[Bug c/27116] New: Incorrect integer division (wrong sign).

2006-04-11 Thread laurent at komite dot net 
The following test demonstrates an incorrect sign in the following division :

#include 

int main (void)
{
volatile long int n;
n = -2;

printf ("%ld\n", (-2147483647L - 1L) / (-n));
return 0;
}

I get a correct result with 4.0.3, and a wrong sign with snapshots 20060325 and
20060408. Also reported in debian : 

http://bugs.debian.org/361883


-- 
   Summary: Incorrect integer division (wrong sign).
   Product: gcc
   Version: 4.2.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: laurent at komite dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27116

[Bug c/27116] [4.2 Regression] Incorrect integer division (wrong sign).

2006-04-11 Thread laurent at komite dot net 


--- Comment #2 from laurent at komite dot net  2006-04-11 15:06 ---

(In reply to comment #1)
> Overflow flag set problem:
> 
>   n = -2;
>   n.10 = n;
>   D.2132 = -08000 / n.10;
> 
> -fwrapv "fixes" the problem.  This is a dup of ...

I'm not sure this is just an overflow problem, it might be more general. As
suggested by a friend, I tried the simple example :

int f (int a, int b)
{
return (-a) / (-b);
}

The assembly and `-fdump-tree-all' output show that both negations are removed,
which is incorrect since the input domain is not symmetric wrt 0.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27116