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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...
+ RegisterOpt<DSAA> X("ds-aa", "Data Structure Graph Based Alias Analysis");
+
+ // Register as an implementation of AliasAnalysis
+ RegisterAnalysisGroup<AliasAnalysis, DSAA> Y;
+}
+
+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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