AliasAnalysis.h revision ddcdcc88631c6bd4ad43d9198b98bc9a829be036
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 identifies memory regions with the Location class. The pointer 20// component specifies the base memory address of the region. The Size specifies 21// the maximum size (in address units) of the memory region, or UnknownSize if 22// the size is not known. The TBAA tag identifies the "type" of the memory 23// reference; see the TypeBasedAliasAnalysis class for details. 24// 25// Some non-obvious details include: 26// - Pointers that point to two completely different objects in memory never 27// alias, regardless of the value of the Size component. 28// - NoAlias doesn't imply inequal pointers. The most obvious example of this 29// is two pointers to constant memory. Even if they are equal, constant 30// memory is never stored to, so there will never be any dependencies. 31// In this and other situations, the pointers may be both NoAlias and 32// MustAlias at the same time. The current API can only return one result, 33// though this is rarely a problem in practice. 34// 35//===----------------------------------------------------------------------===// 36 37#ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H 38#define LLVM_ANALYSIS_ALIAS_ANALYSIS_H 39 40#include "llvm/Support/CallSite.h" 41 42namespace llvm { 43 44class LoadInst; 45class StoreInst; 46class VAArgInst; 47class TargetData; 48class Pass; 49class AnalysisUsage; 50class MemTransferInst; 51class MemIntrinsic; 52 53class AliasAnalysis { 54protected: 55 const TargetData *TD; 56 57private: 58 AliasAnalysis *AA; // Previous Alias Analysis to chain to. 59 60protected: 61 /// InitializeAliasAnalysis - Subclasses must call this method to initialize 62 /// the AliasAnalysis interface before any other methods are called. This is 63 /// typically called by the run* methods of these subclasses. This may be 64 /// called multiple times. 65 /// 66 void InitializeAliasAnalysis(Pass *P); 67 68 /// getAnalysisUsage - All alias analysis implementations should invoke this 69 /// directly (using AliasAnalysis::getAnalysisUsage(AU)). 70 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 71 72public: 73 static char ID; // Class identification, replacement for typeinfo 74 AliasAnalysis() : TD(0), AA(0) {} 75 virtual ~AliasAnalysis(); // We want to be subclassed 76 77 /// UnknownSize - This is a special value which can be used with the 78 /// size arguments in alias queries to indicate that the caller does not 79 /// know the sizes of the potential memory references. 80 static uint64_t const UnknownSize = ~UINT64_C(0); 81 82 /// getTargetData - Return a pointer to the current TargetData object, or 83 /// null if no TargetData object is available. 84 /// 85 const TargetData *getTargetData() const { return TD; } 86 87 /// getTypeStoreSize - Return the TargetData store size for the given type, 88 /// if known, or a conservative value otherwise. 89 /// 90 uint64_t getTypeStoreSize(const Type *Ty); 91 92 //===--------------------------------------------------------------------===// 93 /// Alias Queries... 94 /// 95 96 /// Location - A description of a memory location. 97 struct Location { 98 /// Ptr - The address of the start of the location. 99 const Value *Ptr; 100 /// Size - The maximum size of the location, in address-units, or 101 /// UnknownSize if the size is not known. Note that an unknown size does 102 /// not mean the pointer aliases the entire virtual address space, because 103 /// there are restrictions on stepping out of one object and into another. 104 /// See http://llvm.org/docs/LangRef.html#pointeraliasing 105 uint64_t Size; 106 /// TBAATag - The metadata node which describes the TBAA type of 107 /// the location, or null if there is no known unique tag. 108 const MDNode *TBAATag; 109 110 explicit Location(const Value *P = 0, uint64_t S = UnknownSize, 111 const MDNode *N = 0) 112 : Ptr(P), Size(S), TBAATag(N) {} 113 114 Location getWithNewPtr(const Value *NewPtr) const { 115 Location Copy(*this); 116 Copy.Ptr = NewPtr; 117 return Copy; 118 } 119 120 Location getWithNewSize(uint64_t NewSize) const { 121 Location Copy(*this); 122 Copy.Size = NewSize; 123 return Copy; 124 } 125 126 Location getWithoutTBAATag() const { 127 Location Copy(*this); 128 Copy.TBAATag = 0; 129 return Copy; 130 } 131 }; 132 133 /// getLocation - Fill in Loc with information about the memory reference by 134 /// the given instruction. 135 Location getLocation(const LoadInst *LI); 136 Location getLocation(const StoreInst *SI); 137 Location getLocation(const VAArgInst *VI); 138 static Location getLocationForSource(const MemTransferInst *MTI); 139 static Location getLocationForDest(const MemIntrinsic *MI); 140 141 /// Alias analysis result - Either we know for sure that it does not alias, we 142 /// know for sure it must alias, or we don't know anything: The two pointers 143 /// _might_ alias. This enum is designed so you can do things like: 144 /// if (AA.alias(P1, P2)) { ... } 145 /// to check to see if two pointers might alias. 146 /// 147 /// See docs/AliasAnalysis.html for more information on the specific meanings 148 /// of these values. 149 /// 150 enum AliasResult { 151 NoAlias = 0, ///< No dependencies. 152 MayAlias, ///< Anything goes. 153 PartialAlias, ///< Pointers differ, but pointees overlap. 154 MustAlias ///< Pointers are equal. 155 }; 156 157 /// alias - The main low level interface to the alias analysis implementation. 158 /// Returns an AliasResult indicating whether the two pointers are aliased to 159 /// each other. This is the interface that must be implemented by specific 160 /// alias analysis implementations. 161 virtual AliasResult alias(const Location &LocA, const Location &LocB); 162 163 /// alias - A convenience wrapper. 164 AliasResult alias(const Value *V1, uint64_t V1Size, 165 const Value *V2, uint64_t V2Size) { 166 return alias(Location(V1, V1Size), Location(V2, V2Size)); 167 } 168 169 /// alias - A convenience wrapper. 170 AliasResult alias(const Value *V1, const Value *V2) { 171 return alias(V1, UnknownSize, V2, UnknownSize); 172 } 173 174 /// isNoAlias - A trivial helper function to check to see if the specified 175 /// pointers are no-alias. 176 bool isNoAlias(const Location &LocA, const Location &LocB) { 177 return alias(LocA, LocB) == NoAlias; 178 } 179 180 /// isNoAlias - A convenience wrapper. 181 bool isNoAlias(const Value *V1, uint64_t V1Size, 182 const Value *V2, uint64_t V2Size) { 183 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size)); 184 } 185 186 /// isMustAlias - A convenience wrapper. 187 bool isMustAlias(const Location &LocA, const Location &LocB) { 188 return alias(LocA, LocB) == MustAlias; 189 } 190 191 /// isMustAlias - A convenience wrapper. 192 bool isMustAlias(const Value *V1, const Value *V2) { 193 return alias(V1, 1, V2, 1) == MustAlias; 194 } 195 196 /// pointsToConstantMemory - If the specified memory location is 197 /// known to be constant, return true. If OrLocal is true and the 198 /// specified memory location is known to be "local" (derived from 199 /// an alloca), return true. Otherwise return false. 200 virtual bool pointsToConstantMemory(const Location &Loc, 201 bool OrLocal = false); 202 203 /// pointsToConstantMemory - A convenient wrapper. 204 bool pointsToConstantMemory(const Value *P, bool OrLocal = false) { 205 return pointsToConstantMemory(Location(P), OrLocal); 206 } 207 208 //===--------------------------------------------------------------------===// 209 /// Simple mod/ref information... 210 /// 211 212 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 213 /// bits which may be or'd together. 214 /// 215 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 216 217 /// These values define additional bits used to define the 218 /// ModRefBehavior values. 219 enum { Nowhere = 0, ArgumentPointees = 4, Anywhere = 8 | ArgumentPointees }; 220 221 /// ModRefBehavior - Summary of how a function affects memory in the program. 222 /// Loads from constant globals are not considered memory accesses for this 223 /// interface. Also, functions may freely modify stack space local to their 224 /// invocation without having to report it through these interfaces. 225 enum ModRefBehavior { 226 /// DoesNotAccessMemory - This function does not perform any non-local loads 227 /// or stores to memory. 228 /// 229 /// This property corresponds to the GCC 'const' attribute. 230 /// This property corresponds to the LLVM IR 'readnone' attribute. 231 /// This property corresponds to the IntrNoMem LLVM intrinsic flag. 232 DoesNotAccessMemory = Nowhere | NoModRef, 233 234 /// OnlyReadsArgumentPointees - The only memory references in this function 235 /// (if it has any) are non-volatile loads from objects pointed to by its 236 /// pointer-typed arguments, with arbitrary offsets. 237 /// 238 /// This property corresponds to the IntrReadArgMem LLVM intrinsic flag. 239 OnlyReadsArgumentPointees = ArgumentPointees | Ref, 240 241 /// OnlyAccessesArgumentPointees - The only memory references in this 242 /// function (if it has any) are non-volatile loads and stores from objects 243 /// pointed to by its pointer-typed arguments, with arbitrary offsets. 244 /// 245 /// This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag. 246 OnlyAccessesArgumentPointees = ArgumentPointees | ModRef, 247 248 /// OnlyReadsMemory - This function does not perform any non-local stores or 249 /// volatile loads, but may read from any memory location. 250 /// 251 /// This property corresponds to the GCC 'pure' attribute. 252 /// This property corresponds to the LLVM IR 'readonly' attribute. 253 /// This property corresponds to the IntrReadMem LLVM intrinsic flag. 254 OnlyReadsMemory = Anywhere | Ref, 255 256 /// UnknownModRefBehavior - This indicates that the function could not be 257 /// classified into one of the behaviors above. 258 UnknownModRefBehavior = Anywhere | ModRef 259 }; 260 261 /// getModRefBehavior - Return the behavior when calling the given call site. 262 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 263 264 /// getModRefBehavior - Return the behavior when calling the given function. 265 /// For use when the call site is not known. 