1140451 - Only warn about uncached asm.js compilation if the caching would be useful

Status: REOPENED

(Core :: JavaScript Engine, defect)

Description

[Till Schneidereit [:till]]

In Shumway, we're using Emscripten's Relooper as an asm.js module. The message about successful compilation contains the recommendation to make loading async so caching works:

"Successfully compiled asm.js code (total compilation time 36ms; unable to cache asm.js in synchronous scripts; try loading asm.js via <script async> or createElement('script'))"

However, loading the module from cache takes ~160ms, so doing this would by highly counterproductive. Can we somehow detect this situation and not emit the warning?

I guess more importantly, can we not cache in this situation?

Comment 1

[Luke Wagner [:luke]]

If this is anything like bug 1135296, then most of that 160ms is actually just blocking on some other runnable to finish running on the main thread (as an annoying impl detail of Gecko, we require a few trips to the main thread during cache lookup; some or all of these can be removed in the future).  But this means that caching is still a win b/c it is removing 36ms of main-thread compilation time from the main thread.

A quick experiment to confirm is to see what the load time is with caching for a no-op app that does nothing but load the one relooper script async.

Comment 2

[BMO Automation]

Per policy at https://wiki.mozilla.org/Bug_Triage/Projects/Bug_Handling/Bug_Husbandry#Inactive_Bugs. If this bug is not an enhancement request or a bug not present in a supported release of Firefox, then it may be reopened.