AliasAnalysis.h revision a41af344c2964573318a77e2b43eafd4d3804003
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 34namespace llvm { 35 36class LoadInst; 37class StoreInst; 38class VAArgInst; 39class TargetData; 40class Pass; 41class AnalysisUsage; 42 43class AliasAnalysis { 44protected: 45 const TargetData *TD; 46 AliasAnalysis *AA; // Previous Alias Analysis to chain to. 47 48 /// InitializeAliasAnalysis - Subclasses must call this method to initialize 49 /// the AliasAnalysis interface before any other methods are called. This is 50 /// typically called by the run* methods of these subclasses. This may be 51 /// called multiple times. 52 /// 53 void InitializeAliasAnalysis(Pass *P); 54 55 /// getAnalysisUsage - All alias analysis implementations should invoke this 56 /// directly (using AliasAnalysis::getAnalysisUsage(AU)). 57 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 58 59public: 60 static char ID; // Class identification, replacement for typeinfo 61 AliasAnalysis() : TD(0), AA(0) {} 62 virtual ~AliasAnalysis(); // We want to be subclassed 63 64 /// UnknownSize - This is a special value which can be used with the 65 /// size arguments in alias queries to indicate that the caller does not 66 /// know the sizes of the potential memory references. 67 static unsigned const UnknownSize = ~0u; 68 69 /// getTargetData - Return a pointer to the current TargetData object, or 70 /// null if no TargetData object is available. 71 /// 72 const TargetData *getTargetData() const { return TD; } 73 74 /// getTypeStoreSize - Return the TargetData store size for the given type, 75 /// if known, or a conservative value otherwise. 76 /// 77 unsigned getTypeStoreSize(const Type *Ty); 78 79 //===--------------------------------------------------------------------===// 80 /// Alias Queries... 81 /// 82 83 /// Alias analysis result - Either we know for sure that it does not alias, we 84 /// know for sure it must alias, or we don't know anything: The two pointers 85 /// _might_ alias. This enum is designed so you can do things like: 86 /// if (AA.alias(P1, P2)) { ... } 87 /// to check to see if two pointers might alias. 88 /// 89 /// See docs/AliasAnalysis.html for more information on the specific meanings 90 /// of these values. 91 /// 92 enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; 93 94 /// alias - The main low level interface to the alias analysis implementation. 95 /// Returns a Result indicating whether the two pointers are aliased to each 96 /// other. This is the interface that must be implemented by specific alias 97 /// analysis implementations. 98 /// 99 virtual AliasResult alias(const Value *V1, unsigned V1Size, 100 const Value *V2, unsigned V2Size); 101 102 /// alias - A convenience wrapper for the case where the sizes are unknown. 103 AliasResult alias(const Value *V1, const Value *V2) { 104 return alias(V1, UnknownSize, V2, UnknownSize); 105 } 106 107 /// isNoAlias - A trivial helper function to check to see if the specified 108 /// pointers are no-alias. 109 bool isNoAlias(const Value *V1, unsigned V1Size, 110 const Value *V2, unsigned V2Size) { 111 return alias(V1, V1Size, V2, V2Size) == NoAlias; 112 } 113 114 /// pointsToConstantMemory - If the specified pointer is known to point into 115 /// constant global memory, return true. This allows disambiguation of store 116 /// instructions from constant pointers. 117 /// 118 virtual bool pointsToConstantMemory(const Value *P); 119 120 //===--------------------------------------------------------------------===// 121 /// Simple mod/ref information... 122 /// 123 124 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 125 /// bits which may be or'd together. 126 /// 127 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 128 129 130 /// ModRefBehavior - Summary of how a function affects memory in the program. 131 /// Loads from constant globals are not considered memory accesses for this 132 /// interface. Also, functions may freely modify stack space local to their 133 /// invocation without having to report it through these interfaces. 134 enum ModRefBehavior { 135 // DoesNotAccessMemory - This function does not perform any non-local loads 136 // or stores to memory. 137 // 138 // This property corresponds to the GCC 'const' attribute. 139 DoesNotAccessMemory, 140 141 // AccessesArguments - This function accesses function arguments in well 142 // known (possibly volatile) ways, but does not access any other memory. 143 // 144 // Clients may use the Info parameter of getModRefBehavior to get specific 145 // information about how pointer arguments are used. 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 // 152 // Clients may use the Info parameter of getModRefBehavior to get specific 153 // information about how pointer arguments are used. 154 AccessesArgumentsAndGlobals, 155 156 // OnlyReadsMemory - This function does not perform any non-local stores or 157 // volatile loads, but may read from any memory location. 158 // 159 // This property corresponds to the GCC 'pure' attribute. 160 OnlyReadsMemory, 161 162 // UnknownModRefBehavior - This indicates that the function could not be 163 // classified into one of the behaviors above. 164 UnknownModRefBehavior 165 }; 166 167 /// getModRefBehavior - Return the behavior when calling the given call site. 168 virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); 169 170 /// getModRefBehavior - Return the behavior when calling the given function. 171 /// For use when the call site is not known. 172 virtual ModRefBehavior getModRefBehavior(const Function *F); 173 174 /// getIntrinsicModRefBehavior - Return the modref behavior of the intrinsic 175 /// with the given id. 176 static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid); 177 178 /// doesNotAccessMemory - If the specified call is known to never read or 179 /// write memory, return true. If the call only reads from known-constant 180 /// memory, it is also legal to return true. Calls that unwind the stack 181 /// are legal for this predicate. 182 /// 183 /// Many optimizations (such as CSE and LICM) can be performed on such calls 184 /// without worrying about aliasing properties, and many calls have this 185 /// property (e.g. calls to 'sin' and 'cos'). 186 /// 187 /// This property corresponds to the GCC 'const' attribute. 188 /// 189 bool doesNotAccessMemory(ImmutableCallSite CS) { 190 return getModRefBehavior(CS) == DoesNotAccessMemory; 191 } 192 193 /// doesNotAccessMemory - If the specified function is known to never read or 194 /// write memory, return true. For use when the call site is not known. 195 /// 196 bool doesNotAccessMemory(const Function *F) { 197 return getModRefBehavior(F) == DoesNotAccessMemory; 198 } 199 200 /// onlyReadsMemory - If the specified call is known to only read from 201 /// non-volatile memory (or not access memory at all), return true. Calls 202 /// that unwind the stack are legal for this predicate. 203 /// 204 /// This property allows many common optimizations to be performed in the 205 /// absence of interfering store instructions, such as CSE of strlen calls. 206 /// 207 /// This property corresponds to the GCC 'pure' attribute. 208 /// 209 bool onlyReadsMemory(ImmutableCallSite CS) { 210 ModRefBehavior MRB = getModRefBehavior(CS); 211 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 212 } 213 214 /// onlyReadsMemory - If the specified function is known to only read from 215 /// non-volatile memory (or not access memory at all), return true. For use 216 /// when the call site is not known. 217 /// 218 bool onlyReadsMemory(const Function *F) { 219 ModRefBehavior MRB = getModRefBehavior(F); 220 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 221 } 222 223 224 /// getModRefInfo - Return information about whether or not an instruction may 225 /// read or write memory specified by the pointer operand. An instruction 226 /// that doesn't read or write memory may be trivially LICM'd for example. 227 228 /// getModRefInfo (for call sites) - Return whether information about whether 229 /// a particular call site modifies or reads the memory specified by the 230 /// pointer. 231 /// 232 virtual ModRefResult getModRefInfo(ImmutableCallSite CS, 233 const 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(ImmutableCallSite CS1, 242 ImmutableCallSite CS2); 243 244public: 245 /// Convenience functions... 246 ModRefResult getModRefInfo(const LoadInst *L, const Value *P, unsigned Size); 247 ModRefResult getModRefInfo(const StoreInst *S, const Value *P, unsigned Size); 248 ModRefResult getModRefInfo(const CallInst *C, const Value *P, unsigned Size) { 249 return getModRefInfo(ImmutableCallSite(C), P, Size); 250 } 251 ModRefResult getModRefInfo(const InvokeInst *I, 252 const Value *P, unsigned Size) { 253 return getModRefInfo(ImmutableCallSite(I), P, Size); 254 } 255 ModRefResult getModRefInfo(const VAArgInst* I, 256 const Value* P, unsigned Size) { 257 return AliasAnalysis::ModRef; 258 } 259 ModRefResult getModRefInfo(const Instruction *I, 260 const Value *P, unsigned Size) { 261 switch (I->getOpcode()) { 262 case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, P,Size); 263 case Instruction::Load: return getModRefInfo((const LoadInst*)I, P, Size); 264 case Instruction::Store: return getModRefInfo((const StoreInst*)I, P,Size); 265 case Instruction::Call: return getModRefInfo((const CallInst*)I, P, Size); 266 case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,P,Size); 267 default: return NoModRef; 268 } 269 } 270 271 //===--------------------------------------------------------------------===// 272 /// Higher level methods for querying mod/ref information. 273 /// 274 275 /// canBasicBlockModify - Return true if it is possible for execution of the 276 /// specified basic block to modify the value pointed to by Ptr. 277 /// 278 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 279 280 /// canInstructionRangeModify - Return true if it is possible for the 281 /// execution of the specified instructions to modify the value pointed to by 282 /// Ptr. The instructions to consider are all of the instructions in the 283 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 284 /// 285 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 286 const Value *Ptr, unsigned Size); 287 288 //===--------------------------------------------------------------------===// 289 /// Methods that clients should call when they transform the program to allow 290 /// alias analyses to update their internal data structures. Note that these 291 /// methods may be called on any instruction, regardless of whether or not 292 /// they have pointer-analysis implications. 293 /// 294 295 /// deleteValue - This method should be called whenever an LLVM Value is 296 /// deleted from the program, for example when an instruction is found to be 297 /// redundant and is eliminated. 298 /// 299 virtual void deleteValue(Value *V); 300 301 /// copyValue - This method should be used whenever a preexisting value in the 302 /// program is copied or cloned, introducing a new value. Note that analysis 303 /// implementations should tolerate clients that use this method to introduce 304 /// the same value multiple times: if the analysis already knows about a 305 /// value, it should ignore the request. 306 /// 307 virtual void copyValue(Value *From, Value *To); 308 309 /// replaceWithNewValue - This method is the obvious combination of the two 310 /// above, and it provided as a helper to simplify client code. 311 /// 312 void replaceWithNewValue(Value *Old, Value *New) { 313 copyValue(Old, New); 314 deleteValue(Old); 315 } 316}; 317 318/// isNoAliasCall - Return true if this pointer is returned by a noalias 319/// function. 320bool isNoAliasCall(const Value *V); 321 322/// isIdentifiedObject - Return true if this pointer refers to a distinct and 323/// identifiable object. This returns true for: 324/// Global Variables and Functions (but not Global Aliases) 325/// Allocas and Mallocs 326/// ByVal and NoAlias Arguments 327/// NoAlias returns 328/// 329bool isIdentifiedObject(const Value *V); 330 331} // End llvm namespace 332 333// Because of the way .a files work, we must force the BasicAA implementation to 334// be pulled in if the AliasAnalysis header is included. Otherwise we run 335// the risk of AliasAnalysis being used, but the default implementation not 336// being linked into the tool that uses it. 337FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis) 338FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis) 339 340#endif 341