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+//===- CFLAliasAnalysis.cpp - CFL-Based Alias Analysis Implementation ------==//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a CFL-based context-insensitive alias analysis
+// algorithm. It does not depend on types. The algorithm is a mixture of the one
+// described in "Demand-driven alias analysis for C" by Xin Zheng and Radu
+// Rugina, and "Fast algorithms for Dyck-CFL-reachability with applications to
+// Alias Analysis" by Zhang Q, Lyu M R, Yuan H, and Su Z. -- to summarize the
+// papers, we build a graph of the uses of a variable, where each node is a
+// memory location, and each edge is an action that happened on that memory
+// location. The "actions" can be one of Dereference, Reference, or Assign.
+//
+// Two variables are considered as aliasing iff you can reach one value's node
+// from the other value's node and the language formed by concatenating all of
+// the edge labels (actions) conforms to a context-free grammar.
+//
+// Because this algorithm requires a graph search on each query, we execute the
+// algorithm outlined in "Fast algorithms..." (mentioned above)
+// in order to transform the graph into sets of variables that may alias in
+// ~nlogn time (n = number of variables.), which makes queries take constant
+// time.
+//===----------------------------------------------------------------------===//
+
+#include "StratifiedSets.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/None.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/Passes.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/InstVisitor.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/ValueHandle.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <cassert>
+#include <forward_list>
+#include <memory>
+#include <tuple>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "cfl-aa"
+
+// Try to go from a Value* to a Function*. Never returns nullptr.
+static Optional<Function *> parentFunctionOfValue(Value *);
+
+// Returns possible functions called by the Inst* into the given
+// SmallVectorImpl. Returns true if targets found, false otherwise.
+// This is templated because InvokeInst/CallInst give us the same
+// set of functions that we care about, and I don't like repeating
+// myself.
+template <typename Inst>
+static bool getPossibleTargets(Inst *, SmallVectorImpl<Function *> &);
+
+// Some instructions need to have their users tracked. Instructions like
+// `add` require you to get the users of the Instruction* itself, other
+// instructions like `store` require you to get the users of the first
+// operand. This function gets the "proper" value to track for each
+// type of instruction we support.
+static Optional<Value *> getTargetValue(Instruction *);
+
+// There are certain instructions (i.e. FenceInst, etc.) that we ignore.
+// This notes that we should ignore those.
+static bool hasUsefulEdges(Instruction *);
+
+const StratifiedIndex StratifiedLink::SetSentinel =
+ std::numeric_limits<StratifiedIndex>::max();
+
+namespace {
+// StratifiedInfo Attribute things.
+typedef unsigned StratifiedAttr;
+LLVM_CONSTEXPR unsigned MaxStratifiedAttrIndex = NumStratifiedAttrs;
+LLVM_CONSTEXPR unsigned AttrAllIndex = 0;
+LLVM_CONSTEXPR unsigned AttrGlobalIndex = 1;
+LLVM_CONSTEXPR unsigned AttrUnknownIndex = 2;
+LLVM_CONSTEXPR unsigned AttrFirstArgIndex = 3;
+LLVM_CONSTEXPR unsigned AttrLastArgIndex = MaxStratifiedAttrIndex;
+LLVM_CONSTEXPR unsigned AttrMaxNumArgs = AttrLastArgIndex - AttrFirstArgIndex;
+
+LLVM_CONSTEXPR StratifiedAttr AttrNone = 0;
+LLVM_CONSTEXPR StratifiedAttr AttrUnknown = 1 << AttrUnknownIndex;
+LLVM_CONSTEXPR StratifiedAttr AttrAll = ~AttrNone;
+
+// \brief StratifiedSets call for knowledge of "direction", so this is how we
+// represent that locally.
+enum class Level { Same, Above, Below };
+
+// \brief Edges can be one of four "weights" -- each weight must have an inverse
+// weight (Assign has Assign; Reference has Dereference).
+enum class EdgeType {
+ // The weight assigned when assigning from or to a value. For example, in:
+ // %b = getelementptr %a, 0
+ // ...The relationships are %b assign %a, and %a assign %b. This used to be
+ // two edges, but having a distinction bought us nothing.
+ Assign,
+
+ // The edge used when we have an edge going from some handle to a Value.
+ // Examples of this include:
+ // %b = load %a (%b Dereference %a)
+ // %b = extractelement %a, 0 (%a Dereference %b)
+ Dereference,
+
+ // The edge used when our edge goes from a value to a handle that may have
+ // contained it at some point. Examples:
+ // %b = load %a (%a Reference %b)
+ // %b = extractelement %a, 0 (%b Reference %a)
+ Reference
+};
+
+// \brief Encodes the notion of a "use"
+struct Edge {
+ // \brief Which value the edge is coming from
+ Value *From;
+
+ // \brief Which value the edge is pointing to
+ Value *To;
+
+ // \brief Edge weight
+ EdgeType Weight;
+
+ // \brief Whether we aliased any external values along the way that may be
+ // invisible to the analysis (i.e. landingpad for exceptions, calls for
+ // interprocedural analysis, etc.)
+ StratifiedAttrs AdditionalAttrs;
+
+ Edge(Value *From, Value *To, EdgeType W, StratifiedAttrs A)
+ : From(From), To(To), Weight(W), AdditionalAttrs(A) {}
+};
+
+// \brief Information we have about a function and would like to keep around
+struct FunctionInfo {
+ StratifiedSets<Value *> Sets;
+ // Lots of functions have < 4 returns. Adjust as necessary.
+ SmallVector<Value *, 4> ReturnedValues;
+
+ FunctionInfo(StratifiedSets<Value *> &&S, SmallVector<Value *, 4> &&RV)
+ : Sets(std::move(S)), ReturnedValues(std::move(RV)) {}
+};
+
+struct CFLAliasAnalysis;
+
+struct FunctionHandle : public CallbackVH {
+ FunctionHandle(Function *Fn, CFLAliasAnalysis *CFLAA)
+ : CallbackVH(Fn), CFLAA(CFLAA) {
+ assert(Fn != nullptr);
+ assert(CFLAA != nullptr);
+ }
+
+ ~FunctionHandle() override {}
+
+ void deleted() override { removeSelfFromCache(); }
+ void allUsesReplacedWith(Value *) override { removeSelfFromCache(); }
+
+private:
+ CFLAliasAnalysis *CFLAA;
+
+ void removeSelfFromCache();
+};
+
+struct CFLAliasAnalysis : public ImmutablePass, public AliasAnalysis {
+private:
+ /// \brief Cached mapping of Functions to their StratifiedSets.
+ /// If a function's sets are currently being built, it is marked
+ /// in the cache as an Optional without a value. This way, if we
+ /// have any kind of recursion, it is discernable from a function
+ /// that simply has empty sets.
+ DenseMap<Function *, Optional<FunctionInfo>> Cache;
+ std::forward_list<FunctionHandle> Handles;
+
+public:
+ static char ID;
+
+ CFLAliasAnalysis() : ImmutablePass(ID) {
+ initializeCFLAliasAnalysisPass(*PassRegistry::getPassRegistry());
+ }
+
+ ~CFLAliasAnalysis() override {}
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AliasAnalysis::getAnalysisUsage(AU);
+ }
+
+ void *getAdjustedAnalysisPointer(const void *ID) override {
+ if (ID == &AliasAnalysis::ID)
+ return (AliasAnalysis *)this;
+ return this;
+ }
+
+ /// \brief Inserts the given Function into the cache.
+ void scan(Function *Fn);
+
+ void evict(Function *Fn) { Cache.erase(Fn); }
+
+ /// \brief Ensures that the given function is available in the cache.
+ /// Returns the appropriate entry from the cache.
+ const Optional<FunctionInfo> &ensureCached(Function *Fn) {
+ auto Iter = Cache.find(Fn);
+ if (Iter == Cache.end()) {
+ scan(Fn);
+ Iter = Cache.find(Fn);
+ assert(Iter != Cache.end());
+ assert(Iter->second.hasValue());
+ }
+ return Iter->second;
+ }
+
+ AliasResult query(const MemoryLocation &LocA, const MemoryLocation &LocB);
+
+ AliasResult alias(const MemoryLocation &LocA,
+ const MemoryLocation &LocB) override {
+ if (LocA.Ptr == LocB.Ptr) {
+ if (LocA.Size == LocB.Size) {
+ return MustAlias;
+ } else {
+ return PartialAlias;
+ }
+ }
+
+ // Comparisons between global variables and other constants should be
+ // handled by BasicAA.
+ // TODO: ConstantExpr handling -- CFLAA may report NoAlias when comparing
+ // a GlobalValue and ConstantExpr, but every query needs to have at least
+ // one Value tied to a Function, and neither GlobalValues nor ConstantExprs
+ // are.
+ if (isa<Constant>(LocA.Ptr) && isa<Constant>(LocB.Ptr)) {
+ return AliasAnalysis::alias(LocA, LocB);
+ }
+
+ AliasResult QueryResult = query(LocA, LocB);
+ if (QueryResult == MayAlias)
+ return AliasAnalysis::alias(LocA, LocB);
+
+ return QueryResult;
+ }
+
+ bool doInitialization(Module &M) override;
+};
+
+void FunctionHandle::removeSelfFromCache() {
+ assert(CFLAA != nullptr);
+ auto *Val = getValPtr();
+ CFLAA->evict(cast<Function>(Val));
+ setValPtr(nullptr);
+}
+
+// \brief Gets the edges our graph should have, based on an Instruction*
+class GetEdgesVisitor : public InstVisitor<GetEdgesVisitor, void> {
+ CFLAliasAnalysis &AA;
+ SmallVectorImpl<Edge> &Output;
+
+public:
+ GetEdgesVisitor(CFLAliasAnalysis &AA, SmallVectorImpl<Edge> &Output)
+ : AA(AA), Output(Output) {}
+
+ void visitInstruction(Instruction &) {
+ llvm_unreachable("Unsupported instruction encountered");
+ }
+
+ void visitPtrToIntInst(PtrToIntInst &Inst) {
+ auto *Ptr = Inst.getOperand(0);
+ Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
+ }
+
+ void visitIntToPtrInst(IntToPtrInst &Inst) {
+ auto *Ptr = &Inst;
+ Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
+ }
+
+ void visitCastInst(CastInst &Inst) {
+ Output.push_back(
+ Edge(&Inst, Inst.getOperand(0), EdgeType::Assign, AttrNone));
+ }
+
+ void visitBinaryOperator(BinaryOperator &Inst) {
+ auto *Op1 = Inst.getOperand(0);
+ auto *Op2 = Inst.getOperand(1);
+ Output.push_back(Edge(&Inst, Op1, EdgeType::Assign, AttrNone));
+ Output.push_back(Edge(&Inst, Op2, EdgeType::Assign, AttrNone));
+ }
+
+ void visitAtomicCmpXchgInst(AtomicCmpXchgInst &Inst) {
+ auto *Ptr = Inst.getPointerOperand();
+ auto *Val = Inst.getNewValOperand();
+ Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
+ }
+
+ void visitAtomicRMWInst(AtomicRMWInst &Inst) {
+ auto *Ptr = Inst.getPointerOperand();
+ auto *Val = Inst.getValOperand();
+ Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
+ }
+
+ void visitPHINode(PHINode &Inst) {
+ for (Value *Val : Inst.incoming_values()) {
+ Output.push_back(Edge(&Inst, Val, EdgeType::Assign, AttrNone));
+ }
+ }
+
+ void visitGetElementPtrInst(GetElementPtrInst &Inst) {
+ auto *Op = Inst.getPointerOperand();
+ Output.push_back(Edge(&Inst, Op, EdgeType::Assign, AttrNone));
+ for (auto I = Inst.idx_begin(), E = Inst.idx_end(); I != E; ++I)
+ Output.push_back(Edge(&Inst, *I, EdgeType::Assign, AttrNone));
+ }
+
+ void visitSelectInst(SelectInst &Inst) {
+ // Condition is not processed here (The actual statement producing
+ // the condition result is processed elsewhere). For select, the
+ // condition is evaluated, but not loaded, stored, or assigned
+ // simply as a result of being the condition of a select.
+
+ auto *TrueVal = Inst.getTrueValue();
+ Output.push_back(Edge(&Inst, TrueVal, EdgeType::Assign, AttrNone));
+ auto *FalseVal = Inst.getFalseValue();
+ Output.push_back(Edge(&Inst, FalseVal, EdgeType::Assign, AttrNone));
+ }
+
+ void visitAllocaInst(AllocaInst &) {}
+
+ void visitLoadInst(LoadInst &Inst) {
+ auto *Ptr = Inst.getPointerOperand();
+ auto *Val = &Inst;
+ Output.push_back(Edge(Val, Ptr, EdgeType::Reference, AttrNone));
+ }
+
+ void visitStoreInst(StoreInst &Inst) {
+ auto *Ptr = Inst.getPointerOperand();
+ auto *Val = Inst.getValueOperand();
+ Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
+ }
+
+ void visitVAArgInst(VAArgInst &Inst) {
+ // We can't fully model va_arg here. For *Ptr = Inst.getOperand(0), it does
+ // two things:
+ // 1. Loads a value from *((T*)*Ptr).
+ // 2. Increments (stores to) *Ptr by some target-specific amount.
+ // For now, we'll handle this like a landingpad instruction (by placing the
+ // result in its own group, and having that group alias externals).
+ auto *Val = &Inst;
+ Output.push_back(Edge(Val, Val, EdgeType::Assign, AttrAll));
+ }
+
+ static bool isFunctionExternal(Function *Fn) {
+ return Fn->isDeclaration() || !Fn->hasLocalLinkage();
+ }
+
+ // Gets whether the sets at Index1 above, below, or equal to the sets at
+ // Index2. Returns None if they are not in the same set chain.
+ static Optional<Level> getIndexRelation(const StratifiedSets<Value *> &Sets,
+ StratifiedIndex Index1,
+ StratifiedIndex Index2) {
+ if (Index1 == Index2)
+ return Level::Same;
+
+ const auto *Current = &Sets.getLink(Index1);
+ while (Current->hasBelow()) {
+ if (Current->Below == Index2)
+ return Level::Below;
+ Current = &Sets.getLink(Current->Below);
+ }
+
+ Current = &Sets.getLink(Index1);
+ while (Current->hasAbove()) {
+ if (Current->Above == Index2)
+ return Level::Above;
+ Current = &Sets.getLink(Current->Above);
+ }
+
+ return NoneType();
+ }
+
+ bool
+ tryInterproceduralAnalysis(const SmallVectorImpl<Function *> &Fns,
+ Value *FuncValue,
+ const iterator_range<User::op_iterator> &Args) {
+ const unsigned ExpectedMaxArgs = 8;
+ const unsigned MaxSupportedArgs = 50;
+ assert(Fns.size() > 0);
+
+ // I put this here to give us an upper bound on time taken by IPA. Is it
+ // really (realistically) needed? Keep in mind that we do have an n^2 algo.
+ if (std::distance(Args.begin(), Args.end()) > (int)MaxSupportedArgs)
+ return false;
+
+ // Exit early if we'll fail anyway
+ for (auto *Fn : Fns) {
+ if (isFunctionExternal(Fn) || Fn->isVarArg())
+ return false;
+ auto &MaybeInfo = AA.ensureCached(Fn);
+ if (!MaybeInfo.hasValue())
+ return false;
+ }
+
+ SmallVector<Value *, ExpectedMaxArgs> Arguments(Args.begin(), Args.end());
+ SmallVector<StratifiedInfo, ExpectedMaxArgs> Parameters;
+ for (auto *Fn : Fns) {
+ auto &Info = *AA.ensureCached(Fn);
+ auto &Sets = Info.Sets;
+ auto &RetVals = Info.ReturnedValues;
+
+ Parameters.clear();
+ for (auto &Param : Fn->args()) {
+ auto MaybeInfo = Sets.find(&Param);
+ // Did a new parameter somehow get added to the function/slip by?
