1 //===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source 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/Pass.h" // Need this for IncludeFile
45 AliasAnalysis *AA; // Previous Alias Analysis to chain to.
47 /// InitializeAliasAnalysis - Subclasses must call this method to initialize
48 /// the AliasAnalysis interface before any other methods are called. This is
49 /// typically called by the run* methods of these subclasses. This may be
50 /// called multiple times.
52 void InitializeAliasAnalysis(Pass *P);
54 // getAnalysisUsage - All alias analysis implementations should invoke this
55 // directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that
56 // TargetData is required by the pass.
57 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
60 AliasAnalysis() : TD(0), AA(0) {}
61 virtual ~AliasAnalysis(); // We want to be subclassed
63 /// getTargetData - Every alias analysis implementation depends on the size of
64 /// data items in the current Target. This provides a uniform way to handle
67 const TargetData &getTargetData() const { return *TD; }
69 //===--------------------------------------------------------------------===//
73 /// Alias analysis result - Either we know for sure that it does not alias, we
74 /// know for sure it must alias, or we don't know anything: The two pointers
75 /// _might_ alias. This enum is designed so you can do things like:
76 /// if (AA.alias(P1, P2)) { ... }
77 /// to check to see if two pointers might alias.
79 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
81 /// alias - The main low level interface to the alias analysis implementation.
82 /// Returns a Result indicating whether the two pointers are aliased to each
83 /// other. This is the interface that must be implemented by specific alias
84 /// analysis implementations.
86 virtual AliasResult alias(const Value *V1, unsigned V1Size,
87 const Value *V2, unsigned V2Size);
89 /// getMustAliases - If there are any pointers known that must alias this
90 /// pointer, return them now. This allows alias-set based alias analyses to
91 /// perform a form a value numbering (which is exposed by load-vn). If an
92 /// alias analysis supports this, it should ADD any must aliased pointers to
93 /// the specified vector.
95 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals);
97 /// pointsToConstantMemory - If the specified pointer is known to point into
98 /// constant global memory, return true. This allows disambiguation of store
99 /// instructions from constant pointers.
101 virtual bool pointsToConstantMemory(const Value *P);
103 /// doesNotAccessMemory - If the specified function is known to never read or
104 /// write memory, return true. If the function only reads from known-constant
105 /// memory, it is also legal to return true. Functions that unwind the stack
106 /// are not legal for this predicate.
108 /// Many optimizations (such as CSE and LICM) can be performed on calls to it,
109 /// without worrying about aliasing properties, and many functions have this
110 /// property (e.g. 'sin' and 'cos').
112 /// This property corresponds to the GCC 'const' attribute.
114 virtual bool doesNotAccessMemory(Function *F);
116 /// onlyReadsMemory - If the specified function is known to only read from
117 /// non-volatile memory (or not access memory at all), return true. Functions
118 /// that unwind the stack are not legal for this predicate.
120 /// This property allows many common optimizations to be performed in the
121 /// absence of interfering store instructions, such as CSE of strlen calls.
123 /// This property corresponds to the GCC 'pure' attribute.
125 virtual bool onlyReadsMemory(Function *F);
128 //===--------------------------------------------------------------------===//
129 /// Simple mod/ref information...
132 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
133 /// bits which may be or'd together.
135 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
137 /// getModRefInfo - Return information about whether or not an instruction may
138 /// read or write memory specified by the pointer operand. An instruction
139 /// that doesn't read or write memory may be trivially LICM'd for example.
141 /// getModRefInfo (for call sites) - Return whether information about whether
142 /// a particular call site modifies or reads the memory specified by the
145 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
147 /// getModRefInfo - Return information about whether two call sites may refer
148 /// to the same set of memory locations. This function returns NoModRef if
149 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory
150 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or
151 /// ModRef if CS1 might read or write memory accessed by CS2.
153 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
155 /// hasNoModRefInfoForCalls - Return true if the analysis has no mod/ref
156 /// information for pairs of function calls (other than "pure" and "const"
157 /// functions). This can be used by clients to avoid many pointless queries.
158 /// Remember that if you override this and chain to another analysis, you must
159 /// make sure that it doesn't have mod/ref info either.
161 virtual bool hasNoModRefInfoForCalls() const;
163 /// Convenience functions...
164 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size);
165 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size);
166 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) {
167 return getModRefInfo(CallSite(C), P, Size);
169 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) {
170 return getModRefInfo(CallSite(I), P, Size);
172 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) {
173 switch (I->getOpcode()) {
174 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size);
175 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size);
176 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size);
177 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size);
178 default: return NoModRef;
182 //===--------------------------------------------------------------------===//
183 /// Higher level methods for querying mod/ref information.
186 /// canBasicBlockModify - Return true if it is possible for execution of the
187 /// specified basic block to modify the value pointed to by Ptr.
189 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size);
191 /// canInstructionRangeModify - Return true if it is possible for the
192 /// execution of the specified instructions to modify the value pointed to by
193 /// Ptr. The instructions to consider are all of the instructions in the
194 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
196 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
197 const Value *Ptr, unsigned Size);
199 //===--------------------------------------------------------------------===//
200 /// Methods that clients should call when they transform the program to allow
201 /// alias analyses to update their internal data structures. Note that these
202 /// methods may be called on any instruction, regardless of whether or not
203 /// they have pointer-analysis implications.
206 /// deleteValue - This method should be called whenever an LLVM Value is
207 /// deleted from the program, for example when an instruction is found to be
208 /// redundant and is eliminated.
210 virtual void deleteValue(Value *V);
212 /// copyValue - This method should be used whenever a preexisting value in the
213 /// program is copied or cloned, introducing a new value. Note that analysis
214 /// implementations should tolerate clients that use this method to introduce
215 /// the same value multiple times: if the analysis already knows about a
216 /// value, it should ignore the request.
218 virtual void copyValue(Value *From, Value *To);
220 /// replaceWithNewValue - This method is the obvious combination of the two
221 /// above, and it provided as a helper to simplify client code.
223 void replaceWithNewValue(Value *Old, Value *New) {
229 // Because of the way .a files work, we must force the BasicAA implementation to
230 // be pulled in if the AliasAnalysis header is included. Otherwise we run
231 // the risk of AliasAnalysis being used, but the default implementation not
232 // being linked into the tool that uses it.
234 extern void BasicAAStub();
235 static IncludeFile HDR_INCLUDE_BASICAA_CPP((void*)&BasicAAStub);
237 } // End llvm namespace