xref: /freebsd/contrib/llvm-project/llvm/include/llvm/Analysis/DependenceAnalysis.h (revision 9e5787d2284e187abb5b654d924394a65772e004)
1 //===-- llvm/Analysis/DependenceAnalysis.h -------------------- -*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // DependenceAnalysis is an LLVM pass that analyses dependences between memory
10 // accesses. Currently, it is an implementation of the approach described in
11 //
12 //            Practical Dependence Testing
13 //            Goff, Kennedy, Tseng
14 //            PLDI 1991
15 //
16 // There's a single entry point that analyzes the dependence between a pair
17 // of memory references in a function, returning either NULL, for no dependence,
18 // or a more-or-less detailed description of the dependence between them.
19 //
20 // This pass exists to support the DependenceGraph pass. There are two separate
21 // passes because there's a useful separation of concerns. A dependence exists
22 // if two conditions are met:
23 //
24 //    1) Two instructions reference the same memory location, and
25 //    2) There is a flow of control leading from one instruction to the other.
26 //
27 // DependenceAnalysis attacks the first condition; DependenceGraph will attack
28 // the second (it's not yet ready).
29 //
30 // Please note that this is work in progress and the interface is subject to
31 // change.
32 //
33 // Plausible changes:
34 //    Return a set of more precise dependences instead of just one dependence
35 //    summarizing all.
36 //
37 //===----------------------------------------------------------------------===//
38 
39 #ifndef LLVM_ANALYSIS_DEPENDENCEANALYSIS_H
40 #define LLVM_ANALYSIS_DEPENDENCEANALYSIS_H
41 
42 #include "llvm/ADT/SmallBitVector.h"
43 #include "llvm/IR/Instructions.h"
44 #include "llvm/IR/PassManager.h"
45 #include "llvm/Pass.h"
46 
47 namespace llvm {
48   class AAResults;
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:
77     Dependence(Instruction *Source,
78                Instruction *Destination) :
79       Src(Source),
80       Dst(Destination),
81       NextPredecessor(nullptr),
82       NextSuccessor(nullptr) {}
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.
103       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     ///
109     Instruction *getSrc() const { return Src; }
110 
111     /// getDst - Returns the destination instruction for this dependence.
112     ///
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     ///
133     bool isOrdered() const { return isOutput() || isFlow() || isAnti(); }
134 
135     /// isUnordered - Returns true if dependence is Input
136     ///
137     bool isUnordered() const { return isInput(); }
138 
139     /// isLoopIndependent - Returns true if this is a loop-independent
140     /// dependence.
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).
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).
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.
154     virtual unsigned getLevels() const { return 0; }
155 
156     /// getDirection - Returns the direction associated with a particular
157     /// 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.
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.
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.
170     virtual bool isPeelLast(unsigned Level) const { return false; }
171 
172     /// isSplitable - Returns true if splitting this loop will break
173     /// the dependence.
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.
183     const Dependence *getNextPredecessor() const { return NextPredecessor; }
184 
185     /// getNextSuccessor - Returns the value of the NextSuccessor
186     /// field.
187     const Dependence *getNextSuccessor() const { return NextSuccessor; }
188 
189     /// setNextPredecessor - Sets the value of the NextPredecessor
190     /// field.
191     void setNextPredecessor(const Dependence *pred) { NextPredecessor = pred; }
192 
193     /// setNextSuccessor - Sets the value of the NextSuccessor
194     /// field.
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.
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).
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).
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.
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:
274     DependenceInfo(Function *F, AAResults *AA, ScalarEvolution *SE,
275                    LoopInfo *LI)
276         : AA(AA), SE(SE), LI(LI), F(F) {}
277 
278     /// Handle transitive invalidation when the cached analysis results go away.
279     bool invalidate(Function &F, const PreservedAnalyses &PA,
280                     FunctionAnalysisManager::Invalidator &Inv);
281 
282     /// depends - Tests for a dependence between the Src and Dst instructions.
283     /// Returns NULL if no dependence; otherwise, returns a Dependence (or a
284     /// FullDependence) with as much information as can be gleaned.
285     /// The flag PossiblyLoopIndependent should be set by the caller
286     /// if it appears that control flow can reach from Src to Dst
287     /// without traversing a loop back edge.
288     std::unique_ptr<Dependence> depends(Instruction *Src,
289                                         Instruction *Dst,
290                                         bool PossiblyLoopIndependent);
291 
292     /// getSplitIteration - Give a dependence that's splittable at some
293     /// particular level, return the iteration that should be used to split
294     /// the loop.
295     ///
296     /// Generally, the dependence analyzer will be used to build
297     /// a dependence graph for a function (basically a map from instructions
298     /// to dependences). Looking for cycles in the graph shows us loops
299     /// that cannot be trivially vectorized/parallelized.
300     ///
301     /// We can try to improve the situation by examining all the dependences
302     /// that make up the cycle, looking for ones we can break.
303     /// Sometimes, peeling the first or last iteration of a loop will break
304     /// dependences, and there are flags for those possibilities.
305     /// Sometimes, splitting a loop at some other iteration will do the trick,
306     /// and we've got a flag for that case. Rather than waste the space to
307     /// record the exact iteration (since we rarely know), we provide
308     /// a method that calculates the iteration. It's a drag that it must work
309     /// from scratch, but wonderful in that it's possible.
310     ///
311     /// Here's an example:
312     ///
313     ///    for (i = 0; i < 10; i++)
314     ///        A[i] = ...
315     ///        ... = A[11 - i]
316     ///
317     /// There's a loop-carried flow dependence from the store to the load,
318     /// found by the weak-crossing SIV test. The dependence will have a flag,
319     /// indicating that the dependence can be broken by splitting the loop.
320     /// Calling getSplitIteration will return 5.
321     /// Splitting the loop breaks the dependence, like so:
322     ///
323     ///    for (i = 0; i <= 5; i++)
324     ///        A[i] = ...
325     ///        ... = A[11 - i]
326     ///    for (i = 6; i < 10; i++)
327     ///        A[i] = ...
328     ///        ... = A[11 - i]
329     ///
330     /// breaks the dependence and allows us to vectorize/parallelize
331     /// both loops.
332     const SCEV *getSplitIteration(const Dependence &Dep, unsigned Level);
333 
334     Function *getFunction() const { return F; }
335 
336   private:
337     AAResults *AA;
338     ScalarEvolution *SE;
339     LoopInfo *LI;
340     Function *F;
341 
342     /// Subscript - This private struct represents a pair of subscripts from
343     /// a pair of potentially multi-dimensional array references. We use a
344     /// vector of them to guide subscript partitioning.
345     struct Subscript {
346       const SCEV *Src;
347       const SCEV *Dst;
348       enum ClassificationKind { ZIV, SIV, RDIV, MIV, NonLinear } Classification;
349       SmallBitVector Loops;
350       SmallBitVector GroupLoops;
351       SmallBitVector Group;
352     };
353 
354     struct CoefficientInfo {
355       const SCEV *Coeff;
356       const SCEV *PosPart;
357       const SCEV *NegPart;
358       const SCEV *Iterations;
359     };
360 
361     struct BoundInfo {
362       const SCEV *Iterations;
363       const SCEV *Upper[8];
364       const SCEV *Lower[8];
365       unsigned char Direction;
366       unsigned char DirSet;
367     };
368 
369     /// Constraint - This private class represents a constraint, as defined
370     /// in the paper
371     ///
372     ///           Practical Dependence Testing
373     ///           Goff, Kennedy, Tseng
374     ///           PLDI 1991
375     ///
376     /// There are 5 kinds of constraint, in a hierarchy.
377     ///   1) Any - indicates no constraint, any dependence is possible.
378     ///   2) Line - A line ax + by = c, where a, b, and c are parameters,
379     ///             representing the dependence equation.
380     ///   3) Distance - The value d of the dependence distance;
381     ///   4) Point - A point <x, y> representing the dependence from
382     ///              iteration x to iteration y.
383     ///   5) Empty - No dependence is possible.
384     class Constraint {
385     private:
386       enum ConstraintKind { Empty, Point, Distance, Line, Any } Kind;
387       ScalarEvolution *SE;
388       const SCEV *A;
389       const SCEV *B;
390       const SCEV *C;
391       const Loop *AssociatedLoop;
392 
393     public:
394       /// isEmpty - Return true if the constraint is of kind Empty.
395       bool isEmpty() const { return Kind == Empty; }
396 
397       /// isPoint - Return true if the constraint is of kind Point.
398       bool isPoint() const { return Kind == Point; }
399 
400       /// isDistance - Return true if the constraint is of kind Distance.
401       bool isDistance() const { return Kind == Distance; }
402 
403       /// isLine - Return true if the constraint is of kind Line.
404       /// Since Distance's can also be represented as Lines, we also return
405       /// true if the constraint is of kind Distance.
406       bool isLine() const { return Kind == Line || Kind == Distance; }
407 
408       /// isAny - Return true if the constraint is of kind Any;
409       bool isAny() const { return Kind == Any; }
410 
411       /// getX - If constraint is a point <X, Y>, returns X.
412       /// Otherwise assert.
413       const SCEV *getX() const;
414 
415       /// getY - If constraint is a point <X, Y>, returns Y.
416       /// Otherwise assert.
417       const SCEV *getY() const;
418 
419       /// getA - If constraint is a line AX + BY = C, returns A.
420       /// Otherwise assert.
421       const SCEV *getA() const;
422 
423       /// getB - If constraint is a line AX + BY = C, returns B.
424       /// Otherwise assert.
425       const SCEV *getB() const;
426 
427       /// getC - If constraint is a line AX + BY = C, returns C.
428       /// Otherwise assert.
429       const SCEV *getC() const;
430 
431       /// getD - If constraint is a distance, returns D.
432       /// Otherwise assert.
433       const SCEV *getD() const;
434 
435       /// getAssociatedLoop - Returns the loop associated with this constraint.
436       const Loop *getAssociatedLoop() const;
437 
438       /// setPoint - Change a constraint to Point.
439       void setPoint(const SCEV *X, const SCEV *Y, const Loop *CurrentLoop);
440 
441       /// setLine - Change a constraint to Line.
442       void setLine(const SCEV *A, const SCEV *B,
443                    const SCEV *C, const Loop *CurrentLoop);
444 
445       /// setDistance - Change a constraint to Distance.
446       void setDistance(const SCEV *D, const Loop *CurrentLoop);
447 
448       /// setEmpty - Change a constraint to Empty.
449       void setEmpty();
450 
451       /// setAny - Change a constraint to Any.
452       void setAny(ScalarEvolution *SE);
453 
454       /// dump - For debugging purposes. Dumps the constraint
455       /// out to OS.
456       void dump(raw_ostream &OS) const;
457     };
458 
459     /// establishNestingLevels - Examines the loop nesting of the Src and Dst
460     /// instructions and establishes their shared loops. Sets the variables
461     /// CommonLevels, SrcLevels, and MaxLevels.
462     /// The source and destination instructions needn't be contained in the same
463     /// loop. The routine establishNestingLevels finds the level of most deeply
464     /// nested loop that contains them both, CommonLevels. An instruction that's
465     /// not contained in a loop is at level = 0. MaxLevels is equal to the level
466     /// of the source plus the level of the destination, minus CommonLevels.
467     /// This lets us allocate vectors MaxLevels in length, with room for every
468     /// distinct loop referenced in both the source and destination subscripts.
469     /// The variable SrcLevels is the nesting depth of the source instruction.
470     /// It's used to help calculate distinct loops referenced by the destination.
471     /// Here's the map from loops to levels:
472     ///            0 - unused
473     ///            1 - outermost common loop
474     ///          ... - other common loops
475     /// CommonLevels - innermost common loop
476     ///          ... - loops containing Src but not Dst
477     ///    SrcLevels - innermost loop containing Src but not Dst
478     ///          ... - loops containing Dst but not Src
479     ///    MaxLevels - innermost loop containing Dst but not Src
480     /// Consider the follow code fragment:
481     ///    for (a = ...) {
482     ///      for (b = ...) {
483     ///        for (c = ...) {
484     ///          for (d = ...) {
485     ///            A[] = ...;
486     ///          }
487     ///        }
488     ///        for (e = ...) {
489     ///          for (f = ...) {
490     ///            for (g = ...) {
491     ///              ... = A[];
492     ///            }
493     ///          }
494     ///        }
495     ///      }
496     ///    }
497     /// If we're looking at the possibility of a dependence between the store
498     /// to A (the Src) and the load from A (the Dst), we'll note that they
499     /// have 2 loops in common, so CommonLevels will equal 2 and the direction
500     /// vector for Result will have 2 entries. SrcLevels = 4 and MaxLevels = 7.
501     /// A map from loop names to level indices would look like
502     ///     a - 1
503     ///     b - 2 = CommonLevels
504     ///     c - 3
505     ///     d - 4 = SrcLevels
506     ///     e - 5
507     ///     f - 6
508     ///     g - 7 = MaxLevels
509     void establishNestingLevels(const Instruction *Src,
510                                 const Instruction *Dst);
511 
512     unsigned CommonLevels, SrcLevels, MaxLevels;
513 
514     /// mapSrcLoop - Given one of the loops containing the source, return
515     /// its level index in our numbering scheme.
