1 //===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===//
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 defines the generic AliasAnalysis interface, which is used as the
11 // common interface used by all clients of alias analysis information, and
12 // implemented by all alias analysis implementations. Mod/Ref information is
13 // also captured by this interface.
15 // Implementations of this interface must implement the various virtual methods,
16 // which automatically provides functionality for the entire suite of client
19 // This API identifies memory regions with the Location class. The pointer
20 // component specifies the base memory address of the region. The Size specifies
21 // the maximum size (in address units) of the memory region, or UnknownSize if
22 // the size is not known. The TBAA tag identifies the "type" of the memory
23 // reference; see the TypeBasedAliasAnalysis class for details.
25 // Some non-obvious details include:
26 // - Pointers that point to two completely different objects in memory never
27 // alias, regardless of the value of the Size component.
28 // - NoAlias doesn't imply inequal pointers. The most obvious example of this
29 // is two pointers to constant memory. Even if they are equal, constant
30 // memory is never stored to, so there will never be any dependencies.
31 // In this and other situations, the pointers may be both NoAlias and
32 // MustAlias at the same time. The current API can only return one result,
33 // though this is rarely a problem in practice.
35 //===----------------------------------------------------------------------===//
37 #ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H
38 #define LLVM_ANALYSIS_ALIAS_ANALYSIS_H
40 #include "llvm/Support/CallSite.h"
41 #include "llvm/ADT/DenseMap.h"
51 class MemTransferInst;
59 AliasAnalysis *AA; // Previous Alias Analysis to chain to.
62 /// InitializeAliasAnalysis - Subclasses must call this method to initialize
63 /// the AliasAnalysis interface before any other methods are called. This is
64 /// typically called by the run* methods of these subclasses. This may be
65 /// called multiple times.
67 void InitializeAliasAnalysis(Pass *P);
69 /// getAnalysisUsage - All alias analysis implementations should invoke this
70 /// directly (using AliasAnalysis::getAnalysisUsage(AU)).
71 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
74 static char ID; // Class identification, replacement for typeinfo
75 AliasAnalysis() : TD(0), AA(0) {}
76 virtual ~AliasAnalysis(); // We want to be subclassed
78 /// UnknownSize - This is a special value which can be used with the
79 /// size arguments in alias queries to indicate that the caller does not
80 /// know the sizes of the potential memory references.
81 static uint64_t const UnknownSize = ~UINT64_C(0);
83 /// getTargetData - Return a pointer to the current TargetData object, or
84 /// null if no TargetData object is available.
86 const TargetData *getTargetData() const { return TD; }
88 /// getTypeStoreSize - Return the TargetData store size for the given type,
89 /// if known, or a conservative value otherwise.
91 uint64_t getTypeStoreSize(Type *Ty);
93 //===--------------------------------------------------------------------===//
97 /// Location - A description of a memory location.
99 /// Ptr - The address of the start of the location.
101 /// Size - The maximum size of the location, in address-units, or
102 /// UnknownSize if the size is not known. Note that an unknown size does
103 /// not mean the pointer aliases the entire virtual address space, because
104 /// there are restrictions on stepping out of one object and into another.
105 /// See http://llvm.org/docs/LangRef.html#pointeraliasing
107 /// TBAATag - The metadata node which describes the TBAA type of
108 /// the location, or null if there is no known unique tag.
109 const MDNode *TBAATag;
111 explicit Location(const Value *P = 0, uint64_t S = UnknownSize,
113 : Ptr(P), Size(S), TBAATag(N) {}
115 Location getWithNewPtr(const Value *NewPtr) const {
116 Location Copy(*this);
121 Location getWithNewSize(uint64_t NewSize) const {
122 Location Copy(*this);
127 Location getWithoutTBAATag() const {
128 Location Copy(*this);
134 /// getLocation - Fill in Loc with information about the memory reference by
135 /// the given instruction.
