Date: Fri, 15 May 2015 12:34:46 -0500 From: Pedro Giffuni <pfg@FreeBSD.org> To: Tijl Coosemans <tijl@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r282907 - head/sys/sys Message-ID: <55562E36.1000304@FreeBSD.org> In-Reply-To: <20150515123327.45621037@kalimero.tijl.coosemans.org> References: <201505141549.t4EFnnQg094250@svn.freebsd.org> <20150515123327.45621037@kalimero.tijl.coosemans.org>
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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.
help
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