1126690 - 'arguments' is slow to parse

Status: RESOLVED WORKSFORME

(Core :: JavaScript Engine, defect)

Description

[Neil Fraser]

Attachment: index.html

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:35.0) Gecko/20100101 Firefox/35.0
Build ID: 20150122214805

Steps to reproduce:

1. Open the attached file.
2. Look at console.


Actual results:

The 'slow' function executes ten times slower than the 'fast' function:

slow: 0.88ms
fast: 0.07ms
slow: 0.68ms
fast: 0.06ms

Note that at no time do the generated functions (wrapFunc) ever get called.  This is just as test of how quickly they can be parsed.

This is a minimal test case derived from Google's Blockly where one (using 'arguments') function parses 200 times slower than another function (not using 'arguments').  Firefox only.


Expected results:

Both functions should run at the same speed.  Here's Chrome:
slow: 0.010ms
fast: 0.011ms
slow: 0.022ms
fast: 0.018ms

Comment 1

[ovidiu boca[:Ovidiu]]

Hi, 

I have tested this on Mac OS X 10.10 with Firefox Nightly 46.0a1 and I can't reproduce the issue, the "slow" function is 2 times slower than the "fast" function.  Do you still have this problem?
Please download the Firefox Nightly from here: https://nightly.mozilla.org/ and retest the problem.

Comment 2

[YF (Yang)]

On Windows 10 for me:
35.0.1:
slow: 0.08ms attachment.cgi:14
fast: 0.02ms attachment.cgi:22
slow: 0.02ms attachment.cgi:14
fast: 0.02ms attachment.cgi:22

44.0b4:
slow: 1.24ms attachment.cgi:14
fast: 0.48ms attachment.cgi:22
slow: 0.66ms attachment.cgi:14
fast: 0.41ms attachment.cgi:22

Comment 3

[Jeff Walden [:Waldo]]

Given all the parsing changes that have happened since this was filed, I somewhat doubt this is still relevant.  Profiling to see if this still exists is definitely in order -- but as I'm going on a long vacation now, I can't be the one to deal with it.  :-\

Comment 4

[Neil Fraser]

As the original submitter, I can no longer replicate this issue.  Closing.