AliasAnalysis.h revision e40bb915bae2aecdd1578ea356d5e4c8ac31061c
1//===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 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. 7// 8//===----------------------------------------------------------------------===// 9// 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. 14// 15// Implementations of this interface must implement the various virtual methods, 16// which automatically provides functionality for the entire suite of client 17// APIs. 18// 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. 27// 28//===----------------------------------------------------------------------===// 29 30#ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H 31#define LLVM_ANALYSIS_ALIAS_ANALYSIS_H 32 33#include "llvm/Support/CallSite.h" 34#include "llvm/Pass.h" // Need this for IncludeFile 35 36namespace llvm { 37 38class LoadInst; 39class StoreInst; 40class TargetData; 41 42class AliasAnalysis { 43 const TargetData *TD; 44protected: 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. 49 /// 50 void InitializeAliasAnalysis(Pass *P); 51 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; 56 57public: 58 AliasAnalysis() : TD(0) {} 59 virtual ~AliasAnalysis(); // We want to be subclassed 60 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 63 /// it. 64 /// 65 const TargetData &getTargetData() const { return *TD; } 66 67 //===--------------------------------------------------------------------===// 68 /// Alias Queries... 69 /// 70 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. 76 /// 77 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 78 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. 83 /// 84 virtual AliasResult alias(const Value *V1, unsigned V1Size, 85 const Value *V2, unsigned V2Size) { 86 return MayAlias; 87 } 88 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. 94 /// 95 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) {} 96 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. 100 /// 101 virtual bool pointsToConstantMemory(const Value *P) { return false; } 102 103 /// 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. 107 /// 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'). 111 /// 112 /// This property corresponds to the GCC 'const' attribute. 113 /// 114 virtual bool doesNotAccessMemory(Function *F) { return false; } 115 116 /// 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. 119 /// 120 /// This property allows many common optimizations to be performed in the 121 /// absence of interfering store instructions, such as CSE of strlen calls. 122 /// 123 /// This property corresponds to the GCC 'pure' attribute. 124 /// 125 virtual bool onlyReadsMemory(Function *F) { return doesNotAccessMemory(F); } 126 127 128 //===--------------------------------------------------------------------===// 129 /// Simple mod/ref information... 130 /// 131 132 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 133 /// bits which may be or'd together. 134 /// 135 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 136 137 /// 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. 140 141 /// getModRefInfo (for call sites) - Return whether information about whether 142 /// a particular call site modifies or reads the memory specified by the 143 /// pointer. 144 /// 145 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 146 147 /// 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 they both read 150 /// some of the same memory, Mod if they both write to some of the same 151 /// memory, and ModRef if they read and write to the same memory. 152 /// 153 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 154 155 /// hasNoModRefInfoForCalls - Return true if the analysis has no mod/ref 156 /// information for function calls other than "pure" and "const" functions. 157 /// This can be used by clients to avoid many pointless queries. Remember 158 /// that if you override this and chain to another analysis, you must make 159 /// sure that it doesn't have mod/ref info either. 160 /// 161 virtual bool hasNoModRefInfoForCalls() const { return false; } 162 163 164 /// Convenience functions... 165 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 166 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size); 167 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 168 return getModRefInfo(CallSite(C), P, Size); 169 } 170 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) { 171 return getModRefInfo(CallSite(I), P, Size); 172 } 173 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 174 switch (I->getOpcode()) { 175 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 176 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 177 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 178 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); 179 default: return NoModRef; 180 } 181 } 182 183 /// canBasicBlockModify - Return true if it is possible for execution of the 184 /// specified basic block to modify the value pointed to by Ptr. 185 /// 186 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 187 188 /// canInstructionRangeModify - Return true if it is possible for the 189 /// execution of the specified instructions to modify the value pointed to by 190 /// Ptr. The instructions to consider are all of the instructions in the 191 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 192 /// 193 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 194 const Value *Ptr, unsigned Size); 195}; 196 197// Because of the way .a files work, we must force the BasicAA implementation to 198// be pulled in if the AliasAnalysis header is included. Otherwise we run 199// the risk of AliasAnalysis being used, but the default implementation not 200// being linked into the tool that uses it. 201// 202extern void BasicAAStub(); 203static IncludeFile HDR_INCLUDE_BASICAA_CPP((void*)&BasicAAStub); 204 205} // End llvm namespace 206 207#endif 208