AliasAnalysis.h revision 847a84efd23a2c7d90429b82f6e0f19d1f913d9a
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 /// alias - A convenience wrapper for the case where the sizes are unknown. 98 AliasResult alias(const Value *V1, const Value *V2) { 99 return alias(V1, ~0u, V2, ~0u); 100 } 101 102 /// isNoAlias - A trivial helper function to check to see if the specified 103 /// pointers are no-alias. 104 bool isNoAlias(const Value *V1, unsigned V1Size, 105 const Value *V2, unsigned V2Size) { 106 return alias(V1, V1Size, V2, V2Size) == NoAlias; 107 } 108 109 /// pointsToConstantMemory - If the specified pointer is known to point into 110 /// constant global memory, return true. This allows disambiguation of store 111 /// instructions from constant pointers. 112 /// 113 virtual bool pointsToConstantMemory(const Value *P); 114 115 //===--------------------------------------------------------------------===// 116 /// Simple mod/ref information... 117 /// 118 119 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 120 /// bits which may be or'd together. 121 /// 122 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 123 124 125 /// ModRefBehavior - Summary of how a function affects memory in the program. 126 /// Loads from constant globals are not considered memory accesses for this 127 /// interface. Also, functions may freely modify stack space local to their 128 /// invocation without having to report it through these interfaces. 129 enum ModRefBehavior { 130 // DoesNotAccessMemory - This function does not perform any non-local loads 131 // or stores to memory. 132 // 133 // This property corresponds to the GCC 'const' attribute. 134 DoesNotAccessMemory, 135 136 // AccessesArguments - This function accesses function arguments in well 137 // known (possibly volatile) ways, but does not access any other memory. 138 // 139 // Clients may use the Info parameter of getModRefBehavior to get specific 140 // information about how pointer arguments are used. 141 AccessesArguments, 142 143 // AccessesArgumentsAndGlobals - This function has accesses function 144 // arguments and global variables well known (possibly volatile) ways, but 145 // does not access any other memory. 146 // 147 // Clients may use the Info parameter of getModRefBehavior to get specific 148 // information about how pointer arguments are used. 149 AccessesArgumentsAndGlobals, 150 151 // OnlyReadsMemory - This function does not perform any non-local stores or 152 // volatile loads, but may read from any memory location. 153 // 154 // This property corresponds to the GCC 'pure' attribute. 155 OnlyReadsMemory, 156 157 // UnknownModRefBehavior - This indicates that the function could not be 158 // classified into one of the behaviors above. 159 UnknownModRefBehavior 160 }; 161 162 /// PointerAccessInfo - This struct is used to return results for pointers, 163 /// globals, and the return value of a function. 164 struct PointerAccessInfo { 165 /// V - The value this record corresponds to. This may be an Argument for 166 /// the function, a GlobalVariable, or null, corresponding to the return 167 /// value for the function. 168 Value *V; 169 170 /// ModRefInfo - Whether the pointer is loaded or stored to/from. 171 /// 172 ModRefResult ModRefInfo; 173 }; 174 175 /// getModRefBehavior - Return the behavior when calling the given call site. 176 virtual ModRefBehavior getModRefBehavior(CallSite CS, 177 std::vector<PointerAccessInfo> *Info = 0); 178 179 /// getModRefBehavior - Return the behavior when calling the given function. 180 /// For use when the call site is not known. 181 virtual ModRefBehavior getModRefBehavior(Function *F, 182 std::vector<PointerAccessInfo> *Info = 0); 183 184 /// getModRefBehavior - Return the modref behavior of the intrinsic with the 185 /// given id. 186 static ModRefBehavior getModRefBehavior(unsigned iid); 187 188 /// doesNotAccessMemory - If the specified call is known to never read or 189 /// write memory, return true. If the call only reads from known-constant 190 /// memory, it is also legal to return true. Calls that unwind the stack 191 /// are legal for this predicate. 192 /// 193 /// Many optimizations (such as CSE and LICM) can be performed on such calls 194 /// without worrying about aliasing properties, and many calls have this 195 /// property (e.g. calls to 'sin' and 'cos'). 196 /// 197 /// This property corresponds to the GCC 'const' attribute. 198 /// 199 bool doesNotAccessMemory(CallSite CS) { 200 return getModRefBehavior(CS) == DoesNotAccessMemory; 201 } 202 203 /// doesNotAccessMemory - If the specified function is known to never read or 204 /// write memory, return true. For use when the call site is not known. 205 /// 206 bool doesNotAccessMemory(Function *F) { 207 return getModRefBehavior(F) == DoesNotAccessMemory; 208 } 209 210 /// onlyReadsMemory - If the specified call is known to only read from 211 /// non-volatile memory (or not access memory at all), return true. Calls 212 /// that unwind the stack are legal for this predicate. 213 /// 214 /// This property allows many common optimizations to be performed in the 215 /// absence of interfering store instructions, such as CSE of strlen calls. 216 /// 217 /// This property corresponds to the GCC 'pure' attribute. 