//===- ScopedHashTable.h - A simple scoped hash table -----------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This file implements an efficient scoped hash table, which is useful for

// things like dominator-based optimizations.  This allows clients to do things

// like this:

//

//  ScopedHashTable<int, int> HT;

//  {

//    ScopedHashTableScope<int, int> Scope1(HT);

//    HT.insert(0, 0);

//    HT.insert(1, 1);

//    {

//      ScopedHashTableScope<int, int> Scope2(HT);

//      HT.insert(0, 42);

//    }

//  }

//

// Looking up the value for "0" in the Scope2 block will return 42.  Looking

// up the value for 0 before 42 is inserted or after Scope2 is popped will

// return 0.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_SCOPEDHASHTABLE_H

#define LLVM_ADT_SCOPEDHASHTABLE_H

#include "llvm/ADT/DenseMap.h"

#include "llvm/ADT/DenseMapInfo.h"

#include "llvm/Support/AllocatorBase.h"

#include <cassert>

#include <new>

namespace llvm {

template <typename K, typename V, typename KInfo = DenseMapInfo<K>,

          typename AllocatorTy = MallocAllocator>

class ScopedHashTable;

template <typename K, typename V>

class ScopedHashTableVal {

  ScopedHashTableVal *NextInScope;

  ScopedHashTableVal *NextForKey;

  K Key;

  V Val;

  ScopedHashTableVal(const K &key, const V &val) : Key(key), Val(val) {}

public:

  const K &getKey() const { return Key; }

  const V &getValue() const { return Val; }

  V &getValue() { return Val; }

  ScopedHashTableVal *getNextForKey() { return NextForKey; }

  const ScopedHashTableVal *getNextForKey() const { return NextForKey; }

  ScopedHashTableVal *getNextInScope() { return NextInScope; }

  template <typename AllocatorTy>

  static ScopedHashTableVal *Create(ScopedHashTableVal *nextInScope,

                                    ScopedHashTableVal *nextForKey,

                                    const K &key, const V &val,

                                    AllocatorTy &Allocator) {

    ScopedHashTableVal *New = Allocator.template Allocate<ScopedHashTableVal>();

    // Set up the value.

    new (New) ScopedHashTableVal(key, val);

    New->NextInScope = nextInScope;

    New->NextForKey = nextForKey;

    return New;

  }

  template <typename AllocatorTy> void Destroy(AllocatorTy &Allocator) {

    // Free memory referenced by the item.

    this->~ScopedHashTableVal();

    Allocator.Deallocate(this);

  }

};

template <typename K, typename V, typename KInfo = DenseMapInfo<K>,

          typename AllocatorTy = MallocAllocator>

class ScopedHashTableScope {

  /// HT - The hashtable that we are active for.

  ScopedHashTable<K, V, KInfo, AllocatorTy> &HT;

  /// PrevScope - This is the scope that we are shadowing in HT.

  ScopedHashTableScope *PrevScope;

  /// LastValInScope - This is the last value that was inserted for this scope

  /// or null if none have been inserted yet.

  ScopedHashTableVal<K, V> *LastValInScope;

public:

  ScopedHashTableScope(ScopedHashTable<K, V, KInfo, AllocatorTy> &HT);

  ScopedHashTableScope(ScopedHashTableScope &) = delete;

  ScopedHashTableScope &operator=(ScopedHashTableScope &) = delete;

  ~ScopedHashTableScope();

  ScopedHashTableScope *getParentScope() { return PrevScope; }

  const ScopedHashTableScope *getParentScope() const { return PrevScope; }

private:

  friend class ScopedHashTable<K, V, KInfo, AllocatorTy>;

  ScopedHashTableVal<K, V> *getLastValInScope() {

    return LastValInScope;

  }

  void setLastValInScope(ScopedHashTableVal<K, V> *Val) {

    LastValInScope = Val;

  }

};

template <typename K, typename V, typename KInfo = DenseMapInfo<K>>

class ScopedHashTableIterator {

  ScopedHashTableVal<K, V> *Node;

public:

  ScopedHashTableIterator(ScopedHashTableVal<K, V> *node) : Node(node) {}

  V &operator*() const {

    assert(Node && "Dereference end()");

    return Node->getValue();

  }

  V *operator->() const {

    return &Node->getValue();

  }

  bool operator==(const ScopedHashTableIterator &RHS) const {

    return Node == RHS.Node;

  }

  bool operator!=(const ScopedHashTableIterator &RHS) const {

    return Node != RHS.Node;

  }

  inline ScopedHashTableIterator& operator++() {          // Preincrement

    assert(Node && "incrementing past end()");

    Node = Node->getNextForKey();

    return *this;

  }

  ScopedHashTableIterator operator++(int) {        // Postincrement

    ScopedHashTableIterator tmp = *this; ++*this; return tmp;

  }

};

template <typename K, typename V, typename KInfo, typename AllocatorTy>

class ScopedHashTable {

public:

  /// ScopeTy - This is a helpful typedef that allows clients to get easy access

  /// to the name of the scope for this hash table.

  using ScopeTy = ScopedHashTableScope<K, V, KInfo, AllocatorTy>;

  using size_type = unsigned;

private:

  friend class ScopedHashTableScope<K, V, KInfo, AllocatorTy>;

  using ValTy = ScopedHashTableVal<K, V>;

  DenseMap<K, ValTy*, KInfo> TopLevelMap;

  ScopeTy *CurScope = nullptr;

  AllocatorTy Allocator;

public:

  ScopedHashTable() = default;

  ScopedHashTable(AllocatorTy A) : Allocator(A) {}

  ScopedHashTable(const ScopedHashTable &) = delete;

  ScopedHashTable &operator=(const ScopedHashTable &) = delete;

  ~ScopedHashTable() {

    assert(!CurScope && TopLevelMap.empty() && "Scope imbalance!");

  }

  /// Access to the allocator.

  AllocatorTy &getAllocator() { return Allocator; }

  const AllocatorTy &getAllocator() const { return Allocator; }

  /// Return 1 if the specified key is in the table, 0 otherwise.

  size_type count(const K &Key) const {

    return TopLevelMap.count(Key);

  }

  V lookup(const K &Key) const {

    auto I = TopLevelMap.find(Key);

    if (I != TopLevelMap.end())

      return I->second->getValue();

    return V();

  }

  void insert(const K &Key, const V &Val) {

    insertIntoScope(CurScope, Key, Val);

  }

  using iterator = ScopedHashTableIterator<K, V, KInfo>;

  iterator end() { return iterator(0); }

  iterator begin(const K &Key) {

    typename DenseMap<K, ValTy*, KInfo>::iterator I =

      TopLevelMap.find(Key);

    if (I == TopLevelMap.end()) return end();

    return iterator(I->second);

  }

  ScopeTy *getCurScope() { return CurScope; }

  const ScopeTy *getCurScope() const { return CurScope; }

  /// insertIntoScope - This inserts the specified key/value at the specified

  /// (possibly not the current) scope.  While it is ok to insert into a scope

  /// that isn't the current one, it isn't ok to insert *underneath* an existing

  /// value of the specified key.

  void insertIntoScope(ScopeTy *S, const K &Key, const V &Val) {

    assert(S && "No scope active!");

    ScopedHashTableVal<K, V> *&KeyEntry = TopLevelMap[Key];

    KeyEntry = ValTy::Create(S->getLastValInScope(), KeyEntry, Key, Val,

                             Allocator);

    S->setLastValInScope(KeyEntry);

  }

};

/// ScopedHashTableScope ctor - Install this as the current scope for the hash

/// table.

template <typename K, typename V, typename KInfo, typename Allocator>

ScopedHashTableScope<K, V, KInfo, Allocator>::

  ScopedHashTableScope(ScopedHashTable<K, V, KInfo, Allocator> &ht) : HT(ht) {

  PrevScope = HT.CurScope;

  HT.CurScope = this;

  LastValInScope = nullptr;

}

template <typename K, typename V, typename KInfo, typename Allocator>

ScopedHashTableScope<K, V, KInfo, Allocator>::~ScopedHashTableScope() {

  assert(HT.CurScope == this && "Scope imbalance!");

  HT.CurScope = PrevScope;

  // Pop and delete all values corresponding to this scope.

  while (ScopedHashTableVal<K, V> *ThisEntry = LastValInScope) {

    // Pop this value out of the TopLevelMap.

    if (!ThisEntry->getNextForKey()) {

      assert(HT.TopLevelMap[ThisEntry->getKey()] == ThisEntry &&

             "Scope imbalance!");

      HT.TopLevelMap.erase(ThisEntry->getKey());

    } else {

      ScopedHashTableVal<K, V> *&KeyEntry = HT.TopLevelMap[ThisEntry->getKey()];

      assert(KeyEntry == ThisEntry && "Scope imbalance!");

      KeyEntry = ThisEntry->getNextForKey();

    }

    // Pop this value out of the scope.

    LastValInScope = ThisEntry->getNextInScope();

    // Delete this entry.

    ThisEntry->Destroy(HT.getAllocator());

  }

}

} // end namespace llvm

#endif // LLVM_ADT_SCOPEDHASHTABLE_H