While looking into moving fuzzer comparison logic to shell helpers, I noticed that most of the time spent wasn't in comparing results, but converting the input to BSON for our shell helpers. I've seen this conversion take ~400-500ms for deeply nested objects.

However the input to the shell helper came from a query and is already BSON. The fast-path we have to avoid the extra conversion is not taken. We should investigate why the conversions take so long and if we can avoid unnecessary conversions from BSON to a MozJS structure, back to BSON.

Even if we don't move more logic from JS to C++, this work will still be done when we use any existing helpers in the fuzzer. Here is an example.