From: Qing Zhao <qing.zhao@oracle.com>
To: gcc@gcc.gnu.org, gcc Patches <gcc-patches@gcc.gnu.org>
Subject: A bug in vrp_meet?
Date: Thu, 28 Feb 2019 17:05:00 -0000 [thread overview]
Message-ID: <ABC070F7-B7FC-4114-ABB4-CA3CA662C7AF@oracle.com> (raw)
Hi,
I have been debugging a runtime error caused by value range propagation. and finally located to the following gcc routine:
vrp_meet_1 in gcc/tree-vrp.c
====
/* Meet operation for value ranges. Given two value ranges VR0 and
VR1, store in VR0 a range that contains both VR0 and VR1. This
may not be the smallest possible such range. */
static void
vrp_meet_1 (value_range *vr0, const value_range *vr1)
{
value_range saved;
if (vr0->type == VR_UNDEFINED)
{
set_value_range (vr0, vr1->type, vr1->min, vr1->max, vr1->equiv);
return;
}
if (vr1->type == VR_UNDEFINED)
{
/* VR0 already has the resulting range. */
return;
}
====
In the above, when one of vr0 or vr1 is VR_UNDEFINED, the meet result of these two will be the other VALUE.
This seems not correct to me.
For example, the following is the located incorrect value range propagation: (portion from the dump file *.181t.dom3)
====
Visiting PHI node: i_83 = PHI <_152(20), 0(22)>
Argument #0 (20 -> 10 executable)
_152: UNDEFINED
Argument #1 (22 -> 10 executable)
0: [0, 0]
Meeting
UNDEFINED
and
[0, 0]
to
[0, 0]
Intersecting
[0, 0]
and
[0, 65535]
to
[0, 0]
====
In the above, “i_83” is defined as PHI <_152(20), 0(22)>, the 1st argument is UNDEFINED at this time(but its value range definitely is NOT [0,0]),
and the 2nd argument is 0.
“vrp_meet” generate a VR_RANGE with [0,0] for “i_83” based on the current algorithm. Obviously, this result VR_RANGE with [0,0] does NOT
contain the value ranges for _152.
the result of “vrp_meet” is Not correct. and this incorrect value range result finally caused the runtime error.
I ‘d like to modify the vrp_meet_1 as following:
====
static void
vrp_meet_1 (value_range *vr0, const value_range *vr1)
{
value_range saved;
if (vr0->type == VR_UNDEFINED)
{
/* VR0 already has the resulting range. */
return;
}
if (vr1->type == VR_UNDEFINED)
{
set_value_range_to_undefined (vr0)
return;
}
====
let me know your opinion.
thanks a lot for the help.
Qing
next reply other threads:[~2019-02-28 17:05 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-28 17:05 Qing Zhao [this message]
2019-02-28 19:54 ` Jeff Law
2019-03-01 17:49 ` Qing Zhao
2019-03-01 19:25 ` Richard Biener
2019-03-01 21:02 ` Qing Zhao
2019-03-04 11:45 ` Richard Biener
2019-03-04 16:09 ` Qing Zhao
2019-03-04 22:01 ` Qing Zhao
2019-03-05 9:48 ` Richard Biener
2019-03-05 10:44 ` Richard Biener
2019-03-05 14:45 ` Richard Biener
2019-03-05 21:36 ` Jeff Law
2019-03-06 10:06 ` Richard Biener
2019-03-07 12:47 ` Richard Biener
2019-05-05 21:09 ` Eric Botcazou
2019-05-06 11:27 ` Richard Biener
2019-03-19 19:53 ` Jeff Law
2019-03-20 8:27 ` Richard Biener
2019-03-05 21:27 ` Jeff Law
2019-03-05 21:17 ` Jeff Law
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=ABC070F7-B7FC-4114-ABB4-CA3CA662C7AF@oracle.com \
--to=qing.zhao@oracle.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=gcc@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).