1 //===-- llvm/Analysis/DependenceAnalysis.h -------------------- -*- 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 // DependenceAnalysis is an LLVM pass that analyses dependences between memory 11 // accesses. Currently, it is an implementation of the approach described in 12 // 13 // Practical Dependence Testing 14 // Goff, Kennedy, Tseng 15 // PLDI 1991 16 // 17 // There's a single entry point that analyzes the dependence between a pair 18 // of memory references in a function, returning either NULL, for no dependence, 19 // or a more-or-less detailed description of the dependence between them. 20 // 21 // This pass exists to support the DependenceGraph pass. There are two separate 22 // passes because there's a useful separation of concerns. A dependence exists 23 // if two conditions are met: 24 // 25 // 1) Two instructions reference the same memory location, and 26 // 2) There is a flow of control leading from one instruction to the other. 27 // 28 // DependenceAnalysis attacks the first condition; DependenceGraph will attack 29 // the second (it's not yet ready). 30 // 31 // Please note that this is work in progress and the interface is subject to 32 // change. 33 // 34 // Plausible changes: 35 // Return a set of more precise dependences instead of just one dependence 36 // summarizing all. 37 // 38 //===----------------------------------------------------------------------===// 39 40 #ifndef LLVM_ANALYSIS_DEPENDENCEANALYSIS_H 41 #define LLVM_ANALYSIS_DEPENDENCEANALYSIS_H 42 43 #include "llvm/ADT/SmallBitVector.h" 44 #include "llvm/Analysis/AliasAnalysis.h" 45 #include "llvm/IR/Instructions.h" 46 #include "llvm/Pass.h" 47 48 namespace llvm { 49 template <typename T> class ArrayRef; 50 class Loop; 51 class LoopInfo; 52 class ScalarEvolution; 53 class SCEV; 54 class SCEVConstant; 55 class raw_ostream; 56 57 /// Dependence - This class represents a dependence between two memory 58 /// memory references in a function. It contains minimal information and 59 /// is used in the very common situation where the compiler is unable to 60 /// determine anything beyond the existence of a dependence; that is, it 61 /// represents a confused dependence (see also FullDependence). In most 62 /// cases (for output, flow, and anti dependences), the dependence implies 63 /// an ordering, where the source must precede the destination; in contrast, 64 /// input dependences are unordered. 65 /// 66 /// When a dependence graph is built, each Dependence will be a member of 67 /// the set of predecessor edges for its destination instruction and a set 68 /// if successor edges for its source instruction. These sets are represented 69 /// as singly-linked lists, with the "next" fields stored in the dependence 70 /// itelf. 71 class Dependence { 72 protected: 73 Dependence(Dependence &&) = default; 74 Dependence &operator=(Dependence &&) = default; 75 76 public: Dependence(Instruction * Source,Instruction * Destination)77 Dependence(Instruction *Source, 78 Instruction *Destination) : 79 Src(Source), 80 Dst(Destination), 81 NextPredecessor(nullptr), 82 NextSuccessor(nullptr) {} ~Dependence()83 virtual ~Dependence() {} 84 85 /// Dependence::DVEntry - Each level in the distance/direction vector 86 /// has a direction (or perhaps a union of several directions), and 87 /// perhaps a distance. 88 struct DVEntry { 89 enum { NONE = 0, 90 LT = 1, 91 EQ = 2, 92 LE = 3, 93 GT = 4, 94 NE = 5, 95 GE = 6, 96 ALL = 7 }; 97 unsigned char Direction : 3; // Init to ALL, then refine. 98 bool Scalar : 1; // Init to true. 99 bool PeelFirst : 1; // Peeling the first iteration will break dependence. 100 bool PeelLast : 1; // Peeling the last iteration will break the dependence. 101 bool Splitable : 1; // Splitting the loop will break dependence. 102 const SCEV *Distance; // NULL implies no distance available. DVEntryDVEntry103 DVEntry() : Direction(ALL), Scalar(true), PeelFirst(false), 104 PeelLast(false), Splitable(false), Distance(nullptr) { } 105 }; 106 107 /// getSrc - Returns the source instruction for this dependence. 108 /// getSrc()109 Instruction *getSrc() const { return Src; } 110 111 /// getDst - Returns the destination instruction for this dependence. 112 /// getDst()113 Instruction *getDst() const { return Dst; } 114 115 /// isInput - Returns true if this is an input dependence. 116 /// 117 bool isInput() const; 118 119 /// isOutput - Returns true if this is an output dependence. 120 /// 121 bool isOutput() const; 122 123 /// isFlow - Returns true if this is a flow (aka true) dependence. 124 /// 125 bool isFlow() const; 126 127 /// isAnti - Returns true if this is an anti dependence. 