commit f31bae0330e5787aab3e46af8e72342cb470cc3a
author Benedikt Meurer <bmeurer@chromium.org> Fri Sep 08 18:53:34 2017
committer Commit Bot <commit-bot@chromium.org> Mon Sep 11 06:21:58 2017
tree 92e984e24cd6892bb55b1c58216da0c365837482
parent 6716a7f641fbd520fde38d84daef4121ea978897

[builtins] Add fast-path for JSTypedArray to CreateListFromArrayLike.

It's quite common today to use Function#apply together with typed
arrays, for example to construct a String from character codes (or code
points) within a Uint8Array or Uint16Array, i.e.

  String.fromCharCode.apply(undefined, uint8array)

is seen quite often on the web. But there are other interesting cases
like

  Math.max.apply(undefined, float64array)

to compute the maximum value in a Float64Array, which is definitely not
the fastest implementation, but quite convenient and readable.
Unfortunately these cases hit the super-slow-path of the Function#apply
machinery in V8 currently, because Function#apply doesn't have any
fast-path for TypedArrays.

This CL adds a proper fast-path to CreateListFromArrayLike to the
ElementsAccessor, which can be used as long as the typed array that's
passed wasn't neutered. With this fast-path in place, the performance on
the micro-benchmark mentioned in the issue improves from

  stringFromCharCode: 6386 ms.
  stringFromCodePoint: 8752 ms.

to

  stringFromCharCode: 1932 ms.
  stringFromCodePoint: 4262 ms.

which corresponds to a 2.0x-3.3x improvement.

Bug: v8:2435
Change-Id: I4d39666e53644b11d5856982b005928e26f296fe
Reviewed-on: https://chromium-review.googlesource.com/657405
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47936}