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 "llvm/Support/Compiler.h"
21#include <cstddef>
22#include <functional>
23#include <set>
24#include <utility>
25
26namespace llvm {
27
28/// SmallSet - This maintains a set of unique values, optimizing for the case
29/// when the set is small (less than N).  In this case, the set can be
30/// maintained with no mallocs.  If the set gets large, we expand to using an
31/// std::set to maintain reasonable lookup times.
32///
33/// Note that this set does not provide a way to iterate over members in the
34/// set.
35template <typename T, unsigned N, typename C = std::less<T>>
36class SmallSet {
37  /// Use a SmallVector to hold the elements here (even though it will never
38  /// reach its 'large' stage) to avoid calling the default ctors of elements
39  /// we will never use.
40  SmallVector<T, N> Vector;
41  std::set<T, C> Set;
42  typedef typename SmallVector<T, N>::const_iterator VIterator;
43  typedef typename SmallVector<T, N>::iterator mutable_iterator;
44
45  // In small mode SmallPtrSet uses linear search for the elements, so it is
46  // not a good idea to choose this value too high. You may consider using a
47  // DenseSet<> instead if you expect many elements in the set.
48  static_assert(N <= 32, "N should be small");
49
50public:
51  typedef size_t size_type;
52
53  SmallSet() = default;
54
55  LLVM_NODISCARD bool empty() const {
56    return Vector.empty() && Set.empty();
57  }
58
59  size_type size() const {
60    return isSmall() ? Vector.size() : Set.size();
61  }
62
63  /// count - Return 1 if the element is in the set, 0 otherwise.
64  size_type count(const T &V) const {
65    if (isSmall()) {
66      // Since the collection is small, just do a linear search.
67      return vfind(V) == Vector.end() ? 0 : 1;
68    } else {
69      return Set.count(V);
70    }
71  }
72
73  /// insert - Insert an element into the set if it isn't already there.
74  /// Returns true if the element is inserted (it was not in the set before).
75  /// The first value of the returned pair is unused and provided for
76  /// partial compatibility with the standard library self-associative container
77  /// concept.
78  // FIXME: Add iterators that abstract over the small and large form, and then
79  // return those here.
80  std::pair<NoneType, bool> insert(const T &V) {
81    if (!isSmall())
82      return std::make_pair(None, Set.insert(V).second);
83
84    VIterator I = vfind(V);
85    if (I != Vector.end())    // Don't reinsert if it already exists.
86      return std::make_pair(None, false);
87    if (Vector.size() < N) {
88      Vector.push_back(V);
89      return std::make_pair(None, true);
90    }
91
92    // Otherwise, grow from vector to set.
93    while (!Vector.empty()) {
94      Set.insert(Vector.back());
95      Vector.pop_back();
96    }
97    Set.insert(V);
98    return std::make_pair(None, true);
99  }
100
101  template <typename IterT>
102  void insert(IterT I, IterT E) {
103    for (; I != E; ++I)
104      insert(*I);
105  }
106
107  bool erase(const T &V) {
108    if (!isSmall())
109      return Set.erase(V);
110    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
111      if (*I == V) {
112        Vector.erase(I);
113        return true;
114      }
115    return false;
116  }
117
118  void clear() {
119    Vector.clear();
120    Set.clear();
121  }
122
123private:
124  bool isSmall() const { return Set.empty(); }
125
126  VIterator vfind(const T &V) const {
127    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
128      if (*I == V)
129        return I;
130    return Vector.end();
131  }
132};
133
134/// If this set is of pointer values, transparently switch over to using
135/// SmallPtrSet for performance.
136template <typename PointeeType, unsigned N>
137class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
138
139} // end namespace llvm
140
141#endif // LLVM_ADT_SMALLSET_H
142