1406074 - Slow benchmarks for value mapping tests

Status: RESOLVED INCOMPLETE

(Core :: JavaScript Engine, defect, P3)

Description

[Ryo Hazuki]

User Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0
Build ID: 20170926190823

Steps to reproduce:

The following tests returns weird benchmarks in FF v56 in 64 bits.

http://jsben.ch/o0UDx

Those tests just compare speed between if/else, switch case and value mapper. In all other browsers, the value mapper is the fastest, but not in FF.

People from this forum https://stackoverflow.com/a/8624971/1914034 mentioned that the value mapper test was the fastest in past versions of FF.

Those tests might point out that something is going wrong with FF.


Actual results:

The fastest test was the if/else test.


Expected results:

The fastest test should be the mapper test.

Comment 1

[Ryo Hazuki]

This test shows the same weird behaviour: https://jsperf.com/performance-of-assigning-variables-in-javascript/2

Comment 2

[Jan de Mooij [:jandem]]

The mapper will be faster if you don't create a new object on every call/iteration - move the object literal into the global scope or something.

I expect the if-else/switch to be faster than allocating a brand new object each time just to do a single lookup.