[Bug c/61864] New: Feature Request, -Wcovered-switch-default to identify "dead" default branch

["chengniansun at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61864

            Bug ID: 61864
           Summary: Feature Request, -Wcovered-switch-default to identify
                    "dead" default branch
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chengniansun at gmail dot com

Currently, GCC supports -Wswitch and -Wswitch-enum. But it does not warn on the
case that all the possible values of an enum are covered in a switch, making
the default branch unreachable. 

The following code is extracted and simplified from the SPEC benchmark, the
enum only has three values, which are all covered in the switch. Therefore the
default branch is "dead". 


$: cat t.c
enum clust_strategy {
  CLUSTER_MEAN, CLUSTER_MAX, CLUSTER_MIN
};

int Cluster(enum clust_strategy mode) {
  switch(mode) {
  case CLUSTER_MEAN: break;
  case CLUSTER_MAX: break;
  case CLUSTER_MIN: break;
  default: break;
  }
  return 0;
}
$: clang-trunk -Wcovered-switch-default -c t.c
t.c:10:3: warning: default label in switch which covers all enumeration values
[-Wcovered-switch-default]
  default: break;
  ^
1 warning generated.
$: