Intent to Experiment [more]: Explicit Compile Hints with Magic Comments

[Marja Hölttä]

After getting inconsistent results from our past experiments, we'd like to run a two-arm origin trial combined with a Finch holdback experiment. The two arms are for different implementations of the feature (runtime features JavaScriptCompileHintsMagic and JavaScriptCompileHintsMagicAlways).

To do a two-arm Origin trial, I was told to use 2 origin trials for the same Chromestatus feature. This is the "Intent to Experiment" e-mail for the second one ( JavaScriptCompileHintsMagicAlways ).

Contact emails

ma...@google.com, les...@google.com

Explainer

https://github.com/explainers-by-googlers/explicit-javascript-compile-hints-file-based/blob/main/README.md

Specification

https://explainers-by-googlers.github.io/explicit-javascript-compile-hints-file-based

Summary

Allow attaching information about which functions should be eager parsed & compiled in JavaScript files. The information will be encoded as magic comments. We'll first target launching the file-based explicit compile hints, and as a follow up, investigate selecting individual functions for eager compilation.

Blink component

Blink>JavaScript

TAG review

TAG review status

Not applicable

Chromium Trial Name

JavaScriptCompileHintsMagic

Origin Trial documentation link

https://docs.google.com/document/d/19xTAM4A75tz0xUq_velMzGA4JHEgXpyflUxXTcuNiyE/edit?usp=sharing

Risks

Interoperability and Compatibility

No interoperability / compatibility risks. Other browsers are likely to ignore the hints if they perceive they cannot benefit from them. Ignoring the hint is allowed behavior. We plan to make the hints generic though, so that other browsers can later start to support them too, e.g., if they implement background parsing / compilation.

Gecko: N/A (https://github.com/mozilla/standards-positions/issues/780)

WebKit: N/A (https://github.com/WebKit/standards-positions/issues/172)

Web developers: Positive Positive signals from partners who want to use compile hints to eager-compile core JS files.

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

Goals for experimentation

Reason this experiment is being extended

The origin trial configuration for this feature was broken in M115-M116, and the users weren't able to run the experiments. We did an origin trial in versions 115-117. We modified the feature based on the results (performance measurements by Google Workspace) and we'd now like to do another origin trial with the modified feature, in versions 129-131.

Reason this experiment is being extended

We got inconsistent results from the previous 2 experiments (which had slightly different feature implementations). To investigate further, we're planning to run an experiment where we compare those 2 feature implementations against each other simultaneously, and also add a Finch holdback experiment for already-shipping compile hints features (crowdsourced compile hints and local compile hints) which might interfere with the experiment. In addition, we landed code cache related fixes in M132, and those should also be included in the rerun. The rerun should target versions [132, 134].

Ongoing technical constraints

Debuggability

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

No

The feature doesn't trigger any functional changes and cannot be tested by WPT.

Flag name on about://flags

Finch feature name

None

Non-finch justification

None

Requires code in //chrome?

False

Tracking bug

https://bugs.chromium.org/p/v8/issues/detail?id=13917

Estimated milestones

Origin trial desktop first	115
Origin trial desktop last	117
Origin trial desktop first	132
Origin trial desktop last	134
Origin trial extension 1 end milestone	131
Origin trial extension 2 end milestone	134
Origin trial Android first	132
Origin trial Android last	134

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5100466238652416?gate=6313707028873216

Links to previous Intent discussions

Intent to Experiment: https://groups.google.com/a/chromium.org/g/blink-dev/c/BmN1Wus8V1s/m/3L2uU-wGAgAJ
Intent to Extend Experiment 1: https://groups.google.com/u/1/a/chromium.org/g/blink-dev/c/mwZYYTBJ12g/m/HWsRCkuxAQAJ
Intent to Ship: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAED6dUAN%3DzwdBsziegkniJi2hhF%3DVQ7xUk%2BdvB-6V%2B-TCTdiPg%40mail.gmail.com

This intent message was generated by Chrome Platform Status.

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[Mike Taylor]

LGTM to experiment from 132 to 134 inclusive (let me know if I got that range wrong).

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