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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"
-#include <ostream>
-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(OStream O, const Module *M) const {
- if (O.stream()) print(*O.stream(), M);
- }
- 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);
-
- virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
- virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
-
- private:
- void ResolveFunctionCall(Function *F, const DSCallSite &Call,
- DSNodeHandle &RetVal);
- };
-
- // Register the pass...
- RegisterPass<Steens> X("steens-aa",
- "Steensgaard's alias analysis (DSGraph based)");
-
- // Register as an implementation of AliasAnalysis
- RegisterAnalysisGroup<AliasAnalysis> Y(X);
-}
-
-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);
-
- print(DOUT, &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));
-}
-
-AliasAnalysis::ModRefResult
-Steens::getModRefInfo(CallSite CS1, CallSite CS2)
-{
- return AliasAnalysis::getModRefInfo(CS1,CS2);
-}
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