851621 - 6 seconds spent in AliasedNameToSlot (from EmitAliasedVarOp) while loading large JS codebase

Status: RESOLVED INCOMPLETE

(Core :: JavaScript Engine, defect)

Description

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

We throw the latest VTune at the the monster GDC demo codebase.  Out of 15s of CompileScript() time, 6 seconds of it is spent on line 895 (maybe 894) in BytecodeEmitter.cpp calling AliasedNameToSlot.

This seems bad, potentially low hanging fruit?

Comment 1

[Luke Wagner [:luke]]

We could probably shave off a few cycles (that code was written for simplicity, not performance), but, roughly, the reason we're spending so much time in there is because asm.js contains a huge number of upvar references (every use of the heap or global variable).

Fortunately, bug 851421 will make this all go away for asm.js code, so I'm not sure if we need to worry about this.

Comment 2

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Ah, right! Ok, marking it as dependant.