1//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8///
9/// \file
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/SmallPtrSet.h"
18#include "llvm/ADT/SmallVector.h"
19#include "llvm/ADT/STLExtras.h"
20#include "llvm/ADT/iterator.h"
21#include "llvm/Support/Compiler.h"
22#include "llvm/Support/type_traits.h"
23#include <cstddef>
24#include <functional>
25#include <set>
26#include <type_traits>
27#include <utility>
28
29namespace llvm {
30
31/// SmallSetIterator - This class implements a const_iterator for SmallSet by
32/// delegating to the underlying SmallVector or Set iterators.
33template <typename T, unsigned N, typename C>
34class SmallSetIterator
35    : public iterator_facade_base<SmallSetIterator<T, N, C>,
36                                  std::forward_iterator_tag, T> {
37private:
38  using SetIterTy = typename std::set<T, C>::const_iterator;
39  using VecIterTy = typename SmallVector<T, N>::const_iterator;
40  using SelfTy = SmallSetIterator<T, N, C>;
41
42  /// Iterators to the parts of the SmallSet containing the data. They are set
43  /// depending on isSmall.
44  union {
45    SetIterTy SetIter;
46    VecIterTy VecIter;
47  };
48
49  bool isSmall;
50
51public:
52  SmallSetIterator(SetIterTy SetIter) : SetIter(SetIter), isSmall(false) {}
53
54  SmallSetIterator(VecIterTy VecIter) : VecIter(VecIter), isSmall(true) {}
55
56  // Spell out destructor, copy/move constructor and assignment operators for
57  // MSVC STL, where set<T>::const_iterator is not trivially copy constructible.
58  ~SmallSetIterator() {
59    if (isSmall)
60      VecIter.~VecIterTy();
61    else
62      SetIter.~SetIterTy();
63  }
64
65  SmallSetIterator(const SmallSetIterator &Other) : isSmall(Other.isSmall) {
66    if (isSmall)
67      VecIter = Other.VecIter;
68    else
69      // Use placement new, to make sure SetIter is properly constructed, even
70      // if it is not trivially copy-able (e.g. in MSVC).
71      new (&SetIter) SetIterTy(Other.SetIter);
72  }
73
74  SmallSetIterator(SmallSetIterator &&Other) : isSmall(Other.isSmall) {
75    if (isSmall)
76      VecIter = std::move(Other.VecIter);
77    else
78      // Use placement new, to make sure SetIter is properly constructed, even
79      // if it is not trivially copy-able (e.g. in MSVC).
80      new (&SetIter) SetIterTy(std::move(Other.SetIter));
81  }
82
83  SmallSetIterator& operator=(const SmallSetIterator& Other) {
84    // Call destructor for SetIter, so it gets properly destroyed if it is
85    // not trivially destructible in case we are setting VecIter.
86    if (!isSmall)
87      SetIter.~SetIterTy();
88
89    isSmall = Other.isSmall;
90    if (isSmall)
91      VecIter = Other.VecIter;
92    else
93      new (&SetIter) SetIterTy(Other.SetIter);
94    return *this;
95  }
96
97  SmallSetIterator& operator=(SmallSetIterator&& Other) {
98    // Call destructor for SetIter, so it gets properly destroyed if it is
99    // not trivially destructible in case we are setting VecIter.
100    if (!isSmall)
101      SetIter.~SetIterTy();
102
103    isSmall = Other.isSmall;
104    if (isSmall)
105      VecIter = std::move(Other.VecIter);
106    else
107      new (&SetIter) SetIterTy(std::move(Other.SetIter));
108    return *this;
109  }
110
111  bool operator==(const SmallSetIterator &RHS) const {
112    if (isSmall != RHS.isSmall)
113      return false;
114    if (isSmall)
115      return VecIter == RHS.VecIter;
116    return SetIter == RHS.SetIter;
117  }
118
119  SmallSetIterator &operator++() { // Preincrement
120    if (isSmall)
121      VecIter++;
122    else
123      SetIter++;
124    return *this;
125  }
126
127  const T &operator*() const { return isSmall ? *VecIter : *SetIter; }
128};
129
130/// SmallSet - This maintains a set of unique values, optimizing for the case
131/// when the set is small (less than N).  In this case, the set can be
132/// maintained with no mallocs.  If the set gets large, we expand to using an
133/// std::set to maintain reasonable lookup times.
134template <typename T, unsigned N, typename C = std::less<T>>
135class SmallSet {
136  /// Use a SmallVector to hold the elements here (even though it will never
137  /// reach its 'large' stage) to avoid calling the default ctors of elements
138  /// we will never use.
