AliasAnalysis.h revision 9f27074f42f03af640977006dc7c05005fb77991
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 "llvm/System/IncludeFile.h" 32#include <vector> 33 34namespace llvm { 35 36class LoadInst; 37class StoreInst; 38class VAArgInst; 39class TargetData; 40class Pass; 41class AnalysisUsage; 42 43class AliasAnalysis { 44protected: 45 const TargetData *TD; 46 47private: 48 AliasAnalysis *AA; // Previous Alias Analysis to chain to. 49 50protected: 51 /// InitializeAliasAnalysis - Subclasses must call this method to initialize 52 /// the AliasAnalysis interface before any other methods are called. This is 53 /// typically called by the run* methods of these subclasses. This may be 54 /// called multiple times. 55 /// 56 void InitializeAliasAnalysis(Pass *P); 57 58 /// getAnalysisUsage - All alias analysis implementations should invoke this 59 /// directly (using AliasAnalysis::getAnalysisUsage(AU)). 60 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 61 62public: 63 static char ID; // Class identification, replacement for typeinfo 64 AliasAnalysis() : TD(0), AA(0) {} 65 virtual ~AliasAnalysis(); // We want to be subclassed 66 67 /// UnknownSize - This is a special value which can be used with the 68 /// size arguments in alias queries to indicate that the caller does not 69 /// know the sizes of the potential memory references. 70 static unsigned const UnknownSize = ~0u; 71 72 /// getTargetData - Return a pointer to the current TargetData object, or 73 /// null if no TargetData object is available. 74 /// 75 const TargetData *getTargetData() const { return TD; } 76 77 /// getTypeStoreSize - Return the TargetData store size for the given type, 78 /// if known, or a conservative value otherwise. 79 /// 80 unsigned getTypeStoreSize(const Type *Ty); 81 82 //===--------------------------------------------------------------------===// 83 /// Alias Queries... 84 /// 85 86 /// Location - A description of a memory location. 87 struct Location { 88 /// Ptr - The address of the start of the location. 89 const Value *Ptr; 90 /// Size - The size of the location. 91 unsigned Size; 92 /// TBAATag - The metadata node which describes the TBAA type of 93 /// the location, or null if there is no (unique) tag. 94 const MDNode *TBAATag; 95 96 explicit Location(const Value *P = 0, 97 unsigned S = UnknownSize, 98 const MDNode *N = 0) 99 : Ptr(P), Size(S), TBAATag(N) {} 100 101 Location getWithNewPtr(const Value *NewPtr) const { 102 Location Copy(*this); 103 Copy.Ptr = NewPtr; 104 return Copy; 105 } 106 107 Location getWithoutTBAATag() const { 108 Location Copy(*this); 109 Copy.TBAATag = 0; 110 return Copy; 111 } 112 }; 113 114 /// Alias analysis result - Either we know for sure that it does not alias, we 115 /// know for sure it must alias, or we don't know anything: The two pointers 116 /// _might_ alias. This enum is designed so you can do things like: 117 /// if (AA.alias(P1, P2)) { ... } 118 /// to check to see if two pointers might alias. 119 /// 120 /// See docs/AliasAnalysis.html for more information on the specific meanings 121 /// of these values. 122 /// 123 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 124 125 /// alias - The main low level interface to the alias analysis implementation. 126 /// Returns a Result indicating whether the two pointers are aliased to each 127 /// other. This is the interface that must be implemented by specific alias 128 /// analysis implementations. 129 virtual AliasResult alias(const Location &LocA, const Location &LocB); 130 131 /// alias - A convenience wrapper. 132 AliasResult alias(const Value *V1, unsigned V1Size, 133 const Value *V2, unsigned V2Size) { 134 return alias(Location(V1, V1Size), Location(V2, V2Size)); 135 } 136 137 /// alias - A convenience wrapper. 138 AliasResult alias(const Value *V1, const Value *V2) { 139 return alias(V1, UnknownSize, V2, UnknownSize); 140 } 141 142 /// isNoAlias - A trivial helper function to check to see if the specified 143 /// pointers are no-alias. 144 bool isNoAlias(const Location &LocA, const Location &LocB) { 145 return alias(LocA, LocB) == NoAlias; 146 } 147 148 /// isNoAlias - A convenience wrapper. 149 bool isNoAlias(const Value *V1, unsigned V1Size, 150 const Value *V2, unsigned V2Size) { 151 return isNoAlias(Location(V1, V1Size), Location(V2, V2Size)); 152 } 153 154 /// pointsToConstantMemory - If the specified memory location is known to be 155 /// constant, return true. This allows disambiguation of store 156 /// instructions from constant pointers. 157 /// 158 virtual bool pointsToConstantMemory(const Location &Loc); 159 160 /// pointsToConstantMemory - A convenient wrapper. 161 bool pointsToConstantMemory(const Value *P) { 162 return pointsToConstantMemory(Location(P)); 163 } 164 165 //===--------------------------------------------------------------------===// 166 /// Simple mod/ref information... 167 /// 168 169 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 170 /// bits which may be or'd together. 171 /// 172 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 173 174 175 /// ModRefBehavior - Summary of how a function affects memory in the program. 176 /// Loads from constant globals are not considered memory accesses for this 177 /// interface. Also, functions may freely modify stack space local to their 178 /// invocation without having to report it through these interfaces. 179 enum ModRefBehavior { 180 // DoesNotAccessMemory - This function does not perform any non-local loads 181 // or stores to memory. 182 // 183 // This property corresponds to the GCC 'const' attribute. 184 DoesNotAccessMemory, 185 186 // AccessesArguments - This function accesses function arguments in well 187 // known (possibly volatile) ways, but does not access any other memory. 188 AccessesArguments, 189 190 // AccessesArgumentsAndGlobals - This function has accesses function 191 // arguments and global variables well known (possibly volatile) ways, but 192 // does not access any other memory. 193 AccessesArgumentsAndGlobals, 194 195 // OnlyReadsMemory - This function does not perform any non-local stores or 196 // volatile loads, but may read from any memory location. 197 // 198 // This property corresponds to the GCC 'pure' attribute. 199 OnlyReadsMemory, 200 201 // UnknownModRefBehavior - This indicates that the function could not be 202 // classified into one of the behaviors above. 203 UnknownModRefBehavior 204 }; 205 206 /// getModRefBehavior - Return the behavior when calling the given call site. 207 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 208 209 /// getModRefBehavior - Return the behavior when calling the given function. 210 /// For use when the call site is not known. 211 virtual ModRefBehavior getModRefBehavior(const Function *F); 212 213 /// getIntrinsicModRefBehavior - Return the modref behavior of the intrinsic 214 /// with the given id. Most clients won't need this, because the regular 215 /// getModRefBehavior incorporates this information. 216 static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid); 217 218 /// doesNotAccessMemory - If the specified call is known to never read or 219 /// write memory, return true. If the call only reads from known-constant 220 /// memory, it is also legal to return true. Calls that unwind the stack 221 /// are legal for this predicate. 222 /// 223 /// Many optimizations (such as CSE and LICM) can be performed on such calls 224 /// without worrying about aliasing properties, and many calls have this 225 /// property (e.g. calls to 'sin' and 'cos'). 226 /// 227 /// This property corresponds to the GCC 'const' attribute. 228 /// 229 bool doesNotAccessMemory(ImmutableCallSite CS) { 230 return getModRefBehavior(CS) == DoesNotAccessMemory; 231 } 232 233 /// doesNotAccessMemory - If the specified function is known to never read or 234 /// write memory, return true. For use when the call site is not known. 235 /// 236 bool doesNotAccessMemory(const Function *F) { 237 return getModRefBehavior(F) == DoesNotAccessMemory; 238 } 239 240 /// onlyReadsMemory - If the specified call is known to only read from 241 /// non-volatile memory (or not access memory at all), return true. Calls 242 /// that unwind the stack are legal for this predicate. 243 /// 244 /// This property allows many common optimizations to be performed in the 245 /// absence of interfering store instructions, such as CSE of strlen calls. 246 /// 247 /// This property corresponds to the GCC 'pure' attribute. 248 /// 249 bool onlyReadsMemory(ImmutableCallSite CS) { 250 ModRefBehavior MRB = getModRefBehavior(CS); 251 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 252 } 253 254 /// onlyReadsMemory - If the specified function is known to only read from 255 /// non-volatile memory (or not access memory at all), return true. For use 256 /// when the call site is not known. 257 /// 258 bool onlyReadsMemory(const Function *F) { 259 ModRefBehavior MRB = getModRefBehavior(F); 260 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 261 } 262 263 264 /// getModRefInfo - Return information about whether or not an instruction may 265 /// read or write the specified memory location. An instruction 266 /// that doesn't read or write memory may be trivially LICM'd for example. 267 ModRefResult getModRefInfo(const Instruction *I, 268 const Location &Loc) { 269 switch (I->getOpcode()) { 270 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc); 271 case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc); 272 case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc); 273 case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc); 274 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc); 275 default: return NoModRef; 276 } 277 } 278 279 /// getModRefInfo - A convenience wrapper. 280 ModRefResult getModRefInfo(const Instruction *I, 281 const Value *P, unsigned Size) { 282 return getModRefInfo(I, Location(P, Size)); 283 } 284 285 /// getModRefInfo (for call sites) - Return whether information about whether 286 /// a particular call site modifies or reads the specified memory location. 287 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 288 const Location &Loc); 289 290 /// getModRefInfo (for call sites) - A convenience wrapper. 291 ModRefResult getModRefInfo(ImmutableCallSite CS, 292 const Value *P, unsigned Size) { 293 return getModRefInfo(CS, Location(P, Size)); 294 } 295 296 /// getModRefInfo (for calls) - Return whether information about whether 297 /// a particular call modifies or reads the specified memory location. 298 ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) { 299 return getModRefInfo(ImmutableCallSite(C), Loc); 300 } 301 302 /// getModRefInfo (for calls) - A convenience wrapper. 303 ModRefResult getModRefInfo(const CallInst *C, const Value *P, unsigned Size) { 304 return getModRefInfo(C, Location(P, Size)); 305 } 306 307 /// getModRefInfo (for invokes) - Return whether information about whether 308 /// a particular invoke modifies or reads the specified memory location. 