AliasAnalysis.h revision 42c31a70735e55bf82e66a9315c97d1821c9a798
1//===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// 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, or UnknownSize if the size is not known. 22// Pointers that point to two completely different objects in memory never 23// alias, regardless of the value of the Size component. 24// 25//===----------------------------------------------------------------------===// 26 27#ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H 28#define LLVM_ANALYSIS_ALIAS_ANALYSIS_H 29 30#include "llvm/Support/CallSite.h" 31#include <vector> 32 33namespace llvm { 34 35class LoadInst; 36class StoreInst; 37class VAArgInst; 38class TargetData; 39class Pass; 40class AnalysisUsage; 41 42class AliasAnalysis { 43protected: 44 const TargetData *TD; 45 46private: 47 AliasAnalysis *AA; // Previous Alias Analysis to chain to. 48 49protected: 50 /// InitializeAliasAnalysis - Subclasses must call this method to initialize 51 /// the AliasAnalysis interface before any other methods are called. This is 52 /// typically called by the run* methods of these subclasses. This may be 53 /// called multiple times. 54 /// 55 void InitializeAliasAnalysis(Pass *P); 56 57 /// getAnalysisUsage - All alias analysis implementations should invoke this 58 /// directly (using AliasAnalysis::getAnalysisUsage(AU)). 59 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 60 61public: 62 static char ID; // Class identification, replacement for typeinfo 63 AliasAnalysis() : TD(0), AA(0) {} 64 virtual ~AliasAnalysis(); // We want to be subclassed 65 66 /// UnknownSize - This is a special value which can be used with the 67 /// size arguments in alias queries to indicate that the caller does not 68 /// know the sizes of the potential memory references. 69 static uint64_t const UnknownSize = ~UINT64_C(0); 70 71 /// getTargetData - Return a pointer to the current TargetData object, or 72 /// null if no TargetData object is available. 73 /// 74 const TargetData *getTargetData() const { return TD; } 75 76 /// getTypeStoreSize - Return the TargetData store size for the given type, 77 /// if known, or a conservative value otherwise. 78 /// 79 uint64_t getTypeStoreSize(const Type *Ty); 80 81 //===--------------------------------------------------------------------===// 82 /// Alias Queries... 83 /// 84 85 /// Location - A description of a memory location. 86 struct Location { 87 /// Ptr - The address of the start of the location. 88 const Value *Ptr; 89 /// Size - The maximum size of the location, or UnknownSize if the size is 90 /// not known. Note that an unknown size does not mean the pointer aliases 91 /// the entire virtual address space, because there are restrictions on 92 /// stepping out of one object and into another. 93 /// See http://llvm.org/docs/LangRef.html#pointeraliasing 94 uint64_t Size; 95 /// TBAATag - The metadata node which describes the TBAA type of 96 /// the location, or null if there is no known unique tag. 97 const MDNode *TBAATag; 98 99 explicit Location(const Value *P = 0, 100 uint64_t S = UnknownSize, 101 const MDNode *N = 0) 102 : Ptr(P), Size(S), TBAATag(N) {} 103 104 Location getWithNewPtr(const Value *NewPtr) const { 105 Location Copy(*this); 106 Copy.Ptr = NewPtr; 107 return Copy; 108 } 109 110 Location getWithoutTBAATag() const { 111 Location Copy(*this); 112 Copy.TBAATag = 0; 113 return Copy; 114 } 115 }; 116 117 /// Alias analysis result - Either we know for sure that it does not alias, we 118 /// know for sure it must alias, or we don't know anything: The two pointers 119 /// _might_ alias. This enum is designed so you can do things like: 120 /// if (AA.alias(P1, P2)) { ... } 121 /// to check to see if two pointers might alias. 122 /// 123 /// See docs/AliasAnalysis.html for more information on the specific meanings 124 /// of these values. 125 /// 126 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 127 128 /// alias - The main low level interface to the alias analysis implementation. 129 /// Returns an AliasResult indicating whether the two pointers are aliased to 130 /// each other. This is the interface that must be implemented by specific 131 /// alias analysis implementations. 132 virtual AliasResult alias(const Location &LocA, const Location &LocB); 133 134 /// alias - A convenience wrapper. 