From: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
To: Nicolai Stange <nicstange@gmail.com>
Cc: linux-sparse@vger.kernel.org, Christopher Li <sparse@chrisli.org>,
Josh Triplett <josh@joshtriplett.org>
Subject: Re: [PATCH v2 03/13] expression: examine constness of binops and alike at evaluation only
Date: Tue, 26 Jan 2016 18:24:40 +0100 [thread overview]
Message-ID: <20160126172438.GA989@macpro.local> (raw)
In-Reply-To: <87r3h4bas0.fsf@gmail.com>
On Tue, Jan 26, 2016 at 04:50:07PM +0100, Nicolai Stange wrote:
> Luc Van Oostenryck <luc.vanoostenryck@gmail.com> writes:
>
> > On Mon, Jan 25, 2016 at 03:52:14PM +0100, Nicolai Stange wrote:
> >> + [0 < 0.] = 0, // KO
> >
> > It's not clear to me what the standrad says about this case.
> > What about the constness of 'usual artihmetic conversions' ?
> > Also GCC don't complain on this one.
>
> Within the square brackets, an integer constant expression is needed.
>
> That's 6.6(6). "Floating constants that are immediate operands of casts"
> are allowed. Implicitly promoted types are not, at least to my
> interpretation.
Yes, I saw that the standard isn't explicit about it.
The way I see things is:
- I don't see any reason why an explicit conversion would preserve
constness while an implicit one would not.
- intuitively, when I read the code I see that the result of this
expression is can be known at compile time.
But well ... I have the same issue with [(int) (0 + 0.0)] which
is clearly not allowed by the standard while [(int) 0.0] is.
Maybe those should be relaxed latter and we can invoke 6.6(10):
An implementation may accept other forms of constant expressions
OTOH, who cares about floats ;)
Reading a bit more about it ...
For the designator in the array initializer (but also probably elsewhere)
6.7.8(6) first uses
[ <i>constant-expression<\i> ]
and then
and the expression shall be an integer constant expression.
Can this last 'integer constant expression' be interpreted as 'constant
expression of integer type'?
This could be considered to be coherent with the footnote 99) in 6.6(6)
followed by 6.6(7).
I don't know, it's something for language lawyers.
Luc
next prev parent reply other threads:[~2016-01-26 17:24 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-25 14:47 [PATCH v2 00/13] improve constexpr handling Nicolai Stange
2016-01-25 14:49 ` [PATCH v2 01/13] expression: introduce additional expression constness tracking flags Nicolai Stange
2016-01-25 21:51 ` Luc Van Oostenryck
2016-01-26 15:26 ` Nicolai Stange
2016-01-26 15:37 ` Nicolai Stange
2016-01-25 14:51 ` [PATCH v2 02/13] expression: examine constness of casts at evaluation only Nicolai Stange
2016-01-25 22:02 ` Luc Van Oostenryck
2016-01-26 16:11 ` Nicolai Stange
2016-01-25 14:52 ` [PATCH v2 03/13] expression: examine constness of binops and alike " Nicolai Stange
2016-01-26 0:14 ` Luc Van Oostenryck
2016-01-26 15:50 ` Nicolai Stange
2016-01-26 17:24 ` Luc Van Oostenryck [this message]
2016-01-27 10:42 ` Nicolai Stange
2016-01-27 18:00 ` Luc Van Oostenryck
2016-01-26 0:59 ` Luc Van Oostenryck
2016-01-25 14:53 ` [PATCH v2 04/13] expression: examine constness of preops " Nicolai Stange
2016-01-26 1:10 ` Luc Van Oostenryck
2016-01-25 14:55 ` [PATCH v2 05/13] expression: examine constness of conditionals " Nicolai Stange
2016-01-26 1:16 ` Luc Van Oostenryck
2016-01-25 14:56 ` [PATCH v2 06/13] expression, evaluate: add support for recognizing address constants Nicolai Stange
2016-01-26 1:27 ` Luc Van Oostenryck
2016-01-26 3:10 ` Luc Van Oostenryck
2016-01-25 14:57 ` [PATCH v2 07/13] evaluate: check static storage duration objects' intializers' constness Nicolai Stange
2016-01-26 1:42 ` Luc Van Oostenryck
2016-01-26 16:08 ` Nicolai Stange
2016-01-26 17:56 ` Luc Van Oostenryck
2016-01-26 20:18 ` Luc Van Oostenryck
2016-02-01 3:00 ` Nicolai Stange
2016-01-25 14:59 ` [PATCH v2 08/13] expression: recognize references to labels as address constants Nicolai Stange
2016-01-26 1:45 ` Luc Van Oostenryck
2016-01-25 15:00 ` [PATCH v2 09/13] expression: examine constness of __builtin_offsetof at evaluation only Nicolai Stange
2016-01-26 1:57 ` Luc Van Oostenryck
2016-02-01 3:06 ` Nicolai Stange
2016-01-25 15:02 ` [PATCH v2 10/13] symbol: flag builtins constant_p, safe_p and warning as constexprs Nicolai Stange
2016-01-26 2:00 ` Luc Van Oostenryck
2016-01-25 15:03 ` [PATCH v2 11/13] evaluate: relax some constant expression rules for pointer expressions Nicolai Stange
2016-01-26 2:05 ` Luc Van Oostenryck
2016-01-25 15:04 ` [PATCH v2 12/13] expression, evaluate: support compound literals as address constants Nicolai Stange
2016-01-26 2:07 ` Luc Van Oostenryck
2016-01-25 15:05 ` [PATCH v2 13/13] symbol: do not inherit storage modifiers from base types at examination Nicolai Stange
2016-01-26 2:54 ` Luc Van Oostenryck
2016-01-25 21:01 ` [PATCH v2 00/13] improve constexpr handling Luc Van Oostenryck
2016-01-25 21:26 ` Nicolai Stange
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