avoidable funnels + merges

https://github.com/ember-engines/ember-engines/blob/8f66b5e3b8089cd53884be49f270cac05f9a3d17/lib/engine-addon.js#L319

is often truthy, when it really isn’t needed as maybeMergeTrees via ember-cli/broccoli/merge-trees will return EMPTY_MERGE_TREES. In this location this internal construct leaks out, and results an un-needed funnel.

This optimization “EMPTY_MERGE_TREES” should likely be made to not leak as it does, but likely a short-term fix is to make maybeMergeTrees aware of it, so that downstream code can be made aware.

• fix
• see impact (should often-times remove 1 funnel and 1 merge per engine)
• @rwjblue thoughts?

[rwjblue]

Ya, confirm I had thought we were using broccoli-merge-tree directly. I completely forgot that we used ember-cli’s internal / private one…

[stefanpenner]

Skimming it looks like quite abit of avoidable work happens in engine builds when they encounter these empty trees. This is likely a good source of perf if addressed.