LLVM API Documentation
00001 //===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // This file defines the generic AliasAnalysis interface, which is used as the 00011 // common interface used by all clients of alias analysis information, and 00012 // implemented by all alias analysis implementations. Mod/Ref information is 00013 // also captured by this interface. 00014 // 00015 // Implementations of this interface must implement the various virtual methods, 00016 // which automatically provides functionality for the entire suite of client 00017 // APIs. 00018 // 00019 // This API represents memory as a (Pointer, Size) pair. The Pointer component 00020 // specifies the base memory address of the region, the Size specifies how large 00021 // of an area is being queried. If Size is 0, two pointers only alias if they 00022 // are exactly equal. If size is greater than zero, but small, the two pointers 00023 // alias if the areas pointed to overlap. If the size is very large (ie, ~0U), 00024 // then the two pointers alias if they may be pointing to components of the same 00025 // memory object. Pointers that point to two completely different objects in 00026 // memory never alias, regardless of the value of the Size component. 00027 // 00028 //===----------------------------------------------------------------------===// 00029 00030 #ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H 00031 #define LLVM_ANALYSIS_ALIAS_ANALYSIS_H 00032 00033 #include "llvm/Support/CallSite.h" 00034 #include "llvm/Pass.h" // Need this for IncludeFile 00035 00036 namespace llvm { 00037 00038 class LoadInst; 00039 class StoreInst; 00040 class TargetData; 00041 00042 class AliasAnalysis { 00043 protected: 00044 const TargetData *TD; 00045 AliasAnalysis *AA; // Previous Alias Analysis to chain to. 00046 00047 /// InitializeAliasAnalysis - Subclasses must call this method to initialize 00048 /// the AliasAnalysis interface before any other methods are called. This is 00049 /// typically called by the run* methods of these subclasses. This may be 00050 /// called multiple times. 00051 /// 00052 void InitializeAliasAnalysis(Pass *P); 00053 00054 // getAnalysisUsage - All alias analysis implementations should invoke this 00055 // directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that 00056 // TargetData is required by the pass. 00057 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 00058 00059 public: 00060 AliasAnalysis() : TD(0), AA(0) {} 00061 virtual ~AliasAnalysis(); // We want to be subclassed 00062 00063 /// getTargetData - Every alias analysis implementation depends on the size of 00064 /// data items in the current Target. This provides a uniform way to handle 00065 /// it. 00066 /// 00067 const TargetData &getTargetData() const { return *TD; } 00068 00069 //===--------------------------------------------------------------------===// 00070 /// Alias Queries... 00071 /// 00072 00073 /// Alias analysis result - Either we know for sure that it does not alias, we 00074 /// know for sure it must alias, or we don't know anything: The two pointers 00075 /// _might_ alias. This enum is designed so you can do things like: 00076 /// if (AA.alias(P1, P2)) { ... } 00077 /// to check to see if two pointers might alias. 00078 /// 00079 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 00080 00081 /// alias - The main low level interface to the alias analysis implementation. 00082 /// Returns a Result indicating whether the two pointers are aliased to each 00083 /// other. This is the interface that must be implemented by specific alias 00084 /// analysis implementations. 00085 /// 00086 virtual AliasResult alias(const Value *V1, unsigned V1Size, 00087 const Value *V2, unsigned V2Size); 00088 00089 /// getMustAliases - If there are any pointers known that must alias this 00090 /// pointer, return them now. This allows alias-set based alias analyses to 00091 /// perform a form a value numbering (which is exposed by load-vn). If an 00092 /// alias analysis supports this, it should ADD any must aliased pointers to 00093 /// the specified vector. 00094 /// 00095 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals); 00096 00097 /// pointsToConstantMemory - If the specified pointer is known to point into 00098 /// constant global memory, return true. This allows disambiguation of store 00099 /// instructions from constant pointers. 00100 /// 00101 virtual bool pointsToConstantMemory(const Value *P); 00102 00103 /// doesNotAccessMemory - If the specified function is known to never read or 00104 /// write memory, return true. If the function only reads from known-constant 00105 /// memory, it is also legal to return true. Functions that unwind the stack 00106 /// are not legal for this predicate. 00107 /// 00108 /// Many optimizations (such as CSE and LICM) can be performed on calls to it, 00109 /// without worrying about aliasing properties, and many functions have this 00110 /// property (e.g. 'sin' and 'cos'). 00111 /// 00112 /// This property corresponds to the GCC 'const' attribute. 00113 /// 00114 virtual bool doesNotAccessMemory(Function *F); 00115 00116 /// onlyReadsMemory - If the specified function is known to only read from 00117 /// non-volatile memory (or not access memory at all), return true. Functions 00118 /// that unwind the stack are not legal for this predicate. 