Re: [PATCH v2 3/8] qemu/bswap: Replace bswapXXs() by compiler __builtin_bswap()

[Thomas Huth]

On 28/09/2020 15.19, Philippe Mathieu-Daudé wrote:
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  include/qemu/bswap.h | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/include/qemu/bswap.h b/include/qemu/bswap.h
> index 41131d3d76e..fed96dddd7a 100644
> --- a/include/qemu/bswap.h
> +++ b/include/qemu/bswap.h
> @@ -38,29 +38,31 @@ static inline uint64_t bswap64(uint64_t x)
>  
>  static inline void bswap16s(uint16_t *s)
>  {
> -    *s = bswap16(*s);
> +    *s = __builtin_bswap16(*s);
>  }
>  
>  static inline void bswap32s(uint32_t *s)
>  {
> -    *s = bswap32(*s);
> +    *s = __builtin_bswap32(*s);
>  }
>  
>  static inline void bswap64s(uint64_t *s)
>  {
> -    *s = bswap64(*s);
> +    *s = __builtin_bswap64(*s);
>  }
>  
>  #if defined(HOST_WORDS_BIGENDIAN)
>  #define be_bswap(v, size) (v)
> -#define le_bswap(v, size) glue(bswap, size)(v)
> +#define le_bswap(v, size) glue(__builtin_bswap, size)(v)
>  #define be_bswaps(v, size)
> -#define le_bswaps(p, size) do { *p = glue(bswap, size)(*p); } while(0)
> +#define le_bswaps(p, size) \
> +            do { *p = glue(__builtin_bswap, size)(*p); } while (0)
>  #else
>  #define le_bswap(v, size) (v)
> -#define be_bswap(v, size) glue(bswap, size)(v)
> +#define be_bswap(v, size) glue(__builtin_bswap, size)(v)
>  #define le_bswaps(v, size)
> -#define be_bswaps(p, size) do { *p = glue(bswap, size)(*p); } while(0)
> +#define be_bswaps(p, size) \
> +            do { *p = glue(__builtin_bswap, size)(*p); } while (0)
>  #endif

What's the advantage of the renaming here if bswap is already #defined
to the builtin function (or another useful function from a system
header)? This just looks like code churn to me?

 Thomas