public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/42577] array bounds false positive with -O3, goes away with -O2
Date: Fri, 01 Jan 2010 22:42:00 -0000	[thread overview]
Message-ID: <20100101224200.812.qmail@sourceware.org> (raw)
In-Reply-To: <bug-42577-8137@http.gcc.gnu.org/bugzilla/>



------- Comment #3 from rguenth at gcc dot gnu dot org  2010-01-01 22:42 -------
The array indexing is done with D.25175_104, but

  D.25173_102 = (uint16) cutawaySlot_256;
  D.25174_103 = D.25173_102 + 10;
  D.25175_104 = (int) D.25174_103;
...
  if (D.25174_103 > 9)
    goto <bb 26>;
  else
    goto <bb 30>;

the actual check is done on D.25174_103.  We do not add asserts for
D.25175_104 on the edge to BB30.  D.25174 is unsigned short.

So we end up with

D.25173_102: [0, 1]
D.25174_103: [10, 11]
D.25175_104: [10, 11]

and warn for the access that is dominated by BB30.

So the issue is that we warn for dead code.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42577


  parent reply	other threads:[~2010-01-01 22:42 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-01-01 21:01 [Bug middle-end/42577] New: " matt at use dot net
2010-01-01 21:02 ` [Bug middle-end/42577] " matt at use dot net
2010-01-01 21:16 ` matt at use dot net
2010-01-01 22:42 ` rguenth at gcc dot gnu dot org [this message]
2010-01-02 14:57 ` rguenth at gcc dot gnu dot org
2010-01-02 16:41 ` [Bug middle-end/42577] [4.4/4.5 Regression] " rguenth at gcc dot gnu dot org
2010-01-02 16:42 ` rguenth at gcc dot gnu dot org
2010-01-02 19:15 ` rguenth at gcc dot gnu dot org
2010-01-02 19:15 ` [Bug middle-end/42577] [4.4 " rguenth at gcc dot gnu dot org
2010-01-03 19:58 ` matt at use dot net
2010-01-03 22:33 ` rguenth at gcc dot gnu dot org
2010-01-04  1:04 ` matt at use dot net
2010-01-04 14:26 ` rguenth at gcc dot gnu dot org
2010-01-17 17:39 ` rguenth at gcc dot gnu dot org
2010-01-21 13:18 ` jakub at gcc dot gnu dot org
2010-02-10  1:26 ` matt at use dot net
2010-04-30  9:01 ` jakub at gcc dot gnu dot 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=20100101224200.812.qmail@sourceware.org \
    --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).