128 /// 129 bool isAnti() const; 130 131 /// isOrdered - Returns true if dependence is Output, Flow, or Anti 132 /// isOrdered()133 bool isOrdered() const { return isOutput() || isFlow() || isAnti(); } 134 135 /// isUnordered - Returns true if dependence is Input 136 /// isUnordered()137 bool isUnordered() const { return isInput(); } 138 139 /// isLoopIndependent - Returns true if this is a loop-independent 140 /// dependence. isLoopIndependent()141 virtual bool isLoopIndependent() const { return true; } 142 143 /// isConfused - Returns true if this dependence is confused 144 /// (the compiler understands nothing and makes worst-case 145 /// assumptions). isConfused()146 virtual bool isConfused() const { return true; } 147 148 /// isConsistent - Returns true if this dependence is consistent 149 /// (occurs every time the source and destination are executed). isConsistent()150 virtual bool isConsistent() const { return false; } 151 152 /// getLevels - Returns the number of common loops surrounding the 153 /// source and destination of the dependence. getLevels()154 virtual unsigned getLevels() const { return 0; } 155 156 /// getDirection - Returns the direction associated with a particular 157 /// level. getDirection(unsigned Level)158 virtual unsigned getDirection(unsigned Level) const { return DVEntry::ALL; } 159 160 /// getDistance - Returns the distance (or NULL) associated with a 161 /// particular level. getDistance(unsigned Level)162 virtual const SCEV *getDistance(unsigned Level) const { return nullptr; } 163 164 /// isPeelFirst - Returns true if peeling the first iteration from 165 /// this loop will break this dependence. isPeelFirst(unsigned Level)166 virtual bool isPeelFirst(unsigned Level) const { return false; } 167 168 /// isPeelLast - Returns true if peeling the last iteration from 169 /// this loop will break this dependence. isPeelLast(unsigned Level)170 virtual bool isPeelLast(unsigned Level) const { return false; } 171 172 /// isSplitable - Returns true if splitting this loop will break 173 /// the dependence. isSplitable(unsigned Level)174 virtual bool isSplitable(unsigned Level) const { return false; } 175 176 /// isScalar - Returns true if a particular level is scalar; that is, 177 /// if no subscript in the source or destination mention the induction 178 /// variable associated with the loop at this level. 179 virtual bool isScalar(unsigned Level) const; 180 181 /// getNextPredecessor - Returns the value of the NextPredecessor 182 /// field. getNextPredecessor()183 const Dependence *getNextPredecessor() const { return NextPredecessor; } 184 185 /// getNextSuccessor - Returns the value of the NextSuccessor 186 /// field. getNextSuccessor()187 const Dependence *getNextSuccessor() const { return NextSuccessor; } 188 189 /// setNextPredecessor - Sets the value of the NextPredecessor 190 /// field. setNextPredecessor(const Dependence * pred)191 void setNextPredecessor(const Dependence *pred) { NextPredecessor = pred; } 192 193 /// setNextSuccessor - Sets the value of the NextSuccessor 194 /// field. setNextSuccessor(const Dependence * succ)195 void setNextSuccessor(const Dependence *succ) { NextSuccessor = succ; } 196 197 /// dump - For debugging purposes, dumps a dependence to OS. 198 /// 199 void dump(raw_ostream &OS) const; 200 201 private: 202 Instruction *Src, *Dst; 203 const Dependence *NextPredecessor, *NextSuccessor; 204 friend class DependenceInfo; 205 }; 206 207 /// FullDependence - This class represents a dependence between two memory 208 /// references in a function. It contains detailed information about the 209 /// dependence (direction vectors, etc.) and is used when the compiler is 210 /// able to accurately analyze the interaction of the references; that is, 211 /// it is not a confused dependence (see Dependence). In most cases 212 /// (for output, flow, and anti dependences), the dependence implies an 213 /// ordering, where the source must precede the destination; in contrast, 214 /// input dependences are unordered. 215 class FullDependence final : public Dependence { 216 public: 217 FullDependence(Instruction *Src, Instruction *Dst, bool LoopIndependent, 218 unsigned Levels); 219 220 /// isLoopIndependent - Returns true if this is a loop-independent 221 /// dependence. isLoopIndependent()222 bool isLoopIndependent() const override { return LoopIndependent; } 223 224 /// isConfused - Returns true if this dependence is confused 225 /// (the compiler understands nothing and makes worst-case 226 /// assumptions). isConfused()227 bool isConfused() const override { return false; } 228 229 /// isConsistent - Returns true if this dependence is consistent 230 /// (occurs every time the source and destination are executed). isConsistent()231 bool isConsistent() const override { return Consistent; } 232 233 /// getLevels - Returns the number of common loops surrounding the 234 /// source and destination of the dependence. getLevels()235 unsigned getLevels() const override { return Levels; } 236 237 /// getDirection - Returns the direction associated with a particular 238 /// level. 239 unsigned getDirection(unsigned Level) const override; 240 241 /// getDistance - Returns the distance (or NULL) associated with a 242 /// particular level. 243 const SCEV *getDistance(unsigned Level) const override; 244 245 /// isPeelFirst - Returns true if peeling the first iteration from 246 /// this loop will break this dependence. 247 bool isPeelFirst(unsigned Level) const override; 248 249 /// isPeelLast - Returns true if peeling the last iteration from 250 /// this loop will break this dependence. 251 bool isPeelLast(unsigned Level) const override; 252 253 /// isSplitable - Returns true if splitting the loop will break 254 /// the dependence. 255 bool isSplitable(unsigned Level) const override; 256 257 /// isScalar - Returns true if a particular level is scalar; that is, 258 /// if no subscript in the source or destination mention the induction 259 /// variable associated with the loop at this level. 260 bool isScalar(unsigned Level) const override; 261 262 private: 263 unsigned short Levels; 264 bool LoopIndependent; 265 bool Consistent; // Init to true, then refine. 266 std::unique_ptr<DVEntry[]> DV; 267 friend class DependenceInfo; 268 }; 269 270 /// DependenceInfo - This class is the main dependence-analysis driver. 271 /// 272 class DependenceInfo { 273 public: DependenceInfo(Function * F,AliasAnalysis * AA,ScalarEvolution * SE,LoopInfo * LI)274 DependenceInfo(Function *F, AliasAnalysis *AA, ScalarEvolution *SE, 275 LoopInfo *LI) 276 : AA(AA), SE(SE), LI(LI), F(F) {} 277 278 /// depends - Tests for a dependence between the Src and Dst instructions. 279 /// Returns NULL if no dependence; otherwise, returns a Dependence (or a 280 /// FullDependence) with as much information as can be gleaned. 281 /// The flag PossiblyLoopIndependent should be set by the caller 282 /// if it appears that control flow can reach from Src to Dst 283 /// without traversing a loop back edge. 284 std::unique_ptr<Dependence> depends(Instruction *Src, 285 Instruction *Dst, 286 bool PossiblyLoopIndependent); 287 288 /// getSplitIteration - Give a dependence that's splittable at some 289 /// particular level, return the iteration that should be used to split 290 /// the loop. 291 /// 292 /// Generally, the dependence analyzer will be used to build 293 /// a dependence graph for a function (basically a map from instructions 294 /// to dependences). Looking for cycles in the graph shows us loops 295 /// that cannot be trivially vectorized/parallelized. 296 /// 297 /// We can try to improve the situation by examining all the dependences 298 /// that make up the cycle, looking for ones we can break. 299 /// Sometimes, peeling the first or last iteration of a loop will break 300 /// dependences, and there are flags for those possibilities. 301 /// Sometimes, splitting a loop at some other iteration will do the trick, 302 /// and we've got a flag for that case. Rather than waste the space to 303 /// record the exact iteration (since we rarely know), we provide 304 /// a method that calculates the iteration. It's a drag that it must work 305 /// from scratch, but wonderful in that it's possible. 306 /// 307 /// Here's an example: 308 /// 309 /// for (i = 0; i < 10; i++) 310 /// A[i] = ... 311 /// ... = A[11 - i] 312 /// 313 /// There's a loop-carried flow dependence from the store to the load, 314 /// found by the weak-crossing SIV test. The dependence will have a flag, 315 /// indicating that the dependence can be broken by splitting the loop. 316 /// Calling getSplitIteration will return 5. 317 /// Splitting the loop breaks the dependence, like so: 318 /// 319 /// for (i = 0; i <= 5; i++) 320 /// A[i] = ... 321 /// ... = A[11 - i] 322 /// for (i = 6; i < 10; i++) 323 /// A[i] = ... 324 /// ... = A[11 - i] 325 /// 326 /// breaks the dependence and allows us to vectorize/parallelize 327 /// both loops. 328 const SCEV *getSplitIteration(const Dependence &Dep, unsigned Level); 329 getFunction()330 Function *getFunction() const { return F; } 331 332 private: 333 AliasAnalysis *AA; 334 ScalarEvolution *SE; 335 LoopInfo *LI; 336 Function *F; 337 338 /// Subscript - This private struct represents a pair of subscripts from 339 /// a pair of potentially multi-dimensional array references. We use a 340 /// vector of them to guide subscript partitioning. 341 struct Subscript { 342 const SCEV *Src; 343 const SCEV *Dst; 344 enum ClassificationKind { ZIV, SIV, RDIV, MIV, NonLinear } Classification; 345 SmallBitVector Loops; 346 SmallBitVector GroupLoops; 347 SmallBitVector Group; 348 }; 349 350 struct CoefficientInfo { 351 const SCEV *Coeff; 352 const SCEV *PosPart; 353 const SCEV *NegPart; 354 const SCEV *Iterations; 355 }; 356 357 struct BoundInfo { 358 const SCEV *Iterations; 359 const SCEV *Upper[8]; 360 const SCEV *Lower[8]; 361 unsigned char Direction; 362 unsigned char DirSet; 363 }; 364 365 /// Constraint - This private class represents a constraint, as defined 366 /// in the paper 367 /// 368 /// Practical Dependence Testing 369 /// Goff, Kennedy, Tseng 370 /// PLDI 1991 371 /// 372 /// There are 5 kinds of constraint, in a hierarchy. 