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 /// \file
10 /// This file implements a map that provides insertion order iteration. The
11 /// interface is purposefully minimal. The key is assumed to be cheap to copy
12 /// and 2 copies are kept, one for indexing in a DenseMap, one for iteration in
13 /// a SmallVector.
14 ///
15 //===----------------------------------------------------------------------===//
16 
17 #ifndef LLVM_ADT_MAPVECTOR_H
18 #define LLVM_ADT_MAPVECTOR_H
19 
20 #include "llvm/ADT/DenseMap.h"
21 #include "llvm/ADT/SmallVector.h"
22 #include <cassert>
23 #include <cstddef>
24 #include <iterator>
25 #include <type_traits>
26 #include <utility>
27 
28 namespace llvm {
29 
30 /// This class implements a map that also provides access to all stored values
31 /// in a deterministic order. The values are kept in a SmallVector<*, 0> and the
32 /// mapping is done with DenseMap from Keys to indexes in that vector.
33 template <typename KeyT, typename ValueT,
34           typename MapType = DenseMap<KeyT, unsigned>,
35           typename VectorType = SmallVector<std::pair<KeyT, ValueT>, 0>>
36 class MapVector {
37   MapType Map;
38   VectorType Vector;
39 
40   static_assert(
41       std::is_integral_v<typename MapType::mapped_type>,
42       "The mapped_type of the specified Map must be an integral type");
43 
44 public:
45   using key_type = KeyT;
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_v<ValueT>,
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   template <typename... Ts>
118   std::pair<iterator, bool> try_emplace(const KeyT &Key, Ts &&...Args) {
119     auto [It, Inserted] = Map.insert(std::make_pair(Key, 0));
120     if (Inserted) {
121       It->second = Vector.size();
122       Vector.emplace_back(std::piecewise_construct, std::forward_as_tuple(Key),
123                           std::forward_as_tuple(std::forward<Ts>(Args)...));
124       return std::make_pair(std::prev(end()), true);
125     }
126     return std::make_pair(begin() + It->second, false);
127   }
128   template <typename... Ts>
129   std::pair<iterator, bool> try_emplace(KeyT &&Key, Ts &&...Args) {
130     auto [It, Inserted] = Map.insert(std::make_pair(Key, 0));
131     if (Inserted) {
132       It->second = Vector.size();
133       Vector.emplace_back(std::piecewise_construct,
134                           std::forward_as_tuple(std::move(Key)),
135                           std::forward_as_tuple(std::forward<Ts>(Args)...));
136       return std::make_pair(std::prev(end()), true);
137     }
138     return std::make_pair(begin() + It->second, false);
139   }
140 
141   std::pair<iterator, bool> insert(const std::pair<KeyT, ValueT> &KV) {
142     return try_emplace(KV.first, KV.second);
143   }
144   std::pair<iterator, bool> insert(std::pair<KeyT, ValueT> &&KV) {
145     return try_emplace(std::move(KV.first), std::move(KV.second));
146   }
147 
148   template <typename V>
149   std::pair<iterator, bool> insert_or_assign(const KeyT &Key, V &&Val) {
150     auto Ret = try_emplace(Key, std::forward<V>(Val));
151     if (!Ret.second)
152       Ret.first->second = std::forward<V>(Val);
153     return Ret;
154   }
155   template <typename V>
156   std::pair<iterator, bool> insert_or_assign(KeyT &&Key, V &&Val) {
157     auto Ret = try_emplace(std::move(Key), std::forward<V>(Val));
158     if (!Ret.second)
159       Ret.first->second = std::forward<V>(Val);
160     return Ret;
161   }
162 
163   bool contains(const KeyT &Key) const { return Map.find(Key) != Map.end(); }
164 
165   size_type count(const KeyT &Key) const { return contains(Key) ? 1 : 0; }
166 
167   iterator find(const KeyT &Key) {
168     typename MapType::const_iterator Pos = Map.find(Key);
169     return Pos == Map.end()? Vector.end() :
170                             (Vector.begin() + Pos->second);
171   }
172 
173   const_iterator find(const KeyT &Key) const {
174     typename MapType::const_iterator Pos = Map.find(Key);
175     return Pos == Map.end()? Vector.end() :
176                             (Vector.begin() + Pos->second);
177   }
178 
179   /// Remove the last element from the vector.
180   void pop_back() {
181     typename MapType::iterator Pos = Map.find(Vector.back().first);
182     Map.erase(Pos);
183     Vector.pop_back();
184   }
185 
186   /// Remove the element given by Iterator.
187   ///
188   /// Returns an iterator to the element following the one which was removed,
189   /// which may be end().
190   ///
191   /// \note This is a deceivingly expensive operation (linear time).  It's
192   /// usually better to use \a remove_if() if possible.
193   typename VectorType::iterator erase(typename VectorType::iterator Iterator) {
194     Map.erase(Iterator->first);
195     auto Next = Vector.erase(Iterator);
196     if (Next == Vector.end())
197       return Next;
198 
199     // Update indices in the map.
200     size_t Index = Next - Vector.begin();
201     for (auto &I : Map) {
202       assert(I.second != Index && "Index was already erased!");
203       if (I.second > Index)
204         --I.second;
205     }
206     return Next;
207   }
208 
209   /// Remove all elements with the key value Key.
210   ///
211   /// Returns the number of elements removed.
212   size_type erase(const KeyT &Key) {
213     auto Iterator = find(Key);
214     if (Iterator == end())
215       return 0;
216     erase(Iterator);
217     return 1;
218   }
219 
220   /// Remove the elements that match the predicate.
221   ///
222   /// Erase all elements that match \c Pred in a single pass.  Takes linear
223   /// time.
224   template <class Predicate> void remove_if(Predicate Pred);
225 };
226 
227 template <typename KeyT, typename ValueT, typename MapType, typename VectorType>
228 template <class Function>
229 void MapVector<KeyT, ValueT, MapType, VectorType>::remove_if(Function Pred) {
230   auto O = Vector.begin();
231   for (auto I = O, E = Vector.end(); I != E; ++I) {
232     if (Pred(*I)) {
233       // Erase from the map.
234       Map.erase(I->first);
235       continue;
236     }
237 
238     if (I != O) {
239       // Move the value and update the index in the map.
240       *O = std::move(*I);
241       Map[O->first] = O - Vector.begin();
242     }
243     ++O;
244   }
245   // Erase trailing entries in the vector.
246   Vector.erase(O, Vector.end());
247 }
248 
249 /// A MapVector that performs no allocations if smaller than a certain
250 /// size.
251 template <typename KeyT, typename ValueT, unsigned N>
252 struct SmallMapVector
253     : MapVector<KeyT, ValueT, SmallDenseMap<KeyT, unsigned, N>,
254                 SmallVector<std::pair<KeyT, ValueT>, N>> {
255 };
256 
257 } // end namespace llvm
258 
259 #endif // LLVM_ADT_MAPVECTOR_H
260