On Mon, 8 Jun 2015, Jan Hubicka wrote:
> > Hi,
> > this patchs makes fortran's C_SIGNED_CHAR and C_SIZE_T interoperable with
> > signed char and size_t as standard require. There are two issues here.
> >
> > First Fortran integers are always signed, but the standard insist on the
> > signed integer to match C size_t that is unsigned (if it was ptrdiff_t, we
> > would
> > be better of) and similarly the standard seems to explicitly state that
> > C_SIGNED_CHAR is interoperable with both signed char and unsigned char.
> > I thus globbed all integer types of precision compatible either with char
> > or size_t to be the same regardless the signedness.
> Hmm, actually there is a note:
> NOTE 15.8
> ISO/IEC 9899:1999 specifies that the representations for nonnegative signed
> integers are the same as the corresponding values of unsigned integers.
> Because Fortran does not provide direct support for unsigned kinds of
> integers,
> the ISO C BINDING module does not make accessible named constant s for their
> kind type parameter values. A user can use the signed kinds of integers to
> interoperate with the unsigned types and all their qualified versions
> as
> well. This has the potentially surprising side ect that the C
> type
> unsigned char is interoperable with the type integer with a kind type
> parameter
> of C SIGNED CHAR
>
> This seems to imply that other integer types also should be
> interoperable regardless of the signedness. It is true that
> representation is same for C, but alias sets are not. Perhaps all of
> the C BINDING types shall just be dropped to alias set 0? That would
> also solve the inter-operability of char versus char[1].
Alias-sets of signed and unsigned variants of integer types are the same:
alias_set_type
c_common_get_alias_set (tree t)
{
...
/* The C standard specifically allows aliasing between signed and
unsigned variants of the same type. We treat the signed
variant as canonical. */
if (TREE_CODE (t) == INTEGER_TYPE && TYPE_UNSIGNED (t))
{
tree t1 = c_common_signed_type (t);
/* t1 == t can happen for boolean nodes which are always unsigned.
*/
if (t1 != t)
return get_alias_set (t1);
yes, this should be moved to alias.c ...
Richard.
> I would say that the note is non-normative, so perhaps it can just be
> ignored, too :)
>
> Honza
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Dilip Upmanyu, Graham
Norton, HRB 21284 (AG Nuernberg)
