AliasAnalysis.h revision 8e78cc4e130a8773cc8a2be2a94c4a97317ac383
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#include <vector> 42 43namespace llvm { 44 45class LoadInst; 46class StoreInst; 47class VAArgInst; 48class TargetData; 49class Pass; 50class AnalysisUsage; 51 52class AliasAnalysis { 53protected: 54 const TargetData *TD; 55 56private: 57 AliasAnalysis *AA; // Previous Alias Analysis to chain to. 58 59protected: 60 /// InitializeAliasAnalysis - Subclasses must call this method to initialize 61 /// the AliasAnalysis interface before any other methods are called. This is 62 /// typically called by the run* methods of these subclasses. This may be 63 /// called multiple times. 64 /// 65 void InitializeAliasAnalysis(Pass *P); 66 67 /// getAnalysisUsage - All alias analysis implementations should invoke this 68 /// directly (using AliasAnalysis::getAnalysisUsage(AU)). 69 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 70 71public: 72 static char ID; // Class identification, replacement for typeinfo 73 AliasAnalysis() : TD(0), AA(0) {} 74 virtual ~AliasAnalysis(); // We want to be subclassed 75 76 /// UnknownSize - This is a special value which can be used with the 77 /// size arguments in alias queries to indicate that the caller does not 78 /// know the sizes of the potential memory references. 79 static uint64_t const UnknownSize = ~UINT64_C(0); 80 81 /// getTargetData - Return a pointer to the current TargetData object, or 82 /// null if no TargetData object is available. 83 /// 84 const TargetData *getTargetData() const { return TD; } 85 86 /// getTypeStoreSize - Return the TargetData store size for the given type, 87 /// if known, or a conservative value otherwise. 88 /// 89 uint64_t getTypeStoreSize(const Type *Ty); 90 91 //===--------------------------------------------------------------------===// 92 /// Alias Queries... 93 /// 94 95 /// Location - A description of a memory location. 96 struct Location { 97 /// Ptr - The address of the start of the location. 98 const Value *Ptr; 99 /// Size - The maximum size of the location, or UnknownSize if the size is 100 /// not known. Note that an unknown size does not mean the pointer aliases 101 /// the entire virtual address space, because there are restrictions on 102 /// stepping out of one object and into another. 103 /// See http://llvm.org/docs/LangRef.html#pointeraliasing 104 uint64_t Size; 105 /// TBAATag - The metadata node which describes the TBAA type of 106 /// the location, or null if there is no known unique tag. 107 const MDNode *TBAATag; 108 109 explicit Location(const Value *P = 0, 110 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 /// Alias analysis result - Either we know for sure that it does not alias, we 134 /// know for sure it must alias, or we don't know anything: The two pointers 135 /// _might_ alias. This enum is designed so you can do things like: 136 /// if (AA.alias(P1, P2)) { ... } 137 /// to check to see if two pointers might alias. 138 /// 139 /// See docs/AliasAnalysis.html for more information on the specific meanings 140 /// of these values. 141 /// 142 enum AliasResult { 143 NoAlias = 0, ///< No dependencies. 144 MayAlias = 1, ///< Anything goes. 145 MustAlias = 2 ///< Pointers are equal. 146 }; 147 148 /// alias - The main low level interface to the alias analysis implementation. 149 /// Returns an AliasResult indicating whether the two pointers are aliased to 150 /// each other. This is the interface that must be implemented by specific 151 /// alias analysis implementations. 152 virtual AliasResult alias(const Location &LocA, const Location &LocB); 153 154 /// alias - A convenience wrapper. 155 AliasResult alias(const Value *V1, uint64_t V1Size, 156 const Value *V2, uint64_t V2Size) { 157 return alias(Location(V1, V1Size), Location(V2, V2Size)); 158 } 159 160 /// alias - A convenience wrapper. 161 AliasResult alias(const Value *V1, const Value *V2) { 162 return alias(V1, UnknownSize, V2, UnknownSize); 163 } 164 165 /// isNoAlias - A trivial helper function to check to see if the specified 166 /// pointers are no-alias. 167 bool isNoAlias(const Location &LocA, const Location &LocB) { 168 return alias(LocA, LocB) == NoAlias; 169 } 170 171 /// isNoAlias - A convenience wrapper. 