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* [Bug c/56250] New: Wrong constant folding on unsigned int
@ 2013-02-08 1:39 ishiura-compiler at ml dot kwansei.ac.jp
2013-02-08 1:52 ` [Bug c/56250] " pinskia at gcc dot gnu.org
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: ishiura-compiler at ml dot kwansei.ac.jp @ 2013-02-08 1:39 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56250
Bug #: 56250
Summary: Wrong constant folding on unsigned int
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: ishiura-compiler@ml.kwansei.ac.jp
GCC 4.7.2 and 4.8.0 miscompile the following code where UINT_MAX ==
4294967295.
$ cat bug.c
int main(void)
{
unsigned x = 2;
return ((unsigned) 0 - ( x / 2 ) ) / 2;
}
$ gcc bug.c
$ ./a.out
$ echo $?
0
Unsigned (0-(x/2))/2 should evaluate to 2147483647 instead of 0.
The following code with variable x replaced by "(unsigned) 2" is
correctly compiled.
$ cat nobug.c
int main(void)
{
return ((unsigned) 0 - ( (unsigned) 2 / 2 ) ) / 2;
}
$ gcc nobug.c
$ ./a.out
$ echo $?
255
The miscompile seems to occur on many versions of gcc (4.2 - 4.8, and
even 4.0 and 3.1 on i686-apple-darwin, 4.4 - 4.6 on
i686-linux-gnu-gcc, etc.)
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug c/56250] Wrong constant folding on unsigned int
2013-02-08 1:39 [Bug c/56250] New: Wrong constant folding on unsigned int ishiura-compiler at ml dot kwansei.ac.jp
@ 2013-02-08 1:52 ` pinskia at gcc dot gnu.org
2013-02-08 1:54 ` [Bug middle-end/56250] " pinskia at gcc dot gnu.org
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu.org @ 2013-02-08 1:52 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56250
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-02-08 01:51:39 UTC ---
When I do this:
unsigned x = 2;
unsigned t = (x/2);
unsigned t1 = -t;
unsigned t2 = t2/2;
t2 is 0 which is correct. I don't see why 2147483647 is correct.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug middle-end/56250] Wrong constant folding on unsigned int
2013-02-08 1:39 [Bug c/56250] New: Wrong constant folding on unsigned int ishiura-compiler at ml dot kwansei.ac.jp
2013-02-08 1:52 ` [Bug c/56250] " pinskia at gcc dot gnu.org
@ 2013-02-08 1:54 ` pinskia at gcc dot gnu.org
2013-02-08 1:59 ` ishiura-compiler at ml dot kwansei.ac.jp
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: pinskia at gcc dot gnu.org @ 2013-02-08 1:54 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56250
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
Component|c |middle-end
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-02-08 01:54:23 UTC ---
Actually I get the correct results with the split out one. The problem is
division is being merged together over the negative which is not valid for
wrapping cases.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug middle-end/56250] Wrong constant folding on unsigned int
2013-02-08 1:39 [Bug c/56250] New: Wrong constant folding on unsigned int ishiura-compiler at ml dot kwansei.ac.jp
2013-02-08 1:52 ` [Bug c/56250] " pinskia at gcc dot gnu.org
2013-02-08 1:54 ` [Bug middle-end/56250] " pinskia at gcc dot gnu.org
@ 2013-02-08 1:59 ` ishiura-compiler at ml dot kwansei.ac.jp
2013-02-08 8:31 ` jakub at gcc dot gnu.org
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: ishiura-compiler at ml dot kwansei.ac.jp @ 2013-02-08 1:59 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56250
--- Comment #3 from Ishiura Lab Compiler Team <ishiura-compiler at ml dot kwansei.ac.jp> 2013-02-08 01:59:18 UTC ---
(In reply to comment #1)
> When I do this:
> unsigned x = 2;
> unsigned t = (x/2);
> unsigned t1 = -t;
> unsigned t2 = t2/2;
>
> t2 is 0 which is correct. I don't see why 2147483647 is correct.
The last line should be
unsigned t2 = t1/2;
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug middle-end/56250] Wrong constant folding on unsigned int
2013-02-08 1:39 [Bug c/56250] New: Wrong constant folding on unsigned int ishiura-compiler at ml dot kwansei.ac.jp
` (2 preceding siblings ...)
2013-02-08 1:59 ` ishiura-compiler at ml dot kwansei.ac.jp
@ 2013-02-08 8:31 ` jakub at gcc dot gnu.org
2013-02-08 11:24 ` [Bug tree-optimization/56250] " jakub at gcc dot gnu.org
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2013-02-08 8:31 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56250
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2013-02-08
CC| |jakub at gcc dot gnu.org
AssignedTo|unassigned at gcc dot |jakub at gcc dot gnu.org
|gnu.org |
Ever Confirmed|0 |1
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-08 08:31:03 UTC ---
Bug is in extract_muldiv_1.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/56250] Wrong constant folding on unsigned int
2013-02-08 1:39 [Bug c/56250] New: Wrong constant folding on unsigned int ishiura-compiler at ml dot kwansei.ac.jp
` (3 preceding siblings ...)
2013-02-08 8:31 ` jakub at gcc dot gnu.org
@ 2013-02-08 11:24 ` jakub at gcc dot gnu.org
2013-02-08 15:07 ` jakub at gcc dot gnu.org
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2013-02-08 11:24 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56250
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-08 11:24:02 UTC ---
Created attachment 29394
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29394
gcc48-pr56250.patch
Untested fix.
I believe only division/modulus is problematic, not multiplication, and I think
-fwrapv signed types are fine too. For *_DIV_EXPR/*_MOD_EXPR, I think
wide_type is always NULL_TREE and ctype is always equal to type.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/56250] Wrong constant folding on unsigned int
2013-02-08 1:39 [Bug c/56250] New: Wrong constant folding on unsigned int ishiura-compiler at ml dot kwansei.ac.jp
` (4 preceding siblings ...)
2013-02-08 11:24 ` [Bug tree-optimization/56250] " jakub at gcc dot gnu.org
@ 2013-02-08 15:07 ` jakub at gcc dot gnu.org
2013-02-08 15:24 ` jakub at gcc dot gnu.org
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2013-02-08 15:07 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56250
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-08 15:06:37 UTC ---
Author: jakub
Date: Fri Feb 8 15:06:26 2013
New Revision: 195888
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195888
Log:
PR tree-optimization/56250
* fold-const.c (extract_muldiv_1) <case NEGATE_EXPR>: Don't optimize
if type is unsigned and code isn't MULT_EXPR.
* gcc.c-torture/execute/pr56250.c: New test.
Added:
trunk/gcc/testsuite/gcc.c-torture/execute/pr56250.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/fold-const.c
trunk/gcc/testsuite/ChangeLog
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/56250] Wrong constant folding on unsigned int
2013-02-08 1:39 [Bug c/56250] New: Wrong constant folding on unsigned int ishiura-compiler at ml dot kwansei.ac.jp
` (5 preceding siblings ...)
2013-02-08 15:07 ` jakub at gcc dot gnu.org
@ 2013-02-08 15:24 ` jakub at gcc dot gnu.org
2013-02-19 17:26 ` jakub at gcc dot gnu.org
2013-02-19 17:44 ` jakub at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2013-02-08 15:24 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56250
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-08 15:23:43 UTC ---
Fixed on the trunk so far.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/56250] Wrong constant folding on unsigned int
2013-02-08 1:39 [Bug c/56250] New: Wrong constant folding on unsigned int ishiura-compiler at ml dot kwansei.ac.jp
` (6 preceding siblings ...)
2013-02-08 15:24 ` jakub at gcc dot gnu.org
@ 2013-02-19 17:26 ` jakub at gcc dot gnu.org
2013-02-19 17:44 ` jakub at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2013-02-19 17:26 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56250
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-19 17:26:15 UTC ---
Author: jakub
Date: Tue Feb 19 17:26:04 2013
New Revision: 196147
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196147
Log:
Backported from mainline
2013-02-08 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/56250
* fold-const.c (extract_muldiv_1) <case NEGATE_EXPR>: Don't optimize
if type is unsigned and code isn't MULT_EXPR.
* gcc.c-torture/execute/pr56250.c: New test.
Added:
branches/gcc-4_7-branch/gcc/testsuite/gcc.c-torture/execute/pr56250.c
Modified:
branches/gcc-4_7-branch/gcc/ChangeLog
branches/gcc-4_7-branch/gcc/fold-const.c
branches/gcc-4_7-branch/gcc/testsuite/ChangeLog
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/56250] Wrong constant folding on unsigned int
2013-02-08 1:39 [Bug c/56250] New: Wrong constant folding on unsigned int ishiura-compiler at ml dot kwansei.ac.jp
` (7 preceding siblings ...)
2013-02-19 17:26 ` jakub at gcc dot gnu.org
@ 2013-02-19 17:44 ` jakub at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2013-02-19 17:44 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56250
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution| |FIXED
--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-19 17:43:36 UTC ---
Fixed for 4.7.3+.
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2013-02-19 17:44 UTC | newest]
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2013-02-08 1:39 [Bug c/56250] New: Wrong constant folding on unsigned int ishiura-compiler at ml dot kwansei.ac.jp
2013-02-08 1:52 ` [Bug c/56250] " pinskia at gcc dot gnu.org
2013-02-08 1:54 ` [Bug middle-end/56250] " pinskia at gcc dot gnu.org
2013-02-08 1:59 ` ishiura-compiler at ml dot kwansei.ac.jp
2013-02-08 8:31 ` jakub at gcc dot gnu.org
2013-02-08 11:24 ` [Bug tree-optimization/56250] " jakub at gcc dot gnu.org
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2013-02-19 17:26 ` jakub at gcc dot gnu.org
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