//===- Steensgaard.cpp - Context Insensitive Alias Analysis ---------------===// // // This pass uses the data structure graphs to implement a simple context // insensitive alias analysis. It does this by computing the local analysis // graphs for all of the functions, then merging them together into a single big // graph without cloning. // //===----------------------------------------------------------------------===// #include "llvm/Analysis/DataStructure.h" #include "llvm/Analysis/DSGraph.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Module.h" #include "Support/Statistic.h" namespace { class Steens : public Pass, public AliasAnalysis { DSGraph *ResultGraph; public: Steens() : ResultGraph(0) {} ~Steens() { assert(ResultGraph == 0 && "releaseMemory not called?"); } //------------------------------------------------ // Implement the Pass API // // run - Build up the result graph, representing the pointer graph for the // program. // bool run(Module &M); virtual void releaseMemory() { delete ResultGraph; ResultGraph = 0; } virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); // Does not transform code... AU.addRequired(); // Uses local dsgraph AU.addRequired(); // Chains to another AA impl... } // print - Implement the Pass::print method... void print(std::ostream &O, const Module *M) const { assert(ResultGraph && "Result graph has not yet been computed!"); ResultGraph->writeGraphToFile(O, "steensgaards"); } //------------------------------------------------ // Implement the AliasAnalysis API // // alias - This is the only method here that does anything interesting... Result alias(const Value *V1, const Value *V2) const; /// canCallModify - We are not interprocedural, so we do nothing exciting. /// Result canCallModify(const CallInst &CI, const Value *Ptr) const { return MayAlias; } /// canInvokeModify - We are not interprocedural, so we do nothing exciting. /// Result canInvokeModify(const InvokeInst &I, const Value *Ptr) const { return MayAlias; // We are not interprocedural } private: void ResolveFunctionCall(Function *F, const std::vector &Call, DSNodeHandle &RetVal); }; // Register the pass... RegisterOpt X("steens-aa", "Steensgaard's FlowInsensitive/ConIns alias analysis"); // Register as an implementation of AliasAnalysis RegisterAnalysisGroup Y; } /// ResolveFunctionCall - Resolve the actual arguments of a call to function F /// with the specified call site descriptor. This function links the arguments /// and the return value for the call site context-insensitively. /// void Steens::ResolveFunctionCall(Function *F, const std::vector &Call, DSNodeHandle &RetVal) { assert(ResultGraph != 0 && "Result graph not allocated!"); std::map &ValMap = ResultGraph->getValueMap(); // Handle the return value of the function... which is Call[0] if (Call[0].getNode() && RetVal.getNode()) RetVal.mergeWith(Call[0]); // Loop over all pointer arguments, resolving them to their provided pointers unsigned ArgIdx = 2; // Skip retval and function to call... for (Function::aiterator AI = F->abegin(), AE = F->aend(); AI != AE; ++AI) { std::map::iterator I = ValMap.find(AI); if (I != ValMap.end()) // If its a pointer argument... I->second.addEdgeTo(Call[ArgIdx++]); } assert(ArgIdx == Call.size() && "Argument resolution mismatch!"); } /// run - Build up the result graph, representing the pointer graph for the /// program. /// bool Steens::run(Module &M) { assert(ResultGraph == 0 && "Result graph already allocated!"); LocalDataStructures &LDS = getAnalysis(); // Create a new, empty, graph... ResultGraph = new DSGraph(); // RetValMap - Keep track of the return values for all functions that return // valid pointers. // std::map RetValMap; // Loop over the rest of the module, merging graphs for non-external functions // into this graph. // for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) if (!I->isExternal()) { std::map ValMap; { // Scope to free NodeMap memory ASAP std::map NodeMap; const DSGraph &FDSG = LDS.getDSGraph(*I); DSNodeHandle RetNode = ResultGraph->cloneInto(FDSG, ValMap, NodeMap); // Keep track of the return node of the function's graph if it returns a // value... // if (RetNode.getNode()) RetValMap[I] = RetNode; } // Incorporate the inlined Function's ValueMap into the global ValueMap... std::map &GVM = ResultGraph->getValueMap(); while (!ValMap.empty()) { // Loop over value map, moving entries over... const std::pair &DSN = *ValMap.begin(); std::map::iterator I = GVM.find(DSN.first); if (I == GVM.end()) GVM[DSN.first] = DSN.second; else I->second.mergeWith(DSN.second); ValMap.erase(ValMap.begin()); } } // FIXME: Must recalculate and use the Incomplete markers!! // Now that we have all of the graphs inlined, we can go about eliminating // call nodes... // std::vector > &Calls = ResultGraph->getFunctionCalls(); for (unsigned i = 0; i != Calls.size(); ) { std::vector &CurCall = Calls[i]; // Loop over the called functions, eliminating as many as possible... std::vector CallTargets = CurCall[1].getNode()->getGlobals(); for (unsigned c = 0; c != CallTargets.size(); ) { // If we can eliminate this function call, do so! bool Eliminated = false; if (Function *F = dyn_cast(CallTargets[c])) if (!F->isExternal()) { ResolveFunctionCall(F, CurCall, RetValMap[F]); Eliminated = true; } if (Eliminated) CallTargets.erase(CallTargets.begin()+c); else ++c; // Cannot eliminate this call, skip over it... } if (CallTargets.empty()) // Eliminated all calls? Calls.erase(Calls.begin()+i); // Remove from call list... else ++i; // Skip this call site... } // Update the "incomplete" markers on the nodes, ignoring unknownness due to // incoming arguments... ResultGraph->maskIncompleteMarkers(); ResultGraph->markIncompleteNodes(false); // Remove any nodes that are dead after all of the merging we have done... ResultGraph->removeTriviallyDeadNodes(); DEBUG(print(std::cerr, &M)); return false; } // alias - This is the only method here that does anything interesting... AliasAnalysis::Result Steens::alias(const Value *V1, const Value *V2) const { assert(ResultGraph && "Result grcaph has not yet been computed!"); std::map &GVM = ResultGraph->getValueMap(); std::map::iterator I = GVM.find(const_cast(V1)); if (I != GVM.end() && I->second.getNode()) { DSNodeHandle &V1H = I->second; std::map::iterator J=GVM.find(const_cast(V2)); if (J != GVM.end() && J->second.getNode()) { DSNodeHandle &V2H = J->second; // If the two pointers point to different data structure graph nodes, they // cannot alias! if (V1H.getNode() != V2H.getNode()) return NoAlias; // FIXME: If the two pointers point to the same node, and the offsets are // different, and the LinkIndex vector doesn't alias the section, then the // two pointers do not alias. We need access size information for the two // accesses though! // } } // If we cannot determine alias properties based on our graph, fall back on // some other AA implementation. // return getAnalysis().alias(V1, V2); }