#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/Transforms/Utils/VectorUtils.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Analysis/VectorUtils.h"
using namespace llvm;
#define DEBUG_TYPE "loop-accesses"
VectorizationFactor("force-vector-width", cl::Hidden,
cl::desc("Sets the SIMD width. Zero is autoselect."),
cl::location(VectorizerParams::VectorizationFactor));
-unsigned VectorizerParams::VectorizationFactor = 0;
+unsigned VectorizerParams::VectorizationFactor;
static cl::opt<unsigned, true>
VectorizationInterleave("force-vector-interleave", cl::Hidden,
"Zero is autoselect."),
cl::location(
VectorizerParams::VectorizationInterleave));
-unsigned VectorizerParams::VectorizationInterleave = 0;
-
-/// When performing memory disambiguation checks at runtime do not make more
-/// than this number of comparisons.
-const unsigned VectorizerParams::RuntimeMemoryCheckThreshold = 8;
+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 interesting dependences up to this threshold.
+static cl::opt<unsigned> MaxInterestingDependence(
+ "max-interesting-dependences", cl::Hidden,
+ cl::desc("Maximum number of interesting dependences collected by "
+ "loop-access analysis (default = 100)"),
+ cl::init(100));
+
bool VectorizerParams::isInterleaveForced() {
return ::VectorizationInterleave.getNumOccurrences() > 0;
}
}
const SCEV *llvm::replaceSymbolicStrideSCEV(ScalarEvolution *SE,
- ValueToValueMap &PtrToStride,
+ const ValueToValueMap &PtrToStride,
Value *Ptr, Value *OrigPtr) {
const SCEV *OrigSCEV = SE->getSCEV(Ptr);
// If there is an entry in the map return the SCEV of the pointer with the
// symbolic stride replaced by one.
- ValueToValueMap::iterator SI = PtrToStride.find(OrigPtr ? OrigPtr : Ptr);
+ ValueToValueMap::const_iterator SI =
+ PtrToStride.find(OrigPtr ? OrigPtr : Ptr);
if (SI != PtrToStride.end()) {
Value *StrideVal = SI->second;
return SE->getSCEV(Ptr);
}
-void LoopAccessInfo::RuntimePointerCheck::insert(ScalarEvolution *SE, Loop *Lp,
- Value *Ptr, bool WritePtr,
- unsigned DepSetId,
- unsigned ASId,
- ValueToValueMap &Strides) {
+void LoopAccessInfo::RuntimePointerCheck::insert(
+ Loop *Lp, Value *Ptr, bool WritePtr, unsigned DepSetId, unsigned ASId,
+ const ValueToValueMap &Strides) {
// Get the stride replaced scev.
const SCEV *Sc = replaceSymbolicStrideSCEV(SE, Strides, Ptr);
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Sc);
IsWritePtr.push_back(WritePtr);
DependencySetId.push_back(DepSetId);
AliasSetId.push_back(ASId);
+ Exprs.push_back(Sc);
+}
+
+bool LoopAccessInfo::RuntimePointerCheck::needsChecking(
+ const CheckingPtrGroup &M, const CheckingPtrGroup &N,
+ const SmallVectorImpl<int> *PtrPartition) 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], PtrPartition))
+ 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 LoopAccessInfo::RuntimePointerCheck::CheckingPtrGroup::addPointer(
+ unsigned Index) {
+ // 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(RtCheck.Starts[Index], Low, RtCheck.SE);
+ if (!Min0)
+ return false;
+
+ const SCEV *Min1 = getMinFromExprs(RtCheck.Ends[Index], High, RtCheck.SE);
+ if (!Min1)
+ return false;
+
+ // Update the low bound expression if we've found a new min value.
+ if (Min0 == RtCheck.Starts[Index])
+ Low = RtCheck.Starts[Index];
+
+ // Update the high bound expression if we've found a new max value.
+ if (Min1 != RtCheck.Ends[Index])
+ High = RtCheck.Ends[Index];
+
+ Members.push_back(Index);
+ return true;
+}
+
+void LoopAccessInfo::RuntimePointerCheck::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 don't have the dependency partitions, construct a new
+ // checking pointer group for each pointer.
+ 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 Pointer = 0; Pointer < Pointers.size(); ++Pointer)
+ PositionMap[Pointers[Pointer]] = Pointer;
+
+ // Go through all equivalence classes, get the the "pointer check groups"
+ // and add them to the overall solution.
+ for (auto DI = DepCands.begin(), DE = DepCands.end(); DI != DE; ++DI) {
+ if (!DI->isLeader())
+ continue;
+
+ SmallVector<CheckingPtrGroup, 2> Groups;
+
+ for (auto MI = DepCands.member_begin(DI), ME = DepCands.member_end();
+ MI != ME; ++MI) {
+ unsigned Pointer = PositionMap[MI->getPointer()];
+ bool Merged = false;
+
+ // 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 LoopAccessInfo::RuntimePointerCheck::needsChecking(unsigned I,
- unsigned J) const {
+bool LoopAccessInfo::RuntimePointerCheck::needsChecking(
+ unsigned I, unsigned J, const SmallVectorImpl<int> *PtrPartition) const {
// No need to check if two readonly pointers intersect.
if (!IsWritePtr[I] && !IsWritePtr[J])
return false;
if (AliasSetId[I] != AliasSetId[J])
return false;
+ // If PtrPartition is set omit checks between pointers of the same partition.
