[Bug tree-optimization/32663] [4.3 regression]: revision 126369 went into an infinite loop

[dberlin at dberlin dot org]

------- Comment #7 from dberlin at gcc dot gnu dot org  2007-07-07 20:07 -------
Subject: Re:  [4.3 regression]: revision 126369 went into an infinite loop

On 7 Jul 2007 19:35:01 -0000, hjl at lucon dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
>
>
> ------- Comment #6 from hjl at lucon dot org  2007-07-07 19:35 -------
> If I revert
>
> -         if (lhsval)
> +         if (lhsval && vuse_equiv (lhsval, stmt))
>
> the regression is gone. I suspected that the original code:
>
>           if (lhsval)
>             {
>               set_value_handle (newt, lhsval);
>               if (!is_gimple_min_invariant (lhsval))
>                 add_to_value (lhsval, newt);
>             }
>           else
>             {
>               tree val = vn_lookup_or_add_with_stmt (newt, stmt);
>               vn_add (lhs, val);
>             }
>
> doesnt't handle the case of
>
> if (lhsval && !vuse_equiv (lhsval, stmt))
>

Uh, as it shouldn't.

> If I change it to
>
> --- tree-ssa-pre.c.bad  2007-07-07 08:18:31.000000000 -0700
> +++ tree-ssa-pre.c      2007-07-07 12:33:51.000000000 -0700
> @@ -3362,7 +3362,8 @@ make_values_for_stmt (tree stmt, basic_b
>           else
>             {
>               tree val = vn_lookup_or_add_with_stmt (newt, stmt);
> -             vn_add (lhs, val);
> +             if (!lhsval)
> +               vn_add (lhs, val);
>             }
>
>           add_to_exp_gen (block, newt);
>
> my testcase works.

Only because you are now assigning different value numbers to things
we know to be the same.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32663