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
47namespace 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, Instruction *Destination)
78 : Src(Source), Dst(Destination) {}
79 virtual ~Dependence() = default;
80
81 /// Dependence::DVEntry - Each level in the distance/direction vector
82 /// has a direction (or perhaps a union of several directions), and
83 /// perhaps a distance.
84 struct DVEntry {
85 enum : unsigned char {
86 NONE = 0,
87 LT = 1,
88 EQ = 2,
89 LE = 3,
90 GT = 4,
91 NE = 5,
92 GE = 6,
93 ALL = 7
94 };
95 unsigned char Direction : 3; // Init to ALL, then refine.
96 bool Scalar : 1; // Init to true.
97 bool PeelFirst : 1; // Peeling the first iteration will break dependence.
98 bool PeelLast : 1; // Peeling the last iteration will break the dependence.
99 bool Splitable : 1; // Splitting the loop will break dependence.
100 const SCEV *Distance = nullptr; // NULL implies no distance available.
101 DVEntry()
102 : Direction(ALL), Scalar(true), PeelFirst(false), PeelLast(false),
103 Splitable(false) {}
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 /// Check if the direction vector is negative. A negative direction
164 /// vector means Src and Dst are reversed in the actual program.
165 virtual bool isDirectionNegative() const { return false; }
166
167 /// If the direction vector is negative, normalize the direction
168 /// vector to make it non-negative. Normalization is done by reversing
169 /// Src and Dst, plus reversing the dependence directions and distances
170 /// in the vector.
171 virtual bool normalize(ScalarEvolution *SE) { return false; }
172
173 /// isPeelFirst - Returns true if peeling the first iteration from
174 /// this loop will break this dependence.
175 virtual bool isPeelFirst(unsigned Level) const { return false; }
176
177 /// isPeelLast - Returns true if peeling the last iteration from
178 /// this loop will break this dependence.
179 virtual bool isPeelLast(unsigned Level) const { return false; }
180
181 /// isSplitable - Returns true if splitting this loop will break
182 /// the dependence.
183 virtual bool isSplitable(unsigned Level) const { return false; }
184
185 /// isScalar - Returns true if a particular level is scalar; that is,
186 /// if no subscript in the source or destination mention the induction
187 /// variable associated with the loop at this level.
188 virtual bool isScalar(unsigned Level) const;
189
190 /// getNextPredecessor - Returns the value of the NextPredecessor
191 /// field.
192 const Dependence *getNextPredecessor() const { return NextPredecessor; }
193
194 /// getNextSuccessor - Returns the value of the NextSuccessor
195 /// field.
196 const Dependence *getNextSuccessor() const { return NextSuccessor; }
197
198 /// setNextPredecessor - Sets the value of the NextPredecessor
199 /// field.
200 void setNextPredecessor(const Dependence *pred) { NextPredecessor = pred; }
201
202 /// setNextSuccessor - Sets the value of the NextSuccessor
203 /// field.
204 void setNextSuccessor(const Dependence *succ) { NextSuccessor = succ; }
205
206 /// dump - For debugging purposes, dumps a dependence to OS.
207 ///
208 void dump(raw_ostream &OS) const;
209
210 protected:
211 Instruction *Src, *Dst;
212
213 private:
214 const Dependence *NextPredecessor = nullptr, *NextSuccessor = nullptr;
215 friend class DependenceInfo;
216 };
217
218 /// FullDependence - This class represents a dependence between two memory
219 /// references in a function. It contains detailed information about the
220 /// dependence (direction vectors, etc.) and is used when the compiler is
221 /// able to accurately analyze the interaction of the references; that is,
222 /// it is not a confused dependence (see Dependence). In most cases
223 /// (for output, flow, and anti dependences), the dependence implies an
224 /// ordering, where the source must precede the destination; in contrast,
225 /// input dependences are unordered.
226 class FullDependence final : public Dependence {
227 public:
228 FullDependence(Instruction *Src, Instruction *Dst, bool LoopIndependent,
229 unsigned Levels);
230
231 /// isLoopIndependent - Returns true if this is a loop-independent
232 /// dependence.
233 bool isLoopIndependent() const override { return LoopIndependent; }
234
235 /// isConfused - Returns true if this dependence is confused
236 /// (the compiler understands nothing and makes worst-case
237 /// assumptions).
238 bool isConfused() const override { return false; }
239
240 /// isConsistent - Returns true if this dependence is consistent
241 /// (occurs every time the source and destination are executed).
242 bool isConsistent() const override { return Consistent; }
243
244 /// getLevels - Returns the number of common loops surrounding the
245 /// source and destination of the dependence.
246 unsigned getLevels() const override { return Levels; }
247
248 /// getDirection - Returns the direction associated with a particular
249 /// level.
