AliasAnalysis.h revision db4708cf86cece22539ff022cc0601612dd02ead
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 size of the location. 90 uint64_t Size; 91 /// TBAATag - The metadata node which describes the TBAA type of 92 /// the location, or null if there is no (unique) tag. 93 const MDNode *TBAATag; 94 95 explicit Location(const Value *P = 0, 96 uint64_t S = UnknownSize, 97 const MDNode *N = 0) 98 : Ptr(P), Size(S), TBAATag(N) {} 99 100 Location getWithNewPtr(const Value *NewPtr) const { 101 Location Copy(*this); 102 Copy.Ptr = NewPtr; 103 return Copy; 104 } 105 106 Location getWithoutTBAATag() const { 107 Location Copy(*this); 108 Copy.TBAATag = 0; 109 return Copy; 110 } 111 }; 112 113 /// Alias analysis result - Either we know for sure that it does not alias, we 114 /// know for sure it must alias, or we don't know anything: The two pointers 115 /// _might_ alias. This enum is designed so you can do things like: 116 /// if (AA.alias(P1, P2)) { ... } 117 /// to check to see if two pointers might alias. 118 /// 119 /// See docs/AliasAnalysis.html for more information on the specific meanings 120 /// of these values. 121 /// 122 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 123 124 /// alias - The main low level interface to the alias analysis implementation. 125 /// Returns a Result indicating whether the two pointers are aliased to each 126 /// other. This is the interface that must be implemented by specific alias 127 /// analysis implementations. 128 virtual AliasResult alias(const Location &LocA, const Location &LocB); 129 130 /// alias - A convenience wrapper. 131 AliasResult alias(const Value *V1, uint64_t V1Size, 132 const Value *V2, uint64_t V2Size) { 133 return alias(Location(V1, V1Size), Location(V2, V2Size)); 134 } 135 136 /// alias - A convenience wrapper. 137 AliasResult alias(const Value *V1, const Value *V2) { 138 return alias(V1, UnknownSize, V2, UnknownSize); 139 } 140 141 /// isNoAlias - A trivial helper function to check to see if the specified 142 /// pointers are no-alias. 143 bool isNoAlias(const Location &LocA, const Location &LocB) { 144 return alias(LocA, LocB) == NoAlias; 145 } 146 147 /// isNoAlias - A convenience wrapper. 148 bool isNoAlias(const Value *V1, uint64_t V1Size, 149 const Value *V2, uint64_t V2Size) { 150 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size)); 151 } 152 153 /// pointsToConstantMemory - If the specified memory location is known to be 154 /// constant, return true. This allows disambiguation of store 155 /// instructions from constant pointers. 156 /// 157 virtual bool pointsToConstantMemory(const Location &Loc); 158 159 /// pointsToConstantMemory - A convenient wrapper. 160 bool pointsToConstantMemory(const Value *P) { 161 return pointsToConstantMemory(Location(P)); 162 } 163 164 //===--------------------------------------------------------------------===// 165 /// Simple mod/ref information... 166 /// 167 168 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 169 /// bits which may be or'd together. 170 /// 171 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 172 173 174 /// ModRefBehavior - Summary of how a function affects memory in the program. 175 /// Loads from constant globals are not considered memory accesses for this 176 /// interface. Also, functions may freely modify stack space local to their 177 /// invocation without having to report it through these interfaces. 178 enum ModRefBehavior { 179 // DoesNotAccessMemory - This function does not perform any non-local loads 180 // or stores to memory. 181 // 182 // This property corresponds to the GCC 'const' attribute. 183 DoesNotAccessMemory, 184 185 // AccessesArguments - This function accesses function arguments in well 186 // known (possibly volatile) ways, but does not access any other memory. 187 AccessesArguments, 188 189 // AccessesArgumentsAndGlobals - This function has accesses function 190 // arguments and global variables well known (possibly volatile) ways, but 191 // does not access any other memory. 192 AccessesArgumentsAndGlobals, 193 194 // OnlyReadsMemory - This function does not perform any non-local stores or 195 // volatile loads, but may read from any memory location. 196 // 197 // This property corresponds to the GCC 'pure' attribute. 198 OnlyReadsMemory, 199 200 // UnknownModRefBehavior - This indicates that the function could not be 201 // classified into one of the behaviors above. 202 UnknownModRefBehavior 203 }; 204 205 /// getModRefBehavior - Return the behavior when calling the given call site. 206 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 207 208 /// getModRefBehavior - Return the behavior when calling the given function. 209 /// For use when the call site is not known. 210 virtual ModRefBehavior getModRefBehavior(const Function *F); 211 212 /// getIntrinsicModRefBehavior - Return the modref behavior of the intrinsic 213 /// with the given id. Most clients won't need this, because the regular 214 /// getModRefBehavior incorporates this information. 215 static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid); 216 217 /// doesNotAccessMemory - If the specified call is known to never read or 218 /// write memory, return true. If the call only reads from known-constant 219 /// memory, it is also legal to return true. Calls that unwind the stack 220 /// are legal for this predicate. 221 /// 222 /// Many optimizations (such as CSE and LICM) can be performed on such calls 223 /// without worrying about aliasing properties, and many calls have this 224 /// property (e.g. calls to 'sin' and 'cos'). 225 /// 226 /// This property corresponds to the GCC 'const' attribute. 227 /// 228 bool doesNotAccessMemory(ImmutableCallSite CS) { 229 return getModRefBehavior(CS) == DoesNotAccessMemory; 230 } 231 232 /// doesNotAccessMemory - If the specified function is known to never read or 233 /// write memory, return true. For use when the call site is not known. 234 /// 235 bool doesNotAccessMemory(const Function *F) { 236 return getModRefBehavior(F) == DoesNotAccessMemory; 237 } 238 239 /// onlyReadsMemory - If the specified call is known to only read from 240 /// non-volatile memory (or not access memory at all), return true. Calls 241 /// that unwind the stack are legal for this predicate. 242 /// 243 /// This property allows many common optimizations to be performed in the 244 /// absence of interfering store instructions, such as CSE of strlen calls. 245 /// 246 /// This property corresponds to the GCC 'pure' attribute. 247 /// 248 bool onlyReadsMemory(ImmutableCallSite CS) { 249 ModRefBehavior MRB = getModRefBehavior(CS); 250 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 251 } 252 253 /// onlyReadsMemory - If the specified function is known to only read from 254 /// non-volatile memory (or not access memory at all), return true. For use 255 /// when the call site is not known. 256 /// 257 bool onlyReadsMemory(const Function *F) { 258 ModRefBehavior MRB = getModRefBehavior(F); 259 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 260 } 261 262 263 /// getModRefInfo - Return information about whether or not an instruction may 264 /// read or write the specified memory location. An instruction 265 /// that doesn't read or write memory may be trivially LICM'd for example. 266 ModRefResult getModRefInfo(const Instruction *I, 267 const Location &Loc) { 268 switch (I->getOpcode()) { 269 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc); 270 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc); 271 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc); 272 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc); 273 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc); 274 default: return NoModRef; 275 } 276 } 277 278 /// getModRefInfo - A convenience wrapper. 279 ModRefResult getModRefInfo(const Instruction *I, 280 const Value *P, uint64_t Size) { 281 return getModRefInfo(I, Location(P, Size)); 282 } 283 284 /// getModRefInfo (for call sites) - Return whether information about whether 285 /// a particular call site modifies or reads the specified memory location. 286 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 287 const Location &Loc); 288 289 /// getModRefInfo (for call sites) - A convenience wrapper. 290 ModRefResult getModRefInfo(ImmutableCallSite CS, 291 const Value *P, uint64_t Size) { 292 return getModRefInfo(CS, Location(P, Size)); 293 } 294 295 /// getModRefInfo (for calls) - Return whether information about whether 296 /// a particular call modifies or reads the specified memory location. 297 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) { 298 return getModRefInfo(ImmutableCallSite(C), Loc); 299 } 300 301 /// getModRefInfo (for calls) - A convenience wrapper. 302 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) { 303 return getModRefInfo(C, Location(P, Size)); 304 } 305 306 /// getModRefInfo (for invokes) - Return whether information about whether 307 /// a particular invoke modifies or reads the specified memory location. 308 ModRefResult getModRefInfo(const InvokeInst *I, 309 const Location &Loc) { 310 return getModRefInfo(ImmutableCallSite(I), Loc); 311 } 312 313 /// getModRefInfo (for invokes) - A convenience wrapper. 