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From: "jason at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/58920] New: Overeager optimization based on TREE_THIS_NOTRAP Date: Wed, 30 Oct 2013 03:25:00 -0000 [thread overview] Message-ID: <bug-58920-4@http.gcc.gnu.org/bugzilla/> (raw) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58920 Bug ID: 58920 Summary: Overeager optimization based on TREE_THIS_NOTRAP Product: gcc Version: 4.9.0 Status: UNCONFIRMED Keywords: wrong-code Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: jason at gcc dot gnu.org Created attachment 31108 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31108&action=edit Patch to set TREE_THIS_NOTRAP for C++ references The TREE_THIS_NOTRAP macro came up in email the other day, and it seemed to me that it would be useful to set on C++ references, since they are required to refer to objects; trying to read from a null reference gives undefined behavior. So I tried the attached patch. But it breaks all the ext_pointer tests in libstdc++. Basically, what's happening is that there is a code path which is never taken which leads to an explicit null dereference. The optimizers see this happening within a loop and decide to hoist it out of the loop. So now it is executed before the loop starts, and causes a SEGV. Is this an appropriate optimization?
next reply other threads:[~2013-10-30 3:25 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-10-30 3:25 jason at gcc dot gnu.org [this message] 2013-10-30 3:27 ` [Bug tree-optimization/58920] " jason at gcc dot gnu.org 2013-10-30 4:07 ` pinskia at gcc dot gnu.org 2013-10-30 10:04 ` ebotcazou at gcc dot gnu.org 2013-10-30 10:16 ` rguenth at gcc dot gnu.org 2013-10-30 10:27 ` ebotcazou at gcc dot gnu.org 2013-10-30 10:31 ` rguenth at gcc dot gnu.org 2021-08-13 23:42 ` pinskia at gcc dot gnu.org
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