perf-test-d8.js

var fs = {
  readFile: function(filename, cb) {
    cb(null, {length: 12});
  }
}

for (var i = 0; i < 10000; i++) {
  var __filename = 'perf-test.js';
  printLength(__filename)
}

function printLength (filename) {
  fs.readFile(filename, foo)

  function foo (err, buf)  {
    if (err) return // ignore error - probably just too many fds
     for (var j = 0; j<1000; j++) {
       // Do some work to make the optimization actually worth while
       buf.length++;
    }
    return (filename + ' has length ' + buf.length);
  }
}

~/v8 (master)$ time ./out.gn/x64.debug/d8 perf-test.js --mark_shared_functions_for_tier_up
real	0m0.385s
user	0m0.368s
sys	0m0.020s
~/v8 (master)$ time ./out.gn/x64.debug/d8 perf-test.js 
real	0m1.533s
user	0m1.515s
sys	0m0.026s