Optimization killers: popping an argument by decrementing `arguments.length`?

[Alex Goldsmith]

Howdy.

I was just reading through the Optimization Killers article on the Bluebird wiki, trying to work out whether the following would be optimized:

function get(/* ...k, j, i */) {
   const a = arguments, l = a.length, n = l - 1
   switch (l) {
      case 0: return this
      case 1: return this[a[n]]
      default: return get.apply(this[a[a.length = n]], a) // a.length = n = a.length - 1
   }
}

console.log(get.call({x:{y:{z:'!!!'}}}, 'z','y','x')) // => "!!!"

Shedding an argument in this way isn't really discussed (anywhere that I can find), but it seems like it should be okay (at least it doesn't appear to be leaking).

Any insight would be highly appreciated. Thanks in advance!

[Ben Noordhuis]

Start node or d8 with --trace_opt and it will tell you. My bet is
that you'll see a "Bad value context for arguments value" warning; V8
really doesn't like it when you modify arguments objects.

[Jason Zoo]

Hi,Why I use `d8 --trace_opt` output nothing?  My v8 version is 5.8.

[Ben Noordhuis]

On Tue, Feb 21, 2017 at 7:56 AM, Jason Zoo <zjc...@gmail.com> wrote:
> Hi,Why I use `d8 --trace_opt` output nothing? My v8 version is 5.8.

Try adding --trace_deopt as well.

[Jason Zoo]

also nothing. 

[Jason Zoo]

add --trace as well