public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/53265] Warn when undefined behavior implies smaller iteration count
Date: Wed, 13 Mar 2013 11:01:00 -0000 [thread overview]
Message-ID: <bug-53265-4-eMHvyVpz91@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-53265-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53265
--- Comment #24 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-13 11:00:11 UTC ---
(In reply to comment #23)
> Created attachment 29661 [details]
> gcc48-pr53265.patch
>
> Updated patch as per IRC discussions. Still need to look at longbranch2.C and
> do_1.f90, then test it.
Looks good. Few comments:
+ number_of_latch_executions (loop);
add a comment what side-effect you are interested in.
+
+ /* If we know the exact number of iterations of this loop avoid all the
+ work below and most importantly do not break code with undefined
+ behavior by recording smaller maximum number of iterations. */
+ if (loop->nb_iterations
+ && TREE_CODE (loop->nb_iterations) == INTEGER_CST
+ && loop->any_upper_bound
+ && loop->nb_iterations_upper_bound.ucmp
+ (tree_to_double_int (loop->nb_iterations)) < 0)
+ loop->nb_iterations_upper_bound = tree_to_double_int
(loop->nb_iterations);
We don't avoid any work, so adjust the comment. I'd also simply do:
/* If we know the exact number of iterations record that as the
upper bound as well. This avoids breaking code with undefined
behavior by eventually recording a smaller maximum. */
if (loop->nb_iterations
&& TREE_CODE (loop->nb_iterations) == INTEGER_CST)
{
loop->any_upper_bound = true;
loop->nb_iterations_upper_bound = tree_to_double_int
(loop->nb_iterations);
}
that's always correct.
next prev parent reply other threads:[~2013-03-13 11:01 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-07 14:09 [Bug tree-optimization/53265] New: " amonakov at gcc dot gnu.org
2012-05-07 14:21 ` [Bug tree-optimization/53265] " rguenth at gcc dot gnu.org
2013-01-29 17:23 ` jakub at gcc dot gnu.org
2013-01-31 12:13 ` jakub at gcc dot gnu.org
2013-03-11 10:15 ` rguenth at gcc dot gnu.org
2013-03-11 14:14 ` rguenth at gcc dot gnu.org
2013-03-11 14:16 ` rguenth at gcc dot gnu.org
2013-03-11 14:17 ` rguenth at gcc dot gnu.org
2013-03-11 15:49 ` jakub at gcc dot gnu.org
2013-03-11 15:59 ` rguenth at gcc dot gnu.org
2013-03-11 16:16 ` amonakov at gcc dot gnu.org
2013-03-11 16:42 ` manu at gcc dot gnu.org
2013-03-11 16:50 ` manu at gcc dot gnu.org
2013-03-11 17:11 ` jakub at gcc dot gnu.org
2013-03-12 11:25 ` jakub at gcc dot gnu.org
2013-03-12 11:26 ` jakub at gcc dot gnu.org
2013-03-12 11:30 ` jakub at gcc dot gnu.org
2013-03-12 11:48 ` jakub at gcc dot gnu.org
2013-03-12 12:37 ` jakub at gcc dot gnu.org
2013-03-12 12:41 ` jakub at gcc dot gnu.org
2013-03-12 14:15 ` jakub at gcc dot gnu.org
2013-03-12 20:10 ` jakub at gcc dot gnu.org
2013-03-12 21:48 ` jakub at gcc dot gnu.org
2013-03-13 10:36 ` jakub at gcc dot gnu.org
2013-03-13 11:01 ` rguenth at gcc dot gnu.org [this message]
2013-03-14 9:14 ` jakub at gcc dot gnu.org
2013-03-14 10:55 ` jakub at gcc dot gnu.org
2013-04-29 23:18 ` ppluzhnikov at google dot com
2013-04-30 6:07 ` jakub at gcc dot gnu.org
2013-04-30 6:46 ` jakub at gcc dot gnu.org
2014-02-16 13:14 ` jackie.rosen at hushmail dot com
2023-06-09 16:52 ` 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-53265-4-eMHvyVpz91@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: link
Be 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).