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. If Size is 0, two pointers only alias if they
22 // are exactly equal. If size is greater than zero, but small, the two pointers
23 // alias if the areas pointed to overlap. If the size is very large (ie, ~0U),
24 // then the two pointers alias if they may be pointing to components of the same
25 // memory object. Pointers that point to two completely different objects in
26 // memory never alias, regardless of the value of the Size component.
28 //===----------------------------------------------------------------------===//
30 #ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H
31 #define LLVM_ANALYSIS_ALIAS_ANALYSIS_H
33 #include "llvm/Support/CallSite.h"
34 #include "llvm/System/IncludeFile.h"
49 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 /// getTargetData - Return a pointer to the current TargetData object, or
68 /// null if no TargetData object is available.
70 const TargetData *getTargetData() const { return TD; }
72 /// getTypeStoreSize - Return the TargetData store size for the given type,
73 /// if known, or a conservative value otherwise.
75 unsigned getTypeStoreSize(const Type *Ty);
77 //===--------------------------------------------------------------------===//
81 /// Alias analysis result - Either we know for sure that it does not alias, we
82 /// know for sure it must alias, or we don't know anything: The two pointers
83 /// _might_ alias. This enum is designed so you can do things like:
84 /// if (AA.alias(P1, P2)) { ... }
85 /// to check to see if two pointers might alias.
87 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
89 /// alias - The main low level interface to the alias analysis implementation.
90 /// Returns a Result indicating whether the two pointers are aliased to each
91 /// other. This is the interface that must be implemented by specific alias
92 /// analysis implementations.
94 virtual AliasResult alias(const Value *V1, unsigned V1Size,
95 const Value *V2, unsigned V2Size);
97 /// getMustAliases - If there are any pointers known that must alias this
98 /// pointer, return them now. This allows alias-set based alias analyses to
99 /// perform a form a value numbering (which is exposed by load-vn). If an
100 /// alias analysis supports this, it should ADD any must aliased pointers to
101 /// the specified vector.
103 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals);
105 /// pointsToConstantMemory - If the specified pointer is known to point into
106 /// constant global memory, return true. This allows disambiguation of store
107 /// instructions from constant pointers.
109 virtual bool pointsToConstantMemory(const Value *P);
111 //===--------------------------------------------------------------------===//
112 /// Simple mod/ref information...
115 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
116 /// bits which may be or'd together.
118 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
121 /// ModRefBehavior - Summary of how a function affects memory in the program.
122 /// Loads from constant globals are not considered memory accesses for this
123 /// interface. Also, functions may freely modify stack space local to their
124 /// invocation without having to report it through these interfaces.
125 enum ModRefBehavior {
126 // DoesNotAccessMemory - This function does not perform any non-local loads
127 // or stores to memory.
129 // This property corresponds to the GCC 'const' attribute.
132 // AccessesArguments - This function accesses function arguments in well
133 // known (possibly volatile) ways, but does not access any other memory.
135 // Clients may use the Info parameter of getModRefBehavior to get specific
136 // information about how pointer arguments are used.
139 // AccessesArgumentsAndGlobals - This function has accesses function
140 // arguments and global variables well known (possibly volatile) ways, but
141 // does not access any other memory.
143 // Clients may use the Info parameter of getModRefBehavior to get specific
144 // information about how pointer arguments are used.
145 AccessesArgumentsAndGlobals,
147 // OnlyReadsMemory - This function does not perform any non-local stores or
148 // volatile loads, but may read from any memory location.
150 // This property corresponds to the GCC 'pure' attribute.
153 // UnknownModRefBehavior - This indicates that the function could not be
154 // classified into one of the behaviors above.
155 UnknownModRefBehavior
158 /// PointerAccessInfo - This struct is used to return results for pointers,
159 /// globals, and the return value of a function.
160 struct PointerAccessInfo {
161 /// V - The value this record corresponds to. This may be an Argument for
162 /// the function, a GlobalVariable, or null, corresponding to the return
163 /// value for the function.
166 /// ModRefInfo - Whether the pointer is loaded or stored to/from.
168 ModRefResult ModRefInfo;
170 /// AccessType - Specific fine-grained access information for the argument.
171 /// If none of these classifications is general enough, the
172 /// getModRefBehavior method should not return AccessesArguments*. If a
173 /// record is not returned for a particular argument, the argument is never
174 /// dead and never dereferenced.
176 /// ScalarAccess - The pointer is dereferenced.
180 /// ArrayAccess - The pointer is indexed through as an array of elements.
184 /// ElementAccess ?? P->F only?
186 /// CallsThrough - Indirect calls are made through the specified function
192 /// getModRefBehavior - Return the behavior when calling the given call site.
193 virtual ModRefBehavior getModRefBehavior(CallSite CS,
194 std::vector<PointerAccessInfo> *Info = 0);
196 /// getModRefBehavior - Return the behavior when calling the given function.
197 /// For use when the call site is not known.
198 virtual ModRefBehavior getModRefBehavior(Function *F,
199 std::vector<PointerAccessInfo> *Info = 0);
201 /// doesNotAccessMemory - If the specified call is known to never read or
202 /// write memory, return true. If the call only reads from known-constant
203 /// memory, it is also legal to return true. Calls that unwind the stack
204 /// are legal for this predicate.
