Compare speed of f.call(...) vs. %_CallFunction(..., f) in V8

callfunction.js

// Run with: d8 --allow-natives-syntax callfunction.js

function f1(n, cb, thisArg) {
  for (var i = 0; i < n; i++) {
    cb.call(thisArg, i);
  }
}

function f2(n, cb, thisArg) {
  for (var i = 0; i < n; i++) {
    %_CallFunction(thisArg, i, cb);
  }
}

var start;
var end;

function callback(i) { /* no-op */ }

start = new Date().getTime();
f1(10000000, callback, 42);
end = new Date().getTime();
print("f1", end - start, "ms");

start = new Date().getTime();
f2(10000000, callback, 42);
end = new Date().getTime();
print("f2", end - start, "ms");

Typical output in my machine:

% d8 --allow-natives-syntax callfunction.js
f1 470 ms
f2 48 ms
%

Using %_CallFunction() is consistently an order of magnitude faster.