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DependenceAnalysis.h
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1 //===-- llvm/Analysis/DependenceAnalysis.h -------------------- -*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // DependenceAnalysis is an LLVM pass that analyses dependences between memory
11 // accesses. Currently, it is an implementation of the approach described in
12 //
13 // Practical Dependence Testing
14 // Goff, Kennedy, Tseng
15 // PLDI 1991
16 //
17 // There's a single entry point that analyzes the dependence between a pair
18 // of memory references in a function, returning either NULL, for no dependence,
19 // or a more-or-less detailed description of the dependence between them.
20 //
21 // This pass exists to support the DependenceGraph pass. There are two separate
22 // passes because there's a useful separation of concerns. A dependence exists
23 // if two conditions are met:
24 //
25 // 1) Two instructions reference the same memory location, and
26 // 2) There is a flow of control leading from one instruction to the other.
27 //
28 // DependenceAnalysis attacks the first condition; DependenceGraph will attack
29 // the second (it's not yet ready).
30 //
31 // Please note that this is work in progress and the interface is subject to
32 // change.
33 //
34 // Plausible changes:
35 // Return a set of more precise dependences instead of just one dependence
36 // summarizing all.
37 //
38 //===----------------------------------------------------------------------===//
39 
40 #ifndef LLVM_ANALYSIS_DEPENDENCEANALYSIS_H
41 #define LLVM_ANALYSIS_DEPENDENCEANALYSIS_H
42 
45 #include "llvm/IR/Instructions.h"
46 #include "llvm/Pass.h"
47 
48 namespace llvm {
49 template <typename T> class ArrayRef;
50  class Loop;
51  class LoopInfo;
52  class ScalarEvolution;
53  class SCEV;
54  class SCEVConstant;
55  class raw_ostream;
56 
57  /// Dependence - This class represents a dependence between two memory
58  /// memory references in a function. It contains minimal information and
59  /// is used in the very common situation where the compiler is unable to
60  /// determine anything beyond the existence of a dependence; that is, it
61  /// represents a confused dependence (see also FullDependence). In most
62  /// cases (for output, flow, and anti dependences), the dependence implies
63  /// an ordering, where the source must precede the destination; in contrast,
64  /// input dependences are unordered.
65  ///
66  /// When a dependence graph is built, each Dependence will be a member of
67  /// the set of predecessor edges for its destination instruction and a set
68  /// if successor edges for its source instruction. These sets are represented
69  /// as singly-linked lists, with the "next" fields stored in the dependence
70  /// itelf.
71  class Dependence {
72  protected:
73  Dependence(Dependence &&) = default;
74  Dependence &operator=(Dependence &&) = default;
75 
76  public:
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.
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  ///
273  public:
275  LoopInfo *LI)
276  : AA(AA), SE(SE), LI(LI), F(F) {}
277 
278  /// depends - Tests for a dependence between the Src and Dst instructions.
279  /// Returns NULL if no dependence; otherwise, returns a Dependence (or a
280  /// FullDependence) with as much information as can be gleaned.
281  /// The flag PossiblyLoopIndependent should be set by the caller
282  /// if it appears that control flow can reach from Src to Dst
283  /// without traversing a loop back edge.
284  std::unique_ptr<Dependence> depends(Instruction *Src,
285  Instruction *Dst,
286  bool PossiblyLoopIndependent);
287 
288  /// getSplitIteration - Give a dependence that's splittable at some
289  /// particular level, return the iteration that should be used to split
290  /// the loop.
291  ///
292  /// Generally, the dependence analyzer will be used to build
293  /// a dependence graph for a function (basically a map from instructions
294  /// to dependences). Looking for cycles in the graph shows us loops
295  /// that cannot be trivially vectorized/parallelized.
296  ///
297  /// We can try to improve the situation by examining all the dependences
298  /// that make up the cycle, looking for ones we can break.
299  /// Sometimes, peeling the first or last iteration of a loop will break
300  /// dependences, and there are flags for those possibilities.
