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Diffstat (limited to 'contrib/llvm/lib/Analysis/LoopAccessAnalysis.cpp')
| -rw-r--r-- | contrib/llvm/lib/Analysis/LoopAccessAnalysis.cpp | 1862 |
1 files changed, 1862 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/contrib/llvm/lib/Analysis/LoopAccessAnalysis.cpp new file mode 100644 index 000000000000..8bcdcb862014 --- /dev/null +++ b/contrib/llvm/lib/Analysis/LoopAccessAnalysis.cpp @@ -0,0 +1,1862 @@ +//===- LoopAccessAnalysis.cpp - Loop Access Analysis Implementation --------==// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// The implementation for the loop memory dependence that was originally +// developed for the loop vectorizer. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Analysis/LoopAccessAnalysis.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/ScalarEvolutionExpander.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/DiagnosticInfo.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Analysis/VectorUtils.h" +using namespace llvm; + +#define DEBUG_TYPE "loop-accesses" + +static cl::opt<unsigned, true> +VectorizationFactor("force-vector-width", cl::Hidden, + cl::desc("Sets the SIMD width. Zero is autoselect."), + cl::location(VectorizerParams::VectorizationFactor)); +unsigned VectorizerParams::VectorizationFactor; + +static cl::opt<unsigned, true> +VectorizationInterleave("force-vector-interleave", cl::Hidden, + cl::desc("Sets the vectorization interleave count. " + "Zero is autoselect."), + cl::location( + VectorizerParams::VectorizationInterleave)); +unsigned VectorizerParams::VectorizationInterleave; + +static cl::opt<unsigned, true> RuntimeMemoryCheckThreshold( + "runtime-memory-check-threshold", cl::Hidden, + cl::desc("When performing memory disambiguation checks at runtime do not " + "generate more than this number of comparisons (default = 8)."), + cl::location(VectorizerParams::RuntimeMemoryCheckThreshold), cl::init(8)); +unsigned VectorizerParams::RuntimeMemoryCheckThreshold; + +/// \brief The maximum iterations used to merge memory checks +static cl::opt<unsigned> MemoryCheckMergeThreshold( + "memory-check-merge-threshold", cl::Hidden, + cl::desc("Maximum number of comparisons done when trying to merge " + "runtime memory checks. (default = 100)"), + cl::init(100)); + +/// Maximum SIMD width. +const unsigned VectorizerParams::MaxVectorWidth = 64; + +/// \brief We collect dependences up to this threshold. +static cl::opt<unsigned> + MaxDependences("max-dependences", cl::Hidden, + cl::desc("Maximum number of dependences collected by " + "loop-access analysis (default = 100)"), + cl::init(100)); + +bool VectorizerParams::isInterleaveForced() { + return ::VectorizationInterleave.getNumOccurrences() > 0; +} + +void LoopAccessReport::emitAnalysis(const LoopAccessReport &Message, + const Function *TheFunction, + const Loop *TheLoop, + const char *PassName) { + DebugLoc DL = TheLoop->getStartLoc(); + if (const Instruction *I = Message.getInstr()) + DL = I->getDebugLoc(); + emitOptimizationRemarkAnalysis(TheFunction->getContext(), PassName, + *TheFunction, DL, Message.str()); +} + +Value *llvm::stripIntegerCast(Value *V) { + if (CastInst *CI = dyn_cast<CastInst>(V)) + if (CI->getOperand(0)->getType()->isIntegerTy()) + return CI->getOperand(0); + return V; +} + +const SCEV *llvm::replaceSymbolicStrideSCEV(PredicatedScalarEvolution &PSE, + const ValueToValueMap &PtrToStride, + Value *Ptr, Value *OrigPtr) { + const SCEV *OrigSCEV = PSE.getSCEV(Ptr); + + // If there is an entry in the map return the SCEV of the pointer with the + // symbolic stride replaced by one. + ValueToValueMap::const_iterator SI = + PtrToStride.find(OrigPtr ? OrigPtr : Ptr); + if (SI != PtrToStride.end()) { + Value *StrideVal = SI->second; + + // Strip casts. + StrideVal = stripIntegerCast(StrideVal); + + // Replace symbolic stride by one. + Value *One = ConstantInt::get(StrideVal->getType(), 1); + ValueToValueMap RewriteMap; + RewriteMap[StrideVal] = One; + + ScalarEvolution *SE = PSE.getSE(); + const auto *U = cast<SCEVUnknown>(SE->getSCEV(StrideVal)); + const auto *CT = + static_cast<const SCEVConstant *>(SE->getOne(StrideVal->getType())); + + PSE.addPredicate(*SE->getEqualPredicate(U, CT)); + auto *Expr = PSE.getSCEV(Ptr); + + DEBUG(dbgs() << "LAA: Replacing SCEV: " << *OrigSCEV << " by: " << *Expr + << "\n"); + return Expr; + } + + // Otherwise, just return the SCEV of the original pointer. + return OrigSCEV; +} + +void RuntimePointerChecking::insert(Loop *Lp, Value *Ptr, bool WritePtr, + unsigned DepSetId, unsigned ASId, + const ValueToValueMap &Strides, + PredicatedScalarEvolution &PSE) { + // Get the stride replaced scev. + const SCEV *Sc = replaceSymbolicStrideSCEV(PSE, Strides, Ptr); + const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Sc); + assert(AR && "Invalid addrec expression"); + ScalarEvolution *SE = PSE.getSE(); + const SCEV *Ex = SE->getBackedgeTakenCount(Lp); + + const SCEV *ScStart = AR->getStart(); + const SCEV *ScEnd = AR->evaluateAtIteration(Ex, *SE); + const SCEV *Step = AR->getStepRecurrence(*SE); + + // For expressions with negative step, the upper bound is ScStart and the + // lower bound is ScEnd. + if (const SCEVConstant *CStep = dyn_cast<const SCEVConstant>(Step)) { + if (CStep->getValue()->isNegative()) + std::swap(ScStart, ScEnd); + } else { + // Fallback case: the step is not constant, but the we can still + // get the upper and lower bounds of the interval by using min/max + // expressions. + ScStart = SE->getUMinExpr(ScStart, ScEnd); + ScEnd = SE->getUMaxExpr(AR->getStart(), ScEnd); + } + + Pointers.emplace_back(Ptr, ScStart, ScEnd, WritePtr, DepSetId, ASId, Sc); +} + +SmallVector<RuntimePointerChecking::PointerCheck, 4> +RuntimePointerChecking::generateChecks() const { + SmallVector<PointerCheck, 4> Checks; + + for (unsigned I = 0; I < CheckingGroups.size(); ++I) { + for (unsigned J = I + 1; J < CheckingGroups.size(); ++J) { + const RuntimePointerChecking::CheckingPtrGroup &CGI = CheckingGroups[I]; + const RuntimePointerChecking::CheckingPtrGroup &CGJ = CheckingGroups[J]; + + if (needsChecking(CGI, CGJ)) + Checks.push_back(std::make_pair(&CGI, &CGJ)); + } + } + return Checks; +} + +void RuntimePointerChecking::generateChecks( + MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) { + assert(Checks.empty() && "Checks is not empty"); + groupChecks(DepCands, UseDependencies); + Checks = generateChecks(); +} + +bool RuntimePointerChecking::needsChecking(const CheckingPtrGroup &M, + const CheckingPtrGroup &N) const { + for (unsigned I = 0, EI = M.Members.size(); EI != I; ++I) + for (unsigned J = 0, EJ = N.Members.size(); EJ != J; ++J) + if (needsChecking(M.Members[I], N.Members[J])) + return true; + return false; +} + +/// Compare \p I and \p J and return the minimum. +/// Return nullptr in case we couldn't find an answer. +static const SCEV *getMinFromExprs(const SCEV *I, const SCEV *J, + ScalarEvolution *SE) { + const SCEV *Diff = SE->getMinusSCEV(J, I); + const SCEVConstant *C = dyn_cast<const SCEVConstant>(Diff); + + if (!C) + return nullptr; + if (C->getValue()->isNegative()) + return J; + return I; +} + +bool RuntimePointerChecking::CheckingPtrGroup::addPointer(unsigned Index) { + const SCEV *Start = RtCheck.Pointers[Index].Start; + const SCEV *End = RtCheck.Pointers[Index].End; + + // Compare the starts and ends with the known minimum and maximum + // of this set. We need to know how we compare against the min/max + // of the set in order to be able to emit memchecks. + const SCEV *Min0 = getMinFromExprs(Start, Low, RtCheck.SE); + if (!Min0) + return false; + + const SCEV *Min1 = getMinFromExprs(End, High, RtCheck.SE); + if (!Min1) + return false; + + // Update the low bound expression if we've found a new min value. + if (Min0 == Start) + Low = Start; + + // Update the high bound expression if we've found a new max value. + if (Min1 != End) + High = End; + + Members.push_back(Index); + return true; +} + +void RuntimePointerChecking::groupChecks( + MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) { + // We build the groups from dependency candidates equivalence classes + // because: + // - We know that pointers in the same equivalence class share + // the same underlying object and therefore there is a chance + // that we can compare pointers + // - We wouldn't be able to merge two pointers for which we need + // to emit a memcheck. The classes in DepCands are already + // conveniently built such that no two pointers in the same + // class need checking against each other. + + // We use the following (greedy) algorithm to construct the groups + // For every pointer in the equivalence class: + // For each existing group: + // - if the difference between this pointer and the min/max bounds + // of the group is a constant, then make the pointer part of the + // group and update the min/max bounds of that group as required. + + CheckingGroups.clear(); + + // If we need to check two pointers to the same underlying object + // with a non-constant difference, we shouldn't perform any pointer + // grouping with those pointers. This is because we can easily get + // into cases where the resulting check would return false, even when + // the accesses are safe. + // + // The following example shows this: + // for (i = 0; i < 1000; ++i) + // a[5000 + i * m] = a[i] + a[i + 9000] + // + // Here grouping gives a check of (5000, 5000 + 1000 * m) against + // (0, 10000) which is always false. However, if m is 1, there is no + // dependence. Not grouping the checks for a[i] and a[i + 9000] allows + // us to perform an accurate check in this case. + // + // The above case requires that we have an UnknownDependence between + // accesses to the same underlying object. This cannot happen unless + // ShouldRetryWithRuntimeCheck is set, and therefore UseDependencies + // is also false. In this case we will use the fallback path and create + // separate checking groups for all pointers. + + // If we don't have the dependency partitions, construct a new + // checking pointer group for each pointer. This is also required + // for correctness, because in this case we can have checking between + // pointers to the same underlying object. + if (!UseDependencies) { + for (unsigned I = 0; I < Pointers.size(); ++I) + CheckingGroups.push_back(CheckingPtrGroup(I, *this)); + return; + } + + unsigned TotalComparisons = 0; + + DenseMap<Value *, unsigned> PositionMap; + for (unsigned Index = 0; Index < Pointers.size(); ++Index) + PositionMap[Pointers[Index].PointerValue] = Index; + + // We need to keep track of what pointers we've already seen so we + // don't process them twice. + SmallSet<unsigned, 2> Seen; + + // Go through all equivalence classes, get the "pointer check groups" + // and add them to the overall solution. We use the order in which accesses + // appear in 'Pointers' to enforce determinism. + for (unsigned I = 0; I < Pointers.size(); ++I) { + // We've seen this pointer before, and therefore already processed + // its equivalence class. + if (Seen.count(I)) + continue; + + MemoryDepChecker::MemAccessInfo Access(Pointers[I].PointerValue, + Pointers[I].IsWritePtr); + + SmallVector<CheckingPtrGroup, 2> Groups; + auto LeaderI = DepCands.findValue(DepCands.getLeaderValue(Access)); + + // Because DepCands is constructed by visiting accesses in the order in + // which they appear in alias sets (which is deterministic) and the + // iteration order within an equivalence class member is only dependent on + // the order in which unions and insertions are performed on the + // equivalence class, the iteration order is deterministic. + for (auto MI = DepCands.member_begin(LeaderI), ME = DepCands.member_end(); + MI != ME; ++MI) { + unsigned Pointer = PositionMap[MI->getPointer()]; + bool Merged = false; + // Mark this pointer as seen. + Seen.insert(Pointer); + + // Go through all the existing sets and see if we can find one + // which can include this pointer. + for (CheckingPtrGroup &Group : Groups) { + // Don't perform more than a certain amount of comparisons. + // This should limit the cost of grouping the pointers to something + // reasonable. If we do end up hitting this threshold, the algorithm + // will create separate groups for all remaining pointers. + if (TotalComparisons > MemoryCheckMergeThreshold) + break; + + TotalComparisons++; + + if (Group.addPointer(Pointer)) { + Merged = true; + break; + } + } + + if (!Merged) + // We couldn't add this pointer to any existing set or the threshold + // for the number of comparisons has been reached. Create a new group + // to hold the current pointer. + Groups.push_back(CheckingPtrGroup(Pointer, *this)); + } + + // We've computed the grouped checks for this partition. + // Save the results and continue with the next one. + std::copy(Groups.begin(), Groups.end(), std::back_inserter(CheckingGroups)); + } +} + +bool RuntimePointerChecking::arePointersInSamePartition( + const SmallVectorImpl<int> &PtrToPartition, unsigned PtrIdx1, + unsigned PtrIdx2) { + return (PtrToPartition[PtrIdx1] != -1 && + PtrToPartition[PtrIdx1] == PtrToPartition[PtrIdx2]); +} + +bool RuntimePointerChecking::needsChecking(unsigned I, unsigned J) const { + const PointerInfo &PointerI = Pointers[I]; + const PointerInfo &PointerJ = Pointers[J]; + + // No need to check if two readonly pointers intersect. + if (!PointerI.IsWritePtr && !PointerJ.IsWritePtr) + return false; + + // Only need to check pointers between two different dependency sets. + if (PointerI.DependencySetId == PointerJ.DependencySetId) + return false; + + // Only need to check pointers in the same alias set. + if (PointerI.AliasSetId != PointerJ.AliasSetId) + return false; + + return true; +} + +void RuntimePointerChecking::printChecks( + raw_ostream &OS, const SmallVectorImpl<PointerCheck> &Checks, + unsigned Depth) const { + unsigned N = 0; + for (const auto &Check : Checks) { + const auto &First = Check.first->Members, &Second = Check.second->Members; + + OS.indent(Depth) << "Check " << N++ << ":\n"; + + OS.indent(Depth + 2) << "Comparing group (" << Check.first << "):\n"; + for (unsigned K = 0; K < First.size(); ++K) + OS.indent(Depth + 2) << *Pointers[First[K]].PointerValue << "\n"; + + OS.indent(Depth + 2) << "Against group (" << Check.second << "):\n"; + for (unsigned K = 0; K < Second.size(); ++K) + OS.indent(Depth + 2) << *Pointers[Second[K]].PointerValue << "\n"; + } +} + +void RuntimePointerChecking::print(raw_ostream &OS, unsigned Depth) const { + + OS.indent(Depth) << "Run-time memory checks:\n"; + printChecks(OS, Checks, Depth); + + OS.indent(Depth) << "Grouped accesses:\n"; + for (unsigned I = 0; I < CheckingGroups.size(); ++I) { + const auto &CG = CheckingGroups[I]; + + OS.indent(Depth + 2) << "Group " << &CG << ":\n"; + OS.indent(Depth + 4) << "(Low: " << *CG.Low << " High: " << *CG.High + << ")\n"; + for (unsigned J = 0; J < CG.Members.size(); ++J) { + OS.indent(Depth + 6) << "Member: " << *Pointers[CG.Members[J]].Expr + << "\n"; + } + } +} + +namespace { +/// \brief Analyses memory accesses in a loop. +/// +/// Checks whether run time pointer checks are needed and builds sets for data +/// dependence checking. +class AccessAnalysis { +public: + /// \brief Read or write access location. + typedef PointerIntPair<Value *, 1, bool> MemAccessInfo; + typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet; + + AccessAnalysis(const DataLayout &Dl, AliasAnalysis *AA, LoopInfo *LI, + MemoryDepChecker::DepCandidates &DA, + PredicatedScalarEvolution &PSE) + : DL(Dl), AST(*AA), LI(LI), DepCands(DA), IsRTCheckAnalysisNeeded(false), + PSE(PSE) {} + + /// \brief Register a load and whether it is only read from. + void addLoad(MemoryLocation &Loc, bool IsReadOnly) { + Value *Ptr = const_cast<Value*>(Loc.Ptr); + AST.add(Ptr, MemoryLocation::UnknownSize, Loc.AATags); + Accesses.insert(MemAccessInfo(Ptr, false)); + if (IsReadOnly) + ReadOnlyPtr.insert(Ptr); + } + + /// \brief Register a store. + void addStore(MemoryLocation &Loc) { + Value *Ptr = const_cast<Value*>(Loc.Ptr); + AST.add(Ptr, MemoryLocation::UnknownSize, Loc.AATags); + Accesses.insert(MemAccessInfo(Ptr, true)); + } + + /// \brief Check whether we can check the pointers at runtime for + /// non-intersection. + /// + /// Returns true if we need no check or if we do and we can generate them + /// (i.e. the pointers have computable bounds). + bool canCheckPtrAtRT(RuntimePointerChecking &RtCheck, ScalarEvolution *SE, + Loop *TheLoop, const ValueToValueMap &Strides, + bool ShouldCheckStride = false); + + /// \brief Goes over all memory accesses, checks whether a RT check is needed + /// and builds sets of dependent accesses. + void buildDependenceSets() { + processMemAccesses(); + } + + /// \brief Initial processing of memory accesses determined that we need to + /// perform dependency checking. + /// + /// Note that this can later be cleared if we retry memcheck analysis without + /// dependency checking (i.e. ShouldRetryWithRuntimeCheck). + bool isDependencyCheckNeeded() { return !CheckDeps.empty(); } + + /// We decided that no dependence analysis would be used. Reset the state. + void resetDepChecks(MemoryDepChecker &DepChecker) { + CheckDeps.clear(); + DepChecker.clearDependences(); + } + + MemAccessInfoSet &getDependenciesToCheck() { return CheckDeps; } + +private: + typedef SetVector<MemAccessInfo> PtrAccessSet; + + /// \brief Go over all memory access and check whether runtime pointer checks + /// are needed and build sets of dependency check candidates. + void processMemAccesses(); + + /// Set of all accesses. + PtrAccessSet Accesses; + + const DataLayout &DL; + + /// Set of accesses that need a further dependence check. + MemAccessInfoSet CheckDeps; + + /// Set of pointers that are read only. + SmallPtrSet<Value*, 16> ReadOnlyPtr; + + /// An alias set tracker to partition the access set by underlying object and + //intrinsic property (such as TBAA metadata). + AliasSetTracker AST; + + LoopInfo *LI; + + /// Sets of potentially dependent accesses - members of one set share an + /// underlying pointer. The set "CheckDeps" identfies which sets really need a + /// dependence check. + MemoryDepChecker::DepCandidates &DepCands; + + /// \brief Initial processing of memory accesses determined that we may need + /// to add memchecks. Perform the analysis to determine the necessary checks. + /// + /// Note that, this is different from isDependencyCheckNeeded. When we retry + /// memcheck analysis without dependency checking + /// (i.e. ShouldRetryWithRuntimeCheck), isDependencyCheckNeeded is cleared + /// while this remains set if we have potentially dependent accesses. + bool IsRTCheckAnalysisNeeded; + + /// The SCEV predicate containing all the SCEV-related assumptions. + PredicatedScalarEvolution &PSE; +}; + +} // end anonymous namespace + +/// \brief Check whether a pointer can participate in a runtime bounds check. +static bool hasComputableBounds(PredicatedScalarEvolution &PSE, + const ValueToValueMap &Strides, Value *Ptr, + Loop *L) { + const SCEV *PtrScev = replaceSymbolicStrideSCEV(PSE, Strides, Ptr); + const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev); + if (!AR) + return false; + + return AR->isAffine(); +} + +bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck, + ScalarEvolution *SE, Loop *TheLoop, + const ValueToValueMap &StridesMap, + bool ShouldCheckStride) { + // Find pointers with computable bounds. We are going to use this information + // to place a runtime bound check. + bool CanDoRT = true; + + bool NeedRTCheck = false; + if (!IsRTCheckAnalysisNeeded) return true; + + bool IsDepCheckNeeded = isDependencyCheckNeeded(); + + // We assign a consecutive id to access from different alias sets. + // Accesses between different groups doesn't need to be checked. + unsigned ASId = 1; + for (auto &AS : AST) { + int NumReadPtrChecks = 0; + int NumWritePtrChecks = 0; + + // We assign consecutive id to access from different dependence sets. + // Accesses within the same set don't need a runtime check. + unsigned RunningDepId = 1; + DenseMap<Value *, unsigned> DepSetId; + + for (auto A : AS) { + Value *Ptr = A.getValue(); + bool IsWrite = Accesses.count(MemAccessInfo(Ptr, true)); + MemAccessInfo Access(Ptr, IsWrite); + + if (IsWrite) + ++NumWritePtrChecks; + else + ++NumReadPtrChecks; + + if (hasComputableBounds(PSE, StridesMap, Ptr, TheLoop) && + // When we run after a failing dependency check we have to make sure + // we don't have wrapping pointers. + (!ShouldCheckStride || + isStridedPtr(PSE, Ptr, TheLoop, StridesMap) == 1)) { + // The id of the dependence set. + unsigned DepId; + + if (IsDepCheckNeeded) { + Value *Leader = DepCands.getLeaderValue(Access).getPointer(); + unsigned &LeaderId = DepSetId[Leader]; + if (!LeaderId) + LeaderId = RunningDepId++; + DepId = LeaderId; + } else + // Each access has its own dependence set. + DepId = RunningDepId++; + + RtCheck.insert(TheLoop, Ptr, IsWrite, DepId, ASId, StridesMap, PSE); + + DEBUG(dbgs() << "LAA: Found a runtime check ptr:" << *Ptr << '\n'); + } else { + DEBUG(dbgs() << "LAA: Can't find bounds for ptr:" << *Ptr << '\n'); + CanDoRT = false; + } + } + + // If we have at least two writes or one write and a read then we need to + // check them. But there is no need to checks if there is only one + // dependence set for this alias set. + // + // Note that this function computes CanDoRT and NeedRTCheck independently. + // For example CanDoRT=false, NeedRTCheck=false means that we have a pointer + // for which we couldn't find the bounds but we don't actually need to emit + // any checks so it does not matter. + if (!(IsDepCheckNeeded && CanDoRT && RunningDepId == 2)) + NeedRTCheck |= (NumWritePtrChecks >= 2 || (NumReadPtrChecks >= 1 && + NumWritePtrChecks >= 1)); + + ++ASId; + } + + // If the pointers that we would use for the bounds comparison have different + // address spaces, assume the values aren't directly comparable, so we can't + // use them for the runtime check. We also have to assume they could + // overlap. In the future there should be metadata for whether address spaces + // are disjoint. + unsigned NumPointers = RtCheck.Pointers.size(); + for (unsigned i = 0; i < NumPointers; ++i) { + for (unsigned j = i + 1; j < NumPointers; ++j) { + // Only need to check pointers between two different dependency sets. + if (RtCheck.Pointers[i].DependencySetId == + RtCheck.Pointers[j].DependencySetId) + continue; + // Only need to check pointers in the same alias set. + if (RtCheck.Pointers[i].AliasSetId != RtCheck.Pointers[j].AliasSetId) + continue; + + Value *PtrI = RtCheck.Pointers[i].PointerValue; + Value *PtrJ = RtCheck.Pointers[j].PointerValue; + + unsigned ASi = PtrI->getType()->getPointerAddressSpace(); + unsigned ASj = PtrJ->getType()->getPointerAddressSpace(); + if (ASi != ASj) { + DEBUG(dbgs() << "LAA: Runtime check would require comparison between" + " different address spaces\n"); + return false; + } + } + } + + if (NeedRTCheck && CanDoRT) + RtCheck.generateChecks(DepCands, IsDepCheckNeeded); + + DEBUG(dbgs() << "LAA: We need to do " << RtCheck.getNumberOfChecks() + << " pointer comparisons.\n"); + + RtCheck.Need = NeedRTCheck; + + bool CanDoRTIfNeeded = !NeedRTCheck || CanDoRT; + if (!CanDoRTIfNeeded) + RtCheck.reset(); + return CanDoRTIfNeeded; +} + +void AccessAnalysis::processMemAccesses() { + // We process the set twice: first we process read-write pointers, last we + // process read-only pointers. This allows us to skip dependence tests for + // read-only pointers. + + DEBUG(dbgs() << "LAA: Processing memory accesses...\n"); + DEBUG(dbgs() << " AST: "; AST.dump()); + DEBUG(dbgs() << "LAA: Accesses(" << Accesses.size() << "):\n"); + DEBUG({ + for (auto A : Accesses) + dbgs() << "\t" << *A.getPointer() << " (" << + (A.getInt() ? "write" : (ReadOnlyPtr.count(A.getPointer()) ? + "read-only" : "read")) << ")\n"; + }); + + // The AliasSetTracker has nicely partitioned our pointers by metadata + // compatibility and potential for underlying-object overlap. As a result, we + // only need to check for potential pointer dependencies within each alias + // set. + for (auto &AS : AST) { + // Note that both the alias-set tracker and the alias sets themselves used + // linked lists internally and so the iteration order here is deterministic + // (matching the original instruction order within each set). + + bool SetHasWrite = false; + + // Map of pointers to last access encountered. + typedef DenseMap<Value*, MemAccessInfo> UnderlyingObjToAccessMap; + UnderlyingObjToAccessMap ObjToLastAccess; + + // Set of access to check after all writes have been processed. + PtrAccessSet DeferredAccesses; + + // Iterate over each alias set twice, once to process read/write pointers, + // and then to process read-only pointers. + for (int SetIteration = 0; SetIteration < 2; ++SetIteration) { + bool UseDeferred = SetIteration > 0; + PtrAccessSet &S = UseDeferred ? DeferredAccesses : Accesses; + + for (auto AV : AS) { + Value *Ptr = AV.getValue(); + + // For a single memory access in AliasSetTracker, Accesses may contain + // both read and write, and they both need to be handled for CheckDeps. + for (auto AC : S) { + if (AC.getPointer() != Ptr) + continue; + + bool IsWrite = AC.getInt(); + + // If we're using the deferred access set, then it contains only + // reads. + bool IsReadOnlyPtr = ReadOnlyPtr.count(Ptr) && !IsWrite; + if (UseDeferred && !IsReadOnlyPtr) + continue; + // Otherwise, the pointer must be in the PtrAccessSet, either as a + // read or a write. + assert(((IsReadOnlyPtr && UseDeferred) || IsWrite || + S.count(MemAccessInfo(Ptr, false))) && + "Alias-set pointer not in the access set?"); + + MemAccessInfo Access(Ptr, IsWrite); + DepCands.insert(Access); + + // Memorize read-only pointers for later processing and skip them in + // the first round (they need to be checked after we have seen all + // write pointers). Note: we also mark pointer that are not + // consecutive as "read-only" pointers (so that we check + // "a[b[i]] +="). Hence, we need the second check for "!IsWrite". + if (!UseDeferred && IsReadOnlyPtr) { + DeferredAccesses.insert(Access); + continue; + } + + // If this is a write - check other reads and writes for conflicts. If + // this is a read only check other writes for conflicts (but only if + // there is no other write to the ptr - this is an optimization to + // catch "a[i] = a[i] + " without having to do a dependence check). + if ((IsWrite || IsReadOnlyPtr) && SetHasWrite) { + CheckDeps.insert(Access); + IsRTCheckAnalysisNeeded = true; + } + + if (IsWrite) + SetHasWrite = true; + + // Create sets of pointers connected by a shared alias set and + // underlying object. + typedef SmallVector<Value *, 16> ValueVector; + ValueVector TempObjects; + + GetUnderlyingObjects(Ptr, TempObjects, DL, LI); + DEBUG(dbgs() << "Underlying objects for pointer " << *Ptr << "\n"); + for (Value *UnderlyingObj : TempObjects) { + // nullptr never alias, don't join sets for pointer that have "null" + // in their UnderlyingObjects list. + if (isa<ConstantPointerNull>(UnderlyingObj)) + continue; + + UnderlyingObjToAccessMap::iterator Prev = + ObjToLastAccess.find(UnderlyingObj); + if (Prev != ObjToLastAccess.end()) + DepCands.unionSets(Access, Prev->second); + + ObjToLastAccess[UnderlyingObj] = Access; + DEBUG(dbgs() << " " << *UnderlyingObj << "\n"); + } + } + } + } + } +} + +static bool isInBoundsGep(Value *Ptr) { + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) + return GEP->isInBounds(); + return false; +} + +/// \brief Return true if an AddRec pointer \p Ptr is unsigned non-wrapping, +/// i.e. monotonically increasing/decreasing. +static bool isNoWrapAddRec(Value *Ptr, const SCEVAddRecExpr *AR, + ScalarEvolution *SE, const Loop *L) { + // FIXME: This should probably only return true for NUW. + if (AR->getNoWrapFlags(SCEV::NoWrapMask)) + return true; + + // Scalar evolution does not propagate the non-wrapping flags to values that + // are derived from a non-wrapping induction variable because non-wrapping + // could be flow-sensitive. + // + // Look through the potentially overflowing instruction to try to prove + // non-wrapping for the *specific* value of Ptr. + + // The arithmetic implied by an inbounds GEP can't overflow. + auto *GEP = dyn_cast<GetElementPtrInst>(Ptr); + if (!GEP || !GEP->isInBounds()) + return false; + + // Make sure there is only one non-const index and analyze that. + Value *NonConstIndex = nullptr; + for (auto Index = GEP->idx_begin(); Index != GEP->idx_end(); ++Index) + if (!isa<ConstantInt>(*Index)) { + if (NonConstIndex) + return false; + NonConstIndex = *Index; + } + if (!NonConstIndex) + // The recurrence is on the pointer, ignore for now. + return false; + + // The index in GEP is signed. It is non-wrapping if it's derived from a NSW + // AddRec using a NSW operation. + if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(NonConstIndex)) + if (OBO->hasNoSignedWrap() && + // Assume constant for other the operand so that the AddRec can be + // easily found. + isa<ConstantInt>(OBO->getOperand(1))) { + auto *OpScev = SE->getSCEV(OBO->getOperand(0)); + + if (auto *OpAR = dyn_cast<SCEVAddRecExpr>(OpScev)) + return OpAR->getLoop() == L && OpAR->getNoWrapFlags(SCEV::FlagNSW); + } + + return false; +} + +/// \brief Check whether the access through \p Ptr has a constant stride. +int llvm::isStridedPtr(PredicatedScalarEvolution &PSE, Value *Ptr, + const Loop *Lp, const ValueToValueMap &StridesMap) { + Type *Ty = Ptr->getType(); + assert(Ty->isPointerTy() && "Unexpected non-ptr"); + + // Make sure that the pointer does not point to aggregate types. + auto *PtrTy = cast<PointerType>(Ty); + if (PtrTy->getElementType()->isAggregateType()) { + DEBUG(dbgs() << "LAA: Bad stride - Not a pointer to a scalar type" + << *Ptr << "\n"); + return 0; + } + + const SCEV *PtrScev = replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr); + + const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev); + if (!AR) { + DEBUG(dbgs() << "LAA: Bad stride - Not an AddRecExpr pointer " + << *Ptr << " SCEV: " << *PtrScev << "\n"); + return 0; + } + + // The accesss function must stride over the innermost loop. + if (Lp != AR->getLoop()) { + DEBUG(dbgs() << "LAA: Bad stride - Not striding over innermost loop " << + *Ptr << " SCEV: " << *PtrScev << "\n"); + return 0; + } + + // The address calculation must not wrap. Otherwise, a dependence could be + // inverted. + // An inbounds getelementptr that is a AddRec with a unit stride + // cannot wrap per definition. The unit stride requirement is checked later. + // An getelementptr without an inbounds attribute and unit stride would have + // to access the pointer value "0" which is undefined behavior in address + // space 0, therefore we can also vectorize this case. + bool IsInBoundsGEP = isInBoundsGep(Ptr); + bool IsNoWrapAddRec = isNoWrapAddRec(Ptr, AR, PSE.getSE(), Lp); + bool IsInAddressSpaceZero = PtrTy->getAddressSpace() == 0; + if (!IsNoWrapAddRec && !IsInBoundsGEP && !IsInAddressSpaceZero) { + DEBUG(dbgs() << "LAA: Bad stride - Pointer may wrap in the address space " + << *Ptr << " SCEV: " << *PtrScev << "\n"); + return 0; + } + + // Check the step is constant. + const SCEV *Step = AR->getStepRecurrence(*PSE.getSE()); + + // Calculate the pointer stride and check if it is constant. + const SCEVConstant *C = dyn_cast<SCEVConstant>(Step); + if (!C) { + DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided " << *Ptr << + " SCEV: " << *PtrScev << "\n"); + return 0; + } + + auto &DL = Lp->getHeader()->getModule()->getDataLayout(); + int64_t Size = DL.getTypeAllocSize(PtrTy->getElementType()); + const APInt &APStepVal = C->getAPInt(); + + // Huge step value - give up. + if (APStepVal.getBitWidth() > 64) + return 0; + + int64_t StepVal = APStepVal.getSExtValue(); + + // Strided access. + int64_t Stride = StepVal / Size; + int64_t Rem = StepVal % Size; + if (Rem) + return 0; + + // If the SCEV could wrap but we have an inbounds gep with a unit stride we + // know we can't "wrap around the address space". In case of address space + // zero we know that this won't happen without triggering undefined behavior. + if (!IsNoWrapAddRec && (IsInBoundsGEP || IsInAddressSpaceZero) && + Stride != 1 && Stride != -1) + return 0; + + return Stride; +} + +bool MemoryDepChecker::Dependence::isSafeForVectorization(DepType Type) { + switch (Type) { + case NoDep: + case Forward: + case BackwardVectorizable: + return true; + + case Unknown: + case ForwardButPreventsForwarding: + case Backward: + case BackwardVectorizableButPreventsForwarding: + return false; + } + llvm_unreachable("unexpected DepType!"); +} + +bool MemoryDepChecker::Dependence::isBackward() const { + switch (Type) { + case NoDep: + case Forward: + case ForwardButPreventsForwarding: + case Unknown: + return false; + + case BackwardVectorizable: + case Backward: + case BackwardVectorizableButPreventsForwarding: + return true; + } + llvm_unreachable("unexpected DepType!"); +} + +bool MemoryDepChecker::Dependence::isPossiblyBackward() const { + return isBackward() || Type == Unknown; +} + +bool MemoryDepChecker::Dependence::isForward() const { + switch (Type) { + case Forward: + case ForwardButPreventsForwarding: + return true; + + case NoDep: + case Unknown: + case BackwardVectorizable: + case Backward: + case BackwardVectorizableButPreventsForwarding: + return false; + } + llvm_unreachable("unexpected DepType!"); +} + +bool MemoryDepChecker::couldPreventStoreLoadForward(unsigned Distance, + unsigned TypeByteSize) { + // If loads occur at a distance that is not a multiple of a feasible vector + // factor store-load forwarding does not take place. + // Positive dependences might cause troubles because vectorizing them might + // prevent store-load forwarding making vectorized code run a lot slower. + // a[i] = a[i-3] ^ a[i-8]; + // The stores to a[i:i+1] don't align with the stores to a[i-3:i-2] and + // hence on your typical architecture store-load forwarding does not take + // place. Vectorizing in such cases does not make sense. + // Store-load forwarding distance. + const unsigned NumCyclesForStoreLoadThroughMemory = 8*TypeByteSize; + // Maximum vector factor. + unsigned MaxVFWithoutSLForwardIssues = + VectorizerParams::MaxVectorWidth * TypeByteSize; + if(MaxSafeDepDistBytes < MaxVFWithoutSLForwardIssues) + MaxVFWithoutSLForwardIssues = MaxSafeDepDistBytes; + + for (unsigned vf = 2*TypeByteSize; vf <= MaxVFWithoutSLForwardIssues; + vf *= 2) { + if (Distance % vf && Distance / vf < NumCyclesForStoreLoadThroughMemory) { + MaxVFWithoutSLForwardIssues = (vf >>=1); + break; + } + } + + if (MaxVFWithoutSLForwardIssues< 2*TypeByteSize) { + DEBUG(dbgs() << "LAA: Distance " << Distance << + " that could cause a store-load forwarding conflict\n"); + return true; + } + + if (MaxVFWithoutSLForwardIssues < MaxSafeDepDistBytes && + MaxVFWithoutSLForwardIssues != + VectorizerParams::MaxVectorWidth * TypeByteSize) + MaxSafeDepDistBytes = MaxVFWithoutSLForwardIssues; + return false; +} + +/// \brief Check the dependence for two accesses with the same stride \p Stride. +/// \p Distance is the positive distance and \p TypeByteSize is type size in +/// bytes. +/// +/// \returns true if they are independent. +static bool areStridedAccessesIndependent(unsigned Distance, unsigned Stride, + unsigned TypeByteSize) { + assert(Stride > 1 && "The stride must be greater than 1"); + assert(TypeByteSize > 0 && "The type size in byte must be non-zero"); + assert(Distance > 0 && "The distance must be non-zero"); + + // Skip if the distance is not multiple of type byte size. + if (Distance % TypeByteSize) + return false; + + unsigned ScaledDist = Distance / TypeByteSize; + + // No dependence if the scaled distance is not multiple of the stride. + // E.g. + // for (i = 0; i < 1024 ; i += 4) + // A[i+2] = A[i] + 1; + // + // Two accesses in memory (scaled distance is 2, stride is 4): + // | A[0] | | | | A[4] | | | | + // | | | A[2] | | | | A[6] | | + // + // E.g. + // for (i = 0; i < 1024 ; i += 3) + // A[i+4] = A[i] + 1; + // + // Two accesses in memory (scaled distance is 4, stride is 3): + // | A[0] | | | A[3] | | | A[6] | | | + // | | | | | A[4] | | | A[7] | | + return ScaledDist % Stride; +} + +MemoryDepChecker::Dependence::DepType +MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx, + const MemAccessInfo &B, unsigned BIdx, + const ValueToValueMap &Strides) { + assert (AIdx < BIdx && "Must pass arguments in program order"); + + Value *APtr = A.getPointer(); + Value *BPtr = B.getPointer(); + bool AIsWrite = A.getInt(); + bool BIsWrite = B.getInt(); + + // Two reads are independent. + if (!AIsWrite && !BIsWrite) + return Dependence::NoDep; + + // We cannot check pointers in different address spaces. + if (APtr->getType()->getPointerAddressSpace() != + BPtr->getType()->getPointerAddressSpace()) + return Dependence::Unknown; + + const SCEV *AScev = replaceSymbolicStrideSCEV(PSE, Strides, APtr); + const SCEV *BScev = replaceSymbolicStrideSCEV(PSE, Strides, BPtr); + + int StrideAPtr = isStridedPtr(PSE, APtr, InnermostLoop, Strides); + int StrideBPtr = isStridedPtr(PSE, BPtr, InnermostLoop, Strides); + + const SCEV *Src = AScev; + const SCEV *Sink = BScev; + + // If the induction step is negative we have to invert source and sink of the + // dependence. + if (StrideAPtr < 0) { + //Src = BScev; + //Sink = AScev; + std::swap(APtr, BPtr); + std::swap(Src, Sink); + std::swap(AIsWrite, BIsWrite); + std::swap(AIdx, BIdx); + std::swap(StrideAPtr, StrideBPtr); + } + + const SCEV *Dist = PSE.getSE()->getMinusSCEV(Sink, Src); + + DEBUG(dbgs() << "LAA: Src Scev: " << *Src << "Sink Scev: " << *Sink + << "(Induction step: " << StrideAPtr << ")\n"); + DEBUG(dbgs() << "LAA: Distance for " << *InstMap[AIdx] << " to " + << *InstMap[BIdx] << ": " << *Dist << "\n"); + + // Need accesses with constant stride. We don't want to vectorize + // "A[B[i]] += ..." and similar code or pointer arithmetic that could wrap in + // the address space. + if (!StrideAPtr || !StrideBPtr || StrideAPtr != StrideBPtr){ + DEBUG(dbgs() << "Pointer access with non-constant stride\n"); + return Dependence::Unknown; + } + + const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist); + if (!C) { + DEBUG(dbgs() << "LAA: Dependence because of non-constant distance\n"); + ShouldRetryWithRuntimeCheck = true; + return Dependence::Unknown; + } + + Type *ATy = APtr->getType()->getPointerElementType(); + Type *BTy = BPtr->getType()->getPointerElementType(); + auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout(); + unsigned TypeByteSize = DL.getTypeAllocSize(ATy); + + // Negative distances are not plausible dependencies. + const APInt &Val = C->getAPInt(); + if (Val.isNegative()) { + bool IsTrueDataDependence = (AIsWrite && !BIsWrite); + if (IsTrueDataDependence && + (couldPreventStoreLoadForward(Val.abs().getZExtValue(), TypeByteSize) || + ATy != BTy)) + return Dependence::ForwardButPreventsForwarding; + + DEBUG(dbgs() << "LAA: Dependence is negative: NoDep\n"); + return Dependence::Forward; + } + + // Write to the same location with the same size. + // Could be improved to assert type sizes are the same (i32 == float, etc). + if (Val == 0) { + if (ATy == BTy) + return Dependence::Forward; + DEBUG(dbgs() << "LAA: Zero dependence difference but different types\n"); + return Dependence::Unknown; + } + + assert(Val.isStrictlyPositive() && "Expect a positive value"); + + if (ATy != BTy) { + DEBUG(dbgs() << + "LAA: ReadWrite-Write positive dependency with different types\n"); + return Dependence::Unknown; + } + + unsigned Distance = (unsigned) Val.getZExtValue(); + + unsigned Stride = std::abs(StrideAPtr); + if (Stride > 1 && + areStridedAccessesIndependent(Distance, Stride, TypeByteSize)) { + DEBUG(dbgs() << "LAA: Strided accesses are independent\n"); + return Dependence::NoDep; + } + + // Bail out early if passed-in parameters make vectorization not feasible. + unsigned ForcedFactor = (VectorizerParams::VectorizationFactor ? + VectorizerParams::VectorizationFactor : 1); + unsigned ForcedUnroll = (VectorizerParams::VectorizationInterleave ? + VectorizerParams::VectorizationInterleave : 1); + // The minimum number of iterations for a vectorized/unrolled version. + unsigned MinNumIter = std::max(ForcedFactor * ForcedUnroll, 2U); + + // It's not vectorizable if the distance is smaller than the minimum distance + // needed for a vectroized/unrolled version. Vectorizing one iteration in + // front needs TypeByteSize * Stride. Vectorizing the last iteration needs + // TypeByteSize (No need to plus the last gap distance). + // + // E.g. Assume one char is 1 byte in memory and one int is 4 bytes. + // foo(int *A) { + // int *B = (int *)((char *)A + 14); + // for (i = 0 ; i < 1024 ; i += 2) + // B[i] = A[i] + 1; + // } + // + // Two accesses in memory (stride is 2): + // | A[0] | | A[2] | | A[4] | | A[6] | | + // | B[0] | | B[2] | | B[4] | + // + // Distance