http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55555
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-12-07
09:44:40 UTC ---
I've tried to rewrite this as C, but managed to turn it into something that is
miscompiled at a different spot. The fortran testcase starts having
__builtin_unreachable () in it in the *.cunroll pass, this one already in
*.cunrolli pass. Still, I believe it doesn't do any out of bounds access
anywhere. -O2 on x86_64-linux.
double s[4] = { 1.0, 2.0, 3.0, 4.0 }, pol_x[2] = { 5.0, 6.0 };
__attribute__((noinline)) int
foo (void)
{
double coef_x[8] = { 0, 0, 0, 0, 0, 0, 0, 0 };
int lxp = 0;
if (lxp <= 1)
do
{
double t = pol_x[lxp];
long S;
long l = lxp * 4L - 1;
for (S = 1; S <= 4; S++)
coef_x[S + l] = coef_x[S + l] + s[S - 1] * t;
}
while (lxp++ != 1);
asm volatile ("" : : "r" (coef_x) : "memory");
for (lxp = 0; lxp < 8; lxp++)
if (coef_x[lxp] != ((lxp & 3) + 1) * (5.0 + (lxp >= 4)))
__builtin_abort ();
return 1;
}
int
main ()
{
asm volatile ("" : : : "memory");
if (!foo ())
__builtin_abort ();
return 0;
}
Works with r193067, fails with r193100, haven't tried to bisect exactly, but
would guess this is r193098 again. For the outer loop it prints:
Analyzing # of iterations of loop 1
exit condition [0, + , 1](no_overflow) != 1
bounds on difference of bases: 1 ... 1
result:
# of iterations 1, bounded by 1
Loop 1 iterates 1 times.
Loop 1 iterates at most 1 times.
but that is wrong, the outer loop iterates exactly 2 times.
<bb 3>:
# lxp_1 = PHI <0(2), lxp_21(15)>
...
<bb 6>:
lxp_21 = lxp_1 + 1;
if (lxp_1 != 1)
goto <bb 15>;
else
goto <bb 7>;
<bb 15>:
goto <bb 3>;
If it used lxp_21 in the condition, that would be correct, but it uses the
previous value of the IV.