373 /// 1) Any - indicates no constraint, any dependence is possible. 374 /// 2) Line - A line ax + by = c, where a, b, and c are parameters, 375 /// representing the dependence equation. 376 /// 3) Distance - The value d of the dependence distance; 377 /// 4) Point - A point <x, y> representing the dependence from 378 /// iteration x to iteration y. 379 /// 5) Empty - No dependence is possible. 380 class Constraint { 381 private: 382 enum ConstraintKind { Empty, Point, Distance, Line, Any } Kind; 383 ScalarEvolution *SE; 384 const SCEV *A; 385 const SCEV *B; 386 const SCEV *C; 387 const Loop *AssociatedLoop; 388 389 public: 390 /// isEmpty - Return true if the constraint is of kind Empty. isEmpty()391 bool isEmpty() const { return Kind == Empty; } 392 393 /// isPoint - Return true if the constraint is of kind Point. isPoint()394 bool isPoint() const { return Kind == Point; } 395 396 /// isDistance - Return true if the constraint is of kind Distance. isDistance()397 bool isDistance() const { return Kind == Distance; } 398 399 /// isLine - Return true if the constraint is of kind Line. 400 /// Since Distance's can also be represented as Lines, we also return 401 /// true if the constraint is of kind Distance. isLine()402 bool isLine() const { return Kind == Line || Kind == Distance; } 403 404 /// isAny - Return true if the constraint is of kind Any; isAny()405 bool isAny() const { return Kind == Any; } 406 407 /// getX - If constraint is a point <X, Y>, returns X. 408 /// Otherwise assert. 409 const SCEV *getX() const; 410 411 /// getY - If constraint is a point <X, Y>, returns Y. 412 /// Otherwise assert. 413 const SCEV *getY() const; 414 415 /// getA - If constraint is a line AX + BY = C, returns A. 416 /// Otherwise assert. 417 const SCEV *getA() const; 418 419 /// getB - If constraint is a line AX + BY = C, returns B. 420 /// Otherwise assert. 421 const SCEV *getB() const; 422 423 /// getC - If constraint is a line AX + BY = C, returns C. 424 /// Otherwise assert. 425 const SCEV *getC() const; 426 427 /// getD - If constraint is a distance, returns D. 428 /// Otherwise assert. 429 const SCEV *getD() const; 430 431 /// getAssociatedLoop - Returns the loop associated with this constraint. 432 const Loop *getAssociatedLoop() const; 433 434 /// setPoint - Change a constraint to Point. 435 void setPoint(const SCEV *X, const SCEV *Y, const Loop *CurrentLoop); 436 437 /// setLine - Change a constraint to Line. 438 void setLine(const SCEV *A, const SCEV *B, 439 const SCEV *C, const Loop *CurrentLoop); 440 441 /// setDistance - Change a constraint to Distance. 442 void setDistance(const SCEV *D, const Loop *CurrentLoop); 443 444 /// setEmpty - Change a constraint to Empty. 445 void setEmpty(); 446 447 /// setAny - Change a constraint to Any. 448 void setAny(ScalarEvolution *SE); 449 450 /// dump - For debugging purposes. Dumps the constraint 451 /// out to OS. 452 void dump(raw_ostream &OS) const; 453 }; 454 455 /// establishNestingLevels - Examines the loop nesting of the Src and Dst 456 /// instructions and establishes their shared loops. Sets the variables 457 /// CommonLevels, SrcLevels, and MaxLevels. 458 /// The source and destination instructions needn't be contained in the same 459 /// loop. The routine establishNestingLevels finds the level of most deeply 460 /// nested loop that contains them both, CommonLevels. An instruction that's 461 /// not contained in a loop is at level = 0. MaxLevels is equal to the level 462 /// of the source plus the level of the destination, minus CommonLevels. 463 /// This lets us allocate vectors MaxLevels in length, with room for every 464 /// distinct loop referenced in both the source and destination subscripts. 465 /// The variable SrcLevels is the nesting depth of the source instruction. 466 /// It's used to help calculate distinct loops referenced by the destination. 467 /// Here's the map from loops to levels: 468 /// 0 - unused 469 /// 1 - outermost common loop 470 /// ... - other common loops 471 /// CommonLevels - innermost common loop 472 /// ... - loops containing Src but not Dst 473 /// SrcLevels - innermost loop containing Src but not Dst 474 /// ... - loops containing Dst but not Src 475 /// MaxLevels - innermost loop containing Dst but not Src 476 /// Consider the follow code fragment: 477 /// for (a = ...) { 478 /// for (b = ...) { 479 /// for (c = ...) { 480 /// for (d = ...) { 481 /// A[] = ...; 482 /// } 483 /// } 484 /// for (e = ...) { 485 /// for (f = ...) { 486 /// for (g = ...) { 487 /// ... = A[]; 488 /// } 489 /// } 490 /// } 491 /// } 492 /// } 493 /// If we're looking at the possibility of a dependence between the store 494 /// to A (the Src) and the load from A (the Dst), we'll note that they 495 /// have 2 loops in common, so CommonLevels will equal 2 and the direction 496 /// vector for Result will have 2 entries. SrcLevels = 4 and MaxLevels = 7. 