------- Comment #20 from rguenther at suse dot de 2009-05-06 21:02 -------
Subject: Re: [4.5 Regression] Revision 146817 caused
unaligned access in gcc.dg/torture/pr26565.c
On Wed, 6 May 2009, matz at gcc dot gnu dot org wrote:
> ------- Comment #19 from matz at gcc dot gnu dot org 2009-05-06 20:39 -------
> Something like this implements option 1. It's probably hopelessly inefficient
> (always generating a new type for each packed field), and wrong, and generally
> just a bad idea, but it does fix the testcase, execute.exp still works and
> bootstrap is already in the target libs :)
> And it only deals with packed fields, not those having an aligned() attribute.
>
> Index: c-common.c
> ===================================================================
> --- c-common.c (Revision 147187)
> +++ c-common.c (Arbeitskopie)
> @@ -5813,6 +5813,18 @@ c_init_attributes (void)
> #undef DEF_ATTR_TREE_LIST
> }
>
> +static tree
> +get_aligned_type (tree t, int align)
> +{
> + tree ret;
> + if (TYPE_PACKED (t))
> + return t;
Walking the type variants and searching for what we now build would
fix the inefficiency. And of course this function needs a comment ;)
> + ret = build_variant_type_copy (t);
> + TYPE_ALIGN (ret) = align * BITS_PER_UNIT;
> + TYPE_USER_ALIGN (ret) = 1;
It seems that only ever place_field looks at this flag. How
is the effect of setting it here?
Overall I like this patch.
Richard.
> + return ret;
> +}
> +
> /* Attribute handlers common to C front ends. */
>
> /* Handle a "packed" attribute; arguments as in
> @@ -5837,7 +5849,10 @@ handle_packed_attribute (tree *node, tre
> "%qE attribute ignored for field of type %qT",
> name, TREE_TYPE (*node));
> else
> - DECL_PACKED (*node) = 1;
> + {
> + DECL_PACKED (*node) = 1;
> + TREE_TYPE (*node) = get_aligned_type (TREE_TYPE (*node), 1);
> + }
> }
> /* We can't set DECL_PACKED for a VAR_DECL, because the bit is
> used for DECL_REGISTER. It wouldn't mean anything anyway.
>
>
>
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39954
