Comments on Meeting Notes

Axel Rauschmayer axel at rauschma.de
Tue Dec 11 23:27:19 PST 2012


>>> * It deoptimizes, e.g. a strict-mode function must be optimized to copy
>>> actual parameter values into arguments if it could use the arguments object.
>> 
>> This one I just don't buy at all. In a strict function f, f.arguments
>> is poisoned. f's arguments would only need to be reified if f
>> statically mentions "arguments" or if f has a statically apparent use
>> of the direct eval operator. For all other cases, no arguments object
>> need be created, and therefore no copying is needed.
> 
> Right, that's what I tried to say by "could use the arguments object". Nothing to do with hated f.arguments.
> 
> So every strict function that uses arguments pays a copying price on entry in a naive implementation. Pushing the copies out till just before there might be an aliasing store is an optimization that could be done in a more sophisticated implementation, but engines don't do it currently and feel little pressure to do so. Chicken and egg.


Can you explain? What is this copying price and why don’t non-strict functions have to pay it?

Thanks!

Axel

-- 
Dr. Axel Rauschmayer
axel at rauschma.de

home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com

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