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From: "law at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/58640] [4.9 Regression] wrong code (segfaults) at -O3 on x86_64-linux-gnu
Date: Thu, 10 Oct 2013 20:47:00 -0000	[thread overview]
Message-ID: <bug-58640-4-VtIx7pdLNq@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-58640-4@http.gcc.gnu.org/bugzilla/>

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58640

--- Comment #4 from Jeffrey A. Law <law at redhat dot com> ---
We're ending up with latches from two different loops going to the same
destination due to the jump thread path passing through multiple loops.  This
ultimately causes the unroller to go nuts.

This should be fairly easy to catch & avoid.  And this brings to the forefront
a question that's been slowly building in the back of my mind.

Specifically, given a jump threading path, we have the ability now to lop off
the tail of the path if threading all the way to the tail would ultimately
force cancellation of the jump thread request.  Lopping off the tail may result
in better code than totally cancelling the request.  This testcase is a good
example.

Anyway, I'll be pondering how we want to deal with that as well.


  parent reply	other threads:[~2013-10-10 20:47 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-10-06  5:23 [Bug tree-optimization/58640] New: " su at cs dot ucdavis.edu
2013-10-06 12:31 ` [Bug tree-optimization/58640] " mikpelinux at gmail dot com
2013-10-10 11:59 ` [Bug tree-optimization/58640] [4.9 Regression] " rguenth at gcc dot gnu.org
2013-10-10 19:23 ` law at redhat dot com
2013-10-10 20:09 ` law at redhat dot com
2013-10-10 20:47 ` law at redhat dot com [this message]
2013-10-11  3:07 ` law at redhat dot com
2013-10-11 20:31 ` law at gcc dot gnu.org
2013-10-11 20:32 ` law at redhat dot com
2013-10-12  0:56 ` su at cs dot ucdavis.edu
2013-10-14  9:15 ` rguenth at gcc dot gnu.org
2013-10-14  9:17 ` rguenth at gcc dot gnu.org
2013-11-09  6:02 ` law at redhat dot com
2013-12-08 17:05 ` olegendo at gcc dot gnu.org
2013-12-10  6:55 ` law at redhat dot com
2013-12-10 11:20 ` olegendo at gcc dot gnu.org

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