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 /// Alias analysis result - Either we know for sure that it does not alias, we
87 /// know for sure it must alias, or we don't know anything: The two pointers
88 /// _might_ alias. This enum is designed so you can do things like:
89 /// if (AA.alias(P1, P2)) { ... }
90 /// to check to see if two pointers might alias.
92 /// See docs/AliasAnalysis.html for more information on the specific meanings
95 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
97 /// alias - The main low level interface to the alias analysis implementation.
98 /// Returns a Result indicating whether the two pointers are aliased to each
99 /// other. This is the interface that must be implemented by specific alias
100 /// analysis implementations.
102 virtual AliasResult alias(const Value *V1, unsigned V1Size,
103 const Value *V2, unsigned V2Size);
105 /// alias - A convenience wrapper for the case where the sizes are unknown.
106 AliasResult alias(const Value *V1, const Value *V2) {
107 return alias(V1, UnknownSize, V2, UnknownSize);
110 /// isNoAlias - A trivial helper function to check to see if the specified
111 /// pointers are no-alias.
112 bool isNoAlias(const Value *V1, unsigned V1Size,
113 const Value *V2, unsigned V2Size) {
114 return alias(V1, V1Size, V2, V2Size) == NoAlias;
117 /// pointsToConstantMemory - If the specified pointer is known to point into
118 /// constant global memory, return true. This allows disambiguation of store
119 /// instructions from constant pointers.
121 virtual bool pointsToConstantMemory(const Value *P);
123 //===--------------------------------------------------------------------===//
124 /// Simple mod/ref information...
127 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
128 /// bits which may be or'd together.
130 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
133 /// ModRefBehavior - Summary of how a function affects memory in the program.
134 /// Loads from constant globals are not considered memory accesses for this
135 /// interface. Also, functions may freely modify stack space local to their
136 /// invocation without having to report it through these interfaces.
137 enum ModRefBehavior {
138 // DoesNotAccessMemory - This function does not perform any non-local loads
139 // or stores to memory.
141 // This property corresponds to the GCC 'const' attribute.
144 // AccessesArguments - This function accesses function arguments in well
145 // known (possibly volatile) ways, but does not access any other memory.
148 // AccessesArgumentsAndGlobals - This function has accesses function
149 // arguments and global variables well known (possibly volatile) ways, but
150 // does not access any other memory.
151 AccessesArgumentsAndGlobals,
153 // OnlyReadsMemory - This function does not perform any non-local stores or
154 // volatile loads, but may read from any memory location.
156 // This property corresponds to the GCC 'pure' attribute.
159 // UnknownModRefBehavior - This indicates that the function could not be
160 // classified into one of the behaviors above.
161 UnknownModRefBehavior
164 /// getModRefBehavior - Return the behavior when calling the given call site.
165 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
167 /// getModRefBehavior - Return the behavior when calling the given function.
168 /// For use when the call site is not known.
169 virtual ModRefBehavior getModRefBehavior(const Function *F);
171 /// getIntrinsicModRefBehavior - Return the modref behavior of the intrinsic
172 /// with the given id. Most clients won't need this, because the regular
173 /// getModRefBehavior incorporates this information.
174 static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid);
176 /// doesNotAccessMemory - If the specified call is known to never read or
177 /// write memory, return true. If the call only reads from known-constant
178 /// memory, it is also legal to return true. Calls that unwind the stack
179 /// are legal for this predicate.
181 /// Many optimizations (such as CSE and LICM) can be performed on such calls
182 /// without worrying about aliasing properties, and many calls have this
183 /// property (e.g. calls to 'sin' and 'cos').
185 /// This property corresponds to the GCC 'const' attribute.
187 bool doesNotAccessMemory(ImmutableCallSite CS) {
188 return getModRefBehavior(CS) == DoesNotAccessMemory;
191 /// doesNotAccessMemory - If the specified function is known to never read or
192 /// write memory, return true. For use when the call site is not known.
194 bool doesNotAccessMemory(const Function *F) {
195 return getModRefBehavior(F) == DoesNotAccessMemory;
198 /// onlyReadsMemory - If the specified call is known to only read from
199 /// non-volatile memory (or not access memory at all), return true. Calls
200 /// that unwind the stack are legal for this predicate.
202 /// This property allows many common optimizations to be performed in the
203 /// absence of interfering store instructions, such as CSE of strlen calls.
205 /// This property corresponds to the GCC 'pure' attribute.
207 bool onlyReadsMemory(ImmutableCallSite CS) {
208 ModRefBehavior MRB = getModRefBehavior(CS);
209 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
212 /// onlyReadsMemory - If the specified function is known to only read from
213 /// non-volatile memory (or not access memory at all), return true. For use
214 /// when the call site is not known.
216 bool onlyReadsMemory(const Function *F) {
217 ModRefBehavior MRB = getModRefBehavior(F);
218 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
222 /// getModRefInfo - Return information about whether or not an instruction may
223 /// read or write memory specified by the pointer operand. An instruction
224 /// that doesn't read or write memory may be trivially LICM'd for example.
225 ModRefResult getModRefInfo(const Instruction *I,
226 const Value *P, unsigned Size) {
227 switch (I->getOpcode()) {
228 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, P,Size);
229 case Instruction::Load: return getModRefInfo((const LoadInst*)I, P, Size);
230 case Instruction::Store: return getModRefInfo((const StoreInst*)I, P,Size);
231 case Instruction::Call: return getModRefInfo((const CallInst*)I, P, Size);
232 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,P,Size);
233 default: return NoModRef;
237 /// getModRefInfo (for call sites) - Return whether information about whether
238 /// a particular call site modifies or reads the memory specified by the
240 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
241 const Value *P, unsigned Size);
243 /// getModRefInfo (for calls) - Return whether information about whether
244 /// a particular call modifies or reads the memory specified by the
246 ModRefResult getModRefInfo(const CallInst *C, const Value *P, unsigned Size) {
247 return getModRefInfo(ImmutableCallSite(C), P, Size);
250 /// getModRefInfo (for invokes) - Return whether information about whether
251 /// a particular invoke modifies or reads the memory specified by the
253 ModRefResult getModRefInfo(const InvokeInst *I,
254 const Value *P, unsigned Size) {
255 return getModRefInfo(ImmutableCallSite(I), P, Size);
258 /// getModRefInfo (for loads) - Return whether information about whether
259 /// a particular load modifies or reads the memory specified by the
261 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, unsigned Size);
263 /// getModRefInfo (for stores) - Return whether information about whether
264 /// a particular store modifies or reads the memory specified by the
266 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, unsigned Size);
268 /// getModRefInfo (for va_args) - Return whether information about whether
269 /// a particular va_arg modifies or reads the memory specified by the
271 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, unsigned Size);
273 /// getModRefInfo - Return information about whether two call sites may refer
274 /// to the same set of memory locations. See
275 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo
277 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
278 ImmutableCallSite CS2);
280 //===--------------------------------------------------------------------===//
281 /// Dependence queries.
284 /// DependenceResult - These are the return values for getDependence queries.
285 /// They are defined in terms of "memory", but they are also used to model
286 /// other side effects, such as I/O and volatility.
287 enum DependenceResult {
288 /// ReadThenRead - The instructions are ReadThenReadSome and the second
289 /// instruction reads from exactly the same memory read from by the first.
292 /// ReadThenReadSome - The instructions are Independent, both are read-only,
293 /// and the second instruction reads from a subset of the memory read from
297 /// Independent - Neither instruction reads from or writes to memory written
298 /// to by the other. All enum values lower than this one are special cases
302 /// WriteThenRead - The instructions are WriteThenReadSome and the second
303 /// instruction reads from exactly the same memory written by the first.
306 /// WriteThenReadSome - The first instruction is write-only, the second
307 /// instruction is read-only, and the second only reads from memory
308 /// written to by the first.
311 /// ReadThenWrite - The first instruction is read-only, the second
312 /// instruction is write-only, and the second wrotes to exactly the
313 /// same memory read from by the first.
316 /// WriteThenWrite - The instructions are WriteThenWriteSome, and the
317 /// second instruction writes to exactly the same memory written to by
321 /// WriteSomeThenWrite - Both instructions are write-only, and the second
322 /// instruction writes to a superset of the memory written to by the first.
325 /// Unknown - The relationship between the instructions cannot be
326 /// determined or does not fit into any of the cases defined here.
330 /// DependenceQueryFlags - Flags for refining dependence queries.
331 enum DependenceQueryFlags {
337 /// getDependence - Determine the dependence relationship between the
338 /// instructions. This does not include "register" dependencies; it just
339 /// considers memory references and other side effects.
340 /// WARNING: This is an experimental interface.
341 DependenceResult getDependence(const Instruction *First,
342 const Instruction *Second) {
343 return getDependence(First, Default, Second, Default);
346 /// getDependence - Determine the dependence relationship between the
347 /// instructions. This does not include "register" dependencies; it just
348 /// considers memory references and other side effects. This overload
349 /// accepts additional flags to refine the query.
350 /// WARNING: This is an experimental interface.
351 virtual DependenceResult getDependence(const Instruction *First,
352 DependenceQueryFlags FirstFlags,
353 const Instruction *Second,
354 DependenceQueryFlags SecondFlags);
356 //===--------------------------------------------------------------------===//
357 /// Higher level methods for querying mod/ref information.
360 /// canBasicBlockModify - Return true if it is possible for execution of the
361 /// specified basic block to modify the value pointed to by Ptr.
363 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned 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.
370 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
371 const Value *Ptr, unsigned Size);
373 //===--------------------------------------------------------------------===//
374 /// Methods that clients should call when they transform the program to allow
375 /// alias analyses to update their internal data structures. Note that these
376 /// methods may be called on any instruction, regardless of whether or not
377 /// they have pointer-analysis implications.
380 /// deleteValue - This method should be called whenever an LLVM Value is
381 /// deleted from the program, for example when an instruction is found to be
382 /// redundant and is eliminated.
384 virtual void deleteValue(Value *V);
386 /// copyValue - This method should be used whenever a preexisting value in the
387 /// program is copied or cloned, introducing a new value. Note that analysis
388 /// implementations should tolerate clients that use this method to introduce
389 /// the same value multiple times: if the analysis already knows about a
390 /// value, it should ignore the request.
392 virtual void copyValue(Value *From, Value *To);
394 /// replaceWithNewValue - This method is the obvious combination of the two
395 /// above, and it provided as a helper to simplify client code.
397 void replaceWithNewValue(Value *Old, Value *New) {
403 /// getDependenceViaModRefInfo - Helper function for implementing getDependence
404 /// in implementations which already have getModRefInfo implementations.
405 DependenceResult getDependenceViaModRefInfo(const Instruction *First,
406 DependenceQueryFlags FirstFlags,
407 const Instruction *Second,
408 DependenceQueryFlags SecondFlags);
412 /// isNoAliasCall - Return true if this pointer is returned by a noalias
414 bool isNoAliasCall(const Value *V);
416 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
417 /// identifiable object. This returns true for:
418 /// Global Variables and Functions (but not Global Aliases)
419 /// Allocas and Mallocs
420 /// ByVal and NoAlias Arguments
423 bool isIdentifiedObject(const Value *V);
425 } // End llvm namespace
427 // Because of the way .a files work, we must force the BasicAA implementation to
428 // be pulled in if the AliasAnalysis header is included. Otherwise we run
429 // the risk of AliasAnalysis being used, but the default implementation not
430 // being linked into the tool that uses it.
431 FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis)
432 FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis)