[PATCH] [media] zl10353: use div_u64 instead of do_div

On Sat, 13 Feb 2016, Ard Biesheuvel wrote:

On 12 February 2016 at 22:01, Arnd Bergmann [off-list ref] wrote:

quoted

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