From: Michael Matz <matz@suse.de>
To: Martin Uecker <ma.uecker@gmail.com>
Cc: Richard Biener <richard.guenther@gmail.com>,
"gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Subject: Re: reordering of trapping operations and volatile
Date: Thu, 13 Jan 2022 16:45:03 +0000 (UTC) [thread overview]
Message-ID: <alpine.LSU.2.20.2201131625270.4251@wotan.suse.de> (raw)
In-Reply-To: <bacbe96676729ceafda1ec8077ec3206e4770d82.camel@gmail.com>
Hello,
On Tue, 11 Jan 2022, Martin Uecker via Gcc wrote:
> > Handling all volatile accesses in the
> > very same way would be possible but quite some work I don't
> > see much value in.
>
> I see some value.
>
> But an alternative could be to remove volatile
> from the observable behavior in the standard
> or make it implementation-defined whether it
> is observable or not.
But you are actually arguing for making UB be observable (which then
directly implies an ordering with respect to volatile accesses). That's
much different from making volatile not be observable anymore (which
obviously would be a bad idea), and is also much harder to do, it's
the nature of undefined behaviour to be hard to define :)
Well, what you _actually_ want is an implied dependency between some UB
and volatile accesses (and _only_ those, not e.g. with other UB), and the
difficulty now is to define "some" and to create the dependency without
making that specific UB to be properly observable. I think to define this
all rigorously seems futile (you need a new category between observable
and UB), so it comes down to compiler QoI on a case by case basis.
Ciao,
Michael.
next prev parent reply other threads:[~2022-01-13 16:45 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-08 8:32 Martin Uecker
2022-01-08 12:41 ` Richard Biener
2022-01-08 13:50 ` Martin Uecker
2022-01-08 14:13 ` Marc Glisse
2022-01-08 14:41 ` Eric Botcazou
2022-01-08 15:27 ` Martin Uecker
2022-01-08 17:33 ` Eric Botcazou
2022-01-08 15:03 ` David Brown
2022-01-08 16:42 ` Martin Uecker
2022-01-08 18:35 ` Andrew Pinski
2022-01-08 21:07 ` Martin Uecker
2022-01-10 9:04 ` Richard Biener
2022-01-10 17:36 ` Martin Uecker
2022-01-11 7:11 ` Richard Biener
2022-01-11 8:17 ` Martin Uecker
2022-01-11 9:13 ` Richard Biener
2022-01-11 20:01 ` Martin Uecker
2022-01-13 16:45 ` Michael Matz [this message]
2022-01-13 19:17 ` Martin Uecker
2022-01-14 14:15 ` Michael Matz
2022-01-14 14:58 ` Paul Koning
2022-01-15 21:28 ` Martin Sebor
2022-01-15 21:38 ` Paul Koning
2022-01-16 12:37 ` Martin Uecker
2022-01-14 15:46 ` Martin Uecker
2022-01-14 19:54 ` Jonathan Wakely
2022-01-15 9:00 ` Martin Uecker
2022-01-15 16:33 ` Jonathan Wakely
2022-01-15 18:48 ` Martin Uecker
2022-01-17 14:10 ` Michael Matz
2022-01-18 8:31 ` Richard Biener
2022-01-21 16:21 ` Martin Uecker
2022-01-11 18:17 ` David Brown
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