206 /// Many optimizations (such as CSE and LICM) can be performed on such calls
207 /// without worrying about aliasing properties, and many calls have this
208 /// property (e.g. calls to 'sin' and 'cos').
210 /// This property corresponds to the GCC 'const' attribute.
212 bool doesNotAccessMemory(CallSite CS) {
213 return getModRefBehavior(CS) == DoesNotAccessMemory;
216 /// doesNotAccessMemory - If the specified function is known to never read or
217 /// write memory, return true. For use when the call site is not known.
219 bool doesNotAccessMemory(Function *F) {
220 return getModRefBehavior(F) == DoesNotAccessMemory;
223 /// onlyReadsMemory - If the specified call is known to only read from
224 /// non-volatile memory (or not access memory at all), return true. Calls
225 /// that unwind the stack are legal for this predicate.
227 /// This property allows many common optimizations to be performed in the
228 /// absence of interfering store instructions, such as CSE of strlen calls.
230 /// This property corresponds to the GCC 'pure' attribute.
232 bool onlyReadsMemory(CallSite CS) {
233 ModRefBehavior MRB = getModRefBehavior(CS);
234 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
237 /// onlyReadsMemory - If the specified function is known to only read from
238 /// non-volatile memory (or not access memory at all), return true. For use
239 /// when the call site is not known.
241 bool onlyReadsMemory(Function *F) {
242 ModRefBehavior MRB = getModRefBehavior(F);
243 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
247 /// getModRefInfo - Return information about whether or not an instruction may
248 /// read or write memory specified by the pointer operand. An instruction
249 /// that doesn't read or write memory may be trivially LICM'd for example.
251 /// getModRefInfo (for call sites) - Return whether information about whether
252 /// a particular call site modifies or reads the memory specified by the
255 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
257 /// getModRefInfo - Return information about whether two call sites may refer
258 /// to the same set of memory locations. This function returns NoModRef if
259 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory
260 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or
261 /// ModRef if CS1 might read or write memory accessed by CS2.
263 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
265 /// hasNoModRefInfoForCalls - Return true if the analysis has no mod/ref
266 /// information for pairs of function calls (other than "pure" and "const"
267 /// functions). This can be used by clients to avoid many pointless queries.
268 /// Remember that if you override this and chain to another analysis, you must
269 /// make sure that it doesn't have mod/ref info either.
271 virtual bool hasNoModRefInfoForCalls() const;
274 /// Convenience functions...
275 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size);
276 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size);
277 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) {
278 return getModRefInfo(CallSite(C), P, Size);
280 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) {
281 return getModRefInfo(CallSite(I), P, Size);
283 ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) {
284 return AliasAnalysis::ModRef;
286 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) {
287 switch (I->getOpcode()) {
288 case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size);
289 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size);
290 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size);
291 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size);
292 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size);
293 default: return NoModRef;
297 //===--------------------------------------------------------------------===//
298 /// Higher level methods for querying mod/ref information.
301 /// canBasicBlockModify - Return true if it is possible for execution of the
302 /// specified basic block to modify the value pointed to by Ptr.
304 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size);
306 /// canInstructionRangeModify - Return true if it is possible for the
307 /// execution of the specified instructions to modify the value pointed to by
308 /// Ptr. The instructions to consider are all of the instructions in the
309 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
311 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
312 const Value *Ptr, unsigned Size);
314 //===--------------------------------------------------------------------===//
315 /// Methods that clients should call when they transform the program to allow
316 /// alias analyses to update their internal data structures. Note that these
317 /// methods may be called on any instruction, regardless of whether or not
318 /// they have pointer-analysis implications.
321 /// deleteValue - This method should be called whenever an LLVM Value is
322 /// deleted from the program, for example when an instruction is found to be
323 /// redundant and is eliminated.
325 virtual void deleteValue(Value *V);
327 /// copyValue - This method should be used whenever a preexisting value in the
328 /// program is copied or cloned, introducing a new value. Note that analysis
329 /// implementations should tolerate clients that use this method to introduce
330 /// the same value multiple times: if the analysis already knows about a
331 /// value, it should ignore the request.
333 virtual void copyValue(Value *From, Value *To);
335 /// replaceWithNewValue - This method is the obvious combination of the two
336 /// above, and it provided as a helper to simplify client code.
338 void replaceWithNewValue(Value *Old, Value *New) {
344 /// isNoAliasCall - Return true if this pointer is returned by a noalias
346 bool isNoAliasCall(const Value *V);
348 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
349 /// identifiable object. This returns true for:
350 /// Global Variables and Functions (but not Global Aliases)
351 /// Allocas and Mallocs
352 /// ByVal and NoAlias Arguments
355 bool isIdentifiedObject(const Value *V);
357 } // End llvm namespace
359 // Because of the way .a files work, we must force the BasicAA implementation to
360 // be pulled in if the AliasAnalysis header is included. Otherwise we run
361 // the risk of AliasAnalysis being used, but the default implementation not
362 // being linked into the tool that uses it.
363 FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis)
364 FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis)