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 34 namespace llvm { 35 36 class LoadInst; 37 class StoreInst; 38 class VAArgInst; 39 class TargetData; 40 class Pass; 41 class AnalysisUsage; 42 43 class AliasAnalysis { 44 protected: 45 const TargetData *TD; 46 47 private: 48 AliasAnalysis *AA; // Previous Alias Analysis to chain to. 49 50 protected: 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 62 public: 63 static char ID; // Class identification, replacement for typeinfo AliasAnalysis()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 /// getTargetData()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 /// Alias analysis result - Either we know for sure that it does not alias, we 87 /// know for sure it must alias, or we don't know anything: The two pointers 88 /// _might_ alias. This enum is designed so you can do things like: 89 /// if (AA.alias(P1, P2)) { ... } 90 /// to check to see if two pointers might alias. 91 /// 92 /// See docs/AliasAnalysis.html for more information on the specific meanings 93 /// of these values. 94 /// 95 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 96 97 /// alias - The main low level interface to the alias analysis implementation. 98 /// Returns a Result indicating whether the two pointers are aliased to each 99 /// other. This is the interface that must be implemented by specific alias 100 /// analysis implementations. 101 /// 102 virtual AliasResult alias(const Value *V1, unsigned V1Size, 103 const Value *V2, unsigned V2Size); 104 105 /// alias - A convenience wrapper for the case where the sizes are unknown. alias(const Value * V1,const Value * V2)106 AliasResult alias(const Value *V1, const Value *V2) { 107 return alias(V1, UnknownSize, V2, UnknownSize); 108 } 109 110 /// isNoAlias - A trivial helper function to check to see if the specified 111 /// pointers are no-alias. isNoAlias(const Value * V1,unsigned V1Size,const Value * V2,unsigned V2Size)112 bool isNoAlias(const Value *V1, unsigned V1Size, 113 const Value *V2, unsigned V2Size) { 114 return alias(V1, V1Size, V2, V2Size) == NoAlias; 115 } 116 117 /// pointsToConstantMemory - If the specified pointer is known to point into 118 /// constant global memory, return true. This allows disambiguation of store 119 /// instructions from constant pointers. 120 /// 121 virtual bool pointsToConstantMemory(const Value *P); 122 123 //===--------------------------------------------------------------------===// 124 /// Simple mod/ref information... 125 /// 126 127 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 128 /// bits which may be or'd together. 129 /// 130 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 131 132 133 /// ModRefBehavior - Summary of how a function affects memory in the program. 134 /// Loads from constant globals are not considered memory accesses for this 135 /// interface. Also, functions may freely modify stack space local to their 136 /// invocation without having to report it through these interfaces. 137 enum ModRefBehavior { 138 // DoesNotAccessMemory - This function does not perform any non-local loads 139 // or stores to memory. 140 // 141 // This property corresponds to the GCC 'const' attribute. 142 DoesNotAccessMemory, 143 144 // AccessesArguments - This function accesses function arguments in well 145 // known (possibly volatile) ways, but does not access any other memory. 146 AccessesArguments, 147 148 // AccessesArgumentsAndGlobals - This function has accesses function 149 // arguments and global variables well known (possibly volatile) ways, but 150 // does not access any other memory. 151 AccessesArgumentsAndGlobals, 152 153 // OnlyReadsMemory - This function does not perform any non-local stores or 154 // volatile loads, but may read from any memory location. 155 // 156 // This property corresponds to the GCC 'pure' attribute. 157 OnlyReadsMemory, 158 159 // UnknownModRefBehavior - This indicates that the function could not be 160 // classified into one of the behaviors above. 161 UnknownModRefBehavior 162 }; 163 164 /// getModRefBehavior - Return the behavior when calling the given call site. 165 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 166 167 /// getModRefBehavior - Return the behavior when calling the given function. 168 /// For use when the call site is not known. 169 virtual ModRefBehavior getModRefBehavior(const Function *F); 170 171 /// getIntrinsicModRefBehavior - Return the modref behavior of the intrinsic 172 /// with the given id. Most clients won't need this, because the regular 173 /// getModRefBehavior incorporates this information. 174 static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid); 175 176 /// doesNotAccessMemory - If the specified call is known to never read or 177 /// write memory, return true. If the call only reads from known-constant 178 /// memory, it is also legal to return true. Calls that unwind the stack 179 /// are legal for this predicate. 180 /// 181 /// Many optimizations (such as CSE and LICM) can be performed on such calls 182 /// without worrying about aliasing properties, and many calls have this 183 /// property (e.g. calls to 'sin' and 'cos'). 184 /// 185 /// This property corresponds to the GCC 'const' attribute. 186 /// doesNotAccessMemory(ImmutableCallSite CS)187 bool doesNotAccessMemory(ImmutableCallSite CS) { 188 return getModRefBehavior(CS) == DoesNotAccessMemory; 189 } 190 191 /// doesNotAccessMemory - If the specified function is known to never read or 192 /// write memory, return true. For use when the call site is not known. 193 /// doesNotAccessMemory(const Function * F)194 bool doesNotAccessMemory(const Function *F) { 195 return getModRefBehavior(F) == DoesNotAccessMemory; 196 } 197 198 /// onlyReadsMemory - If the specified call is known to only read from 199 /// non-volatile memory (or not access memory at all), return true. Calls 200 /// that unwind the stack are legal for this predicate. 