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DependenceAnalysis.h
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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 
44 #include "llvm/IR/Instructions.h"
45 #include "llvm/Pass.h"
46 
47 namespace llvm {
48 template <typename T> class ArrayRef;
49  class Loop;
50  class LoopInfo;
51  class ScalarEvolution;
52  class SCEV;
53  class SCEVConstant;
54  class raw_ostream;
55 
56  /// Dependence - This class represents a dependence between two memory
57  /// memory references in a function. It contains minimal information and
58  /// is used in the very common situation where the compiler is unable to
59  /// determine anything beyond the existence of a dependence; that is, it
60  /// represents a confused dependence (see also FullDependence). In most
61  /// cases (for output, flow, and anti dependences), the dependence implies
62  /// an ordering, where the source must precede the destination; in contrast,
63  /// input dependences are unordered.
64  ///
65  /// When a dependence graph is built, each Dependence will be a member of
66  /// the set of predecessor edges for its destination instruction and a set
67  /// if successor edges for its source instruction. These sets are represented
68  /// as singly-linked lists, with the "next" fields stored in the dependence
69  /// itelf.
70  class Dependence {
71  protected:
72  Dependence(Dependence &&) = default;
73  Dependence &operator=(Dependence &&) = default;
74 
75  public:
77  Instruction *Destination) :
78  Src(Source),
79  Dst(Destination),
80  NextPredecessor(nullptr),
81  NextSuccessor(nullptr) {}
82  virtual ~Dependence() {}
83 
84  /// Dependence::DVEntry - Each level in the distance/direction vector
85  /// has a direction (or perhaps a union of several directions), and
86  /// perhaps a distance.
87  struct DVEntry {
88  enum { NONE = 0,
89  LT = 1,
90  EQ = 2,
91  LE = 3,
92  GT = 4,
93  NE = 5,
94  GE = 6,
95  ALL = 7 };
96  unsigned char Direction : 3; // Init to ALL, then refine.
97  bool Scalar : 1; // Init to true.
98  bool PeelFirst : 1; // Peeling the first iteration will break dependence.
99  bool PeelLast : 1; // Peeling the last iteration will break the dependence.
100  bool Splitable : 1; // Splitting the loop will break dependence.
101  const SCEV *Distance; // NULL implies no distance available.
103  PeelLast(false), Splitable(false), Distance(nullptr) { }
104  };
105 
106  /// getSrc - Returns the source instruction for this dependence.
107  ///
108  Instruction *getSrc() const { return Src; }
109 
110  /// getDst - Returns the destination instruction for this dependence.
111  ///
112  Instruction *getDst() const { return Dst; }
113 
114  /// isInput - Returns true if this is an input dependence.
115  ///
116  bool isInput() const;
117 
118  /// isOutput - Returns true if this is an output dependence.
119  ///
120  bool isOutput() const;
121 
122  /// isFlow - Returns true if this is a flow (aka true) dependence.
123  ///
124  bool isFlow() const;
125 
126  /// isAnti - Returns true if this is an anti dependence.
127  ///
128  bool isAnti() const;
129 
130  /// isOrdered - Returns true if dependence is Output, Flow, or Anti
131  ///
132  bool isOrdered() const { return isOutput() || isFlow() || isAnti(); }
133 
134  /// isUnordered - Returns true if dependence is Input
135  ///
136  bool isUnordered() const { return isInput(); }
137 
138  /// isLoopIndependent - Returns true if this is a loop-independent
139  /// dependence.
140  virtual bool isLoopIndependent() const { return true; }
141 
142  /// isConfused - Returns true if this dependence is confused
143  /// (the compiler understands nothing and makes worst-case
144  /// assumptions).
145  virtual bool isConfused() const { return true; }
146 
147  /// isConsistent - Returns true if this dependence is consistent
148  /// (occurs every time the source and destination are executed).
149  virtual bool isConsistent() const { return false; }
150 
151  /// getLevels - Returns the number of common loops surrounding the
152  /// source and destination of the dependence.
153  virtual unsigned getLevels() const { return 0; }
154 
155  /// getDirection - Returns the direction associated with a particular
156  /// level.
157  virtual unsigned getDirection(unsigned Level) const { return DVEntry::ALL; }
158 
159  /// getDistance - Returns the distance (or NULL) associated with a
160  /// particular level.
161  virtual const SCEV *getDistance(unsigned Level) const { return nullptr; }
162 
163  /// isPeelFirst - Returns true if peeling the first iteration from
164  /// this loop will break this dependence.
165  virtual bool isPeelFirst(unsigned Level) const { return false; }
166 
167  /// isPeelLast - Returns true if peeling the last iteration from
168  /// this loop will break this dependence.
169  virtual bool isPeelLast(unsigned Level) const { return false; }
170 
171  /// isSplitable - Returns true if splitting this loop will break
172  /// the dependence.
173  virtual bool isSplitable(unsigned Level) const { return false; }
174 
175  /// isScalar - Returns true if a particular level is scalar; that is,
176  /// if no subscript in the source or destination mention the induction
177  /// variable associated with the loop at this level.
178  virtual bool isScalar(unsigned Level) const;
179 
180  /// getNextPredecessor - Returns the value of the NextPredecessor
181  /// field.
182  const Dependence *getNextPredecessor() const { return NextPredecessor; }
183 
184  /// getNextSuccessor - Returns the value of the NextSuccessor
185  /// field.
186  const Dependence *getNextSuccessor() const { return NextSuccessor; }
187 
188  /// setNextPredecessor - Sets the value of the NextPredecessor
189  /// field.
190  void setNextPredecessor(const Dependence *pred) { NextPredecessor = pred; }
191 
192  /// setNextSuccessor - Sets the value of the NextSuccessor
193  /// field.
194  void setNextSuccessor(const Dependence *succ) { NextSuccessor = succ; }
195 
196  /// dump - For debugging purposes, dumps a dependence to OS.
197  ///
198  void dump(raw_ostream &OS) const;
199 
200  private:
201  Instruction *Src, *Dst;
202  const Dependence *NextPredecessor, *NextSuccessor;
203  friend class DependenceInfo;
204  };
205 
206  /// FullDependence - This class represents a dependence between two memory
207  /// references in a function. It contains detailed information about the
208  /// dependence (direction vectors, etc.) and is used when the compiler is
209  /// able to accurately analyze the interaction of the references; that is,
210  /// it is not a confused dependence (see Dependence). In most cases
211  /// (for output, flow, and anti dependences), the dependence implies an
212  /// ordering, where the source must precede the destination; in contrast,
213  /// input dependences are unordered.
214  class FullDependence final : public Dependence {
215  public:
216  FullDependence(Instruction *Src, Instruction *Dst, bool LoopIndependent,
217  unsigned Levels);
218 
219  /// isLoopIndependent - Returns true if this is a loop-independent
220  /// dependence.
221  bool isLoopIndependent() const override { return LoopIndependent; }
222 
223  /// isConfused - Returns true if this dependence is confused
224  /// (the compiler understands nothing and makes worst-case
225  /// assumptions).
226  bool isConfused() const override { return false; }
227 
228  /// isConsistent - Returns true if this dependence is consistent
229  /// (occurs every time the source and destination are executed).
230  bool isConsistent() const override { return Consistent; }
231 
232  /// getLevels - Returns the number of common loops surrounding the
233  /// source and destination of the dependence.
234  unsigned getLevels() const override { return Levels; }
235 
236  /// getDirection - Returns the direction associated with a particular
237  /// level.
238  unsigned getDirection(unsigned Level) const override;
239 
240  /// getDistance - Returns the distance (or NULL) associated with a
241  /// particular level.
242  const SCEV *getDistance(unsigned Level) const override;
243 
244  /// isPeelFirst - Returns true if peeling the first iteration from
245  /// this loop will break this dependence.
246  bool isPeelFirst(unsigned Level) const override;
247 
248  /// isPeelLast - Returns true if peeling the last iteration from
249  /// this loop will break this dependence.
250  bool isPeelLast(unsigned Level) const override;
251 
252  /// isSplitable - Returns true if splitting the loop will break
253  /// the dependence.
254  bool isSplitable(unsigned Level) const override;
255 
256  /// isScalar - Returns true if a particular level is scalar; that is,
257  /// if no subscript in the source or destination mention the induction
258  /// variable associated with the loop at this level.
259  bool isScalar(unsigned Level) const override;
260 
261  private:
262  unsigned short Levels;
263  bool LoopIndependent;
264  bool Consistent; // Init to true, then refine.
265  std::unique_ptr<DVEntry[]> DV;
266  friend class DependenceInfo;
267  };
268 
269  /// DependenceInfo - This class is the main dependence-analysis driver.
270  ///
272  public:
274  LoopInfo *LI)
275  : AA(AA), SE(SE), LI(LI), F(F) {}
276 
277  /// Handle transitive invalidation when the cached analysis results go away.
278  bool invalidate(Function &F, const PreservedAnalyses &PA,
280 
281  /// depends - Tests for a dependence between the Src and Dst instructions.
282  /// Returns NULL if no dependence; otherwise, returns a Dependence (or a
283  /// FullDependence) with as much information as can be gleaned.
284  /// The flag PossiblyLoopIndependent should be set by the caller
285  /// if it appears that control flow can reach from Src to Dst
286  /// without traversing a loop back edge.
287  std::unique_ptr<Dependence> depends(Instruction *Src,
288  Instruction *Dst,
289  bool PossiblyLoopIndependent);
290 
291  /// getSplitIteration - Give a dependence that's splittable at some
292  /// particular level, return the iteration that should be used to split
293  /// the loop.
294  ///
295  /// Generally, the dependence analyzer will be used to build
296  /// a dependence graph for a function (basically a map from instructions
297  /// to dependences). Looking for cycles in the graph shows us loops
298  /// that cannot be trivially vectorized/parallelized.
299  ///
300  /// We can try to improve the situation by examining all the dependences
301  /// that make up the cycle, looking for ones we can break.
302  /// Sometimes, peeling the first or last iteration of a loop will break
303  /// dependences, and there are flags for those possibilities.
304  /// Sometimes, splitting a loop at some other iteration will do the trick,
305  /// and we've got a flag for that case. Rather than waste the space to
306  /// record the exact iteration (since we rarely know), we provide
307  /// a method that calculates the iteration. It's a drag that it must work
308  /// from scratch, but wonderful in that it's possible.
309  ///
310  /// Here's an example:
311  ///
312  /// for (i = 0; i < 10; i++)
313  /// A[i] = ...
314  /// ... = A[11 - i]
315  ///
316  /// There's a loop-carried flow dependence from the store to the load,
317  /// found by the weak-crossing SIV test. The dependence will have a flag,
318  /// indicating that the dependence can be broken by splitting the loop.
319  /// Calling getSplitIteration will return 5.
320  /// Splitting the loop breaks the dependence, like so:
321  ///
322  /// for (i = 0; i <= 5; i++)
323  /// A[i] = ...