136 Location getLocation(const LoadInst *LI);
137 Location getLocation(const StoreInst *SI);
138 Location getLocation(const VAArgInst *VI);
139 Location getLocation(const AtomicCmpXchgInst *CXI);
140 Location getLocation(const AtomicRMWInst *RMWI);
141 static Location getLocationForSource(const MemTransferInst *MTI);
142 static Location getLocationForDest(const MemIntrinsic *MI);
144 /// Alias analysis result - Either we know for sure that it does not alias, we
145 /// know for sure it must alias, or we don't know anything: The two pointers
146 /// _might_ alias. This enum is designed so you can do things like:
147 /// if (AA.alias(P1, P2)) { ... }
148 /// to check to see if two pointers might alias.
150 /// See docs/AliasAnalysis.html for more information on the specific meanings
154 NoAlias = 0, ///< No dependencies.
155 MayAlias, ///< Anything goes.
156 PartialAlias, ///< Pointers differ, but pointees overlap.
157 MustAlias ///< Pointers are equal.
160 /// alias - The main low level interface to the alias analysis implementation.
161 /// Returns an AliasResult indicating whether the two pointers are aliased to
162 /// each other. This is the interface that must be implemented by specific
163 /// alias analysis implementations.
164 virtual AliasResult alias(const Location &LocA, const Location &LocB);
166 /// alias - A convenience wrapper.
167 AliasResult alias(const Value *V1, uint64_t V1Size,
168 const Value *V2, uint64_t V2Size) {
169 return alias(Location(V1, V1Size), Location(V2, V2Size));
172 /// alias - A convenience wrapper.
173 AliasResult alias(const Value *V1, const Value *V2) {
174 return alias(V1, UnknownSize, V2, UnknownSize);
177 /// isNoAlias - A trivial helper function to check to see if the specified
178 /// pointers are no-alias.
179 bool isNoAlias(const Location &LocA, const Location &LocB) {
180 return alias(LocA, LocB) == NoAlias;
183 /// isNoAlias - A convenience wrapper.
184 bool isNoAlias(const Value *V1, uint64_t V1Size,
185 const Value *V2, uint64_t V2Size) {
186 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size));
189 /// isMustAlias - A convenience wrapper.
190 bool isMustAlias(const Location &LocA, const Location &LocB) {
191 return alias(LocA, LocB) == MustAlias;
194 /// isMustAlias - A convenience wrapper.
195 bool isMustAlias(const Value *V1, const Value *V2) {
196 return alias(V1, 1, V2, 1) == MustAlias;
199 /// pointsToConstantMemory - If the specified memory location is
200 /// known to be constant, return true. If OrLocal is true and the
201 /// specified memory location is known to be "local" (derived from
202 /// an alloca), return true. Otherwise return false.
203 virtual bool pointsToConstantMemory(const Location &Loc,
204 bool OrLocal = false);
206 /// pointsToConstantMemory - A convenient wrapper.
207 bool pointsToConstantMemory(const Value *P, bool OrLocal = false) {
208 return pointsToConstantMemory(Location(P), OrLocal);
211 //===--------------------------------------------------------------------===//
212 /// Simple mod/ref information...
215 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
216 /// bits which may be or'd together.
218 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
220 /// These values define additional bits used to define the
221 /// ModRefBehavior values.
222 enum { Nowhere = 0, ArgumentPointees = 4, Anywhere = 8 | ArgumentPointees };
224 /// ModRefBehavior - Summary of how a function affects memory in the program.
225 /// Loads from constant globals are not considered memory accesses for this
226 /// interface. Also, functions may freely modify stack space local to their
227 /// invocation without having to report it through these interfaces.
228 enum ModRefBehavior {
229 /// DoesNotAccessMemory - This function does not perform any non-local loads
230 /// or stores to memory.
232 /// This property corresponds to the GCC 'const' attribute.
233 /// This property corresponds to the LLVM IR 'readnone' attribute.
234 /// This property corresponds to the IntrNoMem LLVM intrinsic flag.
235 DoesNotAccessMemory = Nowhere | NoModRef,
237 /// OnlyReadsArgumentPointees - The only memory references in this function
238 /// (if it has any) are non-volatile loads from objects pointed to by its
239 /// pointer-typed arguments, with arbitrary offsets.
241 /// This property corresponds to the IntrReadArgMem LLVM intrinsic flag.
242 OnlyReadsArgumentPointees = ArgumentPointees | Ref,
244 /// OnlyAccessesArgumentPointees - The only memory references in this
245 /// function (if it has any) are non-volatile loads and stores from objects
246 /// pointed to by its pointer-typed arguments, with arbitrary offsets.
248 /// This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag.
249 OnlyAccessesArgumentPointees = ArgumentPointees | ModRef,
251 /// OnlyReadsMemory - This function does not perform any non-local stores or
252 /// volatile loads, but may read from any memory location.
254 /// This property corresponds to the GCC 'pure' attribute.
255 /// This property corresponds to the LLVM IR 'readonly' attribute.
256 /// This property corresponds to the IntrReadMem LLVM intrinsic flag.
257 OnlyReadsMemory = Anywhere | Ref,
259 /// UnknownModRefBehavior - This indicates that the function could not be
260 /// classified into one of the behaviors above.
261 UnknownModRefBehavior = Anywhere | ModRef
264 /// getModRefBehavior - Return the behavior when calling the given call site.
265 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
267 /// getModRefBehavior - Return the behavior when calling the given function.
268 /// For use when the call site is not known.
269 virtual ModRefBehavior getModRefBehavior(const Function *F);
271 /// doesNotAccessMemory - If the specified call is known to never read or
272 /// write memory, return true. If the call only reads from known-constant
273 /// memory, it is also legal to return true. Calls that unwind the stack
274 /// are legal for this predicate.
276 /// Many optimizations (such as CSE and LICM) can be performed on such calls
277 /// without worrying about aliasing properties, and many calls have this
278 /// property (e.g. calls to 'sin' and 'cos').
280 /// This property corresponds to the GCC 'const' attribute.
282 bool doesNotAccessMemory(ImmutableCallSite CS) {
283 return getModRefBehavior(CS) == DoesNotAccessMemory;
286 /// doesNotAccessMemory - If the specified function is known to never read or
287 /// write memory, return true. For use when the call site is not known.
289 bool doesNotAccessMemory(const Function *F) {
290 return getModRefBehavior(F) == DoesNotAccessMemory;
293 /// onlyReadsMemory - If the specified call is known to only read from
294 /// non-volatile memory (or not access memory at all), return true. Calls
295 /// that unwind the stack are legal for this predicate.
297 /// This property allows many common optimizations to be performed in the
298 /// absence of interfering store instructions, such as CSE of strlen calls.
300 /// This property corresponds to the GCC 'pure' attribute.
302 bool onlyReadsMemory(ImmutableCallSite CS) {
303 return onlyReadsMemory(getModRefBehavior(CS));
306 /// onlyReadsMemory - If the specified function is known to only read from
307 /// non-volatile memory (or not access memory at all), return true. For use
308 /// when the call site is not known.
310 bool onlyReadsMemory(const Function *F) {
311 return onlyReadsMemory(getModRefBehavior(F));
314 /// onlyReadsMemory - Return true if functions with the specified behavior are
315 /// known to only read from non-volatile memory (or not access memory at all).
317 static bool onlyReadsMemory(ModRefBehavior MRB) {
321 /// onlyAccessesArgPointees - Return true if functions with the specified
322 /// behavior are known to read and write at most from objects pointed to by
323 /// their pointer-typed arguments (with arbitrary offsets).
325 static bool onlyAccessesArgPointees(ModRefBehavior MRB) {
326 return !(MRB & Anywhere & ~ArgumentPointees);
329 /// doesAccessArgPointees - Return true if functions with the specified
330 /// behavior are known to potentially read or write from objects pointed
331 /// to be their pointer-typed arguments (with arbitrary offsets).
333 static bool doesAccessArgPointees(ModRefBehavior MRB) {
334 return (MRB & ModRef) && (MRB & ArgumentPointees);
337 /// getModRefInfo - Return information about whether or not an instruction may
338 /// read or write the specified memory location. An instruction
339 /// that doesn't read or write memory may be trivially LICM'd for example.
340 ModRefResult getModRefInfo(const Instruction *I,
341 const Location &Loc) {
342 switch (I->getOpcode()) {
343 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc);
344 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc);
345 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc);
346 case Instruction::Fence: return getModRefInfo((const FenceInst*)I, Loc);
347 case Instruction::AtomicCmpXchg:
348 return getModRefInfo((const AtomicCmpXchgInst*)I, Loc);
349 case Instruction::AtomicRMW:
350 return getModRefInfo((const AtomicRMWInst*)I, Loc);
351 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc);
352 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc);
353 default: return NoModRef;
357 /// getModRefInfo - A convenience wrapper.
358 ModRefResult getModRefInfo(const Instruction *I,
359 const Value *P, uint64_t Size) {
360 return getModRefInfo(I, Location(P, Size));
363 /// getModRefInfo (for call sites) - Return whether information about whether
364 /// a particular call site modifies or reads the specified memory location.
365 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
366 const Location &Loc);
368 /// getModRefInfo (for call sites) - A convenience wrapper.
369 ModRefResult getModRefInfo(ImmutableCallSite CS,
370 const Value *P, uint64_t Size) {
371 return getModRefInfo(CS, Location(P, Size));
374 /// getModRefInfo (for calls) - Return whether information about whether
375 /// a particular call modifies or reads the specified memory location.
376 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) {
377 return getModRefInfo(ImmutableCallSite(C), Loc);
380 /// getModRefInfo (for calls) - A convenience wrapper.
381 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) {
382 return getModRefInfo(C, Location(P, Size));
385 /// getModRefInfo (for invokes) - Return whether information about whether
386 /// a particular invoke modifies or reads the specified memory location.
387 ModRefResult getModRefInfo(const InvokeInst *I,
388 const Location &Loc) {
389 return getModRefInfo(ImmutableCallSite(I), Loc);
392 /// getModRefInfo (for invokes) - A convenience wrapper.
393 ModRefResult getModRefInfo(const InvokeInst *I,
394 const Value *P, uint64_t Size) {
395 return getModRefInfo(I, Location(P, Size));
398 /// getModRefInfo (for loads) - Return whether information about whether
399 /// a particular load modifies or reads the specified memory location.
400 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc);
402 /// getModRefInfo (for loads) - A convenience wrapper.
403 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) {
404 return getModRefInfo(L, Location(P, Size));
407 /// getModRefInfo (for stores) - Return whether information about whether
408 /// a particular store modifies or reads the specified memory location.
409 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc);
411 /// getModRefInfo (for stores) - A convenience wrapper.
412 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size){
413 return getModRefInfo(S, Location(P, Size));
416 /// getModRefInfo (for fences) - Return whether information about whether
417 /// a particular store modifies or reads the specified memory location.
418 ModRefResult getModRefInfo(const FenceInst *S, const Location &Loc) {
419 // Conservatively correct. (We could possibly be a bit smarter if
420 // Loc is a alloca that doesn't escape.)
424 /// getModRefInfo (for fences) - A convenience wrapper.
425 ModRefResult getModRefInfo(const FenceInst *S, const Value *P, uint64_t Size){
426 return getModRefInfo(S, Location(P, Size));
429 /// getModRefInfo (for cmpxchges) - Return whether information about whether
430 /// a particular cmpxchg modifies or reads the specified memory location.
431 ModRefResult getModRefInfo(const AtomicCmpXchgInst *CX, const Location &Loc);
433 /// getModRefInfo (for cmpxchges) - A convenience wrapper.
434 ModRefResult getModRefInfo(const AtomicCmpXchgInst *CX,
435 const Value *P, unsigned Size) {
436 return getModRefInfo(CX, Location(P, Size));
439 /// getModRefInfo (for atomicrmws) - Return whether information about whether
440 /// a particular atomicrmw modifies or reads the specified memory location.
441 ModRefResult getModRefInfo(const AtomicRMWInst *RMW, const Location &Loc);
443 /// getModRefInfo (for atomicrmws) - A convenience wrapper.
444 ModRefResult getModRefInfo(const AtomicRMWInst *RMW,
445 const Value *P, unsigned Size) {
446 return getModRefInfo(RMW, Location(P, Size));
449 /// getModRefInfo (for va_args) - Return whether information about whether
450 /// a particular va_arg modifies or reads the specified memory location.
