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de6cc372e3
llvm-svn: 20873
301 lines
11 KiB
C++
301 lines
11 KiB
C++
//===- DataStructureAA.cpp - Data Structure Based 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 top-down data structure graphs to implement a simple
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// context sensitive alias analysis.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Module.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/Analysis/DataStructure/DataStructure.h"
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#include "llvm/Analysis/DataStructure/DSGraph.h"
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using namespace llvm;
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namespace {
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class DSAA : public ModulePass, public AliasAnalysis {
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TDDataStructures *TD;
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BUDataStructures *BU;
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// These members are used to cache mod/ref information to make us return
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// results faster, particularly for aa-eval. On the first request of
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// mod/ref information for a particular call site, we compute and store the
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// calculated nodemap for the call site. Any time DSA info is updated we
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// free this information, and when we move onto a new call site, this
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// information is also freed.
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CallSite MapCS;
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std::multimap<DSNode*, const DSNode*> CallerCalleeMap;
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public:
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DSAA() : TD(0) {}
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~DSAA() {
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InvalidateCache();
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}
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void InvalidateCache() {
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MapCS = CallSite();
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CallerCalleeMap.clear();
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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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InitializeAliasAnalysis(this);
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TD = &getAnalysis<TDDataStructures>();
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BU = &getAnalysis<BUDataStructures>();
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return false;
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}
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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.addRequiredTransitive<TDDataStructures>(); // Uses TD Datastructures
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AU.addRequiredTransitive<BUDataStructures>(); // Uses BU Datastructures
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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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ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
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ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
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return AliasAnalysis::getModRefInfo(CS1,CS2);
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}
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virtual void deleteValue(Value *V) {
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InvalidateCache();
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BU->deleteValue(V);
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TD->deleteValue(V);
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}
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virtual void copyValue(Value *From, Value *To) {
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if (From == To) return;
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InvalidateCache();
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BU->copyValue(From, To);
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TD->copyValue(From, To);
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}
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private:
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DSGraph *getGraphForValue(const Value *V);
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};
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// Register the pass...
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RegisterOpt<DSAA> X("ds-aa", "Data Structure Graph Based Alias Analysis");
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// Register as an implementation of AliasAnalysis
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RegisterAnalysisGroup<AliasAnalysis, DSAA> Y;
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}
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ModulePass *llvm::createDSAAPass() { return new DSAA(); }
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// getGraphForValue - Return the DSGraph to use for queries about the specified
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// value...
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//
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DSGraph *DSAA::getGraphForValue(const Value *V) {
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if (const Instruction *I = dyn_cast<Instruction>(V))
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return &TD->getDSGraph(*I->getParent()->getParent());
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else if (const Argument *A = dyn_cast<Argument>(V))
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return &TD->getDSGraph(*A->getParent());
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else if (const BasicBlock *BB = dyn_cast<BasicBlock>(V))
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return &TD->getDSGraph(*BB->getParent());
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return 0;
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}
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AliasAnalysis::AliasResult DSAA::alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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if (V1 == V2) return MustAlias;
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DSGraph *G1 = getGraphForValue(V1);
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DSGraph *G2 = getGraphForValue(V2);
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assert((!G1 || !G2 || G1 == G2) && "Alias query for 2 different functions?");
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// Get the graph to use...
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DSGraph &G = *(G1 ? G1 : (G2 ? G2 : &TD->getGlobalsGraph()));
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const DSGraph::ScalarMapTy &GSM = G.getScalarMap();
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DSGraph::ScalarMapTy::const_iterator I = GSM.find((Value*)V1);
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if (I == GSM.end()) return NoAlias;
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DSGraph::ScalarMapTy::const_iterator J = GSM.find((Value*)V2);
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if (J == GSM.end()) return NoAlias;
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DSNode *N1 = I->second.getNode(), *N2 = J->second.getNode();
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unsigned O1 = I->second.getOffset(), O2 = J->second.getOffset();
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if (N1 == 0 || N2 == 0)
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// Can't tell whether anything aliases null.
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return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
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// We can only make a judgment of one of the nodes is complete...
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if (N1->isComplete() || N2->isComplete()) {
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if (N1 != N2)
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return NoAlias; // Completely different nodes.
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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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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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// FIXME: we could improve on this by checking the globals graph for aliased
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// global queries...
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return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
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}
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/// getModRefInfo - does a callsite modify or reference a value?
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///
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AliasAnalysis::ModRefResult
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DSAA::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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DSNode *N = 0;
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// First step, check our cache.
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if (CS.getInstruction() == MapCS.getInstruction()) {
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{
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const Function *Caller = CS.getInstruction()->getParent()->getParent();
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DSGraph &CallerTDGraph = TD->getDSGraph(*Caller);
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// Figure out which node in the TD graph this pointer corresponds to.
