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 represents memory as a (Pointer, Size) pair. The Pointer component
20 // specifies the base memory address of the region, the Size specifies how large
21 // of an area is being queried, or UnknownSize if the size is not known.
22 // Pointers that point to two completely different objects in memory never
23 // alias, regardless of the value of the Size component.
25 //===----------------------------------------------------------------------===//
27 #ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H
28 #define LLVM_ANALYSIS_ALIAS_ANALYSIS_H
30 #include "llvm/Support/CallSite.h"
47 AliasAnalysis *AA; // Previous Alias Analysis to chain to.
50 /// InitializeAliasAnalysis - Subclasses must call this method to initialize
51 /// the AliasAnalysis interface before any other methods are called. This is
52 /// typically called by the run* methods of these subclasses. This may be
53 /// called multiple times.
55 void InitializeAliasAnalysis(Pass *P);
57 /// getAnalysisUsage - All alias analysis implementations should invoke this
58 /// directly (using AliasAnalysis::getAnalysisUsage(AU)).
59 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
62 static char ID; // Class identification, replacement for typeinfo
63 AliasAnalysis() : TD(0), AA(0) {}
64 virtual ~AliasAnalysis(); // We want to be subclassed
66 /// UnknownSize - This is a special value which can be used with the
67 /// size arguments in alias queries to indicate that the caller does not
68 /// know the sizes of the potential memory references.
69 static uint64_t const UnknownSize = ~UINT64_C(0);
71 /// getTargetData - Return a pointer to the current TargetData object, or
72 /// null if no TargetData object is available.
74 const TargetData *getTargetData() const { return TD; }
76 /// getTypeStoreSize - Return the TargetData store size for the given type,
77 /// if known, or a conservative value otherwise.
79 uint64_t getTypeStoreSize(const Type *Ty);
81 //===--------------------------------------------------------------------===//
85 /// Location - A description of a memory location.
87 /// Ptr - The address of the start of the location.
89 /// Size - The maximum size of the location, or UnknownSize if the size is
90 /// not known. Note that an unknown size does not mean the pointer aliases
91 /// the entire virtual address space, because there are restrictions on
92 /// stepping out of one object and into another.
93 /// See http://llvm.org/docs/LangRef.html#pointeraliasing
95 /// TBAATag - The metadata node which describes the TBAA type of
96 /// the location, or null if there is no known unique tag.
97 const MDNode *TBAATag;
99 explicit Location(const Value *P = 0,
100 uint64_t S = UnknownSize,
102 : Ptr(P), Size(S), TBAATag(N) {}
104 Location getWithNewPtr(const Value *NewPtr) const {
105 Location Copy(*this);
110 Location getWithoutTBAATag() const {
111 Location Copy(*this);
117 /// Alias analysis result - Either we know for sure that it does not alias, we
118 /// know for sure it must alias, or we don't know anything: The two pointers
119 /// _might_ alias. This enum is designed so you can do things like:
120 /// if (AA.alias(P1, P2)) { ... }
121 /// to check to see if two pointers might alias.
123 /// See docs/AliasAnalysis.html for more information on the specific meanings
126 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
128 /// alias - The main low level interface to the alias analysis implementation.
129 /// Returns an AliasResult indicating whether the two pointers are aliased to
130 /// each other. This is the interface that must be implemented by specific
131 /// alias analysis implementations.
132 virtual AliasResult alias(const Location &LocA, const Location &LocB);
134 /// alias - A convenience wrapper.
135 AliasResult alias(const Value *V1, uint64_t V1Size,
136 const Value *V2, uint64_t V2Size) {
137 return alias(Location(V1, V1Size), Location(V2, V2Size));
140 /// alias - A convenience wrapper.
141 AliasResult alias(const Value *V1, const Value *V2) {
142 return alias(V1, UnknownSize, V2, UnknownSize);
145 /// isNoAlias - A trivial helper function to check to see if the specified
146 /// pointers are no-alias.
147 bool isNoAlias(const Location &LocA, const Location &LocB) {
148 return alias(LocA, LocB) == NoAlias;
151 /// isNoAlias - A convenience wrapper.
152 bool isNoAlias(const Value *V1, uint64_t V1Size,
153 const Value *V2, uint64_t V2Size) {
154 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size));
157 /// pointsToConstantMemory - If the specified memory location is
158 /// known to be constant, return true. If OrLocal is true and the
159 /// specified memory location is known to be "local" (derived from
160 /// an alloca), return true. Otherwise return false.
161 virtual bool pointsToConstantMemory(const Location &Loc,
162 bool OrLocal = false);
164 /// pointsToConstantMemory - A convenient wrapper.
165 bool pointsToConstantMemory(const Value *P, bool OrLocal = false) {
166 return pointsToConstantMemory(Location(P), OrLocal);
169 //===--------------------------------------------------------------------===//
170 /// Simple mod/ref information...
173 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
174 /// bits which may be or'd together.
176 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
178 /// These values define additional bits used to define the
179 /// ModRefBehavior values.
