[Bug c/59852] Support sparse-style __attribute__((bitwise)) (type attribute)

[tromey at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59852

--- Comment #5 from Tom Tromey <tromey at gcc dot gnu.org> ---
(In reply to Josh Triplett from comment #4)
> Also note that arithmetic operations between a bitwise and a known-zero
> value do not warn.

I'm curious about this too.
If it means that the warnings should be deferred until after
optimization, then it seems like maybe a difficult problem.
On the other extreme, if this just refers to constant expressions,
making this a purely front-end feature, then it seems more tractable.