301  /// Sometimes, splitting a loop at some other iteration will do the trick,
302  /// and we've got a flag for that case. Rather than waste the space to
303  /// record the exact iteration (since we rarely know), we provide
304  /// a method that calculates the iteration. It's a drag that it must work
305  /// from scratch, but wonderful in that it's possible.
306  ///
307  /// Here's an example:
308  ///
309  /// for (i = 0; i < 10; i++)
310  /// A[i] = ...
311  /// ... = A[11 - i]
312  ///
313  /// There's a loop-carried flow dependence from the store to the load,
314  /// found by the weak-crossing SIV test. The dependence will have a flag,
315  /// indicating that the dependence can be broken by splitting the loop.
316  /// Calling getSplitIteration will return 5.
317  /// Splitting the loop breaks the dependence, like so:
318  ///
319  /// for (i = 0; i <= 5; i++)
320  /// A[i] = ...
321  /// ... = A[11 - i]
322  /// for (i = 6; i < 10; i++)
323  /// A[i] = ...
324  /// ... = A[11 - i]
325  ///
326  /// breaks the dependence and allows us to vectorize/parallelize
327  /// both loops.
328  const SCEV *getSplitIteration(const Dependence &Dep, unsigned Level);
329 
330  Function *getFunction() const { return F; }
331 
332  private:
333  AliasAnalysis *AA;
334  ScalarEvolution *SE;
335  LoopInfo *LI;
336  Function *F;
337 
338  /// Subscript - This private struct represents a pair of subscripts from
339  /// a pair of potentially multi-dimensional array references. We use a
340  /// vector of them to guide subscript partitioning.
341  struct Subscript {
342  const SCEV *Src;
343  const SCEV *Dst;
344  enum ClassificationKind { ZIV, SIV, RDIV, MIV, NonLinear } Classification;
346  SmallBitVector GroupLoops;
347  SmallBitVector Group;
348  };
349 
350  struct CoefficientInfo {
351  const SCEV *Coeff;
352  const SCEV *PosPart;
353  const SCEV *NegPart;
354  const SCEV *Iterations;
355  };
356 
357  struct BoundInfo {
358  const SCEV *Iterations;
359  const SCEV *Upper[8];
360  const SCEV *Lower[8];
361  unsigned char Direction;
362  unsigned char DirSet;
363  };
364 
365  /// Constraint - This private class represents a constraint, as defined
366  /// in the paper
367  ///
368  /// Practical Dependence Testing
369  /// Goff, Kennedy, Tseng
370  /// PLDI 1991
371  ///
372  /// There are 5 kinds of constraint, in a hierarchy.
373  /// 1) Any - indicates no constraint, any dependence is possible.
374  /// 2) Line - A line ax + by = c, where a, b, and c are parameters,
375  /// representing the dependence equation.
376  /// 3) Distance - The value d of the dependence distance;
377  /// 4) Point - A point <x, y> representing the dependence from
378  /// iteration x to iteration y.
379  /// 5) Empty - No dependence is possible.
380  class Constraint {
381  private:
382  enum ConstraintKind { Empty, Point, Distance, Line, Any } Kind;
383  ScalarEvolution *SE;
384  const SCEV *A;
385  const SCEV *B;
386  const SCEV *C;
387  const Loop *AssociatedLoop;
388 
389  public:
390  /// isEmpty - Return true if the constraint is of kind Empty.
391  bool isEmpty() const { return Kind == Empty; }
392 
393  /// isPoint - Return true if the constraint is of kind Point.
394  bool isPoint() const { return Kind == Point; }
395 
396  /// isDistance - Return true if the constraint is of kind Distance.
397  bool isDistance() const { return Kind == Distance; }
398 
399  /// isLine - Return true if the constraint is of kind Line.
400  /// Since Distance's can also be represented as Lines, we also return
401  /// true if the constraint is of kind Distance.
402  bool isLine() const { return Kind == Line || Kind == Distance; }
403 
404  /// isAny - Return true if the constraint is of kind Any;
405  bool isAny() const { return Kind == Any; }
406 
407  /// getX - If constraint is a point <X, Y>, returns X.
408  /// Otherwise assert.
