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