1 //===- CFLAliasAnalysis.cpp - CFL-Based Alias Analysis Implementation ------==//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements a CFL-based context-insensitive alias analysis
11 // algorithm. It does not depend on types. The algorithm is a mixture of the one
12 // described in "Demand-driven alias analysis for C" by Xin Zheng and Radu
13 // Rugina, and "Fast algorithms for Dyck-CFL-reachability with applications to
14 // Alias Analysis" by Zhang Q, Lyu M R, Yuan H, and Su Z. -- to summarize the
15 // papers, we build a graph of the uses of a variable, where each node is a
16 // memory location, and each edge is an action that happened on that memory
17 // location. The "actions" can be one of Dereference, Reference, Assign, or
20 // Two variables are considered as aliasing iff you can reach one value's node
21 // from the other value's node and the language formed by concatenating all of
22 // the edge labels (actions) conforms to a context-free grammar.
24 // Because this algorithm requires a graph search on each query, we execute the
25 // algorithm outlined in "Fast algorithms..." (mentioned above)
26 // in order to transform the graph into sets of variables that may alias in
27 // ~nlogn time (n = number of variables.), which makes queries take constant
29 //===----------------------------------------------------------------------===//
31 #include "StratifiedSets.h"
32 #include "llvm/ADT/BitVector.h"
33 #include "llvm/ADT/DenseMap.h"
34 #include "llvm/ADT/None.h"
35 #include "llvm/ADT/Optional.h"
36 #include "llvm/Analysis/AliasAnalysis.h"
37 #include "llvm/Analysis/Passes.h"
38 #include "llvm/IR/Constants.h"
39 #include "llvm/IR/Function.h"
40 #include "llvm/IR/InstVisitor.h"
41 #include "llvm/IR/Instructions.h"
42 #include "llvm/IR/ValueHandle.h"
43 #include "llvm/Pass.h"
44 #include "llvm/Support/Allocator.h"
45 #include "llvm/Support/Compiler.h"
46 #include "llvm/Support/Debug.h"
47 #include "llvm/Support/ErrorHandling.h"
51 #include <forward_list>
56 #define DEBUG_TYPE "cfl-aa"
58 // Try to go from a Value* to a Function*. Never returns nullptr.
59 static Optional<Function *> parentFunctionOfValue(Value *);
61 // Returns possible functions called by the Inst* into the given
62 // SmallVectorImpl. Returns true if targets found, false otherwise.
63 // This is templated because InvokeInst/CallInst give us the same
64 // set of functions that we care about, and I don't like repeating
66 template <typename Inst>
67 static bool getPossibleTargets(Inst *, SmallVectorImpl<Function *> &);
69 // Some instructions need to have their users tracked. Instructions like
70 // `add` require you to get the users of the Instruction* itself, other
71 // instructions like `store` require you to get the users of the first
72 // operand. This function gets the "proper" value to track for each
73 // type of instruction we support.
74 static Optional<Value *> getTargetValue(Instruction *);
76 // There are certain instructions (i.e. FenceInst, etc.) that we ignore.
77 // This notes that we should ignore those.
78 static bool hasUsefulEdges(Instruction *);
80 const StratifiedIndex StratifiedLink::SetSentinel =
81 std::numeric_limits<StratifiedIndex>::max();
84 // StratifiedInfo Attribute things.
85 typedef unsigned StratifiedAttr;
86 LLVM_CONSTEXPR unsigned MaxStratifiedAttrIndex = NumStratifiedAttrs;
87 LLVM_CONSTEXPR unsigned AttrAllIndex = 0;
88 LLVM_CONSTEXPR unsigned AttrGlobalIndex = 1;
89 LLVM_CONSTEXPR unsigned AttrUnknownIndex = 2;
90 LLVM_CONSTEXPR unsigned AttrFirstArgIndex = 3;
91 LLVM_CONSTEXPR unsigned AttrLastArgIndex = MaxStratifiedAttrIndex;
92 LLVM_CONSTEXPR unsigned AttrMaxNumArgs = AttrLastArgIndex - AttrFirstArgIndex;
94 LLVM_CONSTEXPR StratifiedAttr AttrNone = 0;
95 LLVM_CONSTEXPR StratifiedAttr AttrUnknown = 1 << AttrUnknownIndex;
96 LLVM_CONSTEXPR StratifiedAttr AttrAll = ~AttrNone;
98 // \brief StratifiedSets call for knowledge of "direction", so this is how we
99 // represent that locally.
100 enum class Level { Same, Above, Below };
102 // \brief Edges can be one of four "weights" -- each weight must have an inverse
103 // weight (Assign has Assign; Reference has Dereference).
104 enum class EdgeType {
105 // The weight assigned when assigning from or to a value. For example, in:
106 // %b = getelementptr %a, 0
107 // ...The relationships are %b assign %a, and %a assign %b. This used to be
108 // two edges, but having a distinction bought us nothing.
111 // The edge used when we have an edge going from some handle to a Value.
112 // Examples of this include:
113 // %b = load %a (%b Dereference %a)
114 // %b = extractelement %a, 0 (%a Dereference %b)
117 // The edge used when our edge goes from a value to a handle that may have
118 // contained it at some point. Examples:
119 // %b = load %a (%a Reference %b)
120 // %b = extractelement %a, 0 (%b Reference %a)
124 // \brief Encodes the notion of a "use"
126 // \brief Which value the edge is coming from
129 // \brief Which value the edge is pointing to
132 // \brief Edge weight
135 // \brief Whether we aliased any external values along the way that may be
136 // invisible to the analysis (i.e. landingpad for exceptions, calls for
137 // interprocedural analysis, etc.)
