AliasAnalysis.h revision 541481f34c7ffd49c0b55b56eab3753fda17c3e5
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 /// isNoAlias - A trivial helper function to check to see if the specified 98 /// pointers are no-alias. 99 bool isNoAlias(const Value *V1, unsigned V1Size, 100 const Value *V2, unsigned V2Size) { 101 return alias(V1, V1Size, V2, V2Size) == NoAlias; 102 } 103 104 /// pointsToConstantMemory - If the specified pointer is known to point into 105 /// constant global memory, return true. This allows disambiguation of store 106 /// instructions from constant pointers. 107 /// 108 virtual bool pointsToConstantMemory(const Value *P); 109 110 //===--------------------------------------------------------------------===// 111 /// Simple mod/ref information... 112 /// 113 114 /// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are 115 /// bits which may be or'd together. 116 /// 117 enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 }; 118 119 120 /// ModRefBehavior - Summary of how a function affects memory in the program. 121 /// Loads from constant globals are not considered memory accesses for this 122 /// interface. Also, functions may freely modify stack space local to their 123 /// invocation without having to report it through these interfaces. 124 enum ModRefBehavior { 125 // DoesNotAccessMemory - This function does not perform any non-local loads 126 // or stores to memory. 127 // 128 // This property corresponds to the GCC 'const' attribute. 129 DoesNotAccessMemory, 130 131 // AccessesArguments - This function accesses function arguments in well 132 // known (possibly volatile) ways, but does not access any other memory. 133 // 134 // Clients may use the Info parameter of getModRefBehavior to get specific 135 // information about how pointer arguments are used. 136 AccessesArguments, 137 138 // AccessesArgumentsAndGlobals - This function has accesses function 139 // arguments and global variables well known (possibly volatile) ways, but 140 // does not access any other memory. 141 // 142 // Clients may use the Info parameter of getModRefBehavior to get specific 143 // information about how pointer arguments are used. 144 AccessesArgumentsAndGlobals, 145 146 // OnlyReadsMemory - This function does not perform any non-local stores or 147 // volatile loads, but may read from any memory location. 148 // 149 // This property corresponds to the GCC 'pure' attribute. 150 OnlyReadsMemory, 151 152 // UnknownModRefBehavior - This indicates that the function could not be 153 // classified into one of the behaviors above. 154 UnknownModRefBehavior 155 }; 156 157 /// PointerAccessInfo - This struct is used to return results for pointers, 158 /// globals, and the return value of a function. 159 struct PointerAccessInfo { 160 /// V - The value this record corresponds to. This may be an Argument for 161 /// the function, a GlobalVariable, or null, corresponding to the return 162 /// value for the function. 163 Value *V; 164 165 /// ModRefInfo - Whether the pointer is loaded or stored to/from. 166 /// 167 ModRefResult ModRefInfo; 168 }; 169 170 /// getModRefBehavior - Return the behavior when calling the given call site. 171 virtual ModRefBehavior getModRefBehavior(CallSite CS, 172 std::vector<PointerAccessInfo> *Info = 0); 173 174 /// getModRefBehavior - Return the behavior when calling the given function. 175 /// For use when the call site is not known. 176 virtual ModRefBehavior getModRefBehavior(Function *F, 177 std::vector<PointerAccessInfo> *Info = 0); 178 179 /// getModRefBehavior - Return the modref behavior of the intrinsic with the 180 /// given id. 181 static ModRefBehavior getModRefBehavior(unsigned iid); 182 183 /// doesNotAccessMemory - If the specified call is known to never read or 184 /// write memory, return true. If the call only reads from known-constant 185 /// memory, it is also legal to return true. Calls that unwind the stack 186 /// are legal for this predicate. 187 /// 188 /// Many optimizations (such as CSE and LICM) can be performed on such calls 189 /// without worrying about aliasing properties, and many calls have this 190 /// property (e.g. calls to 'sin' and 'cos'). 191 /// 192 /// This property corresponds to the GCC 'const' attribute. 193 /// 194 bool doesNotAccessMemory(CallSite CS) { 195 return getModRefBehavior(CS) == DoesNotAccessMemory; 196 } 197 198 /// doesNotAccessMemory - If the specified function is known to never read or 199 /// write memory, return true. For use when the call site is not known. 200 /// 201 bool doesNotAccessMemory(Function *F) { 202 return getModRefBehavior(F) == DoesNotAccessMemory; 203 } 204 205 /// onlyReadsMemory - If the specified call is known to only read from 206 /// non-volatile memory (or not access memory at all), return true. Calls 207 /// that unwind the stack are legal for this predicate. 208 /// 209 /// This property allows many common optimizations to be performed in the 210 /// absence of interfering store instructions, such as CSE of strlen calls. 211 /// 212 /// This property corresponds to the GCC 'pure' attribute. 213 /// 214 bool onlyReadsMemory(CallSite CS) { 215 ModRefBehavior MRB = getModRefBehavior(CS); 216 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 217 } 218 219 /// onlyReadsMemory - If the specified function is known to only read from 220 /// non-volatile memory (or not access memory at all), return true. For use 221 /// when the call site is not known. 222 /// 223 bool onlyReadsMemory(Function *F) { 224 ModRefBehavior MRB = getModRefBehavior(F); 225 return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; 226 } 227 228 229 /// getModRefInfo - Return information about whether or not an instruction may 230 /// read or write memory specified by the pointer operand. An instruction 231 /// that doesn't read or write memory may be trivially LICM'd for example. 232 233 /// getModRefInfo (for call sites) - Return whether information about whether 234 /// a particular call site modifies or reads the memory specified by the 235 /// pointer. 236 /// 237 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); 238 239 /// getModRefInfo - Return information about whether two call sites may refer 240 /// to the same set of memory locations. This function returns NoModRef if 241 /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory 242 /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or 243 /// ModRef if CS1 might read or write memory accessed by CS2. 244 /// 245 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); 246 247public: 248 /// Convenience functions... 249 ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); 250 ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size); 251 ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { 252 return getModRefInfo(CallSite(C), P, Size); 253 } 254 ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) { 255 return getModRefInfo(CallSite(I), P, Size); 256 } 257 ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) { 258 return AliasAnalysis::ModRef; 259 } 260 ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { 261 switch (I->getOpcode()) { 262 case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size); 263 case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); 264 case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); 265 case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); 266 case Instruction::Invoke: return getModRefInfo((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, if Interprocedural is false 327/// NoAlias returns, if Interprocedural is false 328/// 329bool isIdentifiedObject(const Value *V, bool Interprocedural = false); 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