1 //===- LoopAccessAnalysis.cpp - Loop Access Analysis Implementation --------==//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // The implementation for the loop memory dependence that was originally
11 // developed for the loop vectorizer.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Analysis/LoopAccessAnalysis.h"
16 #include "llvm/Analysis/LoopInfo.h"
17 #include "llvm/Analysis/LoopPassManager.h"
18 #include "llvm/Analysis/ScalarEvolutionExpander.h"
19 #include "llvm/Analysis/TargetLibraryInfo.h"
20 #include "llvm/Analysis/ValueTracking.h"
21 #include "llvm/Analysis/VectorUtils.h"
22 #include "llvm/IR/DiagnosticInfo.h"
23 #include "llvm/IR/Dominators.h"
24 #include "llvm/IR/IRBuilder.h"
25 #include "llvm/IR/PassManager.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/raw_ostream.h"
30 #define DEBUG_TYPE "loop-accesses"
32 static cl::opt<unsigned, true>
33 VectorizationFactor("force-vector-width", cl::Hidden,
34 cl::desc("Sets the SIMD width. Zero is autoselect."),
35 cl::location(VectorizerParams::VectorizationFactor));
36 unsigned VectorizerParams::VectorizationFactor;
38 static cl::opt<unsigned, true>
39 VectorizationInterleave("force-vector-interleave", cl::Hidden,
40 cl::desc("Sets the vectorization interleave count. "
41 "Zero is autoselect."),
43 VectorizerParams::VectorizationInterleave));
44 unsigned VectorizerParams::VectorizationInterleave;
46 static cl::opt<unsigned, true> RuntimeMemoryCheckThreshold(
47 "runtime-memory-check-threshold", cl::Hidden,
48 cl::desc("When performing memory disambiguation checks at runtime do not "
49 "generate more than this number of comparisons (default = 8)."),
50 cl::location(VectorizerParams::RuntimeMemoryCheckThreshold), cl::init(8));
51 unsigned VectorizerParams::RuntimeMemoryCheckThreshold;
53 /// \brief The maximum iterations used to merge memory checks
54 static cl::opt<unsigned> MemoryCheckMergeThreshold(
55 "memory-check-merge-threshold", cl::Hidden,
56 cl::desc("Maximum number of comparisons done when trying to merge "
57 "runtime memory checks. (default = 100)"),
60 /// Maximum SIMD width.
61 const unsigned VectorizerParams::MaxVectorWidth = 64;
63 /// \brief We collect dependences up to this threshold.
64 static cl::opt<unsigned>
65 MaxDependences("max-dependences", cl::Hidden,
66 cl::desc("Maximum number of dependences collected by "
67 "loop-access analysis (default = 100)"),
70 /// This enables versioning on the strides of symbolically striding memory
71 /// accesses in code like the following.
72 /// for (i = 0; i < N; ++i)
73 /// A[i * Stride1] += B[i * Stride2] ...
75 /// Will be roughly translated to
76 /// if (Stride1 == 1 && Stride2 == 1) {
77 /// for (i = 0; i < N; i+=4)
81 static cl::opt<bool> EnableMemAccessVersioning(
82 "enable-mem-access-versioning", cl::init(true), cl::Hidden,
83 cl::desc("Enable symbolic stride memory access versioning"));
85 /// \brief Enable store-to-load forwarding conflict detection. This option can
86 /// be disabled for correctness testing.
87 static cl::opt<bool> EnableForwardingConflictDetection(
88 "store-to-load-forwarding-conflict-detection", cl::Hidden,
89 cl::desc("Enable conflict detection in loop-access analysis"),
92 bool VectorizerParams::isInterleaveForced() {
93 return ::VectorizationInterleave.getNumOccurrences() > 0;
96 void LoopAccessReport::emitAnalysis(const LoopAccessReport &Message,
97 const Function *TheFunction,
99 const char *PassName) {
100 DebugLoc DL = TheLoop->getStartLoc();
101 if (const Instruction *I = Message.getInstr())
102 DL = I->getDebugLoc();
103 emitOptimizationRemarkAnalysis(TheFunction->getContext(), PassName,
104 *TheFunction, DL, Message.str());
107 Value *llvm::stripIntegerCast(Value *V) {
108 if (auto *CI = dyn_cast<CastInst>(V))
109 if (CI->getOperand(0)->getType()->isIntegerTy())
110 return CI->getOperand(0);
114 const SCEV *llvm::replaceSymbolicStrideSCEV(PredicatedScalarEvolution &PSE,
115 const ValueToValueMap &PtrToStride,
116 Value *Ptr, Value *OrigPtr) {
117 const SCEV *OrigSCEV = PSE.getSCEV(Ptr);
119 // If there is an entry in the map return the SCEV of the pointer with the
120 // symbolic stride replaced by one.
121 ValueToValueMap::const_iterator SI =
122 PtrToStride.find(OrigPtr ? OrigPtr : Ptr);
123 if (SI != PtrToStride.end()) {
124 Value *StrideVal = SI->second;
127 StrideVal = stripIntegerCast(StrideVal);
129 // Replace symbolic stride by one.
130 Value *One = ConstantInt::get(StrideVal->getType(), 1);
131 ValueToValueMap RewriteMap;
132 RewriteMap[StrideVal] = One;
134 ScalarEvolution *SE = PSE.getSE();
135 const auto *U = cast<SCEVUnknown>(SE->getSCEV(StrideVal));
137 static_cast<const SCEVConstant *>(SE->getOne(StrideVal->getType()));
139 PSE.addPredicate(*SE->getEqualPredicate(U, CT));
140 auto *Expr = PSE.getSCEV(Ptr);
142 DEBUG(dbgs() << "LAA: Replacing SCEV: " << *OrigSCEV << " by: " << *Expr
147 // Otherwise, just return the SCEV of the original pointer.
151 void RuntimePointerChecking::insert(Loop *Lp, Value *Ptr, bool WritePtr,
152 unsigned DepSetId, unsigned ASId,
153 const ValueToValueMap &Strides,
154 PredicatedScalarEvolution &PSE) {
155 // Get the stride replaced scev.
156 const SCEV *Sc = replaceSymbolicStrideSCEV(PSE, Strides, Ptr);
157 ScalarEvolution *SE = PSE.getSE();
162 if (SE->isLoopInvariant(Sc, Lp))
163 ScStart = ScEnd = Sc;
165 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Sc);
166 assert(AR && "Invalid addrec expression");
167 const SCEV *Ex = PSE.getBackedgeTakenCount();
169 ScStart = AR->getStart();
170 ScEnd = AR->evaluateAtIteration(Ex, *SE);
171 const SCEV *Step = AR->getStepRecurrence(*SE);
173 // For expressions with negative step, the upper bound is ScStart and the
174 // lower bound is ScEnd.
175 if (const auto *CStep = dyn_cast<SCEVConstant>(Step)) {
176 if (CStep->getValue()->isNegative())
177 std::swap(ScStart, ScEnd);
179 // Fallback case: the step is not constant, but the we can still
180 // get the upper and lower bounds of the interval by using min/max
182 ScStart = SE->getUMinExpr(ScStart, ScEnd);
183 ScEnd = SE->getUMaxExpr(AR->getStart(), ScEnd);
187 Pointers.emplace_back(Ptr, ScStart, ScEnd, WritePtr, DepSetId, ASId, Sc);
190 SmallVector<RuntimePointerChecking::PointerCheck, 4>
191 RuntimePointerChecking::generateChecks() const {
192 SmallVector<PointerCheck, 4> Checks;
194 for (unsigned I = 0; I < CheckingGroups.size(); ++I) {
195 for (unsigned J = I + 1; J < CheckingGroups.size(); ++J) {
196 const RuntimePointerChecking::CheckingPtrGroup &CGI = CheckingGroups[I];
197 const RuntimePointerChecking::CheckingPtrGroup &CGJ = CheckingGroups[J];
199 if (needsChecking(CGI, CGJ))
200 Checks.push_back(std::make_pair(&CGI, &CGJ));
206 void RuntimePointerChecking::generateChecks(
207 MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) {
208 assert(Checks.empty() && "Checks is not empty");
209 groupChecks(DepCands, UseDependencies);
210 Checks = generateChecks();
213 bool RuntimePointerChecking::needsChecking(const CheckingPtrGroup &M,
214 const CheckingPtrGroup &N) const {
215 for (unsigned I = 0, EI = M.Members.size(); EI != I; ++I)
216 for (unsigned J = 0, EJ = N.Members.size(); EJ != J; ++J)
217 if (needsChecking(M.Members[I], N.Members[J]))
222 /// Compare \p I and \p J and return the minimum.
223 /// Return nullptr in case we couldn't find an answer.
224 static const SCEV *getMinFromExprs(const SCEV *I, const SCEV *J,
225 ScalarEvolution *SE) {
226 const SCEV *Diff = SE->getMinusSCEV(J, I);
227 const SCEVConstant *C = dyn_cast<const SCEVConstant>(Diff);
231 if (C->getValue()->isNegative())
236 bool RuntimePointerChecking::CheckingPtrGroup::addPointer(unsigned Index) {
237 const SCEV *Start = RtCheck.Pointers[Index].Start;
238 const SCEV *End = RtCheck.Pointers[Index].End;
240 // Compare the starts and ends with the known minimum and maximum
241 // of this set. We need to know how we compare against the min/max
242 // of the set in order to be able to emit memchecks.
243 const SCEV *Min0 = getMinFromExprs(Start, Low, RtCheck.SE);
247 const SCEV *Min1 = getMinFromExprs(End, High, RtCheck.SE);
251 // Update the low bound expression if we've found a new min value.
255 // Update the high bound expression if we've found a new max value.
259 Members.push_back(Index);
263 void RuntimePointerChecking::groupChecks(
264 MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) {
265 // We build the groups from dependency candidates equivalence classes
267 // - We know that pointers in the same equivalence class share
268 // the same underlying object and therefore there is a chance
269 // that we can compare pointers
270 // - We wouldn't be able to merge two pointers for which we need
271 // to emit a memcheck. The classes in DepCands are already
272 // conveniently built such that no two pointers in the same
273 // class need checking against each other.
275 // We use the following (greedy) algorithm to construct the groups
276 // For every pointer in the equivalence class:
277 // For each existing group:
278 // - if the difference between this pointer and the min/max bounds
279 // of the group is a constant, then make the pointer part of the
280 // group and update the min/max bounds of that group as required.
282 CheckingGroups.clear();
284 // If we need to check two pointers to the same underlying object
285 // with a non-constant difference, we shouldn't perform any pointer
286 // grouping with those pointers. This is because we can easily get
287 // into cases where the resulting check would return false, even when
288 // the accesses are safe.
290 // The following example shows this:
291 // for (i = 0; i < 1000; ++i)
292 // a[5000 + i * m] = a[i] + a[i + 9000]
294 // Here grouping gives a check of (5000, 5000 + 1000 * m) against
295 // (0, 10000) which is always false. However, if m is 1, there is no
296 // dependence. Not grouping the checks for a[i] and a[i + 9000] allows
297 // us to perform an accurate check in this case.
299 // The above case requires that we have an UnknownDependence between
300 // accesses to the same underlying object. This cannot happen unless
301 // ShouldRetryWithRuntimeCheck is set, and therefore UseDependencies
302 // is also false. In this case we will use the fallback path and create
303 // separate checking groups for all pointers.
305 // If we don't have the dependency partitions, construct a new
306 // checking pointer group for each pointer. This is also required
307 // for correctness, because in this case we can have checking between
308 // pointers to the same underlying object.
309 if (!UseDependencies) {
310 for (unsigned I = 0; I < Pointers.size(); ++I)
311 CheckingGroups.push_back(CheckingPtrGroup(I, *this));
315 unsigned TotalComparisons = 0;
317 DenseMap<Value *, unsigned> PositionMap;
318 for (unsigned Index = 0; Index < Pointers.size(); ++Index)
319 PositionMap[Pointers[Index].PointerValue] = Index;
321 // We need to keep track of what pointers we've already seen so we
322 // don't process them twice.
323 SmallSet<unsigned, 2> Seen;
325 // Go through all equivalence classes, get the "pointer check groups"
326 // and add them to the overall solution. We use the order in which accesses
327 // appear in 'Pointers' to enforce determinism.
328 for (unsigned I = 0; I < Pointers.size(); ++I) {
329 // We've seen this pointer before, and therefore already processed
330 // its equivalence class.
334 MemoryDepChecker::MemAccessInfo Access(Pointers[I].PointerValue,
335 Pointers[I].IsWritePtr);
337 SmallVector<CheckingPtrGroup, 2> Groups;
338 auto LeaderI = DepCands.findValue(DepCands.getLeaderValue(Access));
340 // Because DepCands is constructed by visiting accesses in the order in
341 // which they appear in alias sets (which is deterministic) and the
342 // iteration order within an equivalence class member is only dependent on
343 // the order in which unions and insertions are performed on the
344 // equivalence class, the iteration order is deterministic.
345 for (auto MI = DepCands.member_begin(LeaderI), ME = DepCands.member_end();
347 unsigned Pointer = PositionMap[MI->getPointer()];
349 // Mark this pointer as seen.
350 Seen.insert(Pointer);
352 // Go through all the existing sets and see if we can find one
353 // which can include this pointer.
354 for (CheckingPtrGroup &Group : Groups) {
355 // Don't perform more than a certain amount of comparisons.
356 // This should limit the cost of grouping the pointers to something
357 // reasonable. If we do end up hitting this threshold, the algorithm
358 // will create separate groups for all remaining pointers.
359 if (TotalComparisons > MemoryCheckMergeThreshold)
364 if (Group.addPointer(Pointer)) {
371 // We couldn't add this pointer to any existing set or the threshold
372 // for the number of comparisons has been reached. Create a new group
373 // to hold the current pointer.
374 Groups.push_back(CheckingPtrGroup(Pointer, *this));
377 // We've computed the grouped checks for this partition.
378 // Save the results and continue with the next one.
379 std::copy(Groups.begin(), Groups.end(), std::back_inserter(CheckingGroups));
383 bool RuntimePointerChecking::arePointersInSamePartition(
384 const SmallVectorImpl<int> &PtrToPartition, unsigned PtrIdx1,
386 return (PtrToPartition[PtrIdx1] != -1 &&
387 PtrToPartition[PtrIdx1] == PtrToPartition[PtrIdx2]);
390 bool RuntimePointerChecking::needsChecking(unsigned I, unsigned J) const {
391 const PointerInfo &PointerI = Pointers[I];
392 const PointerInfo &PointerJ = Pointers[J];
394 // No need to check if two readonly pointers intersect.
395 if (!PointerI.IsWritePtr && !PointerJ.IsWritePtr)
398 // Only need to check pointers between two different dependency sets.
399 if (PointerI.DependencySetId == PointerJ.DependencySetId)
402 // Only need to check pointers in the same alias set.
403 if (PointerI.AliasSetId != PointerJ.AliasSetId)
409 void RuntimePointerChecking::printChecks(
410 raw_ostream &OS, const SmallVectorImpl<PointerCheck> &Checks,
411 unsigned Depth) const {
413 for (const auto &Check : Checks) {
414 const auto &First = Check.first->Members, &Second = Check.second->Members;
416 OS.indent(Depth) << "Check " << N++ << ":\n";
418 OS.indent(Depth + 2) << "Comparing group (" << Check.first << "):\n";
419 for (unsigned K = 0; K < First.size(); ++K)
420 OS.indent(Depth + 2) << *Pointers[First[K]].PointerValue << "\n";
422 OS.indent(Depth + 2) << "Against group (" << Check.second << "):\n";
423 for (unsigned K = 0; K < Second.size(); ++K)
424 OS.indent(Depth + 2) << *Pointers[Second[K]].PointerValue << "\n";
428 void RuntimePointerChecking::print(raw_ostream &OS, unsigned Depth) const {
430 OS.indent(Depth) << "Run-time memory checks:\n";
431 printChecks(OS, Checks, Depth);
433 OS.indent(Depth) << "Grouped accesses:\n";
434 for (unsigned I = 0; I < CheckingGroups.size(); ++I) {
435 const auto &CG = CheckingGroups[I];
437 OS.indent(Depth + 2) << "Group " << &CG << ":\n";
438 OS.indent(Depth + 4) << "(Low: " << *CG.Low << " High: " << *CG.High
440 for (unsigned J = 0; J < CG.Members.size(); ++J) {
441 OS.indent(Depth + 6) << "Member: " << *Pointers[CG.Members[J]].Expr
448 /// \brief Analyses memory accesses in a loop.
450 /// Checks whether run time pointer checks are needed and builds sets for data
451 /// dependence checking.
452 class AccessAnalysis {
454 /// \brief Read or write access location.
455 typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
456 typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet;
458 AccessAnalysis(const DataLayout &Dl, AliasAnalysis *AA, LoopInfo *LI,
459 MemoryDepChecker::DepCandidates &DA,
460 PredicatedScalarEvolution &PSE)
461 : DL(Dl), AST(*AA), LI(LI), DepCands(DA), IsRTCheckAnalysisNeeded(false),
464 /// \brief Register a load and whether it is only read from.
465 void addLoad(MemoryLocation &Loc, bool IsReadOnly) {
466 Value *Ptr = const_cast<Value*>(Loc.Ptr);
467 AST.add(Ptr, MemoryLocation::UnknownSize, Loc.AATags);
468 Accesses.insert(MemAccessInfo(Ptr, false));
470 ReadOnlyPtr.insert(Ptr);
473 /// \brief Register a store.
474 void addStore(MemoryLocation &Loc) {
475 Value *Ptr = const_cast<Value*>(Loc.Ptr);
476 AST.add(Ptr, MemoryLocation::UnknownSize, Loc.AATags);
477 Accesses.insert(MemAccessInfo(Ptr, true));
480 /// \brief Check whether we can check the pointers at runtime for
481 /// non-intersection.
483 /// Returns true if we need no check or if we do and we can generate them
484 /// (i.e. the pointers have computable bounds).
485 bool canCheckPtrAtRT(RuntimePointerChecking &RtCheck, ScalarEvolution *SE,
486 Loop *TheLoop, const ValueToValueMap &Strides,
487 bool ShouldCheckWrap = false);
489 /// \brief Goes over all memory accesses, checks whether a RT check is needed
490 /// and builds sets of dependent accesses.
491 void buildDependenceSets() {
492 processMemAccesses();
495 /// \brief Initial processing of memory accesses determined that we need to
496 /// perform dependency checking.
498 /// Note that this can later be cleared if we retry memcheck analysis without
499 /// dependency checking (i.e. ShouldRetryWithRuntimeCheck).
500 bool isDependencyCheckNeeded() { return !CheckDeps.empty(); }
502 /// We decided that no dependence analysis would be used. Reset the state.
503 void resetDepChecks(MemoryDepChecker &DepChecker) {
505 DepChecker.clearDependences();
508 MemAccessInfoSet &getDependenciesToCheck() { return CheckDeps; }
511 typedef SetVector<MemAccessInfo> PtrAccessSet;
513 /// \brief Go over all memory access and check whether runtime pointer checks
514 /// are needed and build sets of dependency check candidates.
515 void processMemAccesses();
517 /// Set of all accesses.
518 PtrAccessSet Accesses;
520 const DataLayout &DL;
522 /// Set of accesses that need a further dependence check.
523 MemAccessInfoSet CheckDeps;
525 /// Set of pointers that are read only.
526 SmallPtrSet<Value*, 16> ReadOnlyPtr;
528 /// An alias set tracker to partition the access set by underlying object and
529 //intrinsic property (such as TBAA metadata).
534 /// Sets of potentially dependent accesses - members of one set share an
535 /// underlying pointer. The set "CheckDeps" identfies which sets really need a
536 /// dependence check.
537 MemoryDepChecker::DepCandidates &DepCands;
539 /// \brief Initial processing of memory accesses determined that we may need
540 /// to add memchecks. Perform the analysis to determine the necessary checks.
542 /// Note that, this is different from isDependencyCheckNeeded. When we retry
543 /// memcheck analysis without dependency checking
544 /// (i.e. ShouldRetryWithRuntimeCheck), isDependencyCheckNeeded is cleared
545 /// while this remains set if we have potentially dependent accesses.
546 bool IsRTCheckAnalysisNeeded;
548 /// The SCEV predicate containing all the SCEV-related assumptions.
549 PredicatedScalarEvolution &PSE;
552 } // end anonymous namespace
554 /// \brief Check whether a pointer can participate in a runtime bounds check.
555 static bool hasComputableBounds(PredicatedScalarEvolution &PSE,
556 const ValueToValueMap &Strides, Value *Ptr,
558 const SCEV *PtrScev = replaceSymbolicStrideSCEV(PSE, Strides, Ptr);
560 // The bounds for loop-invariant pointer is trivial.
561 if (PSE.getSE()->isLoopInvariant(PtrScev, L))
564 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
568 return AR->isAffine();
571 /// \brief Check whether a pointer address cannot wrap.
572 static bool isNoWrap(PredicatedScalarEvolution &PSE,
573 const ValueToValueMap &Strides, Value *Ptr, Loop *L) {
574 const SCEV *PtrScev = PSE.getSCEV(Ptr);
575 if (PSE.getSE()->isLoopInvariant(PtrScev, L))
578 int64_t Stride = getPtrStride(PSE, Ptr, L, Strides);
582 bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck,
583 ScalarEvolution *SE, Loop *TheLoop,
584 const ValueToValueMap &StridesMap,
585 bool ShouldCheckWrap) {
586 // Find pointers with computable bounds. We are going to use this information
587 // to place a runtime bound check.
590 bool NeedRTCheck = false;
591 if (!IsRTCheckAnalysisNeeded) return true;
593 bool IsDepCheckNeeded = isDependencyCheckNeeded();
595 // We assign a consecutive id to access from different alias sets.
596 // Accesses between different groups doesn't need to be checked.
598 for (auto &AS : AST) {
599 int NumReadPtrChecks = 0;
600 int NumWritePtrChecks = 0;
602 // We assign consecutive id to access from different dependence sets.
603 // Accesses within the same set don't need a runtime check.
604 unsigned RunningDepId = 1;
605 DenseMap<Value *, unsigned> DepSetId;
608 Value *Ptr = A.getValue();
609 bool IsWrite = Accesses.count(MemAccessInfo(Ptr, true));
610 MemAccessInfo Access(Ptr, IsWrite);
617 if (hasComputableBounds(PSE, StridesMap, Ptr, TheLoop) &&
618 // When we run after a failing dependency check we have to make sure
619 // we don't have wrapping pointers.
620 (!ShouldCheckWrap || isNoWrap(PSE, StridesMap, Ptr, TheLoop))) {
621 // The id of the dependence set.
624 if (IsDepCheckNeeded) {
625 Value *Leader = DepCands.getLeaderValue(Access).getPointer();
626 unsigned &LeaderId = DepSetId[Leader];
628 LeaderId = RunningDepId++;
631 // Each access has its own dependence set.
632 DepId = RunningDepId++;
634 RtCheck.insert(TheLoop, Ptr, IsWrite, DepId, ASId, StridesMap, PSE);
636 DEBUG(dbgs() << "LAA: Found a runtime check ptr:" << *Ptr << '\n');
638 DEBUG(dbgs() << "LAA: Can't find bounds for ptr:" << *Ptr << '\n');
643 // If we have at least two writes or one write and a read then we need to
644 // check them. But there is no need to checks if there is only one
645 // dependence set for this alias set.
647 // Note that this function computes CanDoRT and NeedRTCheck independently.
648 // For example CanDoRT=false, NeedRTCheck=false means that we have a pointer
649 // for which we couldn't find the bounds but we don't actually need to emit
650 // any checks so it does not matter.
651 if (!(IsDepCheckNeeded && CanDoRT && RunningDepId == 2))
652 NeedRTCheck |= (NumWritePtrChecks >= 2 || (NumReadPtrChecks >= 1 &&
653 NumWritePtrChecks >= 1));
658 // If the pointers that we would use for the bounds comparison have different
659 // address spaces, assume the values aren't directly comparable, so we can't
660 // use them for the runtime check. We also have to assume they could
661 // overlap. In the future there should be metadata for whether address spaces
663 unsigned NumPointers = RtCheck.Pointers.size();
664 for (unsigned i = 0; i < NumPointers; ++i) {
665 for (unsigned j = i + 1; j < NumPointers; ++j) {
666 // Only need to check pointers between two different dependency sets.
667 if (RtCheck.Pointers[i].DependencySetId ==
668 RtCheck.Pointers[j].DependencySetId)
670 // Only need to check pointers in the same alias set.
671 if (RtCheck.Pointers[i].AliasSetId != RtCheck.Pointers[j].AliasSetId)
674 Value *PtrI = RtCheck.Pointers[i].PointerValue;
675 Value *PtrJ = RtCheck.Pointers[j].PointerValue;
677 unsigned ASi = PtrI->getType()->getPointerAddressSpace();
678 unsigned ASj = PtrJ->getType()->getPointerAddressSpace();
680 DEBUG(dbgs() << "LAA: Runtime check would require comparison between"
681 " different address spaces\n");
687 if (NeedRTCheck && CanDoRT)
688 RtCheck.generateChecks(DepCands, IsDepCheckNeeded);
690 DEBUG(dbgs() << "LAA: We need to do " << RtCheck.getNumberOfChecks()
691 << " pointer comparisons.\n");
693 RtCheck.Need = NeedRTCheck;
695 bool CanDoRTIfNeeded = !NeedRTCheck || CanDoRT;
696 if (!CanDoRTIfNeeded)
698 return CanDoRTIfNeeded;
701 void AccessAnalysis::processMemAccesses() {
702 // We process the set twice: first we process read-write pointers, last we
703 // process read-only pointers. This allows us to skip dependence tests for
704 // read-only pointers.
706 DEBUG(dbgs() << "LAA: Processing memory accesses...\n");
707 DEBUG(dbgs() << " AST: "; AST.dump());
708 DEBUG(dbgs() << "LAA: Accesses(" << Accesses.size() << "):\n");
710 for (auto A : Accesses)
711 dbgs() << "\t" << *A.getPointer() << " (" <<
712 (A.getInt() ? "write" : (ReadOnlyPtr.count(A.getPointer()) ?
713 "read-only" : "read")) << ")\n";
716 // The AliasSetTracker has nicely partitioned our pointers by metadata
717 // compatibility and potential for underlying-object overlap. As a result, we
718 // only need to check for potential pointer dependencies within each alias
720 for (auto &AS : AST) {
721 // Note that both the alias-set tracker and the alias sets themselves used
722 // linked lists internally and so the iteration order here is deterministic
723 // (matching the original instruction order within each set).
725 bool SetHasWrite = false;
727 // Map of pointers to last access encountered.
728 typedef DenseMap<Value*, MemAccessInfo> UnderlyingObjToAccessMap;
729 UnderlyingObjToAccessMap ObjToLastAccess;
731 // Set of access to check after all writes have been processed.
732 PtrAccessSet DeferredAccesses;
734 // Iterate over each alias set twice, once to process read/write pointers,
735 // and then to process read-only pointers.
736 for (int SetIteration = 0; SetIteration < 2; ++SetIteration) {
737 bool UseDeferred = SetIteration > 0;
738 PtrAccessSet &S = UseDeferred ? DeferredAccesses : Accesses;
741 Value *Ptr = AV.getValue();
743 // For a single memory access in AliasSetTracker, Accesses may contain
744 // both read and write, and they both need to be handled for CheckDeps.
746 if (AC.getPointer() != Ptr)
749 bool IsWrite = AC.getInt();
751 // If we're using the deferred access set, then it contains only
753 bool IsReadOnlyPtr = ReadOnlyPtr.count(Ptr) && !IsWrite;
754 if (UseDeferred && !IsReadOnlyPtr)
756 // Otherwise, the pointer must be in the PtrAccessSet, either as a
758 assert(((IsReadOnlyPtr && UseDeferred) || IsWrite ||
759 S.count(MemAccessInfo(Ptr, false))) &&
760 "Alias-set pointer not in the access set?");
762 MemAccessInfo Access(Ptr, IsWrite);
763 DepCands.insert(Access);
765 // Memorize read-only pointers for later processing and skip them in
766 // the first round (they need to be checked after we have seen all
767 // write pointers). Note: we also mark pointer that are not
768 // consecutive as "read-only" pointers (so that we check
769 // "a[b[i]] +="). Hence, we need the second check for "!IsWrite".
770 if (!UseDeferred && IsReadOnlyPtr) {
771 DeferredAccesses.insert(Access);
775 // If this is a write - check other reads and writes for conflicts. If
776 // this is a read only check other writes for conflicts (but only if
777 // there is no other write to the ptr - this is an optimization to
778 // catch "a[i] = a[i] + " without having to do a dependence check).
779 if ((IsWrite || IsReadOnlyPtr) && SetHasWrite) {
780 CheckDeps.insert(Access);
781 IsRTCheckAnalysisNeeded = true;
787 // Create sets of pointers connected by a shared alias set and
788 // underlying object.
789 typedef SmallVector<Value *, 16> ValueVector;
790 ValueVector TempObjects;
792 GetUnderlyingObjects(Ptr, TempObjects, DL, LI);
793 DEBUG(dbgs() << "Underlying objects for pointer " << *Ptr << "\n");
794 for (Value *UnderlyingObj : TempObjects) {
795 // nullptr never alias, don't join sets for pointer that have "null"
796 // in their UnderlyingObjects list.
797 if (isa<ConstantPointerNull>(UnderlyingObj))
800 UnderlyingObjToAccessMap::iterator Prev =
801 ObjToLastAccess.find(UnderlyingObj);
802 if (Prev != ObjToLastAccess.end())
803 DepCands.unionSets(Access, Prev->second);
805 ObjToLastAccess[UnderlyingObj] = Access;
806 DEBUG(dbgs() << " " << *UnderlyingObj << "\n");
814 static bool isInBoundsGep(Value *Ptr) {
815 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr))
816 return GEP->isInBounds();
820 /// \brief Return true if an AddRec pointer \p Ptr is unsigned non-wrapping,
821 /// i.e. monotonically increasing/decreasing.
