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• feat(transformer/async-to-generator): handle this within arrows function #7074
• perf(transformer/arrow-function): store scope_id to avoid going through scopes #7041 👈
• ci(transformer): enable unfinished plugins in benchmark #7040
• main

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CodSpeed Performance Report

Merging #7041 will not alter performance

_{Comparing 10-31-perf_transformer_arrow-function_change_to_a_correct_scope_id_when_inserting_this (d320f62) with main (9f611a1)}

Summary

✅ 30 untouched benchmarks

I've broken out the change to using AstBuilder::alloc_function_with_scope_id into a separate PR #7055. That change is good, but incidental to main thrust of this PR.

I'm not sure if this is a good idea or not. It makes entering/exiting functions more expensive, in order to make resolving this bindings cheaper.

ThisVar is 24 bytes, and it creates one for every function. Whereas previously SparseStack only took 1 byte (a bool) for each function (except for functions which need _this inserted into them, which take a further 24 bytes).

On the positive side, you avoid having to search up the tree to find the scope of the parent function when you do find a this within an arrow function. Note: That search only happens on 1st this within that parent function.

So whether this change is a perf improvement or not depends on which is more common: functions, or this within arrow functions (in particular, a single this). The answer will depend on the nature of the code being transformed.

On our benchmarks, it appears to be mostly negative (-0.1% to -0.3%) and it's hard to see if it's positive or negative on RadixUIAdoptionSection.jsx benchmark, as that one is so noisy. But either way, it doesn't make much difference.

If you want to merge this, I don't object. If you want to close it, I don't object either!

One last thing: If you do close it, please don't see it as wasted time. Often the only way to find out if something improves perf or not is to try, and often the result is unexpected - things you think will have marginal impact can surprisingly win you 5%, and other things you had high hopes for do nothing. So we need to experiment.

Thanks for taking your precious time on this! Yes, we can't determine which way now, I will leave it until I move the implementation of ArrowFunction to the common module, in that time we can use it in async-to-generator and async-generator-functions plugins where we may get more samples to verify which one is better.

Closing as we don't see a noticeable performance improvement