benchmark: util._extend vs object.assign

To copy the values of all enumerable own properties from-
a source object to a target object, node still use-
`util._extend`, though newer standard `Object.assign`
is available. This is because `util._extend` is found to
be faster than `Object.assign`. This benchmark test is
to keep track of how performance compare.

PR-URL: #7255
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>

benchmark/misc/util-extend-vs-object-assign.js

@@ -0,0 +1,40 @@
+'use strict';
+
+const common = require('../common.js');
+const util = require('util');
+const v8 = require('v8');
+
+const bench = common.createBenchmark(main, {
+  type: ['extend', 'assign'],
+  n: [10e4]
+});
+
+function main(conf) {
+  let fn;
+  const n = conf.n | 0;
+  let v8command;
+
+  if (conf.type === 'extend') {
+    fn = util._extend;
+    v8command = '%OptimizeFunctionOnNextCall(util._extend)';
+  } else if (conf.type === 'assign') {
+    fn = Object.assign;
+    // Object.assign is built-in, cannot be optimized
+    v8command = '';
+  }
+
+  // Force-optimize the method to test so that the benchmark doesn't
+  // get disrupted by the optimizer kicking in halfway through.
+  for (var i = 0; i < conf.type.length * 10; i += 1)
+    fn({}, process.env);
+
+  v8.setFlagsFromString('--allow_natives_syntax');
+  eval(v8command);
+
+  var obj = new Proxy({}, { set: function(a, b, c) { return true; } });
+
+  bench.start();
+  for (var j = 0; j < n; j += 1)
+    fn(obj, process.env);
+  bench.end(n);
+}