js: benchmark for typed arrays, refs https://github.com/nim-lang/Nim/pull/16850

[timotheecour]

@xflywind is this benchmark flawed / representative?

benchmark refs https://github.com/nim-lang/Nim/pull/16850#discussion_r566711862

Example

import times, macros

macro getArray(): untyped =
  result = newTree(nnkBracket)
  let m = 10
  for i in 0..<m:
    result.add newLit 3

proc main()=
  let n = 10000000
  let t = now()
  var x = 0
  for i in 0..<n:
    let a = getArray()
    for j in a: # same conclusions w: for j in 0..<a.len:
      x += a[j]
  let t2 = now()
  echo (t2 - t, x)

for i in 0..<3:
  echo i
  main()

before PR https://github.com/nim-lang/Nim/pull/16850

nim r -b:js -d:danger main

0 (144 milliseconds, 300000000) 1 (148 milliseconds, 300000000) 2 (174 milliseconds, 300000000)

after PR

0 (1 second and 469 milliseconds, 300000000) 1 (1 second and 441 milliseconds, 300000000) 2 (1 second and 424 milliseconds, 300000000)

links

• https://stackoverflow.com/questions/13328658/are-the-advantages-of-typed-arrays-in-javascript-is-that-they-work-the-same-or-s#comment18254017_13334497

  You are right, however these days most normal arrays are typed too, to avoid the cost of autoboxing. If you only store int's, then you get an int array (in modern JS engines). Type checking can also be needed for typed arrays, in case you try to store a non-number to one. – JL235 Nov 13 '12 at 21:48

[timotheecour]

weird:

• typeArray is a bit slower than array in this example which initializes the array/typed array just once

• and that's true even if we change in generated code var a_704643094 = new Int32Array([3, 3, 3, 3, 3, 3, 3, 3, 3, 3, ...]); to var a_704643094 = new Int32Array(10);

  when defined case2b:
  #[
  ]#
  import times, macros
  macro getArray(): untyped =
  result = newTree(nnkBracket)
  let m = 10
  for i in 0..<m:
    result.add newLit 3
  
  proc main()=
  let n = 10000000
  let t = now()
  var x = 0
  let a = getArray()
  for i in 0..<n:
    for j in a:
      x += a[j]
  let t2 = now()
  echo (t2 - t, x)
  
  for i in 0..<3:
  echo i
  main()