180 enum { Nowhere = 0, ArgumentPointees = 4, Anywhere = 8 | ArgumentPointees };
182 /// ModRefBehavior - Summary of how a function affects memory in the program.
183 /// Loads from constant globals are not considered memory accesses for this
184 /// interface. Also, functions may freely modify stack space local to their
185 /// invocation without having to report it through these interfaces.
186 enum ModRefBehavior {
187 /// DoesNotAccessMemory - This function does not perform any non-local loads
188 /// or stores to memory.
190 /// This property corresponds to the GCC 'const' attribute.
191 /// This property corresponds to the LLVM IR 'readnone' attribute.
192 /// This property corresponds to the IntrNoMem LLVM intrinsic flag.
193 DoesNotAccessMemory = Nowhere | NoModRef,
195 /// OnlyReadsArgumentPointees - The only memory references in this function
196 /// (if it has any) are non-volatile loads from objects pointed to by its
197 /// pointer-typed arguments, with arbitrary offsets.
199 /// This property corresponds to the IntrReadArgMem LLVM intrinsic flag.
200 OnlyReadsArgumentPointees = ArgumentPointees | Ref,
202 /// OnlyAccessesArgumentPointees - The only memory references in this
203 /// function (if it has any) are non-volatile loads and stores from objects
204 /// pointed to by its pointer-typed arguments, with arbitrary offsets.
206 /// This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag.
207 OnlyAccessesArgumentPointees = ArgumentPointees | ModRef,
209 /// OnlyReadsMemory - This function does not perform any non-local stores or
210 /// volatile loads, but may read from any memory location.
212 /// This property corresponds to the GCC 'pure' attribute.
213 /// This property corresponds to the LLVM IR 'readonly' attribute.
214 /// This property corresponds to the IntrReadMem LLVM intrinsic flag.
215 OnlyReadsMemory = Anywhere | Ref,
217 /// UnknownModRefBehavior - This indicates that the function could not be
218 /// classified into one of the behaviors above.
219 UnknownModRefBehavior = Anywhere | ModRef
222 /// getModRefBehavior - Return the behavior when calling the given call site.
223 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
225 /// getModRefBehavior - Return the behavior when calling the given function.
226 /// For use when the call site is not known.
227 virtual ModRefBehavior getModRefBehavior(const Function *F);
229 /// doesNotAccessMemory - If the specified call is known to never read or
230 /// write memory, return true. If the call only reads from known-constant
231 /// memory, it is also legal to return true. Calls that unwind the stack
232 /// are legal for this predicate.
234 /// Many optimizations (such as CSE and LICM) can be performed on such calls
235 /// without worrying about aliasing properties, and many calls have this
236 /// property (e.g. calls to 'sin' and 'cos').
238 /// This property corresponds to the GCC 'const' attribute.
240 bool doesNotAccessMemory(ImmutableCallSite CS) {
241 return getModRefBehavior(CS) == DoesNotAccessMemory;
244 /// doesNotAccessMemory - If the specified function is known to never read or
245 /// write memory, return true. For use when the call site is not known.
247 bool doesNotAccessMemory(const Function *F) {
248 return getModRefBehavior(F) == DoesNotAccessMemory;
251 /// onlyReadsMemory - If the specified call is known to only read from
252 /// non-volatile memory (or not access memory at all), return true. Calls
253 /// that unwind the stack are legal for this predicate.
255 /// This property allows many common optimizations to be performed in the
256 /// absence of interfering store instructions, such as CSE of strlen calls.
258 /// This property corresponds to the GCC 'pure' attribute.
260 bool onlyReadsMemory(ImmutableCallSite CS) {
261 return onlyReadsMemory(getModRefBehavior(CS));
264 /// onlyReadsMemory - If the specified function is known to only read from
265 /// non-volatile memory (or not access memory at all), return true. For use
266 /// when the call site is not known.
268 bool onlyReadsMemory(const Function *F) {
269 return onlyReadsMemory(getModRefBehavior(F));
272 /// onlyReadsMemory - Return true if functions with the specified behavior are
273 /// known to only read from non-volatile memory (or not access memory at all).
275 static bool onlyReadsMemory(ModRefBehavior MRB) {
279 /// onlyAccessesArgPointees - Return true if functions with the specified
280 /// behavior are known to read and write at most from objects pointed to by
281 /// their pointer-typed arguments (with arbitrary offsets).
283 static bool onlyAccessesArgPointees(ModRefBehavior MRB) {
284 return !(MRB & Anywhere & ~ArgumentPointees);
287 /// doesAccessArgPointees - Return true if functions with the specified
288 /// behavior are known to potentially read or write from objects pointed
289 /// to be their pointer-typed arguments (with arbitrary offsets).
291 static bool doesAccessArgPointees(ModRefBehavior MRB) {
292 return (MRB & ModRef) && (MRB & ArgumentPointees);
295 /// getModRefInfo - Return information about whether or not an instruction may
296 /// read or write the specified memory location. An instruction
297 /// that doesn't read or write memory may be trivially LICM'd for example.
