Optimizing handling for variadic function arguments

benchmark

#!/bin/bash
node benchmark.js

benchmark.js

var Benchmark = require('benchmark')
var suite = new Benchmark.Suite()

var handlers = require('./callback-handlers')

var cb = () => {}
var err = { code: 0 }
var result = 'async result'

// add tests
handlers.forEach(function (f) {
  suite.add(f.name, function () {
    f(cb, err, result)
  })
})

// add listeners and run async
suite
  .on('cycle', function (event) {
    console.log(String(event.target))
  })
  .on('complete', function () {
    console.log('And the winner is... ' + suite.filter('fastest').map('name') + '!')
  })
  .run({ async: true })

callback-handlers.js

function cbSliceArguments (callback, err) {
  if (err && err.code !== 0) {
    return callback(err)
  }

  var args = Array.prototype.slice.call(arguments, 2)
  args.unshift(null) // set err to null

  callback.apply(undefined, args)
}

function cbArrayConstructor (callback, err) {
  if (err && err.code !== 0) {
    return callback(err)
  }

  var args = Array.apply(null, arguments)
  args.shift() // remove callback argument
  args[0] = null // set err to null

  callback.apply(undefined, args)
}

function cbIterateArguments (callback, err) {
  if (err && err.code !== 0) {
    return callback(err)
  }

  var len = arguments.length
  var args = [null]
  for (var i = 2; i < len; i++) {
    args[i - 1] = arguments[i]
  }

  callback.apply(undefined, args)
}

function cbIterateArgumentsUsingPush (callback, err) {
  if (err && err.code !== 0) {
    return callback(err)
  }

  var len = arguments.length
  var args = [null]
  for (var i = 2; i < len; i++) {
    args.push(arguments[i])
  }

  callback.apply(undefined, args)
}

function cbSpreadOperator (callback, err, ...args) {
  if (err && err.code !== 0) {
    return callback(err)
  }

  callback(null, ...args)
}

function cbNaive (callback, err, arg1, arg2, arg3) {
  if (err && err.code !== 0) {
    return callback(err)
  }

  callback(null, arg1, arg2, arg3)
}

module.exports = [
  cbSliceArguments,
  cbArrayConstructor,
  cbIterateArguments,
  cbIterateArgumentsUsingPush,
  cbSpreadOperator,
  cbNaive
]

optimize

#!/bin/bash
if [ "$1" == "-v" ]; then
  node --trace_opt --trace_deopt --allow-natives-syntax optimize.js
else
  node --trace_opt --trace_deopt --allow-natives-syntax optimize.js | grep "^#"
fi

optimize.js

var handlers = require('./callback-handlers')

function status(f) {
  switch(%GetOptimizationStatus(f)) {
    case 1: return '\033[32moptimized\033[0m'
    case 2: return '\033[31mnot optimized\033[0m'
    case 3: return '\033[32malways optimized\033[0m'
    case 4: return '\033[31mnever optimized\033[0m'
    case 6: return 'maybe deoptimized'
    case 7: return '\033[32moptimized by TurboFan\033[0m'
    default: 'unknown'
  }
}

function printStatus(f) {
  console.log('# Function %s is %s', f.name, status(f))
}

var cb = function () {}
var error = { code: 0 }
var result = 'some value'

handlers.forEach((f) => {
  // 2 calls are needed to go from uninitialized -> pre-monomorphic -> monomorphic
  f(cb, error, result)
  f(cb, error, result)

  ;%OptimizeFunctionOnNextCall(f)
  f(cb, error, result)
  printStatus(f)
})