324  /// ... = A[11 - i]
325  /// for (i = 6; i < 10; i++)
326  /// A[i] = ...
327  /// ... = A[11 - i]
328  ///
329  /// breaks the dependence and allows us to vectorize/parallelize
330  /// both loops.
331  const SCEV *getSplitIteration(const Dependence &Dep, unsigned Level);
332 
333  Function *getFunction() const { return F; }
334 
335  private:
336  AliasAnalysis *AA;
337  ScalarEvolution *SE;
338  LoopInfo *LI;
339  Function *F;
340 
341  /// Subscript - This private struct represents a pair of subscripts from
342  /// a pair of potentially multi-dimensional array references. We use a
343  /// vector of them to guide subscript partitioning.
344  struct Subscript {
345  const SCEV *Src;
346  const SCEV *Dst;
347  enum ClassificationKind { ZIV, SIV, RDIV, MIV, NonLinear } Classification;
349  SmallBitVector GroupLoops;
350  SmallBitVector Group;
351  };
352 
353  struct CoefficientInfo {
354  const SCEV *Coeff;
355  const SCEV *PosPart;
356  const SCEV *NegPart;
357  const SCEV *Iterations;
358  };
359 
360  struct BoundInfo {
361  const SCEV *Iterations;
362  const SCEV *Upper[8];
363  const SCEV *Lower[8];
364  unsigned char Direction;
365  unsigned char DirSet;
366  };
367 
368  /// Constraint - This private class represents a constraint, as defined
369  /// in the paper
370  ///
371  /// Practical Dependence Testing
372  /// Goff, Kennedy, Tseng
373  /// PLDI 1991
374  ///
375  /// There are 5 kinds of constraint, in a hierarchy.
376  /// 1) Any - indicates no constraint, any dependence is possible.
377  /// 2) Line - A line ax + by = c, where a, b, and c are parameters,
378  /// representing the dependence equation.
379  /// 3) Distance - The value d of the dependence distance;
380  /// 4) Point - A point <x, y> representing the dependence from
381  /// iteration x to iteration y.
382  /// 5) Empty - No dependence is possible.
383  class Constraint {
384  private:
385  enum ConstraintKind { Empty, Point, Distance, Line, Any } Kind;
386  ScalarEvolution *SE;
387  const SCEV *A;
388  const SCEV *B;
389  const SCEV *C;
390  const Loop *AssociatedLoop;
391 
392  public:
393  /// isEmpty - Return true if the constraint is of kind Empty.
394  bool isEmpty() const { return Kind == Empty; }
395 
396  /// isPoint - Return true if the constraint is of kind Point.
397  bool isPoint() const { return Kind == Point; }
398 
399  /// isDistance - Return true if the constraint is of kind Distance.
400  bool isDistance() const { return Kind == Distance; }
401 
402  /// isLine - Return true if the constraint is of kind Line.
403  /// Since Distance's can also be represented as Lines, we also return
404  /// true if the constraint is of kind Distance.
405  bool isLine() const { return Kind == Line || Kind == Distance; }
406 
407  /// isAny - Return true if the constraint is of kind Any;
408  bool isAny() const { return Kind == Any; }
409 
410  /// getX - If constraint is a point <X, Y>, returns X.
411  /// Otherwise assert.
412  const SCEV *getX() const;
413 
414  /// getY - If constraint is a point <X, Y>, returns Y.
415  /// Otherwise assert.
416  const SCEV *getY() const;
417 
418  /// getA - If constraint is a line AX + BY = C, returns A.
419  /// Otherwise assert.
420  const SCEV *getA() const;
421 
422  /// getB - If constraint is a line AX + BY = C, returns B.
423  /// Otherwise assert.
424  const SCEV *getB() const;
425 
426  /// getC - If constraint is a line AX + BY = C, returns C.
427  /// Otherwise assert.
428  const SCEV *getC() const;
429 
430  /// getD - If constraint is a distance, returns D.
431  /// Otherwise assert.
432  const SCEV *getD() const;
433 
434  /// getAssociatedLoop - Returns the loop associated with this constraint.
435  const Loop *getAssociatedLoop() const;
436 
437  /// setPoint - Change a constraint to Point.
438  void setPoint(const SCEV *X, const SCEV *Y, const Loop *CurrentLoop);
439 
440  /// setLine - Change a constraint to Line.
441  void setLine(const SCEV *A, const SCEV *B,
442  const SCEV *C, const Loop *CurrentLoop);
443 
444  /// setDistance - Change a constraint to Distance.
445  void setDistance(const SCEV *D, const Loop *CurrentLoop);
446 
447  /// setEmpty - Change a constraint to Empty.
448  void setEmpty();
449 
450  /// setAny - Change a constraint to Any.
451  void setAny(ScalarEvolution *SE);
452 
453  /// dump - For debugging purposes. Dumps the constraint
454  /// out to OS.
455  void dump(raw_ostream &OS) const;
456  };
457 
458  /// establishNestingLevels - Examines the loop nesting of the Src and Dst
459  /// instructions and establishes their shared loops. Sets the variables
460  /// CommonLevels, SrcLevels, and MaxLevels.
461  /// The source and destination instructions needn't be contained in the same
462  /// loop. The routine establishNestingLevels finds the level of most deeply
463  /// nested loop that contains them both, CommonLevels. An instruction that's
464  /// not contained in a loop is at level = 0. MaxLevels is equal to the level
465  /// of the source plus the level of the destination, minus CommonLevels.
466  /// This lets us allocate vectors MaxLevels in length, with room for every
467  /// distinct loop referenced in both the source and destination subscripts.
468  /// The variable SrcLevels is the nesting depth of the source instruction.
469  /// It's used to help calculate distinct loops referenced by the destination.
470  /// Here's the map from loops to levels:
471  /// 0 - unused
472  /// 1 - outermost common loop
473  /// ... - other common loops
474  /// CommonLevels - innermost common loop
475  /// ... - loops containing Src but not Dst
476  /// SrcLevels - innermost loop containing Src but not Dst
477  /// ... - loops containing Dst but not Src
478  /// MaxLevels - innermost loop containing Dst but not Src
479  /// Consider the follow code fragment:
480  /// for (a = ...) {
481  /// for (b = ...) {
482  /// for (c = ...) {
483  /// for (d = ...) {
484  /// A[] = ...;
485  /// }
486  /// }
487  /// for (e = ...) {
488  /// for (f = ...) {
489  /// for (g = ...) {
490  /// ... = A[];
491  /// }
492  /// }
493  /// }
494  /// }
495  /// }
496  /// If we're looking at the possibility of a dependence between the store
497  /// to A (the Src) and the load from A (the Dst), we'll note that they
498  /// have 2 loops in common, so CommonLevels will equal 2 and the direction
499  /// vector for Result will have 2 entries. SrcLevels = 4 and MaxLevels = 7.
500  /// A map from loop names to level indices would look like
501  /// a - 1
502  /// b - 2 = CommonLevels
503  /// c - 3
504  /// d - 4 = SrcLevels
505  /// e - 5
506  /// f - 6
507  /// g - 7 = MaxLevels
508  void establishNestingLevels(const Instruction *Src,
509  const Instruction *Dst);
510 
511  unsigned CommonLevels, SrcLevels, MaxLevels;
512 
513  /// mapSrcLoop - Given one of the loops containing the source, return
514  /// its level index in our numbering scheme.
515  unsigned mapSrcLoop(const Loop *SrcLoop) const;
516 
517  /// mapDstLoop - Given one of the loops containing the destination,
518  /// return its level index in our numbering scheme.
519  unsigned mapDstLoop(const Loop *DstLoop) const;
520 
521  /// isLoopInvariant - Returns true if Expression is loop invariant
522  /// in LoopNest.
523  bool isLoopInvariant(const SCEV *Expression, const Loop *LoopNest) const;
524 
525  /// Makes sure all subscript pairs share the same integer type by
526  /// sign-extending as necessary.
527  /// Sign-extending a subscript is safe because getelementptr assumes the
528  /// array subscripts are signed.
529  void unifySubscriptType(ArrayRef<Subscript *> Pairs);
530 
531  /// removeMatchingExtensions - Examines a subscript pair.
532  /// If the source and destination are identically sign (or zero)
533  /// extended, it strips off the extension in an effort to
534  /// simplify the actual analysis.
535  void removeMatchingExtensions(Subscript *Pair);
536 
537  /// collectCommonLoops - Finds the set of loops from the LoopNest that
538  /// have a level <= CommonLevels and are referred to by the SCEV Expression.
539  void collectCommonLoops(const SCEV *Expression,
540  const Loop *LoopNest,
541  SmallBitVector &Loops) const;
542 
543  /// checkSrcSubscript - Examines the SCEV Src, returning true iff it's
544  /// linear. Collect the set of loops mentioned by Src.
545  bool checkSrcSubscript(const SCEV *Src,
546  const Loop *LoopNest,
547  SmallBitVector &Loops);
548 
549  /// checkDstSubscript - Examines the SCEV Dst, returning true iff it's
550  /// linear. Collect the set of loops mentioned by Dst.
551  bool checkDstSubscript(const SCEV *Dst,
552  const Loop *LoopNest,
553  SmallBitVector &Loops);
554 
555  /// isKnownPredicate - Compare X and Y using the predicate Pred.
556  /// Basically a wrapper for SCEV::isKnownPredicate,
557  /// but tries harder, especially in the presence of sign and zero
558  /// extensions and symbolics.
559  bool isKnownPredicate(ICmpInst::Predicate Pred,
560  const SCEV *X,
561  const SCEV *Y) const;
562 
563  /// isKnownLessThan - Compare to see if S is less than Size
564  /// Another wrapper for isKnownNegative(S - max(Size, 1)) with some extra
565  /// checking if S is an AddRec and we can prove lessthan using the loop
566  /// bounds.
567  bool isKnownLessThan(const SCEV *S, const SCEV *Size) const;
568 
569  /// isKnownNonNegative - Compare to see if S is known not to be negative
570  /// Uses the fact that S comes from Ptr, which may be an inbound GEP,
571  /// Proving there is no wrapping going on.
572  bool isKnownNonNegative(const SCEV *S, const Value *Ptr) const;
573 
574  /// collectUpperBound - All subscripts are the same type (on my machine,
575  /// an i64). The loop bound may be a smaller type. collectUpperBound
576  /// find the bound, if available, and zero extends it to the Type T.
577  /// (I zero extend since the bound should always be >= 0.)
578  /// If no upper bound is available, return NULL.
579  const SCEV *collectUpperBound(const Loop *l, Type *T) const;
580 
581  /// collectConstantUpperBound - Calls collectUpperBound(), then
582  /// attempts to cast it to SCEVConstant. If the cast fails,
583  /// returns NULL.
584  const SCEVConstant *collectConstantUpperBound(const Loop *l, Type *T) const;
585 
586  /// classifyPair - Examines the subscript pair (the Src and Dst SCEVs)
587  /// and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear.
588  /// Collects the associated loops in a set.
