Added ImmutableList, a companion ADT to ImmutableSet and ImmutableMap that is used to represent a purely functional list.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52911 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/ImmutableList.h

@@ -0,0 +1,175 @@
+//==--- ImmutableList.h - Immutable (functional) list interface --*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the ImmutableList class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_IMLIST_H
+#define LLVM_ADT_IMLIST_H
+
+#include "llvm/Support/Allocator.h"
+#include "llvm/ADT/FoldingSet.h"
+#include "llvm/Support/DataTypes.h"
+#include <cassert>
+
+namespace llvm {
+
+template <typename T> class ImmutableListFactory;
+  
+template <typename T>
+class ImmutableListImpl : public FoldingSetNode {
+  T Head;
+  ImmutableListImpl* Tail;
+
+  ImmutableListImpl(const T& head, ImmutableListImpl* tail = 0)
+    : Head(head), Tail(tail) {}
+  
+  friend class ImmutableListFactory<T>;
+  
+  // Do not implement.
+  void operator=(const ImmutableListImpl&);
+  ImmutableListImpl(const ImmutableListImpl&);
+  
+public:
+  const T& getHead() const { return Head; }
+  ImmutableListImpl* getTail() const { return Tail; }
+  
+  static inline void Profile(FoldingSetNodeID& ID, const T& H,
+                             ImmutableListImpl* L){
+    ID.AddPointer(L);
+    ID.Add(H);
+  }
+  
+  void Profile(FoldingSetNodeID& ID) {
+    Profile(ID, Head, Tail);
+  }
+};
+  
+/// ImmutableList - This class represents an immutable (functional) list.
+///  It is implemented as a smart pointer (wraps ImmutableListImpl), so it
+///  it is intended to always be copied by value as if it were a pointer.
+///  This interface matches ImmutableSet and ImmutableMap.  ImmutableList
+///  objects should almost never be created directly, and instead should
+///  be created by ImmutableListFactory objects that manage the lifetime
+///  of a group of lists.  When the factory object is reclaimed, all lists
+///  created by that factory are released as well.
+template <typename T>
+class ImmutableList {
+public:
+  typedef T value_type;
+  typedef ImmutableListFactory<T> Factory;
+
+private:
+  ImmutableListImpl<T>* X;
+
+public:
+  // This constructor should normally only be called by ImmutableListFactory<T>.
+  // There may be cases, however, when one needs to extract the internal pointer
+  // and reconstruct a list object from that pointer.
+  ImmutableList(ImmutableListImpl<T>* x) : X(x) {}
+
+  ImmutableListImpl<T>* getInternalPointer() const {
+    return X;
+  }
+  
+  class iterator {
+    ImmutableListImpl<T>* L;
+  public:
+    iterator() : L(0) {}
+    iterator(ImmutableList l) : L(l.getInternalPointer()) {}
+    
+    iterator& operator++() { L = L->Tail; }
+    bool operator==(const iterator& I) const { return L == I.L; }
+    ImmutableList operator*() const { return L; }
+  };
+
+  iterator begin() const { return iterator(X); }
+  iterator end() const { return iterator(); }
+
+  bool isEmpty() const { return !X; }
+  
+  bool isEqual(const ImmutableList& L) const { return X == L.X; }  
+  bool operator==(const ImmutableList& L) const { return isEqual(L); }
+
+  const T& getHead() {
+    assert (!isEmpty() && "Cannot get the head of an empty list.");
+    return X->getHead();
+  }
+  
+  ImmutableList getTail() {
+    return X ? X->getTail() : 0;
+  }  
+};
+  
+template <typename T>
+class ImmutableListFactory {
+  typedef ImmutableListImpl<T> ListTy;  
+  typedef FoldingSet<ListTy>   CacheTy;
+  
+  CacheTy Cache;
+  uintptr_t Allocator;
+  
+  bool ownsAllocator() const {
+    return Allocator & 0x1 ? false : true;
+  }
+  
+  BumpPtrAllocator& getAllocator() const { 
+    return *reinterpret_cast<BumpPtrAllocator*>(Allocator & ~0x1);
+  }  
+
+public:
+  ImmutableListFactory()
+    : Allocator(reinterpret_cast<uintptr_t>(new BumpPtrAllocator())) {}
+  
+  ImmutableListFactory(BumpPtrAllocator& Alloc)
+  : Allocator(reinterpret_cast<uintptr_t>(&Alloc) | 0x1) {}
+  
+  ~ImmutableListFactory() {
+    if (ownsAllocator()) delete &getAllocator();
+  }
+  
+  ImmutableList<T> Concat(const T& Head, ImmutableList<T> Tail) {
+    // Profile the new list to see if it already exists in our cache.
+    FoldingSetNodeID ID;
+    void* InsertPos;
+    
+    ListTy* TailImpl = Tail.getInternalPointer();
+    ListTy::Profile(ID, Head, TailImpl);
+    ListTy* L = Cache.FindNodeOrInsertPos(ID, InsertPos);
+    
+    if (!L) {
+      // The list does not exist in our cache.  Create it.
+      BumpPtrAllocator& A = getAllocator();
+      L = (ListTy*) A.Allocate<ListTy>();
+      new (L) ListTy(Head, TailImpl);
+    
+      // Insert the new list into the cache.
+      Cache.InsertNode(L, InsertPos);
+    }
+    
+    return L;
+  }
+  
+  ImmutableList<T> Add(const T& D, ImmutableList<T> L) {
+    return Concat(D, L);
+  }
+  
+  ImmutableList<T> GetEmptyList() const {
+    return ImmutableList<T>(0);
+  }
+  
+  ImmutableList<T> Create(const T& X) {
+    return Concat(X, GetEmptyList());
+  }
+};
+  
+} // end llvm namespace
+
+#endif