AliasAnalysis.h revision 66e08cf79a052dd75bf6fa2f94abd4c0a18cb019
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 /// pointsToConstantMemory - If the specified pointer is known to point into 98 /// constant global memory, return true. This allows disambiguation of store 99 /// instructions from constant pointers. 100 /// 101 virtual bool pointsToConstantMemory(const Value *P); 102 103 //===--------------------------------------------------------------------===// 104 /// Simple mod/ref information... 105 /// 106 107 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 108 /// bits which may be or'd together. 109 /// 110 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 111 112 113 /// ModRefBehavior - Summary of how a function affects memory in the program. 114 /// Loads from constant globals are not considered memory accesses for this 115 /// interface. Also, functions may freely modify stack space local to their 116 /// invocation without having to report it through these interfaces. 117 enum ModRefBehavior { 118 // DoesNotAccessMemory - This function does not perform any non-local loads 119 // or stores to memory. 120 // 121 // This property corresponds to the GCC 'const' attribute. 122 DoesNotAccessMemory, 123 124 // AccessesArguments - This function accesses function arguments in well 125 // known (possibly volatile) ways, but does not access any other memory. 126 // 127 // Clients may use the Info parameter of getModRefBehavior to get specific 128 // information about how pointer arguments are used. 129 AccessesArguments, 130 131 // AccessesArgumentsAndGlobals - This function has accesses function 132 // arguments and global variables well known (possibly volatile) ways, but 133 // 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 AccessesArgumentsAndGlobals, 138 139 // OnlyReadsMemory - This function does not perform any non-local stores or 140 // volatile loads, but may read from any memory location. 141 // 142 // This property corresponds to the GCC 'pure' attribute. 143 OnlyReadsMemory, 144 145 // UnknownModRefBehavior - This indicates that the function could not be 146 // classified into one of the behaviors above. 147 UnknownModRefBehavior 148 }; 149 150 /// PointerAccessInfo - This struct is used to return results for pointers, 151 /// globals, and the return value of a function. 152 struct PointerAccessInfo { 153 /// V - The value this record corresponds to. This may be an Argument for 154 /// the function, a GlobalVariable, or null, corresponding to the return 155 /// value for the function. 156 Value *V; 157 158 /// ModRefInfo - Whether the pointer is loaded or stored to/from. 159 /// 160 ModRefResult ModRefInfo; 161 162 /// AccessType - Specific fine-grained access information for the argument. 163 /// If none of these classifications is general enough, the 164 /// getModRefBehavior method should not return AccessesArguments*. If a 165 /// record is not returned for a particular argument, the argument is never 166 /// dead and never dereferenced. 167 enum AccessType { 168 /// ScalarAccess - The pointer is dereferenced. 169 /// 170 ScalarAccess, 171 172 /// ArrayAccess - The pointer is indexed through as an array of elements. 173 /// 174 ArrayAccess, 175 176 /// ElementAccess ?? P->F only? 177 178 /// CallsThrough - Indirect calls are made through the specified function 179 /// pointer. 180 CallsThrough 181 }; 182 }; 183 184 /// getModRefBehavior - Return the behavior when calling the given call site. 185 virtual ModRefBehavior getModRefBehavior(CallSite CS, 186 std::vector<PointerAccessInfo> *Info = 0); 187 188 /// getModRefBehavior - Return the behavior when calling the given function. 189 /// For use when the call site is not known. 190 virtual ModRefBehavior getModRefBehavior(Function *F, 191 std::vector<PointerAccessInfo> *Info = 0); 192 193 /// doesNotAccessMemory - If the specified call is known to never read or 194 /// write memory, return true. If the call only reads from known-constant 195 /// memory, it is also legal to return true. Calls that unwind the stack 196 /// are legal for this predicate. 197 /// 198 /// Many optimizations (such as CSE and LICM) can be performed on such calls 199 /// without worrying about aliasing properties, and many calls have this 200 /// property (e.g. calls to 'sin' and 'cos'). 201 /// 202 /// This property corresponds to the GCC 'const' attribute. 203 /// 204 bool doesNotAccessMemory(CallSite CS) { 205 return getModRefBehavior(CS) == DoesNotAccessMemory; 206 } 207 208 /// doesNotAccessMemory - If the specified function is known to never read or 209 /// write memory, return true. For use when the call site is not known. 210 /// 211 bool doesNotAccessMemory(Function *F) { 212 return getModRefBehavior(F) == DoesNotAccessMemory; 213 } 214 215 /// onlyReadsMemory - If the specified call is known to only read from 216 /// non-volatile memory (or not access memory at all), return true. Calls 217 /// that unwind the stack are legal for this predicate. 218 /// 219 /// This property allows many common optimizations to be performed in the 220 /// absence of interfering store instructions, such as CSE of strlen calls. 221 /// 222 /// This property corresponds to the GCC 'pure' attribute. 