451 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc);
453 /// getModRefInfo (for va_args) - A convenience wrapper.
454 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size){
455 return getModRefInfo(I, Location(P, Size));
458 /// getModRefInfo - Return information about whether two call sites may refer
459 /// to the same set of memory locations. See
460 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo
462 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
463 ImmutableCallSite CS2);
465 //===--------------------------------------------------------------------===//
466 /// Higher level methods for querying mod/ref information.
469 /// canBasicBlockModify - Return true if it is possible for execution of the
470 /// specified basic block to modify the value pointed to by Ptr.
471 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc);
473 /// canBasicBlockModify - A convenience wrapper.
474 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){
475 return canBasicBlockModify(BB, Location(P, Size));
478 /// canInstructionRangeModify - Return true if it is possible for the
479 /// execution of the specified instructions to modify the value pointed to by
480 /// Ptr. The instructions to consider are all of the instructions in the
481 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
482 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
483 const Location &Loc);
485 /// canInstructionRangeModify - A convenience wrapper.
486 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
487 const Value *Ptr, uint64_t Size) {
488 return canInstructionRangeModify(I1, I2, Location(Ptr, Size));
491 //===--------------------------------------------------------------------===//
492 /// Methods that clients should call when they transform the program to allow
493 /// alias analyses to update their internal data structures. Note that these
494 /// methods may be called on any instruction, regardless of whether or not
495 /// they have pointer-analysis implications.
498 /// deleteValue - This method should be called whenever an LLVM Value is
499 /// deleted from the program, for example when an instruction is found to be
500 /// redundant and is eliminated.
502 virtual void deleteValue(Value *V);
504 /// copyValue - This method should be used whenever a preexisting value in the
505 /// program is copied or cloned, introducing a new value. Note that analysis
506 /// implementations should tolerate clients that use this method to introduce
507 /// the same value multiple times: if the analysis already knows about a
508 /// value, it should ignore the request.
510 virtual void copyValue(Value *From, Value *To);
512 /// addEscapingUse - This method should be used whenever an escaping use is
513 /// added to a pointer value. Analysis implementations may either return
514 /// conservative responses for that value in the future, or may recompute
515 /// some or all internal state to continue providing precise responses.
517 /// Escaping uses are considered by anything _except_ the following:
518 /// - GEPs or bitcasts of the pointer
519 /// - Loads through the pointer
520 /// - Stores through (but not of) the pointer
521 virtual void addEscapingUse(Use &U);
523 /// replaceWithNewValue - This method is the obvious combination of the two
524 /// above, and it provided as a helper to simplify client code.
526 void replaceWithNewValue(Value *Old, Value *New) {
532 // Specialize DenseMapInfo for Location.
534 struct DenseMapInfo<AliasAnalysis::Location> {
535 static inline AliasAnalysis::Location getEmptyKey() {
537 AliasAnalysis::Location(DenseMapInfo<const Value *>::getEmptyKey(),
540 static inline AliasAnalysis::Location getTombstoneKey() {
542 AliasAnalysis::Location(DenseMapInfo<const Value *>::getTombstoneKey(),
545 static unsigned getHashValue(const AliasAnalysis::Location &Val) {
546 return DenseMapInfo<const Value *>::getHashValue(Val.Ptr) ^
547 DenseMapInfo<uint64_t>::getHashValue(Val.Size) ^
548 DenseMapInfo<const MDNode *>::getHashValue(Val.TBAATag);
550 static bool isEqual(const AliasAnalysis::Location &LHS,
551 const AliasAnalysis::Location &RHS) {
552 return LHS.Ptr == RHS.Ptr &&
553 LHS.Size == RHS.Size &&
554 LHS.TBAATag == RHS.TBAATag;
558 /// isNoAliasCall - Return true if this pointer is returned by a noalias
560 bool isNoAliasCall(const Value *V);
562 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
563 /// identifiable object. This returns true for:
564 /// Global Variables and Functions (but not Global Aliases)
565 /// Allocas and Mallocs
566 /// ByVal and NoAlias Arguments
569 bool isIdentifiedObject(const Value *V);
571 } // End llvm namespace