AliasAnalysis.h revision 5753a4a0033da4add45f2e9930a4e1159d92a869
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 /// getMustAliases - If there are any pointers known that must alias this 98 /// pointer, return them now. This allows alias-set based alias analyses to 99 /// perform a form a value numbering (which is exposed by load-vn). If an 100 /// alias analysis supports this, it should ADD any must aliased pointers to 101 /// the specified vector. 102 /// 103 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals); 104 105 /// pointsToConstantMemory - If the specified pointer is known to point into 106 /// constant global memory, return true. This allows disambiguation of store 107 /// instructions from constant pointers. 108 /// 109 virtual bool pointsToConstantMemory(const Value *P); 110 111 //===--------------------------------------------------------------------===// 112 /// Simple mod/ref information... 113 /// 114 115 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 116 /// bits which may be or'd together. 117 /// 118 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 119 120 121 /// ModRefBehavior - Summary of how a function affects memory in the program. 122 /// Loads from constant globals are not considered memory accesses for this 123 /// interface. Also, functions may freely modify stack space local to their 124 /// invocation without having to report it through these interfaces. 125 enum ModRefBehavior { 126 // DoesNotAccessMemory - This function does not perform any non-local loads 127 // or stores to memory. 128 // 129 // This property corresponds to the GCC 'const' attribute. 130 DoesNotAccessMemory, 131 132 // AccessesArguments - This function accesses function arguments in well 133 // known (possibly volatile) ways, but does not access any other memory. 134 // 135 // Clients may use the Info parameter of getModRefBehavior to get specific 136 // information about how pointer arguments are used. 137 AccessesArguments, 138 139 // AccessesArgumentsAndGlobals - This function has accesses function 140 // arguments and global variables well known (possibly volatile) ways, but 141 // does not access any other memory. 142 // 143 // Clients may use the Info parameter of getModRefBehavior to get specific 144 // information about how pointer arguments are used. 145 AccessesArgumentsAndGlobals, 146 147 // OnlyReadsMemory - This function does not perform any non-local stores or 148 // volatile loads, but may read from any memory location. 149 // 150 // This property corresponds to the GCC 'pure' attribute. 151 OnlyReadsMemory, 152 153 // UnknownModRefBehavior - This indicates that the function could not be 154 // classified into one of the behaviors above. 155 UnknownModRefBehavior 156 }; 157 158 /// PointerAccessInfo - This struct is used to return results for pointers, 159 /// globals, and the return value of a function. 160 struct PointerAccessInfo { 161 /// V - The value this record corresponds to. This may be an Argument for 162 /// the function, a GlobalVariable, or null, corresponding to the return 163 /// value for the function. 164 Value *V; 165 166 /// ModRefInfo - Whether the pointer is loaded or stored to/from. 167 /// 168 ModRefResult ModRefInfo; 169 170 /// AccessType - Specific fine-grained access information for the argument. 171 /// If none of these classifications is general enough, the 172 /// getModRefBehavior method should not return AccessesArguments*. If a 173 /// record is not returned for a particular argument, the argument is never 174 /// dead and never dereferenced. 175 enum AccessType { 176 /// ScalarAccess - The pointer is dereferenced. 177 /// 178 ScalarAccess, 179 180 /// ArrayAccess - The pointer is indexed through as an array of elements. 181 /// 182 ArrayAccess, 183 184 /// ElementAccess ?? P->F only? 185 186 /// CallsThrough - Indirect calls are made through the specified function 187 /// pointer. 188 CallsThrough 189 }; 190 }; 191 192 /// getModRefBehavior - Return the behavior when calling the given call site. 193 virtual ModRefBehavior getModRefBehavior(CallSite CS, 194 std::vector<PointerAccessInfo> *Info = 0); 195 196 /// getModRefBehavior - Return the behavior when calling the given function. 197 /// For use when the call site is not known. 198 virtual ModRefBehavior getModRefBehavior(Function *F, 199 std::vector<PointerAccessInfo> *Info = 0); 200 201 /// doesNotAccessMemory - If the specified call is known to never read or 202 /// write memory, return true. If the call only reads from known-constant 203 /// memory, it is also legal to return true. Calls that unwind the stack 204 /// are legal for this predicate. 205 /// 206 /// Many optimizations (such as CSE and LICM) can be performed on such calls 207 /// without worrying about aliasing properties, and many calls have this 208 /// property (e.g. calls to 'sin' and 'cos'). 209 /// 210 /// This property corresponds to the GCC 'const' attribute. 211 /// 212 bool doesNotAccessMemory(CallSite CS) { 213 return getModRefBehavior(CS) == DoesNotAccessMemory; 214 } 215 216 /// doesNotAccessMemory - If the specified function is known to never read or 217 /// write memory, return true. For use when the call site is not known. 218 /// 219 bool doesNotAccessMemory(Function *F) { 220 return getModRefBehavior(F) == DoesNotAccessMemory; 221 } 222 223 /// onlyReadsMemory - If the specified call is known to only read from 224 /// non-volatile memory (or not access memory at all), return true. Calls 225 /// that unwind the stack are legal for this predicate. 226 /// 227 /// This property allows many common optimizations to be performed in the 228 /// absence of interfering store instructions, such as CSE of strlen calls. 229 /// 230 /// This property corresponds to the GCC 'pure' attribute. 