138 StratifiedAttrs AdditionalAttrs;
140 Edge(Value *From, Value *To, EdgeType W, StratifiedAttrs A)
141 : From(From), To(To), Weight(W), AdditionalAttrs(A) {}
144 // \brief Information we have about a function and would like to keep around
145 struct FunctionInfo {
146 StratifiedSets<Value *> Sets;
147 // Lots of functions have < 4 returns. Adjust as necessary.
148 SmallVector<Value *, 4> ReturnedValues;
150 FunctionInfo(StratifiedSets<Value *> &&S,
151 SmallVector<Value *, 4> &&RV)
152 : Sets(std::move(S)), ReturnedValues(std::move(RV)) {}
155 struct CFLAliasAnalysis;
157 struct FunctionHandle : public CallbackVH {
158 FunctionHandle(Function *Fn, CFLAliasAnalysis *CFLAA)
159 : CallbackVH(Fn), CFLAA(CFLAA) {
160 assert(Fn != nullptr);
161 assert(CFLAA != nullptr);
164 virtual ~FunctionHandle() {}
166 void deleted() override { removeSelfFromCache(); }
167 void allUsesReplacedWith(Value *) override { removeSelfFromCache(); }
170 CFLAliasAnalysis *CFLAA;
172 void removeSelfFromCache();
175 struct CFLAliasAnalysis : public ImmutablePass, public AliasAnalysis {
177 /// \brief Cached mapping of Functions to their StratifiedSets.
178 /// If a function's sets are currently being built, it is marked
179 /// in the cache as an Optional without a value. This way, if we
180 /// have any kind of recursion, it is discernable from a function
181 /// that simply has empty sets.
182 DenseMap<Function *, Optional<FunctionInfo>> Cache;
183 std::forward_list<FunctionHandle> Handles;
188 CFLAliasAnalysis() : ImmutablePass(ID) {
189 initializeCFLAliasAnalysisPass(*PassRegistry::getPassRegistry());
192 virtual ~CFLAliasAnalysis() {}
194 void getAnalysisUsage(AnalysisUsage &AU) const override {
195 AliasAnalysis::getAnalysisUsage(AU);
198 void *getAdjustedAnalysisPointer(const void *ID) override {
199 if (ID == &AliasAnalysis::ID)
200 return (AliasAnalysis *)this;
204 /// \brief Inserts the given Function into the cache.
205 void scan(Function *Fn);
207 void evict(Function *Fn) { Cache.erase(Fn); }
209 /// \brief Ensures that the given function is available in the cache.
210 /// Returns the appropriate entry from the cache.
211 const Optional<FunctionInfo> &ensureCached(Function *Fn) {
212 auto Iter = Cache.find(Fn);
213 if (Iter == Cache.end()) {
215 Iter = Cache.find(Fn);
216 assert(Iter != Cache.end());
217 assert(Iter->second.hasValue());
222 AliasResult query(const Location &LocA, const Location &LocB);
224 AliasResult alias(const Location &LocA, const Location &LocB) override {
225 if (LocA.Ptr == LocB.Ptr) {
226 if (LocA.Size == LocB.Size) {
233 // Comparisons between global variables and other constants should be
234 // handled by BasicAA.
235 // TODO: ConstantExpr handling -- CFLAA may report NoAlias when comparing
236 // a GlobalValue and ConstantExpr, but every query needs to have at least
237 // one Value tied to a Function, and neither GlobalValues nor ConstantExprs
239 if (isa<Constant>(LocA.Ptr) && isa<Constant>(LocB.Ptr)) {
240 return AliasAnalysis::alias(LocA, LocB);
243 AliasResult QueryResult = query(LocA, LocB);
244 if (QueryResult == MayAlias)
245 return AliasAnalysis::alias(LocA, LocB);
250 bool doInitialization(Module &M) override;
253 void FunctionHandle::removeSelfFromCache() {
254 assert(CFLAA != nullptr);
255 auto *Val = getValPtr();
256 CFLAA->evict(cast<Function>(Val));
260 // \brief Gets the edges our graph should have, based on an Instruction*
261 class GetEdgesVisitor : public InstVisitor<GetEdgesVisitor, void> {
262 CFLAliasAnalysis &AA;
263 SmallVectorImpl<Edge> &Output;
266 GetEdgesVisitor(CFLAliasAnalysis &AA, SmallVectorImpl<Edge> &Output)
267 : AA(AA), Output(Output) {}
269 void visitInstruction(Instruction &) {
270 llvm_unreachable("Unsupported instruction encountered");
273 void visitPtrToIntInst(PtrToIntInst &Inst) {
274 auto *Ptr = Inst.getOperand(0);
275 Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
278 void visitIntToPtrInst(IntToPtrInst &Inst) {
280 Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
283 void visitCastInst(CastInst &Inst) {
284 Output.push_back(Edge(&Inst, Inst.getOperand(0), EdgeType::Assign,
288 void visitBinaryOperator(BinaryOperator &Inst) {
289 auto *Op1 = Inst.getOperand(0);
290 auto *Op2 = Inst.getOperand(1);
291 Output.push_back(Edge(&Inst, Op1, EdgeType::Assign, AttrNone));
292 Output.push_back(Edge(&Inst, Op2, EdgeType::Assign, AttrNone));
295 void visitAtomicCmpXchgInst(AtomicCmpXchgInst &Inst) {
296 auto *Ptr = Inst.getPointerOperand();
297 auto *Val = Inst.getNewValOperand();
298 Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
301 void visitAtomicRMWInst(AtomicRMWInst &Inst) {
302 auto *Ptr = Inst.getPointerOperand();
303 auto *Val = Inst.getValOperand();
304 Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
307 void visitPHINode(PHINode &Inst) {
308 for (unsigned I = 0, E = Inst.getNumIncomingValues(); I != E; ++I) {
309 Value *Val = Inst.getIncomingValue(I);
310 Output.push_back(Edge(&Inst, Val, EdgeType::Assign, AttrNone));
314 void visitGetElementPtrInst(GetElementPtrInst &Inst) {
315 auto *Op = Inst.getPointerOperand();
316 Output.push_back(Edge(&Inst, Op, EdgeType::Assign, AttrNone));
317 for (auto I = Inst.idx_begin(), E = Inst.idx_end(); I != E; ++I)
318 Output.push_back(Edge(&Inst, *I, EdgeType::Assign, AttrNone));
321 void visitSelectInst(SelectInst &Inst) {
322 // Condition is not processed here (The actual statement producing
323 // the condition result is processed elsewhere). For select, the
324 // condition is evaluated, but not loaded, stored, or assigned
325 // simply as a result of being the condition of a select.