266 virtual ModRefBehavior getModRefBehavior(const Function *F); 267 268 /// doesNotAccessMemory - If the specified call is known to never read or 269 /// write memory, return true. If the call only reads from known-constant 270 /// memory, it is also legal to return true. Calls that unwind the stack 271 /// are legal for this predicate. 272 /// 273 /// Many optimizations (such as CSE and LICM) can be performed on such calls 274 /// without worrying about aliasing properties, and many calls have this 275 /// property (e.g. calls to 'sin' and 'cos'). 276 /// 277 /// This property corresponds to the GCC 'const' attribute. 278 /// 279 bool doesNotAccessMemory(ImmutableCallSite CS) { 280 return getModRefBehavior(CS) == DoesNotAccessMemory; 281 } 282 283 /// doesNotAccessMemory - If the specified function is known to never read or 284 /// write memory, return true. For use when the call site is not known. 285 /// 286 bool doesNotAccessMemory(const Function *F) { 287 return getModRefBehavior(F) == DoesNotAccessMemory; 288 } 289 290 /// onlyReadsMemory - If the specified call is known to only read from 291 /// non-volatile memory (or not access memory at all), return true. Calls 292 /// that unwind the stack are legal for this predicate. 293 /// 294 /// This property allows many common optimizations to be performed in the 295 /// absence of interfering store instructions, such as CSE of strlen calls. 296 /// 297 /// This property corresponds to the GCC 'pure' attribute. 298 /// 299 bool onlyReadsMemory(ImmutableCallSite CS) { 300 return onlyReadsMemory(getModRefBehavior(CS)); 301 } 302 303 /// onlyReadsMemory - If the specified function is known to only read from 304 /// non-volatile memory (or not access memory at all), return true. For use 305 /// when the call site is not known. 306 /// 307 bool onlyReadsMemory(const Function *F) { 308 return onlyReadsMemory(getModRefBehavior(F)); 309 } 310 311 /// onlyReadsMemory - Return true if functions with the specified behavior are 312 /// known to only read from non-volatile memory (or not access memory at all). 313 /// 314 static bool onlyReadsMemory(ModRefBehavior MRB) { 315 return !(MRB & Mod); 316 } 317 318 /// onlyAccessesArgPointees - Return true if functions with the specified 319 /// behavior are known to read and write at most from objects pointed to by 320 /// their pointer-typed arguments (with arbitrary offsets). 321 /// 322 static bool onlyAccessesArgPointees(ModRefBehavior MRB) { 323 return !(MRB & Anywhere & ~ArgumentPointees); 324 } 325 326 /// doesAccessArgPointees - Return true if functions with the specified 327 /// behavior are known to potentially read or write from objects pointed 328 /// to be their pointer-typed arguments (with arbitrary offsets). 329 /// 330 static bool doesAccessArgPointees(ModRefBehavior MRB) { 331 return (MRB & ModRef) && (MRB & ArgumentPointees); 332 } 333 334 /// getModRefInfo - Return information about whether or not an instruction may 335 /// read or write the specified memory location. An instruction 336 /// that doesn't read or write memory may be trivially LICM'd for example. 337 ModRefResult getModRefInfo(const Instruction *I, 338 const Location &Loc) { 339 switch (I->getOpcode()) { 340 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc); 341 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc); 342 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc); 343 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc); 344 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc); 345 default: return NoModRef; 346 } 347 } 348 349 /// getModRefInfo - A convenience wrapper. 350 ModRefResult getModRefInfo(const Instruction *I, 351 const Value *P, uint64_t Size) { 352 return getModRefInfo(I, Location(P, Size)); 353 } 354 355 /// getModRefInfo (for call sites) - Return whether information about whether 356 /// a particular call site modifies or reads the specified memory location. 357 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 358 const Location &Loc); 359 360 /// getModRefInfo (for call sites) - A convenience wrapper. 361 ModRefResult getModRefInfo(ImmutableCallSite CS, 362 const Value *P, uint64_t Size) { 363 return getModRefInfo(CS, Location(P, Size)); 364 } 365 366 /// getModRefInfo (for calls) - Return whether information about whether 367 /// a particular call modifies or reads the specified memory location. 368 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) { 369 return getModRefInfo(ImmutableCallSite(C), Loc); 370 } 371 372 /// getModRefInfo (for calls) - A convenience wrapper. 373 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) { 374 return getModRefInfo(C, Location(P, Size)); 375 } 376 377 /// getModRefInfo (for invokes) - Return whether information about whether 378 /// a particular invoke modifies or reads the specified memory location. 379 ModRefResult getModRefInfo(const InvokeInst *I, 380 const Location &Loc) { 381 return getModRefInfo(ImmutableCallSite(I), Loc); 382 } 383 384 /// getModRefInfo (for invokes) - A convenience wrapper. 