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