AliasAnalysis.h revision 6c25c920e66aa2d8f6b48454bc9770087ff7939a
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 known to be 158 /// constant, return true. This allows disambiguation of store 159 /// instructions from constant pointers. 160 /// 161 virtual bool pointsToConstantMemory(const Location &Loc); 162 163 /// pointsToConstantMemory - A convenient wrapper. 164 bool pointsToConstantMemory(const Value *P) { 165 return pointsToConstantMemory(Location(P)); 166 } 167 168 //===--------------------------------------------------------------------===// 169 /// Simple mod/ref information... 170 /// 171 172 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 173 /// bits which may be or'd together. 174 /// 175 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 176 177 178 /// ModRefBehavior - Summary of how a function affects memory in the program. 179 /// Loads from constant globals are not considered memory accesses for this 180 /// interface. Also, functions may freely modify stack space local to their 181 /// invocation without having to report it through these interfaces. 182 enum ModRefBehavior { 183 // DoesNotAccessMemory - This function does not perform any non-local loads 184 // or stores to memory. 185 // 186 // This property corresponds to the GCC 'const' attribute. 187 DoesNotAccessMemory, 188 189 // AccessesArguments - This function accesses function arguments in well 190 // known (possibly volatile) ways, but does not access any other memory. 191 AccessesArguments, 192 193 // AccessesArgumentsAndGlobals - This function has accesses function 194 // arguments and global variables well known (possibly volatile) ways, but 195 // does not access any other memory. 196 AccessesArgumentsAndGlobals, 197 198 // OnlyReadsMemory - This function does not perform any non-local stores or 199 // volatile loads, but may read from any memory location. 200 // 201 // This property corresponds to the GCC 'pure' attribute. 202 OnlyReadsMemory, 203 204 // UnknownModRefBehavior - This indicates that the function could not be 205 // classified into one of the behaviors above. 206 UnknownModRefBehavior 207 }; 208 209 /// getModRefBehavior - Return the behavior when calling the given call site. 210 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 211 212 /// getModRefBehavior - Return the behavior when calling the given function. 213 /// For use when the call site is not known. 214 virtual ModRefBehavior getModRefBehavior(const Function *F); 215 216 /// getIntrinsicModRefBehavior - Return the modref behavior of the intrinsic 217 /// with the given id. Most clients won't need this, because the regular 218 /// getModRefBehavior incorporates this information. 219 static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid); 220 221 /// doesNotAccessMemory - If the specified call is known to never read or 222 /// write memory, return true. If the call only reads from known-constant 223 /// memory, it is also legal to return true. Calls that unwind the stack 224 /// are legal for this predicate. 225 /// 226 /// Many optimizations (such as CSE and LICM) can be performed on such calls 227 /// without worrying about aliasing properties, and many calls have this 228 /// property (e.g. calls to 'sin' and 'cos'). 229 /// 230 /// This property corresponds to the GCC 'const' attribute. 231 /// 232 bool doesNotAccessMemory(ImmutableCallSite CS) { 233 return getModRefBehavior(CS) == DoesNotAccessMemory; 234 } 235 236 /// doesNotAccessMemory - If the specified function is known to never read or 237 /// write memory, return true. For use when the call site is not known. 238 /// 239 bool doesNotAccessMemory(const Function *F) { 240 return getModRefBehavior(F) == DoesNotAccessMemory; 241 } 242 243 /// onlyReadsMemory - If the specified call is known to only read from 244 /// non-volatile memory (or not access memory at all), return true. Calls 245 /// that unwind the stack are legal for this predicate. 246 /// 247 /// This property allows many common optimizations to be performed in the 248 /// absence of interfering store instructions, such as CSE of strlen calls. 249 /// 250 /// This property corresponds to the GCC 'pure' attribute. 251 /// 252 bool onlyReadsMemory(ImmutableCallSite CS) { 253 ModRefBehavior MRB = getModRefBehavior(CS); 254 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 255 } 256 257 /// onlyReadsMemory - If the specified function is known to only read from 258 /// non-volatile memory (or not access memory at all), return true. For use 259 /// when the call site is not known. 260 /// 261 bool onlyReadsMemory(const Function *F) { 262 ModRefBehavior MRB = getModRefBehavior(F); 263 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 264 } 265 266 267 /// getModRefInfo - Return information about whether or not an instruction may 268 /// read or write the specified memory location. An instruction 269 /// that doesn't read or write memory may be trivially LICM'd for example. 270 ModRefResult getModRefInfo(const Instruction *I, 271 const Location &Loc) { 272 switch (I->getOpcode()) { 273 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc); 274 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc); 275 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc); 276 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc); 277 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc); 278 default: return NoModRef; 279 } 280 } 281 282 /// getModRefInfo - A convenience wrapper. 283 ModRefResult getModRefInfo(const Instruction *I, 284 const Value *P, uint64_t Size) { 285 return getModRefInfo(I, Location(P, Size)); 286 } 287 288 /// getModRefInfo (for call sites) - Return whether information about whether 289 /// a particular call site modifies or reads the specified memory location. 