1//===- LoopAccessAnalysis.cpp - Loop Access Analysis Implementation --------==//
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// The implementation for the loop memory dependence that was originally
11// developed for the loop vectorizer.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/Analysis/LoopAccessAnalysis.h"
16#include "llvm/Analysis/LoopInfo.h"
17#include "llvm/Analysis/ScalarEvolutionExpander.h"
18#include "llvm/Analysis/TargetLibraryInfo.h"
19#include "llvm/Analysis/ValueTracking.h"
20#include "llvm/IR/DiagnosticInfo.h"
21#include "llvm/IR/Dominators.h"
22#include "llvm/IR/IRBuilder.h"
23#include "llvm/Support/Debug.h"
24#include "llvm/Support/raw_ostream.h"
25#include "llvm/Transforms/Utils/VectorUtils.h"
26using namespace llvm;
27
28#define DEBUG_TYPE "loop-accesses"
29
30static cl::opt<unsigned, true>
31VectorizationFactor("force-vector-width", cl::Hidden,
32                    cl::desc("Sets the SIMD width. Zero is autoselect."),
33                    cl::location(VectorizerParams::VectorizationFactor));
34unsigned VectorizerParams::VectorizationFactor;
35
36static cl::opt<unsigned, true>
37VectorizationInterleave("force-vector-interleave", cl::Hidden,
38                        cl::desc("Sets the vectorization interleave count. "
39                                 "Zero is autoselect."),
40                        cl::location(
41                            VectorizerParams::VectorizationInterleave));
42unsigned VectorizerParams::VectorizationInterleave;
43
44static cl::opt<unsigned, true> RuntimeMemoryCheckThreshold(
45    "runtime-memory-check-threshold", cl::Hidden,
46    cl::desc("When performing memory disambiguation checks at runtime do not "
47             "generate more than this number of comparisons (default = 8)."),
48    cl::location(VectorizerParams::RuntimeMemoryCheckThreshold), cl::init(8));
49unsigned VectorizerParams::RuntimeMemoryCheckThreshold;
50
51/// Maximum SIMD width.
52const unsigned VectorizerParams::MaxVectorWidth = 64;
53
54/// \brief We collect interesting dependences up to this threshold.
55static cl::opt<unsigned> MaxInterestingDependence(
56    "max-interesting-dependences", cl::Hidden,
57    cl::desc("Maximum number of interesting dependences collected by "
58             "loop-access analysis (default = 100)"),
59    cl::init(100));
60
61bool VectorizerParams::isInterleaveForced() {
62  return ::VectorizationInterleave.getNumOccurrences() > 0;
63}
64
65void LoopAccessReport::emitAnalysis(const LoopAccessReport &Message,
66                                    const Function *TheFunction,
67                                    const Loop *TheLoop,
68                                    const char *PassName) {
69  DebugLoc DL = TheLoop->getStartLoc();
70  if (const Instruction *I = Message.getInstr())
71    DL = I->getDebugLoc();
72  emitOptimizationRemarkAnalysis(TheFunction->getContext(), PassName,
73                                 *TheFunction, DL, Message.str());
74}
75
76Value *llvm::stripIntegerCast(Value *V) {
77  if (CastInst *CI = dyn_cast<CastInst>(V))
78    if (CI->getOperand(0)->getType()->isIntegerTy())
79      return CI->getOperand(0);
80  return V;
81}
82
83const SCEV *llvm::replaceSymbolicStrideSCEV(ScalarEvolution *SE,
84                                            const ValueToValueMap &PtrToStride,
85                                            Value *Ptr, Value *OrigPtr) {
86
87  const SCEV *OrigSCEV = SE->getSCEV(Ptr);
88
89  // If there is an entry in the map return the SCEV of the pointer with the
90  // symbolic stride replaced by one.
91  ValueToValueMap::const_iterator SI =
92      PtrToStride.find(OrigPtr ? OrigPtr : Ptr);
93  if (SI != PtrToStride.end()) {
94    Value *StrideVal = SI->second;
95
96    // Strip casts.
97    StrideVal = stripIntegerCast(StrideVal);
98
99    // Replace symbolic stride by one.
100    Value *One = ConstantInt::get(StrideVal->getType(), 1);
101    ValueToValueMap RewriteMap;
102    RewriteMap[StrideVal] = One;
103
104    const SCEV *ByOne =
105        SCEVParameterRewriter::rewrite(OrigSCEV, *SE, RewriteMap, true);
106    DEBUG(dbgs() << "LAA: Replacing SCEV: " << *OrigSCEV << " by: " << *ByOne
107                 << "\n");
108    return ByOne;
109  }
110
111  // Otherwise, just return the SCEV of the original pointer.
112  return SE->getSCEV(Ptr);
113}
114
115void LoopAccessInfo::RuntimePointerCheck::insert(
116    ScalarEvolution *SE, Loop *Lp, Value *Ptr, bool WritePtr, unsigned DepSetId,
117    unsigned ASId, const ValueToValueMap &Strides) {
118  // Get the stride replaced scev.
119  const SCEV *Sc = replaceSymbolicStrideSCEV(SE, Strides, Ptr);
120  const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Sc);
121  assert(AR && "Invalid addrec expression");
122  const SCEV *Ex = SE->getBackedgeTakenCount(Lp);
123  const SCEV *ScEnd = AR->evaluateAtIteration(Ex, *SE);
124  Pointers.push_back(Ptr);
125  Starts.push_back(AR->getStart());
126  Ends.push_back(ScEnd);
127  IsWritePtr.push_back(WritePtr);
128  DependencySetId.push_back(DepSetId);
129  AliasSetId.push_back(ASId);
130}
131
132bool LoopAccessInfo::RuntimePointerCheck::needsChecking(
133    unsigned I, unsigned J, const SmallVectorImpl<int> *PtrPartition) const {
134  // No need to check if two readonly pointers intersect.
135  if (!IsWritePtr[I] && !IsWritePtr[J])
136    return false;
137
138  // Only need to check pointers between two different dependency sets.
139  if (DependencySetId[I] == DependencySetId[J])
140    return false;
141
142  // Only need to check pointers in the same alias set.
143  if (AliasSetId[I] != AliasSetId[J])
144    return false;
145
146  // If PtrPartition is set omit checks between pointers of the same partition.
147  // Partition number -1 means that the pointer is used in multiple partitions.
148  // In this case we can't omit the check.
149  if (PtrPartition && (*PtrPartition)[I] != -1 &&
150      (*PtrPartition)[I] == (*PtrPartition)[J])
151    return false;
152
153  return true;
154}
155
156void LoopAccessInfo::RuntimePointerCheck::print(
157    raw_ostream &OS, unsigned Depth,
158    const SmallVectorImpl<int> *PtrPartition) const {
159  unsigned NumPointers = Pointers.size();
160  if (NumPointers == 0)
161    return;
162
163  OS.indent(Depth) << "Run-time memory checks:\n";
164  unsigned N = 0;
165  for (unsigned I = 0; I < NumPointers; ++I)
166    for (unsigned J = I + 1; J < NumPointers; ++J)
167      if (needsChecking(I, J, PtrPartition)) {
168        OS.indent(Depth) << N++ << ":\n";
169        OS.indent(Depth + 2) << *Pointers[I];
170        if (PtrPartition)
171          OS << " (Partition: " << (*PtrPartition)[I] << ")";
172        OS << "\n";
173        OS.indent(Depth + 2) << *Pointers[J];
174        if (PtrPartition)
175          OS << " (Partition: " << (*PtrPartition)[J] << ")";
176        OS << "\n";
177      }
178}
179
180bool LoopAccessInfo::RuntimePointerCheck::needsAnyChecking(
181    const SmallVectorImpl<int> *PtrPartition) const {
182  unsigned NumPointers = Pointers.size();
183
184  for (unsigned I = 0; I < NumPointers; ++I)
185    for (unsigned J = I + 1; J < NumPointers; ++J)
186      if (needsChecking(I, J, PtrPartition))
187        return true;
188  return false;
189}
190
191namespace {
192/// \brief Analyses memory accesses in a loop.
193///
194/// Checks whether run time pointer checks are needed and builds sets for data
195/// dependence checking.
196class AccessAnalysis {
197public:
198  /// \brief Read or write access location.
199  typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
200  typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet;
201
202  AccessAnalysis(const DataLayout &Dl, AliasAnalysis *AA,
203                 MemoryDepChecker::DepCandidates &DA)
204      : DL(Dl), AST(*AA), DepCands(DA), IsRTCheckNeeded(false) {}
205
206  /// \brief Register a load  and whether it is only read from.
207  void addLoad(AliasAnalysis::Location &Loc, bool IsReadOnly) {
208    Value *Ptr = const_cast<Value*>(Loc.Ptr);
209    AST.add(Ptr, AliasAnalysis::UnknownSize, Loc.AATags);
210    Accesses.insert(MemAccessInfo(Ptr, false));
211    if (IsReadOnly)
212      ReadOnlyPtr.insert(Ptr);
213  }
214
215  /// \brief Register a store.
216  void addStore(AliasAnalysis::Location &Loc) {
217    Value *Ptr = const_cast<Value*>(Loc.Ptr);
218    AST.add(Ptr, AliasAnalysis::UnknownSize, Loc.AATags);
219    Accesses.insert(MemAccessInfo(Ptr, true));
220  }
221
222  /// \brief Check whether we can check the pointers at runtime for
223  /// non-intersection.
224  bool canCheckPtrAtRT(LoopAccessInfo::RuntimePointerCheck &RtCheck,
225                       unsigned &NumComparisons, ScalarEvolution *SE,
226                       Loop *TheLoop, const ValueToValueMap &Strides,
227                       bool ShouldCheckStride = false);
228
229  /// \brief Goes over all memory accesses, checks whether a RT check is needed
230  /// and builds sets of dependent accesses.
231  void buildDependenceSets() {
232    processMemAccesses();
233  }
234
235  bool isRTCheckNeeded() { return IsRTCheckNeeded; }
236
237  bool isDependencyCheckNeeded() { return !CheckDeps.empty(); }
238  void resetDepChecks() { CheckDeps.clear(); }
239
240  MemAccessInfoSet &getDependenciesToCheck() { return CheckDeps; }
241
242private:
243  typedef SetVector<MemAccessInfo> PtrAccessSet;
244
245  /// \brief Go over all memory access and check whether runtime pointer checks
246  /// are needed /// and build sets of dependency check candidates.
247  void processMemAccesses();
248
249  /// Set of all accesses.
250  PtrAccessSet Accesses;
251
252  const DataLayout &DL;
253
254  /// Set of accesses that need a further dependence check.
255  MemAccessInfoSet CheckDeps;
256
257  /// Set of pointers that are read only.
258  SmallPtrSet<Value*, 16> ReadOnlyPtr;
259
260  /// An alias set tracker to partition the access set by underlying object and
261  //intrinsic property (such as TBAA metadata).
262  AliasSetTracker AST;
263
264  /// Sets of potentially dependent accesses - members of one set share an
265  /// underlying pointer. The set "CheckDeps" identfies which sets really need a
266  /// dependence check.
267  MemoryDepChecker::DepCandidates &DepCands;
268
269  bool IsRTCheckNeeded;
270};
271
272} // end anonymous namespace
273
274/// \brief Check whether a pointer can participate in a runtime bounds check.
275static bool hasComputableBounds(ScalarEvolution *SE,
276                                const ValueToValueMap &Strides, Value *Ptr) {
277  const SCEV *PtrScev = replaceSymbolicStrideSCEV(SE, Strides, Ptr);
278  const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
279  if (!AR)
280    return false;
281
282  return AR->isAffine();
283}
284
285/// \brief Check the stride of the pointer and ensure that it does not wrap in
286/// the address space.
287static int isStridedPtr(ScalarEvolution *SE, Value *Ptr, const Loop *Lp,
288                        const ValueToValueMap &StridesMap);
289
290bool AccessAnalysis::canCheckPtrAtRT(
291    LoopAccessInfo::RuntimePointerCheck &RtCheck, unsigned &NumComparisons,
292    ScalarEvolution *SE, Loop *TheLoop, const ValueToValueMap &StridesMap,
293    bool ShouldCheckStride) {
294  // Find pointers with computable bounds. We are going to use this information
295  // to place a runtime bound check.
296  bool CanDoRT = true;
297
298  bool IsDepCheckNeeded = isDependencyCheckNeeded();
299  NumComparisons = 0;
300
301  // We assign a consecutive id to access from different alias sets.
302  // Accesses between different groups doesn't need to be checked.
303  unsigned ASId = 1;
304  for (auto &AS : AST) {
305    unsigned NumReadPtrChecks = 0;
306    unsigned NumWritePtrChecks = 0;
307
308    // We assign consecutive id to access from different dependence sets.
309    // Accesses within the same set don't need a runtime check.
310    unsigned RunningDepId = 1;
311    DenseMap<Value *, unsigned> DepSetId;
312
313    for (auto A : AS) {
314      Value *Ptr = A.getValue();
315      bool IsWrite = Accesses.count(MemAccessInfo(Ptr, true));
316      MemAccessInfo Access(Ptr, IsWrite);
317
318      if (IsWrite)
319        ++NumWritePtrChecks;
320      else
321        ++NumReadPtrChecks;
322
323      if (hasComputableBounds(SE, StridesMap, Ptr) &&
324          // When we run after a failing dependency check we have to make sure
325          // we don't have wrapping pointers.
326          (!ShouldCheckStride ||
327           isStridedPtr(SE, Ptr, TheLoop, StridesMap) == 1)) {
328        // The id of the dependence set.
329        unsigned DepId;
330
331        if (IsDepCheckNeeded) {
332          Value *Leader = DepCands.getLeaderValue(Access).getPointer();
333          unsigned &LeaderId = DepSetId[Leader];
334          if (!LeaderId)
335            LeaderId = RunningDepId++;
336          DepId = LeaderId;
337        } else
338          // Each access has its own dependence set.
339          DepId = RunningDepId++;
340
341        RtCheck.insert(SE, TheLoop, Ptr, IsWrite, DepId, ASId, StridesMap);
342
343        DEBUG(dbgs() << "LAA: Found a runtime check ptr:" << *Ptr << '\n');
344      } else {
345        CanDoRT = false;
346      }
347    }
348
349    if (IsDepCheckNeeded && CanDoRT && RunningDepId == 2)
350      NumComparisons += 0; // Only one dependence set.
351    else {
352      NumComparisons += (NumWritePtrChecks * (NumReadPtrChecks +
353                                              NumWritePtrChecks - 1));
354    }
355
356    ++ASId;
357  }
358
359  // If the pointers that we would use for the bounds comparison have different
360  // address spaces, assume the values aren't directly comparable, so we can't
361  // use them for the runtime check. We also have to assume they could
362  // overlap. In the future there should be metadata for whether address spaces
363  // are disjoint.
364  unsigned NumPointers = RtCheck.Pointers.size();
365  for (unsigned i = 0; i < NumPointers; ++i) {
366    for (unsigned j = i + 1; j < NumPointers; ++j) {
367      // Only need to check pointers between two different dependency sets.
368      if (RtCheck.DependencySetId[i] == RtCheck.DependencySetId[j])
369       continue;
370      // Only need to check pointers in the same alias set.
371      if (RtCheck.AliasSetId[i] != RtCheck.AliasSetId[j])
372        continue;
373
374      Value *PtrI = RtCheck.Pointers[i];
375      Value *PtrJ = RtCheck.Pointers[j];
376
377      unsigned ASi = PtrI->getType()->getPointerAddressSpace();
378      unsigned ASj = PtrJ->getType()->getPointerAddressSpace();
379      if (ASi != ASj) {
380        DEBUG(dbgs() << "LAA: Runtime check would require comparison between"
381                       " different address spaces\n");
382        return false;
383      }
384    }
385  }
386
387  return CanDoRT;
388}
389
390void AccessAnalysis::processMemAccesses() {
391  // We process the set twice: first we process read-write pointers, last we
392  // process read-only pointers. This allows us to skip dependence tests for
393  // read-only pointers.
394
395  DEBUG(dbgs() << "LAA: Processing memory accesses...\n");
396  DEBUG(dbgs() << "  AST: "; AST.dump());
397  DEBUG(dbgs() << "LAA:   Accesses(" << Accesses.size() << "):\n");
398  DEBUG({
399    for (auto A : Accesses)
400      dbgs() << "\t" << *A.getPointer() << " (" <<
401                (A.getInt() ? "write" : (ReadOnlyPtr.count(A.getPointer()) ?
402                                         "read-only" : "read")) << ")\n";
403  });
404
405  // The AliasSetTracker has nicely partitioned our pointers by metadata
406  // compatibility and potential for underlying-object overlap. As a result, we
407  // only need to check for potential pointer dependencies within each alias
408  // set.
409  for (auto &AS : AST) {
410    // Note that both the alias-set tracker and the alias sets themselves used
411    // linked lists internally and so the iteration order here is deterministic
412    // (matching the original instruction order within each set).
413
414    bool SetHasWrite = false;
415
416    // Map of pointers to last access encountered.
417    typedef DenseMap<Value*, MemAccessInfo> UnderlyingObjToAccessMap;
418    UnderlyingObjToAccessMap ObjToLastAccess;
419
420    // Set of access to check after all writes have been processed.
421    PtrAccessSet DeferredAccesses;
422
423    // Iterate over each alias set twice, once to process read/write pointers,
424    // and then to process read-only pointers.
425    for (int SetIteration = 0; SetIteration < 2; ++SetIteration) {
426      bool UseDeferred = SetIteration > 0;
427      PtrAccessSet &S = UseDeferred ? DeferredAccesses : Accesses;
428
429      for (auto AV : AS) {
430        Value *Ptr = AV.getValue();
431
432        // For a single memory access in AliasSetTracker, Accesses may contain
433        // both read and write, and they both need to be handled for CheckDeps.
434        for (auto AC : S) {
435          if (AC.getPointer() != Ptr)
436            continue;
437
438          bool IsWrite = AC.getInt();
439
440          // If we're using the deferred access set, then it contains only
441          // reads.
442          bool IsReadOnlyPtr = ReadOnlyPtr.count(Ptr) && !IsWrite;
443          if (UseDeferred && !IsReadOnlyPtr)
444            continue;
445          // Otherwise, the pointer must be in the PtrAccessSet, either as a
446          // read or a write.
447          assert(((IsReadOnlyPtr && UseDeferred) || IsWrite ||
448                  S.count(MemAccessInfo(Ptr, false))) &&
449                 "Alias-set pointer not in the access set?");
450
451          MemAccessInfo Access(Ptr, IsWrite);
452          DepCands.insert(Access);
453
454          // Memorize read-only pointers for later processing and skip them in
455          // the first round (they need to be checked after we have seen all
456          // write pointers). Note: we also mark pointer that are not
457          // consecutive as "read-only" pointers (so that we check
458          // "a[b[i]] +="). Hence, we need the second check for "!IsWrite".
459          if (!UseDeferred && IsReadOnlyPtr) {
460            DeferredAccesses.insert(Access);
461            continue;
462          }
463
464          // If this is a write - check other reads and writes for conflicts. If
465          // this is a read only check other writes for conflicts (but only if
466          // there is no other write to the ptr - this is an optimization to
467          // catch "a[i] = a[i] + " without having to do a dependence check).
468          if ((IsWrite || IsReadOnlyPtr) && SetHasWrite) {
469            CheckDeps.insert(Access);
470            IsRTCheckNeeded = true;
471          }
472
473          if (IsWrite)
474            SetHasWrite = true;
475
476          // Create sets of pointers connected by a shared alias set and
477          // underlying object.
478          typedef SmallVector<Value *, 16> ValueVector;
479          ValueVector TempObjects;
480          GetUnderlyingObjects(Ptr, TempObjects, DL);
481          for (Value *UnderlyingObj : TempObjects) {
482            UnderlyingObjToAccessMap::iterator Prev =
483                ObjToLastAccess.find(UnderlyingObj);
484            if (Prev != ObjToLastAccess.end())
485              DepCands.unionSets(Access, Prev->second);
486
487            ObjToLastAccess[UnderlyingObj] = Access;
488          }
489        }
490      }
491    }
492  }
493}
494
495static bool isInBoundsGep(Value *Ptr) {
496  if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr))
497    return GEP->isInBounds();
498  return false;
499}
500
501/// \brief Check whether the access through \p Ptr has a constant stride.
502static int isStridedPtr(ScalarEvolution *SE, Value *Ptr, const Loop *Lp,
503                        const ValueToValueMap &StridesMap) {
504  const Type *Ty = Ptr->getType();
505  assert(Ty->isPointerTy() && "Unexpected non-ptr");
506
507  // Make sure that the pointer does not point to aggregate types.
508  const PointerType *PtrTy = cast<PointerType>(Ty);
509  if (PtrTy->getElementType()->isAggregateType()) {
510    DEBUG(dbgs() << "LAA: Bad stride - Not a pointer to a scalar type"
511          << *Ptr << "\n");
512    return 0;
513  }
514
515  const SCEV *PtrScev = replaceSymbolicStrideSCEV(SE, StridesMap, Ptr);
516
517  const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
518  if (!AR) {
519    DEBUG(dbgs() << "LAA: Bad stride - Not an AddRecExpr pointer "
520          << *Ptr << " SCEV: " << *PtrScev << "\n");
521    return 0;
522  }
523
524  // The accesss function must stride over the innermost loop.
525  if (Lp != AR->getLoop()) {
526    DEBUG(dbgs() << "LAA: Bad stride - Not striding over innermost loop " <<
527          *Ptr << " SCEV: " << *PtrScev << "\n");
528  }
529
530  // The address calculation must not wrap. Otherwise, a dependence could be
531  // inverted.
532  // An inbounds getelementptr that is a AddRec with a unit stride
533  // cannot wrap per definition. The unit stride requirement is checked later.
534  // An getelementptr without an inbounds attribute and unit stride would have
535  // to access the pointer value "0" which is undefined behavior in address
536  // space 0, therefore we can also vectorize this case.
537  bool IsInBoundsGEP = isInBoundsGep(Ptr);
538  bool IsNoWrapAddRec = AR->getNoWrapFlags(SCEV::NoWrapMask);
539  bool IsInAddressSpaceZero = PtrTy->getAddressSpace() == 0;
540  if (!IsNoWrapAddRec && !IsInBoundsGEP && !IsInAddressSpaceZero) {
541    DEBUG(dbgs() << "LAA: Bad stride - Pointer may wrap in the address space "
542          << *Ptr << " SCEV: " << *PtrScev << "\n");
543    return 0;
544  }
545
546  // Check the step is constant.
547  const SCEV *Step = AR->getStepRecurrence(*SE);
548
549  // Calculate the pointer stride and check if it is consecutive.
550  const SCEVConstant *C = dyn_cast<SCEVConstant>(Step);
551  if (!C) {
552    DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided " << *Ptr <<
553          " SCEV: " << *PtrScev << "\n");
554    return 0;
555  }
556
557  auto &DL = Lp->getHeader()->getModule()->getDataLayout();
558  int64_t Size = DL.getTypeAllocSize(PtrTy->getElementType());
559  const APInt &APStepVal = C->getValue()->getValue();
560
561  // Huge step value - give up.
562  if (APStepVal.getBitWidth() > 64)
563    return 0;
564
565  int64_t StepVal = APStepVal.getSExtValue();
566
567  // Strided access.
568  int64_t Stride = StepVal / Size;
569  int64_t Rem = StepVal % Size;
570  if (Rem)
571    return 0;
572
573  // If the SCEV could wrap but we have an inbounds gep with a unit stride we
574  // know we can't "wrap around the address space". In case of address space
575  // zero we know that this won't happen without triggering undefined behavior.
576  if (!IsNoWrapAddRec && (IsInBoundsGEP || IsInAddressSpaceZero) &&
577      Stride != 1 && Stride != -1)
578    return 0;
579
580  return Stride;
581}
582
583bool MemoryDepChecker::Dependence::isSafeForVectorization(DepType Type) {
584  switch (Type) {
585  case NoDep:
586  case Forward:
587  case BackwardVectorizable:
588    return true;
589
590  case Unknown:
591  case ForwardButPreventsForwarding:
592  case Backward:
593  case BackwardVectorizableButPreventsForwarding:
594    return false;
595  }
596  llvm_unreachable("unexpected DepType!");
597}
598
599bool MemoryDepChecker::Dependence::isInterestingDependence(DepType Type) {
600  switch (Type) {
601  case NoDep:
602  case Forward:
603    return false;
604
605  case BackwardVectorizable:
606  case Unknown:
607  case ForwardButPreventsForwarding:
608  case Backward:
609  case BackwardVectorizableButPreventsForwarding:
610    return true;
611  }
612  llvm_unreachable("unexpected DepType!");
613}
614
615bool MemoryDepChecker::Dependence::isPossiblyBackward() const {
616  switch (Type) {
617  case NoDep:
618  case Forward:
619  case ForwardButPreventsForwarding:
620    return false;
621
622  case Unknown:
623  case BackwardVectorizable:
624  case Backward:
625  case BackwardVectorizableButPreventsForwarding:
626    return true;
627  }
628  llvm_unreachable("unexpected DepType!");
629}
630
631bool MemoryDepChecker::couldPreventStoreLoadForward(unsigned Distance,
632                                                    unsigned TypeByteSize) {
633  // If loads occur at a distance that is not a multiple of a feasible vector
634  // factor store-load forwarding does not take place.
635  // Positive dependences might cause troubles because vectorizing them might
636  // prevent store-load forwarding making vectorized code run a lot slower.
637  //   a[i] = a[i-3] ^ a[i-8];
638  //   The stores to a[i:i+1] don't align with the stores to a[i-3:i-2] and
639  //   hence on your typical architecture store-load forwarding does not take
640  //   place. Vectorizing in such cases does not make sense.
641  // Store-load forwarding distance.
642  const unsigned NumCyclesForStoreLoadThroughMemory = 8*TypeByteSize;
643  // Maximum vector factor.
644  unsigned MaxVFWithoutSLForwardIssues =
645    VectorizerParams::MaxVectorWidth * TypeByteSize;
646  if(MaxSafeDepDistBytes < MaxVFWithoutSLForwardIssues)
647    MaxVFWithoutSLForwardIssues = MaxSafeDepDistBytes;
648
649  for (unsigned vf = 2*TypeByteSize; vf <= MaxVFWithoutSLForwardIssues;
650       vf *= 2) {
651    if (Distance % vf && Distance / vf < NumCyclesForStoreLoadThroughMemory) {
652      MaxVFWithoutSLForwardIssues = (vf >>=1);
653      break;
654    }
655  }
656
657  if (MaxVFWithoutSLForwardIssues< 2*TypeByteSize) {
658    DEBUG(dbgs() << "LAA: Distance " << Distance <<
659          " that could cause a store-load forwarding conflict\n");
660    return true;
661  }
662
663  if (MaxVFWithoutSLForwardIssues < MaxSafeDepDistBytes &&
664      MaxVFWithoutSLForwardIssues !=
665      VectorizerParams::MaxVectorWidth * TypeByteSize)
666    MaxSafeDepDistBytes = MaxVFWithoutSLForwardIssues;
667  return false;
668}
669
670MemoryDepChecker::Dependence::DepType
671MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
672                              const MemAccessInfo &B, unsigned BIdx,
673                              const ValueToValueMap &Strides) {
674  assert (AIdx < BIdx && "Must pass arguments in program order");
675
676  Value *APtr = A.getPointer();
677  Value *BPtr = B.getPointer();
678  bool AIsWrite = A.getInt();
679  bool BIsWrite = B.getInt();
680
681  // Two reads are independent.
682  if (!AIsWrite && !BIsWrite)
683    return Dependence::NoDep;
684
685  // We cannot check pointers in different address spaces.
686  if (APtr->getType()->getPointerAddressSpace() !=
687      BPtr->getType()->getPointerAddressSpace())
688    return Dependence::Unknown;
689
690  const SCEV *AScev = replaceSymbolicStrideSCEV(SE, Strides, APtr);
691  const SCEV *BScev = replaceSymbolicStrideSCEV(SE, Strides, BPtr);
692
693  int StrideAPtr = isStridedPtr(SE, APtr, InnermostLoop, Strides);
694  int StrideBPtr = isStridedPtr(SE, BPtr, InnermostLoop, Strides);
695
696  const SCEV *Src = AScev;
697  const SCEV *Sink = BScev;
698
699  // If the induction step is negative we have to invert source and sink of the
700  // dependence.
701  if (StrideAPtr < 0) {
702    //Src = BScev;
703    //Sink = AScev;
704    std::swap(APtr, BPtr);
705    std::swap(Src, Sink);
706    std::swap(AIsWrite, BIsWrite);
707    std::swap(AIdx, BIdx);
708    std::swap(StrideAPtr, StrideBPtr);
709  }
710
711  const SCEV *Dist = SE->getMinusSCEV(Sink, Src);
712
713  DEBUG(dbgs() << "LAA: Src Scev: " << *Src << "Sink Scev: " << *Sink
714        << "(Induction step: " << StrideAPtr <<  ")\n");
715  DEBUG(dbgs() << "LAA: Distance for " << *InstMap[AIdx] << " to "
716        << *InstMap[BIdx] << ": " << *Dist << "\n");
717
718  // Need consecutive accesses. We don't want to vectorize
719  // "A[B[i]] += ..." and similar code or pointer arithmetic that could wrap in
720  // the address space.
