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Re: linux says it is a bug
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Hannes Frederic Sowa <hannes at stressinduktion dot org>
- Cc: Andrew Haley <aph at redhat dot com>, Jonathan Wakely <jwakely dot gcc at gmail dot com>, lin zuojian <manjian2006 at gmail dot com>, GCC Development <gcc at gcc dot gnu dot org>
- Date: Tue, 4 Mar 2014 12:08:19 +0100
- Subject: Re: linux says it is a bug
- Authentication-results: sourceware.org; auth=none
- References: <20140304064026 dot GE8019 at ubuntu> <CAFiYyc3bVGgG=dmozPG5m4Vx_oJbR=rR=TsZfj+01dvXmWiJmw at mail dot gmail dot com> <20140304091703 dot GE17043 at order dot stressinduktion dot org> <CAH6eHdQ2mrDYm5s2FiGWdQnp7V_cV0JdwGA381SXzp3D79j+=Q at mail dot gmail dot com> <20140304092420 dot GF17043 at order dot stressinduktion dot org> <53159C47 dot 5040901 at redhat dot com> <20140304093337 dot GG17043 at order dot stressinduktion dot org>
On Tue, Mar 4, 2014 at 10:33 AM, Hannes Frederic Sowa
<hannes@stressinduktion.org> wrote:
> On Tue, Mar 04, 2014 at 09:26:31AM +0000, Andrew Haley wrote:
>> On 03/04/2014 09:24 AM, Hannes Frederic Sowa wrote:
>> >> > So the bug was probably fixed more than 15 years ago.
>> > Probably :)
>> >
>> > But the __volatile__ shoud do no harm and shouldn't influence code
>> > generation in any way, no?
>>
>> Of course it will: it's a barrier.
>
> Sure. My question was about the volatile marker. asm("":::"memory") should act
> as the barrier alone.
__asm__("":::"memory")
is a memory barrier
volatile __asm__("":::"memory")
is a memory barrier and a barrier for other volatile instructions.
Nothing more, nothing less.
Neither is a "optimization barrier" or "compiler barrier" or whatever
name you invent.
Richard.