[Bug c/17170] New: -Wdefault-bitfield-sign

[terra at gnome dot org]

I would like to see -Wdefault-bitfield-sign turn on warnings when bitfields
are declared in ways that are likely bugs:

struct oink {
  int foo : 5;        // warning: the signedness of foo is implementation defined
  signed int bar : 5; // no warning
  int : 5;            // no warning (since no name)
  int booze : 1;      // warning: dubious signed one-bit bitfield
  signed int baz : 1; // no warning.
};

(A signed bitfield on width one can contain {-1;0} or {0} depending on integer
representation.  The latter allows for impressive optimizations, but surely
someone meant to use unsigned.)

Adding "signed" or "unsigned" as shown would silence the warnings.  Further,
I would assume that foo's warning above would be silenced by the use of one
of

`-fsigned-bitfields'
`-funsigned-bitfields'
`-fno-signed-bitfields'
`-fno-unsigned-bitfields'

booze's warning should remain, though.

-- 
           Summary: -Wdefault-bitfield-sign
           Product: gcc
           Version: 3.4.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: terra at gnome dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17170