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 size of the location.
91 /// TBAATag - The metadata node which describes the TBAA type of
92 /// the location, or null if there is no (unique) tag.
93 const MDNode *TBAATag;
95 explicit Location(const Value *P = 0,
96 uint64_t S = UnknownSize,
98 : Ptr(P), Size(S), TBAATag(N) {}
100 Location getWithNewPtr(const Value *NewPtr) const {
101 Location Copy(*this);
106 Location getWithoutTBAATag() const {
107 Location Copy(*this);
113 /// Alias analysis result - Either we know for sure that it does not alias, we
114 /// know for sure it must alias, or we don't know anything: The two pointers
115 /// _might_ alias. This enum is designed so you can do things like:
116 /// if (AA.alias(P1, P2)) { ... }
117 /// to check to see if two pointers might alias.
119 /// See docs/AliasAnalysis.html for more information on the specific meanings
122 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
124 /// alias - The main low level interface to the alias analysis implementation.
125 /// Returns a Result indicating whether the two pointers are aliased to each
126 /// other. This is the interface that must be implemented by specific alias
127 /// analysis implementations.
128 virtual AliasResult alias(const Location &LocA, const Location &LocB);
130 /// alias - A convenience wrapper.
131 AliasResult alias(const Value *V1, uint64_t V1Size,
132 const Value *V2, uint64_t V2Size) {
133 return alias(Location(V1, V1Size), Location(V2, V2Size));
136 /// alias - A convenience wrapper.
137 AliasResult alias(const Value *V1, const Value *V2) {
138 return alias(V1, UnknownSize, V2, UnknownSize);
141 /// isNoAlias - A trivial helper function to check to see if the specified
142 /// pointers are no-alias.
143 bool isNoAlias(const Location &LocA, const Location &LocB) {
144 return alias(LocA, LocB) == NoAlias;
147 /// isNoAlias - A convenience wrapper.
148 bool isNoAlias(const Value *V1, uint64_t V1Size,
149 const Value *V2, uint64_t V2Size) {
150 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size));
153 /// pointsToConstantMemory - If the specified memory location is known to be
154 /// constant, return true. This allows disambiguation of store
155 /// instructions from constant pointers.
157 virtual bool pointsToConstantMemory(const Location &Loc);
159 /// pointsToConstantMemory - A convenient wrapper.
160 bool pointsToConstantMemory(const Value *P) {
161 return pointsToConstantMemory(Location(P));
164 //===--------------------------------------------------------------------===//
165 /// Simple mod/ref information...
168 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
169 /// bits which may be or'd together.
171 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
174 /// ModRefBehavior - Summary of how a function affects memory in the program.
175 /// Loads from constant globals are not considered memory accesses for this
176 /// interface. Also, functions may freely modify stack space local to their
177 /// invocation without having to report it through these interfaces.
178 enum ModRefBehavior {
179 // DoesNotAccessMemory - This function does not perform any non-local loads
180 // or stores to memory.
182 // This property corresponds to the GCC 'const' attribute.
185 // AccessesArguments - This function accesses function arguments in well
186 // known (possibly volatile) ways, but does not access any other memory.
189 // AccessesArgumentsAndGlobals - This function has accesses function
190 // arguments and global variables well known (possibly volatile) ways, but
191 // does not access any other memory.
192 AccessesArgumentsAndGlobals,
194 // OnlyReadsMemory - This function does not perform any non-local stores or
195 // volatile loads, but may read from any memory location.
197 // This property corresponds to the GCC 'pure' attribute.
200 // UnknownModRefBehavior - This indicates that the function could not be
201 // classified into one of the behaviors above.
202 UnknownModRefBehavior
205 /// getModRefBehavior - Return the behavior when calling the given call site.
206 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
208 /// getModRefBehavior - Return the behavior when calling the given function.
209 /// For use when the call site is not known.
210 virtual ModRefBehavior getModRefBehavior(const Function *F);
212 /// getIntrinsicModRefBehavior - Return the modref behavior of the intrinsic
213 /// with the given id. Most clients won't need this, because the regular
214 /// getModRefBehavior incorporates this information.
215 static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid);
217 /// doesNotAccessMemory - If the specified call is known to never read or
218 /// write memory, return true. If the call only reads from known-constant
219 /// memory, it is also legal to return true. Calls that unwind the stack
220 /// are legal for this predicate.
222 /// Many optimizations (such as CSE and LICM) can be performed on such calls
223 /// without worrying about aliasing properties, and many calls have this
224 /// property (e.g. calls to 'sin' and 'cos').
226 /// This property corresponds to the GCC 'const' attribute.
228 bool doesNotAccessMemory(ImmutableCallSite CS) {
229 return getModRefBehavior(CS) == DoesNotAccessMemory;
232 /// doesNotAccessMemory - If the specified function is known to never read or
233 /// write memory, return true. For use when the call site is not known.
235 bool doesNotAccessMemory(const Function *F) {
236 return getModRefBehavior(F) == DoesNotAccessMemory;
239 /// onlyReadsMemory - If the specified call is known to only read from
240 /// non-volatile memory (or not access memory at all), return true. Calls
241 /// that unwind the stack are legal for this predicate.
243 /// This property allows many common optimizations to be performed in the
244 /// absence of interfering store instructions, such as CSE of strlen calls.
246 /// This property corresponds to the GCC 'pure' attribute.
248 bool onlyReadsMemory(ImmutableCallSite CS) {
249 ModRefBehavior MRB = getModRefBehavior(CS);
250 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
253 /// onlyReadsMemory - If the specified function is known to only read from
254 /// non-volatile memory (or not access memory at all), return true. For use
255 /// when the call site is not known.
257 bool onlyReadsMemory(const Function *F) {
258 ModRefBehavior MRB = getModRefBehavior(F);
259 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
263 /// getModRefInfo - Return information about whether or not an instruction may
264 /// read or write the specified memory location. An instruction
265 /// that doesn't read or write memory may be trivially LICM'd for example.
266 ModRefResult getModRefInfo(const Instruction *I,
267 const Location &Loc) {
268 switch (I->getOpcode()) {
269 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc);
270 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc);
271 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc);
272 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc);
273 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc);
274 default: return NoModRef;
278 /// getModRefInfo - A convenience wrapper.
279 ModRefResult getModRefInfo(const Instruction *I,
280 const Value *P, uint64_t Size) {
281 return getModRefInfo(I, Location(P, Size));
284 /// getModRefInfo (for call sites) - Return whether information about whether
285 /// a particular call site modifies or reads the specified memory location.
286 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
287 const Location &Loc);
289 /// getModRefInfo (for call sites) - A convenience wrapper.
290 ModRefResult getModRefInfo(ImmutableCallSite CS,
291 const Value *P, uint64_t Size) {
292 return getModRefInfo(CS, Location(P, Size));
295 /// getModRefInfo (for calls) - Return whether information about whether
296 /// a particular call modifies or reads the specified memory location.
297 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) {
298 return getModRefInfo(ImmutableCallSite(C), Loc);
301 /// getModRefInfo (for calls) - A convenience wrapper.
302 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) {
303 return getModRefInfo(C, Location(P, Size));
306 /// getModRefInfo (for invokes) - Return whether information about whether
307 /// a particular invoke modifies or reads the specified memory location.
308 ModRefResult getModRefInfo(const InvokeInst *I,
309 const Location &Loc) {
310 return getModRefInfo(ImmutableCallSite(I), Loc);
313 /// getModRefInfo (for invokes) - A convenience wrapper.
314 ModRefResult getModRefInfo(const InvokeInst *I,
315 const Value *P, uint64_t Size) {
316 return getModRefInfo(I, Location(P, Size));
319 /// getModRefInfo (for loads) - Return whether information about whether
320 /// a particular load modifies or reads the specified memory location.
321 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc);
323 /// getModRefInfo (for loads) - A convenience wrapper.
324 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) {
325 return getModRefInfo(L, Location(P, Size));
328 /// getModRefInfo (for stores) - Return whether information about whether
329 /// a particular store modifies or reads the specified memory location.
330 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc);
332 /// getModRefInfo (for stores) - A convenience wrapper.
333 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) {
334 return getModRefInfo(S, Location(P, Size));
337 /// getModRefInfo (for va_args) - Return whether information about whether
338 /// a particular va_arg modifies or reads the specified memory location.
339 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc);
341 /// getModRefInfo (for va_args) - A convenience wrapper.
342 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) {
343 return getModRefInfo(I, Location(P, Size));
346 /// getModRefInfo - Return information about whether two call sites may refer
347 /// to the same set of memory locations. See
348 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo
350 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
351 ImmutableCallSite CS2);
353 //===--------------------------------------------------------------------===//
354 /// Higher level methods for querying mod/ref information.
357 /// canBasicBlockModify - Return true if it is possible for execution of the
358 /// specified basic block to modify the value pointed to by Ptr.
359 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc);
361 /// canBasicBlockModify - A convenience wrapper.
362 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){
363 return canBasicBlockModify(BB, Location(P, Size));
366 /// canInstructionRangeModify - Return true if it is possible for the
367 /// execution of the specified instructions to modify the value pointed to by
368 /// Ptr. The instructions to consider are all of the instructions in the
369 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
370 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
371 const Location &Loc);
373 /// canInstructionRangeModify - A convenience wrapper.
374 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
375 const Value *Ptr, uint64_t Size) {
376 return canInstructionRangeModify(I1, I2, Location(Ptr, Size));
379 //===--------------------------------------------------------------------===//
380 /// Methods that clients should call when they transform the program to allow
381 /// alias analyses to update their internal data structures. Note that these
382 /// methods may be called on any instruction, regardless of whether or not
383 /// they have pointer-analysis implications.
386 /// deleteValue - This method should be called whenever an LLVM Value is
387 /// deleted from the program, for example when an instruction is found to be
388 /// redundant and is eliminated.
390 virtual void deleteValue(Value *V);
392 /// copyValue - This method should be used whenever a preexisting value in the
393 /// program is copied or cloned, introducing a new value. Note that analysis
394 /// implementations should tolerate clients that use this method to introduce
395 /// the same value multiple times: if the analysis already knows about a
396 /// value, it should ignore the request.
398 virtual void copyValue(Value *From, Value *To);
400 /// replaceWithNewValue - This method is the obvious combination of the two
401 /// above, and it provided as a helper to simplify client code.
403 void replaceWithNewValue(Value *Old, Value *New) {
409 /// isNoAliasCall - Return true if this pointer is returned by a noalias
411 bool isNoAliasCall(const Value *V);
413 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
414 /// identifiable object. This returns true for:
415 /// Global Variables and Functions (but not Global Aliases)
416 /// Allocas and Mallocs
417 /// ByVal and NoAlias Arguments
420 bool isIdentifiedObject(const Value *V);
422 } // End llvm namespace