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* [Bug middle-end/23666] New: Fold does not reduce C - ~a into a + (C+1)
@ 2005-09-01 1:42 pinskia at gcc dot gnu dot org
2005-09-01 6:20 ` [Bug middle-end/23666] " falk at debian dot org
` (2 more replies)
0 siblings, 3 replies; 11+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-09-01 1:42 UTC (permalink / raw)
To: gcc-bugs
The asm for the following two functions should be the same.
int f(int a)
{
return 10 - ~a;
}
int f1(int a)
{
return a + 11;
}
Found while reading LLVM's instruction combiner.
--
Summary: Fold does not reduce C - ~a into a + (C+1)
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P2
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: pinskia at gcc dot gnu dot org
CC: gcc-bugs at gcc dot gnu dot org
OtherBugsDependingO 19987
nThis:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug middle-end/23666] Fold does not reduce C - ~a into a + (C+1)
2005-09-01 1:42 [Bug middle-end/23666] New: Fold does not reduce C - ~a into a + (C+1) pinskia at gcc dot gnu dot org
@ 2005-09-01 6:20 ` falk at debian dot org
2005-09-01 12:00 ` pinskia at gcc dot gnu dot org
2005-09-17 2:11 ` pinskia at gcc dot gnu dot org
2 siblings, 0 replies; 11+ messages in thread
From: falk at debian dot org @ 2005-09-01 6:20 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From falk at debian dot org 2005-09-01 06:19 -------
Works for me on alphaev68-unknown-linux-gnu
tiw with 4.1.0 20050819.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug middle-end/23666] Fold does not reduce C - ~a into a + (C+1)
2005-09-01 1:42 [Bug middle-end/23666] New: Fold does not reduce C - ~a into a + (C+1) pinskia at gcc dot gnu dot org
2005-09-01 6:20 ` [Bug middle-end/23666] " falk at debian dot org
@ 2005-09-01 12:00 ` pinskia at gcc dot gnu dot org
2005-09-17 2:11 ` pinskia at gcc dot gnu dot org
2 siblings, 0 replies; 11+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-09-01 12:00 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-09-01 11:59 -------
(In reply to comment #1)
> Works for me on alphaev68-unknown-linux-gnu
> tiw with 4.1.0 20050819.
And does not with 4.1.0 20050901 on i686-pc-linux-gnu or on powerpc-darwin.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug middle-end/23666] Fold does not reduce C - ~a into a + (C+1)
2005-09-01 1:42 [Bug middle-end/23666] New: Fold does not reduce C - ~a into a + (C+1) pinskia at gcc dot gnu dot org
2005-09-01 6:20 ` [Bug middle-end/23666] " falk at debian dot org
2005-09-01 12:00 ` pinskia at gcc dot gnu dot org
@ 2005-09-17 2:11 ` pinskia at gcc dot gnu dot org
2 siblings, 0 replies; 11+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-09-17 2:11 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-09-17 02:11 -------
Confirmed.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed| |1
Last reconfirmed|0000-00-00 00:00:00 |2005-09-17 02:11:51
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug middle-end/23666] Fold does not reduce C - ~a into a + (C+1)
[not found] <bug-23666-6528@http.gcc.gnu.org/bugzilla/>
` (5 preceding siblings ...)
2005-11-30 16:48 ` pinskia at gcc dot gnu dot org
@ 2006-10-22 15:12 ` rguenth at gcc dot gnu dot org
6 siblings, 0 replies; 11+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2006-10-22 15:12 UTC (permalink / raw)
To: gcc-bugs
------- Comment #10 from rguenth at gcc dot gnu dot org 2006-10-22 15:12 -------
With the patch for 23295 we get the behavior as noted in comment #7. This is
due
to negate_expr_p (correctly) containing
case BIT_NOT_EXPR:
return INTEGRAL_TYPE_P (type)
&& (TYPE_UNSIGNED (type)
|| (flag_wrapv && !flag_trapv));
as negating ~7ffffff will result in signed overflow which is undefined without
flag_wrapv.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug middle-end/23666] Fold does not reduce C - ~a into a + (C+1)
[not found] <bug-23666-6528@http.gcc.gnu.org/bugzilla/>
` (4 preceding siblings ...)
2005-11-29 0:39 ` pinskia at gcc dot gnu dot org
@ 2005-11-30 16:48 ` pinskia at gcc dot gnu dot org
2006-10-22 15:12 ` rguenth at gcc dot gnu dot org
6 siblings, 0 replies; 11+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-11-30 16:48 UTC (permalink / raw)
To: gcc-bugs
------- Comment #9 from pinskia at gcc dot gnu dot org 2005-11-30 16:48 -------
This is exactly the same issue as PR 23295 now (I should copy some of the
comments from here to there).
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
BugsThisDependsOn| |23295
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug middle-end/23666] Fold does not reduce C - ~a into a + (C+1)
[not found] <bug-23666-6528@http.gcc.gnu.org/bugzilla/>
` (3 preceding siblings ...)
2005-11-27 22:26 ` pinskia at gcc dot gnu dot org
@ 2005-11-29 0:39 ` pinskia at gcc dot gnu dot org
2005-11-30 16:48 ` pinskia at gcc dot gnu dot org
2006-10-22 15:12 ` rguenth at gcc dot gnu dot org
6 siblings, 0 replies; 11+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-11-29 0:39 UTC (permalink / raw)
To: gcc-bugs
------- Comment #8 from pinskia at gcc dot gnu dot org 2005-11-29 00:39 -------
I am not going to fix this now as it exposes too many VRP issues and other
issues.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|pinskia at gcc dot gnu dot |unassigned at gcc dot gnu
|org |dot org
Status|ASSIGNED |NEW
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug middle-end/23666] Fold does not reduce C - ~a into a + (C+1)
[not found] <bug-23666-6528@http.gcc.gnu.org/bugzilla/>
` (2 preceding siblings ...)
2005-11-26 22:53 ` pinskia at gcc dot gnu dot org
@ 2005-11-27 22:26 ` pinskia at gcc dot gnu dot org
2005-11-29 0:39 ` pinskia at gcc dot gnu dot org
` (2 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-11-27 22:26 UTC (permalink / raw)
To: gcc-bugs
------- Comment #7 from pinskia at gcc dot gnu dot org 2005-11-27 22:26 -------
After the patch which I am about to test, we get this with -fwrapv (yes that is
weird we get it with something which should be cause optimizations not to
happen and not the other way around).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug middle-end/23666] Fold does not reduce C - ~a into a + (C+1)
[not found] <bug-23666-6528@http.gcc.gnu.org/bugzilla/>
2005-11-26 21:43 ` pinskia at gcc dot gnu dot org
2005-11-26 22:38 ` pinskia at gcc dot gnu dot org
@ 2005-11-26 22:53 ` pinskia at gcc dot gnu dot org
2005-11-27 22:26 ` pinskia at gcc dot gnu dot org
` (3 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-11-26 22:53 UTC (permalink / raw)
To: gcc-bugs
------- Comment #6 from pinskia at gcc dot gnu dot org 2005-11-26 22:53 -------
Actually it is just a check for flag_wrapv which looks to be wrong as far as I
can tell.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug middle-end/23666] Fold does not reduce C - ~a into a + (C+1)
[not found] <bug-23666-6528@http.gcc.gnu.org/bugzilla/>
2005-11-26 21:43 ` pinskia at gcc dot gnu dot org
@ 2005-11-26 22:38 ` pinskia at gcc dot gnu dot org
2005-11-26 22:53 ` pinskia at gcc dot gnu dot org
` (4 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-11-26 22:38 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from pinskia at gcc dot gnu dot org 2005-11-26 22:38 -------
Actually there is two things that need to be done, first is what I said in
comment # 4 and then the second thing is for MINUS_EXPR to use those functions
instead of checking explicatly for NEGATE_EXPR.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug middle-end/23666] Fold does not reduce C - ~a into a + (C+1)
[not found] <bug-23666-6528@http.gcc.gnu.org/bugzilla/>
@ 2005-11-26 21:43 ` pinskia at gcc dot gnu dot org
2005-11-26 22:38 ` pinskia at gcc dot gnu dot org
` (5 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-11-26 21:43 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from pinskia at gcc dot gnu dot org 2005-11-26 21:43 -------
The problem here is my fault, slightly. Fold is converting -(~a) in the
NEGATE_EXPR but not in the generic functions to do the negation. I will do the
patch for this one. (I am saying that -(~a) is more complex than a+1 which is
true).
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|unassigned at gcc dot gnu |pinskia at gcc dot gnu dot
|dot org |org
Status|NEW |ASSIGNED
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23666
^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2006-10-22 15:12 UTC | newest]
Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2005-09-01 1:42 [Bug middle-end/23666] New: Fold does not reduce C - ~a into a + (C+1) pinskia at gcc dot gnu dot org
2005-09-01 6:20 ` [Bug middle-end/23666] " falk at debian dot org
2005-09-01 12:00 ` pinskia at gcc dot gnu dot org
2005-09-17 2:11 ` pinskia at gcc dot gnu dot org
[not found] <bug-23666-6528@http.gcc.gnu.org/bugzilla/>
2005-11-26 21:43 ` pinskia at gcc dot gnu dot org
2005-11-26 22:38 ` pinskia at gcc dot gnu dot org
2005-11-26 22:53 ` pinskia at gcc dot gnu dot org
2005-11-27 22:26 ` pinskia at gcc dot gnu dot org
2005-11-29 0:39 ` pinskia at gcc dot gnu dot org
2005-11-30 16:48 ` pinskia at gcc dot gnu dot org
2006-10-22 15:12 ` rguenth at gcc dot gnu dot org
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