721  if (!StrideAPtr || !StrideBPtr || StrideAPtr != StrideBPtr){
722    DEBUG(dbgs() << "Non-consecutive pointer access\n");
723    return Dependence::Unknown;
724  }
725
726  const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist);
727  if (!C) {
728    DEBUG(dbgs() << "LAA: Dependence because of non-constant distance\n");
729    ShouldRetryWithRuntimeCheck = true;
730    return Dependence::Unknown;
731  }
732
733  Type *ATy = APtr->getType()->getPointerElementType();
734  Type *BTy = BPtr->getType()->getPointerElementType();
735  auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout();
736  unsigned TypeByteSize = DL.getTypeAllocSize(ATy);
737
738  // Negative distances are not plausible dependencies.
739  const APInt &Val = C->getValue()->getValue();
740  if (Val.isNegative()) {
741    bool IsTrueDataDependence = (AIsWrite && !BIsWrite);
742    if (IsTrueDataDependence &&
743        (couldPreventStoreLoadForward(Val.abs().getZExtValue(), TypeByteSize) ||
744         ATy != BTy))
745      return Dependence::ForwardButPreventsForwarding;
746
747    DEBUG(dbgs() << "LAA: Dependence is negative: NoDep\n");
748    return Dependence::Forward;
749  }
750
751  // Write to the same location with the same size.
752  // Could be improved to assert type sizes are the same (i32 == float, etc).
753  if (Val == 0) {
754    if (ATy == BTy)
755      return Dependence::NoDep;
756    DEBUG(dbgs() << "LAA: Zero dependence difference but different types\n");
757    return Dependence::Unknown;
758  }
759
760  assert(Val.isStrictlyPositive() && "Expect a positive value");
761
762  if (ATy != BTy) {
763    DEBUG(dbgs() <<
764          "LAA: ReadWrite-Write positive dependency with different types\n");
765    return Dependence::Unknown;
766  }
767
768  unsigned Distance = (unsigned) Val.getZExtValue();
769
770  // Bail out early if passed-in parameters make vectorization not feasible.
771  unsigned ForcedFactor = (VectorizerParams::VectorizationFactor ?
772                           VectorizerParams::VectorizationFactor : 1);
773  unsigned ForcedUnroll = (VectorizerParams::VectorizationInterleave ?
774                           VectorizerParams::VectorizationInterleave : 1);
775
776  // The distance must be bigger than the size needed for a vectorized version
777  // of the operation and the size of the vectorized operation must not be
778  // bigger than the currrent maximum size.
779  if (Distance < 2*TypeByteSize ||
780      2*TypeByteSize > MaxSafeDepDistBytes ||
781      Distance < TypeByteSize * ForcedUnroll * ForcedFactor) {
782    DEBUG(dbgs() << "LAA: Failure because of Positive distance "
783        << Val.getSExtValue() << '\n');
784    return Dependence::Backward;
785  }
786
787  // Positive distance bigger than max vectorization factor.
788  MaxSafeDepDistBytes = Distance < MaxSafeDepDistBytes ?
789    Distance : MaxSafeDepDistBytes;
790
791  bool IsTrueDataDependence = (!AIsWrite && BIsWrite);
792  if (IsTrueDataDependence &&
793      couldPreventStoreLoadForward(Distance, TypeByteSize))
794    return Dependence::BackwardVectorizableButPreventsForwarding;
795
796  DEBUG(dbgs() << "LAA: Positive distance " << Val.getSExtValue() <<
797        " with max VF = " << MaxSafeDepDistBytes / TypeByteSize << '\n');
798
799  return Dependence::BackwardVectorizable;
800}
801
802bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets,
803                                   MemAccessInfoSet &CheckDeps,
804                                   const ValueToValueMap &Strides) {
805
806  MaxSafeDepDistBytes = -1U;
807  while (!CheckDeps.empty()) {
808    MemAccessInfo CurAccess = *CheckDeps.begin();
809
810    // Get the relevant memory access set.
811    EquivalenceClasses<MemAccessInfo>::iterator I =
812      AccessSets.findValue(AccessSets.getLeaderValue(CurAccess));
813
814    // Check accesses within this set.
815    EquivalenceClasses<MemAccessInfo>::member_iterator AI, AE;
816    AI = AccessSets.member_begin(I), AE = AccessSets.member_end();
817
818    // Check every access pair.
819    while (AI != AE) {
820      CheckDeps.erase(*AI);
821      EquivalenceClasses<MemAccessInfo>::member_iterator OI = std::next(AI);
822      while (OI != AE) {
823        // Check every accessing instruction pair in program order.
824        for (std::vector<unsigned>::iterator I1 = Accesses[*AI].begin(),
825             I1E = Accesses[*AI].end(); I1 != I1E; ++I1)
826          for (std::vector<unsigned>::iterator I2 = Accesses[*OI].begin(),
827               I2E = Accesses[*OI].end(); I2 != I2E; ++I2) {
828            auto A = std::make_pair(&*AI, *I1);
829            auto B = std::make_pair(&*OI, *I2);
830
831            assert(*I1 != *I2);
832            if (*I1 > *I2)
833              std::swap(A, B);
834
835            Dependence::DepType Type =
836                isDependent(*A.first, A.second, *B.first, B.second, Strides);
837            SafeForVectorization &= Dependence::isSafeForVectorization(Type);
838
839            // Gather dependences unless we accumulated MaxInterestingDependence
840            // dependences.  In that case return as soon as we find the first
841            // unsafe dependence.  This puts a limit on this quadratic
842            // algorithm.
843            if (RecordInterestingDependences) {
844              if (Dependence::isInterestingDependence(Type))
845                InterestingDependences.push_back(
846                    Dependence(A.second, B.second, Type));
847
848              if (InterestingDependences.size() >= MaxInterestingDependence) {
849                RecordInterestingDependences = false;
850                InterestingDependences.clear();
851                DEBUG(dbgs() << "Too many dependences, stopped recording\n");
852              }
853            }
854            if (!RecordInterestingDependences && !SafeForVectorization)
855              return false;
856          }
857        ++OI;
858      }
859      AI++;
860    }
861  }
862
863  DEBUG(dbgs() << "Total Interesting Dependences: "
864               << InterestingDependences.size() << "\n");
865  return SafeForVectorization;
866}
867
868SmallVector<Instruction *, 4>
869MemoryDepChecker::getInstructionsForAccess(Value *Ptr, bool isWrite) const {
870  MemAccessInfo Access(Ptr, isWrite);
871  auto &IndexVector = Accesses.find(Access)->second;
872
873  SmallVector<Instruction *, 4> Insts;
874  std::transform(IndexVector.begin(), IndexVector.end(),
875                 std::back_inserter(Insts),
876                 [&](unsigned Idx) { return this->InstMap[Idx]; });
877  return Insts;
878}
879
880const char *MemoryDepChecker::Dependence::DepName[] = {
881    "NoDep", "Unknown", "Forward", "ForwardButPreventsForwarding", "Backward",
882    "BackwardVectorizable", "BackwardVectorizableButPreventsForwarding"};
883
884void MemoryDepChecker::Dependence::print(
885    raw_ostream &OS, unsigned Depth,
886    const SmallVectorImpl<Instruction *> &Instrs) const {
887  OS.indent(Depth) << DepName[Type] << ":\n";
888  OS.indent(Depth + 2) << *Instrs[Source] << " -> \n";
889  OS.indent(Depth + 2) << *Instrs[Destination] << "\n";
890}
891
892bool LoopAccessInfo::canAnalyzeLoop() {
893    // We can only analyze innermost loops.
894  if (!TheLoop->empty()) {
895    emitAnalysis(LoopAccessReport() << "loop is not the innermost loop");
896    return false;
897  }
898
899  // We must have a single backedge.
