RE: [PATCH 02/25] tracing: Improve "if" macro code generation

[David Laight]

From: Linus Torvalds 
> Sent: 20 March 2019 17:26
> To: David Laight
> On Wed, Mar 20, 2019 at 4:17 AM David Laight <David.Laight@xxxxxxxxxx> wrote:
> >
> > >               ______r = !!(cond);                                     \
> >
> >         Is that (or maybe just the !!) needed any more??
> 
> It is, because the 'cond' expression might not be an int, it could be
> a test for a pointer being non-NULL, or an u64 being non-zero, and not
> having the "!!" would mean that you'd get a warning or drop bits when
> assigning to 'int'.
> 
> And you do need the new temporary variable to avoid double evaluation
> the way that code is written.

As usual I'd opened my mouth before checking the full context :-)

>           ______r = !!(cond);                                     
> -		______f.miss_hit[______r]++;					\
> +		______r ? ______f.miss_hit[1]++ : ______f.miss_hit[0]++;\
>  		______r;						\

Actually you can avoid double evaluation by doing:

		(cond) ? (______f.miss_hit[1]++, 1) : (______f.miss_hit[0]++, 0)

With luck the compiler will move the increment to after the branch target.

for (_____ = ____; _____ < ______; _____++) :-)

	David

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