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"
31 #include "llvm/System/IncludeFile.h"
48 AliasAnalysis *AA; // Previous Alias Analysis to chain to.
51 /// InitializeAliasAnalysis - Subclasses must call this method to initialize
52 /// the AliasAnalysis interface before any other methods are called. This is
53 /// typically called by the run* methods of these subclasses. This may be
54 /// called multiple times.
56 void InitializeAliasAnalysis(Pass *P);
58 /// getAnalysisUsage - All alias analysis implementations should invoke this
59 /// directly (using AliasAnalysis::getAnalysisUsage(AU)).
60 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
63 static char ID; // Class identification, replacement for typeinfo
64 AliasAnalysis() : TD(0), AA(0) {}
65 virtual ~AliasAnalysis(); // We want to be subclassed
67 /// UnknownSize - This is a special value which can be used with the
68 /// size arguments in alias queries to indicate that the caller does not
69 /// know the sizes of the potential memory references.
70 static unsigned const UnknownSize = ~0u;
72 /// getTargetData - Return a pointer to the current TargetData object, or
73 /// null if no TargetData object is available.
75 const TargetData *getTargetData() const { return TD; }
77 /// getTypeStoreSize - Return the TargetData store size for the given type,
78 /// if known, or a conservative value otherwise.
80 unsigned getTypeStoreSize(const Type *Ty);
82 //===--------------------------------------------------------------------===//
86 /// Location - A description of a memory location.
88 /// Ptr - The address of the start of the location.
90 /// Size - The size of the location.
92 /// TBAATag - The metadata node which describes the TBAA type of
93 /// the location, or null if there is no (unique) tag.
94 const MDNode *TBAATag;
96 explicit Location(const Value *P = 0,
97 unsigned S = UnknownSize,
99 : Ptr(P), Size(S), TBAATag(N) {}
102 /// Alias analysis result - Either we know for sure that it does not alias, we
103 /// know for sure it must alias, or we don't know anything: The two pointers
104 /// _might_ alias. This enum is designed so you can do things like:
105 /// if (AA.alias(P1, P2)) { ... }
106 /// to check to see if two pointers might alias.
108 /// See docs/AliasAnalysis.html for more information on the specific meanings
111 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
113 /// alias - The main low level interface to the alias analysis implementation.
114 /// Returns a Result indicating whether the two pointers are aliased to each
115 /// other. This is the interface that must be implemented by specific alias
116 /// analysis implementations.
117 virtual AliasResult alias(const Location &LocA, const Location &LocB);
119 /// alias - A convenience wrapper.
120 AliasResult alias(const Value *V1, unsigned V1Size,
121 const Value *V2, unsigned V2Size) {
122 return alias(Location(V1, V1Size), Location(V2, V2Size));
125 /// alias - A convenience wrapper.
126 AliasResult alias(const Value *V1, const Value *V2) {
127 return alias(V1, UnknownSize, V2, UnknownSize);
130 /// isNoAlias - A trivial helper function to check to see if the specified
131 /// pointers are no-alias.
132 bool isNoAlias(const Location &LocA, const Location &LocB) {
133 return alias(LocA, LocB) == NoAlias;
136 /// isNoAlias - A convenience wrapper.
137 bool isNoAlias(const Value *V1, unsigned V1Size,
138 const Value *V2, unsigned V2Size) {
139 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size));
142 /// pointsToConstantMemory - If the specified memory location is known to be
143 /// constant, return true. This allows disambiguation of store
144 /// instructions from constant pointers.
146 virtual bool pointsToConstantMemory(const Location &Loc);
148 /// pointsToConstantMemory - A convenient wrapper.
149 bool pointsToConstantMemory(const Value *P) {
150 return pointsToConstantMemory(Location(P));
153 //===--------------------------------------------------------------------===//
154 /// Simple mod/ref information...
157 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
158 /// bits which may be or'd together.
160 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
163 /// ModRefBehavior - Summary of how a function affects memory in the program.
164 /// Loads from constant globals are not considered memory accesses for this
165 /// interface. Also, functions may freely modify stack space local to their
166 /// invocation without having to report it through these interfaces.
167 enum ModRefBehavior {
168 // DoesNotAccessMemory - This function does not perform any non-local loads
169 // or stores to memory.
