[gcc r12-2824] libstdc++: [_GLIBCXX_DEBUG] Avoid allocator operator== when always equal

[Franथईois Dumont]

https://gcc.gnu.org/g:1354603bf7d2ef8cd0cb1f76e801732020502987

commit r12-2824-g1354603bf7d2ef8cd0cb1f76e801732020502987
Author: François Dumont <fdumont@gcc.gnu.org>
Date:   Mon Aug 9 11:55:43 2021 +0200

    libstdc++: [_GLIBCXX_DEBUG] Avoid allocator operator== when always equal
    
    Use std::allocator_traits::is_always_equal to find out if we need to compare
    allocator instances on safe container allocator aware move constructor.
    
    libstdc++-v3/ChangeLog:
    
            * include/debug/safe_container.h
            (_Safe_container(_Safe_container&&, const _Alloc&, std::true_type)): New.
            (_Safe_container(_Safe_container&&, const _Alloc&, std::false_type)): New.
            (_Safe_container(_Safe_container&&, const _Alloc&)): Use latters.

Diff:
---
 libstdc++-v3/include/debug/safe_container.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/debug/safe_container.h b/libstdc++-v3/include/debug/safe_container.h
index d9636c29e9b..97c47167fe8 100644
--- a/libstdc++-v3/include/debug/safe_container.h
+++ b/libstdc++-v3/include/debug/safe_container.h
@@ -57,7 +57,12 @@ namespace __gnu_debug
       _Safe_container(const _Safe_container&) = default;
       _Safe_container(_Safe_container&&) = default;
 
-      _Safe_container(_Safe_container&& __x, const _Alloc& __a)
+    private:
+      _Safe_container(_Safe_container&& __x, const _Alloc&, std::true_type)
+      : _Safe_container(std::move(__x))
+      { }
+
+      _Safe_container(_Safe_container&& __x, const _Alloc& __a, std::false_type)
       : _Safe_container()
       {
 	if (__x._M_cont().get_allocator() == __a)
@@ -65,6 +70,12 @@ namespace __gnu_debug
 	else
 	  __x._M_invalidate_all();
       }
+
+    protected:
+      _Safe_container(_Safe_container&& __x, const _Alloc& __a)
+      : _Safe_container(std::move(__x), __a,
+		      typename std::allocator_traits<_Alloc>::is_always_equal{})
+      { }
 #endif
 
     public: