AliasAnalysis.h revision 1c56b730a6313886076d7b293a126ae5576f5288
1//===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===// 2// 3// This file defines the generic AliasAnalysis interface, which is used as the 4// common interface used by all clients of alias analysis information, and 5// implemented by all alias analysis implementations. Mod/Ref information is 6// also captured by this interface. 7// 8// Implementations of this interface must implement the various virtual methods, 9// which automatically provides functionality for the entire suite of client 10// APIs. 11// 12// This API represents memory as a (Pointer, Size) pair. The Pointer component 13// specifies the base memory address of the region, the Size specifies how large 14// of an area is being queried. If Size is 0, two pointers only alias if they 15// are exactly equal. If size is greater than zero, but small, the two pointers 16// alias if the areas pointed to overlap. If the size is very large (ie, ~0U), 17// then the two pointers alias if they may be pointing to components of the same 18// memory object. Pointers that point to two completely different objects in 19// memory never alias, regardless of the value of the Size component. 20// 21//===----------------------------------------------------------------------===// 22 23#ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H 24#define LLVM_ANALYSIS_ALIAS_ANALYSIS_H 25 26#include "llvm/Support/CallSite.h" 27class LoadInst; 28class StoreInst; 29class TargetData; 30class AnalysisUsage; 31class Pass; 32 33class AliasAnalysis { 34 const TargetData *TD; 35protected: 36 /// InitializeAliasAnalysis - Subclasses must call this method to initialize 37 /// the AliasAnalysis interface before any other methods are called. This is 38 /// typically called by the run* methods of these subclasses. This may be 39 /// called multiple times. 40 /// 41 void InitializeAliasAnalysis(Pass *P); 42 43 // getAnalysisUsage - All alias analysis implementations should invoke this 44 // directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that 45 // TargetData is required by the pass. 46 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 47 48public: 49 AliasAnalysis() : TD(0) {} 50 virtual ~AliasAnalysis(); // We want to be subclassed 51 52 /// getTargetData - Every alias analysis implementation depends on the size of 53 /// data items in the current Target. This provides a uniform way to handle 54 /// it. 55 const TargetData &getTargetData() const { return *TD; } 56 57 //===--------------------------------------------------------------------===// 58 /// Alias Queries... 59 /// 60 61 /// Alias analysis result - Either we know for sure that it does not alias, we 62 /// know for sure it must alias, or we don't know anything: The two pointers 63 /// _might_ alias. This enum is designed so you can do things like: 64 /// if (AA.alias(P1, P2)) { ... } 65 /// to check to see if two pointers might alias. 66 /// 67 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 68 69 /// alias - The main low level interface to the alias analysis implementation. 70 /// Returns a Result indicating whether the two pointers are aliased to each 71 /// other. This is the interface that must be implemented by specific alias 72 /// analysis implementations. 73 /// 74 virtual AliasResult alias(const Value *V1, unsigned V1Size, 75 const Value *V2, unsigned V2Size) { 76 return MayAlias; 77 } 78 79 //===--------------------------------------------------------------------===// 80 /// Simple mod/ref information... 81 /// 82 83 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 84 /// bits which may be or'd together. 85 /// 86 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 87 88 /// getModRefInfo - Return information about whether or not an instruction may 89 /// read or write memory specified by the pointer operand. An instruction 90 /// that doesn't read or write memory may be trivially LICM'd for example. 91 92 /// getModRefInfo (for call sites) - Return whether information about whether 93 /// a particular call site modifies or reads the memory specified by the 94 /// pointer. 95 /// 96 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) { 97 return ModRef; 98 } 99 100 /// getModRefInfo - Return information about whether two call sites may refer 101 /// to the same set of memory locations. This function returns NoModRef if 102 /// the two calls refer to disjoint memory locations, Ref if they both read 103 /// some of the same memory, Mod if they both write to some of the same 104 /// memory, and ModRef if they read and write to the same memory. 105 /// 106 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) { 107 return ModRef; 108 } 109 110 /// Convenience functions... 111 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 112 ModRefResult getModRefInfo(StoreInst*S, Value *P, unsigned Size); 113 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 114 return getModRefInfo(CallSite(C), P, Size); 115 } 116 ModRefResult getModRefInfo(InvokeInst*I, Value *P, unsigned Size) { 117 return getModRefInfo(CallSite(I), P, Size); 118 } 119 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 120 switch (I->getOpcode()) { 121 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 122 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 123 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 124 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); 125 default: return NoModRef; 126 } 127 } 128 129 /// canBasicBlockModify - Return true if it is possible for execution of the 130 /// specified basic block to modify the value pointed to by Ptr. 131 /// 132 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 133 134 /// canInstructionRangeModify - Return true if it is possible for the 135 /// execution of the specified instructions to modify the value pointed to by 136 /// Ptr. The instructions to consider are all of the instructions in the 137 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 138 /// 139 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 140 const Value *Ptr, unsigned Size); 141}; 142 143#endif 144