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 { NONE = 0,
86 LT = 1,
87 EQ = 2,
88 LE = 3,
89 GT = 4,
90 NE = 5,
91 GE = 6,
92 ALL = 7 };
93 unsigned char Direction : 3; // Init to ALL, then refine.
94 bool Scalar : 1; // Init to true.
95 bool PeelFirst : 1; // Peeling the first iteration will break dependence.
96 bool PeelLast : 1; // Peeling the last iteration will break the dependence.
97 bool Splitable : 1; // Splitting the loop will break dependence.
98 const SCEV *Distance = nullptr; // NULL implies no distance available.
99 DVEntry()
100 : Direction(ALL), Scalar(true), PeelFirst(false), PeelLast(false),
101 Splitable(false) {}
102 };
103
104 /// getSrc - Returns the source instruction for this dependence.
105 ///
106 Instruction *getSrc() const { return Src; }
107
108 /// getDst - Returns the destination instruction for this dependence.
109 ///
110 Instruction *getDst() const { return Dst; }
111
112 /// isInput - Returns true if this is an input dependence.
113 ///
114 bool isInput() const;
115
116 /// isOutput - Returns true if this is an output dependence.
117 ///
118 bool isOutput() const;
119
120 /// isFlow - Returns true if this is a flow (aka true) dependence.
121 ///
122 bool isFlow() const;
123
124 /// isAnti - Returns true if this is an anti dependence.
125 ///
126 bool isAnti() const;
127
128 /// isOrdered - Returns true if dependence is Output, Flow, or Anti
129 ///
130 bool isOrdered() const { return isOutput() || isFlow() || isAnti(); }
131
132 /// isUnordered - Returns true if dependence is Input
133 ///
134 bool isUnordered() const { return isInput(); }
135
136 /// isLoopIndependent - Returns true if this is a loop-independent
137 /// dependence.
138 virtual bool isLoopIndependent() const { return true; }
139
140 /// isConfused - Returns true if this dependence is confused
141 /// (the compiler understands nothing and makes worst-case
142 /// assumptions).
143 virtual bool isConfused() const { return true; }
144
145 /// isConsistent - Returns true if this dependence is consistent
146 /// (occurs every time the source and destination are executed).
147 virtual bool isConsistent() const { return false; }
148
149 /// getLevels - Returns the number of common loops surrounding the
150 /// source and destination of the dependence.
151 virtual unsigned getLevels() const { return 0; }
152
153 /// getDirection - Returns the direction associated with a particular
154 /// level.
155 virtual unsigned getDirection(unsigned Level) const { return DVEntry::ALL; }
156
157 /// getDistance - Returns the distance (or NULL) associated with a
158 /// particular level.
159 virtual const SCEV *getDistance(unsigned Level) const { return nullptr; }
160
161 /// Check if the direction vector is negative. A negative direction
162 /// vector means Src and Dst are reversed in the actual program.
163 virtual bool isDirectionNegative() const { return false; }
164
165 /// If the direction vector is negative, normalize the direction
166 /// vector to make it non-negative. Normalization is done by reversing
167 /// Src and Dst, plus reversing the dependence directions and distances
168 /// in the vector.
169 virtual bool normalize(ScalarEvolution *SE) { return false; }
170
171 /// isPeelFirst - Returns true if peeling the first iteration from
172 /// this loop will break this dependence.
173 virtual bool isPeelFirst(unsigned Level) const { return false; }
174
175 /// isPeelLast - Returns true if peeling the last iteration from
176 /// this loop will break this dependence.
177 virtual bool isPeelLast(unsigned Level) const { return false; }
178
179 /// isSplitable - Returns true if splitting this loop will break
180 /// the dependence.
181 virtual bool isSplitable(unsigned Level) const { return false; }
182
183 /// isScalar - Returns true if a particular level is scalar; that is,
184 /// if no subscript in the source or destination mention the induction
185 /// variable associated with the loop at this level.
186 virtual bool isScalar(unsigned Level) const;
187
188 /// getNextPredecessor - Returns the value of the NextPredecessor
189 /// field.
190 const Dependence *getNextPredecessor() const { return NextPredecessor; }
191
192 /// getNextSuccessor - Returns the value of the NextSuccessor
193 /// field.
194 const Dependence *getNextSuccessor() const { return NextSuccessor; }
195
196 /// setNextPredecessor - Sets the value of the NextPredecessor
197 /// field.
198 void setNextPredecessor(const Dependence *pred) { NextPredecessor = pred; }
199
200 /// setNextSuccessor - Sets the value of the NextSuccessor
201 /// field.
202 void setNextSuccessor(const Dependence *succ) { NextSuccessor = succ; }
203
204 /// dump - For debugging purposes, dumps a dependence to OS.
205 ///
206 void dump(raw_ostream &OS) const;
207
208 protected:
209 Instruction *Src, *Dst;
210
211 private:
212 const Dependence *NextPredecessor = nullptr, *NextSuccessor = nullptr;
213 friend class DependenceInfo;
214 };
215
216 /// FullDependence - This class represents a dependence between two memory
217 /// references in a function. It contains detailed information about the
218 /// dependence (direction vectors, etc.) and is used when the compiler is
219 /// able to accurately analyze the interaction of the references; that is,
220 /// it is not a confused dependence (see Dependence). In most cases
221 /// (for output, flow, and anti dependences), the dependence implies an
222 /// ordering, where the source must precede the destination; in contrast,
223 /// input dependences are unordered.
224 class FullDependence final : public Dependence {
225 public:
226 FullDependence(Instruction *Src, Instruction *Dst, bool LoopIndependent,
227 unsigned Levels);
228
229 /// isLoopIndependent - Returns true if this is a loop-independent
230 /// dependence.
231 bool isLoopIndependent() const override { return LoopIndependent; }
232
233 /// isConfused - Returns true if this dependence is confused
234 /// (the compiler understands nothing and makes worst-case
235 /// assumptions).
236 bool isConfused() const override { return false; }
237
238 /// isConsistent - Returns true if this dependence is consistent
239 /// (occurs every time the source and destination are executed).
240 bool isConsistent() const override { return Consistent; }
241
242 /// getLevels - Returns the number of common loops surrounding the
243 /// source and destination of the dependence.
244 unsigned getLevels() const override { return Levels; }
245
246 /// getDirection - Returns the direction associated with a particular
247 /// level.
248 unsigned getDirection(unsigned Level) const override;
249
250 /// getDistance - Returns the distance (or NULL) associated with a
251 /// particular level.
252 const SCEV *getDistance(unsigned Level) const override;
253
254 /// Check if the direction vector is negative. A negative direction
255 /// vector means Src and Dst are reversed in the actual program.
256 bool isDirectionNegative() const override;
257
258 /// If the direction vector is negative, normalize the direction
259 /// vector to make it non-negative. Normalization is done by reversing
260 /// Src and Dst, plus reversing the dependence directions and distances
261 /// in the vector.
262 bool normalize(ScalarEvolution *SE) override;
263
264 /// isPeelFirst - Returns true if peeling the first iteration from
265 /// this loop will break this dependence.
266 bool isPeelFirst(unsigned Level) const override;
267
268 /// isPeelLast - Returns true if peeling the last iteration from
269 /// this loop will break this dependence.
270 bool isPeelLast(unsigned Level) const override;
271
272 /// isSplitable - Returns true if splitting the loop will break
273 /// the dependence.
274 bool isSplitable(unsigned Level) const override;
275
276 /// isScalar - Returns true if a particular level is scalar; that is,
277 /// if no subscript in the source or destination mention the induction
278 /// variable associated with the loop at this level.
279 bool isScalar(unsigned Level) const override;
280
281 private:
282 unsigned short Levels;
283 bool LoopIndependent;
284 bool Consistent; // Init to true, then refine.
285 std::unique_ptr<DVEntry[]> DV;
286 friend class DependenceInfo;
287 };
288
289 /// DependenceInfo - This class is the main dependence-analysis driver.
290 ///
291 class DependenceInfo {
292 public:
293 DependenceInfo(Function *F, AAResults *AA, ScalarEvolution *SE,
294 LoopInfo *LI)
295 : AA(AA), SE(SE), LI(LI), F(F) {}
296
297 /// Handle transitive invalidation when the cached analysis results go away.
298 bool invalidate(Function &F, const PreservedAnalyses &PA,
299 FunctionAnalysisManager::Invalidator &Inv);
300
301 /// depends - Tests for a dependence between the Src and Dst instructions.
302 /// Returns NULL if no dependence; otherwise, returns a Dependence (or a
303 /// FullDependence) with as much information as can be gleaned.
304 /// The flag PossiblyLoopIndependent should be set by the caller
305 /// if it appears that control flow can reach from Src to Dst
306 /// without traversing a loop back edge.
307 std::unique_ptr<Dependence> depends(Instruction *Src,
308 Instruction *Dst,
309 bool PossiblyLoopIndependent);
310
311 /// getSplitIteration - Give a dependence that's splittable at some
312 /// particular level, return the iteration that should be used to split
313 /// the loop.
314 ///
315 /// Generally, the dependence analyzer will be used to build
316 /// a dependence graph for a function (basically a map from instructions
317 /// to dependences). Looking for cycles in the graph shows us loops
318 /// that cannot be trivially vectorized/parallelized.
319 ///
320 /// We can try to improve the situation by examining all the dependences
321 /// that make up the cycle, looking for ones we can break.
322 /// Sometimes, peeling the first or last iteration of a loop will break
323 /// dependences, and there are flags for those possibilities.
324 /// Sometimes, splitting a loop at some other iteration will do the trick,
325 /// and we've got a flag for that case. Rather than waste the space to
326 /// record the exact iteration (since we rarely know), we provide
327 /// a method that calculates the iteration. It's a drag that it must work
328 /// from scratch, but wonderful in that it's possible.