822 static bool isNoWrapAddRec(Value *Ptr, const SCEVAddRecExpr *AR,
823 PredicatedScalarEvolution &PSE, const Loop *L) {
824 // FIXME: This should probably only return true for NUW.
825 if (AR->getNoWrapFlags(SCEV::NoWrapMask))
828 // Scalar evolution does not propagate the non-wrapping flags to values that
829 // are derived from a non-wrapping induction variable because non-wrapping
830 // could be flow-sensitive.
832 // Look through the potentially overflowing instruction to try to prove
833 // non-wrapping for the *specific* value of Ptr.
835 // The arithmetic implied by an inbounds GEP can't overflow.
836 auto *GEP = dyn_cast<GetElementPtrInst>(Ptr);
837 if (!GEP || !GEP->isInBounds())
840 // Make sure there is only one non-const index and analyze that.
841 Value *NonConstIndex = nullptr;
842 for (Value *Index : make_range(GEP->idx_begin(), GEP->idx_end()))
843 if (!isa<ConstantInt>(Index)) {
846 NonConstIndex = Index;
849 // The recurrence is on the pointer, ignore for now.
852 // The index in GEP is signed. It is non-wrapping if it's derived from a NSW
853 // AddRec using a NSW operation.
854 if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(NonConstIndex))
855 if (OBO->hasNoSignedWrap() &&
856 // Assume constant for other the operand so that the AddRec can be
858 isa<ConstantInt>(OBO->getOperand(1))) {
859 auto *OpScev = PSE.getSCEV(OBO->getOperand(0));
861 if (auto *OpAR = dyn_cast<SCEVAddRecExpr>(OpScev))
862 return OpAR->getLoop() == L && OpAR->getNoWrapFlags(SCEV::FlagNSW);
868 /// \brief Check whether the access through \p Ptr has a constant stride.
869 int64_t llvm::getPtrStride(PredicatedScalarEvolution &PSE, Value *Ptr,
870 const Loop *Lp, const ValueToValueMap &StridesMap,
872 Type *Ty = Ptr->getType();
873 assert(Ty->isPointerTy() && "Unexpected non-ptr");
875 // Make sure that the pointer does not point to aggregate types.
876 auto *PtrTy = cast<PointerType>(Ty);
877 if (PtrTy->getElementType()->isAggregateType()) {
878 DEBUG(dbgs() << "LAA: Bad stride - Not a pointer to a scalar type" << *Ptr
883 const SCEV *PtrScev = replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr);
885 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
887 AR = PSE.getAsAddRec(Ptr);
890 DEBUG(dbgs() << "LAA: Bad stride - Not an AddRecExpr pointer " << *Ptr
891 << " SCEV: " << *PtrScev << "\n");
895 // The accesss function must stride over the innermost loop.
896 if (Lp != AR->getLoop()) {
897 DEBUG(dbgs() << "LAA: Bad stride - Not striding over innermost loop " <<
898 *Ptr << " SCEV: " << *AR << "\n");
902 // The address calculation must not wrap. Otherwise, a dependence could be
904 // An inbounds getelementptr that is a AddRec with a unit stride
905 // cannot wrap per definition. The unit stride requirement is checked later.
906 // An getelementptr without an inbounds attribute and unit stride would have
907 // to access the pointer value "0" which is undefined behavior in address
908 // space 0, therefore we can also vectorize this case.
909 bool IsInBoundsGEP = isInBoundsGep(Ptr);
910 bool IsNoWrapAddRec =
911 PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW) ||
912 isNoWrapAddRec(Ptr, AR, PSE, Lp);
913 bool IsInAddressSpaceZero = PtrTy->getAddressSpace() == 0;
914 if (!IsNoWrapAddRec && !IsInBoundsGEP && !IsInAddressSpaceZero) {
916 PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW);
917 IsNoWrapAddRec = true;
918 DEBUG(dbgs() << "LAA: Pointer may wrap in the address space:\n"
919 << "LAA: Pointer: " << *Ptr << "\n"
920 << "LAA: SCEV: " << *AR << "\n"
921 << "LAA: Added an overflow assumption\n");
923 DEBUG(dbgs() << "LAA: Bad stride - Pointer may wrap in the address space "
924 << *Ptr << " SCEV: " << *AR << "\n");
929 // Check the step is constant.
930 const SCEV *Step = AR->getStepRecurrence(*PSE.getSE());
932 // Calculate the pointer stride and check if it is constant.
933 const SCEVConstant *C = dyn_cast<SCEVConstant>(Step);
935 DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided " << *Ptr <<
936 " SCEV: " << *AR << "\n");
940 auto &DL = Lp->getHeader()->getModule()->getDataLayout();
941 int64_t Size = DL.getTypeAllocSize(PtrTy->getElementType());
942 const APInt &APStepVal = C->getAPInt();
944 // Huge step value - give up.
945 if (APStepVal.getBitWidth() > 64)
948 int64_t StepVal = APStepVal.getSExtValue();
951 int64_t Stride = StepVal / Size;
952 int64_t Rem = StepVal % Size;
956 // If the SCEV could wrap but we have an inbounds gep with a unit stride we
957 // know we can't "wrap around the address space". In case of address space
958 // zero we know that this won't happen without triggering undefined behavior.
959 if (!IsNoWrapAddRec && (IsInBoundsGEP || IsInAddressSpaceZero) &&
960 Stride != 1 && Stride != -1) {
962 // We can avoid this case by adding a run-time check.
963 DEBUG(dbgs() << "LAA: Non unit strided pointer which is not either "
964 << "inbouds or in address space 0 may wrap:\n"
965 << "LAA: Pointer: " << *Ptr << "\n"
966 << "LAA: SCEV: " << *AR << "\n"
967 << "LAA: Added an overflow assumption\n");
968 PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW);
976 /// Take the pointer operand from the Load/Store instruction.
977 /// Returns NULL if this is not a valid Load/Store instruction.
978 static Value *getPointerOperand(Value *I) {
979 if (auto *LI = dyn_cast<LoadInst>(I))
980 return LI->getPointerOperand();
981 if (auto *SI = dyn_cast<StoreInst>(I))
982 return SI->getPointerOperand();
986 /// Take the address space operand from the Load/Store instruction.
987 /// Returns -1 if this is not a valid Load/Store instruction.
988 static unsigned getAddressSpaceOperand(Value *I) {
989 if (LoadInst *L = dyn_cast<LoadInst>(I))
990 return L->getPointerAddressSpace();
991 if (StoreInst *S = dyn_cast<StoreInst>(I))
992 return S->getPointerAddressSpace();
996 /// Returns true if the memory operations \p A and \p B are consecutive.
997 bool llvm::isConsecutiveAccess(Value *A, Value *B, const DataLayout &DL,
998 ScalarEvolution &SE, bool CheckType) {
999 Value *PtrA = getPointerOperand(A);
1000 Value *PtrB = getPointerOperand(B);
1001 unsigned ASA = getAddressSpaceOperand(A);
1002 unsigned ASB = getAddressSpaceOperand(B);
1004 // Check that the address spaces match and that the pointers are valid.
1005 if (!PtrA || !PtrB || (ASA != ASB))
1008 // Make sure that A and B are different pointers.
1012 // Make sure that A and B have the same type if required.
1013 if(CheckType && PtrA->getType() != PtrB->getType())
1016 unsigned PtrBitWidth = DL.getPointerSizeInBits(ASA);
1017 Type *Ty = cast<PointerType>(PtrA->getType())->getElementType();
1018 APInt Size(PtrBitWidth, DL.getTypeStoreSize(Ty));
1020 APInt OffsetA(PtrBitWidth, 0), OffsetB(PtrBitWidth, 0);
1021 PtrA = PtrA->stripAndAccumulateInBoundsConstantOffsets(DL, OffsetA);
1022 PtrB = PtrB->stripAndAccumulateInBoundsConstantOffsets(DL, OffsetB);
1024 // OffsetDelta = OffsetB - OffsetA;
1025 const SCEV *OffsetSCEVA = SE.getConstant(OffsetA);
1026 const SCEV *OffsetSCEVB = SE.getConstant(OffsetB);
1027 const SCEV *OffsetDeltaSCEV = SE.getMinusSCEV(OffsetSCEVB, OffsetSCEVA);
1028 const SCEVConstant *OffsetDeltaC = dyn_cast<SCEVConstant>(OffsetDeltaSCEV);
1029 const APInt &OffsetDelta = OffsetDeltaC->getAPInt();
1030 // Check if they are based on the same pointer. That makes the offsets
1033 return OffsetDelta == Size;
1035 // Compute the necessary base pointer delta to have the necessary final delta
1036 // equal to the size.
1037 // BaseDelta = Size - OffsetDelta;
1038 const SCEV *SizeSCEV = SE.getConstant(Size);
1039 const SCEV *BaseDelta = SE.getMinusSCEV(SizeSCEV, OffsetDeltaSCEV);
1041 // Otherwise compute the distance with SCEV between the base pointers.
1042 const SCEV *PtrSCEVA = SE.getSCEV(PtrA);
1043 const SCEV *PtrSCEVB = SE.getSCEV(PtrB);
1044 const SCEV *X = SE.getAddExpr(PtrSCEVA, BaseDelta);
1045 return X == PtrSCEVB;
1048 bool MemoryDepChecker::Dependence::isSafeForVectorization(DepType Type) {
1052 case BackwardVectorizable:
1056 case ForwardButPreventsForwarding:
1058 case BackwardVectorizableButPreventsForwarding:
1061 llvm_unreachable("unexpected DepType!");
1064 bool MemoryDepChecker::Dependence::isBackward() const {
1068 case ForwardButPreventsForwarding:
1072 case BackwardVectorizable:
1074 case BackwardVectorizableButPreventsForwarding:
1077 llvm_unreachable("unexpected DepType!");
1080 bool MemoryDepChecker::Dependence::isPossiblyBackward() const {
1081 return isBackward() || Type == Unknown;
1084 bool MemoryDepChecker::Dependence::isForward() const {
1087 case ForwardButPreventsForwarding:
1092 case BackwardVectorizable:
1094 case BackwardVectorizableButPreventsForwarding:
1097 llvm_unreachable("unexpected DepType!");
1100 bool MemoryDepChecker::couldPreventStoreLoadForward(uint64_t Distance,
1101 uint64_t TypeByteSize) {
1102 // If loads occur at a distance that is not a multiple of a feasible vector
1103 // factor store-load forwarding does not take place.
