It's relatively like and it does happen on the web that code like Object.assign(obj, {a: 1, b: 3}) will turn the object literal into an unboxed object. This current always takes a slow path. In my patch for this I am not sure if we need to copy the layout.properties(), because those might change during execution? This makes unboxed objects as a source about as fast as native objects, maybe a bit slower.

> In my patch for this I am not sure if we need to copy the layout.properties(), because those might change during execution? Brian can you answer this for me? Thanks

(In reply to Tom Schuster [:evilpie] from comment #0) > In my patch for this I am not sure if we need to copy the > layout.properties(), because those might change during execution? The properties in a group's unboxed layout do not change after construction.

Thanks Brian. I was actually wondering what keeps the UnboxedLayout alive, but I didn't phrase that well. During the iteration we might change from unboxed to native.

(In reply to Tom Schuster [:evilpie] from comment #3) > Created attachment 8923553 [details] [diff] [review] > Optimize Object.assign from an unboxed object > > Thanks Brian. I was actually wondering what keeps the UnboxedLayout alive, > but I didn't phrase that well. During the iteration we might change from > unboxed to native. Well, the unboxed layout is owned by / stored in the object group which refers to it, and since that group is rooted in the patch things should be fine.

Comment on attachment 8923553 [details] [diff] [review] Optimize Object.assign from an unboxed object Review of attachment 8923553 [details] [diff] [review]: ----------------------------------------------------------------- \o/ very nice to have this fixed!

Pushed by evilpies@gmail.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/8cbf1345efd1 Optimize Object.assign with unboxed objects. r=jandem

Backed out for failing spidermonkey non-unified at js/src/vm/UnboxedObject.h:263:33: inline function 'const js::UnboxedLayout& js::UnboxedPlainObject::layout() const' used but never defined: https://hg.mozilla.org/integration/mozilla-inbound/rev/4154937d7b4e4d217f37cb6d06fd51e5012cbe84 Push with failure: https://treeherder.mozilla.org/#/jobs?repo=mozilla-inbound&revision=8cbf1345efd1e9fb1f6a729af5a115431fcd4c15&filter-resultStatus=usercancel&filter-resultStatus=runnable&filter-resultStatus=retry&filter-resultStatus=testfailed&filter-resultStatus=busted&filter-resultStatus=exception Failure log: https://treeherder.mozilla.org/logviewer.html#?job_id=141112011&repo=mozilla-inbound > js/src/vm/UnboxedObject.h:263:33: error: inline function 'const js::UnboxedLayout& js::UnboxedPlainObject::layout() const' used but never defined [-Werror]

Pushed by evilpies@gmail.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/2aaa2d20e7aa Optimize Object.assign with unboxed objects. r=jandem