516     unsigned mapSrcLoop(const Loop *SrcLoop) const;
517 
518     /// mapDstLoop - Given one of the loops containing the destination,
519     /// return its level index in our numbering scheme.
520     unsigned mapDstLoop(const Loop *DstLoop) const;
521 
522     /// isLoopInvariant - Returns true if Expression is loop invariant
523     /// in LoopNest.
524     bool isLoopInvariant(const SCEV *Expression, const Loop *LoopNest) const;
525 
526     /// Makes sure all subscript pairs share the same integer type by
527     /// sign-extending as necessary.
528     /// Sign-extending a subscript is safe because getelementptr assumes the
529     /// array subscripts are signed.
530     void unifySubscriptType(ArrayRef<Subscript *> Pairs);
531 
532     /// removeMatchingExtensions - Examines a subscript pair.
533     /// If the source and destination are identically sign (or zero)
534     /// extended, it strips off the extension in an effort to
535     /// simplify the actual analysis.
536     void removeMatchingExtensions(Subscript *Pair);
537 
538     /// collectCommonLoops - Finds the set of loops from the LoopNest that
539     /// have a level <= CommonLevels and are referred to by the SCEV Expression.
540     void collectCommonLoops(const SCEV *Expression,
541                             const Loop *LoopNest,
542                             SmallBitVector &Loops) const;
543 
544     /// checkSrcSubscript - Examines the SCEV Src, returning true iff it's
545     /// linear. Collect the set of loops mentioned by Src.
546     bool checkSrcSubscript(const SCEV *Src,
547                            const Loop *LoopNest,
548                            SmallBitVector &Loops);
549 
550     /// checkDstSubscript - Examines the SCEV Dst, returning true iff it's
551     /// linear. Collect the set of loops mentioned by Dst.
552     bool checkDstSubscript(const SCEV *Dst,
553                            const Loop *LoopNest,
554                            SmallBitVector &Loops);
555 
556     /// isKnownPredicate - Compare X and Y using the predicate Pred.
557     /// Basically a wrapper for SCEV::isKnownPredicate,
558     /// but tries harder, especially in the presence of sign and zero
559     /// extensions and symbolics.
560     bool isKnownPredicate(ICmpInst::Predicate Pred,
561                           const SCEV *X,
562                           const SCEV *Y) const;
563 
564     /// isKnownLessThan - Compare to see if S is less than Size
565     /// Another wrapper for isKnownNegative(S - max(Size, 1)) with some extra
566     /// checking if S is an AddRec and we can prove lessthan using the loop
567     /// bounds.
568     bool isKnownLessThan(const SCEV *S, const SCEV *Size) const;
569 
570     /// isKnownNonNegative - Compare to see if S is known not to be negative
571     /// Uses the fact that S comes from Ptr, which may be an inbound GEP,
572     /// Proving there is no wrapping going on.
573     bool isKnownNonNegative(const SCEV *S, const Value *Ptr) const;
574 
575     /// collectUpperBound - All subscripts are the same type (on my machine,
576     /// an i64). The loop bound may be a smaller type. collectUpperBound
577     /// find the bound, if available, and zero extends it to the Type T.
578     /// (I zero extend since the bound should always be >= 0.)
579     /// If no upper bound is available, return NULL.
580     const SCEV *collectUpperBound(const Loop *l, Type *T) const;
581 
582     /// collectConstantUpperBound - Calls collectUpperBound(), then
583     /// attempts to cast it to SCEVConstant. If the cast fails,
584     /// returns NULL.
585     const SCEVConstant *collectConstantUpperBound(const Loop *l, Type *T) const;
586 
587     /// classifyPair - Examines the subscript pair (the Src and Dst SCEVs)
588     /// and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear.
589     /// Collects the associated loops in a set.
590     Subscript::ClassificationKind classifyPair(const SCEV *Src,
591                                            const Loop *SrcLoopNest,
592                                            const SCEV *Dst,
593                                            const Loop *DstLoopNest,
594                                            SmallBitVector &Loops);
595 
596     /// testZIV - Tests the ZIV subscript pair (Src and Dst) for dependence.
597     /// Returns true if any possible dependence is disproved.
598     /// If there might be a dependence, returns false.
599     /// If the dependence isn't proven to exist,
600     /// marks the Result as inconsistent.
601     bool testZIV(const SCEV *Src,
602                  const SCEV *Dst,
603                  FullDependence &Result) const;
604 
605     /// testSIV - Tests the SIV subscript pair (Src and Dst) for dependence.
606     /// Things of the form [c1 + a1*i] and [c2 + a2*j], where
607     /// i and j are induction variables, c1 and c2 are loop invariant,
608     /// and a1 and a2 are constant.
609     /// Returns true if any possible dependence is disproved.
610     /// If there might be a dependence, returns false.
611     /// Sets appropriate direction vector entry and, when possible,
612     /// the distance vector entry.
613     /// If the dependence isn't proven to exist,
614     /// marks the Result as inconsistent.
615     bool testSIV(const SCEV *Src,
616                  const SCEV *Dst,
617                  unsigned &Level,
618                  FullDependence &Result,
619                  Constraint &NewConstraint,
620                  const SCEV *&SplitIter) const;
621 
622     /// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence.
623     /// Things of the form [c1 + a1*i] and [c2 + a2*j]
624     /// where i and j are induction variables, c1 and c2 are loop invariant,
625     /// and a1 and a2 are constant.
626     /// With minor algebra, this test can also be used for things like
627     /// [c1 + a1*i + a2*j][c2].
628     /// Returns true if any possible dependence is disproved.
629     /// If there might be a dependence, returns false.
630     /// Marks the Result as inconsistent.
631     bool testRDIV(const SCEV *Src,
632                   const SCEV *Dst,
633                   FullDependence &Result) const;
634 
635     /// testMIV - Tests the MIV subscript pair (Src and Dst) for dependence.
636     /// Returns true if dependence disproved.
637     /// Can sometimes refine direction vectors.
638     bool testMIV(const SCEV *Src,
639                  const SCEV *Dst,
640                  const SmallBitVector &Loops,
641                  FullDependence &Result) const;
642 
643     /// strongSIVtest - Tests the strong SIV subscript pair (Src and Dst)
644     /// for dependence.
645     /// Things of the form [c1 + a*i] and [c2 + a*i],
646     /// where i is an induction variable, c1 and c2 are loop invariant,
647     /// and a is a constant
648     /// Returns true if any possible dependence is disproved.
649     /// If there might be a dependence, returns false.
650     /// Sets appropriate direction and distance.
651     bool strongSIVtest(const SCEV *Coeff,
652                        const SCEV *SrcConst,
653                        const SCEV *DstConst,
654                        const Loop *CurrentLoop,
655                        unsigned Level,
656                        FullDependence &Result,
657                        Constraint &NewConstraint) const;
658 
659     /// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair
660     /// (Src and Dst) for dependence.
661     /// Things of the form [c1 + a*i] and [c2 - a*i],
662     /// where i is an induction variable, c1 and c2 are loop invariant,
663     /// and a is a constant.
664     /// Returns true if any possible dependence is disproved.
665     /// If there might be a dependence, returns false.
666     /// Sets appropriate direction entry.
667     /// Set consistent to false.
668     /// Marks the dependence as splitable.
669     bool weakCrossingSIVtest(const SCEV *SrcCoeff,
670                              const SCEV *SrcConst,
671                              const SCEV *DstConst,
672                              const Loop *CurrentLoop,
673                              unsigned Level,
674                              FullDependence &Result,
675                              Constraint &NewConstraint,
676                              const SCEV *&SplitIter) const;
677 
678     /// ExactSIVtest - Tests the SIV subscript pair
679     /// (Src and Dst) for dependence.
680     /// Things of the form [c1 + a1*i] and [c2 + a2*i],
681     /// where i is an induction variable, c1 and c2 are loop invariant,
682     /// and a1 and a2 are constant.
683     /// Returns true if any possible dependence is disproved.
684     /// If there might be a dependence, returns false.
685     /// Sets appropriate direction entry.
686     /// Set consistent to false.
687     bool exactSIVtest(const SCEV *SrcCoeff,
688                       const SCEV *DstCoeff,
689                       const SCEV *SrcConst,
690                       const SCEV *DstConst,
691                       const Loop *CurrentLoop,
692                       unsigned Level,
693                       FullDependence &Result,
694                       Constraint &NewConstraint) const;
695 
696     /// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair
697     /// (Src and Dst) for dependence.
698     /// Things of the form [c1] and [c2 + a*i],
699     /// where i is an induction variable, c1 and c2 are loop invariant,
700     /// and a is a constant. See also weakZeroDstSIVtest.
701     /// Returns true if any possible dependence is disproved.
702     /// If there might be a dependence, returns false.
