From: Eliot Moss <moss@cs.umass.edu>
To: cygwin <cygwin@cygwin.com>
Subject: Re: gcc and 128-bit compare/exchange
Date: Sun, 8 Mar 2020 22:59:51 -0400 [thread overview]
Message-ID: <f27b324f-049c-7830-68cd-14813aab6eed@cs.umass.edu> (raw)
In-Reply-To: <ab69ca04-06a2-eeb9-4771-e37432b59a77@cs.umass.edu>
On 3/8/2020 10:29 PM, Eliot Moss wrote:
> This is probably to the gcc maintainer ...
>
> I am running on a processor that has compare/exchange 128-bit (cx16 capability),
> and I compiler with -mcx16 and -latomic. I'm on the latest release cygwin gcc
> (9.2.0-3, I believe) and the corresponding libatomic. I have a program with
> this in it:
>
> __atomic_compare_exchange((__int128 *)&s1, (__int128 *)&z, (__int128 *)&s2, 0, __ATOMIC_SEQ_CST,
> __ATOMIC_SEQ_CST);
>
> This compiles to a call (nice if it would inline, but ...) to
> __atomic_compare_exchange_16, which uses mutex's, not the CMPXCHG16B
> instruction I was hoping for. Note I am doing dynamic linking,
> which on at least one other platform results in dynamic selection
> of a lib_at implementation of the compare/exchange, which does use
> the desired instruction.
>
> Is this a limitation of cygwin gcc, or should I be doing something
> different to achieve the desired effect?
>
> Obviously it would be best not to going an asm inline if I can avoid it,
> but I suppose I can dig into the libatomic source to get the right
> incantation for it if need be ...
A quick followup: I was able to get __sync_val_compare_and_swap_16 to work
(and its bool form). That will do for now, though of course it's deprecated.
Regards - EM
next prev parent reply other threads:[~2020-03-09 2:59 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-09 2:29 Eliot Moss
2020-03-09 2:59 ` Eliot Moss [this message]
2020-03-10 20:35 ` Brian Inglis
2020-03-10 21:13 ` Eliot Moss
2020-03-11 5:31 ` Brian Inglis
2020-03-11 6:13 ` Eliot Moss
2020-03-11 16:30 ` Brian Inglis
2020-03-12 3:36 ` Eliot Moss
2020-03-12 21:13 ` Brian Inglis
2020-03-12 22:49 ` Eliot Moss
2020-03-13 5:35 ` Brian Inglis
2020-03-11 17:31 ` Achim Gratz
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