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* [Bug middle-end/35307] New: Missing Simplication for div op
@ 2008-02-23 5:17 xinliangli at gmail dot com
2008-02-23 19:58 ` [Bug middle-end/35307] " segher at kernel dot crashing dot org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: xinliangli at gmail dot com @ 2008-02-23 5:17 UTC (permalink / raw)
To: gcc-bugs
The following rule is good to have:
int i, i, k;
i/j/k ===> i/(j*k)
--
Summary: Missing Simplication for div op
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: xinliangli at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35307
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/35307] Missing Simplication for div op
2008-02-23 5:17 [Bug middle-end/35307] New: Missing Simplication for div op xinliangli at gmail dot com
@ 2008-02-23 19:58 ` segher at kernel dot crashing dot org
2008-02-23 20:01 ` pinskia at gcc dot gnu dot org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: segher at kernel dot crashing dot org @ 2008-02-23 19:58 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from segher at kernel dot crashing dot org 2008-02-23 19:57 -------
Not equivalent in the presence of overflow.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35307
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/35307] Missing Simplication for div op
2008-02-23 5:17 [Bug middle-end/35307] New: Missing Simplication for div op xinliangli at gmail dot com
2008-02-23 19:58 ` [Bug middle-end/35307] " segher at kernel dot crashing dot org
@ 2008-02-23 20:01 ` pinskia at gcc dot gnu dot org
2008-02-24 22:17 ` rguenth at gcc dot gnu dot org
2008-02-26 16:17 ` segher at kernel dot crashing dot org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2008-02-23 20:01 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from pinskia at gcc dot gnu dot org 2008-02-23 20:00 -------
(In reply to comment #1)
> Not equivalent in the presence of overflow.
You mean defined overflow :).
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
Keywords| |missed-optimization
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35307
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/35307] Missing Simplication for div op
2008-02-23 5:17 [Bug middle-end/35307] New: Missing Simplication for div op xinliangli at gmail dot com
2008-02-23 19:58 ` [Bug middle-end/35307] " segher at kernel dot crashing dot org
2008-02-23 20:01 ` pinskia at gcc dot gnu dot org
@ 2008-02-24 22:17 ` rguenth at gcc dot gnu dot org
2008-02-26 16:17 ` segher at kernel dot crashing dot org
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2008-02-24 22:17 UTC (permalink / raw)
To: gcc-bugs
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2008-02-24 22:16:29
date| |
Version|unknown |4.3.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35307
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/35307] Missing Simplication for div op
2008-02-23 5:17 [Bug middle-end/35307] New: Missing Simplication for div op xinliangli at gmail dot com
` (2 preceding siblings ...)
2008-02-24 22:17 ` rguenth at gcc dot gnu dot org
@ 2008-02-26 16:17 ` segher at kernel dot crashing dot org
3 siblings, 0 replies; 5+ messages in thread
From: segher at kernel dot crashing dot org @ 2008-02-26 16:17 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from segher at kernel dot crashing dot org 2008-02-26 16:16 -------
> > Not equivalent in the presence of overflow.
>
> You mean defined overflow :).
No, I mean overflow.
Let's assume int is 16-bit (just to keep the numbers smallish);
now take i=1, j=1000, k=1000. i/j/k is perfectly well-defined,
but i/(j*k) overflows in the j*k computation.
Segher
--
segher at kernel dot crashing dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |segher at kernel dot
| |crashing dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35307
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2008-02-26 16:17 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2008-02-23 5:17 [Bug middle-end/35307] New: Missing Simplication for div op xinliangli at gmail dot com
2008-02-23 19:58 ` [Bug middle-end/35307] " segher at kernel dot crashing dot org
2008-02-23 20:01 ` pinskia at gcc dot gnu dot org
2008-02-24 22:17 ` rguenth at gcc dot gnu dot org
2008-02-26 16:17 ` segher at kernel dot crashing dot org
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