327 auto *TrueVal = Inst.getTrueValue();
328 Output.push_back(Edge(&Inst, TrueVal, EdgeType::Assign, AttrNone));
329 auto *FalseVal = Inst.getFalseValue();
330 Output.push_back(Edge(&Inst, FalseVal, EdgeType::Assign, AttrNone));
333 void visitAllocaInst(AllocaInst &) {}
335 void visitLoadInst(LoadInst &Inst) {
336 auto *Ptr = Inst.getPointerOperand();
338 Output.push_back(Edge(Val, Ptr, EdgeType::Reference, AttrNone));
341 void visitStoreInst(StoreInst &Inst) {
342 auto *Ptr = Inst.getPointerOperand();
343 auto *Val = Inst.getValueOperand();
344 Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
347 void visitVAArgInst(VAArgInst &Inst) {
348 // We can't fully model va_arg here. For *Ptr = Inst.getOperand(0), it does
350 // 1. Loads a value from *((T*)*Ptr).
351 // 2. Increments (stores to) *Ptr by some target-specific amount.
352 // For now, we'll handle this like a landingpad instruction (by placing the
353 // result in its own group, and having that group alias externals).
355 Output.push_back(Edge(Val, Val, EdgeType::Assign, AttrAll));
358 static bool isFunctionExternal(Function *Fn) {
359 return Fn->isDeclaration() || !Fn->hasLocalLinkage();
362 // Gets whether the sets at Index1 above, below, or equal to the sets at
363 // Index2. Returns None if they are not in the same set chain.
364 static Optional<Level> getIndexRelation(const StratifiedSets<Value *> &Sets,
365 StratifiedIndex Index1,
366 StratifiedIndex Index2) {
367 if (Index1 == Index2)
370 const auto *Current = &Sets.getLink(Index1);
371 while (Current->hasBelow()) {
372 if (Current->Below == Index2)
374 Current = &Sets.getLink(Current->Below);
377 Current = &Sets.getLink(Index1);
378 while (Current->hasAbove()) {
379 if (Current->Above == Index2)
381 Current = &Sets.getLink(Current->Above);
388 tryInterproceduralAnalysis(const SmallVectorImpl<Function *> &Fns,
390 const iterator_range<User::op_iterator> &Args) {
391 const unsigned ExpectedMaxArgs = 8;
392 const unsigned MaxSupportedArgs = 50;
393 assert(Fns.size() > 0);
395 // I put this here to give us an upper bound on time taken by IPA. Is it
396 // really (realistically) needed? Keep in mind that we do have an n^2 algo.
397 if (std::distance(Args.begin(), Args.end()) > (int)MaxSupportedArgs)
400 // Exit early if we'll fail anyway
401 for (auto *Fn : Fns) {
402 if (isFunctionExternal(Fn) || Fn->isVarArg())
404 auto &MaybeInfo = AA.ensureCached(Fn);
405 if (!MaybeInfo.hasValue())
409 SmallVector<Value *, ExpectedMaxArgs> Arguments(Args.begin(), Args.end());
410 SmallVector<StratifiedInfo, ExpectedMaxArgs> Parameters;
411 for (auto *Fn : Fns) {
412 auto &Info = *AA.ensureCached(Fn);
413 auto &Sets = Info.Sets;
414 auto &RetVals = Info.ReturnedValues;
417 for (auto &Param : Fn->args()) {
418 auto MaybeInfo = Sets.find(&Param);
419 // Did a new parameter somehow get added to the function/slip by?
420 if (!MaybeInfo.hasValue())
422 Parameters.push_back(*MaybeInfo);
425 // Adding an edge from argument -> return value for each parameter that
426 // may alias the return value
427 for (unsigned I = 0, E = Parameters.size(); I != E; ++I) {
428 auto &ParamInfo = Parameters[I];
429 auto &ArgVal = Arguments[I];
430 bool AddEdge = false;
431 StratifiedAttrs Externals;
432 for (unsigned X = 0, XE = RetVals.size(); X != XE; ++X) {
433 auto MaybeInfo = Sets.find(RetVals[X]);
434 if (!MaybeInfo.hasValue())
437 auto &RetInfo = *MaybeInfo;
438 auto RetAttrs = Sets.getLink(RetInfo.Index).Attrs;
439 auto ParamAttrs = Sets.getLink(ParamInfo.Index).Attrs;
441 getIndexRelation(Sets, ParamInfo.Index, RetInfo.Index);
442 if (MaybeRelation.hasValue()) {
444 Externals |= RetAttrs | ParamAttrs;
448 Output.push_back(Edge(FuncValue, ArgVal, EdgeType::Assign,
449 StratifiedAttrs().flip()));
452 if (Parameters.size() != Arguments.size())
455 // Adding edges between arguments for arguments that may end up aliasing
456 // each other. This is necessary for functions such as
457 // void foo(int** a, int** b) { *a = *b; }
458 // (Technically, the proper sets for this would be those below
459 // Arguments[I] and Arguments[X], but our algorithm will produce
460 // extremely similar, and equally correct, results either way)
461 for (unsigned I = 0, E = Arguments.size(); I != E; ++I) {
462 auto &MainVal = Arguments[I];
463 auto &MainInfo = Parameters[I];
464 auto &MainAttrs = Sets.getLink(MainInfo.Index).Attrs;
465 for (unsigned X = I + 1; X != E; ++X) {
466 auto &SubInfo = Parameters[X];
467 auto &SubVal = Arguments[X];
468 auto &SubAttrs = Sets.getLink(SubInfo.Index).Attrs;
470 getIndexRelation(Sets, MainInfo.Index, SubInfo.Index);
472 if (!MaybeRelation.hasValue())
475 auto NewAttrs = SubAttrs | MainAttrs;
476 Output.push_back(Edge(MainVal, SubVal, EdgeType::Assign, NewAttrs));
483 template <typename InstT> void visitCallLikeInst(InstT &Inst) {
484 SmallVector<Function *, 4> Targets;
485 if (getPossibleTargets(&Inst, Targets)) {
486 if (tryInterproceduralAnalysis(Targets, &Inst, Inst.arg_operands()))
488 // Cleanup from interprocedural analysis
492 for (Value *V : Inst.arg_operands())
493 Output.push_back(Edge(&Inst, V, EdgeType::Assign, AttrAll));
496 void visitCallInst(CallInst &Inst) { visitCallLikeInst(Inst); }
498 void visitInvokeInst(InvokeInst &Inst) { visitCallLikeInst(Inst); }
500 // Because vectors/aggregates are immutable and unaddressable,
501 // there's nothing we can do to coax a value out of them, other
502 // than calling Extract{Element,Value}. We can effectively treat
503 // them as pointers to arbitrary memory locations we can store in
505 void visitExtractElementInst(ExtractElementInst &Inst) {
506 auto *Ptr = Inst.getVectorOperand();
508 Output.push_back(Edge(Val, Ptr, EdgeType::Reference, AttrNone));
511 void visitInsertElementInst(InsertElementInst &Inst) {
512 auto *Vec = Inst.getOperand(0);
513 auto *Val = Inst.getOperand(1);
514 Output.push_back(Edge(&Inst, Vec, EdgeType::Assign, AttrNone));
515 Output.push_back(Edge(&Inst, Val, EdgeType::Dereference, AttrNone));
518 void visitLandingPadInst(LandingPadInst &Inst) {
519 // Exceptions come from "nowhere", from our analysis' perspective.
520 // So we place the instruction its own group, noting that said group may
522 Output.push_back(Edge(&Inst, &Inst, EdgeType::Assign, AttrAll));
525 void visitInsertValueInst(InsertValueInst &Inst) {
526 auto *Agg = Inst.getOperand(0);
527 auto *Val = Inst.getOperand(1);
528 Output.push_back(Edge(&Inst, Agg, EdgeType::Assign, AttrNone));
529 Output.push_back(Edge(&Inst, Val, EdgeType::Dereference, AttrNone));
532 void visitExtractValueInst(ExtractValueInst &Inst) {
533 auto *Ptr = Inst.getAggregateOperand();
534 Output.push_back(Edge(&Inst, Ptr, EdgeType::Reference, AttrNone));
537 void visitShuffleVectorInst(ShuffleVectorInst &Inst) {
538 auto *From1 = Inst.getOperand(0);
539 auto *From2 = Inst.getOperand(1);
540 Output.push_back(Edge(&Inst, From1, EdgeType::Assign, AttrNone));
541 Output.push_back(Edge(&Inst, From2, EdgeType::Assign, AttrNone));
545 // For a given instruction, we need to know which Value* to get the
546 // users of in order to build our graph. In some cases (i.e. add),
547 // we simply need the Instruction*. In other cases (i.e. store),
548 // finding the users of the Instruction* is useless; we need to find
549 // the users of the first operand. This handles determining which
550 // value to follow for us.
552 // Note: we *need* to keep this in sync with GetEdgesVisitor. Add
553 // something to GetEdgesVisitor, add it here -- remove something from
554 // GetEdgesVisitor, remove it here.
555 class GetTargetValueVisitor
556 : public InstVisitor<GetTargetValueVisitor, Value *> {
558 Value *visitInstruction(Instruction &Inst) { return &Inst; }
560 Value *visitStoreInst(StoreInst &Inst) { return Inst.getPointerOperand(); }
562 Value *visitAtomicCmpXchgInst(AtomicCmpXchgInst &Inst) {
563 return Inst.getPointerOperand();
566 Value *visitAtomicRMWInst(AtomicRMWInst &Inst) {
567 return Inst.getPointerOperand();
570 Value *visitInsertElementInst(InsertElementInst &Inst) {
571 return Inst.getOperand(0);
574 Value *visitInsertValueInst(InsertValueInst &Inst) {
575 return Inst.getAggregateOperand();
579 // Set building requires a weighted bidirectional graph.
580 template <typename EdgeTypeT> class WeightedBidirectionalGraph {
582 typedef std::size_t Node;
585 const static Node StartNode = Node(0);
591 Edge(const EdgeTypeT &W, const Node &N)
592 : Weight(W), Other(N) {}
594 bool operator==(const Edge &E) const {
595 return Weight == E.Weight && Other == E.Other;
598 bool operator!=(const Edge &E) const { return !operator==(E); }
602 std::vector<Edge> Edges;
605 std::vector<NodeImpl> NodeImpls;
607 bool inbounds(Node NodeIndex) const { return NodeIndex < NodeImpls.size(); }
609 const NodeImpl &getNode(Node N) const { return NodeImpls[N]; }
610 NodeImpl &getNode(Node N) { return NodeImpls[N]; }
613 // ----- Various Edge iterators for the graph ----- //
615 // \brief Iterator for edges. Because this graph is bidirected, we don't
616 // allow modificaiton of the edges using this iterator. Additionally, the
617 // iterator becomes invalid if you add edges to or from the node you're
618 // getting the edges of.
619 struct EdgeIterator : public std::iterator<std::forward_iterator_tag,
620 std::tuple<EdgeTypeT, Node *>> {
621 EdgeIterator(const typename std::vector<Edge>::const_iterator &Iter)
624 EdgeIterator(NodeImpl &Impl) : Current(Impl.begin()) {}
626 EdgeIterator &operator++() {
631 EdgeIterator operator++(int) {
632 EdgeIterator Copy(Current);
637 std::tuple<EdgeTypeT, Node> &operator*() {
638 Store = std::make_tuple(Current->Weight, Current->Other);
642 bool operator==(const EdgeIterator &Other) const {
643 return Current == Other.Current;
646 bool operator!=(const EdgeIterator &Other) const {
647 return !operator==(Other);
651 typename std::vector<Edge>::const_iterator Current;
652 std::tuple<EdgeTypeT, Node> Store;
655 // Wrapper for EdgeIterator with begin()/end() calls.
656 struct EdgeIterable {
657 EdgeIterable(const std::vector<Edge> &Edges)
658 : BeginIter(Edges.begin()), EndIter(Edges.end()) {}
660 EdgeIterator begin() { return EdgeIterator(BeginIter); }
662 EdgeIterator end() { return EdgeIterator(EndIter); }
665 typename std::vector<Edge>::const_iterator BeginIter;
666 typename std::vector<Edge>::const_iterator EndIter;
669 // ----- Actual graph-related things ----- //
671 WeightedBidirectionalGraph() {}
673 WeightedBidirectionalGraph(WeightedBidirectionalGraph<EdgeTypeT> &&Other)
674 : NodeImpls(std::move(Other.NodeImpls)) {}
676 WeightedBidirectionalGraph<EdgeTypeT> &
677 operator=(WeightedBidirectionalGraph<EdgeTypeT> &&Other) {
678 NodeImpls = std::move(Other.NodeImpls);
683 auto Index = NodeImpls.size();
684 auto NewNode = Node(Index);
685 NodeImpls.push_back(NodeImpl());
689 void addEdge(Node From, Node To, const EdgeTypeT &Weight,
690 const EdgeTypeT &ReverseWeight) {
691 assert(inbounds(From));
692 assert(inbounds(To));
693 auto &FromNode = getNode(From);
694 auto &ToNode = getNode(To);
695 FromNode.Edges.push_back(Edge(Weight, To));
696 ToNode.Edges.push_back(Edge(ReverseWeight, From));
699 EdgeIterable edgesFor(const Node &N) const {
700 const auto &Node = getNode(N);
701 return EdgeIterable(Node.Edges);
704 bool empty() const { return NodeImpls.empty(); }
705 std::size_t size() const { return NodeImpls.size(); }
707 // \brief Gets an arbitrary node in the graph as a starting point for
709 Node getEntryNode() {
710 assert(inbounds(StartNode));
715 typedef WeightedBidirectionalGraph<std::pair<EdgeType, StratifiedAttrs>> GraphT;
716 typedef DenseMap<Value *, GraphT::Node> NodeMapT;
719 // -- Setting up/registering CFLAA pass -- //
720 char CFLAliasAnalysis::ID = 0;
722 INITIALIZE_AG_PASS(CFLAliasAnalysis, AliasAnalysis, "cfl-aa",
723 "CFL-Based AA implementation", false, true, false)
725 ImmutablePass *llvm::createCFLAliasAnalysisPass() {
726 return new CFLAliasAnalysis();
729 //===----------------------------------------------------------------------===//
730 // Function declarations that require types defined in the namespace above
731 //===----------------------------------------------------------------------===//
733 // Given an argument number, returns the appropriate Attr index to set.
734 static StratifiedAttr argNumberToAttrIndex(StratifiedAttr);
736 // Given a Value, potentially return which AttrIndex it maps to.
737 static Optional<StratifiedAttr> valueToAttrIndex(Value *Val);
739 // Gets the inverse of a given EdgeType.
740 static EdgeType flipWeight(EdgeType);
742 // Gets edges of the given Instruction*, writing them to the SmallVector*.
743 static void argsToEdges(CFLAliasAnalysis &, Instruction *,
744 SmallVectorImpl<Edge> &);
746 // Gets the "Level" that one should travel in StratifiedSets
747 // given an EdgeType.
748 static Level directionOfEdgeType(EdgeType);
750 // Builds the graph needed for constructing the StratifiedSets for the
752 static void buildGraphFrom(CFLAliasAnalysis &, Function *,
753 SmallVectorImpl<Value *> &, NodeMapT &, GraphT &);
755 // Gets the edges of a ConstantExpr as if it was an Instruction. This
756 // function also acts on any nested ConstantExprs, adding the edges
757 // of those to the given SmallVector as well.
758 static void constexprToEdges(CFLAliasAnalysis &, ConstantExpr &,
759 SmallVectorImpl<Edge> &);
761 // Given an Instruction, this will add it to the graph, along with any
762 // Instructions that are potentially only available from said Instruction
763 // For example, given the following line:
764 // %0 = load i16* getelementptr ([1 x i16]* @a, 0, 0), align 2
765 // addInstructionToGraph would add both the `load` and `getelementptr`
766 // instructions to the graph appropriately.
767 static void addInstructionToGraph(CFLAliasAnalysis &, Instruction &,
768 SmallVectorImpl<Value *> &, NodeMapT &,
771 // Notes whether it would be pointless to add the given Value to our sets.
772 static bool canSkipAddingToSets(Value *Val);
774 // Builds the graph + StratifiedSets for a function.
775 static FunctionInfo buildSetsFrom(CFLAliasAnalysis &, Function *);
777 static Optional<Function *> parentFunctionOfValue(Value *Val) {
778 if (auto *Inst = dyn_cast<Instruction>(Val)) {
779 auto *Bb = Inst->getParent();
780 return Bb->getParent();
783 if (auto *Arg = dyn_cast<Argument>(Val))
784 return Arg->getParent();
788 template <typename Inst>
789 static bool getPossibleTargets(Inst *Call,
790 SmallVectorImpl<Function *> &Output) {
791 if (auto *Fn = Call->getCalledFunction()) {
792 Output.push_back(Fn);
796 // TODO: If the call is indirect, we might be able to enumerate all potential
797 // targets of the call and return them, rather than just failing.
801 static Optional<Value *> getTargetValue(Instruction *Inst) {
802 GetTargetValueVisitor V;
803 return V.visit(Inst);
806 static bool hasUsefulEdges(Instruction *Inst) {
807 bool IsNonInvokeTerminator =
808 isa<TerminatorInst>(Inst) && !isa<InvokeInst>(Inst);
809 return !isa<CmpInst>(Inst) && !isa<FenceInst>(Inst) && !IsNonInvokeTerminator;
812 static Optional<StratifiedAttr> valueToAttrIndex(Value *Val) {
813 if (isa<GlobalValue>(Val))
814 return AttrGlobalIndex;
816 if (auto *Arg = dyn_cast<Argument>(Val))
817 // Only pointer arguments should have the argument attribute,
818 // because things can't escape through scalars without us seeing a
819 // cast, and thus, interaction with them doesn't matter.
820 if (!Arg->hasNoAliasAttr() && Arg->getType()->isPointerTy())
821 return argNumberToAttrIndex(Arg->getArgNo());
825 static StratifiedAttr argNumberToAttrIndex(unsigned ArgNum) {
826 if (ArgNum >= AttrMaxNumArgs)
828 return ArgNum + AttrFirstArgIndex;
831 static EdgeType flipWeight(EdgeType Initial) {
833 case EdgeType::Assign:
834 return EdgeType::Assign;
835 case EdgeType::Dereference:
836 return EdgeType::Reference;
837 case EdgeType::Reference:
838 return EdgeType::Dereference;
840 llvm_unreachable("Incomplete coverage of EdgeType enum");
843 static void argsToEdges(CFLAliasAnalysis &Analysis, Instruction *Inst,
844 SmallVectorImpl<Edge> &Output) {
845 assert(hasUsefulEdges(Inst) &&
846 "Expected instructions to have 'useful' edges");
847 GetEdgesVisitor v(Analysis, Output);
851 static Level directionOfEdgeType(EdgeType Weight) {
853 case EdgeType::Reference:
855 case EdgeType::Dereference:
857 case EdgeType::Assign:
860 llvm_unreachable("Incomplete switch coverage");
863 static void constexprToEdges(CFLAliasAnalysis &Analysis,
864 ConstantExpr &CExprToCollapse,
865 SmallVectorImpl<Edge> &Results) {
866 SmallVector<ConstantExpr *, 4> Worklist;
867 Worklist.push_back(&CExprToCollapse);
869 SmallVector<Edge, 8> ConstexprEdges;
870 while (!Worklist.empty()) {
871 auto *CExpr = Worklist.pop_back_val();
872 std::unique_ptr<Instruction> Inst(CExpr->getAsInstruction());
874 if (!hasUsefulEdges(Inst.get()))
877 ConstexprEdges.clear();
878 argsToEdges(Analysis, Inst.get(), ConstexprEdges);
879 for (auto &Edge : ConstexprEdges) {
880 if (Edge.From == Inst.get())
882 else if (auto *Nested = dyn_cast<ConstantExpr>(Edge.From))
883 Worklist.push_back(Nested);
885 if (Edge.To == Inst.get())
887 else if (auto *Nested = dyn_cast<ConstantExpr>(Edge.To))
888 Worklist.push_back(Nested);
891 Results.append(ConstexprEdges.begin(), ConstexprEdges.end());
895 static void addInstructionToGraph(CFLAliasAnalysis &Analysis, Instruction &Inst,
896 SmallVectorImpl<Value *> &ReturnedValues,
897 NodeMapT &Map, GraphT &Graph) {
898 const auto findOrInsertNode = [&Map, &Graph](Value *Val) {
899 auto Pair = Map.insert(std::make_pair(Val, GraphT::Node()));
900 auto &Iter = Pair.first;
902 auto NewNode = Graph.addNode();
903 Iter->second = NewNode;
908 // We don't want the edges of most "return" instructions, but we *do* want
909 // to know what can be returned.
910 if (isa<ReturnInst>(&Inst))
911 ReturnedValues.push_back(&Inst);
913 if (!hasUsefulEdges(&Inst))
916 SmallVector<Edge, 8> Edges;
917 argsToEdges(Analysis, &Inst, Edges);
919 // In the case of an unused alloca (or similar), edges may be empty. Note
920 // that it exists so we can potentially answer NoAlias.
922 auto MaybeVal = getTargetValue(&Inst);
923 assert(MaybeVal.hasValue());
924 auto *Target = *MaybeVal;
925 findOrInsertNode(Target);
929 const auto addEdgeToGraph = [&Graph, &findOrInsertNode](const Edge &E) {
930 auto To = findOrInsertNode(E.To);
931 auto From = findOrInsertNode(E.From);
932 auto FlippedWeight = flipWeight(E.Weight);
933 auto Attrs = E.AdditionalAttrs;
934 Graph.addEdge(From, To, std::make_pair(E.Weight, Attrs),
935 std::make_pair(FlippedWeight, Attrs));
938 SmallVector<ConstantExpr *, 4> ConstantExprs;
939 for (const Edge &E : Edges) {
941 if (auto *Constexpr = dyn_cast<ConstantExpr>(E.To))
942 ConstantExprs.push_back(Constexpr);
943 if (auto *Constexpr = dyn_cast<ConstantExpr>(E.From))
944 ConstantExprs.push_back(Constexpr);
947 for (ConstantExpr *CE : ConstantExprs) {
949 constexprToEdges(Analysis, *CE, Edges);
950 std::for_each(Edges.begin(), Edges.end(), addEdgeToGraph);
954 // Aside: We may remove graph construction entirely, because it doesn't really
955 // buy us much that we don't already have. I'd like to add interprocedural
956 // analysis prior to this however, in case that somehow requires the graph
957 // produced by this for efficient execution
958 static void buildGraphFrom(CFLAliasAnalysis &Analysis, Function *Fn,
959 SmallVectorImpl<Value *> &ReturnedValues,
960 NodeMapT &Map, GraphT &Graph) {
961 for (auto &Bb : Fn->getBasicBlockList())
962 for (auto &Inst : Bb.getInstList())
963 addInstructionToGraph(Analysis, Inst, ReturnedValues, Map, Graph);
966 static bool canSkipAddingToSets(Value *Val) {
967 // Constants can share instances, which may falsely unify multiple
969 // store i32* null, i32** %ptr1
970 // store i32* null, i32** %ptr2
971 // clearly ptr1 and ptr2 should not be unified into the same set, so
972 // we should filter out the (potentially shared) instance to
974 if (isa<Constant>(Val)) {
975 bool Container = isa<ConstantVector>(Val) || isa<ConstantArray>(Val) ||
976 isa<ConstantStruct>(Val);
977 // TODO: Because all of these things are constant, we can determine whether
978 // the data is *actually* mutable at graph building time. This will probably
979 // come for free/cheap with offset awareness.
