AliasAnalysis.h revision 075fb5d68fcb55d26e44c48f07dfdbbfa21ccb2a
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 getWithNewSize(uint64_t NewSize) const { 111 Location Copy(*this); 112 Copy.Size = NewSize; 113 return Copy; 114 } 115 116 Location getWithoutTBAATag() const { 117 Location Copy(*this); 118 Copy.TBAATag = 0; 119 return Copy; 120 } 121 }; 122 123 /// Alias analysis result - Either we know for sure that it does not alias, we 124 /// know for sure it must alias, or we don't know anything: The two pointers 125 /// _might_ alias. This enum is designed so you can do things like: 126 /// if (AA.alias(P1, P2)) { ... } 127 /// to check to see if two pointers might alias. 128 /// 129 /// See docs/AliasAnalysis.html for more information on the specific meanings 130 /// of these values. 131 /// 132 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 133 134 /// alias - The main low level interface to the alias analysis implementation. 135 /// Returns an AliasResult indicating whether the two pointers are aliased to 136 /// each other. This is the interface that must be implemented by specific 137 /// alias analysis implementations. 138 virtual AliasResult alias(const Location &LocA, const Location &LocB); 139 140 /// alias - A convenience wrapper. 141 AliasResult alias(const Value *V1, uint64_t V1Size, 142 const Value *V2, uint64_t V2Size) { 143 return alias(Location(V1, V1Size), Location(V2, V2Size)); 144 } 145 146 /// alias - A convenience wrapper. 147 AliasResult alias(const Value *V1, const Value *V2) { 148 return alias(V1, UnknownSize, V2, UnknownSize); 149 } 150 151 /// isNoAlias - A trivial helper function to check to see if the specified 152 /// pointers are no-alias. 153 bool isNoAlias(const Location &LocA, const Location &LocB) { 154 return alias(LocA, LocB) == NoAlias; 155 } 156 157 /// isNoAlias - A convenience wrapper. 158 bool isNoAlias(const Value *V1, uint64_t V1Size, 159 const Value *V2, uint64_t V2Size) { 160 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size)); 161 } 162 163 /// pointsToConstantMemory - If the specified memory location is 164 /// known to be constant, return true. If OrLocal is true and the 165 /// specified memory location is known to be "local" (derived from 166 /// an alloca), return true. Otherwise return false. 167 virtual bool pointsToConstantMemory(const Location &Loc, 168 bool OrLocal = false); 169 170 /// pointsToConstantMemory - A convenient wrapper. 171 bool pointsToConstantMemory(const Value *P, bool OrLocal = false) { 172 return pointsToConstantMemory(Location(P), OrLocal); 173 } 174 175 //===--------------------------------------------------------------------===// 176 /// Simple mod/ref information... 177 /// 178 179 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 180 /// bits which may be or'd together. 181 /// 182 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 183 184 /// These values define additional bits used to define the 185 /// ModRefBehavior values. 186 enum { Nowhere = 0, ArgumentPointees = 4, Anywhere = 8 | ArgumentPointees }; 187 188 /// ModRefBehavior - Summary of how a function affects memory in the program. 189 /// Loads from constant globals are not considered memory accesses for this 190 /// interface. Also, functions may freely modify stack space local to their 191 /// invocation without having to report it through these interfaces. 192 enum ModRefBehavior { 193 /// DoesNotAccessMemory - This function does not perform any non-local loads 194 /// or stores to memory. 195 /// 196 /// This property corresponds to the GCC 'const' attribute. 197 /// This property corresponds to the LLVM IR 'readnone' attribute. 198 /// This property corresponds to the IntrNoMem LLVM intrinsic flag. 199 DoesNotAccessMemory = Nowhere | NoModRef, 200 201 /// OnlyReadsArgumentPointees - The only memory references in this function 202 /// (if it has any) are non-volatile loads from objects pointed to by its 203 /// pointer-typed arguments, with arbitrary offsets. 204 /// 205 /// This property corresponds to the IntrReadArgMem LLVM intrinsic flag. 206 OnlyReadsArgumentPointees = ArgumentPointees | Ref, 207 208 /// OnlyAccessesArgumentPointees - The only memory references in this 209 /// function (if it has any) are non-volatile loads and stores from objects 210 /// pointed to by its pointer-typed arguments, with arbitrary offsets. 211 /// 212 /// This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag. 213 OnlyAccessesArgumentPointees = ArgumentPointees | ModRef, 214 215 /// OnlyReadsMemory - This function does not perform any non-local stores or 216 /// volatile loads, but may read from any memory location. 217 /// 218 /// This property corresponds to the GCC 'pure' attribute. 219 /// This property corresponds to the LLVM IR 'readonly' attribute. 220 /// This property corresponds to the IntrReadMem LLVM intrinsic flag. 221 OnlyReadsMemory = Anywhere | Ref, 222 223 /// UnknownModRefBehavior - This indicates that the function could not be 224 /// classified into one of the behaviors above. 