1415161 - JSContext::findVersion slows down CheckPatternSyntax

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement)

Description

[Jan de Mooij [:jandem]]

Attachment: Patch

New candidate for silliest perf bug of the year. CheckPatternSyntax initializes a CompileOptions but doesn't pass a JSVersion, so the CompileOptions constructor ends up calling JSContext::findVersion which can be really slow because it walks the stack.

Hopefully we can remove JSVersion soon, but for now here's a patch to use JSVERSION_DEFAULT in CheckPatternSyntax.

This improves the micro-benchmark below from 223 ms to 200 ms.

function f() {
    var t = new Date;
    for (let i = 0; i < 1000000; i++) {
        re = new RegExp("foo");
    }
    print(new Date - t);
}
f();

Comment 1

[Jan de Mooij [:jandem]]

(I think there's more we can optimize here btw; looking into that still.)

Comment 2

[André Bargull [:anba]]

Comment on attachment 8925915 [details] [diff] [review]
Patch

Review of attachment 8925915 [details] [diff] [review]:
-----------------------------------------------------------------

Oh wow, I'm kind of speechless right now! :-)

Comment 3

[Jan de Mooij [:jandem]]

Oh I should fix the Maybe<CompileOptions> in RegExpObject::create too I guess.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/d82266d06a5b
Get rid of slow JSContext::findVersion calls when parsing regular expressions. r=anba

Comment 5

[Eliza Balazs [:ebalazs_]]

https://hg.mozilla.org/mozilla-central/rev/d82266d06a5b