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 /// isNoAlias - A trivial helper function to check to see if the specified
98 /// pointers are no-alias.
99 bool isNoAlias(const Value *V1, unsigned V1Size,
100 const Value *V2, unsigned V2Size) {
101 return alias(V1, V1Size, V2, V2Size) == NoAlias;
104 /// pointsToConstantMemory - If the specified pointer is known to point into
105 /// constant global memory, return true. This allows disambiguation of store
106 /// instructions from constant pointers.
108 virtual bool pointsToConstantMemory(const Value *P);
110 //===--------------------------------------------------------------------===//
111 /// Simple mod/ref information...
114 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
115 /// bits which may be or'd together.
117 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
120 /// ModRefBehavior - Summary of how a function affects memory in the program.
121 /// Loads from constant globals are not considered memory accesses for this
122 /// interface. Also, functions may freely modify stack space local to their
123 /// invocation without having to report it through these interfaces.
124 enum ModRefBehavior {
125 // DoesNotAccessMemory - This function does not perform any non-local loads
126 // or stores to memory.
128 // This property corresponds to the GCC 'const' attribute.
131 // AccessesArguments - This function accesses function arguments in well
132 // known (possibly volatile) ways, but does not access any other memory.
134 // Clients may use the Info parameter of getModRefBehavior to get specific
135 // information about how pointer arguments are used.
138 // AccessesArgumentsAndGlobals - This function has accesses function
139 // arguments and global variables well known (possibly volatile) ways, but
140 // does not access any other memory.
142 // Clients may use the Info parameter of getModRefBehavior to get specific
143 // information about how pointer arguments are used.
144 AccessesArgumentsAndGlobals,
146 // OnlyReadsMemory - This function does not perform any non-local stores or
147 // volatile loads, but may read from any memory location.
149 // This property corresponds to the GCC 'pure' attribute.
152 // UnknownModRefBehavior - This indicates that the function could not be
153 // classified into one of the behaviors above.
154 UnknownModRefBehavior
157 /// PointerAccessInfo - This struct is used to return results for pointers,
158 /// globals, and the return value of a function.
159 struct PointerAccessInfo {
160 /// V - The value this record corresponds to. This may be an Argument for
161 /// the function, a GlobalVariable, or null, corresponding to the return
162 /// value for the function.
165 /// ModRefInfo - Whether the pointer is loaded or stored to/from.
167 ModRefResult ModRefInfo;
170 /// getModRefBehavior - Return the behavior when calling the given call site.
171 virtual ModRefBehavior getModRefBehavior(CallSite CS,
172 std::vector<PointerAccessInfo> *Info = 0);
174 /// getModRefBehavior - Return the behavior when calling the given function.
175 /// For use when the call site is not known.
176 virtual ModRefBehavior getModRefBehavior(Function *F,
177 std::vector<PointerAccessInfo> *Info = 0);
179 /// getModRefBehavior - Return the modref behavior of the intrinsic with the
181 static ModRefBehavior getModRefBehavior(unsigned iid);
183 /// doesNotAccessMemory - If the specified call is known to never read or
184 /// write memory, return true. If the call only reads from known-constant
185 /// memory, it is also legal to return true. Calls that unwind the stack
186 /// are legal for this predicate.
188 /// Many optimizations (such as CSE and LICM) can be performed on such calls
189 /// without worrying about aliasing properties, and many calls have this
190 /// property (e.g. calls to 'sin' and 'cos').
192 /// This property corresponds to the GCC 'const' attribute.
194 bool doesNotAccessMemory(CallSite CS) {
195 return getModRefBehavior(CS) == DoesNotAccessMemory;
198 /// doesNotAccessMemory - If the specified function is known to never read or
199 /// write memory, return true. For use when the call site is not known.
201 bool doesNotAccessMemory(Function *F) {
202 return getModRefBehavior(F) == DoesNotAccessMemory;
205 /// onlyReadsMemory - If the specified call is known to only read from
206 /// non-volatile memory (or not access memory at all), return true. Calls
207 /// that unwind the stack are legal for this predicate.
209 /// This property allows many common optimizations to be performed in the
210 /// absence of interfering store instructions, such as CSE of strlen calls.
212 /// This property corresponds to the GCC 'pure' attribute.
214 bool onlyReadsMemory(CallSite CS) {
215 ModRefBehavior MRB = getModRefBehavior(CS);
216 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
219 /// onlyReadsMemory - If the specified function is known to only read from
220 /// non-volatile memory (or not access memory at all), return true. For use
221 /// when the call site is not known.
223 bool onlyReadsMemory(Function *F) {
224 ModRefBehavior MRB = getModRefBehavior(F);
225 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
229 /// getModRefInfo - Return information about whether or not an instruction may
230 /// read or write memory specified by the pointer operand. An instruction
231 /// that doesn't read or write memory may be trivially LICM'd for example.
233 /// getModRefInfo (for call sites) - Return whether information about whether
234 /// a particular call site modifies or reads the memory specified by the
237 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
239 /// getModRefInfo - Return information about whether two call sites may refer
240 /// to the same set of memory locations. This function returns NoModRef if
241 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory
242 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or
243 /// ModRef if CS1 might read or write memory accessed by CS2.
245 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
248 /// Convenience functions...
249 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size);
250 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size);
251 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) {
252 return getModRefInfo(CallSite(C), P, Size);
254 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) {
255 return getModRefInfo(CallSite(I), P, Size);
257 ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) {
258 return AliasAnalysis::ModRef;
260 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) {
261 switch (I->getOpcode()) {
262 case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size);
263 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size);
264 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size);
265 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size);
266 case Instruction::Invoke: return getModRefInfo((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)