1986187 - Emit JSOp::TypeofEq for typeof x > "u"

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P3)

Description

[Tooru Fujisawa [:arai]]

It turns out that esbuild minifies typeof x === "undefined" into typeof x>"u", which means the JSOp::TypeofEq optimization no longer works on the code minified with it.

https://esbuild.github.io/try/#dAAwLjI1LjkALS1taW5pZnkAdHlwZW9mIHggPT09ICJ1bmRlZmluZWQi

We could extend the support for JSOp::TypeofEq to also match the minified code, so that the minified code still works in the same speed.

JSC already landed a patch to emit an optimized ops for the the minified code: https://bugs.webkit.org/show_bug.cgi?id=298148

Comment 1

[Tooru Fujisawa [:arai]]

Attachment: Bug 1986187 - Emit JSOp::TypeofEq for typeof x > "u". r?jandem!

Comment 2

[Tom S. (please needinfo tschuster)]

So this minfier basically made it impossible to introduce any new type in JavaScript that is lexographically lager than an "u"?

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/ec3b954f2c4f
https://hg.mozilla.org/integration/autoland/rev/2fb1b25f39e2
Emit JSOp::TypeofEq for typeof x > "u". r=jandem

Comment 4

[Iulian Moraru]

https://hg.mozilla.org/mozilla-central/rev/2fb1b25f39e2