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"
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(const 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 static Location getLocationForSource(const MemTransferInst *MTI);
140 static Location getLocationForDest(const MemIntrinsic *MI);
142 /// Alias analysis result - Either we know for sure that it does not alias, we
143 /// know for sure it must alias, or we don't know anything: The two pointers
144 /// _might_ alias. This enum is designed so you can do things like:
145 /// if (AA.alias(P1, P2)) { ... }
146 /// to check to see if two pointers might alias.
148 /// See docs/AliasAnalysis.html for more information on the specific meanings
152 NoAlias = 0, ///< No dependencies.
153 MayAlias, ///< Anything goes.
154 PartialAlias, ///< Pointers differ, but pointees overlap.
155 MustAlias ///< Pointers are equal.
158 /// alias - The main low level interface to the alias analysis implementation.
159 /// Returns an AliasResult indicating whether the two pointers are aliased to
160 /// each other. This is the interface that must be implemented by specific
161 /// alias analysis implementations.
162 virtual AliasResult alias(const Location &LocA, const Location &LocB);
164 /// alias - A convenience wrapper.
165 AliasResult alias(const Value *V1, uint64_t V1Size,
166 const Value *V2, uint64_t V2Size) {
167 return alias(Location(V1, V1Size), Location(V2, V2Size));
170 /// alias - A convenience wrapper.
171 AliasResult alias(const Value *V1, const Value *V2) {
172 return alias(V1, UnknownSize, V2, UnknownSize);
175 /// isNoAlias - A trivial helper function to check to see if the specified
176 /// pointers are no-alias.
177 bool isNoAlias(const Location &LocA, const Location &LocB) {
178 return alias(LocA, LocB) == NoAlias;
181 /// isNoAlias - A convenience wrapper.
182 bool isNoAlias(const Value *V1, uint64_t V1Size,
183 const Value *V2, uint64_t V2Size) {
184 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size));
187 /// isMustAlias - A convenience wrapper.
188 bool isMustAlias(const Location &LocA, const Location &LocB) {
189 return alias(LocA, LocB) == MustAlias;
192 /// isMustAlias - A convenience wrapper.
193 bool isMustAlias(const Value *V1, const Value *V2) {
194 return alias(V1, 1, V2, 1) == MustAlias;
197 /// pointsToConstantMemory - If the specified memory location is
198 /// known to be constant, return true. If OrLocal is true and the
199 /// specified memory location is known to be "local" (derived from
200 /// an alloca), return true. Otherwise return false.
201 virtual bool pointsToConstantMemory(const Location &Loc,
202 bool OrLocal = false);
204 /// pointsToConstantMemory - A convenient wrapper.
205 bool pointsToConstantMemory(const Value *P, bool OrLocal = false) {
206 return pointsToConstantMemory(Location(P), OrLocal);
209 //===--------------------------------------------------------------------===//
210 /// Simple mod/ref information...
213 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
214 /// bits which may be or'd together.
216 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
218 /// These values define additional bits used to define the
219 /// ModRefBehavior values.
220 enum { Nowhere = 0, ArgumentPointees = 4, Anywhere = 8 | ArgumentPointees };
222 /// ModRefBehavior - Summary of how a function affects memory in the program.
223 /// Loads from constant globals are not considered memory accesses for this
224 /// interface. Also, functions may freely modify stack space local to their
225 /// invocation without having to report it through these interfaces.
226 enum ModRefBehavior {
227 /// DoesNotAccessMemory - This function does not perform any non-local loads
228 /// or stores to memory.
230 /// This property corresponds to the GCC 'const' attribute.
231 /// This property corresponds to the LLVM IR 'readnone' attribute.
232 /// This property corresponds to the IntrNoMem LLVM intrinsic flag.
233 DoesNotAccessMemory = Nowhere | NoModRef,
235 /// OnlyReadsArgumentPointees - The only memory references in this function
236 /// (if it has any) are non-volatile loads from objects pointed to by its
237 /// pointer-typed arguments, with arbitrary offsets.
239 /// This property corresponds to the IntrReadArgMem LLVM intrinsic flag.
240 OnlyReadsArgumentPointees = ArgumentPointees | Ref,
242 /// OnlyAccessesArgumentPointees - The only memory references in this
243 /// function (if it has any) are non-volatile loads and stores from objects
244 /// pointed to by its pointer-typed arguments, with arbitrary offsets.
