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/PointerIntPair.h" 19 #include "llvm/ADT/SmallPtrSet.h" 20 #include "llvm/Analysis/AliasAnalysis.h" 21 #include "llvm/IR/BasicBlock.h" 22 #include "llvm/IR/ValueHandle.h" 23 #include "llvm/Pass.h" 24 25 namespace llvm { 26 class Function; 27 class FunctionPass; 28 class Instruction; 29 class CallSite; 30 class AliasAnalysis; 31 class DataLayout; 32 class MemoryDependenceAnalysis; 33 class PredIteratorCache; 34 class DominatorTree; 35 class PHITransAddr; 36 37 /// MemDepResult - A memory dependence query can return one of three different 38 /// answers, described below. 39 class MemDepResult { 40 enum DepType { 41 /// Invalid - Clients of MemDep never see this. 42 Invalid = 0, 43 44 /// Clobber - This is a dependence on the specified instruction which 45 /// clobbers the desired value. The pointer member of the MemDepResult 46 /// pair holds the instruction that clobbers the memory. For example, 47 /// this occurs when we see a may-aliased store to the memory location we 48 /// care about. 49 /// 50 /// There are several cases that may be interesting here: 51 /// 1. Loads are clobbered by may-alias stores. 52 /// 2. Loads are considered clobbered by partially-aliased loads. The 53 /// client may choose to analyze deeper into these cases. 54 Clobber, 55 56 /// Def - This is a dependence on the specified instruction which 57 /// defines/produces the desired memory location. The pointer member of 58 /// the MemDepResult pair holds the instruction that defines the memory. 59 /// Cases of interest: 60 /// 1. This could be a load or store for dependence queries on 61 /// load/store. The value loaded or stored is the produced value. 62 /// Note that the pointer operand may be different than that of the 63 /// queried pointer due to must aliases and phi translation. Note 64 /// that the def may not be the same type as the query, the pointers 65 /// may just be must aliases. 66 /// 2. For loads and stores, this could be an allocation instruction. In 67 /// this case, the load is loading an undef value or a store is the 68 /// first store to (that part of) the allocation. 69 /// 3. Dependence queries on calls return Def only when they are 70 /// readonly calls or memory use intrinsics with identical callees 71 /// and no intervening clobbers. No validation is done that the 72 /// operands to the calls are the same. 73 Def, 74 75 /// Other - This marker indicates that the query has no known dependency 76 /// in the specified block. More detailed state info is encoded in the 77 /// upper part of the pair (i.e. the Instruction*) 78 Other 79 }; 80 /// If DepType is "Other", the upper part of the pair 81 /// (i.e. the Instruction* part) is instead used to encode more detailed 82 /// type information as follows 83 enum OtherType { 84 /// NonLocal - This marker indicates that the query has no dependency in 85 /// the specified block. To find out more, the client should query other 86 /// predecessor blocks. 87 NonLocal = 0x4, 88 /// NonFuncLocal - This marker indicates that the query has no 89 /// dependency in the specified function. 90 NonFuncLocal = 0x8, 91 /// Unknown - This marker indicates that the query dependency 92 /// is unknown. 93 Unknown = 0xc 94 }; 95 96 typedef PointerIntPair<Instruction*, 2, DepType> PairTy; 97 PairTy Value; 98 explicit MemDepResult(PairTy V) : Value(V) {} 99 public: 100 MemDepResult() : Value(nullptr, Invalid) {} 101 102 /// get methods: These are static ctor methods for creating various 103 /// MemDepResult kinds. 104 static MemDepResult getDef(Instruction *Inst) { 105 assert(Inst && "Def requires inst"); 106 return MemDepResult(PairTy(Inst, Def)); 107 } 108 static MemDepResult getClobber(Instruction *Inst) { 109 assert(Inst && "Clobber requires inst"); 110 return MemDepResult(PairTy(Inst, Clobber)); 111 } 112 static MemDepResult getNonLocal() { 113 return MemDepResult( 114 PairTy(reinterpret_cast<Instruction*>(NonLocal), Other)); 115 } 116 static MemDepResult getNonFuncLocal() { 117 return MemDepResult( 118 PairTy(reinterpret_cast<Instruction*>(NonFuncLocal), Other)); 119 } 120 static MemDepResult getUnknown() { 121 return MemDepResult( 122 PairTy(reinterpret_cast<Instruction*>(Unknown), Other)); 123 } 124 125 /// isClobber - Return true if this MemDepResult represents a query that is 126 /// an instruction clobber dependency. 127 bool isClobber() const { return Value.getInt() == Clobber; } 128 129 /// isDef - Return true if this MemDepResult represents a query that is 130 /// an instruction definition dependency. 131 bool isDef() const { return Value.getInt() == Def; } 132 133 /// isNonLocal - Return true if this MemDepResult represents a query that 134 /// is transparent to the start of the block, but where a non-local hasn't 135 /// been done. 136 bool isNonLocal() const { 137 return Value.getInt() == Other 138 && Value.getPointer() == reinterpret_cast<Instruction*>(NonLocal); 139 } 140 141 /// isNonFuncLocal - Return true if this MemDepResult represents a query 142 /// that is transparent to the start of the function. 143 bool isNonFuncLocal() const { 144 return Value.getInt() == Other 145 && Value.getPointer() == reinterpret_cast<Instruction*>(NonFuncLocal); 146 } 147 148 /// isUnknown - Return true if this MemDepResult represents a query which 149 /// cannot and/or will not be computed. 150 bool isUnknown() const { 151 return Value.getInt() == Other 152 && Value.getPointer() == reinterpret_cast<Instruction*>(Unknown); 153 } 154 155 /// getInst() - If this is a normal dependency, return the instruction that 156 /// is depended on. Otherwise, return null. 157 Instruction *getInst() const { 158 if (Value.getInt() == Other) return nullptr; 159 return Value.getPointer(); 160 } 161 162 bool operator==(const MemDepResult &M) const { return Value == M.Value; } 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 private: 167 friend class MemoryDependenceAnalysis; 168 /// Dirty - Entries with this marker occur in a LocalDeps map or 169 /// NonLocalDeps map when the instruction they previously referenced was 170 /// removed from MemDep. In either case, the entry may include an 171 /// instruction pointer. If so, the pointer is an instruction in the 172 /// block where scanning can start from, saving some work. 173 /// 174 /// In a default-constructed MemDepResult object, the type will be Dirty 175 /// and the instruction pointer will be null. 176 /// 177 178 /// isDirty - Return true if this is a MemDepResult in its dirty/invalid. 179 /// state. 180 bool isDirty() const { return Value.getInt() == Invalid; } 181 182 static MemDepResult getDirty(Instruction *Inst) { 183 return MemDepResult(PairTy(Inst, Invalid)); 184 } 185 }; 186 187 /// NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache. For 188 /// each BasicBlock (the BB entry) it keeps a MemDepResult. 189 class NonLocalDepEntry { 190 BasicBlock *BB; 191 MemDepResult Result; 192 public: 193 NonLocalDepEntry(BasicBlock *bb, MemDepResult result) 194 : BB(bb), Result(result) {} 195 196 // This is used for searches. 197 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {} 198 199 // BB is the sort key, it can't be changed. 200 BasicBlock *getBB() const { return BB; } 201 202 void setResult(const MemDepResult &R) { Result = R; } 203 204 const MemDepResult &getResult() const { return Result; } 205 206 bool operator<(const NonLocalDepEntry &RHS) const { 207 return BB < RHS.BB; 208 } 209 }; 210 211 /// NonLocalDepResult - This is a result from a NonLocal dependence query. 212 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the 213 /// (potentially phi translated) address that was live in the block. 214 class NonLocalDepResult { 215 NonLocalDepEntry Entry; 216 Value *Address; 217 public: 218 NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address) 219 : Entry(bb, result), Address(address) {} 220 221 // BB is the sort key, it can't be changed. 222 BasicBlock *getBB() const { return Entry.getBB(); } 223 224 void setResult(const MemDepResult &R, Value *Addr) { 225 Entry.setResult(R); 226 Address = Addr; 227 } 228 229 const MemDepResult &getResult() const { return Entry.getResult(); } 230 231 /// getAddress - Return the address of this pointer in this block. This can 232 /// be different than the address queried for the non-local result because 233 /// of phi translation. This returns null if the address was not available 234 /// in a block (i.e. because phi translation failed) or if this is a cached 235 /// result and that address was deleted. 236 /// 237 /// The address is always null for a non-local 'call' dependence. 238 Value *getAddress() const { return Address; } 239 }; 240 241 /// MemoryDependenceAnalysis - This is an analysis that determines, for a 242 /// given memory operation, what preceding memory operations it depends on. 243 /// It builds on alias analysis information, and tries to provide a lazy, 244 /// caching interface to a common kind of alias information query. 245 /// 246 /// The dependency information returned is somewhat unusual, but is pragmatic. 247 /// If queried about a store or call that might modify memory, the analysis 248 /// will return the instruction[s] that may either load from that memory or 249 /// store to it. If queried with a load or call that can never modify memory, 250 /// the analysis will return calls and stores that might modify the pointer, 251 /// but generally does not return loads unless a) they are volatile, or 252 /// b) they load from *must-aliased* pointers. Returning a dependence on 253 /// must-alias'd pointers instead of all pointers interacts well with the 254 /// internal caching mechanism. 255 /// 256 class MemoryDependenceAnalysis : public FunctionPass { 257 // A map from instructions to their dependency. 258 typedef DenseMap<Instruction*, MemDepResult> LocalDepMapType; 259 LocalDepMapType LocalDeps; 260 261 public: 262 typedef std::vector<NonLocalDepEntry> NonLocalDepInfo; 263 private: 264 /// ValueIsLoadPair - This is a pair<Value*, bool> where the bool is true if 265 /// the dependence is a read only dependence, false if read/write. 266 typedef PointerIntPair<const Value*, 1, bool> ValueIsLoadPair; 267 268 /// BBSkipFirstBlockPair - This pair is used when caching information for a 269 /// block. If the pointer is null, the cache value is not a full query that 270 /// starts at the specified block. If non-null, the bool indicates whether 271 /// or not the contents of the block was skipped. 272 typedef PointerIntPair<BasicBlock*, 1, bool> BBSkipFirstBlockPair; 273 274 /// NonLocalPointerInfo - This record is the information kept for each 275 /// (value, is load) pair. 276 struct NonLocalPointerInfo { 277 /// Pair - The pair of the block and the skip-first-block flag. 278 BBSkipFirstBlockPair Pair; 279 /// NonLocalDeps - The results of the query for each relevant block. 280 NonLocalDepInfo NonLocalDeps; 281 /// Size - The maximum size of the dereferences of the 282 /// pointer. May be UnknownSize if the sizes are unknown. 283 uint64_t Size; 284 /// TBAATag - The TBAA tag associated with dereferences of the 285 /// pointer. May be null if there are no tags or conflicting tags. 286 const MDNode *TBAATag; 287 288 NonLocalPointerInfo() 289 : Size(AliasAnalysis::UnknownSize), TBAATag(nullptr) {} 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 const DataLayout *DL; 327 DominatorTree *DT; 328 std::unique_ptr<PredIteratorCache> PredCache; 329 330 public: 331 MemoryDependenceAnalysis(); 332 ~MemoryDependenceAnalysis(); 333 static char ID; 334 335 /// Pass Implementation stuff. This doesn't do any analysis eagerly. 336 bool runOnFunction(Function &) override; 337 338 /// Clean up memory in between runs 339 void releaseMemory() override; 340 341 /// getAnalysisUsage - Does not modify anything. It uses Value Numbering 342 /// and Alias Analysis. 343 /// 344 void getAnalysisUsage(AnalysisUsage &AU) const override; 345 346 /// getDependency - Return the instruction on which a memory operation 347 /// depends. See the class comment for more details. It is illegal to call 348 /// this on non-memory instructions. 349 MemDepResult getDependency(Instruction *QueryInst); 350 351 /// getNonLocalCallDependency - Perform a full dependency query for the 352 /// specified call, returning the set of blocks that the value is 353 /// potentially live across. The returned set of results will include a 354 /// "NonLocal" result for all blocks where the value is live across. 