[Libguestfs] [PATCH libnbd] lib: Use GCC hints to move debug and error handling code out of hot paths.

[Eric Blake]

On 11/2/19 4:24 PM, Richard W.M. Jones wrote:
> ---
>   generator/generator |  6 +++---
>   lib/crypto.c        |  2 +-
>   lib/internal.h      | 14 +++++++++++++-
>   3 files changed, 17 insertions(+), 5 deletions(-)
> 

> +++ b/lib/internal.h
> @@ -40,6 +40,18 @@
>   #include "states.h"
>   #include "unlocked.h"
>   
> +/* Define unlikely macro, but only for GCC.  These are used to move
> + * debug and error handling code out of hot paths, making the hot path
> + * into common functions use less instruction cache.
> + */
> +#if defined(__GNUC__)
> +#define unlikely(x) __builtin_expect (!!(x), 0)
> +#define if_debug(h) if (unlikely ((h)->debug))
> +#else
> +#define unlikely(x) (x)
> +#define if_debug(h) if ((h)->debug)
> +#endif

Same question about applicability to clang as for nbdkit, otherwise 
looks fine.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org