1 //===-- llvm/Analysis/DependenceAnalysis.h -------------------- -*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // DependenceAnalysis is an LLVM pass that analyses dependences between memory
11 // accesses. Currently, it is an implementation of the approach described in
13 // Practical Dependence Testing
14 // Goff, Kennedy, Tseng
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.
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:
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.
28 // DependenceAnalysis attacks the first condition; DependenceGraph will attack
29 // the second (it's not yet ready).
31 // Please note that this is work in progress and the interface is subject to
35 // Return a set of more precise dependences instead of just one dependence
38 //===----------------------------------------------------------------------===//
40 #ifndef LLVM_ANALYSIS_DEPENDENCEANALYSIS_H
41 #define LLVM_ANALYSIS_DEPENDENCEANALYSIS_H
43 #include "llvm/ADT/SmallBitVector.h"
44 #include "llvm/Analysis/AliasAnalysis.h"
45 #include "llvm/IR/Instructions.h"
46 #include "llvm/Pass.h"
49 template <typename T> class ArrayRef;
52 class ScalarEvolution;
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.
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
73 Dependence(const Dependence &) = default;
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;
82 Dependence(Instruction *Source,
83 Instruction *Destination) :
86 NextPredecessor(nullptr),
87 NextSuccessor(nullptr) {}
88 virtual ~Dependence() {}
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.
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) { }
112 /// getSrc - Returns the source instruction for this dependence.
114 Instruction *getSrc() const { return Src; }
116 /// getDst - Returns the destination instruction for this dependence.
118 Instruction *getDst() const { return Dst; }
120 /// isInput - Returns true if this is an input dependence.
122 bool isInput() const;
124 /// isOutput - Returns true if this is an output dependence.
126 bool isOutput() const;
128 /// isFlow - Returns true if this is a flow (aka true) dependence.
132 /// isAnti - Returns true if this is an anti dependence.
136 /// isOrdered - Returns true if dependence is Output, Flow, or Anti
138 bool isOrdered() const { return isOutput() || isFlow() || isAnti(); }
140 /// isUnordered - Returns true if dependence is Input
142 bool isUnordered() const { return isInput(); }
144 /// isLoopIndependent - Returns true if this is a loop-independent
146 virtual bool isLoopIndependent() const { return true; }
148 /// isConfused - Returns true if this dependence is confused
149 /// (the compiler understands nothing and makes worst-case
151 virtual bool isConfused() const { return true; }
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; }
157 /// getLevels - Returns the number of common loops surrounding the
158 /// source and destination of the dependence.
159 virtual unsigned getLevels() const { return 0; }
161 /// getDirection - Returns the direction associated with a particular
163 virtual unsigned getDirection(unsigned Level) const { return DVEntry::ALL; }
165 /// getDistance - Returns the distance (or NULL) associated with a
166 /// particular level.
167 virtual const SCEV *getDistance(unsigned Level) const { return nullptr; }
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; }
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; }
177 /// isSplitable - Returns true if splitting this loop will break
179 virtual bool isSplitable(unsigned Level) const { return false; }
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;
186 /// getNextPredecessor - Returns the value of the NextPredecessor
188 const Dependence *getNextPredecessor() const { return NextPredecessor; }
190 /// getNextSuccessor - Returns the value of the NextSuccessor
192 const Dependence *getNextSuccessor() const { return NextSuccessor; }
194 /// setNextPredecessor - Sets the value of the NextPredecessor
196 void setNextPredecessor(const Dependence *pred) { NextPredecessor = pred; }
198 /// setNextSuccessor - Sets the value of the NextSuccessor
200 void setNextSuccessor(const Dependence *succ) { NextSuccessor = succ; }
202 /// dump - For debugging purposes, dumps a dependence to OS.
204 void dump(raw_ostream &OS) const;
207 Instruction *Src, *Dst;
208 const Dependence *NextPredecessor, *NextSuccessor;
209 friend class DependenceInfo;
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 {
222 FullDependence(Instruction *Src, Instruction *Dst, bool LoopIndependent,
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)) {}
230 /// isLoopIndependent - Returns true if this is a loop-independent
232 bool isLoopIndependent() const override { return LoopIndependent; }
234 /// isConfused - Returns true if this dependence is confused
235 /// (the compiler understands nothing and makes worst-case
237 bool isConfused() const override { return false; }
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; }
243 /// getLevels - Returns the number of common loops surrounding the
244 /// source and destination of the dependence.
245 unsigned getLevels() const override { return Levels; }
247 /// getDirection - Returns the direction associated with a particular
249 unsigned getDirection(unsigned Level) const override;
251 /// getDistance - Returns the distance (or NULL) associated with a
252 /// particular level.
253 const SCEV *getDistance(unsigned Level) const override;
255 /// isPeelFirst - Returns true if peeling the first iteration from
256 /// this loop will break this dependence.
257 bool isPeelFirst(unsigned Level) const override;
259 /// isPeelLast - Returns true if peeling the last iteration from
260 /// this loop will break this dependence.
261 bool isPeelLast(unsigned Level) const override;
263 /// isSplitable - Returns true if splitting the loop will break
265 bool isSplitable(unsigned Level) const override;
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;
273 unsigned short Levels;
274 bool LoopIndependent;
275 bool Consistent; // Init to true, then refine.
276 std::unique_ptr<DVEntry[]> DV;
277 friend class DependenceInfo;
280 /// DependenceInfo - This class is the main dependence-analysis driver.
282 class DependenceInfo {
284 DependenceInfo(Function *F, AliasAnalysis *AA, ScalarEvolution *SE,
286 : AA(AA), SE(SE), LI(LI), F(F) {}
288 /// depends - Tests for a dependence between the Src and Dst instructions.
289 /// Returns NULL if no dependence; otherwise, returns a Dependence (or a
290 /// FullDependence) with as much information as can be gleaned.
291 /// The flag PossiblyLoopIndependent should be set by the caller
292 /// if it appears that control flow can reach from Src to Dst
293 /// without traversing a loop back edge.
294 std::unique_ptr<Dependence> depends(Instruction *Src,
296 bool PossiblyLoopIndependent);
298 /// getSplitIteration - Give a dependence that's splittable at some
299 /// particular level, return the iteration that should be used to split
302 /// Generally, the dependence analyzer will be used to build
303 /// a dependence graph for a function (basically a map from instructions
304 /// to dependences). Looking for cycles in the graph shows us loops
305 /// that cannot be trivially vectorized/parallelized.
307 /// We can try to improve the situation by examining all the dependences
308 /// that make up the cycle, looking for ones we can break.
309 /// Sometimes, peeling the first or last iteration of a loop will break
310 /// dependences, and there are flags for those possibilities.
311 /// Sometimes, splitting a loop at some other iteration will do the trick,
312 /// and we've got a flag for that case. Rather than waste the space to
313 /// record the exact iteration (since we rarely know), we provide
314 /// a method that calculates the iteration. It's a drag that it must work
315 /// from scratch, but wonderful in that it's possible.
317 /// Here's an example:
319 /// for (i = 0; i < 10; i++)
323 /// There's a loop-carried flow dependence from the store to the load,
324 /// found by the weak-crossing SIV test. The dependence will have a flag,
325 /// indicating that the dependence can be broken by splitting the loop.
326 /// Calling getSplitIteration will return 5.
327 /// Splitting the loop breaks the dependence, like so:
329 /// for (i = 0; i <= 5; i++)
332 /// for (i = 6; i < 10; i++)
336 /// breaks the dependence and allows us to vectorize/parallelize
338 const SCEV *getSplitIteration(const Dependence &Dep, unsigned Level);
340 Function *getFunction() const { return F; }
348 /// Subscript - This private struct represents a pair of subscripts from
349 /// a pair of potentially multi-dimensional array references. We use a
350 /// vector of them to guide subscript partitioning.
354 enum ClassificationKind { ZIV, SIV, RDIV, MIV, NonLinear } Classification;
355 SmallBitVector Loops;
356 SmallBitVector GroupLoops;
357 SmallBitVector Group;
360 struct CoefficientInfo {
364 const SCEV *Iterations;
368 const SCEV *Iterations;
369 const SCEV *Upper[8];
370 const SCEV *Lower[8];
371 unsigned char Direction;
372 unsigned char DirSet;
375 /// Constraint - This private class represents a constraint, as defined
378 /// Practical Dependence Testing
379 /// Goff, Kennedy, Tseng
382 /// There are 5 kinds of constraint, in a hierarchy.
383 /// 1) Any - indicates no constraint, any dependence is possible.
384 /// 2) Line - A line ax + by = c, where a, b, and c are parameters,
385 /// representing the dependence equation.
386 /// 3) Distance - The value d of the dependence distance;
387 /// 4) Point - A point <x, y> representing the dependence from
388 /// iteration x to iteration y.
389 /// 5) Empty - No dependence is possible.
392 enum ConstraintKind { Empty, Point, Distance, Line, Any } Kind;
397 const Loop *AssociatedLoop;
400 /// isEmpty - Return true if the constraint is of kind Empty.
401 bool isEmpty() const { return Kind == Empty; }
403 /// isPoint - Return true if the constraint is of kind Point.
404 bool isPoint() const { return Kind == Point; }
406 /// isDistance - Return true if the constraint is of kind Distance.
407 bool isDistance() const { return Kind == Distance; }
409 /// isLine - Return true if the constraint is of kind Line.
410 /// Since Distance's can also be represented as Lines, we also return
411 /// true if the constraint is of kind Distance.
412 bool isLine() const { return Kind == Line || Kind == Distance; }
414 /// isAny - Return true if the constraint is of kind Any;
415 bool isAny() const { return Kind == Any; }
417 /// getX - If constraint is a point <X, Y>, returns X.
418 /// Otherwise assert.
419 const SCEV *getX() const;
421 /// getY - If constraint is a point <X, Y>, returns Y.
422 /// Otherwise assert.
423 const SCEV *getY() const;
425 /// getA - If constraint is a line AX + BY = C, returns A.
426 /// Otherwise assert.
427 const SCEV *getA() const;
429 /// getB - If constraint is a line AX + BY = C, returns B.
430 /// Otherwise assert.
431 const SCEV *getB() const;
433 /// getC - If constraint is a line AX + BY = C, returns C.
434 /// Otherwise assert.
435 const SCEV *getC() const;
437 /// getD - If constraint is a distance, returns D.
438 /// Otherwise assert.
439 const SCEV *getD() const;
441 /// getAssociatedLoop - Returns the loop associated with this constraint.
442 const Loop *getAssociatedLoop() const;
444 /// setPoint - Change a constraint to Point.
445 void setPoint(const SCEV *X, const SCEV *Y, const Loop *CurrentLoop);
447 /// setLine - Change a constraint to Line.
448 void setLine(const SCEV *A, const SCEV *B,
449 const SCEV *C, const Loop *CurrentLoop);
451 /// setDistance - Change a constraint to Distance.
452 void setDistance(const SCEV *D, const Loop *CurrentLoop);
454 /// setEmpty - Change a constraint to Empty.
457 /// setAny - Change a constraint to Any.
458 void setAny(ScalarEvolution *SE);
460 /// dump - For debugging purposes. Dumps the constraint
462 void dump(raw_ostream &OS) const;
465 /// establishNestingLevels - Examines the loop nesting of the Src and Dst
466 /// instructions and establishes their shared loops. Sets the variables
467 /// CommonLevels, SrcLevels, and MaxLevels.
468 /// The source and destination instructions needn't be contained in the same
469 /// loop. The routine establishNestingLevels finds the level of most deeply
470 /// nested loop that contains them both, CommonLevels. An instruction that's
471 /// not contained in a loop is at level = 0. MaxLevels is equal to the level
472 /// of the source plus the level of the destination, minus CommonLevels.
473 /// This lets us allocate vectors MaxLevels in length, with room for every
474 /// distinct loop referenced in both the source and destination subscripts.
475 /// The variable SrcLevels is the nesting depth of the source instruction.
476 /// It's used to help calculate distinct loops referenced by the destination.
477 /// Here's the map from loops to levels:
479 /// 1 - outermost common loop
480 /// ... - other common loops
481 /// CommonLevels - innermost common loop
482 /// ... - loops containing Src but not Dst
483 /// SrcLevels - innermost loop containing Src but not Dst
484 /// ... - loops containing Dst but not Src
485 /// MaxLevels - innermost loop containing Dst but not Src
486 /// Consider the follow code fragment:
503 /// If we're looking at the possibility of a dependence between the store
504 /// to A (the Src) and the load from A (the Dst), we'll note that they
505 /// have 2 loops in common, so CommonLevels will equal 2 and the direction
506 /// vector for Result will have 2 entries. SrcLevels = 4 and MaxLevels = 7.
507 /// A map from loop names to level indices would look like
509 /// b - 2 = CommonLevels
511 /// d - 4 = SrcLevels
514 /// g - 7 = MaxLevels
515 void establishNestingLevels(const Instruction *Src,
516 const Instruction *Dst);
518 unsigned CommonLevels, SrcLevels, MaxLevels;
520 /// mapSrcLoop - Given one of the loops containing the source, return
521 /// its level index in our numbering scheme.
522 unsigned mapSrcLoop(const Loop *SrcLoop) const;
524 /// mapDstLoop - Given one of the loops containing the destination,
525 /// return its level index in our numbering scheme.
526 unsigned mapDstLoop(const Loop *DstLoop) const;
528 /// isLoopInvariant - Returns true if Expression is loop invariant
530 bool isLoopInvariant(const SCEV *Expression, const Loop *LoopNest) const;
532 /// Makes sure all subscript pairs share the same integer type by
533 /// sign-extending as necessary.
534 /// Sign-extending a subscript is safe because getelementptr assumes the
535 /// array subscripts are signed.
536 void unifySubscriptType(ArrayRef<Subscript *> Pairs);
538 /// removeMatchingExtensions - Examines a subscript pair.
539 /// If the source and destination are identically sign (or zero)
540 /// extended, it strips off the extension in an effort to
541 /// simplify the actual analysis.
542 void removeMatchingExtensions(Subscript *Pair);
544 /// collectCommonLoops - Finds the set of loops from the LoopNest that
545 /// have a level <= CommonLevels and are referred to by the SCEV Expression.
546 void collectCommonLoops(const SCEV *Expression,
547 const Loop *LoopNest,
548 SmallBitVector &Loops) const;
550 /// checkSrcSubscript - Examines the SCEV Src, returning true iff it's
551 /// linear. Collect the set of loops mentioned by Src.
552 bool checkSrcSubscript(const SCEV *Src,
553 const Loop *LoopNest,
554 SmallBitVector &Loops);
556 /// checkDstSubscript - Examines the SCEV Dst, returning true iff it's
557 /// linear. Collect the set of loops mentioned by Dst.
558 bool checkDstSubscript(const SCEV *Dst,
559 const Loop *LoopNest,
560 SmallBitVector &Loops);
562 /// isKnownPredicate - Compare X and Y using the predicate Pred.
563 /// Basically a wrapper for SCEV::isKnownPredicate,
564 /// but tries harder, especially in the presence of sign and zero
565 /// extensions and symbolics.
