Example of Babel issue #5656

output.js

var log = function log() {
  var _console;

  return (_console = console).log.apply(_console, arguments);
};

function test_opt() {
  log.apply(undefined, arguments);
}

function test_deopt() {
  for (var _len = arguments.length, args = Array(_len), _key = 0; _key < _len; _key++) {
    args[_key] = arguments[_key];
  }

  var fn = function fn() {
    return log.apply(undefined, arguments);
  };
  fn.apply(undefined, args);
}