Re: C++0x Memory model and gcc

[Richard Guenther <richard dot guenther at gmail dot com>]

On Thu, May 6, 2010 at 5:43 PM, Andrew MacLeod <amacleod@redhat.com> wrote:
> I've been working for a while on understanding how the new memory model and
> Atomics work, and what the impacts are on GCC.
>
> It would be ideal to get as many of these changes into GCC 4.6 as possible.
> I've started work on some of the modifications and testing, ?and the overall
> impact on GCC shouldn't be *too* bad :-)
>
> The plan is to localize the changes as much as possible, and any intrusive
> bits like optimization changes will be controlled by a flag enabling us to
> keep the current behaviour when we want it.
>
> I've put together a document summarizing how the memory model works, and how
> I propose to make the changes. I've converted it to wiki pages. ?Maybe no
> one will laugh at my choice of document format this time :-)
>
> The document is linked off the Atomics wiki page, or directly ?here:
> ?http://gcc.gnu.org/wiki/Atomic/GCCMM
>
> It consists mainly of describing the 2 primary aspects of the memory model
> which affects us
> - Optimization changes to avoid introducing new data races
> - Implementation of atomic variables and synchronization modes
> as well as a new infrastructure to test these types of things.
>
> I'm sure I've screwed something up while doing it, and I will proofread it
> later today again and tweak it further.
>
> Please point out anything that isn't clear, ?or is downright wrong.
> Especially in the testing methodology since its all new stuff.
> Suggestions for improvements on any of the plan are welcome as well.

First let me say that the C++ memory model is crap when it
forces data-races to be avoided for unannotated data like
the examples for packed data.

Well, I hope that instead of just disabling optimizations you
will help to improve their implementation to be able to optimize
in a conformant manner.

Richard.

> Andrew
>
>
>
>