2027064 - Slower than JSC at calling `Date.now = () => +new Date('2023-05-12T08:35:00');`

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P3)

Description

[Markus Stange [:mstange]]

Attachment: microbenchmark

On the Perf-Dashboard subtest of sp3, Date.now has been stubbed out as follows:

Date.now = () => +new Date('2023-05-12T08:35:00');

https://github.com/WebKit/Speedometer/blob/6cd673574812cf63ec1b497b15ec7397f0356cfc/resources/perf.webkit.org/public/v3/index.html#L39

On the attached microbenchmark, I get 435ms in Firefox and 231ms in Safari Technology Preview 227, i.e. Safari being 1.9x faster.

Doubling our speed here may give us a 1% win on the Perf-Dashboard subtest.

See bug 2026748 comment 4 for more context.

Comment 1

[Iain Ireland [:iain]]

In the linked comment I mention two possible approaches for speeding this up: a one-element cache when parsing Dates, and CacheIR support for converting Dates to number. I got Claude to prototype the second approach; it brings us within ~15% of jsc. If we also do the one-element cache, I think we should be significantly faster.

Comment 2

[Worcester12345]

Should this bug get the "PERF" key word? I can do it if someone can fix that for me. Thank you.

Comment 3

[Markus Stange [:mstange]]

This looks well and truly fixed now. Thanks anba and Iain!

I now get 64ms in Firefox, down from 435ms and way lower than Safari's ~200ms.