566 bool isKnownPredicate(ICmpInst::Predicate Pred,
568 const SCEV *Y) const;
570 /// collectUpperBound - All subscripts are the same type (on my machine,
571 /// an i64). The loop bound may be a smaller type. collectUpperBound
572 /// find the bound, if available, and zero extends it to the Type T.
573 /// (I zero extend since the bound should always be >= 0.)
574 /// If no upper bound is available, return NULL.
575 const SCEV *collectUpperBound(const Loop *l, Type *T) const;
577 /// collectConstantUpperBound - Calls collectUpperBound(), then
578 /// attempts to cast it to SCEVConstant. If the cast fails,
580 const SCEVConstant *collectConstantUpperBound(const Loop *l, Type *T) const;
582 /// classifyPair - Examines the subscript pair (the Src and Dst SCEVs)
583 /// and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear.
584 /// Collects the associated loops in a set.
585 Subscript::ClassificationKind classifyPair(const SCEV *Src,
586 const Loop *SrcLoopNest,
588 const Loop *DstLoopNest,
589 SmallBitVector &Loops);
591 /// testZIV - Tests the ZIV subscript pair (Src and Dst) for dependence.
592 /// Returns true if any possible dependence is disproved.
593 /// If there might be a dependence, returns false.
594 /// If the dependence isn't proven to exist,
595 /// marks the Result as inconsistent.
596 bool testZIV(const SCEV *Src,
598 FullDependence &Result) const;
600 /// testSIV - Tests the SIV subscript pair (Src and Dst) for dependence.
601 /// Things of the form [c1 + a1*i] and [c2 + a2*j], where
602 /// i and j are induction variables, c1 and c2 are loop invariant,
603 /// and a1 and a2 are constant.
604 /// Returns true if any possible dependence is disproved.
605 /// If there might be a dependence, returns false.
606 /// Sets appropriate direction vector entry and, when possible,
607 /// the distance vector entry.
608 /// If the dependence isn't proven to exist,
609 /// marks the Result as inconsistent.
610 bool testSIV(const SCEV *Src,
613 FullDependence &Result,
614 Constraint &NewConstraint,
615 const SCEV *&SplitIter) const;
617 /// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence.
618 /// Things of the form [c1 + a1*i] and [c2 + a2*j]
619 /// where i and j are induction variables, c1 and c2 are loop invariant,
620 /// and a1 and a2 are constant.
621 /// With minor algebra, this test can also be used for things like
622 /// [c1 + a1*i + a2*j][c2].
623 /// Returns true if any possible dependence is disproved.
624 /// If there might be a dependence, returns false.
625 /// Marks the Result as inconsistent.
626 bool testRDIV(const SCEV *Src,
628 FullDependence &Result) const;
630 /// testMIV - Tests the MIV subscript pair (Src and Dst) for dependence.
631 /// Returns true if dependence disproved.
632 /// Can sometimes refine direction vectors.
633 bool testMIV(const SCEV *Src,
635 const SmallBitVector &Loops,
636 FullDependence &Result) const;
638 /// strongSIVtest - Tests the strong SIV subscript pair (Src and Dst)
640 /// Things of the form [c1 + a*i] and [c2 + a*i],
641 /// where i is an induction variable, c1 and c2 are loop invariant,
642 /// and a is a constant
643 /// Returns true if any possible dependence is disproved.
644 /// If there might be a dependence, returns false.
645 /// Sets appropriate direction and distance.
646 bool strongSIVtest(const SCEV *Coeff,
647 const SCEV *SrcConst,
648 const SCEV *DstConst,
649 const Loop *CurrentLoop,
651 FullDependence &Result,
652 Constraint &NewConstraint) const;
654 /// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair
655 /// (Src and Dst) for dependence.
656 /// Things of the form [c1 + a*i] and [c2 - a*i],
657 /// where i is an induction variable, c1 and c2 are loop invariant,
658 /// and a is a constant.
659 /// Returns true if any possible dependence is disproved.
660 /// If there might be a dependence, returns false.
661 /// Sets appropriate direction entry.
662 /// Set consistent to false.
663 /// Marks the dependence as splitable.
664 bool weakCrossingSIVtest(const SCEV *SrcCoeff,
665 const SCEV *SrcConst,
666 const SCEV *DstConst,
667 const Loop *CurrentLoop,
669 FullDependence &Result,
670 Constraint &NewConstraint,
671 const SCEV *&SplitIter) const;
673 /// ExactSIVtest - Tests the SIV subscript pair
674 /// (Src and Dst) for dependence.
675 /// Things of the form [c1 + a1*i] and [c2 + a2*i],
676 /// where i is an induction variable, c1 and c2 are loop invariant,
677 /// and a1 and a2 are constant.
678 /// Returns true if any possible dependence is disproved.
679 /// If there might be a dependence, returns false.
680 /// Sets appropriate direction entry.
681 /// Set consistent to false.
682 bool exactSIVtest(const SCEV *SrcCoeff,
683 const SCEV *DstCoeff,
684 const SCEV *SrcConst,
685 const SCEV *DstConst,
686 const Loop *CurrentLoop,
688 FullDependence &Result,
689 Constraint &NewConstraint) const;
691 /// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair
692 /// (Src and Dst) for dependence.
693 /// Things of the form [c1] and [c2 + a*i],
694 /// where i is an induction variable, c1 and c2 are loop invariant,
695 /// and a is a constant. See also weakZeroDstSIVtest.
696 /// Returns true if any possible dependence is disproved.
697 /// If there might be a dependence, returns false.
698 /// Sets appropriate direction entry.
699 /// Set consistent to false.
700 /// If loop peeling will break the dependence, mark appropriately.
701 bool weakZeroSrcSIVtest(const SCEV *DstCoeff,
702 const SCEV *SrcConst,
703 const SCEV *DstConst,
704 const Loop *CurrentLoop,
706 FullDependence &Result,
707 Constraint &NewConstraint) const;
709 /// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair
710 /// (Src and Dst) for dependence.
711 /// Things of the form [c1 + a*i] and [c2],
712 /// where i is an induction variable, c1 and c2 are loop invariant,
713 /// and a is a constant. See also weakZeroSrcSIVtest.
714 /// Returns true if any possible dependence is disproved.
715 /// If there might be a dependence, returns false.
716 /// Sets appropriate direction entry.
717 /// Set consistent to false.
718 /// If loop peeling will break the dependence, mark appropriately.
719 bool weakZeroDstSIVtest(const SCEV *SrcCoeff,
720 const SCEV *SrcConst,
721 const SCEV *DstConst,
722 const Loop *CurrentLoop,
724 FullDependence &Result,
725 Constraint &NewConstraint) const;
727 /// exactRDIVtest - Tests the RDIV subscript pair for dependence.
728 /// Things of the form [c1 + a*i] and [c2 + b*j],
729 /// where i and j are induction variable, c1 and c2 are loop invariant,
730 /// and a and b are constants.
731 /// Returns true if any possible dependence is disproved.
732 /// Marks the result as inconsistent.
733 /// Works in some cases that symbolicRDIVtest doesn't,
735 bool exactRDIVtest(const SCEV *SrcCoeff,
736 const SCEV *DstCoeff,
737 const SCEV *SrcConst,
738 const SCEV *DstConst,
741 FullDependence &Result) const;
743 /// symbolicRDIVtest - Tests the RDIV subscript pair for dependence.
744 /// Things of the form [c1 + a*i] and [c2 + b*j],
745 /// where i and j are induction variable, c1 and c2 are loop invariant,
746 /// and a and b are constants.
747 /// Returns true if any possible dependence is disproved.
748 /// Marks the result as inconsistent.
749 /// Works in some cases that exactRDIVtest doesn't,
750 /// and vice versa. Can also be used as a backup for
751 /// ordinary SIV tests.
752 bool symbolicRDIVtest(const SCEV *SrcCoeff,
753 const SCEV *DstCoeff,
754 const SCEV *SrcConst,
755 const SCEV *DstConst,
757 const Loop *DstLoop) const;
759 /// gcdMIVtest - Tests an MIV subscript pair for dependence.
760 /// Returns true if any possible dependence is disproved.
761 /// Marks the result as inconsistent.
762 /// Can sometimes disprove the equal direction for 1 or more loops.
763 // Can handle some symbolics that even the SIV tests don't get,
764 /// so we use it as a backup for everything.
765 bool gcdMIVtest(const SCEV *Src,
767 FullDependence &Result) const;
769 /// banerjeeMIVtest - Tests an MIV subscript pair for dependence.
770 /// Returns true if any possible dependence is disproved.
771 /// Marks the result as inconsistent.
772 /// Computes directions.
773 bool banerjeeMIVtest(const SCEV *Src,
775 const SmallBitVector &Loops,
776 FullDependence &Result) const;
778 /// collectCoefficientInfo - Walks through the subscript,
779 /// collecting each coefficient, the associated loop bounds,
780 /// and recording its positive and negative parts for later use.
781 CoefficientInfo *collectCoeffInfo(const SCEV *Subscript,
783 const SCEV *&Constant) const;
785 /// getPositivePart - X^+ = max(X, 0).
787 const SCEV *getPositivePart(const SCEV *X) const;
789 /// getNegativePart - X^- = min(X, 0).
791 const SCEV *getNegativePart(const SCEV *X) const;
793 /// getLowerBound - Looks through all the bounds info and
794 /// computes the lower bound given the current direction settings
796 const SCEV *getLowerBound(BoundInfo *Bound) const;
798 /// getUpperBound - Looks through all the bounds info and
799 /// computes the upper bound given the current direction settings
801 const SCEV *getUpperBound(BoundInfo *Bound) const;
803 /// exploreDirections - Hierarchically expands the direction vector
804 /// search space, combining the directions of discovered dependences
805 /// in the DirSet field of Bound. Returns the number of distinct
806 /// dependences discovered. If the dependence is disproved,
807 /// it will return 0.
808 unsigned exploreDirections(unsigned Level,
812 const SmallBitVector &Loops,
813 unsigned &DepthExpanded,
814 const SCEV *Delta) const;
816 /// testBounds - Returns true iff the current bounds are plausible.
817 bool testBounds(unsigned char DirKind,
820 const SCEV *Delta) const;
822 /// findBoundsALL - Computes the upper and lower bounds for level K
823 /// using the * direction. Records them in Bound.
824 void findBoundsALL(CoefficientInfo *A,
829 /// findBoundsLT - Computes the upper and lower bounds for level K
830 /// using the < direction. Records them in Bound.
831 void findBoundsLT(CoefficientInfo *A,
836 /// findBoundsGT - Computes the upper and lower bounds for level K
837 /// using the > direction. Records them in Bound.
838 void findBoundsGT(CoefficientInfo *A,
843 /// findBoundsEQ - Computes the upper and lower bounds for level K
844 /// using the = direction. Records them in Bound.
845 void findBoundsEQ(CoefficientInfo *A,
850 /// intersectConstraints - Updates X with the intersection
851 /// of the Constraints X and Y. Returns true if X has changed.
852 bool intersectConstraints(Constraint *X,
853 const Constraint *Y);
855 /// propagate - Review the constraints, looking for opportunities
856 /// to simplify a subscript pair (Src and Dst).
857 /// Return true if some simplification occurs.
858 /// If the simplification isn't exact (that is, if it is conservative
859 /// in terms of dependence), set consistent to false.
860 bool propagate(const SCEV *&Src,
862 SmallBitVector &Loops,
863 SmallVectorImpl<Constraint> &Constraints,
866 /// propagateDistance - Attempt to propagate a distance
867 /// constraint into a subscript pair (Src and Dst).
