1 //===- llvm/Analysis/LoopAccessAnalysis.h -----------------------*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file defines the interface for the loop memory dependence framework that 10 // was originally developed for the Loop Vectorizer. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_ANALYSIS_LOOPACCESSANALYSIS_H 15 #define LLVM_ANALYSIS_LOOPACCESSANALYSIS_H 16 17 #include "llvm/ADT/EquivalenceClasses.h" 18 #include "llvm/Analysis/LoopAnalysisManager.h" 19 #include "llvm/Analysis/ScalarEvolutionExpressions.h" 20 #include "llvm/IR/DiagnosticInfo.h" 21 #include "llvm/Pass.h" 22 23 namespace llvm { 24 25 class AAResults; 26 class DataLayout; 27 class Loop; 28 class LoopAccessInfo; 29 class OptimizationRemarkEmitter; 30 class raw_ostream; 31 class SCEV; 32 class SCEVUnionPredicate; 33 class Value; 34 35 /// Collection of parameters shared beetween the Loop Vectorizer and the 36 /// Loop Access Analysis. 37 struct VectorizerParams { 38 /// Maximum SIMD width. 39 static const unsigned MaxVectorWidth; 40 41 /// VF as overridden by the user. 42 static unsigned VectorizationFactor; 43 /// Interleave factor as overridden by the user. 44 static unsigned VectorizationInterleave; 45 /// True if force-vector-interleave was specified by the user. 46 static bool isInterleaveForced(); 47 48 /// \When performing memory disambiguation checks at runtime do not 49 /// make more than this number of comparisons. 50 static unsigned RuntimeMemoryCheckThreshold; 51 }; 52 53 /// Checks memory dependences among accesses to the same underlying 54 /// object to determine whether there vectorization is legal or not (and at 55 /// which vectorization factor). 56 /// 57 /// Note: This class will compute a conservative dependence for access to 58 /// different underlying pointers. Clients, such as the loop vectorizer, will 59 /// sometimes deal these potential dependencies by emitting runtime checks. 60 /// 61 /// We use the ScalarEvolution framework to symbolically evalutate access 62 /// functions pairs. Since we currently don't restructure the loop we can rely 63 /// on the program order of memory accesses to determine their safety. 64 /// At the moment we will only deem accesses as safe for: 65 /// * A negative constant distance assuming program order. 66 /// 67 /// Safe: tmp = a[i + 1]; OR a[i + 1] = x; 68 /// a[i] = tmp; y = a[i]; 69 /// 70 /// The latter case is safe because later checks guarantuee that there can't 71 /// be a cycle through a phi node (that is, we check that "x" and "y" is not 72 /// the same variable: a header phi can only be an induction or a reduction, a 73 /// reduction can't have a memory sink, an induction can't have a memory 74 /// source). This is important and must not be violated (or we have to 75 /// resort to checking for cycles through memory). 76 /// 77 /// * A positive constant distance assuming program order that is bigger 78 /// than the biggest memory access. 79 /// 80 /// tmp = a[i] OR b[i] = x 81 /// a[i+2] = tmp y = b[i+2]; 82 /// 83 /// Safe distance: 2 x sizeof(a[0]), and 2 x sizeof(b[0]), respectively. 84 /// 85 /// * Zero distances and all accesses have the same size. 86 /// 87 class MemoryDepChecker { 88 public: 89 typedef PointerIntPair<Value *, 1, bool> MemAccessInfo; 90 typedef SmallVector<MemAccessInfo, 8> MemAccessInfoList; 91 /// Set of potential dependent memory accesses. 92 typedef EquivalenceClasses<MemAccessInfo> DepCandidates; 93 94 /// Type to keep track of the status of the dependence check. The order of 95 /// the elements is important and has to be from most permissive to least 96 /// permissive. 97 enum class VectorizationSafetyStatus { 98 // Can vectorize safely without RT checks. All dependences are known to be 99 // safe. 100 Safe, 101 // Can possibly vectorize with RT checks to overcome unknown dependencies. 102 PossiblySafeWithRtChecks, 103 // Cannot vectorize due to known unsafe dependencies. 104 Unsafe, 105 }; 106 107 /// Dependece between memory access instructions. 108 struct Dependence { 109 /// The type of the dependence. 110 enum DepType { 111 // No dependence. 112 NoDep, 113 // We couldn't determine the direction or the distance. 114 Unknown, 115 // Lexically forward. 116 // 117 // FIXME: If we only have loop-independent forward dependences (e.g. a 118 // read and write of A[i]), LAA will locally deem the dependence "safe" 119 // without querying the MemoryDepChecker. Therefore we can miss 120 // enumerating loop-independent forward dependences in 121 // getDependences. Note that as soon as there are different 122 // indices used to access the same array, the MemoryDepChecker *is* 123 // queried and the dependence list is complete. 124 Forward, 125 // Forward, but if vectorized, is likely to prevent store-to-load 126 // forwarding. 127 ForwardButPreventsForwarding, 128 // Lexically backward. 129 Backward, 130 // Backward, but the distance allows a vectorization factor of 131 // MaxSafeDepDistBytes. 132 BackwardVectorizable, 133 // Same, but may prevent store-to-load forwarding. 134 BackwardVectorizableButPreventsForwarding 135 }; 136 137 /// String version of the types. 138 static const char *DepName[]; 139 140 /// Index of the source of the dependence in the InstMap vector. 141 unsigned Source; 142 /// Index of the destination of the dependence in the InstMap vector. 143 unsigned Destination; 144 /// The type of the dependence. 145 DepType Type; 146 147 Dependence(unsigned Source, unsigned Destination, DepType Type) 148 : Source(Source), Destination(Destination), Type(Type) {} 149 150 /// Return the source instruction of the dependence. 151 Instruction *getSource(const LoopAccessInfo &LAI) const; 152 /// Return the destination instruction of the dependence. 153 Instruction *getDestination(const LoopAccessInfo &LAI) const; 154 155 /// Dependence types that don't prevent vectorization. 156 static VectorizationSafetyStatus isSafeForVectorization(DepType Type); 157 158 /// Lexically forward dependence. 159 bool isForward() const; 160 /// Lexically backward dependence. 161 bool isBackward() const; 162 163 /// May be a lexically backward dependence type (includes Unknown). 164 bool isPossiblyBackward() const; 165 166 /// Print the dependence. \p Instr is used to map the instruction 167 /// indices to instructions. 168 void print(raw_ostream &OS, unsigned Depth, 169 const SmallVectorImpl<Instruction *> &Instrs) const; 170 }; 171 172 MemoryDepChecker(PredicatedScalarEvolution &PSE, const Loop *L) 173 : PSE(PSE), InnermostLoop(L), AccessIdx(0), MaxSafeDepDistBytes(0), 174 MaxSafeVectorWidthInBits(-1U), 175 FoundNonConstantDistanceDependence(false), 176 Status(VectorizationSafetyStatus::Safe), RecordDependences(true) {} 177 178 /// Register the location (instructions are given increasing numbers) 179 /// of a write access. 180 void addAccess(StoreInst *SI) { 181 Value *Ptr = SI->getPointerOperand(); 182 Accesses[MemAccessInfo(Ptr, true)].push_back(AccessIdx); 183 InstMap.push_back(SI); 184 ++AccessIdx; 185 } 186 187 /// Register the location (instructions are given increasing numbers) 188 /// of a write access. 189 void addAccess(LoadInst *LI) { 190 Value *Ptr = LI->getPointerOperand(); 191 Accesses[MemAccessInfo(Ptr, false)].push_back(AccessIdx); 192 InstMap.push_back(LI); 193 ++AccessIdx; 194 } 195 196 /// Check whether the dependencies between the accesses are safe. 197 /// 198 /// Only checks sets with elements in \p CheckDeps. 199 bool areDepsSafe(DepCandidates &AccessSets, MemAccessInfoList &CheckDeps, 200 const ValueToValueMap &Strides); 201 202 /// No memory dependence was encountered that would inhibit 203 /// vectorization. 204 bool isSafeForVectorization() const { 205 return Status == VectorizationSafetyStatus::Safe; 206 } 207 208 /// Return true if the number of elements that are safe to operate on 209 /// simultaneously is not bounded. 