861069 - Baseline JIT landing has almost completely broken JIT Inspector

Status: RESOLVED INCOMPLETE

(Core :: JavaScript Engine, defect)

Description

[Katelyn Gadd (:kael)]

The JIT Inspector addon (https://addons.mozilla.org/en-US/firefox/addon/jit-inspector/?src=api) has historically been extremely useful for understanding JS performance in Firefox and it exposes lots of useful data.

As of Firefox 23 (nightly), almost every part of JIT Inspector seems to have broken. Most of the views now show nothing instead of showing the variety of data they used to show. For example, monomorphic vs polymorphic values, stub calls, etc don't seem to consistently show up in the gathered data anymore.

It seems like the problem is that baseline jitted code is not generating this information, but I can't be sure.

I understand if the JIT Inspector addon is unsupported or otherwise impossible to maintain, but it is unfortunate to lose it. Much of the data it provides is unavailable in any other form so this makes it much harder to understand and troubleshoot performance issues.

If JIT Inspector is broken for good by Baseline, it should probably be marked as incompatible with Firefox 23 and up.