329 ///
330 /// Here's an example:
331 ///
332 /// for (i = 0; i < 10; i++)
333 /// A[i] = ...
334 /// ... = A[11 - i]
335 ///
336 /// There's a loop-carried flow dependence from the store to the load,
337 /// found by the weak-crossing SIV test. The dependence will have a flag,
338 /// indicating that the dependence can be broken by splitting the loop.
339 /// Calling getSplitIteration will return 5.
340 /// Splitting the loop breaks the dependence, like so:
341 ///
342 /// for (i = 0; i <= 5; i++)
343 /// A[i] = ...
344 /// ... = A[11 - i]
345 /// for (i = 6; i < 10; i++)
346 /// A[i] = ...
347 /// ... = A[11 - i]
348 ///
349 /// breaks the dependence and allows us to vectorize/parallelize
350 /// both loops.
351 const SCEV *getSplitIteration(const Dependence &Dep, unsigned Level);
352
353 Function *getFunction() const { return F; }
354
355 private:
356 AAResults *AA;
357 ScalarEvolution *SE;
358 LoopInfo *LI;
359 Function *F;
360
361 /// Subscript - This private struct represents a pair of subscripts from
362 /// a pair of potentially multi-dimensional array references. We use a
363 /// vector of them to guide subscript partitioning.
364 struct Subscript {
365 const SCEV *Src;
366 const SCEV *Dst;
367 enum ClassificationKind { ZIV, SIV, RDIV, MIV, NonLinear } Classification;
368 SmallBitVector Loops;
369 SmallBitVector GroupLoops;
370 SmallBitVector Group;
371 };
372
373 struct CoefficientInfo {
374 const SCEV *Coeff;
375 const SCEV *PosPart;
376 const SCEV *NegPart;
377 const SCEV *Iterations;
378 };
379
380 struct BoundInfo {
381 const SCEV *Iterations;
382 const SCEV *Upper[8];
383 const SCEV *Lower[8];
384 unsigned char Direction;
385 unsigned char DirSet;
386 };
387
388 /// Constraint - This private class represents a constraint, as defined
389 /// in the paper
390 ///
391 /// Practical Dependence Testing
392 /// Goff, Kennedy, Tseng
393 /// PLDI 1991
394 ///
395 /// There are 5 kinds of constraint, in a hierarchy.
396 /// 1) Any - indicates no constraint, any dependence is possible.
397 /// 2) Line - A line ax + by = c, where a, b, and c are parameters,
398 /// representing the dependence equation.
399 /// 3) Distance - The value d of the dependence distance;
400 /// 4) Point - A point <x, y> representing the dependence from
401 /// iteration x to iteration y.
402 /// 5) Empty - No dependence is possible.
403 class Constraint {
404 private:
405 enum ConstraintKind { Empty, Point, Distance, Line, Any } Kind;
406 ScalarEvolution *SE;
407 const SCEV *A;
408 const SCEV *B;
409 const SCEV *C;
410 const Loop *AssociatedLoop;
411
412 public:
413 /// isEmpty - Return true if the constraint is of kind Empty.
414 bool isEmpty() const { return Kind == Empty; }
415
416 /// isPoint - Return true if the constraint is of kind Point.
417 bool isPoint() const { return Kind == Point; }
418
419 /// isDistance - Return true if the constraint is of kind Distance.
420 bool isDistance() const { return Kind == Distance; }
421
422 /// isLine - Return true if the constraint is of kind Line.
423 /// Since Distance's can also be represented as Lines, we also return
424 /// true if the constraint is of kind Distance.
425 bool isLine() const { return Kind == Line || Kind == Distance; }
426
427 /// isAny - Return true if the constraint is of kind Any;
428 bool isAny() const { return Kind == Any; }
429
430 /// getX - If constraint is a point <X, Y>, returns X.
431 /// Otherwise assert.
432 const SCEV *getX() const;
433
434 /// getY - If constraint is a point <X, Y>, returns Y.
435 /// Otherwise assert.
436 const SCEV *getY() const;
437
438 /// getA - If constraint is a line AX + BY = C, returns A.
439 /// Otherwise assert.
440 const SCEV *getA() const;
441
442 /// getB - If constraint is a line AX + BY = C, returns B.
443 /// Otherwise assert.
444 const SCEV *getB() const;
445
446 /// getC - If constraint is a line AX + BY = C, returns C.
447 /// Otherwise assert.
448 const SCEV *getC() const;
449
450 /// getD - If constraint is a distance, returns D.
451 /// Otherwise assert.
452 const SCEV *getD() const;
453
454 /// getAssociatedLoop - Returns the loop associated with this constraint.
455 const Loop *getAssociatedLoop() const;
456
457 /// setPoint - Change a constraint to Point.
458 void setPoint(const SCEV *X, const SCEV *Y, const Loop *CurrentLoop);
459
460 /// setLine - Change a constraint to Line.
461 void setLine(const SCEV *A, const SCEV *B,
462 const SCEV *C, const Loop *CurrentLoop);
463
464 /// setDistance - Change a constraint to Distance.