172 bool isNoAlias(const Value *V1, uint64_t V1Size, 173 const Value *V2, uint64_t V2Size) { 174 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size)); 175 } 176 177 /// pointsToConstantMemory - If the specified memory location is 178 /// known to be constant, return true. If OrLocal is true and the 179 /// specified memory location is known to be "local" (derived from 180 /// an alloca), return true. Otherwise return false. 181 virtual bool pointsToConstantMemory(const Location &Loc, 182 bool OrLocal = false); 183 184 /// pointsToConstantMemory - A convenient wrapper. 185 bool pointsToConstantMemory(const Value *P, bool OrLocal = false) { 186 return pointsToConstantMemory(Location(P), OrLocal); 187 } 188 189 //===--------------------------------------------------------------------===// 190 /// Simple mod/ref information... 191 /// 192 193 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 194 /// bits which may be or'd together. 195 /// 196 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 197 198 /// These values define additional bits used to define the 199 /// ModRefBehavior values. 200 enum { Nowhere = 0, ArgumentPointees = 4, Anywhere = 8 | ArgumentPointees }; 201 202 /// ModRefBehavior - Summary of how a function affects memory in the program. 203 /// Loads from constant globals are not considered memory accesses for this 204 /// interface. Also, functions may freely modify stack space local to their 205 /// invocation without having to report it through these interfaces. 206 enum ModRefBehavior { 207 /// DoesNotAccessMemory - This function does not perform any non-local loads 208 /// or stores to memory. 209 /// 210 /// This property corresponds to the GCC 'const' attribute. 211 /// This property corresponds to the LLVM IR 'readnone' attribute. 212 /// This property corresponds to the IntrNoMem LLVM intrinsic flag. 213 DoesNotAccessMemory = Nowhere | NoModRef, 214 215 /// OnlyReadsArgumentPointees - The only memory references in this function 216 /// (if it has any) are non-volatile loads from objects pointed to by its 217 /// pointer-typed arguments, with arbitrary offsets. 218 /// 219 /// This property corresponds to the IntrReadArgMem LLVM intrinsic flag. 220 OnlyReadsArgumentPointees = ArgumentPointees | Ref, 221 222 /// OnlyAccessesArgumentPointees - The only memory references in this 223 /// function (if it has any) are non-volatile loads and stores from objects 224 /// pointed to by its pointer-typed arguments, with arbitrary offsets. 225 /// 226 /// This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag. 227 OnlyAccessesArgumentPointees = ArgumentPointees | ModRef, 228 229 /// OnlyReadsMemory - This function does not perform any non-local stores or 230 /// volatile loads, but may read from any memory location. 231 /// 232 /// This property corresponds to the GCC 'pure' attribute. 233 /// This property corresponds to the LLVM IR 'readonly' attribute. 234 /// This property corresponds to the IntrReadMem LLVM intrinsic flag. 235 OnlyReadsMemory = Anywhere | Ref, 236 237 /// UnknownModRefBehavior - This indicates that the function could not be 238 /// classified into one of the behaviors above. 239 UnknownModRefBehavior = Anywhere | ModRef 240 }; 241 242 /// getModRefBehavior - Return the behavior when calling the given call site. 243 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 244 245 /// getModRefBehavior - Return the behavior when calling the given function. 246 /// For use when the call site is not known. 247 virtual ModRefBehavior getModRefBehavior(const Function *F); 248 249 /// doesNotAccessMemory - If the specified call is known to never read or 250 /// write memory, return true. If the call only reads from known-constant 251 /// memory, it is also legal to return true. Calls that unwind the stack 252 /// are legal for this predicate. 253 /// 254 /// Many optimizations (such as CSE and LICM) can be performed on such calls 255 /// without worrying about aliasing properties, and many calls have this 256 /// property (e.g. calls to 'sin' and 'cos'). 257 /// 258 /// This property corresponds to the GCC 'const' attribute. 259 /// 260 bool doesNotAccessMemory(ImmutableCallSite CS) { 261 return getModRefBehavior(CS) == DoesNotAccessMemory; 262 } 263 264 /// doesNotAccessMemory - If the specified function is known to never read or 265 /// write memory, return true. For use when the call site is not known. 