+ // Partition number -1 means that the pointer is used in multiple partitions.
+ // In this case we can't omit the check.
+ if (PtrPartition && (*PtrPartition)[I] != -1 &&
+ (*PtrPartition)[I] == (*PtrPartition)[J])
+ return false;
+
return true;
}
+void LoopAccessInfo::RuntimePointerCheck::print(
+ raw_ostream &OS, unsigned Depth,
+ const SmallVectorImpl<int> *PtrPartition) const {
+
+ OS.indent(Depth) << "Run-time memory checks:\n";
+
+ unsigned N = 0;
+ for (unsigned I = 0; I < CheckingGroups.size(); ++I)
+ for (unsigned J = I + 1; J < CheckingGroups.size(); ++J)
+ if (needsChecking(CheckingGroups[I], CheckingGroups[J], PtrPartition)) {
+ OS.indent(Depth) << "Check " << N++ << ":\n";
+ OS.indent(Depth + 2) << "Comparing group " << I << ":\n";
+
+ for (unsigned K = 0; K < CheckingGroups[I].Members.size(); ++K) {
+ OS.indent(Depth + 2) << *Pointers[CheckingGroups[I].Members[K]]
+ << "\n";
+ if (PtrPartition)
+ OS << " (Partition: "
+ << (*PtrPartition)[CheckingGroups[I].Members[K]] << ")"
+ << "\n";
+ }
+
+ OS.indent(Depth + 2) << "Against group " << J << ":\n";
+
+ for (unsigned K = 0; K < CheckingGroups[J].Members.size(); ++K) {
+ OS.indent(Depth + 2) << *Pointers[CheckingGroups[J].Members[K]]
+ << "\n";
+ if (PtrPartition)
+ OS << " (Partition: "
+ << (*PtrPartition)[CheckingGroups[J].Members[K]] << ")"
+ << "\n";
+ }
+ }
+
+ OS.indent(Depth) << "Grouped accesses:\n";
+ for (unsigned I = 0; I < CheckingGroups.size(); ++I) {
+ OS.indent(Depth + 2) << "Group " << I << ":\n";
+ OS.indent(Depth + 4) << "(Low: " << *CheckingGroups[I].Low
+ << " High: " << *CheckingGroups[I].High << ")\n";
+ for (unsigned J = 0; J < CheckingGroups[I].Members.size(); ++J) {
+ OS.indent(Depth + 6) << "Member: " << *Exprs[CheckingGroups[I].Members[J]]
+ << "\n";
+ }
+ }
+}
+
+unsigned LoopAccessInfo::RuntimePointerCheck::getNumberOfChecks(
+ const SmallVectorImpl<int> *PtrPartition) const {
+
+ unsigned NumPartitions = CheckingGroups.size();
+ unsigned CheckCount = 0;
+
+ for (unsigned I = 0; I < NumPartitions; ++I)
+ for (unsigned J = I + 1; J < NumPartitions; ++J)
+ if (needsChecking(CheckingGroups[I], CheckingGroups[J], PtrPartition))
+ CheckCount++;
+ return CheckCount;
+}
+
+bool LoopAccessInfo::RuntimePointerCheck::needsAnyChecking(
+ const SmallVectorImpl<int> *PtrPartition) const {
+ unsigned NumPointers = Pointers.size();
+
+ for (unsigned I = 0; I < NumPointers; ++I)
+ for (unsigned J = I + 1; J < NumPointers; ++J)
+ if (needsChecking(I, J, PtrPartition))
+ return true;
+ return false;
+}
+
namespace {
/// \brief Analyses memory accesses in a loop.
///
typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet;
- /// \brief Set of potential dependent memory accesses.
- typedef EquivalenceClasses<MemAccessInfo> DepCandidates;
-
- AccessAnalysis(const DataLayout *Dl, AliasAnalysis *AA, DepCandidates &DA) :
- DL(Dl), AST(*AA), DepCands(DA), IsRTCheckNeeded(false) {}
+ AccessAnalysis(const DataLayout &Dl, AliasAnalysis *AA, LoopInfo *LI,
+ MemoryDepChecker::DepCandidates &DA)
+ : DL(Dl), AST(*AA), LI(LI), DepCands(DA), IsRTCheckNeeded(false) {}
/// \brief Register a load and whether it is only read from.
- void addLoad(AliasAnalysis::Location &Loc, bool IsReadOnly) {
+ void addLoad(MemoryLocation &Loc, bool IsReadOnly) {
Value *Ptr = const_cast<Value*>(Loc.Ptr);
- AST.add(Ptr, AliasAnalysis::UnknownSize, Loc.AATags);
+ AST.add(Ptr, MemoryLocation::UnknownSize, Loc.AATags);
Accesses.insert(MemAccessInfo(Ptr, false));
if (IsReadOnly)
ReadOnlyPtr.insert(Ptr);
}
/// \brief Register a store.
- void addStore(AliasAnalysis::Location &Loc) {
+ void addStore(MemoryLocation &Loc) {
Value *Ptr = const_cast<Value*>(Loc.Ptr);
- AST.add(Ptr, AliasAnalysis::UnknownSize, Loc.AATags);
+ 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.
+ /// non-intersection. Returns true when we have 0 pointers
+ /// (a check on 0 pointers for non-intersection will always return true).
bool canCheckPtrAtRT(LoopAccessInfo::RuntimePointerCheck &RtCheck,
- unsigned &NumComparisons,
- ScalarEvolution *SE, Loop *TheLoop,
- ValueToValueMap &Strides,
+ bool &NeedRTCheck, ScalarEvolution *SE, Loop *TheLoop,
+ const ValueToValueMap &Strides,
bool ShouldCheckStride = false);
/// \brief Goes over all memory accesses, checks whether a RT check is needed
bool isRTCheckNeeded() { return IsRTCheckNeeded; }
bool isDependencyCheckNeeded() { return !CheckDeps.empty(); }
- void resetDepChecks() { CheckDeps.clear(); }
+
+ /// We decided that no dependence analysis would be used. Reset the state.
+ void resetDepChecks(MemoryDepChecker &DepChecker) {
+ CheckDeps.clear();
+ DepChecker.clearInterestingDependences();
+ }
MemAccessInfoSet &getDependenciesToCheck() { return CheckDeps; }
/// 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;
- const DataLayout *DL;
-
/// 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.
- DepCandidates &DepCands;
+ MemoryDepChecker::DepCandidates &DepCands;
bool IsRTCheckNeeded;
};
} // end anonymous namespace
/// \brief Check whether a pointer can participate in a runtime bounds check.
-static bool hasComputableBounds(ScalarEvolution *SE, ValueToValueMap &Strides,
- Value *Ptr) {
+static bool hasComputableBounds(ScalarEvolution *SE,
+ const ValueToValueMap &Strides, Value *Ptr) {
const SCEV *PtrScev = replaceSymbolicStrideSCEV(SE, Strides, Ptr);
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
if (!AR)
return AR->isAffine();
}
-/// \brief Check the stride of the pointer and ensure that it does not wrap in
-/// the address space.
-static int isStridedPtr(ScalarEvolution *SE, const DataLayout *DL, Value *Ptr,
- const Loop *Lp, ValueToValueMap &StridesMap);
-
bool AccessAnalysis::canCheckPtrAtRT(
- LoopAccessInfo::RuntimePointerCheck &RtCheck,
- unsigned &NumComparisons, ScalarEvolution *SE, Loop *TheLoop,
- ValueToValueMap &StridesMap, bool ShouldCheckStride) {
+ LoopAccessInfo::RuntimePointerCheck &RtCheck, bool &NeedRTCheck,
+ 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;
+ NeedRTCheck = false;
+ if (!IsRTCheckNeeded) return true;
+
bool IsDepCheckNeeded = isDependencyCheckNeeded();
- NumComparisons = 0;
// 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) {
- unsigned NumReadPtrChecks = 0;
- unsigned 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;
bool IsWrite = Accesses.count(MemAccessInfo(Ptr, true));
MemAccessInfo Access(Ptr, IsWrite);
- if (IsWrite)
- ++NumWritePtrChecks;
- else
- ++NumReadPtrChecks;
-
if (hasComputableBounds(SE, StridesMap, Ptr) &&
- // When we run after a failing dependency check we have to make sure we
- // don't have wrapping pointers.
+ // When we run after a failing dependency check we have to make sure
+ // we don't have wrapping pointers.
(!ShouldCheckStride ||
- isStridedPtr(SE, DL, Ptr, TheLoop, StridesMap) == 1)) {
+ isStridedPtr(SE, Ptr, TheLoop, StridesMap) == 1)) {
// The id of the dependence set.
unsigned DepId;
// Each access has its own dependence set.
DepId = RunningDepId++;
- RtCheck.insert(SE, TheLoop, Ptr, IsWrite, DepId, ASId, StridesMap);
+ RtCheck.insert(TheLoop, Ptr, IsWrite, DepId, ASId, StridesMap);
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 (IsDepCheckNeeded && CanDoRT && RunningDepId == 2)
- NumComparisons += 0; // Only one dependence set.
- else {
- NumComparisons += (NumWritePtrChecks * (NumReadPtrChecks +
- NumWritePtrChecks - 1));
- }
-
++ASId;
}
+ // We need a runtime check if there are any accesses that need checking.
+ // However, some accesses cannot be checked (for example because we
+ // can't determine their bounds). In these cases we would need a check
+ // but wouldn't be able to add it.
+ NeedRTCheck = !CanDoRT || RtCheck.needsAnyChecking(nullptr);
+
// 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
}
}
+ if (NeedRTCheck && CanDoRT)
+ RtCheck.groupChecks(DepCands, IsDepCheckNeeded);
+
return CanDoRT;
}
DEBUG(dbgs() << "LAA: Processing memory accesses...\n");
DEBUG(dbgs() << " AST: "; AST.dump());
- DEBUG(dbgs() << "LAA: Accesses:\n");
+ DEBUG(dbgs() << "LAA: Accesses(" << Accesses.size() << "):\n");
DEBUG({
for (auto A : Accesses)
dbgs() << "\t" << *A.getPointer() << " (" <<
// underlying object.
typedef SmallVector<Value *, 16> ValueVector;
ValueVector TempObjects;
- GetUnderlyingObjects(Ptr, TempObjects, DL);
+
+ GetUnderlyingObjects(Ptr, TempObjects, DL, LI);
+ DEBUG(dbgs() << "Underlying objects for pointer " << *Ptr << "\n");
for (Value *UnderlyingObj : TempObjects) {
UnderlyingObjToAccessMap::iterator Prev =
ObjToLastAccess.find(UnderlyingObj);
DepCands.unionSets(Access, Prev->second);
ObjToLastAccess[UnderlyingObj] = Access;
+ DEBUG(dbgs() << " " << *UnderlyingObj << "\n");
}
}
}
}
}
-namespace {
-/// \brief Checks memory dependences among accesses to the same underlying
-/// object to determine whether there vectorization is legal or not (and at
-/// which vectorization factor).
