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"
24 class Steens : public Pass, public AliasAnalysis {
26 DSGraph *GlobalsGraph; // FIXME: Eliminate globals graph stuff from DNE
28 Steens() : ResultGraph(0), GlobalsGraph(0) {}
31 assert(ResultGraph == 0 && "releaseMemory not called?");
34 //------------------------------------------------
35 // Implement the Pass API
38 // run - Build up the result graph, representing the pointer graph for the
43 virtual void releaseMyMemory() { delete ResultGraph; ResultGraph = 0; }
45 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
46 AliasAnalysis::getAnalysisUsage(AU);
47 AU.setPreservesAll(); // Does not transform code...
48 AU.addRequired<LocalDataStructures>(); // Uses local dsgraph
49 AU.addRequired<AliasAnalysis>(); // Chains to another AA impl...
52 // print - Implement the Pass::print method...
53 void print(std::ostream &O, const Module *M) const {
54 assert(ResultGraph && "Result graph has not yet been computed!");
55 ResultGraph->writeGraphToFile(O, "steensgaards");
58 //------------------------------------------------
59 // Implement the AliasAnalysis API
62 // alias - This is the only method here that does anything interesting...
63 AliasResult alias(const Value *V1, unsigned V1Size,
64 const Value *V2, unsigned V2Size);
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 DSGraph::ScalarMapTy &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 DSGraph::ScalarMapTy::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 InitializeAliasAnalysis(this);
109 assert(ResultGraph == 0 && "Result graph already allocated!");
110 LocalDataStructures &LDS = getAnalysis<LocalDataStructures>();
112 // Create a new, empty, graph...
113 ResultGraph = new DSGraph();
114 GlobalsGraph = new DSGraph();
115 ResultGraph->setGlobalsGraph(GlobalsGraph);
116 ResultGraph->setPrintAuxCalls();
118 // RetValMap - Keep track of the return values for all functions that return
121 DSGraph::ReturnNodesTy RetValMap;
123 // Loop over the rest of the module, merging graphs for non-external functions
127 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
128 if (!I->isExternal()) {
129 DSGraph::ScalarMapTy ValMap;
130 { // Scope to free NodeMap memory ASAP
131 DSGraph::NodeMapTy NodeMap;
132 const DSGraph &FDSG = LDS.getDSGraph(*I);
133 ResultGraph->cloneInto(FDSG, ValMap, RetValMap, NodeMap);
136 // Incorporate the inlined Function's ScalarMap into the global
138 DSGraph::ScalarMapTy &GVM = ResultGraph->getScalarMap();
139 for (DSGraph::ScalarMapTy::iterator I = ValMap.begin(),
140 E = ValMap.end(); I != E; ++I)
141 GVM[I->first].mergeWith(I->second);
143 if ((++Count & 1) == 0) // Prune nodes out every other time...
144 ResultGraph->removeTriviallyDeadNodes();
147 // FIXME: Must recalculate and use the Incomplete markers!!
149 // Now that we have all of the graphs inlined, we can go about eliminating
152 std::vector<DSCallSite> &Calls =
153 ResultGraph->getAuxFunctionCalls();
154 assert(Calls.empty() && "Aux call list is already in use??");
156 // Start with a copy of the original call sites...
157 Calls = ResultGraph->getFunctionCalls();
159 for (unsigned i = 0; i != Calls.size(); ) {
160 DSCallSite &CurCall = Calls[i];
162 // Loop over the called functions, eliminating as many as possible...
163 std::vector<GlobalValue*> CallTargets;
164 if (CurCall.isDirectCall())
165 CallTargets.push_back(CurCall.getCalleeFunc());
167 CallTargets = CurCall.getCalleeNode()->getGlobals();
169 for (unsigned c = 0; c != CallTargets.size(); ) {
170 // If we can eliminate this function call, do so!
171 bool Eliminated = false;
172 if (Function *F = dyn_cast<Function>(CallTargets[c]))
173 if (!F->isExternal()) {
174 ResolveFunctionCall(F, CurCall, RetValMap[F]);
178 CallTargets[c] = CallTargets.back();
179 CallTargets.pop_back();
181 ++c; // Cannot eliminate this call, skip over it...
184 if (CallTargets.empty()) { // Eliminated all calls?
185 CurCall = Calls.back(); // Remove entry
188 ++i; // Skip this call site...
193 // Update the "incomplete" markers on the nodes, ignoring unknownness due to
194 // incoming arguments...
195 ResultGraph->maskIncompleteMarkers();
196 ResultGraph->markIncompleteNodes(DSGraph::IgnoreFormalArgs);
198 // Remove any nodes that are dead after all of the merging we have done...
199 // FIXME: We should be able to disable the globals graph for steens!
200 ResultGraph->removeDeadNodes(DSGraph::KeepUnreachableGlobals);
202 DEBUG(print(std::cerr, &M));
206 // alias - This is the only method here that does anything interesting...
207 AliasAnalysis::AliasResult Steens::alias(const Value *V1, unsigned V1Size,
208 const Value *V2, unsigned V2Size) {
209 // FIXME: HANDLE Size argument!
210 assert(ResultGraph && "Result graph has not been computed yet!");
212 DSGraph::ScalarMapTy &GSM = ResultGraph->getScalarMap();
214 DSGraph::ScalarMapTy::iterator I = GSM.find(const_cast<Value*>(V1));
215 if (I != GSM.end() && I->second.getNode()) {
216 DSNodeHandle &V1H = I->second;
217 DSGraph::ScalarMapTy::iterator J=GSM.find(const_cast<Value*>(V2));
218 if (J != GSM.end() && J->second.getNode()) {
219 DSNodeHandle &V2H = J->second;
220 // If the two pointers point to different data structure graph nodes, they
222 if (V1H.getNode() != V2H.getNode()) // FIXME: Handle incompleteness!
225 // FIXME: If the two pointers point to the same node, and the offsets are
226 // different, and the LinkIndex vector doesn't alias the section, then the
227 // two pointers do not alias. We need access size information for the two
233 // If we cannot determine alias properties based on our graph, fall back on
234 // some other AA implementation.
236 return getAnalysis<AliasAnalysis>().alias(V1, V1Size, V2, V2Size);