589  Subscript::ClassificationKind classifyPair(const SCEV *Src,
590  const Loop *SrcLoopNest,
591  const SCEV *Dst,
592  const Loop *DstLoopNest,
593  SmallBitVector &Loops);
594 
595  /// testZIV - Tests the ZIV subscript pair (Src and Dst) for dependence.
596  /// Returns true if any possible dependence is disproved.
597  /// If there might be a dependence, returns false.
598  /// If the dependence isn't proven to exist,
599  /// marks the Result as inconsistent.
600  bool testZIV(const SCEV *Src,
601  const SCEV *Dst,
602  FullDependence &Result) const;
603 
604  /// testSIV - Tests the SIV subscript pair (Src and Dst) for dependence.
605  /// Things of the form [c1 + a1*i] and [c2 + a2*j], where
606  /// i and j are induction variables, c1 and c2 are loop invariant,
607  /// and a1 and a2 are constant.
608  /// Returns true if any possible dependence is disproved.
609  /// If there might be a dependence, returns false.
610  /// Sets appropriate direction vector entry and, when possible,
611  /// the distance vector entry.
612  /// If the dependence isn't proven to exist,
613  /// marks the Result as inconsistent.
614  bool testSIV(const SCEV *Src,
615  const SCEV *Dst,
616  unsigned &Level,
617  FullDependence &Result,
618  Constraint &NewConstraint,
619  const SCEV *&SplitIter) const;
620 
621  /// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence.
622  /// Things of the form [c1 + a1*i] and [c2 + a2*j]
623  /// where i and j are induction variables, c1 and c2 are loop invariant,
624  /// and a1 and a2 are constant.
625  /// With minor algebra, this test can also be used for things like
626  /// [c1 + a1*i + a2*j][c2].
627  /// Returns true if any possible dependence is disproved.
628  /// If there might be a dependence, returns false.
629  /// Marks the Result as inconsistent.
630  bool testRDIV(const SCEV *Src,
631  const SCEV *Dst,
632  FullDependence &Result) const;
633 
634  /// testMIV - Tests the MIV subscript pair (Src and Dst) for dependence.
635  /// Returns true if dependence disproved.
636  /// Can sometimes refine direction vectors.
637  bool testMIV(const SCEV *Src,
638  const SCEV *Dst,
639  const SmallBitVector &Loops,
640  FullDependence &Result) const;
641 
642  /// strongSIVtest - Tests the strong SIV subscript pair (Src and Dst)
643  /// for dependence.
644  /// Things of the form [c1 + a*i] and [c2 + a*i],
645  /// where i is an induction variable, c1 and c2 are loop invariant,
646  /// and a is a constant
647  /// Returns true if any possible dependence is disproved.
648  /// If there might be a dependence, returns false.
649  /// Sets appropriate direction and distance.
650  bool strongSIVtest(const SCEV *Coeff,
651  const SCEV *SrcConst,
652  const SCEV *DstConst,
653  const Loop *CurrentLoop,
654  unsigned Level,
655  FullDependence &Result,
656  Constraint &NewConstraint) const;
657 
658  /// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair
659  /// (Src and Dst) for dependence.
660  /// Things of the form [c1 + a*i] and [c2 - a*i],
661  /// where i is an induction variable, c1 and c2 are loop invariant,
662  /// and a is a constant.
663  /// Returns true if any possible dependence is disproved.
664  /// If there might be a dependence, returns false.
665  /// Sets appropriate direction entry.
666  /// Set consistent to false.
667  /// Marks the dependence as splitable.
668  bool weakCrossingSIVtest(const SCEV *SrcCoeff,
669  const SCEV *SrcConst,
670  const SCEV *DstConst,
671  const Loop *CurrentLoop,
672  unsigned Level,
673  FullDependence &Result,
674  Constraint &NewConstraint,
675  const SCEV *&SplitIter) const;
676 
677  /// ExactSIVtest - Tests the SIV subscript pair
678  /// (Src and Dst) for dependence.
679  /// Things of the form [c1 + a1*i] and [c2 + a2*i],
680  /// where i is an induction variable, c1 and c2 are loop invariant,
681  /// and a1 and a2 are constant.
682  /// Returns true if any possible dependence is disproved.
683  /// If there might be a dependence, returns false.
684  /// Sets appropriate direction entry.
685  /// Set consistent to false.
686  bool exactSIVtest(const SCEV *SrcCoeff,
687  const SCEV *DstCoeff,
688  const SCEV *SrcConst,
689  const SCEV *DstConst,
690  const Loop *CurrentLoop,
691  unsigned Level,
692  FullDependence &Result,
693  Constraint &NewConstraint) const;
694 
695  /// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair
696  /// (Src and Dst) for dependence.
697  /// Things of the form [c1] and [c2 + a*i],
698  /// where i is an induction variable, c1 and c2 are loop invariant,
699  /// and a is a constant. See also weakZeroDstSIVtest.
700  /// Returns true if any possible dependence is disproved.
701  /// If there might be a dependence, returns false.
702  /// Sets appropriate direction entry.
703  /// Set consistent to false.
704  /// If loop peeling will break the dependence, mark appropriately.
705  bool weakZeroSrcSIVtest(const SCEV *DstCoeff,
706  const SCEV *SrcConst,
707  const SCEV *DstConst,
708  const Loop *CurrentLoop,
709  unsigned Level,
710  FullDependence &Result,
711  Constraint &NewConstraint) const;
712 
713  /// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair
714  /// (Src and Dst) for dependence.
