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/ADT/ArrayRef.h" 45 #include "llvm/Analysis/AliasAnalysis.h" 46 #include "llvm/IR/Instructions.h" 47 #include "llvm/Pass.h" 48 49 namespace llvm { 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(const Dependence &) = default; 74 75 // FIXME: When we move to MSVC 2015 as the base compiler for Visual Studio 76 // support, uncomment this line to allow a defaulted move constructor for 77 // Dependence. Currently, FullDependence relies on the copy constructor, but 78 // that is acceptable given the triviality of the class. 79 // Dependence(Dependence &&) = default; 80 81 public: 82 Dependence(Instruction *Source, 83 Instruction *Destination) : 84 Src(Source), 85 Dst(Destination), 86 NextPredecessor(nullptr), 87 NextSuccessor(nullptr) {} 88 virtual ~Dependence() {} 89 90 /// Dependence::DVEntry - Each level in the distance/direction vector 91 /// has a direction (or perhaps a union of several directions), and 92 /// perhaps a distance. 93 struct DVEntry { 94 enum { NONE = 0, 95 LT = 1, 96 EQ = 2, 97 LE = 3, 98 GT = 4, 99 NE = 5, 100 GE = 6, 101 ALL = 7 }; 102 unsigned char Direction : 3; // Init to ALL, then refine. 103 bool Scalar : 1; // Init to true. 104 bool PeelFirst : 1; // Peeling the first iteration will break dependence. 105 bool PeelLast : 1; // Peeling the last iteration will break the dependence. 106 bool Splitable : 1; // Splitting the loop will break dependence. 107 const SCEV *Distance; // NULL implies no distance available. 108 DVEntry() : Direction(ALL), Scalar(true), PeelFirst(false), 109 PeelLast(false), Splitable(false), Distance(nullptr) { } 110 }; 111 112 /// getSrc - Returns the source instruction for this dependence. 113 /// 114 Instruction *getSrc() const { return Src; } 115 116 /// getDst - Returns the destination instruction for this dependence. 117 /// 118 Instruction *getDst() const { return Dst; } 119 120 /// isInput - Returns true if this is an input dependence. 121 /// 122 bool isInput() const; 123 124 /// isOutput - Returns true if this is an output dependence. 125 /// 126 bool isOutput() const; 127 128 /// isFlow - Returns true if this is a flow (aka true) dependence. 129 /// 130 bool isFlow() const; 131 132 /// isAnti - Returns true if this is an anti dependence. 133 /// 134 bool isAnti() const; 135 136 /// isOrdered - Returns true if dependence is Output, Flow, or Anti 137 /// 138 bool isOrdered() const { return isOutput() || isFlow() || isAnti(); } 139 140 /// isUnordered - Returns true if dependence is Input 141 /// 142 bool isUnordered() const { return isInput(); } 143 144 /// isLoopIndependent - Returns true if this is a loop-independent 145 /// dependence. 146 virtual bool isLoopIndependent() const { return true; } 147 148 /// isConfused - Returns true if this dependence is confused 149 /// (the compiler understands nothing and makes worst-case 150 /// assumptions). 151 virtual bool isConfused() const { return true; } 152 153 /// isConsistent - Returns true if this dependence is consistent 154 /// (occurs every time the source and destination are executed). 155 virtual bool isConsistent() const { return false; } 156 157 /// getLevels - Returns the number of common loops surrounding the 158 /// source and destination of the dependence. 159 virtual unsigned getLevels() const { return 0; } 160 161 /// getDirection - Returns the direction associated with a particular 162 /// level. 163 virtual unsigned getDirection(unsigned Level) const { return DVEntry::ALL; } 164 165 /// getDistance - Returns the distance (or NULL) associated with a 166 /// particular level. 167 virtual const SCEV *getDistance(unsigned Level) const { return nullptr; } 168 169 /// isPeelFirst - Returns true if peeling the first iteration from 170 /// this loop will break this dependence. 171 virtual bool isPeelFirst(unsigned Level) const { return false; } 172 173 /// isPeelLast - Returns true if peeling the last iteration from 174 /// this loop will break this dependence. 175 virtual bool isPeelLast(unsigned Level) const { return false; } 176 177 /// isSplitable - Returns true if splitting this loop will break 178 /// the dependence. 179 virtual bool isSplitable(unsigned Level) const { return false; } 180 181 /// isScalar - Returns true if a particular level is scalar; that is, 182 /// if no subscript in the source or destination mention the induction 183 /// variable associated with the loop at this level. 