AliasAnalysis.h revision 794fd75c67a2cdc128d67342c6d88a504d186896
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/System/IncludeFile.h" 35#include <vector> 36 37namespace llvm { 38 39class LoadInst; 40class StoreInst; 41class VAArgInst; 42class TargetData; 43class Pass; 44class AnalysisUsage; 45 46class AliasAnalysis { 47protected: 48 const TargetData *TD; 49 AliasAnalysis *AA; // Previous Alias Analysis to chain to. 50 51 /// InitializeAliasAnalysis - Subclasses must call this method to initialize 52 /// the AliasAnalysis interface before any other methods are called. This is 53 /// typically called by the run* methods of these subclasses. This may be 54 /// called multiple times. 55 /// 56 void InitializeAliasAnalysis(Pass *P); 57 58 // getAnalysisUsage - All alias analysis implementations should invoke this 59 // directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that 60 // TargetData is required by the pass. 61 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 62 63public: 64 static const int ID; // Class identification, replacement for typeinfo 65 AliasAnalysis() : TD(0), AA(0) {} 66 virtual ~AliasAnalysis(); // We want to be subclassed 67 68 /// getTargetData - Every alias analysis implementation depends on the size of 69 /// data items in the current Target. This provides a uniform way to handle 70 /// it. 71 /// 72 const TargetData &getTargetData() const { return *TD; } 73 74 //===--------------------------------------------------------------------===// 75 /// Alias Queries... 76 /// 77 78 /// Alias analysis result - Either we know for sure that it does not alias, we 79 /// know for sure it must alias, or we don't know anything: The two pointers 80 /// _might_ alias. This enum is designed so you can do things like: 81 /// if (AA.alias(P1, P2)) { ... } 82 /// to check to see if two pointers might alias. 83 /// 84 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 85 86 /// alias - The main low level interface to the alias analysis implementation. 87 /// Returns a Result indicating whether the two pointers are aliased to each 88 /// other. This is the interface that must be implemented by specific alias 89 /// analysis implementations. 90 /// 91 virtual AliasResult alias(const Value *V1, unsigned V1Size, 92 const Value *V2, unsigned V2Size); 93 94 /// getMustAliases - If there are any pointers known that must alias this 95 /// pointer, return them now. This allows alias-set based alias analyses to 96 /// perform a form a value numbering (which is exposed by load-vn). If an 97 /// alias analysis supports this, it should ADD any must aliased pointers to 98 /// the specified vector. 99 /// 100 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals); 101 102 /// pointsToConstantMemory - If the specified pointer is known to point into 103 /// constant global memory, return true. This allows disambiguation of store 104 /// instructions from constant pointers. 105 /// 106 virtual bool pointsToConstantMemory(const Value *P); 107 108 //===--------------------------------------------------------------------===// 109 /// Simple mod/ref information... 110 /// 111 112 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 113 /// bits which may be or'd together. 114 /// 115 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 116 117 118 /// ModRefBehavior - Summary of how a function affects memory in the program. 119 /// Loads from constant globals are not considered memory accesses for this 120 /// interface. Also, functions may freely modify stack space local to their 121 /// invocation without having to report it through these interfaces. 122 enum ModRefBehavior { 123 // DoesNotAccessMemory - This function does not perform any non-local loads 124 // or stores to memory. 125 // 126 // This property corresponds to the GCC 'const' attribute. 127 DoesNotAccessMemory, 128 129 // AccessesArguments - This function accesses function arguments in 130 // non-volatile and well known ways, but does not access any other memory. 131 // 132 // Clients may call getArgumentAccesses to get specific information about 133 // how pointer arguments are used. 134 AccessesArguments, 135 136 // AccessesArgumentsAndGlobals - This function has accesses function 137 // arguments and global variables in non-volatile and well-known ways, but 138 // does not access any other memory. 139 // 140 // Clients may call getArgumentAccesses to get specific information about 141 // how pointer arguments and globals are used. 142 AccessesArgumentsAndGlobals, 143 144 // OnlyReadsMemory - This function does not perform any non-local stores or 145 // volatile loads, but may read from any memory location. 146 // 147 // This property corresponds to the GCC 'pure' attribute. 148 OnlyReadsMemory, 149 150 // UnknownModRefBehavior - This indicates that the function could not be 151 // classified into one of the behaviors above. 152 UnknownModRefBehavior 153 }; 154 155 /// PointerAccessInfo - This struct is used to return results for pointers, 156 /// globals, and the return value of a function. 157 struct PointerAccessInfo { 158 /// V - The value this record corresponds to. This may be an Argument for 159 /// the function, a GlobalVariable, or null, corresponding to the return 160 /// value for the function. 161 Value *V; 162 163 /// ModRefInfo - Whether the pointer is loaded or stored to/from. 164 /// 165 ModRefResult ModRefInfo; 166 167 /// AccessType - Specific fine-grained access information for the argument. 168 /// If none of these classifications is general enough, the 169 /// getModRefBehavior method should not return AccessesArguments*. If a 170 /// record is not returned for a particular argument, the argument is never 171 /// dead and never dereferenced. 172 enum AccessType { 173 /// ScalarAccess - The pointer is dereferenced. 174 /// 175 ScalarAccess, 176 177 /// ArrayAccess - The pointer is indexed through as an array of elements. 178 /// 179 ArrayAccess, 180 181 /// ElementAccess ?? P->F only? 182 183 /// CallsThrough - Indirect calls are made through the specified function 184 /// pointer. 185 CallsThrough 186 }; 187 }; 188 189 /// getModRefBehavior - Return the behavior of the specified function if 190 /// called from the specified call site. The call site may be null in which 191 /// case the most generic behavior of this function should be returned. 