Re: [RFC PATCH v4] compiler.h: remove GCC < 3 __builtin_expect fallback

[Claudio Fontana <cfontana@suse.de>]

On 12/11/20 2:13 PM, Philippe Mathieu-Daudé wrote:
> Since commit efc6c07 ("configure: Add a test for the minimum compiler
> version"), QEMU explicitely depends on GCC >= 4.8.
> 
> (clang >= 3.4 advertizes itself as GCC >= 4.2 compatible and supports
> __builtin_expect too)
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> [PMD: #error if likely/unlikely already defined]
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> Supersedes: <20201210134752.780923-4-marcandre.lureau@redhat.com>
> ---
>  include/qemu/compiler.h | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
> index c76281f3540..ae1aee79c8d 100644
> --- a/include/qemu/compiler.h
> +++ b/include/qemu/compiler.h
> @@ -43,14 +43,11 @@
>  #define tostring(s)	#s
>  #endif
>  
> -#ifndef likely
> -#if __GNUC__ < 3
> -#define __builtin_expect(x, n) (x)
> +#if defined(likely) || defined(unlikely)
> +#error building with likely/unlikely is not supported

I'd put the argument of #error as a single string constant delimited by quotes ",
doesn't matter in this case though as there are no problem characters in the string.

>  #endif
> -
>  #define likely(x)   __builtin_expect(!!(x), 1)
>  #define unlikely(x)   __builtin_expect(!!(x), 0)
> -#endif
>  
>  #ifndef container_of
>  #define container_of(ptr, type, member) ({                      \
> 

Reviewed-by: Claudio Fontana <cfontana@suse.de>