https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77886
Bug ID: 77886 Summary: -Wimplicit-fallthrough: breaks duff's device Product: gcc Version: 7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: marc.mutz at kdab dot com Target Milestone: --- The recent addition (or activation) of -Wimplicit-fallthrough breaks Duff's Device: int n = (count + 7) / 8; switch (count & 0x07) { case 0: do { *dest++ = value; case 7: *dest++ = value; case 6: *dest++ = value; case 5: *dest++ = value; case 4: *dest++ = value; case 3: *dest++ = value; case 2: *dest++ = value; case 1: *dest++ = value; } while (--n > 0); } adding all those pesky // fall through comments makes the code unreadable, the more so as GCC doesn"t accept it as a trailing comment after each line but insists on having it on a line of its own.