Having failed to find a working profiler on npm I ended up webpacking nqp-js-on-js and profiling it directly in Chrome.
I implemented them.
The second big slowdown was actually the slurp() function.
MoarVM doesn't handle concatenation large amounts of huge strings very well so the cross compiler so instead of concatenating bits of javascript code it's often much faster to write them to disk and then slurp it back in.
On the nqp-js-on-js due to a misset buffer size slurp turned out sluggish.
…

nqp-js-on-js (NQP compiled to JavaScript and running on node.js) passes it's test suit (almost, there is a bug with how regexes compiled at runtime capture stuff which I haven't yet figured out).
While nqp-js-on-js compiles parts of rakudo (with a minor bug fix) it turn out for some reason it's unacceptably slow on some of the larger files (like Perl6::World).
As such I have turned my attention to figuring out what's the problem and speeding nqp-js-on-js up.
Hopefully the next blog posts will be more detailed and contain the description of some nifty optimizations.