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 getWithNewSize(uint64_t NewSize) const {
111 Location Copy(*this);
116 Location getWithoutTBAATag() const {
117 Location Copy(*this);
123 /// Alias analysis result - Either we know for sure that it does not alias, we
124 /// know for sure it must alias, or we don't know anything: The two pointers
125 /// _might_ alias. This enum is designed so you can do things like:
126 /// if (AA.alias(P1, P2)) { ... }
127 /// to check to see if two pointers might alias.
129 /// See docs/AliasAnalysis.html for more information on the specific meanings
132 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
134 /// alias - The main low level interface to the alias analysis implementation.
135 /// Returns an AliasResult indicating whether the two pointers are aliased to
136 /// each other. This is the interface that must be implemented by specific
137 /// alias analysis implementations.
138 virtual AliasResult alias(const Location &LocA, const Location &LocB);
140 /// alias - A convenience wrapper.
141 AliasResult alias(const Value *V1, uint64_t V1Size,
142 const Value *V2, uint64_t V2Size) {
143 return alias(Location(V1, V1Size), Location(V2, V2Size));
146 /// alias - A convenience wrapper.
147 AliasResult alias(const Value *V1, const Value *V2) {
148 return alias(V1, UnknownSize, V2, UnknownSize);
151 /// isNoAlias - A trivial helper function to check to see if the specified
152 /// pointers are no-alias.
153 bool isNoAlias(const Location &LocA, const Location &LocB) {
154 return alias(LocA, LocB) == NoAlias;
157 /// isNoAlias - A convenience wrapper.
158 bool isNoAlias(const Value *V1, uint64_t V1Size,
159 const Value *V2, uint64_t V2Size) {
160 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size));
163 /// pointsToConstantMemory - If the specified memory location is
164 /// known to be constant, return true. If OrLocal is true and the
165 /// specified memory location is known to be "local" (derived from
166 /// an alloca), return true. Otherwise return false.
167 virtual bool pointsToConstantMemory(const Location &Loc,
168 bool OrLocal = false);
170 /// pointsToConstantMemory - A convenient wrapper.
171 bool pointsToConstantMemory(const Value *P, bool OrLocal = false) {
172 return pointsToConstantMemory(Location(P), OrLocal);
175 //===--------------------------------------------------------------------===//
176 /// Simple mod/ref information...
179 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
180 /// bits which may be or'd together.
182 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
184 /// These values define additional bits used to define the
185 /// ModRefBehavior values.
186 enum { Nowhere = 0, ArgumentPointees = 4, Anywhere = 8 | ArgumentPointees };
188 /// ModRefBehavior - Summary of how a function affects memory in the program.
189 /// Loads from constant globals are not considered memory accesses for this
190 /// interface. Also, functions may freely modify stack space local to their
191 /// invocation without having to report it through these interfaces.
192 enum ModRefBehavior {
193 /// DoesNotAccessMemory - This function does not perform any non-local loads
194 /// or stores to memory.
196 /// This property corresponds to the GCC 'const' attribute.
197 /// This property corresponds to the LLVM IR 'readnone' attribute.
198 /// This property corresponds to the IntrNoMem LLVM intrinsic flag.
199 DoesNotAccessMemory = Nowhere | NoModRef,
201 /// OnlyReadsArgumentPointees - The only memory references in this function
202 /// (if it has any) are non-volatile loads from objects pointed to by its
203 /// pointer-typed arguments, with arbitrary offsets.
205 /// This property corresponds to the IntrReadArgMem LLVM intrinsic flag.
206 OnlyReadsArgumentPointees = ArgumentPointees | Ref,
208 /// OnlyAccessesArgumentPointees - The only memory references in this
209 /// function (if it has any) are non-volatile loads and stores from objects
210 /// pointed to by its pointer-typed arguments, with arbitrary offsets.
212 /// This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag.
213 OnlyAccessesArgumentPointees = ArgumentPointees | ModRef,
215 /// OnlyReadsMemory - This function does not perform any non-local stores or
216 /// volatile loads, but may read from any memory location.
218 /// This property corresponds to the GCC 'pure' attribute.
219 /// This property corresponds to the LLVM IR 'readonly' attribute.