385 ModRefResult getModRefInfo(const InvokeInst *I, 386 const Value *P, uint64_t Size) { 387 return getModRefInfo(I, Location(P, Size)); 388 } 389 390 /// getModRefInfo (for loads) - Return whether information about whether 391 /// a particular load modifies or reads the specified memory location. 392 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc); 393 394 /// getModRefInfo (for loads) - A convenience wrapper. 395 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) { 396 return getModRefInfo(L, Location(P, Size)); 397 } 398 399 /// getModRefInfo (for stores) - Return whether information about whether 400 /// a particular store modifies or reads the specified memory location. 401 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc); 402 403 /// getModRefInfo (for stores) - A convenience wrapper. 404 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size){ 405 return getModRefInfo(S, Location(P, Size)); 406 } 407 408 /// getModRefInfo (for va_args) - Return whether information about whether 409 /// a particular va_arg modifies or reads the specified memory location. 410 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc); 411 412 /// getModRefInfo (for va_args) - A convenience wrapper. 413 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size){ 414 return getModRefInfo(I, Location(P, Size)); 415 } 416 417 /// getModRefInfo - Return information about whether two call sites may refer 418 /// to the same set of memory locations. See 419 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo 420 /// for details. 421 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 422 ImmutableCallSite CS2); 423 424 //===--------------------------------------------------------------------===// 425 /// Higher level methods for querying mod/ref information. 426 /// 427 428 /// canBasicBlockModify - Return true if it is possible for execution of the 429 /// specified basic block to modify the value pointed to by Ptr. 430 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc); 431 432 /// canBasicBlockModify - A convenience wrapper. 433 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){ 434 return canBasicBlockModify(BB, Location(P, Size)); 435 } 436 437 /// canInstructionRangeModify - Return true if it is possible for the 438 /// execution of the specified instructions to modify the value pointed to by 439 /// Ptr. The instructions to consider are all of the instructions in the 440 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 441 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 442 const Location &Loc); 443 444 /// canInstructionRangeModify - A convenience wrapper. 445 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 446 const Value *Ptr, uint64_t Size) { 447 return canInstructionRangeModify(I1, I2, Location(Ptr, Size)); 448 } 449 450 //===--------------------------------------------------------------------===// 451 /// Methods that clients should call when they transform the program to allow 452 /// alias analyses to update their internal data structures. Note that these 453 /// methods may be called on any instruction, regardless of whether or not 454 /// they have pointer-analysis implications. 455 /// 456 457 /// deleteValue - This method should be called whenever an LLVM Value is 458 /// deleted from the program, for example when an instruction is found to be 459 /// redundant and is eliminated. 460 /// 461 virtual void deleteValue(Value *V); 462 463 /// copyValue - This method should be used whenever a preexisting value in the 464 /// program is copied or cloned, introducing a new value. Note that analysis 465 /// implementations should tolerate clients that use this method to introduce 466 /// the same value multiple times: if the analysis already knows about a 467 /// value, it should ignore the request. 468 /// 469 virtual void copyValue(Value *From, Value *To); 470 471 /// addEscapingUse - This method should be used whenever an escaping use is 472 /// added to a pointer value. Analysis implementations may either return 473 /// conservative responses for that value in the future, or may recompute 474 /// some or all internal state to continue providing precise responses. 475 /// 476 /// Escaping uses are considered by anything _except_ the following: 477 /// - GEPs or bitcasts of the pointer 478 /// - Loads through the pointer 479 /// - Stores through (but not of) the pointer 480 virtual void addEscapingUse(Use &U); 481 482 /// replaceWithNewValue - This method is the obvious combination of the two 483 /// above, and it provided as a helper to simplify client code. 484 /// 485 void replaceWithNewValue(Value *Old, Value *New) { 486 copyValue(Old, New); 487 deleteValue(Old); 488 } 489}; 490 491/// isNoAliasCall - Return true if this pointer is returned by a noalias 492/// function. 493bool isNoAliasCall(const Value *V); 494 495/// isIdentifiedObject - Return true if this pointer refers to a distinct and 496/// identifiable object. This returns true for: 497/// Global Variables and Functions (but not Global Aliases) 498/// Allocas and Mallocs 499/// ByVal and NoAlias Arguments 500/// NoAlias returns 501/// 502bool isIdentifiedObject(const Value *V); 503 504} // End llvm namespace 505 506#endif 507