-///
-/// This class works under the assumption that we already checked that memory
-/// locations with different underlying pointers are "must-not alias".
-/// We use the ScalarEvolution framework to symbolically evalutate access
-/// functions pairs. Since we currently don't restructure the loop we can rely
-/// on the program order of memory accesses to determine their safety.
-/// At the moment we will only deem accesses as safe for:
-/// * A negative constant distance assuming program order.
-///
-/// Safe: tmp = a[i + 1]; OR a[i + 1] = x;
-/// a[i] = tmp; y = a[i];
-///
-/// The latter case is safe because later checks guarantuee that there can't
-/// be a cycle through a phi node (that is, we check that "x" and "y" is not
-/// the same variable: a header phi can only be an induction or a reduction, a
-/// reduction can't have a memory sink, an induction can't have a memory
-/// source). This is important and must not be violated (or we have to
-/// resort to checking for cycles through memory).
-///
-/// * A positive constant distance assuming program order that is bigger
-/// than the biggest memory access.
-///
-/// tmp = a[i] OR b[i] = x
-/// a[i+2] = tmp y = b[i+2];
-///
-/// Safe distance: 2 x sizeof(a[0]), and 2 x sizeof(b[0]), respectively.
-///
-/// * Zero distances and all accesses have the same size.
-///
-class MemoryDepChecker {
-public:
- typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
- typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet;
-
- MemoryDepChecker(ScalarEvolution *Se, const DataLayout *Dl, const Loop *L)
- : SE(Se), DL(Dl), InnermostLoop(L), AccessIdx(0),
- ShouldRetryWithRuntimeCheck(false) {}
-
- /// \brief Register the location (instructions are given increasing numbers)
- /// of a write access.
- void addAccess(StoreInst *SI) {
- Value *Ptr = SI->getPointerOperand();
- Accesses[MemAccessInfo(Ptr, true)].push_back(AccessIdx);
- InstMap.push_back(SI);
- ++AccessIdx;
- }
-
- /// \brief Register the location (instructions are given increasing numbers)
- /// of a write access.
- void addAccess(LoadInst *LI) {
- Value *Ptr = LI->getPointerOperand();
- Accesses[MemAccessInfo(Ptr, false)].push_back(AccessIdx);
- InstMap.push_back(LI);
- ++AccessIdx;
- }
+static bool isInBoundsGep(Value *Ptr) {
+ if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr))
+ return GEP->isInBounds();
+ return false;
+}
- /// \brief Check whether the dependencies between the accesses are safe.
- ///
- /// Only checks sets with elements in \p CheckDeps.
- bool areDepsSafe(AccessAnalysis::DepCandidates &AccessSets,
- MemAccessInfoSet &CheckDeps, ValueToValueMap &Strides);
+/// \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;
- /// \brief The maximum number of bytes of a vector register we can vectorize
- /// the accesses safely with.
- unsigned getMaxSafeDepDistBytes() { return MaxSafeDepDistBytes; }
+ // 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.
- /// \brief In same cases when the dependency check fails we can still
- /// vectorize the loop with a dynamic array access check.
- bool shouldRetryWithRuntimeCheck() { return ShouldRetryWithRuntimeCheck; }
+ // The arithmetic implied by an inbounds GEP can't overflow.
+ auto *GEP = dyn_cast<GetElementPtrInst>(Ptr);
+ if (!GEP || !GEP->isInBounds())
+ return false;
-private:
- ScalarEvolution *SE;
- const DataLayout *DL;
- const Loop *InnermostLoop;
-
- /// \brief Maps access locations (ptr, read/write) to program order.
- DenseMap<MemAccessInfo, std::vector<unsigned> > Accesses;
-
- /// \brief Memory access instructions in program order.
- SmallVector<Instruction *, 16> InstMap;
-
- /// \brief The program order index to be used for the next instruction.
- unsigned AccessIdx;
-
- // We can access this many bytes in parallel safely.
- unsigned MaxSafeDepDistBytes;
-
- /// \brief If we see a non-constant dependence distance we can still try to
- /// vectorize this loop with runtime checks.
- bool ShouldRetryWithRuntimeCheck;
-
- /// \brief Check whether there is a plausible dependence between the two
- /// accesses.
- ///
- /// Access \p A must happen before \p B in program order. The two indices
- /// identify the index into the program order map.
- ///
- /// This function checks whether there is a plausible dependence (or the
- /// absence of such can't be proved) between the two accesses. If there is a
- /// plausible dependence but the dependence distance is bigger than one
- /// element access it records this distance in \p MaxSafeDepDistBytes (if this
- /// distance is smaller than any other distance encountered so far).
- /// Otherwise, this function returns true signaling a possible dependence.
- bool isDependent(const MemAccessInfo &A, unsigned AIdx,
- const MemAccessInfo &B, unsigned BIdx,
- ValueToValueMap &Strides);
-
- /// \brief Check whether the data dependence could prevent store-load
- /// forwarding.
- bool couldPreventStoreLoadForward(unsigned Distance, unsigned TypeByteSize);
-};
+ // 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;
-} // end anonymous namespace
+ // 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);
+ }
-static bool isInBoundsGep(Value *Ptr) {
- if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr))
- return GEP->isInBounds();
return false;
}
/// \brief Check whether the access through \p Ptr has a constant stride.
-static int isStridedPtr(ScalarEvolution *SE, const DataLayout *DL, Value *Ptr,
- const Loop *Lp, ValueToValueMap &StridesMap) {
+int llvm::isStridedPtr(ScalarEvolution *SE, Value *Ptr, const Loop *Lp,
+ const ValueToValueMap &StridesMap) {
const Type *Ty = Ptr->getType();
assert(Ty->isPointerTy() && "Unexpected non-ptr");
// 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 = AR->getNoWrapFlags(SCEV::NoWrapMask);
+ bool IsNoWrapAddRec = isNoWrapAddRec(Ptr, AR, SE, Lp);
bool IsInAddressSpaceZero = PtrTy->getAddressSpace() == 0;
if (!IsNoWrapAddRec && !IsInBoundsGEP && !IsInAddressSpaceZero) {
DEBUG(dbgs() << "LAA: Bad stride - Pointer may wrap in the address space "
return 0;
}
- int64_t Size = DL->getTypeAllocSize(PtrTy->getElementType());
+ auto &DL = Lp->getHeader()->getModule()->getDataLayout();
+ int64_t Size = DL.getTypeAllocSize(PtrTy->getElementType());
const APInt &APStepVal = C->getValue()->getValue();
// Huge step value - give up.
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::isInterestingDependence(DepType Type) {
+ switch (Type) {
+ case NoDep:
+ case Forward:
+ return false;
+
+ case BackwardVectorizable:
+ case Unknown:
+ case ForwardButPreventsForwarding:
+ case Backward:
+ case BackwardVectorizableButPreventsForwarding:
+ return true;
+ }
+ llvm_unreachable("unexpected DepType!");
+}
+
+bool MemoryDepChecker::Dependence::isPossiblyBackward() const {
+ switch (Type) {
+ case NoDep:
+ case Forward:
+ case ForwardButPreventsForwarding:
+ return false;
+
+ case Unknown:
+ case BackwardVectorizable:
+ case Backward:
+ case BackwardVectorizableButPreventsForwarding:
+ return true;
+ }
+ 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
return false;
}
-bool MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
- const MemAccessInfo &B, unsigned BIdx,
- ValueToValueMap &Strides) {
+/// \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();
// Two reads are independent.
if (!AIsWrite && !BIsWrite)
- return false;
+ return Dependence::NoDep;
// We cannot check pointers in different address spaces.
if (APtr->getType()->getPointerAddressSpace() !=
BPtr->getType()->getPointerAddressSpace())
- return true;
+ return Dependence::Unknown;
const SCEV *AScev = replaceSymbolicStrideSCEV(SE, Strides, APtr);
const SCEV *BScev = replaceSymbolicStrideSCEV(SE, Strides, BPtr);
- int StrideAPtr = isStridedPtr(SE, DL, APtr, InnermostLoop, Strides);
- int StrideBPtr = isStridedPtr(SE, DL, BPtr, InnermostLoop, Strides);
+ int StrideAPtr = isStridedPtr(SE, APtr, InnermostLoop, Strides);
+ int StrideBPtr = isStridedPtr(SE, BPtr, InnermostLoop, Strides);
const SCEV *Src = AScev;
const SCEV *Sink = BScev;
// the address space.
if (!StrideAPtr || !StrideBPtr || StrideAPtr != StrideBPtr){
DEBUG(dbgs() << "Non-consecutive pointer access\n");
- return true;
+ 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 true;
+ return Dependence::Unknown;
}
Type *ATy = APtr->getType()->getPointerElementType();
Type *BTy = BPtr->getType()->getPointerElementType();
- unsigned TypeByteSize = DL->getTypeAllocSize(ATy);
+ auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout();
+ unsigned TypeByteSize = DL.getTypeAllocSize(ATy);
// Negative distances are not plausible dependencies.
const APInt &Val = C->getValue()->getValue();
if (IsTrueDataDependence &&
(couldPreventStoreLoadForward(Val.abs().getZExtValue(), TypeByteSize) ||
ATy != BTy))
- return true;
+ return Dependence::ForwardButPreventsForwarding;
DEBUG(dbgs() << "LAA: Dependence is negative: NoDep\n");
- return false;
+ 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 false;
+ return Dependence::NoDep;
DEBUG(dbgs() << "LAA: Zero dependence difference but different types\n");
- return true;
+ return Dependence::Unknown;
}
assert(Val.isStrictlyPositive() && "Expect a positive value");
- // Positive distance bigger than max vectorization factor.
if (ATy != BTy) {
DEBUG(dbgs() <<
"LAA: ReadWrite-Write positive dependency with different types\n");
- return false;
+ return Dependence::Unknown;
}
unsigned Distance = (unsigned) Val.getZExtValue();
+ unsigned Stride = std::abs(StrideAPtr);
+ if (Stride > 1 &&
+ areStridedAccessesIndependent(Distance, Stride, TypeByteSize))
+ 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;
+ }
- // The distance must be bigger than the size needed for a vectorized version
- // of the operation and the size of the vectorized operation must not be
- // bigger than the currrent maximum size.
