[gcc(refs/vendors/redhat/heads/gcc-10-branch)] libstdc++: uninitialized_construct_using_allocator should use construct_at (LWG 3321)

[Jakub Jelinek]

https://gcc.gnu.org/g:5f3641d0c430523d839298a6876f907523811485

commit 5f3641d0c430523d839298a6876f907523811485
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Feb 19 12:14:54 2020 +0000

    libstdc++: uninitialized_construct_using_allocator should use construct_at (LWG 3321)
    
            * include/std/memory (uninitialized_construct_using_allocator): Use
            std::construct_at (LWG 3321).

Diff:
---
 libstdc++-v3/ChangeLog          | 3 +++
 libstdc++-v3/include/std/memory | 7 ++++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index eb83c632adc..5408a89c7fb 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,8 @@
 2020-02-19  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/memory (uninitialized_construct_using_allocator): Use
+	std::construct_at (LWG 3321).
+
 	* include/std/memory_resource (polymorphic_allocator::allocate_bytes)
 	(polymorphic_allocator::allocate_object)
 	(polymorphic_allocator::new_object): Add nodiscard attribute (LWG3304).
diff --git a/libstdc++-v3/include/std/memory b/libstdc++-v3/include/std/memory
index 14aedb70dac..aaee6e42c1a 100644
--- a/libstdc++-v3/include/std/memory
+++ b/libstdc++-v3/include/std/memory
@@ -387,9 +387,10 @@ get_pointer_safety() noexcept { return pointer_safety::relaxed; }
     uninitialized_construct_using_allocator(_Tp* __p, const _Alloc& __a,
 					    _Args&&... __args)
     {
-      void* __vp = const_cast<void*>(static_cast<const volatile void*>(__p));
-      return ::new(__vp) _Tp(std::make_obj_using_allocator<_Tp>(__a,
-	    std::forward<_Args>(__args)...));
+      return std::apply([&](auto&&... __xs) {
+	return std::construct_at(__p, std::forward<decltype(__xs)>(__xs)...);
+      }, std::uses_allocator_construction_args<_Tp>(__a,
+	std::forward<_Args>(__args)...));
     }
 // @}