[EXTERNAL] [PATCH 2/2] ntdll: Move InterlockedCompareExchange128 support to winnt.h.

[Puetz Kevin A]

There's no __sync_bool_compare_and_swap_16 in ARMv8.0
(or even with ARMv8.1, support wasn't added until until GCC 10).

This of course broke our builds when it was added; for now I'd been working
around it with the attached patch, which substitutes the -latomic 
__atomic_compare_exchange_16, which is allowed to be based on a lock
if there's no lockfree implementation (e.g.  the specified -march or GCC lack
support for the ARMv8.1 CASP* instructions).

I was waiting to hear back from our BSP guys whether we'd eventually get
support on the final hardware/toolchain or not before raising this upstream,
to see know if I had an issue that needed a "real" fix or just a short-term 
impediment (in which case I had a viable workaround in the meantime).
 
But if you're moving it into external API too, then it seems like it's time to at
least point out what I've learned.

Microsoft only promises InterlockedCompareExchange128 on amd64;
It's nice to offer it anywhere an underlying compiler intrinsic exists, but
that needs to test defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16).
And I think RtlInterlocked*SList needs some kind of fallback.
What I did with -latomic seems sane, but should get a ./configure check
since you wouldn't need to link -latomic if the compiler has the intrinsic.

> -----Original Message-----
> From: wine-devel <wine-devel-bounces at winehq.org> On Behalf Of Jacek
> Caban
> Sent: Friday, July 31, 2020 8:38 AM
> To: wine-devel <wine-devel at winehq.org>
> Subject: [EXTERNAL] [PATCH 2/2] ntdll: Move
> InterlockedCompareExchange128 support to winnt.h.
> 
> [EXTERNAL EMAIL]: This message was generated from an external source. Do
> not follow guidance, click links, or open attachments unless you recognize
> the sender and know the content is safe.
> 
> Also properly declare intrinsic on msvc.
> 
> Signed-off-by: Jacek Caban <jacek at codeweavers.com>
> ---
>   dlls/ntdll/rtl.c | 26 ++++----------------------
>   include/winnt.h  | 32 ++++++++++++++++++++++++++++++++
>   2 files changed, 36 insertions(+), 22 deletions(-)
> 

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