- if (Distance < 2*TypeByteSize ||
- 2*TypeByteSize > MaxSafeDepDistBytes ||
- Distance < TypeByteSize * ForcedUnroll * ForcedFactor) {
- DEBUG(dbgs() << "LAA: Failure because of Positive distance "
- << Val.getSExtValue() << '\n');
- return true;
+ // 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;
}
- MaxSafeDepDistBytes = Distance < MaxSafeDepDistBytes ?
- Distance : MaxSafeDepDistBytes;
+ // 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 true;
+ return Dependence::BackwardVectorizableButPreventsForwarding;
- DEBUG(dbgs() << "LAA: Positive distance " << Val.getSExtValue() <<
- " with max VF = " << MaxSafeDepDistBytes / TypeByteSize << '\n');
+ DEBUG(dbgs() << "LAA: Positive distance " << Val.getSExtValue()
+ << " with max VF = "
+ << MaxSafeDepDistBytes / (TypeByteSize * Stride) << '\n');
- return false;
+ return Dependence::BackwardVectorizable;
}
-bool MemoryDepChecker::areDepsSafe(AccessAnalysis::DepCandidates &AccessSets,
+bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets,
MemAccessInfoSet &CheckDeps,
- ValueToValueMap &Strides) {
+ const ValueToValueMap &Strides) {
MaxSafeDepDistBytes = -1U;
while (!CheckDeps.empty()) {
I1E = Accesses[*AI].end(); I1 != I1E; ++I1)
for (std::vector<unsigned>::iterator I2 = Accesses[*OI].begin(),
I2E = Accesses[*OI].end(); I2 != I2E; ++I2) {
- if (*I1 < *I2 && isDependent(*AI, *I1, *OI, *I2, Strides))
- return false;
- if (*I2 < *I1 && isDependent(*OI, *I2, *AI, *I1, Strides))
+ 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 MaxInterestingDependence
+ // dependences. In that case return as soon as we find the first
+ // unsafe dependence. This puts a limit on this quadratic
+ // algorithm.
+ if (RecordInterestingDependences) {
+ if (Dependence::isInterestingDependence(Type))
+ InterestingDependences.push_back(
+ Dependence(A.second, B.second, Type));
+
+ if (InterestingDependences.size() >= MaxInterestingDependence) {
+ RecordInterestingDependences = false;
+ InterestingDependences.clear();
+ DEBUG(dbgs() << "Too many dependences, stopped recording\n");
+ }
+ }
+ if (!RecordInterestingDependences && !SafeForVectorization)
return false;
}
++OI;
AI++;
}
}
- return true;
+
+ DEBUG(dbgs() << "Total Interesting Dependences: "
+ << InterestingDependences.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");
// 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");
// 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;
}
- // We need to have a loop header.
- DEBUG(dbgs() << "LAA: Found a loop: " <<
- TheLoop->getHeader()->getName() << '\n');
-
// ScalarEvolution needs to be able to find the exit count.
const SCEV *ExitCount = SE->getBackedgeTakenCount(TheLoop);
if (ExitCount == SE->getCouldNotCompute()) {
return true;
}
-void LoopAccessInfo::analyzeLoop(ValueToValueMap &Strides) {
+void LoopAccessInfo::analyzeLoop(const ValueToValueMap &Strides) {
typedef SmallVector<Value*, 16> ValueVector;
typedef SmallPtrSet<Value*, 16> ValueSet;
PtrRtCheck.Need = false;
const bool IsAnnotatedParallel = TheLoop->isAnnotatedParallel();
- MemoryDepChecker DepChecker(SE, DL, TheLoop);
// For each block.
for (Loop::block_iterator bb = TheLoop->block_begin(),
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)
return;
}
- AccessAnalysis::DepCandidates DependentAccesses;
- AccessAnalysis Accesses(DL, AA, DependentAccesses);
+ MemoryDepChecker::DepCandidates DependentAccesses;
+ AccessAnalysis Accesses(TheLoop->getHeader()->getModule()->getDataLayout(),
+ AA, LI, DependentAccesses);
// 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 (I = Stores.begin(), IE = Stores.end(); I != IE; ++I) {
StoreInst *ST = cast<StoreInst>(*I);
Value* Ptr = ST->getPointerOperand();
-
- if (isUniform(Ptr)) {
- emitAnalysis(
- LoopAccessReport(ST)
- << "write to a loop invariant address could not be vectorized");
- DEBUG(dbgs() << "LAA: We don't allow storing to uniform addresses\n");
- CanVecMem = false;
- return;
- }
-
+ // 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;
- AliasAnalysis::Location Loc = AA->getLocation(ST);
+ 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.
// 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(SE, DL, Ptr, TheLoop, Strides)) {
+ if (Seen.insert(Ptr).second || !isStridedPtr(SE, Ptr, TheLoop, Strides)) {
++NumReads;
IsReadOnlyPtr = true;
}
- AliasAnalysis::Location Loc = AA->getLocation(LD);
+ 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.
// Build dependence sets and check whether we need a runtime pointer bounds
// check.
Accesses.buildDependenceSets();
- bool NeedRTCheck = Accesses.isRTCheckNeeded();
// Find pointers with computable bounds. We are going to use this information
// to place a runtime bound check.
- unsigned NumComparisons = 0;
- bool CanDoRT = false;
- if (NeedRTCheck)
- CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE, TheLoop,
- Strides);
-
- DEBUG(dbgs() << "LAA: We need to do " << NumComparisons <<
- " pointer comparisons.\n");
-
- // If we only have one set of dependences to check pointers among we don't
- // need a runtime check.
- if (NumComparisons == 0 && NeedRTCheck)
- NeedRTCheck = false;
-
- // Check that we did not collect too many pointers or found an unsizeable
- // pointer.
- if (!CanDoRT ||
- NumComparisons > VectorizerParams::RuntimeMemoryCheckThreshold) {
- PtrRtCheck.reset();
- CanDoRT = false;
- }
+ bool NeedRTCheck;
+ bool CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck,
+ NeedRTCheck, SE,
+ TheLoop, Strides);
- if (CanDoRT) {
- DEBUG(dbgs() << "LAA: We can perform a memory runtime check if needed.\n");
- }
+ DEBUG(dbgs() << "LAA: We need to do "
+ << PtrRtCheck.getNumberOfChecks(nullptr)
+ << " pointer comparisons.\n");
- if (NeedRTCheck && !CanDoRT) {
+ // Check that we found the bounds for the pointer.
+ if (CanDoRT)
+ DEBUG(dbgs() << "LAA: We can perform a memory runtime check if needed.\n");
+ else if (NeedRTCheck) {
emitAnalysis(LoopAccessReport() << "cannot identify array bounds");
DEBUG(dbgs() << "LAA: We can't vectorize because we can't find " <<
"the array bounds.\n");
NeedRTCheck = true;
// Clear the dependency checks. We assume they are not needed.
- Accesses.resetDepChecks();
+ Accesses.resetDepChecks(DepChecker);
PtrRtCheck.reset();
PtrRtCheck.Need = true;
- CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE,
+ CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NeedRTCheck, SE,
TheLoop, Strides, true);
- // Check that we did not collect too many pointers or found an unsizeable
- // pointer.
- if (!CanDoRT ||
- NumComparisons > VectorizerParams::RuntimeMemoryCheckThreshold) {
- if (!CanDoRT && NumComparisons > 0)
- emitAnalysis(LoopAccessReport()
- << "cannot check memory dependencies at runtime");
- else
- emitAnalysis(LoopAccessReport()
- << NumComparisons << " exceeds limit of "
- << VectorizerParams::RuntimeMemoryCheckThreshold
- << " dependent memory operations checked at runtime");
+
+ // Check that we found the bounds for the pointer.
+ if (NeedRTCheck && !CanDoRT) {
+ emitAnalysis(LoopAccessReport()
+ << "cannot check memory dependencies at runtime");
DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n");
PtrRtCheck.reset();
CanVecMem = false;
}
}
- if (!CanVecMem)
+ if (CanVecMem)
+ DEBUG(dbgs() << "LAA: No unsafe dependent memory operations in loop. We"
+ << (NeedRTCheck ? "" : " don't")
+ << " need a runtime memory check.\n");
+ else {
emitAnalysis(LoopAccessReport() <<
"unsafe dependent memory operations in loop");
-
- DEBUG(dbgs() << "LAA: We" << (NeedRTCheck ? "" : " don't") <<
- " need a runtime memory check.\n");
+ DEBUG(dbgs() << "LAA: unsafe dependent memory operations in loop\n");
+ }
}
bool LoopAccessInfo::blockNeedsPredication(BasicBlock *BB, Loop *TheLoop,
Report = Message;
}
-bool LoopAccessInfo::isUniform(Value *V) {
+bool LoopAccessInfo::isUniform(Value *V) const {
return (SE->isLoopInvariant(SE->getSCEV(V), TheLoop));
}
return nullptr;
}
-std::pair<Instruction *, Instruction *>
-LoopAccessInfo::addRuntimeCheck(Instruction *Loc) {
- Instruction *tnullptr = nullptr;
+std::pair<Instruction *, Instruction *> LoopAccessInfo::addRuntimeCheck(
+ Instruction *Loc, const SmallVectorImpl<int> *PtrPartition) const {
if (!PtrRtCheck.Need)
- return std::pair<Instruction *, Instruction *>(tnullptr, tnullptr);
+ return std::make_pair(nullptr, nullptr);
- unsigned NumPointers = PtrRtCheck.Pointers.size();
- SmallVector<TrackingVH<Value> , 2> Starts;
- SmallVector<TrackingVH<Value> , 2> Ends;
+ SmallVector<TrackingVH<Value>, 2> Starts;
+ SmallVector<TrackingVH<Value>, 2> Ends;
LLVMContext &Ctx = Loc->getContext();
- SCEVExpander Exp(*SE, "induction");
+ SCEVExpander Exp(*SE, DL, "induction");
Instruction *FirstInst = nullptr;
- for (unsigned i = 0; i < NumPointers; ++i) {
- Value *Ptr = PtrRtCheck.Pointers[i];
+ for (unsigned i = 0; i < PtrRtCheck.CheckingGroups.size(); ++i) {
+ const RuntimePointerCheck::CheckingPtrGroup &CG =
+ PtrRtCheck.CheckingGroups[i];
+ Value *Ptr = PtrRtCheck.Pointers[CG.Members[0]];
const SCEV *Sc = SE->getSCEV(Ptr);
if (SE->isLoopInvariant(Sc, TheLoop)) {
- DEBUG(dbgs() << "LAA: Adding RT check for a loop invariant ptr:" <<
- *Ptr <<"\n");
+ DEBUG(dbgs() << "LAA: Adding RT check for a loop invariant ptr:" << *Ptr
+ << "\n");
Starts.push_back(Ptr);
Ends.push_back(Ptr);
} else {
- DEBUG(dbgs() << "LAA: Adding RT check for range:" << *Ptr << '\n');
unsigned AS = Ptr->getType()->getPointerAddressSpace();
// Use this type for pointer arithmetic.
Type *PtrArithTy = Type::getInt8PtrTy(Ctx, AS);
+ Value *Start = nullptr, *End = nullptr;
- Value *Start = Exp.expandCodeFor(PtrRtCheck.Starts[i], PtrArithTy, Loc);
- Value *End = Exp.expandCodeFor(PtrRtCheck.Ends[i], PtrArithTy, Loc);
+ 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");
Starts.push_back(Start);
Ends.push_back(End);
}
IRBuilder<> ChkBuilder(Loc);
// Our instructions might fold to a constant.
Value *MemoryRuntimeCheck = nullptr;
- for (unsigned i = 0; i < NumPointers; ++i) {
- for (unsigned j = i+1; j < NumPointers; ++j) {
- if (!PtrRtCheck.needsChecking(i, j))
+ for (unsigned i = 0; i < PtrRtCheck.CheckingGroups.size(); ++i) {
+ for (unsigned j = i + 1; j < PtrRtCheck.CheckingGroups.size(); ++j) {
+ const RuntimePointerCheck::CheckingPtrGroup &CGI =
+ PtrRtCheck.CheckingGroups[i];
+ const RuntimePointerCheck::CheckingPtrGroup &CGJ =
+ PtrRtCheck.CheckingGroups[j];
+
+ if (!PtrRtCheck.needsChecking(CGI, CGJ, PtrPartition))
continue;
unsigned AS0 = Starts[i]->getType()->getPointerAddressSpace();
}
}
+ 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.
}
LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE,
- const DataLayout *DL,
+ const DataLayout &DL,
const TargetLibraryInfo *TLI, AliasAnalysis *AA,
- DominatorTree *DT, ValueToValueMap &Strides)
- : TheLoop(L), SE(SE), DL(DL), TLI(TLI), AA(AA), DT(DT), NumLoads(0),
- NumStores(0), MaxSafeDepDistBytes(-1U), CanVecMem(false) {
+ DominatorTree *DT, LoopInfo *LI,
+ const ValueToValueMap &Strides)
+ : PtrRtCheck(SE), DepChecker(SE, L), TheLoop(L), SE(SE), DL(DL), TLI(TLI),
+ AA(AA), DT(DT), LI(LI), NumLoads(0), NumStores(0),
+ MaxSafeDepDistBytes(-1U), CanVecMem(false),
+ StoreToLoopInvariantAddress(false) {
if (canAnalyzeLoop())
analyzeLoop(Strides);
}
-LoopAccessInfo &LoopAccessAnalysis::getInfo(Loop *L, ValueToValueMap &Strides) {
+void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const {
+ if (CanVecMem) {
+ if (PtrRtCheck.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 *InterestingDependences = DepChecker.getInterestingDependences()) {
+ OS.indent(Depth) << "Interesting Dependences:\n";
+ for (auto &Dep : *InterestingDependences) {
+ Dep.print(OS, Depth + 2, DepChecker.getMemoryInstructions());
+ OS << "\n";
+ }
+ } else
+ OS.indent(Depth) << "Too many interesting dependences, not recorded\n";
+
+ // List the pair of accesses need run-time checks to prove independence.
+ PtrRtCheck.print(OS, Depth);
+ OS << "\n";
+
+ OS.indent(Depth) << "Store to invariant address was "
+ << (StoreToLoopInvariantAddress ? "" : "not ")
+ << "found in loop.\n";
+}
+
+const LoopAccessInfo &
+LoopAccessAnalysis::getInfo(Loop *L, const ValueToValueMap &Strides) {
auto &LAI = LoopAccessInfoMap[L];
#ifndef NDEBUG
#endif
if (!LAI) {
- LAI = llvm::make_unique<LoopAccessInfo>(L, SE, DL, TLI, AA, DT, Strides);
+ 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<ScalarEvolution>();
- DL = F.getParent()->getDataLayout();
auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
TLI = TLIP ? &TLIP->getTLI() : nullptr;
AA = &getAnalysis<AliasAnalysis>();
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
return false;
}
AU.addRequired<ScalarEvolution>();
AU.addRequired<AliasAnalysis>();
AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addRequired<LoopInfoWrapperPass>();
AU.setPreservesAll();
}
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_END(LoopAccessAnalysis, LAA_NAME, laa_name, false, true)
namespace llvm {