forked from OSchip/llvm-project
276 lines
9.9 KiB
C++
276 lines
9.9 KiB
C++
//===- Steensgaard.cpp - Context Insensitive Alias Analysis ---------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass uses the data structure graphs to implement a simple context
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// insensitive alias analysis. It does this by computing the local analysis
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// graphs for all of the functions, then merging them together into a single big
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// graph without cloning.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/DataStructure/DataStructure.h"
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#include "llvm/Analysis/DataStructure/DSGraph.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/Module.h"
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#include "llvm/Support/Debug.h"
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#include <iostream>
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using namespace llvm;
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namespace {
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class Steens : public ModulePass, public AliasAnalysis {
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DSGraph *ResultGraph;
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EquivalenceClasses<GlobalValue*> GlobalECs; // Always empty
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public:
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Steens() : ResultGraph(0) {}
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~Steens() {
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releaseMyMemory();
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assert(ResultGraph == 0 && "releaseMemory not called?");
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}
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//------------------------------------------------
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// Implement the Pass API
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//
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// run - Build up the result graph, representing the pointer graph for the
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// program.
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//
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bool runOnModule(Module &M);
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virtual void releaseMyMemory() { delete ResultGraph; ResultGraph = 0; }
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AliasAnalysis::getAnalysisUsage(AU);
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AU.setPreservesAll(); // Does not transform code...
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AU.addRequired<LocalDataStructures>(); // Uses local dsgraph
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}
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// print - Implement the Pass::print method...
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void print(std::ostream &O, const Module *M) const {
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assert(ResultGraph && "Result graph has not yet been computed!");
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ResultGraph->writeGraphToFile(O, "steensgaards");
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}
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//------------------------------------------------
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// Implement the AliasAnalysis API
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//
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AliasResult alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size);
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virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
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virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
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private:
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void ResolveFunctionCall(Function *F, const DSCallSite &Call,
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DSNodeHandle &RetVal);
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};
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// Register the pass...
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RegisterPass<Steens> X("steens-aa",
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"Steensgaard's alias analysis (DSGraph based)");
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// Register as an implementation of AliasAnalysis
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RegisterAnalysisGroup<AliasAnalysis> Y(X);
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}
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ModulePass *llvm::createSteensgaardPass() { return new Steens(); }
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/// ResolveFunctionCall - Resolve the actual arguments of a call to function F
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/// with the specified call site descriptor. This function links the arguments
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/// and the return value for the call site context-insensitively.
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///
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void Steens::ResolveFunctionCall(Function *F, const DSCallSite &Call,
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DSNodeHandle &RetVal) {
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assert(ResultGraph != 0 && "Result graph not allocated!");
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DSGraph::ScalarMapTy &ValMap = ResultGraph->getScalarMap();
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// Handle the return value of the function...
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if (Call.getRetVal().getNode() && RetVal.getNode())
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RetVal.mergeWith(Call.getRetVal());
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// Loop over all pointer arguments, resolving them to their provided pointers
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unsigned PtrArgIdx = 0;
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for (Function::arg_iterator AI = F->arg_begin(), AE = F->arg_end();
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AI != AE && PtrArgIdx < Call.getNumPtrArgs(); ++AI) {
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DSGraph::ScalarMapTy::iterator I = ValMap.find(AI);
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if (I != ValMap.end()) // If its a pointer argument...
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I->second.mergeWith(Call.getPtrArg(PtrArgIdx++));
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}
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}
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/// run - Build up the result graph, representing the pointer graph for the
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/// program.
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///
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bool Steens::runOnModule(Module &M) {
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InitializeAliasAnalysis(this);
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assert(ResultGraph == 0 && "Result graph already allocated!");
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LocalDataStructures &LDS = getAnalysis<LocalDataStructures>();
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// Create a new, empty, graph...
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ResultGraph = new DSGraph(GlobalECs, getTargetData());
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ResultGraph->spliceFrom(LDS.getGlobalsGraph());
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// Loop over the rest of the module, merging graphs for non-external functions
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// into this graph.
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//
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for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
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if (!I->isExternal())
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ResultGraph->spliceFrom(LDS.getDSGraph(*I));
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ResultGraph->removeTriviallyDeadNodes();
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// FIXME: Must recalculate and use the Incomplete markers!!
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// Now that we have all of the graphs inlined, we can go about eliminating
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// call nodes...
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//
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std::list<DSCallSite> &Calls = ResultGraph->getAuxFunctionCalls();
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assert(Calls.empty() && "Aux call list is already in use??");
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// Start with a copy of the original call sites.
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Calls = ResultGraph->getFunctionCalls();
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for (std::list<DSCallSite>::iterator CI = Calls.begin(), E = Calls.end();
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CI != E;) {
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DSCallSite &CurCall = *CI++;
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// Loop over the called functions, eliminating as many as possible...