900  if (TheLoop->getNumBackEdges() != 1) {
901    emitAnalysis(
902        LoopAccessReport() <<
903        "loop control flow is not understood by analyzer");
904    return false;
905  }
906
907  // We must have a single exiting block.
908  if (!TheLoop->getExitingBlock()) {
909    emitAnalysis(
910        LoopAccessReport() <<
911        "loop control flow is not understood by analyzer");
912    return false;
913  }
914
915  // We only handle bottom-tested loops, i.e. loop in which the condition is
916  // checked at the end of each iteration. With that we can assume that all
917  // instructions in the loop are executed the same number of times.
918  if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) {
919    emitAnalysis(
920        LoopAccessReport() <<
921        "loop control flow is not understood by analyzer");
922    return false;
923  }
924
925  // We need to have a loop header.
926  DEBUG(dbgs() << "LAA: Found a loop: " <<
927        TheLoop->getHeader()->getName() << '\n');
928
929  // ScalarEvolution needs to be able to find the exit count.
930  const SCEV *ExitCount = SE->getBackedgeTakenCount(TheLoop);
931  if (ExitCount == SE->getCouldNotCompute()) {
932    emitAnalysis(LoopAccessReport() <<
933                 "could not determine number of loop iterations");
934    DEBUG(dbgs() << "LAA: SCEV could not compute the loop exit count.\n");
935    return false;
936  }
937
938  return true;
939}
940
941void LoopAccessInfo::analyzeLoop(const ValueToValueMap &Strides) {
942
943  typedef SmallVector<Value*, 16> ValueVector;
944  typedef SmallPtrSet<Value*, 16> ValueSet;
945
946  // Holds the Load and Store *instructions*.
947  ValueVector Loads;
948  ValueVector Stores;
949
950  // Holds all the different accesses in the loop.
951  unsigned NumReads = 0;
952  unsigned NumReadWrites = 0;
953
954  PtrRtCheck.Pointers.clear();
955  PtrRtCheck.Need = false;
956
957  const bool IsAnnotatedParallel = TheLoop->isAnnotatedParallel();
958
959  // For each block.
960  for (Loop::block_iterator bb = TheLoop->block_begin(),
961       be = TheLoop->block_end(); bb != be; ++bb) {
962
963    // Scan the BB and collect legal loads and stores.
964    for (BasicBlock::iterator it = (*bb)->begin(), e = (*bb)->end(); it != e;
965         ++it) {
966
967      // If this is a load, save it. If this instruction can read from memory
968      // but is not a load, then we quit. Notice that we don't handle function
969      // calls that read or write.
970      if (it->mayReadFromMemory()) {
971        // Many math library functions read the rounding mode. We will only
972        // vectorize a loop if it contains known function calls that don't set
973        // the flag. Therefore, it is safe to ignore this read from memory.
974        CallInst *Call = dyn_cast<CallInst>(it);
975        if (Call && getIntrinsicIDForCall(Call, TLI))
976          continue;
977
978        // If the function has an explicit vectorized counterpart, we can safely
979        // assume that it can be vectorized.
980        if (Call && !Call->isNoBuiltin() && Call->getCalledFunction() &&
981            TLI->isFunctionVectorizable(Call->getCalledFunction()->getName()))
982          continue;
983
984        LoadInst *Ld = dyn_cast<LoadInst>(it);
985        if (!Ld || (!Ld->isSimple() && !IsAnnotatedParallel)) {
986          emitAnalysis(LoopAccessReport(Ld)
987                       << "read with atomic ordering or volatile read");
988          DEBUG(dbgs() << "LAA: Found a non-simple load.\n");
989          CanVecMem = false;
990          return;
991        }
992        NumLoads++;
993        Loads.push_back(Ld);
994        DepChecker.addAccess(Ld);
995        continue;
996      }
997
998      // Save 'store' instructions. Abort if other instructions write to memory.
999      if (it->mayWriteToMemory()) {
1000        StoreInst *St = dyn_cast<StoreInst>(it);
1001        if (!St) {
1002          emitAnalysis(LoopAccessReport(it) <<
1003                       "instruction cannot be vectorized");
1004          CanVecMem = false;
1005          return;
1006        }
1007        if (!St->isSimple() && !IsAnnotatedParallel) {
1008          emitAnalysis(LoopAccessReport(St)
1009                       << "write with atomic ordering or volatile write");
1010          DEBUG(dbgs() << "LAA: Found a non-simple store.\n");
1011          CanVecMem = false;
1012          return;
1013        }
1014        NumStores++;
1015        Stores.push_back(St);
1016        DepChecker.addAccess(St);
1017      }
1018    } // Next instr.
1019  } // Next block.
1020
1021  // Now we have two lists that hold the loads and the stores.
1022  // Next, we find the pointers that they use.
1023
1024  // Check if we see any stores. If there are no stores, then we don't
1025  // care if the pointers are *restrict*.
1026  if (!Stores.size()) {
1027    DEBUG(dbgs() << "LAA: Found a read-only loop!\n");
1028    CanVecMem = true;
1029    return;
1030  }
1031
1032  MemoryDepChecker::DepCandidates DependentAccesses;
1033  AccessAnalysis Accesses(TheLoop->getHeader()->getModule()->getDataLayout(),
1034                          AA, DependentAccesses);
1035
1036  // Holds the analyzed pointers. We don't want to call GetUnderlyingObjects
1037  // multiple times on the same object. If the ptr is accessed twice, once
1038  // for read and once for write, it will only appear once (on the write
1039  // list). This is okay, since we are going to check for conflicts between
1040  // writes and between reads and writes, but not between reads and reads.
1041  ValueSet Seen;
1042
1043  ValueVector::iterator I, IE;
1044  for (I = Stores.begin(), IE = Stores.end(); I != IE; ++I) {
1045    StoreInst *ST = cast<StoreInst>(*I);
1046    Value* Ptr = ST->getPointerOperand();
1047    // Check for store to loop invariant address.
1048    StoreToLoopInvariantAddress |= isUniform(Ptr);
1049    // If we did *not* see this pointer before, insert it to  the read-write
1050    // list. At this phase it is only a 'write' list.
1051    if (Seen.insert(Ptr).second) {
1052      ++NumReadWrites;
1053
1054      AliasAnalysis::Location Loc = AA->getLocation(ST);
1055      // The TBAA metadata could have a control dependency on the predication
1056      // condition, so we cannot rely on it when determining whether or not we
1057      // need runtime pointer checks.
1058      if (blockNeedsPredication(ST->getParent(), TheLoop, DT))
1059        Loc.AATags.TBAA = nullptr;
1060
1061      Accesses.addStore(Loc);
1062    }
1063  }
1064
1065  if (IsAnnotatedParallel) {
1066    DEBUG(dbgs()
1067          << "LAA: A loop annotated parallel, ignore memory dependency "
1068          << "checks.\n");
1069    CanVecMem = true;
1070    return;
1071  }
1072
1073  for (I = Loads.begin(), IE = Loads.end(); I != IE; ++I) {
1074    LoadInst *LD = cast<LoadInst>(*I);
1075    Value* Ptr = LD->getPointerOperand();
1076    // If we did *not* see this pointer before, insert it to the
1077    // read list. If we *did* see it before, then it is already in
1078    // the read-write list. This allows us to vectorize expressions
1079    // such as A[i] += x;  Because the address of A[i] is a read-write
1080    // pointer. This only works if the index of A[i] is consecutive.
1081    // If the address of i is unknown (for example A[B[i]]) then we may
1082    // read a few words, modify, and write a few words, and some of the
1083    // words may be written to the same address.