201 /// 202 /// This property allows many common optimizations to be performed in the 203 /// absence of interfering store instructions, such as CSE of strlen calls. 204 /// 205 /// This property corresponds to the GCC 'pure' attribute. 206 /// onlyReadsMemory(ImmutableCallSite CS)207 bool onlyReadsMemory(ImmutableCallSite CS) { 208 ModRefBehavior MRB = getModRefBehavior(CS); 209 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 210 } 211 212 /// onlyReadsMemory - If the specified function is known to only read from 213 /// non-volatile memory (or not access memory at all), return true. For use 214 /// when the call site is not known. 215 /// onlyReadsMemory(const Function * F)216 bool onlyReadsMemory(const Function *F) { 217 ModRefBehavior MRB = getModRefBehavior(F); 218 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 219 } 220 221 222 /// getModRefInfo - Return information about whether or not an instruction may 223 /// read or write memory specified by the pointer operand. An instruction 224 /// that doesn't read or write memory may be trivially LICM'd for example. 225 226 /// getModRefInfo (for call sites) - Return whether information about whether 227 /// a particular call site modifies or reads the memory specified by the 228 /// pointer. 229 /// 230 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 231 const Value *P, unsigned Size); 232 233 /// getModRefInfo - Return information about whether two call sites may refer 234 /// to the same set of memory locations. See 235 /// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo 236 /// for details. 237 virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, 238 ImmutableCallSite CS2); 239 240 public: 241 /// Convenience functions... 242 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, unsigned Size); 243 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, unsigned Size); 244 ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, unsigned Size); getModRefInfo(const CallInst * C,const Value * P,unsigned Size)245 ModRefResult getModRefInfo(const CallInst *C, const Value *P, unsigned Size) { 246 return getModRefInfo(ImmutableCallSite(C), P, Size); 247 } getModRefInfo(const InvokeInst * I,const Value * P,unsigned Size)248 ModRefResult getModRefInfo(const InvokeInst *I, 249 const Value *P, unsigned Size) { 250 return getModRefInfo(ImmutableCallSite(I), P, Size); 251 } getModRefInfo(const Instruction * I,const Value * P,unsigned Size)252 ModRefResult getModRefInfo(const Instruction *I, 253 const Value *P, unsigned Size) { 254 switch (I->getOpcode()) { 255 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, P,Size); 256 case Instruction::Load: return getModRefInfo((const LoadInst*)I, P, Size); 257 case Instruction::Store: return getModRefInfo((const StoreInst*)I, P,Size); 258 case Instruction::Call: return getModRefInfo((const CallInst*)I, P, Size); 259 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,P,Size); 260 default: return NoModRef; 261 } 262 } 263 264 //===--------------------------------------------------------------------===// 265 /// Higher level methods for querying mod/ref information. 266 /// 267 268 /// canBasicBlockModify - Return true if it is possible for execution of the 269 /// specified basic block to modify the value pointed to by Ptr. 270 /// 271 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 272 273 /// canInstructionRangeModify - Return true if it is possible for the 274 /// execution of the specified instructions to modify the value pointed to by 275 /// Ptr. The instructions to consider are all of the instructions in the 276 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 277 /// 278 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 279 const Value *Ptr, unsigned Size); 280 281 //===--------------------------------------------------------------------===// 282 /// Methods that clients should call when they transform the program to allow 283 /// alias analyses to update their internal data structures. Note that these 284 /// methods may be called on any instruction, regardless of whether or not 285 /// they have pointer-analysis implications. 286 /// 287 288 /// deleteValue - This method should be called whenever an LLVM Value is 289 /// deleted from the program, for example when an instruction is found to be 290 /// redundant and is eliminated. 291 /// 292 virtual void deleteValue(Value *V); 293 294 /// copyValue - This method should be used whenever a preexisting value in the 295 /// program is copied or cloned, introducing a new value. Note that analysis 296 /// implementations should tolerate clients that use this method to introduce 297 /// the same value multiple times: if the analysis already knows about a 298 /// value, it should ignore the request. 299 /// 300 virtual void copyValue(Value *From, Value *To); 301 302 /// replaceWithNewValue - This method is the obvious combination of the two 303 /// above, and it provided as a helper to simplify client code. 304 /// replaceWithNewValue(Value * Old,Value * New)305 void replaceWithNewValue(Value *Old, Value *New) { 306 copyValue(Old, New); 307 deleteValue(Old); 308 } 309 }; 310 311 /// isNoAliasCall - Return true if this pointer is returned by a noalias 312 /// function. 313 bool isNoAliasCall(const Value *V); 314 315 /// isIdentifiedObject - Return true if this pointer refers to a distinct and 316 /// identifiable object. This returns true for: 317 /// Global Variables and Functions (but not Global Aliases) 318 /// Allocas and Mallocs 319 /// ByVal and NoAlias Arguments 320 /// NoAlias returns 321 /// 322 bool isIdentifiedObject(const Value *V); 323 324 } // End llvm namespace 325 326 // Because of the way .a files work, we must force the BasicAA implementation to 327 // be pulled in if the AliasAnalysis header is included. Otherwise we run 328 // the risk of AliasAnalysis being used, but the default implementation not 329 // being linked into the tool that uses it. 330 FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis) 331 FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis) 332 333 #endif 334