libc++ patch for max_align_t

[Chandler Carruth]

Thanks, submitted in r201843 after testing with a Clang, GCC 4.8 (has
::max_align_t) and GCC 4.6 (does not have ::max_align_t).


On Wed, Feb 19, 2014 at 11:16 PM, Marshall Clow <mclow.lists at gmail.com>wrote:

> On Feb 19, 2014, at 3:11 PM, Chandler Carruth <chandlerc at google.com>
> wrote:
>
> Attached in my patch to do this minimum of work to get std::max_align_t.
> It's dirt simple, if deeply unfortunate in the specific definition in
> provides on many platforms. I think it is no worse than the current
> behavior.
>
> If we want to support a host which is neither Clang nor GCC and does not
> provide a ::max_align_t, we can do so incrementally atop this I think.
>
>
> LGTM.
>
> — Marshall
>
>
>
> -Chandler
>
>
> On Sun, Feb 16, 2014 at 12:14 AM, Chandler Carruth <chandlerc at google.com>wrote:
>
>> FYI, i'm preparing patches to this effect.
>>
>>
>> On Sat, Feb 15, 2014 at 11:13 PM, Richard Smith <richard at metafoo.co.uk>wrote:
>>
>>> This seems to be going in the wrong direction.
>>>
>>> * max_align_t needs to be in <stddef.h> as well as in <cstddef>
>>> * <stddef.h> is provided by the compiler, not by the standard library
>>> * max_align_t is de facto part of the platform's ABI. It's not enough to
>>> get the alignment right, you also need to get the size and mangled name of
>>> the type right (and possibly other things too).
>>>
>>> IMO, the right thing to do here is to add a definition to max_align_t to
>>> Clang's lib/Headers/stddef.h, and add a using declaration to libc++'s
>>> cstddef to pull it into namespace std.
>>>
>>>
>>> On Mon, Feb 10, 2014 at 1:16 PM, Howard Hinnant <
>>> howard.hinnant at gmail.com> wrote:
>>>
>>>> On Feb 10, 2014, at 2:25 PM, Howard Hinnant <howard.hinnant at gmail.com>
>>>> wrote:
>>>>
>>>> >> It seems like the old behavior follows the standard more closely. If
>>>> Len
>>>> >> == 17, then _any_ c++ object with size no greater than Len includes
>>>> >> objects of size 16 and some objects of size 16 maybe have an
>>>> alignment
>>>> >> requirement of 16.
>>>> >
>>>> > Ok, I'm convinced, thanks.
>>>>
>>>> I've enclosed a slightly updated patch.  I've added float as Kal
>>>> suggested, but haven't added uintmax_t because of not wanting to couple
>>>> <cstddef> to <cstddint>.  I have not modified the behavior, thanks to Kal.
>>>>
>>>> std::__find_max_align<std::__all_types, 1>::value = 1
>>>> std::__find_max_align<std::__all_types, 2>::value = 2
>>>> std::__find_max_align<std::__all_types, 3>::value = 2
>>>> std::__find_max_align<std::__all_types, 4>::value = 4
>>>> std::__find_max_align<std::__all_types, 5>::value = 4
>>>> std::__find_max_align<std::__all_types, 6>::value = 4
>>>> std::__find_max_align<std::__all_types, 7>::value = 4
>>>> std::__find_max_align<std::__all_types, 8>::value = 8
>>>> std::__find_max_align<std::__all_types, 9>::value = 8
>>>> std::__find_max_align<std::__all_types, 10>::value = 8
>>>> std::__find_max_align<std::__all_types, 11>::value = 8
>>>> std::__find_max_align<std::__all_types, 12>::value = 8
>>>> std::__find_max_align<std::__all_types, 13>::value = 8
>>>> std::__find_max_align<std::__all_types, 14>::value = 8
>>>> std::__find_max_align<std::__all_types, 15>::value = 8
>>>> std::__find_max_align<std::__all_types, 16>::value = 16
>>>> std::__find_max_align<std::__all_types, 17>::value = 16
>>>> std::__find_max_align<std::__all_types, 18>::value = 16
>>>> std::__find_max_align<std::__all_types, 19>::value = 16
>>>> std::__find_max_align<std::__all_types, 20>::value = 16
>>>> std::__find_max_align<std::__all_types, 21>::value = 16
>>>> std::__find_max_align<std::__all_types, 22>::value = 16
>>>> std::__find_max_align<std::__all_types, 23>::value = 16
>>>> std::__find_max_align<std::__all_types, 24>::value = 16
>>>> std::__find_max_align<std::__all_types, 25>::value = 16
>>>> std::__find_max_align<std::__all_types, 26>::value = 16
>>>> std::__find_max_align<std::__all_types, 27>::value = 16
>>>> std::__find_max_align<std::__all_types, 28>::value = 16
>>>> std::__find_max_align<std::__all_types, 29>::value = 16
>>>> std::__find_max_align<std::__all_types, 30>::value = 16
>>>> std::__find_max_align<std::__all_types, 31>::value = 16
>>>> std::__find_max_align<std::__all_types, 32>::value = 16
>>>> std::__find_max_align<std::__all_types, 33>::value = 16
>>>> ...
>>>>
>>>> Howard
>>>>
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>>>>
>>>>
>>>
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>>>
>>
> <fix-max-align-t.patch>
>
>
>
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