if(false) vs if(isNaN) benchmark

[Joseph Rushton Wakeling]

Hi all,

A trivial little benchmark for comparing the performance of a function using
if(!booleanValue) as a conditional, versus one using if(isNan(x)).

Run with dmd -O -release -inline -noboundscheck on my system, I find the two are
virtually equivalent, with it taking about 30ms for 1 million if(!boolean)
versus about 31 for a million if(isNaN(floatingpoint)).

With ldmd2 and the same optimizations, I get about 25 compared to 27-28 ms for
the two cases, again with a million realizations of each.

Finally, with gdmd I get 30ms for a million if(!boolean) versus about 150ms for
a million if(isNaN(floatingpoint)).

Code attached, feel free to critique.  Generally I think these results show that
the difference between checking a boolean and checking isNan are negligible, but
I'm surprised at the relatively bad performance with gdmd and I wonder if
there's some particular reason for this.

The relevance is to a fix I'm preparing for this bug:
http://d.puremagic.com/issues/show_bug.cgi?id=10322

See also: http://forum.dlang.org/post/lcrwybqszclitzravrqo@forum.dlang.org

Thanks in advance for any feedback :-)

Best wishes,

    -- Joe
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