171 // This property corresponds to the GCC 'const' attribute.
174 // AccessesArguments - This function accesses function arguments in well
175 // known (possibly volatile) ways, but does not access any other memory.
178 // AccessesArgumentsAndGlobals - This function has accesses function
179 // arguments and global variables well known (possibly volatile) ways, but
180 // does not access any other memory.
181 AccessesArgumentsAndGlobals,
183 // OnlyReadsMemory - This function does not perform any non-local stores or
184 // volatile loads, but may read from any memory location.
186 // This property corresponds to the GCC 'pure' attribute.
189 // UnknownModRefBehavior - This indicates that the function could not be
190 // classified into one of the behaviors above.
191 UnknownModRefBehavior
194 /// getModRefBehavior - Return the behavior when calling the given call site.
195 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
197 /// getModRefBehavior - Return the behavior when calling the given function.
198 /// For use when the call site is not known.
199 virtual ModRefBehavior getModRefBehavior(const Function *F);
201 /// getIntrinsicModRefBehavior - Return the modref behavior of the intrinsic
202 /// with the given id. Most clients won't need this, because the regular
203 /// getModRefBehavior incorporates this information.
204 static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid);
206 /// doesNotAccessMemory - If the specified call is known to never read or
207 /// write memory, return true. If the call only reads from known-constant
208 /// memory, it is also legal to return true. Calls that unwind the stack
209 /// are legal for this predicate.
211 /// Many optimizations (such as CSE and LICM) can be performed on such calls
212 /// without worrying about aliasing properties, and many calls have this
213 /// property (e.g. calls to 'sin' and 'cos').
215 /// This property corresponds to the GCC 'const' attribute.
217 bool doesNotAccessMemory(ImmutableCallSite CS) {
218 return getModRefBehavior(CS) == DoesNotAccessMemory;
221 /// doesNotAccessMemory - If the specified function is known to never read or
222 /// write memory, return true. For use when the call site is not known.
224 bool doesNotAccessMemory(const Function *F) {
225 return getModRefBehavior(F) == DoesNotAccessMemory;
228 /// onlyReadsMemory - If the specified call is known to only read from
229 /// non-volatile memory (or not access memory at all), return true. Calls
230 /// that unwind the stack are legal for this predicate.
232 /// This property allows many common optimizations to be performed in the
233 /// absence of interfering store instructions, such as CSE of strlen calls.
235 /// This property corresponds to the GCC 'pure' attribute.
237 bool onlyReadsMemory(ImmutableCallSite CS) {
238 ModRefBehavior MRB = getModRefBehavior(CS);
239 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
242 /// onlyReadsMemory - If the specified function is known to only read from
243 /// non-volatile memory (or not access memory at all), return true. For use
244 /// when the call site is not known.
246 bool onlyReadsMemory(const Function *F) {
247 ModRefBehavior MRB = getModRefBehavior(F);
248 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
252 /// getModRefInfo - Return information about whether or not an instruction may
253 /// read or write the specified memory location. An instruction
254 /// that doesn't read or write memory may be trivially LICM'd for example.
255 ModRefResult getModRefInfo(const Instruction *I,
256 const Location &Loc) {
257 switch (I->getOpcode()) {
258 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc);
259 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc);
260 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc);
261 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc);
262 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc);
263 default: return NoModRef;
267 /// getModRefInfo - A convenience wrapper.
268 ModRefResult getModRefInfo(const Instruction *I,
269 const Value *P, unsigned Size) {
270 return getModRefInfo(I, Location(P, Size));
273 /// getModRefInfo (for call sites) - Return whether information about whether
274 /// a particular call site modifies or reads the specified memory location.
275 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
276 const Location &Loc);
278 /// getModRefInfo (for call sites) - A convenience wrapper.
279 ModRefResult getModRefInfo(ImmutableCallSite CS,
280 const Value *P, unsigned Size) {
281 return getModRefInfo(CS, Location(P, Size));
284 /// getModRefInfo (for calls) - Return whether information about whether
285 /// a particular call modifies or reads the specified memory location.
286 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) {
287 return getModRefInfo(ImmutableCallSite(C), Loc);
290 /// getModRefInfo (for calls) - A convenience wrapper.
