Messages in this thread | | | Date | Sat, 13 Feb 2016 16:57:41 -0500 (EST) | From | Nicolas Pitre <> | Subject | Re: [PATCH] [media] zl10353: use div_u64 instead of do_div |
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On Sat, 13 Feb 2016, Ard Biesheuvel wrote:
> On 12 February 2016 at 22:01, Arnd Bergmann <arnd@arndb.de> wrote: > > However, I did stumble over an older patch I did now, which I could > > not remember what it was good for. It does fix the problem, and > > it seems to be a better solution. > > > > Arnd > > > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > > index b5acbb404854..b5ff9881bef8 100644 > > --- a/include/linux/compiler.h > > +++ b/include/linux/compiler.h > > @@ -148,7 +148,7 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); > > */ > > #define if(cond, ...) __trace_if( (cond , ## __VA_ARGS__) ) > > #define __trace_if(cond) \ > > - if (__builtin_constant_p((cond)) ? !!(cond) : \ > > + if (__builtin_constant_p(!!(cond)) ? !!(cond) : \ > > ({ \ > > int ______r; \ > > static struct ftrace_branch_data \ > > > > I remember seeing this patch, but I don't remember the exact context. > But when you think about it, !!cond can be a build time constant even > if cond is not, as long as you can prove statically that cond != 0. So
You're right. I just tested it and to my surprise gcc is smart enough to figure that case out.
> I think this change is obviously correct, and an improvement since it > will remove the profiling overhead of branches that are not true > branches in the first place.
Indeed.
Nicolas
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