314 ModRefResult getModRefInfo(const InvokeInst *I, 315 const Value *P, uint64_t Size) { 316 return getModRefInfo(I, Location(P, Size)); 317 } 318 319 /// getModRefInfo (for loads) - Return whether information about whether 320 /// a particular load modifies or reads the specified memory location. 321 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc); 322 323 /// getModRefInfo (for loads) - A convenience wrapper. 324 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) { 325 return getModRefInfo(L, Location(P, Size)); 326 } 327 328 /// getModRefInfo (for stores) - Return whether information about whether 329 /// a particular store modifies or reads the specified memory location. 330 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc); 331 332 /// getModRefInfo (for stores) - A convenience wrapper. 333 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) { 334 return getModRefInfo(S, Location(P, Size)); 335 } 336 337 /// getModRefInfo (for va_args) - Return whether information about whether 338 /// a particular va_arg modifies or reads the specified memory location. 339 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc); 340 341 /// getModRefInfo (for va_args) - A convenience wrapper. 342 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) { 343 return getModRefInfo(I, Location(P, Size)); 344 } 345 346 /// getModRefInfo - Return information about whether two call sites may refer 347 /// to the same set of memory locations. See 348 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo 349 /// for details. 350 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 351 ImmutableCallSite CS2); 352 353 //===--------------------------------------------------------------------===// 354 /// Higher level methods for querying mod/ref information. 355 /// 356 357 /// canBasicBlockModify - Return true if it is possible for execution of the 358 /// specified basic block to modify the value pointed to by Ptr. 359 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc); 360 361 /// canBasicBlockModify - A convenience wrapper. 362 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){ 363 return canBasicBlockModify(BB, Location(P, Size)); 364 } 365 366 /// canInstructionRangeModify - Return true if it is possible for the 367 /// execution of the specified instructions to modify the value pointed to by 368 /// Ptr. The instructions to consider are all of the instructions in the 369 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 370 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 371 const Location &Loc); 372 373 /// canInstructionRangeModify - A convenience wrapper. 374 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 375 const Value *Ptr, uint64_t Size) { 376 return canInstructionRangeModify(I1, I2, Location(Ptr, Size)); 377 } 378 379 //===--------------------------------------------------------------------===// 380 /// Methods that clients should call when they transform the program to allow 381 /// alias analyses to update their internal data structures. Note that these 382 /// methods may be called on any instruction, regardless of whether or not 383 /// they have pointer-analysis implications. 384 /// 385 386 /// deleteValue - This method should be called whenever an LLVM Value is 387 /// deleted from the program, for example when an instruction is found to be 388 /// redundant and is eliminated. 389 /// 390 virtual void deleteValue(Value *V); 391 392 /// copyValue - This method should be used whenever a preexisting value in the 393 /// program is copied or cloned, introducing a new value. Note that analysis 394 /// implementations should tolerate clients that use this method to introduce 395 /// the same value multiple times: if the analysis already knows about a 396 /// value, it should ignore the request. 397 /// 398 virtual void copyValue(Value *From, Value *To); 399 400 /// replaceWithNewValue - This method is the obvious combination of the two 401 /// above, and it provided as a helper to simplify client code. 402 /// 403 void replaceWithNewValue(Value *Old, Value *New) { 404 copyValue(Old, New); 405 deleteValue(Old); 406 } 407}; 408 409/// isNoAliasCall - Return true if this pointer is returned by a noalias 410/// function. 411bool isNoAliasCall(const Value *V); 412 413/// isIdentifiedObject - Return true if this pointer refers to a distinct and 414/// identifiable object. This returns true for: 415/// Global Variables and Functions (but not Global Aliases) 416/// Allocas and Mallocs 417/// ByVal and NoAlias Arguments 418/// NoAlias returns 419/// 420bool isIdentifiedObject(const Value *V); 421 422} // End llvm namespace 423 424#endif 425