497 /// A map from loop names to level indices would look like 498 /// a - 1 499 /// b - 2 = CommonLevels 500 /// c - 3 501 /// d - 4 = SrcLevels 502 /// e - 5 503 /// f - 6 504 /// g - 7 = MaxLevels 505 void establishNestingLevels(const Instruction *Src, 506 const Instruction *Dst); 507 508 unsigned CommonLevels, SrcLevels, MaxLevels; 509 510 /// mapSrcLoop - Given one of the loops containing the source, return 511 /// its level index in our numbering scheme. 512 unsigned mapSrcLoop(const Loop *SrcLoop) const; 513 514 /// mapDstLoop - Given one of the loops containing the destination, 515 /// return its level index in our numbering scheme. 516 unsigned mapDstLoop(const Loop *DstLoop) const; 517 518 /// isLoopInvariant - Returns true if Expression is loop invariant 519 /// in LoopNest. 520 bool isLoopInvariant(const SCEV *Expression, const Loop *LoopNest) const; 521 522 /// Makes sure all subscript pairs share the same integer type by 523 /// sign-extending as necessary. 524 /// Sign-extending a subscript is safe because getelementptr assumes the 525 /// array subscripts are signed. 526 void unifySubscriptType(ArrayRef<Subscript *> Pairs); 527 528 /// removeMatchingExtensions - Examines a subscript pair. 529 /// If the source and destination are identically sign (or zero) 530 /// extended, it strips off the extension in an effort to 531 /// simplify the actual analysis. 532 void removeMatchingExtensions(Subscript *Pair); 533 534 /// collectCommonLoops - Finds the set of loops from the LoopNest that 535 /// have a level <= CommonLevels and are referred to by the SCEV Expression. 536 void collectCommonLoops(const SCEV *Expression, 537 const Loop *LoopNest, 538 SmallBitVector &Loops) const; 539 540 /// checkSrcSubscript - Examines the SCEV Src, returning true iff it's 541 /// linear. Collect the set of loops mentioned by Src. 542 bool checkSrcSubscript(const SCEV *Src, 543 const Loop *LoopNest, 544 SmallBitVector &Loops); 545 546 /// checkDstSubscript - Examines the SCEV Dst, returning true iff it's 547 /// linear. Collect the set of loops mentioned by Dst. 548 bool checkDstSubscript(const SCEV *Dst, 549 const Loop *LoopNest, 550 SmallBitVector &Loops); 551 552 /// isKnownPredicate - Compare X and Y using the predicate Pred. 553 /// Basically a wrapper for SCEV::isKnownPredicate, 554 /// but tries harder, especially in the presence of sign and zero 555 /// extensions and symbolics. 556 bool isKnownPredicate(ICmpInst::Predicate Pred, 557 const SCEV *X, 558 const SCEV *Y) const; 559 560 /// isKnownLessThan - Compare to see if S is less than Size 561 /// Another wrapper for isKnownNegative(S - max(Size, 1)) with some extra 562 /// checking if S is an AddRec and we can prove lessthan using the loop 563 /// bounds. 564 bool isKnownLessThan(const SCEV *S, const SCEV *Size) const; 565 566 /// isKnownNonNegative - Compare to see if S is known not to be negative 567 /// Uses the fact that S comes from Ptr, which may be an inbound GEP, 568 /// Proving there is no wrapping going on. 569 bool isKnownNonNegative(const SCEV *S, const Value *Ptr) const; 570 571 /// collectUpperBound - All subscripts are the same type (on my machine, 572 /// an i64). The loop bound may be a smaller type. collectUpperBound 573 /// find the bound, if available, and zero extends it to the Type T. 574 /// (I zero extend since the bound should always be >= 0.) 575 /// If no upper bound is available, return NULL. 576 const SCEV *collectUpperBound(const Loop *l, Type *T) const; 577 578 /// collectConstantUpperBound - Calls collectUpperBound(), then 579 /// attempts to cast it to SCEVConstant. If the cast fails, 580 /// returns NULL. 581 const SCEVConstant *collectConstantUpperBound(const Loop *l, Type *T) const; 582 583 /// classifyPair - Examines the subscript pair (the Src and Dst SCEVs) 584 /// and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear. 585 /// Collects the associated loops in a set. 586 Subscript::ClassificationKind classifyPair(const SCEV *Src, 587 const Loop *SrcLoopNest, 588 const SCEV *Dst, 589 const Loop *DstLoopNest, 590 SmallBitVector &Loops); 591 592 /// testZIV - Tests the ZIV subscript pair (Src and Dst) for dependence. 593 /// Returns true if any possible dependence is disproved. 594 /// If there might be a dependence, returns false. 595 /// If the dependence isn't proven to exist, 596 /// marks the Result as inconsistent. 597 bool testZIV(const SCEV *Src, 598 const SCEV *Dst, 599 FullDependence &Result) const; 600 601 /// testSIV - Tests the SIV subscript pair (Src and Dst) for dependence. 602 /// Things of the form [c1 + a1*i] and [c2 + a2*j], where 603 /// i and j are induction variables, c1 and c2 are loop invariant, 604 /// and a1 and a2 are constant. 