libc++ patch for max_align_t

[Chandler Carruth]

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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