Sorry to bump in, but I am interested if those are good beginner bugs, would that be OK?
Thanks, Ting ----- Original Message ----- > From: "Kannan Vijayan" <[email protected]> > To: [email protected] > Sent: Wednesday, July 30, 2014 9:44:12 PM > Subject: Re: [JS-internals] 'in' operator is slow? > > The simple reason is that we don't optimize this case in Ion yet. > > Looking at IonBuilder's handling of JSOP_IN, it optimizes the case where > the property being checked for is a dense element and the object is > well-known, but it doesn't optimize property checks. > > The "full treatment" of this op would include the following: > > 1. Optimize property checks using Type-Inference. This will only work > for definite properties. > 2. Optimize property checks using Baseline IC stubs, inlining shape > guards into the main jitcode body. > 3. Optimize property checks using Ion ICs. > > These are, in fact, really good beginner bugs. Most of the logic here > will be equivalent to the GetProp implementations, except instead of > returning the value from the property slot, it will return true/false.. > so there's a good existing reference for how to implement this. > > Kannan > > > On 2014-07-30, 9:25 AM, Nicholas Nethercote wrote: > > Hi, > > > > The following jsperf microbenchmark suggests that |p in o| is much > > slower than |o.p !== undefined|: http://jsperf.com/in-vs-not-undefined > > > > Can someone explain why? > > http://stackoverflow.com/questions/13866442/why-is-javascripts-in-operator-consistently-slower-than-strict-member-compari > > discusses this, but I'm not entirely convinced. Maybe the ToString() > > required for 'in' explains it? > > > > Thanks. > > > > Nick > > _______________________________________________ > > dev-tech-js-engine-internals mailing list > > [email protected] > > https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals > > _______________________________________________ > dev-tech-js-engine-internals mailing list > [email protected] > https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals > _______________________________________________ dev-tech-js-engine-internals mailing list [email protected] https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals
