tree.h (CASE_LOW_SEEN, [...]): New macros for manipulating temporary visit flags on CASE_LABEL_EXPRs.
* tree.h (CASE_LOW_SEEN, CASE_HIGH_SEEN): New macros for manipulating
temporary visit flags on CASE_LABEL_EXPRs.
* c-common.c (match_case_to_enum): Add function comment. Avoid
O(N) loop, by looking up both CASE_LOW_SEEN and CASE_HIGH_SEEN.
(c_do_switch_warnings): Reorganize to record CASE_LOW_SEEN and
CASE_HIGH_SEEN for enumerated types. If the switch expression is
a constant, only warn if that constant value isn't handled.
* gcc.dg/Wswitch-enum-2.c: New test case.
* gcc.dg/Wswitch-enum-3.c: Likewise.