298 ModRefResult getModRefInfo(const Instruction *I,
299 const Location &Loc) {
300 switch (I->getOpcode()) {
301 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc);
302 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc);
303 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc);
304 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc);
305 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc);
306 default: return NoModRef;
310 /// getModRefInfo - A convenience wrapper.
311 ModRefResult getModRefInfo(const Instruction *I,
312 const Value *P, uint64_t Size) {
313 return getModRefInfo(I, Location(P, Size));
316 /// getModRefInfo (for call sites) - Return whether information about whether
317 /// a particular call site modifies or reads the specified memory location.
318 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
319 const Location &Loc);
321 /// getModRefInfo (for call sites) - A convenience wrapper.
322 ModRefResult getModRefInfo(ImmutableCallSite CS,
323 const Value *P, uint64_t Size) {
324 return getModRefInfo(CS, Location(P, Size));
327 /// getModRefInfo (for calls) - Return whether information about whether
328 /// a particular call modifies or reads the specified memory location.
329 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) {
330 return getModRefInfo(ImmutableCallSite(C), Loc);
333 /// getModRefInfo (for calls) - A convenience wrapper.
334 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) {
335 return getModRefInfo(C, Location(P, Size));
338 /// getModRefInfo (for invokes) - Return whether information about whether
339 /// a particular invoke modifies or reads the specified memory location.
340 ModRefResult getModRefInfo(const InvokeInst *I,
341 const Location &Loc) {
342 return getModRefInfo(ImmutableCallSite(I), Loc);
345 /// getModRefInfo (for invokes) - A convenience wrapper.
346 ModRefResult getModRefInfo(const InvokeInst *I,
347 const Value *P, uint64_t Size) {
348 return getModRefInfo(I, Location(P, Size));
351 /// getModRefInfo (for loads) - Return whether information about whether
352 /// a particular load modifies or reads the specified memory location.
353 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc);
355 /// getModRefInfo (for loads) - A convenience wrapper.
356 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) {
357 return getModRefInfo(L, Location(P, Size));
360 /// getModRefInfo (for stores) - Return whether information about whether
361 /// a particular store modifies or reads the specified memory location.
362 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc);
364 /// getModRefInfo (for stores) - A convenience wrapper.
365 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) {
366 return getModRefInfo(S, Location(P, Size));
369 /// getModRefInfo (for va_args) - Return whether information about whether
370 /// a particular va_arg modifies or reads the specified memory location.
371 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc);
373 /// getModRefInfo (for va_args) - A convenience wrapper.
374 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) {
375 return getModRefInfo(I, Location(P, Size));
378 /// getModRefInfo - Return information about whether two call sites may refer
379 /// to the same set of memory locations. See
380 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo
382 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
383 ImmutableCallSite CS2);
385 //===--------------------------------------------------------------------===//
386 /// Higher level methods for querying mod/ref information.
389 /// canBasicBlockModify - Return true if it is possible for execution of the
390 /// specified basic block to modify the value pointed to by Ptr.
391 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc);
393 /// canBasicBlockModify - A convenience wrapper.
394 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){
395 return canBasicBlockModify(BB, Location(P, Size));
398 /// canInstructionRangeModify - Return true if it is possible for the
399 /// execution of the specified instructions to modify the value pointed to by
400 /// Ptr. The instructions to consider are all of the instructions in the
401 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
402 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
403 const Location &Loc);
405 /// canInstructionRangeModify - A convenience wrapper.
406 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
407 const Value *Ptr, uint64_t Size) {
408 return canInstructionRangeModify(I1, I2, Location(Ptr, Size));
411 //===--------------------------------------------------------------------===//
412 /// Methods that clients should call when they transform the program to allow
413 /// alias analyses to update their internal data structures. Note that these
414 /// methods may be called on any instruction, regardless of whether or not
415 /// they have pointer-analysis implications.
418 /// deleteValue - This method should be called whenever an LLVM Value is
419 /// deleted from the program, for example when an instruction is found to be
420 /// redundant and is eliminated.
422 virtual void deleteValue(Value *V);
424 /// copyValue - This method should be used whenever a preexisting value in the
425 /// program is copied or cloned, introducing a new value. Note that analysis
426 /// implementations should tolerate clients that use this method to introduce
427 /// the same value multiple times: if the analysis already knows about a
428 /// value, it should ignore the request.
430 virtual void copyValue(Value *From, Value *To);
432 /// replaceWithNewValue - This method is the obvious combination of the two
433 /// above, and it provided as a helper to simplify client code.
435 void replaceWithNewValue(Value *Old, Value *New) {
441 /// isNoAliasCall - Return true if this pointer is returned by a noalias
443 bool isNoAliasCall(const Value *V);
445 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
446 /// identifiable object. This returns true for:
447 /// Global Variables and Functions (but not Global Aliases)
448 /// Allocas and Mallocs
449 /// ByVal and NoAlias Arguments
452 bool isIdentifiedObject(const Value *V);
454 } // End llvm namespace