+ if (!MaybeInfo.hasValue())
+ return false;
+ Parameters.push_back(*MaybeInfo);
+ }
+
+ // Adding an edge from argument -> return value for each parameter that
+ // may alias the return value
+ for (unsigned I = 0, E = Parameters.size(); I != E; ++I) {
+ auto &ParamInfo = Parameters[I];
+ auto &ArgVal = Arguments[I];
+ bool AddEdge = false;
+ StratifiedAttrs Externals;
+ for (unsigned X = 0, XE = RetVals.size(); X != XE; ++X) {
+ auto MaybeInfo = Sets.find(RetVals[X]);
+ if (!MaybeInfo.hasValue())
+ return false;
+
+ auto &RetInfo = *MaybeInfo;
+ auto RetAttrs = Sets.getLink(RetInfo.Index).Attrs;
+ auto ParamAttrs = Sets.getLink(ParamInfo.Index).Attrs;
+ auto MaybeRelation =
+ getIndexRelation(Sets, ParamInfo.Index, RetInfo.Index);
+ if (MaybeRelation.hasValue()) {
+ AddEdge = true;
+ Externals |= RetAttrs | ParamAttrs;
+ }
+ }
+ if (AddEdge)
+ Output.push_back(Edge(FuncValue, ArgVal, EdgeType::Assign,
+ StratifiedAttrs().flip()));
+ }
+
+ if (Parameters.size() != Arguments.size())
+ return false;
+
+ // Adding edges between arguments for arguments that may end up aliasing
+ // each other. This is necessary for functions such as
+ // void foo(int** a, int** b) { *a = *b; }
+ // (Technically, the proper sets for this would be those below
+ // Arguments[I] and Arguments[X], but our algorithm will produce
+ // extremely similar, and equally correct, results either way)
+ for (unsigned I = 0, E = Arguments.size(); I != E; ++I) {
+ auto &MainVal = Arguments[I];
+ auto &MainInfo = Parameters[I];
+ auto &MainAttrs = Sets.getLink(MainInfo.Index).Attrs;
+ for (unsigned X = I + 1; X != E; ++X) {
+ auto &SubInfo = Parameters[X];
+ auto &SubVal = Arguments[X];
+ auto &SubAttrs = Sets.getLink(SubInfo.Index).Attrs;
+ auto MaybeRelation =
+ getIndexRelation(Sets, MainInfo.Index, SubInfo.Index);
+
+ if (!MaybeRelation.hasValue())
+ continue;
+
+ auto NewAttrs = SubAttrs | MainAttrs;
+ Output.push_back(Edge(MainVal, SubVal, EdgeType::Assign, NewAttrs));
+ }
+ }
+ }
+ return true;
+ }
+
+ template <typename InstT> void visitCallLikeInst(InstT &Inst) {
+ SmallVector<Function *, 4> Targets;
+ if (getPossibleTargets(&Inst, Targets)) {
+ if (tryInterproceduralAnalysis(Targets, &Inst, Inst.arg_operands()))
+ return;
+ // Cleanup from interprocedural analysis
+ Output.clear();
+ }
+
+ for (Value *V : Inst.arg_operands())
+ Output.push_back(Edge(&Inst, V, EdgeType::Assign, AttrAll));
+ }
+
+ void visitCallInst(CallInst &Inst) { visitCallLikeInst(Inst); }
+
+ void visitInvokeInst(InvokeInst &Inst) { visitCallLikeInst(Inst); }
+
+ // Because vectors/aggregates are immutable and unaddressable,
+ // there's nothing we can do to coax a value out of them, other
+ // than calling Extract{Element,Value}. We can effectively treat
+ // them as pointers to arbitrary memory locations we can store in
+ // and load from.
+ void visitExtractElementInst(ExtractElementInst &Inst) {
+ auto *Ptr = Inst.getVectorOperand();
+ auto *Val = &Inst;
+ Output.push_back(Edge(Val, Ptr, EdgeType::Reference, AttrNone));
+ }
+
+ void visitInsertElementInst(InsertElementInst &Inst) {
+ auto *Vec = Inst.getOperand(0);
+ auto *Val = Inst.getOperand(1);
+ Output.push_back(Edge(&Inst, Vec, EdgeType::Assign, AttrNone));
+ Output.push_back(Edge(&Inst, Val, EdgeType::Dereference, AttrNone));
+ }
+
+ void visitLandingPadInst(LandingPadInst &Inst) {
+ // Exceptions come from "nowhere", from our analysis' perspective.
+ // So we place the instruction its own group, noting that said group may
+ // alias externals
+ Output.push_back(Edge(&Inst, &Inst, EdgeType::Assign, AttrAll));
+ }
+
+ void visitInsertValueInst(InsertValueInst &Inst) {
+ auto *Agg = Inst.getOperand(0);
+ auto *Val = Inst.getOperand(1);
+ Output.push_back(Edge(&Inst, Agg, EdgeType::Assign, AttrNone));
+ Output.push_back(Edge(&Inst, Val, EdgeType::Dereference, AttrNone));
+ }
+
+ void visitExtractValueInst(ExtractValueInst &Inst) {
+ auto *Ptr = Inst.getAggregateOperand();
+ Output.push_back(Edge(&Inst, Ptr, EdgeType::Reference, AttrNone));
+ }
+
+ void visitShuffleVectorInst(ShuffleVectorInst &Inst) {
+ auto *From1 = Inst.getOperand(0);
+ auto *From2 = Inst.getOperand(1);
+ Output.push_back(Edge(&Inst, From1, EdgeType::Assign, AttrNone));
+ Output.push_back(Edge(&Inst, From2, EdgeType::Assign, AttrNone));
+ }
+
+ void visitConstantExpr(ConstantExpr *CE) {
+ switch (CE->getOpcode()) {
+ default:
+ llvm_unreachable("Unknown instruction type encountered!");
+// Build the switch statement using the Instruction.def file.
+#define HANDLE_INST(NUM, OPCODE, CLASS) \
+ case Instruction::OPCODE: \
+ visit##OPCODE(*(CLASS *)CE); \
+ break;
+#include "llvm/IR/Instruction.def"
+ }
+ }
+};
+
+// For a given instruction, we need to know which Value* to get the
+// users of in order to build our graph. In some cases (i.e. add),
+// we simply need the Instruction*. In other cases (i.e. store),
+// finding the users of the Instruction* is useless; we need to find
+// the users of the first operand. This handles determining which
+// value to follow for us.
+//
+// Note: we *need* to keep this in sync with GetEdgesVisitor. Add
+// something to GetEdgesVisitor, add it here -- remove something from
+// GetEdgesVisitor, remove it here.
+class GetTargetValueVisitor
+ : public InstVisitor<GetTargetValueVisitor, Value *> {
+public:
+ Value *visitInstruction(Instruction &Inst) { return &Inst; }
+
+ Value *visitStoreInst(StoreInst &Inst) { return Inst.getPointerOperand(); }
+
+ Value *visitAtomicCmpXchgInst(AtomicCmpXchgInst &Inst) {
+ return Inst.getPointerOperand();
+ }
+
+ Value *visitAtomicRMWInst(AtomicRMWInst &Inst) {
+ return Inst.getPointerOperand();
+ }
+
+ Value *visitInsertElementInst(InsertElementInst &Inst) {
+ return Inst.getOperand(0);
+ }
+
+ Value *visitInsertValueInst(InsertValueInst &Inst) {
+ return Inst.getAggregateOperand();
+ }
+};
+
+// Set building requires a weighted bidirectional graph.
