AliasAnalysis.h revision 6df60a9effe4d20a48cfd9d105c0ab3c5dc3e690
1//===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source 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/Support/IncludeFile.h" 35 36namespace llvm { 37 38class LoadInst; 39class StoreInst; 40class VAArgInst; 41class TargetData; 42class Pass; 43class AnalysisUsage; 44 45class AliasAnalysis { 46protected: 47 const TargetData *TD; 48 AliasAnalysis *AA; // Previous Alias Analysis to chain to. 49 50 /// InitializeAliasAnalysis - Subclasses must call this method to initialize 51 /// the AliasAnalysis interface before any other methods are called. This is 52 /// typically called by the run* methods of these subclasses. This may be 53 /// called multiple times. 54 /// 55 void InitializeAliasAnalysis(Pass *P); 56 57 // getAnalysisUsage - All alias analysis implementations should invoke this 58 // directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that 59 // TargetData is required by the pass. 60 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 61 62public: 63 AliasAnalysis() : TD(0), AA(0) {} 64 virtual ~AliasAnalysis(); // We want to be subclassed 65 66 /// getTargetData - Every alias analysis implementation depends on the size of 67 /// data items in the current Target. This provides a uniform way to handle 68 /// it. 69 /// 70 const TargetData &getTargetData() const { return *TD; } 71 72 //===--------------------------------------------------------------------===// 73 /// Alias Queries... 74 /// 75 76 /// Alias analysis result - Either we know for sure that it does not alias, we 77 /// know for sure it must alias, or we don't know anything: The two pointers 78 /// _might_ alias. This enum is designed so you can do things like: 79 /// if (AA.alias(P1, P2)) { ... } 80 /// to check to see if two pointers might alias. 81 /// 82 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 83 84 /// alias - The main low level interface to the alias analysis implementation. 85 /// Returns a Result indicating whether the two pointers are aliased to each 86 /// other. This is the interface that must be implemented by specific alias 87 /// analysis implementations. 88 /// 89 virtual AliasResult alias(const Value *V1, unsigned V1Size, 90 const Value *V2, unsigned V2Size); 91 92 /// getMustAliases - If there are any pointers known that must alias this 93 /// pointer, return them now. This allows alias-set based alias analyses to 94 /// perform a form a value numbering (which is exposed by load-vn). If an 95 /// alias analysis supports this, it should ADD any must aliased pointers to 96 /// the specified vector. 97 /// 98 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals); 99 100 /// pointsToConstantMemory - If the specified pointer is known to point into 101 /// constant global memory, return true. This allows disambiguation of store 102 /// instructions from constant pointers. 103 /// 104 virtual bool pointsToConstantMemory(const Value *P); 105 106 //===--------------------------------------------------------------------===// 107 /// Simple mod/ref information... 108 /// 109 110 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 111 /// bits which may be or'd together. 112 /// 113 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 114 115 116 /// ModRefBehavior - Summary of how a function affects memory in the program. 117 /// Loads from constant globals are not considered memory accesses for this 118 /// interface. Also, functions may freely modify stack space local to their 119 /// invocation without having to report it through these interfaces. 120 enum ModRefBehavior { 121 // DoesNotAccessMemory - This function does not perform any non-local loads 122 // or stores to memory. 123 // 124 // This property corresponds to the GCC 'const' attribute. 125 DoesNotAccessMemory, 126 127 // AccessesArguments - This function accesses function arguments in 128 // non-volatile and well known ways, but does not access any other memory. 129 // 130 // Clients may call getArgumentAccesses to get specific information about 131 // how pointer arguments are used. 132 AccessesArguments, 133 134 // AccessesArgumentsAndGlobals - This function has accesses function 135 // arguments and global variables in non-volatile and well-known ways, but 136 // does not access any other memory. 137 // 138 // Clients may call getArgumentAccesses to get specific information about 139 // how pointer arguments and globals are used. 140 AccessesArgumentsAndGlobals, 141 142 // OnlyReadsMemory - This function does not perform any non-local stores or 143 // volatile loads, but may read from any memory location. 144 // 145 // This property corresponds to the GCC 'pure' attribute. 146 OnlyReadsMemory, 147 148 // UnknownModRefBehavior - This indicates that the function could not be 149 // classified into one of the behaviors above. 150 UnknownModRefBehavior 151 }; 152 153 /// PointerAccessInfo - This struct is used to return results for pointers, 154 /// globals, and the return value of a function. 155 struct PointerAccessInfo { 156 /// V - The value this record corresponds to. This may be an Argument for 157 /// the function, a GlobalVariable, or null, corresponding to the return 158 /// value for the function. 159 Value *V; 160 161 /// ModRefInfo - Whether the pointer is loaded or stored to/from. 162 /// 163 ModRefResult ModRefInfo; 164 165 /// AccessType - Specific fine-grained access information for the argument. 166 /// If none of these classifications is general enough, the 167 /// getModRefBehavior method should not return AccessesArguments*. If a 168 /// record is not returned for a particular argument, the argument is never 169 /// dead and never dereferenced. 170 enum AccessType { 171 /// ScalarAccess - The pointer is dereferenced. 172 /// 173 ScalarAccess, 174 175 /// ArrayAccess - The pointer is indexed through as an array of elements. 176 /// 177 ArrayAccess, 178 179 /// ElementAccess ?? P->F only? 180 181 /// CallsThrough - Indirect calls are made through the specified function 182 /// pointer. 183 CallsThrough 184 }; 185 }; 186 187 /// getModRefBehavior - Return the behavior of the specified function if 188 /// called from the specified call site. The call site may be null in which 189 /// case the most generic behavior of this function should be returned. 