Re: [PATCH 1/4] compiler.h: introduce unused_expression() macro

[Konstantin Khlebnikov]

H. Peter Anvin wrote:
> On 04/25/2012 04:26 AM, Konstantin Khlebnikov wrote:
> > Sometimes we want to check some expressions correctness in compile-time without
> > generating extra code. "(void)(e)" does not work if expression has side-effects.
> > This patch introduces macro unused_expression() which helps in this situation.
> >
> > Cast to "long" required because sizeof does not work for bit-fields.
> >
> > Signed-off-by: Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx>
> > ---
> >   include/linux/compiler.h |    2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> > index 923d093..46fbda3 100644
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -310,4 +310,6 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
> >    */
> >   #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
> >
> > +#define unused_expression(e) ((void)(sizeof((__force long)(e))))
> > +
>
> OK, bikeshedding a bit:
>
> "unused_expression()" doesn't sound like something that inhibits side
> effects, especially since "unused" applied to an argument or variable
> means "don't make a fuss over this not being used."
>
> 	-hpa

Ok, in v2 I'll rename it into BUILD_BUG_ON_INVALID()
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