include/llvm/ADT/ScopedHashTable.h

   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
  39 namespace llvm {
  40
  41 template <typename K, typename V, typename KInfo = DenseMapInfo<K>,
  42           typename AllocatorTy = MallocAllocator>
  43 class ScopedHashTable;
  44
  45 template <typename K, typename V>
  46 class 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
  54 public:
  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
  83 template <typename K, typename V, typename KInfo = DenseMapInfo<K>,
  84           typename AllocatorTy = MallocAllocator>
  85 class 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
  96 public:
  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
 105 private:
 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
 117 template <typename K, typename V, typename KInfo = DenseMapInfo<K>>
 118 class ScopedHashTableIterator {
 119   ScopedHashTableVal<K, V> *Node;
 120
 121 public:
 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
 149 template <typename K, typename V, typename KInfo, typename AllocatorTy>
 150 class ScopedHashTable {
 151 public:
 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
 157 private:
 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
 167 public:
 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.
 227 template <typename K, typename V, typename KInfo, typename Allocator>
 228 ScopedHashTableScope<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
 235 template <typename K, typename V, typename KInfo, typename Allocator>
 236 ScopedHashTableScope<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