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 AssumptionCache; 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; MemDepResult(PairTy V)99 explicit MemDepResult(PairTy V) : Value(V) {} 100 public: MemDepResult()101 MemDepResult() : Value(nullptr, Invalid) {} 102 103 /// get methods: These are static ctor methods for creating various 104 /// MemDepResult kinds. getDef(Instruction * Inst)105 static MemDepResult getDef(Instruction *Inst) { 106 assert(Inst && "Def requires inst"); 107 return MemDepResult(PairTy(Inst, Def)); 108 } getClobber(Instruction * Inst)109 static MemDepResult getClobber(Instruction *Inst) { 110 assert(Inst && "Clobber requires inst"); 111 return MemDepResult(PairTy(Inst, Clobber)); 112 } getNonLocal()113 static MemDepResult getNonLocal() { 114 return MemDepResult( 115 PairTy(reinterpret_cast<Instruction*>(NonLocal), Other)); 116 } getNonFuncLocal()117 static MemDepResult getNonFuncLocal() { 118 return MemDepResult( 119 PairTy(reinterpret_cast<Instruction*>(NonFuncLocal), Other)); 120 } getUnknown()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. isClobber()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. isDef()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. isNonLocal()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. isNonFuncLocal()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. isUnknown()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. getInst()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 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. isDirty()181 bool isDirty() const { return Value.getInt() == Invalid; } 182 getDirty(Instruction * Inst)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: NonLocalDepEntry(BasicBlock * bb,MemDepResult result)194 NonLocalDepEntry(BasicBlock *bb, MemDepResult result) 195 : BB(bb), Result(result) {} 196 197 // This is used for searches. NonLocalDepEntry(BasicBlock * bb)198 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {} 199 200 // BB is the sort key, it can't be changed. getBB()201 BasicBlock *getBB() const { return BB; } 202 setResult(const MemDepResult & R)203 void setResult(const MemDepResult &R) { Result = R; } 204 getResult()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: NonLocalDepResult(BasicBlock * bb,MemDepResult result,Value * address)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. getBB()223 BasicBlock *getBB() const { return Entry.getBB(); } 224 setResult(const MemDepResult & R,Value * Addr)225 void setResult(const MemDepResult &R, Value *Addr) { 226 Entry.setResult(R); 227 Address = Addr; 228 } 229 getResult()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. getAddress()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 /// AATags - The AA tags associated with dereferences of the 286 /// pointer. The members may be null if there are no tags or 287 /// conflicting tags. 288 AAMDNodes AATags; 289 NonLocalPointerInfoNonLocalPointerInfo290 NonLocalPointerInfo() : Size(AliasAnalysis::UnknownSize) {} 291 }; 292 293 /// CachedNonLocalPointerInfo - This map stores the cached results of doing 294 /// a pointer lookup at the bottom of a block. The key of this map is the 295 /// pointer+isload bit, the value is a list of <bb->result> mappings. 296 typedef DenseMap<ValueIsLoadPair, 297 NonLocalPointerInfo> CachedNonLocalPointerInfo; 298 CachedNonLocalPointerInfo NonLocalPointerDeps; 299 300 // A map from instructions to their non-local pointer dependencies. 301 typedef DenseMap<Instruction*, 302 SmallPtrSet<ValueIsLoadPair, 4> > ReverseNonLocalPtrDepTy; 303 ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps; 304 305 306 /// PerInstNLInfo - This is the instruction we keep for each cached access 307 /// that we have for an instruction. The pointer is an owning pointer and 308 /// the bool indicates whether we have any dirty bits in the set. 309 typedef std::pair<NonLocalDepInfo, bool> PerInstNLInfo; 310 311 // A map from instructions to their non-local dependencies. 312 typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType; 313 314 NonLocalDepMapType NonLocalDeps; 315 316 // A reverse mapping from dependencies to the dependees. This is 317 // used when removing instructions to keep the cache coherent. 318 typedef DenseMap<Instruction*, 319 SmallPtrSet<Instruction*, 4> > ReverseDepMapType; 320 ReverseDepMapType ReverseLocalDeps; 321 322 // A reverse mapping from dependencies to the non-local dependees. 323 ReverseDepMapType ReverseNonLocalDeps; 324 325 /// Current AA implementation, just a cache. 326 AliasAnalysis *AA; 327 const DataLayout *DL; 328 DominatorTree *DT; 329 AssumptionCache *AC; 330 std::unique_ptr<PredIteratorCache> PredCache; 331 332 public: 333 MemoryDependenceAnalysis(); 334 ~MemoryDependenceAnalysis(); 335 static char ID; 336 337 /// Pass Implementation stuff. This doesn't do any analysis eagerly. 338 bool runOnFunction(Function &) override; 339 340 /// Clean up memory in between runs 341 void releaseMemory() override; 342 343 /// getAnalysisUsage - Does not modify anything. It uses Value Numbering 344 /// and Alias Analysis. 345 /// 346 void getAnalysisUsage(AnalysisUsage &AU) const override; 347 348 /// getDependency - Return the instruction on which a memory operation 349 /// depends. See the class comment for more details. It is illegal to call 350 /// this on non-memory instructions. 351 MemDepResult getDependency(Instruction *QueryInst); 352 353 /// getNonLocalCallDependency - Perform a full dependency query for the 354 /// specified call, returning the set of blocks that the value is 355 /// potentially live across. The returned set of results will include a 356 /// "NonLocal" result for all blocks where the value is live across. 357 /// 358 /// This method assumes the instruction returns a "NonLocal" dependency 359 /// within its own block. 360 /// 361 /// This returns a reference to an internal data structure that may be 362 /// invalidated on the next non-local query or when an instruction is 363 /// removed. Clients must copy this data if they want it around longer than 364 /// that. 365 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS); 366 367 368 /// getNonLocalPointerDependency - Perform a full dependency query for an 369 /// access to the QueryInst's specified memory location, returning the set 370 /// of instructions that either define or clobber the value. 371 /// 372 /// Warning: For a volatile query instruction, the dependencies will be 373 /// accurate, and thus usable for reordering, but it is never legal to 374 /// remove the query instruction. 375 /// 376 /// This method assumes the pointer has a "NonLocal" dependency within 377 /// QueryInst's parent basic block. 378 void getNonLocalPointerDependency(Instruction *QueryInst, 379 SmallVectorImpl<NonLocalDepResult> &Result); 380 381 /// removeInstruction - Remove an instruction from the dependence analysis, 382 /// updating the dependence of instructions that previously depended on it. 383 void removeInstruction(Instruction *InstToRemove); 384 385 /// invalidateCachedPointerInfo - This method is used to invalidate cached 386 /// information about the specified pointer, because it may be too 387 /// conservative in memdep. This is an optional call that can be used when 388 /// the client detects an equivalence between the pointer and some other 389 /// value and replaces the other value with ptr. This can make Ptr available 390 /// in more places that cached info does not necessarily keep. 391 void invalidateCachedPointerInfo(Value *Ptr); 392 393 /// invalidateCachedPredecessors - Clear the PredIteratorCache info. 394 /// This needs to be done when the CFG changes, e.g., due to splitting 395 /// critical edges. 396 void invalidateCachedPredecessors(); 397 398 /// getPointerDependencyFrom - Return the instruction on which a memory 399 /// location depends. If isLoad is true, this routine ignores may-aliases 400 /// with read-only operations. If isLoad is false, this routine ignores 401 /// may-aliases with reads from read-only locations. If possible, pass 402 /// the query instruction as well; this function may take advantage of 403 /// the metadata annotated to the query instruction to refine the result. 404 /// 405 /// Note that this is an uncached query, and thus may be inefficient. 406 /// 407 MemDepResult getPointerDependencyFrom(const AliasAnalysis::Location &Loc, 408 bool isLoad, 409 BasicBlock::iterator ScanIt, 410 BasicBlock *BB, 411 Instruction *QueryInst = nullptr); 412 413 414 /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that 415 /// looks at a memory location for a load (specified by MemLocBase, Offs, 416 /// and Size) and compares it against a load. If the specified load could 417 /// be safely widened to a larger integer load that is 1) still efficient, 418 /// 2) safe for the target, and 3) would provide the specified memory 419 /// location value, then this function returns the size in bytes of the 420 /// load width to use. If not, this returns zero. 421 static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase, 422 int64_t MemLocOffs, 423 unsigned MemLocSize, 424 const LoadInst *LI, 425 const DataLayout &DL); 426 427 private: 428 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall, 429 BasicBlock::iterator ScanIt, 430 BasicBlock *BB); 431 bool getNonLocalPointerDepFromBB(const PHITransAddr &Pointer, 432 const AliasAnalysis::Location &Loc, 433 bool isLoad, BasicBlock *BB, 434 SmallVectorImpl<NonLocalDepResult> &Result, 435 DenseMap<BasicBlock*, Value*> &Visited, 436 bool SkipFirstBlock = false); 437 MemDepResult GetNonLocalInfoForBlock(const AliasAnalysis::Location &Loc, 438 bool isLoad, BasicBlock *BB, 439 NonLocalDepInfo *Cache, 440 unsigned NumSortedEntries); 441 442 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P); 443 444 /// verifyRemoved - Verify that the specified instruction does not occur 445 /// in our internal data structures. 446 void verifyRemoved(Instruction *Inst) const; 447 448 }; 449 450 } // End llvm namespace 451 452 #endif 453