291 ModRefResult getModRefInfo(const CallInst *C, const Value *P, unsigned Size) {
292 return getModRefInfo(C, Location(P, Size));
295 /// getModRefInfo (for invokes) - Return whether information about whether
296 /// a particular invoke modifies or reads the specified memory location.
297 ModRefResult getModRefInfo(const InvokeInst *I,
298 const Location &Loc) {
299 return getModRefInfo(ImmutableCallSite(I), Loc);
302 /// getModRefInfo (for invokes) - A convenience wrapper.
303 ModRefResult getModRefInfo(const InvokeInst *I,
304 const Value *P, unsigned Size) {
305 return getModRefInfo(I, Location(P, Size));
308 /// getModRefInfo (for loads) - Return whether information about whether
309 /// a particular load modifies or reads the specified memory location.
310 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc);
312 /// getModRefInfo (for loads) - A convenience wrapper.
313 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, unsigned Size) {
314 return getModRefInfo(L, Location(P, Size));
317 /// getModRefInfo (for stores) - Return whether information about whether
318 /// a particular store modifies or reads the specified memory location.
319 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc);
321 /// getModRefInfo (for stores) - A convenience wrapper.
322 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, unsigned Size) {
323 return getModRefInfo(S, Location(P, Size));
326 /// getModRefInfo (for va_args) - Return whether information about whether
327 /// a particular va_arg modifies or reads the specified memory location.
328 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc);
330 /// getModRefInfo (for va_args) - A convenience wrapper.
331 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, unsigned Size) {
332 return getModRefInfo(I, Location(P, Size));
335 /// getModRefInfo - Return information about whether two call sites may refer
336 /// to the same set of memory locations. See
337 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo
339 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
340 ImmutableCallSite CS2);
342 //===--------------------------------------------------------------------===//
343 /// Higher level methods for querying mod/ref information.
346 /// canBasicBlockModify - Return true if it is possible for execution of the
347 /// specified basic block to modify the value pointed to by Ptr.
348 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc);
350 /// canBasicBlockModify - A convenience wrapper.
351 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size){
352 return canBasicBlockModify(BB, Location(P, Size));
355 /// canInstructionRangeModify - Return true if it is possible for the
356 /// execution of the specified instructions to modify the value pointed to by
357 /// Ptr. The instructions to consider are all of the instructions in the
358 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
359 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
360 const Location &Loc);
362 /// canInstructionRangeModify - A convenience wrapper.
363 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
364 const Value *Ptr, unsigned Size) {
365 return canInstructionRangeModify(I1, I2, Location(Ptr, Size));
368 //===--------------------------------------------------------------------===//
369 /// Methods that clients should call when they transform the program to allow
370 /// alias analyses to update their internal data structures. Note that these
371 /// methods may be called on any instruction, regardless of whether or not
372 /// they have pointer-analysis implications.
375 /// deleteValue - This method should be called whenever an LLVM Value is
376 /// deleted from the program, for example when an instruction is found to be
377 /// redundant and is eliminated.
379 virtual void deleteValue(Value *V);
381 /// copyValue - This method should be used whenever a preexisting value in the
382 /// program is copied or cloned, introducing a new value. Note that analysis
383 /// implementations should tolerate clients that use this method to introduce
384 /// the same value multiple times: if the analysis already knows about a
385 /// value, it should ignore the request.
387 virtual void copyValue(Value *From, Value *To);
389 /// replaceWithNewValue - This method is the obvious combination of the two
390 /// above, and it provided as a helper to simplify client code.
392 void replaceWithNewValue(Value *Old, Value *New) {
398 /// isNoAliasCall - Return true if this pointer is returned by a noalias
400 bool isNoAliasCall(const Value *V);
402 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
403 /// identifiable object. This returns true for:
404 /// Global Variables and Functions (but not Global Aliases)
405 /// Allocas and Mallocs
406 /// ByVal and NoAlias Arguments
409 bool isIdentifiedObject(const Value *V);
411 } // End llvm namespace
413 // Because of the way .a files work, we must force the BasicAA implementation to
414 // be pulled in if the AliasAnalysis header is included. Otherwise we run
415 // the risk of AliasAnalysis being used, but the default implementation not
416 // being linked into the tool that uses it.
417 FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis)
418 FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis)