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+//===- Steensgaard.cpp - Context Insensitive Alias Analysis ---------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// 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/DataStructure.h"
+#include "llvm/Analysis/DataStructure/DSGraph.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/Passes.h"
+#include "llvm/Module.h"
+#include "llvm/Support/Debug.h"
+using namespace llvm;
+
+namespace {
+ class Steens : public ModulePass, public AliasAnalysis {
+ DSGraph *ResultGraph;
+
+ EquivalenceClasses<GlobalValue*> GlobalECs; // Always empty
+ public:
+ Steens() : ResultGraph(0) {}
+ ~Steens() {
+ releaseMyMemory();
+ assert(ResultGraph == 0 && "releaseMemory not called?");
+ }
+
+ //------------------------------------------------
+ // Implement the Pass API
+ //
+
+ // run - Build up the result graph, representing the pointer graph for the
+ // program.
+ //
+ bool runOnModule(Module &M);
+
+ virtual void releaseMyMemory() { delete ResultGraph; ResultGraph = 0; }
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AliasAnalysis::getAnalysisUsage(AU);
+ AU.setPreservesAll(); // Does not transform code...
+ AU.addRequired<LocalDataStructures>(); // Uses local dsgraph
+ }
+
+ // 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
+ //
+
+ AliasResult alias(const Value *V1, unsigned V1Size,
+ const Value *V2, unsigned V2Size);
+
+ ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
+
+ private:
+ void ResolveFunctionCall(Function *F, const DSCallSite &Call,
+ DSNodeHandle &RetVal);
+ };
+
+ // Register the pass...
+ RegisterOpt<Steens> X("steens-aa",
+ "Steensgaard's alias analysis (DSGraph based)");
+
+ // Register as an implementation of AliasAnalysis
+ RegisterAnalysisGroup<AliasAnalysis, Steens> Y;
+}
+
+ModulePass *llvm::createSteensgaardPass() { return new Steens(); }
+
+/// 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 DSCallSite &Call,
+ DSNodeHandle &RetVal) {
+ assert(ResultGraph != 0 && "Result graph not allocated!");
+ DSGraph::ScalarMapTy &ValMap = ResultGraph->getScalarMap();
+
+ // Handle the return value of the function...
+ if (Call.getRetVal().getNode() && RetVal.getNode())
+ RetVal.mergeWith(Call.getRetVal());
+
+ // Loop over all pointer arguments, resolving them to their provided pointers
+ unsigned PtrArgIdx = 0;
+ for (Function::arg_iterator AI = F->arg_begin(), AE = F->arg_end();
+ AI != AE && PtrArgIdx < Call.getNumPtrArgs(); ++AI) {
+ DSGraph::ScalarMapTy::iterator I = ValMap.find(AI);
+ if (I != ValMap.end()) // If its a pointer argument...
+ I->second.mergeWith(Call.getPtrArg(PtrArgIdx++));
+ }
+}
+
+
+/// run - Build up the result graph, representing the pointer graph for the
+/// program.
+///
+bool Steens::runOnModule(Module &M) {
+ InitializeAliasAnalysis(this);
+ assert(ResultGraph == 0 && "Result graph already allocated!");
+ LocalDataStructures &LDS = getAnalysis<LocalDataStructures>();
+
+ // Create a new, empty, graph...
+ ResultGraph = new DSGraph(GlobalECs, getTargetData());
+ ResultGraph->spliceFrom(LDS.getGlobalsGraph());
+
+ // 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())
+ ResultGraph->spliceFrom(LDS.getDSGraph(*I));
+
+ ResultGraph->removeTriviallyDeadNodes();
+
+ // 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::list<DSCallSite> &Calls = ResultGraph->getAuxFunctionCalls();
+ assert(Calls.empty() && "Aux call list is already in use??");
+
+ // Start with a copy of the original call sites.
+ Calls = ResultGraph->getFunctionCalls();
+
+ for (std::list<DSCallSite>::iterator CI = Calls.begin(), E = Calls.end();
+ CI != E;) {
+ DSCallSite &CurCall = *CI++;
+
+ // Loop over the called functions, eliminating as many as possible...
+ std::vector<Function*> CallTargets;
+ if (CurCall.isDirectCall())
+ CallTargets.push_back(CurCall.getCalleeFunc());
+ else
+ CurCall.getCalleeNode()->addFullFunctionList(CallTargets);
+
+ for (unsigned c = 0; c != CallTargets.size(); ) {
+ // If we can eliminate this function call, do so!