210 bool isSafeForAnyVectorWidth() const { 211 return MaxSafeVectorWidthInBits == UINT_MAX; 212 } 213 214 /// The maximum number of bytes of a vector register we can vectorize 215 /// the accesses safely with. 216 uint64_t getMaxSafeDepDistBytes() { return MaxSafeDepDistBytes; } 217 218 /// Return the number of elements that are safe to operate on 219 /// simultaneously, multiplied by the size of the element in bits. 220 uint64_t getMaxSafeVectorWidthInBits() const { 221 return MaxSafeVectorWidthInBits; 222 } 223 224 /// In same cases when the dependency check fails we can still 225 /// vectorize the loop with a dynamic array access check. 226 bool shouldRetryWithRuntimeCheck() const { 227 return FoundNonConstantDistanceDependence && 228 Status == VectorizationSafetyStatus::PossiblySafeWithRtChecks; 229 } 230 231 /// Returns the memory dependences. If null is returned we exceeded 232 /// the MaxDependences threshold and this information is not 233 /// available. 234 const SmallVectorImpl<Dependence> *getDependences() const { 235 return RecordDependences ? &Dependences : nullptr; 236 } 237 238 void clearDependences() { Dependences.clear(); } 239 240 /// The vector of memory access instructions. The indices are used as 241 /// instruction identifiers in the Dependence class. 242 const SmallVectorImpl<Instruction *> &getMemoryInstructions() const { 243 return InstMap; 244 } 245 246 /// Generate a mapping between the memory instructions and their 247 /// indices according to program order. 248 DenseMap<Instruction *, unsigned> generateInstructionOrderMap() const { 249 DenseMap<Instruction *, unsigned> OrderMap; 250 251 for (unsigned I = 0; I < InstMap.size(); ++I) 252 OrderMap[InstMap[I]] = I; 253 254 return OrderMap; 255 } 256 257 /// Find the set of instructions that read or write via \p Ptr. 258 SmallVector<Instruction *, 4> getInstructionsForAccess(Value *Ptr, 259 bool isWrite) const; 260 261 private: 262 /// A wrapper around ScalarEvolution, used to add runtime SCEV checks, and 263 /// applies dynamic knowledge to simplify SCEV expressions and convert them 264 /// to a more usable form. We need this in case assumptions about SCEV 265 /// expressions need to be made in order to avoid unknown dependences. For 266 /// example we might assume a unit stride for a pointer in order to prove 267 /// that a memory access is strided and doesn't wrap. 268 PredicatedScalarEvolution &PSE; 269 const Loop *InnermostLoop; 270 271 /// Maps access locations (ptr, read/write) to program order. 272 DenseMap<MemAccessInfo, std::vector<unsigned> > Accesses; 273 274 /// Memory access instructions in program order. 275 SmallVector<Instruction *, 16> InstMap; 276 277 /// The program order index to be used for the next instruction. 278 unsigned AccessIdx; 279 280 // We can access this many bytes in parallel safely. 281 uint64_t MaxSafeDepDistBytes; 282 283 /// Number of elements (from consecutive iterations) that are safe to 284 /// operate on simultaneously, multiplied by the size of the element in bits. 285 /// The size of the element is taken from the memory access that is most 286 /// restrictive. 287 uint64_t MaxSafeVectorWidthInBits; 288 289 /// If we see a non-constant dependence distance we can still try to 290 /// vectorize this loop with runtime checks. 291 bool FoundNonConstantDistanceDependence; 292 293 /// Result of the dependence checks, indicating whether the checked 294 /// dependences are safe for vectorization, require RT checks or are known to 295 /// be unsafe. 296 VectorizationSafetyStatus Status; 297 298 //// True if Dependences reflects the dependences in the 299 //// loop. If false we exceeded MaxDependences and 300 //// Dependences is invalid. 301 bool RecordDependences; 302 303 /// Memory dependences collected during the analysis. Only valid if 304 /// RecordDependences is true. 305 SmallVector<Dependence, 8> Dependences; 306 307 /// Check whether there is a plausible dependence between the two 308 /// accesses. 309 /// 310 /// Access \p A must happen before \p B in program order. The two indices 311 /// identify the index into the program order map. 312 /// 313 /// This function checks whether there is a plausible dependence (or the 314 /// absence of such can't be proved) between the two accesses. If there is a 315 /// plausible dependence but the dependence distance is bigger than one 316 /// element access it records this distance in \p MaxSafeDepDistBytes (if this 317 /// distance is smaller than any other distance encountered so far). 318 /// Otherwise, this function returns true signaling a possible dependence. 319 Dependence::DepType isDependent(const MemAccessInfo &A, unsigned AIdx, 320 const MemAccessInfo &B, unsigned BIdx, 321 const ValueToValueMap &Strides); 322 323 /// Check whether the data dependence could prevent store-load 324 /// forwarding. 325 /// 326 /// \return false if we shouldn't vectorize at all or avoid larger 327 /// vectorization factors by limiting MaxSafeDepDistBytes. 328 bool couldPreventStoreLoadForward(uint64_t Distance, uint64_t TypeByteSize); 329 330 /// Updates the current safety status with \p S. We can go from Safe to 331 /// either PossiblySafeWithRtChecks or Unsafe and from 332 /// PossiblySafeWithRtChecks to Unsafe. 333 void mergeInStatus(VectorizationSafetyStatus S); 334 }; 335 336 class RuntimePointerChecking; 337 /// A grouping of pointers. A single memcheck is required between 338 /// two groups. 339 struct RuntimeCheckingPtrGroup { 340 /// Create a new pointer checking group containing a single 341 /// pointer, with index \p Index in RtCheck. 342 RuntimeCheckingPtrGroup(unsigned Index, RuntimePointerChecking &RtCheck); 343 344 /// Tries to add the pointer recorded in RtCheck at index 345 /// \p Index to this pointer checking group. We can only add a pointer 346 /// to a checking group if we will still be able to get 347 /// the upper and lower bounds of the check. Returns true in case 348 /// of success, false otherwise. 349 bool addPointer(unsigned Index); 350 351 /// Constitutes the context of this pointer checking group. For each 352 /// pointer that is a member of this group we will retain the index 353 /// at which it appears in RtCheck. 354 RuntimePointerChecking &RtCheck; 355 /// The SCEV expression which represents the upper bound of all the 356 /// pointers in this group. 357 const SCEV *High; 358 /// The SCEV expression which represents the lower bound of all the 359 /// pointers in this group. 360 const SCEV *Low; 361 /// Indices of all the pointers that constitute this grouping. 362 SmallVector<unsigned, 2> Members; 363 }; 364 365 /// A memcheck which made up of a pair of grouped pointers. 366 typedef std::pair<const RuntimeCheckingPtrGroup *, 367 const RuntimeCheckingPtrGroup *> 368 RuntimePointerCheck; 369 370 /// Holds information about the memory runtime legality checks to verify 371 /// that a group of pointers do not overlap. 372 class RuntimePointerChecking { 373 friend struct RuntimeCheckingPtrGroup; 374 375 public: 376 struct PointerInfo { 377 /// Holds the pointer value that we need to check. 378 TrackingVH<Value> PointerValue; 379 /// Holds the smallest byte address accessed by the pointer throughout all 380 /// iterations of the loop. 381 const SCEV *Start; 382 /// Holds the largest byte address accessed by the pointer throughout all 383 /// iterations of the loop, plus 1. 384 const SCEV *End; 385 /// Holds the information if this pointer is used for writing to memory. 386 bool IsWritePtr; 387 /// Holds the id of the set of pointers that could be dependent because of a 388 /// shared underlying object. 389 unsigned DependencySetId; 390 /// Holds the id of the disjoint alias set to which this pointer belongs. 391 unsigned AliasSetId; 392 /// SCEV for the access. 393 const SCEV *Expr; 394 395 PointerInfo(Value *PointerValue, const SCEV *Start, const SCEV *End, 396 bool IsWritePtr, unsigned DependencySetId, unsigned AliasSetId, 397 const SCEV *Expr) 398 : PointerValue(PointerValue), Start(Start), End(End), 399 IsWritePtr(IsWritePtr), DependencySetId(DependencySetId), 400 AliasSetId(AliasSetId), Expr(Expr) {} 401 }; 402 403 RuntimePointerChecking(ScalarEvolution *SE) : Need(false), SE(SE) {} 404 405 /// Reset the state of the pointer runtime information. 406 void reset() { 407 Need = false; 408 Pointers.clear(); 409 Checks.clear(); 410 } 411 412 /// Insert a pointer and calculate the start and end SCEVs. 413 /// We need \p PSE in order to compute the SCEV expression of the pointer 414 /// according to the assumptions that we've made during the analysis. 415 /// The method might also version the pointer stride according to \p Strides, 416 /// and add new predicates to \p PSE. 417 void insert(Loop *Lp, Value *Ptr, bool WritePtr, unsigned DepSetId, 418 unsigned ASId, const ValueToValueMap &Strides, 419 PredicatedScalarEvolution &PSE); 420 421 /// No run-time memory checking is necessary. 422 bool empty() const { return Pointers.empty(); } 423 424 /// Generate the checks and store it. This also performs the grouping 425 /// of pointers to reduce the number of memchecks necessary. 426 void generateChecks(MemoryDepChecker::DepCandidates &DepCands, 427 bool UseDependencies); 428 429 /// Returns the checks that generateChecks created. 430 const SmallVectorImpl<RuntimePointerCheck> &getChecks() const { 431 return Checks; 432 } 433 434 /// Decide if we need to add a check between two groups of pointers, 435 /// according to needsChecking. 436 bool needsChecking(const RuntimeCheckingPtrGroup &M, 437 const RuntimeCheckingPtrGroup &N) const; 438 439 /// Returns the number of run-time checks required according to 440 /// needsChecking. 441 unsigned getNumberOfChecks() const { return Checks.size(); } 442 443 /// Print the list run-time memory checks necessary. 444 void print(raw_ostream &OS, unsigned Depth = 0) const; 445 446 /// Print \p Checks. 447 void printChecks(raw_ostream &OS, 448 const SmallVectorImpl<RuntimePointerCheck> &Checks, 449 unsigned Depth = 0) const; 450 451 /// This flag indicates if we need to add the runtime check. 452 bool Need; 453 454 /// Information about the pointers that may require checking. 455 SmallVector<PointerInfo, 2> Pointers; 456 457 /// Holds a partitioning of pointers into "check groups". 458 SmallVector<RuntimeCheckingPtrGroup, 2> CheckingGroups; 459 460 /// Check if pointers are in the same partition 461 /// 462 /// \p PtrToPartition contains the partition number for pointers (-1 if the 463 /// pointer belongs to multiple partitions). 464 static bool 465 arePointersInSamePartition(const SmallVectorImpl<int> &PtrToPartition, 466 unsigned PtrIdx1, unsigned PtrIdx2); 467 468 /// Decide whether we need to issue a run-time check for pointer at 469 /// index \p I and \p J to prove their independence. 470 bool needsChecking(unsigned I, unsigned J) const; 471 472 /// Return PointerInfo for pointer at index \p PtrIdx. 473 const PointerInfo &getPointerInfo(unsigned PtrIdx) const { 474 return Pointers[PtrIdx]; 475 } 476 477 ScalarEvolution *getSE() const { return SE; } 478 479 private: 480 /// Groups pointers such that a single memcheck is required 481 /// between two different groups. This will clear the CheckingGroups vector 482 /// and re-compute it. We will only group dependecies if \p UseDependencies 483 /// is true, otherwise we will create a separate group for each pointer. 484 void groupChecks(MemoryDepChecker::DepCandidates &DepCands, 485 bool UseDependencies); 486 487 /// Generate the checks and return them. 488 SmallVector<RuntimePointerCheck, 4> generateChecks() const; 489 490 /// Holds a pointer to the ScalarEvolution analysis. 491 ScalarEvolution *SE; 492 493 /// Set of run-time checks required to establish independence of 494 /// otherwise may-aliasing pointers in the loop. 495 SmallVector<RuntimePointerCheck, 4> Checks; 496 }; 497 498 /// Drive the analysis of memory accesses in the loop 499 /// 500 /// This class is responsible for analyzing the memory accesses of a loop. It 501 /// collects the accesses and then its main helper the AccessAnalysis class 502 /// finds and categorizes the dependences in buildDependenceSets. 503 /// 504 /// For memory dependences that can be analyzed at compile time, it determines 505 /// whether the dependence is part of cycle inhibiting vectorization. This work 506 /// is delegated to the MemoryDepChecker class. 507 /// 508 /// For memory dependences that cannot be determined at compile time, it 509 /// generates run-time checks to prove independence. This is done by 510 /// AccessAnalysis::canCheckPtrAtRT and the checks are maintained by the 511 /// RuntimePointerCheck class. 512 /// 513 /// If pointers can wrap or can't be expressed as affine AddRec expressions by 514 /// ScalarEvolution, we will generate run-time checks by emitting a 515 /// SCEVUnionPredicate. 516 /// 517 /// Checks for both memory dependences and the SCEV predicates contained in the 518 /// PSE must be emitted in order for the results of this analysis to be valid. 519 class LoopAccessInfo { 520 public: 521 LoopAccessInfo(Loop *L, ScalarEvolution *SE, const TargetLibraryInfo *TLI, 522 AAResults *AA, DominatorTree *DT, LoopInfo *LI); 523 524 /// Return true we can analyze the memory accesses in the loop and there are 525 /// no memory dependence cycles. 526 bool canVectorizeMemory() const { return CanVecMem; } 527 528 /// Return true if there is a convergent operation in the loop. There may 529 /// still be reported runtime pointer checks that would be required, but it is 530 /// not legal to insert them. 531 bool hasConvergentOp() const { return HasConvergentOp; } 532 533 const RuntimePointerChecking *getRuntimePointerChecking() const { 534 return PtrRtChecking.get(); 535 } 536 537 /// Number of memchecks required to prove independence of otherwise 538 /// may-alias pointers. 539 unsigned getNumRuntimePointerChecks() const { 540 return PtrRtChecking->getNumberOfChecks(); 541 } 542 543 /// Return true if the block BB needs to be predicated in order for the loop 544 /// to be vectorized. 545 static bool blockNeedsPredication(BasicBlock *BB, Loop *TheLoop, 546 DominatorTree *DT); 547 548 /// Returns true if the value V is uniform within the loop. 549 bool isUniform(Value *V) const; 550 551 uint64_t getMaxSafeDepDistBytes() const { return MaxSafeDepDistBytes; } 552 unsigned getNumStores() const { return NumStores; } 553 unsigned getNumLoads() const { return NumLoads;} 554 555 /// The diagnostics report generated for the analysis. E.g. why we 556 /// couldn't analyze the loop. 557 const OptimizationRemarkAnalysis *getReport() const { return Report.get(); } 558 559 /// the Memory Dependence Checker which can determine the 560 /// loop-independent and loop-carried dependences between memory accesses. 561 const MemoryDepChecker &getDepChecker() const { return *DepChecker; } 562 563 /// Return the list of instructions that use \p Ptr to read or write 564 /// memory. 565 SmallVector<Instruction *, 4> getInstructionsForAccess(Value *Ptr, 566 bool isWrite) const { 567 return DepChecker->getInstructionsForAccess(Ptr, isWrite); 568 } 569 570 /// If an access has a symbolic strides, this maps the pointer value to 571 /// the stride symbol. 572 const ValueToValueMap &getSymbolicStrides() const { return SymbolicStrides; } 573 574 /// Pointer has a symbolic stride. 575 bool hasStride(Value *V) const { return StrideSet.count(V); } 576 577 /// Print the information about the memory accesses in the loop. 578 void print(raw_ostream &OS, unsigned Depth = 0) const; 579 580 /// If the loop has memory dependence involving an invariant address, i.e. two 581 /// stores or a store and a load, then return true, else return false. 582 bool hasDependenceInvolvingLoopInvariantAddress() const { 583 return HasDependenceInvolvingLoopInvariantAddress; 584 } 585 586 /// Used to add runtime SCEV checks. Simplifies SCEV expressions and converts 587 /// them to a more usable form. All SCEV expressions during the analysis 588 /// should be re-written (and therefore simplified) according to PSE. 589 /// A user of LoopAccessAnalysis will need to emit the runtime checks 590 /// associated with this predicate. 591 const PredicatedScalarEvolution &getPSE() const { return *PSE; } 592 593 private: 594 /// Analyze the loop. 595 void analyzeLoop(AAResults *AA, LoopInfo *LI, 596 const TargetLibraryInfo *TLI, DominatorTree *DT); 597 598 /// Check if the structure of the loop allows it to be analyzed by this 599 /// pass. 600 bool canAnalyzeLoop(); 601 602 /// Save the analysis remark. 603 /// 604 /// LAA does not directly emits the remarks. Instead it stores it which the 605 /// client can retrieve and presents as its own analysis 606 /// (e.g. -Rpass-analysis=loop-vectorize). 607 OptimizationRemarkAnalysis &recordAnalysis(StringRef RemarkName, 608 Instruction *Instr = nullptr); 609 610 /// Collect memory access with loop invariant strides. 611 /// 612 /// Looks for accesses like "a[i * StrideA]" where "StrideA" is loop 613 /// invariant. 614 void collectStridedAccess(Value *LoadOrStoreInst); 615 616 std::unique_ptr<PredicatedScalarEvolution> PSE; 617 618 /// We need to check that all of the pointers in this list are disjoint 619 /// at runtime. Using std::unique_ptr to make using move ctor simpler. 620 std::unique_ptr<RuntimePointerChecking> PtrRtChecking; 621 622 /// the Memory Dependence Checker which can determine the 623 /// loop-independent and loop-carried dependences between memory accesses. 624 std::unique_ptr<MemoryDepChecker> DepChecker; 625 626 Loop *TheLoop; 627 628 unsigned NumLoads; 629 unsigned NumStores; 630 631 uint64_t MaxSafeDepDistBytes; 632 633 /// Cache the result of analyzeLoop. 634 bool CanVecMem; 635 bool HasConvergentOp; 636 637 /// Indicator that there are non vectorizable stores to a uniform address. 638 bool HasDependenceInvolvingLoopInvariantAddress; 639 640 /// The diagnostics report generated for the analysis. E.g. why we 641 /// couldn't analyze the loop. 642 std::unique_ptr<OptimizationRemarkAnalysis> Report; 643 644 /// If an access has a symbolic strides, this maps the pointer value to 645 /// the stride symbol. 646 ValueToValueMap SymbolicStrides; 647 648 /// Set of symbolic strides values. 649 SmallPtrSet<Value *, 8> StrideSet; 650 }; 651 652 Value *stripIntegerCast(Value *V); 653 654 /// Return the SCEV corresponding to a pointer with the symbolic stride 655 /// replaced with constant one, assuming the SCEV predicate associated with 656 /// \p PSE is true. 657 /// 658 /// If necessary this method will version the stride of the pointer according 659 /// to \p PtrToStride and therefore add further predicates to \p PSE. 660 /// 661 /// If \p OrigPtr is not null, use it to look up the stride value instead of \p 662 /// Ptr. \p PtrToStride provides the mapping between the pointer value and its 663 /// stride as collected by LoopVectorizationLegality::collectStridedAccess. 664 const SCEV *replaceSymbolicStrideSCEV(PredicatedScalarEvolution &PSE, 665 const ValueToValueMap &PtrToStride, 666 Value *Ptr, Value *OrigPtr = nullptr); 667 668 /// If the pointer has a constant stride return it in units of its 669 /// element size. Otherwise return zero. 670 /// 671 /// Ensure that it does not wrap in the address space, assuming the predicate 672 /// associated with \p PSE is true. 673 /// 674 /// If necessary this method will version the stride of the pointer according 675 /// to \p PtrToStride and therefore add further predicates to \p PSE. 676 /// The \p Assume parameter indicates if we are allowed to make additional 677 /// run-time assumptions. 678 int64_t getPtrStride(PredicatedScalarEvolution &PSE, Value *Ptr, const Loop *Lp, 679 const ValueToValueMap &StridesMap = ValueToValueMap(), 680 bool Assume = false, bool ShouldCheckWrap = true); 681 682 /// Attempt to sort the pointers in \p VL and return the sorted indices 683 /// in \p SortedIndices, if reordering is required. 684 /// 685 /// Returns 'true' if sorting is legal, otherwise returns 'false'. 686 /// 687 /// For example, for a given \p VL of memory accesses in program order, a[i+4], 688 /// a[i+0], a[i+1] and a[i+7], this function will sort the \p VL and save the 689 /// sorted indices in \p SortedIndices as a[i+0], a[i+1], a[i+4], a[i+7] and 690 /// saves the mask for actual memory accesses in program order in 691 /// \p SortedIndices as <1,2,0,3> 692 bool sortPtrAccesses(ArrayRef<Value *> VL, const DataLayout &DL, 693 ScalarEvolution &SE, 694 SmallVectorImpl<unsigned> &SortedIndices); 695 696 /// Returns true if the memory operations \p A and \p B are consecutive. 697 /// This is a simple API that does not depend on the analysis pass. 698 bool isConsecutiveAccess(Value *A, Value *B, const DataLayout &DL, 699 ScalarEvolution &SE, bool CheckType = true); 700 701 /// This analysis provides dependence information for the memory accesses 702 /// of a loop. 703 /// 704 /// It runs the analysis for a loop on demand. This can be initiated by 705 /// querying the loop access info via LAA::getInfo. getInfo return a 706 /// LoopAccessInfo object. See this class for the specifics of what information 707 /// is provided. 708 class LoopAccessLegacyAnalysis : public FunctionPass { 709 public: 710 static char ID; 711 712 LoopAccessLegacyAnalysis(); 713 714 bool runOnFunction(Function &F) override; 715 716 void getAnalysisUsage(AnalysisUsage &AU) const override; 717 718 /// Query the result of the loop access information for the loop \p L. 719 /// 720 /// If there is no cached result available run the analysis. 721 const LoopAccessInfo &getInfo(Loop *L); 722 723 void releaseMemory() override { 724 // Invalidate the cache when the pass is freed. 725 LoopAccessInfoMap.clear(); 726 } 727 728 /// Print the result of the analysis when invoked with -analyze. 729 void print(raw_ostream &OS, const Module *M = nullptr) const override; 730 731 private: 732 /// The cache. 733 DenseMap<Loop *, std::unique_ptr<LoopAccessInfo>> LoopAccessInfoMap; 734 735 // The used analysis passes. 736 ScalarEvolution *SE = nullptr; 737 const TargetLibraryInfo *TLI = nullptr; 738 AAResults *AA = nullptr; 739 DominatorTree *DT = nullptr; 740 LoopInfo *LI = nullptr; 741 }; 742 743 /// This analysis provides dependence information for the memory 744 /// accesses of a loop. 745 /// 746 /// It runs the analysis for a loop on demand. This can be initiated by 747 /// querying the loop access info via AM.getResult<LoopAccessAnalysis>. 748 /// getResult return a LoopAccessInfo object. See this class for the 749 /// specifics of what information is provided. 750 class LoopAccessAnalysis 751 : public AnalysisInfoMixin<LoopAccessAnalysis> { 752 friend AnalysisInfoMixin<LoopAccessAnalysis>; 753 static AnalysisKey Key; 754 755 public: 756 typedef LoopAccessInfo Result; 757 758 Result run(Loop &L, LoopAnalysisManager &AM, LoopStandardAnalysisResults &AR); 759 }; 760 761 inline Instruction *MemoryDepChecker::Dependence::getSource( 762 const LoopAccessInfo &LAI) const { 763 return LAI.getDepChecker().getMemoryInstructions()[Source]; 764 } 765 766 inline Instruction *MemoryDepChecker::Dependence::getDestination( 767 const LoopAccessInfo &LAI) const { 768 return LAI.getDepChecker().getMemoryInstructions()[Destination]; 769 } 770 771 } // End llvm namespace 772 773 #endif 774