135 AliasResult alias(const Value *V1, uint64_t V1Size, 136 const Value *V2, uint64_t V2Size) { 137 return alias(Location(V1, V1Size), Location(V2, V2Size)); 138 } 139 140 /// alias - A convenience wrapper. 141 AliasResult alias(const Value *V1, const Value *V2) { 142 return alias(V1, UnknownSize, V2, UnknownSize); 143 } 144 145 /// isNoAlias - A trivial helper function to check to see if the specified 146 /// pointers are no-alias. 147 bool isNoAlias(const Location &LocA, const Location &LocB) { 148 return alias(LocA, LocB) == NoAlias; 149 } 150 151 /// isNoAlias - A convenience wrapper. 152 bool isNoAlias(const Value *V1, uint64_t V1Size, 153 const Value *V2, uint64_t V2Size) { 154 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size)); 155 } 156 157 /// pointsToConstantMemory - If the specified memory location is 158 /// known to be constant, return true. If OrLocal is true and the 159 /// specified memory location is known to be "local" (derived from 160 /// an alloca), return true. Otherwise return false. 161 virtual bool pointsToConstantMemory(const Location &Loc, 162 bool OrLocal = false); 163 164 /// pointsToConstantMemory - A convenient wrapper. 165 bool pointsToConstantMemory(const Value *P, bool OrLocal = false) { 166 return pointsToConstantMemory(Location(P), OrLocal); 167 } 168 169 //===--------------------------------------------------------------------===// 170 /// Simple mod/ref information... 171 /// 172 173 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 174 /// bits which may be or'd together. 175 /// 176 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 177 178 /// These values define additional bits used to define the 179 /// ModRefBehavior values. 180 enum { Nowhere = 0, ArgumentPointees = 4, Anywhere = 8 | ArgumentPointees }; 181 182 /// ModRefBehavior - Summary of how a function affects memory in the program. 183 /// Loads from constant globals are not considered memory accesses for this 184 /// interface. Also, functions may freely modify stack space local to their 185 /// invocation without having to report it through these interfaces. 186 enum ModRefBehavior { 187 /// DoesNotAccessMemory - This function does not perform any non-local loads 188 /// or stores to memory. 189 /// 190 /// This property corresponds to the GCC 'const' attribute. 191 /// This property corresponds to the LLVM IR 'readnone' attribute. 192 /// This property corresponds to the IntrNoMem LLVM intrinsic flag. 193 DoesNotAccessMemory = Nowhere | NoModRef, 194 195 /// AccessesArgumentsReadonly - This function loads through function 196 /// arguments and does not perform any non-local stores or volatile 197 /// loads. 198 /// 199 /// This property corresponds to the IntrReadArgMem LLVM intrinsic flag. 200 AccessesArgumentsReadonly = ArgumentPointees | Ref, 201 202 /// AccessesArguments - This function accesses function arguments in well 203 /// known (possibly volatile) ways, but does not access any other memory. 204 /// 205 /// This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag. 206 AccessesArguments = ArgumentPointees | ModRef, 207 208 /// OnlyReadsMemory - This function does not perform any non-local stores or 209 /// volatile loads, but may read from any memory location. 210 /// 211 /// This property corresponds to the GCC 'pure' attribute. 212 /// This property corresponds to the LLVM IR 'readonly' attribute. 213 /// This property corresponds to the IntrReadMem LLVM intrinsic flag. 214 OnlyReadsMemory = Anywhere | Ref, 215 216 /// UnknownModRefBehavior - This indicates that the function could not be 217 /// classified into one of the behaviors above. 218 UnknownModRefBehavior = Anywhere | ModRef 219 }; 220 221 /// getModRefBehavior - Return the behavior when calling the given call site. 222 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 223 224 /// getModRefBehavior - Return the behavior when calling the given function. 225 /// For use when the call site is not known. 226 virtual ModRefBehavior getModRefBehavior(const Function *F); 227 228 /// doesNotAccessMemory - If the specified call is known to never read or 229 /// write memory, return true. If the call only reads from known-constant 230 /// memory, it is also legal to return true. Calls that unwind the stack 231 /// are legal for this predicate. 