MapVector.h revision 353358
1//===- llvm/ADT/MapVector.h - Map w/ deterministic value order --*- 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 implements a map that provides insertion order iteration. The
10// interface is purposefully minimal. The key is assumed to be cheap to copy
11// and 2 copies are kept, one for indexing in a DenseMap, one for iteration in
12// a std::vector.
13//
14//===----------------------------------------------------------------------===//
15
16#ifndef LLVM_ADT_MAPVECTOR_H
17#define LLVM_ADT_MAPVECTOR_H
18
19#include "llvm/ADT/DenseMap.h"
20#include "llvm/ADT/SmallVector.h"
21#include <algorithm>
22#include <cassert>
23#include <cstddef>
24#include <iterator>
25#include <type_traits>
26#include <utility>
27#include <vector>
28
29namespace llvm {
30
31/// This class implements a map that also provides access to all stored values
32/// in a deterministic order. The values are kept in a std::vector and the
33/// mapping is done with DenseMap from Keys to indexes in that vector.
34template<typename KeyT, typename ValueT,
35         typename MapType = DenseMap<KeyT, unsigned>,
36         typename VectorType = std::vector<std::pair<KeyT, ValueT>>>
37class MapVector {
38  MapType Map;
39  VectorType Vector;
40
41  static_assert(
42      std::is_integral<typename MapType::mapped_type>::value,
43      "The mapped_type of the specified Map must be an integral type");
44
45public:
46  using value_type = typename VectorType::value_type;
47  using size_type = typename VectorType::size_type;
48
49  using iterator = typename VectorType::iterator;
50  using const_iterator = typename VectorType::const_iterator;
51  using reverse_iterator = typename VectorType::reverse_iterator;
52  using const_reverse_iterator = typename VectorType::const_reverse_iterator;
53
54  /// Clear the MapVector and return the underlying vector.
55  VectorType takeVector() {
56    Map.clear();
57    return std::move(Vector);
58  }
59
60  size_type size() const { return Vector.size(); }
61
62  /// Grow the MapVector so that it can contain at least \p NumEntries items
63  /// before resizing again.
64  void reserve(size_type NumEntries) {
65    Map.reserve(NumEntries);
66    Vector.reserve(NumEntries);
67  }
68
69  iterator begin() { return Vector.begin(); }
70  const_iterator begin() const { return Vector.begin(); }
71  iterator end() { return Vector.end(); }
72  const_iterator end() const { return Vector.end(); }
73
74  reverse_iterator rbegin() { return Vector.rbegin(); }
75  const_reverse_iterator rbegin() const { return Vector.rbegin(); }
76  reverse_iterator rend() { return Vector.rend(); }
77  const_reverse_iterator rend() const { return Vector.rend(); }
78
79  bool empty() const {
80    return Vector.empty();
81  }
82
83  std::pair<KeyT, ValueT>       &front()       { return Vector.front(); }
84  const std::pair<KeyT, ValueT> &front() const { return Vector.front(); }
85  std::pair<KeyT, ValueT>       &back()        { return Vector.back(); }
86  const std::pair<KeyT, ValueT> &back()  const { return Vector.back(); }
87
88  void clear() {
89    Map.clear();
90    Vector.clear();
91  }
92
93  void swap(MapVector &RHS) {
94    std::swap(Map, RHS.Map);
95    std::swap(Vector, RHS.Vector);
96  }
97
98  ValueT &operator[](const KeyT &Key) {
99    std::pair<KeyT, typename MapType::mapped_type> Pair = std::make_pair(Key, 0);
100    std::pair<typename MapType::iterator, bool> Result = Map.insert(Pair);
101    auto &I = Result.first->second;
102    if (Result.second) {
103      Vector.push_back(std::make_pair(Key, ValueT()));
104      I = Vector.size() - 1;
105    }
106    return Vector[I].second;
107  }
108
109  // Returns a copy of the value.  Only allowed if ValueT is copyable.
110  ValueT lookup(const KeyT &Key) const {
111    static_assert(std::is_copy_constructible<ValueT>::value,
112                  "Cannot call lookup() if ValueT is not copyable.");
113    typename MapType::const_iterator Pos = Map.find(Key);
114    return Pos == Map.end()? ValueT() : Vector[Pos->second].second;
115  }
116
117  std::pair<iterator, bool> insert(const std::pair<KeyT, ValueT> &KV) {
118    std::pair<KeyT, typename MapType::mapped_type> Pair = std::make_pair(KV.first, 0);
119    std::pair<typename MapType::iterator, bool> Result = Map.insert(Pair);
120    auto &I = Result.first->second;
121    if (Result.second) {
122      Vector.push_back(std::make_pair(KV.first, KV.second));
123      I = Vector.size() - 1;
124      return std::make_pair(std::prev(end()), true);
125    }
126    return std::make_pair(begin() + I, false);
127  }
128
129  std::pair<iterator, bool> insert(std::pair<KeyT, ValueT> &&KV) {
130    // Copy KV.first into the map, then move it into the vector.
131    std::pair<KeyT, typename MapType::mapped_type> Pair = std::make_pair(KV.first, 0);
132    std::pair<typename MapType::iterator, bool> Result = Map.insert(Pair);
133    auto &I = Result.first->second;
134    if (Result.second) {
135      Vector.push_back(std::move(KV));
136      I = Vector.size() - 1;
137      return std::make_pair(std::prev(end()), true);
138    }
139    return std::make_pair(begin() + I, false);
140  }
141
142  size_type count(const KeyT &Key) const {
143    typename MapType::const_iterator Pos = Map.find(Key);
144    return Pos == Map.end()? 0 : 1;
145  }
146
147  iterator find(const KeyT &Key) {
148    typename MapType::const_iterator Pos = Map.find(Key);
149    return Pos == Map.end()? Vector.end() :
150                            (Vector.begin() + Pos->second);
151  }
152
153  const_iterator find(const KeyT &Key) const {
154    typename MapType::const_iterator Pos = Map.find(Key);
155    return Pos == Map.end()? Vector.end() :
156                            (Vector.begin() + Pos->second);
157  }
158
159  /// Remove the last element from the vector.
160  void pop_back() {
161    typename MapType::iterator Pos = Map.find(Vector.back().first);
162    Map.erase(Pos);
163    Vector.pop_back();
164  }
165
166  /// Remove the element given by Iterator.
167  ///
168  /// Returns an iterator to the element following the one which was removed,
169  /// which may be end().
170  ///
171  /// \note This is a deceivingly expensive operation (linear time).  It's
172  /// usually better to use \a remove_if() if possible.
173  typename VectorType::iterator erase(typename VectorType::iterator Iterator) {
174    Map.erase(Iterator->first);
175    auto Next = Vector.erase(Iterator);
176    if (Next == Vector.end())
177      return Next;
178
179    // Update indices in the map.
180    size_t Index = Next - Vector.begin();
181    for (auto &I : Map) {
182      assert(I.second != Index && "Index was already erased!");
183      if (I.second > Index)
184        --I.second;
185    }
186    return Next;
187  }
188
189  /// Remove all elements with the key value Key.
190  ///
191  /// Returns the number of elements removed.
192  size_type erase(const KeyT &Key) {
193    auto Iterator = find(Key);
194    if (Iterator == end())
195      return 0;
196    erase(Iterator);
197    return 1;
198  }
199
200  /// Remove the elements that match the predicate.
201  ///
202  /// Erase all elements that match \c Pred in a single pass.  Takes linear
203  /// time.
204  template <class Predicate> void remove_if(Predicate Pred);
205};
206
207template <typename KeyT, typename ValueT, typename MapType, typename VectorType>
208template <class Function>
209void MapVector<KeyT, ValueT, MapType, VectorType>::remove_if(Function Pred) {
210  auto O = Vector.begin();
211  for (auto I = O, E = Vector.end(); I != E; ++I) {
212    if (Pred(*I)) {
213      // Erase from the map.
214      Map.erase(I->first);
215      continue;
216    }
217
218    if (I != O) {
219      // Move the value and update the index in the map.
220      *O = std::move(*I);
221      Map[O->first] = O - Vector.begin();
222    }
223    ++O;
224  }
225  // Erase trailing entries in the vector.
226  Vector.erase(O, Vector.end());
227}
228
229/// A MapVector that performs no allocations if smaller than a certain
230/// size.
231template <typename KeyT, typename ValueT, unsigned N>
232struct SmallMapVector
233    : MapVector<KeyT, ValueT, SmallDenseMap<KeyT, unsigned, N>,
234                SmallVector<std::pair<KeyT, ValueT>, N>> {
235};
236
237} // end namespace llvm
238
239#endif // LLVM_ADT_MAPVECTOR_H
240