Add include/llvm/ADT/UsuallyTinyPtrVector.h which is a vector that

optimizes the case where there is only one element.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152090 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/ADT/UsuallyTinyPtrVector.h b/include/llvm/ADT/UsuallyTinyPtrVector.h
new file mode 100644 (file)
index 0000000..cfa147e
--- /dev/null
+++ b/include/llvm/ADT/UsuallyTinyPtrVector.h
@@ -0,0 +1,137 @@
+//===-- UsuallyTinyPtrVector.h - Pointer vector class -----------*- 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 UsuallyTinyPtrVector class, which is a vector that
+//  optimizes the case where there is only one element.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_USUALLY_TINY_PTR_VECTOR_H
+#define LLVM_ADT_USUALLY_TINY_PTR_VECTOR_H
+
+#include <vector>
+
+namespace llvm {
+
+/// \brief A vector class template that is optimized for storing a single 
+/// pointer element.
+template<typename T>
+class UsuallyTinyPtrVector {
+  /// \brief Storage for the vector.
+  ///
+  /// When the low bit is zero, this is a T *. When the
+  /// low bit is one, this is a std::vector<T *> *.
+  mutable uintptr_t Storage;
+
+  typedef std::vector<T*> vector_type;
+
+public:
+  UsuallyTinyPtrVector() : Storage(0) { }
+  explicit UsuallyTinyPtrVector(T *Element) 
+    : Storage(reinterpret_cast<uintptr_t>(Element)) { }
+  
+  bool empty() const { return !Storage; }
+
+  typedef const T **iterator;
+  iterator begin() const;
+  iterator end() const;
+  size_t size() const;
+
+  void push_back(T *Method);
+  iterator erase(const iterator ElementPos);
+  void Destroy();
+};
+
+template<typename T>
+typename UsuallyTinyPtrVector<T>::iterator 
+UsuallyTinyPtrVector<T>::begin() const {
+  if ((Storage & 0x01) == 0)
+    return reinterpret_cast<iterator>(&Storage);
+
+  vector_type *Vec = reinterpret_cast<vector_type *>(Storage & ~0x01);
+  return &Vec->front();
+}
+
+template<typename T>
+typename UsuallyTinyPtrVector<T>::iterator 
+UsuallyTinyPtrVector<T>::end() const {
+  if ((Storage & 0x01) == 0) {
+    if (Storage == 0)
+      return reinterpret_cast<iterator>(&Storage);
+
+    return reinterpret_cast<iterator>(&Storage) + 1;
+  }
+
+  vector_type *Vec = reinterpret_cast<vector_type *>(Storage & ~0x01);
+  return &Vec->front() + Vec->size();
+}
+
+template<typename T>
+size_t UsuallyTinyPtrVector<T>::size() const {
+  if ((Storage & 0x01) == 0)
+    return (Storage == 0) ? 0 : 1;
+
+  vector_type *Vec = reinterpret_cast<vector_type *>(Storage & ~0x01);
+  return Vec->size();
+}
+
+template<typename T>
+void UsuallyTinyPtrVector<T>::push_back(T *Element) {
+  if (Storage == 0) {
+    // 0 -> 1 element.
+    Storage = reinterpret_cast<uintptr_t>(Element);
+    return;
+  }
+
+  vector_type *Vec;
+  if ((Storage & 0x01) == 0) {
+    // 1 -> 2 elements. Allocate a new vector and push the element into that
+    // vector.
+    Vec = new vector_type;
+    Vec->push_back(reinterpret_cast<T *>(Storage));
+    Storage = reinterpret_cast<uintptr_t>(Vec) | 0x01;
+  } else
+    Vec = reinterpret_cast<vector_type *>(Storage & ~0x01);
+
+  // Add the new element to the vector.
+  Vec->push_back(Element);
+}
+
+template<typename T>
+typename UsuallyTinyPtrVector<T>::iterator
+UsuallyTinyPtrVector<T>::erase(
+  const typename UsuallyTinyPtrVector<T>::iterator ElementPos) {
+  // only one item
+  if ((Storage & 0x01) == 0) {
+    // if the element is found remove it
+    if (ElementPos == reinterpret_cast<T **>(&Storage))
+      Storage = 0;
+  } else {
+    // multiple items in a vector; just do the erase, there is no
+    // benefit to collapsing back to a pointer
+    vector_type *Vec = reinterpret_cast<vector_type *>(Storage & ~0x01);
+    unsigned index = ElementPos -
+         const_cast<typename UsuallyTinyPtrVector<T>::iterator>(&Vec->front());
+    if (index < Vec->size())
+      return const_cast<typename UsuallyTinyPtrVector<T>::iterator>(
+                                         &*(Vec->erase(Vec->begin() + index)));
+  }
+  return end();
+}
+
+template<typename T>
+void UsuallyTinyPtrVector<T>::Destroy() {
+  if (Storage & 0x01)
+    delete reinterpret_cast<vector_type *>(Storage & ~0x01);
+  
+  Storage = 0;
+}
+
+}
+#endif