On Sat, Feb 22, 2020 at 10:25 AM Ian Lepore <i...@freebsd.org> wrote: > > On Sat, 2020-02-22 at 16:20 +0000, Kyle Evans wrote: > > Author: kevans > > Date: Sat Feb 22 16:20:04 2020 > > New Revision: 358248 > > URL: https://svnweb.freebsd.org/changeset/base/358248 > > > > Log: > > vm_radix: prefer __builtin_unreachable() to an unreachable panic() > > > > This provides the needed hint to GCC and offers an annotation for readers > > to > > observe that it's in-fact impossible to hit this point. We'll get hit > > with a > > a -Wswitch error if the enum applicable to the switch above were to get > > expanded without the new value(s) being handled. > > > > Modified: > > head/sys/vm/vm_radix.c > > > > Modified: head/sys/vm/vm_radix.c > > ============================================================================== > > --- head/sys/vm/vm_radix.c Sat Feb 22 13:23:27 2020 (r358247) > > +++ head/sys/vm/vm_radix.c Sat Feb 22 16:20:04 2020 (r358248) > > @@ -208,8 +208,7 @@ vm_radix_node_load(smrnode_t *p, enum vm_radix_access > > case SMR: > > return (smr_entered_load(p, vm_radix_smr)); > > } > > - /* This is unreachable, silence gcc. */ > > - panic("vm_radix_node_get: Unknown access type"); > > + __unreachable(); > > } > > > > static __inline void > > What does __unreachable() do if the code ever becomes reachable? Like > if a new enum value is added and this switch doesn't get updated? >
__unreachable doesn't help here, but the compiler will error out on the switch() if all enum values aren't addressed and there's no default: case. IMO, compilers could/should become smart enough to error if there's an explicit __builtin_unreachable() and they can trivially determine that all paths will terminate before this, independent of -Werror=switch*. _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
