public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "torvald at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/59448] Code generation doesn't respect C11 address-dependency Date: Mon, 17 Feb 2014 21:03:00 -0000 [thread overview] Message-ID: <bug-59448-4-wqkYHr19o5@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-59448-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59448 --- Comment #12 from torvald at gcc dot gnu.org --- (In reply to algrant from comment #11) > Where do you get that this is racy if the access to data is not atomic? In threadB(), you do: f = flag.load(std::memory_order_consume); // B.A d = *(&data + f - f); // B.B That reads from data irrespective of the value of f, so will read when data is actually not "owned" by threadB. You can either make the accesses to data atomic, or move the load from data to after checking that flag equals 1. > By > design, release/acquire and release/consume sequences don't require > wholesale changes to the way the data payload (in the general case, multiple > fields within a structure) is first constructed and then used. 1.10#13 > makes clear that as a result of the intra-thread sequencing between atomic > and non-atomic operations (1.9#14), and the inter-thread ordering between > atomic operations (1.10 various), there is a resulting ordering on > operations to "ordinary" (sic) objects. Please see the references to the > C++ standard in the source example, for the chain of reasoning here. I'm very much aware of the rules, I believe. But as far as you can see, there's a data race in your test program, which results in undefined behavior.
next prev parent reply other threads:[~2014-02-17 21:03 UTC|newest] Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-12-10 12:07 [Bug target/59448] New: ARM code " algrant at acm dot org 2013-12-10 14:19 ` [Bug c/59448] Code " rearnsha at gcc dot gnu.org 2013-12-10 16:43 ` algrant at acm dot org 2013-12-10 17:47 ` joseph at codesourcery dot com 2013-12-12 18:07 ` [Bug middle-end/59448] " algrant at acm dot org 2013-12-16 14:38 ` joseph at codesourcery dot com 2014-01-20 8:52 ` algrant at acm dot org 2014-01-20 9:02 ` pinskia at gcc dot gnu.org 2014-01-20 10:13 ` algrant at acm dot org 2014-01-20 14:21 ` joseph at codesourcery dot com 2014-01-23 22:28 ` torvald at gcc dot gnu.org 2014-02-17 10:26 ` algrant at acm dot org 2014-02-17 21:03 ` torvald at gcc dot gnu.org [this message] 2014-02-17 22:22 ` algrant at acm dot org 2014-10-28 10:56 ` ramana at gcc dot gnu.org 2014-10-28 12:48 ` amacleod at redhat dot com 2014-10-28 13:43 ` joseph at codesourcery dot com 2014-10-28 17:37 ` t.p.northover at gmail dot com 2014-10-29 1:48 ` joseph at codesourcery dot com 2014-10-29 9:23 ` torvald at gcc dot gnu.org 2014-10-30 21:08 ` torvald at gcc dot gnu.org 2014-10-30 22:16 ` filter-gcc at preshing dot com 2014-11-24 12:13 ` filter-gcc at preshing dot com 2015-01-14 13:59 ` amacleod at redhat dot com 2022-01-15 1:47 ` pinskia at gcc dot gnu.org 2022-01-15 1:53 ` pinskia at gcc dot gnu.org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=bug-59448-4-wqkYHr19o5@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).