LCOV - code coverage report
Current view: top level - include/llvm/ADT - SparseMultiSet.h (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 236 400 59.0 %
Date: 2018-10-20 13:21:21 Functions: 22 101 21.8 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===- llvm/ADT/SparseMultiSet.h - Sparse multiset --------------*- C++ -*-===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : //
      10             : // This file defines the SparseMultiSet class, which adds multiset behavior to
      11             : // the SparseSet.
      12             : //
      13             : // A sparse multiset holds a small number of objects identified by integer keys
      14             : // from a moderately sized universe. The sparse multiset uses more memory than
      15             : // other containers in order to provide faster operations. Any key can map to
      16             : // multiple values. A SparseMultiSetNode class is provided, which serves as a
      17             : // convenient base class for the contents of a SparseMultiSet.
      18             : //
      19             : //===----------------------------------------------------------------------===//
      20             : 
      21             : #ifndef LLVM_ADT_SPARSEMULTISET_H
      22             : #define LLVM_ADT_SPARSEMULTISET_H
      23             : 
      24             : #include "llvm/ADT/STLExtras.h"
      25             : #include "llvm/ADT/SmallVector.h"
      26             : #include "llvm/ADT/SparseSet.h"
      27             : #include <cassert>
      28             : #include <cstdint>
      29             : #include <cstdlib>
      30             : #include <iterator>
      31             : #include <limits>
      32             : #include <utility>
      33             : 
      34             : namespace llvm {
      35             : 
      36             : /// Fast multiset implementation for objects that can be identified by small
      37             : /// unsigned keys.
      38             : ///
      39             : /// SparseMultiSet allocates memory proportional to the size of the key
      40             : /// universe, so it is not recommended for building composite data structures.
      41             : /// It is useful for algorithms that require a single set with fast operations.
      42             : ///
      43             : /// Compared to DenseSet and DenseMap, SparseMultiSet provides constant-time
      44             : /// fast clear() as fast as a vector.  The find(), insert(), and erase()
      45             : /// operations are all constant time, and typically faster than a hash table.
      46             : /// The iteration order doesn't depend on numerical key values, it only depends
      47             : /// on the order of insert() and erase() operations.  Iteration order is the
      48             : /// insertion order. Iteration is only provided over elements of equivalent
      49             : /// keys, but iterators are bidirectional.
      50             : ///
      51             : /// Compared to BitVector, SparseMultiSet<unsigned> uses 8x-40x more memory, but
      52             : /// offers constant-time clear() and size() operations as well as fast iteration
      53             : /// independent on the size of the universe.
      54             : ///
      55             : /// SparseMultiSet contains a dense vector holding all the objects and a sparse
      56             : /// array holding indexes into the dense vector.  Most of the memory is used by
      57             : /// the sparse array which is the size of the key universe. The SparseT template
      58             : /// parameter provides a space/speed tradeoff for sets holding many elements.
      59             : ///
      60             : /// When SparseT is uint32_t, find() only touches up to 3 cache lines, but the
      61             : /// sparse array uses 4 x Universe bytes.
      62             : ///
      63             : /// When SparseT is uint8_t (the default), find() touches up to 3+[N/256] cache
      64             : /// lines, but the sparse array is 4x smaller.  N is the number of elements in
      65             : /// the set.
      66             : ///
      67             : /// For sets that may grow to thousands of elements, SparseT should be set to
      68             : /// uint16_t or uint32_t.
      69             : ///
      70             : /// Multiset behavior is provided by providing doubly linked lists for values
      71             : /// that are inlined in the dense vector. SparseMultiSet is a good choice when
      72             : /// one desires a growable number of entries per key, as it will retain the
      73             : /// SparseSet algorithmic properties despite being growable. Thus, it is often a
      74             : /// better choice than a SparseSet of growable containers or a vector of
      75             : /// vectors. SparseMultiSet also keeps iterators valid after erasure (provided
      76             : /// the iterators don't point to the element erased), allowing for more
      77             : /// intuitive and fast removal.
      78             : ///
      79             : /// @tparam ValueT      The type of objects in the set.
      80             : /// @tparam KeyFunctorT A functor that computes an unsigned index from KeyT.
      81             : /// @tparam SparseT     An unsigned integer type. See above.