290 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 291 const Location &Loc); 292 293 /// getModRefInfo (for call sites) - A convenience wrapper. 294 ModRefResult getModRefInfo(ImmutableCallSite CS, 295 const Value *P, uint64_t Size) { 296 return getModRefInfo(CS, Location(P, Size)); 297 } 298 299 /// getModRefInfo (for calls) - Return whether information about whether 300 /// a particular call modifies or reads the specified memory location. 301 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) { 302 return getModRefInfo(ImmutableCallSite(C), Loc); 303 } 304 305 /// getModRefInfo (for calls) - A convenience wrapper. 306 ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) { 307 return getModRefInfo(C, Location(P, Size)); 308 } 309 310 /// getModRefInfo (for invokes) - Return whether information about whether 311 /// a particular invoke modifies or reads the specified memory location. 312 ModRefResult getModRefInfo(const InvokeInst *I, 313 const Location &Loc) { 314 return getModRefInfo(ImmutableCallSite(I), Loc); 315 } 316 317 /// getModRefInfo (for invokes) - A convenience wrapper. 318 ModRefResult getModRefInfo(const InvokeInst *I, 319 const Value *P, uint64_t Size) { 320 return getModRefInfo(I, Location(P, Size)); 321 } 322 323 /// getModRefInfo (for loads) - Return whether information about whether 324 /// a particular load modifies or reads the specified memory location. 325 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc); 326 327 /// getModRefInfo (for loads) - A convenience wrapper. 328 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) { 329 return getModRefInfo(L, Location(P, Size)); 330 } 331 332 /// getModRefInfo (for stores) - Return whether information about whether 333 /// a particular store modifies or reads the specified memory location. 334 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc); 335 336 /// getModRefInfo (for stores) - A convenience wrapper. 337 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size) { 338 return getModRefInfo(S, Location(P, Size)); 339 } 340 341 /// getModRefInfo (for va_args) - Return whether information about whether 342 /// a particular va_arg modifies or reads the specified memory location. 343 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc); 344 345 /// getModRefInfo (for va_args) - A convenience wrapper. 346 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size) { 347 return getModRefInfo(I, Location(P, Size)); 348 } 349 350 /// getModRefInfo - Return information about whether two call sites may refer 351 /// to the same set of memory locations. See 352 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo 353 /// for details. 354 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 355 ImmutableCallSite CS2); 356 357 //===--------------------------------------------------------------------===// 358 /// Higher level methods for querying mod/ref information. 359 /// 360 361 /// canBasicBlockModify - Return true if it is possible for execution of the 362 /// specified basic block to modify the value pointed to by Ptr. 363 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc); 364 365 /// canBasicBlockModify - A convenience wrapper. 366 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){ 367 return canBasicBlockModify(BB, Location(P, Size)); 368 } 369 370 /// canInstructionRangeModify - Return true if it is possible for the 371 /// execution of the specified instructions to modify the value pointed to by 372 /// Ptr. The instructions to consider are all of the instructions in the 373 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 374 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 375 const Location &Loc); 376 377 /// canInstructionRangeModify - A convenience wrapper. 378 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 379 const Value *Ptr, uint64_t Size) { 380 return canInstructionRangeModify(I1, I2, Location(Ptr, Size)); 381 } 382 383 //===--------------------------------------------------------------------===// 384 /// Methods that clients should call when they transform the program to allow 385 /// alias analyses to update their internal data structures. Note that these 386 /// methods may be called on any instruction, regardless of whether or not 387 /// they have pointer-analysis implications. 388 /// 389 390 /// deleteValue - This method should be called whenever an LLVM Value is 391 /// deleted from the program, for example when an instruction is found to be 392 /// redundant and is eliminated. 393 /// 394 virtual void deleteValue(Value *V); 395 396 /// copyValue - This method should be used whenever a preexisting value in the 397 /// program is copied or cloned, introducing a new value. Note that analysis 398 /// implementations should tolerate clients that use this method to introduce 399 /// the same value multiple times: if the analysis already knows about a 400 /// value, it should ignore the request. 401 /// 402 virtual void copyValue(Value *From, Value *To); 403 404 /// replaceWithNewValue - This method is the obvious combination of the two 405 /// above, and it provided as a helper to simplify client code. 406 /// 407 void replaceWithNewValue(Value *Old, Value *New) { 408 copyValue(Old, New); 409 deleteValue(Old); 410 } 411}; 412 413/// isNoAliasCall - Return true if this pointer is returned by a noalias 414/// function. 415bool isNoAliasCall(const Value *V); 416 417/// isIdentifiedObject - Return true if this pointer refers to a distinct and 418/// identifiable object. This returns true for: 419/// Global Variables and Functions (but not Global Aliases) 420/// Allocas and Mallocs 421/// ByVal and NoAlias Arguments 422/// NoAlias returns 423/// 424bool isIdentifiedObject(const Value *V); 425 426} // End llvm namespace 427 428#endif 429