220 /// This property corresponds to the IntrReadMem LLVM intrinsic flag.
221 OnlyReadsMemory = Anywhere | Ref,
223 /// UnknownModRefBehavior - This indicates that the function could not be
224 /// classified into one of the behaviors above.
225 UnknownModRefBehavior = Anywhere | ModRef
228 /// getModRefBehavior - Return the behavior when calling the given call site.
229 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
231 /// getModRefBehavior - Return the behavior when calling the given function.
232 /// For use when the call site is not known.
233 virtual ModRefBehavior getModRefBehavior(const Function *F);
235 /// doesNotAccessMemory - If the specified call is known to never read or
236 /// write memory, return true. If the call only reads from known-constant
237 /// memory, it is also legal to return true. Calls that unwind the stack
238 /// are legal for this predicate.
240 /// Many optimizations (such as CSE and LICM) can be performed on such calls
241 /// without worrying about aliasing properties, and many calls have this
242 /// property (e.g. calls to 'sin' and 'cos').
244 /// This property corresponds to the GCC 'const' attribute.
246 bool doesNotAccessMemory(ImmutableCallSite CS) {
247 return getModRefBehavior(CS) == DoesNotAccessMemory;
250 /// doesNotAccessMemory - If the specified function is known to never read or
251 /// write memory, return true. For use when the call site is not known.
253 bool doesNotAccessMemory(const Function *F) {
254 return getModRefBehavior(F) == DoesNotAccessMemory;
257 /// onlyReadsMemory - If the specified call is known to only read from
258 /// non-volatile memory (or not access memory at all), return true. Calls
259 /// that unwind the stack are legal for this predicate.
261 /// This property allows many common optimizations to be performed in the
262 /// absence of interfering store instructions, such as CSE of strlen calls.
264 /// This property corresponds to the GCC 'pure' attribute.
266 bool onlyReadsMemory(ImmutableCallSite CS) {
267 return onlyReadsMemory(getModRefBehavior(CS));
270 /// onlyReadsMemory - If the specified function is known to only read from
271 /// non-volatile memory (or not access memory at all), return true. For use
272 /// when the call site is not known.
274 bool onlyReadsMemory(const Function *F) {
275 return onlyReadsMemory(getModRefBehavior(F));
278 /// onlyReadsMemory - Return true if functions with the specified behavior are
279 /// known to only read from non-volatile memory (or not access memory at all).
281 static bool onlyReadsMemory(ModRefBehavior MRB) {
285 /// onlyAccessesArgPointees - Return true if functions with the specified
286 /// behavior are known to read and write at most from objects pointed to by
287 /// their pointer-typed arguments (with arbitrary offsets).
289 static bool onlyAccessesArgPointees(ModRefBehavior MRB) {
290 return !(MRB & Anywhere & ~ArgumentPointees);
293 /// doesAccessArgPointees - Return true if functions with the specified
294 /// behavior are known to potentially read or write from objects pointed
295 /// to be their pointer-typed arguments (with arbitrary offsets).
297 static bool doesAccessArgPointees(ModRefBehavior MRB) {
298 return (MRB & ModRef) && (MRB & ArgumentPointees);
301 /// getModRefInfo - Return information about whether or not an instruction may
302 /// read or write the specified memory location. An instruction
303 /// that doesn't read or write memory may be trivially LICM'd for example.
304 ModRefResult getModRefInfo(const Instruction *I,
305 const Location &Loc) {
306 switch (I->getOpcode()) {
307 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc);
308 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc);
309 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc);
310 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc);
311 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc);
312 default: return NoModRef;
316 /// getModRefInfo - A convenience wrapper.
317 ModRefResult getModRefInfo(const Instruction *I,
318 const Value *P, uint64_t Size) {
319 return getModRefInfo(I, Location(P, Size));
322 /// getModRefInfo (for call sites) - Return whether information about whether
323 /// a particular call site modifies or reads the specified memory location.
324 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
325 const Location &Loc);
327 /// getModRefInfo (for call sites) - A convenience wrapper.