246 /// This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag.
247 OnlyAccessesArgumentPointees = ArgumentPointees | ModRef,
249 /// OnlyReadsMemory - This function does not perform any non-local stores or
250 /// volatile loads, but may read from any memory location.
252 /// This property corresponds to the GCC 'pure' attribute.
253 /// This property corresponds to the LLVM IR 'readonly' attribute.
254 /// This property corresponds to the IntrReadMem LLVM intrinsic flag.
255 OnlyReadsMemory = Anywhere | Ref,
257 /// UnknownModRefBehavior - This indicates that the function could not be
258 /// classified into one of the behaviors above.
259 UnknownModRefBehavior = Anywhere | ModRef
262 /// getModRefBehavior - Return the behavior when calling the given call site.
263 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
265 /// getModRefBehavior - Return the behavior when calling the given function.
266 /// For use when the call site is not known.
267 virtual ModRefBehavior getModRefBehavior(const Function *F);
269 /// doesNotAccessMemory - If the specified call is known to never read or
270 /// write memory, return true. If the call only reads from known-constant
271 /// memory, it is also legal to return true. Calls that unwind the stack
272 /// are legal for this predicate.
274 /// Many optimizations (such as CSE and LICM) can be performed on such calls
275 /// without worrying about aliasing properties, and many calls have this
276 /// property (e.g. calls to 'sin' and 'cos').
278 /// This property corresponds to the GCC 'const' attribute.
280 bool doesNotAccessMemory(ImmutableCallSite CS) {
281 return getModRefBehavior(CS) == DoesNotAccessMemory;
284 /// doesNotAccessMemory - If the specified function is known to never read or
285 /// write memory, return true. For use when the call site is not known.
287 bool doesNotAccessMemory(const Function *F) {
288 return getModRefBehavior(F) == DoesNotAccessMemory;
291 /// onlyReadsMemory - If the specified call is known to only read from
292 /// non-volatile memory (or not access memory at all), return true. Calls
293 /// that unwind the stack are legal for this predicate.
295 /// This property allows many common optimizations to be performed in the
296 /// absence of interfering store instructions, such as CSE of strlen calls.
298 /// This property corresponds to the GCC 'pure' attribute.
300 bool onlyReadsMemory(ImmutableCallSite CS) {
301 return onlyReadsMemory(getModRefBehavior(CS));
304 /// onlyReadsMemory - If the specified function is known to only read from
305 /// non-volatile memory (or not access memory at all), return true. For use
306 /// when the call site is not known.
308 bool onlyReadsMemory(const Function *F) {
309 return onlyReadsMemory(getModRefBehavior(F));
312 /// onlyReadsMemory - Return true if functions with the specified behavior are
313 /// known to only read from non-volatile memory (or not access memory at all).
315 static bool onlyReadsMemory(ModRefBehavior MRB) {
319 /// onlyAccessesArgPointees - Return true if functions with the specified
320 /// behavior are known to read and write at most from objects pointed to by
321 /// their pointer-typed arguments (with arbitrary offsets).
323 static bool onlyAccessesArgPointees(ModRefBehavior MRB) {
324 return !(MRB & Anywhere & ~ArgumentPointees);
327 /// doesAccessArgPointees - Return true if functions with the specified
328 /// behavior are known to potentially read or write from objects pointed
329 /// to be their pointer-typed arguments (with arbitrary offsets).
331 static bool doesAccessArgPointees(ModRefBehavior MRB) {
332 return (MRB & ModRef) && (MRB & ArgumentPointees);
335 /// getModRefInfo - Return information about whether or not an instruction may
336 /// read or write the specified memory location. An instruction
337 /// that doesn't read or write memory may be trivially LICM'd for example.
338 ModRefResult getModRefInfo(const Instruction *I,
339 const Location &Loc) {
340 switch (I->getOpcode()) {
341 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc);
342 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc);
343 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc);
344 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc);
345 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc);
346 default: return NoModRef;
350 /// getModRefInfo - A convenience wrapper.
351 ModRefResult getModRefInfo(const Instruction *I,
352 const Value *P, uint64_t Size) {
353 return getModRefInfo(I, Location(P, Size));
356 /// getModRefInfo (for call sites) - Return whether information about whether
357 /// a particular call site modifies or reads the specified memory location.