232 /// 233 /// Many optimizations (such as CSE and LICM) can be performed on such calls 234 /// without worrying about aliasing properties, and many calls have this 235 /// property (e.g. calls to 'sin' and 'cos'). 236 /// 237 /// This property corresponds to the GCC 'const' attribute. 238 /// 239 bool doesNotAccessMemory(ImmutableCallSite CS) { 240 return getModRefBehavior(CS) == DoesNotAccessMemory; 241 } 242 243 /// doesNotAccessMemory - If the specified function is known to never read or 244 /// write memory, return true. For use when the call site is not known. 245 /// 246 bool doesNotAccessMemory(const Function *F) { 247 return getModRefBehavior(F) == DoesNotAccessMemory; 248 } 249 250 /// onlyReadsMemory - If the specified call is known to only read from 251 /// non-volatile memory (or not access memory at all), return true. Calls 252 /// that unwind the stack are legal for this predicate. 253 /// 254 /// This property allows many common optimizations to be performed in the 255 /// absence of interfering store instructions, such as CSE of strlen calls. 256 /// 257 /// This property corresponds to the GCC 'pure' attribute. 258 /// 259 bool onlyReadsMemory(ImmutableCallSite CS) { 260 return onlyReadsMemory(getModRefBehavior(CS)); 261 } 262 263 /// onlyReadsMemory - If the specified function is known to only read from 264 /// non-volatile memory (or not access memory at all), return true. For use 265 /// when the call site is not known. 266 /// 267 bool onlyReadsMemory(const Function *F) { 268 return onlyReadsMemory(getModRefBehavior(F)); 269 } 270 271 /// onlyReadsMemory - If the functions with the specified behavior are known 272 /// to only read from non-volatile memory (or not access memory at all), return 273 /// true. For use when the call site is not known. 274 /// 275 static bool onlyReadsMemory(ModRefBehavior MRB) { 276 return !(MRB & Mod); 277 } 278 279 /// getModRefInfo - Return information about whether or not an instruction may 280 /// read or write the specified memory location. An instruction 281 /// that doesn't read or write memory may be trivially LICM'd for example. 282 ModRefResult getModRefInfo(const Instruction *I, 283 const Location &Loc) { 284 switch (I->getOpcode()) { 285 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc); 286 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc); 287 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc); 288 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc); 289 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc); 290 default: return NoModRef; 291 } 292 } 293 294 /// getModRefInfo - A convenience wrapper. 295 ModRefResult getModRefInfo(const Instruction *I, 296 const Value *P, uint64_t Size) { 297 return getModRefInfo(I, Location(P, Size)); 298 } 299 300 /// getModRefInfo (for call sites) - Return whether information about whether 301 /// a particular call site modifies or reads the specified memory location. 302 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 303 const Location &Loc); 304 305 /// getModRefInfo (for call sites) - A convenience wrapper. 306 ModRefResult getModRefInfo(ImmutableCallSite CS, 307 const Value *P, uint64_t Size) { 308 return getModRefInfo(CS, Location(P, Size)); 309 } 310 311 /// getModRefInfo (for calls) - Return whether information about whether 312 /// a particular call modifies or reads the specified memory location. 313 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) { 314 return getModRefInfo(ImmutableCallSite(C), Loc); 315 } 316 317 /// getModRefInfo (for calls) - A convenience wrapper. 318 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) { 319 return getModRefInfo(C, Location(P, Size)); 320 } 321 322 /// getModRefInfo (for invokes) - Return whether information about whether 323 /// a particular invoke modifies or reads the specified memory location. 324 ModRefResult getModRefInfo(const InvokeInst *I, 325 const Location &Loc) { 326 return getModRefInfo(ImmutableCallSite(I), Loc); 327 } 328 329 /// getModRefInfo (for invokes) - A convenience wrapper. 330 ModRefResult getModRefInfo(const InvokeInst *I, 331 const Value *P, uint64_t Size) { 332 return getModRefInfo(I, Location(P, Size)); 333 } 334 335 /// getModRefInfo (for loads) - Return whether information about whether 336 /// a particular load modifies or reads the specified memory location. 