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 
29 namespace 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.
34 template<typename KeyT, typename ValueT,
35          typename MapType = DenseMap<KeyT, unsigned>,
36          typename VectorType = std::vector<std::pair<KeyT, ValueT>>>
37 class 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 
45 public:
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.
takeVector()55   VectorType takeVector() {
56     Map.clear();
57     return std::move(Vector);
58   }
59 
size()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.
reserve(size_type NumEntries)64   void reserve(size_type NumEntries) {
65     Map.reserve(NumEntries);
66     Vector.reserve(NumEntries);
67   }
68 
begin()69   iterator begin() { return Vector.begin(); }
begin()70   const_iterator begin() const { return Vector.begin(); }
end()71   iterator end() { return Vector.end(); }
end()72   const_iterator end() const { return Vector.end(); }
73 
rbegin()74   reverse_iterator rbegin() { return Vector.rbegin(); }
rbegin()75   const_reverse_iterator rbegin() const { return Vector.rbegin(); }
rend()76   reverse_iterator rend() { return Vector.rend(); }
rend()77   const_reverse_iterator rend() const { return Vector.rend(); }
78 
empty()79   bool empty() const {
80     return Vector.empty();
81   }
82 
front()83   std::pair<KeyT, ValueT>       &front()       { return Vector.front(); }
front()84   const std::pair<KeyT, ValueT> &front() const { return Vector.front(); }
back()85   std::pair<KeyT, ValueT>       &back()        { return Vector.back(); }
back()86   const std::pair<KeyT, ValueT> &back()  const { return Vector.back(); }
87 
clear()88   void clear() {
89     Map.clear();
90     Vector.clear();
91   }
92 
swap(MapVector & RHS)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.
lookup(const KeyT & Key)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 
insert(const std::pair<KeyT,ValueT> & KV)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 
insert(std::pair<KeyT,ValueT> && KV)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 
count(const KeyT & Key)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 
find(const KeyT & Key)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 
find(const KeyT & Key)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.
pop_back()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.
erase(typename VectorType::iterator Iterator)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.
erase(const KeyT & Key)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 
207 template <typename KeyT, typename ValueT, typename MapType, typename VectorType>
208 template <class Function>
remove_if(Function Pred)209 void 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.
231 template <typename KeyT, typename ValueT, unsigned N>
232 struct 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