358 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
359 const Location &Loc);
361 /// getModRefInfo (for call sites) - A convenience wrapper.
362 ModRefResult getModRefInfo(ImmutableCallSite CS,
363 const Value *P, uint64_t Size) {
364 return getModRefInfo(CS, Location(P, Size));
367 /// getModRefInfo (for calls) - Return whether information about whether
368 /// a particular call modifies or reads the specified memory location.
369 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) {
370 return getModRefInfo(ImmutableCallSite(C), Loc);
373 /// getModRefInfo (for calls) - A convenience wrapper.
374 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) {
375 return getModRefInfo(C, Location(P, Size));
378 /// getModRefInfo (for invokes) - Return whether information about whether
379 /// a particular invoke modifies or reads the specified memory location.
380 ModRefResult getModRefInfo(const InvokeInst *I,
381 const Location &Loc) {
382 return getModRefInfo(ImmutableCallSite(I), Loc);
385 /// getModRefInfo (for invokes) - A convenience wrapper.
386 ModRefResult getModRefInfo(const InvokeInst *I,
387 const Value *P, uint64_t Size) {
388 return getModRefInfo(I, Location(P, Size));
391 /// getModRefInfo (for loads) - Return whether information about whether
392 /// a particular load modifies or reads the specified memory location.
393 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc);
395 /// getModRefInfo (for loads) - A convenience wrapper.
396 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) {
397 return getModRefInfo(L, Location(P, Size));
400 /// getModRefInfo (for stores) - Return whether information about whether
401 /// a particular store modifies or reads the specified memory location.
402 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc);
404 /// getModRefInfo (for stores) - A convenience wrapper.
405 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) {
406 return getModRefInfo(S, Location(P, Size));
409 /// getModRefInfo (for va_args) - Return whether information about whether
410 /// a particular va_arg modifies or reads the specified memory location.
411 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc);
413 /// getModRefInfo (for va_args) - A convenience wrapper.
414 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) {
415 return getModRefInfo(I, Location(P, Size));
418 /// getModRefInfo - Return information about whether two call sites may refer
419 /// to the same set of memory locations. See
420 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo
422 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
423 ImmutableCallSite CS2);
425 //===--------------------------------------------------------------------===//
426 /// Higher level methods for querying mod/ref information.
429 /// canBasicBlockModify - Return true if it is possible for execution of the
430 /// specified basic block to modify the value pointed to by Ptr.
431 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc);
433 /// canBasicBlockModify - A convenience wrapper.
434 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){
435 return canBasicBlockModify(BB, Location(P, Size));
438 /// canInstructionRangeModify - Return true if it is possible for the
439 /// execution of the specified instructions to modify the value pointed to by
440 /// Ptr. The instructions to consider are all of the instructions in the
441 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
442 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
443 const Location &Loc);
445 /// canInstructionRangeModify - A convenience wrapper.
446 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
447 const Value *Ptr, uint64_t Size) {
448 return canInstructionRangeModify(I1, I2, Location(Ptr, Size));
451 //===--------------------------------------------------------------------===//
452 /// Methods that clients should call when they transform the program to allow
453 /// alias analyses to update their internal data structures. Note that these
454 /// methods may be called on any instruction, regardless of whether or not
455 /// they have pointer-analysis implications.
458 /// deleteValue - This method should be called whenever an LLVM Value is
459 /// deleted from the program, for example when an instruction is found to be
460 /// redundant and is eliminated.
462 virtual void deleteValue(Value *V);
464 /// copyValue - This method should be used whenever a preexisting value in the
465 /// program is copied or cloned, introducing a new value. Note that analysis
466 /// implementations should tolerate clients that use this method to introduce
467 /// the same value multiple times: if the analysis already knows about a
468 /// value, it should ignore the request.
470 virtual void copyValue(Value *From, Value *To);
472 /// replaceWithNewValue - This method is the obvious combination of the two
473 /// above, and it provided as a helper to simplify client code.
475 void replaceWithNewValue(Value *Old, Value *New) {
481 /// isNoAliasCall - Return true if this pointer is returned by a noalias
483 bool isNoAliasCall(const Value *V);
485 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
486 /// identifiable object. This returns true for:
487 /// Global Variables and Functions (but not Global Aliases)
488 /// Allocas and Mallocs
489 /// ByVal and NoAlias Arguments
492 bool isIdentifiedObject(const Value *V);
494 } // End llvm namespace