public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/51885] g++ compiler options -O2 and -O3 modifies program results
Date: Wed, 18 Jan 2012 10:09:00 -0000 [thread overview]
Message-ID: <bug-51885-4-Qy6Xvxpciw@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-51885-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51885
Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |manu at gcc dot gnu.org
--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-01-18 10:02:04 UTC ---
(In reply to comment #2)
> The reinterpret_cast definitely results in undefined behaviour, because it
> accesses the float objects through a different type, violating [basic.lval]/10
>
> And indeed, -fno-strict-aliasing makes the problem go away.
It definitely does not make the problem go away, it merely hides it. The
undefined behavior does not disappear just by using command-line options.
On the other hand, is it possible to cast a float pointer to a uint32 pointer
and use it for anything that does not invoke undefined behaviour?
GCC gives a warning with -Wstrict-aliasing=1 but no with other levels.
next prev parent reply other threads:[~2012-01-18 10:02 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-17 18:59 [Bug c++/51885] New: " laurentlouis.maurin at wanadoo dot fr
2012-01-17 18:59 ` [Bug c++/51885] " paolo.carlini at oracle dot com
2012-01-17 20:00 ` redi at gcc dot gnu.org
2012-01-18 10:09 ` manu at gcc dot gnu.org [this message]
2012-01-20 20:04 ` laurentlouis.maurin at wanadoo dot fr
2012-01-20 20:06 ` redi 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-51885-4-Qy6Xvxpciw@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).