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std::vector<Function*> CallTargets;
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if (CurCall.isDirectCall())
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CallTargets.push_back(CurCall.getCalleeFunc());
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else
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CurCall.getCalleeNode()->addFullFunctionList(CallTargets);
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for (unsigned c = 0; c != CallTargets.size(); ) {
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// If we can eliminate this function call, do so!
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Function *F = CallTargets[c];
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if (!F->isExternal()) {
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ResolveFunctionCall(F, CurCall, ResultGraph->getReturnNodes()[F]);
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CallTargets[c] = CallTargets.back();
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CallTargets.pop_back();
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} else
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++c; // Cannot eliminate this call, skip over it...
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}
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if (CallTargets.empty()) { // Eliminated all calls?
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std::list<DSCallSite>::iterator I = CI;
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Calls.erase(--I); // Remove entry
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}
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}
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// Remove our knowledge of what the return values of the functions are, except
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// for functions that are externally visible from this module (e.g. main). We
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// keep these functions so that their arguments are marked incomplete.
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for (DSGraph::ReturnNodesTy::iterator I =
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ResultGraph->getReturnNodes().begin(),
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E = ResultGraph->getReturnNodes().end(); I != E; )
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if (I->first->hasInternalLinkage())
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ResultGraph->getReturnNodes().erase(I++);
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else
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++I;
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// Update the "incomplete" markers on the nodes, ignoring unknownness due to
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// incoming arguments...
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ResultGraph->maskIncompleteMarkers();
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ResultGraph->markIncompleteNodes(DSGraph::IgnoreGlobals |
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DSGraph::MarkFormalArgs);
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// Remove any nodes that are dead after all of the merging we have done...
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// FIXME: We should be able to disable the globals graph for steens!
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//ResultGraph->removeDeadNodes(DSGraph::KeepUnreachableGlobals);
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DEBUG(print(std::cerr, &M));
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return false;
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}
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AliasAnalysis::AliasResult Steens::alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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assert(ResultGraph && "Result graph has not been computed yet!");
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DSGraph::ScalarMapTy &GSM = ResultGraph->getScalarMap();
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DSGraph::ScalarMapTy::iterator I = GSM.find(const_cast<Value*>(V1));
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DSGraph::ScalarMapTy::iterator J = GSM.find(const_cast<Value*>(V2));
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if (I != GSM.end() && !I->second.isNull() &&
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J != GSM.end() && !J->second.isNull()) {
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DSNodeHandle &V1H = I->second;
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DSNodeHandle &V2H = J->second;
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// If at least one of the nodes is complete, we can say something about
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// this. If one is complete and the other isn't, then they are obviously
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// different nodes. If they are both complete, we can't say anything
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// useful.
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if (I->second.getNode()->isComplete() ||
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J->second.getNode()->isComplete()) {
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// If the two pointers point to different data structure graph nodes, they
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// cannot alias!
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if (V1H.getNode() != V2H.getNode())
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return NoAlias;
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// See if they point to different offsets... if so, we may be able to
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// determine that they do not alias...
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unsigned O1 = I->second.getOffset(), O2 = J->second.getOffset();
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if (O1 != O2) {
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if (O2 < O1) { // Ensure that O1 <= O2
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std::swap(V1, V2);
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std::swap(O1, O2);
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std::swap(V1Size, V2Size);
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}
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if (O1+V1Size <= O2)
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return NoAlias;
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}
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}
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}
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// If we cannot determine alias properties based on our graph, fall back on
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// some other AA implementation.
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//
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return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
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}
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AliasAnalysis::ModRefResult
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Steens::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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AliasAnalysis::ModRefResult Result = ModRef;
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// Find the node in question.
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DSGraph::ScalarMapTy &GSM = ResultGraph->getScalarMap();
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DSGraph::ScalarMapTy::iterator I = GSM.find(P);
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if (I != GSM.end() && !I->second.isNull()) {
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DSNode *N = I->second.getNode();
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if (N->isComplete()) {
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// If this is a direct call to an external function, and if the pointer
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// points to a complete node, the external function cannot modify or read
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// the value (we know it's not passed out of the program!).
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if (Function *F = CS.getCalledFunction())
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if (F->isExternal())
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return NoModRef;
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// Otherwise, if the node is complete, but it is only M or R, return this.
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// This can be useful for globals that should be marked const but are not.
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if (!N->isModified())
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Result = (ModRefResult)(Result & ~Mod);
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if (!N->isRead())
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Result = (ModRefResult)(Result & ~Ref);
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}
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}
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return (ModRefResult)(Result & AliasAnalysis::getModRefInfo(CS, P, Size));
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}
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AliasAnalysis::ModRefResult
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Steens::getModRefInfo(CallSite CS1, CallSite CS2)
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{
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return AliasAnalysis::getModRefInfo(CS1,CS2);
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}
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