AliasAnalysis.h revision 902da265f684b00b76c669c2a7cbc0f209cda187
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 }; 177 178 179 /// ModRefBehavior - Summary of how a function affects memory in the program. 180 /// Loads from constant globals are not considered memory accesses for this 181 /// interface. Also, functions may freely modify stack space local to their 182 /// invocation without having to report it through these interfaces. 183 enum ModRefBehavior { 184 // DoesNotAccessMemory - This function does not perform any non-local loads 185 // or stores to memory. 186 // 187 // This property corresponds to the GCC 'const' attribute. 188 // This property corresponds to the LLVM IR 'readnone' attribute. 189 // This property corresponds to the IntrNoMem LLVM intrinsic flag. 190 DoesNotAccessMemory, 191 192 // AccessesArguments - This function accesses function arguments in well 193 // known (possibly volatile) ways, but does not access any other memory. 194 // 195 // This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag. 196 AccessesArguments, 197 198 // AccessesArgumentsAndGlobals - This function has accesses function 199 // arguments and global variables well known (possibly volatile) ways, but 200 // does not access any other memory. 201 AccessesArgumentsAndGlobals, 202 203 // OnlyReadsMemory - This function does not perform any non-local stores or 204 // volatile loads, but may read from any memory location. 205 // 206 // This property corresponds to the GCC 'pure' attribute. 207 // This property corresponds to the LLVM IR 'readonly' attribute. 208 // This property corresponds to the IntrReadMem LLVM intrinsic flag. 209 OnlyReadsMemory, 210 211 // UnknownModRefBehavior - This indicates that the function could not be 212 // classified into one of the behaviors above. 213 UnknownModRefBehavior 214 }; 215 216 /// getModRefBehavior - Return the behavior when calling the given call site. 217 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 218 219 /// getModRefBehavior - Return the behavior when calling the given function. 220 /// For use when the call site is not known. 221 virtual ModRefBehavior getModRefBehavior(const Function *F); 222 223 /// doesNotAccessMemory - If the specified call is known to never read or 224 /// write memory, return true. If the call only reads from known-constant 225 /// memory, it is also legal to return true. Calls that unwind the stack 226 /// are legal for this predicate. 227 /// 228 /// Many optimizations (such as CSE and LICM) can be performed on such calls 229 /// without worrying about aliasing properties, and many calls have this 230 /// property (e.g. calls to 'sin' and 'cos'). 231 /// 232 /// This property corresponds to the GCC 'const' attribute. 233 /// 234 bool doesNotAccessMemory(ImmutableCallSite CS) { 235 return getModRefBehavior(CS) == DoesNotAccessMemory; 236 } 237 238 /// doesNotAccessMemory - If the specified function is known to never read or 239 /// write memory, return true. For use when the call site is not known. 240 /// 241 bool doesNotAccessMemory(const Function *F) { 242 return getModRefBehavior(F) == DoesNotAccessMemory; 243 } 244 245 /// onlyReadsMemory - If the specified call is known to only read from 246 /// non-volatile memory (or not access memory at all), return true. Calls 247 /// that unwind the stack are legal for this predicate. 248 /// 249 /// This property allows many common optimizations to be performed in the 250 /// absence of interfering store instructions, such as CSE of strlen calls. 251 /// 252 /// This property corresponds to the GCC 'pure' attribute. 253 /// 254 bool onlyReadsMemory(ImmutableCallSite CS) { 255 ModRefBehavior MRB = getModRefBehavior(CS); 256 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 257 } 258 259 /// onlyReadsMemory - If the specified function is known to only read from 260 /// non-volatile memory (or not access memory at all), return true. For use 261 /// when the call site is not known. 262 /// 263 bool onlyReadsMemory(const Function *F) { 264 ModRefBehavior MRB = getModRefBehavior(F); 265 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 266 } 267 268 269 /// getModRefInfo - Return information about whether or not an instruction may 270 /// read or write the specified memory location. An instruction 271 /// that doesn't read or write memory may be trivially LICM'd for example. 272 ModRefResult getModRefInfo(const Instruction *I, 273 const Location &Loc) { 274 switch (I->getOpcode()) { 275 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc); 276 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc); 277 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc); 278 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc); 279 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc); 280 default: return NoModRef; 281 } 282 } 283 284 /// getModRefInfo - A convenience wrapper. 285 ModRefResult getModRefInfo(const Instruction *I, 286 const Value *P, uint64_t Size) { 287 return getModRefInfo(I, Location(P, Size)); 288 } 289 290 /// getModRefInfo (for call sites) - Return whether information about whether 291 /// a particular call site modifies or reads the specified memory location. 292 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 293 const Location &Loc); 294 295 /// getModRefInfo (for call sites) - A convenience wrapper. 