Re: [PATCH v3 03/13] compiler.h: remove GCC < 3 __builtin_expect fallback

[Philippe Mathieu-Daudé]

On 12/10/20 2:47 PM, marcandre.lureau@redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> 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>
> ---
>  include/qemu/compiler.h | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
> index c76281f354..226ead6c90 100644
> --- a/include/qemu/compiler.h
> +++ b/include/qemu/compiler.h
> @@ -44,10 +44,6 @@
>  #endif
>  
>  #ifndef likely
> -#if __GNUC__ < 3
> -#define __builtin_expect(x, n) (x)
> -#endif
> -
>  #define likely(x)   __builtin_expect(!!(x), 1)
>  #define unlikely(x)   __builtin_expect(!!(x), 0)
>  #endif
> 

Trying with GCC 10:
warning: implicit declaration of function ‘likely’
[-Wimplicit-function-declaration]

Clang 10:
warning: implicit declaration of function 'likely' is invalid in C99
[-Wimplicit-function-declaration]

Shouldn't it becleaner to test in the configure script or Meson that
likely() and unlikely() are not defined, and define them here
unconditionally?

Regards,

Phil.