Re: [PATCH] Use sufficient alignment when expanding VCE (PR target/35366)

["Richard Guenther" <richard dot guenther at gmail dot com>]

On Tue, Nov 11, 2008 at 7:30 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> This is another patch for PR35366, either of the patches fixes the failure,
> but IMHO we want both.  If for whatever reason VIEW_CONVERT_EXPR <double, STRING_CST>
> (or some other VCE) isn't folded, and the TREE_TYPE of the VCE needs bigger
> alignment than the inner operand, the inner constant is emitted with a small
> alignment, but it is actually accessed as if the alignment was big enough
> for the outer type.  The following patch makes sure an inner constant
> is sufficiently aligned.
>
> Ok for trunk?

Is it always possible to force the alignment of the inner object?  I think
the same problem may exist for V_C_E <double> (*p) when we cannot
influence the alignment of *p.  So shouldn't we make sure to have the
correct MEM_ALIGN instead?  Or does it work in that case already?

Richard.

> 2008-11-11  Jakub Jelinek  <jakub@redhat.com>
>
>        PR target/35366
>        * expr.c (expand_expr_addr_expr_1): If EXP needs bigger alignment
>        than INNER and INNER is a constant, forcibly align INNER as much
>        as needed.
>
> --- gcc/expr.c.jj       2008-10-29 23:16:25.000000000 +0100
> +++ gcc/expr.c  2008-11-11 14:24:56.000000000 +0100
> @@ -6862,6 +6862,16 @@ expand_expr_addr_expr_1 (tree exp, rtx t
>   gcc_assert (inner != exp);
>
>   subtarget = offset || bitpos ? NULL_RTX : target;
> +  /* For VIEW_CONVERT_EXPR, where the outer alignment is bigger than
> +     inner alignment, force the inner to be sufficiently aligned.  */
> +  if (CONSTANT_CLASS_P (inner)
> +      && TYPE_ALIGN (TREE_TYPE (inner)) < TYPE_ALIGN (TREE_TYPE (exp)))
> +    {
> +      inner = copy_node (inner);
> +      TREE_TYPE (inner) = copy_node (TREE_TYPE (inner));
> +      TYPE_ALIGN (TREE_TYPE (inner)) = TYPE_ALIGN (TREE_TYPE (exp));
> +      TYPE_USER_ALIGN (TREE_TYPE (inner)) = 1;
> +    }
>   result = expand_expr_addr_expr_1 (inner, subtarget, tmode, modifier);
>
>   if (offset)
>
>        Jakub
>