1104 // Positive dependences might cause troubles because vectorizing them might
1105 // prevent store-load forwarding making vectorized code run a lot slower.
1106 // a[i] = a[i-3] ^ a[i-8];
1107 // The stores to a[i:i+1] don't align with the stores to a[i-3:i-2] and
1108 // hence on your typical architecture store-load forwarding does not take
1109 // place. Vectorizing in such cases does not make sense.
1110 // Store-load forwarding distance.
1112 // After this many iterations store-to-load forwarding conflicts should not
1113 // cause any slowdowns.
1114 const uint64_t NumItersForStoreLoadThroughMemory = 8 * TypeByteSize;
1115 // Maximum vector factor.
1116 uint64_t MaxVFWithoutSLForwardIssues = std::min(
1117 VectorizerParams::MaxVectorWidth * TypeByteSize, MaxSafeDepDistBytes);
1119 // Compute the smallest VF at which the store and load would be misaligned.
1120 for (uint64_t VF = 2 * TypeByteSize; VF <= MaxVFWithoutSLForwardIssues;
1122 // If the number of vector iteration between the store and the load are
1123 // small we could incur conflicts.
1124 if (Distance % VF && Distance / VF < NumItersForStoreLoadThroughMemory) {
1125 MaxVFWithoutSLForwardIssues = (VF >>= 1);
1130 if (MaxVFWithoutSLForwardIssues < 2 * TypeByteSize) {
1131 DEBUG(dbgs() << "LAA: Distance " << Distance
1132 << " that could cause a store-load forwarding conflict\n");
1136 if (MaxVFWithoutSLForwardIssues < MaxSafeDepDistBytes &&
1137 MaxVFWithoutSLForwardIssues !=
1138 VectorizerParams::MaxVectorWidth * TypeByteSize)
1139 MaxSafeDepDistBytes = MaxVFWithoutSLForwardIssues;
1143 /// \brief Check the dependence for two accesses with the same stride \p Stride.
1144 /// \p Distance is the positive distance and \p TypeByteSize is type size in
1147 /// \returns true if they are independent.
1148 static bool areStridedAccessesIndependent(uint64_t Distance, uint64_t Stride,
1149 uint64_t TypeByteSize) {
1150 assert(Stride > 1 && "The stride must be greater than 1");
1151 assert(TypeByteSize > 0 && "The type size in byte must be non-zero");
1152 assert(Distance > 0 && "The distance must be non-zero");
1154 // Skip if the distance is not multiple of type byte size.
1155 if (Distance % TypeByteSize)
1158 uint64_t ScaledDist = Distance / TypeByteSize;
1160 // No dependence if the scaled distance is not multiple of the stride.
1162 // for (i = 0; i < 1024 ; i += 4)
1163 // A[i+2] = A[i] + 1;
1165 // Two accesses in memory (scaled distance is 2, stride is 4):
1166 // | A[0] | | | | A[4] | | | |
1167 // | | | A[2] | | | | A[6] | |
1170 // for (i = 0; i < 1024 ; i += 3)
1171 // A[i+4] = A[i] + 1;
1173 // Two accesses in memory (scaled distance is 4, stride is 3):
1174 // | A[0] | | | A[3] | | | A[6] | | |
1175 // | | | | | A[4] | | | A[7] | |
1176 return ScaledDist % Stride;
1179 MemoryDepChecker::Dependence::DepType
1180 MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
1181 const MemAccessInfo &B, unsigned BIdx,
1182 const ValueToValueMap &Strides) {
1183 assert (AIdx < BIdx && "Must pass arguments in program order");
1185 Value *APtr = A.getPointer();
1186 Value *BPtr = B.getPointer();
1187 bool AIsWrite = A.getInt();
1188 bool BIsWrite = B.getInt();
1190 // Two reads are independent.
1191 if (!AIsWrite && !BIsWrite)
1192 return Dependence::NoDep;
1194 // We cannot check pointers in different address spaces.
1195 if (APtr->getType()->getPointerAddressSpace() !=
1196 BPtr->getType()->getPointerAddressSpace())
1197 return Dependence::Unknown;
1199 int64_t StrideAPtr = getPtrStride(PSE, APtr, InnermostLoop, Strides, true);
1200 int64_t StrideBPtr = getPtrStride(PSE, BPtr, InnermostLoop, Strides, true);
1202 const SCEV *Src = PSE.getSCEV(APtr);
1203 const SCEV *Sink = PSE.getSCEV(BPtr);
1205 // If the induction step is negative we have to invert source and sink of the
1207 if (StrideAPtr < 0) {
1208 std::swap(APtr, BPtr);
1209 std::swap(Src, Sink);
1210 std::swap(AIsWrite, BIsWrite);
1211 std::swap(AIdx, BIdx);
1212 std::swap(StrideAPtr, StrideBPtr);
1215 const SCEV *Dist = PSE.getSE()->getMinusSCEV(Sink, Src);
1217 DEBUG(dbgs() << "LAA: Src Scev: " << *Src << "Sink Scev: " << *Sink
1218 << "(Induction step: " << StrideAPtr << ")\n");
1219 DEBUG(dbgs() << "LAA: Distance for " << *InstMap[AIdx] << " to "
1220 << *InstMap[BIdx] << ": " << *Dist << "\n");
1222 // Need accesses with constant stride. We don't want to vectorize
1223 // "A[B[i]] += ..." and similar code or pointer arithmetic that could wrap in
1224 // the address space.
1225 if (!StrideAPtr || !StrideBPtr || StrideAPtr != StrideBPtr){
1226 DEBUG(dbgs() << "Pointer access with non-constant stride\n");
1227 return Dependence::Unknown;
1230 const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist);
1232 DEBUG(dbgs() << "LAA: Dependence because of non-constant distance\n");
1233 ShouldRetryWithRuntimeCheck = true;
1234 return Dependence::Unknown;
1237 Type *ATy = APtr->getType()->getPointerElementType();
1238 Type *BTy = BPtr->getType()->getPointerElementType();
1239 auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout();
1240 uint64_t TypeByteSize = DL.getTypeAllocSize(ATy);
1242 const APInt &Val = C->getAPInt();
1243 int64_t Distance = Val.getSExtValue();
1244 uint64_t Stride = std::abs(StrideAPtr);
1246 // Attempt to prove strided accesses independent.
1247 if (std::abs(Distance) > 0 && Stride > 1 && ATy == BTy &&
1248 areStridedAccessesIndependent(std::abs(Distance), Stride, TypeByteSize)) {
1249 DEBUG(dbgs() << "LAA: Strided accesses are independent\n");
1250 return Dependence::NoDep;
1253 // Negative distances are not plausible dependencies.
1254 if (Val.isNegative()) {
1255 bool IsTrueDataDependence = (AIsWrite && !BIsWrite);
1256 if (IsTrueDataDependence && EnableForwardingConflictDetection &&
1257 (couldPreventStoreLoadForward(Val.abs().getZExtValue(), TypeByteSize) ||
1259 DEBUG(dbgs() << "LAA: Forward but may prevent st->ld forwarding\n");
1260 return Dependence::ForwardButPreventsForwarding;
1263 DEBUG(dbgs() << "LAA: Dependence is negative\n");
1264 return Dependence::Forward;
1267 // Write to the same location with the same size.
1268 // Could be improved to assert type sizes are the same (i32 == float, etc).
1271 return Dependence::Forward;
1272 DEBUG(dbgs() << "LAA: Zero dependence difference but different types\n");
1273 return Dependence::Unknown;
1276 assert(Val.isStrictlyPositive() && "Expect a positive value");
1280 "LAA: ReadWrite-Write positive dependency with different types\n");
1281 return Dependence::Unknown;
1284 // Bail out early if passed-in parameters make vectorization not feasible.
1285 unsigned ForcedFactor = (VectorizerParams::VectorizationFactor ?
1286 VectorizerParams::VectorizationFactor : 1);
1287 unsigned ForcedUnroll = (VectorizerParams::VectorizationInterleave ?
1288 VectorizerParams::VectorizationInterleave : 1);
1289 // The minimum number of iterations for a vectorized/unrolled version.
1290 unsigned MinNumIter = std::max(ForcedFactor * ForcedUnroll, 2U);
1292 // It's not vectorizable if the distance is smaller than the minimum distance
1293 // needed for a vectroized/unrolled version. Vectorizing one iteration in
1294 // front needs TypeByteSize * Stride. Vectorizing the last iteration needs
1295 // TypeByteSize (No need to plus the last gap distance).
1297 // E.g. Assume one char is 1 byte in memory and one int is 4 bytes.
1299 // int *B = (int *)((char *)A + 14);
1300 // for (i = 0 ; i < 1024 ; i += 2)
1304 // Two accesses in memory (stride is 2):
1305 // | A[0] | | A[2] | | A[4] | | A[6] | |
1306 // | B[0] | | B[2] | | B[4] |
1308 // Distance needs for vectorizing iterations except the last iteration:
1309 // 4 * 2 * (MinNumIter - 1). Distance needs for the last iteration: 4.
1310 // So the minimum distance needed is: 4 * 2 * (MinNumIter - 1) + 4.
1312 // If MinNumIter is 2, it is vectorizable as the minimum distance needed is
1313 // 12, which is less than distance.
1315 // If MinNumIter is 4 (Say if a user forces the vectorization factor to be 4),
1316 // the minimum distance needed is 28, which is greater than distance. It is
1317 // not safe to do vectorization.
1318 uint64_t MinDistanceNeeded =
1319 TypeByteSize * Stride * (MinNumIter - 1) + TypeByteSize;
1320 if (MinDistanceNeeded > static_cast<uint64_t>(Distance)) {
1321 DEBUG(dbgs() << "LAA: Failure because of positive distance " << Distance
1323 return Dependence::Backward;
1326 // Unsafe if the minimum distance needed is greater than max safe distance.
1327 if (MinDistanceNeeded > MaxSafeDepDistBytes) {
1328 DEBUG(dbgs() << "LAA: Failure because it needs at least "
1329 << MinDistanceNeeded << " size in bytes");
1330 return Dependence::Backward;
1333 // Positive distance bigger than max vectorization factor.
1334 // FIXME: Should use max factor instead of max distance in bytes, which could
1335 // not handle different types.
1336 // E.g. Assume one char is 1 byte in memory and one int is 4 bytes.
1337 // void foo (int *A, char *B) {
1338 // for (unsigned i = 0; i < 1024; i++) {
1339 // A[i+2] = A[i] + 1;
1340 // B[i+2] = B[i] + 1;
1344 // This case is currently unsafe according to the max safe distance. If we
1345 // analyze the two accesses on array B, the max safe dependence distance
1346 // is 2. Then we analyze the accesses on array A, the minimum distance needed
1347 // is 8, which is less than 2 and forbidden vectorization, But actually
1348 // both A and B could be vectorized by 2 iterations.
1349 MaxSafeDepDistBytes =
1350 std::min(static_cast<uint64_t>(Distance), MaxSafeDepDistBytes);
1352 bool IsTrueDataDependence = (!AIsWrite && BIsWrite);
1353 if (IsTrueDataDependence && EnableForwardingConflictDetection &&
1354 couldPreventStoreLoadForward(Distance, TypeByteSize))
1355 return Dependence::BackwardVectorizableButPreventsForwarding;
1357 DEBUG(dbgs() << "LAA: Positive distance " << Val.getSExtValue()
1358 << " with max VF = "
1359 << MaxSafeDepDistBytes / (TypeByteSize * Stride) << '\n');
1361 return Dependence::BackwardVectorizable;
1364 bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets,
1365 MemAccessInfoSet &CheckDeps,
1366 const ValueToValueMap &Strides) {
1368 MaxSafeDepDistBytes = -1;
1369 while (!CheckDeps.empty()) {
1370 MemAccessInfo CurAccess = *CheckDeps.begin();
1372 // Get the relevant memory access set.
1373 EquivalenceClasses<MemAccessInfo>::iterator I =
1374 AccessSets.findValue(AccessSets.getLeaderValue(CurAccess));
1376 // Check accesses within this set.
1377 EquivalenceClasses<MemAccessInfo>::member_iterator AI =
1378 AccessSets.member_begin(I);
1379 EquivalenceClasses<MemAccessInfo>::member_iterator AE =
1380 AccessSets.member_end();
1382 // Check every access pair.
1384 CheckDeps.erase(*AI);
1385 EquivalenceClasses<MemAccessInfo>::member_iterator OI = std::next(AI);
1387 // Check every accessing instruction pair in program order.
1388 for (std::vector<unsigned>::iterator I1 = Accesses[*AI].begin(),
1389 I1E = Accesses[*AI].end(); I1 != I1E; ++I1)
1390 for (std::vector<unsigned>::iterator I2 = Accesses[*OI].begin(),
1391 I2E = Accesses[*OI].end(); I2 != I2E; ++I2) {
1392 auto A = std::make_pair(&*AI, *I1);
1393 auto B = std::make_pair(&*OI, *I2);
1399 Dependence::DepType Type =
1400 isDependent(*A.first, A.second, *B.first, B.second, Strides);
1401 SafeForVectorization &= Dependence::isSafeForVectorization(Type);
1403 // Gather dependences unless we accumulated MaxDependences
1404 // dependences. In that case return as soon as we find the first
1405 // unsafe dependence. This puts a limit on this quadratic
1407 if (RecordDependences) {
1408 if (Type != Dependence::NoDep)
1409 Dependences.push_back(Dependence(A.second, B.second, Type));
1411 if (Dependences.size() >= MaxDependences) {
1412 RecordDependences = false;
1413 Dependences.clear();
1414 DEBUG(dbgs() << "Too many dependences, stopped recording\n");
1417 if (!RecordDependences && !SafeForVectorization)
1426 DEBUG(dbgs() << "Total Dependences: " << Dependences.size() << "\n");
1427 return SafeForVectorization;
1430 SmallVector<Instruction *, 4>
1431 MemoryDepChecker::getInstructionsForAccess(Value *Ptr, bool isWrite) const {
1432 MemAccessInfo Access(Ptr, isWrite);
1433 auto &IndexVector = Accesses.find(Access)->second;
1435 SmallVector<Instruction *, 4> Insts;
1436 std::transform(IndexVector.begin(), IndexVector.end(),
1437 std::back_inserter(Insts),
1438 [&](unsigned Idx) { return this->InstMap[Idx]; });
1442 const char *MemoryDepChecker::Dependence::DepName[] = {
1443 "NoDep", "Unknown", "Forward", "ForwardButPreventsForwarding", "Backward",
1444 "BackwardVectorizable", "BackwardVectorizableButPreventsForwarding"};
1446 void MemoryDepChecker::Dependence::print(
1447 raw_ostream &OS, unsigned Depth,
1448 const SmallVectorImpl<Instruction *> &Instrs) const {
1449 OS.indent(Depth) << DepName[Type] << ":\n";
1450 OS.indent(Depth + 2) << *Instrs[Source] << " -> \n";
1451 OS.indent(Depth + 2) << *Instrs[Destination] << "\n";
1454 bool LoopAccessInfo::canAnalyzeLoop() {
1455 // We need to have a loop header.
1456 DEBUG(dbgs() << "LAA: Found a loop in "
1457 << TheLoop->getHeader()->getParent()->getName() << ": "
1458 << TheLoop->getHeader()->getName() << '\n');
1460 // We can only analyze innermost loops.
1461 if (!TheLoop->empty()) {
1462 DEBUG(dbgs() << "LAA: loop is not the innermost loop\n");
1463 emitAnalysis(LoopAccessReport() << "loop is not the innermost loop");
1467 // We must have a single backedge.
1468 if (TheLoop->getNumBackEdges() != 1) {
1469 DEBUG(dbgs() << "LAA: loop control flow is not understood by analyzer\n");
1471 LoopAccessReport() <<
1472 "loop control flow is not understood by analyzer");
1476 // We must have a single exiting block.
1477 if (!TheLoop->getExitingBlock()) {
1478 DEBUG(dbgs() << "LAA: loop control flow is not understood by analyzer\n");
1480 LoopAccessReport() <<
1481 "loop control flow is not understood by analyzer");
1485 // We only handle bottom-tested loops, i.e. loop in which the condition is
1486 // checked at the end of each iteration. With that we can assume that all
1487 // instructions in the loop are executed the same number of times.
1488 if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) {
1489 DEBUG(dbgs() << "LAA: loop control flow is not understood by analyzer\n");
1491 LoopAccessReport() <<
1492 "loop control flow is not understood by analyzer");
1496 // ScalarEvolution needs to be able to find the exit count.
1497 const SCEV *ExitCount = PSE->getBackedgeTakenCount();
1498 if (ExitCount == PSE->getSE()->getCouldNotCompute()) {
1499 emitAnalysis(LoopAccessReport()
1500 << "could not determine number of loop iterations");
1501 DEBUG(dbgs() << "LAA: SCEV could not compute the loop exit count.\n");
1508 void LoopAccessInfo::analyzeLoop(AliasAnalysis *AA, LoopInfo *LI,
1509 const TargetLibraryInfo *TLI,
1510 DominatorTree *DT) {
1511 typedef SmallPtrSet<Value*, 16> ValueSet;
1513 // Holds the Load and Store instructions.
1514 SmallVector<LoadInst *, 16> Loads;
1515 SmallVector<StoreInst *, 16> Stores;
1517 // Holds all the different accesses in the loop.
1518 unsigned NumReads = 0;
1519 unsigned NumReadWrites = 0;
1521 PtrRtChecking->Pointers.clear();
1522 PtrRtChecking->Need = false;
1524 const bool IsAnnotatedParallel = TheLoop->isAnnotatedParallel();
1527 for (BasicBlock *BB : TheLoop->blocks()) {
1528 // Scan the BB and collect legal loads and stores.
1529 for (Instruction &I : *BB) {
1530 // If this is a load, save it. If this instruction can read from memory
1531 // but is not a load, then we quit. Notice that we don't handle function
1532 // calls that read or write.
1533 if (I.mayReadFromMemory()) {
1534 // Many math library functions read the rounding mode. We will only
1535 // vectorize a loop if it contains known function calls that don't set
1536 // the flag. Therefore, it is safe to ignore this read from memory.
1537 auto *Call = dyn_cast<CallInst>(&I);
1538 if (Call && getVectorIntrinsicIDForCall(Call, TLI))
1541 // If the function has an explicit vectorized counterpart, we can safely
1542 // assume that it can be vectorized.
1543 if (Call && !Call->isNoBuiltin() && Call->getCalledFunction() &&
1544 TLI->isFunctionVectorizable(Call->getCalledFunction()->getName()))
1547 auto *Ld = dyn_cast<LoadInst>(&I);
1548 if (!Ld || (!Ld->isSimple() && !IsAnnotatedParallel)) {
1549 emitAnalysis(LoopAccessReport(Ld)
1550 << "read with atomic ordering or volatile read");
1551 DEBUG(dbgs() << "LAA: Found a non-simple load.\n");
1556 Loads.push_back(Ld);
1557 DepChecker->addAccess(Ld);
1558 if (EnableMemAccessVersioning)
1559 collectStridedAccess(Ld);
1563 // Save 'store' instructions. Abort if other instructions write to memory.
1564 if (I.mayWriteToMemory()) {
1565 auto *St = dyn_cast<StoreInst>(&I);
1567 emitAnalysis(LoopAccessReport(St)
1568 << "instruction cannot be vectorized");
1572 if (!St->isSimple() && !IsAnnotatedParallel) {
1573 emitAnalysis(LoopAccessReport(St)
1574 << "write with atomic ordering or volatile write");
1575 DEBUG(dbgs() << "LAA: Found a non-simple store.\n");
1580 Stores.push_back(St);
1581 DepChecker->addAccess(St);
1582 if (EnableMemAccessVersioning)
1583 collectStridedAccess(St);
1588 // Now we have two lists that hold the loads and the stores.
1589 // Next, we find the pointers that they use.
1591 // Check if we see any stores. If there are no stores, then we don't
1592 // care if the pointers are *restrict*.
1593 if (!Stores.size()) {
1594 DEBUG(dbgs() << "LAA: Found a read-only loop!\n");
1599 MemoryDepChecker::DepCandidates DependentAccesses;
1600 AccessAnalysis Accesses(TheLoop->getHeader()->getModule()->getDataLayout(),
1601 AA, LI, DependentAccesses, *PSE);
1603 // Holds the analyzed pointers. We don't want to call GetUnderlyingObjects
1604 // multiple times on the same object. If the ptr is accessed twice, once
1605 // for read and once for write, it will only appear once (on the write
1606 // list). This is okay, since we are going to check for conflicts between
1607 // writes and between reads and writes, but not between reads and reads.
1610 for (StoreInst *ST : Stores) {
1611 Value *Ptr = ST->getPointerOperand();
1612 // Check for store to loop invariant address.
1613 StoreToLoopInvariantAddress |= isUniform(Ptr);
1614 // If we did *not* see this pointer before, insert it to the read-write
1615 // list. At this phase it is only a 'write' list.
1616 if (Seen.insert(Ptr).second) {
1619 MemoryLocation Loc = MemoryLocation::get(ST);
1620 // The TBAA metadata could have a control dependency on the predication
1621 // condition, so we cannot rely on it when determining whether or not we
1622 // need runtime pointer checks.
1623 if (blockNeedsPredication(ST->getParent(), TheLoop, DT))
1624 Loc.AATags.TBAA = nullptr;
1626 Accesses.addStore(Loc);
1630 if (IsAnnotatedParallel) {
1632 << "LAA: A loop annotated parallel, ignore memory dependency "
1638 for (LoadInst *LD : Loads) {
1639 Value *Ptr = LD->getPointerOperand();
1640 // If we did *not* see this pointer before, insert it to the
1641 // read list. If we *did* see it before, then it is already in
1642 // the read-write list. This allows us to vectorize expressions
1643 // such as A[i] += x; Because the address of A[i] is a read-write
1644 // pointer. This only works if the index of A[i] is consecutive.
1645 // If the address of i is unknown (for example A[B[i]]) then we may
1646 // read a few words, modify, and write a few words, and some of the
1647 // words may be written to the same address.
1648 bool IsReadOnlyPtr = false;
1649 if (Seen.insert(Ptr).second ||
1650 !getPtrStride(*PSE, Ptr, TheLoop, SymbolicStrides)) {
1652 IsReadOnlyPtr = true;
1655 MemoryLocation Loc = MemoryLocation::get(LD);
1656 // The TBAA metadata could have a control dependency on the predication
1657 // condition, so we cannot rely on it when determining whether or not we
1658 // need runtime pointer checks.
1659 if (blockNeedsPredication(LD->getParent(), TheLoop, DT))
1660 Loc.AATags.TBAA = nullptr;
1662 Accesses.addLoad(Loc, IsReadOnlyPtr);
1665 // If we write (or read-write) to a single destination and there are no
1666 // other reads in this loop then is it safe to vectorize.
1667 if (NumReadWrites == 1 && NumReads == 0) {
1668 DEBUG(dbgs() << "LAA: Found a write-only loop!\n");
1673 // Build dependence sets and check whether we need a runtime pointer bounds
1675 Accesses.buildDependenceSets();
1677 // Find pointers with computable bounds. We are going to use this information
1678 // to place a runtime bound check.
1679 bool CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(*PtrRtChecking, PSE->getSE(),
1680 TheLoop, SymbolicStrides);
1681 if (!CanDoRTIfNeeded) {
1682 emitAnalysis(LoopAccessReport() << "cannot identify array bounds");
1683 DEBUG(dbgs() << "LAA: We can't vectorize because we can't find "
1684 << "the array bounds.\n");
1689 DEBUG(dbgs() << "LAA: We can perform a memory runtime check if needed.\n");
1692 if (Accesses.isDependencyCheckNeeded()) {
1693 DEBUG(dbgs() << "LAA: Checking memory dependencies\n");
1694 CanVecMem = DepChecker->areDepsSafe(
1695 DependentAccesses, Accesses.getDependenciesToCheck(), SymbolicStrides);
1696 MaxSafeDepDistBytes = DepChecker->getMaxSafeDepDistBytes();
1698 if (!CanVecMem && DepChecker->shouldRetryWithRuntimeCheck()) {
1699 DEBUG(dbgs() << "LAA: Retrying with memory checks\n");
1701 // Clear the dependency checks. We assume they are not needed.
1702 Accesses.resetDepChecks(*DepChecker);
1704 PtrRtChecking->reset();
1705 PtrRtChecking->Need = true;
1707 auto *SE = PSE->getSE();
1708 CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(*PtrRtChecking, SE, TheLoop,
1709 SymbolicStrides, true);
1711 // Check that we found the bounds for the pointer.
1712 if (!CanDoRTIfNeeded) {
1713 emitAnalysis(LoopAccessReport()
1714 << "cannot check memory dependencies at runtime");
1715 DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n");
1725 DEBUG(dbgs() << "LAA: No unsafe dependent memory operations in loop. We"
1726 << (PtrRtChecking->Need ? "" : " don't")
1727 << " need runtime memory checks.\n");
1731 << "unsafe dependent memory operations in loop. Use "
1732 "#pragma loop distribute(enable) to allow loop distribution "
1733 "to attempt to isolate the offending operations into a separate "
1735 DEBUG(dbgs() << "LAA: unsafe dependent memory operations in loop\n");
1739 bool LoopAccessInfo::blockNeedsPredication(BasicBlock *BB, Loop *TheLoop,
1740 DominatorTree *DT) {
1741 assert(TheLoop->contains(BB) && "Unknown block used");
1743 // Blocks that do not dominate the latch need predication.
1744 BasicBlock* Latch = TheLoop->getLoopLatch();
1745 return !DT->dominates(BB, Latch);
1748 void LoopAccessInfo::emitAnalysis(LoopAccessReport &Message) {
1749 assert(!Report && "Multiple reports generated");
1753 bool LoopAccessInfo::isUniform(Value *V) const {
1754 return (PSE->getSE()->isLoopInvariant(PSE->getSE()->getSCEV(V), TheLoop));
1757 // FIXME: this function is currently a duplicate of the one in
1758 // LoopVectorize.cpp.
1759 static Instruction *getFirstInst(Instruction *FirstInst, Value *V,
1763 if (Instruction *I = dyn_cast<Instruction>(V))
1764 return I->getParent() == Loc->getParent() ? I : nullptr;
1769 /// \brief IR Values for the lower and upper bounds of a pointer evolution. We
1770 /// need to use value-handles because SCEV expansion can invalidate previously
1771 /// expanded values. Thus expansion of a pointer can invalidate the bounds for
1773 struct PointerBounds {
1774 TrackingVH<Value> Start;
1775 TrackingVH<Value> End;
1777 } // end anonymous namespace
1779 /// \brief Expand code for the lower and upper bound of the pointer group \p CG
1780 /// in \p TheLoop. \return the values for the bounds.
1781 static PointerBounds
1782 expandBounds(const RuntimePointerChecking::CheckingPtrGroup *CG, Loop *TheLoop,
1783 Instruction *Loc, SCEVExpander &Exp, ScalarEvolution *SE,
1784 const RuntimePointerChecking &PtrRtChecking) {
1785 Value *Ptr = PtrRtChecking.Pointers[CG->Members[0]].PointerValue;
1786 const SCEV *Sc = SE->getSCEV(Ptr);
1788 if (SE->isLoopInvariant(Sc, TheLoop)) {
1789 DEBUG(dbgs() << "LAA: Adding RT check for a loop invariant ptr:" << *Ptr
1793 unsigned AS = Ptr->getType()->getPointerAddressSpace();
1794 LLVMContext &Ctx = Loc->getContext();
1796 // Use this type for pointer arithmetic.
1797 Type *PtrArithTy = Type::getInt8PtrTy(Ctx, AS);
1798 Value *Start = nullptr, *End = nullptr;
1800 DEBUG(dbgs() << "LAA: Adding RT check for range:\n");
1801 Start = Exp.expandCodeFor(CG->Low, PtrArithTy, Loc);
1802 End = Exp.expandCodeFor(CG->High, PtrArithTy, Loc);
1803 DEBUG(dbgs() << "Start: " << *CG->Low << " End: " << *CG->High << "\n");
1804 return {Start, End};
1808 /// \brief Turns a collection of checks into a collection of expanded upper and
1809 /// lower bounds for both pointers in the check.
1810 static SmallVector<std::pair<PointerBounds, PointerBounds>, 4> expandBounds(
1811 const SmallVectorImpl<RuntimePointerChecking::PointerCheck> &PointerChecks,
1812 Loop *L, Instruction *Loc, ScalarEvolution *SE, SCEVExpander &Exp,
1813 const RuntimePointerChecking &PtrRtChecking) {
1814 SmallVector<std::pair<PointerBounds, PointerBounds>, 4> ChecksWithBounds;
1816 // Here we're relying on the SCEV Expander's cache to only emit code for the
1817 // same bounds once.
1819 PointerChecks.begin(), PointerChecks.end(),
1820 std::back_inserter(ChecksWithBounds),
1821 [&](const RuntimePointerChecking::PointerCheck &Check) {
1823 First = expandBounds(Check.first, L, Loc, Exp, SE, PtrRtChecking),
1824 Second = expandBounds(Check.second, L, Loc, Exp, SE, PtrRtChecking);
1825 return std::make_pair(First, Second);
1828 return ChecksWithBounds;
1831 std::pair<Instruction *, Instruction *> LoopAccessInfo::addRuntimeChecks(
1833 const SmallVectorImpl<RuntimePointerChecking::PointerCheck> &PointerChecks)
1835 const DataLayout &DL = TheLoop->getHeader()->getModule()->getDataLayout();
1836 auto *SE = PSE->getSE();
1837 SCEVExpander Exp(*SE, DL, "induction");
1838 auto ExpandedChecks =
1839 expandBounds(PointerChecks, TheLoop, Loc, SE, Exp, *PtrRtChecking);
1841 LLVMContext &Ctx = Loc->getContext();
1842 Instruction *FirstInst = nullptr;
1843 IRBuilder<> ChkBuilder(Loc);
1844 // Our instructions might fold to a constant.
1845 Value *MemoryRuntimeCheck = nullptr;
1847 for (const auto &Check : ExpandedChecks) {
1848 const PointerBounds &A = Check.first, &B = Check.second;
1849 // Check if two pointers (A and B) conflict where conflict is computed as:
1850 // start(A) <= end(B) && start(B) <= end(A)
1851 unsigned AS0 = A.Start->getType()->getPointerAddressSpace();
1852 unsigned AS1 = B.Start->getType()->getPointerAddressSpace();
1854 assert((AS0 == B.End->getType()->getPointerAddressSpace()) &&
1855 (AS1 == A.End->getType()->getPointerAddressSpace()) &&
1856 "Trying to bounds check pointers with different address spaces");
1858 Type *PtrArithTy0 = Type::getInt8PtrTy(Ctx, AS0);
1859 Type *PtrArithTy1 = Type::getInt8PtrTy(Ctx, AS1);
1861 Value *Start0 = ChkBuilder.CreateBitCast(A.Start, PtrArithTy0, "bc");
1862 Value *Start1 = ChkBuilder.CreateBitCast(B.Start, PtrArithTy1, "bc");
1863 Value *End0 = ChkBuilder.CreateBitCast(A.End, PtrArithTy1, "bc");
1864 Value *End1 = ChkBuilder.CreateBitCast(B.End, PtrArithTy0, "bc");
1866 Value *Cmp0 = ChkBuilder.CreateICmpULE(Start0, End1, "bound0");
1867 FirstInst = getFirstInst(FirstInst, Cmp0, Loc);
1868 Value *Cmp1 = ChkBuilder.CreateICmpULE(Start1, End0, "bound1");
1869 FirstInst = getFirstInst(FirstInst, Cmp1, Loc);
1870 Value *IsConflict = ChkBuilder.CreateAnd(Cmp0, Cmp1, "found.conflict");
1871 FirstInst = getFirstInst(FirstInst, IsConflict, Loc);
1872 if (MemoryRuntimeCheck) {
1874 ChkBuilder.CreateOr(MemoryRuntimeCheck, IsConflict, "conflict.rdx");
1875 FirstInst = getFirstInst(FirstInst, IsConflict, Loc);
1877 MemoryRuntimeCheck = IsConflict;
1880 if (!MemoryRuntimeCheck)
1881 return std::make_pair(nullptr, nullptr);
1883 // We have to do this trickery because the IRBuilder might fold the check to a
1884 // constant expression in which case there is no Instruction anchored in a
1886 Instruction *Check = BinaryOperator::CreateAnd(MemoryRuntimeCheck,
1887 ConstantInt::getTrue(Ctx));
1888 ChkBuilder.Insert(Check, "memcheck.conflict");
1889 FirstInst = getFirstInst(FirstInst, Check, Loc);
1890 return std::make_pair(FirstInst, Check);
1893 std::pair<Instruction *, Instruction *>
1894 LoopAccessInfo::addRuntimeChecks(Instruction *Loc) const {
1895 if (!PtrRtChecking->Need)
1896 return std::make_pair(nullptr, nullptr);
1898 return addRuntimeChecks(Loc, PtrRtChecking->getChecks());
1901 void LoopAccessInfo::collectStridedAccess(Value *MemAccess) {
1902 Value *Ptr = nullptr;
1903 if (LoadInst *LI = dyn_cast<LoadInst>(MemAccess))
1904 Ptr = LI->getPointerOperand();
1905 else if (StoreInst *SI = dyn_cast<StoreInst>(MemAccess))
1906 Ptr = SI->getPointerOperand();
1910 Value *Stride = getStrideFromPointer(Ptr, PSE->getSE(), TheLoop);
1914 DEBUG(dbgs() << "LAA: Found a strided access that we can version");
1915 DEBUG(dbgs() << " Ptr: " << *Ptr << " Stride: " << *Stride << "\n");
1916 SymbolicStrides[Ptr] = Stride;
1917 StrideSet.insert(Stride);
1920 LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE,
1921 const TargetLibraryInfo *TLI, AliasAnalysis *AA,
1922 DominatorTree *DT, LoopInfo *LI)
1923 : PSE(llvm::make_unique<PredicatedScalarEvolution>(*SE, *L)),
1924 PtrRtChecking(llvm::make_unique<RuntimePointerChecking>(SE)),
1925 DepChecker(llvm::make_unique<MemoryDepChecker>(*PSE, L)), TheLoop(L),
1926 NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1), CanVecMem(false),
1927 StoreToLoopInvariantAddress(false) {
1928 if (canAnalyzeLoop())
1929 analyzeLoop(AA, LI, TLI, DT);
1932 void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const {
1934 OS.indent(Depth) << "Memory dependences are safe";
1935 if (MaxSafeDepDistBytes != -1ULL)
1936 OS << " with a maximum dependence distance of " << MaxSafeDepDistBytes
1938 if (PtrRtChecking->Need)
1939 OS << " with run-time checks";
1944 OS.indent(Depth) << "Report: " << Report->str() << "\n";
1946 if (auto *Dependences = DepChecker->getDependences()) {
1947 OS.indent(Depth) << "Dependences:\n";
1948 for (auto &Dep : *Dependences) {
1949 Dep.print(OS, Depth + 2, DepChecker->getMemoryInstructions());
1953 OS.indent(Depth) << "Too many dependences, not recorded\n";
1955 // List the pair of accesses need run-time checks to prove independence.
1956 PtrRtChecking->print(OS, Depth);
1959 OS.indent(Depth) << "Store to invariant address was "
1960 << (StoreToLoopInvariantAddress ? "" : "not ")
1961 << "found in loop.\n";
1963 OS.indent(Depth) << "SCEV assumptions:\n";
1964 PSE->getUnionPredicate().print(OS, Depth);
1968 OS.indent(Depth) << "Expressions re-written:\n";
1969 PSE->print(OS, Depth);
1972 const LoopAccessInfo &LoopAccessLegacyAnalysis::getInfo(Loop *L) {
1973 auto &LAI = LoopAccessInfoMap[L];
1976 LAI = llvm::make_unique<LoopAccessInfo>(L, SE, TLI, AA, DT, LI);
1981 void LoopAccessLegacyAnalysis::print(raw_ostream &OS, const Module *M) const {
1982 LoopAccessLegacyAnalysis &LAA = *const_cast<LoopAccessLegacyAnalysis *>(this);
1984 for (Loop *TopLevelLoop : *LI)
1985 for (Loop *L : depth_first(TopLevelLoop)) {
1986 OS.indent(2) << L->getHeader()->getName() << ":\n";
1987 auto &LAI = LAA.getInfo(L);
1992 bool LoopAccessLegacyAnalysis::runOnFunction(Function &F) {
1993 SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
1994 auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
1995 TLI = TLIP ? &TLIP->getTLI() : nullptr;
1996 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
1997 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
1998 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
2003 void LoopAccessLegacyAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
2004 AU.addRequired<ScalarEvolutionWrapperPass>();
2005 AU.addRequired<AAResultsWrapperPass>();
2006 AU.addRequired<DominatorTreeWrapperPass>();
2007 AU.addRequired<LoopInfoWrapperPass>();
2009 AU.setPreservesAll();
2012 char LoopAccessLegacyAnalysis::ID = 0;
2013 static const char laa_name[] = "Loop Access Analysis";
2014 #define LAA_NAME "loop-accesses"
2016 INITIALIZE_PASS_BEGIN(LoopAccessLegacyAnalysis, LAA_NAME, laa_name, false, true)
2017 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
2018 INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
2019 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
2020 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
2021 INITIALIZE_PASS_END(LoopAccessLegacyAnalysis, LAA_NAME, laa_name, false, true)
2023 char LoopAccessAnalysis::PassID;
2025 LoopAccessInfo LoopAccessAnalysis::run(Loop &L, AnalysisManager<Loop> &AM) {
2026 const AnalysisManager<Function> &FAM =
2027 AM.getResult<FunctionAnalysisManagerLoopProxy>(L).getManager();
2028 Function &F = *L.getHeader()->getParent();
2029 auto *SE = FAM.getCachedResult<ScalarEvolutionAnalysis>(F);
2030 auto *TLI = FAM.getCachedResult<TargetLibraryAnalysis>(F);
2031 auto *AA = FAM.getCachedResult<AAManager>(F);
2032 auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(F);
2033 auto *LI = FAM.getCachedResult<LoopAnalysis>(F);
2036 "ScalarEvolution must have been cached at a higher level");
2038 report_fatal_error("AliasAnalysis must have been cached at a higher level");
2040 report_fatal_error("DominatorTree must have been cached at a higher level");
2042 report_fatal_error("LoopInfo must have been cached at a higher level");
2043 return LoopAccessInfo(&L, SE, TLI, AA, DT, LI);
2046 PreservedAnalyses LoopAccessInfoPrinterPass::run(Loop &L,
2047 AnalysisManager<Loop> &AM) {
2048 Function &F = *L.getHeader()->getParent();
2049 auto &LAI = AM.getResult<LoopAccessAnalysis>(L);
2050 OS << "Loop access info in function '" << F.getName() << "':\n";
2051 OS.indent(2) << L.getHeader()->getName() << ":\n";
2053 return PreservedAnalyses::all();
2057 Pass *createLAAPass() {
2058 return new LoopAccessLegacyAnalysis();