Share ebo helper throughout lib

[François Dumont <frs dot dumont at gmail dot com>]

Hi

    It has already been noticed that there are 2 ebo helpers in the 
lib. Here is a patch to use 1.


    * include/bits/ebo_helper.h: New.
    * include/Makefile.am: Add latter.
    * include/Makefile.in: Regenerate.
    * include/bits/hashtable_policy.h: Adapt.
    * include/bits/shared_ptr_base.h: Adapt.

Tested under linux x86_64.

Ok to commit ?

François

diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
index 70db3cb..98c1a6c 100644
--- a/libstdc++-v3/include/Makefile.am
+++ b/libstdc++-v3/include/Makefile.am
@@ -105,6 +105,7 @@ bits_headers = \
 	${bits_srcdir}/concept_check.h \
 	${bits_srcdir}/cpp_type_traits.h \
 	${bits_srcdir}/deque.tcc \
+	${bits_srcdir}/ebo_helper.h \
 	${bits_srcdir}/enable_special_members.h \
 	${bits_srcdir}/forward_list.h \
 	${bits_srcdir}/forward_list.tcc \
diff --git a/libstdc++-v3/include/Makefile.in b/libstdc++-v3/include/Makefile.in
index 0e1cbe4..35093bc 100644
--- a/libstdc++-v3/include/Makefile.in
+++ b/libstdc++-v3/include/Makefile.in
@@ -398,6 +398,7 @@ bits_headers = \
 	${bits_srcdir}/concept_check.h \
 	${bits_srcdir}/cpp_type_traits.h \
 	${bits_srcdir}/deque.tcc \
+	${bits_srcdir}/ebo_helper.h \
 	${bits_srcdir}/enable_special_members.h \
 	${bits_srcdir}/forward_list.h \
 	${bits_srcdir}/forward_list.tcc \
diff --git a/libstdc++-v3/include/bits/ebo_helper.h b/libstdc++-v3/include/bits/ebo_helper.h
new file mode 100644
index 0000000..5b9073a
--- /dev/null
+++ b/libstdc++-v3/include/bits/ebo_helper.h
@@ -0,0 +1,114 @@
+// Ebo helper header -*- C++ -*-
+
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file bits/ebo_helper.h
+ *  This is an internal header file, included by other library headers.
+ *  Do not attempt to use it directly.
+ *  @headername{unordered_map,unordered_set,memory}
+ */
+
+#ifndef _EBO_HELPER_H
+#define _EBO_HELPER_H 1
+
+#include <bits/move.h>
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+namespace __detail
+{
+  /**
+   *  Primary class template _Ebo_helper.
+   *
+   *  Helper class using EBO when it is not forbidden (the type is not
+   *  final) and when it is worth it (the type is empty.)
+   */
+  template<int _Nm, typename _Tp,
+	   bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>
+    struct _Ebo_helper;
+
+  /// Specialization using EBO.
+  template<int _Nm, typename _Tp>
+    struct _Ebo_helper<_Nm, _Tp, true>
+    : private _Tp
+    {
+      _Ebo_helper() = default;
+      _Ebo_helper(const _Tp& __tp)
+      : _Tp(__tp)
+      { }
+
+      _Ebo_helper(_Tp&& __tp)
+      : _Tp(std::move(__tp))
+      { }
+
+      template<typename _OtherTp>
+	_Ebo_helper(_OtherTp&& __tp)
+	: _Tp(std::forward<_OtherTp>(__tp))
+	{ }
+
+      static const _Tp&
+      _S_cget(const _Ebo_helper& __eboh)
+      { return __eboh; }
+
+      static _Tp&
+      _S_get(_Ebo_helper& __eboh)
+      { return __eboh; }
+    };
+
+  /// Specialization not using EBO.
+  template<int _Nm, typename _Tp>
+    struct _Ebo_helper<_Nm, _Tp, false>
+    {
+      _Ebo_helper() = default;
+      _Ebo_helper(const _Tp& __tp)
+      : _M_tp(__tp)
+      { }
+
+      _Ebo_helper(_Tp&& __tp)
+      : _M_tp(std::move(__tp))
+      { }
+
+      template<typename _OtherTp>
+	_Ebo_helper(_OtherTp&& __tp)
+	: _M_tp(std::forward<_OtherTp>(__tp))
+	{ }
+
+      static const _Tp&
+      _S_cget(const _Ebo_helper& __eboh)
+      { return __eboh._M_tp; }
+
+      static _Tp&
+      _S_get(_Ebo_helper& __eboh)
+      { return __eboh._M_tp; }
+
+    private:
+      _Tp _M_tp;
+    };
+}
+
+_GLIBCXX_END_NAMESPACE_VERSION
+}
+
+#endif
diff --git a/libstdc++-v3/include/bits/hashtable_policy.h b/libstdc++-v3/include/bits/hashtable_policy.h
index 3ff6b14..62f6fd1 100644
--- a/libstdc++-v3/include/bits/hashtable_policy.h
+++ b/libstdc++-v3/include/bits/hashtable_policy.h
@@ -34,6 +34,7 @@
 #include <tuple>		// for std::tuple, std::forward_as_tuple
 #include <cstdint>		// for std::uint_fast64_t
 #include <bits/stl_algobase.h>	// for std::min.
+#include <bits/ebo_helper.h>
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
@@ -1088,59 +1089,8 @@ namespace __detail
       }
     };
 
-  /**
-   *  Primary class template _Hashtable_ebo_helper.
-   *
-   *  Helper class using EBO when it is not forbidden (the type is not
-   *  final) and when it is worth it (the type is empty.)
-   */
-  template<int _Nm, typename _Tp,
-	   bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>
-    struct _Hashtable_ebo_helper;
-
-  /// Specialization using EBO.
-  template<int _Nm, typename _Tp>
-    struct _Hashtable_ebo_helper<_Nm, _Tp, true>
-    : private _Tp
-    {
-      _Hashtable_ebo_helper() = default;
-
-      template<typename _OtherTp>
-	_Hashtable_ebo_helper(_OtherTp&& __tp)
-	  : _Tp(std::forward<_OtherTp>(__tp))
-	{ }
-
-      static const _Tp&
-      _S_cget(const _Hashtable_ebo_helper& __eboh)
-      { return static_cast<const _Tp&>(__eboh); }
-
-      static _Tp&
-      _S_get(_Hashtable_ebo_helper& __eboh)
-      { return static_cast<_Tp&>(__eboh); }
-    };
-
-  /// Specialization not using EBO.
   template<int _Nm, typename _Tp>
-    struct _Hashtable_ebo_helper<_Nm, _Tp, false>
-    {
-      _Hashtable_ebo_helper() = default;
-
-      template<typename _OtherTp>
-	_Hashtable_ebo_helper(_OtherTp&& __tp)
-	  : _M_tp(std::forward<_OtherTp>(__tp))
-	{ }
-
-      static const _Tp&
-      _S_cget(const _Hashtable_ebo_helper& __eboh)
-      { return __eboh._M_tp; }
-
-      static _Tp&
-      _S_get(_Hashtable_ebo_helper& __eboh)
-      { return __eboh._M_tp; }
-
-    private:
-      _Tp _M_tp;
-    };
+    using _Hashtable_ebo_helper = _Ebo_helper<_Nm, _Tp>;
 
   /**
    *  Primary class template _Local_iterator_base.
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h
index 870aeb9..191e4be 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -53,6 +53,7 @@
 #include <bits/allocated_ptr.h>
 #include <bits/refwrap.h>
 #include <bits/stl_function.h>
+#include <bits/ebo_helper.h>
 #include <ext/aligned_buffer.h>
 
 namespace std _GLIBCXX_VISIBILITY(default)
@@ -403,35 +404,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inline void
     _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }
 
-  template<int _Nm, typename _Tp,
-	   bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>
-    struct _Sp_ebo_helper;
-
-  /// Specialization using EBO.
-  template<int _Nm, typename _Tp>
-    struct _Sp_ebo_helper<_Nm, _Tp, true> : private _Tp
-    {
-      explicit _Sp_ebo_helper(const _Tp& __tp) : _Tp(__tp) { }
-      explicit _Sp_ebo_helper(_Tp&& __tp) : _Tp(std::move(__tp)) { }
-
-      static _Tp&
-      _S_get(_Sp_ebo_helper& __eboh) { return static_cast<_Tp&>(__eboh); }
-    };
-
-  /// Specialization not using EBO.
   template<int _Nm, typename _Tp>
-    struct _Sp_ebo_helper<_Nm, _Tp, false>
-    {
-      explicit _Sp_ebo_helper(const _Tp& __tp) : _M_tp(__tp) { }
-      explicit _Sp_ebo_helper(_Tp&& __tp) : _M_tp(std::move(__tp)) { }
-
-      static _Tp&
-      _S_get(_Sp_ebo_helper& __eboh)
-      { return __eboh._M_tp; }
-
-    private:
-      _Tp _M_tp;
-    };
+    using _Sp_ebo_helper = __detail::_Ebo_helper<_Nm, _Tp>;
 
   // Support for custom deleter and/or allocator
   template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>