> One thing that wasn't clear to me from this post is why they still need the C++ interpreter at all.
A lot of code on the web is very cold (executed once or twice) and for such code the Baseline Interpreter would add some overhead (requires allocating a JitScript storing the IC data for example and we would then spend more time in IC code as well). It's possible this could be mitigated or fixed with additional work, but we need to keep the C++ interpreter anyway (not all platforms have a JIT backend and it's useful for differential testing) so it's not a priority right now.
Can you run the baseline interpreter with the costly parts disabled? Even if the code then runs approx. the same speed (and at same cost) of the C++ interpreter, you‘d save maintaining a bunch of code. I assume implementing the missing backends offsets maintenance costs in the long term.
A lot of code on the web is very cold (executed once or twice) and for such code the Baseline Interpreter would add some overhead (requires allocating a JitScript storing the IC data for example and we would then spend more time in IC code as well). It's possible this could be mitigated or fixed with additional work, but we need to keep the C++ interpreter anyway (not all platforms have a JIT backend and it's useful for differential testing) so it's not a priority right now.