GVM[I->first].mergeWith(I->second);
136 if ((++Count & 1) == 0) // Prune nodes out every other time...
137 ResultGraph->removeTriviallyDeadNodes();
140 // FIXME: Must recalculate and use the Incomplete markers!!
142 // Now that we have all of the graphs inlined, we can go about eliminating
145 std::vector<DSCallSite> &Calls =
146 ResultGraph->getAuxFunctionCalls();
147 assert(Calls.empty() && "Aux call list is already in use??");
149 // Start with a copy of the original call sites...
150 Calls = ResultGraph->getFunctionCalls();
152 for (unsigned i = 0; i != Calls.size(); ) {
153 DSCallSite &CurCall = Calls[i];
155 // Loop over the called functions, eliminating as many as possible...
156 std::vector<GlobalValue*> CallTargets;
157 if (CurCall.isDirectCall())
158 CallTargets.push_back(CurCall.getCalleeFunc());
160 CallTargets = CurCall.getCalleeNode()->getGlobals();
162 for (unsigned c = 0; c != CallTargets.size(); ) {
163 // If we can eliminate this function call, do so!
164 bool Eliminated = false;
165 if (Function *F = dyn_cast<Function>(CallTargets[c]))
166 if (!F->isExternal()) {
167 ResolveFunctionCall(F, CurCall, RetValMap[F]);
171 CallTargets[c] = CallTargets.back();
172 CallTargets.pop_back();
174 ++c; // Cannot eliminate this call, skip over it...
177 if (CallTargets.empty()) { // Eliminated all calls?
178 CurCall = Calls.back(); // Remove entry
181 ++i; // Skip this call site...
186 // Update the "incomplete" markers on the nodes, ignoring unknownness due to
187 // incoming arguments...
188 ResultGraph->maskIncompleteMarkers();
189 ResultGraph->markIncompleteNodes(DSGraph::IgnoreFormalArgs);
191 // Remove any nodes that are dead after all of the merging we have done...
192 // FIXME: We should be able to disable the globals graph for steens!
193 ResultGraph->removeDeadNodes(DSGraph::KeepUnreachableGlobals);
195 DEBUG(print(std::cerr, &M));
199 // alias - This is the only method here that does anything interesting...
200 AliasAnalysis::AliasResult Steens::alias(const Value *V1, unsigned V1Size,
201 const Value *V2, unsigned V2Size) {
202 // FIXME: HANDLE Size argument!
203 assert(ResultGraph && "Result graph has not been computed yet!");
205 DSGraph::ScalarMapTy &GSM = ResultGraph->getScalarMap();
207 DSGraph::ScalarMapTy::iterator I = GSM.find(const_cast<Value*>(V1));
208 if (I != GSM.end() && I->second.getNode()) {
209 DSNodeHandle &V1H = I->second;
210 DSGraph::ScalarMapTy::iterator J=GSM.find(const_cast<Value*>(V2));
211 if (J != GSM.end() && J->second.getNode()) {
212 DSNodeHandle &V2H = J->second;
213 // If the two pointers point to different data structure graph nodes, they
215 if (V1H.getNode() != V2H.getNode()) // FIXME: Handle incompleteness!
218 // FIXME: If the two pointers point to the same node, and the offsets are
219 // different, and the LinkIndex vector doesn't alias the section, then the
220 // two pointers do not alias. We need access size information for the two
226 // If we cannot determine alias properties based on our graph, fall back on
227 // some other AA implementation.
229 return getAnalysis<AliasAnalysis>().alias(V1, V1Size, V2, V2Size);