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DSScalarMap &CallerSM = CallerTDGraph.getScalarMap();
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DSScalarMap::iterator NI = CallerSM.find(P);
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if (NI == CallerSM.end()) {
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InvalidateCache();
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return DSAA::getModRefInfo(CS, P, Size);
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}
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N = NI->second.getNode();
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}
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HaveMappingInfo:
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assert(N && "Null pointer in scalar map??");
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typedef std::multimap<DSNode*, const DSNode*>::iterator NodeMapIt;
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std::pair<NodeMapIt, NodeMapIt> Range = CallerCalleeMap.equal_range(N);
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// Loop over all of the nodes in the callee that correspond to "N", keeping
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// track of aggregate mod/ref info.
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bool NeverReads = true, NeverWrites = true;
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for (; Range.first != Range.second; ++Range.first) {
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if (Range.first->second->isModified())
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NeverWrites = false;
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if (Range.first->second->isRead())
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NeverReads = false;
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if (NeverReads == false && NeverWrites == false)
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return AliasAnalysis::getModRefInfo(CS, P, Size);
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}
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ModRefResult Result = ModRef;
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if (NeverWrites) // We proved it was not modified.
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Result = ModRefResult(Result & ~Mod);
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if (NeverReads) // We proved it was not read.
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Result = ModRefResult(Result & ~Ref);
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return ModRefResult(Result & AliasAnalysis::getModRefInfo(CS, P, Size));
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}
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// Any cached info we have is for the wrong function.
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InvalidateCache();
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Function *F = CS.getCalledFunction();
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if (!F) return AliasAnalysis::getModRefInfo(CS, P, Size);
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if (F->isExternal()) {
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// If we are calling an external function, and if this global doesn't escape
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// the portion of the program we have analyzed, we can draw conclusions
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// based on whether the global escapes the program.
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Function *Caller = CS.getInstruction()->getParent()->getParent();
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DSGraph *G = &TD->getDSGraph(*Caller);
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DSScalarMap::iterator NI = G->getScalarMap().find(P);
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if (NI == G->getScalarMap().end()) {
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// If it wasn't in the local function graph, check the global graph. This
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// can occur for globals who are locally reference but hoisted out to the
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// globals graph despite that.
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G = G->getGlobalsGraph();
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NI = G->getScalarMap().find(P);
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if (NI == G->getScalarMap().end())
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return AliasAnalysis::getModRefInfo(CS, P, Size);
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}
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// If we found a node and it's complete, it cannot be passed out to the
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// called function.
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if (NI->second.getNode()->isComplete())
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return NoModRef;
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return AliasAnalysis::getModRefInfo(CS, P, Size);
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}
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// Get the graphs for the callee and caller. Note that we want the BU graph
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// for the callee because we don't want all caller's effects incorporated!
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const Function *Caller = CS.getInstruction()->getParent()->getParent();
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DSGraph &CallerTDGraph = TD->getDSGraph(*Caller);
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DSGraph &CalleeBUGraph = BU->getDSGraph(*F);
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// Figure out which node in the TD graph this pointer corresponds to.
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DSScalarMap &CallerSM = CallerTDGraph.getScalarMap();
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DSScalarMap::iterator NI = CallerSM.find(P);
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if (NI == CallerSM.end()) {
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ModRefResult Result = ModRef;
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if (isa<ConstantPointerNull>(P) || isa<UndefValue>(P))
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return NoModRef; // null is never modified :)
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else {
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assert(isa<GlobalVariable>(P) &&
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cast<GlobalVariable>(P)->getType()->getElementType()->isFirstClassType() &&
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"This isn't a global that DSA inconsiderately dropped "
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"from the graph?");
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DSGraph &GG = *CallerTDGraph.getGlobalsGraph();
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DSScalarMap::iterator NI = GG.getScalarMap().find(P);
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if (NI != GG.getScalarMap().end() && !NI->second.isNull()) {
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// Otherwise, if the node is only M or R, return this. This can be
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// useful for globals that should be marked const but are not.
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DSNode *N = NI->second.getNode();
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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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if (Result == NoModRef) return Result;
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return ModRefResult(Result & AliasAnalysis::getModRefInfo(CS, P, Size));
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}
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// Compute the mapping from nodes in the callee graph to the nodes in the
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// caller graph for this call site.
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DSGraph::NodeMapTy CalleeCallerMap;
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DSCallSite DSCS = CallerTDGraph.getDSCallSiteForCallSite(CS);
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CallerTDGraph.computeCalleeCallerMapping(DSCS, *F, CalleeBUGraph,
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CalleeCallerMap);
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// Remember the mapping and the call site for future queries.
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MapCS = CS;
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// Invert the mapping into CalleeCallerInvMap.
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for (DSGraph::NodeMapTy::iterator I = CalleeCallerMap.begin(),
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E = CalleeCallerMap.end(); I != E; ++I)
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CallerCalleeMap.insert(std::make_pair(I->second.getNode(), I->first));
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N = NI->second.getNode();
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goto HaveMappingInfo;
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}
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