Re: [gimple] assignments to volatile

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

On Sat, Jun 26, 2010 at 5:46 AM, Mark Mitchell <mark@codesourcery.com> wrote:
> Mike Stump wrote:
>
>> I'd like to understand how you interpret the standard.
>
> I simply think it does not say. ?I don't think it says make a copy. ?I
> don't think it says don't make a copy. ?I understand how you are reading
> it, but I think you're finding meaning where none is necessarily
> present. ?I'll be persuaded if you show me a consensus of people on the
> standards reflector, but you didn't want to ask on the reflector.
>
> If it is unspecified, I'd rather not do the read. ?I don't argue the
> standard mandates not doing the read, but I feel that it's better
> behavior. ?I think it's odd to do a read from "y" in "x = y = z", but I
> think it's *very* odd to do a read from "y" in the case of "x ? y = z :
> ...", which is what Nathan says we presently do.
>
>> Other compilers might differ on the re-read. ?Even if they did, I'd
>> still object to changing gcc to match them. ?I'd rather talk with
>> their implementors and figure out if they think they conform to the
>> standard or not, and if not, why? ?Could be just a simple bug in
>> their compiler that they would fix.
>
> I don't find that likely. ?Changing this behavior will change the
> meaning of existing programs in mysterious ways. ?I doubt you'll find
> compiler implementors eager to do that. ?But, we can't know until we
> test the compilers. ?Maybe they all agree with you.
>
> Backwards compatibility is also the best reason not to change GCC; even
> if the standard unambiguously mandated that we change, it might not make
> sense to change, since it might break code that's worked with GCC for a
> long time.

What did GCC do for all these cases pre-tree-ssa?

Richard.