184 virtual bool isScalar(unsigned Level) const; 185 186 /// getNextPredecessor - Returns the value of the NextPredecessor 187 /// field. 188 const Dependence *getNextPredecessor() const { return NextPredecessor; } 189 190 /// getNextSuccessor - Returns the value of the NextSuccessor 191 /// field. 192 const Dependence *getNextSuccessor() const { return NextSuccessor; } 193 194 /// setNextPredecessor - Sets the value of the NextPredecessor 195 /// field. 196 void setNextPredecessor(const Dependence *pred) { NextPredecessor = pred; } 197 198 /// setNextSuccessor - Sets the value of the NextSuccessor 199 /// field. 200 void setNextSuccessor(const Dependence *succ) { NextSuccessor = succ; } 201 202 /// dump - For debugging purposes, dumps a dependence to OS. 203 /// 204 void dump(raw_ostream &OS) const; 205 206 private: 207 Instruction *Src, *Dst; 208 const Dependence *NextPredecessor, *NextSuccessor; 209 friend class DependenceAnalysis; 210 }; 211 212 /// FullDependence - This class represents a dependence between two memory 213 /// references in a function. It contains detailed information about the 214 /// dependence (direction vectors, etc.) and is used when the compiler is 215 /// able to accurately analyze the interaction of the references; that is, 216 /// it is not a confused dependence (see Dependence). In most cases 217 /// (for output, flow, and anti dependences), the dependence implies an 218 /// ordering, where the source must precede the destination; in contrast, 219 /// input dependences are unordered. 220 class FullDependence final : public Dependence { 221 public: 222 FullDependence(Instruction *Src, Instruction *Dst, bool LoopIndependent, 223 unsigned Levels); 224 225 FullDependence(FullDependence &&RHS) 226 : Dependence(std::move(RHS)), Levels(RHS.Levels), 227 LoopIndependent(RHS.LoopIndependent), Consistent(RHS.Consistent), 228 DV(std::move(RHS.DV)) {} 229 230 /// isLoopIndependent - Returns true if this is a loop-independent 231 /// dependence. 232 bool isLoopIndependent() const override { return LoopIndependent; } 233 234 /// isConfused - Returns true if this dependence is confused 235 /// (the compiler understands nothing and makes worst-case 236 /// assumptions). 237 bool isConfused() const override { return false; } 238 239 /// isConsistent - Returns true if this dependence is consistent 240 /// (occurs every time the source and destination are executed). 241 bool isConsistent() const override { return Consistent; } 242 243 /// getLevels - Returns the number of common loops surrounding the 244 /// source and destination of the dependence. 245 unsigned getLevels() const override { return Levels; } 246 247 /// getDirection - Returns the direction associated with a particular 248 /// level. 249 unsigned getDirection(unsigned Level) const override; 250 251 /// getDistance - Returns the distance (or NULL) associated with a 252 /// particular level. 253 const SCEV *getDistance(unsigned Level) const override; 254 255 /// isPeelFirst - Returns true if peeling the first iteration from 256 /// this loop will break this dependence. 257 bool isPeelFirst(unsigned Level) const override; 258 259 /// isPeelLast - Returns true if peeling the last iteration from 260 /// this loop will break this dependence. 261 bool isPeelLast(unsigned Level) const override; 262 263 /// isSplitable - Returns true if splitting the loop will break 264 /// the dependence. 265 bool isSplitable(unsigned Level) const override; 266 267 /// isScalar - Returns true if a particular level is scalar; that is, 268 /// if no subscript in the source or destination mention the induction 269 /// variable associated with the loop at this level. 270 bool isScalar(unsigned Level) const override; 271 272 private: 273 unsigned short Levels; 274 bool LoopIndependent; 275 bool Consistent; // Init to true, then refine. 276 std::unique_ptr<DVEntry[]> DV; 277 friend class DependenceAnalysis; 278 }; 279 280 /// DependenceAnalysis - This class is the main dependence-analysis driver. 281 /// 282 class DependenceAnalysis : public FunctionPass { 283 void operator=(const DependenceAnalysis &) = delete; 284 DependenceAnalysis(const DependenceAnalysis &) = delete; 285 286 public: 287 /// depends - Tests for a dependence between the Src and Dst instructions. 