409  const SCEV *getX() const;
410 
411  /// getY - If constraint is a point <X, Y>, returns Y.
412  /// Otherwise assert.
413  const SCEV *getY() const;
414 
415  /// getA - If constraint is a line AX + BY = C, returns A.
416  /// Otherwise assert.
417  const SCEV *getA() const;
418 
419  /// getB - If constraint is a line AX + BY = C, returns B.
420  /// Otherwise assert.
421  const SCEV *getB() const;
422 
423  /// getC - If constraint is a line AX + BY = C, returns C.
424  /// Otherwise assert.
425  const SCEV *getC() const;
426 
427  /// getD - If constraint is a distance, returns D.
428  /// Otherwise assert.
429  const SCEV *getD() const;
430 
431  /// getAssociatedLoop - Returns the loop associated with this constraint.
432  const Loop *getAssociatedLoop() const;
433 
434  /// setPoint - Change a constraint to Point.
435  void setPoint(const SCEV *X, const SCEV *Y, const Loop *CurrentLoop);
436 
437  /// setLine - Change a constraint to Line.
438  void setLine(const SCEV *A, const SCEV *B,
439  const SCEV *C, const Loop *CurrentLoop);
440 
441  /// setDistance - Change a constraint to Distance.
442  void setDistance(const SCEV *D, const Loop *CurrentLoop);
443 
444  /// setEmpty - Change a constraint to Empty.
445  void setEmpty();
446 
447  /// setAny - Change a constraint to Any.
448  void setAny(ScalarEvolution *SE);
449 
450  /// dump - For debugging purposes. Dumps the constraint
451  /// out to OS.
452  void dump(raw_ostream &OS) const;
453  };
454 
455  /// establishNestingLevels - Examines the loop nesting of the Src and Dst
456  /// instructions and establishes their shared loops. Sets the variables
457  /// CommonLevels, SrcLevels, and MaxLevels.
458  /// The source and destination instructions needn't be contained in the same
459  /// loop. The routine establishNestingLevels finds the level of most deeply
460  /// nested loop that contains them both, CommonLevels. An instruction that's
461  /// not contained in a loop is at level = 0. MaxLevels is equal to the level
462  /// of the source plus the level of the destination, minus CommonLevels.
463  /// This lets us allocate vectors MaxLevels in length, with room for every
464  /// distinct loop referenced in both the source and destination subscripts.
465  /// The variable SrcLevels is the nesting depth of the source instruction.
466  /// It's used to help calculate distinct loops referenced by the destination.
467  /// Here's the map from loops to levels:
468  /// 0 - unused
469  /// 1 - outermost common loop
470  /// ... - other common loops
471  /// CommonLevels - innermost common loop
472  /// ... - loops containing Src but not Dst
473  /// SrcLevels - innermost loop containing Src but not Dst
474  /// ... - loops containing Dst but not Src
475  /// MaxLevels - innermost loop containing Dst but not Src
476  /// Consider the follow code fragment:
477  /// for (a = ...) {
478  /// for (b = ...) {
479  /// for (c = ...) {
480  /// for (d = ...) {
481  /// A[] = ...;
482  /// }
483  /// }
484  /// for (e = ...) {
485  /// for (f = ...) {
486  /// for (g = ...) {
487  /// ... = A[];
488  /// }
489  /// }
490  /// }
491  /// }
492  /// }
493  /// If we're looking at the possibility of a dependence between the store
494  /// to A (the Src) and the load from A (the Dst), we'll note that they
495  /// have 2 loops in common, so CommonLevels will equal 2 and the direction
496  /// vector for Result will have 2 entries. SrcLevels = 4 and MaxLevels = 7.
497  /// A map from loop names to level indices would look like
498  /// a - 1
499  /// b - 2 = CommonLevels
500  /// c - 3
501  /// d - 4 = SrcLevels
502  /// e - 5
503  /// f - 6
504  /// g - 7 = MaxLevels
505  void establishNestingLevels(const Instruction *Src,
506  const Instruction *Dst);
507 
508  unsigned CommonLevels, SrcLevels, MaxLevels;
509 
510  /// mapSrcLoop - Given one of the loops containing the source, return
511  /// its level index in our numbering scheme.
512  unsigned mapSrcLoop(const Loop *SrcLoop) const;
513 
514  /// mapDstLoop - Given one of the loops containing the destination,
515  /// return its level index in our numbering scheme.
516  unsigned mapDstLoop(const Loop *DstLoop) const;
517 
518  /// isLoopInvariant - Returns true if Expression is loop invariant
519  /// in LoopNest.
520  bool isLoopInvariant(const SCEV *Expression, const Loop *LoopNest) const;
521 
522  /// Makes sure all subscript pairs share the same integer type by
523  /// sign-extending as necessary.
524  /// Sign-extending a subscript is safe because getelementptr assumes the
525  /// array subscripts are signed.
526  void unifySubscriptType(ArrayRef<Subscript *> Pairs);
527 
528  /// removeMatchingExtensions - Examines a subscript pair.
529  /// If the source and destination are identically sign (or zero)
530  /// extended, it strips off the extension in an effort to
531  /// simplify the actual analysis.
532  void removeMatchingExtensions(Subscript *Pair);
533 
534  /// collectCommonLoops - Finds the set of loops from the LoopNest that
535  /// have a level <= CommonLevels and are referred to by the SCEV Expression.
536  void collectCommonLoops(const SCEV *Expression,
537  const Loop *LoopNest,
538  SmallBitVector &Loops) const;
539 
540  /// checkSrcSubscript - Examines the SCEV Src, returning true iff it's
541  /// linear. Collect the set of loops mentioned by Src.
542  bool checkSrcSubscript(const SCEV *Src,
543  const Loop *LoopNest,
544  SmallBitVector &Loops);
545 
546  /// checkDstSubscript - Examines the SCEV Dst, returning true iff it's
547  /// linear. Collect the set of loops mentioned by Dst.
548  bool checkDstSubscript(const SCEV *Dst,
549  const Loop *LoopNest,
550  SmallBitVector &Loops);
551 
552  /// isKnownPredicate - Compare X and Y using the predicate Pred.
553  /// Basically a wrapper for SCEV::isKnownPredicate,
554  /// but tries harder, especially in the presence of sign and zero
555  /// extensions and symbolics.
556  bool isKnownPredicate(ICmpInst::Predicate Pred,
557  const SCEV *X,
558  const SCEV *Y) const;
559 
560  /// collectUpperBound - All subscripts are the same type (on my machine,
561  /// an i64). The loop bound may be a smaller type. collectUpperBound
562  /// find the bound, if available, and zero extends it to the Type T.
563  /// (I zero extend since the bound should always be >= 0.)
564  /// If no upper bound is available, return NULL.
565  const SCEV *collectUpperBound(const Loop *l, Type *T) const;
566 
567  /// collectConstantUpperBound - Calls collectUpperBound(), then
568  /// attempts to cast it to SCEVConstant. If the cast fails,
569  /// returns NULL.
570  const SCEVConstant *collectConstantUpperBound(const Loop *l, Type *T) const;
571 
572  /// classifyPair - Examines the subscript pair (the Src and Dst SCEVs)
573  /// and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear.
574  /// Collects the associated loops in a set.
575  Subscript::ClassificationKind classifyPair(const SCEV *Src,
576  const Loop *SrcLoopNest,
577  const SCEV *Dst,
578  const Loop *DstLoopNest,
579  SmallBitVector &Loops);
580 
581  /// testZIV - Tests the ZIV subscript pair (Src and Dst) for dependence.
582  /// Returns true if any possible dependence is disproved.
583  /// If there might be a dependence, returns false.
584  /// If the dependence isn't proven to exist,
585  /// marks the Result as inconsistent.
586  bool testZIV(const SCEV *Src,
587  const SCEV *Dst,
588  FullDependence &Result) const;
589 
590  /// testSIV - Tests the SIV subscript pair (Src and Dst) for dependence.
591  /// Things of the form [c1 + a1*i] and [c2 + a2*j], where
592  /// i and j are induction variables, c1 and c2 are loop invariant,
593  /// and a1 and a2 are constant.
