Re: [PATCH v4 03/16] qemu/compiler.h: Add optimize_away

[David Hildenbrand]

On 24.09.19 00:59, Richard Henderson wrote:
> Use this as a compile-time assert that a particular
> code path is not reachable.
> 
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  include/qemu/compiler.h | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
> index 20780e722d..6604ccea92 100644
> --- a/include/qemu/compiler.h
> +++ b/include/qemu/compiler.h
> @@ -221,4 +221,19 @@
>  #define QEMU_GENERIC9(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC8(x, 
> __VA_ARGS__))
>  #define QEMU_GENERIC10(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC9(x, 
> __VA_ARGS__))
>  
> +/**
> + * optimize_away()

I would have used the compiler-speak "optimized_out()" instead.

> + *
> + * The compiler, during optimization, is expected to prove that a call
> + * to this function cannot be reached and remove it.  If the compiler
> + * supports QEMU_ERROR, this will be reported at compile time; otherwise
> + * this will be reported at link time, due to the missing symbol.
> + */
> +#ifdef __OPTIMIZE__
> +extern void QEMU_NORETURN QEMU_ERROR("code path is reachable")
> +    optimize_away(void);
> +#else
> +#define optimize_away()  g_assert_not_reached()
> +#endif
> +
>  #endif /* COMPILER_H */
> 

Apart from that looks good to me.

-- 

Thanks,

David / dhildenb