703     /// Sets appropriate direction entry.
704     /// Set consistent to false.
705     /// If loop peeling will break the dependence, mark appropriately.
706     bool weakZeroSrcSIVtest(const SCEV *DstCoeff,
707                             const SCEV *SrcConst,
708                             const SCEV *DstConst,
709                             const Loop *CurrentLoop,
710                             unsigned Level,
711                             FullDependence &Result,
712                             Constraint &NewConstraint) const;
713 
714     /// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair
715     /// (Src and Dst) for dependence.
716     /// Things of the form [c1 + a*i] and [c2],
717     /// where i is an induction variable, c1 and c2 are loop invariant,
718     /// and a is a constant. See also weakZeroSrcSIVtest.
719     /// Returns true if any possible dependence is disproved.
720     /// If there might be a dependence, returns false.
721     /// Sets appropriate direction entry.
722     /// Set consistent to false.
723     /// If loop peeling will break the dependence, mark appropriately.
724     bool weakZeroDstSIVtest(const SCEV *SrcCoeff,
725                             const SCEV *SrcConst,
726                             const SCEV *DstConst,
727                             const Loop *CurrentLoop,
728                             unsigned Level,
729                             FullDependence &Result,
730                             Constraint &NewConstraint) const;
731 
732     /// exactRDIVtest - Tests the RDIV subscript pair for dependence.
733     /// Things of the form [c1 + a*i] and [c2 + b*j],
734     /// where i and j are induction variable, c1 and c2 are loop invariant,
735     /// and a and b are constants.
736     /// Returns true if any possible dependence is disproved.
737     /// Marks the result as inconsistent.
738     /// Works in some cases that symbolicRDIVtest doesn't,
739     /// and vice versa.
740     bool exactRDIVtest(const SCEV *SrcCoeff,
741                        const SCEV *DstCoeff,
742                        const SCEV *SrcConst,
743                        const SCEV *DstConst,
744                        const Loop *SrcLoop,
745                        const Loop *DstLoop,
746                        FullDependence &Result) const;
747 
748     /// symbolicRDIVtest - Tests the RDIV subscript pair for dependence.
749     /// Things of the form [c1 + a*i] and [c2 + b*j],
750     /// where i and j are induction variable, c1 and c2 are loop invariant,
751     /// and a and b are constants.
752     /// Returns true if any possible dependence is disproved.
753     /// Marks the result as inconsistent.
754     /// Works in some cases that exactRDIVtest doesn't,
755     /// and vice versa. Can also be used as a backup for
756     /// ordinary SIV tests.
757     bool symbolicRDIVtest(const SCEV *SrcCoeff,
758                           const SCEV *DstCoeff,
759                           const SCEV *SrcConst,
760                           const SCEV *DstConst,
761                           const Loop *SrcLoop,
762                           const Loop *DstLoop) const;
763 
764     /// gcdMIVtest - Tests an MIV subscript pair for dependence.
765     /// Returns true if any possible dependence is disproved.
766     /// Marks the result as inconsistent.
767     /// Can sometimes disprove the equal direction for 1 or more loops.
768     //  Can handle some symbolics that even the SIV tests don't get,
769     /// so we use it as a backup for everything.
770     bool gcdMIVtest(const SCEV *Src,
771                     const SCEV *Dst,
772                     FullDependence &Result) const;
773 
774     /// banerjeeMIVtest - Tests an MIV subscript pair for dependence.
775     /// Returns true if any possible dependence is disproved.
776     /// Marks the result as inconsistent.
777     /// Computes directions.
778     bool banerjeeMIVtest(const SCEV *Src,
779                          const SCEV *Dst,
780                          const SmallBitVector &Loops,
781                          FullDependence &Result) const;
782 
783     /// collectCoefficientInfo - Walks through the subscript,
784     /// collecting each coefficient, the associated loop bounds,
785     /// and recording its positive and negative parts for later use.
786     CoefficientInfo *collectCoeffInfo(const SCEV *Subscript,
787                                       bool SrcFlag,
788                                       const SCEV *&Constant) const;
789 
790     /// getPositivePart - X^+ = max(X, 0).
791     ///
792     const SCEV *getPositivePart(const SCEV *X) const;
793 
794     /// getNegativePart - X^- = min(X, 0).
795     ///
796     const SCEV *getNegativePart(const SCEV *X) const;
797 
798     /// getLowerBound - Looks through all the bounds info and
799     /// computes the lower bound given the current direction settings
800     /// at each level.
801     const SCEV *getLowerBound(BoundInfo *Bound) const;
802 
803     /// getUpperBound - Looks through all the bounds info and
804     /// computes the upper bound given the current direction settings
805     /// at each level.
806     const SCEV *getUpperBound(BoundInfo *Bound) const;
807 
808     /// exploreDirections - Hierarchically expands the direction vector
809     /// search space, combining the directions of discovered dependences
810     /// in the DirSet field of Bound. Returns the number of distinct
811     /// dependences discovered. If the dependence is disproved,
812     /// it will return 0.
813     unsigned exploreDirections(unsigned Level,
814                                CoefficientInfo *A,
815                                CoefficientInfo *B,
816                                BoundInfo *Bound,
817                                const SmallBitVector &Loops,
818                                unsigned &DepthExpanded,
819                                const SCEV *Delta) const;
820 
821     /// testBounds - Returns true iff the current bounds are plausible.
822     bool testBounds(unsigned char DirKind,
823                     unsigned Level,
824                     BoundInfo *Bound,
825                     const SCEV *Delta) const;
826 
827     /// findBoundsALL - Computes the upper and lower bounds for level K
828     /// using the * direction. Records them in Bound.
829     void findBoundsALL(CoefficientInfo *A,
830                        CoefficientInfo *B,
831                        BoundInfo *Bound,
832                        unsigned K) const;
833 
834     /// findBoundsLT - Computes the upper and lower bounds for level K
835     /// using the < direction. Records them in Bound.
836     void findBoundsLT(CoefficientInfo *A,
837                       CoefficientInfo *B,
838                       BoundInfo *Bound,
839                       unsigned K) const;
840 
841     /// findBoundsGT - Computes the upper and lower bounds for level K
842     /// using the > direction. Records them in Bound.
843     void findBoundsGT(CoefficientInfo *A,
844                       CoefficientInfo *B,
845                       BoundInfo *Bound,
846                       unsigned K) const;
847 
848     /// findBoundsEQ - Computes the upper and lower bounds for level K
849     /// using the = direction. Records them in Bound.
850     void findBoundsEQ(CoefficientInfo *A,
851                       CoefficientInfo *B,
852                       BoundInfo *Bound,
853                       unsigned K) const;
854 
855     /// intersectConstraints - Updates X with the intersection
856     /// of the Constraints X and Y. Returns true if X has changed.
857     bool intersectConstraints(Constraint *X,
858                               const Constraint *Y);
859 
860     /// propagate - Review the constraints, looking for opportunities
861     /// to simplify a subscript pair (Src and Dst).
862     /// Return true if some simplification occurs.
863     /// If the simplification isn't exact (that is, if it is conservative
864     /// in terms of dependence), set consistent to false.
865     bool propagate(const SCEV *&Src,
866                    const SCEV *&Dst,
867                    SmallBitVector &Loops,
868                    SmallVectorImpl<Constraint> &Constraints,
869                    bool &Consistent);
870 
871     /// propagateDistance - Attempt to propagate a distance
872     /// constraint into a subscript pair (Src and Dst).
873     /// Return true if some simplification occurs.
874     /// If the simplification isn't exact (that is, if it is conservative
875     /// in terms of dependence), set consistent to false.
876     bool propagateDistance(const SCEV *&Src,
877                            const SCEV *&Dst,
878                            Constraint &CurConstraint,
879                            bool &Consistent);
880 
881     /// propagatePoint - Attempt to propagate a point
882     /// constraint into a subscript pair (Src and Dst).
883     /// Return true if some simplification occurs.
884     bool propagatePoint(const SCEV *&Src,
885                         const SCEV *&Dst,
886                         Constraint &CurConstraint);
887 
888     /// propagateLine - Attempt to propagate a line
889     /// constraint into a subscript pair (Src and Dst).
890     /// Return true if some simplification occurs.
891     /// If the simplification isn't exact (that is, if it is conservative
892     /// in terms of dependence), set consistent to false.
893     bool propagateLine(const SCEV *&Src,
894                        const SCEV *&Dst,
895                        Constraint &CurConstraint,
896                        bool &Consistent);
897 
898     /// findCoefficient - Given a linear SCEV,
899     /// return the coefficient corresponding to specified loop.
900     /// If there isn't one, return the SCEV constant 0.
901     /// For example, given a*i + b*j + c*k, returning the coefficient
902     /// corresponding to the j loop would yield b.
