[gcc r13-2698] libstdc++: Remove __alloc_neq helper

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:15943285867a6952dbc5a603c434e61bfe32296f

commit r13-2698-g15943285867a6952dbc5a603c434e61bfe32296f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Sep 16 11:39:41 2022 +0100

    libstdc++: Remove __alloc_neq helper
    
    This class template and partial specialization were added 15 years ago
    to optimize allocator equality comparisons in std::list. I think it's
    safe to assume that GCC is now capable of optimizing an inline
    operator!= that just returns false at least as well as an inline member
    function that just returns false.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/allocator.h (__alloc_neq): Remove.
            * include/bits/stl_list.h (list::_M_check_equal_allocators):
            Compare allocators directly, without __alloc_neq.

Diff:
---
 libstdc++-v3/include/bits/allocator.h | 17 -----------------
 libstdc++-v3/include/bits/stl_list.h  |  5 ++---
 2 files changed, 2 insertions(+), 20 deletions(-)

diff --git a/libstdc++-v3/include/bits/allocator.h b/libstdc++-v3/include/bits/allocator.h
index 28abf13eba9..c39166e24fe 100644
--- a/libstdc++-v3/include/bits/allocator.h
+++ b/libstdc++-v3/include/bits/allocator.h
@@ -298,23 +298,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
     };
 
-  // Optimize for stateless allocators.
-  template<typename _Alloc, bool = __is_empty(_Alloc)>
-    struct __alloc_neq
-    {
-      static bool
-      _S_do_it(const _Alloc&, const _Alloc&)
-      { return false; }
-    };
-
-  template<typename _Alloc>
-    struct __alloc_neq<_Alloc, false>
-    {
-      static bool
-      _S_do_it(const _Alloc& __one, const _Alloc& __two)
-      { return __one != __two; }
-    };
-
 #if __cplusplus >= 201103L
   template<typename _Tp, bool
     = __or_<is_copy_constructible<typename _Tp::value_type>,
diff --git a/libstdc++-v3/include/bits/stl_list.h b/libstdc++-v3/include/bits/stl_list.h
index b8bd46191fc..a73ca60df5a 100644
--- a/libstdc++-v3/include/bits/stl_list.h
+++ b/libstdc++-v3/include/bits/stl_list.h
@@ -2026,10 +2026,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
       // To implement the splice (and merge) bits of N1599.
       void
-      _M_check_equal_allocators(list& __x) _GLIBCXX_NOEXCEPT
+      _M_check_equal_allocators(const list& __x) _GLIBCXX_NOEXCEPT
       {
-	if (std::__alloc_neq<typename _Base::_Node_alloc_type>::
-	    _S_do_it(_M_get_Node_allocator(), __x._M_get_Node_allocator()))
+	if (_M_get_Node_allocator() != __x._M_get_Node_allocator())
 	  __builtin_abort();
       }