Re: [PATCH v2 5/5] perf metric: Don't compute unused events.

[Jiri Olsa]

On Tue, Nov 17, 2020 at 09:03:35PM -0800, Ian Rogers wrote:

SNIP

> +			ids__free($1.ids);
> +			ids__free($3.ids);
> +		}
> +	} else {
> +		$$.val = NAN;
> +		$$.ids = ids__union($1.ids, $3.ids);
> +	}
> +}
> +| expr '*' expr
> +{
> +	if (!compute_ids || (isfinite($1.val) && isfinite($3.val))) {
> +		$$.val = $1.val * $3.val;
> +		$$.ids = NULL;
> +		if (compute_ids) {
> +			ids__free($1.ids);
> +			ids__free($3.ids);
> +		}
> +	} else {
> +		$$.val = NAN;
> +		$$.ids = ids__union($1.ids, $3.ids);
> +	}
> +}
> +| expr '/' expr
> +{
> +	if (fpclassify($3.val) == FP_ZERO) {
> +		pr_debug("division by zero\n");
> +		YYABORT;
> +	} else if (!compute_ids || (isfinite($1.val) && isfinite($3.val))) {
> +		$$.val = $1.val / $3.val;
> +		$$.ids = NULL;

hum, I'm confused with this.. compute_ids with finite values?
why do we erase ids then? also val should be NAN then, no?
could you please put in some comment with reasoning?

thanks,
jirka