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.
173 static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid);
175 /// doesNotAccessMemory - If the specified call is known to never read or
176 /// write memory, return true. If the call only reads from known-constant
177 /// memory, it is also legal to return true. Calls that unwind the stack
178 /// are legal for this predicate.
180 /// Many optimizations (such as CSE and LICM) can be performed on such calls
181 /// without worrying about aliasing properties, and many calls have this
182 /// property (e.g. calls to 'sin' and 'cos').
184 /// This property corresponds to the GCC 'const' attribute.
186 bool doesNotAccessMemory(ImmutableCallSite CS) {
187 return getModRefBehavior(CS) == DoesNotAccessMemory;
190 /// doesNotAccessMemory - If the specified function is known to never read or
191 /// write memory, return true. For use when the call site is not known.
193 bool doesNotAccessMemory(const Function *F) {
194 return getModRefBehavior(F) == DoesNotAccessMemory;
197 /// onlyReadsMemory - If the specified call is known to only read from
198 /// non-volatile memory (or not access memory at all), return true. Calls
199 /// that unwind the stack are legal for this predicate.
201 /// This property allows many common optimizations to be performed in the
202 /// absence of interfering store instructions, such as CSE of strlen calls.
204 /// This property corresponds to the GCC 'pure' attribute.
206 bool onlyReadsMemory(ImmutableCallSite CS) {
207 ModRefBehavior MRB = getModRefBehavior(CS);
208 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
211 /// onlyReadsMemory - If the specified function is known to only read from
212 /// non-volatile memory (or not access memory at all), return true. For use
213 /// when the call site is not known.
215 bool onlyReadsMemory(const Function *F) {
216 ModRefBehavior MRB = getModRefBehavior(F);
217 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
221 /// getModRefInfo - Return information about whether or not an instruction may
222 /// read or write memory specified by the pointer operand. An instruction
223 /// that doesn't read or write memory may be trivially LICM'd for example.
225 /// getModRefInfo (for call sites) - Return whether information about whether
226 /// a particular call site modifies or reads the memory specified by the
229 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
230 const Value *P, unsigned Size);
232 /// getModRefInfo - Return information about whether two call sites may refer
233 /// to the same set of memory locations. This function returns NoModRef if
234 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory
235 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or
236 /// ModRef if CS1 might read or write memory accessed by CS2.
238 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
239 ImmutableCallSite CS2);
242 /// Convenience functions...
243 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, unsigned Size);
244 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, unsigned Size);
245 ModRefResult getModRefInfo(const CallInst *C, const Value *P, unsigned Size) {
246 return getModRefInfo(ImmutableCallSite(C), P, Size);
248 ModRefResult getModRefInfo(const InvokeInst *I,
249 const Value *P, unsigned Size) {
250 return getModRefInfo(ImmutableCallSite(I), P, Size);
252 ModRefResult getModRefInfo(const VAArgInst* I,
253 const Value* P, unsigned Size) {
254 return AliasAnalysis::ModRef;
256 ModRefResult getModRefInfo(const Instruction *I,
257 const Value *P, unsigned Size) {
258 switch (I->getOpcode()) {
259 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, P,Size);
260 case Instruction::Load: return getModRefInfo((const LoadInst*)I, P, Size);
261 case Instruction::Store: return getModRefInfo((const StoreInst*)I, P,Size);
262 case Instruction::Call: return getModRefInfo((const CallInst*)I, P, Size);
263 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,P,Size);
264 default: return NoModRef;
268 //===--------------------------------------------------------------------===//
269 /// Higher level methods for querying mod/ref information.
272 /// canBasicBlockModify - Return true if it is possible for execution of the
273 /// specified basic block to modify the value pointed to by Ptr.
275 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size);
277 /// canInstructionRangeModify - Return true if it is possible for the
278 /// execution of the specified instructions to modify the value pointed to by
279 /// Ptr. The instructions to consider are all of the instructions in the
280 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
282 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
283 const Value *Ptr, unsigned Size);
285 //===--------------------------------------------------------------------===//
286 /// Methods that clients should call when they transform the program to allow
287 /// alias analyses to update their internal data structures. Note that these
288 /// methods may be called on any instruction, regardless of whether or not
289 /// they have pointer-analysis implications.
292 /// deleteValue - This method should be called whenever an LLVM Value is
293 /// deleted from the program, for example when an instruction is found to be
294 /// redundant and is eliminated.
296 virtual void deleteValue(Value *V);
298 /// copyValue - This method should be used whenever a preexisting value in the
299 /// program is copied or cloned, introducing a new value. Note that analysis
300 /// implementations should tolerate clients that use this method to introduce
301 /// the same value multiple times: if the analysis already knows about a
302 /// value, it should ignore the request.
304 virtual void copyValue(Value *From, Value *To);
306 /// replaceWithNewValue - This method is the obvious combination of the two
307 /// above, and it provided as a helper to simplify client code.
309 void replaceWithNewValue(Value *Old, Value *New) {
315 /// isNoAliasCall - Return true if this pointer is returned by a noalias
317 bool isNoAliasCall(const Value *V);
319 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
320 /// identifiable object. This returns true for:
321 /// Global Variables and Functions (but not Global Aliases)
322 /// Allocas and Mallocs
323 /// ByVal and NoAlias Arguments
326 bool isIdentifiedObject(const Value *V);
328 } // End llvm namespace
330 // Because of the way .a files work, we must force the BasicAA implementation to
331 // be pulled in if the AliasAnalysis header is included. Otherwise we run
332 // the risk of AliasAnalysis being used, but the default implementation not
333 // being linked into the tool that uses it.
334 FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis)
335 FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis)