AliasAnalysis.h revision 6be2bd516a3022721480f8fee6986617baf0944f
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. If Size is 0, two pointers only alias if they 22// are exactly equal. If size is greater than zero, but small, the two pointers 23// alias if the areas pointed to overlap. If the size is very large (ie, ~0U), 24// then the two pointers alias if they may be pointing to components of the same 25// memory object. Pointers that point to two completely different objects in 26// memory never alias, regardless of the value of the Size component. 27// 28//===----------------------------------------------------------------------===// 29 30#ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H 31#define LLVM_ANALYSIS_ALIAS_ANALYSIS_H 32 33#include "llvm/Support/CallSite.h" 34#include "llvm/System/IncludeFile.h" 35#include <vector> 36 37namespace llvm { 38 39class LoadInst; 40class StoreInst; 41class VAArgInst; 42class TargetData; 43class Pass; 44class AnalysisUsage; 45 46class AliasAnalysis { 47protected: 48 const TargetData *TD; 49 AliasAnalysis *AA; // Previous Alias Analysis to chain to. 50 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 /// getTargetData - Return a pointer to the current TargetData object, or 68 /// null if no TargetData object is available. 69 /// 70 const TargetData *getTargetData() const { return TD; } 71 72 /// getTypeStoreSize - Return the TargetData store size for the given type, 73 /// if known, or a conservative value otherwise. 74 /// 75 unsigned getTypeStoreSize(const Type *Ty); 76 77 //===--------------------------------------------------------------------===// 78 /// Alias Queries... 79 /// 80 81 /// Alias analysis result - Either we know for sure that it does not alias, we 82 /// know for sure it must alias, or we don't know anything: The two pointers 83 /// _might_ alias. This enum is designed so you can do things like: 84 /// if (AA.alias(P1, P2)) { ... } 85 /// to check to see if two pointers might alias. 86 /// 87 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 88 89 /// alias - The main low level interface to the alias analysis implementation. 90 /// Returns a Result indicating whether the two pointers are aliased to each 91 /// other. This is the interface that must be implemented by specific alias 92 /// analysis implementations. 93 /// 94 virtual AliasResult alias(const Value *V1, unsigned V1Size, 95 const Value *V2, unsigned V2Size); 96 97 /// isNoAlias - A trivial helper function to check to see if the specified 98 /// pointers are no-alias. 99 bool isNoAlias(const Value *V1, unsigned V1Size, 100 const Value *V2, unsigned V2Size) { 101 return alias(V1, V1Size, V2, V2Size) == NoAlias; 102 } 103 104 /// pointsToConstantMemory - If the specified pointer is known to point into 105 /// constant global memory, return true. This allows disambiguation of store 106 /// instructions from constant pointers. 107 /// 108 virtual bool pointsToConstantMemory(const Value *P); 109 110 //===--------------------------------------------------------------------===// 111 /// Simple mod/ref information... 112 /// 113 114 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 115 /// bits which may be or'd together. 116 /// 117 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 118 119 120 /// ModRefBehavior - Summary of how a function affects memory in the program. 121 /// Loads from constant globals are not considered memory accesses for this 122 /// interface. Also, functions may freely modify stack space local to their 123 /// invocation without having to report it through these interfaces. 124 enum ModRefBehavior { 125 // DoesNotAccessMemory - This function does not perform any non-local loads 126 // or stores to memory. 127 // 128 // This property corresponds to the GCC 'const' attribute. 129 DoesNotAccessMemory, 130 131 // AccessesArguments - This function accesses function arguments in well 132 // known (possibly volatile) ways, but does not access any other memory. 133 // 134 // Clients may use the Info parameter of getModRefBehavior to get specific 135 // information about how pointer arguments are used. 136 AccessesArguments, 137 138 // AccessesArgumentsAndGlobals - This function has accesses function 139 // arguments and global variables well known (possibly volatile) ways, but 140 // does not access any other memory. 141 // 142 // Clients may use the Info parameter of getModRefBehavior to get specific 143 // information about how pointer arguments are used. 144 AccessesArgumentsAndGlobals, 145 146 // OnlyReadsMemory - This function does not perform any non-local stores or 147 // volatile loads, but may read from any memory location. 148 // 149 // This property corresponds to the GCC 'pure' attribute. 150 OnlyReadsMemory, 151 152 // UnknownModRefBehavior - This indicates that the function could not be 153 // classified into one of the behaviors above. 154 UnknownModRefBehavior 155 }; 156 157 /// PointerAccessInfo - This struct is used to return results for pointers, 158 /// globals, and the return value of a function. 159 struct PointerAccessInfo { 160 /// V - The value this record corresponds to. This may be an Argument for 161 /// the function, a GlobalVariable, or null, corresponding to the return 162 /// value for the function. 163 Value *V; 164 165 /// ModRefInfo - Whether the pointer is loaded or stored to/from. 166 /// 167 ModRefResult ModRefInfo; 168 169 /// AccessType - Specific fine-grained access information for the argument. 170 /// If none of these classifications is general enough, the 171 /// getModRefBehavior method should not return AccessesArguments*. If a 172 /// record is not returned for a particular argument, the argument is never 173 /// dead and never dereferenced. 174 enum AccessType { 175 /// ScalarAccess - The pointer is dereferenced. 176 /// 177 ScalarAccess, 178 179 /// ArrayAccess - The pointer is indexed through as an array of elements. 180 /// 181 ArrayAccess, 182 183 /// ElementAccess ?? P->F only? 184 185 /// CallsThrough - Indirect calls are made through the specified function 186 /// pointer. 187 CallsThrough 188 }; 189 }; 190 191 /// getModRefBehavior - Return the behavior when calling the given call site. 192 virtual ModRefBehavior getModRefBehavior(CallSite CS, 193 std::vector<PointerAccessInfo> *Info = 0); 194 195 /// getModRefBehavior - Return the behavior when calling the given function. 196 /// For use when the call site is not known. 197 virtual ModRefBehavior getModRefBehavior(Function *F, 198 std::vector<PointerAccessInfo> *Info = 0); 199 200 /// getModRefBehavior - Return the modref behavior of the intrinsic with the 201 /// given id. 202 static ModRefBehavior getModRefBehavior(unsigned iid); 203 204 /// doesNotAccessMemory - If the specified call is known to never read or 205 /// write memory, return true. If the call only reads from known-constant 206 /// memory, it is also legal to return true. Calls that unwind the stack 207 /// are legal for this predicate. 208 /// 209 /// Many optimizations (such as CSE and LICM) can be performed on such calls 210 /// without worrying about aliasing properties, and many calls have this 211 /// property (e.g. calls to 'sin' and 'cos'). 212 /// 213 /// This property corresponds to the GCC 'const' attribute. 214 /// 215 bool doesNotAccessMemory(CallSite CS) { 216 return getModRefBehavior(CS) == DoesNotAccessMemory; 217 } 218 219 /// doesNotAccessMemory - If the specified function is known to never read or 220 /// write memory, return true. For use when the call site is not known. 221 /// 222 bool doesNotAccessMemory(Function *F) { 223 return getModRefBehavior(F) == DoesNotAccessMemory; 224 } 225 226 /// onlyReadsMemory - If the specified call is known to only read from 227 /// non-volatile memory (or not access memory at all), return true. Calls 228 /// that unwind the stack are legal for this predicate. 229 /// 230 /// This property allows many common optimizations to be performed in the 231 /// absence of interfering store instructions, such as CSE of strlen calls. 232 /// 233 /// This property corresponds to the GCC 'pure' attribute. 234 /// 235 bool onlyReadsMemory(CallSite CS) { 236 ModRefBehavior MRB = getModRefBehavior(CS); 237 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 238 } 239 240 /// onlyReadsMemory - If the specified function is known to only read from 241 /// non-volatile memory (or not access memory at all), return true. For use 242 /// when the call site is not known. 243 /// 244 bool onlyReadsMemory(Function *F) { 245 ModRefBehavior MRB = getModRefBehavior(F); 246 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 247 } 248 249 250 /// getModRefInfo - Return information about whether or not an instruction may 251 /// read or write memory specified by the pointer operand. An instruction 252 /// that doesn't read or write memory may be trivially LICM'd for example. 253 254 /// getModRefInfo (for call sites) - Return whether information about whether 255 /// a particular call site modifies or reads the memory specified by the 256 /// pointer. 257 /// 258 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 259 260 /// getModRefInfo - Return information about whether two call sites may refer 261 /// to the same set of memory locations. This function returns NoModRef if 262 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory 263 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or 264 /// ModRef if CS1 might read or write memory accessed by CS2. 265 /// 266 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 267 268public: 269 /// Convenience functions... 270 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 271 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size); 272 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 273 return getModRefInfo(CallSite(C), P, Size); 274 } 275 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) { 276 return getModRefInfo(CallSite(I), P, Size); 277 } 278 ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) { 279 return AliasAnalysis::ModRef; 280 } 281 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 282 switch (I->getOpcode()) { 283 case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size); 284 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 285 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 286 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 287 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); 288 default: return NoModRef; 289 } 290 } 291 292 //===--------------------------------------------------------------------===// 293 /// Higher level methods for querying mod/ref information. 294 /// 295 296 /// canBasicBlockModify - Return true if it is possible for execution of the 297 /// specified basic block to modify the value pointed to by Ptr. 298 /// 299 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 300 301 /// canInstructionRangeModify - Return true if it is possible for the 302 /// execution of the specified instructions to modify the value pointed to by 303 /// Ptr. The instructions to consider are all of the instructions in the 304 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 305 /// 306 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 307 const Value *Ptr, unsigned Size); 308 309 //===--------------------------------------------------------------------===// 310 /// Methods that clients should call when they transform the program to allow 311 /// alias analyses to update their internal data structures. Note that these 312 /// methods may be called on any instruction, regardless of whether or not 313 /// they have pointer-analysis implications. 314 /// 315 316 /// deleteValue - This method should be called whenever an LLVM Value is 317 /// deleted from the program, for example when an instruction is found to be 318 /// redundant and is eliminated. 319 /// 320 virtual void deleteValue(Value *V); 321 322 /// copyValue - This method should be used whenever a preexisting value in the 323 /// program is copied or cloned, introducing a new value. Note that analysis 324 /// implementations should tolerate clients that use this method to introduce 325 /// the same value multiple times: if the analysis already knows about a 326 /// value, it should ignore the request. 327 /// 328 virtual void copyValue(Value *From, Value *To); 329 330 /// replaceWithNewValue - This method is the obvious combination of the two 331 /// above, and it provided as a helper to simplify client code. 332 /// 333 void replaceWithNewValue(Value *Old, Value *New) { 334 copyValue(Old, New); 335 deleteValue(Old); 336 } 337}; 338 339/// isNoAliasCall - Return true if this pointer is returned by a noalias 340/// function. 341bool isNoAliasCall(const Value *V); 342 343/// isIdentifiedObject - Return true if this pointer refers to a distinct and 344/// identifiable object. This returns true for: 345/// Global Variables and Functions (but not Global Aliases) 346/// Allocas and Mallocs 347/// ByVal and NoAlias Arguments, if Interprocedural is false 348/// NoAlias returns, if Interprocedural is false 349/// 350bool isIdentifiedObject(const Value *V, bool Interprocedural = false); 351 352} // End llvm namespace 353 354// Because of the way .a files work, we must force the BasicAA implementation to 355// be pulled in if the AliasAnalysis header is included. Otherwise we run 356// the risk of AliasAnalysis being used, but the default implementation not 357// being linked into the tool that uses it. 358FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis) 359FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis) 360 361#endif 362