On Wed, 25 Apr 2012 15:26:23 +0400 Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> 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)))) > + btw, please let's not add undocumented stuff, particularly obscure undocumented stuff. I typed this in: --- a/include/linux/compiler.h~compilerh-introduce-unused_expression-macro-fix +++ a/include/linux/compiler.h @@ -310,6 +310,11 @@ void ftrace_likely_update(struct ftrace_ */ #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) +/* + * unused_expression() permits the compiler to check the validity of the + * expression but avoids the generation of any code, even if that expression + * has side-effects. + */ #define unused_expression(e) ((void)(sizeof((__force long)(e)))) #endif /* __LINUX_COMPILER_H */ but then decided I didn't want to apply the patches (yet?). -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