868 /// Return true if some simplification occurs.
869 /// If the simplification isn't exact (that is, if it is conservative
870 /// in terms of dependence), set consistent to false.
871 bool propagateDistance(const SCEV *&Src,
873 Constraint &CurConstraint,
876 /// propagatePoint - Attempt to propagate a point
877 /// constraint into a subscript pair (Src and Dst).
878 /// Return true if some simplification occurs.
879 bool propagatePoint(const SCEV *&Src,
881 Constraint &CurConstraint);
883 /// propagateLine - Attempt to propagate a line
884 /// constraint into a subscript pair (Src and Dst).
885 /// Return true if some simplification occurs.
886 /// If the simplification isn't exact (that is, if it is conservative
887 /// in terms of dependence), set consistent to false.
888 bool propagateLine(const SCEV *&Src,
890 Constraint &CurConstraint,
893 /// findCoefficient - Given a linear SCEV,
894 /// return the coefficient corresponding to specified loop.
895 /// If there isn't one, return the SCEV constant 0.
896 /// For example, given a*i + b*j + c*k, returning the coefficient
897 /// corresponding to the j loop would yield b.
898 const SCEV *findCoefficient(const SCEV *Expr,
899 const Loop *TargetLoop) const;
901 /// zeroCoefficient - Given a linear SCEV,
902 /// return the SCEV given by zeroing out the coefficient
903 /// corresponding to the specified loop.
904 /// For example, given a*i + b*j + c*k, zeroing the coefficient
905 /// corresponding to the j loop would yield a*i + c*k.
906 const SCEV *zeroCoefficient(const SCEV *Expr,
907 const Loop *TargetLoop) const;
909 /// addToCoefficient - Given a linear SCEV Expr,
910 /// return the SCEV given by adding some Value to the
911 /// coefficient corresponding to the specified TargetLoop.
912 /// For example, given a*i + b*j + c*k, adding 1 to the coefficient
913 /// corresponding to the j loop would yield a*i + (b+1)*j + c*k.
914 const SCEV *addToCoefficient(const SCEV *Expr,
915 const Loop *TargetLoop,
916 const SCEV *Value) const;
918 /// updateDirection - Update direction vector entry
919 /// based on the current constraint.
920 void updateDirection(Dependence::DVEntry &Level,
921 const Constraint &CurConstraint) const;
923 bool tryDelinearize(Instruction *Src, Instruction *Dst,
924 SmallVectorImpl<Subscript> &Pair);
925 }; // class DependenceInfo
927 /// \brief AnalysisPass to compute dependence information in a function
928 class DependenceAnalysis : public AnalysisInfoMixin<DependenceAnalysis> {
930 typedef DependenceInfo Result;
931 Result run(Function &F, FunctionAnalysisManager &FAM);
935 friend struct AnalysisInfoMixin<DependenceAnalysis>;
936 }; // class DependenceAnalysis
938 /// \brief Legacy pass manager pass to access dependence information
939 class DependenceAnalysisWrapperPass : public FunctionPass {
941 static char ID; // Class identification, replacement for typeinfo
942 DependenceAnalysisWrapperPass() : FunctionPass(ID) {
943 initializeDependenceAnalysisWrapperPassPass(
944 *PassRegistry::getPassRegistry());
947 bool runOnFunction(Function &F) override;
948 void releaseMemory() override;
949 void getAnalysisUsage(AnalysisUsage &) const override;
950 void print(raw_ostream &, const Module * = nullptr) const override;
951 DependenceInfo &getDI() const;
954 std::unique_ptr<DependenceInfo> info;
955 }; // class DependenceAnalysisWrapperPass
957 /// createDependenceAnalysisPass - This creates an instance of the
958 /// DependenceAnalysis wrapper pass.
959 FunctionPass *createDependenceAnalysisWrapperPass();