From: Richard Henderson <rth@redhat.com>
To: Jakub Jelinek <jakub@redhat.com>
Cc: gcc-patches@gcc.gnu.org, amacleod@redhat.com
Subject: Re: [cxx-mem-model][PATCH 0/9] Convert i386 to new atomic optabs.
Date: Fri, 28 Oct 2011 15:25:00 -0000 [thread overview]
Message-ID: <4EAAC321.9000108@redhat.com> (raw)
In-Reply-To: <20111028110616.GS1052@tyan-ft48-01.lab.bos.redhat.com>
On 10/28/2011 04:06 AM, Jakub Jelinek wrote:
> It just wants a guarantee that the builtin will actually be implemented
> in hw. I guess if __sync_fetch_op (new/old) isn't supported but
> __sync_compare_and_swap_* is, we could just use the former and let
> optabs.c deal with that. But we have to handle the CAS case anyway
> for most of the operations that don't have a __sync_fetch_op defined
> (and for the cases where we e.g. VCE floating point data to integer
> of the same size for CAS).
I was just thinking that the data structure with the 6 optabs that we're
exporting from optabs.c is somewhat over the top, when simply testing
can_compare_and_swap_p is just about equivalent.
On reflection, I think I'll revert that patch and try it with just that
one test...
> BTW, I believe all #pragma omp atomic ops we want in the relaxed model
> or weaker, I think OpenMP only guarantees that the memory is modified
> or loaded atomically (that you don't see half of something and half of
> something else), there is nothing that requires ordering the atomic
> vs. any other memory location stores/loads.
... possibly with switching to the new builtins in relaxed mode?
r~
next prev parent reply other threads:[~2011-10-28 14:59 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-28 4:08 Richard Henderson
2011-10-28 4:08 ` [PATCH 3/9] Introduce and use can_compare_and_swap_p Richard Henderson
2011-10-28 4:08 ` [PATCH 7/9] Update omp for new atomic optabs Richard Henderson
2011-10-28 4:08 ` [PATCH 1/9] Fix thinko in gen_mem_thread_fence operand Richard Henderson
2011-10-28 4:08 ` [PATCH 2/9] Handle expanding insns with 8 operands Richard Henderson
2011-10-28 5:11 ` [PATCH 6/9] Update cppbuiltins for atomic-compare-and-swap Richard Henderson
2011-10-28 5:11 ` [PATCH 9/9] Update ChangeLogs Richard Henderson
2011-10-28 5:20 ` [PATCH 8/9] Convert i386 backend to new atomic patterns Richard Henderson
2011-10-28 5:30 ` [PATCH 5/9] Add missing atomic optab initializations Richard Henderson
2011-10-28 5:40 ` [PATCH 4/9] Rewrite all compare-and-swap in terms of expand_atomic_compare_and_swap Richard Henderson
2011-10-28 11:29 ` [cxx-mem-model][PATCH 0/9] Convert i386 to new atomic optabs Jakub Jelinek
2011-10-28 15:25 ` Richard Henderson [this message]
2011-10-29 17:28 ` Andrew MacLeod
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