250 unsigned getDirection(unsigned Level) const override;
251
252 /// getDistance - Returns the distance (or NULL) associated with a
253 /// particular level.
254 const SCEV *getDistance(unsigned Level) const override;
255
256 /// Check if the direction vector is negative. A negative direction
257 /// vector means Src and Dst are reversed in the actual program.
258 bool isDirectionNegative() const override;
259
260 /// If the direction vector is negative, normalize the direction
261 /// vector to make it non-negative. Normalization is done by reversing
262 /// Src and Dst, plus reversing the dependence directions and distances
263 /// in the vector.
264 bool normalize(ScalarEvolution *SE) override;
265
266 /// isPeelFirst - Returns true if peeling the first iteration from
267 /// this loop will break this dependence.
268 bool isPeelFirst(unsigned Level) const override;
269
270 /// isPeelLast - Returns true if peeling the last iteration from
271 /// this loop will break this dependence.
272 bool isPeelLast(unsigned Level) const override;
273
274 /// isSplitable - Returns true if splitting the loop will break
275 /// the dependence.
276 bool isSplitable(unsigned Level) const override;
277
278 /// isScalar - Returns true if a particular level is scalar; that is,
279 /// if no subscript in the source or destination mention the induction
280 /// variable associated with the loop at this level.
281 bool isScalar(unsigned Level) const override;
282
283 private:
284 unsigned short Levels;
285 bool LoopIndependent;
286 bool Consistent; // Init to true, then refine.
287 std::unique_ptr<DVEntry[]> DV;
288 friend class DependenceInfo;
289 };
290
291 /// DependenceInfo - This class is the main dependence-analysis driver.
292 ///
293 class DependenceInfo {
294 public:
295 DependenceInfo(Function *F, AAResults *AA, ScalarEvolution *SE,
296 LoopInfo *LI)
297 : AA(AA), SE(SE), LI(LI), F(F) {}
298
299 /// Handle transitive invalidation when the cached analysis results go away.
300 bool invalidate(Function &F, const PreservedAnalyses &PA,
301 FunctionAnalysisManager::Invalidator &Inv);
302
303 /// depends - Tests for a dependence between the Src and Dst instructions.
304 /// Returns NULL if no dependence; otherwise, returns a Dependence (or a
305 /// FullDependence) with as much information as can be gleaned.
306 /// The flag PossiblyLoopIndependent should be set by the caller
307 /// if it appears that control flow can reach from Src to Dst
308 /// without traversing a loop back edge.
309 std::unique_ptr<Dependence> depends(Instruction *Src,
310 Instruction *Dst,
311 bool PossiblyLoopIndependent);
312
313 /// getSplitIteration - Give a dependence that's splittable at some
314 /// particular level, return the iteration that should be used to split
315 /// the loop.
316 ///
317 /// Generally, the dependence analyzer will be used to build
318 /// a dependence graph for a function (basically a map from instructions
319 /// to dependences). Looking for cycles in the graph shows us loops
320 /// that cannot be trivially vectorized/parallelized.
321 ///
322 /// We can try to improve the situation by examining all the dependences
323 /// that make up the cycle, looking for ones we can break.
324 /// Sometimes, peeling the first or last iteration of a loop will break
325 /// dependences, and there are flags for those possibilities.
326 /// Sometimes, splitting a loop at some other iteration will do the trick,
327 /// and we've got a flag for that case. Rather than waste the space to
328 /// record the exact iteration (since we rarely know), we provide
329 /// a method that calculates the iteration. It's a drag that it must work
330 /// from scratch, but wonderful in that it's possible.
331 ///
332 /// Here's an example:
333 ///
334 /// for (i = 0; i < 10; i++)
335 /// A[i] = ...
336 /// ... = A[11 - i]
337 ///
338 /// There's a loop-carried flow dependence from the store to the load,
339 /// found by the weak-crossing SIV test. The dependence will have a flag,
340 /// indicating that the dependence can be broken by splitting the loop.
341 /// Calling getSplitIteration will return 5.
342 /// Splitting the loop breaks the dependence, like so:
343 ///
344 /// for (i = 0; i <= 5; i++)
345 /// A[i] = ...
346 /// ... = A[11 - i]
347 /// for (i = 6; i < 10; i++)
348 /// A[i] = ...
349 /// ... = A[11 - i]
350 ///
351 /// breaks the dependence and allows us to vectorize/parallelize
352 /// both loops.
353 const SCEV *getSplitIteration(const Dependence &Dep, unsigned Level);
354
355 Function *getFunction() const { return F; }
356
357 private:
358 AAResults *AA;
359 ScalarEvolution *SE;
360 LoopInfo *LI;
361 Function *F;
362
363 /// Subscript - This private struct represents a pair of subscripts from
364 /// a pair of potentially multi-dimensional array references. We use a
365 /// vector of them to guide subscript partitioning.
366 struct Subscript {
367 const SCEV *Src;
368 const SCEV *Dst;
369 enum ClassificationKind { ZIV, SIV, RDIV, MIV, NonLinear } Classification;
370 SmallBitVector Loops;
371 SmallBitVector GroupLoops;
372 SmallBitVector Group;
373 };
374
375 struct CoefficientInfo {
376 const SCEV *Coeff;
377 const SCEV *PosPart;
378 const SCEV *NegPart;
379 const SCEV *Iterations;
380 };
381
382 struct BoundInfo {
383 const SCEV *Iterations;
384 const SCEV *Upper[8];
385 const SCEV *Lower[8];
386 unsigned char Direction;
387 unsigned char DirSet;
388 };
389
390 /// Constraint - This private class represents a constraint, as defined
391 /// in the paper
392 ///
393 /// Practical Dependence Testing
394 /// Goff, Kennedy, Tseng
395 /// PLDI 1991
396 ///
397 /// There are 5 kinds of constraint, in a hierarchy.
398 /// 1) Any - indicates no constraint, any dependence is possible.
399 /// 2) Line - A line ax + by = c, where a, b, and c are parameters,
400 /// representing the dependence equation.
401 /// 3) Distance - The value d of the dependence distance;
402 /// 4) Point - A point <x, y> representing the dependence from
403 /// iteration x to iteration y.
404 /// 5) Empty - No dependence is possible.
405 class Constraint {
406 private:
407 enum ConstraintKind { Empty, Point, Distance, Line, Any } Kind;
408 ScalarEvolution *SE;
409 const SCEV *A;
410 const SCEV *B;
411 const SCEV *C;
412 const Loop *AssociatedLoop;
413
414 public:
415 /// isEmpty - Return true if the constraint is of kind Empty.
416 bool isEmpty() const { return Kind == Empty; }
417
418 /// isPoint - Return true if the constraint is of kind Point.
419 bool isPoint() const { return Kind == Point; }
420
421 /// isDistance - Return true if the constraint is of kind Distance.
422 bool isDistance() const { return Kind == Distance; }
423
424 /// isLine - Return true if the constraint is of kind Line.
425 /// Since Distance's can also be represented as Lines, we also return
426 /// true if the constraint is of kind Distance.
427 bool isLine() const { return Kind == Line || Kind == Distance; }
428
429 /// isAny - Return true if the constraint is of kind Any;
430 bool isAny() const { return Kind == Any; }
431
432 /// getX - If constraint is a point <X, Y>, returns X.
433 /// Otherwise assert.
434 const SCEV *getX() const;
435
436 /// getY - If constraint is a point <X, Y>, returns Y.
437 /// Otherwise assert.
438 const SCEV *getY() const;
439
440 /// getA - If constraint is a line AX + BY = C, returns A.
441 /// Otherwise assert.
442 const SCEV *getA() const;
443
444 /// getB - If constraint is a line AX + BY = C, returns B.
445 /// Otherwise assert.
446 const SCEV *getB() const;
447
448 /// getC - If constraint is a line AX + BY = C, returns C.
449 /// Otherwise assert.
450 const SCEV *getC() const;
451
452 /// getD - If constraint is a distance, returns D.
453 /// Otherwise assert.
454 const SCEV *getD() const;
455
456 /// getAssociatedLoop - Returns the loop associated with this constraint.
457 const Loop *getAssociatedLoop() const;
458
459 /// setPoint - Change a constraint to Point.
460 void setPoint(const SCEV *X, const SCEV *Y, const Loop *CurrentLoop);
461
462 /// setLine - Change a constraint to Line.
463 void setLine(const SCEV *A, const SCEV *B,
464 const SCEV *C, const Loop *CurrentLoop);
465
466 /// setDistance - Change a constraint to Distance.
467 void setDistance(const SCEV *D, const Loop *CurrentLoop);
468
469 /// setEmpty - Change a constraint to Empty.
470 void setEmpty();
471
472 /// setAny - Change a constraint to Any.
473 void setAny(ScalarEvolution *SE);
474
475 /// dump - For debugging purposes. Dumps the constraint
476 /// out to OS.
477 void dump(raw_ostream &OS) const;
478 };
479
480 /// establishNestingLevels - Examines the loop nesting of the Src and Dst
481 /// instructions and establishes their shared loops. Sets the variables
482 /// CommonLevels, SrcLevels, and MaxLevels.
483 /// The source and destination instructions needn't be contained in the same
484 /// loop. The routine establishNestingLevels finds the level of most deeply
485 /// nested loop that contains them both, CommonLevels. An instruction that's
486 /// not contained in a loop is at level = 0. MaxLevels is equal to the level
487 /// of the source plus the level of the destination, minus CommonLevels.
488 /// This lets us allocate vectors MaxLevels in length, with room for every
489 /// distinct loop referenced in both the source and destination subscripts.
490 /// The variable SrcLevels is the nesting depth of the source instruction.
491 /// It's used to help calculate distinct loops referenced by the destination.
492 /// Here's the map from loops to levels:
493 /// 0 - unused
494 /// 1 - outermost common loop
495 /// ... - other common loops
496 /// CommonLevels - innermost common loop
497 /// ... - loops containing Src but not Dst
498 /// SrcLevels - innermost loop containing Src but not Dst
499 /// ... - loops containing Dst but not Src
500 /// MaxLevels - innermost loop containing Dst but not Src
501 /// Consider the follow code fragment:
502 /// for (a = ...) {
503 /// for (b = ...) {
504 /// for (c = ...) {
505 /// for (d = ...) {
506 /// A[] = ...;
507 /// }
508 /// }
509 /// for (e = ...) {
510 /// for (f = ...) {
511 /// for (g = ...) {
512 /// ... = A[];
513 /// }
514 /// }
515 /// }
516 /// }
517 /// }
518 /// If we're looking at the possibility of a dependence between the store
519 /// to A (the Src) and the load from A (the Dst), we'll note that they
520 /// have 2 loops in common, so CommonLevels will equal 2 and the direction
521 /// vector for Result will have 2 entries. SrcLevels = 4 and MaxLevels = 7.
522 /// A map from loop names to level indices would look like
523 /// a - 1
524 /// b - 2 = CommonLevels
525 /// c - 3
526 /// d - 4 = SrcLevels
527 /// e - 5
528 /// f - 6
529 /// g - 7 = MaxLevels
530 void establishNestingLevels(const Instruction *Src,
531 const Instruction *Dst);
532
533 unsigned CommonLevels, SrcLevels, MaxLevels;
534
535 /// mapSrcLoop - Given one of the loops containing the source, return
536 /// its level index in our numbering scheme.
537 unsigned mapSrcLoop(const Loop *SrcLoop) const;
538
539 /// mapDstLoop - Given one of the loops containing the destination,
540 /// return its level index in our numbering scheme.
541 unsigned mapDstLoop(const Loop *DstLoop) const;
542
543 /// isLoopInvariant - Returns true if Expression is loop invariant
544 /// in LoopNest.
545 bool isLoopInvariant(const SCEV *Expression, const Loop *LoopNest) const;
546
547 /// Makes sure all subscript pairs share the same integer type by
548 /// sign-extending as necessary.
549 /// Sign-extending a subscript is safe because getelementptr assumes the
550 /// array subscripts are signed.
551 void unifySubscriptType(ArrayRef<Subscript *> Pairs);
552
553 /// removeMatchingExtensions - Examines a subscript pair.
554 /// If the source and destination are identically sign (or zero)
555 /// extended, it strips off the extension in an effort to
556 /// simplify the actual analysis.
557 void removeMatchingExtensions(Subscript *Pair);
558
559 /// collectCommonLoops - Finds the set of loops from the LoopNest that
560 /// have a level <= CommonLevels and are referred to by the SCEV Expression.
561 void collectCommonLoops(const SCEV *Expression,
562 const Loop *LoopNest,
563 SmallBitVector &Loops) const;
564
565 /// checkSrcSubscript - Examines the SCEV Src, returning true iff it's
566 /// linear. Collect the set of loops mentioned by Src.
567 bool checkSrcSubscript(const SCEV *Src,
568 const Loop *LoopNest,
569 SmallBitVector &Loops);
570
571 /// checkDstSubscript - Examines the SCEV Dst, returning true iff it's
572 /// linear. Collect the set of loops mentioned by Dst.
573 bool checkDstSubscript(const SCEV *Dst,
574 const Loop *LoopNest,
575 SmallBitVector &Loops);
576
577 /// isKnownPredicate - Compare X and Y using the predicate Pred.
578 /// Basically a wrapper for SCEV::isKnownPredicate,
579 /// but tries harder, especially in the presence of sign and zero
580 /// extensions and symbolics.
581 bool isKnownPredicate(ICmpInst::Predicate Pred,
582 const SCEV *X,
583 const SCEV *Y) const;
584
585 /// isKnownLessThan - Compare to see if S is less than Size
586 /// Another wrapper for isKnownNegative(S - max(Size, 1)) with some extra
587 /// checking if S is an AddRec and we can prove lessthan using the loop
588 /// bounds.
589 bool isKnownLessThan(const SCEV *S, const SCEV *Size) const;
590
591 /// isKnownNonNegative - Compare to see if S is known not to be negative
592 /// Uses the fact that S comes from Ptr, which may be an inbound GEP,
593 /// Proving there is no wrapping going on.
594 bool isKnownNonNegative(const SCEV *S, const Value *Ptr) const;
595
596 /// collectUpperBound - All subscripts are the same type (on my machine,
597 /// an i64). The loop bound may be a smaller type. collectUpperBound
598 /// find the bound, if available, and zero extends it to the Type T.
599 /// (I zero extend since the bound should always be >= 0.)
600 /// If no upper bound is available, return NULL.
601 const SCEV *collectUpperBound(const Loop *l, Type *T) const;
602
603 /// collectConstantUpperBound - Calls collectUpperBound(), then
604 /// attempts to cast it to SCEVConstant. If the cast fails,
605 /// returns NULL.
606 const SCEVConstant *collectConstantUpperBound(const Loop *l, Type *T) const;
607
608 /// classifyPair - Examines the subscript pair (the Src and Dst SCEVs)
609 /// and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear.
610 /// Collects the associated loops in a set.
611 Subscript::ClassificationKind classifyPair(const SCEV *Src,
612 const Loop *SrcLoopNest,
613 const SCEV *Dst,
614 const Loop *DstLoopNest,
615 SmallBitVector &Loops);
616
617 /// testZIV - Tests the ZIV subscript pair (Src and Dst) for dependence.
618 /// Returns true if any possible dependence is disproved.
619 /// If there might be a dependence, returns false.
620 /// If the dependence isn't proven to exist,
621 /// marks the Result as inconsistent.
622 bool testZIV(const SCEV *Src,
623 const SCEV *Dst,
624 FullDependence &Result) const;
625
626 /// testSIV - Tests the SIV subscript pair (Src and Dst) for dependence.
627 /// Things of the form [c1 + a1*i] and [c2 + a2*j], where
628 /// i and j are induction variables, c1 and c2 are loop invariant,
629 /// and a1 and a2 are constant.
630 /// Returns true if any possible dependence is disproved.
631 /// If there might be a dependence, returns false.
632 /// Sets appropriate direction vector entry and, when possible,
633 /// the distance vector entry.
634 /// If the dependence isn't proven to exist,
635 /// marks the Result as inconsistent.
636 bool testSIV(const SCEV *Src,
637 const SCEV *Dst,
638 unsigned &Level,
639 FullDependence &Result,
640 Constraint &NewConstraint,
641 const SCEV *&SplitIter) const;
642
643 /// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence.
644 /// Things of the form [c1 + a1*i] and [c2 + a2*j]
645 /// where i and j are induction variables, c1 and c2 are loop invariant,
646 /// and a1 and a2 are constant.
647 /// With minor algebra, this test can also be used for things like
648 /// [c1 + a1*i + a2*j][c2].
649 /// Returns true if any possible dependence is disproved.
650 /// If there might be a dependence, returns false.
651 /// Marks the Result as inconsistent.
652 bool testRDIV(const SCEV *Src,
653 const SCEV *Dst,
654 FullDependence &Result) const;
655
656 /// testMIV - Tests the MIV subscript pair (Src and Dst) for dependence.
657 /// Returns true if dependence disproved.
658 /// Can sometimes refine direction vectors.
659 bool testMIV(const SCEV *Src,
660 const SCEV *Dst,
661 const SmallBitVector &Loops,
662 FullDependence &Result) const;
663
664 /// strongSIVtest - Tests the strong SIV subscript pair (Src and Dst)
665 /// for dependence.
666 /// Things of the form [c1 + a*i] and [c2 + a*i],
667 /// where i is an induction variable, c1 and c2 are loop invariant,
668 /// and a is a constant
669 /// Returns true if any possible dependence is disproved.
670 /// If there might be a dependence, returns false.
671 /// Sets appropriate direction and distance.
672 bool strongSIVtest(const SCEV *Coeff,
673 const SCEV *SrcConst,
674 const SCEV *DstConst,
675 const Loop *CurrentLoop,
676 unsigned Level,
677 FullDependence &Result,
678 Constraint &NewConstraint) const;
679
680 /// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair
681 /// (Src and Dst) for dependence.
682 /// Things of the form [c1 + a*i] and [c2 - a*i],
683 /// where i is an induction variable, c1 and c2 are loop invariant,
684 /// and a is a constant.
685 /// Returns true if any possible dependence is disproved.
686 /// If there might be a dependence, returns false.
687 /// Sets appropriate direction entry.
688 /// Set consistent to false.
689 /// Marks the dependence as splitable.
690 bool weakCrossingSIVtest(const SCEV *SrcCoeff,
691 const SCEV *SrcConst,
692 const SCEV *DstConst,
693 const Loop *CurrentLoop,
694 unsigned Level,
695 FullDependence &Result,
696 Constraint &NewConstraint,
697 const SCEV *&SplitIter) const;
698
699 /// ExactSIVtest - Tests the SIV subscript pair
700 /// (Src and Dst) for dependence.
701 /// Things of the form [c1 + a1*i] and [c2 + a2*i],
702 /// where i is an induction variable, c1 and c2 are loop invariant,
703 /// and a1 and a2 are constant.
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 bool exactSIVtest(const SCEV *SrcCoeff,
709 const SCEV *DstCoeff,
710 const SCEV *SrcConst,
711 const SCEV *DstConst,
712 const Loop *CurrentLoop,
713 unsigned Level,
714 FullDependence &Result,
715 Constraint &NewConstraint) const;
716
717 /// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair
718 /// (Src and Dst) for dependence.
719 /// Things of the form [c1] and [c2 + a*i],
720 /// where i is an induction variable, c1 and c2 are loop invariant,
721 /// and a is a constant. See also weakZeroDstSIVtest.
722 /// Returns true if any possible dependence is disproved.
723 /// If there might be a dependence, returns false.
724 /// Sets appropriate direction entry.
725 /// Set consistent to false.
726 /// If loop peeling will break the dependence, mark appropriately.
727 bool weakZeroSrcSIVtest(const SCEV *DstCoeff,
728 const SCEV *SrcConst,
729 const SCEV *DstConst,
730 const Loop *CurrentLoop,
731 unsigned Level,
732 FullDependence &Result,
733 Constraint &NewConstraint) const;
734
735 /// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair
736 /// (Src and Dst) for dependence.
737 /// Things of the form [c1 + a*i] and [c2],
738 /// where i is an induction variable, c1 and c2 are loop invariant,
739 /// and a is a constant. See also weakZeroSrcSIVtest.
740 /// Returns true if any possible dependence is disproved.
741 /// If there might be a dependence, returns false.
742 /// Sets appropriate direction entry.
743 /// Set consistent to false.
744 /// If loop peeling will break the dependence, mark appropriately.
745 bool weakZeroDstSIVtest(const SCEV *SrcCoeff,
746 const SCEV *SrcConst,
747 const SCEV *DstConst,
748 const Loop *CurrentLoop,
749 unsigned Level,
750 FullDependence &Result,
751 Constraint &NewConstraint) const;
752
753 /// exactRDIVtest - Tests the RDIV subscript pair for dependence.
754 /// Things of the form [c1 + a*i] and [c2 + b*j],
755 /// where i and j are induction variable, c1 and c2 are loop invariant,
756 /// and a and b are constants.
757 /// Returns true if any possible dependence is disproved.
758 /// Marks the result as inconsistent.
759 /// Works in some cases that symbolicRDIVtest doesn't,
760 /// and vice versa.
761 bool exactRDIVtest(const SCEV *SrcCoeff,
762 const SCEV *DstCoeff,
763 const SCEV *SrcConst,
764 const SCEV *DstConst,
765 const Loop *SrcLoop,
766 const Loop *DstLoop,
767 FullDependence &Result) const;
768
769 /// symbolicRDIVtest - Tests the RDIV subscript pair for dependence.
770 /// Things of the form [c1 + a*i] and [c2 + b*j],
771 /// where i and j are induction variable, c1 and c2 are loop invariant,
772 /// and a and b are constants.
773 /// Returns true if any possible dependence is disproved.
774 /// Marks the result as inconsistent.
775 /// Works in some cases that exactRDIVtest doesn't,
776 /// and vice versa. Can also be used as a backup for
777 /// ordinary SIV tests.
778 bool symbolicRDIVtest(const SCEV *SrcCoeff,
779 const SCEV *DstCoeff,
780 const SCEV *SrcConst,
781 const SCEV *DstConst,
782 const Loop *SrcLoop,
783 const Loop *DstLoop) const;
784
785 /// gcdMIVtest - Tests an MIV subscript pair for dependence.
786 /// Returns true if any possible dependence is disproved.
787 /// Marks the result as inconsistent.
788 /// Can sometimes disprove the equal direction for 1 or more loops.
789 // Can handle some symbolics that even the SIV tests don't get,
790 /// so we use it as a backup for everything.
791 bool gcdMIVtest(const SCEV *Src,
792 const SCEV *Dst,
793 FullDependence &Result) const;
794
795 /// banerjeeMIVtest - Tests an MIV subscript pair for dependence.
796 /// Returns true if any possible dependence is disproved.
797 /// Marks the result as inconsistent.
798 /// Computes directions.
799 bool banerjeeMIVtest(const SCEV *Src,
800 const SCEV *Dst,
801 const SmallBitVector &Loops,
802 FullDependence &Result) const;
803
804 /// collectCoefficientInfo - Walks through the subscript,
805 /// collecting each coefficient, the associated loop bounds,
806 /// and recording its positive and negative parts for later use.
807 CoefficientInfo *collectCoeffInfo(const SCEV *Subscript,
808 bool SrcFlag,
809 const SCEV *&Constant) const;
810
811 /// getPositivePart - X^+ = max(X, 0).
812 ///
813 const SCEV *getPositivePart(const SCEV *X) const;
814
815 /// getNegativePart - X^- = min(X, 0).
816 ///
817 const SCEV *getNegativePart(const SCEV *X) const;
818
819 /// getLowerBound - Looks through all the bounds info and
820 /// computes the lower bound given the current direction settings
821 /// at each level.
822 const SCEV *getLowerBound(BoundInfo *Bound) const;
823
824 /// getUpperBound - Looks through all the bounds info and
825 /// computes the upper bound given the current direction settings
826 /// at each level.
827 const SCEV *getUpperBound(BoundInfo *Bound) const;
828
829 /// exploreDirections - Hierarchically expands the direction vector
830 /// search space, combining the directions of discovered dependences
831 /// in the DirSet field of Bound. Returns the number of distinct
832 /// dependences discovered. If the dependence is disproved,
833 /// it will return 0.
834 unsigned exploreDirections(unsigned Level,
835 CoefficientInfo *A,
836 CoefficientInfo *B,
837 BoundInfo *Bound,
838 const SmallBitVector &Loops,
839 unsigned &DepthExpanded,
840 const SCEV *Delta) const;
841
842 /// testBounds - Returns true iff the current bounds are plausible.
843 bool testBounds(unsigned char DirKind,
844 unsigned Level,
845 BoundInfo *Bound,
846 const SCEV *Delta) const;
847
848 /// findBoundsALL - Computes the upper and lower bounds for level K
849 /// using the * direction. Records them in Bound.
850 void findBoundsALL(CoefficientInfo *A,
851 CoefficientInfo *B,
852 BoundInfo *Bound,
853 unsigned K) const;
854
855 /// findBoundsLT - Computes the upper and lower bounds for level K
856 /// using the < direction. Records them in Bound.
857 void findBoundsLT(CoefficientInfo *A,
858 CoefficientInfo *B,
859 BoundInfo *Bound,
860 unsigned K) const;
861
862 /// findBoundsGT - Computes the upper and lower bounds for level K
863 /// using the > direction. Records them in Bound.
864 void findBoundsGT(CoefficientInfo *A,
865 CoefficientInfo *B,
866 BoundInfo *Bound,
867 unsigned K) const;
868
869 /// findBoundsEQ - Computes the upper and lower bounds for level K
870 /// using the = direction. Records them in Bound.
871 void findBoundsEQ(CoefficientInfo *A,
872 CoefficientInfo *B,
873 BoundInfo *Bound,
874 unsigned K) const;
875
876 /// intersectConstraints - Updates X with the intersection
877 /// of the Constraints X and Y. Returns true if X has changed.
878 bool intersectConstraints(Constraint *X,
879 const Constraint *Y);
880
881 /// propagate - Review the constraints, looking for opportunities
882 /// to simplify a subscript pair (Src and Dst).
883 /// Return true if some simplification occurs.
884 /// If the simplification isn't exact (that is, if it is conservative
885 /// in terms of dependence), set consistent to false.
886 bool propagate(const SCEV *&Src,
887 const SCEV *&Dst,
888 SmallBitVector &Loops,
889 SmallVectorImpl<Constraint> &Constraints,
890 bool &Consistent);
891
892 /// propagateDistance - Attempt to propagate a distance
893 /// constraint into a subscript pair (Src and Dst).
894 /// Return true if some simplification occurs.
895 /// If the simplification isn't exact (that is, if it is conservative
896 /// in terms of dependence), set consistent to false.
897 bool propagateDistance(const SCEV *&Src,
898 const SCEV *&Dst,
899 Constraint &CurConstraint,
900 bool &Consistent);
901
902 /// propagatePoint - Attempt to propagate a point
903 /// constraint into a subscript pair (Src and Dst).
904 /// Return true if some simplification occurs.
905 bool propagatePoint(const SCEV *&Src,
906 const SCEV *&Dst,
907 Constraint &CurConstraint);
908
909 /// propagateLine - Attempt to propagate a line
910 /// constraint into a subscript pair (Src and Dst).
911 /// Return true if some simplification occurs.
912 /// If the simplification isn't exact (that is, if it is conservative
913 /// in terms of dependence), set consistent to false.
914 bool propagateLine(const SCEV *&Src,
915 const SCEV *&Dst,
916 Constraint &CurConstraint,
917 bool &Consistent);
918
919 /// findCoefficient - Given a linear SCEV,
920 /// return the coefficient corresponding to specified loop.
921 /// If there isn't one, return the SCEV constant 0.
922 /// For example, given a*i + b*j + c*k, returning the coefficient
923 /// corresponding to the j loop would yield b.
924 const SCEV *findCoefficient(const SCEV *Expr,
925 const Loop *TargetLoop) const;
926
927 /// zeroCoefficient - Given a linear SCEV,
928 /// return the SCEV given by zeroing out the coefficient
929 /// corresponding to the specified loop.
930 /// For example, given a*i + b*j + c*k, zeroing the coefficient
931 /// corresponding to the j loop would yield a*i + c*k.
932 const SCEV *zeroCoefficient(const SCEV *Expr,
933 const Loop *TargetLoop) const;
934
935 /// addToCoefficient - Given a linear SCEV Expr,
936 /// return the SCEV given by adding some Value to the
937 /// coefficient corresponding to the specified TargetLoop.
938 /// For example, given a*i + b*j + c*k, adding 1 to the coefficient
939 /// corresponding to the j loop would yield a*i + (b+1)*j + c*k.
940 const SCEV *addToCoefficient(const SCEV *Expr,
941 const Loop *TargetLoop,
942 const SCEV *Value) const;
943
944 /// updateDirection - Update direction vector entry
945 /// based on the current constraint.
946 void updateDirection(Dependence::DVEntry &Level,
947 const Constraint &CurConstraint) const;
948
949 /// Given a linear access function, tries to recover subscripts
950 /// for each dimension of the array element access.
951 bool tryDelinearize(Instruction *Src, Instruction *Dst,
952 SmallVectorImpl<Subscript> &Pair);
953
954 /// Tries to delinearize \p Src and \p Dst access functions for a fixed size
955 /// multi-dimensional array. Calls tryDelinearizeFixedSizeImpl() to
956 /// delinearize \p Src and \p Dst separately,
957 bool tryDelinearizeFixedSize(Instruction *Src, Instruction *Dst,
958 const SCEV *SrcAccessFn,
959 const SCEV *DstAccessFn,
960 SmallVectorImpl<const SCEV *> &SrcSubscripts,
961 SmallVectorImpl<const SCEV *> &DstSubscripts);
962
963 /// Tries to delinearize access function for a multi-dimensional array with
964 /// symbolic runtime sizes.
965 /// Returns true upon success and false otherwise.
966 bool tryDelinearizeParametricSize(
967 Instruction *Src, Instruction *Dst, const SCEV *SrcAccessFn,
968 const SCEV *DstAccessFn, SmallVectorImpl<const SCEV *> &SrcSubscripts,
969 SmallVectorImpl<const SCEV *> &DstSubscripts);
970
971 /// checkSubscript - Helper function for checkSrcSubscript and
972 /// checkDstSubscript to avoid duplicate code
973 bool checkSubscript(const SCEV *Expr, const Loop *LoopNest,
974 SmallBitVector &Loops, bool IsSrc);
975 }; // class DependenceInfo
976
977 /// AnalysisPass to compute dependence information in a function
978 class DependenceAnalysis : public AnalysisInfoMixin<DependenceAnalysis> {
979 public:
980 typedef DependenceInfo Result;
981 Result run(Function &F, FunctionAnalysisManager &FAM);
982
983 private:
984 static AnalysisKey Key;
985 friend struct AnalysisInfoMixin<DependenceAnalysis>;
986 }; // class DependenceAnalysis
987
988 /// Printer pass to dump DA results.
989 struct DependenceAnalysisPrinterPass
990 : public PassInfoMixin<DependenceAnalysisPrinterPass> {
991 DependenceAnalysisPrinterPass(raw_ostream &OS,
992 bool NormalizeResults = false)
993 : OS(OS), NormalizeResults(NormalizeResults) {}
994
995 PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM);
996
997 static bool isRequired() { return true; }
998
999 private:
1000 raw_ostream &OS;
1001 bool NormalizeResults;
1002 }; // class DependenceAnalysisPrinterPass
1003
1004 /// Legacy pass manager pass to access dependence information
1005 class DependenceAnalysisWrapperPass : public FunctionPass {
1006 public:
1007 static char ID; // Class identification, replacement for typeinfo
1008 DependenceAnalysisWrapperPass();
1009
1010 bool runOnFunction(Function &F) override;
1011 void releaseMemory() override;
1012 void getAnalysisUsage(AnalysisUsage &) const override;
1013 void print(raw_ostream &, const Module * = nullptr) const override;
1014 DependenceInfo &getDI() const;
1015
1016 private:
1017 std::unique_ptr<DependenceInfo> info;
1018 }; // class DependenceAnalysisWrapperPass
1019
1020 /// createDependenceAnalysisPass - This creates an instance of the
1021 /// DependenceAnalysis wrapper pass.
1022 FunctionPass *createDependenceAnalysisWrapperPass();
1023
1024} // namespace llvm
1025
1026#endif
1027

source code of llvm/include/llvm/Analysis/DependenceAnalysis.h