Re: CFR: a new __unreachable() builtin
2015-05-13 18:09 GMT+02:00 David Chisnall david.chisn...@cl.cam.ac.uk:
LLVM uses this quite heavily, in a macro that expands to something equivalent
to assert(0 unreachable reached!”) in debug mode and
__builtin_unreachable() in release mode. When you’re debugging, you get
errors if you reach unreachable code and in deployment the compiler gets a
useful hint for optimisation.
Too bad we can't use this trick in our own assert(). You'd need to
define assert() like this:
#define assert(expr) do { \
if (!(expr)) \
__builtin_unreachable(); \
} while (0)
Unfortunately, this would cause the expression to be evaluated, which
is not allowed.
--
Ed Schouten e...@nuxi.nl
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CFR: a new __unreachable() builtin
Hello; I am looking at the cdefs in other BSDs hoping to avoid adopting the same definitions with incompatible names and I noticed NetBSD is using a new __builtin_unreachable (void) function from gcc 4.6: https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html Apparently it was interesting enough that clang implemented it too so I created a code review differential for it. https://reviews.freebsd.org/D2536 I don't want to add new C definitions unless they are going to be used so feel free to comment on the convenience or not of having it. Pedro. ___ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to freebsd-current-unsubscr...@freebsd.org
Re: CFR: a new __unreachable() builtin
On 13 May 2015, at 17:05, Pedro Giffuni p...@freebsd.org wrote: Hello; I am looking at the cdefs in other BSDs hoping to avoid adopting the same definitions with incompatible names and I noticed NetBSD is using a new __builtin_unreachable (void) function from gcc 4.6: https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html Apparently it was interesting enough that clang implemented it too so I created a code review differential for it. https://reviews.freebsd.org/D2536 I don't want to add new C definitions unless they are going to be used so feel free to comment on the convenience or not of having it. LLVM uses this quite heavily, in a macro that expands to something equivalent to assert(0 unreachable reached!”) in debug mode and __builtin_unreachable() in release mode. When you’re debugging, you get errors if you reach unreachable code and in deployment the compiler gets a useful hint for optimisation. David ___ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to freebsd-current-unsubscr...@freebsd.org