218 /// 219 bool onlyReadsMemory(CallSite CS) { 220 ModRefBehavior MRB = getModRefBehavior(CS); 221 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 222 } 223 224 /// onlyReadsMemory - If the specified function is known to only read from 225 /// non-volatile memory (or not access memory at all), return true. For use 226 /// when the call site is not known. 227 /// 228 bool onlyReadsMemory(Function *F) { 229 ModRefBehavior MRB = getModRefBehavior(F); 230 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 231 } 232 233 234 /// getModRefInfo - Return information about whether or not an instruction may 235 /// read or write memory specified by the pointer operand. An instruction 236 /// that doesn't read or write memory may be trivially LICM'd for example. 237 238 /// getModRefInfo (for call sites) - Return whether information about whether 239 /// a particular call site modifies or reads the memory specified by the 240 /// pointer. 241 /// 242 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 243 244 /// getModRefInfo - Return information about whether two call sites may refer 245 /// to the same set of memory locations. This function returns NoModRef if 246 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory 247 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or 248 /// ModRef if CS1 might read or write memory accessed by CS2. 249 /// 250 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 251 252public: 253 /// Convenience functions... 254 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 255 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size); 256 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 257 return getModRefInfo(CallSite(C), P, Size); 258 } 259 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) { 260 return getModRefInfo(CallSite(I), P, Size); 261 } 262 ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) { 263 return AliasAnalysis::ModRef; 264 } 265 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 266 switch (I->getOpcode()) { 267 case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size); 268 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 269 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 270 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 271 case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); 272 default: return NoModRef; 273 } 274 } 275 276 //===--------------------------------------------------------------------===// 277 /// Higher level methods for querying mod/ref information. 278 /// 279 280 /// canBasicBlockModify - Return true if it is possible for execution of the 281 /// specified basic block to modify the value pointed to by Ptr. 282 /// 283 bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size); 284 285 /// canInstructionRangeModify - Return true if it is possible for the 286 /// execution of the specified instructions to modify the value pointed to by 287 /// Ptr. The instructions to consider are all of the instructions in the 288 /// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block. 289 /// 290 bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, 291 const Value *Ptr, unsigned Size); 292 293 //===--------------------------------------------------------------------===// 294 /// Methods that clients should call when they transform the program to allow 295 /// alias analyses to update their internal data structures. Note that these 296 /// methods may be called on any instruction, regardless of whether or not 297 /// they have pointer-analysis implications. 298 /// 299 300 /// deleteValue - This method should be called whenever an LLVM Value is 301 /// deleted from the program, for example when an instruction is found to be 302 /// redundant and is eliminated. 303 /// 304 virtual void deleteValue(Value *V); 305 306 /// copyValue - This method should be used whenever a preexisting value in the 307 /// program is copied or cloned, introducing a new value. Note that analysis 308 /// implementations should tolerate clients that use this method to introduce 309 /// the same value multiple times: if the analysis already knows about a 310 /// value, it should ignore the request. 311 /// 312 virtual void copyValue(Value *From, Value *To); 313 314 /// replaceWithNewValue - This method is the obvious combination of the two 315 /// above, and it provided as a helper to simplify client code. 316 /// 317 void replaceWithNewValue(Value *Old, Value *New) { 318 copyValue(Old, New); 319 deleteValue(Old); 320 } 321}; 322 323/// isNoAliasCall - Return true if this pointer is returned by a noalias 324/// function. 325bool isNoAliasCall(const Value *V); 326 327/// isIdentifiedObject - Return true if this pointer refers to a distinct and 328/// identifiable object. This returns true for: 329/// Global Variables and Functions (but not Global Aliases) 330/// Allocas and Mallocs 331/// ByVal and NoAlias Arguments 332/// NoAlias returns 333/// 334bool isIdentifiedObject(const Value *V); 335 336} // End llvm namespace 337 338// Because of the way .a files work, we must force the BasicAA implementation to 339// be pulled in if the AliasAnalysis header is included. Otherwise we run 340// the risk of AliasAnalysis being used, but the default implementation not 341// being linked into the tool that uses it. 342FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis) 343FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis) 344 345#endif 346