[lttng-dev] [PATCH 1/3] urcu: avoid "expression result unused" from clang

[Mathieu Desnoyers]

* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> The last expression result is unused and clang will complain.
> The trick in the patch supresses the complaint

Hrm, but with this patch, gcc complains:

rculfhash.c:1921:3: warning: variable '_w' set but not used
[-Wunused-but-set-variable]

using

gcc version 4.7.2 (Debian 4.7.2-4)

Thoughts ?

Thanks,

Mathieu

> 
> Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
> ---
>  urcu/system.h        |    5 ++++-
>  2 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/urcu/system.h b/urcu/system.h
> index 2a45f22..6b7b0af 100644
> --- a/urcu/system.h
> +++ b/urcu/system.h
> @@ -46,12 +46,15 @@
>  /*
>   * Store v into x, where x is located in shared memory. Performs the
>   * required cache flush after writing. Returns v.
> + * "_w" here avoids the warning from clang:
> + * 	warning: expression result unused [-Wunused-value]
>   */
>  #define CMM_STORE_SHARED(x, v)		\
>  	({				\
>  		__typeof__(x) _v = _CMM_STORE_SHARED(x, v);	\
> +		__typeof__(x) _w;	\
>  		cmm_smp_wmc();		\
> -		_v;			\
> +		_w = _v;		\
>  	})
>  
>  #endif /* _URCU_SYSTEM_H */
> -- 
> 1.7.4.4
> 
> 
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-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com