+template <typename EdgeTypeT> class WeightedBidirectionalGraph {
+public:
+ typedef std::size_t Node;
+
+private:
+ const static Node StartNode = Node(0);
+
+ struct Edge {
+ EdgeTypeT Weight;
+ Node Other;
+
+ Edge(const EdgeTypeT &W, const Node &N) : Weight(W), Other(N) {}
+
+ bool operator==(const Edge &E) const {
+ return Weight == E.Weight && Other == E.Other;
+ }
+
+ bool operator!=(const Edge &E) const { return !operator==(E); }
+ };
+
+ struct NodeImpl {
+ std::vector<Edge> Edges;
+ };
+
+ std::vector<NodeImpl> NodeImpls;
+
+ bool inbounds(Node NodeIndex) const { return NodeIndex < NodeImpls.size(); }
+
+ const NodeImpl &getNode(Node N) const { return NodeImpls[N]; }
+ NodeImpl &getNode(Node N) { return NodeImpls[N]; }
+
+public:
+ // ----- Various Edge iterators for the graph ----- //
+
+ // \brief Iterator for edges. Because this graph is bidirected, we don't
+ // allow modificaiton of the edges using this iterator. Additionally, the
+ // iterator becomes invalid if you add edges to or from the node you're
+ // getting the edges of.
+ struct EdgeIterator : public std::iterator<std::forward_iterator_tag,
+ std::tuple<EdgeTypeT, Node *>> {
+ EdgeIterator(const typename std::vector<Edge>::const_iterator &Iter)
+ : Current(Iter) {}
+
+ EdgeIterator(NodeImpl &Impl) : Current(Impl.begin()) {}
+
+ EdgeIterator &operator++() {
+ ++Current;
+ return *this;
+ }
+
+ EdgeIterator operator++(int) {
+ EdgeIterator Copy(Current);
+ operator++();
+ return Copy;
+ }
+
+ std::tuple<EdgeTypeT, Node> &operator*() {
+ Store = std::make_tuple(Current->Weight, Current->Other);
+ return Store;
+ }
+
+ bool operator==(const EdgeIterator &Other) const {
+ return Current == Other.Current;
+ }
+
+ bool operator!=(const EdgeIterator &Other) const {
+ return !operator==(Other);
+ }
+
+ private:
+ typename std::vector<Edge>::const_iterator Current;
+ std::tuple<EdgeTypeT, Node> Store;
+ };
+
+ // Wrapper for EdgeIterator with begin()/end() calls.
+ struct EdgeIterable {
+ EdgeIterable(const std::vector<Edge> &Edges)
+ : BeginIter(Edges.begin()), EndIter(Edges.end()) {}
+
+ EdgeIterator begin() { return EdgeIterator(BeginIter); }
+
+ EdgeIterator end() { return EdgeIterator(EndIter); }
+
+ private:
+ typename std::vector<Edge>::const_iterator BeginIter;
+ typename std::vector<Edge>::const_iterator EndIter;
+ };
+
+ // ----- Actual graph-related things ----- //
+
+ WeightedBidirectionalGraph() {}
+
+ WeightedBidirectionalGraph(WeightedBidirectionalGraph<EdgeTypeT> &&Other)
+ : NodeImpls(std::move(Other.NodeImpls)) {}
+
+ WeightedBidirectionalGraph<EdgeTypeT> &
+ operator=(WeightedBidirectionalGraph<EdgeTypeT> &&Other) {
+ NodeImpls = std::move(Other.NodeImpls);
+ return *this;
+ }
+
+ Node addNode() {
+ auto Index = NodeImpls.size();
+ auto NewNode = Node(Index);
+ NodeImpls.push_back(NodeImpl());
+ return NewNode;
+ }
+
+ void addEdge(Node From, Node To, const EdgeTypeT &Weight,
+ const EdgeTypeT &ReverseWeight) {
+ assert(inbounds(From));
+ assert(inbounds(To));
+ auto &FromNode = getNode(From);
+ auto &ToNode = getNode(To);
+ FromNode.Edges.push_back(Edge(Weight, To));
+ ToNode.Edges.push_back(Edge(ReverseWeight, From));
+ }
+
+ EdgeIterable edgesFor(const Node &N) const {
+ const auto &Node = getNode(N);
+ return EdgeIterable(Node.Edges);
+ }
+
+ bool empty() const { return NodeImpls.empty(); }
+ std::size_t size() const { return NodeImpls.size(); }
+
+ // \brief Gets an arbitrary node in the graph as a starting point for
+ // traversal.
+ Node getEntryNode() {
+ assert(inbounds(StartNode));
+ return StartNode;
+ }
+};
+
+typedef WeightedBidirectionalGraph<std::pair<EdgeType, StratifiedAttrs>> GraphT;
+typedef DenseMap<Value *, GraphT::Node> NodeMapT;
+}
+
+// -- Setting up/registering CFLAA pass -- //
+char CFLAliasAnalysis::ID = 0;
+
+INITIALIZE_AG_PASS(CFLAliasAnalysis, AliasAnalysis, "cfl-aa",
+ "CFL-Based AA implementation", false, true, false)
+
+ImmutablePass *llvm::createCFLAliasAnalysisPass() {
+ return new CFLAliasAnalysis();
+}
+
+//===----------------------------------------------------------------------===//
+// Function declarations that require types defined in the namespace above
+//===----------------------------------------------------------------------===//
+
+// Given an argument number, returns the appropriate Attr index to set.
+static StratifiedAttr argNumberToAttrIndex(StratifiedAttr);
+
+// Given a Value, potentially return which AttrIndex it maps to.
+static Optional<StratifiedAttr> valueToAttrIndex(Value *Val);
+
+// Gets the inverse of a given EdgeType.
+static EdgeType flipWeight(EdgeType);
+
+// Gets edges of the given Instruction*, writing them to the SmallVector*.
