431908 - ActionMonkey: Use Tamarin Tracing's strings to implement SpiderMonkey strings

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, defect)

Description

[Jim Blandy :jimb]

Once we have Tamarin Tracing in the ActionMonkey tree, our first step should be to change SpiderMonkey to use TT's strings.

This will regress performance, as TT strings don't have SM's optimizations (deflated string cache; quick append; quick substring), but taking this smaller step allows us to do full in-browser tests sooner.  Bug 427154 should restore that performance.

Comment 1

[Brendan Eich [:brendan]]

Hi Jim, I'm wondering if this is taking too much risk in one gulp. The problems include lack of test coverage (we have a lot, but nothing near total), including performance tests.

Ideally we would have a near-to-release-shape state of ActionMonkey, near meaning a month or two. Is this even close to true now with ActionMonkey as it is? Even if not, every large calculated regression requiring multiple followup fixes takes us farther away from that point. I've seen projects lose the thread and never get back to near the (undertested, but user-tested in perma-beta) quasi-releasable point.

Why is it a goal to run in-browser JS tests on TT string code as it is today?

/be

Comment 2

[Benjamin Smedberg]

I again thought we were doing this the other way 'round: giving TT the spidermonkey string optimizations, and *then* unifying the types. Am I confused again? Bug 427154

Comment 3

[Jim Blandy :jimb]

Rob Sayre, Brian Crowder, Jason Orendorff, and Jim Blandy had a meeting in person about this strategy this morning; we'll be posting to tamarin-devel, and meeting again with more information tomorrow.

Rob explained to Jason and Jim that Mozilla's experience is that any performance regression at all, even temporarily, is a losing strategy.  So we'll be working with that constraint.

Comment 4

[Robert Sayre]

today's spidermonkey vs. tamarin-tracing numbers:

http://spreadsheets.google.com/pub?key=pF_tMaWf14QyDcEpQFxyoIg

Comment 5

[Jason Orendorff [:jorendorff]]

Mass-WONTFIXing ActionMonkey bugs.