190 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS, 191 std::vector<PointerAccessInfo> *Info = 0); 192 193 /// doesNotAccessMemory - If the specified function is known to never read or 194 /// write memory, return true. If the function only reads from known-constant 195 /// memory, it is also legal to return true. Functions that unwind the stack 196 /// are not legal for this predicate. 197 /// 198 /// Many optimizations (such as CSE and LICM) can be performed on calls to it, 199 /// without worrying about aliasing properties, and many functions have this 200 /// property (e.g. 'sin' and 'cos'). 201 /// 202 /// This property corresponds to the GCC 'const' attribute. 203 /// 204 bool doesNotAccessMemory(Function *F) { 205 return getModRefBehavior(F, CallSite()) == DoesNotAccessMemory; 206 } 207 208 /// onlyReadsMemory - If the specified function is known to only read from 209 /// non-volatile memory (or not access memory at all), return true. Functions 210 /// that unwind the stack are not legal for this predicate. 211 /// 212 /// This property allows many common optimizations to be performed in the 213 /// absence of interfering store instructions, such as CSE of strlen calls. 214 /// 215 /// This property corresponds to the GCC 'pure' attribute. 216 /// 217 bool onlyReadsMemory(Function *F) { 218 /// FIXME: If the analysis returns more precise info, we can reduce it to 219 /// this. 220 ModRefBehavior MRB = getModRefBehavior(F, CallSite()); 221 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 222 } 223 224 225 /// getModRefInfo - Return information about whether or not an instruction may 226 /// read or write memory specified by the pointer operand. An instruction 227 /// that doesn't read or write memory may be trivially LICM'd for example. 228 229 /// getModRefInfo (for call sites) - Return whether information about whether 230 /// a particular call site modifies or reads the memory specified by the 231 /// pointer. 232 /// 233 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 234 235 /// getModRefInfo - Return information about whether two call sites may refer 236 /// to the same set of memory locations. This function returns NoModRef if 237 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory 238 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or 239 /// ModRef if CS1 might read or write memory accessed by CS2. 240 /// 241 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 242 243 /// hasNoModRefInfoForCalls - Return true if the analysis has no mod/ref 244 /// information for pairs of function calls (other than "pure" and "const" 245 /// functions). This can be used by clients to avoid many pointless queries. 246 /// Remember that if you override this and chain to another analysis, you must 247 /// make sure that it doesn't have mod/ref info either. 248 /// 249 virtual bool hasNoModRefInfoForCalls() const; 250 251 /// Convenience functions... 252 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 253 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size); 254 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 255 return getModRefInfo(CallSite(C), P, Size); 256 } 257 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) { 258 return getModRefInfo(CallSite(I), P, Size); 259 } 260 ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) { 261 return AliasAnalysis::Mod; 262 } 263 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 264 switch (I->getOpcode()) { 265 case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size); 266 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 267 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 268 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 269 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); 270 default: return NoModRef; 271 } 272 } 273 274 //===--------------------------------------------------------------------===// 275 /// Higher level methods for querying mod/ref information. 276 /// 277 278 /// canBasicBlockModify - Return true if it is possible for execution of the 279 /// specified basic block to modify the value pointed to by Ptr. 280 /// 281 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 282 283 /// canInstructionRangeModify - Return true if it is possible for the 284 /// execution of the specified instructions to modify the value pointed to by 285 /// Ptr. The instructions to consider are all of the instructions in the 286 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 287 /// 288 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 289 const Value *Ptr, unsigned Size); 290 291 //===--------------------------------------------------------------------===// 292 /// Methods that clients should call when they transform the program to allow 293 /// alias analyses to update their internal data structures. Note that these 294 /// methods may be called on any instruction, regardless of whether or not 295 /// they have pointer-analysis implications. 296 /// 297 298 /// deleteValue - This method should be called whenever an LLVM Value is 299 /// deleted from the program, for example when an instruction is found to be 300 /// redundant and is eliminated. 301 /// 302 virtual void deleteValue(Value *V); 303 304 /// copyValue - This method should be used whenever a preexisting value in the 305 /// program is copied or cloned, introducing a new value. Note that analysis 306 /// implementations should tolerate clients that use this method to introduce 307 /// the same value multiple times: if the analysis already knows about a 308 /// value, it should ignore the request. 309 /// 310 virtual void copyValue(Value *From, Value *To); 311 312 /// replaceWithNewValue - This method is the obvious combination of the two 313 /// above, and it provided as a helper to simplify client code. 314 /// 315 void replaceWithNewValue(Value *Old, Value *New) { 316 copyValue(Old, New); 317 deleteValue(Old); 318 } 319}; 320 321// Because of the way .a files work, we must force the BasicAA implementation to 322// be pulled in if the AliasAnalysis header is included. Otherwise we run 323// the risk of AliasAnalysis being used, but the default implementation not 324// being linked into the tool that uses it. 325// 326extern int BasicAAStub; 327static IncludeFile HDR_INCLUDE_BASICAA_CPP(&BasicAAStub); 328 329} // End llvm namespace 330 331#endif 332