On Tue, 11 Dec 2012, Jakub Jelinek wrote:
> Hi!
>
> The following testcase on x86_64 (or the f90-intrinsic-bitsize.f on 32-bit
> HWI) with -Os shows a bug in discover_iteration_bound_by_body_walk. If some
> bound is a -1, -1 HWI, then adding double_int_one to it overflows into 0, 0
> HWI and we can return that as maximum number of iterations. We need to
> ignore such bounds instead.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Ok.
Thanks,
Richard.
> 2012-12-11 Jakub Jelinek <ja...@redhat.com>
>
> PR fortran/55633
> * tree-ssa-loop-niter.c (discover_iteration_bound_by_body_walk):
> Ignore bounds on which bound += double_int_one overflowed.
>
> * gcc.dg/torture/pr55633.c: New test.
>
> --- gcc/tree-ssa-loop-niter.c.jj 2012-11-21 16:00:09.000000000 +0100
> +++ gcc/tree-ssa-loop-niter.c 2012-12-11 10:56:49.890396498 +0100
> @@ -3011,7 +3011,12 @@ discover_iteration_bound_by_body_walk (s
> /* Exit terminates loop at given iteration, while non-exits produce
> undefined
> effect on the next iteration. */
> if (!elt->is_exit)
> - bound += double_int_one;
> + {
> + bound += double_int_one;
> + /* If an overflow occurred, ignore the result. */
> + if (bound.is_zero ())
> + continue;
> + }
>
> if (!loop->any_upper_bound
> || bound.ult (loop->nb_iterations_upper_bound))
> @@ -3037,7 +3042,12 @@ discover_iteration_bound_by_body_walk (s
> {
> double_int bound = elt->bound;
> if (!elt->is_exit)
> - bound += double_int_one;
> + {
> + bound += double_int_one;
> + /* If an overflow occurred, ignore the result. */
> + if (bound.is_zero ())
> + continue;
> + }
>
> if (!loop->any_upper_bound
> || bound.ult (loop->nb_iterations_upper_bound))
> --- gcc/testsuite/gcc.dg/torture/pr55633.c.jj 2012-12-11 11:12:19.567069030
> +0100
> +++ gcc/testsuite/gcc.dg/torture/pr55633.c 2012-12-11 11:12:04.000000000
> +0100
> @@ -0,0 +1,39 @@
> +/* PR fortran/55633 */
> +/* { dg-do run { target int128 } } */
> +
> +extern void abort (void);
> +
> +__attribute__((noinline, noclone)) void
> +bar (__int128_t *x)
> +{
> + int c = sizeof (__int128_t) * __CHAR_BIT__;
> + if (c > 127)
> + c = 127;
> + if (*x != c)
> + abort ();
> +}
> +
> +__attribute__((noinline)) void
> +foo (void)
> +{
> + __int128_t m, ma;
> + ma = 0;
> + m = 0;
> + m = ~m;
> + do
> + {
> + if (m == 0 || ma > 126)
> + break;
> + ma = ma + 1;
> + m = ((__uint128_t) m) >> 1;
> + }
> + while (1);
> + bar (&ma);
> +}
> +
> +int
> +main ()
> +{
> + foo ();
> + return 0;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imend