980 bool CanStoreMutableData =
981 isa<GlobalValue>(Val) || isa<ConstantExpr>(Val) || Container;
982 return !CanStoreMutableData;
988 static FunctionInfo buildSetsFrom(CFLAliasAnalysis &Analysis, Function *Fn) {
991 SmallVector<Value *, 4> ReturnedValues;
993 buildGraphFrom(Analysis, Fn, ReturnedValues, Map, Graph);
995 DenseMap<GraphT::Node, Value *> NodeValueMap;
996 NodeValueMap.resize(Map.size());
997 for (const auto &Pair : Map)
998 NodeValueMap.insert(std::make_pair(Pair.second, Pair.first));
1000 const auto findValueOrDie = [&NodeValueMap](GraphT::Node Node) {
1001 auto ValIter = NodeValueMap.find(Node);
1002 assert(ValIter != NodeValueMap.end());
1003 return ValIter->second;
1006 StratifiedSetsBuilder<Value *> Builder;
1008 SmallVector<GraphT::Node, 16> Worklist;
1009 for (auto &Pair : Map) {
1012 auto *Value = Pair.first;
1014 auto InitialNode = Pair.second;
1015 Worklist.push_back(InitialNode);
1016 while (!Worklist.empty()) {
1017 auto Node = Worklist.pop_back_val();
1018 auto *CurValue = findValueOrDie(Node);
1019 if (canSkipAddingToSets(CurValue))
1022 for (const auto &EdgeTuple : Graph.edgesFor(Node)) {
1023 auto Weight = std::get<0>(EdgeTuple);
1024 auto Label = Weight.first;
1025 auto &OtherNode = std::get<1>(EdgeTuple);
1026 auto *OtherValue = findValueOrDie(OtherNode);
1028 if (canSkipAddingToSets(OtherValue))
1032 switch (directionOfEdgeType(Label)) {
1034 Added = Builder.addAbove(CurValue, OtherValue);
1037 Added = Builder.addBelow(CurValue, OtherValue);
1040 Added = Builder.addWith(CurValue, OtherValue);
1044 auto Aliasing = Weight.second;
1045 if (auto MaybeCurIndex = valueToAttrIndex(CurValue))
1046 Aliasing.set(*MaybeCurIndex);
1047 if (auto MaybeOtherIndex = valueToAttrIndex(OtherValue))
1048 Aliasing.set(*MaybeOtherIndex);
1049 Builder.noteAttributes(CurValue, Aliasing);
1050 Builder.noteAttributes(OtherValue, Aliasing);
1053 Worklist.push_back(OtherNode);
1058 // There are times when we end up with parameters not in our graph (i.e. if
1059 // it's only used as the condition of a branch). Other bits of code depend on
1060 // things that were present during construction being present in the graph.
1061 // So, we add all present arguments here.
1062 for (auto &Arg : Fn->args()) {
1063 if (!Builder.add(&Arg))
1066 auto Attrs = valueToAttrIndex(&Arg);
1067 if (Attrs.hasValue())
1068 Builder.noteAttributes(&Arg, *Attrs);
1071 return FunctionInfo(Builder.build(), std::move(ReturnedValues));
1074 void CFLAliasAnalysis::scan(Function *Fn) {
1075 auto InsertPair = Cache.insert(std::make_pair(Fn, Optional<FunctionInfo>()));
1077 assert(InsertPair.second &&
1078 "Trying to scan a function that has already been cached");
1080 FunctionInfo Info(buildSetsFrom(*this, Fn));
1081 Cache[Fn] = std::move(Info);
1082 Handles.push_front(FunctionHandle(Fn, this));
1085 AliasAnalysis::AliasResult
1086 CFLAliasAnalysis::query(const AliasAnalysis::Location &LocA,
1087 const AliasAnalysis::Location &LocB) {
1088 auto *ValA = const_cast<Value *>(LocA.Ptr);
1089 auto *ValB = const_cast<Value *>(LocB.Ptr);
1091 Function *Fn = nullptr;
1092 auto MaybeFnA = parentFunctionOfValue(ValA);
1093 auto MaybeFnB = parentFunctionOfValue(ValB);
1094 if (!MaybeFnA.hasValue() && !MaybeFnB.hasValue()) {
1095 // The only times this is known to happen are when globals + InlineAsm
1097 DEBUG(dbgs() << "CFLAA: could not extract parent function information.\n");
1098 return AliasAnalysis::MayAlias;
1101 if (MaybeFnA.hasValue()) {
1103 assert((!MaybeFnB.hasValue() || *MaybeFnB == *MaybeFnA) &&
1104 "Interprocedural queries not supported");
1109 assert(Fn != nullptr);
1110 auto &MaybeInfo = ensureCached(Fn);
1111 assert(MaybeInfo.hasValue());
1113 auto &Sets = MaybeInfo->Sets;
1114 auto MaybeA = Sets.find(ValA);
1115 if (!MaybeA.hasValue())
1116 return AliasAnalysis::MayAlias;
1118 auto MaybeB = Sets.find(ValB);
1119 if (!MaybeB.hasValue())
1120 return AliasAnalysis::MayAlias;
1122 auto SetA = *MaybeA;
1123 auto SetB = *MaybeB;
1124 auto AttrsA = Sets.getLink(SetA.Index).Attrs;
1125 auto AttrsB = Sets.getLink(SetB.Index).Attrs;
1127 // Stratified set attributes are used as markets to signify whether a member
1128 // of a StratifiedSet (or a member of a set above the current set) has
1129 // interacted with either arguments or globals. "Interacted with" meaning
1130 // its value may be different depending on the value of an argument or
1131 // global. The thought behind this is that, because arguments and globals
1132 // may alias each other, if AttrsA and AttrsB have touched args/globals,
1133 // we must conservatively say that they alias. However, if at least one of
1134 // the sets has no values that could legally be altered by changing the value
1135 // of an argument or global, then we don't have to be as conservative.
1136 if (AttrsA.any() && AttrsB.any())
1137 return AliasAnalysis::MayAlias;
1139 // We currently unify things even if the accesses to them may not be in
1140 // bounds, so we can't return partial alias here because we don't
1141 // know whether the pointer is really within the object or not.
1142 // IE Given an out of bounds GEP and an alloca'd pointer, we may
1143 // unify the two. We can't return partial alias for this case.
1144 // Since we do not currently track enough information to
1147 if (SetA.Index == SetB.Index)
1148 return AliasAnalysis::MayAlias;
1150 return AliasAnalysis::NoAlias;
1153 bool CFLAliasAnalysis::doInitialization(Module &M) {
1154 InitializeAliasAnalysis(this, &M.getDataLayout());