225 UnknownModRefBehavior = Anywhere | ModRef 226 }; 227 228 /// getModRefBehavior - Return the behavior when calling the given call site. 229 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 230 231 /// getModRefBehavior - Return the behavior when calling the given function. 232 /// For use when the call site is not known. 233 virtual ModRefBehavior getModRefBehavior(const Function *F); 234 235 /// doesNotAccessMemory - If the specified call is known to never read or 236 /// write memory, return true. If the call only reads from known-constant 237 /// memory, it is also legal to return true. Calls that unwind the stack 238 /// are legal for this predicate. 239 /// 240 /// Many optimizations (such as CSE and LICM) can be performed on such calls 241 /// without worrying about aliasing properties, and many calls have this 242 /// property (e.g. calls to 'sin' and 'cos'). 243 /// 244 /// This property corresponds to the GCC 'const' attribute. 245 /// 246 bool doesNotAccessMemory(ImmutableCallSite CS) { 247 return getModRefBehavior(CS) == DoesNotAccessMemory; 248 } 249 250 /// doesNotAccessMemory - If the specified function is known to never read or 251 /// write memory, return true. For use when the call site is not known. 252 /// 253 bool doesNotAccessMemory(const Function *F) { 254 return getModRefBehavior(F) == DoesNotAccessMemory; 255 } 256 257 /// onlyReadsMemory - If the specified call is known to only read from 258 /// non-volatile memory (or not access memory at all), return true. Calls 259 /// that unwind the stack are legal for this predicate. 260 /// 261 /// This property allows many common optimizations to be performed in the 262 /// absence of interfering store instructions, such as CSE of strlen calls. 263 /// 264 /// This property corresponds to the GCC 'pure' attribute. 265 /// 266 bool onlyReadsMemory(ImmutableCallSite CS) { 267 return onlyReadsMemory(getModRefBehavior(CS)); 268 } 269 270 /// onlyReadsMemory - If the specified function is known to only read from 271 /// non-volatile memory (or not access memory at all), return true. For use 272 /// when the call site is not known. 273 /// 274 bool onlyReadsMemory(const Function *F) { 275 return onlyReadsMemory(getModRefBehavior(F)); 276 } 277 278 /// onlyReadsMemory - Return true if functions with the specified behavior are 279 /// known to only read from non-volatile memory (or not access memory at all). 280 /// 281 static bool onlyReadsMemory(ModRefBehavior MRB) { 282 return !(MRB & Mod); 283 } 284 285 /// onlyAccessesArgPointees - Return true if functions with the specified 286 /// behavior are known to read and write at most from objects pointed to by 287 /// their pointer-typed arguments (with arbitrary offsets). 288 /// 289 static bool onlyAccessesArgPointees(ModRefBehavior MRB) { 290 return !(MRB & Anywhere & ~ArgumentPointees); 291 } 292 293 /// doesAccessArgPointees - Return true if functions with the specified 294 /// behavior are known to potentially read or write from objects pointed 295 /// to be their pointer-typed arguments (with arbitrary offsets). 296 /// 297 static bool doesAccessArgPointees(ModRefBehavior MRB) { 298 return (MRB & ModRef) && (MRB & ArgumentPointees); 299 } 300 301 /// getModRefInfo - Return information about whether or not an instruction may 302 /// read or write the specified memory location. An instruction 303 /// that doesn't read or write memory may be trivially LICM'd for example. 304 ModRefResult getModRefInfo(const Instruction *I, 305 const Location &Loc) { 306 switch (I->getOpcode()) { 307 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc); 308 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc); 309 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc); 310 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc); 311 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc); 312 default: return NoModRef; 313 } 314 } 315 316 /// getModRefInfo - A convenience wrapper. 317 ModRefResult getModRefInfo(const Instruction *I, 318 const Value *P, uint64_t Size) { 319 return getModRefInfo(I, Location(P, Size)); 320 } 321 322 /// getModRefInfo (for call sites) - Return whether information about whether 323 /// a particular call site modifies or reads the specified memory location. 324 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 325 const Location &Loc); 326 327 /// getModRefInfo (for call sites) - A convenience wrapper. 328 ModRefResult getModRefInfo(ImmutableCallSite CS, 329 const Value *P, uint64_t Size) { 330 return getModRefInfo(CS, Location(P, Size)); 331 } 332 333 /// getModRefInfo (for calls) - Return whether information about whether 334 /// a particular call modifies or reads the specified memory location. 335 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) { 336 return getModRefInfo(ImmutableCallSite(C), Loc); 337 } 338 339 /// getModRefInfo (for calls) - A convenience wrapper. 340 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) { 341 return getModRefInfo(C, Location(P, Size)); 342 } 343 344 /// getModRefInfo (for invokes) - Return whether information about whether 345 /// a particular invoke modifies or reads the specified memory location. 346 ModRefResult getModRefInfo(const InvokeInst *I, 347 const Location &Loc) { 348 return getModRefInfo(ImmutableCallSite(I), Loc); 349 } 350 351 /// getModRefInfo (for invokes) - A convenience wrapper. 352 ModRefResult getModRefInfo(const InvokeInst *I, 353 const Value *P, uint64_t Size) { 354 return getModRefInfo(I, Location(P, Size)); 355 } 356 357 /// getModRefInfo (for loads) - Return whether information about whether 358 /// a particular load modifies or reads the specified memory location. 359 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc); 360 361 /// getModRefInfo (for loads) - A convenience wrapper. 362 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) { 363 return getModRefInfo(L, Location(P, Size)); 364 } 365 366 /// getModRefInfo (for stores) - Return whether information about whether 367 /// a particular store modifies or reads the specified memory location. 368 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc); 369 370 /// getModRefInfo (for stores) - A convenience wrapper. 371 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) { 372 return getModRefInfo(S, Location(P, Size)); 373 } 374 375 /// getModRefInfo (for va_args) - Return whether information about whether 376 /// a particular va_arg modifies or reads the specified memory location. 377 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc); 378 379 /// getModRefInfo (for va_args) - A convenience wrapper. 380 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) { 381 return getModRefInfo(I, Location(P, Size)); 382 } 383 384 /// getModRefInfo - Return information about whether two call sites may refer 385 /// to the same set of memory locations. See 386 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo 387 /// for details. 388 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 389 ImmutableCallSite CS2); 390 391 //===--------------------------------------------------------------------===// 392 /// Higher level methods for querying mod/ref information. 393 /// 394 395 /// canBasicBlockModify - Return true if it is possible for execution of the 396 /// specified basic block to modify the value pointed to by Ptr. 397 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc); 398 399 /// canBasicBlockModify - A convenience wrapper. 400 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){ 401 return canBasicBlockModify(BB, Location(P, Size)); 402 } 403 404 /// canInstructionRangeModify - Return true if it is possible for the 405 /// execution of the specified instructions to modify the value pointed to by 406 /// Ptr. The instructions to consider are all of the instructions in the 407 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 408 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 409 const Location &Loc); 410 411 /// canInstructionRangeModify - A convenience wrapper. 412 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 413 const Value *Ptr, uint64_t Size) { 414 return canInstructionRangeModify(I1, I2, Location(Ptr, Size)); 415 } 416 417 //===--------------------------------------------------------------------===// 418 /// Methods that clients should call when they transform the program to allow 419 /// alias analyses to update their internal data structures. Note that these 420 /// methods may be called on any instruction, regardless of whether or not 421 /// they have pointer-analysis implications. 422 /// 423 424 /// deleteValue - This method should be called whenever an LLVM Value is 425 /// deleted from the program, for example when an instruction is found to be 426 /// redundant and is eliminated. 427 /// 428 virtual void deleteValue(Value *V); 429 430 /// copyValue - This method should be used whenever a preexisting value in the 431 /// program is copied or cloned, introducing a new value. Note that analysis 432 /// implementations should tolerate clients that use this method to introduce 433 /// the same value multiple times: if the analysis already knows about a 434 /// value, it should ignore the request. 435 /// 436 virtual void copyValue(Value *From, Value *To); 437 438 /// replaceWithNewValue - This method is the obvious combination of the two 439 /// above, and it provided as a helper to simplify client code. 440 /// 441 void replaceWithNewValue(Value *Old, Value *New) { 442 copyValue(Old, New); 443 deleteValue(Old); 444 } 445}; 446 447/// isNoAliasCall - Return true if this pointer is returned by a noalias 448/// function. 449bool isNoAliasCall(const Value *V); 450 451/// isIdentifiedObject - Return true if this pointer refers to a distinct and 452/// identifiable object. This returns true for: 453/// Global Variables and Functions (but not Global Aliases) 454/// Allocas and Mallocs 455/// ByVal and NoAlias Arguments 456/// NoAlias returns 457/// 458bool isIdentifiedObject(const Value *V); 459 460} // End llvm namespace 461 462#endif 463