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"
46 AliasAnalysis *AA; // Previous Alias Analysis to chain to.
48 /// InitializeAliasAnalysis - Subclasses must call this method to initialize
49 /// the AliasAnalysis interface before any other methods are called. This is
50 /// typically called by the run* methods of these subclasses. This may be
51 /// called multiple times.
53 void InitializeAliasAnalysis(Pass *P);
55 /// getAnalysisUsage - All alias analysis implementations should invoke this
56 /// directly (using AliasAnalysis::getAnalysisUsage(AU)).
57 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
60 static char ID; // Class identification, replacement for typeinfo
61 AliasAnalysis() : TD(0), AA(0) {}
62 virtual ~AliasAnalysis(); // We want to be subclassed
64 /// UnknownSize - This is a special value which can be used with the
65 /// size arguments in alias queries to indicate that the caller does not
66 /// know the sizes of the potential memory references.
67 static unsigned const UnknownSize = ~0u;
69 /// getTargetData - Return a pointer to the current TargetData object, or
70 /// null if no TargetData object is available.
72 const TargetData *getTargetData() const { return TD; }
74 /// getTypeStoreSize - Return the TargetData store size for the given type,
75 /// if known, or a conservative value otherwise.
77 unsigned getTypeStoreSize(const Type *Ty);
79 //===--------------------------------------------------------------------===//
83 /// Alias analysis result - Either we know for sure that it does not alias, we
84 /// know for sure it must alias, or we don't know anything: The two pointers
85 /// _might_ alias. This enum is designed so you can do things like:
86 /// if (AA.alias(P1, P2)) { ... }
87 /// to check to see if two pointers might alias.
89 /// See docs/AliasAnalysis.html for more information on the specific meanings
92 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
94 /// alias - The main low level interface to the alias analysis implementation.
95 /// Returns a Result indicating whether the two pointers are aliased to each
96 /// other. This is the interface that must be implemented by specific alias
97 /// analysis implementations.
99 virtual AliasResult alias(const Value *V1, unsigned V1Size,
100 const Value *V2, unsigned V2Size);
102 /// alias - A convenience wrapper for the case where the sizes are unknown.
103 AliasResult alias(const Value *V1, const Value *V2) {
104 return alias(V1, UnknownSize, V2, UnknownSize);
107 /// isNoAlias - A trivial helper function to check to see if the specified
108 /// pointers are no-alias.
109 bool isNoAlias(const Value *V1, unsigned V1Size,
110 const Value *V2, unsigned V2Size) {
111 return alias(V1, V1Size, V2, V2Size) == NoAlias;
114 /// pointsToConstantMemory - If the specified pointer is known to point into
115 /// constant global memory, return true. This allows disambiguation of store
116 /// instructions from constant pointers.
118 virtual bool pointsToConstantMemory(const Value *P);
120 //===--------------------------------------------------------------------===//
121 /// Simple mod/ref information...
124 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
125 /// bits which may be or'd together.
127 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
130 /// ModRefBehavior - Summary of how a function affects memory in the program.
131 /// Loads from constant globals are not considered memory accesses for this
132 /// interface. Also, functions may freely modify stack space local to their
133 /// invocation without having to report it through these interfaces.
134 enum ModRefBehavior {
135 // DoesNotAccessMemory - This function does not perform any non-local loads
136 // or stores to memory.
138 // This property corresponds to the GCC 'const' attribute.
141 // AccessesArguments - This function accesses function arguments in well
142 // known (possibly volatile) ways, but does not access any other memory.
144 // Clients may use the Info parameter of getModRefBehavior to get specific
145 // information about how pointer arguments are used.
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.
152 // Clients may use the Info parameter of getModRefBehavior to get specific
153 // information about how pointer arguments are used.
154 AccessesArgumentsAndGlobals,
156 // OnlyReadsMemory - This function does not perform any non-local stores or
157 // volatile loads, but may read from any memory location.
159 // This property corresponds to the GCC 'pure' attribute.
162 // UnknownModRefBehavior - This indicates that the function could not be
163 // classified into one of the behaviors above.
164 UnknownModRefBehavior
167 /// getModRefBehavior - Return the behavior when calling the given call site.
168 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
170 /// getModRefBehavior - Return the behavior when calling the given function.
171 /// For use when the call site is not known.
172 virtual ModRefBehavior getModRefBehavior(const Function *F);
174 /// getIntrinsicModRefBehavior - Return the modref behavior of the intrinsic
175 /// with the given id.
176 static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid);
178 /// doesNotAccessMemory - If the specified call is known to never read or
179 /// write memory, return true. If the call only reads from known-constant
180 /// memory, it is also legal to return true. Calls that unwind the stack
181 /// are legal for this predicate.
183 /// Many optimizations (such as CSE and LICM) can be performed on such calls
184 /// without worrying about aliasing properties, and many calls have this
185 /// property (e.g. calls to 'sin' and 'cos').
187 /// This property corresponds to the GCC 'const' attribute.
189 bool doesNotAccessMemory(ImmutableCallSite CS) {
190 return getModRefBehavior(CS) == DoesNotAccessMemory;
193 /// doesNotAccessMemory - If the specified function is known to never read or
194 /// write memory, return true. For use when the call site is not known.
196 bool doesNotAccessMemory(const Function *F) {
197 return getModRefBehavior(F) == DoesNotAccessMemory;
200 /// onlyReadsMemory - If the specified call is known to only read from
201 /// non-volatile memory (or not access memory at all), return true. Calls
202 /// that unwind the stack are legal for this predicate.
204 /// This property allows many common optimizations to be performed in the
205 /// absence of interfering store instructions, such as CSE of strlen calls.
207 /// This property corresponds to the GCC 'pure' attribute.
209 bool onlyReadsMemory(ImmutableCallSite CS) {
210 ModRefBehavior MRB = getModRefBehavior(CS);
211 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
214 /// onlyReadsMemory - If the specified function is known to only read from
215 /// non-volatile memory (or not access memory at all), return true. For use
216 /// when the call site is not known.
218 bool onlyReadsMemory(const Function *F) {
219 ModRefBehavior MRB = getModRefBehavior(F);
220 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
224 /// getModRefInfo - Return information about whether or not an instruction may
225 /// read or write memory specified by the pointer operand. An instruction
226 /// that doesn't read or write memory may be trivially LICM'd for example.
228 /// getModRefInfo (for call sites) - Return whether information about whether
229 /// a particular call site modifies or reads the memory specified by the
232 virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
233 const Value *P, unsigned Size);
235 /// getModRefInfo - Return information about whether two call sites may refer
236 /// to the same set of memory locations. This function returns NoModRef if
237 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory
238 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or
239 /// ModRef if CS1 might read or write memory accessed by CS2.
241 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
242 ImmutableCallSite CS2);
245 /// Convenience functions...
246 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, unsigned Size);
247 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, unsigned Size);
248 ModRefResult getModRefInfo(const CallInst *C, const Value *P, unsigned Size) {
249 return getModRefInfo(ImmutableCallSite(C), P, Size);
251 ModRefResult getModRefInfo(const InvokeInst *I,
252 const Value *P, unsigned Size) {
253 return getModRefInfo(ImmutableCallSite(I), P, Size);
255 ModRefResult getModRefInfo(const VAArgInst* I,
256 const Value* P, unsigned Size) {
257 return AliasAnalysis::ModRef;
259 ModRefResult getModRefInfo(const Instruction *I,
260 const Value *P, unsigned Size) {
261 switch (I->getOpcode()) {
262 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, P,Size);
263 case Instruction::Load: return getModRefInfo((const LoadInst*)I, P, Size);
264 case Instruction::Store: return getModRefInfo((const StoreInst*)I, P,Size);
265 case Instruction::Call: return getModRefInfo((const CallInst*)I, P, Size);
266 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,P,Size);
267 default: return NoModRef;
271 //===--------------------------------------------------------------------===//
272 /// Higher level methods for querying mod/ref information.
275 /// canBasicBlockModify - Return true if it is possible for execution of the
276 /// specified basic block to modify the value pointed to by Ptr.
278 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size);
280 /// canInstructionRangeModify - Return true if it is possible for the
281 /// execution of the specified instructions to modify the value pointed to by
282 /// Ptr. The instructions to consider are all of the instructions in the
283 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
285 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
286 const Value *Ptr, unsigned Size);
288 //===--------------------------------------------------------------------===//
289 /// Methods that clients should call when they transform the program to allow
290 /// alias analyses to update their internal data structures. Note that these
291 /// methods may be called on any instruction, regardless of whether or not
292 /// they have pointer-analysis implications.
295 /// deleteValue - This method should be called whenever an LLVM Value is
296 /// deleted from the program, for example when an instruction is found to be
297 /// redundant and is eliminated.
299 virtual void deleteValue(Value *V);
301 /// copyValue - This method should be used whenever a preexisting value in the
302 /// program is copied or cloned, introducing a new value. Note that analysis
303 /// implementations should tolerate clients that use this method to introduce
304 /// the same value multiple times: if the analysis already knows about a
305 /// value, it should ignore the request.
307 virtual void copyValue(Value *From, Value *To);
309 /// replaceWithNewValue - This method is the obvious combination of the two
310 /// above, and it provided as a helper to simplify client code.
312 void replaceWithNewValue(Value *Old, Value *New) {
318 /// isNoAliasCall - Return true if this pointer is returned by a noalias
320 bool isNoAliasCall(const Value *V);
322 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
323 /// identifiable object. This returns true for:
324 /// Global Variables and Functions (but not Global Aliases)
325 /// Allocas and Mallocs
326 /// ByVal and NoAlias Arguments
329 bool isIdentifiedObject(const Value *V);
331 } // End llvm namespace
333 // Because of the way .a files work, we must force the BasicAA implementation to
334 // be pulled in if the AliasAnalysis header is included. Otherwise we run
335 // the risk of AliasAnalysis being used, but the default implementation not
336 // being linked into the tool that uses it.
337 FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis)
338 FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis)