1 //===- llvm/Analysis/MemoryDependenceAnalysis.h - Memory Deps --*- 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 MemoryDependenceAnalysis analysis pass. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_ANALYSIS_MEMORYDEPENDENCEANALYSIS_H 15 #define LLVM_ANALYSIS_MEMORYDEPENDENCEANALYSIS_H 16 17 #include "llvm/ADT/DenseMap.h" 18 #include "llvm/ADT/OwningPtr.h" 19 #include "llvm/ADT/PointerIntPair.h" 20 #include "llvm/ADT/SmallPtrSet.h" 21 #include "llvm/Analysis/AliasAnalysis.h" 22 #include "llvm/IR/BasicBlock.h" 23 #include "llvm/Pass.h" 24 #include "llvm/Support/ValueHandle.h" 25 26 namespace llvm { 27 class Function; 28 class FunctionPass; 29 class Instruction; 30 class CallSite; 31 class AliasAnalysis; 32 class DataLayout; 33 class MemoryDependenceAnalysis; 34 class PredIteratorCache; 35 class DominatorTree; 36 class PHITransAddr; 37 38 /// MemDepResult - A memory dependence query can return one of three different 39 /// answers, described below. 40 class MemDepResult { 41 enum DepType { 42 /// Invalid - Clients of MemDep never see this. 43 Invalid = 0, 44 45 /// Clobber - This is a dependence on the specified instruction which 46 /// clobbers the desired value. The pointer member of the MemDepResult 47 /// pair holds the instruction that clobbers the memory. For example, 48 /// this occurs when we see a may-aliased store to the memory location we 49 /// care about. 50 /// 51 /// There are several cases that may be interesting here: 52 /// 1. Loads are clobbered by may-alias stores. 53 /// 2. Loads are considered clobbered by partially-aliased loads. The 54 /// client may choose to analyze deeper into these cases. 55 Clobber, 56 57 /// Def - This is a dependence on the specified instruction which 58 /// defines/produces the desired memory location. The pointer member of 59 /// the MemDepResult pair holds the instruction that defines the memory. 60 /// Cases of interest: 61 /// 1. This could be a load or store for dependence queries on 62 /// load/store. The value loaded or stored is the produced value. 63 /// Note that the pointer operand may be different than that of the 64 /// queried pointer due to must aliases and phi translation. Note 65 /// that the def may not be the same type as the query, the pointers 66 /// may just be must aliases. 67 /// 2. For loads and stores, this could be an allocation instruction. In 68 /// this case, the load is loading an undef value or a store is the 69 /// first store to (that part of) the allocation. 70 /// 3. Dependence queries on calls return Def only when they are 71 /// readonly calls or memory use intrinsics with identical callees 72 /// and no intervening clobbers. No validation is done that the 73 /// operands to the calls are the same. 74 Def, 75 76 /// Other - This marker indicates that the query has no known dependency 77 /// in the specified block. More detailed state info is encoded in the 78 /// upper part of the pair (i.e. the Instruction*) 79 Other 80 }; 81 /// If DepType is "Other", the upper part of the pair 82 /// (i.e. the Instruction* part) is instead used to encode more detailed 83 /// type information as follows 84 enum OtherType { 85 /// NonLocal - This marker indicates that the query has no dependency in 86 /// the specified block. To find out more, the client should query other 87 /// predecessor blocks. 88 NonLocal = 0x4, 89 /// NonFuncLocal - This marker indicates that the query has no 90 /// dependency in the specified function. 91 NonFuncLocal = 0x8, 92 /// Unknown - This marker indicates that the query dependency 93 /// is unknown. 94 Unknown = 0xc 95 }; 96 97 typedef PointerIntPair<Instruction*, 2, DepType> PairTy; 98 PairTy Value; 99 explicit MemDepResult(PairTy V) : Value(V) {} 100 public: 101 MemDepResult() : Value(0, Invalid) {} 102 103 /// get methods: These are static ctor methods for creating various 104 /// MemDepResult kinds. 105 static MemDepResult getDef(Instruction *Inst) { 106 assert(Inst && "Def requires inst"); 107 return MemDepResult(PairTy(Inst, Def)); 108 } 109 static MemDepResult getClobber(Instruction *Inst) { 110 assert(Inst && "Clobber requires inst"); 111 return MemDepResult(PairTy(Inst, Clobber)); 112 } 113 static MemDepResult getNonLocal() { 114 return MemDepResult( 115 PairTy(reinterpret_cast<Instruction*>(NonLocal), Other)); 116 } 117 static MemDepResult getNonFuncLocal() { 118 return MemDepResult( 119 PairTy(reinterpret_cast<Instruction*>(NonFuncLocal), Other)); 120 } 121 static MemDepResult getUnknown() { 122 return MemDepResult( 123 PairTy(reinterpret_cast<Instruction*>(Unknown), Other)); 124 } 125 126 /// isClobber - Return true if this MemDepResult represents a query that is 127 /// an instruction clobber dependency. 128 bool isClobber() const { return Value.getInt() == Clobber; } 129 130 /// isDef - Return true if this MemDepResult represents a query that is 131 /// an instruction definition dependency. 132 bool isDef() const { return Value.getInt() == Def; } 133 134 /// isNonLocal - Return true if this MemDepResult represents a query that 135 /// is transparent to the start of the block, but where a non-local hasn't 136 /// been done. 137 bool isNonLocal() const { 138 return Value.getInt() == Other 139 && Value.getPointer() == reinterpret_cast<Instruction*>(NonLocal); 140 } 141 142 /// isNonFuncLocal - Return true if this MemDepResult represents a query 143 /// that is transparent to the start of the function. 144 bool isNonFuncLocal() const { 145 return Value.getInt() == Other 146 && Value.getPointer() == reinterpret_cast<Instruction*>(NonFuncLocal); 147 } 148 149 /// isUnknown - Return true if this MemDepResult represents a query which 150 /// cannot and/or will not be computed. 151 bool isUnknown() const { 152 return Value.getInt() == Other 153 && Value.getPointer() == reinterpret_cast<Instruction*>(Unknown); 154 } 155 156 /// getInst() - If this is a normal dependency, return the instruction that 157 /// is depended on. Otherwise, return null. 158 Instruction *getInst() const { 159 if (Value.getInt() == Other) return NULL; 160 return Value.getPointer(); 161 } 162 163 bool operator==(const MemDepResult &M) const { return Value == M.Value; } 164 bool operator!=(const MemDepResult &M) const { return Value != M.Value; } 165 bool operator<(const MemDepResult &M) const { return Value < M.Value; } 166 bool operator>(const MemDepResult &M) const { return Value > M.Value; } 167 private: 168 friend class MemoryDependenceAnalysis; 169 /// Dirty - Entries with this marker occur in a LocalDeps map or 170 /// NonLocalDeps map when the instruction they previously referenced was 171 /// removed from MemDep. In either case, the entry may include an 172 /// instruction pointer. If so, the pointer is an instruction in the 173 /// block where scanning can start from, saving some work. 174 /// 175 /// In a default-constructed MemDepResult object, the type will be Dirty 176 /// and the instruction pointer will be null. 177 /// 178 179 /// isDirty - Return true if this is a MemDepResult in its dirty/invalid. 180 /// state. 181 bool isDirty() const { return Value.getInt() == Invalid; } 182 183 static MemDepResult getDirty(Instruction *Inst) { 184 return MemDepResult(PairTy(Inst, Invalid)); 185 } 186 }; 187 188 /// NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache. For 189 /// each BasicBlock (the BB entry) it keeps a MemDepResult. 190 class NonLocalDepEntry { 191 BasicBlock *BB; 192 MemDepResult Result; 193 public: 194 NonLocalDepEntry(BasicBlock *bb, MemDepResult result) 195 : BB(bb), Result(result) {} 196 197 // This is used for searches. 198 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {} 199 200 // BB is the sort key, it can't be changed. 201 BasicBlock *getBB() const { return BB; } 202 203 void setResult(const MemDepResult &R) { Result = R; } 204 205 const MemDepResult &getResult() const { return Result; } 206 207 bool operator<(const NonLocalDepEntry &RHS) const { 208 return BB < RHS.BB; 209 } 210 }; 211 212 /// NonLocalDepResult - This is a result from a NonLocal dependence query. 213 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the 214 /// (potentially phi translated) address that was live in the block. 215 class NonLocalDepResult { 216 NonLocalDepEntry Entry; 217 Value *Address; 218 public: 219 NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address) 220 : Entry(bb, result), Address(address) {} 221 222 // BB is the sort key, it can't be changed. 223 BasicBlock *getBB() const { return Entry.getBB(); } 224 225 void setResult(const MemDepResult &R, Value *Addr) { 226 Entry.setResult(R); 227 Address = Addr; 228 } 229 230 const MemDepResult &getResult() const { return Entry.getResult(); } 231 232 /// getAddress - Return the address of this pointer in this block. This can 233 /// be different than the address queried for the non-local result because 234 /// of phi translation. This returns null if the address was not available 235 /// in a block (i.e. because phi translation failed) or if this is a cached 236 /// result and that address was deleted. 237 /// 238 /// The address is always null for a non-local 'call' dependence. 239 Value *getAddress() const { return Address; } 240 }; 241 242 /// MemoryDependenceAnalysis - This is an analysis that determines, for a 243 /// given memory operation, what preceding memory operations it depends on. 244 /// It builds on alias analysis information, and tries to provide a lazy, 245 /// caching interface to a common kind of alias information query. 246 /// 247 /// The dependency information returned is somewhat unusual, but is pragmatic. 248 /// If queried about a store or call that might modify memory, the analysis 249 /// will return the instruction[s] that may either load from that memory or 250 /// store to it. If queried with a load or call that can never modify memory, 251 /// the analysis will return calls and stores that might modify the pointer, 252 /// but generally does not return loads unless a) they are volatile, or 253 /// b) they load from *must-aliased* pointers. Returning a dependence on 254 /// must-alias'd pointers instead of all pointers interacts well with the 255 /// internal caching mechanism. 256 /// 257 class MemoryDependenceAnalysis : public FunctionPass { 258 // A map from instructions to their dependency. 259 typedef DenseMap<Instruction*, MemDepResult> LocalDepMapType; 260 LocalDepMapType LocalDeps; 261 262 public: 263 typedef std::vector<NonLocalDepEntry> NonLocalDepInfo; 264 private: 265 /// ValueIsLoadPair - This is a pair<Value*, bool> where the bool is true if 266 /// the dependence is a read only dependence, false if read/write. 267 typedef PointerIntPair<const Value*, 1, bool> ValueIsLoadPair; 268 269 /// BBSkipFirstBlockPair - This pair is used when caching information for a 270 /// block. If the pointer is null, the cache value is not a full query that 271 /// starts at the specified block. If non-null, the bool indicates whether 272 /// or not the contents of the block was skipped. 273 typedef PointerIntPair<BasicBlock*, 1, bool> BBSkipFirstBlockPair; 274 275 /// NonLocalPointerInfo - This record is the information kept for each 276 /// (value, is load) pair. 277 struct NonLocalPointerInfo { 278 /// Pair - The pair of the block and the skip-first-block flag. 279 BBSkipFirstBlockPair Pair; 280 /// NonLocalDeps - The results of the query for each relevant block. 281 NonLocalDepInfo NonLocalDeps; 282 /// Size - The maximum size of the dereferences of the 283 /// pointer. May be UnknownSize if the sizes are unknown. 284 uint64_t Size; 285 /// TBAATag - The TBAA tag associated with dereferences of the 286 /// pointer. May be null if there are no tags or conflicting tags. 287 const MDNode *TBAATag; 288 289 NonLocalPointerInfo() : Size(AliasAnalysis::UnknownSize), TBAATag(0) {} 290 }; 291 292 /// CachedNonLocalPointerInfo - This map stores the cached results of doing 293 /// a pointer lookup at the bottom of a block. The key of this map is the 294 /// pointer+isload bit, the value is a list of <bb->result> mappings. 295 typedef DenseMap<ValueIsLoadPair, 296 NonLocalPointerInfo> CachedNonLocalPointerInfo; 297 CachedNonLocalPointerInfo NonLocalPointerDeps; 298 299 // A map from instructions to their non-local pointer dependencies. 300 typedef DenseMap<Instruction*, 301 SmallPtrSet<ValueIsLoadPair, 4> > ReverseNonLocalPtrDepTy; 302 ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps; 303 304 305 /// PerInstNLInfo - This is the instruction we keep for each cached access 306 /// that we have for an instruction. The pointer is an owning pointer and 307 /// the bool indicates whether we have any dirty bits in the set. 308 typedef std::pair<NonLocalDepInfo, bool> PerInstNLInfo; 309 310 // A map from instructions to their non-local dependencies. 311 typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType; 312 313 NonLocalDepMapType NonLocalDeps; 314 315 // A reverse mapping from dependencies to the dependees. This is 316 // used when removing instructions to keep the cache coherent. 317 typedef DenseMap<Instruction*, 318 SmallPtrSet<Instruction*, 4> > ReverseDepMapType; 319 ReverseDepMapType ReverseLocalDeps; 320 321 // A reverse mapping from dependencies to the non-local dependees. 322 ReverseDepMapType ReverseNonLocalDeps; 323 324 /// Current AA implementation, just a cache. 325 AliasAnalysis *AA; 326 DataLayout *TD; 327 DominatorTree *DT; 328 OwningPtr<PredIteratorCache> PredCache; 329 public: 330 MemoryDependenceAnalysis(); 331 ~MemoryDependenceAnalysis(); 332 static char ID; 333 334 /// Pass Implementation stuff. This doesn't do any analysis eagerly. 335 bool runOnFunction(Function &); 336 337 /// Clean up memory in between runs 338 void releaseMemory(); 339 340 /// getAnalysisUsage - Does not modify anything. It uses Value Numbering 341 /// and Alias Analysis. 