builtins-date-based-on-std-stringstream.cc

// ES6 section 20.3.4.41.1 ToDateString(tv)
std::string ToDateString(double time_val, DateCache* date_cache,
                         ToDateStringMode mode = kDateAndTime) {
  std::stringstream ss;
  ss.sync_with_stdio(false); // to speed up by enabling buffering
  if (std::isnan(time_val)) {
    ss << "Invalid Date";
    return ss.str();
  }
  int64_t time_ms = static_cast<int64_t>(time_val);
  int64_t local_time_ms = date_cache->ToLocal(time_ms);
  int year, month, day, weekday, hour, min, sec, ms;
  date_cache->BreakDownTime(local_time_ms, &year, &month, &day, &weekday, &hour,
                            &min, &sec, &ms);
  int timezone_offset = -date_cache->TimezoneOffset(time_ms);
  int timezone_hour = std::abs(timezone_offset) / 60;
  int timezone_min = std::abs(timezone_offset) % 60;
  const char* local_timezone = date_cache->LocalTimezone(time_ms);
  switch (mode) {
    case kDateOnly:
      ss << kShortWeekDays[weekday] << ' ' << kShortMonths[month] << ' '
          << std::setfill('0') << std::setw(2) << day << ' '
          << std::setfill('0') << std::setw(4) << year;
      return ss.str();
    case kTimeOnly:
      ss << std::setfill('0') << std::setw(2) << hour << ':'
          << std::setfill('0') << std::setw(2) << min << ':'
          << std::setfill('0') << std::setw(2) << sec
          << " GMT" << ((timezone_offset < 0) ? '-' : '+')
          << std::setfill('0') << std::setw(2) << timezone_hour
          << std::setfill('0') << std::setw(2) << timezone_min
          << " (" << local_timezone << ')';
      return ss.str();
    case kDateAndTime:
      ss << kShortWeekDays[weekday] << ' ' << kShortMonths[month] << ' '
          << std::setfill('0') << std::setw(2) << day << ' '
          << std::setfill('0') << std::setw(4) << year << ' '
          << std::setfill('0') << std::setw(2) << hour << ':'
          << std::setfill('0') << std::setw(2) << min << ':'
          << std::setfill('0') << std::setw(2) << sec
          << " GMT" << ((timezone_offset < 0) ? '-' : '+')
          << std::setfill('0') << std::setw(2) << timezone_hour
          << std::setfill('0') << std::setw(2) << timezone_min
          << " (" << local_timezone << ')';
      return ss.str();
  }
  UNREACHABLE();
}

results-with-ssoallocator.txt

bikineev@bikineev-OptiPlex-7040:~/git/v8/out/release-perf$ perf stat ./d8 test.js                                                                              

 Performance counter stats for './d8 test.js':

       9352,901636      task-clock (msec)         #    1,001 CPUs utilized          
             1 774      context-switches          #    0,190 K/sec                  
                35      cpu-migrations            #    0,004 K/sec                  
             3 857      page-faults               #    0,412 K/sec                  
    34 412 867 769      cycles                    #    3,679 GHz                    
   <not supported>      stalled-cycles-frontend  
   <not supported>      stalled-cycles-backend   
   104 841 056 197      instructions              #    3,05  insns per cycle        
    17 071 710 498      branches                  # 1825,285 M/sec                  
        30 876 662      branch-misses             #    0,18% of all branches        

       9,341967976 seconds time elapsed

results-with-std-stringstream.txt

bikineev@bikineev-OptiPlex-7040:~/git/v8/out/release-perf$ perf stat ./d8 test.js 

 Performance counter stats for './d8 test.js':

      16384,025031      task-clock (msec)         #    1,001 CPUs utilized          
             1 789      context-switches          #    0,109 K/sec                  
                44      cpu-migrations            #    0,003 K/sec                  
             3 854      page-faults               #    0,235 K/sec                  
    61 220 099 717      cycles                    #    3,737 GHz                    
   <not supported>      stalled-cycles-frontend  
   <not supported>      stalled-cycles-backend   
   155 779 362 573      instructions              #    2,54  insns per cycle        
    27 703 189 915      branches                  # 1690,866 M/sec                  
        47 186 522      branch-misses             #    0,17% of all branches        

      16,373651309 seconds time elapsed

test.js

(function f() { var s; for (var i = 0; i < 10000000; i++) { s = new Date().toString() } return s })();