ScopedHashTable.h revision 360660 
1//===- ScopedHashTable.h - A simple scoped hash table -----------*- 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 an efficient scoped hash table, which is useful for
10// things like dominator-based optimizations.  This allows clients to do things
11// like this:
12//
13//  ScopedHashTable<int, int> HT;
14//  {
15//    ScopedHashTableScope<int, int> Scope1(HT);
16//    HT.insert(0, 0);
17//    HT.insert(1, 1);
18//    {
19//      ScopedHashTableScope<int, int> Scope2(HT);
20//      HT.insert(0, 42);
21//    }
22//  }
23//
24// Looking up the value for "0" in the Scope2 block will return 42.  Looking
25// up the value for 0 before 42 is inserted or after Scope2 is popped will
26// return 0.
27//
28//===----------------------------------------------------------------------===//
29
30#ifndef LLVM_ADT_SCOPEDHASHTABLE_H
31#define LLVM_ADT_SCOPEDHASHTABLE_H
32
33#include "llvm/ADT/DenseMap.h"
34#include "llvm/ADT/DenseMapInfo.h"
35#include "llvm/Support/Allocator.h"
36#include <cassert>
37#include <new>
38
39namespace llvm {
40
41template <typename K, typename V, typename KInfo = DenseMapInfo<K>,
42          typename AllocatorTy = MallocAllocator>
43class ScopedHashTable;
44
45template <typename K, typename V>
46class ScopedHashTableVal {
47  ScopedHashTableVal *NextInScope;
48  ScopedHashTableVal *NextForKey;
49  K Key;
50  V Val;
51
52  ScopedHashTableVal(const K &key, const V &val) : Key(key), Val(val) {}
53
54public:
55  const K &getKey() const { return Key; }
56  const V &getValue() const { return Val; }
57  V &getValue() { return Val; }
58
59  ScopedHashTableVal *getNextForKey() { return NextForKey; }
60  const ScopedHashTableVal *getNextForKey() const { return NextForKey; }
61  ScopedHashTableVal *getNextInScope() { return NextInScope; }
62
63  template <typename AllocatorTy>
64  static ScopedHashTableVal *Create(ScopedHashTableVal *nextInScope,
65                                    ScopedHashTableVal *nextForKey,
66                                    const K &key, const V &val,
67                                    AllocatorTy &Allocator) {
68    ScopedHashTableVal *New = Allocator.template Allocate<ScopedHashTableVal>();
69    // Set up the value.
70    new (New) ScopedHashTableVal(key, val);
71    New->NextInScope = nextInScope;
72    New->NextForKey = nextForKey;
73    return New;
74  }
75
76  template <typename AllocatorTy> void Destroy(AllocatorTy &Allocator) {
77    // Free memory referenced by the item.
78    this->~ScopedHashTableVal();
79    Allocator.Deallocate(this);
80  }
81};
82
83template <typename K, typename V, typename KInfo = DenseMapInfo<K>,
84          typename AllocatorTy = MallocAllocator>
85class ScopedHashTableScope {
86  /// HT - The hashtable that we are active for.
87  ScopedHashTable<K, V, KInfo, AllocatorTy> &HT;
88
89  /// PrevScope - This is the scope that we are shadowing in HT.
90  ScopedHashTableScope *PrevScope;
91
92  /// LastValInScope - This is the last value that was inserted for this scope
93  /// or null if none have been inserted yet.
94  ScopedHashTableVal<K, V> *LastValInScope;
95
96public:
97  ScopedHashTableScope(ScopedHashTable<K, V, KInfo, AllocatorTy> &HT);
98  ScopedHashTableScope(ScopedHashTableScope &) = delete;
99  ScopedHashTableScope &operator=(ScopedHashTableScope &) = delete;
100  ~ScopedHashTableScope();
101
102  ScopedHashTableScope *getParentScope() { return PrevScope; }
103  const ScopedHashTableScope *getParentScope() const { return PrevScope; }
104
105private:
106  friend class ScopedHashTable<K, V, KInfo, AllocatorTy>;
107
108  ScopedHashTableVal<K, V> *getLastValInScope() {
109    return LastValInScope;
110  }
111
112  void setLastValInScope(ScopedHashTableVal<K, V> *Val) {
113    LastValInScope = Val;
114  }
115};
116
117template <typename K, typename V, typename KInfo = DenseMapInfo<K>>
118class ScopedHashTableIterator {
119  ScopedHashTableVal<K, V> *Node;
120
121public:
122  ScopedHashTableIterator(ScopedHashTableVal<K, V> *node) : Node(node) {}
123
124  V &operator*() const {
125    assert(Node && "Dereference end()");
126    return Node->getValue();
127  }
128  V *operator->() const {
129    return &Node->getValue();
130  }
131
132  bool operator==(const ScopedHashTableIterator &RHS) const {
133    return Node == RHS.Node;
134  }
135  bool operator!=(const ScopedHashTableIterator &RHS) const {
136    return Node != RHS.Node;
137  }
138
139  inline ScopedHashTableIterator& operator++() {          // Preincrement
140    assert(Node && "incrementing past end()");
141    Node = Node->getNextForKey();
142    return *this;
143  }
144  ScopedHashTableIterator operator++(int) {        // Postincrement
145    ScopedHashTableIterator tmp = *this; ++*this; return tmp;
146  }
147};
148
149template <typename K, typename V, typename KInfo, typename AllocatorTy>
150class ScopedHashTable {
151public:
152  /// ScopeTy - This is a helpful typedef that allows clients to get easy access
153  /// to the name of the scope for this hash table.
154  using ScopeTy = ScopedHashTableScope<K, V, KInfo, AllocatorTy>;
155  using size_type = unsigned;
156
157private:
158  friend class ScopedHashTableScope<K, V, KInfo, AllocatorTy>;
159
160  using ValTy = ScopedHashTableVal<K, V>;
161
162  DenseMap<K, ValTy*, KInfo> TopLevelMap;
163  ScopeTy *CurScope = nullptr;
164
165  AllocatorTy Allocator;
166
167public:
168  ScopedHashTable() = default;
169  ScopedHashTable(AllocatorTy A) : Allocator(A) {}
170  ScopedHashTable(const ScopedHashTable &) = delete;
171  ScopedHashTable &operator=(const ScopedHashTable &) = delete;
172
173  ~ScopedHashTable() {
174    assert(!CurScope && TopLevelMap.empty() && "Scope imbalance!");
175  }
176
177  /// Access to the allocator.
178  AllocatorTy &getAllocator() { return Allocator; }
179  const AllocatorTy &getAllocator() const { return Allocator; }
180
181  /// Return 1 if the specified key is in the table, 0 otherwise.
182  size_type count(const K &Key) const {
183    return TopLevelMap.count(Key);
184  }
185
186  V lookup(const K &Key) const {
187    auto I = TopLevelMap.find(Key);
188    if (I != TopLevelMap.end())
189      return I->second->getValue();
190
191    return V();
192  }
193
194  void insert(const K &Key, const V &Val) {
195    insertIntoScope(CurScope, Key, Val);
196  }
197
198  using iterator = ScopedHashTableIterator<K, V, KInfo>;
199
200  iterator end() { return iterator(0); }
201
202  iterator begin(const K &Key) {
203    typename DenseMap<K, ValTy*, KInfo>::iterator I =
204      TopLevelMap.find(Key);
205    if (I == TopLevelMap.end()) return end();
206    return iterator(I->second);
207  }
208
209  ScopeTy *getCurScope() { return CurScope; }
210  const ScopeTy *getCurScope() const { return CurScope; }
211
212  /// insertIntoScope - This inserts the specified key/value at the specified
213  /// (possibly not the current) scope.  While it is ok to insert into a scope
214  /// that isn't the current one, it isn't ok to insert *underneath* an existing
215  /// value of the specified key.
216  void insertIntoScope(ScopeTy *S, const K &Key, const V &Val) {
217    assert(S && "No scope active!");
218    ScopedHashTableVal<K, V> *&KeyEntry = TopLevelMap[Key];
219    KeyEntry = ValTy::Create(S->getLastValInScope(), KeyEntry, Key, Val,
220                             Allocator);
221    S->setLastValInScope(KeyEntry);
222  }
223};
224
225/// ScopedHashTableScope ctor - Install this as the current scope for the hash
226/// table.
227template <typename K, typename V, typename KInfo, typename Allocator>
228ScopedHashTableScope<K, V, KInfo, Allocator>::
229  ScopedHashTableScope(ScopedHashTable<K, V, KInfo, Allocator> &ht) : HT(ht) {
230  PrevScope = HT.CurScope;
231  HT.CurScope = this;
232  LastValInScope = nullptr;
233}
234
235template <typename K, typename V, typename KInfo, typename Allocator>
236ScopedHashTableScope<K, V, KInfo, Allocator>::~ScopedHashTableScope() {
237  assert(HT.CurScope == this && "Scope imbalance!");
238  HT.CurScope = PrevScope;
239
240  // Pop and delete all values corresponding to this scope.
241  while (ScopedHashTableVal<K, V> *ThisEntry = LastValInScope) {
242    // Pop this value out of the TopLevelMap.
243    if (!ThisEntry->getNextForKey()) {
244      assert(HT.TopLevelMap[ThisEntry->getKey()] == ThisEntry &&
245             "Scope imbalance!");
246      HT.TopLevelMap.erase(ThisEntry->getKey());
247    } else {
248      ScopedHashTableVal<K, V> *&KeyEntry = HT.TopLevelMap[ThisEntry->getKey()];
249      assert(KeyEntry == ThisEntry && "Scope imbalance!");
250      KeyEntry = ThisEntry->getNextForKey();
251    }
252
253    // Pop this value out of the scope.
254    LastValInScope = ThisEntry->getNextInScope();
255
256    // Delete this entry.
257    ThisEntry->Destroy(HT.getAllocator());
258  }
259}
260
261} // end namespace llvm
262
263#endif // LLVM_ADT_SCOPEDHASHTABLE_H
264