1084    bool IsReadOnlyPtr = false;
1085    if (Seen.insert(Ptr).second || !isStridedPtr(SE, Ptr, TheLoop, Strides)) {
1086      ++NumReads;
1087      IsReadOnlyPtr = true;
1088    }
1089
1090    AliasAnalysis::Location Loc = AA->getLocation(LD);
1091    // The TBAA metadata could have a control dependency on the predication
1092    // condition, so we cannot rely on it when determining whether or not we
1093    // need runtime pointer checks.
1094    if (blockNeedsPredication(LD->getParent(), TheLoop, DT))
1095      Loc.AATags.TBAA = nullptr;
1096
1097    Accesses.addLoad(Loc, IsReadOnlyPtr);
1098  }
1099
1100  // If we write (or read-write) to a single destination and there are no
1101  // other reads in this loop then is it safe to vectorize.
1102  if (NumReadWrites == 1 && NumReads == 0) {
1103    DEBUG(dbgs() << "LAA: Found a write-only loop!\n");
1104    CanVecMem = true;
1105    return;
1106  }
1107
1108  // Build dependence sets and check whether we need a runtime pointer bounds
1109  // check.
1110  Accesses.buildDependenceSets();
1111  bool NeedRTCheck = Accesses.isRTCheckNeeded();
1112
1113  // Find pointers with computable bounds. We are going to use this information
1114  // to place a runtime bound check.
1115  bool CanDoRT = false;
1116  if (NeedRTCheck)
1117    CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE, TheLoop,
1118                                       Strides);
1119
1120  DEBUG(dbgs() << "LAA: We need to do " << NumComparisons <<
1121        " pointer comparisons.\n");
1122
1123  // If we only have one set of dependences to check pointers among we don't
1124  // need a runtime check.
1125  if (NumComparisons == 0 && NeedRTCheck)
1126    NeedRTCheck = false;
1127
1128  // Check that we found the bounds for the pointer.
1129  if (CanDoRT)
1130    DEBUG(dbgs() << "LAA: We can perform a memory runtime check if needed.\n");
1131  else if (NeedRTCheck) {
1132    emitAnalysis(LoopAccessReport() << "cannot identify array bounds");
1133    DEBUG(dbgs() << "LAA: We can't vectorize because we can't find " <<
1134          "the array bounds.\n");
1135    PtrRtCheck.reset();
1136    CanVecMem = false;
1137    return;
1138  }
1139
1140  PtrRtCheck.Need = NeedRTCheck;
1141
1142  CanVecMem = true;
1143  if (Accesses.isDependencyCheckNeeded()) {
1144    DEBUG(dbgs() << "LAA: Checking memory dependencies\n");
1145    CanVecMem = DepChecker.areDepsSafe(
1146        DependentAccesses, Accesses.getDependenciesToCheck(), Strides);
1147    MaxSafeDepDistBytes = DepChecker.getMaxSafeDepDistBytes();
1148
1149    if (!CanVecMem && DepChecker.shouldRetryWithRuntimeCheck()) {
1150      DEBUG(dbgs() << "LAA: Retrying with memory checks\n");
1151      NeedRTCheck = true;
1152
1153      // Clear the dependency checks. We assume they are not needed.
1154      Accesses.resetDepChecks();
1155
1156      PtrRtCheck.reset();
1157      PtrRtCheck.Need = true;
1158
1159      CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE,
1160                                         TheLoop, Strides, true);
1161      // Check that we found the bounds for the pointer.
1162      if (!CanDoRT && NumComparisons > 0) {
1163        emitAnalysis(LoopAccessReport()
1164                     << "cannot check memory dependencies at runtime");
1165        DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n");
1166        PtrRtCheck.reset();
1167        CanVecMem = false;
1168        return;
1169      }
1170
1171      CanVecMem = true;
1172    }
1173  }
1174
1175  if (CanVecMem)
1176    DEBUG(dbgs() << "LAA: No unsafe dependent memory operations in loop.  We"
1177                 << (NeedRTCheck ? "" : " don't")
1178                 << " need a runtime memory check.\n");
1179  else {
1180    emitAnalysis(LoopAccessReport() <<
1181                 "unsafe dependent memory operations in loop");
1182    DEBUG(dbgs() << "LAA: unsafe dependent memory operations in loop\n");
1183  }
1184}
1185
1186bool LoopAccessInfo::blockNeedsPredication(BasicBlock *BB, Loop *TheLoop,
1187                                           DominatorTree *DT)  {
1188  assert(TheLoop->contains(BB) && "Unknown block used");
1189
1190  // Blocks that do not dominate the latch need predication.
1191  BasicBlock* Latch = TheLoop->getLoopLatch();
1192  return !DT->dominates(BB, Latch);
1193}
1194
1195void LoopAccessInfo::emitAnalysis(LoopAccessReport &Message) {
1196  assert(!Report && "Multiple reports generated");
1197  Report = Message;
1198}
1199
1200bool LoopAccessInfo::isUniform(Value *V) const {
1201  return (SE->isLoopInvariant(SE->getSCEV(V), TheLoop));
1202}
1203
1204// FIXME: this function is currently a duplicate of the one in
1205// LoopVectorize.cpp.
1206static Instruction *getFirstInst(Instruction *FirstInst, Value *V,
1207                                 Instruction *Loc) {
1208  if (FirstInst)
1209    return FirstInst;
1210  if (Instruction *I = dyn_cast<Instruction>(V))
1211    return I->getParent() == Loc->getParent() ? I : nullptr;
1212  return nullptr;
1213}
1214
1215std::pair<Instruction *, Instruction *> LoopAccessInfo::addRuntimeCheck(
1216    Instruction *Loc, const SmallVectorImpl<int> *PtrPartition) const {
1217  if (!PtrRtCheck.Need)
1218    return std::make_pair(nullptr, nullptr);
1219
1220  unsigned NumPointers = PtrRtCheck.Pointers.size();
1221  SmallVector<TrackingVH<Value> , 2> Starts;
1222  SmallVector<TrackingVH<Value> , 2> Ends;
1223
1224  LLVMContext &Ctx = Loc->getContext();
1225  SCEVExpander Exp(*SE, DL, "induction");
1226  Instruction *FirstInst = nullptr;
1227
1228  for (unsigned i = 0; i < NumPointers; ++i) {
1229    Value *Ptr = PtrRtCheck.Pointers[i];
1230    const SCEV *Sc = SE->getSCEV(Ptr);
1231
1232    if (SE->isLoopInvariant(Sc, TheLoop)) {
1233      DEBUG(dbgs() << "LAA: Adding RT check for a loop invariant ptr:" <<
1234            *Ptr <<"\n");
1235      Starts.push_back(Ptr);
1236      Ends.push_back(Ptr);
1237    } else {
1238      DEBUG(dbgs() << "LAA: Adding RT check for range:" << *Ptr << '\n');
1239      unsigned AS = Ptr->getType()->getPointerAddressSpace();
1240
1241      // Use this type for pointer arithmetic.
1242      Type *PtrArithTy = Type::getInt8PtrTy(Ctx, AS);
1243
1244      Value *Start = Exp.expandCodeFor(PtrRtCheck.Starts[i], PtrArithTy, Loc);
1245      Value *End = Exp.expandCodeFor(PtrRtCheck.Ends[i], PtrArithTy, Loc);
1246      Starts.push_back(Start);
1247      Ends.push_back(End);
1248    }
1249  }
1250
1251  IRBuilder<> ChkBuilder(Loc);
1252  // Our instructions might fold to a constant.
1253  Value *MemoryRuntimeCheck = nullptr;
1254  for (unsigned i = 0; i < NumPointers; ++i) {
1255    for (unsigned j = i+1; j < NumPointers; ++j) {
1256      if (!PtrRtCheck.needsChecking(i, j, PtrPartition))
1257        continue;
1258
1259      unsigned AS0 = Starts[i]->getType()->getPointerAddressSpace();
1260      unsigned AS1 = Starts[j]->getType()->getPointerAddressSpace();
1261
1262      assert((AS0 == Ends[j]->getType()->getPointerAddressSpace()) &&
1263             (AS1 == Ends[i]->getType()->getPointerAddressSpace()) &&
1264             "Trying to bounds check pointers with different address spaces");
1265
1266      Type *PtrArithTy0 = Type::getInt8PtrTy(Ctx, AS0);
1267      Type *PtrArithTy1 = Type::getInt8PtrTy(Ctx, AS1);
1268
1269      Value *Start0 = ChkBuilder.CreateBitCast(Starts[i], PtrArithTy0, "bc");
1270      Value *Start1 = ChkBuilder.CreateBitCast(Starts[j], PtrArithTy1, "bc");
1271      Value *End0 =   ChkBuilder.CreateBitCast(Ends[i],   PtrArithTy1, "bc");
1272      Value *End1 =   ChkBuilder.CreateBitCast(Ends[j],   PtrArithTy0, "bc");
1273
1274      Value *Cmp0 = ChkBuilder.CreateICmpULE(Start0, End1, "bound0");
1275      FirstInst = getFirstInst(FirstInst, Cmp0, Loc);
1276      Value *Cmp1 = ChkBuilder.CreateICmpULE(Start1, End0, "bound1");
1277      FirstInst = getFirstInst(FirstInst, Cmp1, Loc);
1278      Value *IsConflict = ChkBuilder.CreateAnd(Cmp0, Cmp1, "found.conflict");
1279      FirstInst = getFirstInst(FirstInst, IsConflict, Loc);
1280      if (MemoryRuntimeCheck) {
1281        IsConflict = ChkBuilder.CreateOr(MemoryRuntimeCheck, IsConflict,
1282                                         "conflict.rdx");
1283        FirstInst = getFirstInst(FirstInst, IsConflict, Loc);
1284      }
1285      MemoryRuntimeCheck = IsConflict;
1286    }
1287  }
1288
1289  if (!MemoryRuntimeCheck)
1290    return std::make_pair(nullptr, nullptr);
1291
1292  // We have to do this trickery because the IRBuilder might fold the check to a
1293  // constant expression in which case there is no Instruction anchored in a
1294  // the block.
1295  Instruction *Check = BinaryOperator::CreateAnd(MemoryRuntimeCheck,
1296                                                 ConstantInt::getTrue(Ctx));
1297  ChkBuilder.Insert(Check, "memcheck.conflict");
1298  FirstInst = getFirstInst(FirstInst, Check, Loc);
1299  return std::make_pair(FirstInst, Check);
1300}
1301
1302LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE,
1303                               const DataLayout &DL,
1304                               const TargetLibraryInfo *TLI, AliasAnalysis *AA,
1305                               DominatorTree *DT,
1306                               const ValueToValueMap &Strides)
1307    : DepChecker(SE, L), NumComparisons(0), TheLoop(L), SE(SE), DL(DL),
1308      TLI(TLI), AA(AA), DT(DT), NumLoads(0), NumStores(0),
1309      MaxSafeDepDistBytes(-1U), CanVecMem(false),
1310      StoreToLoopInvariantAddress(false) {
1311  if (canAnalyzeLoop())
1312    analyzeLoop(Strides);
1313}
1314
1315void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const {
1316  if (CanVecMem) {
1317    if (PtrRtCheck.Need)
1318      OS.indent(Depth) << "Memory dependences are safe with run-time checks\n";
1319    else
1320      OS.indent(Depth) << "Memory dependences are safe\n";
1321  }
1322
1323  OS.indent(Depth) << "Store to invariant address was "
1324                   << (StoreToLoopInvariantAddress ? "" : "not ")
1325                   << "found in loop.\n";
1326
1327  if (Report)
1328    OS.indent(Depth) << "Report: " << Report->str() << "\n";
1329
1330  if (auto *InterestingDependences = DepChecker.getInterestingDependences()) {
1331    OS.indent(Depth) << "Interesting Dependences:\n";
1332    for (auto &Dep : *InterestingDependences) {
1333      Dep.print(OS, Depth + 2, DepChecker.getMemoryInstructions());
1334      OS << "\n";
1335    }
1336  } else
1337    OS.indent(Depth) << "Too many interesting dependences, not recorded\n";
1338
1339  // List the pair of accesses need run-time checks to prove independence.
1340  PtrRtCheck.print(OS, Depth);
1341  OS << "\n";
1342}
1343
1344const LoopAccessInfo &
1345LoopAccessAnalysis::getInfo(Loop *L, const ValueToValueMap &Strides) {
1346  auto &LAI = LoopAccessInfoMap[L];
1347
1348#ifndef NDEBUG
1349  assert((!LAI || LAI->NumSymbolicStrides == Strides.size()) &&
1350         "Symbolic strides changed for loop");
1351#endif
1352
1353  if (!LAI) {
1354    const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
1355    LAI = llvm::make_unique<LoopAccessInfo>(L, SE, DL, TLI, AA, DT, Strides);
1356#ifndef NDEBUG
1357    LAI->NumSymbolicStrides = Strides.size();
1358#endif
1359  }
1360  return *LAI.get();
1361}
1362
1363void LoopAccessAnalysis::print(raw_ostream &OS, const Module *M) const {
1364  LoopAccessAnalysis &LAA = *const_cast<LoopAccessAnalysis *>(this);
1365
1366  LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
1367  ValueToValueMap NoSymbolicStrides;
1368
1369  for (Loop *TopLevelLoop : *LI)
1370    for (Loop *L : depth_first(TopLevelLoop)) {
1371      OS.indent(2) << L->getHeader()->getName() << ":\n";
1372      auto &LAI = LAA.getInfo(L, NoSymbolicStrides);
1373      LAI.print(OS, 4);
1374    }
1375}
1376
1377bool LoopAccessAnalysis::runOnFunction(Function &F) {
1378  SE = &getAnalysis<ScalarEvolution>();
1379  auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
1380  TLI = TLIP ? &TLIP->getTLI() : nullptr;
1381  AA = &getAnalysis<AliasAnalysis>();
1382  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
1383
1384  return false;
1385}
1386
1387void LoopAccessAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
1388    AU.addRequired<ScalarEvolution>();
1389    AU.addRequired<AliasAnalysis>();
1390    AU.addRequired<DominatorTreeWrapperPass>();
1391    AU.addRequired<LoopInfoWrapperPass>();
1392
1393    AU.setPreservesAll();
1394}
1395
1396char LoopAccessAnalysis::ID = 0;
1397static const char laa_name[] = "Loop Access Analysis";
1398#define LAA_NAME "loop-accesses"
1399
1400INITIALIZE_PASS_BEGIN(LoopAccessAnalysis, LAA_NAME, laa_name, false, true)
1401INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
1402INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
1403INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
1404INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
1405INITIALIZE_PASS_END(LoopAccessAnalysis, LAA_NAME, laa_name, false, true)
1406
1407namespace llvm {
1408  Pass *createLAAPass() {
1409    return new LoopAccessAnalysis();
1410  }
1411}
1412