https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127722
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Maybe something like this is concise and brief enough:
GCC does not warn about adjacent case labels with no statement between them,
so that the fallthrough attribute is not needed for common patterns like:
case 0:
case 1:
do_something(i);
break;
N.B. I used "adjacent" not "consecutive" to avoid any possible confusion about
whether it means the constants are consecutive integers. That is, "case 1: case
3:" are adjacent, despite 1 and 3 not being consecutive numbers.
