AliasAnalysis.h revision 762e8e846f0ad50ffea56216c5ea20db1c95b756
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" 35 36namespace llvm { 37 38class LoadInst; 39class StoreInst; 40class TargetData; 41class AnalysisUsage; 42class Pass; 43 44class AliasAnalysis { 45 const TargetData *TD; 46protected: 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. 51 /// 52 void InitializeAliasAnalysis(Pass *P); 53 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; 58 59public: 60 AliasAnalysis() : TD(0) {} 61 virtual ~AliasAnalysis(); // We want to be subclassed 62 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 65 /// it. 66 const TargetData &getTargetData() const { return *TD; } 67 68 //===--------------------------------------------------------------------===// 69 /// Alias Queries... 70 /// 71 72 /// Alias analysis result - Either we know for sure that it does not alias, we 73 /// know for sure it must alias, or we don't know anything: The two pointers 74 /// _might_ alias. This enum is designed so you can do things like: 75 /// if (AA.alias(P1, P2)) { ... } 76 /// to check to see if two pointers might alias. 77 /// 78 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 79 80 /// alias - The main low level interface to the alias analysis implementation. 81 /// Returns a Result indicating whether the two pointers are aliased to each 82 /// other. This is the interface that must be implemented by specific alias 83 /// analysis implementations. 84 /// 85 virtual AliasResult alias(const Value *V1, unsigned V1Size, 86 const Value *V2, unsigned V2Size) { 87 return MayAlias; 88 } 89 90 /// getMustAliases - If there are any pointers known that must alias this 91 /// pointer, return them now. This allows alias-set based alias analyses to 92 /// perform a form a value numbering (which is exposed by load-vn). If an 93 /// alias analysis supports this, it should ADD any must aliased pointers to 94 /// the specified vector. 95 /// 96 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) {} 97 98 /// pointsToConstantMemory - If the specified pointer is known to point into 99 /// constant global memory, return true. This allows disambiguation of store 100 /// instructions from constant pointers. 101 /// 102 virtual bool pointsToConstantMemory(const Value *P) { return false; } 103 104 //===--------------------------------------------------------------------===// 105 /// Simple mod/ref information... 106 /// 107 108 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 109 /// bits which may be or'd together. 110 /// 111 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 112 113 /// getModRefInfo - Return information about whether or not an instruction may 114 /// read or write memory specified by the pointer operand. An instruction 115 /// that doesn't read or write memory may be trivially LICM'd for example. 116 117 /// getModRefInfo (for call sites) - Return whether information about whether 118 /// a particular call site modifies or reads the memory specified by the 119 /// pointer. 120 /// 121 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) { 122 // If P points to a constant memory location, the call definitely could not 123 // modify the memory location. 124 return pointsToConstantMemory(P) ? Ref : ModRef; 125 } 126 127 /// getModRefInfo - Return information about whether two call sites may refer 128 /// to the same set of memory locations. This function returns NoModRef if 129 /// the two calls refer to disjoint memory locations, Ref if they both read 130 /// some of the same memory, Mod if they both write to some of the same 131 /// memory, and ModRef if they read and write to the same memory. 132 /// 133 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) { 134 return ModRef; 135 } 136 137 /// Convenience functions... 138 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 139 ModRefResult getModRefInfo(StoreInst*S, Value *P, unsigned Size); 140 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 141 return getModRefInfo(CallSite(C), P, Size); 142 } 143 ModRefResult getModRefInfo(InvokeInst*I, Value *P, unsigned Size) { 144 return getModRefInfo(CallSite(I), P, Size); 145 } 146 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 147 switch (I->getOpcode()) { 148 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 149 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 150 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 151 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); 152 default: return NoModRef; 153 } 154 } 155 156 /// canBasicBlockModify - Return true if it is possible for execution of the 157 /// specified basic block to modify the value pointed to by Ptr. 158 /// 159 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 160 161 /// canInstructionRangeModify - Return true if it is possible for the 162 /// execution of the specified instructions to modify the value pointed to by 163 /// Ptr. The instructions to consider are all of the instructions in the 164 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 165 /// 166 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 167 const Value *Ptr, unsigned Size); 168}; 169 170// Because of the way .a files work, we must force the BasicAA implementation to 171// be pulled in if the AliasAnalysis header is included. Otherwise we run 172// the risk of AliasAnalysis being used, but the default implementation not 173// being linked into the tool that uses it. 174// 175extern void BasicAAStub(); 176static IncludeFile HDR_INCLUDE_BASICAA_CPP((void*)&BasicAAStub); 177 178} // End llvm namespace 179 180#endif 181