1643750 - Optimize Object.prototype.toString for primitives

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P3)

Description

[Ted Campbell [:tcampbell]]

This is a bit silly, but there is noticeable time on sites like reddit spent converting primitives to objects in order to call toString.

eg.

function c(e) {
  return "[object Object]" === Object.prototype.toString.call(e);
}

We currently handle this by calling obj_toString but this is allocating objects. As a short-term fix, I'll add a fast path there. In the future with WarpBuilder, we should be able to do a better job.

Comment 1

[Ted Campbell [:tcampbell]]

Attachment: Bug 1643750 - Optimize Object.prototype.toString for primitives. r?jandem

While this is a bit silly, the code does come up in the wild. We avoid
allocating objects for primitives we can can show that the global prototypes
were not tampered with.

Comment 2

[Ted Campbell [:tcampbell]]

Here is a patch that improves that case. It became more complex than I wanted though. In future it would be good to have a transpile-able IC

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/8c3873698dcb
Optimize Object.prototype.toString for primitives. r=jandem

Comment 4

[Bogdan Tara[:bogdan_tara | bogdant]]

https://hg.mozilla.org/mozilla-central/rev/8c3873698dcb