309 ModRefResult getModRefInfo(const InvokeInst *I, 310 const Location &Loc) { 311 return getModRefInfo(ImmutableCallSite(I), Loc); 312 } 313 314 /// getModRefInfo (for invokes) - A convenience wrapper. 315 ModRefResult getModRefInfo(const InvokeInst *I, 316 const Value *P, unsigned Size) { 317 return getModRefInfo(I, Location(P, Size)); 318 } 319 320 /// getModRefInfo (for loads) - Return whether information about whether 321 /// a particular load modifies or reads the specified memory location. 322 ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc); 323 324 /// getModRefInfo (for loads) - A convenience wrapper. 325 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, unsigned Size) { 326 return getModRefInfo(L, Location(P, Size)); 327 } 328 329 /// getModRefInfo (for stores) - Return whether information about whether 330 /// a particular store modifies or reads the specified memory location. 331 ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc); 332 333 /// getModRefInfo (for stores) - A convenience wrapper. 334 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, unsigned Size) { 335 return getModRefInfo(S, Location(P, Size)); 336 } 337 338 /// getModRefInfo (for va_args) - Return whether information about whether 339 /// a particular va_arg modifies or reads the specified memory location. 340 ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc); 341 342 /// getModRefInfo (for va_args) - A convenience wrapper. 343 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, unsigned Size) { 344 return getModRefInfo(I, Location(P, Size)); 345 } 346 347 /// getModRefInfo - Return information about whether two call sites may refer 348 /// to the same set of memory locations. See 349 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo 350 /// for details. 351 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 352 ImmutableCallSite CS2); 353 354 //===--------------------------------------------------------------------===// 355 /// Higher level methods for querying mod/ref information. 356 /// 357 358 /// canBasicBlockModify - Return true if it is possible for execution of the 359 /// specified basic block to modify the value pointed to by Ptr. 360 bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc); 361 362 /// canBasicBlockModify - A convenience wrapper. 363 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size){ 364 return canBasicBlockModify(BB, Location(P, Size)); 365 } 366 367 /// canInstructionRangeModify - Return true if it is possible for the 368 /// execution of the specified instructions to modify the value pointed to by 369 /// Ptr. The instructions to consider are all of the instructions in the 370 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 371 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 372 const Location &Loc); 373 374 /// canInstructionRangeModify - A convenience wrapper. 375 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 376 const Value *Ptr, unsigned Size) { 377 return canInstructionRangeModify(I1, I2, Location(Ptr, Size)); 378 } 379 380 //===--------------------------------------------------------------------===// 381 /// Methods that clients should call when they transform the program to allow 382 /// alias analyses to update their internal data structures. Note that these 383 /// methods may be called on any instruction, regardless of whether or not 384 /// they have pointer-analysis implications. 385 /// 386 387 /// deleteValue - This method should be called whenever an LLVM Value is 388 /// deleted from the program, for example when an instruction is found to be 389 /// redundant and is eliminated. 390 /// 391 virtual void deleteValue(Value *V); 392 393 /// copyValue - This method should be used whenever a preexisting value in the 394 /// program is copied or cloned, introducing a new value. Note that analysis 395 /// implementations should tolerate clients that use this method to introduce 396 /// the same value multiple times: if the analysis already knows about a 397 /// value, it should ignore the request. 398 /// 399 virtual void copyValue(Value *From, Value *To); 400 401 /// replaceWithNewValue - This method is the obvious combination of the two 402 /// above, and it provided as a helper to simplify client code. 403 /// 404 void replaceWithNewValue(Value *Old, Value *New) { 405 copyValue(Old, New); 406 deleteValue(Old); 407 } 408}; 409 410/// isNoAliasCall - Return true if this pointer is returned by a noalias 411/// function. 412bool isNoAliasCall(const Value *V); 413 414/// isIdentifiedObject - Return true if this pointer refers to a distinct and 415/// identifiable object. This returns true for: 416/// Global Variables and Functions (but not Global Aliases) 417/// Allocas and Mallocs 418/// ByVal and NoAlias Arguments 419/// NoAlias returns 420/// 421bool isIdentifiedObject(const Value *V); 422 423} // End llvm namespace 424 425// Because of the way .a files work, we must force the BasicAA implementation to 426// be pulled in if the AliasAnalysis header is included. Otherwise we run 427// the risk of AliasAnalysis being used, but the default implementation not 428// being linked into the tool that uses it. 429FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis) 430FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis) 431 432#endif 433