465 void setDistance(const SCEV *D, const Loop *CurrentLoop);
466
467 /// setEmpty - Change a constraint to Empty.
468 void setEmpty();
469
470 /// setAny - Change a constraint to Any.
471 void setAny(ScalarEvolution *SE);
472
473 /// dump - For debugging purposes. Dumps the constraint
474 /// out to OS.
475 void dump(raw_ostream &OS) const;
476 };
477
478 /// establishNestingLevels - Examines the loop nesting of the Src and Dst
479 /// instructions and establishes their shared loops. Sets the variables
480 /// CommonLevels, SrcLevels, and MaxLevels.
481 /// The source and destination instructions needn't be contained in the same
482 /// loop. The routine establishNestingLevels finds the level of most deeply
483 /// nested loop that contains them both, CommonLevels. An instruction that's
484 /// not contained in a loop is at level = 0. MaxLevels is equal to the level
485 /// of the source plus the level of the destination, minus CommonLevels.
486 /// This lets us allocate vectors MaxLevels in length, with room for every
487 /// distinct loop referenced in both the source and destination subscripts.
488 /// The variable SrcLevels is the nesting depth of the source instruction.
489 /// It's used to help calculate distinct loops referenced by the destination.
490 /// Here's the map from loops to levels:
491 /// 0 - unused
492 /// 1 - outermost common loop
493 /// ... - other common loops
494 /// CommonLevels - innermost common loop
495 /// ... - loops containing Src but not Dst
496 /// SrcLevels - innermost loop containing Src but not Dst
497 /// ... - loops containing Dst but not Src
498 /// MaxLevels - innermost loop containing Dst but not Src
499 /// Consider the follow code fragment:
500 /// for (a = ...) {
501 /// for (b = ...) {
502 /// for (c = ...) {
503 /// for (d = ...) {
504 /// A[] = ...;
505 /// }
506 /// }
507 /// for (e = ...) {
508 /// for (f = ...) {
509 /// for (g = ...) {
510 /// ... = A[];
511 /// }
512 /// }
513 /// }
514 /// }
515 /// }
516 /// If we're looking at the possibility of a dependence between the store
517 /// to A (the Src) and the load from A (the Dst), we'll note that they
518 /// have 2 loops in common, so CommonLevels will equal 2 and the direction
519 /// vector for Result will have 2 entries. SrcLevels = 4 and MaxLevels = 7.
520 /// A map from loop names to level indices would look like
521 /// a - 1
522 /// b - 2 = CommonLevels
523 /// c - 3
524 /// d - 4 = SrcLevels
525 /// e - 5
526 /// f - 6
527 /// g - 7 = MaxLevels
528 void establishNestingLevels(const Instruction *Src,
529 const Instruction *Dst);
530
531 unsigned CommonLevels, SrcLevels, MaxLevels;
532
533 /// mapSrcLoop - Given one of the loops containing the source, return
534 /// its level index in our numbering scheme.
535 unsigned mapSrcLoop(const Loop *SrcLoop) const;
536
537 /// mapDstLoop - Given one of the loops containing the destination,
538 /// return its level index in our numbering scheme.
539 unsigned mapDstLoop(const Loop *DstLoop) const;
540
541 /// isLoopInvariant - Returns true if Expression is loop invariant
542 /// in LoopNest.
543 bool isLoopInvariant(const SCEV *Expression, const Loop *LoopNest) const;
544
545 /// Makes sure all subscript pairs share the same integer type by
546 /// sign-extending as necessary.
547 /// Sign-extending a subscript is safe because getelementptr assumes the
548 /// array subscripts are signed.
549 void unifySubscriptType(ArrayRef<Subscript *> Pairs);
550
551 /// removeMatchingExtensions - Examines a subscript pair.
552 /// If the source and destination are identically sign (or zero)
553 /// extended, it strips off the extension in an effort to
554 /// simplify the actual analysis.
555 void removeMatchingExtensions(Subscript *Pair);
556
557 /// collectCommonLoops - Finds the set of loops from the LoopNest that
558 /// have a level <= CommonLevels and are referred to by the SCEV Expression.
559 void collectCommonLoops(const SCEV *Expression,
560 const Loop *LoopNest,
561 SmallBitVector &Loops) const;
562
563 /// checkSrcSubscript - Examines the SCEV Src, returning true iff it's
564 /// linear. Collect the set of loops mentioned by Src.
565 bool checkSrcSubscript(const SCEV *Src,
566 const Loop *LoopNest,
567 SmallBitVector &Loops);
568
569 /// checkDstSubscript - Examines the SCEV Dst, returning true iff it's
570 /// linear. Collect the set of loops mentioned by Dst.
571 bool checkDstSubscript(const SCEV *Dst,
572 const Loop *LoopNest,
573 SmallBitVector &Loops);
574
575 /// isKnownPredicate - Compare X and Y using the predicate Pred.
576 /// Basically a wrapper for SCEV::isKnownPredicate,
577 /// but tries harder, especially in the presence of sign and zero
578 /// extensions and symbolics.
579 bool isKnownPredicate(ICmpInst::Predicate Pred,
580 const SCEV *X,
581 const SCEV *Y) const;
582
583 /// isKnownLessThan - Compare to see if S is less than Size
584 /// Another wrapper for isKnownNegative(S - max(Size, 1)) with some extra
585 /// checking if S is an AddRec and we can prove lessthan using the loop
586 /// bounds.
587 bool isKnownLessThan(const SCEV *S, const SCEV *Size) const;
588
589 /// isKnownNonNegative - Compare to see if S is known not to be negative
590 /// Uses the fact that S comes from Ptr, which may be an inbound GEP,
591 /// Proving there is no wrapping going on.
592 bool isKnownNonNegative(const SCEV *S, const Value *Ptr) const;
593
594 /// collectUpperBound - All subscripts are the same type (on my machine,
595 /// an i64). The loop bound may be a smaller type. collectUpperBound
596 /// find the bound, if available, and zero extends it to the Type T.
597 /// (I zero extend since the bound should always be >= 0.)
598 /// If no upper bound is available, return NULL.
599 const SCEV *collectUpperBound(const Loop *l, Type *T) const;
600
601 /// collectConstantUpperBound - Calls collectUpperBound(), then
602 /// attempts to cast it to SCEVConstant. If the cast fails,
603 /// returns NULL.
604 const SCEVConstant *collectConstantUpperBound(const Loop *l, Type *T) const;
605
606 /// classifyPair - Examines the subscript pair (the Src and Dst SCEVs)
607 /// and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear.
608 /// Collects the associated loops in a set.
609 Subscript::ClassificationKind classifyPair(const SCEV *Src,
610 const Loop *SrcLoopNest,
611 const SCEV *Dst,
612 const Loop *DstLoopNest,
613 SmallBitVector &Loops);
614
615 /// testZIV - Tests the ZIV subscript pair (Src and Dst) for dependence.
616 /// Returns true if any possible dependence is disproved.
617 /// If there might be a dependence, returns false.
618 /// If the dependence isn't proven to exist,
619 /// marks the Result as inconsistent.
620 bool testZIV(const SCEV *Src,
621 const SCEV *Dst,
622 FullDependence &Result) const;
623
624 /// testSIV - Tests the SIV subscript pair (Src and Dst) for dependence.
625 /// Things of the form [c1 + a1*i] and [c2 + a2*j], where
626 /// i and j are induction variables, c1 and c2 are loop invariant,
627 /// and a1 and a2 are constant.
628 /// Returns true if any possible dependence is disproved.
629 /// If there might be a dependence, returns false.
630 /// Sets appropriate direction vector entry and, when possible,
631 /// the distance vector entry.
632 /// If the dependence isn't proven to exist,
633 /// marks the Result as inconsistent.
634 bool testSIV(const SCEV *Src,
635 const SCEV *Dst,
636 unsigned &Level,
637 FullDependence &Result,
638 Constraint &NewConstraint,
639 const SCEV *&SplitIter) const;
640
641 /// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence.
642 /// Things of the form [c1 + a1*i] and [c2 + a2*j]
643 /// where i and j are induction variables, c1 and c2 are loop invariant,
644 /// and a1 and a2 are constant.
645 /// With minor algebra, this test can also be used for things like
646 /// [c1 + a1*i + a2*j][c2].
647 /// Returns true if any possible dependence is disproved.
648 /// If there might be a dependence, returns false.
649 /// Marks the Result as inconsistent.
650 bool testRDIV(const SCEV *Src,
651 const SCEV *Dst,
652 FullDependence &Result) const;
653
654 /// testMIV - Tests the MIV subscript pair (Src and Dst) for dependence.
655 /// Returns true if dependence disproved.
656 /// Can sometimes refine direction vectors.
657 bool testMIV(const SCEV *Src,
658 const SCEV *Dst,
659 const SmallBitVector &Loops,
660 FullDependence &Result) const;
661
662 /// strongSIVtest - Tests the strong SIV subscript pair (Src and Dst)
663 /// for dependence.
664 /// Things of the form [c1 + a*i] and [c2 + a*i],
665 /// where i is an induction variable, c1 and c2 are loop invariant,
666 /// and a is a constant
667 /// Returns true if any possible dependence is disproved.
668 /// If there might be a dependence, returns false.
669 /// Sets appropriate direction and distance.
670 bool strongSIVtest(const SCEV *Coeff,
671 const SCEV *SrcConst,
672 const SCEV *DstConst,
673 const Loop *CurrentLoop,
674 unsigned Level,
675 FullDependence &Result,
676 Constraint &NewConstraint) const;
677
678 /// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair
679 /// (Src and Dst) for dependence.
680 /// Things of the form [c1 + a*i] and [c2 - a*i],
681 /// where i is an induction variable, c1 and c2 are loop invariant,
682 /// and a is a constant.
683 /// Returns true if any possible dependence is disproved.
684 /// If there might be a dependence, returns false.
685 /// Sets appropriate direction entry.
686 /// Set consistent to false.
687 /// Marks the dependence as splitable.
688 bool weakCrossingSIVtest(const SCEV *SrcCoeff,
689 const SCEV *SrcConst,
690 const SCEV *DstConst,
691 const Loop *CurrentLoop,
692 unsigned Level,
693 FullDependence &Result,
694 Constraint &NewConstraint,
695 const SCEV *&SplitIter) const;
696
697 /// ExactSIVtest - Tests the SIV subscript pair
698 /// (Src and Dst) for dependence.
699 /// Things of the form [c1 + a1*i] and [c2 + a2*i],
700 /// where i is an induction variable, c1 and c2 are loop invariant,
701 /// and a1 and a2 are constant.
702 /// Returns true if any possible dependence is disproved.
703 /// If there might be a dependence, returns false.
704 /// Sets appropriate direction entry.
705 /// Set consistent to false.
706 bool exactSIVtest(const SCEV *SrcCoeff,
707 const SCEV *DstCoeff,
708 const SCEV *SrcConst,
709 const SCEV *DstConst,
710 const Loop *CurrentLoop,
711 unsigned Level,
712 FullDependence &Result,
713 Constraint &NewConstraint) const;
714
715 /// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair
716 /// (Src and Dst) for dependence.
717 /// Things of the form [c1] and [c2 + a*i],
718 /// where i is an induction variable, c1 and c2 are loop invariant,
719 /// and a is a constant. See also weakZeroDstSIVtest.
720 /// Returns true if any possible dependence is disproved.
721 /// If there might be a dependence, returns false.
722 /// Sets appropriate direction entry.
723 /// Set consistent to false.
724 /// If loop peeling will break the dependence, mark appropriately.
725 bool weakZeroSrcSIVtest(const SCEV *DstCoeff,
726 const SCEV *SrcConst,
727 const SCEV *DstConst,
728 const Loop *CurrentLoop,
729 unsigned Level,
730 FullDependence &Result,
731 Constraint &NewConstraint) const;
732
733 /// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair
734 /// (Src and Dst) for dependence.
735 /// Things of the form [c1 + a*i] and [c2],
736 /// where i is an induction variable, c1 and c2 are loop invariant,
737 /// and a is a constant. See also weakZeroSrcSIVtest.
738 /// Returns true if any possible dependence is disproved.
739 /// If there might be a dependence, returns false.
740 /// Sets appropriate direction entry.
741 /// Set consistent to false.
742 /// If loop peeling will break the dependence, mark appropriately.
743 bool weakZeroDstSIVtest(const SCEV *SrcCoeff,
744 const SCEV *SrcConst,
745 const SCEV *DstConst,
746 const Loop *CurrentLoop,
747 unsigned Level,
748 FullDependence &Result,
749 Constraint &NewConstraint) const;
750
751 /// exactRDIVtest - Tests the RDIV subscript pair for dependence.
752 /// Things of the form [c1 + a*i] and [c2 + b*j],
753 /// where i and j are induction variable, c1 and c2 are loop invariant,
754 /// and a and b are constants.
755 /// Returns true if any possible dependence is disproved.
756 /// Marks the result as inconsistent.
757 /// Works in some cases that symbolicRDIVtest doesn't,
758 /// and vice versa.
759 bool exactRDIVtest(const SCEV *SrcCoeff,
760 const SCEV *DstCoeff,
761 const SCEV *SrcConst,
762 const SCEV *DstConst,
763 const Loop *SrcLoop,
764 const Loop *DstLoop,
765 FullDependence &Result) const;
766
767 /// symbolicRDIVtest - Tests the RDIV subscript pair for dependence.
768 /// Things of the form [c1 + a*i] and [c2 + b*j],
769 /// where i and j are induction variable, c1 and c2 are loop invariant,
770 /// and a and b are constants.
771 /// Returns true if any possible dependence is disproved.
772 /// Marks the result as inconsistent.
773 /// Works in some cases that exactRDIVtest doesn't,
774 /// and vice versa. Can also be used as a backup for
775 /// ordinary SIV tests.
776 bool symbolicRDIVtest(const SCEV *SrcCoeff,
777 const SCEV *DstCoeff,
778 const SCEV *SrcConst,
779 const SCEV *DstConst,
780 const Loop *SrcLoop,
781 const Loop *DstLoop) const;
782
783 /// gcdMIVtest - Tests an MIV subscript pair for dependence.
784 /// Returns true if any possible dependence is disproved.
785 /// Marks the result as inconsistent.
786 /// Can sometimes disprove the equal direction for 1 or more loops.
787 // Can handle some symbolics that even the SIV tests don't get,
788 /// so we use it as a backup for everything.
789 bool gcdMIVtest(const SCEV *Src,
790 const SCEV *Dst,
791 FullDependence &Result) const;
792
793 /// banerjeeMIVtest - Tests an MIV subscript pair for dependence.
794 /// Returns true if any possible dependence is disproved.
795 /// Marks the result as inconsistent.
796 /// Computes directions.
797 bool banerjeeMIVtest(const SCEV *Src,
798 const SCEV *Dst,
799 const SmallBitVector &Loops,
800 FullDependence &Result) const;
801
802 /// collectCoefficientInfo - Walks through the subscript,
803 /// collecting each coefficient, the associated loop bounds,
804 /// and recording its positive and negative parts for later use.
805 CoefficientInfo *collectCoeffInfo(const SCEV *Subscript,
806 bool SrcFlag,
807 const SCEV *&Constant) const;
808
809 /// getPositivePart - X^+ = max(X, 0).
810 ///
811 const SCEV *getPositivePart(const SCEV *X) const;
812
813 /// getNegativePart - X^- = min(X, 0).
814 ///
815 const SCEV *getNegativePart(const SCEV *X) const;
816
817 /// getLowerBound - Looks through all the bounds info and
818 /// computes the lower bound given the current direction settings
819 /// at each level.
820 const SCEV *getLowerBound(BoundInfo *Bound) const;
821
822 /// getUpperBound - Looks through all the bounds info and
823 /// computes the upper bound given the current direction settings
824 /// at each level.
825 const SCEV *getUpperBound(BoundInfo *Bound) const;
826
827 /// exploreDirections - Hierarchically expands the direction vector
828 /// search space, combining the directions of discovered dependences
829 /// in the DirSet field of Bound. Returns the number of distinct
830 /// dependences discovered. If the dependence is disproved,
831 /// it will return 0.
832 unsigned exploreDirections(unsigned Level,
833 CoefficientInfo *A,
834 CoefficientInfo *B,
835 BoundInfo *Bound,
836 const SmallBitVector &Loops,
837 unsigned &DepthExpanded,
838 const SCEV *Delta) const;
839
840 /// testBounds - Returns true iff the current bounds are plausible.
841 bool testBounds(unsigned char DirKind,
842 unsigned Level,
843 BoundInfo *Bound,
844 const SCEV *Delta) const;
845
846 /// findBoundsALL - Computes the upper and lower bounds for level K
847 /// using the * direction. Records them in Bound.
848 void findBoundsALL(CoefficientInfo *A,
849 CoefficientInfo *B,
850 BoundInfo *Bound,
851 unsigned K) const;
852
853 /// findBoundsLT - Computes the upper and lower bounds for level K
854 /// using the < direction. Records them in Bound.
855 void findBoundsLT(CoefficientInfo *A,
856 CoefficientInfo *B,
857 BoundInfo *Bound,
858 unsigned K) const;
859
860 /// findBoundsGT - Computes the upper and lower bounds for level K
861 /// using the > direction. Records them in Bound.
862 void findBoundsGT(CoefficientInfo *A,
863 CoefficientInfo *B,
864 BoundInfo *Bound,
865 unsigned K) const;
866
867 /// findBoundsEQ - Computes the upper and lower bounds for level K
868 /// using the = direction. Records them in Bound.
869 void findBoundsEQ(CoefficientInfo *A,
870 CoefficientInfo *B,
871 BoundInfo *Bound,
872 unsigned K) const;
873
874 /// intersectConstraints - Updates X with the intersection
875 /// of the Constraints X and Y. Returns true if X has changed.
876 bool intersectConstraints(Constraint *X,
877 const Constraint *Y);
878
879 /// propagate - Review the constraints, looking for opportunities
880 /// to simplify a subscript pair (Src and Dst).
881 /// Return true if some simplification occurs.
882 /// If the simplification isn't exact (that is, if it is conservative
883 /// in terms of dependence), set consistent to false.
884 bool propagate(const SCEV *&Src,
885 const SCEV *&Dst,
886 SmallBitVector &Loops,
887 SmallVectorImpl<Constraint> &Constraints,
888 bool &Consistent);
889
890 /// propagateDistance - Attempt to propagate a distance
891 /// constraint into a subscript pair (Src and Dst).
892 /// Return true if some simplification occurs.
893 /// If the simplification isn't exact (that is, if it is conservative
894 /// in terms of dependence), set consistent to false.
895 bool propagateDistance(const SCEV *&Src,
896 const SCEV *&Dst,
897 Constraint &CurConstraint,
898 bool &Consistent);
899
900 /// propagatePoint - Attempt to propagate a point
901 /// constraint into a subscript pair (Src and Dst).
902 /// Return true if some simplification occurs.
903 bool propagatePoint(const SCEV *&Src,
904 const SCEV *&Dst,
905 Constraint &CurConstraint);
906
907 /// propagateLine - Attempt to propagate a line
908 /// constraint into a subscript pair (Src and Dst).
909 /// Return true if some simplification occurs.
910 /// If the simplification isn't exact (that is, if it is conservative
911 /// in terms of dependence), set consistent to false.
912 bool propagateLine(const SCEV *&Src,
913 const SCEV *&Dst,
914 Constraint &CurConstraint,
915 bool &Consistent);
916
917 /// findCoefficient - Given a linear SCEV,
918 /// return the coefficient corresponding to specified loop.
919 /// If there isn't one, return the SCEV constant 0.
920 /// For example, given a*i + b*j + c*k, returning the coefficient
921 /// corresponding to the j loop would yield b.
922 const SCEV *findCoefficient(const SCEV *Expr,
923 const Loop *TargetLoop) const;
924
925 /// zeroCoefficient - Given a linear SCEV,
926 /// return the SCEV given by zeroing out the coefficient
927 /// corresponding to the specified loop.
928 /// For example, given a*i + b*j + c*k, zeroing the coefficient
929 /// corresponding to the j loop would yield a*i + c*k.
930 const SCEV *zeroCoefficient(const SCEV *Expr,
931 const Loop *TargetLoop) const;
932
933 /// addToCoefficient - Given a linear SCEV Expr,
934 /// return the SCEV given by adding some Value to the
935 /// coefficient corresponding to the specified TargetLoop.
936 /// For example, given a*i + b*j + c*k, adding 1 to the coefficient
937 /// corresponding to the j loop would yield a*i + (b+1)*j + c*k.
938 const SCEV *addToCoefficient(const SCEV *Expr,
939 const Loop *TargetLoop,
940 const SCEV *Value) const;
941
942 /// updateDirection - Update direction vector entry
943 /// based on the current constraint.
944 void updateDirection(Dependence::DVEntry &Level,
945 const Constraint &CurConstraint) const;
946
947 /// Given a linear access function, tries to recover subscripts
948 /// for each dimension of the array element access.
949 bool tryDelinearize(Instruction *Src, Instruction *Dst,
950 SmallVectorImpl<Subscript> &Pair);
951
952 /// Tries to delinearize \p Src and \p Dst access functions for a fixed size
953 /// multi-dimensional array. Calls tryDelinearizeFixedSizeImpl() to
954 /// delinearize \p Src and \p Dst separately,
955 bool tryDelinearizeFixedSize(Instruction *Src, Instruction *Dst,
956 const SCEV *SrcAccessFn,
957 const SCEV *DstAccessFn,
958 SmallVectorImpl<const SCEV *> &SrcSubscripts,
959 SmallVectorImpl<const SCEV *> &DstSubscripts);
960
961 /// Tries to delinearize access function for a multi-dimensional array with
962 /// symbolic runtime sizes.
963 /// Returns true upon success and false otherwise.
964 bool tryDelinearizeParametricSize(
965 Instruction *Src, Instruction *Dst, const SCEV *SrcAccessFn,
966 const SCEV *DstAccessFn, SmallVectorImpl<const SCEV *> &SrcSubscripts,
967 SmallVectorImpl<const SCEV *> &DstSubscripts);
968
969 /// checkSubscript - Helper function for checkSrcSubscript and
970 /// checkDstSubscript to avoid duplicate code
971 bool checkSubscript(const SCEV *Expr, const Loop *LoopNest,
972 SmallBitVector &Loops, bool IsSrc);
973 }; // class DependenceInfo
974
975 /// AnalysisPass to compute dependence information in a function
976 class DependenceAnalysis : public AnalysisInfoMixin<DependenceAnalysis> {
977 public:
978 typedef DependenceInfo Result;
979 Result run(Function &F, FunctionAnalysisManager &FAM);
980
981 private:
982 static AnalysisKey Key;
983 friend struct AnalysisInfoMixin<DependenceAnalysis>;
984 }; // class DependenceAnalysis
985
986 /// Printer pass to dump DA results.
987 struct DependenceAnalysisPrinterPass
988 : public PassInfoMixin<DependenceAnalysisPrinterPass> {
989 DependenceAnalysisPrinterPass(raw_ostream &OS,
990 bool NormalizeResults = false)
991 : OS(OS), NormalizeResults(NormalizeResults) {}
992
993 PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM);
994
995 private:
996 raw_ostream &OS;
997 bool NormalizeResults;
998 }; // class DependenceAnalysisPrinterPass
999
1000 /// Legacy pass manager pass to access dependence information
1001 class DependenceAnalysisWrapperPass : public FunctionPass {
1002 public:
1003 static char ID; // Class identification, replacement for typeinfo
1004 DependenceAnalysisWrapperPass();
1005
1006 bool runOnFunction(Function &F) override;
1007 void releaseMemory() override;
1008 void getAnalysisUsage(AnalysisUsage &) const override;
1009 void print(raw_ostream &, const Module * = nullptr) const override;
1010 DependenceInfo &getDI() const;
1011
1012 private:
1013 std::unique_ptr<DependenceInfo> info;
1014 }; // class DependenceAnalysisWrapperPass
1015
1016 /// createDependenceAnalysisPass - This creates an instance of the
1017 /// DependenceAnalysis wrapper pass.
1018 FunctionPass *createDependenceAnalysisWrapperPass();
1019
1020} // namespace llvm
1021
1022#endif
1023

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