605 /// Returns true if any possible dependence is disproved. 606 /// If there might be a dependence, returns false. 607 /// Sets appropriate direction vector entry and, when possible, 608 /// the distance vector entry. 609 /// If the dependence isn't proven to exist, 610 /// marks the Result as inconsistent. 611 bool testSIV(const SCEV *Src, 612 const SCEV *Dst, 613 unsigned &Level, 614 FullDependence &Result, 615 Constraint &NewConstraint, 616 const SCEV *&SplitIter) const; 617 618 /// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence. 619 /// Things of the form [c1 + a1*i] and [c2 + a2*j] 620 /// where i and j are induction variables, c1 and c2 are loop invariant, 621 /// and a1 and a2 are constant. 622 /// With minor algebra, this test can also be used for things like 623 /// [c1 + a1*i + a2*j][c2]. 624 /// Returns true if any possible dependence is disproved. 625 /// If there might be a dependence, returns false. 626 /// Marks the Result as inconsistent. 627 bool testRDIV(const SCEV *Src, 628 const SCEV *Dst, 629 FullDependence &Result) const; 630 631 /// testMIV - Tests the MIV subscript pair (Src and Dst) for dependence. 632 /// Returns true if dependence disproved. 633 /// Can sometimes refine direction vectors. 634 bool testMIV(const SCEV *Src, 635 const SCEV *Dst, 636 const SmallBitVector &Loops, 637 FullDependence &Result) const; 638 639 /// strongSIVtest - Tests the strong SIV subscript pair (Src and Dst) 640 /// for dependence. 641 /// Things of the form [c1 + a*i] and [c2 + a*i], 642 /// where i is an induction variable, c1 and c2 are loop invariant, 643 /// and a is a constant 644 /// Returns true if any possible dependence is disproved. 645 /// If there might be a dependence, returns false. 646 /// Sets appropriate direction and distance. 647 bool strongSIVtest(const SCEV *Coeff, 648 const SCEV *SrcConst, 649 const SCEV *DstConst, 650 const Loop *CurrentLoop, 651 unsigned Level, 652 FullDependence &Result, 653 Constraint &NewConstraint) const; 654 655 /// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair 656 /// (Src and Dst) for dependence. 657 /// Things of the form [c1 + a*i] and [c2 - a*i], 658 /// where i is an induction variable, c1 and c2 are loop invariant, 659 /// and a is a constant. 660 /// Returns true if any possible dependence is disproved. 661 /// If there might be a dependence, returns false. 662 /// Sets appropriate direction entry. 663 /// Set consistent to false. 664 /// Marks the dependence as splitable. 665 bool weakCrossingSIVtest(const SCEV *SrcCoeff, 666 const SCEV *SrcConst, 667 const SCEV *DstConst, 668 const Loop *CurrentLoop, 669 unsigned Level, 670 FullDependence &Result, 671 Constraint &NewConstraint, 672 const SCEV *&SplitIter) const; 673 674 /// ExactSIVtest - Tests the SIV subscript pair 675 /// (Src and Dst) for dependence. 676 /// Things of the form [c1 + a1*i] and [c2 + a2*i], 677 /// where i is an induction variable, c1 and c2 are loop invariant, 678 /// and a1 and a2 are constant. 679 /// Returns true if any possible dependence is disproved. 680 /// If there might be a dependence, returns false. 681 /// Sets appropriate direction entry. 682 /// Set consistent to false. 683 bool exactSIVtest(const SCEV *SrcCoeff, 684 const SCEV *DstCoeff, 685 const SCEV *SrcConst, 686 const SCEV *DstConst, 687 const Loop *CurrentLoop, 688 unsigned Level, 689 FullDependence &Result, 690 Constraint &NewConstraint) const; 691 692 /// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair 693 /// (Src and Dst) for dependence. 694 /// Things of the form [c1] and [c2 + a*i], 695 /// where i is an induction variable, c1 and c2 are loop invariant, 696 /// and a is a constant. See also weakZeroDstSIVtest. 697 /// Returns true if any possible dependence is disproved. 698 /// If there might be a dependence, returns false. 699 /// Sets appropriate direction entry. 700 /// Set consistent to false. 701 /// If loop peeling will break the dependence, mark appropriately. 702 bool weakZeroSrcSIVtest(const SCEV *DstCoeff, 703 const SCEV *SrcConst, 704 const SCEV *DstConst, 705 const Loop *CurrentLoop, 706 unsigned Level, 707 FullDependence &Result, 708 Constraint &NewConstraint) const; 709 710 /// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair 711 /// (Src and Dst) for dependence. 712 /// Things of the form [c1 + a*i] and [c2], 713 /// where i is an induction variable, c1 and c2 are loop invariant, 714 /// and a is a constant. See also weakZeroSrcSIVtest. 715 /// Returns true if any possible dependence is disproved. 716 /// If there might be a dependence, returns false. 717 /// Sets appropriate direction entry. 718 /// Set consistent to false. 719 /// If loop peeling will break the dependence, mark appropriately. 