288 /// Returns NULL if no dependence; otherwise, returns a Dependence (or a 289 /// FullDependence) with as much information as can be gleaned. 290 /// The flag PossiblyLoopIndependent should be set by the caller 291 /// if it appears that control flow can reach from Src to Dst 292 /// without traversing a loop back edge. 293 std::unique_ptr<Dependence> depends(Instruction *Src, 294 Instruction *Dst, 295 bool PossiblyLoopIndependent); 296 297 /// getSplitIteration - Give a dependence that's splittable at some 298 /// particular level, return the iteration that should be used to split 299 /// the loop. 300 /// 301 /// Generally, the dependence analyzer will be used to build 302 /// a dependence graph for a function (basically a map from instructions 303 /// to dependences). Looking for cycles in the graph shows us loops 304 /// that cannot be trivially vectorized/parallelized. 305 /// 306 /// We can try to improve the situation by examining all the dependences 307 /// that make up the cycle, looking for ones we can break. 308 /// Sometimes, peeling the first or last iteration of a loop will break 309 /// dependences, and there are flags for those possibilities. 310 /// Sometimes, splitting a loop at some other iteration will do the trick, 311 /// and we've got a flag for that case. Rather than waste the space to 312 /// record the exact iteration (since we rarely know), we provide 313 /// a method that calculates the iteration. It's a drag that it must work 314 /// from scratch, but wonderful in that it's possible. 315 /// 316 /// Here's an example: 317 /// 318 /// for (i = 0; i < 10; i++) 319 /// A[i] = ... 320 /// ... = A[11 - i] 321 /// 322 /// There's a loop-carried flow dependence from the store to the load, 323 /// found by the weak-crossing SIV test. The dependence will have a flag, 324 /// indicating that the dependence can be broken by splitting the loop. 325 /// Calling getSplitIteration will return 5. 326 /// Splitting the loop breaks the dependence, like so: 327 /// 328 /// for (i = 0; i <= 5; i++) 329 /// A[i] = ... 330 /// ... = A[11 - i] 331 /// for (i = 6; i < 10; i++) 332 /// A[i] = ... 333 /// ... = A[11 - i] 334 /// 335 /// breaks the dependence and allows us to vectorize/parallelize 336 /// both loops. 337 const SCEV *getSplitIteration(const Dependence &Dep, unsigned Level); 338 339 private: 340 AliasAnalysis *AA; 341 ScalarEvolution *SE; 342 LoopInfo *LI; 343 Function *F; 344 345 /// Subscript - This private struct represents a pair of subscripts from 346 /// a pair of potentially multi-dimensional array references. We use a 347 /// vector of them to guide subscript partitioning. 348 struct Subscript { 349 const SCEV *Src; 350 const SCEV *Dst; 351 enum ClassificationKind { ZIV, SIV, RDIV, MIV, NonLinear } Classification; 352 SmallBitVector Loops; 353 SmallBitVector GroupLoops; 354 SmallBitVector Group; 355 }; 356 357 struct CoefficientInfo { 358 const SCEV *Coeff; 359 const SCEV *PosPart; 360 const SCEV *NegPart; 361 const SCEV *Iterations; 362 }; 363 364 struct BoundInfo { 365 const SCEV *Iterations; 366 const SCEV *Upper[8]; 367 const SCEV *Lower[8]; 368 unsigned char Direction; 369 unsigned char DirSet; 370 }; 371 372 /// Constraint - This private class represents a constraint, as defined 373 /// in the paper 374 /// 375 /// Practical Dependence Testing 376 /// Goff, Kennedy, Tseng 377 /// PLDI 1991 378 /// 379 /// There are 5 kinds of constraint, in a hierarchy. 380 /// 1) Any - indicates no constraint, any dependence is possible. 381 /// 2) Line - A line ax + by = c, where a, b, and c are parameters, 382 /// representing the dependence equation. 383 /// 3) Distance - The value d of the dependence distance; 384 /// 4) Point - A point <x, y> representing the dependence from 385 /// iteration x to iteration y. 386 /// 5) Empty - No dependence is possible. 387 class Constraint { 388 private: 389 enum ConstraintKind { Empty, Point, Distance, Line, Any } Kind; 390 ScalarEvolution *SE; 391 const SCEV *A; 392 const SCEV *B; 393 const SCEV *C; 394 const Loop *AssociatedLoop; 395 396 public: 397 /// isEmpty - Return true if the constraint is of kind Empty. 398 bool isEmpty() const { return Kind == Empty; } 399 400 /// isPoint - Return true if the constraint is of kind Point. 401 bool isPoint() const { return Kind == Point; } 402 403 /// isDistance - Return true if the constraint is of kind Distance. 404 bool isDistance() const { return Kind == Distance; } 405 406 /// isLine - Return true if the constraint is of kind Line. 407 /// Since Distance's can also be represented as Lines, we also return 408 /// true if the constraint is of kind Distance. 409 bool isLine() const { return Kind == Line || Kind == Distance; } 410 411 /// isAny - Return true if the constraint is of kind Any; 412 bool isAny() const { return Kind == Any; } 413 414 /// getX - If constraint is a point <X, Y>, returns X. 415 /// Otherwise assert. 416 const SCEV *getX() const; 417 418 /// getY - If constraint is a point <X, Y>, returns Y. 419 /// Otherwise assert. 420 const SCEV *getY() const; 421 422 /// getA - If constraint is a line AX + BY = C, returns A. 423 /// Otherwise assert. 424 const SCEV *getA() const; 425 426 /// getB - If constraint is a line AX + BY = C, returns B. 427 /// Otherwise assert. 428 const SCEV *getB() const; 429 430 /// getC - If constraint is a line AX + BY = C, returns C. 431 /// Otherwise assert. 432 const SCEV *getC() const; 433 434 /// getD - If constraint is a distance, returns D. 435 /// Otherwise assert. 436 const SCEV *getD() const; 437 438 /// getAssociatedLoop - Returns the loop associated with this constraint. 439 const Loop *getAssociatedLoop() const; 440 441 /// setPoint - Change a constraint to Point. 442 void setPoint(const SCEV *X, const SCEV *Y, const Loop *CurrentLoop); 443 444 /// setLine - Change a constraint to Line. 445 void setLine(const SCEV *A, const SCEV *B, 446 const SCEV *C, const Loop *CurrentLoop); 447 448 /// setDistance - Change a constraint to Distance. 449 void setDistance(const SCEV *D, const Loop *CurrentLoop); 450 451 /// setEmpty - Change a constraint to Empty. 452 void setEmpty(); 453 454 /// setAny - Change a constraint to Any. 455 void setAny(ScalarEvolution *SE); 456 457 /// dump - For debugging purposes. Dumps the constraint 458 /// out to OS. 459 void dump(raw_ostream &OS) const; 460 }; 461 462 /// establishNestingLevels - Examines the loop nesting of the Src and Dst 463 /// instructions and establishes their shared loops. Sets the variables 464 /// CommonLevels, SrcLevels, and MaxLevels. 465 /// The source and destination instructions needn't be contained in the same 466 /// loop. The routine establishNestingLevels finds the level of most deeply 467 /// nested loop that contains them both, CommonLevels. An instruction that's 468 /// not contained in a loop is at level = 0. MaxLevels is equal to the level 469 /// of the source plus the level of the destination, minus CommonLevels. 470 /// This lets us allocate vectors MaxLevels in length, with room for every 471 /// distinct loop referenced in both the source and destination subscripts. 472 /// The variable SrcLevels is the nesting depth of the source instruction. 473 /// It's used to help calculate distinct loops referenced by the destination. 474 /// Here's the map from loops to levels: 475 /// 0 - unused 476 /// 1 - outermost common loop 477 /// ... - other common loops 478 /// CommonLevels - innermost common loop 479 /// ... - loops containing Src but not Dst 480 /// SrcLevels - innermost loop containing Src but not Dst 481 /// ... - loops containing Dst but not Src 482 /// MaxLevels - innermost loop containing Dst but not Src 483 /// Consider the follow code fragment: 484 /// for (a = ...) { 485 /// for (b = ...) { 486 /// for (c = ...) { 487 /// for (d = ...) { 488 /// A[] = ...; 489 /// } 490 /// } 491 /// for (e = ...) { 492 /// for (f = ...) { 493 /// for (g = ...) { 494 /// ... = A[]; 495 /// } 496 /// } 497 /// } 498 /// } 499 /// } 500 /// If we're looking at the possibility of a dependence between the store 501 /// to A (the Src) and the load from A (the Dst), we'll note that they 502 /// have 2 loops in common, so CommonLevels will equal 2 and the direction 503 /// vector for Result will have 2 entries. SrcLevels = 4 and MaxLevels = 7. 504 /// A map from loop names to level indices would look like 505 /// a - 1 506 /// b - 2 = CommonLevels 507 /// c - 3 508 /// d - 4 = SrcLevels 509 /// e - 5 510 /// f - 6 511 /// g - 7 = MaxLevels 512 void establishNestingLevels(const Instruction *Src, 513 const Instruction *Dst); 514 515 unsigned CommonLevels, SrcLevels, MaxLevels; 516 517 /// mapSrcLoop - Given one of the loops containing the source, return 518 /// its level index in our numbering scheme. 