650073 - Make empty loops faster

Status: RESOLVED WORKSFORME

(Core :: JavaScript Engine, defect)

Description

[David Mandelin [:dmandelin]]

V8 has faster empty loops (from 0 to N-1) than both JM and TM. I'm pretty sure the reason is that we don't keep loop iteration variables in registers. This probably matters a bit for the V8 benchmarks, and it would be good to do this in general.

This will be much easier to do in IonMonkey.

Comment 1

[Florian Bender]

Does this still apply? I checked with an empty loop check (assuming by empty loop you mean a loop without any statement) somebody put on jsperf[1] for a quick comparision (I know it's not optimal). In this test, Firefox is >40% faster (> 570 ops/sec) than Chrome (< 400 ops/sec) on my MBA 2012.


[1] http://jsperf.com/empty-loop-is-jsperf-com-fair

Comment 2

[Dan Gohman [:sunfish]]

I think we can call this done. We have IonMonkey now and it does keep loop iteration variables in registers.