328 ModRefResult getModRefInfo(ImmutableCallSite CS,
329 const Value *P, uint64_t Size) {
330 return getModRefInfo(CS, Location(P, Size));
333 /// getModRefInfo (for calls) - Return whether information about whether
334 /// a particular call modifies or reads the specified memory location.
335 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) {
336 return getModRefInfo(ImmutableCallSite(C), Loc);
339 /// getModRefInfo (for calls) - A convenience wrapper.
340 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) {
341 return getModRefInfo(C, Location(P, Size));
344 /// getModRefInfo (for invokes) - Return whether information about whether
345 /// a particular invoke modifies or reads the specified memory location.
346 ModRefResult getModRefInfo(const InvokeInst *I,
347 const Location &Loc) {
348 return getModRefInfo(ImmutableCallSite(I), Loc);
351 /// getModRefInfo (for invokes) - A convenience wrapper.
352 ModRefResult getModRefInfo(const InvokeInst *I,
353 const Value *P, uint64_t Size) {
354 return getModRefInfo(I, Location(P, Size));
357 /// getModRefInfo (for loads) - Return whether information about whether
358 /// a particular load modifies or reads the specified memory location.
359 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc);
361 /// getModRefInfo (for loads) - A convenience wrapper.
362 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) {
363 return getModRefInfo(L, Location(P, Size));
366 /// getModRefInfo (for stores) - Return whether information about whether
367 /// a particular store modifies or reads the specified memory location.
368 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc);
370 /// getModRefInfo (for stores) - A convenience wrapper.
371 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) {
372 return getModRefInfo(S, Location(P, Size));
375 /// getModRefInfo (for va_args) - Return whether information about whether
376 /// a particular va_arg modifies or reads the specified memory location.
377 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc);
379 /// getModRefInfo (for va_args) - A convenience wrapper.
380 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) {
381 return getModRefInfo(I, Location(P, Size));
384 /// getModRefInfo - Return information about whether two call sites may refer
385 /// to the same set of memory locations. See
386 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo
388 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
389 ImmutableCallSite CS2);
391 //===--------------------------------------------------------------------===//
392 /// Higher level methods for querying mod/ref information.
395 /// canBasicBlockModify - Return true if it is possible for execution of the
396 /// specified basic block to modify the value pointed to by Ptr.
397 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc);
399 /// canBasicBlockModify - A convenience wrapper.
400 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){
401 return canBasicBlockModify(BB, Location(P, Size));
404 /// canInstructionRangeModify - Return true if it is possible for the
405 /// execution of the specified instructions to modify the value pointed to by
406 /// Ptr. The instructions to consider are all of the instructions in the
407 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
408 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
409 const Location &Loc);
411 /// canInstructionRangeModify - A convenience wrapper.
412 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
413 const Value *Ptr, uint64_t Size) {
414 return canInstructionRangeModify(I1, I2, Location(Ptr, Size));
417 //===--------------------------------------------------------------------===//
418 /// Methods that clients should call when they transform the program to allow
419 /// alias analyses to update their internal data structures. Note that these
420 /// methods may be called on any instruction, regardless of whether or not
421 /// they have pointer-analysis implications.
424 /// deleteValue - This method should be called whenever an LLVM Value is
425 /// deleted from the program, for example when an instruction is found to be
426 /// redundant and is eliminated.
428 virtual void deleteValue(Value *V);
430 /// copyValue - This method should be used whenever a preexisting value in the
431 /// program is copied or cloned, introducing a new value. Note that analysis
432 /// implementations should tolerate clients that use this method to introduce
433 /// the same value multiple times: if the analysis already knows about a
434 /// value, it should ignore the request.
436 virtual void copyValue(Value *From, Value *To);
438 /// replaceWithNewValue - This method is the obvious combination of the two
439 /// above, and it provided as a helper to simplify client code.
441 void replaceWithNewValue(Value *Old, Value *New) {
447 /// isNoAliasCall - Return true if this pointer is returned by a noalias
449 bool isNoAliasCall(const Value *V);
451 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
452 /// identifiable object. This returns true for:
453 /// Global Variables and Functions (but not Global Aliases)
454 /// Allocas and Mallocs
455 /// ByVal and NoAlias Arguments
458 bool isIdentifiedObject(const Value *V);
460 } // End llvm namespace