519 unsigned mapSrcLoop(const Loop *SrcLoop) const; 520 521 /// mapDstLoop - Given one of the loops containing the destination, 522 /// return its level index in our numbering scheme. 523 unsigned mapDstLoop(const Loop *DstLoop) const; 524 525 /// isLoopInvariant - Returns true if Expression is loop invariant 526 /// in LoopNest. 527 bool isLoopInvariant(const SCEV *Expression, const Loop *LoopNest) const; 528 529 /// Makes sure all subscript pairs share the same integer type by 530 /// sign-extending as necessary. 531 /// Sign-extending a subscript is safe because getelementptr assumes the 532 /// array subscripts are signed. 533 void unifySubscriptType(ArrayRef<Subscript *> Pairs); 534 535 /// removeMatchingExtensions - Examines a subscript pair. 536 /// If the source and destination are identically sign (or zero) 537 /// extended, it strips off the extension in an effort to 538 /// simplify the actual analysis. 539 void removeMatchingExtensions(Subscript *Pair); 540 541 /// collectCommonLoops - Finds the set of loops from the LoopNest that 542 /// have a level <= CommonLevels and are referred to by the SCEV Expression. 543 void collectCommonLoops(const SCEV *Expression, 544 const Loop *LoopNest, 545 SmallBitVector &Loops) const; 546 547 /// checkSrcSubscript - Examines the SCEV Src, returning true iff it's 548 /// linear. Collect the set of loops mentioned by Src. 549 bool checkSrcSubscript(const SCEV *Src, 550 const Loop *LoopNest, 551 SmallBitVector &Loops); 552 553 /// checkDstSubscript - Examines the SCEV Dst, returning true iff it's 554 /// linear. Collect the set of loops mentioned by Dst. 555 bool checkDstSubscript(const SCEV *Dst, 556 const Loop *LoopNest, 557 SmallBitVector &Loops); 558 559 /// isKnownPredicate - Compare X and Y using the predicate Pred. 560 /// Basically a wrapper for SCEV::isKnownPredicate, 561 /// but tries harder, especially in the presence of sign and zero 562 /// extensions and symbolics. 563 bool isKnownPredicate(ICmpInst::Predicate Pred, 564 const SCEV *X, 565 const SCEV *Y) const; 566 567 /// collectUpperBound - All subscripts are the same type (on my machine, 568 /// an i64). The loop bound may be a smaller type. collectUpperBound 569 /// find the bound, if available, and zero extends it to the Type T. 570 /// (I zero extend since the bound should always be >= 0.) 571 /// If no upper bound is available, return NULL. 572 const SCEV *collectUpperBound(const Loop *l, Type *T) const; 573 574 /// collectConstantUpperBound - Calls collectUpperBound(), then 575 /// attempts to cast it to SCEVConstant. If the cast fails, 576 /// returns NULL. 577 const SCEVConstant *collectConstantUpperBound(const Loop *l, Type *T) const; 578 579 /// classifyPair - Examines the subscript pair (the Src and Dst SCEVs) 580 /// and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear. 581 /// Collects the associated loops in a set. 582 Subscript::ClassificationKind classifyPair(const SCEV *Src, 583 const Loop *SrcLoopNest, 584 const SCEV *Dst, 585 const Loop *DstLoopNest, 586 SmallBitVector &Loops); 587 588 /// testZIV - Tests the ZIV subscript pair (Src and Dst) for dependence. 589 /// Returns true if any possible dependence is disproved. 590 /// If there might be a dependence, returns false. 591 /// If the dependence isn't proven to exist, 592 /// marks the Result as inconsistent. 593 bool testZIV(const SCEV *Src, 594 const SCEV *Dst, 595 FullDependence &Result) const; 596 597 /// testSIV - Tests the SIV subscript pair (Src and Dst) for dependence. 598 /// Things of the form [c1 + a1*i] and [c2 + a2*j], where 599 /// i and j are induction variables, c1 and c2 are loop invariant, 600 /// and a1 and a2 are constant. 601 /// Returns true if any possible dependence is disproved. 602 /// If there might be a dependence, returns false. 603 /// Sets appropriate direction vector entry and, when possible, 604 /// the distance vector entry. 605 /// If the dependence isn't proven to exist, 606 /// marks the Result as inconsistent. 607 bool testSIV(const SCEV *Src, 608 const SCEV *Dst, 609 unsigned &Level, 610 FullDependence &Result, 611 Constraint &NewConstraint, 612 const SCEV *&SplitIter) const; 613 614 /// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence. 615 /// Things of the form [c1 + a1*i] and [c2 + a2*j] 616 /// where i and j are induction variables, c1 and c2 are loop invariant, 617 /// and a1 and a2 are constant. 