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/PredIteratorCache.h" 23 #include "llvm/IR/ValueHandle.h" 24 #include "llvm/Pass.h" 25 26 namespace llvm { 27 class Function; 28 class FunctionPass; 29 class Instruction; 30 class CallSite; 31 class AssumptionCache; 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) {} 99 100 public: 101 MemDepResult() : Value(nullptr, 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 nullptr; 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; } 167 168 private: 169 friend class MemoryDependenceAnalysis; 170 /// Dirty - Entries with this marker occur in a LocalDeps map or 171 /// NonLocalDeps map when the instruction they previously referenced was 172 /// removed from MemDep. In either case, the entry may include an 173 /// instruction pointer. If so, the pointer is an instruction in the 174 /// block where scanning can start from, saving some work. 175 /// 176 /// In a default-constructed MemDepResult object, the type will be Dirty 177 /// and the instruction pointer will be null. 178 /// 179 180 /// isDirty - Return true if this is a MemDepResult in its dirty/invalid. 181 /// state. 182 bool isDirty() const { return Value.getInt() == Invalid; } 183 184 static MemDepResult getDirty(Instruction *Inst) { 185 return MemDepResult(PairTy(Inst, Invalid)); 186 } 187 }; 188 189 /// NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache. For 190 /// each BasicBlock (the BB entry) it keeps a MemDepResult. 191 class NonLocalDepEntry { 192 BasicBlock *BB; 193 MemDepResult Result; 194 195 public: 196 NonLocalDepEntry(BasicBlock *bb, MemDepResult result) 197 : BB(bb), Result(result) {} 198 199 // This is used for searches. 200 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {} 201 202 // BB is the sort key, it can't be changed. 203 BasicBlock *getBB() const { return BB; } 204 205 void setResult(const MemDepResult &R) { Result = R; } 206 207 const MemDepResult &getResult() const { return Result; } 208 209 bool operator<(const NonLocalDepEntry &RHS) const { 210 return BB < RHS.BB; 211 } 212 }; 213 214 /// NonLocalDepResult - This is a result from a NonLocal dependence query. 215 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the 216 /// (potentially phi translated) address that was live in the block. 217 class NonLocalDepResult { 218 NonLocalDepEntry Entry; 219 Value *Address; 220 221 public: 222 NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address) 223 : Entry(bb, result), Address(address) {} 224 225 // BB is the sort key, it can't be changed. 226 BasicBlock *getBB() const { return Entry.getBB(); } 227 228 void setResult(const MemDepResult &R, Value *Addr) { 229 Entry.setResult(R); 230 Address = Addr; 231 } 232 233 const MemDepResult &getResult() const { return Entry.getResult(); } 234 235 /// getAddress - Return the address of this pointer in this block. This can 236 /// be different than the address queried for the non-local result because 237 /// of phi translation. This returns null if the address was not available 238 /// in a block (i.e. because phi translation failed) or if this is a cached 239 /// result and that address was deleted. 240 /// 241 /// The address is always null for a non-local 'call' dependence. 242 Value *getAddress() const { return Address; } 243 }; 244 245 /// MemoryDependenceAnalysis - This is an analysis that determines, for a 246 /// given memory operation, what preceding memory operations it depends on. 247 /// It builds on alias analysis information, and tries to provide a lazy, 248 /// caching interface to a common kind of alias information query. 249 /// 250 /// The dependency information returned is somewhat unusual, but is pragmatic. 251 /// If queried about a store or call that might modify memory, the analysis 252 /// will return the instruction[s] that may either load from that memory or 253 /// store to it. If queried with a load or call that can never modify memory, 254 /// the analysis will return calls and stores that might modify the pointer, 255 /// but generally does not return loads unless a) they are volatile, or 256 /// b) they load from *must-aliased* pointers. Returning a dependence on 257 /// must-alias'd pointers instead of all pointers interacts well with the 258 /// internal caching mechanism. 259 /// 260 class MemoryDependenceAnalysis : public FunctionPass { 261 // A map from instructions to their dependency. 262 typedef DenseMap<Instruction*, MemDepResult> LocalDepMapType; 263 LocalDepMapType LocalDeps; 264 265 public: 266 typedef std::vector<NonLocalDepEntry> NonLocalDepInfo; 267 268 private: 269 /// ValueIsLoadPair - This is a pair<Value*, bool> where the bool is true if 270 /// the dependence is a read only dependence, false if read/write. 271 typedef PointerIntPair<const Value*, 1, bool> ValueIsLoadPair; 272 273 /// BBSkipFirstBlockPair - This pair is used when caching information for a 274 /// block. If the pointer is null, the cache value is not a full query that 275 /// starts at the specified block. If non-null, the bool indicates whether 276 /// or not the contents of the block was skipped. 277 typedef PointerIntPair<BasicBlock*, 1, bool> BBSkipFirstBlockPair; 278 279 /// NonLocalPointerInfo - This record is the information kept for each 280 /// (value, is load) pair. 281 struct NonLocalPointerInfo { 282 /// Pair - The pair of the block and the skip-first-block flag. 283 BBSkipFirstBlockPair Pair; 284 /// NonLocalDeps - The results of the query for each relevant block. 285 NonLocalDepInfo NonLocalDeps; 286 /// Size - The maximum size of the dereferences of the 287 /// pointer. May be UnknownSize if the sizes are unknown. 288 uint64_t Size; 289 /// AATags - The AA tags associated with dereferences of the 290 /// pointer. The members may be null if there are no tags or 291 /// conflicting tags. 292 AAMDNodes AATags; 293 294 NonLocalPointerInfo() : Size(MemoryLocation::UnknownSize) {} 295 }; 296 297 /// CachedNonLocalPointerInfo - This map stores the cached results of doing 298 /// a pointer lookup at the bottom of a block. The key of this map is the 299 /// pointer+isload bit, the value is a list of <bb->result> mappings. 300 typedef DenseMap<ValueIsLoadPair, 301 NonLocalPointerInfo> CachedNonLocalPointerInfo; 302 CachedNonLocalPointerInfo NonLocalPointerDeps; 303 304 // A map from instructions to their non-local pointer dependencies. 305 typedef DenseMap<Instruction*, 306 SmallPtrSet<ValueIsLoadPair, 4> > ReverseNonLocalPtrDepTy; 307 ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps; 308 309 /// PerInstNLInfo - This is the instruction we keep for each cached access 310 /// that we have for an instruction. The pointer is an owning pointer and 311 /// the bool indicates whether we have any dirty bits in the set. 312 typedef std::pair<NonLocalDepInfo, bool> PerInstNLInfo; 313 314 // A map from instructions to their non-local dependencies. 315 typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType; 316 317 NonLocalDepMapType NonLocalDeps; 318 319 // A reverse mapping from dependencies to the dependees. This is 320 // used when removing instructions to keep the cache coherent. 321 typedef DenseMap<Instruction*, 322 SmallPtrSet<Instruction*, 4> > ReverseDepMapType; 323 ReverseDepMapType ReverseLocalDeps; 324 325 // A reverse mapping from dependencies to the non-local dependees. 326 ReverseDepMapType ReverseNonLocalDeps; 327 328 /// Current AA implementation, just a cache. 329 AliasAnalysis *AA; 330 DominatorTree *DT; 331 AssumptionCache *AC; 332 const TargetLibraryInfo *TLI; 333 PredIteratorCache PredCache; 334 335 public: 336 MemoryDependenceAnalysis(); 337 ~MemoryDependenceAnalysis() override; 338 static char ID; 339 340 /// Pass Implementation stuff. This doesn't do any analysis eagerly. 341 bool runOnFunction(Function &) override; 342 343 /// Clean up memory in between runs 344 void releaseMemory() override; 345 346 /// getAnalysisUsage - Does not modify anything. It uses Value Numbering 347 /// and Alias Analysis. 348 /// 349 void getAnalysisUsage(AnalysisUsage &AU) const override; 350 351 /// getDependency - Return the instruction on which a memory operation 352 /// depends. See the class comment for more details. It is illegal to call 353 /// this on non-memory instructions. 354 MemDepResult getDependency(Instruction *QueryInst); 355 356 /// getNonLocalCallDependency - Perform a full dependency query for the 357 /// specified call, returning the set of blocks that the value is 358 /// potentially live across. The returned set of results will include a 359 /// "NonLocal" result for all blocks where the value is live across. 360 /// 361 /// This method assumes the instruction returns a "NonLocal" dependency 362 /// within its own block. 363 /// 364 /// This returns a reference to an internal data structure that may be 365 /// invalidated on the next non-local query or when an instruction is 366 /// removed. Clients must copy this data if they want it around longer than 367 /// that. 368 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS); 369 370 /// getNonLocalPointerDependency - Perform a full dependency query for an 371 /// access to the QueryInst's specified memory location, returning the set 372 /// of instructions that either define or clobber the value. 373 /// 374 /// Warning: For a volatile query instruction, the dependencies will be 375 /// accurate, and thus usable for reordering, but it is never legal to 376 /// remove the query instruction. 377 /// 378 /// This method assumes the pointer has a "NonLocal" dependency within 379 /// QueryInst's parent basic block. 380 void getNonLocalPointerDependency(Instruction *QueryInst, 381 SmallVectorImpl<NonLocalDepResult> &Result); 382 383 /// removeInstruction - Remove an instruction from the dependence analysis, 384 /// updating the dependence of instructions that previously depended on it. 385 void removeInstruction(Instruction *InstToRemove); 386 387 /// invalidateCachedPointerInfo - This method is used to invalidate cached 388 /// information about the specified pointer, because it may be too 389 /// conservative in memdep. This is an optional call that can be used when 390 /// the client detects an equivalence between the pointer and some other 391 /// value and replaces the other value with ptr. This can make Ptr available 392 /// in more places that cached info does not necessarily keep. 393 void invalidateCachedPointerInfo(Value *Ptr); 394 395 /// invalidateCachedPredecessors - Clear the PredIteratorCache info. 396 /// This needs to be done when the CFG changes, e.g., due to splitting 397 /// critical edges. 398 void invalidateCachedPredecessors(); 399 400 /// \brief Return the instruction on which a memory location depends. 401 /// If isLoad is true, this routine ignores may-aliases with read-only 402 /// operations. If isLoad is false, this routine ignores may-aliases 403 /// with reads from read-only locations. If possible, pass the query 404 /// instruction as well; this function may take advantage of the metadata 405 /// annotated to the query instruction to refine the result. 406 /// 407 /// Note that this is an uncached query, and thus may be inefficient. 408 /// 409 MemDepResult getPointerDependencyFrom(const MemoryLocation &Loc, 410 bool isLoad, 411 BasicBlock::iterator ScanIt, 412 BasicBlock *BB, 413 Instruction *QueryInst = nullptr); 414 415 MemDepResult getSimplePointerDependencyFrom(const MemoryLocation &MemLoc, 416 bool isLoad, 417 BasicBlock::iterator ScanIt, 418 BasicBlock *BB, 419 Instruction *QueryInst); 420 421 /// This analysis looks for other loads and stores with invariant.group 422 /// metadata and the same pointer operand. Returns Unknown if it does not 423 /// find anything, and Def if it can be assumed that 2 instructions load or 424 /// store the same value. 425 /// FIXME: This analysis works only on single block because of restrictions 426 /// at the call site. 427 MemDepResult getInvariantGroupPointerDependency(LoadInst *LI, 428 BasicBlock *BB); 429 430 /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that 431 /// looks at a memory location for a load (specified by MemLocBase, Offs, 432 /// and Size) and compares it against a load. If the specified load could 433 /// be safely widened to a larger integer load that is 1) still efficient, 434 /// 2) safe for the target, and 3) would provide the specified memory 435 /// location value, then this function returns the size in bytes of the 436 /// load width to use. If not, this returns zero. 437 static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase, 438 int64_t MemLocOffs, 439 unsigned MemLocSize, 440 const LoadInst *LI); 441 442 private: 443 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall, 444 BasicBlock::iterator ScanIt, 445 BasicBlock *BB); 446 bool getNonLocalPointerDepFromBB(Instruction *QueryInst, 447 const PHITransAddr &Pointer, 448 const MemoryLocation &Loc, bool isLoad, 449 BasicBlock *BB, 450 SmallVectorImpl<NonLocalDepResult> &Result, 451 DenseMap<BasicBlock *, Value *> &Visited, 452 bool SkipFirstBlock = false); 453 MemDepResult GetNonLocalInfoForBlock(Instruction *QueryInst, 454 const MemoryLocation &Loc, bool isLoad, 455 BasicBlock *BB, NonLocalDepInfo *Cache, 456 unsigned NumSortedEntries); 457 458 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P); 459 460 /// verifyRemoved - Verify that the specified instruction does not occur 461 /// in our internal data structures. 462 void verifyRemoved(Instruction *Inst) const; 463 }; 464 465 } // End llvm namespace 466 467 #endif 468