192 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS, 193 std::vector<PointerAccessInfo> *Info = 0); 194 195 /// doesNotAccessMemory - If the specified function is known to never read or 196 /// write memory, return true. If the function only reads from known-constant 197 /// memory, it is also legal to return true. Functions that unwind the stack 198 /// are not legal for this predicate. 199 /// 200 /// Many optimizations (such as CSE and LICM) can be performed on calls to it, 201 /// without worrying about aliasing properties, and many functions have this 202 /// property (e.g. 'sin' and 'cos'). 203 /// 204 /// This property corresponds to the GCC 'const' attribute. 205 /// 206 bool doesNotAccessMemory(Function *F) { 207 return getModRefBehavior(F, CallSite()) == DoesNotAccessMemory; 208 } 209 210 /// onlyReadsMemory - If the specified function is known to only read from 211 /// non-volatile memory (or not access memory at all), return true. Functions 212 /// that unwind the stack are not legal for this predicate. 213 /// 214 /// This property allows many common optimizations to be performed in the 215 /// absence of interfering store instructions, such as CSE of strlen calls. 216 /// 217 /// This property corresponds to the GCC 'pure' attribute. 218 /// 219 bool onlyReadsMemory(Function *F) { 220 /// FIXME: If the analysis returns more precise info, we can reduce it to 221 /// this. 222 ModRefBehavior MRB = getModRefBehavior(F, CallSite()); 223 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 224 } 225 226 227 /// getModRefInfo - Return information about whether or not an instruction may 228 /// read or write memory specified by the pointer operand. An instruction 229 /// that doesn't read or write memory may be trivially LICM'd for example. 230 231 /// getModRefInfo (for call sites) - Return whether information about whether 232 /// a particular call site modifies or reads the memory specified by the 233 /// pointer. 234 /// 235 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 236 237 /// getModRefInfo - Return information about whether two call sites may refer 238 /// to the same set of memory locations. This function returns NoModRef if 239 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory 240 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or 241 /// ModRef if CS1 might read or write memory accessed by CS2. 242 /// 243 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 244 245 /// hasNoModRefInfoForCalls - Return true if the analysis has no mod/ref 246 /// information for pairs of function calls (other than "pure" and "const" 247 /// functions). This can be used by clients to avoid many pointless queries. 248 /// Remember that if you override this and chain to another analysis, you must 249 /// make sure that it doesn't have mod/ref info either. 250 /// 251 virtual bool hasNoModRefInfoForCalls() const; 252 253 /// Convenience functions... 254 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 255 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size); 256 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 257 return getModRefInfo(CallSite(C), P, Size); 258 } 259 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) { 260 return getModRefInfo(CallSite(I), P, Size); 261 } 262 ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) { 263 return AliasAnalysis::Mod; 264 } 265 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 266 switch (I->getOpcode()) { 267 case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size); 268 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 269 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 270 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 271 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); 272 default: return NoModRef; 273 } 274 } 275 276 //===--------------------------------------------------------------------===// 277 /// Higher level methods for querying mod/ref information. 278 /// 279 280 /// canBasicBlockModify - Return true if it is possible for execution of the 281 /// specified basic block to modify the value pointed to by Ptr. 282 /// 283 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 284 285 /// canInstructionRangeModify - Return true if it is possible for the 286 /// execution of the specified instructions to modify the value pointed to by 287 /// Ptr. The instructions to consider are all of the instructions in the 288 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 289 /// 290 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 291 const Value *Ptr, unsigned Size); 292 293 //===--------------------------------------------------------------------===// 294 /// Methods that clients should call when they transform the program to allow 295 /// alias analyses to update their internal data structures. Note that these 296 /// methods may be called on any instruction, regardless of whether or not 297 /// they have pointer-analysis implications. 298 /// 299 300 /// deleteValue - This method should be called whenever an LLVM Value is 301 /// deleted from the program, for example when an instruction is found to be 302 /// redundant and is eliminated. 303 /// 304 virtual void deleteValue(Value *V); 305 306 /// copyValue - This method should be used whenever a preexisting value in the 307 /// program is copied or cloned, introducing a new value. Note that analysis 308 /// implementations should tolerate clients that use this method to introduce 309 /// the same value multiple times: if the analysis already knows about a 310 /// value, it should ignore the request. 311 /// 312 virtual void copyValue(Value *From, Value *To); 313 314 /// replaceWithNewValue - This method is the obvious combination of the two 315 /// above, and it provided as a helper to simplify client code. 316 /// 317 void replaceWithNewValue(Value *Old, Value *New) { 318 copyValue(Old, New); 319 deleteValue(Old); 320 } 321}; 322 323} // End llvm namespace 324 325// Because of the way .a files work, we must force the BasicAA implementation to 326// be pulled in if the AliasAnalysis header is included. Otherwise we run 327// the risk of AliasAnalysis being used, but the default implementation not 328// being linked into the tool that uses it. 329FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis) 330FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis) 331 332#endif 333