618 /// With minor algebra, this test can also be used for things like 619 /// [c1 + a1*i + a2*j][c2]. 620 /// Returns true if any possible dependence is disproved. 621 /// If there might be a dependence, returns false. 622 /// Marks the Result as inconsistent. 623 bool testRDIV(const SCEV *Src, 624 const SCEV *Dst, 625 FullDependence &Result) const; 626 627 /// testMIV - Tests the MIV subscript pair (Src and Dst) for dependence. 628 /// Returns true if dependence disproved. 629 /// Can sometimes refine direction vectors. 630 bool testMIV(const SCEV *Src, 631 const SCEV *Dst, 632 const SmallBitVector &Loops, 633 FullDependence &Result) const; 634 635 /// strongSIVtest - Tests the strong SIV subscript pair (Src and Dst) 636 /// for dependence. 637 /// Things of the form [c1 + a*i] and [c2 + a*i], 638 /// where i is an induction variable, c1 and c2 are loop invariant, 639 /// and a is a constant 640 /// Returns true if any possible dependence is disproved. 641 /// If there might be a dependence, returns false. 642 /// Sets appropriate direction and distance. 643 bool strongSIVtest(const SCEV *Coeff, 644 const SCEV *SrcConst, 645 const SCEV *DstConst, 646 const Loop *CurrentLoop, 647 unsigned Level, 648 FullDependence &Result, 649 Constraint &NewConstraint) const; 650 651 /// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair 652 /// (Src and Dst) for dependence. 653 /// Things of the form [c1 + a*i] and [c2 - a*i], 654 /// where i is an induction variable, c1 and c2 are loop invariant, 655 /// and a is a constant. 656 /// Returns true if any possible dependence is disproved. 657 /// If there might be a dependence, returns false. 658 /// Sets appropriate direction entry. 659 /// Set consistent to false. 660 /// Marks the dependence as splitable. 661 bool weakCrossingSIVtest(const SCEV *SrcCoeff, 662 const SCEV *SrcConst, 663 const SCEV *DstConst, 664 const Loop *CurrentLoop, 665 unsigned Level, 666 FullDependence &Result, 667 Constraint &NewConstraint, 668 const SCEV *&SplitIter) const; 669 670 /// ExactSIVtest - Tests the SIV subscript pair 671 /// (Src and Dst) for dependence. 672 /// Things of the form [c1 + a1*i] and [c2 + a2*i], 673 /// where i is an induction variable, c1 and c2 are loop invariant, 674 /// and a1 and a2 are constant. 675 /// Returns true if any possible dependence is disproved. 676 /// If there might be a dependence, returns false. 677 /// Sets appropriate direction entry. 678 /// Set consistent to false. 679 bool exactSIVtest(const SCEV *SrcCoeff, 680 const SCEV *DstCoeff, 681 const SCEV *SrcConst, 682 const SCEV *DstConst, 683 const Loop *CurrentLoop, 684 unsigned Level, 685 FullDependence &Result, 686 Constraint &NewConstraint) const; 687 688 /// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair 689 /// (Src and Dst) for dependence. 690 /// Things of the form [c1] and [c2 + a*i], 691 /// where i is an induction variable, c1 and c2 are loop invariant, 692 /// and a is a constant. See also weakZeroDstSIVtest. 693 /// Returns true if any possible dependence is disproved. 694 /// If there might be a dependence, returns false. 695 /// Sets appropriate direction entry. 696 /// Set consistent to false. 697 /// If loop peeling will break the dependence, mark appropriately. 698 bool weakZeroSrcSIVtest(const SCEV *DstCoeff, 699 const SCEV *SrcConst, 700 const SCEV *DstConst, 701 const Loop *CurrentLoop, 702 unsigned Level, 703 FullDependence &Result, 704 Constraint &NewConstraint) const; 705 706 /// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair 707 /// (Src and Dst) for dependence. 708 /// Things of the form [c1 + a*i] and [c2], 709 /// where i is an induction variable, c1 and c2 are loop invariant, 710 /// and a is a constant. See also weakZeroSrcSIVtest. 711 /// Returns true if any possible dependence is disproved. 712 /// If there might be a dependence, returns false. 713 /// Sets appropriate direction entry. 714 /// Set consistent to false. 715 /// If loop peeling will break the dependence, mark appropriately. 716 bool weakZeroDstSIVtest(const SCEV *SrcCoeff, 717 const SCEV *SrcConst, 718 const SCEV *DstConst, 719 const Loop *CurrentLoop, 720 unsigned Level, 721 FullDependence &Result, 722 Constraint &NewConstraint) const; 723 724 /// exactRDIVtest - Tests the RDIV subscript pair for dependence. 725 /// Things of the form [c1 + a*i] and [c2 + b*j], 726 /// where i and j are induction variable, c1 and c2 are loop invariant, 727 /// and a and b are constants. 728 /// Returns true if any possible dependence is disproved. 729 /// Marks the result as inconsistent. 730 /// Works in some cases that symbolicRDIVtest doesn't, 731 /// and vice versa. 732 bool exactRDIVtest(const SCEV *SrcCoeff, 733 const SCEV *DstCoeff, 734 const SCEV *SrcConst, 735 const SCEV *DstConst, 736 const Loop *SrcLoop, 737 const Loop *DstLoop, 738 FullDependence &Result) const; 739 740 /// symbolicRDIVtest - Tests the RDIV subscript pair for dependence. 741 /// Things of the form [c1 + a*i] and [c2 + b*j], 742 /// where i and j are induction variable, c1 and c2 are loop invariant, 743 /// and a and b are constants. 744 /// Returns true if any possible dependence is disproved. 745 /// Marks the result as inconsistent. 746 /// Works in some cases that exactRDIVtest doesn't, 747 /// and vice versa. Can also be used as a backup for 748 /// ordinary SIV tests. 749 bool symbolicRDIVtest(const SCEV *SrcCoeff, 750 const SCEV *DstCoeff, 751 const SCEV *SrcConst, 752 const SCEV *DstConst, 753 const Loop *SrcLoop, 754 const Loop *DstLoop) const; 755 756 /// gcdMIVtest - Tests an MIV subscript pair for dependence. 757 /// Returns true if any possible dependence is disproved. 758 /// Marks the result as inconsistent. 759 /// Can sometimes disprove the equal direction for 1 or more loops. 760 // Can handle some symbolics that even the SIV tests don't get, 761 /// so we use it as a backup for everything. 762 bool gcdMIVtest(const SCEV *Src, 763 const SCEV *Dst, 764 FullDependence &Result) const; 765 766 /// banerjeeMIVtest - Tests an MIV subscript pair for dependence. 767 /// Returns true if any possible dependence is disproved. 768 /// Marks the result as inconsistent. 769 /// Computes directions. 770 bool banerjeeMIVtest(const SCEV *Src, 771 const SCEV *Dst, 772 const SmallBitVector &Loops, 773 FullDependence &Result) const; 774 775 /// collectCoefficientInfo - Walks through the subscript, 776 /// collecting each coefficient, the associated loop bounds, 777 /// and recording its positive and negative parts for later use. 778 CoefficientInfo *collectCoeffInfo(const SCEV *Subscript, 779 bool SrcFlag, 780 const SCEV *&Constant) const; 781 782 /// getPositivePart - X^+ = max(X, 0). 783 /// 784 const SCEV *getPositivePart(const SCEV *X) const; 785 786 /// getNegativePart - X^- = min(X, 0). 787 /// 788 const SCEV *getNegativePart(const SCEV *X) const; 789 790 /// getLowerBound - Looks through all the bounds info and 791 /// computes the lower bound given the current direction settings 792 /// at each level. 793 const SCEV *getLowerBound(BoundInfo *Bound) const; 794 795 /// getUpperBound - Looks through all the bounds info and 796 /// computes the upper bound given the current direction settings 797 /// at each level. 798 const SCEV *getUpperBound(BoundInfo *Bound) const; 799 800 /// exploreDirections - Hierarchically expands the direction vector 801 /// search space, combining the directions of discovered dependences 802 /// in the DirSet field of Bound. Returns the number of distinct 803 /// dependences discovered. If the dependence is disproved, 804 /// it will return 0. 805 unsigned exploreDirections(unsigned Level, 806 CoefficientInfo *A, 807 CoefficientInfo *B, 808 BoundInfo *Bound, 809 const SmallBitVector &Loops, 810 unsigned &DepthExpanded, 811 const SCEV *Delta) const; 812 813 /// testBounds - Returns true iff the current bounds are plausible. 814 bool testBounds(unsigned char DirKind, 815 unsigned Level, 816 BoundInfo *Bound, 817 const SCEV *Delta) const; 818 819 /// findBoundsALL - Computes the upper and lower bounds for level K 820 /// using the * direction. Records them in Bound. 821 void findBoundsALL(CoefficientInfo *A, 822 CoefficientInfo *B, 823 BoundInfo *Bound, 824 unsigned K) const; 825 826 /// findBoundsLT - Computes the upper and lower bounds for level K 827 /// using the < direction. Records them in Bound. 828 void findBoundsLT(CoefficientInfo *A, 829 CoefficientInfo *B, 830 BoundInfo *Bound, 831 unsigned K) const; 832 833 /// findBoundsGT - Computes the upper and lower bounds for level K 834 /// using the > direction. Records them in Bound. 835 void findBoundsGT(CoefficientInfo *A, 836 CoefficientInfo *B, 837 BoundInfo *Bound, 838 unsigned K) const; 839 840 /// findBoundsEQ - Computes the upper and lower bounds for level K 841 /// using the = direction. Records them in Bound. 842 void findBoundsEQ(CoefficientInfo *A, 843 CoefficientInfo *B, 844 BoundInfo *Bound, 845 unsigned K) const; 846 847 /// intersectConstraints - Updates X with the intersection 848 /// of the Constraints X and Y. Returns true if X has changed. 849 bool intersectConstraints(Constraint *X, 850 const Constraint *Y); 851 852 /// propagate - Review the constraints, looking for opportunities 853 /// to simplify a subscript pair (Src and Dst). 854 /// Return true if some simplification occurs. 855 /// If the simplification isn't exact (that is, if it is conservative 856 /// in terms of dependence), set consistent to false. 857 bool propagate(const SCEV *&Src, 858 const SCEV *&Dst, 859 SmallBitVector &Loops, 860 SmallVectorImpl<Constraint> &Constraints, 861 bool &Consistent); 862 863 /// propagateDistance - Attempt to propagate a distance 864 /// constraint into a subscript pair (Src and Dst). 865 /// Return true if some simplification occurs. 866 /// If the simplification isn't exact (that is, if it is conservative 867 /// in terms of dependence), set consistent to false. 868 bool propagateDistance(const SCEV *&Src, 869 const SCEV *&Dst, 870 Constraint &CurConstraint, 871 bool &Consistent); 872 873 /// propagatePoint - Attempt to propagate a point 874 /// constraint into a subscript pair (Src and Dst). 875 /// Return true if some simplification occurs. 876 bool propagatePoint(const SCEV *&Src, 877 const SCEV *&Dst, 878 Constraint &CurConstraint); 879 880 /// propagateLine - Attempt to propagate a line 881 /// constraint into a subscript pair (Src and Dst). 882 /// Return true if some simplification occurs. 883 /// If the simplification isn't exact (that is, if it is conservative 884 /// in terms of dependence), set consistent to false. 885 bool propagateLine(const SCEV *&Src, 886 const SCEV *&Dst, 887 Constraint &CurConstraint, 888 bool &Consistent); 889 890 /// findCoefficient - Given a linear SCEV, 891 /// return the coefficient corresponding to specified loop. 892 /// If there isn't one, return the SCEV constant 0. 893 /// For example, given a*i + b*j + c*k, returning the coefficient 894 /// corresponding to the j loop would yield b. 895 const SCEV *findCoefficient(const SCEV *Expr, 896 const Loop *TargetLoop) const; 897 898 /// zeroCoefficient - Given a linear SCEV, 899 /// return the SCEV given by zeroing out the coefficient 900 /// corresponding to the specified loop. 901 /// For example, given a*i + b*j + c*k, zeroing the coefficient 902 /// corresponding to the j loop would yield a*i + c*k. 903 const SCEV *zeroCoefficient(const SCEV *Expr, 904 const Loop *TargetLoop) const; 905 906 /// addToCoefficient - Given a linear SCEV Expr, 907 /// return the SCEV given by adding some Value to the 908 /// coefficient corresponding to the specified TargetLoop. 909 /// For example, given a*i + b*j + c*k, adding 1 to the coefficient 910 /// corresponding to the j loop would yield a*i + (b+1)*j + c*k. 911 const SCEV *addToCoefficient(const SCEV *Expr, 912 const Loop *TargetLoop, 913 const SCEV *Value) const; 914 915 /// updateDirection - Update direction vector entry 916 /// based on the current constraint. 917 void updateDirection(Dependence::DVEntry &Level, 918 const Constraint &CurConstraint) const; 919 920 bool tryDelinearize(Instruction *Src, Instruction *Dst, 921 SmallVectorImpl<Subscript> &Pair); 922 923 public: 924 static char ID; // Class identification, replacement for typeinfo 925 DependenceAnalysis() : FunctionPass(ID) { 926 initializeDependenceAnalysisPass(*PassRegistry::getPassRegistry()); 927 } 928 929 bool runOnFunction(Function &F) override; 930 void releaseMemory() override; 931 void getAnalysisUsage(AnalysisUsage &) const override; 932 void print(raw_ostream &, const Module * = nullptr) const override; 933 }; // class DependenceAnalysis 934 935 /// createDependenceAnalysisPass - This creates an instance of the 936 /// DependenceAnalysis pass. 937 FunctionPass *createDependenceAnalysisPass(); 938 939 } // namespace llvm 940 941 #endif 942
