1815503 - Optimize away `SetElementMegamorphic` inside for-in loops when possible

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P2)

Description

[Alex Thayer [:alexical] (she/her)]

In bug 1799025, Iain optimized away megamorphic hasprop/getelem ops by using information cached on the iterator to just get the slot directly. We should be able to do the same thing for SetElementMegamorphic and SetPropertyCache.

My initial patch for this saw a nice little 2.25% win on React-Redux-TodoMVC and a 1.5% win on React-TodoMVC from this: https://treeherder.mozilla.org/perfherder/comparesubtest?originalProject=try&newProject=try&newRevision=38cb033e4e080a0a3f4cf810ca9a9a6d10503efa&originalSignature=3451139&newSignature=3451139&framework=13&originalRevision=487d5fad0b7e8785ce652405a06084349d875658&page=1&showOnlyComparable=1

Comment 1

[Alex Thayer [:alexical] (she/her)]

Attachment: Bug 1815503 - Optimize away `SetElementMegamorphic` inside for-in loops when possible r?iain

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/6ff2f3fcd5fd
Optimize away `SetElementMegamorphic` inside for-in loops when possible r=iain

Comment 3

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/6ff2f3fcd5fd