[dpdk-dev] [PATCH] eal/common: better likely() and unlikely()

[Wiles, Keith]

> On Nov 19, 2017, at 4:16 PM, Aleksey Baulin <aleksey.baulin at gmail.com> wrote:
> 
> A warning is issued when using an argument to likely() or unlikely()
> builtins which is evaluated to a pointer value, as __builtin_expect()
> expects a 'long int' type for its first argument. With this fix
> a pointer value is converted to an integer with the value of 0 or 1.
> 
> Signed-off-by: Aleksey Baulin <Aleksey.Baulin at gmail.com>
> ---
> lib/librte_eal/common/include/rte_branch_prediction.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/librte_eal/common/include/rte_branch_prediction.h b/lib/librte_eal/common/include/rte_branch_prediction.h
> index a6a56d1..2e7dc69 100644
> --- a/lib/librte_eal/common/include/rte_branch_prediction.h
> +++ b/lib/librte_eal/common/include/rte_branch_prediction.h
> @@ -50,7 +50,7 @@
>  *
>  */
> #ifndef likely
> -#define likely(x)  __builtin_expect((x),1)
> +#define likely(x)	__builtin_expect(!!(x), 1)
> #endif /* likely */
> 
> /**
> @@ -64,7 +64,7 @@
>  *
>  */
> #ifndef unlikely
> -#define unlikely(x)  __builtin_expect((x),0)
> +#define unlikely(x)	__builtin_expect(!!(x), 0)

I have not looked at the generated code, but does this add some extra instruction now to do the !!(x) ?

> #endif /* unlikely */
> 
> #endif /* _RTE_BRANCH_PREDICTION_H_ */
> -- 
> 2.7.4
> 

Regards,
Keith