[PATCH] PR libstdc++/77691 fix resource_adaptor failures due to max_align_t bugs

[Jonathan Wakely]

On 22/05/19 21:40 +0100, Jonathan Wakely wrote:
>Remove the hardcoded whitelist of allocators expected to return memory
>aligned to alignof(max_align_t), because that doesn't work when the
>platform's malloc() and GCC's max_align_t do not agree what the largest
>fundamental alignment is. It's also sub-optimal for user-defined
>allocators that return memory suitable for any fundamental alignment.
>
>Instead use a hardcoded list of alignments that are definitely supported
>by the platform malloc, and use a copy of the allocator rebound to a POD
>type with the requested alignment. Only allocate an oversized
>buffer to use with std::align for alignments larger than any of the
>hardcoded values.
>
>For 32-bit Solaris x86 do not include alignof(max_align_t) in the
>hardcoded values.
>
>	PR libstdc++/77691
>	* include/experimental/memory_resource: Add system header pragma.
>	(__resource_adaptor_common::__guaranteed_alignment): Remove.
>	(__resource_adaptor_common::_Types)
>	(__resource_adaptor_common::__new_list)
>	(__resource_adaptor_common::_New_list)
>	(__resource_adaptor_common::_Alignments)
>	(__resource_adaptor_common::_Fund_align_types): New utilities for
>	creating a list of types with fundamental alignments.
>	(__resource_adaptor_imp::do_allocate): Call new _M_allocate function.
>	(__resource_adaptor_imp::do_deallocate): Call new _M_deallocate
>	function.
>	(__resource_adaptor_imp::_M_allocate): New function that first tries
>	to use an allocator rebound to a type with a fundamental alignment.
>	(__resource_adaptor_imp::_M_deallocate): Likewise for deallocation.
>	* testsuite/experimental/memory_resource/new_delete_resource.cc:
>	Adjust expected allocation sizes.
>	* testsuite/experimental/memory_resource/resource_adaptor.cc: Remove
>	xfail.

Gah, that's the wrong ChangeLog, from an earlier version of the patch.
The right one is in the ChangeLog file, but the svn commit has the
wrong info, sorry.

The correct one is:

        PR libstdc++/77691
        * include/experimental/memory_resource: Add system header pragma and
        do not define anything unless compiled as C++14 or later.
        (__resource_adaptor_common::__guaranteed_alignment): Remove.
        (__resource_adaptor_imp::do_allocate): If the requested alignment
        is a fundamental alignment then either allocate directly from _M_alloc
        or call the new _M_allocate function.
        (__resource_adaptor_imp::do_deallocate): Likewise for deallocation.
        (__resource_adaptor_imp::_M_allocate): New function that uses a copy
        of the allocator rebound to a POD type with the specified alignment.
        (__resource_adaptor_imp::_M_deallocate): Likewise for deallocation.
        * testsuite/experimental/memory_resource/new_delete_resource.cc:
        Adjust expected allocation sizes.
        * testsuite/experimental/memory_resource/resource_adaptor.cc: Remove
        xfail for Solaris x86.