Re: [committed] avoid assuming array indices are zero-based (PR 92952)

[Jakub Jelinek]

On Mon, Dec 16, 2019 at 03:28:29PM -0700, Martin Sebor wrote:
> PR middle-end/92952 - gfortran.dg/lto/pr87689 FAILs
> 
> gcc/ChangeLog:
> 
>       PR middle-end/92952
>       * builtins.c (compute_objsize): Adjust offset by the array low bound.
> 
> Index: gcc/builtins.c
> ===================================================================
> --- gcc/builtins.c    (revision 279443)
> +++ gcc/builtins.c    (working copy)
> @@ -3999,6 +3999,16 @@ compute_objsize (tree dest, int ostype, tree *pdec
>            above.  */
>         if (TREE_CODE (dest) == ARRAY_REF)
>           {
> +           tree lowbnd = array_ref_low_bound (dest);
> +           if (!integer_zerop (lowbnd) && tree_fits_uhwi_p (lowbnd))
> +             {
> +               /* Adjust the offset by the low bound of the array
> +                  domain (normally zero but 1 in Fortran).  */
> +               unsigned HOST_WIDE_INT lb = tree_to_uhwi (lowbnd);
> +               offrng[0] -= lb;
> +               offrng[1] -= lb;
> +             }

I don't understand why uhwi is used.  offrng is an array of wide_int with
precision of sizetype, so why not instead:
              if (!integer_zerop (lowbnd) && TREE_CODE (lowbnd) == INTEGER_CST)
                {
                  /* Adjust the offset by the low bound of the array
                     domain (normally zero but 1 in Fortran).  */
                  wide_int lb = wi::to_wide (lowbnd, sizprec);
                  offrng[0] -= lb;
                  offrng[1] -= lb;
                }
?

        Jakub