+static void argsToEdges(CFLAliasAnalysis &, Instruction *,
+ SmallVectorImpl<Edge> &);
+
+// Gets edges of the given ConstantExpr*, writing them to the SmallVector*.
+static void argsToEdges(CFLAliasAnalysis &, ConstantExpr *,
+ SmallVectorImpl<Edge> &);
+
+// Gets the "Level" that one should travel in StratifiedSets
+// given an EdgeType.
+static Level directionOfEdgeType(EdgeType);
+
+// Builds the graph needed for constructing the StratifiedSets for the
+// given function
+static void buildGraphFrom(CFLAliasAnalysis &, Function *,
+ SmallVectorImpl<Value *> &, NodeMapT &, GraphT &);
+
+// Gets the edges of a ConstantExpr as if it was an Instruction. This
+// function also acts on any nested ConstantExprs, adding the edges
+// of those to the given SmallVector as well.
+static void constexprToEdges(CFLAliasAnalysis &, ConstantExpr &,
+ SmallVectorImpl<Edge> &);
+
+// Given an Instruction, this will add it to the graph, along with any
+// Instructions that are potentially only available from said Instruction
+// For example, given the following line:
+// %0 = load i16* getelementptr ([1 x i16]* @a, 0, 0), align 2
+// addInstructionToGraph would add both the `load` and `getelementptr`
+// instructions to the graph appropriately.
+static void addInstructionToGraph(CFLAliasAnalysis &, Instruction &,
+ SmallVectorImpl<Value *> &, NodeMapT &,
+ GraphT &);
+
+// Notes whether it would be pointless to add the given Value to our sets.
+static bool canSkipAddingToSets(Value *Val);
+
+// Builds the graph + StratifiedSets for a function.
+static FunctionInfo buildSetsFrom(CFLAliasAnalysis &, Function *);
+
+static Optional<Function *> parentFunctionOfValue(Value *Val) {
+ if (auto *Inst = dyn_cast<Instruction>(Val)) {
+ auto *Bb = Inst->getParent();
+ return Bb->getParent();
+ }
+
+ if (auto *Arg = dyn_cast<Argument>(Val))
+ return Arg->getParent();
+ return NoneType();
+}
+
+template <typename Inst>
+static bool getPossibleTargets(Inst *Call,
+ SmallVectorImpl<Function *> &Output) {
+ if (auto *Fn = Call->getCalledFunction()) {
+ Output.push_back(Fn);
+ return true;
+ }
+
+ // TODO: If the call is indirect, we might be able to enumerate all potential
+ // targets of the call and return them, rather than just failing.
+ return false;
+}
+
+static Optional<Value *> getTargetValue(Instruction *Inst) {
+ GetTargetValueVisitor V;
+ return V.visit(Inst);
+}
+
+static bool hasUsefulEdges(Instruction *Inst) {
+ bool IsNonInvokeTerminator =
+ isa<TerminatorInst>(Inst) && !isa<InvokeInst>(Inst);
+ return !isa<CmpInst>(Inst) && !isa<FenceInst>(Inst) && !IsNonInvokeTerminator;
+}
+
+static bool hasUsefulEdges(ConstantExpr *CE) {
+ // ConstantExpr doens't have terminators, invokes, or fences, so only needs
+ // to check for compares.
+ return CE->getOpcode() != Instruction::ICmp &&
+ CE->getOpcode() != Instruction::FCmp;
+}
+
+static Optional<StratifiedAttr> valueToAttrIndex(Value *Val) {
+ if (isa<GlobalValue>(Val))
+ return AttrGlobalIndex;
+
+ if (auto *Arg = dyn_cast<Argument>(Val))
+ // Only pointer arguments should have the argument attribute,
+ // because things can't escape through scalars without us seeing a
+ // cast, and thus, interaction with them doesn't matter.
+ if (!Arg->hasNoAliasAttr() && Arg->getType()->isPointerTy())
+ return argNumberToAttrIndex(Arg->getArgNo());
+ return NoneType();
+}
+
+static StratifiedAttr argNumberToAttrIndex(unsigned ArgNum) {
+ if (ArgNum >= AttrMaxNumArgs)
+ return AttrAllIndex;
+ return ArgNum + AttrFirstArgIndex;
+}
+
+static EdgeType flipWeight(EdgeType Initial) {
+ switch (Initial) {
+ case EdgeType::Assign:
+ return EdgeType::Assign;
+ case EdgeType::Dereference:
+ return EdgeType::Reference;
+ case EdgeType::Reference:
+ return EdgeType::Dereference;
+ }
+ llvm_unreachable("Incomplete coverage of EdgeType enum");
+}
+
+static void argsToEdges(CFLAliasAnalysis &Analysis, Instruction *Inst,
+ SmallVectorImpl<Edge> &Output) {
+ assert(hasUsefulEdges(Inst) &&
+ "Expected instructions to have 'useful' edges");
+ GetEdgesVisitor v(Analysis, Output);
+ v.visit(Inst);
+}
+
+static void argsToEdges(CFLAliasAnalysis &Analysis, ConstantExpr *CE,
+ SmallVectorImpl<Edge> &Output) {
+ assert(hasUsefulEdges(CE) && "Expected constant expr to have 'useful' edges");
+ GetEdgesVisitor v(Analysis, Output);
+ v.visitConstantExpr(CE);
+}
+
+static Level directionOfEdgeType(EdgeType Weight) {
+ switch (Weight) {
+ case EdgeType::Reference:
+ return Level::Above;
+ case EdgeType::Dereference:
+ return Level::Below;
+ case EdgeType::Assign:
+ return Level::Same;
+ }
+ llvm_unreachable("Incomplete switch coverage");
+}
+
+static void constexprToEdges(CFLAliasAnalysis &Analysis,
+ ConstantExpr &CExprToCollapse,
+ SmallVectorImpl<Edge> &Results) {
+ SmallVector<ConstantExpr *, 4> Worklist;
+ Worklist.push_back(&CExprToCollapse);
+
+ SmallVector<Edge, 8> ConstexprEdges;
+ SmallPtrSet<ConstantExpr *, 4> Visited;
+ while (!Worklist.empty()) {
+ auto *CExpr = Worklist.pop_back_val();
+
+ if (!hasUsefulEdges(CExpr))
+ continue;
+
+ ConstexprEdges.clear();
+ argsToEdges(Analysis, CExpr, ConstexprEdges);
+ for (auto &Edge : ConstexprEdges) {
+ if (auto *Nested = dyn_cast<ConstantExpr>(Edge.From))
+ if (Visited.insert(Nested).second)
+ Worklist.push_back(Nested);
+
+ if (auto *Nested = dyn_cast<ConstantExpr>(Edge.To))
+ if (Visited.insert(Nested).second)
+ Worklist.push_back(Nested);
+ }
+
+ Results.append(ConstexprEdges.begin(), ConstexprEdges.end());
+ }
+}
+
+static void addInstructionToGraph(CFLAliasAnalysis &Analysis, Instruction &Inst,
+ SmallVectorImpl<Value *> &ReturnedValues,
+ NodeMapT &Map, GraphT &Graph) {
+ const auto findOrInsertNode = [&Map, &Graph](Value *Val) {
+ auto Pair = Map.insert(std::make_pair(Val, GraphT::Node()));
+ auto &Iter = Pair.first;
+ if (Pair.second) {
+ auto NewNode = Graph.addNode();
+ Iter->second = NewNode;
+ }
+ return Iter->second;
+ };
+
+ // We don't want the edges of most "return" instructions, but we *do* want
+ // to know what can be returned.