223 /// 224 bool onlyReadsMemory(CallSite CS) { 225 ModRefBehavior MRB = getModRefBehavior(CS); 226 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 227 } 228 229 /// onlyReadsMemory - If the specified function is known to only read from 230 /// non-volatile memory (or not access memory at all), return true. For use 231 /// when the call site is not known. 232 /// 233 bool onlyReadsMemory(Function *F) { 234 ModRefBehavior MRB = getModRefBehavior(F); 235 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 236 } 237 238 239 /// getModRefInfo - Return information about whether or not an instruction may 240 /// read or write memory specified by the pointer operand. An instruction 241 /// that doesn't read or write memory may be trivially LICM'd for example. 242 243 /// getModRefInfo (for call sites) - Return whether information about whether 244 /// a particular call site modifies or reads the memory specified by the 245 /// pointer. 246 /// 247 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 248 249 /// getModRefInfo - Return information about whether two call sites may refer 250 /// to the same set of memory locations. This function returns NoModRef if 251 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory 252 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or 253 /// ModRef if CS1 might read or write memory accessed by CS2. 254 /// 255 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 256 257public: 258 /// Convenience functions... 259 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 260 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size); 261 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 262 return getModRefInfo(CallSite(C), P, Size); 263 } 264 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) { 265 return getModRefInfo(CallSite(I), P, Size); 266 } 267 ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) { 268 return AliasAnalysis::ModRef; 269 } 270 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 271 switch (I->getOpcode()) { 272 case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size); 273 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 274 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 275 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 276 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); 277 default: return NoModRef; 278 } 279 } 280 281 //===--------------------------------------------------------------------===// 282 /// Higher level methods for querying mod/ref information. 283 /// 284 285 /// canBasicBlockModify - Return true if it is possible for execution of the 286 /// specified basic block to modify the value pointed to by Ptr. 287 /// 288 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 289 290 /// canInstructionRangeModify - Return true if it is possible for the 291 /// execution of the specified instructions to modify the value pointed to by 292 /// Ptr. The instructions to consider are all of the instructions in the 293 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 294 /// 295 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 296 const Value *Ptr, unsigned Size); 297 298 //===--------------------------------------------------------------------===// 299 /// Methods that clients should call when they transform the program to allow 300 /// alias analyses to update their internal data structures. Note that these 301 /// methods may be called on any instruction, regardless of whether or not 302 /// they have pointer-analysis implications. 303 /// 304 305 /// deleteValue - This method should be called whenever an LLVM Value is 306 /// deleted from the program, for example when an instruction is found to be 307 /// redundant and is eliminated. 308 /// 309 virtual void deleteValue(Value *V); 310 311 /// copyValue - This method should be used whenever a preexisting value in the 312 /// program is copied or cloned, introducing a new value. Note that analysis 313 /// implementations should tolerate clients that use this method to introduce 314 /// the same value multiple times: if the analysis already knows about a 315 /// value, it should ignore the request. 316 /// 317 virtual void copyValue(Value *From, Value *To); 318 319 /// replaceWithNewValue - This method is the obvious combination of the two 320 /// above, and it provided as a helper to simplify client code. 321 /// 322 void replaceWithNewValue(Value *Old, Value *New) { 323 copyValue(Old, New); 324 deleteValue(Old); 325 } 326}; 327 328/// isNoAliasCall - Return true if this pointer is returned by a noalias 329/// function. 330bool isNoAliasCall(const Value *V); 331 332/// isIdentifiedObject - Return true if this pointer refers to a distinct and 333/// identifiable object. This returns true for: 334/// Global Variables and Functions (but not Global Aliases) 335/// Allocas and Mallocs 336/// ByVal and NoAlias Arguments 337/// NoAlias returns 338/// 339bool isIdentifiedObject(const Value *V); 340 341} // End llvm namespace 342 343// Because of the way .a files work, we must force the BasicAA implementation to 344// be pulled in if the AliasAnalysis header is included. Otherwise we run 345// the risk of AliasAnalysis being used, but the default implementation not 346// being linked into the tool that uses it. 347FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis) 348FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis) 349 350#endif 351