Re: GCC in-line assembly and the removal of -mcx16

[Jonathan Wakely <jwakely dot gcc at gmail dot com>]

On 28 May 2017 at 12:15, Toebs Douglass wrote:
> I would like to write a little about the new libatomic mechanism for
> What I see however is that there is a way for me to avoid these costs
> and return to the simple situation.  My code has an abstraction layer,
> and I can implement inline assembly for double-word CAS on 64-bit
> platforms and use that instead of __atomic and __sync.

On x86_64 can't you just use __sync_val_compare_and_swap with -mcx16?

Since GCC 4.6 this always emits cmpxchg16b when compiled with -mcx16:

int main()
{
  __int128 i = 0;
  __sync_val_compare_and_swap(&i, 0, 1);
}

That still works with GCC 7.