needs for vectorizing iterations except the last iteration: + // 4 * 2 * (MinNumIter - 1). Distance needs for the last iteration: 4. + // So the minimum distance needed is: 4 * 2 * (MinNumIter - 1) + 4. + // + // If MinNumIter is 2, it is vectorizable as the minimum distance needed is + // 12, which is less than distance. + // + // If MinNumIter is 4 (Say if a user forces the vectorization factor to be 4), + // the minimum distance needed is 28, which is greater than distance. It is + // not safe to do vectorization. + unsigned MinDistanceNeeded = + TypeByteSize * Stride * (MinNumIter - 1) + TypeByteSize; + if (MinDistanceNeeded > Distance) { + DEBUG(dbgs() << "LAA: Failure because of positive distance " << Distance + << '\n'); + return Dependence::Backward; + } + + // Unsafe if the minimum distance needed is greater than max safe distance. + if (MinDistanceNeeded > MaxSafeDepDistBytes) { + DEBUG(dbgs() << "LAA: Failure because it needs at least " + << MinDistanceNeeded << " size in bytes"); + return Dependence::Backward; + } + + // Positive distance bigger than max vectorization factor. + // FIXME: Should use max factor instead of max distance in bytes, which could + // not handle different types. + // E.g. Assume one char is 1 byte in memory and one int is 4 bytes. + // void foo (int *A, char *B) { + // for (unsigned i = 0; i < 1024; i++) { + // A[i+2] = A[i] + 1; + // B[i+2] = B[i] + 1; + // } + // } + // + // This case is currently unsafe according to the max safe distance. If we + // analyze the two accesses on array B, the max safe dependence distance + // is 2. Then we analyze the accesses on array A, the minimum distance needed + // is 8, which is less than 2 and forbidden vectorization, But actually + // both A and B could be vectorized by 2 iterations. + MaxSafeDepDistBytes = + Distance < MaxSafeDepDistBytes ? Distance : MaxSafeDepDistBytes; + + bool IsTrueDataDependence = (!AIsWrite && BIsWrite); + if (IsTrueDataDependence && + couldPreventStoreLoadForward(Distance, TypeByteSize)) + return Dependence::BackwardVectorizableButPreventsForwarding; + + DEBUG(dbgs() << "LAA: Positive distance " << Val.getSExtValue() + << " with max VF = " + << MaxSafeDepDistBytes / (TypeByteSize * Stride) << '\n'); + + return Dependence::BackwardVectorizable; +} + +bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets, + MemAccessInfoSet &CheckDeps, + const ValueToValueMap &Strides) { + + MaxSafeDepDistBytes = -1U; + while (!CheckDeps.empty()) { + MemAccessInfo CurAccess = *CheckDeps.begin(); + + // Get the relevant memory access set. + EquivalenceClasses<MemAccessInfo>::iterator I = + AccessSets.findValue(AccessSets.getLeaderValue(CurAccess)); + + // Check accesses within this set. + EquivalenceClasses<MemAccessInfo>::member_iterator AI, AE; + AI = AccessSets.member_begin(I), AE = AccessSets.member_end(); + + // Check every access pair. + while (AI != AE) { + CheckDeps.erase(*AI); + EquivalenceClasses<MemAccessInfo>::member_iterator OI = std::next(AI); + while (OI != AE) { + // Check every accessing instruction pair in program order. + for (std::vector<unsigned>::iterator I1 = Accesses[*AI].begin(), + I1E = Accesses[*AI].end(); I1 != I1E; ++I1) + for (std::vector<unsigned>::iterator I2 = Accesses[*OI].begin(), + I2E = Accesses[*OI].end(); I2 != I2E; ++I2) { + auto A = std::make_pair(&*AI, *I1); + auto B = std::make_pair(&*OI, *I2); + + assert(*I1 != *I2); + if (*I1 > *I2) + std::swap(A, B); + + Dependence::DepType Type = + isDependent(*A.first, A.second, *B.first, B.second, Strides); + SafeForVectorization &= Dependence::isSafeForVectorization(Type); + + // Gather dependences unless we accumulated MaxDependences + // dependences. In that case return as soon as we find the first + // unsafe dependence. This puts a limit on this quadratic + // algorithm. + if (RecordDependences) { + if (Type != Dependence::NoDep) + Dependences.push_back(Dependence(A.second, B.second, Type)); + + if (Dependences.size() >= MaxDependences) { + RecordDependences = false; + Dependences.clear(); + DEBUG(dbgs() << "Too many dependences, stopped recording\n"); + } + } + if (!RecordDependences && !SafeForVectorization) + return false; + } + ++OI; + } + AI++; + } + } + + DEBUG(dbgs() << "Total Dependences: " << Dependences.size() << "\n"); + return SafeForVectorization; +} + +SmallVector<Instruction *, 4> +MemoryDepChecker::getInstructionsForAccess(Value *Ptr, bool isWrite) const { + MemAccessInfo Access(Ptr, isWrite); + auto &IndexVector = Accesses.find(Access)->second; + + SmallVector<Instruction *, 4> Insts; + std::transform(IndexVector.begin(), IndexVector.end(), + std::back_inserter(Insts), + [&](unsigned Idx) { return this->InstMap[Idx]; }); + return Insts; +} + +const char *MemoryDepChecker::Dependence::DepName[] = { + "NoDep", "Unknown", "Forward", "ForwardButPreventsForwarding", "Backward", + "BackwardVectorizable", "BackwardVectorizableButPreventsForwarding"}; + +void MemoryDepChecker::Dependence::print( + raw_ostream &OS, unsigned Depth, + const SmallVectorImpl<Instruction *> &Instrs) const { + OS.indent(Depth) << DepName[Type] << ":\n"; + OS.indent(Depth + 2) << *Instrs[Source] << " -> \n"; + OS.indent(Depth + 2) << *Instrs[Destination] << "\n"; +} + +bool LoopAccessInfo::canAnalyzeLoop() { + // We need to have a loop header. + DEBUG(dbgs() << "LAA: Found a loop: " << + TheLoop->getHeader()->getName() << '\n'); + + // We can only analyze innermost loops. + if (!TheLoop->empty()) { + DEBUG(dbgs() << "LAA: loop is not the innermost loop\n"); + emitAnalysis(LoopAccessReport() << "loop is not the innermost loop"); + return false; + } + + // We must have a single backedge. + if (TheLoop->getNumBackEdges() != 1) { + DEBUG(dbgs() << "LAA: loop control flow is not understood by analyzer\n"); + emitAnalysis( + LoopAccessReport() << + "loop control flow is not understood by analyzer"); + return false; + } + + // We must have a single exiting block. + if (!TheLoop->getExitingBlock()) { + DEBUG(dbgs() << "LAA: loop control flow is not understood by analyzer\n"); + emitAnalysis( + LoopAccessReport() << + "loop control flow is not understood by analyzer"); + return false; + } + + // We only handle bottom-tested loops, i.e. loop in which the condition is + // checked at the end of each iteration. With that we can assume that all + // instructions in the loop are executed the same number of times. + if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) { + DEBUG(dbgs() << "LAA: loop control flow is not understood by analyzer\n"); + emitAnalysis( + LoopAccessReport() << + "loop control flow is not understood by analyzer"); + return false; + } + + // ScalarEvolution needs to be able to find the exit count. + const SCEV *ExitCount = PSE.getSE()->getBackedgeTakenCount(TheLoop); + if (ExitCount == PSE.getSE()->getCouldNotCompute()) { + emitAnalysis(LoopAccessReport() + << "could not determine number of loop iterations"); + DEBUG(dbgs() << "LAA: SCEV could not compute the loop exit count.\n"); + return false; + } + + return true; +} + +void LoopAccessInfo::analyzeLoop(const ValueToValueMap &Strides) { + + typedef SmallVector<Value*, 16> ValueVector; + typedef SmallPtrSet<Value*, 16> ValueSet; + + // Holds the Load and Store *instructions*. + ValueVector Loads; + ValueVector Stores; + + // Holds all the different accesses in the loop. + unsigned NumReads = 0; + unsigned NumReadWrites = 0; + + PtrRtChecking.Pointers.clear(); + PtrRtChecking.Need = false; + + const bool IsAnnotatedParallel = TheLoop->isAnnotatedParallel(); + + // For each block. + for (Loop::block_iterator bb = TheLoop->block_begin(), + be = TheLoop->block_end(); bb != be; ++bb) { + + // Scan the BB and collect legal loads and stores. + for (BasicBlock::iterator it = (*bb)->begin(), e = (*bb)->end(); it != e; + ++it) { + + // If this is a load, save it. If this instruction can read from memory + // but is not a load, then we quit. Notice that we don't handle function + // calls that read or write. + if (it->mayReadFromMemory()) { + // Many math library functions read the rounding mode. We will only + // vectorize a loop if it contains known function calls that don't set + // the flag. Therefore, it is safe to ignore this read from memory. + CallInst *Call = dyn_cast<CallInst>(it); + if (Call && getIntrinsicIDForCall(Call, TLI)) + continue; + + // If the function has an explicit vectorized counterpart, we can safely + // assume that it can be vectorized. + if (Call && !Call->isNoBuiltin() && Call->getCalledFunction() && + TLI->isFunctionVectorizable(Call->getCalledFunction()->getName())) + continue; + + LoadInst *Ld = dyn_cast<LoadInst>(it); + if (!Ld || (!Ld->isSimple() && !IsAnnotatedParallel)) { + emitAnalysis(LoopAccessReport(Ld) + << "read with atomic ordering or volatile read"); + DEBUG(dbgs() << "LAA: Found a non-simple load.\n"); + CanVecMem = false; + return; + } + NumLoads++; + Loads.push_back(Ld); + DepChecker.addAccess(Ld); + continue; + } + + // Save 'store' instructions. Abort if other instructions write to memory. + if (it->mayWriteToMemory()) { + StoreInst *St = dyn_cast<StoreInst>(it); + if (!St) { + emitAnalysis(LoopAccessReport(&*it) << + "instruction cannot be vectorized"); + CanVecMem = false; + return; + } + if (!St->isSimple() && !IsAnnotatedParallel) { + emitAnalysis(LoopAccessReport(St) + << "write with atomic ordering or volatile write"); + DEBUG(dbgs() << "LAA: Found a non-simple store.\n"); + CanVecMem = false; + return; + } + NumStores++; + Stores.push_back(St); + DepChecker.addAccess(St); + } + } // Next instr. + } // Next block. + + // Now we have two lists that hold the loads and the stores. + // Next, we find the pointers that they use. + + // Check if we see any stores. If there are no stores, then we don't + // care if the pointers are *restrict*. + if (!Stores.size()) { + DEBUG(dbgs() << "LAA: Found a read-only loop!\n"); + CanVecMem = true; + return; + } + + MemoryDepChecker::DepCandidates DependentAccesses; + AccessAnalysis Accesses(TheLoop->getHeader()->getModule()->getDataLayout(), + AA, LI, DependentAccesses, PSE); + + // Holds the analyzed pointers. We don't want to call GetUnderlyingObjects + // multiple times on the same object. If the ptr is accessed twice, once + // for read and once for write, it will only appear once (on the write + // list). This is okay, since we are going to check for conflicts between + // writes and between reads and writes, but not between reads and reads. + ValueSet Seen; + + ValueVector::iterator I, IE; + for (I = Stores.begin(), IE = Stores.end(); I != IE; ++I) { + StoreInst *ST = cast<StoreInst>(*I); + Value* Ptr = ST->getPointerOperand(); + // Check for store to loop invariant address. + StoreToLoopInvariantAddress |= isUniform(Ptr); + // If we did *not* see this pointer before, insert it to the read-write + // list. At this phase it is only a 'write' list. + if (Seen.insert(Ptr).second) { + ++NumReadWrites; + + MemoryLocation Loc = MemoryLocation::get(ST); + // The TBAA metadata could have a control dependency on the predication + // condition, so we cannot rely on it when determining whether or not we + // need runtime pointer checks. + if (blockNeedsPredication(ST->getParent(), TheLoop, DT)) + Loc.AATags.TBAA = nullptr; + + Accesses.addStore(Loc); + } + } + + if (IsAnnotatedParallel) { + DEBUG(dbgs() + << "LAA: A loop annotated parallel, ignore memory dependency " + << "checks.\n"); + CanVecMem = true; + return; + } + + for (I = Loads.begin(), IE = Loads.end(); I != IE; ++I) { + LoadInst *LD = cast<LoadInst>(*I); + Value* Ptr = LD->getPointerOperand(); + // If we did *not* see this pointer before, insert it to the + // read list. If we *did* see it before, then it is already in + // the read-write list. This allows us to vectorize expressions + // such as A[i] += x; Because the address of A[i] is a read-write + // pointer. This only works if the index of A[i] is consecutive. + // If the address of i is unknown (for example A[B[i]]) then we may + // read a few words, modify, and write a few words, and some of the + // words may be written to the same address. + bool IsReadOnlyPtr = false; + if (Seen.insert(Ptr).second || !isStridedPtr(PSE, Ptr, TheLoop, Strides)) { + ++NumReads; + IsReadOnlyPtr = true; + } + + MemoryLocation Loc = MemoryLocation::get(LD); + // The TBAA metadata could have a control dependency on the predication + // condition, so we cannot rely on it when determining whether or not we + // need runtime pointer checks. + if (blockNeedsPredication(LD->getParent(), TheLoop, DT)) + Loc.AATags.TBAA = nullptr; + + Accesses.addLoad(Loc, IsReadOnlyPtr); + } + + // If we write (or read-write) to a single destination and there are no + // other reads in this loop then is it safe to vectorize. + if (NumReadWrites == 1 && NumReads == 0) { + DEBUG(dbgs() << "LAA: Found a write-only loop!\n"); + CanVecMem = true; + return; + } + + // Build dependence sets and check whether we need a runtime pointer bounds + // check. + Accesses.buildDependenceSets(); + + // Find pointers with computable bounds. We are going to use this information + // to place a runtime bound check. + bool CanDoRTIfNeeded = + Accesses.canCheckPtrAtRT(PtrRtChecking, PSE.getSE(), TheLoop, Strides); + if (!CanDoRTIfNeeded) { + emitAnalysis(LoopAccessReport() << "cannot identify array bounds"); + DEBUG(dbgs() << "LAA: We can't vectorize because we can't find " + << "the array bounds.\n"); + CanVecMem = false; + return; + } + + DEBUG(dbgs() << "LAA: We can perform a memory runtime check if needed.\n"); + + CanVecMem = true; + if (Accesses.isDependencyCheckNeeded()) { + DEBUG(dbgs() << "LAA: Checking memory dependencies\n"); + CanVecMem = DepChecker.areDepsSafe( + DependentAccesses, Accesses.getDependenciesToCheck(), Strides); + MaxSafeDepDistBytes = DepChecker.getMaxSafeDepDistBytes(); + + if (!CanVecMem && DepChecker.shouldRetryWithRuntimeCheck()) { + DEBUG(dbgs() << "LAA: Retrying with memory checks\n"); + + // Clear the dependency checks. We assume they are not needed. + Accesses.resetDepChecks(DepChecker); + + PtrRtChecking.reset(); + PtrRtChecking.Need = true; + + auto *SE = PSE.getSE(); + CanDoRTIfNeeded = + Accesses.canCheckPtrAtRT(PtrRtChecking, SE, TheLoop, Strides, true); + + // Check that we found the bounds for the pointer. + if (!CanDoRTIfNeeded) { + emitAnalysis(LoopAccessReport() + << "cannot check memory dependencies at runtime"); + DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n"); + CanVecMem = false; + return; + } + + CanVecMem = true; + } + } + + if (CanVecMem) + DEBUG(dbgs() << "LAA: No unsafe dependent memory operations in loop. We" + << (PtrRtChecking.Need ? "" : " don't") + << " need runtime memory checks.\n"); + else { + emitAnalysis(LoopAccessReport() << + "unsafe dependent memory operations in loop"); + DEBUG(dbgs() << "LAA: unsafe dependent memory operations in loop\n"); + } +} + +bool LoopAccessInfo::blockNeedsPredication(BasicBlock *BB, Loop *TheLoop, + DominatorTree *DT) { + assert(TheLoop->contains(BB) && "Unknown block used"); + + // Blocks that do not dominate the latch need predication. + BasicBlock* Latch = TheLoop->getLoopLatch(); + return !DT->dominates(BB, Latch); +} + +void LoopAccessInfo::emitAnalysis(LoopAccessReport &Message) { + assert(!Report && "Multiple reports generated"); + Report = Message; +} + +bool LoopAccessInfo::isUniform(Value *V) const { + return (PSE.getSE()->isLoopInvariant(PSE.getSE()->getSCEV(V), TheLoop)); +} + +// FIXME: this function is currently a duplicate of the one in +// LoopVectorize.cpp. +static Instruction *getFirstInst(Instruction *FirstInst, Value *V, + Instruction *Loc) { + if (FirstInst) + return FirstInst; + if (Instruction *I = dyn_cast<Instruction>(V)) + return I->getParent() == Loc->getParent() ? I : nullptr; + return nullptr; +} + +namespace { +/// \brief IR Values for the lower and upper bounds of a pointer evolution. We +/// need to use value-handles because SCEV expansion can invalidate previously +/// expanded values. Thus expansion of a pointer can invalidate the bounds for +/// a previous one. +struct PointerBounds { + TrackingVH<Value> Start; + TrackingVH<Value> End; +}; +} // end anonymous namespace + +/// \brief Expand code for the lower and upper bound of the pointer group \p CG +/// in \p TheLoop. \return the values for the bounds. +static PointerBounds +expandBounds(const RuntimePointerChecking::CheckingPtrGroup *CG, Loop *TheLoop, + Instruction *Loc, SCEVExpander &Exp, ScalarEvolution *SE, + const RuntimePointerChecking &PtrRtChecking) { + Value *Ptr = PtrRtChecking.Pointers[CG->Members[0]].PointerValue; + const SCEV *Sc = SE->getSCEV(Ptr); + + if (SE->isLoopInvariant(Sc, TheLoop)) { + DEBUG(dbgs() << "LAA: Adding RT check for a loop invariant ptr:" << *Ptr + << "\n"); + return {Ptr, Ptr}; + } else { + unsigned AS = Ptr->getType()->getPointerAddressSpace(); + LLVMContext &Ctx = Loc->getContext(); + + // Use this type for pointer arithmetic. + Type *PtrArithTy = Type::getInt8PtrTy(Ctx, AS); + Value *Start = nullptr, *End = nullptr; + + DEBUG(dbgs() << "LAA: Adding RT check for range:\n"); + Start = Exp.expandCodeFor(CG->Low, PtrArithTy, Loc); + End = Exp.expandCodeFor(CG->High, PtrArithTy, Loc); + DEBUG(dbgs() << "Start: " << *CG->Low << " End: " << *CG->High << "\n"); + return {Start, End}; + } +} + +/// \brief Turns a collection of checks into a collection of expanded upper and +/// lower bounds for both pointers in the check. +static SmallVector<std::pair<PointerBounds, PointerBounds>, 4> expandBounds( + const SmallVectorImpl<RuntimePointerChecking::PointerCheck> &PointerChecks, + Loop *L, Instruction *Loc, ScalarEvolution *SE, SCEVExpander &Exp, + const RuntimePointerChecking &PtrRtChecking) { + SmallVector<std::pair<PointerBounds, PointerBounds>, 4> ChecksWithBounds; + + // Here we're relying on the SCEV Expander's cache to only emit code for the + // same bounds once. + std::transform( + PointerChecks.begin(), PointerChecks.end(), + std::back_inserter(ChecksWithBounds), + [&](const RuntimePointerChecking::PointerCheck &Check) { + PointerBounds + First = expandBounds(Check.first, L, Loc, Exp, SE, PtrRtChecking), + Second = expandBounds(Check.second, L, Loc, Exp, SE, PtrRtChecking); + return std::make_pair(First, Second); + }); + + return ChecksWithBounds; +} + +std::pair<Instruction *, Instruction *> LoopAccessInfo::addRuntimeChecks( + Instruction *Loc, + const SmallVectorImpl<RuntimePointerChecking::PointerCheck> &PointerChecks) + const { + auto *SE = PSE.getSE(); + SCEVExpander Exp(*SE, DL, "induction"); + auto ExpandedChecks = + expandBounds(PointerChecks, TheLoop, Loc, SE, Exp, PtrRtChecking); + + LLVMContext &Ctx = Loc->getContext(); + Instruction *FirstInst = nullptr; + IRBuilder<> ChkBuilder(Loc); + // Our instructions might fold to a constant. + Value *MemoryRuntimeCheck = nullptr; + + for (const auto &Check : ExpandedChecks) { + const PointerBounds &A = Check.first, &B = Check.second; + // Check if two pointers (A and B) conflict where conflict is computed as: + // start(A) <= end(B) && start(B) <= end(A) + unsigned AS0 = A.Start->getType()->getPointerAddressSpace(); + unsigned AS1 = B.Start->getType()->getPointerAddressSpace(); + + assert((AS0 == B.End->getType()->getPointerAddressSpace()) && + (AS1 == A.End->getType()->getPointerAddressSpace()) && + "Trying to bounds check pointers with different address spaces"); + + Type *PtrArithTy0 = Type::getInt8PtrTy(Ctx, AS0); + Type *PtrArithTy1 = Type::getInt8PtrTy(Ctx, AS1); + + Value *Start0 = ChkBuilder.CreateBitCast(A.Start, PtrArithTy0, "bc"); + Value *Start1 = ChkBuilder.CreateBitCast(B.Start, PtrArithTy1, "bc"); + Value *End0 = ChkBuilder.CreateBitCast(A.End, PtrArithTy1, "bc"); + Value *End1 = ChkBuilder.CreateBitCast(B.End, PtrArithTy0, "bc"); + + Value *Cmp0 = ChkBuilder.CreateICmpULE(Start0, End1, "bound0"); + FirstInst = getFirstInst(FirstInst, Cmp0, Loc); + Value *Cmp1 = ChkBuilder.CreateICmpULE(Start1, End0, "bound1"); + FirstInst = getFirstInst(FirstInst, Cmp1, Loc); + Value *IsConflict = ChkBuilder.CreateAnd(Cmp0, Cmp1, "found.conflict"); + FirstInst = getFirstInst(FirstInst, IsConflict, Loc); + if (MemoryRuntimeCheck) { + IsConflict = + ChkBuilder.CreateOr(MemoryRuntimeCheck, IsConflict, "conflict.rdx"); + FirstInst = getFirstInst(FirstInst, IsConflict, Loc); + } + MemoryRuntimeCheck = IsConflict; + } + + if (!MemoryRuntimeCheck) + return std::make_pair(nullptr, nullptr); + + // We have to do this trickery because the IRBuilder might fold the check to a + // constant expression in which case there is no Instruction anchored in a + // the block. + Instruction *Check = BinaryOperator::CreateAnd(MemoryRuntimeCheck, + ConstantInt::getTrue(Ctx)); + ChkBuilder.Insert(Check, "memcheck.conflict"); + FirstInst = getFirstInst(FirstInst, Check, Loc); + return std::make_pair(FirstInst, Check); +} + +std::pair<Instruction *, Instruction *> +LoopAccessInfo::addRuntimeChecks(Instruction *Loc) const { + if (!PtrRtChecking.Need) + return std::make_pair(nullptr, nullptr); + + return addRuntimeChecks(Loc, PtrRtChecking.getChecks()); +} + +LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE, + const DataLayout &DL, + const TargetLibraryInfo *TLI, AliasAnalysis *AA, + DominatorTree *DT, LoopInfo *LI, + const ValueToValueMap &Strides) + : PSE(*SE), PtrRtChecking(SE), DepChecker(PSE, L), TheLoop(L), DL(DL), + TLI(TLI), AA(AA), DT(DT), LI(LI), NumLoads(0), NumStores(0), + MaxSafeDepDistBytes(-1U), CanVecMem(false), + StoreToLoopInvariantAddress(false) { + if (canAnalyzeLoop()) + analyzeLoop(Strides); +} + +void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const { + if (CanVecMem) { + if (PtrRtChecking.Need) + OS.indent(Depth) << "Memory dependences are safe with run-time checks\n"; + else + OS.indent(Depth) << "Memory dependences are safe\n"; + } + + if (Report) + OS.indent(Depth) << "Report: " << Report->str() << "\n"; + + if (auto *Dependences = DepChecker.getDependences()) { + OS.indent(Depth) << "Dependences:\n"; + for (auto &Dep : *Dependences) { + Dep.print(OS, Depth + 2, DepChecker.getMemoryInstructions()); + OS << "\n"; + } + } else + OS.indent(Depth) << "Too many dependences, not recorded\n"; + + // List the pair of accesses need run-time checks to prove independence. + PtrRtChecking.print(OS, Depth); + OS << "\n"; + + OS.indent(Depth) << "Store to invariant address was " + << (StoreToLoopInvariantAddress ? "" : "not ") + << "found in loop.\n"; + + OS.indent(Depth) << "SCEV assumptions:\n"; + PSE.getUnionPredicate().print(OS, Depth); +} + +const LoopAccessInfo & +LoopAccessAnalysis::getInfo(Loop *L, const ValueToValueMap &Strides) { + auto &LAI = LoopAccessInfoMap[L]; + +#ifndef NDEBUG + assert((!LAI || LAI->NumSymbolicStrides == Strides.size()) && + "Symbolic strides changed for loop"); +#endif + + if (!LAI) { + const DataLayout &DL = L->getHeader()->getModule()->getDataLayout(); + LAI = + llvm::make_unique<LoopAccessInfo>(L, SE, DL, TLI, AA, DT, LI, Strides); +#ifndef NDEBUG + LAI->NumSymbolicStrides = Strides.size(); +#endif + } + return *LAI.get(); +} + +void LoopAccessAnalysis::print(raw_ostream &OS, const Module *M) const { + LoopAccessAnalysis &LAA = *const_cast<LoopAccessAnalysis *>(this); + + ValueToValueMap NoSymbolicStrides; + + for (Loop *TopLevelLoop : *LI) + for (Loop *L : depth_first(TopLevelLoop)) { + OS.indent(2) << L->getHeader()->getName() << ":\n"; + auto &LAI = LAA.getInfo(L, NoSymbolicStrides); + LAI.print(OS, 4); + } +} + +bool LoopAccessAnalysis::runOnFunction(Function &F) { + SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE(); + auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>(); + TLI = TLIP ? &TLIP->getTLI() : nullptr; + AA = &getAnalysis<AAResultsWrapperPass>().getAAResults(); + DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); + + return false; +} + +void LoopAccessAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired<ScalarEvolutionWrapperPass>(); + AU.addRequired<AAResultsWrapperPass>(); + AU.addRequired<DominatorTreeWrapperPass>(); + AU.addRequired<LoopInfoWrapperPass>(); + + AU.setPreservesAll(); +} + +char LoopAccessAnalysis::ID = 0; +static const char laa_name[] = "Loop Access Analysis"; +#define LAA_NAME "loop-accesses" + +INITIALIZE_PASS_BEGIN(LoopAccessAnalysis, LAA_NAME, laa_name, false, true) +INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) +INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) +INITIALIZE_PASS_END(LoopAccessAnalysis, LAA_NAME, laa_name, false, true) + +namespace llvm { + Pass *createLAAPass() { + return new LoopAccessAnalysis(); + } +} |