+ static unsigned RuntimeMemoryCheckThreshold;
+};
+
+/// \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).
+///
+/// Note: This class will compute a conservative dependence for access to
+/// different underlying pointers. Clients, such as the loop vectorizer, will
+/// sometimes deal these potential dependencies by emitting runtime checks.
+///
+/// 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;
+ /// \brief Set of potential dependent memory accesses.
+ typedef EquivalenceClasses<MemAccessInfo> DepCandidates;
+
+ /// \brief Dependece between memory access instructions.
+ struct Dependence {
+ /// \brief The type of the dependence.
+ enum DepType {
+ // No dependence.
+ NoDep,
+ // We couldn't determine the direction or the distance.
+ Unknown,
+ // Lexically forward.
+ Forward,
+ // Forward, but if vectorized, is likely to prevent store-to-load
+ // forwarding.
+ ForwardButPreventsForwarding,
+ // Lexically backward.
+ Backward,
+ // Backward, but the distance allows a vectorization factor of
+ // MaxSafeDepDistBytes.
+ BackwardVectorizable,
+ // Same, but may prevent store-to-load forwarding.
+ BackwardVectorizableButPreventsForwarding
+ };
+
+ /// \brief String version of the types.
+ static const char *DepName[];
+
+ /// \brief Index of the source of the dependence in the InstMap vector.
+ unsigned Source;
+ /// \brief Index of the destination of the dependence in the InstMap vector.
+ unsigned Destination;
+ /// \brief The type of the dependence.
+ DepType Type;
+
+ Dependence(unsigned Source, unsigned Destination, DepType Type)
+ : Source(Source), Destination(Destination), Type(Type) {}
+
+ /// \brief Dependence types that don't prevent vectorization.
+ static bool isSafeForVectorization(DepType Type);
+
+ /// \brief Dependence types that can be queried from the analysis.
+ static bool isInterestingDependence(DepType Type);
+
+ /// \brief Lexically backward dependence types.
+ bool isPossiblyBackward() const;
+
+ /// \brief Print the dependence. \p Instr is used to map the instruction
+ /// indices to instructions.
+ void print(raw_ostream &OS, unsigned Depth,
+ const SmallVectorImpl<Instruction *> &Instrs) const;
+ };
+
+ MemoryDepChecker(ScalarEvolution *Se, const Loop *L)
+ : SE(Se), InnermostLoop(L), AccessIdx(0),
+ ShouldRetryWithRuntimeCheck(false), SafeForVectorization(true),
+ RecordInterestingDependences(true) {}
+
+ /// \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;
+ }
+
+ /// \brief Check whether the dependencies between the accesses are safe.
+ ///
+ /// Only checks sets with elements in \p CheckDeps.
+ bool areDepsSafe(DepCandidates &AccessSets, MemAccessInfoSet &CheckDeps,
+ const ValueToValueMap &Strides);
+
+ /// \brief No memory dependence was encountered that would inhibit
+ /// vectorization.
+ bool isSafeForVectorization() const { return SafeForVectorization; }
+
+ /// \brief The maximum number of bytes of a vector register we can vectorize
+ /// the accesses safely with.
+ unsigned getMaxSafeDepDistBytes() { return MaxSafeDepDistBytes; }
+
+ /// \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; }
+
+ /// \brief Returns the interesting dependences. If null is returned we
+ /// exceeded the MaxInterestingDependence threshold and this information is
+ /// not available.
+ const SmallVectorImpl<Dependence> *getInterestingDependences() const {
+ return RecordInterestingDependences ? &InterestingDependences : nullptr;
+ }
+
+ void clearInterestingDependences() { InterestingDependences.clear(); }
+
+ /// \brief The vector of memory access instructions. The indices are used as
+ /// instruction identifiers in the Dependence class.
+ const SmallVectorImpl<Instruction *> &getMemoryInstructions() const {
+ return InstMap;
+ }
+
+ /// \brief Find the set of instructions that read or write via \p Ptr.
+ SmallVector<Instruction *, 4> getInstructionsForAccess(Value *Ptr,
+ bool isWrite) const;
+
+private:
+ ScalarEvolution *SE;
+ 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 No memory dependence was encountered that would inhibit
+ /// vectorization.
+ bool SafeForVectorization;
+
+ //// \brief True if InterestingDependences reflects the dependences in the
+ //// loop. If false we exceeded MaxInterestingDependence and
+ //// InterestingDependences is invalid.
+ bool RecordInterestingDependences;
+
+ /// \brief Interesting memory dependences collected during the analysis as
+ /// defined by isInterestingDependence. Only valid if
+ /// RecordInterestingDependences is true.
+ SmallVector<Dependence, 8> InterestingDependences;
+
+ /// \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.
+ Dependence::DepType isDependent(const MemAccessInfo &A, unsigned AIdx,
+ const MemAccessInfo &B, unsigned BIdx,
+ const ValueToValueMap &Strides);
+
+ /// \brief Check whether the data dependence could prevent store-load
+ /// forwarding.
+ bool couldPreventStoreLoadForward(unsigned Distance, unsigned TypeByteSize);
+};
+
+/// \brief Holds information about the memory runtime legality checks to verify
+/// that a group of pointers do not overlap.
+class RuntimePointerChecking {
+public:
+ struct PointerInfo {
+ /// Holds the pointer value that we need to check.
+ TrackingVH<Value> PointerValue;
+ /// Holds the pointer value at the beginning of the loop.
+ const SCEV *Start;
+ /// Holds the pointer value at the end of the loop.
+ const SCEV *End;
+ /// Holds the information if this pointer is used for writing to memory.
+ bool IsWritePtr;
+ /// Holds the id of the set of pointers that could be dependent because of a
+ /// shared underlying object.
+ unsigned DependencySetId;
+ /// Holds the id of the disjoint alias set to which this pointer belongs.
+ unsigned AliasSetId;
+ /// SCEV for the access.
+ const SCEV *Expr;
+
+ PointerInfo(Value *PointerValue, const SCEV *Start, const SCEV *End,
+ bool IsWritePtr, unsigned DependencySetId, unsigned AliasSetId,
+ const SCEV *Expr)
+ : PointerValue(PointerValue), Start(Start), End(End),
+ IsWritePtr(IsWritePtr), DependencySetId(DependencySetId),
+ AliasSetId(AliasSetId), Expr(Expr) {}
+ };
+
+ RuntimePointerChecking(ScalarEvolution *SE) : Need(false), SE(SE) {}
+
+ /// Reset the state of the pointer runtime information.
+ void reset() {
+ Need = false;
+ Pointers.clear();
+ }
+
+ /// Insert a pointer and calculate the start and end SCEVs.
+ void insert(Loop *Lp, Value *Ptr, bool WritePtr, unsigned DepSetId,
+ unsigned ASId, const ValueToValueMap &Strides);
+
+ /// \brief No run-time memory checking is necessary.
+ bool empty() const { return Pointers.empty(); }
+
+ /// A grouping of pointers. A single memcheck is required between
+ /// two groups.
+ struct CheckingPtrGroup {
+ /// \brief Create a new pointer checking group containing a single
+ /// pointer, with index \p Index in RtCheck.
+ CheckingPtrGroup(unsigned Index, RuntimePointerChecking &RtCheck)
+ : RtCheck(RtCheck), High(RtCheck.Pointers[Index].End),
+ Low(RtCheck.Pointers[Index].Start) {
+ Members.push_back(Index);
+ }
+
+ /// \brief Tries to add the pointer recorded in RtCheck at index
+ /// \p Index to this pointer checking group. We can only add a pointer
+ /// to a checking group if we will still be able to get
+ /// the upper and lower bounds of the check. Returns true in case
+ /// of success, false otherwise.
+ bool addPointer(unsigned Index);
+
+ /// Constitutes the context of this pointer checking group. For each
+ /// pointer that is a member of this group we will retain the index
+ /// at which it appears in RtCheck.
+ RuntimePointerChecking &RtCheck;
+ /// The SCEV expression which represents the upper bound of all the
+ /// pointers in this group.
+ const SCEV *High;
+ /// The SCEV expression which represents the lower bound of all the
+ /// pointers in this group.
+ const SCEV *Low;
+ /// Indices of all the pointers that constitute this grouping.
+ SmallVector<unsigned, 2> Members;
+ };
+
+ /// \brief Groups pointers such that a single memcheck is required
+ /// between two different groups. This will clear the CheckingGroups vector
+ /// and re-compute it. We will only group dependecies if \p UseDependencies
+ /// is true, otherwise we will create a separate group for each pointer.
+ void groupChecks(MemoryDepChecker::DepCandidates &DepCands,
+ bool UseDependencies);
+
+ /// \brief Decide if we need to add a check between two groups of pointers,
+ /// according to needsChecking.
+ bool needsChecking(const CheckingPtrGroup &M, const CheckingPtrGroup &N,
+ const SmallVectorImpl<int> *PtrPartition) const;
+
+ /// \brief Return true if any pointer requires run-time checking according
+ /// to needsChecking.
+ bool needsAnyChecking(const SmallVectorImpl<int> *PtrPartition) const;
+
+ /// \brief Returns the number of run-time checks required according to
+ /// needsChecking.
+ unsigned getNumberOfChecks(const SmallVectorImpl<int> *PtrPartition) const;
+
+ /// \brief Print the list run-time memory checks necessary.
+ ///
+ /// If \p PtrPartition is set, it contains the partition number for
+ /// pointers (-1 if the pointer belongs to multiple partitions). In this
+ /// case omit checks between pointers belonging to the same partition.
+ void print(raw_ostream &OS, unsigned Depth = 0,
+ const SmallVectorImpl<int> *PtrPartition = nullptr) const;
+
+ /// This flag indicates if we need to add the runtime check.
+ bool Need;
+
+ /// Information about the pointers that may require checking.
+ SmallVector<PointerInfo, 2> Pointers;
+
+ /// Holds a partitioning of pointers into "check groups".
+ SmallVector<CheckingPtrGroup, 2> CheckingGroups;
+
+ /// \brief Check if pointers are in the same partition
+ ///
+ /// \p PtrToPartition contains the partition number for pointers (-1 if the
+ /// pointer belongs to multiple partitions).
+ static bool
+ arePointersInSamePartition(const SmallVectorImpl<int> &PtrToPartition,
+ unsigned PtrIdx1, unsigned PtrIdx2);
+
+private:
+ /// \brief Decide whether we need to issue a run-time check for pointer at
+ /// index \p I and \p J to prove their independence.
+ ///
+ /// If \p PtrPartition is set, it contains the partition number for
+ /// pointers (-1 if the pointer belongs to multiple partitions). In this
+ /// case omit checks between pointers belonging to the same partition.
+ bool needsChecking(unsigned I, unsigned J,
+ const SmallVectorImpl<int> *PtrPartition) const;
+
+ /// Holds a pointer to the ScalarEvolution analysis.
+ ScalarEvolution *SE;