Re: [PATCH] ifplugd: using the __builtin_expect?

[Maksym Kryzhanovskyy]

On 08.7.2010 02:37:35, Denys Vlasenko wrote:
> On Wednesday 07 July 2010 12:58, Maksym Kryzhanovskyy wrote:
> > Hi Denis,
> > 
> > can we use the __builtin_expect function in busybox?
> > In the previous patch for ifplugd it might be usefull
> > (see attachment).
> 
> -       if (!G.detect_link_func) {
> +       if (__builtin_expect(G.detect_link_func == NULL, 0)) {
> 
> I don't see any changes in size, only obfuscated code.


Yes, it's not for reducing the size of ifplugd, but we wanted to ask gcc to
optimize the if statment for a negative result (moreover, it costs nothing in
terms of size):

if (!G.detect_link_func) { // predominantly negative throughout life of ifplugd


This may be unlikely() if it is more readable as Marek Polacek
and Bernhard Fischer-Reutner offers:

#define unlikely(x) __builtin_expect(!!(x), 0)
if (unlikely(G.detect_link_func == NULL)) {


If it is actually needed..


Max.

> -- 
> vda
> 
> 
>