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// This file defines the SmallSet class.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_ADT_SMALLSET_H
14#define LLVM_ADT_SMALLSET_H
15
16#include "llvm/ADT/None.h"
17#include "llvm/ADT/SmallPtrSet.h"
18#include "llvm/ADT/SmallVector.h"
19#include "llvm/ADT/iterator.h"
20#include "llvm/Support/Compiler.h"
21#include "llvm/Support/type_traits.h"
22#include <cstddef>
23#include <functional>
24#include <set>
25#include <type_traits>
26#include <utility>
27
28namespace llvm {
29
30/// SmallSetIterator - This class implements a const_iterator for SmallSet by
31/// delegating to the underlying SmallVector or Set iterators.
32template <typename T, unsigned N, typename C>
33class SmallSetIterator
34 : public iterator_facade_base<SmallSetIterator<T, N, C>,
35 std::forward_iterator_tag, T> {
36private:
37 using SetIterTy = typename std::set<T, C>::const_iterator;
38 using VecIterTy = typename SmallVector<T, N>::const_iterator;
39 using SelfTy = SmallSetIterator<T, N, C>;
40
41 /// Iterators to the parts of the SmallSet containing the data. They are set
42 /// depending on isSmall.
43 union {
44 SetIterTy SetIter;
45 VecIterTy VecIter;
46 };
47
48 bool isSmall;
49
50public:
51 SmallSetIterator(SetIterTy SetIter) : SetIter(SetIter), isSmall(false) {}
52
53 SmallSetIterator(VecIterTy VecIter) : VecIter(VecIter), isSmall(true) {}
54
55 // Spell out destructor, copy/move constructor and assignment operators for
56 // MSVC STL, where set<T>::const_iterator is not trivially copy constructible.
57 ~SmallSetIterator() {
58 if (isSmall)
59 VecIter.~VecIterTy();
60 else
61 SetIter.~SetIterTy();
62 }
63
64 SmallSetIterator(const SmallSetIterator &Other) : isSmall(Other.isSmall) {
65 if (isSmall)
66 VecIter = Other.VecIter;
67 else
68 // Use placement new, to make sure SetIter is properly constructed, even
69 // if it is not trivially copy-able (e.g. in MSVC).
70 new (&SetIter) SetIterTy(Other.SetIter);
71 }
72
73 SmallSetIterator(SmallSetIterator &&Other) : isSmall(Other.isSmall) {
74 if (isSmall)
75 VecIter = std::move(Other.VecIter);
76 else
77 // Use placement new, to make sure SetIter is properly constructed, even
78 // if it is not trivially copy-able (e.g. in MSVC).
79 new (&SetIter) SetIterTy(std::move(Other.SetIter));
80 }
81
82 SmallSetIterator& operator=(const SmallSetIterator& Other) {
83 // Call destructor for SetIter, so it gets properly destroyed if it is
84 // not trivially destructible in case we are setting VecIter.
85 if (!isSmall)
86 SetIter.~SetIterTy();
87
88 isSmall = Other.isSmall;
89 if (isSmall)
90 VecIter = Other.VecIter;
91 else
92 new (&SetIter) SetIterTy(Other.SetIter);
93 return *this;
94 }
95
96 SmallSetIterator& operator=(SmallSetIterator&& Other) {
97 // Call destructor for SetIter, so it gets properly destroyed if it is
98 // not trivially destructible in case we are setting VecIter.
99 if (!isSmall)
100 SetIter.~SetIterTy();
101
102 isSmall = Other.isSmall;
103 if (isSmall)
104 VecIter = std::move(Other.VecIter);
105 else
106 new (&SetIter) SetIterTy(std::move(Other.SetIter));
107 return *this;
108 }
109
110 bool operator==(const SmallSetIterator &RHS) const {
111 if (isSmall != RHS.isSmall)
112 return false;
113 if (isSmall)
114 return VecIter == RHS.VecIter;
115 return SetIter == RHS.SetIter;
116 }
117
118 SmallSetIterator &operator++() { // Preincrement
119 if (isSmall)
120 VecIter++;
121 else
122 SetIter++;
123 return *this;
124 }
125
126 const T &operator*() const { return isSmall ? *VecIter : *SetIter; }
127};
128
129/// SmallSet - This maintains a set of unique values, optimizing for the case
130/// when the set is small (less than N). In this case, the set can be
131/// maintained with no mallocs. If the set gets large, we expand to using an
132/// std::set to maintain reasonable lookup times.
