[libc++] Optimize __tree::__erase_unique

Author: philnik777

libcxx/docs/ReleaseNotes/22.rst

@@ -45,6 +45,8 @@ Improvements and New Features
 
 - The performance of ``map::map(const map&)`` has been improved up to 2.3x
 - The performance of ``map::operator=(const map&)`` has been improved by up to 11x
+- The performance of ``map::erase`` and ``set::erase`` has been improved by up to 2x
+- The performance of ``find(key)`` in all associative containers has been improved by up to 2.3x
 
 Deprecations and Removals
 -------------------------

libcxx/include/__tree

@@ -1009,9 +1009,22 @@ public:
   __insert_node_at(__end_node_pointer __parent, __node_base_pointer& __child, __node_base_pointer __new_node) _NOEXCEPT;
 
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI iterator find(const _Key& __v);
+  _LIBCPP_HIDE_FROM_ABI iterator find(const _Key& __key) {
+    __end_node_pointer __parent;
+    __node_base_pointer __match = __find_equal(__parent, __key);
+    if (__match == nullptr)
+      return end();
+    return iterator(static_cast<__node_pointer>(__match));
+  }
+
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI const_iterator find(const _Key& __v) const;
+  _LIBCPP_HIDE_FROM_ABI const_iterator find(const _Key& __key) const {
+    __end_node_pointer __parent;
+    __node_base_pointer __match = __find_equal(__parent, __key);
+    if (__match == nullptr)
+      return end();
+    return const_iterator(static_cast<__node_pointer>(__match));
+  }
 
   template <class _Key>
   _LIBCPP_HIDE_FROM_ABI size_type __count_unique(const _Key& __k) const;
@@ -2031,25 +2044,6 @@ __tree<_Tp, _Compare, _Allocator>::__erase_multi(const _Key& __k) {
   return __r;
 }
 
-template <class _Tp, class _Compare, class _Allocator>
-template <class _Key>
-typename __tree<_Tp, _Compare, _Allocator>::iterator __tree<_Tp, _Compare, _Allocator>::find(const _Key& __v) {
-  iterator __p = __lower_bound(__v, __root(), __end_node());
-  if (__p != end() && !value_comp()(__v, *__p))
-    return __p;
-  return end();
-}
-
-template <class _Tp, class _Compare, class _Allocator>
-template <class _Key>
-typename __tree<_Tp, _Compare, _Allocator>::const_iterator
-__tree<_Tp, _Compare, _Allocator>::find(const _Key& __v) const {
-  const_iterator __p = __lower_bound(__v, __root(), __end_node());
-  if (__p != end() && !value_comp()(__v, *__p))
-    return __p;
-  return end();
-}
-
 template <class _Tp, class _Compare, class _Allocator>
 template <class _Key>
 typename __tree<_Tp, _Compare, _Allocator>::size_type