From: "Joseph S. Myers" <joseph@codesourcery.com>
To: DJ Delorie <dj@redhat.com>
Cc: <richard.guenther@gmail.com>, <gcc@gcc.gnu.org>
Subject: Re: proposal to make SIZE_TYPE more flexible
Date: Thu, 09 Jan 2014 03:23:00 -0000 [thread overview]
Message-ID: <Pine.LNX.4.64.1401090214160.8625@digraph.polyomino.org.uk> (raw)
In-Reply-To: <201401090031.s090VGm9003938@greed.delorie.com>
On Wed, 8 Jan 2014, DJ Delorie wrote:
> > I think a patch is more useful once believe feature-complete, which
> > means replacing the __int128 support with the new mechanism.
>
> One of the side-effects of taking out the existing __int128 support is
> that __int128 isn't in the integer_type_kind list, so isn't a type
> that is usable for constants. This breaks int128-4.C, which assumes a
> 128-bit integer constant. If I add generic support for intN types in
I don't see constants in that test.
It's not possible to write constants of type __int128 anyway. It *is*
possible to build them up using expressions casting narrower constants to
__int128. If you write a constant with a large value (with or without a
suffix) that won't fit in target intmax_t / uintmax_t (or target long /
unsigned long for C90), then you should get a pedwarn (and some larger
type, maybe widest_integer_literal_type_node /
widest_unsigned_literal_type_node, will be used if available).
> i_t_k[], then we'll get (for example) 20-bit constants, which might
> not be what we want. The only other option is to special-case
> __int128 if we find it in the __intN list.
Integer constant types should be taken from the int / long / long long
(and unsigned variants) list. If a constant can't fit in any type ISO C
allows for it, then it's reasonable to go on the extended types wider than
long long, in increasing order of size, but __int20 is never relevant for
constants as it's always narrower than long.
> Thoughts?
It's desirable anyway to have a way of representing what might be a
standard type from integer_type_kind, or an extended type, given that it
would be good for macros such as SIZE_TYPE to evaluate to enumerated
values not magic strings. Maybe a reserved space of itk_* values just
like reserving RID_* values?
> Also, I noted a few tests check for the int128-specific error message
> when the type is not supported, but as per our previous discussion,
> the __int128 keyword just doesn't exist if the type isn't supported.
> Do we need to discern between "not supported with these options" and
> "not supported ever" ?
I don't think there's a need to distinguish, although I don't think it
would be particularly harmful to have an __int128 keyword present without
a corresponding type for targets not supporting __int128, if that helps
diagnostics, as long as nothing else special-cases __int128.
(Draft TS 18661-3 has the interesting peculiarity that the keywords
_FloatN for N = 16, 32, 64 or >= 128 and a multiple of 32, _DecimalN for N
>= 32 and a multiple of 32, and _Float32x, _Float64x, _Float128x,
_Decimal64x, _Decimal128x always exist as keywords whether or not the
corresponding types are supported. Implementing that would I suppose
require special checks to handle arbitrary _FloatN and _DecimalN (for
valid N) as keywords - an infinite number of keywords - much as we handle
_Imaginary as a keyword without otherwise implementing it.)
--
Joseph S. Myers
joseph@codesourcery.com
next prev parent reply other threads:[~2014-01-09 2:31 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-30 4:28 DJ Delorie
2013-10-30 15:53 ` Joseph S. Myers
2013-10-30 19:18 ` DJ Delorie
2013-10-30 20:49 ` Joseph S. Myers
2013-10-30 22:19 ` DJ Delorie
2013-10-30 22:51 ` Joseph S. Myers
2013-11-14 1:58 ` DJ Delorie
2013-11-14 13:26 ` Joseph S. Myers
2013-11-14 18:12 ` DJ Delorie
2013-11-14 18:37 ` Joseph S. Myers
2013-11-14 18:48 ` DJ Delorie
2013-11-14 21:40 ` Joseph S. Myers
2013-11-15 1:47 ` DJ Delorie
2013-11-15 1:56 ` Joseph S. Myers
2013-11-15 23:38 ` DJ Delorie
2013-11-16 11:23 ` Richard Biener
2013-11-16 12:26 ` Joseph S. Myers
2013-11-21 22:41 ` DJ Delorie
2013-11-21 22:59 ` Joseph S. Myers
2013-11-22 8:29 ` DJ Delorie
2013-11-22 12:43 ` Joseph S. Myers
2013-11-22 19:33 ` DJ Delorie
2013-11-22 21:00 ` Joseph S. Myers
2013-11-22 21:19 ` DJ Delorie
2013-11-23 0:41 ` Joseph S. Myers
2013-12-10 3:35 ` DJ Delorie
2013-12-10 17:17 ` Joseph S. Myers
2013-12-10 18:10 ` DJ Delorie
2013-12-10 18:38 ` Joseph S. Myers
2013-12-10 18:42 ` DJ Delorie
2013-12-11 9:27 ` Richard Biener
2013-12-20 4:58 ` DJ Delorie
2013-12-20 12:42 ` Joseph S. Myers
2013-12-20 19:47 ` DJ Delorie
2013-12-20 21:53 ` Joseph S. Myers
2013-12-20 21:59 ` DJ Delorie
2013-12-20 22:15 ` Joseph S. Myers
2013-12-20 22:40 ` DJ Delorie
2013-12-21 1:01 ` Joseph S. Myers
2014-01-09 2:31 ` DJ Delorie
2014-01-09 3:23 ` Joseph S. Myers [this message]
2014-01-09 7:02 ` DJ Delorie
2014-01-09 16:22 ` Joseph S. Myers
2014-01-15 12:48 ` DJ Delorie
2014-01-28 21:52 ` DJ Delorie
2014-01-28 21:58 ` Joseph S. Myers
2014-01-28 22:24 ` DJ Delorie
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