133template <typename T, unsigned N, typename C = std::less<T>>
134class SmallSet {
135 /// Use a SmallVector to hold the elements here (even though it will never
136 /// reach its 'large' stage) to avoid calling the default ctors of elements
137 /// we will never use.
138 SmallVector<T, N> Vector;
139 std::set<T, C> Set;
140
141 using VIterator = typename SmallVector<T, N>::const_iterator;
142 using mutable_iterator = typename SmallVector<T, N>::iterator;
143
144 // In small mode SmallPtrSet uses linear search for the elements, so it is
145 // not a good idea to choose this value too high. You may consider using a
146 // DenseSet<> instead if you expect many elements in the set.
147 static_assert(N <= 32, "N should be small");
148
149public:
150 using size_type = size_t;
151 using const_iterator = SmallSetIterator<T, N, C>;
152
153 SmallSet() = default;
154
155 LLVM_NODISCARD bool empty() const {
156 return Vector.empty() && Set.empty();
157 }
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 true if the element is inserted (it was not in the set before).
175 /// The first value of the returned pair is unused and provided for
176 /// partial compatibility with the standard library self-associative container
177 /// concept.
178 // FIXME: Add iterators that abstract over the small and large form, and then
179 // return those here.
180 std::pair<NoneType, bool> insert(const T &V) {
181 if (!isSmall())
182 return std::make_pair(None, Set.insert(V).second);
183
184 VIterator I = vfind(V);
185 if (I != Vector.end()) // Don't reinsert if it already exists.
186 return std::make_pair(None, false);
187 if (Vector.size() < N) {
188 Vector.push_back(V);
189 return std::make_pair(None, true);
190 }
191
192 // Otherwise, grow from vector to set.
193 while (!Vector.empty()) {
194 Set.insert(Vector.back());
195 Vector.pop_back();
196 }
197 Set.insert(V);
198 return std::make_pair(None, true);
199 }
200
201 template <typename IterT>
202 void insert(IterT I, IterT E) {
203 for (; I != E; ++I)
204 insert(*I);
205 }
206
207 bool erase(const T &V) {
208 if (!isSmall())
209 return Set.erase(V);
210 for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
211 if (*I == V) {
212 Vector.erase(I);
213 return true;
214 }
215 return false;
216 }
217
218 void clear() {
219 Vector.clear();
220 Set.clear();
221 }
222
223 const_iterator begin() const {
224 if (isSmall())
225 return {Vector.begin()};
226 return {Set.begin()};
227 }
228
229 const_iterator end() const {
230 if (isSmall())
231 return {Vector.end()};
232 return {Set.end()};
233 }
234
235 /// Check if the SmallSet contains the given element.
236 bool contains(const T &V) const {
237 if (isSmall())
238 return vfind(V) != Vector.end();
239 return Set.find(V) != Set.end();
240 }
241
242private:
243 bool isSmall() const { return Set.empty(); }
244
245 VIterator vfind(const T &V) const {
246 for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
247 if (*I == V)
248 return I;
249 return Vector.end();
250 }
251};
252
253/// If this set is of pointer values, transparently switch over to using
254/// SmallPtrSet for performance.
255template <typename PointeeType, unsigned N>
256class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
257
258/// Equality comparison for SmallSet.
259///
260/// Iterates over elements of LHS confirming that each element is also a member
261/// of RHS, and that RHS contains no additional values.
262/// Equivalent to N calls to RHS.count.
263/// For small-set mode amortized complexity is O(N^2)
264/// For large-set mode amortized complexity is linear, worst case is O(N^2) (if
265/// every hash collides).
266template <typename T, unsigned LN, unsigned RN, typename C>
267bool operator==(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) {
268 if (LHS.size() != RHS.size())
269 return false;
270
271 // All elements in LHS must also be in RHS
272 return all_of(LHS, [&RHS](const T &E) { return RHS.count(E); });
273}
274
275/// Inequality comparison for SmallSet.
276///
277/// Equivalent to !(LHS == RHS). See operator== for performance notes.
278template <typename T, unsigned LN, unsigned RN, typename C>
279bool operator!=(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) {
280 return !(LHS == RHS);
281}
282
283} // end namespace llvm
284
285#endif // LLVM_ADT_SMALLSET_H
286