+ if (isa<ReturnInst>(&Inst))
+ ReturnedValues.push_back(&Inst);
+
+ if (!hasUsefulEdges(&Inst))
+ return;
+
+ SmallVector<Edge, 8> Edges;
+ argsToEdges(Analysis, &Inst, Edges);
+
+ // In the case of an unused alloca (or similar), edges may be empty. Note
+ // that it exists so we can potentially answer NoAlias.
+ if (Edges.empty()) {
+ auto MaybeVal = getTargetValue(&Inst);
+ assert(MaybeVal.hasValue());
+ auto *Target = *MaybeVal;
+ findOrInsertNode(Target);
+ return;
+ }
+
+ const auto addEdgeToGraph = [&Graph, &findOrInsertNode](const Edge &E) {
+ auto To = findOrInsertNode(E.To);
+ auto From = findOrInsertNode(E.From);
+ auto FlippedWeight = flipWeight(E.Weight);
+ auto Attrs = E.AdditionalAttrs;
+ Graph.addEdge(From, To, std::make_pair(E.Weight, Attrs),
+ std::make_pair(FlippedWeight, Attrs));
+ };
+
+ SmallVector<ConstantExpr *, 4> ConstantExprs;
+ for (const Edge &E : Edges) {
+ addEdgeToGraph(E);
+ if (auto *Constexpr = dyn_cast<ConstantExpr>(E.To))
+ ConstantExprs.push_back(Constexpr);
+ if (auto *Constexpr = dyn_cast<ConstantExpr>(E.From))
+ ConstantExprs.push_back(Constexpr);
+ }
+
+ for (ConstantExpr *CE : ConstantExprs) {
+ Edges.clear();
+ constexprToEdges(Analysis, *CE, Edges);
+ std::for_each(Edges.begin(), Edges.end(), addEdgeToGraph);
+ }
+}
+
+// Aside: We may remove graph construction entirely, because it doesn't really
+// buy us much that we don't already have. I'd like to add interprocedural
+// analysis prior to this however, in case that somehow requires the graph
+// produced by this for efficient execution
+static void buildGraphFrom(CFLAliasAnalysis &Analysis, Function *Fn,
+ SmallVectorImpl<Value *> &ReturnedValues,
+ NodeMapT &Map, GraphT &Graph) {
+ for (auto &Bb : Fn->getBasicBlockList())
+ for (auto &Inst : Bb.getInstList())
+ addInstructionToGraph(Analysis, Inst, ReturnedValues, Map, Graph);
+}
+
+static bool canSkipAddingToSets(Value *Val) {
+ // Constants can share instances, which may falsely unify multiple
+ // sets, e.g. in
+ // store i32* null, i32** %ptr1
+ // store i32* null, i32** %ptr2
+ // clearly ptr1 and ptr2 should not be unified into the same set, so
+ // we should filter out the (potentially shared) instance to
+ // i32* null.
+ if (isa<Constant>(Val)) {
+ bool Container = isa<ConstantVector>(Val) || isa<ConstantArray>(Val) ||
+ isa<ConstantStruct>(Val);
+ // TODO: Because all of these things are constant, we can determine whether
+ // the data is *actually* mutable at graph building time. This will probably
+ // come for free/cheap with offset awareness.
+ bool CanStoreMutableData =
+ isa<GlobalValue>(Val) || isa<ConstantExpr>(Val) || Container;
+ return !CanStoreMutableData;
+ }
+
+ return false;
+}
+
+static FunctionInfo buildSetsFrom(CFLAliasAnalysis &Analysis, Function *Fn) {
+ NodeMapT Map;
+ GraphT Graph;
+ SmallVector<Value *, 4> ReturnedValues;
+
+ buildGraphFrom(Analysis, Fn, ReturnedValues, Map, Graph);
+
+ DenseMap<GraphT::Node, Value *> NodeValueMap;
+ NodeValueMap.resize(Map.size());
+ for (const auto &Pair : Map)
+ NodeValueMap.insert(std::make_pair(Pair.second, Pair.first));
+
+ const auto findValueOrDie = [&NodeValueMap](GraphT::Node Node) {
+ auto ValIter = NodeValueMap.find(Node);
+ assert(ValIter != NodeValueMap.end());
+ return ValIter->second;
+ };
+
+ StratifiedSetsBuilder<Value *> Builder;
+
+ SmallVector<GraphT::Node, 16> Worklist;
+ for (auto &Pair : Map) {
+ Worklist.clear();
+
+ auto *Value = Pair.first;
+ Builder.add(Value);
+ auto InitialNode = Pair.second;
+ Worklist.push_back(InitialNode);
+ while (!Worklist.empty()) {
+ auto Node = Worklist.pop_back_val();
+ auto *CurValue = findValueOrDie(Node);
+ if (canSkipAddingToSets(CurValue))
+ continue;
+
+ for (const auto &EdgeTuple : Graph.edgesFor(Node)) {
+ auto Weight = std::get<0>(EdgeTuple);
+ auto Label = Weight.first;
+ auto &OtherNode = std::get<1>(EdgeTuple);
+ auto *OtherValue = findValueOrDie(OtherNode);
+
+ if (canSkipAddingToSets(OtherValue))
+ continue;
+
+ bool Added;
+ switch (directionOfEdgeType(Label)) {
+ case Level::Above:
+ Added = Builder.addAbove(CurValue, OtherValue);
+ break;
+ case Level::Below:
+ Added = Builder.addBelow(CurValue, OtherValue);
+ break;
+ case Level::Same:
+ Added = Builder.addWith(CurValue, OtherValue);
+ break;
+ }
+
+ auto Aliasing = Weight.second;
+ if (auto MaybeCurIndex = valueToAttrIndex(CurValue))
+ Aliasing.set(*MaybeCurIndex);
+ if (auto MaybeOtherIndex = valueToAttrIndex(OtherValue))
+ Aliasing.set(*MaybeOtherIndex);
+ Builder.noteAttributes(CurValue, Aliasing);
+ Builder.noteAttributes(OtherValue, Aliasing);
+
+ if (Added)
+ Worklist.push_back(OtherNode);
+ }
+ }
+ }
+
+ // There are times when we end up with parameters not in our graph (i.e. if
+ // it's only used as the condition of a branch). Other bits of code depend on
+ // things that were present during construction being present in the graph.
+ // So, we add all present arguments here.
+ for (auto &Arg : Fn->args()) {
+ if (!Builder.add(&Arg))
+ continue;
+
+ auto Attrs = valueToAttrIndex(&Arg);
+ if (Attrs.hasValue())
+ Builder.noteAttributes(&Arg, *Attrs);
+ }
+
+ return FunctionInfo(Builder.build(), std::move(ReturnedValues));
+}
+
+void CFLAliasAnalysis::scan(Function *Fn) {
+ auto InsertPair = Cache.insert(std::make_pair(Fn, Optional<FunctionInfo>()));
+ (void)InsertPair;
+ assert(InsertPair.second &&
+ "Trying to scan a function that has already been cached");
+
+ FunctionInfo Info(buildSetsFrom(*this, Fn));
+ Cache[Fn] = std::move(Info);
+ Handles.push_front(FunctionHandle(Fn, this));
+}
+
+AliasResult CFLAliasAnalysis::query(const MemoryLocation &LocA,
+ const MemoryLocation &LocB) {
+ auto *ValA = const_cast<Value *>(LocA.Ptr);
+ auto *ValB = const_cast<Value *>(LocB.Ptr);
+
+ Function *Fn = nullptr;
+ auto MaybeFnA = parentFunctionOfValue(ValA);
+ auto MaybeFnB = parentFunctionOfValue(ValB);
+ if (!MaybeFnA.hasValue() && !MaybeFnB.hasValue()) {
+ // The only times this is known to happen are when globals + InlineAsm
+ // are involved
+ DEBUG(dbgs() << "CFLAA: could not extract parent function information.\n");
+ return MayAlias;
+ }
+
+ if (MaybeFnA.hasValue()) {
+ Fn = *MaybeFnA;
+ assert((!MaybeFnB.hasValue() || *MaybeFnB == *MaybeFnA) &&
+ "Interprocedural queries not supported");
+ } else {
+ Fn = *MaybeFnB;
+ }
+
+ assert(Fn != nullptr);
+ auto &MaybeInfo = ensureCached(Fn);
+ assert(MaybeInfo.hasValue());
+
+ auto &Sets = MaybeInfo->Sets;
+ auto MaybeA = Sets.find(ValA);
+ if (!MaybeA.hasValue())
+ return MayAlias;
+
+ auto MaybeB = Sets.find(ValB);
+ if (!MaybeB.hasValue())
+ return MayAlias;
+
+ auto SetA = *MaybeA;
+ auto SetB = *MaybeB;
+ auto AttrsA = Sets.getLink(SetA.Index).Attrs;
+ auto AttrsB = Sets.getLink(SetB.Index).Attrs;
+
+ // Stratified set attributes are used as markets to signify whether a member
+ // of a StratifiedSet (or a member of a set above the current set) has
+ // interacted with either arguments or globals. "Interacted with" meaning
+ // its value may be different depending on the value of an argument or
+ // global. The thought behind this is that, because arguments and globals
+ // may alias each other, if AttrsA and AttrsB have touched args/globals,
+ // we must conservatively say that they alias. However, if at least one of
+ // the sets has no values that could legally be altered by changing the value
+ // of an argument or global, then we don't have to be as conservative.
+ if (AttrsA.any() && AttrsB.any())
+ return MayAlias;
+
+ // We currently unify things even if the accesses to them may not be in
+ // bounds, so we can't return partial alias here because we don't
+ // know whether the pointer is really within the object or not.
+ // IE Given an out of bounds GEP and an alloca'd pointer, we may
+ // unify the two. We can't return partial alias for this case.
+ // Since we do not currently track enough information to
+ // differentiate
+
+ if (SetA.Index == SetB.Index)
+ return MayAlias;
+
+ return NoAlias;
+}
+
+bool CFLAliasAnalysis::doInitialization(Module &M) {
+ InitializeAliasAnalysis(this, &M.getDataLayout());
+ return true;
+}
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