llvm/ADT/ScopedHashTable.h

0001 //===- ScopedHashTable.h - A simple scoped hash table -----------*- C++ -*-===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008 //
0009 // This file implements an efficient scoped hash table, which is useful for
0010 // things like dominator-based optimizations.  This allows clients to do things
0011 // like this:
0012 //
0013 //  ScopedHashTable<int, int> HT;
0014 //  {
0015 //    ScopedHashTableScope<int, int> Scope1(HT);
0016 //    HT.insert(0, 0);
0017 //    HT.insert(1, 1);
0018 //    {
0019 //      ScopedHashTableScope<int, int> Scope2(HT);
0020 //      HT.insert(0, 42);
0021 //    }
0022 //  }
0023 //
0024 // Looking up the value for "0" in the Scope2 block will return 42.  Looking
0025 // up the value for 0 before 42 is inserted or after Scope2 is popped will
0026 // return 0.
0027 //
0028 //===----------------------------------------------------------------------===//
0029
0030 #ifndef LLVM_ADT_SCOPEDHASHTABLE_H
0031 #define LLVM_ADT_SCOPEDHASHTABLE_H
0032
0033 #include "llvm/ADT/DenseMap.h"
0034 #include "llvm/ADT/DenseMapInfo.h"
0035 #include "llvm/Support/AllocatorBase.h"
0036 #include <cassert>
0037 #include <new>
0038
0039 namespace llvm {
0040
0041 template <typename K, typename V, typename KInfo = DenseMapInfo<K>,
0042           typename AllocatorTy = MallocAllocator>
0043 class ScopedHashTable;
0044
0045 template <typename K, typename V>
0046 class ScopedHashTableVal {
0047   ScopedHashTableVal *NextInScope;
0048   ScopedHashTableVal *NextForKey;
0049   K Key;
0050   V Val;
0051
0052   ScopedHashTableVal(const K &key, const V &val) : Key(key), Val(val) {}
0053
0054 public:
0055   const K &getKey() const { return Key; }
0056   const V &getValue() const { return Val; }
0057   V &getValue() { return Val; }
0058
0059   ScopedHashTableVal *getNextForKey() { return NextForKey; }
0060   const ScopedHashTableVal *getNextForKey() const { return NextForKey; }
0061   ScopedHashTableVal *getNextInScope() { return NextInScope; }
0062
0063   template <typename AllocatorTy>
0064   static ScopedHashTableVal *Create(ScopedHashTableVal *nextInScope,
0065                                     ScopedHashTableVal *nextForKey,
0066                                     const K &key, const V &val,
0067                                     AllocatorTy &Allocator) {
0068     ScopedHashTableVal *New = Allocator.template Allocate<ScopedHashTableVal>();
0069     // Set up the value.
0070     new (New) ScopedHashTableVal(key, val);
0071     New->NextInScope = nextInScope;
0072     New->NextForKey = nextForKey;
0073     return New;
0074   }
0075
0076   template <typename AllocatorTy> void Destroy(AllocatorTy &Allocator) {
0077     // Free memory referenced by the item.
0078     this->~ScopedHashTableVal();
0079     Allocator.Deallocate(this);
0080   }
0081 };
0082
0083 template <typename K, typename V, typename KInfo = DenseMapInfo<K>,
0084           typename AllocatorTy = MallocAllocator>
0085 class ScopedHashTableScope {
0086   /// HT - The hashtable that we are active for.
0087   ScopedHashTable<K, V, KInfo, AllocatorTy> &HT;
0088
0089   /// PrevScope - This is the scope that we are shadowing in HT.
0090   ScopedHashTableScope *PrevScope;
0091
0092   /// LastValInScope - This is the last value that was inserted for this scope
0093   /// or null if none have been inserted yet.
0094   ScopedHashTableVal<K, V> *LastValInScope;
0095
0096 public:
0097   ScopedHashTableScope(ScopedHashTable<K, V, KInfo, AllocatorTy> &HT);
0098   ScopedHashTableScope(ScopedHashTableScope &) = delete;
0099   ScopedHashTableScope &operator=(ScopedHashTableScope &) = delete;
0100   ~ScopedHashTableScope();
0101
0102   ScopedHashTableScope *getParentScope() { return PrevScope; }
0103   const ScopedHashTableScope *getParentScope() const { return PrevScope; }
0104
0105 private:
0106   friend class ScopedHashTable<K, V, KInfo, AllocatorTy>;
0107
0108   ScopedHashTableVal<K, V> *getLastValInScope() {
0109     return LastValInScope;
0110   }
0111
0112   void setLastValInScope(ScopedHashTableVal<K, V> *Val) {
0113     LastValInScope = Val;
0114   }
0115 };
0116
0117 template <typename K, typename V, typename KInfo = DenseMapInfo<K>>
0118 class ScopedHashTableIterator {
0119   ScopedHashTableVal<K, V> *Node;
0120
0121 public:
0122   ScopedHashTableIterator(ScopedHashTableVal<K, V> *node) : Node(node) {}
0123
0124   V &operator*() const {
0125     assert(Node && "Dereference end()");
0126     return Node->getValue();
0127   }
0128   V *operator->() const {
0129     return &Node->getValue();
0130   }
0131
0132   bool operator==(const ScopedHashTableIterator &RHS) const {
0133     return Node == RHS.Node;
0134   }
0135   bool operator!=(const ScopedHashTableIterator &RHS) const {
0136     return Node != RHS.Node;
0137   }
0138
0139   inline ScopedHashTableIterator& operator++() {          // Preincrement
0140     assert(Node && "incrementing past end()");
0141     Node = Node->getNextForKey();
0142     return *this;
0143   }
0144   ScopedHashTableIterator operator++(int) {        // Postincrement
0145     ScopedHashTableIterator tmp = *this; ++*this; return tmp;
0146   }
0147 };
0148
0149 template <typename K, typename V, typename KInfo, typename AllocatorTy>
0150 class ScopedHashTable : detail::AllocatorHolder<AllocatorTy> {
0151   using AllocTy = detail::AllocatorHolder<AllocatorTy>;
0152
0153 public:
0154   /// ScopeTy - This is a helpful typedef that allows clients to get easy access
0155   /// to the name of the scope for this hash table.
0156   using ScopeTy = ScopedHashTableScope<K, V, KInfo, AllocatorTy>;
0157   using size_type = unsigned;
0158
0159 private:
0160   friend class ScopedHashTableScope<K, V, KInfo, AllocatorTy>;
0161
0162   using ValTy = ScopedHashTableVal<K, V>;
0163
0164   DenseMap<K, ValTy*, KInfo> TopLevelMap;
0165   ScopeTy *CurScope = nullptr;
0166
0167 public:
0168   ScopedHashTable() = default;
0169   ScopedHashTable(AllocatorTy A) : AllocTy(A) {}
0170   ScopedHashTable(const ScopedHashTable &) = delete;
0171   ScopedHashTable &operator=(const ScopedHashTable &) = delete;
0172
0173   ~ScopedHashTable() {
0174     assert(!CurScope && TopLevelMap.empty() && "Scope imbalance!");
0175   }
0176
0177   /// Access to the allocator.
0178   using AllocTy::getAllocator;
0179
0180   /// Return 1 if the specified key is in the table, 0 otherwise.
0181   size_type count(const K &Key) const {
0182     return TopLevelMap.count(Key);
0183   }
0184
0185   V lookup(const K &Key) const {
0186     auto I = TopLevelMap.find(Key);
0187     if (I != TopLevelMap.end())
0188       return I->second->getValue();
0189
0190     return V();
0191   }
0192
0193   void insert(const K &Key, const V &Val) {
0194     insertIntoScope(CurScope, Key, Val);
0195   }
0196
0197   using iterator = ScopedHashTableIterator<K, V, KInfo>;
0198
0199   iterator end() { return iterator(nullptr); }
0200
0201   iterator begin(const K &Key) {
0202     typename DenseMap<K, ValTy*, KInfo>::iterator I =
0203       TopLevelMap.find(Key);
0204     if (I == TopLevelMap.end()) return end();
0205     return iterator(I->second);
0206   }
0207
0208   ScopeTy *getCurScope() { return CurScope; }
0209   const ScopeTy *getCurScope() const { return CurScope; }
0210
0211   /// insertIntoScope - This inserts the specified key/value at the specified
0212   /// (possibly not the current) scope.  While it is ok to insert into a scope
0213   /// that isn't the current one, it isn't ok to insert *underneath* an existing
0214   /// value of the specified key.
0215   void insertIntoScope(ScopeTy *S, const K &Key, const V &Val) {
0216     assert(S && "No scope active!");
0217     ScopedHashTableVal<K, V> *&KeyEntry = TopLevelMap[Key];
0218     KeyEntry = ValTy::Create(S->getLastValInScope(), KeyEntry, Key, Val,
0219                              getAllocator());
0220     S->setLastValInScope(KeyEntry);
0221   }
0222 };
0223
0224 /// ScopedHashTableScope ctor - Install this as the current scope for the hash
0225 /// table.
0226 template <typename K, typename V, typename KInfo, typename Allocator>
0227 ScopedHashTableScope<K, V, KInfo, Allocator>::
0228   ScopedHashTableScope(ScopedHashTable<K, V, KInfo, Allocator> &ht) : HT(ht) {
0229   PrevScope = HT.CurScope;
0230   HT.CurScope = this;
0231   LastValInScope = nullptr;
0232 }
0233
0234 template <typename K, typename V, typename KInfo, typename Allocator>
0235 ScopedHashTableScope<K, V, KInfo, Allocator>::~ScopedHashTableScope() {
0236   assert(HT.CurScope == this && "Scope imbalance!");
0237   HT.CurScope = PrevScope;
0238
0239   // Pop and delete all values corresponding to this scope.
0240   while (ScopedHashTableVal<K, V> *ThisEntry = LastValInScope) {
0241     // Pop this value out of the TopLevelMap.
0242     if (!ThisEntry->getNextForKey()) {
0243       assert(HT.TopLevelMap[ThisEntry->getKey()] == ThisEntry &&
0244              "Scope imbalance!");
0245       HT.TopLevelMap.erase(ThisEntry->getKey());
0246     } else {
0247       ScopedHashTableVal<K, V> *&KeyEntry = HT.TopLevelMap[ThisEntry->getKey()];
0248       assert(KeyEntry == ThisEntry && "Scope imbalance!");
0249       KeyEntry = ThisEntry->getNextForKey();
0250     }
0251
0252     // Pop this value out of the scope.
0253     LastValInScope = ThisEntry->getNextInScope();
0254
0255     // Delete this entry.
0256     ThisEntry->Destroy(HT.getAllocator());
0257   }
0258 }
0259
0260 } // end namespace llvm
0261
0262 #endif // LLVM_ADT_SCOPEDHASHTABLE_H