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
43  using VIterator = typename SmallVector<T, N>::const_iterator;
44  using mutable_iterator = typename SmallVector<T, N>::iterator;
45
46  // In small mode SmallPtrSet uses linear search for the elements, so it is
47  // not a good idea to choose this value too high. You may consider using a
48  // DenseSet<> instead if you expect many elements in the set.
49  static_assert(N <= 32, "N should be small");
50
51public:
52  using size_type = size_t;
53
54  SmallSet() = default;
55
56  LLVM_NODISCARD bool empty() const {
57    return Vector.empty() && Set.empty();
58  }
59
60  size_type size() const {
61    return isSmall() ? Vector.size() : Set.size();
62  }
63
64  /// count - Return 1 if the element is in the set, 0 otherwise.
65  size_type count(const T &V) const {
66    if (isSmall()) {
67      // Since the collection is small, just do a linear search.
68      return vfind(V) == Vector.end() ? 0 : 1;
69    } else {
70      return Set.count(V);
71    }
72  }
73
74  /// insert - Insert an element into the set if it isn't already there.
75  /// Returns true if the element is inserted (it was not in the set before).
76  /// The first value of the returned pair is unused and provided for
77  /// partial compatibility with the standard library self-associative container
78  /// concept.
79  // FIXME: Add iterators that abstract over the small and large form, and then
80  // return those here.
81  std::pair<NoneType, bool> insert(const T &V) {
82    if (!isSmall())
83      return std::make_pair(None, Set.insert(V).second);
84
85    VIterator I = vfind(V);
86    if (I != Vector.end())    // Don't reinsert if it already exists.
87      return std::make_pair(None, false);
88    if (Vector.size() < N) {
89      Vector.push_back(V);
90      return std::make_pair(None, true);
91    }
92
93    // Otherwise, grow from vector to set.
94    while (!Vector.empty()) {
95      Set.insert(Vector.back());
96      Vector.pop_back();
97    }
98    Set.insert(V);
99    return std::make_pair(None, true);
100  }
101
102  template <typename IterT>
103  void insert(IterT I, IterT E) {
104    for (; I != E; ++I)
105      insert(*I);
106  }
107
108  bool erase(const T &V) {
109    if (!isSmall())
110      return Set.erase(V);
111    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
112      if (*I == V) {
113        Vector.erase(I);
114        return true;
115      }
116    return false;
117  }
118
119  void clear() {
120    Vector.clear();
121    Set.clear();
122  }
123
124private:
125  bool isSmall() const { return Set.empty(); }
126
127  VIterator vfind(const T &V) const {
128    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
129      if (*I == V)
130        return I;
131    return Vector.end();
132  }
133};
134
135/// If this set is of pointer values, transparently switch over to using
136/// SmallPtrSet for performance.
137template <typename PointeeType, unsigned N>
138class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
139
140} // end namespace llvm
141
142#endif // LLVM_ADT_SMALLSET_H
143