296 ModRefResult getModRefInfo(ImmutableCallSite CS, 297 const Value *P, uint64_t Size) { 298 return getModRefInfo(CS, Location(P, Size)); 299 } 300 301 /// getModRefInfo (for calls) - Return whether information about whether 302 /// a particular call modifies or reads the specified memory location. 303 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) { 304 return getModRefInfo(ImmutableCallSite(C), Loc); 305 } 306 307 /// getModRefInfo (for calls) - A convenience wrapper. 308 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) { 309 return getModRefInfo(C, Location(P, Size)); 310 } 311 312 /// getModRefInfo (for invokes) - Return whether information about whether 313 /// a particular invoke modifies or reads the specified memory location. 314 ModRefResult getModRefInfo(const InvokeInst *I, 315 const Location &Loc) { 316 return getModRefInfo(ImmutableCallSite(I), Loc); 317 } 318 319 /// getModRefInfo (for invokes) - A convenience wrapper. 320 ModRefResult getModRefInfo(const InvokeInst *I, 321 const Value *P, uint64_t Size) { 322 return getModRefInfo(I, Location(P, Size)); 323 } 324 325 /// getModRefInfo (for loads) - Return whether information about whether 326 /// a particular load modifies or reads the specified memory location. 327 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc); 328 329 /// getModRefInfo (for loads) - A convenience wrapper. 330 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) { 331 return getModRefInfo(L, Location(P, Size)); 332 } 333 334 /// getModRefInfo (for stores) - Return whether information about whether 335 /// a particular store modifies or reads the specified memory location. 336 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc); 337 338 /// getModRefInfo (for stores) - A convenience wrapper. 339 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) { 340 return getModRefInfo(S, Location(P, Size)); 341 } 342 343 /// getModRefInfo (for va_args) - Return whether information about whether 344 /// a particular va_arg modifies or reads the specified memory location. 345 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc); 346 347 /// getModRefInfo (for va_args) - A convenience wrapper. 348 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) { 349 return getModRefInfo(I, Location(P, Size)); 350 } 351 352 /// getModRefInfo - Return information about whether two call sites may refer 353 /// to the same set of memory locations. See 354 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo 355 /// for details. 356 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 357 ImmutableCallSite CS2); 358 359 //===--------------------------------------------------------------------===// 360 /// Higher level methods for querying mod/ref information. 361 /// 362 363 /// canBasicBlockModify - Return true if it is possible for execution of the 364 /// specified basic block to modify the value pointed to by Ptr. 365 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc); 366 367 /// canBasicBlockModify - A convenience wrapper. 368 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){ 369 return canBasicBlockModify(BB, Location(P, Size)); 370 } 371 372 /// canInstructionRangeModify - Return true if it is possible for the 373 /// execution of the specified instructions to modify the value pointed to by 374 /// Ptr. The instructions to consider are all of the instructions in the 375 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 376 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 377 const Location &Loc); 378 379 /// canInstructionRangeModify - A convenience wrapper. 380 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 381 const Value *Ptr, uint64_t Size) { 382 return canInstructionRangeModify(I1, I2, Location(Ptr, Size)); 383 } 384 385 //===--------------------------------------------------------------------===// 386 /// Methods that clients should call when they transform the program to allow 387 /// alias analyses to update their internal data structures. Note that these 388 /// methods may be called on any instruction, regardless of whether or not 389 /// they have pointer-analysis implications. 390 /// 391 392 /// deleteValue - This method should be called whenever an LLVM Value is 393 /// deleted from the program, for example when an instruction is found to be 394 /// redundant and is eliminated. 395 /// 396 virtual void deleteValue(Value *V); 397 398 /// copyValue - This method should be used whenever a preexisting value in the 399 /// program is copied or cloned, introducing a new value. Note that analysis 400 /// implementations should tolerate clients that use this method to introduce 401 /// the same value multiple times: if the analysis already knows about a 402 /// value, it should ignore the request. 403 /// 404 virtual void copyValue(Value *From, Value *To); 405 406 /// replaceWithNewValue - This method is the obvious combination of the two 407 /// above, and it provided as a helper to simplify client code. 408 /// 409 void replaceWithNewValue(Value *Old, Value *New) { 410 copyValue(Old, New); 411 deleteValue(Old); 412 } 413}; 414 415/// isNoAliasCall - Return true if this pointer is returned by a noalias 416/// function. 417bool isNoAliasCall(const Value *V); 418 419/// isIdentifiedObject - Return true if this pointer refers to a distinct and 420/// identifiable object. This returns true for: 421/// Global Variables and Functions (but not Global Aliases) 422/// Allocas and Mallocs 423/// ByVal and NoAlias Arguments 424/// NoAlias returns 425/// 426bool isIdentifiedObject(const Value *V); 427 428} // End llvm namespace 429 430#endif 431