1//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- 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 SmallSet class.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_ADT_SMALLSET_H
15#define LLVM_ADT_SMALLSET_H
16
17#include "llvm/ADT/None.h"
18#include "llvm/ADT/SmallPtrSet.h"
19#include "llvm/ADT/SmallVector.h"
20#include <set>
21
22namespace llvm {
23
24/// SmallSet - This maintains a set of unique values, optimizing for the case
25/// when the set is small (less than N).  In this case, the set can be
26/// maintained with no mallocs.  If the set gets large, we expand to using an
27/// std::set to maintain reasonable lookup times.
28///
29/// Note that this set does not provide a way to iterate over members in the
30/// set.
31template <typename T, unsigned N,  typename C = std::less<T> >
32class SmallSet {
33  /// Use a SmallVector to hold the elements here (even though it will never
34  /// reach its 'large' stage) to avoid calling the default ctors of elements
35  /// we will never use.
36  SmallVector<T, N> Vector;
37  std::set<T, C> Set;
38  typedef typename SmallVector<T, N>::const_iterator VIterator;
39  typedef typename SmallVector<T, N>::iterator mutable_iterator;
40
41  // In small mode SmallPtrSet uses linear search for the elements, so it is
42  // not a good idea to choose this value too high. You may consider using a
43  // DenseSet<> instead if you expect many elements in the set.
44  static_assert(N <= 32, "N should be small");
45
46public:
47  typedef size_t size_type;
48  SmallSet() {}
49
50  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const {
51    return Vector.empty() && Set.empty();
52  }
53
54  size_type size() const {
55    return isSmall() ? Vector.size() : Set.size();
56  }
57
58  /// count - Return 1 if the element is in the set, 0 otherwise.
59  size_type count(const T &V) const {
60    if (isSmall()) {
61      // Since the collection is small, just do a linear search.
62      return vfind(V) == Vector.end() ? 0 : 1;
63    } else {
64      return Set.count(V);
65    }
66  }
67
68  /// insert - Insert an element into the set if it isn't already there.
69  /// Returns true if the element is inserted (it was not in the set before).
70  /// The first value of the returned pair is unused and provided for
71  /// partial compatibility with the standard library self-associative container
72  /// concept.
73  // FIXME: Add iterators that abstract over the small and large form, and then
74  // return those here.
75  std::pair<NoneType, bool> insert(const T &V) {
76    if (!isSmall())
77      return std::make_pair(None, Set.insert(V).second);
78
79    VIterator I = vfind(V);
80    if (I != Vector.end())    // Don't reinsert if it already exists.
81      return std::make_pair(None, false);
82    if (Vector.size() < N) {
83      Vector.push_back(V);
84      return std::make_pair(None, true);
85    }
86
87    // Otherwise, grow from vector to set.
88    while (!Vector.empty()) {
89      Set.insert(Vector.back());
90      Vector.pop_back();
91    }
92    Set.insert(V);
93    return std::make_pair(None, true);
94  }
95
96  template <typename IterT>
97  void insert(IterT I, IterT E) {
98    for (; I != E; ++I)
99      insert(*I);
100  }
101
102  bool erase(const T &V) {
103    if (!isSmall())
104      return Set.erase(V);
105    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
106      if (*I == V) {
107        Vector.erase(I);
108        return true;
109      }
110    return false;
111  }
112
113  void clear() {
114    Vector.clear();
115    Set.clear();
116  }
117
118private:
119  bool isSmall() const { return Set.empty(); }
120
121  VIterator vfind(const T &V) const {
122    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
123      if (*I == V)
124        return I;
125    return Vector.end();
126  }
127};
128
129/// If this set is of pointer values, transparently switch over to using
130/// SmallPtrSet for performance.
131template <typename PointeeType, unsigned N>
132class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
133
134} // end namespace llvm
135
136#endif
137