Re: [PATCH] Fold (int *)&a + 4 to a[1] using offset_int (PR middle-end/81695)

[Richard Biener <richard dot guenther at gmail dot com>]

On Fri, Aug 4, 2017 at 10:38 AM, Marek Polacek <polacek@redhat.com> wrote:
> We were crashing because size_binop_loc got operands of different types:
> sizetype and ssizetype.  Richi suggested performing the computation in
> offset_int which my patch tries to do.  Unsure about the sdiv_trunc part,
> what do I use instead of EXACT_DIV_EXPR?

Use wi::divmod_trunc and check for a zero remainder.  If the remainder is not
zero we may not fold.

Ok with that change.

Thanks,
Richard.

> Bootstrapped/regtested on x86_64-linux, ok for trunk?  Testing on ppc64le
> in progress.
>
> 2017-08-04  Marek Polacek  <polacek@redhat.com>
>
>         PR middle-end/81695
>         * fold-const.c (fold_indirect_ref_1): For ((int *)&a + 4 -> a[1],
>         perform the computation in offset_int.
>
>         * gcc.dg/pr81695.c: New test.
>
> diff --git gcc/fold-const.c gcc/fold-const.c
> index ed6c289a64b..64a84eb0197 100644
> --- gcc/fold-const.c
> +++ gcc/fold-const.c
> @@ -14106,14 +14106,17 @@ fold_indirect_ref_1 (location_t loc, tree type, tree op0)
>                    && type == TREE_TYPE (op00type))
>             {
>               tree type_domain = TYPE_DOMAIN (op00type);
> -             tree min_val = size_zero_node;
> -             if (type_domain && TYPE_MIN_VALUE (type_domain))
> -               min_val = TYPE_MIN_VALUE (type_domain);
> -             op01 = size_binop_loc (loc, EXACT_DIV_EXPR, op01,
> -                                    TYPE_SIZE_UNIT (type));
> -             op01 = size_binop_loc (loc, PLUS_EXPR, op01, min_val);
> -             return build4_loc (loc, ARRAY_REF, type, op00, op01,
> -                                NULL_TREE, NULL_TREE);
> +             tree min = TYPE_MIN_VALUE (type_domain);
> +             if (min && TREE_CODE (min) == INTEGER_CST)
> +               {
> +                 offset_int off = wi::to_offset (op01);
> +                 offset_int el_sz = wi::to_offset (TYPE_SIZE_UNIT (type));
> +                 off = wi::sdiv_trunc (off, el_sz);
> +                 off = off + wi::to_offset (min);
> +                 op01 = wide_int_to_tree (sizetype, off);
> +                 return build4_loc (loc, ARRAY_REF, type, op00, op01,
> +                                    NULL_TREE, NULL_TREE);
> +               }
>             }
>         }
>      }
> diff --git gcc/testsuite/gcc.dg/pr81695.c gcc/testsuite/gcc.dg/pr81695.c
> index e69de29bb2d..c3452580f1c 100644
> --- gcc/testsuite/gcc.dg/pr81695.c
> +++ gcc/testsuite/gcc.dg/pr81695.c
> @@ -0,0 +1,11 @@
> +/* PR middle-end/81695 */
> +/* { dg-do compile } */
> +/* { dg-options "" } */
> +
> +int z[] = { };
> +
> +int
> +main (void)
> +{
> +  __builtin_printf ("%d\n", *(z + 1));
> +}
>
>         Marek