715  /// Things of the form [c1 + a*i] and [c2],
716  /// where i is an induction variable, c1 and c2 are loop invariant,
717  /// and a is a constant. See also weakZeroSrcSIVtest.
718  /// Returns true if any possible dependence is disproved.
719  /// If there might be a dependence, returns false.
720  /// Sets appropriate direction entry.
721  /// Set consistent to false.
722  /// If loop peeling will break the dependence, mark appropriately.
723  bool weakZeroDstSIVtest(const SCEV *SrcCoeff,
724  const SCEV *SrcConst,
725  const SCEV *DstConst,
726  const Loop *CurrentLoop,
727  unsigned Level,
728  FullDependence &Result,
729  Constraint &NewConstraint) const;
730 
731  /// exactRDIVtest - Tests the RDIV subscript pair for dependence.
732  /// Things of the form [c1 + a*i] and [c2 + b*j],
733  /// where i and j are induction variable, c1 and c2 are loop invariant,
734  /// and a and b are constants.
735  /// Returns true if any possible dependence is disproved.
736  /// Marks the result as inconsistent.
737  /// Works in some cases that symbolicRDIVtest doesn't,
738  /// and vice versa.
739  bool exactRDIVtest(const SCEV *SrcCoeff,
740  const SCEV *DstCoeff,
741  const SCEV *SrcConst,
742  const SCEV *DstConst,
743  const Loop *SrcLoop,
744  const Loop *DstLoop,
745  FullDependence &Result) const;
746 
747  /// symbolicRDIVtest - Tests the RDIV subscript pair for dependence.
748  /// Things of the form [c1 + a*i] and [c2 + b*j],
749  /// where i and j are induction variable, c1 and c2 are loop invariant,
750  /// and a and b are constants.
751  /// Returns true if any possible dependence is disproved.
752  /// Marks the result as inconsistent.
753  /// Works in some cases that exactRDIVtest doesn't,
754  /// and vice versa. Can also be used as a backup for
755  /// ordinary SIV tests.
756  bool symbolicRDIVtest(const SCEV *SrcCoeff,
757  const SCEV *DstCoeff,
758  const SCEV *SrcConst,
759  const SCEV *DstConst,
760  const Loop *SrcLoop,
761  const Loop *DstLoop) const;
762 
763  /// gcdMIVtest - Tests an MIV subscript pair for dependence.
764  /// Returns true if any possible dependence is disproved.
765  /// Marks the result as inconsistent.
766  /// Can sometimes disprove the equal direction for 1 or more loops.
767  // Can handle some symbolics that even the SIV tests don't get,
768  /// so we use it as a backup for everything.
769  bool gcdMIVtest(const SCEV *Src,
770  const SCEV *Dst,
771  FullDependence &Result) const;
772 
773  /// banerjeeMIVtest - Tests an MIV subscript pair for dependence.
774  /// Returns true if any possible dependence is disproved.
775  /// Marks the result as inconsistent.
776  /// Computes directions.
777  bool banerjeeMIVtest(const SCEV *Src,
778  const SCEV *Dst,
779  const SmallBitVector &Loops,
780  FullDependence &Result) const;
781 
782  /// collectCoefficientInfo - Walks through the subscript,
783  /// collecting each coefficient, the associated loop bounds,
784  /// and recording its positive and negative parts for later use.
785  CoefficientInfo *collectCoeffInfo(const SCEV *Subscript,
786  bool SrcFlag,
787  const SCEV *&Constant) const;
788 
789  /// getPositivePart - X^+ = max(X, 0).
790  ///
791  const SCEV *getPositivePart(const SCEV *X) const;
792 
793  /// getNegativePart - X^- = min(X, 0).
794  ///
795  const SCEV *getNegativePart(const SCEV *X) const;
796 
797  /// getLowerBound - Looks through all the bounds info and
798  /// computes the lower bound given the current direction settings
799  /// at each level.
800  const SCEV *getLowerBound(BoundInfo *Bound) const;
801 
802  /// getUpperBound - Looks through all the bounds info and
803  /// computes the upper bound given the current direction settings
804  /// at each level.
805  const SCEV *getUpperBound(BoundInfo *Bound) const;
806 
807  /// exploreDirections - Hierarchically expands the direction vector
808  /// search space, combining the directions of discovered dependences
809  /// in the DirSet field of Bound. Returns the number of distinct
810  /// dependences discovered. If the dependence is disproved,
811  /// it will return 0.
812  unsigned exploreDirections(unsigned Level,
813  CoefficientInfo *A,
814  CoefficientInfo *B,
815  BoundInfo *Bound,
816  const SmallBitVector &Loops,
817  unsigned &DepthExpanded,
818  const SCEV *Delta) const;
819 
820  /// testBounds - Returns true iff the current bounds are plausible.
821  bool testBounds(unsigned char DirKind,
822  unsigned Level,
823  BoundInfo *Bound,
824  const SCEV *Delta) const;
825 
826  /// findBoundsALL - Computes the upper and lower bounds for level K
827  /// using the * direction. Records them in Bound.
828  void findBoundsALL(CoefficientInfo *A,
829  CoefficientInfo *B,
830  BoundInfo *Bound,
831  unsigned K) const;
832 
833  /// findBoundsLT - Computes the upper and lower bounds for level K
834  /// using the < direction. Records them in Bound.
835  void findBoundsLT(CoefficientInfo *A,
836  CoefficientInfo *B,
837  BoundInfo *Bound,
838  unsigned K) const;
839 
840  /// findBoundsGT - Computes the upper and lower bounds for level K
841  /// using the > direction. Records them in Bound.
