1//===- llvm/ADT/SmallPtrSet.h - 'Normally small' pointer set ----*- 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 SmallPtrSet class.  See the doxygen comment for
11// SmallPtrSetImplBase for more details on the algorithm used.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ADT_SMALLPTRSET_H
16#define LLVM_ADT_SMALLPTRSET_H
17
18#include "llvm/Support/Compiler.h"
19#include "llvm/Support/DataTypes.h"
20#include "llvm/Support/PointerLikeTypeTraits.h"
21#include <cassert>
22#include <cstddef>
23#include <cstring>
24#include <iterator>
25#include <utility>
26
27namespace llvm {
28
29class SmallPtrSetIteratorImpl;
30
31/// SmallPtrSetImplBase - This is the common code shared among all the
32/// SmallPtrSet<>'s, which is almost everything.  SmallPtrSet has two modes, one
33/// for small and one for large sets.
34///
35/// Small sets use an array of pointers allocated in the SmallPtrSet object,
36/// which is treated as a simple array of pointers.  When a pointer is added to
37/// the set, the array is scanned to see if the element already exists, if not
38/// the element is 'pushed back' onto the array.  If we run out of space in the
39/// array, we grow into the 'large set' case.  SmallSet should be used when the
40/// sets are often small.  In this case, no memory allocation is used, and only
41/// light-weight and cache-efficient scanning is used.
42///
43/// Large sets use a classic exponentially-probed hash table.  Empty buckets are
44/// represented with an illegal pointer value (-1) to allow null pointers to be
45/// inserted.  Tombstones are represented with another illegal pointer value
46/// (-2), to allow deletion.  The hash table is resized when the table is 3/4 or
47/// more.  When this happens, the table is doubled in size.
48///
49class SmallPtrSetImplBase {
50  friend class SmallPtrSetIteratorImpl;
51
52protected:
53  /// SmallArray - Points to a fixed size set of buckets, used in 'small mode'.
54  const void **SmallArray;
55  /// CurArray - This is the current set of buckets.  If equal to SmallArray,
56  /// then the set is in 'small mode'.
57  const void **CurArray;
58  /// CurArraySize - The allocated size of CurArray, always a power of two.
59  unsigned CurArraySize;
60
61  // If small, this is # elts allocated consecutively
62  unsigned NumElements;
63  unsigned NumTombstones;
64
65  // Helpers to copy and move construct a SmallPtrSet.
66  SmallPtrSetImplBase(const void **SmallStorage, const SmallPtrSetImplBase &that);
67  SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize,
68                  SmallPtrSetImplBase &&that);
69  explicit SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize) :
70    SmallArray(SmallStorage), CurArray(SmallStorage), CurArraySize(SmallSize) {
71    assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
72           "Initial size must be a power of two!");
73    clear();
74  }
75  ~SmallPtrSetImplBase();
76
77public:
78  typedef unsigned size_type;
79  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const { return size() == 0; }
80  size_type size() const { return NumElements; }
81
82  void clear() {
83    // If the capacity of the array is huge, and the # elements used is small,
84    // shrink the array.
85    if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32)
86      return shrink_and_clear();
87
88    // Fill the array with empty markers.
89    memset(CurArray, -1, CurArraySize*sizeof(void*));
90    NumElements = 0;
91    NumTombstones = 0;
92  }
93
94protected:
95  static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
96  static void *getEmptyMarker() {
97    // Note that -1 is chosen to make clear() efficiently implementable with
98    // memset and because it's not a valid pointer value.
99    return reinterpret_cast<void*>(-1);
100  }
101
102  /// insert_imp - This returns true if the pointer was new to the set, false if
103  /// it was already in the set.  This is hidden from the client so that the
104  /// derived class can check that the right type of pointer is passed in.
105  std::pair<const void *const *, bool> insert_imp(const void *Ptr);
106
107  /// erase_imp - If the set contains the specified pointer, remove it and
108  /// return true, otherwise return false.  This is hidden from the client so
109  /// that the derived class can check that the right type of pointer is passed
110  /// in.
111  bool erase_imp(const void * Ptr);
112
113  bool count_imp(const void * Ptr) const {
114    if (isSmall()) {
115      // Linear search for the item.
116      for (const void *const *APtr = SmallArray,
117                      *const *E = SmallArray+NumElements; APtr != E; ++APtr)
118        if (*APtr == Ptr)
119          return true;
120      return false;
121    }
122
123    // Big set case.
124    return *FindBucketFor(Ptr) == Ptr;
125  }
126
127private:
128  bool isSmall() const { return CurArray == SmallArray; }
129
130  const void * const *FindBucketFor(const void *Ptr) const;
131  void shrink_and_clear();
132
133  /// Grow - Allocate a larger backing store for the buckets and move it over.
134  void Grow(unsigned NewSize);
135
136  void operator=(const SmallPtrSetImplBase &RHS) = delete;
137
138protected:
139  /// swap - Swaps the elements of two sets.
140  /// Note: This method assumes that both sets have the same small size.
141  void swap(SmallPtrSetImplBase &RHS);
142
143  void CopyFrom(const SmallPtrSetImplBase &RHS);
144  void MoveFrom(unsigned SmallSize, SmallPtrSetImplBase &&RHS);
145};
146
147/// SmallPtrSetIteratorImpl - This is the common base class shared between all
148/// instances of SmallPtrSetIterator.
149class SmallPtrSetIteratorImpl {
150protected:
151  const void *const *Bucket;
152  const void *const *End;
153
154public:
155  explicit SmallPtrSetIteratorImpl(const void *const *BP, const void*const *E)
156    : Bucket(BP), End(E) {
157      AdvanceIfNotValid();
158  }
159
160  bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
161    return Bucket == RHS.Bucket;
162  }
163  bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
164    return Bucket != RHS.Bucket;
165  }
166
167protected:
168  /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket
169  /// that is.   This is guaranteed to stop because the end() bucket is marked
170  /// valid.
171  void AdvanceIfNotValid() {
172    assert(Bucket <= End);
173    while (Bucket != End &&
174           (*Bucket == SmallPtrSetImplBase::getEmptyMarker() ||
175            *Bucket == SmallPtrSetImplBase::getTombstoneMarker()))
176      ++Bucket;
177  }
178};
179
180/// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
181template<typename PtrTy>
182class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
183  typedef PointerLikeTypeTraits<PtrTy> PtrTraits;
184
185public:
186  typedef PtrTy                     value_type;
187  typedef PtrTy                     reference;
188  typedef PtrTy                     pointer;
189  typedef std::ptrdiff_t            difference_type;
190  typedef std::forward_iterator_tag iterator_category;
191
192  explicit SmallPtrSetIterator(const void *const *BP, const void *const *E)
193    : SmallPtrSetIteratorImpl(BP, E) {}
194
195  // Most methods provided by baseclass.
196
197  const PtrTy operator*() const {
198    assert(Bucket < End);
199    return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket));
200  }
201
202  inline SmallPtrSetIterator& operator++() {          // Preincrement
203    ++Bucket;
204    AdvanceIfNotValid();
205    return *this;
206  }
207
208  SmallPtrSetIterator operator++(int) {        // Postincrement
209    SmallPtrSetIterator tmp = *this; ++*this; return tmp;
210  }
211};
212
213/// RoundUpToPowerOfTwo - This is a helper template that rounds N up to the next
214/// power of two (which means N itself if N is already a power of two).
215template<unsigned N>
216struct RoundUpToPowerOfTwo;
217
218/// RoundUpToPowerOfTwoH - If N is not a power of two, increase it.  This is a
219/// helper template used to implement RoundUpToPowerOfTwo.
220template<unsigned N, bool isPowerTwo>
221struct RoundUpToPowerOfTwoH {
222  enum { Val = N };
223};
224template<unsigned N>
225struct RoundUpToPowerOfTwoH<N, false> {
226  enum {
227    // We could just use NextVal = N+1, but this converges faster.  N|(N-1) sets
228    // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
229    Val = RoundUpToPowerOfTwo<(N|(N-1)) + 1>::Val
230  };
231};
232
233template<unsigned N>
234struct RoundUpToPowerOfTwo {
235  enum { Val = RoundUpToPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
236};
237
238/// \brief A templated base class for \c SmallPtrSet which provides the
239/// typesafe interface that is common across all small sizes.
240///
241/// This is particularly useful for passing around between interface boundaries
242/// to avoid encoding a particular small size in the interface boundary.
243template <typename PtrType>
244class SmallPtrSetImpl : public SmallPtrSetImplBase {
245  typedef PointerLikeTypeTraits<PtrType> PtrTraits;
246
247  SmallPtrSetImpl(const SmallPtrSetImpl &) = delete;
248
249protected:
250  // Constructors that forward to the base.
251  SmallPtrSetImpl(const void **SmallStorage, const SmallPtrSetImpl &that)
252      : SmallPtrSetImplBase(SmallStorage, that) {}
253  SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize,
254                  SmallPtrSetImpl &&that)
255      : SmallPtrSetImplBase(SmallStorage, SmallSize, std::move(that)) {}
256  explicit SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize)
257      : SmallPtrSetImplBase(SmallStorage, SmallSize) {}
258
259public:
260  typedef SmallPtrSetIterator<PtrType> iterator;
261  typedef SmallPtrSetIterator<PtrType> const_iterator;
262
263  /// Inserts Ptr if and only if there is no element in the container equal to
264  /// Ptr. The bool component of the returned pair is true if and only if the
265  /// insertion takes place, and the iterator component of the pair points to
266  /// the element equal to Ptr.
267  std::pair<iterator, bool> insert(PtrType Ptr) {
268    auto p = insert_imp(PtrTraits::getAsVoidPointer(Ptr));
269    return std::make_pair(iterator(p.first, CurArray + CurArraySize), p.second);
270  }
271
272  /// erase - If the set contains the specified pointer, remove it and return
273  /// true, otherwise return false.
274  bool erase(PtrType Ptr) {
275    return erase_imp(PtrTraits::getAsVoidPointer(Ptr));
276  }
277
278  /// count - Return 1 if the specified pointer is in the set, 0 otherwise.
279  size_type count(PtrType Ptr) const {
280    return count_imp(PtrTraits::getAsVoidPointer(Ptr)) ? 1 : 0;
281  }
282
283  template <typename IterT>
284  void insert(IterT I, IterT E) {
285    for (; I != E; ++I)
286      insert(*I);
287  }
288
289  inline iterator begin() const {
290    return iterator(CurArray, CurArray+CurArraySize);
291  }
292  inline iterator end() const {
293    return iterator(CurArray+CurArraySize, CurArray+CurArraySize);
294  }
295};
296
297/// SmallPtrSet - This class implements a set which is optimized for holding
298/// SmallSize or less elements.  This internally rounds up SmallSize to the next
299/// power of two if it is not already a power of two.  See the comments above
300/// SmallPtrSetImplBase for details of the algorithm.
301template<class PtrType, unsigned SmallSize>
302class SmallPtrSet : public SmallPtrSetImpl<PtrType> {
303  typedef SmallPtrSetImpl<PtrType> BaseT;
304
305  // Make sure that SmallSize is a power of two, round up if not.
306  enum { SmallSizePowTwo = RoundUpToPowerOfTwo<SmallSize>::Val };
307  /// SmallStorage - Fixed size storage used in 'small mode'.
308  const void *SmallStorage[SmallSizePowTwo];
309
310public:
311  SmallPtrSet() : BaseT(SmallStorage, SmallSizePowTwo) {}
312  SmallPtrSet(const SmallPtrSet &that) : BaseT(SmallStorage, that) {}
313  SmallPtrSet(SmallPtrSet &&that)
314      : BaseT(SmallStorage, SmallSizePowTwo, std::move(that)) {}
315
316  template<typename It>
317  SmallPtrSet(It I, It E) : BaseT(SmallStorage, SmallSizePowTwo) {
318    this->insert(I, E);
319  }
320
321  SmallPtrSet<PtrType, SmallSize> &
322  operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) {
323    if (&RHS != this)
324      this->CopyFrom(RHS);
325    return *this;
326  }
327
328  SmallPtrSet<PtrType, SmallSize>&
329  operator=(SmallPtrSet<PtrType, SmallSize> &&RHS) {
330    if (&RHS != this)
331      this->MoveFrom(SmallSizePowTwo, std::move(RHS));
332    return *this;
333  }
334
335  /// swap - Swaps the elements of two sets.
336  void swap(SmallPtrSet<PtrType, SmallSize> &RHS) {
337    SmallPtrSetImplBase::swap(RHS);
338  }
339};
340}
341
342namespace std {
343  /// Implement std::swap in terms of SmallPtrSet swap.
344  template<class T, unsigned N>
345  inline void swap(llvm::SmallPtrSet<T, N> &LHS, llvm::SmallPtrSet<T, N> &RHS) {
346    LHS.swap(RHS);
347  }
348}
349
350#endif
351