From: "Joseph S. Myers" <joseph@codesourcery.com>
To: Aldy Hernandez <aldyh@redhat.com>
Cc: Richard Henderson <rth@redhat.com>,
gcc-patches <gcc-patches@gcc.gnu.org>,
Jeff Law <law@redhat.com>
Subject: Re: [cxx-mem-model] disallow load data races (1 of some)
Date: Thu, 24 Mar 2011 21:51:00 -0000 [thread overview]
Message-ID: <Pine.LNX.4.64.1103242148430.11151@digraph.polyomino.org.uk> (raw)
In-Reply-To: <4D8BB82F.3060901@redhat.com>
On Thu, 24 Mar 2011, Aldy Hernandez wrote:
> This work is independent of the C++ memory model. It is just to prevent the
> optimizers from introducing new data races due to code movement. This initial
> pass is just to make the optimizations data race safe so that if you have a
> program which is proven to be free of data races, you can run the optimizers
> and it will still be data race free after the optimizers have been run.
>
> See the following summary by Andrew (which in turn is based on a paper by Hans
> Boehm):
>
> http://gcc.gnu.org/wiki/Atomic/GCCMM/DataRaces
But hoisting global in this case doesn't result in a data race, since the
loop always accesses global and contains no synchronisation code. If it
were only accessed conditionally, as in the examples under "Avoiding
Speculation" on that page, then there would be a race in hoisting it, but
not for the code you gave; any data races with the hoisting would still
have been present without it.
--
Joseph S. Myers
joseph@codesourcery.com
next prev parent reply other threads:[~2011-03-24 21:51 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-24 17:33 Aldy Hernandez
2011-03-24 19:58 ` Richard Henderson
2011-03-24 21:31 ` Aldy Hernandez
2011-03-24 21:51 ` Joseph S. Myers [this message]
2011-03-24 23:57 ` Andrew MacLeod
2011-03-25 10:03 ` Richard Guenther
2011-03-25 12:58 ` Aldy Hernandez
2011-03-25 15:27 ` Michael Matz
2011-03-25 15:33 ` Jeff Law
2011-03-25 15:35 ` Jakub Jelinek
2011-03-25 15:46 ` Richard Guenther
2011-03-29 16:52 ` Aldy Hernandez
2011-03-31 13:12 ` Jeff Law
2011-03-31 13:32 ` Richard Guenther
2011-03-31 13:32 ` Jeff Law
2011-03-31 21:07 ` Michael Matz
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