svn commit: r282907 - head/sys/sys

[Pedro Giffuni]

On 05/15/15 05:33, Tijl Coosemans wrote:
> Modified: head/sys/sys/cdefs.h
> ==============================================================================
> --- head/sys/sys/cdefs.h	Thu May 14 15:14:03 2015	(r282906)
> +++ head/sys/sys/cdefs.h	Thu May 14 15:49:48 2015	(r282907)
> @@ -388,6 +388,12 @@
>   #define	__alloc_size(x)
>   #endif
>   
> +#if __has_builtin(__builtin_unreachable) || __GNUC_PREREQ__(4, 6)
> +#define	__unreachable()	__builtin_unreachable()
> +#else
> +#define	__unreachable()	do {} while (/*CONSTCOND*/0)
> __builtin_unreachable() can be used in expressions so I think it's better
> to replace do-while with ((void)0).  You can then do things like this:
>
> #define assume(e)  ((e) ? (void)0 : __unreachable())
> (like assert(e) but without error)
Looks reasonable, thanks!

FWIW, there was some discussion about having a debugging
macro that warns when such unreachable code is reached.
We are just not sure where such a macro belongs, probably
not in cdefs.

Pedro.