http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46675
--- Comment #14 from Uros Bizjak <ubizjak at gmail dot com> 2010-11-28 15:07:39
UTC ---
Hm, no. The patch in comment #13 is not correct fix.
However, the comment of bound_difference says that no overflows are assumed:
/* Stores the bounds on the value of the expression X - Y in LOOP to BNDS.
The subtraction is considered to be performed in arbitrary precision,
without overflows.
We do not attempt to be too clever regarding the value ranges of X and
Y; most of the time, they are just integers or ssa names offsetted by
integer. However, we try to use the information contained in the
comparisons before the loop (usually created by loop header copying). */
static void
bound_difference (struct loop *loop, tree x, tree y, bounds *bnds)
And we have an overflow here (slightly modified test):
--cut here--
#define OFFS 1
extern void abort (void);
int j;
void
__attribute__((noinline))
foo (int n)
{
int npairs, i;
npairs = n - (-__INT_MAX__ - OFFS);
if (npairs > 0)
for (i = 0; i < npairs; i++)
j++;
}
int
main ()
{
foo (5 - __INT_MAX__ - OFFS);
if (j != 5)
abort ();
return 0;
}
--cut here--
An interesting fact, the testcase is miscompiled only for OFFS={1,2,3}.