266 /// 267 bool doesNotAccessMemory(const Function *F) { 268 return getModRefBehavior(F) == DoesNotAccessMemory; 269 } 270 271 /// onlyReadsMemory - If the specified call is known to only read from 272 /// non-volatile memory (or not access memory at all), return true. Calls 273 /// that unwind the stack are legal for this predicate. 274 /// 275 /// This property allows many common optimizations to be performed in the 276 /// absence of interfering store instructions, such as CSE of strlen calls. 277 /// 278 /// This property corresponds to the GCC 'pure' attribute. 279 /// 280 bool onlyReadsMemory(ImmutableCallSite CS) { 281 return onlyReadsMemory(getModRefBehavior(CS)); 282 } 283 284 /// onlyReadsMemory - If the specified function is known to only read from 285 /// non-volatile memory (or not access memory at all), return true. For use 286 /// when the call site is not known. 287 /// 288 bool onlyReadsMemory(const Function *F) { 289 return onlyReadsMemory(getModRefBehavior(F)); 290 } 291 292 /// onlyReadsMemory - Return true if functions with the specified behavior are 293 /// known to only read from non-volatile memory (or not access memory at all). 294 /// 295 static bool onlyReadsMemory(ModRefBehavior MRB) { 296 return !(MRB & Mod); 297 } 298 299 /// onlyAccessesArgPointees - Return true if functions with the specified 300 /// behavior are known to read and write at most from objects pointed to by 301 /// their pointer-typed arguments (with arbitrary offsets). 302 /// 303 static bool onlyAccessesArgPointees(ModRefBehavior MRB) { 304 return !(MRB & Anywhere & ~ArgumentPointees); 305 } 306 307 /// doesAccessArgPointees - Return true if functions with the specified 308 /// behavior are known to potentially read or write from objects pointed 309 /// to be their pointer-typed arguments (with arbitrary offsets). 310 /// 311 static bool doesAccessArgPointees(ModRefBehavior MRB) { 312 return (MRB & ModRef) && (MRB & ArgumentPointees); 313 } 314 315 /// getModRefInfo - Return information about whether or not an instruction may 316 /// read or write the specified memory location. An instruction 317 /// that doesn't read or write memory may be trivially LICM'd for example. 318 ModRefResult getModRefInfo(const Instruction *I, 319 const Location &Loc) { 320 switch (I->getOpcode()) { 321 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc); 322 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc); 323 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc); 324 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc); 325 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc); 326 default: return NoModRef; 327 } 328 } 329 330 /// getModRefInfo - A convenience wrapper. 331 ModRefResult getModRefInfo(const Instruction *I, 332 const Value *P, uint64_t Size) { 333 return getModRefInfo(I, Location(P, Size)); 334 } 335 336 /// getModRefInfo (for call sites) - Return whether information about whether 337 /// a particular call site modifies or reads the specified memory location. 338 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 339 const Location &Loc); 340 341 /// getModRefInfo (for call sites) - A convenience wrapper. 342 ModRefResult getModRefInfo(ImmutableCallSite CS, 343 const Value *P, uint64_t Size) { 344 return getModRefInfo(CS, Location(P, Size)); 345 } 346 347 /// getModRefInfo (for calls) - Return whether information about whether 348 /// a particular call modifies or reads the specified memory location. 349 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) { 350 return getModRefInfo(ImmutableCallSite(C), Loc); 351 } 352 353 /// getModRefInfo (for calls) - A convenience wrapper. 354 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) { 355 return getModRefInfo(C, Location(P, Size)); 356 } 357 358 /// getModRefInfo (for invokes) - Return whether information about whether 359 /// a particular invoke modifies or reads the specified memory location. 360 ModRefResult getModRefInfo(const InvokeInst *I, 361 const Location &Loc) { 362 return getModRefInfo(ImmutableCallSite(I), Loc); 363 } 364 365 /// getModRefInfo (for invokes) - A convenience wrapper. 366 ModRefResult getModRefInfo(const InvokeInst *I, 367 const Value *P, uint64_t Size) { 368 return getModRefInfo(I, Location(P, Size)); 369 } 370 371 /// getModRefInfo (for loads) - Return whether information about whether 372 /// a particular load modifies or reads the specified memory location. 