[PATCH] Add a new type attribute always_alias (PR79671)

[Sandra Loosemore]

On 04/05/2017 03:02 PM, Bernd Edlinger wrote:
> On 04/05/17 19:22, Bernd Edlinger wrote:
>> On 04/05/17 18:08, Jakub Jelinek wrote:
>>
>> Yes, exactly.  I really want to reach the deadline for gcc-7.
>> Fixing the name is certainly the most important first step,
>> and if everybody agrees on "typeless_storage", for the name
>> I can start with adjusting the name, and look into how
>> to use a spare type-flag that should be a mechanical change.
>>
>
> Jakub, I just renamed the attribute and reworked the patch
> as you suggested, reg-testing is not yet completed, but
> it looks good so far.  I also added a few more tests.
>
> I have changed the documentation as Richi suggested, but
> I am not too sure what to say here.
>

> Index: gcc/doc/extend.texi
> ===================================================================
> --- gcc/doc/extend.texi	(revision 246678)
> +++ gcc/doc/extend.texi	(working copy)
> @@ -6656,6 +6656,11 @@ declaration, the above program would abort when co
>  @option{-fstrict-aliasing}, which is on by default at @option{-O2} or
>  above.
>
> +@item typeless_storage
> +@cindex @code{typeless_storage} type attribute
> +An object declared with a type with this attribute behaves like a
> +character type with respect to aliasing semantics.
> +
>  @item packed
>  @cindex @code{packed} type attribute
>  This attribute, attached to @code{struct} or @code{union} type


"An object ....  behaves like a character type"?  I think you mean "as 
if it had character type".  Or maybe something simpler like "A type 
declared with this attribute has the same aliasing semantics as 
@code{char} type."

-Sandra