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From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/41244] "&data[i] - data" isn't converted to "i"
Date: Thu, 03 Sep 2009 14:12:00 -0000 [thread overview]
Message-ID: <20090903141237.13233.qmail@sourceware.org> (raw)
In-Reply-To: <bug-41244-14164@http.gcc.gnu.org/bugzilla/>
------- Comment #2 from rguenth at gcc dot gnu dot org 2009-09-03 14:12 -------
Because the index arithmetic is done unsigned.
return (int) ((unsigned int) i * 212) /[ex] 212;
We lost the information that i * 212 cannot overflow.
Simpler testcase:
extern int data[];
int find(int i)
{
return &data[i] - data;
}
from which we enter c_fully_fold_internal with
((int) ((int *) &data + (unsigned int) ((unsigned int) i * 4)) - (int) &data)
/[ex] 4
addressed on the no-undefined-overflow branch.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Keywords| |missed-optimization
Last reconfirmed|0000-00-00 00:00:00 |2009-09-03 14:12:37
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41244
next prev parent reply other threads:[~2009-09-03 14:12 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-03 13:49 [Bug tree-optimization/41244] New: " zsojka at seznam dot cz
2009-09-03 13:51 ` [Bug tree-optimization/41244] " zsojka at seznam dot cz
2009-09-03 14:12 ` rguenth at gcc dot gnu dot org [this message]
[not found] <bug-41244-4@http.gcc.gnu.org/bugzilla/>
2021-09-14 22:03 ` pinskia at gcc dot gnu.org
2021-10-09 21:19 ` pinskia at gcc dot gnu.org
2023-06-11 19:44 ` pinskia at gcc dot gnu.org
2023-06-11 23:54 ` pinskia at gcc dot gnu.org
2023-06-12 0:30 ` pinskia at gcc dot gnu.org
2023-06-12 1:33 ` pinskia at gcc dot gnu.org
2023-06-12 2:12 ` pinskia at gcc dot gnu.org
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