231 /// 232 bool onlyReadsMemory(CallSite CS) { 233 ModRefBehavior MRB = getModRefBehavior(CS); 234 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 235 } 236 237 /// onlyReadsMemory - If the specified function is known to only read from 238 /// non-volatile memory (or not access memory at all), return true. For use 239 /// when the call site is not known. 240 /// 241 bool onlyReadsMemory(Function *F) { 242 ModRefBehavior MRB = getModRefBehavior(F); 243 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 244 } 245 246 247 /// getModRefInfo - Return information about whether or not an instruction may 248 /// read or write memory specified by the pointer operand. An instruction 249 /// that doesn't read or write memory may be trivially LICM'd for example. 250 251 /// getModRefInfo (for call sites) - Return whether information about whether 252 /// a particular call site modifies or reads the memory specified by the 253 /// pointer. 254 /// 255 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 256 257 /// getModRefInfo - Return information about whether two call sites may refer 258 /// to the same set of memory locations. This function returns NoModRef if 259 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory 260 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or 261 /// ModRef if CS1 might read or write memory accessed by CS2. 262 /// 263 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 264 265 /// hasNoModRefInfoForCalls - Return true if the analysis has no mod/ref 266 /// information for pairs of function calls (other than "pure" and "const" 267 /// functions). This can be used by clients to avoid many pointless queries. 268 /// Remember that if you override this and chain to another analysis, you must 269 /// make sure that it doesn't have mod/ref info either. 270 /// 271 virtual bool hasNoModRefInfoForCalls() const; 272 273public: 274 /// Convenience functions... 275 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 276 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size); 277 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 278 return getModRefInfo(CallSite(C), P, Size); 279 } 280 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) { 281 return getModRefInfo(CallSite(I), P, Size); 282 } 283 ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) { 284 return AliasAnalysis::ModRef; 285 } 286 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 287 switch (I->getOpcode()) { 288 case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size); 289 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 290 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 291 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 292 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); 293 default: return NoModRef; 294 } 295 } 296 297 //===--------------------------------------------------------------------===// 298 /// Higher level methods for querying mod/ref information. 299 /// 300 301 /// canBasicBlockModify - Return true if it is possible for execution of the 302 /// specified basic block to modify the value pointed to by Ptr. 303 /// 304 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 305 306 /// canInstructionRangeModify - Return true if it is possible for the 307 /// execution of the specified instructions to modify the value pointed to by 308 /// Ptr. The instructions to consider are all of the instructions in the 309 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 310 /// 311 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 312 const Value *Ptr, unsigned Size); 313 314 //===--------------------------------------------------------------------===// 315 /// Methods that clients should call when they transform the program to allow 316 /// alias analyses to update their internal data structures. Note that these 317 /// methods may be called on any instruction, regardless of whether or not 318 /// they have pointer-analysis implications. 319 /// 320 321 /// deleteValue - This method should be called whenever an LLVM Value is 322 /// deleted from the program, for example when an instruction is found to be 323 /// redundant and is eliminated. 324 /// 325 virtual void deleteValue(Value *V); 326 327 /// copyValue - This method should be used whenever a preexisting value in the 328 /// program is copied or cloned, introducing a new value. Note that analysis 329 /// implementations should tolerate clients that use this method to introduce 330 /// the same value multiple times: if the analysis already knows about a 331 /// value, it should ignore the request. 332 /// 333 virtual void copyValue(Value *From, Value *To); 334 335 /// replaceWithNewValue - This method is the obvious combination of the two 336 /// above, and it provided as a helper to simplify client code. 337 /// 338 void replaceWithNewValue(Value *Old, Value *New) { 339 copyValue(Old, New); 340 deleteValue(Old); 341 } 342}; 343 344/// isNoAliasCall - Return true if this pointer is returned by a noalias 345/// function. 346bool isNoAliasCall(const Value *V); 347 348/// isIdentifiedObject - Return true if this pointer refers to a distinct and 349/// identifiable object. This returns true for: 350/// Global Variables and Functions (but not Global Aliases) 351/// Allocas and Mallocs 352/// ByVal and NoAlias Arguments 353/// NoAlias returns 354/// 355bool isIdentifiedObject(const Value *V); 356 357} // End llvm namespace 358 359// Because of the way .a files work, we must force the BasicAA implementation to 360// be pulled in if the AliasAnalysis header is included. Otherwise we run 361// the risk of AliasAnalysis being used, but the default implementation not 362// being linked into the tool that uses it. 363FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis) 364FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis) 365 366#endif 367