1664826 - Update js::StaticStrings optimization to support $, _

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P3)

Description

[Ted Campbell [:tcampbell]]

In the js::StaticStrings optimization, we fast-path length-2 strings whose characters are matched by this. This covers the usual alpha-numeric ASCII set and also [ and ~. In JS the rule for identifiers allows $ and _ and minifiers use this. We should change the the set of small-chars to match this. The lookup during atomization is table-based so this change does not have an impact on lookup complexity.

For example, on the cadmium_core bundle that Netflix loads, this change fast-paths 3000 atomize calls in the parser.

Comment 1

[Ted Campbell [:tcampbell]]

Attachment: Bug 1664826 - Update StaticStrings small-chars to include '$', '_'

The $ and _ characters are legal JS identifiers and can show up a fair
bit in large minified code-bases. This changes the {to,from}SmallChar which
is used during StaticStrings::init. We already use a table-based lookup
while atomizing so there isn't additional perf cost during atomization.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/2267cc975235
Update StaticStrings small-chars to include '$', '_' r=djvj

Comment 3

[Cosmin Sabou [:CosminS]]

Backed out for valgrind bustages about ParserAtom.cpp.

Push with failures: https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=pending%2Crunning%2Ctestfailed%2Cbusted%2Cexception&revision=71d14ede1fcb8eaf54659c37226dd78eb23ed6ac&searchStr=valgrind

Failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=315868064&repo=autoland&lineNumber=66784

Backout link: https://hg.mozilla.org/integration/autoland/rev/b2d8201169eaddec051abaae7685656b2bd2a3fb

Comment 4

[Ted Campbell [:tcampbell]]

(backout reason is in Bug 1664312)

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/931771ff71c2
Update StaticStrings small-chars to include '$', '_' r=djvj

Comment 6

[Bogdan Tara[:bogdan_tara | bogdant]]

https://hg.mozilla.org/mozilla-central/rev/931771ff71c2