842  void findBoundsGT(CoefficientInfo *A,
843  CoefficientInfo *B,
844  BoundInfo *Bound,
845  unsigned K) const;
846 
847  /// findBoundsEQ - Computes the upper and lower bounds for level K
848  /// using the = direction. Records them in Bound.
849  void findBoundsEQ(CoefficientInfo *A,
850  CoefficientInfo *B,
851  BoundInfo *Bound,
852  unsigned K) const;
853 
854  /// intersectConstraints - Updates X with the intersection
855  /// of the Constraints X and Y. Returns true if X has changed.
856  bool intersectConstraints(Constraint *X,
857  const Constraint *Y);
858 
859  /// propagate - Review the constraints, looking for opportunities
860  /// to simplify a subscript pair (Src and Dst).
861  /// Return true if some simplification occurs.
862  /// If the simplification isn't exact (that is, if it is conservative
863  /// in terms of dependence), set consistent to false.
864  bool propagate(const SCEV *&Src,
865  const SCEV *&Dst,
866  SmallBitVector &Loops,
867  SmallVectorImpl<Constraint> &Constraints,
868  bool &Consistent);
869 
870  /// propagateDistance - Attempt to propagate a distance
871  /// constraint into a subscript pair (Src and Dst).
872  /// Return true if some simplification occurs.
873  /// If the simplification isn't exact (that is, if it is conservative
874  /// in terms of dependence), set consistent to false.
875  bool propagateDistance(const SCEV *&Src,
876  const SCEV *&Dst,
877  Constraint &CurConstraint,
878  bool &Consistent);
879 
880  /// propagatePoint - Attempt to propagate a point
881  /// constraint into a subscript pair (Src and Dst).
882  /// Return true if some simplification occurs.
883  bool propagatePoint(const SCEV *&Src,
884  const SCEV *&Dst,
885  Constraint &CurConstraint);
886 
887  /// propagateLine - Attempt to propagate a line
888  /// constraint into a subscript pair (Src and Dst).
889  /// Return true if some simplification occurs.
890  /// If the simplification isn't exact (that is, if it is conservative
891  /// in terms of dependence), set consistent to false.
892  bool propagateLine(const SCEV *&Src,
893  const SCEV *&Dst,
894  Constraint &CurConstraint,
895  bool &Consistent);
896 
897  /// findCoefficient - Given a linear SCEV,
898  /// return the coefficient corresponding to specified loop.
899  /// If there isn't one, return the SCEV constant 0.
900  /// For example, given a*i + b*j + c*k, returning the coefficient
901  /// corresponding to the j loop would yield b.
902  const SCEV *findCoefficient(const SCEV *Expr,
903  const Loop *TargetLoop) const;
904 
905  /// zeroCoefficient - Given a linear SCEV,
906  /// return the SCEV given by zeroing out the coefficient
907  /// corresponding to the specified loop.
908  /// For example, given a*i + b*j + c*k, zeroing the coefficient
909  /// corresponding to the j loop would yield a*i + c*k.
910  const SCEV *zeroCoefficient(const SCEV *Expr,
911  const Loop *TargetLoop) const;
912 
913  /// addToCoefficient - Given a linear SCEV Expr,
914  /// return the SCEV given by adding some Value to the
915  /// coefficient corresponding to the specified TargetLoop.
916  /// For example, given a*i + b*j + c*k, adding 1 to the coefficient
917  /// corresponding to the j loop would yield a*i + (b+1)*j + c*k.
918  const SCEV *addToCoefficient(const SCEV *Expr,
919  const Loop *TargetLoop,
920  const SCEV *Value) const;
921 
922  /// updateDirection - Update direction vector entry
923  /// based on the current constraint.
924  void updateDirection(Dependence::DVEntry &Level,
925  const Constraint &CurConstraint) const;
926 
927  bool tryDelinearize(Instruction *Src, Instruction *Dst,
929  }; // class DependenceInfo
930 
931  /// AnalysisPass to compute dependence information in a function
932  class DependenceAnalysis : public AnalysisInfoMixin<DependenceAnalysis> {
933  public:
935  Result run(Function &F, FunctionAnalysisManager &FAM);
936 
937  private:
938  static AnalysisKey Key;
940  }; // class DependenceAnalysis
941 
942  /// Printer pass to dump DA results.
944  : public PassInfoMixin<DependenceAnalysisPrinterPass> {
946 
948 
949  private:
950  raw_ostream &OS;
951  }; // class DependenceAnalysisPrinterPass
952 
953  /// Legacy pass manager pass to access dependence information
955  public:
956  static char ID; // Class identification, replacement for typeinfo
960  }
961 
962  bool runOnFunction(Function &F) override;
963  void releaseMemory() override;
964  void getAnalysisUsage(AnalysisUsage &) const override;
965  void print(raw_ostream &, const Module * = nullptr) const override;
966  DependenceInfo &getDI() const;
967 
968  private:
969  std::unique_ptr<DependenceInfo> info;
970  }; // class DependenceAnalysisWrapperPass
971 
972  /// createDependenceAnalysisPass - This creates an instance of the
973  /// DependenceAnalysis wrapper pass.
975 
976 } // namespace llvm
977 
978 #endif
Dependence(Dependence &&)=default
DependenceInfo(Function *F, AliasAnalysis *AA, ScalarEvolution *SE, LoopInfo *LI)
uint64_t CallInst * C
FunctionPass * createDependenceAnalysisWrapperPass()
createDependenceAnalysisPass - This creates an instance of the DependenceAnalysis wrapper pass...
Definition: Any.h:26
static GCMetadataPrinterRegistry::Add< ErlangGCPrinter > X("erlang", "erlang-compatible garbage collector")
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
bool isUnordered() const
isUnordered - Returns true if dependence is Input
This is a &#39;bitvector&#39; (really, a variable-sized bit array), optimized for the case when the array is ...
virtual const SCEV * getDistance(unsigned Level) const
getDistance - Returns the distance (or NULL) associated with a particular level.
AnalysisPass to compute dependence information in a function.
This class represents lattice values for constants.
Definition: AllocatorList.h:23
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:65
Legacy pass manager pass to access dependence information.
virtual bool isConsistent() const
isConsistent - Returns true if this dependence is consistent (occurs every time the source and destin...
The main scalar evolution driver.
virtual bool isConfused() const
isConfused - Returns true if this dependence is confused (the compiler understands nothing and makes ...
F(f)
block Block Frequency true
DependenceInfo - This class is the main dependence-analysis driver.
void dump(raw_ostream &OS) const
dump - For debugging purposes, dumps a dependence to OS.
const Dependence * getNextSuccessor() const
getNextSuccessor - Returns the value of the NextSuccessor field.
bool isConsistent() const override
isConsistent - Returns true if this dependence is consistent (occurs every time the source and destin...
static GCMetadataPrinterRegistry::Add< OcamlGCMetadataPrinter > Y("ocaml", "ocaml 3.10-compatible collector")
Hexagon Hardware Loops
virtual bool isScalar(unsigned Level) const
isScalar - Returns true if a particular level is scalar; that is, if no subscript in the source or de...
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:41
void initializeDependenceAnalysisWrapperPassPass(PassRegistry &)
bool isFlow() const
isFlow - Returns true if this is a flow (aka true) dependence.
Key
PAL metadata keys.
A CRTP mix-in to automatically provide informational APIs needed for passes.
Definition: PassManager.h:372
Instruction * getSrc() const
getSrc - Returns the source instruction for this dependence.
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory)...
Definition: APInt.h:32
unsigned getLevels() const override
getLevels - Returns the number of common loops surrounding the source and destination of the dependen...
bool isKnownNonNegative(const Value *V, const DataLayout &DL, unsigned Depth=0, AssumptionCache *AC=nullptr, const Instruction *CxtI=nullptr, const DominatorTree *DT=nullptr, bool UseInstrInfo=true)
Returns true if the give value is known to be non-negative.
const Dependence * getNextPredecessor() const
getNextPredecessor - Returns the value of the NextPredecessor field.
bool isLoopIndependent() const override
isLoopIndependent - Returns true if this is a loop-independent dependence.
bool isOutput() const
isOutput - Returns true if this is an output dependence.
void setNextPredecessor(const Dependence *pred)
setNextPredecessor - Sets the value of the NextPredecessor field.
static bool runOnFunction(Function &F, bool PostInlining)
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:153
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:45
This is an important base class in LLVM.
Definition: Constant.h:41
bool isConfused() const override
isConfused - Returns true if this dependence is confused (the compiler understands nothing and makes ...
A CRTP mix-in that provides informational APIs needed for analysis passes.
Definition: PassManager.h:389
Printer pass to dump DA results.
Represent the analysis usage information of a pass.
Predicate
This enumeration lists the possible predicates for CmpInst subclasses.
Definition: InstrTypes.h:732
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:284
virtual bool isPeelLast(unsigned Level) const
isPeelLast - Returns true if peeling the last iteration from this loop will break this dependence...
static void print(raw_ostream &Out, object::Archive::Kind Kind, T Val)
lazy value info
hexagon gen pred
Dependence & operator=(Dependence &&)=default
virtual unsigned getLevels() const
getLevels - Returns the number of common loops surrounding the source and destination of the dependen...
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
virtual unsigned getDirection(unsigned Level) const
getDirection - Returns the direction associated with a particular level.
Dependence(Instruction *Source, Instruction *Destination)
bool isOrdered() const
isOrdered - Returns true if dependence is Output, Flow, or Anti
static void propagate(InstantiatedValue From, InstantiatedValue To, MatchState State, ReachabilitySet &ReachSet, std::vector< WorkListItem > &WorkList)
virtual bool isLoopIndependent() const
isLoopIndependent - Returns true if this is a loop-independent dependence.
Function * getFunction() const
bool isAnti() const
isAnti - Returns true if this is an anti dependence.
This class represents an analyzed expression in the program.
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:506
virtual bool isSplitable(unsigned Level) const
isSplitable - Returns true if splitting this loop will break the dependence.
FullDependence - This class represents a dependence between two memory references in a function...
uint32_t Size
Definition: Profile.cpp:46
Dependence::DVEntry - Each level in the distance/direction vector has a direction (or perhaps a union...
Instruction * getDst() const
getDst - Returns the destination instruction for this dependence.
Loop::LoopBounds::Direction Direction
Definition: LoopInfo.cpp:226
API to communicate dependencies between analyses during invalidation.
Definition: PassManager.h:648
bool isInput() const
isInput - Returns true if this is an input dependence.
LLVM Value Representation.
Definition: Value.h:72
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:45
A container for analyses that lazily runs them and caches their results.
Dependence - This class represents a dependence between two memory memory references in a function...
void setNextSuccessor(const Dependence *succ)
setNextSuccessor - Sets the value of the NextSuccessor field.
virtual bool isPeelFirst(unsigned Level) const
isPeelFirst - Returns true if peeling the first iteration from this loop will break this dependence...
A special type used by analysis passes to provide an address that identifies that particular analysis...
Definition: PassManager.h:70
This class represents a constant integer value.