00119 /// 00120 /// This property allows many common optimizations to be performed in the 00121 /// absence of interfering store instructions, such as CSE of strlen calls. 00122 /// 00123 /// This property corresponds to the GCC 'pure' attribute. 00124 /// 00125 virtual bool onlyReadsMemory(Function *F); 00126 00127 00128 //===--------------------------------------------------------------------===// 00129 /// Simple mod/ref information... 00130 /// 00131 00132 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 00133 /// bits which may be or'd together. 00134 /// 00135 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 00136 00137 /// getModRefInfo - Return information about whether or not an instruction may 00138 /// read or write memory specified by the pointer operand. An instruction 00139 /// that doesn't read or write memory may be trivially LICM'd for example. 00140 00141 /// getModRefInfo (for call sites) - Return whether information about whether 00142 /// a particular call site modifies or reads the memory specified by the 00143 /// pointer. 00144 /// 00145 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 00146 00147 /// getModRefInfo - Return information about whether two call sites may refer 00148 /// to the same set of memory locations. This function returns NoModRef if 00149 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory 00150 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or 00151 /// ModRef if CS1 might read or write memory accessed by CS2. 00152 /// 00153 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 00154 00155 /// hasNoModRefInfoForCalls - Return true if the analysis has no mod/ref 00156 /// information for pairs of function calls (other than "pure" and "const" 00157 /// functions). This can be used by clients to avoid many pointless queries. 00158 /// Remember that if you override this and chain to another analysis, you must 00159 /// make sure that it doesn't have mod/ref info either. 00160 /// 00161 virtual bool hasNoModRefInfoForCalls() const; 00162 00163 /// Convenience functions... 00164 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 00165 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size); 00166 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 00167 return getModRefInfo(CallSite(C), P, Size); 00168 } 00169 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) { 00170 return getModRefInfo(CallSite(I), P, Size); 00171 } 00172 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 00173 switch (I->getOpcode()) { 00174 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 00175 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 00176 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 00177 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); 00178 default: return NoModRef; 00179 } 00180 } 00181 00182 //===--------------------------------------------------------------------===// 00183 /// Higher level methods for querying mod/ref information. 00184 /// 00185 00186 /// canBasicBlockModify - Return true if it is possible for execution of the 00187 /// specified basic block to modify the value pointed to by Ptr. 00188 /// 00189 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 00190 00191 /// canInstructionRangeModify - Return true if it is possible for the 00192 /// execution of the specified instructions to modify the value pointed to by 00193 /// Ptr. The instructions to consider are all of the instructions in the 00194 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 00195 /// 00196 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 00197 const Value *Ptr, unsigned Size); 00198 00199 //===--------------------------------------------------------------------===// 00200 /// Methods that clients should call when they transform the program to allow 00201 /// alias analyses to update their internal data structures. Note that these 00202 /// methods may be called on any instruction, regardless of whether or not 00203 /// they have pointer-analysis implications. 00204 /// 00205 00206 /// deleteValue - This method should be called whenever an LLVM Value is 00207 /// deleted from the program, for example when an instruction is found to be 00208 /// redundant and is eliminated. 00209 /// 00210 virtual void deleteValue(Value *V); 00211 00212 /// copyValue - This method should be used whenever a preexisting value in the 00213 /// program is copied or cloned, introducing a new value. Note that analysis 00214 /// implementations should tolerate clients that use this method to introduce 00215 /// the same value multiple times: if the analysis already knows about a 00216 /// value, it should ignore the request. 00217 /// 00218 virtual void copyValue(Value *From, Value *To); 00219 00220 /// replaceWithNewValue - This method is the obvious combination of the two 00221 /// above, and it provided as a helper to simplify client code. 00222 /// 00223 void replaceWithNewValue(Value *Old, Value *New) { 00224 copyValue(Old, New); 00225 deleteValue(Old); 00226 } 00227 }; 00228 00229 // Because of the way .a files work, we must force the BasicAA implementation to 00230 // be pulled in if the AliasAnalysis header is included. Otherwise we run 00231 // the risk of AliasAnalysis being used, but the default implementation not 00232 // being linked into the tool that uses it. 00233 // 00234 extern void BasicAAStub(); 00235 static IncludeFile HDR_INCLUDE_BASICAA_CPP((void*)&BasicAAStub); 00236 00237 } // End llvm namespace 00238 00239 #endif