[Bug c/28901] New: -Wunused-variable ignores unused const initialised variables

["mikpe at csd dot uu dot se" <gcc-bugzilla@gcc.gnu.org>]

gcc -Wunused-variable -c test.c, where test.c contains the
following code, fails to warn that variable a is unused:
--begin-test.c-
static const int a = 27;
static const int b = 42;
const int *f(void) { return &b; }
--end-test.c--
However, gcc -Wunused-variable -c -Dconst= test.c does 
produce the warning I wanted:
test.c:1: warning: 'a' defined but not used

The problem is that for some reason, -Wunused-variable ignores
const variables, and there doesn't seem to be any alternative
warning option or variable attribute to request unused warnings
for const variables.

In the application where this was observed, there is a large number
of initialised const arrays-of-structs encoding final-state
information for a state transition engine. Other const variables
and functions encode the fairly complex transition rules. A copy-paste
error in the transition rules led to some final states not being
reachable, i.e., there were no references to those variables, but
-Wunused-variable (implied by -Wall) failed to notice that.


-- 
           Summary: -Wunused-variable ignores unused const initialised
                    variables
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mikpe at csd dot uu dot se


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28901