From: Vincent Lefevre <vincent+gcc@vinc17.org>
To: gcc-help@gcc.gnu.org
Subject: Re: False positive from -Warray-bounds?
Date: Fri, 30 Dec 2011 00:16:00 -0000 [thread overview]
Message-ID: <20111229235727.GU5641@xvii.vinc17.org> (raw)
In-Reply-To: <mcrr4zn3qsn.fsf@dhcp-172-18-216-180.mtv.corp.google.com>
On 2011-12-29 15:24:08 -0800, Ian Lance Taylor wrote:
> I guess it's a matter of perspective. What that text is intended to say
> is: the compiler can prove that the array access is out of bounds.
... based on an incorrect hypothesis (that the path can be reached).
With an incorrect hypothesis, one can prove anything. So, I don't
think that would be a valid proof.
For instance, compiling the following code with -O2 -Warray-bounds -c
triggers the warning.
unsigned int f(unsigned int value)
{
unsigned int i = (value & 0xffff);
return (i == 0xffff ? 0xffffffff : i);
}
static int arr1[10];
void t(unsigned int s)
{
if (s >> 1 == 0)
{
arr1[f(s)] = 0;
arr1[f(s)] = 0;
}
}
--
Vincent Lefèvre <vincent@vinc17.net> - Web: <http://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / Arénaire project (LIP, ENS-Lyon)
next prev parent reply other threads:[~2011-12-29 23:57 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-29 22:02 Lars Gullik Bjønnes
2011-12-29 22:45 ` Ian Lance Taylor
2011-12-29 23:03 ` Lars Gullik Bjønnes
2011-12-29 23:57 ` Ian Lance Taylor
2011-12-30 0:16 ` Vincent Lefevre [this message]
2011-12-30 0:21 ` Vincent Lefevre
2011-12-30 0:38 ` Ian Lance Taylor
2011-12-30 5:00 ` Vincent Lefevre
2011-12-30 8:29 ` Ian Lance Taylor
2011-12-30 12:08 ` David Brown
2011-12-30 19:44 ` Vincent Lefevre
2011-12-29 23:24 ` Vincent Lefevre
2011-12-30 0:19 ` Ian Lance Taylor
2011-12-29 23:17 ` Vincent Lefevre
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