594  /// Returns true if any possible dependence is disproved.
595  /// If there might be a dependence, returns false.
596  /// Sets appropriate direction vector entry and, when possible,
597  /// the distance vector entry.
598  /// If the dependence isn't proven to exist,
599  /// marks the Result as inconsistent.
600  bool testSIV(const SCEV *Src,
601  const SCEV *Dst,
602  unsigned &Level,
603  FullDependence &Result,
604  Constraint &NewConstraint,
605  const SCEV *&SplitIter) const;
606 
607  /// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence.
608  /// Things of the form [c1 + a1*i] and [c2 + a2*j]
609  /// where i and j are induction variables, c1 and c2 are loop invariant,
610  /// and a1 and a2 are constant.
611  /// With minor algebra, this test can also be used for things like
612  /// [c1 + a1*i + a2*j][c2].
613  /// Returns true if any possible dependence is disproved.
614  /// If there might be a dependence, returns false.
615  /// Marks the Result as inconsistent.
616  bool testRDIV(const SCEV *Src,
617  const SCEV *Dst,
618  FullDependence &Result) const;
619 
620  /// testMIV - Tests the MIV subscript pair (Src and Dst) for dependence.
621  /// Returns true if dependence disproved.
622  /// Can sometimes refine direction vectors.
623  bool testMIV(const SCEV *Src,
624  const SCEV *Dst,
625  const SmallBitVector &Loops,
626  FullDependence &Result) const;
627 
628  /// strongSIVtest - Tests the strong SIV subscript pair (Src and Dst)
629  /// for dependence.
630  /// Things of the form [c1 + a*i] and [c2 + a*i],
631  /// where i is an induction variable, c1 and c2 are loop invariant,
632  /// and a is a constant
633  /// Returns true if any possible dependence is disproved.
634  /// If there might be a dependence, returns false.
635  /// Sets appropriate direction and distance.
636  bool strongSIVtest(const SCEV *Coeff,
637  const SCEV *SrcConst,
638  const SCEV *DstConst,
639  const Loop *CurrentLoop,
640  unsigned Level,
641  FullDependence &Result,
642  Constraint &NewConstraint) const;
643 
644  /// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair
645  /// (Src and Dst) for dependence.
646  /// Things of the form [c1 + a*i] and [c2 - a*i],
647  /// where i is an induction variable, c1 and c2 are loop invariant,
648  /// and a is a constant.
649  /// Returns true if any possible dependence is disproved.
650  /// If there might be a dependence, returns false.
651  /// Sets appropriate direction entry.
652  /// Set consistent to false.
653  /// Marks the dependence as splitable.
654  bool weakCrossingSIVtest(const SCEV *SrcCoeff,
655  const SCEV *SrcConst,
656  const SCEV *DstConst,
657  const Loop *CurrentLoop,
658  unsigned Level,
659  FullDependence &Result,
660  Constraint &NewConstraint,
661  const SCEV *&SplitIter) const;
662 
663  /// ExactSIVtest - Tests the SIV subscript pair
664  /// (Src and Dst) for dependence.
665  /// Things of the form [c1 + a1*i] and [c2 + a2*i],
666  /// where i is an induction variable, c1 and c2 are loop invariant,
667  /// and a1 and a2 are constant.
668  /// Returns true if any possible dependence is disproved.
669  /// If there might be a dependence, returns false.
670  /// Sets appropriate direction entry.
671  /// Set consistent to false.
672  bool exactSIVtest(const SCEV *SrcCoeff,
673  const SCEV *DstCoeff,
674  const SCEV *SrcConst,
675  const SCEV *DstConst,
676  const Loop *CurrentLoop,
677  unsigned Level,
678  FullDependence &Result,
679  Constraint &NewConstraint) const;
680 
681  /// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair
682  /// (Src and Dst) for dependence.
683  /// Things of the form [c1] and [c2 + a*i],
684  /// where i is an induction variable, c1 and c2 are loop invariant,
685  /// and a is a constant. See also weakZeroDstSIVtest.
686  /// Returns true if any possible dependence is disproved.
687  /// If there might be a dependence, returns false.
688  /// Sets appropriate direction entry.
689  /// Set consistent to false.
690  /// If loop peeling will break the dependence, mark appropriately.
691  bool weakZeroSrcSIVtest(const SCEV *DstCoeff,
692  const SCEV *SrcConst,
693  const SCEV *DstConst,
694  const Loop *CurrentLoop,
695  unsigned Level,
696  FullDependence &Result,
697  Constraint &NewConstraint) const;
698 
699  /// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair
700  /// (Src and Dst) for dependence.
701  /// Things of the form [c1 + a*i] and [c2],
702  /// where i is an induction variable, c1 and c2 are loop invariant,
703  /// and a is a constant. See also weakZeroSrcSIVtest.
704  /// Returns true if any possible dependence is disproved.
705  /// If there might be a dependence, returns false.
706  /// Sets appropriate direction entry.
707  /// Set consistent to false.
708  /// If loop peeling will break the dependence, mark appropriately.
709  bool weakZeroDstSIVtest(const SCEV *SrcCoeff,
710  const SCEV *SrcConst,
711  const SCEV *DstConst,
712  const Loop *CurrentLoop,
713  unsigned Level,
714  FullDependence &Result,
715  Constraint &NewConstraint) const;
716 
717  /// exactRDIVtest - Tests the RDIV subscript pair for dependence.
718  /// Things of the form [c1 + a*i] and [c2 + b*j],
719  /// where i and j are induction variable, c1 and c2 are loop invariant,
720  /// and a and b are constants.
721  /// Returns true if any possible dependence is disproved.
722  /// Marks the result as inconsistent.
723  /// Works in some cases that symbolicRDIVtest doesn't,
724  /// and vice versa.
725  bool exactRDIVtest(const SCEV *SrcCoeff,
726  const SCEV *DstCoeff,
727  const SCEV *SrcConst,
728  const SCEV *DstConst,
729  const Loop *SrcLoop,
730  const Loop *DstLoop,
731  FullDependence &Result) const;
732 
733  /// symbolicRDIVtest - Tests the RDIV subscript pair for dependence.
734  /// Things of the form [c1 + a*i] and [c2 + b*j],
735  /// where i and j are induction variable, c1 and c2 are loop invariant,
736  /// and a and b are constants.
737  /// Returns true if any possible dependence is disproved.
738  /// Marks the result as inconsistent.
739  /// Works in some cases that exactRDIVtest doesn't,
740  /// and vice versa. Can also be used as a backup for
741  /// ordinary SIV tests.
742  bool symbolicRDIVtest(const SCEV *SrcCoeff,
743  const SCEV *DstCoeff,
744  const SCEV *SrcConst,
745  const SCEV *DstConst,
746  const Loop *SrcLoop,
747  const Loop *DstLoop) const;
748 
749  /// gcdMIVtest - Tests an MIV subscript pair for dependence.
750  /// Returns true if any possible dependence is disproved.
751  /// Marks the result as inconsistent.
752  /// Can sometimes disprove the equal direction for 1 or more loops.
753  // Can handle some symbolics that even the SIV tests don't get,
754  /// so we use it as a backup for everything.
755  bool gcdMIVtest(const SCEV *Src,
756  const SCEV *Dst,
757  FullDependence &Result) const;
758 
759  /// banerjeeMIVtest - Tests an MIV subscript pair for dependence.
760  /// Returns true if any possible dependence is disproved.
761  /// Marks the result as inconsistent.
762  /// Computes directions.
763  bool banerjeeMIVtest(const SCEV *Src,
764  const SCEV *Dst,
765  const SmallBitVector &Loops,
766  FullDependence &Result) const;
767 
768  /// collectCoefficientInfo - Walks through the subscript,
769  /// collecting each coefficient, the associated loop bounds,
770  /// and recording its positive and negative parts for later use.
771  CoefficientInfo *collectCoeffInfo(const SCEV *Subscript,
772  bool SrcFlag,
773  const SCEV *&Constant) const;
774 
775  /// getPositivePart - X^+ = max(X, 0).
776  ///
777  const SCEV *getPositivePart(const SCEV *X) const;
778 
779  /// getNegativePart - X^- = min(X, 0).
780  ///
781  const SCEV *getNegativePart(const SCEV *X) const;
782 
783  /// getLowerBound - Looks through all the bounds info and
784  /// computes the lower bound given the current direction settings
785  /// at each level.
786  const SCEV *getLowerBound(BoundInfo *Bound) const;
787 
788  /// getUpperBound - Looks through all the bounds info and
789  /// computes the upper bound given the current direction settings
790  /// at each level.
791  const SCEV *getUpperBound(BoundInfo *Bound) const;
792 
793  /// exploreDirections - Hierarchically expands the direction vector
794  /// search space, combining the directions of discovered dependences
795  /// in the DirSet field of Bound. Returns the number of distinct
796  /// dependences discovered. If the dependence is disproved,
797  /// it will return 0.
798  unsigned exploreDirections(unsigned Level,
799  CoefficientInfo *A,
800  CoefficientInfo *B,
801  BoundInfo *Bound,
802  const SmallBitVector &Loops,
803  unsigned &DepthExpanded,
804  const SCEV *Delta) const;
805 
806  /// testBounds - Returns true iff the current bounds are plausible.
807  bool testBounds(unsigned char DirKind,
808  unsigned Level,
809  BoundInfo *Bound,
810  const SCEV *Delta) const;
811 
812  /// findBoundsALL - Computes the upper and lower bounds for level K
813  /// using the * direction. Records them in Bound.
814  void findBoundsALL(CoefficientInfo *A,
815  CoefficientInfo *B,
816  BoundInfo *Bound,
817  unsigned K) const;
818 
819  /// findBoundsLT - Computes the upper and lower bounds for level K
820  /// using the < direction. Records them in Bound.
821  void findBoundsLT(CoefficientInfo *A,
822  CoefficientInfo *B,
823  BoundInfo *Bound,
824  unsigned K) const;
825 
826  /// findBoundsGT - Computes the upper and lower bounds for level K
827  /// using the > direction. Records them in Bound.
828  void findBoundsGT(CoefficientInfo *A,
829  CoefficientInfo *B,
830  BoundInfo *Bound,
831  unsigned K) const;
832 
833  /// findBoundsEQ - Computes the upper and lower bounds for level K
834  /// using the = direction. Records them in Bound.
835  void findBoundsEQ(CoefficientInfo *A,
836  CoefficientInfo *B,
837  BoundInfo *Bound,
838  unsigned K) const;
839 
840  /// intersectConstraints - Updates X with the intersection
841  /// of the Constraints X and Y. Returns true if X has changed.
842  bool intersectConstraints(Constraint *X,
843  const Constraint *Y);
844 
845  /// propagate - Review the constraints, looking for opportunities
846  /// to simplify a subscript pair (Src and Dst).
847  /// Return true if some simplification occurs.
848  /// If the simplification isn't exact (that is, if it is conservative
849  /// in terms of dependence), set consistent to false.
850  bool propagate(const SCEV *&Src,
851  const SCEV *&Dst,
852  SmallBitVector &Loops,
853  SmallVectorImpl<Constraint> &Constraints,
854  bool &Consistent);
855 
856  /// propagateDistance - Attempt to propagate a distance
857  /// constraint into a subscript pair (Src and Dst).
858  /// Return true if some simplification occurs.
859  /// If the simplification isn't exact (that is, if it is conservative
860  /// in terms of dependence), set consistent to false.
861  bool propagateDistance(const SCEV *&Src,
862  const SCEV *&Dst,
863  Constraint &CurConstraint,
864  bool &Consistent);
865 
866  /// propagatePoint - Attempt to propagate a point
867  /// constraint into a subscript pair (Src and Dst).
868  /// Return true if some simplification occurs.
869  bool propagatePoint(const SCEV *&Src,
870  const SCEV *&Dst,
871  Constraint &CurConstraint);
872 
873  /// propagateLine - Attempt to propagate a line
874  /// constraint into a subscript pair (Src and Dst).
875  /// Return true if some simplification occurs.
876  /// If the simplification isn't exact (that is, if it is conservative
877  /// in terms of dependence), set consistent to false.
878  bool propagateLine(const SCEV *&Src,
879  const SCEV *&Dst,
880  Constraint &CurConstraint,
881  bool &Consistent);
882 
883  /// findCoefficient - Given a linear SCEV,
884  /// return the coefficient corresponding to specified loop.
885  /// If there isn't one, return the SCEV constant 0.
886  /// For example, given a*i + b*j + c*k, returning the coefficient
887  /// corresponding to the j loop would yield b.
888  const SCEV *findCoefficient(const SCEV *Expr,
889  const Loop *TargetLoop) const;
890 
891  /// zeroCoefficient - Given a linear SCEV,
892  /// return the SCEV given by zeroing out the coefficient
893  /// corresponding to the specified loop.
894  /// For example, given a*i + b*j + c*k, zeroing the coefficient
895  /// corresponding to the j loop would yield a*i + c*k.
896  const SCEV *zeroCoefficient(const SCEV *Expr,
897  const Loop *TargetLoop) const;
898 
899  /// addToCoefficient - Given a linear SCEV Expr,
900  /// return the SCEV given by adding some Value to the
901  /// coefficient corresponding to the specified TargetLoop.
902  /// For example, given a*i + b*j + c*k, adding 1 to the coefficient
903  /// corresponding to the j loop would yield a*i + (b+1)*j + c*k.
904  const SCEV *addToCoefficient(const SCEV *Expr,
905  const Loop *TargetLoop,
906  const SCEV *Value) const;
907 
908  /// updateDirection - Update direction vector entry
909  /// based on the current constraint.
910  void updateDirection(Dependence::DVEntry &Level,
911  const Constraint &CurConstraint) const;
912 
913  bool tryDelinearize(Instruction *Src, Instruction *Dst,
915  }; // class DependenceInfo
916 
917  /// \brief AnalysisPass to compute dependence information in a function
918  class DependenceAnalysis : public AnalysisInfoMixin<DependenceAnalysis> {
919  public:
921  Result run(Function &F, FunctionAnalysisManager &FAM);
922 
923  private:
924  static AnalysisKey Key;
926  }; // class DependenceAnalysis
927 
928  /// \brief Legacy pass manager pass to access dependence information
930  public:
931  static char ID; // Class identification, replacement for typeinfo
935  }
936 
937  bool runOnFunction(Function &F) override;
938  void releaseMemory() override;
939  void getAnalysisUsage(AnalysisUsage &) const override;
940  void print(raw_ostream &, const Module * = nullptr) const override;
941  DependenceInfo &getDI() const;
942 
943  private:
944  std::unique_ptr<DependenceInfo> info;
945  }; // class DependenceAnalysisWrapperPass
946 
947  /// createDependenceAnalysisPass - This creates an instance of the
948  /// DependenceAnalysis wrapper pass.
950 
951 } // namespace llvm
952 
953 #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...
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
static bool isLoopInvariant(Value *V, const Loop *L, const DominatorTree *DT)
Perform a quick domtree based check for loop invariance assuming that V is used within the loop...
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.
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:63
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)
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:42
void initializeDependenceAnalysisWrapperPassPass(PassRegistry &)
bool isFlow() const
isFlow - Returns true if this is a flow (aka true) dependence.
Key
PAL metadata keys.
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:33
unsigned getLevels() const override
getLevels - Returns the number of common loops surrounding the source and destination of the dependen...
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")
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:46
This is an important base class in LLVM.
Definition: Constant.h:42
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:382
Represent the analysis usage information of a pass.
Predicate
This enumeration lists the possible predicates for CmpInst subclasses.
Definition: InstrTypes.h:853
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:285
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.
Basic Alias true
This class represents an analyzed expression in the program.
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:439
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...
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.
bool isInput() const
isInput - Returns true if this is an input dependence.
const unsigned Kind
LLVM Value Representation.
Definition: Value.h:73
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:44
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.