139  SmallVector<T, N> Vector;
140  std::set<T, C> Set;
141
142  using VIterator = typename SmallVector<T, N>::const_iterator;
143  using SIterator = typename std::set<T, C>::const_iterator;
144  using mutable_iterator = typename SmallVector<T, N>::iterator;
145
146  // In small mode SmallPtrSet uses linear search for the elements, so it is
147  // not a good idea to choose this value too high. You may consider using a
148  // DenseSet<> instead if you expect many elements in the set.
149  static_assert(N <= 32, "N should be small");
150
151public:
152  using size_type = size_t;
153  using const_iterator = SmallSetIterator<T, N, C>;
154
155  SmallSet() = default;
156
157  [[nodiscard]] bool empty() const { return Vector.empty() && Set.empty(); }
158
159  size_type size() const {
160    return isSmall() ? Vector.size() : Set.size();
161  }
162
163  /// count - Return 1 if the element is in the set, 0 otherwise.
164  size_type count(const T &V) const {
165    if (isSmall()) {
166      // Since the collection is small, just do a linear search.
167      return vfind(V) == Vector.end() ? 0 : 1;
168    } else {
169      return Set.count(V);
170    }
171  }
172
173  /// insert - Insert an element into the set if it isn't already there.
174  /// Returns a pair. The first value of it is an iterator to the inserted
175  /// element or the existing element in the set. The second value is true
176  /// if the element is inserted (it was not in the set before).
177  std::pair<const_iterator, bool> insert(const T &V) {
178    if (!isSmall()) {
179      auto [I, Inserted] = Set.insert(V);
180      return std::make_pair(const_iterator(I), Inserted);
181    }
182
183    VIterator I = vfind(V);
184    if (I != Vector.end())    // Don't reinsert if it already exists.
185      return std::make_pair(const_iterator(I), false);
186    if (Vector.size() < N) {
187      Vector.push_back(V);
188      return std::make_pair(const_iterator(std::prev(Vector.end())), true);
189    }
190
191    // Otherwise, grow from vector to set.
192    while (!Vector.empty()) {
193      Set.insert(Vector.back());
194      Vector.pop_back();
195    }
196    return std::make_pair(const_iterator(Set.insert(V).first), true);
197  }
198
199  template <typename IterT>
200  void insert(IterT I, IterT E) {
201    for (; I != E; ++I)
202      insert(*I);
203  }
204
205  bool erase(const T &V) {
206    if (!isSmall())
207      return Set.erase(V);
208    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
209      if (*I == V) {
210        Vector.erase(I);
211        return true;
212      }
213    return false;
214  }
215
216  void clear() {
217    Vector.clear();
218    Set.clear();
219  }
220
221  const_iterator begin() const {
222    if (isSmall())
223      return {Vector.begin()};
224    return {Set.begin()};
225  }
226
227  const_iterator end() const {
228    if (isSmall())
229      return {Vector.end()};
230    return {Set.end()};
231  }
232
233  /// Check if the SmallSet contains the given element.
234  bool contains(const T &V) const {
235    if (isSmall())
236      return vfind(V) != Vector.end();
237    return Set.find(V) != Set.end();
238  }
239
240private:
241  bool isSmall() const { return Set.empty(); }
242
243  VIterator vfind(const T &V) const {
244    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
245      if (*I == V)
246        return I;
247    return Vector.end();
248  }
249};
250
251/// If this set is of pointer values, transparently switch over to using
252/// SmallPtrSet for performance.
253template <typename PointeeType, unsigned N>
254class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
255
256/// Equality comparison for SmallSet.
257///
258/// Iterates over elements of LHS confirming that each element is also a member
259/// of RHS, and that RHS contains no additional values.
260/// Equivalent to N calls to RHS.count.
261/// For small-set mode amortized complexity is O(N^2)
262/// For large-set mode amortized complexity is linear, worst case is O(N^2) (if
263/// every hash collides).
264template <typename T, unsigned LN, unsigned RN, typename C>
265bool operator==(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) {
266  if (LHS.size() != RHS.size())
267    return false;
268
269  // All elements in LHS must also be in RHS
270  return all_of(LHS, [&RHS](const T &E) { return RHS.count(E); });
271}
272
273/// Inequality comparison for SmallSet.
274///
275/// Equivalent to !(LHS == RHS). See operator== for performance notes.
276template <typename T, unsigned LN, unsigned RN, typename C>
277bool operator!=(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) {
278  return !(LHS == RHS);
279}
280
281} // end namespace llvm
282
283#endif // LLVM_ADT_SMALLSET_H
284