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.h"
18 #include "llvm/Analysis/DSGraph.h"
19 #include "llvm/Analysis/AliasAnalysis.h"
20 #include "llvm/Module.h"
21 #include "Support/Debug.h"
25 class Steens : public Pass, public AliasAnalysis {
27 DSGraph *GlobalsGraph; // FIXME: Eliminate globals graph stuff from DNE
29 Steens() : ResultGraph(0), GlobalsGraph(0) {}
32 assert(ResultGraph == 0 && "releaseMemory not called?");
35 //------------------------------------------------
36 // Implement the Pass API
39 // run - Build up the result graph, representing the pointer graph for the
44 virtual void releaseMyMemory() { delete ResultGraph; ResultGraph = 0; }
46 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
47 AliasAnalysis::getAnalysisUsage(AU);
48 AU.setPreservesAll(); // Does not transform code...
49 AU.addRequired<LocalDataStructures>(); // Uses local dsgraph
50 AU.addRequired<AliasAnalysis>(); // Chains to another AA impl...
53 // print - Implement the Pass::print method...
54 void print(std::ostream &O, const Module *M) const {
55 assert(ResultGraph && "Result graph has not yet been computed!");
56 ResultGraph->writeGraphToFile(O, "steensgaards");
59 //------------------------------------------------
60 // Implement the AliasAnalysis API
63 // alias - This is the only method here that does anything interesting...
64 AliasResult alias(const Value *V1, unsigned V1Size,
65 const Value *V2, unsigned V2Size);
67 bool pointsToConstantMemory(const Value *P) {
68 return getAnalysis<AliasAnalysis>().pointsToConstantMemory(P);
72 void ResolveFunctionCall(Function *F, const DSCallSite &Call,
73 DSNodeHandle &RetVal);
76 // Register the pass...
77 RegisterOpt<Steens> X("steens-aa",
78 "Steensgaard's alias analysis (DSGraph based)");
80 // Register as an implementation of AliasAnalysis
81 RegisterAnalysisGroup<AliasAnalysis, Steens> Y;
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::aiterator AI = F->abegin(), AE = F->aend();
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::run(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(getTargetData());
118 GlobalsGraph = new DSGraph(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
131 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
132 if (!I->isExternal()) {
133 DSGraph::ScalarMapTy ValMap;
134 { // Scope to free NodeMap memory ASAP
135 DSGraph::NodeMapTy NodeMap;
136 const DSGraph &FDSG = LDS.getDSGraph(*I);
137 ResultGraph->cloneInto(FDSG, ValMap, RetValMap, NodeMap,
138 DSGraph::UpdateInlinedGlobals);
141 // Incorporate the inlined Function's ScalarMap into the global
143 DSGraph::ScalarMapTy &GVM = ResultGraph->getScalarMap();
144 for (DSGraph::ScalarMapTy::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...
198 // Update the "incomplete" markers on the nodes, ignoring unknownness due to
199 // incoming arguments...
200 ResultGraph->maskIncompleteMarkers();
201 ResultGraph->markIncompleteNodes(DSGraph::IgnoreFormalArgs);
203 // Remove any nodes that are dead after all of the merging we have done...
204 // FIXME: We should be able to disable the globals graph for steens!
205 ResultGraph->removeDeadNodes(DSGraph::KeepUnreachableGlobals);
207 DEBUG(print(std::cerr, &M));
211 // alias - This is the only method here that does anything interesting...
212 AliasAnalysis::AliasResult Steens::alias(const Value *V1, unsigned V1Size,
213 const Value *V2, unsigned V2Size) {
214 // FIXME: HANDLE Size argument!
215 assert(ResultGraph && "Result graph has not been computed yet!");
217 DSGraph::ScalarMapTy &GSM = ResultGraph->getScalarMap();
219 DSGraph::ScalarMapTy::iterator I = GSM.find(const_cast<Value*>(V1));
220 if (I != GSM.end() && I->second.getNode()) {
221 DSNodeHandle &V1H = I->second;
222 DSGraph::ScalarMapTy::iterator J=GSM.find(const_cast<Value*>(V2));
223 if (J != GSM.end() && J->second.getNode()) {
224 DSNodeHandle &V2H = J->second;
225 // If the two pointers point to different data structure graph nodes, they
227 if (V1H.getNode() != V2H.getNode()) // FIXME: Handle incompleteness!
230 // FIXME: If the two pointers point to the same node, and the offsets are
231 // different, and the LinkIndex vector doesn't alias the section, then the
232 // two pointers do not alias. We need access size information for the two
238 // If we cannot determine alias properties based on our graph, fall back on
239 // some other AA implementation.
241 return getAnalysis<AliasAnalysis>().alias(V1, V1Size, V2, V2Size);