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 known to be
158 /// constant, return true. This allows disambiguation of store
159 /// instructions from constant pointers.
161 virtual bool pointsToConstantMemory(const Location &Loc);
163 /// pointsToConstantMemory - A convenient wrapper.
164 bool pointsToConstantMemory(const Value *P) {
165 return pointsToConstantMemory(Location(P));
168 //===--------------------------------------------------------------------===//
169 /// Simple mod/ref information...
172 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
173 /// bits which may be or'd together.
175 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
178 /// ModRefBehavior - Summary of how a function affects memory in the program.
179 /// Loads from constant globals are not considered memory accesses for this
180 /// interface. Also, functions may freely modify stack space local to their
181 /// invocation without having to report it through these interfaces.
182 enum ModRefBehavior {
183 // DoesNotAccessMemory - This function does not perform any non-local loads
184 // or stores to memory.
186 // This property corresponds to the GCC 'const' attribute.
189 // AccessesArguments - This function accesses function arguments in well
190 // known (possibly volatile) ways, but does not access any other memory.
193 // AccessesArgumentsAndGlobals - This function has accesses function
194 // arguments and global variables well known (possibly volatile) ways, but
195 // does not access any other memory.
196 AccessesArgumentsAndGlobals,
198 // OnlyReadsMemory - This function does not perform any non-local stores or
199 // volatile loads, but may read from any memory location.
201 // This property corresponds to the GCC 'pure' attribute.
204 // UnknownModRefBehavior - This indicates that the function could not be
205 // classified into one of the behaviors above.
206 UnknownModRefBehavior
209 /// getModRefBehavior - Return the behavior when calling the given call site.
210 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
212 /// getModRefBehavior - Return the behavior when calling the given function.
213 /// For use when the call site is not known.
214 virtual ModRefBehavior getModRefBehavior(const Function *F);
216 /// doesNotAccessMemory - If the specified call is known to never read or
217 /// write memory, return true. If the call only reads from known-constant
218 /// memory, it is also legal to return true. Calls that unwind the stack
219 /// are legal for this predicate.
221 /// Many optimizations (such as CSE and LICM) can be performed on such calls
222 /// without worrying about aliasing properties, and many calls have this
223 /// property (e.g. calls to 'sin' and 'cos').
225 /// This property corresponds to the GCC 'const' attribute.
227 bool doesNotAccessMemory(ImmutableCallSite CS) {
228 return getModRefBehavior(CS) == DoesNotAccessMemory;
231 /// doesNotAccessMemory - If the specified function is known to never read or
232 /// write memory, return true. For use when the call site is not known.
234 bool doesNotAccessMemory(const Function *F) {
235 return getModRefBehavior(F) == DoesNotAccessMemory;
238 /// onlyReadsMemory - If the specified call is known to only read from
239 /// non-volatile memory (or not access memory at all), return true. Calls
240 /// that unwind the stack are legal for this predicate.
242 /// This property allows many common optimizations to be performed in the
243 /// absence of interfering store instructions, such as CSE of strlen calls.
245 /// This property corresponds to the GCC 'pure' attribute.
247 bool onlyReadsMemory(ImmutableCallSite CS) {
248 ModRefBehavior MRB = getModRefBehavior(CS);
249 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
252 /// onlyReadsMemory - If the specified function is known to only read from
253 /// non-volatile memory (or not access memory at all), return true. For use
254 /// when the call site is not known.
256 bool onlyReadsMemory(const Function *F) {
257 ModRefBehavior MRB = getModRefBehavior(F);
258 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
262 /// getModRefInfo - Return information about whether or not an instruction may
263 /// read or write the specified memory location. An instruction
264 /// that doesn't read or write memory may be trivially LICM'd for example.
265 ModRefResult getModRefInfo(const Instruction *I,
266 const Location &Loc) {
267 switch (I->getOpcode()) {
268 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc);
269 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc);
270 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc);
271 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc);
272 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc);
273 default: return NoModRef;
277 /// getModRefInfo - A convenience wrapper.
278 ModRefResult getModRefInfo(const Instruction *I,
279 const Value *P, uint64_t Size) {
280 return getModRefInfo(I, Location(P, Size));
283 /// getModRefInfo (for call sites) - Return whether information about whether
284 /// a particular call site modifies or reads the specified memory location.
285 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
286 const Location &Loc);
288 /// getModRefInfo (for call sites) - A convenience wrapper.
289 ModRefResult getModRefInfo(ImmutableCallSite CS,
290 const Value *P, uint64_t Size) {
291 return getModRefInfo(CS, Location(P, Size));
294 /// getModRefInfo (for calls) - Return whether information about whether
295 /// a particular call modifies or reads the specified memory location.
296 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) {
297 return getModRefInfo(ImmutableCallSite(C), Loc);
300 /// getModRefInfo (for calls) - A convenience wrapper.
301 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) {
302 return getModRefInfo(C, Location(P, Size));
305 /// getModRefInfo (for invokes) - Return whether information about whether
306 /// a particular invoke modifies or reads the specified memory location.
307 ModRefResult getModRefInfo(const InvokeInst *I,
308 const Location &Loc) {
309 return getModRefInfo(ImmutableCallSite(I), Loc);
312 /// getModRefInfo (for invokes) - A convenience wrapper.
313 ModRefResult getModRefInfo(const InvokeInst *I,
314 const Value *P, uint64_t Size) {
315 return getModRefInfo(I, Location(P, Size));
318 /// getModRefInfo (for loads) - Return whether information about whether
319 /// a particular load modifies or reads the specified memory location.
320 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc);
322 /// getModRefInfo (for loads) - A convenience wrapper.
323 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) {
324 return getModRefInfo(L, Location(P, Size));
327 /// getModRefInfo (for stores) - Return whether information about whether
328 /// a particular store modifies or reads the specified memory location.
329 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc);
331 /// getModRefInfo (for stores) - A convenience wrapper.
332 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) {
333 return getModRefInfo(S, Location(P, Size));
336 /// getModRefInfo (for va_args) - Return whether information about whether
337 /// a particular va_arg modifies or reads the specified memory location.
338 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc);
340 /// getModRefInfo (for va_args) - A convenience wrapper.
341 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) {
342 return getModRefInfo(I, Location(P, Size));
345 /// getModRefInfo - Return information about whether two call sites may refer
346 /// to the same set of memory locations. See
347 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo
349 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
350 ImmutableCallSite CS2);
352 //===--------------------------------------------------------------------===//
353 /// Higher level methods for querying mod/ref information.
356 /// canBasicBlockModify - Return true if it is possible for execution of the
357 /// specified basic block to modify the value pointed to by Ptr.
358 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc);
360 /// canBasicBlockModify - A convenience wrapper.
361 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){
362 return canBasicBlockModify(BB, Location(P, Size));
365 /// canInstructionRangeModify - Return true if it is possible for the
366 /// execution of the specified instructions to modify the value pointed to by
367 /// Ptr. The instructions to consider are all of the instructions in the
368 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
369 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
370 const Location &Loc);
372 /// canInstructionRangeModify - A convenience wrapper.
373 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
374 const Value *Ptr, uint64_t Size) {
375 return canInstructionRangeModify(I1, I2, Location(Ptr, Size));
378 //===--------------------------------------------------------------------===//
379 /// Methods that clients should call when they transform the program to allow
380 /// alias analyses to update their internal data structures. Note that these
381 /// methods may be called on any instruction, regardless of whether or not
382 /// they have pointer-analysis implications.
385 /// deleteValue - This method should be called whenever an LLVM Value is
386 /// deleted from the program, for example when an instruction is found to be
387 /// redundant and is eliminated.
389 virtual void deleteValue(Value *V);
391 /// copyValue - This method should be used whenever a preexisting value in the
392 /// program is copied or cloned, introducing a new value. Note that analysis
393 /// implementations should tolerate clients that use this method to introduce
394 /// the same value multiple times: if the analysis already knows about a
395 /// value, it should ignore the request.
397 virtual void copyValue(Value *From, Value *To);
399 /// replaceWithNewValue - This method is the obvious combination of the two
400 /// above, and it provided as a helper to simplify client code.
402 void replaceWithNewValue(Value *Old, Value *New) {
408 /// isNoAliasCall - Return true if this pointer is returned by a noalias
410 bool isNoAliasCall(const Value *V);
412 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
413 /// identifiable object. This returns true for:
414 /// Global Variables and Functions (but not Global Aliases)
415 /// Allocas and Mallocs
416 /// ByVal and NoAlias Arguments
419 bool isIdentifiedObject(const Value *V);
421 } // End llvm namespace