Complex Iterators are Slow
They might be convenient, but the design of JavaScript Iterators is inherently slow for complex iteration as it prevents your compiler from inlining code.
Inlining can have a dramatic effect on performance. So it's worth paying attention to. When performance tuning, you can use the --trace-turbo-inlining flag to ask TurboFan (one of V8's optimising compilers) to report when it inlines a function.
TurboFan and other optimising compilers can be encouraged to inline calls to your function by keeping it small and simple (and calling it many times). But in this post, I want to consider when inlining fails.
I've padded the add() function from earlier with useless code to prevent TurboFan inlining it. I wasn't scientific about the process, I just typed until it stopped inlining.
Of course, normally, inlining is prevented not by pointless padding but by necessary work. Iteration in Timi, for example, can involve complicated walks up and down the tree and the code is - necessarily - too complex to be inlined.
