Have physical equality inspect Javascript objects #25
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OlivierNicole
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Currently in wasm, physical equality behaves differently from in Javascript: Javascript objects are boxed, and non-equality of the pointers causes the values to be physically not equal. This can be an issue for some folks who rely on the JS-object-inspecting semantics of physical equality to implement things such as memoizing. This restores the fact that physical equality inspects Javascript objects. Other values are unaffected. This entails to pay an additional cost of between one and two Wasm runtime type tests in physical equality. A quick benchmark performing a few million `(==)` in an array of integers show a slowdown of 20~25 %. Since typical programs should perform physical equality much less frequently, we expect the overhead to be in the noise in practice. That being said, we may want to make this behaviour opt-in using a flag. Co-authored-by: Jérôme Vouillon <jerome.vouillon@gmail.com>
OlivierNicole
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I think I'm going to merge this PR as is. We'll add an opt out flag later if necessary. Could you make sure that all the files are properly formatted? |
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It should be now. |
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Currently in wasm, physical equality behaves differently from in Javascript: Javascript objects are boxed, and non-equality of the pointers causes the values to be physically not equal. This can be an issue for some folks who rely on the JS-object-inspecting semantics of physical equality to implement things such as memoizing.
This restores the fact that physical equality inspects Javascript objects. Other values are unaffected. This entails to pay an additional cost of between one and two Wasm runtime type tests in physical equality. A quick benchmark performing a few million
(==)in an array of integers show a slowdown of 20~25 %. Since typical programs should perform physical equality much less frequently, we expect the overhead to be in the noise in practice.That being said, we may want to make this behaviour opt-in using a flag.