Re: Libatomic 16B

[Alexander Monakov <amonakov@ispras.ru>]

On Fri, 25 Feb 2022, Florian Weimer via Gcc-help wrote:

> * Xi Ruoyao via Gcc-help:
> 
> > On Fri, 2022-02-25 at 09:35 +0100, Stefan Ring via Gcc-help wrote:
> >> On Thu, Feb 24, 2022 at 9:39 PM Satish Vasudeva via Gcc-help
> >> <gcc-help@gcc.gnu.org> wrote:
> >> > 
> >> > Please let into this intel architecture manual , section 8.1.1
> >> > 
> >> > https://cdrdv2.intel.com/v1/dl/getContent/671190
> >> > 
> >> > I think Intel claims 16B operations are atomic , unless I am missing
> >> > something.
> >> 
> >> Interesting. This seems to be a somewhat recent addition, and the
> >> mailing list discussion linked to above predates it. Coincidentally, I
> >> pulled a copy of the Intel manuals at almost exactly the same time as
> >> this discussion, and sure enough, it does not yet contain the
> >> paragraph about 16 byte operations.
> >
> > It seems an addition in Dec 2021 revision:
> > https://cdrdv2.intel.com/v1/dl/getContent/671294
> >
> > Create an issue in bugzilla then?
> 
> Yes please.  I should have read the whole thread first. 8-)
> 
> The AMD manual doesn't say this yet, so any optimization needs to be
> restricted to Intel CPUs for now.  I'll reach out to AMD to get
> clarification.

This StackOverflow question has evidence that both Intel (Core Duo) and
AMD (Opteron 2435) can tear 128-bit loads. So neither manufacturer can
give a retroactive guarantee.

https://stackoverflow.com/questions/7646018/sse-instructions-which-cpus-can-do-atomic-16b-memory-operations

Alexander