720 bool weakZeroDstSIVtest(const SCEV *SrcCoeff, 721 const SCEV *SrcConst, 722 const SCEV *DstConst, 723 const Loop *CurrentLoop, 724 unsigned Level, 725 FullDependence &Result, 726 Constraint &NewConstraint) const; 727 728 /// exactRDIVtest - Tests the RDIV subscript pair for dependence. 729 /// Things of the form [c1 + a*i] and [c2 + b*j], 730 /// where i and j are induction variable, c1 and c2 are loop invariant, 731 /// and a and b are constants. 732 /// Returns true if any possible dependence is disproved. 733 /// Marks the result as inconsistent. 734 /// Works in some cases that symbolicRDIVtest doesn't, 735 /// and vice versa. 736 bool exactRDIVtest(const SCEV *SrcCoeff, 737 const SCEV *DstCoeff, 738 const SCEV *SrcConst, 739 const SCEV *DstConst, 740 const Loop *SrcLoop, 741 const Loop *DstLoop, 742 FullDependence &Result) const; 743 744 /// symbolicRDIVtest - Tests the RDIV subscript pair for dependence. 745 /// Things of the form [c1 + a*i] and [c2 + b*j], 746 /// where i and j are induction variable, c1 and c2 are loop invariant, 747 /// and a and b are constants. 748 /// Returns true if any possible dependence is disproved. 749 /// Marks the result as inconsistent. 750 /// Works in some cases that exactRDIVtest doesn't, 751 /// and vice versa. Can also be used as a backup for 752 /// ordinary SIV tests. 753 bool symbolicRDIVtest(const SCEV *SrcCoeff, 754 const SCEV *DstCoeff, 755 const SCEV *SrcConst, 756 const SCEV *DstConst, 757 const Loop *SrcLoop, 758 const Loop *DstLoop) const; 759 760 /// gcdMIVtest - Tests an MIV subscript pair for dependence. 761 /// Returns true if any possible dependence is disproved. 762 /// Marks the result as inconsistent. 763 /// Can sometimes disprove the equal direction for 1 or more loops. 764 // Can handle some symbolics that even the SIV tests don't get, 765 /// so we use it as a backup for everything. 766 bool gcdMIVtest(const SCEV *Src, 767 const SCEV *Dst, 768 FullDependence &Result) const; 769 770 /// banerjeeMIVtest - Tests an MIV subscript pair for dependence. 771 /// Returns true if any possible dependence is disproved. 772 /// Marks the result as inconsistent. 773 /// Computes directions. 774 bool banerjeeMIVtest(const SCEV *Src, 775 const SCEV *Dst, 776 const SmallBitVector &Loops, 777 FullDependence &Result) const; 778 779 /// collectCoefficientInfo - Walks through the subscript, 780 /// collecting each coefficient, the associated loop bounds, 781 /// and recording its positive and negative parts for later use. 782 CoefficientInfo *collectCoeffInfo(const SCEV *Subscript, 783 bool SrcFlag, 784 const SCEV *&Constant) const; 785 786 /// getPositivePart - X^+ = max(X, 0). 787 /// 788 const SCEV *getPositivePart(const SCEV *X) const; 789 790 /// getNegativePart - X^- = min(X, 0). 791 /// 792 const SCEV *getNegativePart(const SCEV *X) const; 793 794 /// getLowerBound - Looks through all the bounds info and 795 /// computes the lower bound given the current direction settings 796 /// at each level. 797 const SCEV *getLowerBound(BoundInfo *Bound) const; 798 799 /// getUpperBound - Looks through all the bounds info and 800 /// computes the upper bound given the current direction settings 801 /// at each level. 802 const SCEV *getUpperBound(BoundInfo *Bound) const; 803 804 /// exploreDirections - Hierarchically expands the direction vector 805 /// search space, combining the directions of discovered dependences 806 /// in the DirSet field of Bound. Returns the number of distinct 807 /// dependences discovered. If the dependence is disproved, 808 /// it will return 0. 809 unsigned exploreDirections(unsigned Level, 810 CoefficientInfo *A, 811 CoefficientInfo *B, 812 BoundInfo *Bound, 813 const SmallBitVector &Loops, 814 unsigned &DepthExpanded, 815 const SCEV *Delta) const; 816 817 /// testBounds - Returns true iff the current bounds are plausible. 818 bool testBounds(unsigned char DirKind, 819 unsigned Level, 820 BoundInfo *Bound, 821 const SCEV *Delta) const; 822 823 /// findBoundsALL - Computes the upper and lower bounds for level K 824 /// using the * direction. Records them in Bound. 825 void findBoundsALL(CoefficientInfo *A, 826 CoefficientInfo *B, 827 BoundInfo *Bound, 828 unsigned K) const; 829 830 /// findBoundsLT - Computes the upper and lower bounds for level K 831 /// using the < direction. Records them in Bound. 832 void findBoundsLT(CoefficientInfo *A, 833 CoefficientInfo *B, 834 BoundInfo *Bound, 835 unsigned K) const; 836 837 /// findBoundsGT - Computes the upper and lower bounds for level K 838 /// using the > direction. Records them in Bound. 839 void findBoundsGT(CoefficientInfo *A, 840 CoefficientInfo *B, 841 BoundInfo *Bound, 842 unsigned K) const; 843 844 /// findBoundsEQ - Computes the upper and lower bounds for level K 845 /// using the = direction. Records them in Bound. 846 void findBoundsEQ(CoefficientInfo *A, 847 CoefficientInfo *B, 848 BoundInfo *Bound, 849 unsigned K) const; 850 851 /// intersectConstraints - Updates X with the intersection 852 /// of the Constraints X and Y. Returns true if X has changed. 853 bool intersectConstraints(Constraint *X, 854 const Constraint *Y); 855 856 /// propagate - Review the constraints, looking for opportunities 857 /// to simplify a subscript pair (Src and Dst). 858 /// Return true if some simplification occurs. 859 /// If the simplification isn't exact (that is, if it is conservative 860 /// in terms of dependence), set consistent to false. 861 bool propagate(const SCEV *&Src, 862 const SCEV *&Dst, 863 SmallBitVector &Loops, 864 SmallVectorImpl<Constraint> &Constraints, 865 bool &Consistent); 866 867 /// propagateDistance - Attempt to propagate a distance 868 /// constraint into a subscript pair (Src and Dst). 869 /// Return true if some simplification occurs. 870 /// If the simplification isn't exact (that is, if it is conservative 871 /// in terms of dependence), set consistent to false. 872 bool propagateDistance(const SCEV *&Src, 873 const SCEV *&Dst, 874 Constraint &CurConstraint, 875 bool &Consistent); 876 877 /// propagatePoint - Attempt to propagate a point 878 /// constraint into a subscript pair (Src and Dst). 879 /// Return true if some simplification occurs. 880 bool propagatePoint(const SCEV *&Src, 881 const SCEV *&Dst, 882 Constraint &CurConstraint); 883 884 /// propagateLine - Attempt to propagate a line 885 /// constraint into a subscript pair (Src and Dst). 886 /// Return true if some simplification occurs. 887 /// If the simplification isn't exact (that is, if it is conservative 888 /// in terms of dependence), set consistent to false. 889 bool propagateLine(const SCEV *&Src, 890 const SCEV *&Dst, 891 Constraint &CurConstraint, 892 bool &Consistent); 893 894 /// findCoefficient - Given a linear SCEV, 895 /// return the coefficient corresponding to specified loop. 896 /// If there isn't one, return the SCEV constant 0. 897 /// For example, given a*i + b*j + c*k, returning the coefficient 898 /// corresponding to the j loop would yield b. 899 const SCEV *findCoefficient(const SCEV *Expr, 900 const Loop *TargetLoop) const; 901 902 /// zeroCoefficient - Given a linear SCEV, 903 /// return the SCEV given by zeroing out the coefficient 904 /// corresponding to the specified loop. 905 /// For example, given a*i + b*j + c*k, zeroing the coefficient 906 /// corresponding to the j loop would yield a*i + c*k. 907 const SCEV *zeroCoefficient(const SCEV *Expr, 908 const Loop *TargetLoop) const; 909 910 /// addToCoefficient - Given a linear SCEV Expr, 911 /// return the SCEV given by adding some Value to the 912 /// coefficient corresponding to the specified TargetLoop. 913 /// For example, given a*i + b*j + c*k, adding 1 to the coefficient 914 /// corresponding to the j loop would yield a*i + (b+1)*j + c*k. 915 const SCEV *addToCoefficient(const SCEV *Expr, 916 const Loop *TargetLoop, 917 const SCEV *Value) const; 918 919 /// updateDirection - Update direction vector entry 920 /// based on the current constraint. 921 void updateDirection(Dependence::DVEntry &Level, 922 const Constraint &CurConstraint) const; 923 924 bool tryDelinearize(Instruction *Src, Instruction *Dst, 925 SmallVectorImpl<Subscript> &Pair); 926 }; // class DependenceInfo 927 928 /// AnalysisPass to compute dependence information in a function 929 class DependenceAnalysis : public AnalysisInfoMixin<DependenceAnalysis> { 930 public: 931 typedef DependenceInfo Result; 932 Result run(Function &F, FunctionAnalysisManager &FAM); 933 934 private: 935 static AnalysisKey Key; 936 friend struct AnalysisInfoMixin<DependenceAnalysis>; 937 }; // class DependenceAnalysis 938 939 /// Printer pass to dump DA results. 940 struct DependenceAnalysisPrinterPass 941 : public PassInfoMixin<DependenceAnalysisPrinterPass> { 942 DependenceAnalysisPrinterPass(raw_ostream &OS) : OS(OS) {} 943 944 PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM); 945 946 private: 947 raw_ostream &OS; 948 }; // class DependenceAnalysisPrinterPass 949 950 /// Legacy pass manager pass to access dependence information 951 class DependenceAnalysisWrapperPass : public FunctionPass { 952 public: 953 static char ID; // Class identification, replacement for typeinfo 954 DependenceAnalysisWrapperPass() : FunctionPass(ID) { 955 initializeDependenceAnalysisWrapperPassPass( 956 *PassRegistry::getPassRegistry()); 957 } 958 959 bool runOnFunction(Function &F) override; 960 void releaseMemory() override; 961 void getAnalysisUsage(AnalysisUsage &) const override; 962 void print(raw_ostream &, const Module * = nullptr) const override; 963 DependenceInfo &getDI() const; 964 965 private: 966 std::unique_ptr<DependenceInfo> info; 967 }; // class DependenceAnalysisWrapperPass 968 969 /// createDependenceAnalysisPass - This creates an instance of the 970 /// DependenceAnalysis wrapper pass. 971 FunctionPass *createDependenceAnalysisWrapperPass(); 972 973 } // namespace llvm 974 975 #endif 976