355 /// 356 /// This method assumes the instruction returns a "NonLocal" dependency 357 /// within its own block. 358 /// 359 /// This returns a reference to an internal data structure that may be 360 /// invalidated on the next non-local query or when an instruction is 361 /// removed. Clients must copy this data if they want it around longer than 362 /// that. 363 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS); 364 365 366 /// getNonLocalPointerDependency - Perform a full dependency query for an 367 /// access to the specified (non-volatile) memory location, returning the 368 /// set of instructions that either define or clobber the value. 369 /// 370 /// This method assumes the pointer has a "NonLocal" dependency within BB. 371 void getNonLocalPointerDependency(const AliasAnalysis::Location &Loc, 372 bool isLoad, BasicBlock *BB, 373 SmallVectorImpl<NonLocalDepResult> &Result); 374 375 /// removeInstruction - Remove an instruction from the dependence analysis, 376 /// updating the dependence of instructions that previously depended on it. 377 void removeInstruction(Instruction *InstToRemove); 378 379 /// invalidateCachedPointerInfo - This method is used to invalidate cached 380 /// information about the specified pointer, because it may be too 381 /// conservative in memdep. This is an optional call that can be used when 382 /// the client detects an equivalence between the pointer and some other 383 /// value and replaces the other value with ptr. This can make Ptr available 384 /// in more places that cached info does not necessarily keep. 385 void invalidateCachedPointerInfo(Value *Ptr); 386 387 /// invalidateCachedPredecessors - Clear the PredIteratorCache info. 388 /// This needs to be done when the CFG changes, e.g., due to splitting 389 /// critical edges. 390 void invalidateCachedPredecessors(); 391 392 /// getPointerDependencyFrom - Return the instruction on which a memory 393 /// location depends. If isLoad is true, this routine ignores may-aliases 394 /// with read-only operations. If isLoad is false, this routine ignores 395 /// may-aliases with reads from read-only locations. If possible, pass 396 /// the query instruction as well; this function may take advantage of 397 /// the metadata annotated to the query instruction to refine the result. 398 /// 399 /// Note that this is an uncached query, and thus may be inefficient. 400 /// 401 MemDepResult getPointerDependencyFrom(const AliasAnalysis::Location &Loc, 402 bool isLoad, 403 BasicBlock::iterator ScanIt, 404 BasicBlock *BB, 405 Instruction *QueryInst = nullptr); 406 407 408 /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that 409 /// looks at a memory location for a load (specified by MemLocBase, Offs, 410 /// and Size) and compares it against a load. If the specified load could 411 /// be safely widened to a larger integer load that is 1) still efficient, 412 /// 2) safe for the target, and 3) would provide the specified memory 413 /// location value, then this function returns the size in bytes of the 414 /// load width to use. If not, this returns zero. 415 static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase, 416 int64_t MemLocOffs, 417 unsigned MemLocSize, 418 const LoadInst *LI, 419 const DataLayout &DL); 420 421 private: 422 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall, 423 BasicBlock::iterator ScanIt, 424 BasicBlock *BB); 425 bool getNonLocalPointerDepFromBB(const PHITransAddr &Pointer, 426 const AliasAnalysis::Location &Loc, 427 bool isLoad, BasicBlock *BB, 428 SmallVectorImpl<NonLocalDepResult> &Result, 429 DenseMap<BasicBlock*, Value*> &Visited, 430 bool SkipFirstBlock = false); 431 MemDepResult GetNonLocalInfoForBlock(const AliasAnalysis::Location &Loc, 432 bool isLoad, BasicBlock *BB, 433 NonLocalDepInfo *Cache, 434 unsigned NumSortedEntries); 435 436 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P); 437 438 /// verifyRemoved - Verify that the specified instruction does not occur 439 /// in our internal data structures. 440 void verifyRemoved(Instruction *Inst) const; 441 442 }; 443 444 } // End llvm namespace 445 446 #endif 447