342 /// 343 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 344 345 /// getDependency - Return the instruction on which a memory operation 346 /// depends. See the class comment for more details. It is illegal to call 347 /// this on non-memory instructions. 348 MemDepResult getDependency(Instruction *QueryInst); 349 350 /// getNonLocalCallDependency - Perform a full dependency query for the 351 /// specified call, returning the set of blocks that the value is 352 /// potentially live across. The returned set of results will include a 353 /// "NonLocal" result for all blocks where the value is live across. 354 /// 355 /// This method assumes the instruction returns a "NonLocal" dependency 356 /// within its own block. 357 /// 358 /// This returns a reference to an internal data structure that may be 359 /// invalidated on the next non-local query or when an instruction is 360 /// removed. Clients must copy this data if they want it around longer than 361 /// that. 362 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS); 363 364 365 /// getNonLocalPointerDependency - Perform a full dependency query for an 366 /// access to the specified (non-volatile) memory location, returning the 367 /// set of instructions that either define or clobber the value. 368 /// 369 /// This method assumes the pointer has a "NonLocal" dependency within BB. 370 void getNonLocalPointerDependency(const AliasAnalysis::Location &Loc, 371 bool isLoad, BasicBlock *BB, 372 SmallVectorImpl<NonLocalDepResult> &Result); 373 374 /// removeInstruction - Remove an instruction from the dependence analysis, 375 /// updating the dependence of instructions that previously depended on it. 376 void removeInstruction(Instruction *InstToRemove); 377 378 /// invalidateCachedPointerInfo - This method is used to invalidate cached 379 /// information about the specified pointer, because it may be too 380 /// conservative in memdep. This is an optional call that can be used when 381 /// the client detects an equivalence between the pointer and some other 382 /// value and replaces the other value with ptr. This can make Ptr available 383 /// in more places that cached info does not necessarily keep. 384 void invalidateCachedPointerInfo(Value *Ptr); 385 386 /// invalidateCachedPredecessors - Clear the PredIteratorCache info. 387 /// This needs to be done when the CFG changes, e.g., due to splitting 388 /// critical edges. 389 void invalidateCachedPredecessors(); 390 391 /// getPointerDependencyFrom - Return the instruction on which a memory 392 /// location depends. If isLoad is true, this routine ignores may-aliases 393 /// with read-only operations. If isLoad is false, this routine ignores 394 /// may-aliases with reads from read-only locations. If possible, pass 395 /// the query instruction as well; this function may take advantage of 396 /// the metadata annotated to the query instruction to refine the result. 397 /// 398 /// Note that this is an uncached query, and thus may be inefficient. 399 /// 400 MemDepResult getPointerDependencyFrom(const AliasAnalysis::Location &Loc, 401 bool isLoad, 402 BasicBlock::iterator ScanIt, 403 BasicBlock *BB, 404 Instruction *QueryInst = 0); 405 406 407 /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that 408 /// looks at a memory location for a load (specified by MemLocBase, Offs, 409 /// and Size) and compares it against a load. If the specified load could 410 /// be safely widened to a larger integer load that is 1) still efficient, 411 /// 2) safe for the target, and 3) would provide the specified memory 412 /// location value, then this function returns the size in bytes of the 413 /// load width to use. If not, this returns zero. 414 static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase, 415 int64_t MemLocOffs, 416 unsigned MemLocSize, 417 const LoadInst *LI, 418 const DataLayout &TD); 419 420 private: 421 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall, 422 BasicBlock::iterator ScanIt, 423 BasicBlock *BB); 424 bool getNonLocalPointerDepFromBB(const PHITransAddr &Pointer, 425 const AliasAnalysis::Location &Loc, 426 bool isLoad, BasicBlock *BB, 427 SmallVectorImpl<NonLocalDepResult> &Result, 428 DenseMap<BasicBlock*, Value*> &Visited, 429 bool SkipFirstBlock = false); 430 MemDepResult GetNonLocalInfoForBlock(const AliasAnalysis::Location &Loc, 431 bool isLoad, BasicBlock *BB, 432 NonLocalDepInfo *Cache, 433 unsigned NumSortedEntries); 434 435 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P); 436 437 /// verifyRemoved - Verify that the specified instruction does not occur 438 /// in our internal data structures. 439 void verifyRemoved(Instruction *Inst) const; 440 441 }; 442 443 } // End llvm namespace 444 445 #endif 446