337 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc); 338 339 /// getModRefInfo (for loads) - A convenience wrapper. 340 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) { 341 return getModRefInfo(L, Location(P, Size)); 342 } 343 344 /// getModRefInfo (for stores) - Return whether information about whether 345 /// a particular store modifies or reads the specified memory location. 346 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc); 347 348 /// getModRefInfo (for stores) - A convenience wrapper. 349 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) { 350 return getModRefInfo(S, Location(P, Size)); 351 } 352 353 /// getModRefInfo (for va_args) - Return whether information about whether 354 /// a particular va_arg modifies or reads the specified memory location. 355 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc); 356 357 /// getModRefInfo (for va_args) - A convenience wrapper. 358 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) { 359 return getModRefInfo(I, Location(P, Size)); 360 } 361 362 /// getModRefInfo - Return information about whether two call sites may refer 363 /// to the same set of memory locations. See 364 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo 365 /// for details. 366 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 367 ImmutableCallSite CS2); 368 369 //===--------------------------------------------------------------------===// 370 /// Higher level methods for querying mod/ref information. 371 /// 372 373 /// canBasicBlockModify - Return true if it is possible for execution of the 374 /// specified basic block to modify the value pointed to by Ptr. 375 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc); 376 377 /// canBasicBlockModify - A convenience wrapper. 378 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){ 379 return canBasicBlockModify(BB, Location(P, Size)); 380 } 381 382 /// canInstructionRangeModify - Return true if it is possible for the 383 /// execution of the specified instructions to modify the value pointed to by 384 /// Ptr. The instructions to consider are all of the instructions in the 385 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 386 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 387 const Location &Loc); 388 389 /// canInstructionRangeModify - A convenience wrapper. 390 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 391 const Value *Ptr, uint64_t Size) { 392 return canInstructionRangeModify(I1, I2, Location(Ptr, Size)); 393 } 394 395 //===--------------------------------------------------------------------===// 396 /// Methods that clients should call when they transform the program to allow 397 /// alias analyses to update their internal data structures. Note that these 398 /// methods may be called on any instruction, regardless of whether or not 399 /// they have pointer-analysis implications. 400 /// 401 402 /// deleteValue - This method should be called whenever an LLVM Value is 403 /// deleted from the program, for example when an instruction is found to be 404 /// redundant and is eliminated. 405 /// 406 virtual void deleteValue(Value *V); 407 408 /// copyValue - This method should be used whenever a preexisting value in the 409 /// program is copied or cloned, introducing a new value. Note that analysis 410 /// implementations should tolerate clients that use this method to introduce 411 /// the same value multiple times: if the analysis already knows about a 412 /// value, it should ignore the request. 413 /// 414 virtual void copyValue(Value *From, Value *To); 415 416 /// replaceWithNewValue - This method is the obvious combination of the two 417 /// above, and it provided as a helper to simplify client code. 418 /// 419 void replaceWithNewValue(Value *Old, Value *New) { 420 copyValue(Old, New); 421 deleteValue(Old); 422 } 423}; 424 425/// isNoAliasCall - Return true if this pointer is returned by a noalias 426/// function. 427bool isNoAliasCall(const Value *V); 428 429/// isIdentifiedObject - Return true if this pointer refers to a distinct and 430/// identifiable object. This returns true for: 431/// Global Variables and Functions (but not Global Aliases) 432/// Allocas and Mallocs 433/// ByVal and NoAlias Arguments 434/// NoAlias returns 435/// 436bool isIdentifiedObject(const Value *V); 437 438} // End llvm namespace 439 440#endif 441