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From: "law at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/58387] [4.9 Regression] wrong code at -Os and above on x86_64-linux-gnu (both 32-bit and 64-bit modes)
Date: Fri, 13 Sep 2013 16:33:00 -0000	[thread overview]
Message-ID: <bug-58387-4-46rvrtRbpd@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-58387-4@http.gcc.gnu.org/bugzilla/>

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58387

--- Comment #18 from Jeffrey A. Law <law at redhat dot com> ---
I'll also note that the plan for the isolated paths that exhibit undefined
behaviour is to have them trap/abort at the statement which triggers the
undefined behaviour.

The original patch from 2011 actually eliminated the undefined behaviour path
entirely, that's incorrect in that earlier code in the path might have
observable side effects (such as a printf call).  It would also make more
problems with "optimization unstable code".

By unconditionally trapping/aborting at the statement which triggered the
undefined behaviour (say a null pointer dereference), we still get any prior
observable side effects on the path and we halt the program at the point of
undefined behaviour, thus avoiding the multitude of problems around
"optimization unstable code".


  parent reply	other threads:[~2013-09-13 16:33 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-09-10 23:10 [Bug middle-end/58387] New: " su at cs dot ucdavis.edu
2013-09-11  5:17 ` [Bug middle-end/58387] " jakub at gcc dot gnu.org
2013-09-11  5:22 ` su at cs dot ucdavis.edu
2013-09-11  6:13 ` jakub at gcc dot gnu.org
2013-09-11  7:10 ` su at cs dot ucdavis.edu
2013-09-11 15:04 ` su at cs dot ucdavis.edu
2013-09-11 16:50 ` [Bug middle-end/58387] [4.9 Regression] " hjl.tools at gmail dot com
2013-09-12 21:19 ` hjl.tools at gmail dot com
2013-09-12 21:29 ` law at redhat dot com
2013-09-13  3:35 ` law at redhat dot com
2013-09-13  6:02 ` law at redhat dot com
2013-09-13  7:10 ` su at cs dot ucdavis.edu
2013-09-13 11:10 ` markus at trippelsdorf dot de
2013-09-13 15:28 ` law at redhat dot com
2013-09-13 15:48 ` su at cs dot ucdavis.edu
2013-09-13 16:02 ` law at redhat dot com
2013-09-13 16:25 ` joseph at codesourcery dot com
2013-09-13 16:33 ` law at redhat dot com [this message]
2013-09-13 17:31 ` glisse at gcc dot gnu.org
2013-09-13 18:00 ` law at redhat dot com
2013-09-13 19:18 ` glisse at gcc dot gnu.org
2013-09-17 18:39 ` law at redhat dot com

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