      82             : ///
      83             : template<typename ValueT,
      84             :          typename KeyFunctorT = identity<unsigned>,
      85             :          typename SparseT = uint8_t>
      86             : class SparseMultiSet {
      87             :   static_assert(std::numeric_limits<SparseT>::is_integer &&
      88             :                 !std::numeric_limits<SparseT>::is_signed,
      89             :                 "SparseT must be an unsigned integer type");
      90             : 
      91             :   /// The actual data that's stored, as a doubly-linked list implemented via
      92             :   /// indices into the DenseVector.  The doubly linked list is implemented
      93             :   /// circular in Prev indices, and INVALID-terminated in Next indices. This
      94             :   /// provides efficient access to list tails. These nodes can also be
      95             :   /// tombstones, in which case they are actually nodes in a single-linked
      96             :   /// freelist of recyclable slots.
      97             :   struct SMSNode {
      98             :     static const unsigned INVALID = ~0U;
      99             : 
     100             :     ValueT Data;
     101             :     unsigned Prev;
     102             :     unsigned Next;
     103             : 
     104     8175385 :     SMSNode(ValueT D, unsigned P, unsigned N) : Data(D), Prev(P), Next(N) {}
     105             : 
     106             :     /// List tails have invalid Nexts.
     107           0 :     bool isTail() const {
     108           0 :       return Next == INVALID;
     109             :     }
     110           0 : 
     111           0 :     /// Whether this node is a tombstone node, and thus is in our freelist.
     112             :     bool isTombstone() const {
     113           0 :       return Prev == INVALID;
     114           0 :     }
     115             : 
     116           0 :     /// Since the list is circular in Prev, all non-tombstone nodes have a valid
     117           0 :     /// Prev.
     118           0 :     bool isValid() const { return Prev != INVALID; }
     119             :   };
     120             : 
     121             :   using KeyT = typename KeyFunctorT::argument_type;
     122             :   using DenseT = SmallVector<SMSNode, 8>;
     123             :   DenseT Dense;
     124           0 :   SparseT *Sparse = nullptr;
     125             :   unsigned Universe = 0;
     126             :   KeyFunctorT KeyIndexOf;
     127           0 :   SparseSetValFunctor<KeyT, ValueT, KeyFunctorT> ValIndexOf;
     128             : 
     129             :   /// We have a built-in recycler for reusing tombstone slots. This recycler
     130             :   /// puts a singly-linked free list into tombstone slots, allowing us quick
     131             :   /// erasure, iterator preservation, and dense size.
     132             :   unsigned FreelistIdx = SMSNode::INVALID;
     133             :   unsigned NumFree = 0;
     134             : 
     135           0 :   unsigned sparseIndex(const ValueT &Val) const {
     136             :     assert(ValIndexOf(Val) < Universe &&
     137             :            "Invalid key in set. Did object mutate?");
     138           0 :     return ValIndexOf(Val);
     139             :   }
     140           0 :   unsigned sparseIndex(const SMSNode &N) const { return sparseIndex(N.Data); }
     141           0 : 
     142             :   /// Whether the given entry is the head of the list. List heads's previous
     143             :   /// pointers are to the tail of the list, allowing for efficient access to the
     144           0 :   /// list tail. D must be a valid entry node.
     145           0 :   bool isHead(const SMSNode &D) const {
     146           0 :     assert(D.isValid() && "Invalid node for head");
     147     2693687 :     return Dense[D.Prev].isTail();
     148             :   }
     149           0 : 
     150             :   /// Whether the given entry is a singleton entry, i.e. the only entry with
     151           0 :   /// that key.
     152           0 :   bool isSingleton(const SMSNode &N) const {
     153             :     assert(N.isValid() && "Invalid node for singleton");
     154           0 :     // Is N its own predecessor?
     155             :     return &Dense[N.Prev] == &N;
     156        2770 :   }
     157           0 : 
     158             :   /// Add in the given SMSNode. Uses a free entry in our freelist if
     159           0 :   /// available. Returns the index of the added node.
