v8-bailout-reasons

This was written in 2014, when Crankshaft was still the JIT in V8. Turbofan was shipped in late 2016 and made primary in 2017. It's a much better JIT - it is tolerant to many more code patterns, including ES6 features - but IRHydra2 no longer works with Turbofan, so this type of introspection is more difficult to do. A few years ago I hand-tuned some kdb+/q interop code on Crankshaft using IRHydra2 and d8. The results were impressive: about 10x by just shuffling code around to be friendlier to the JIT. It was fun, but more than a little mysterious. Tuning on Crankshaft was all about avoiding bailout (https://github.com/vhf/v8-bailout-reasons/blob/master/README...). Tuning for Turbofan is less about "gotchas" and more about making sure your functions don't go megamorphic. Using TypeScript or Flow helps you do this just to get your code to

Any team with enough developers using Node should develop a handful who can understand the v8 internals and help troubleshoot real-world performance problems. The most helpful resource I've found about v8 specific performance is the bluebird optimization killers wiki: https://github.com/petkaantonov/bluebird/wiki/Optimization-k... wiki, and the v8 bailout reasons repo: https://github.com/vhf/v8-bailout-reasons

The two expressions are equivalent. V8 cannot compile that logic into optimized bytecode due to a violation in its code engine that conflicts with other optimization logic. So instead of fast compiled code the code in the local scope of that expression is slow string interpreted code. https://github.com/vhf/v8-bailout-reasons

Thanks! The linked repo [1] is also great: [1] https://github.com/vhf/v8-bailout-reasons