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 /// PointerAccessInfo - This struct is used to return results for pointers,
168 /// globals, and the return value of a function.
169 struct PointerAccessInfo {
170 /// V - The value this record corresponds to. This may be an Argument for
171 /// the function, a GlobalVariable, or null, corresponding to the return
172 /// value for the function.
175 /// ModRefInfo - Whether the pointer is loaded or stored to/from.
177 ModRefResult ModRefInfo;
180 /// getModRefBehavior - Return the behavior when calling the given call site.
181 virtual ModRefBehavior getModRefBehavior(CallSite CS,
182 std::vector<PointerAccessInfo> *Info = 0);
184 /// getModRefBehavior - Return the behavior when calling the given function.
185 /// For use when the call site is not known.
186 virtual ModRefBehavior getModRefBehavior(Function *F,
187 std::vector<PointerAccessInfo> *Info = 0);
189 /// getModRefBehavior - Return the modref behavior of the intrinsic with the
191 static ModRefBehavior getModRefBehavior(unsigned iid);
193 /// doesNotAccessMemory - If the specified call is known to never read or
194 /// write memory, return true. If the call only reads from known-constant
195 /// memory, it is also legal to return true. Calls that unwind the stack
196 /// are legal for this predicate.
198 /// Many optimizations (such as CSE and LICM) can be performed on such calls
199 /// without worrying about aliasing properties, and many calls have this
200 /// property (e.g. calls to 'sin' and 'cos').
202 /// This property corresponds to the GCC 'const' attribute.
204 bool doesNotAccessMemory(CallSite CS) {
205 return getModRefBehavior(CS) == DoesNotAccessMemory;
208 /// doesNotAccessMemory - If the specified function is known to never read or
209 /// write memory, return true. For use when the call site is not known.
211 bool doesNotAccessMemory(Function *F) {
212 return getModRefBehavior(F) == DoesNotAccessMemory;
215 /// onlyReadsMemory - If the specified call is known to only read from
216 /// non-volatile memory (or not access memory at all), return true. Calls
217 /// that unwind the stack are legal for this predicate.
219 /// This property allows many common optimizations to be performed in the
220 /// absence of interfering store instructions, such as CSE of strlen calls.
222 /// This property corresponds to the GCC 'pure' attribute.
224 bool onlyReadsMemory(CallSite CS) {
225 ModRefBehavior MRB = getModRefBehavior(CS);
226 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
229 /// onlyReadsMemory - If the specified function is known to only read from
230 /// non-volatile memory (or not access memory at all), return true. For use
231 /// when the call site is not known.
233 bool onlyReadsMemory(Function *F) {
234 ModRefBehavior MRB = getModRefBehavior(F);
235 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
239 /// getModRefInfo - Return information about whether or not an instruction may
240 /// read or write memory specified by the pointer operand. An instruction
241 /// that doesn't read or write memory may be trivially LICM'd for example.
243 /// getModRefInfo (for call sites) - Return whether information about whether
244 /// a particular call site modifies or reads the memory specified by the
247 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
249 /// getModRefInfo - Return information about whether two call sites may refer
250 /// to the same set of memory locations. This function returns NoModRef if
251 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory
252 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or
253 /// ModRef if CS1 might read or write memory accessed by CS2.
255 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
258 /// Convenience functions...
259 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size);
260 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size);
261 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) {
262 return getModRefInfo(CallSite(C), P, Size);
264 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) {
265 return getModRefInfo(CallSite(I), P, Size);
267 ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) {
268 return AliasAnalysis::ModRef;
270 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) {
271 switch (I->getOpcode()) {
272 case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size);
273 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size);
274 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size);
275 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size);
276 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size);
277 default: return NoModRef;
281 //===--------------------------------------------------------------------===//
282 /// Higher level methods for querying mod/ref information.
285 /// canBasicBlockModify - Return true if it is possible for execution of the
286 /// specified basic block to modify the value pointed to by Ptr.
288 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size);
290 /// canInstructionRangeModify - Return true if it is possible for the
291 /// execution of the specified instructions to modify the value pointed to by
292 /// Ptr. The instructions to consider are all of the instructions in the
293 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
295 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
296 const Value *Ptr, unsigned Size);
298 //===--------------------------------------------------------------------===//
299 /// Methods that clients should call when they transform the program to allow
300 /// alias analyses to update their internal data structures. Note that these
301 /// methods may be called on any instruction, regardless of whether or not
302 /// they have pointer-analysis implications.
305 /// deleteValue - This method should be called whenever an LLVM Value is
306 /// deleted from the program, for example when an instruction is found to be
307 /// redundant and is eliminated.
309 virtual void deleteValue(Value *V);
311 /// copyValue - This method should be used whenever a preexisting value in the
312 /// program is copied or cloned, introducing a new value. Note that analysis
313 /// implementations should tolerate clients that use this method to introduce
314 /// the same value multiple times: if the analysis already knows about a
315 /// value, it should ignore the request.
317 virtual void copyValue(Value *From, Value *To);
319 /// replaceWithNewValue - This method is the obvious combination of the two
320 /// above, and it provided as a helper to simplify client code.
322 void replaceWithNewValue(Value *Old, Value *New) {
328 /// isNoAliasCall - Return true if this pointer is returned by a noalias
330 bool isNoAliasCall(const Value *V);
332 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
333 /// identifiable object. This returns true for:
334 /// Global Variables and Functions (but not Global Aliases)
335 /// Allocas and Mallocs
336 /// ByVal and NoAlias Arguments
339 bool isIdentifiedObject(const Value *V);
341 } // End llvm namespace
343 // Because of the way .a files work, we must force the BasicAA implementation to
344 // be pulled in if the AliasAnalysis header is included. Otherwise we run
345 // the risk of AliasAnalysis being used, but the default implementation not
346 // being linked into the tool that uses it.
347 FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis)
348 FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis)