Add a simple, but efficient, generic scoped hash table

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52112 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/ScopedHashTable.h

@@ -0,0 +1,193 @@
+//===- ScopedHashTable.h - A simple scoped hash table ---------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// 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 <cassert>
+#include "llvm/ADT/DenseMap.h"
+
+namespace llvm {
+
+template <typename K, typename V>
+class ScopedHashTable;
+
+template <typename K, typename V>
+class ScopedHashTableVal {
+  ScopedHashTableVal *NextInScope;
+  ScopedHashTableVal *NextForKey;
+  K Key;
+  V Val;
+public:
+  ScopedHashTableVal(ScopedHashTableVal *nextInScope, 
+                     ScopedHashTableVal *nextForKey, const K &key, const V &val)
+    : NextInScope(nextInScope), NextForKey(nextForKey), Key(key), Val(val) {
+  }
+  
+  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; }
+public:
+  ScopedHashTableVal *getNextInScope() { return NextInScope; }
+};
+
+template <typename K, typename V>
+class ScopedHashTableScope {
+  /// HT - The hashtable that we are active for.
+  ScopedHashTable<K, V> &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;
+  void operator=(ScopedHashTableScope&);       // DO NOT IMPLEMENT
+  ScopedHashTableScope(ScopedHashTableScope&); // DO NOT IMPLEMENT
+public:
+  ScopedHashTableScope(ScopedHashTable<K, V> &HT);
+  ~ScopedHashTableScope();
+  
+private:
+  friend class ScopedHashTable<K, V>;
+  ScopedHashTableVal<K, V> *getLastValInScope() { return LastValInScope; }
+  void setLastValInScope(ScopedHashTableVal<K,V> *Val) { LastValInScope = Val; }
+};
+
+
+template <typename K, typename V>
+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>
+class ScopedHashTable {
+  DenseMap<K, ScopedHashTableVal<K,V>*> TopLevelMap;
+  ScopedHashTableScope<K, V> *CurScope;
+  ScopedHashTable(const ScopedHashTable&); // NOT YET IMPLEMENTED
+  void operator=(const ScopedHashTable&);  // NOT YET IMPLEMENTED
+  friend class ScopedHashTableScope<K, V>;
+public:
+  ScopedHashTable() : CurScope(0) {}
+  ~ScopedHashTable() {
+    assert(CurScope == 0 && TopLevelMap.empty() && "Scope imbalance!");
+  }
+  
+  void insert(const K &Key, const V &Val) {
+    assert(CurScope && "No scope active!");
+    
+    ScopedHashTableVal<K,V> *&KeyEntry = TopLevelMap[Key];
+    
+    KeyEntry = new ScopedHashTableVal<K,V>(CurScope->getLastValInScope(),
+                                           KeyEntry, Key, Val);
+    CurScope->setLastValInScope(KeyEntry);
+  }
+  
+  typedef ScopedHashTableIterator<K, V> iterator;
+
+  iterator end() { return iterator(0); }
+
+  iterator begin(const K &Key) {
+    typename DenseMap<K, ScopedHashTableVal<K,V>*>::iterator I = 
+      TopLevelMap.find(Key);
+    if (I == TopLevelMap.end()) return end();
+    return iterator(I->second);
+  }
+};
+
+/// ScopedHashTableScope ctor - Install this as the current scope for the hash
+/// table.
+template <typename K, typename V>
+ScopedHashTableScope<K, V>::ScopedHashTableScope(ScopedHashTable<K, V> &ht)
+  : HT(ht) {
+  PrevScope = HT.CurScope;
+  HT.CurScope = this;
+  LastValInScope = 0;
+}
+
+template <typename K, typename V>
+ScopedHashTableScope<K, V>::~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() == 0) {
+      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.
+    delete ThisEntry;
+  }
+}
+
+} // end namespace llvm
+
+#endif