373 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc); 374 375 /// getModRefInfo (for loads) - A convenience wrapper. 376 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) { 377 return getModRefInfo(L, Location(P, Size)); 378 } 379 380 /// getModRefInfo (for stores) - Return whether information about whether 381 /// a particular store modifies or reads the specified memory location. 382 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc); 383 384 /// getModRefInfo (for stores) - A convenience wrapper. 385 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) { 386 return getModRefInfo(S, Location(P, Size)); 387 } 388 389 /// getModRefInfo (for va_args) - Return whether information about whether 390 /// a particular va_arg modifies or reads the specified memory location. 391 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc); 392 393 /// getModRefInfo (for va_args) - A convenience wrapper. 394 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) { 395 return getModRefInfo(I, Location(P, Size)); 396 } 397 398 /// getModRefInfo - Return information about whether two call sites may refer 399 /// to the same set of memory locations. See 400 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo 401 /// for details. 402 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 403 ImmutableCallSite CS2); 404 405 //===--------------------------------------------------------------------===// 406 /// Higher level methods for querying mod/ref information. 407 /// 408 409 /// canBasicBlockModify - Return true if it is possible for execution of the 410 /// specified basic block to modify the value pointed to by Ptr. 411 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc); 412 413 /// canBasicBlockModify - A convenience wrapper. 414 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){ 415 return canBasicBlockModify(BB, Location(P, Size)); 416 } 417 418 /// canInstructionRangeModify - Return true if it is possible for the 419 /// execution of the specified instructions to modify the value pointed to by 420 /// Ptr. The instructions to consider are all of the instructions in the 421 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 422 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 423 const Location &Loc); 424 425 /// canInstructionRangeModify - A convenience wrapper. 426 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 427 const Value *Ptr, uint64_t Size) { 428 return canInstructionRangeModify(I1, I2, Location(Ptr, Size)); 429 } 430 431 //===--------------------------------------------------------------------===// 432 /// Methods that clients should call when they transform the program to allow 433 /// alias analyses to update their internal data structures. Note that these 434 /// methods may be called on any instruction, regardless of whether or not 435 /// they have pointer-analysis implications. 436 /// 437 438 /// deleteValue - This method should be called whenever an LLVM Value is 439 /// deleted from the program, for example when an instruction is found to be 440 /// redundant and is eliminated. 441 /// 442 virtual void deleteValue(Value *V); 443 444 /// copyValue - This method should be used whenever a preexisting value in the 445 /// program is copied or cloned, introducing a new value. Note that analysis 446 /// implementations should tolerate clients that use this method to introduce 447 /// the same value multiple times: if the analysis already knows about a 448 /// value, it should ignore the request. 449 /// 450 virtual void copyValue(Value *From, Value *To); 451 452 /// replaceWithNewValue - This method is the obvious combination of the two 453 /// above, and it provided as a helper to simplify client code. 454 /// 455 void replaceWithNewValue(Value *Old, Value *New) { 456 copyValue(Old, New); 457 deleteValue(Old); 458 } 459}; 460 461/// isNoAliasCall - Return true if this pointer is returned by a noalias 462/// function. 463bool isNoAliasCall(const Value *V); 464 465/// isIdentifiedObject - Return true if this pointer refers to a distinct and 466/// identifiable object. This returns true for: 467/// Global Variables and Functions (but not Global Aliases) 468/// Allocas and Mallocs 469/// ByVal and NoAlias Arguments 470/// NoAlias returns 471/// 472bool isIdentifiedObject(const Value *V); 473 474} // End llvm namespace 475 476#endif 477