     160     1581057 :   unsigned addValue(const ValueT& V, unsigned Prev, unsigned Next) {
     161     1581057 :     if (NumFree == 0) {
     162     1581057 :       Dense.push_back(SMSNode(V, Prev, Next));
     163     1581806 :       return Dense.size() - 1;
     164           0 :     }
     165           0 : 
     166             :     // Peel off a free slot
     167           0 :     unsigned Idx = FreelistIdx;
     168           0 :     unsigned NextFree = Dense[Idx].Next;
     169           0 :     assert(Dense[Idx].isTombstone() && "Non-tombstone free?");
     170             : 
     171    15625516 :     Dense[Idx] = SMSNode(V, Prev, Next);
     172           0 :     FreelistIdx = NextFree;
     173           0 :     --NumFree;
     174           0 :     return Idx;
     175           0 :   }
     176             : 
     177           0 :   /// Make the current index a new tombstone. Pushes it onto the freelist.
     178             :   void makeTombstone(unsigned Idx) {
     179          15 :     Dense[Idx].Prev = SMSNode::INVALID;
     180             :     Dense[Idx].Next = FreelistIdx;
     181           0 :     FreelistIdx = Idx;
     182             :     ++NumFree;
     183           0 :   }
     184           3 : 
     185           3 : public:
     186           3 :   using value_type = ValueT;
     187           3 :   using reference = ValueT &;
     188             :   using const_reference = const ValueT &;
     189             :   using pointer = ValueT *;
     190             :   using const_pointer = const ValueT *;
     191     3781981 :   using size_type = unsigned;
     192           0 : 
     193      167111 :   SparseMultiSet() = default;
     194             :   SparseMultiSet(const SparseMultiSet &) = delete;
     195           0 :   SparseMultiSet &operator=(const SparseMultiSet &) = delete;
     196    10336356 :   ~SparseMultiSet() { free(Sparse); }
     197     9231909 : 
     198     6594325 :   /// Set the universe size which determines the largest key the set can hold.
     199     6594325 :   /// The universe must be sized before any elements can be added.
     200           3 :   ///
     201           3 :   /// @param U Universe size. All object keys must be less than U.
     202           3 :   ///
     203     2637587 :   void setUniverse(unsigned U) {
     204     2637584 :     // It's not hard to resize the universe on a non-empty set, but it doesn't
     205             :     // seem like a likely use case, so we can add that code when we need it.
     206             :     assert(empty() && "Can only resize universe on an empty map");
     207     2637584 :     // Hysteresis prevents needless reallocations.
     208     2637584 :     if (U >= Universe/4 && U <= Universe)
     209     2637584 :       return;
     210     2637584 :     free(Sparse);
     211           0 :     // The Sparse array doesn't actually need to be initialized, so malloc
     212     2392078 :     // would be enough here, but that will cause tools like valgrind to
     213     2392078 :     // complain about branching on uninitialized data.
     214     1441228 :     Sparse = static_cast<SparseT*>(safe_calloc(U, sizeof(SparseT)));
     215     1441228 :     Universe = U;
     216           0 :   }
     217           0 : 
     218           0 :   /// Our iterators are iterators over the collection of objects that share a
     219      950850 :   /// key.
     220      950850 :   template<typename SMSPtrTy>
     221             :   class iterator_base : public std::iterator<std::bidirectional_iterator_tag,
     222             :                                              ValueT> {
     223      950850 :     friend class SparseMultiSet;
     224      950850 : 
     225      950850 :     SMSPtrTy SMS;
     226      950850 :     unsigned Idx;
     227           0 :     unsigned SparseIdx;
     228      685276 : 
     229      685276 :     iterator_base(SMSPtrTy P, unsigned I, unsigned SI)
     230      685276 :       : SMS(P), Idx(I), SparseIdx(SI) {}
     231      685276 : 
     232             :     /// Whether our iterator has fallen outside our dense vector.
     233             :     bool isEnd() const {
     234             :       if (Idx == SMSNode::INVALID)
     235           0 :         return true;
     236           0 : 
     237           0 :       assert(Idx < SMS->Dense.size() && "Out of range, non-INVALID Idx?");
     238           0 :       return false;
     239           0 :     }
     240           0 : 
     241           0 :     /// Whether our iterator is properly keyed, i.e. the SparseIdx is valid
     242           0 :     bool isKeyed() const { return SparseIdx < SMS->Universe; }
     243             : 
     244     6924623 :     unsigned Prev() const { return SMS->Dense[Idx].Prev; }
     245    23336563 :     unsigned Next() const { return SMS->Dense[Idx].Next; }
     246     4467821 : 
     247     4467821 :     void setPrev(unsigned P) { SMS->Dense[Idx].Prev = P; }
     248             :     void setNext(unsigned N) { SMS->Dense[Idx].Next = N; }
     249           6 : 
     250             :   public:
     251     1686734 :     using super = std::iterator<std::bidirectional_iterator_tag, ValueT>;
     252     1686740 :     using value_type = typename super::value_type;
     253             :     using difference_type = typename super::difference_type;
     254             :     using pointer = typename super::pointer;
     255     1686734 :     using reference = typename super::reference;
     256     1686734 : 
     257     1686734 :     reference operator*() const {
     258     1686734 :       assert(isKeyed() && SMS->sparseIndex(SMS->Dense[Idx].Data) == SparseIdx &&
     259           0 :              "Dereferencing iterator of invalid key or index");
     260             : 
     261    17204381 :       return SMS->Dense[Idx].Data;
     262             :     }
     263           0 :     pointer operator->() const { return &operator*(); }
     264           0 : 
     265           0 :     /// Comparison operators
     266           0 :     bool operator==(const iterator_base &RHS) const {
     267             :       // end compares equal
     268    23185202 :       if (SMS == RHS.SMS && Idx == RHS.Idx) {
     269             :         assert((isEnd() || SparseIdx == RHS.SparseIdx) &&
     270           0 :                "Same dense entry, but different keys?");
     271           0 :         return true;
     272             :       }
     273           0 : 
     274             :       return false;
     275             :     }
     276             : 
     277      937336 :     bool operator!=(const iterator_base &RHS) const {
     278           0 :       return !operator==(RHS);
     279           0 :     }
     280           0 : 
     281             :     /// Increment and decrement operators
     282             :     iterator_base &operator--() { // predecrement - Back up
     283             :       assert(isKeyed() && "Decrementing an invalid iterator");
     284           0 :       assert((isEnd() || !SMS->isHead(SMS->Dense[Idx])) &&
     285           0 :              "Decrementing head of list");
     286             : 
     287           0 :       // If we're at the end, then issue a new find()
     288             :       if (isEnd())
     289             :         Idx = SMS->findIndex(SparseIdx).Prev();
     290             :       else
     291             :         Idx = Prev();
     292           0 : 
     293           0 :       return *this;
     294           0 :     }
     295             :     iterator_base &operator++() { // preincrement - Advance
     296             :       assert(!isEnd() && isKeyed() && "Incrementing an invalid/end iterator");
     297             :       Idx = Next();
     298           0 :       return *this;
     299           0 :     }
     300             :     iterator_base operator--(int) { // postdecrement
     301           0 :       iterator_base I(*this);
     302             :       --*this;
     303             :       return I;
     304             :     }
     305             :     iterator_base operator++(int) { // postincrement
     306           0 :       iterator_base I(*this);
     307           0 :       ++*this;
     308           0 :       return I;
     309             :     }
     310             :   };
     311             : 
     312           0 :   using iterator = iterator_base<SparseMultiSet *>;
     313           0 :   using const_iterator = iterator_base<const SparseMultiSet *>;
     314             : 
     315           0 :   // Convenience types
     316             :   using RangePair = std::pair<iterator, iterator>;
     317           0 : 
     318           0 :   /// Returns an iterator past this container. Note that such an iterator cannot
     319           0 :   /// be decremented, but will compare equal to other end iterators.
     320           0 :   iterator end() { return iterator(this, SMSNode::INVALID, SMSNode::INVALID); }
     321           0 :   const_iterator end() const {
     322           0 :     return const_iterator(this, SMSNode::INVALID, SMSNode::INVALID);
     323             :   }
     324             : 
     325             :   /// Returns true if the set is empty.
     326           0 :   ///
     327           0 :   /// This is not the same as BitVector::empty().
     328          16 :   ///
     329          29 :   bool empty() const { return size() == 0; }
     330             : 
     331           4 :   /// Returns the number of elements in the set.
     332             :   ///
     333             :   /// This is not the same as BitVector::size() which returns the size of the
     334           0 :   /// universe.
     335           0 :   ///
     336           0 :   size_type size() const {
     337             :     assert(NumFree <= Dense.size() && "Out-of-bounds free entries");
     338             :     return Dense.size() - NumFree;
     339             :   }
     340           0 : 
     341           0 :   /// Clears the set.  This is a very fast constant time operation.
     342             :   ///
     343             :   void clear() {
     344             :     // Sparse does not need to be cleared, see find().
     345           7 :     Dense.clear();
     346      124424 :     NumFree = 0;
     347      124424 :     FreelistIdx = SMSNode::INVALID;
     348             :   }
     349             : 
     350             :   /// Find an element by its index.
     351           0 :   ///
     352             :   /// @param   Idx A valid index to find.
     353           0 :   /// @returns An iterator to the element identified by key, or end().
     354             :   ///
     355     4399764 :   iterator findIndex(unsigned Idx) {
     356             :     assert(Idx < Universe && "Key out of range");
     357           0 :     const unsigned Stride = std::numeric_limits<SparseT>::max() + 1u;
     358     6216201 :     for (unsigned i = Sparse[Idx], e = Dense.size(); i < e; i += Stride) {
     359     4510124 :       const unsigned FoundIdx = sparseIndex(Dense[i]);
     360           0 :       // Check that we're pointing at the correct entry and that it is the head
     361           0 :       // of a valid list.
     362     4510124 :       if (Idx == FoundIdx && Dense[i].isValid() && isHead(Dense[i]))
     363     2693687 :         return iterator(this, i, Idx);
     364        2204 :       // Stride is 0 when SparseT >= unsigned.  We don't need to loop.
     365             :       if (!Stride)
     366             :         break;
     367           0 :     }
     368             :     return end();
     369             :   }
     370     2218736 : 
     371     6413390 :   /// Find an element by its key.
     372           0 :   ///
     373        7182 :   /// @param   Key A valid key to find.
     374           0 :   /// @returns An iterator to the element identified by key, or end().
     375             :   ///
     376           0 :   iterator find(const KeyT &Key) {
     377     2818707 :     return findIndex(KeyIndexOf(Key));
     378             :   }
     379             : 
     380             :   const_iterator find(const KeyT &Key) const {
     381             :     iterator I = const_cast<SparseMultiSet*>(this)->findIndex(KeyIndexOf(Key));
     382           0 :     return const_iterator(I.SMS, I.Idx, KeyIndexOf(Key));
     383           0 :   }
     384           0 : 
     385             :   /// Returns the number of elements identified by Key. This will be linear in
     386             :   /// the number of elements of that key.
     387     8493789 :   size_type count(const KeyT &Key) const {
     388             :     unsigned Ret = 0;
     389           0 :     for (const_iterator It = find(Key); It != end(); ++It)
     390             :       ++Ret;
     391             : 
     392           0 :     return Ret;
     393           0 :   }
     394           0 : 
     395           0 :   /// Returns true if this set contains an element identified by Key.
     396             :   bool contains(const KeyT &Key) const {
     397           0 :     return find(Key) != end();
     398             :   }
     399           0 : 
     400             :   /// Return the head and tail of the subset's list, otherwise returns end().
     401           0 :   iterator getHead(const KeyT &Key) { return find(Key); }
     402           0 :   iterator getTail(const KeyT &Key) {
     403             :     iterator I = find(Key);
     404           0 :     if (I != end())
     405           0 :       I = iterator(this, I.Prev(), KeyIndexOf(Key));
     406             :     return I;
     407        1158 :   }
     408             : 
     409             :   /// The bounds of the range of items sharing Key K. First member is the head
     410           0 :   /// of the list, and the second member is a decrementable end iterator for
     411             :   /// that key.
     412    73018561 :   RangePair equal_range(const KeyT &K) {
     413             :     iterator B = find(K);
     414          14 :     iterator E = iterator(this, SMSNode::INVALID, B.SparseIdx);
     415           0 :     return make_pair(B, E);
     416             :   }
     417             : 
     418          20 :   /// Insert a new element at the tail of the subset list. Returns an iterator
     419             :   /// to the newly added entry.
     420     1581057 :   iterator insert(const ValueT &Val) {
     421             :     unsigned Idx = sparseIndex(Val);
     422     1581057 :     iterator I = findIndex(Idx);
     423             : 
     424     1581077 :     unsigned NodeIdx = addValue(Val, SMSNode::INVALID, SMSNode::INVALID);
     425           7 : 
     426             :     if (I == end()) {
     427          26 :       // Make a singleton list
     428      810989 :       Sparse[Idx] = NodeIdx;
     429      811009 :       Dense[NodeIdx].Prev = NodeIdx;
     430      810989 :       return iterator(this, NodeIdx, Idx);
     431             :     }
     432           0 : 
     433           9 :     // Stick it at the end.
     434             :     unsigned HeadIdx = I.Idx;
     435           0 :     unsigned TailIdx = I.Prev();
     436     1540136 :     Dense[TailIdx].Next = NodeIdx;
     437      770068 :     Dense[HeadIdx].Prev = NodeIdx;
     438      770069 :     Dense[NodeIdx].Prev = TailIdx;
     439           0 : 
     440      770068 :     return iterator(this, NodeIdx, Idx);
     441             :   }
     442           0 : 
     443             :   /// Erases an existing element identified by a valid iterator.
     444             :   ///
     445           0 :   /// This invalidates iterators pointing at the same entry, but erase() returns
     446             :   /// an iterator pointing to the next element in the subset's list. This makes
     447             :   /// it possible to erase selected elements while iterating over the subset:
     448             :   ///
     449             :   ///   tie(I, E) = Set.equal_range(Key);
     450           0 :   ///   while (I != E)
     451             :   ///     if (test(*I))
     452           0 :   ///       I = Set.erase(I);
     453             :   ///     else
     454             :   ///       ++I;
     455           0 :   ///
     456             :   /// Note that if the last element in the subset list is erased, this will
     457             :   /// return an end iterator which can be decremented to get the new tail (if it
     458             :   /// exists):
     459             :   ///
     460             :   ///  tie(B, I) = Set.equal_range(Key);
     461             :   ///  for (bool isBegin = B == I; !isBegin; /* empty */) {
     462           0 :   ///    isBegin = (--I) == B;
     463             :   ///    if (test(I))
     464             :   ///      break;
     465           2 :   ///    I = erase(I);
     466        1158 :   ///  }
     467             :   iterator erase(iterator I) {
     468             :     assert(I.isKeyed() && !I.isEnd() && !Dense[I.Idx].isTombstone() &&
     469             :            "erasing invalid/end/tombstone iterator");
     470             : 
     471             :     // First, unlink the node from its list. Then swap the node out with the
     472        1158 :     // dense vector's last entry
     473        1158 :     iterator NextI = unlink(Dense[I.Idx]);
     474          13 : 
     475           0 :     // Put in a tombstone.
     476             :     makeTombstone(I.Idx);
     477        1158 : 
     478             :     return NextI;
     479             :   }
     480             : 
     481             :   /// Erase all elements with the given key. This invalidates all
     482           1 :   /// iterators of that key.
     483           1 :   void eraseAll(const KeyT &K) {
     484             :     for (iterator I = find(K); I != end(); /* empty */)
     485             :       I = erase(I);
     486             :   }
     487             : 
     488             : private:
     489             :   /// Unlink the node from its list. Returns the next node in the list.
     490             :   iterator unlink(const SMSNode &N) {
     491        1494 :     if (isSingleton(N)) {
     492             :       // Singleton is already unlinked
     493             :       assert(N.Next == SMSNode::INVALID && "Singleton has next?");
     494        3514 :       return iterator(this, SMSNode::INVALID, ValIndexOf(N.Data));
     495        2769 :     }
     496             : 
     497             :     if (isHead(N)) {
     498        2769 :       // If we're the head, then update the sparse array and our next.
     499         749 :       Sparse[sparseIndex(N)] = N.Next;
     500             :       Dense[N.Next].Prev = N.Prev;
     501             :       return iterator(this, N.Next, ValIndexOf(N.Data));
     502             :     }
     503             : 
     504             :     if (N.isTail()) {
     505             :       // If we're the tail, then update our head and our previous.
     506           8 :       findIndex(sparseIndex(N)).setPrev(N.Prev);
     507             :       Dense[N.Prev].Next = N.Next;
     508             : 
     509          10 :       // Give back an end iterator that can be decremented
     510           7 :       iterator I(this, N.Prev, ValIndexOf(N.Data));
     511             :       return ++I;
     512             :     }
     513           7 : 
     514           5 :     // Otherwise, just drop us
     515             :     Dense[N.Next].Prev = N.Prev;
     516             :     Dense[N.Prev].Next = N.Next;
     517             :     return iterator(this, N.Next, ValIndexOf(N.Data));
     518             :   }
     519             : };
     520             : 
     521        1486 : } // end namespace llvm
     522             : 
     523             : #endif // LLVM_ADT_SPARSEMULTISET_H

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