903     const SCEV *findCoefficient(const SCEV *Expr,
904                                 const Loop *TargetLoop) const;
905 
906     /// zeroCoefficient - Given a linear SCEV,
907     /// return the SCEV given by zeroing out the coefficient
908     /// corresponding to the specified loop.
909     /// For example, given a*i + b*j + c*k, zeroing the coefficient
910     /// corresponding to the j loop would yield a*i + c*k.
911     const SCEV *zeroCoefficient(const SCEV *Expr,
912                                 const Loop *TargetLoop) const;
913 
914     /// addToCoefficient - Given a linear SCEV Expr,
915     /// return the SCEV given by adding some Value to the
916     /// coefficient corresponding to the specified TargetLoop.
917     /// For example, given a*i + b*j + c*k, adding 1 to the coefficient
918     /// corresponding to the j loop would yield a*i + (b+1)*j + c*k.
919     const SCEV *addToCoefficient(const SCEV *Expr,
920                                  const Loop *TargetLoop,
921                                  const SCEV *Value)  const;
922 
923     /// updateDirection - Update direction vector entry
924     /// based on the current constraint.
925     void updateDirection(Dependence::DVEntry &Level,
926                          const Constraint &CurConstraint) const;
927 
928     /// Given a linear access function, tries to recover subscripts
929     /// for each dimension of the array element access.
930     bool tryDelinearize(Instruction *Src, Instruction *Dst,
931                         SmallVectorImpl<Subscript> &Pair);
932 
933     /// Tries to delinearize access function for a fixed size multi-dimensional
934     /// array, by deriving subscripts from GEP instructions. Returns true upon
935     /// success and false otherwise.
936     bool tryDelinearizeFixedSize(Instruction *Src, Instruction *Dst,
937                                  const SCEV *SrcAccessFn,
938                                  const SCEV *DstAccessFn,
939                                  SmallVectorImpl<const SCEV *> &SrcSubscripts,
940                                  SmallVectorImpl<const SCEV *> &DstSubscripts);
941 
942     /// Tries to delinearize access function for a multi-dimensional array with
943     /// symbolic runtime sizes.
944     /// Returns true upon success and false otherwise.
945     bool tryDelinearizeParametricSize(
946         Instruction *Src, Instruction *Dst, const SCEV *SrcAccessFn,
947         const SCEV *DstAccessFn, SmallVectorImpl<const SCEV *> &SrcSubscripts,
948         SmallVectorImpl<const SCEV *> &DstSubscripts);
949 
950     /// checkSubscript - Helper function for checkSrcSubscript and
951     /// checkDstSubscript to avoid duplicate code
952     bool checkSubscript(const SCEV *Expr, const Loop *LoopNest,
953                         SmallBitVector &Loops, bool IsSrc);
954   }; // class DependenceInfo
955 
956   /// AnalysisPass to compute dependence information in a function
957   class DependenceAnalysis : public AnalysisInfoMixin<DependenceAnalysis> {
958   public:
959     typedef DependenceInfo Result;
960     Result run(Function &F, FunctionAnalysisManager &FAM);
961 
962   private:
963     static AnalysisKey Key;
964     friend struct AnalysisInfoMixin<DependenceAnalysis>;
965   }; // class DependenceAnalysis
966 
967   /// Printer pass to dump DA results.
968   struct DependenceAnalysisPrinterPass
969       : public PassInfoMixin<DependenceAnalysisPrinterPass> {
970     DependenceAnalysisPrinterPass(raw_ostream &OS) : OS(OS) {}
971 
972     PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM);
973 
974   private:
975     raw_ostream &OS;
976   }; // class DependenceAnalysisPrinterPass
977 
978   /// Legacy pass manager pass to access dependence information
979   class DependenceAnalysisWrapperPass : public FunctionPass {
980   public:
981     static char ID; // Class identification, replacement for typeinfo
982     DependenceAnalysisWrapperPass();
983 
984     bool runOnFunction(Function &F) override;
985     void releaseMemory() override;
986     void getAnalysisUsage(AnalysisUsage &) const override;
987     void print(raw_ostream &, const Module * = nullptr) const override;
988     DependenceInfo &getDI() const;
989 
990   private:
991     std::unique_ptr<DependenceInfo> info;
992   }; // class DependenceAnalysisWrapperPass
993 
994   /// createDependenceAnalysisPass - This creates an instance of the
995   /// DependenceAnalysis wrapper pass.
996   FunctionPass *createDependenceAnalysisWrapperPass();
997 
998 } // namespace llvm
999 
1000 #endif
1001