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dns: allow v8 to optimize lookup() #8942

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mscdex
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@mscdex mscdex commented Dec 25, 2014

Reassigning the values of parameter variables causes
v8 to disable function optimization.

exports.lookup = function(domain, family, callback) {
exports.lookup = function(domain, family_, callback_) {
var family = family_,
callback = callback;
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Should this be callback = callback_?

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Yes, sorry.

@cjihrig
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cjihrig commented Dec 25, 2014

I thought v8 could still optimize writes to named function arguments, but couldn't handle writes to arguments (need to test though).

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mscdex commented Dec 25, 2014

It can't optimize any function that contains any usage of arguments and also mutates parameter variable values. This is mentioned in bluebird's "Optimization killers" and I also saw it while checking for deoptimizations in my own code with node v0.10.

@Fishrock123
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I thought v8 could still optimize writes to named function arguments, but couldn't handle writes to arguments (need to test though).

I was also under this impression. I know writing to arguments is bad, but I always do like fn(param) { param = param || 'thing' }.

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This is mentioned in bluebird's "Optimization killers"

Hmm, only says when you also use arguments in the same function. Interesting. Weird.

@cjihrig
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cjihrig commented Dec 25, 2014

Ah, the problem is that is also reads arguments. I think you can get around that just by enabling strict mode.

Using `arguments` and reassigning parameter variable
values causes v8 to disable function optimization.
@jasnell
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jasnell commented Aug 27, 2015

@mscdex ... is this still something you think needs to be done in v0.10?

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mscdex commented Aug 27, 2015

@jasnell Well, it's an optimization. If anything it might make lookups a tad faster. If it doesn't apply cleanly to v0.10 anymore I guess I wouldn't worry about it.

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jasnell commented Aug 27, 2015

So long as CI passes, LGTM

jasnell pushed a commit that referenced this pull request Aug 27, 2015
Using `arguments` and reassigning parameter variable
values causes v8 to disable function optimization.

PR-URL: #8942
Reviewed-By: jasnell - James M Snell <jasnell@gmail.com>
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jasnell commented Aug 27, 2015

Landed in 6502160

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5 participants