From: Jason Merrill <jason@redhat.com>
To: David Edelsohn <dje.gcc@gmail.com>
Cc: Ramana Radhakrishnan <ramana.radhakrishnan@foss.arm.com>,
"gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>,
Jim Wilson <wilson@tuliptree.org>,
Steve Ellcey <sellcey@mips.com>,
Richard Henderson <rth@redhat.com>,
Steve Munroe <munroesj@linux.vnet.ibm.com>
Subject: Re: [RFC / CFT] PR c++/66192 - Remove TARGET_RELAXED_ORDERING and use load acquires.
Date: Fri, 22 May 2015 14:42:00 -0000 [thread overview]
Message-ID: <555F3D09.2070700@redhat.com> (raw)
In-Reply-To: <CAGWvnykzukDM2aG_QmbeCyOh7+u6xF8snOc13GUHG2RULoQU-g@mail.gmail.com>
On 05/22/2015 09:55 AM, David Edelsohn wrote:
> On Fri, May 22, 2015 at 9:40 AM, Jason Merrill <jason@redhat.com> wrote:
>> On 05/22/2015 07:23 AM, Ramana Radhakrishnan wrote:
>>>
>>> + /* Load the guard value only through an atomic acquire load. */
>>> + guard = build_atomic_load (guard, MEMMODEL_ACQUIRE);
>>> +
>>> /* Check to see if the GUARD is zero. */
>>> guard = get_guard_bits (guard);
>>
>>
>> I wonder if these calls should be reversed, to express that we're only
>> trying to atomically load a byte (on non-ARM targets)?
>
> That expresses the semantics more directly, but will that lead to less
> efficient code on some RISC architectures?
I'm not sure. I would expect that the target would use a larger load
and mask it if that is better for performance, but I don't know.
I do notice that get_guard_bits after build_atomic_load just won't work
on non-ARM targets, as it ends up trying to take the address of a value.
Jason
next prev parent reply other threads:[~2015-05-22 14:28 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-22 11:26 Ramana Radhakrishnan
2015-05-22 11:37 ` Ramana Radhakrishnan
2015-05-22 13:49 ` Jason Merrill
2015-05-22 14:15 ` David Edelsohn
2015-05-22 14:42 ` Jason Merrill [this message]
2015-05-22 15:42 ` Ramana Radhakrishnan
2015-05-22 17:48 ` David Edelsohn
2015-05-22 18:19 ` Jason Merrill
2015-05-22 19:49 ` Richard Henderson
2015-05-29 13:32 ` Ramana Radhakrishnan
2015-05-29 16:34 ` Richard Henderson
2015-05-29 16:36 ` Richard Henderson
2015-05-29 20:53 ` Jason Merrill
2015-06-04 9:46 ` Ramana Radhakrishnan
2015-06-02 14:42 ` David Edelsohn
2015-05-22 14:28 ` Ramana Radhakrishnan
2015-05-24 18:55 Uros Bizjak
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