+ Function *F = CallTargets[c];
+ if (!F->isExternal()) {
+ ResolveFunctionCall(F, CurCall, ResultGraph->getReturnNodes()[F]);
+ CallTargets[c] = CallTargets.back();
+ CallTargets.pop_back();
+ } else
+ ++c; // Cannot eliminate this call, skip over it...
+ }
+
+ if (CallTargets.empty()) { // Eliminated all calls?
+ std::list<DSCallSite>::iterator I = CI;
+ Calls.erase(--I); // Remove entry
+ }
+ }
+
+ // Remove our knowledge of what the return values of the functions are, except
+ // for functions that are externally visible from this module (e.g. main). We
+ // keep these functions so that their arguments are marked incomplete.
+ for (DSGraph::ReturnNodesTy::iterator I =
+ ResultGraph->getReturnNodes().begin(),
+ E = ResultGraph->getReturnNodes().end(); I != E; )
+ if (I->first->hasInternalLinkage())
+ ResultGraph->getReturnNodes().erase(I++);
+ else
+ ++I;
+
+ // Update the "incomplete" markers on the nodes, ignoring unknownness due to
+ // incoming arguments...
+ ResultGraph->maskIncompleteMarkers();
+ ResultGraph->markIncompleteNodes(DSGraph::IgnoreGlobals |
+ DSGraph::MarkFormalArgs);
+
+ // Remove any nodes that are dead after all of the merging we have done...
+ // FIXME: We should be able to disable the globals graph for steens!
+ //ResultGraph->removeDeadNodes(DSGraph::KeepUnreachableGlobals);
+
+ DEBUG(print(std::cerr, &M));
+ return false;
+}
+
+AliasAnalysis::AliasResult Steens::alias(const Value *V1, unsigned V1Size,
+ const Value *V2, unsigned V2Size) {
+ assert(ResultGraph && "Result graph has not been computed yet!");
+
+ DSGraph::ScalarMapTy &GSM = ResultGraph->getScalarMap();
+
+ DSGraph::ScalarMapTy::iterator I = GSM.find(const_cast<Value*>(V1));
+ DSGraph::ScalarMapTy::iterator J = GSM.find(const_cast<Value*>(V2));
+ if (I != GSM.end() && !I->second.isNull() &&
+ J != GSM.end() && !J->second.isNull()) {
+ DSNodeHandle &V1H = I->second;
+ DSNodeHandle &V2H = J->second;
+
+ // If at least one of the nodes is complete, we can say something about
+ // this. If one is complete and the other isn't, then they are obviously
+ // different nodes. If they are both complete, we can't say anything
+ // useful.
+ if (I->second.getNode()->isComplete() ||
+ J->second.getNode()->isComplete()) {
+ // If the two pointers point to different data structure graph nodes, they
+ // cannot alias!
+ if (V1H.getNode() != V2H.getNode())
+ return NoAlias;
+
+ // See if they point to different offsets... if so, we may be able to
+ // determine that they do not alias...
+ unsigned O1 = I->second.getOffset(), O2 = J->second.getOffset();
+ if (O1 != O2) {
+ if (O2 < O1) { // Ensure that O1 <= O2
+ std::swap(V1, V2);
+ std::swap(O1, O2);
+ std::swap(V1Size, V2Size);
+ }
+
+ if (O1+V1Size <= O2)
+ return NoAlias;
+ }
+ }
+ }
+
+ // If we cannot determine alias properties based on our graph, fall back on
+ // some other AA implementation.
+ //
+ return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
+}
+
+AliasAnalysis::ModRefResult
+Steens::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
+ AliasAnalysis::ModRefResult Result = ModRef;
+
+ // Find the node in question.
+ DSGraph::ScalarMapTy &GSM = ResultGraph->getScalarMap();
+ DSGraph::ScalarMapTy::iterator I = GSM.find(P);
+
+ if (I != GSM.end() && !I->second.isNull()) {
+ DSNode *N = I->second.getNode();
+ if (N->isComplete()) {
+ // If this is a direct call to an external function, and if the pointer
+ // points to a complete node, the external function cannot modify or read
+ // the value (we know it's not passed out of the program!).
+ if (Function *F = CS.getCalledFunction())
+ if (F->isExternal())
+ return NoModRef;
+
+ // Otherwise, if the node is complete, but it is only M or R, return this.
+ // This can be useful for globals that should be marked const but are not.
+ if (!N->isModified())
+ Result = (ModRefResult)(Result & ~Mod);
+ if (!N->isRead())
+ Result = (ModRefResult)(Result & ~Ref);
+ }
+ }
+
+ return (ModRefResult)(Result & AliasAnalysis::getModRefInfo(CS, P, Size));
+}
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