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 /// InitializeAliasAnalysis - Subclasses must call this method to initialize
46 /// the AliasAnalysis interface before any other methods are called. This is
47 /// typically called by the run* methods of these subclasses. This may be
48 /// called multiple times.
50 void InitializeAliasAnalysis(Pass *P);
52 // getAnalysisUsage - All alias analysis implementations should invoke this
53 // directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that
54 // TargetData is required by the pass.
55 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
58 AliasAnalysis() : TD(0) {}
59 virtual ~AliasAnalysis(); // We want to be subclassed
61 /// getTargetData - Every alias analysis implementation depends on the size of
62 /// data items in the current Target. This provides a uniform way to handle
65 const TargetData &getTargetData() const { return *TD; }
67 //===--------------------------------------------------------------------===//
71 /// Alias analysis result - Either we know for sure that it does not alias, we
72 /// know for sure it must alias, or we don't know anything: The two pointers
73 /// _might_ alias. This enum is designed so you can do things like:
74 /// if (AA.alias(P1, P2)) { ... }
75 /// to check to see if two pointers might alias.
77 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
79 /// alias - The main low level interface to the alias analysis implementation.
80 /// Returns a Result indicating whether the two pointers are aliased to each
81 /// other. This is the interface that must be implemented by specific alias
82 /// analysis implementations.
84 virtual AliasResult alias(const Value *V1, unsigned V1Size,
85 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) { return false; }
103 //===--------------------------------------------------------------------===//
104 /// Simple mod/ref information...
107 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
108 /// bits which may be or'd together.
110 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
112 /// getModRefInfo - Return information about whether or not an instruction may
113 /// read or write memory specified by the pointer operand. An instruction
114 /// that doesn't read or write memory may be trivially LICM'd for example.
116 /// getModRefInfo (for call sites) - Return whether information about whether
117 /// a particular call site modifies or reads the memory specified by the
120 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
121 // If P points to a constant memory location, the call definitely could not
122 // modify the memory location.
123 return pointsToConstantMemory(P) ? Ref : ModRef;
126 /// getModRefInfo - Return information about whether two call sites may refer
127 /// to the same set of memory locations. This function returns NoModRef if
128 /// the two calls refer to disjoint memory locations, Ref if they both read
129 /// some of the same memory, Mod if they both write to some of the same
130 /// memory, and ModRef if they read and write to the same memory.
132 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
136 /// Convenience functions...
137 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size);
138 ModRefResult getModRefInfo(StoreInst*S, Value *P, unsigned Size);
139 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) {
140 return getModRefInfo(CallSite(C), P, Size);
142 ModRefResult getModRefInfo(InvokeInst*I, Value *P, unsigned Size) {
143 return getModRefInfo(CallSite(I), P, Size);
145 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) {
146 switch (I->getOpcode()) {
147 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size);
148 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size);
149 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size);
150 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size);
151 default: return NoModRef;
155 /// canBasicBlockModify - Return true if it is possible for execution of the
156 /// specified basic block to modify the value pointed to by Ptr.
158 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size);
160 /// canInstructionRangeModify - Return true if it is possible for the
161 /// execution of the specified instructions to modify the value pointed to by
162 /// Ptr. The instructions to consider are all of the instructions in the
163 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
165 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
166 const Value *Ptr, unsigned Size);
169 // Because of the way .a files work, we must force the BasicAA implementation to
170 // be pulled in if the AliasAnalysis header is included. Otherwise we run
171 // the risk of AliasAnalysis being used, but the default implementation not
172 // being linked into the tool that uses it.
174 extern void BasicAAStub();
175 static IncludeFile HDR_INCLUDE_BASICAA_CPP((void*)&BasicAAStub);
177 } // End llvm namespace