735088 - Stop using crappy hash functions in the JS engine

Status: RESOLVED INACTIVE

(Core :: JavaScript Engine, defect)

Description

[Justin Lebar (not reading bugmail)]

Split off from bug 729940.  There, we stopped using crappy hash functions in Gecko.  But we didn't land for JS because of some small perf regressions which I'm still working out.

Comment 1

[Justin Lebar (not reading bugmail)]

Watch the Windows Dromaeo results below to see if simplifying the hash function from goldenratio * (rol(hash, 5) ^ val) to 33 * (hash ^ val) improves perf.

https://tbpl.mozilla.org/?tree=Try&rev=284fb758b848

Comment 2

[Luke Wagner [:luke]]

On the subject, it would be nice to remove JS_ROTATE_LEFT32 to remove the temptation in the future...

Comment 3

[Justin Lebar (not reading bugmail)]

> Watch the Windows Dromaeo results below to see if simplifying the hash function from goldenratio * 
> (rol(hash, 5) ^ val) to 33 * (hash ^ val) improves perf.

I'm kicking more runs of Dromaeo, but it appears to be right beneath the cusp of statistically equal performance.

I really wonder why JS should be so sensitive to the hash function used here...