Initialize cached time zone offset after snapshot is created, not before. Fix...

src/date.js

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 103 matching lines @@
   // the actual year if it is in the range 1970..2037
   if (t >= 0 && t <= 2.1e12) return t;
 
   var day = MakeDay(EquivalentYear(YEAR_FROM_TIME(t)),
                     MONTH_FROM_TIME(t),
                     DATE_FROM_TIME(t));
   return MakeDate(day, TimeWithinDay(t));
 }
 
 
-// Because computing the DST offset is a pretty expensive operation
-// we keep a cache of last computed offset along with a time interval
+// local_time_offset is initialized when the DST_offset_cache is missed.
+// It must not be used until after a call to DaylightSavingsOffset().
+// In this way, only one check, for a DST cache miss, is needed.
+var local_time_offset;
+
+
+// Because computing the DST offset is an expensive operation,
+// we keep a cache of the last computed DST offset along with a time interval
 // where we know the cache is valid.
+// When the cache is valid, local_time_offset is also valid.
 var DST_offset_cache = {
   // Cached DST offset.
   offset: 0,
   // Time interval where the cached offset is valid.
   start: 0, end: -1,
   // Size of next interval expansion.
   increment: 0
 };
 
 
 // NOTE: The implementation relies on the fact that no time zones have
 // more than one daylight savings offset change per month.
 // If this function is called with NaN it returns NaN.
 function DaylightSavingsOffset(t) {
   // Load the cache object from the builtins object.
   var cache = DST_offset_cache;
 
   // Cache the start and the end in local variables for fast access.
   var start = cache.start;
   var end = cache.end;
 
   if (start <= t) {
     // If the time fits in the cached interval, return the cached offset.
     if (t <= end) return cache.offset;
 
+    // If the cache misses, the local_time_offset may not be initialized.
+    if (IS_UNDEFINED(local_time_offset)) {
+      local_time_offset = %DateLocalTimeOffset();
+    }
+
     // Compute a possible new interval end.
     var new_end = end + cache.increment;
 
     if (t <= new_end) {
       var end_offset = %DateDaylightSavingsOffset(EquivalentTime(new_end));
       if (cache.offset == end_offset) {
         // If the offset at the end of the new interval still matches
         // the offset in the cache, we grow the cached time interval
         // and return the offset.
         cache.end = new_end;
@@ skipping 16 matching lines @@
           cache.increment /= 3;
           cache.end = t;
         }
         // Update the offset in the cache and return it.
         cache.offset = offset;
         return offset;
       }
     }
   }
 
+  // If the cache misses, the local_time_offset may not be initialized.
+  if (IS_UNDEFINED(local_time_offset)) {
+    local_time_offset = %DateLocalTimeOffset();
+  }
   // Compute the DST offset for the time and shrink the cache interval
   // to only contain the time. This allows fast repeated DST offset
   // computations for the same time.
   var offset = %DateDaylightSavingsOffset(EquivalentTime(t));
   cache.offset = offset;
   cache.start = cache.end = t;
   cache.increment = msPerMonth;
   return offset;
 }
 
@@ skipping 10 matching lines @@
   timezone_cache_time = t;
   timezone_cache_timezone = timezone;
   return timezone;
 }
 
 
 function WeekDay(time) {
   return Modulo(DAY(time) + 4, 7);
 }
 
-var local_time_offset = %DateLocalTimeOffset();
 
 function LocalTime(time) {
   if (NUMBER_IS_NAN(time)) return time;
-  return time + local_time_offset + DaylightSavingsOffset(time);
+  // DaylightSavingsOffset called before local_time_offset used.
+  return time + DaylightSavingsOffset(time) + local_time_offset;
 }
 
 function LocalTimeNoCheck(time) {
   if (time < -MAX_TIME_MS || time > MAX_TIME_MS) {
     return $NaN;
   }
 
   // Inline the DST offset cache checks for speed.
+  // The cache is hit, or DaylightSavingsOffset is called,
+  // before local_time_offset is used.
   var cache = DST_offset_cache;
   if (cache.start <= time && time <= cache.end) {
     var dst_offset = cache.offset;
   } else {
     var dst_offset = DaylightSavingsOffset(time);
   }
   return time + local_time_offset + dst_offset;
 }
 
 
 function UTC(time) {
   if (NUMBER_IS_NAN(time)) return time;
+  // local_time_offset is needed before the call to DaylightSavingsOffset,
+  // so it may be uninitialized.
+  if (IS_UNDEFINED(local_time_offset)) {
+    local_time_offset = %DateLocalTimeOffset();
+  }
   var tmp = time - local_time_offset;
   return tmp - DaylightSavingsOffset(tmp);
 }
 
 
 // ECMA 262 - 15.9.1.11
 function MakeTime(hour, min, sec, ms) {
   if (!$isFinite(hour)) return $NaN;
   if (!$isFinite(min)) return $NaN;
   if (!$isFinite(sec)) return $NaN;
@@ skipping 306 matching lines @@
 
 function TimeString(time) {
   return TwoDigitString(HOUR_FROM_TIME(time)) + ':'
       + TwoDigitString(MIN_FROM_TIME(time)) + ':'
       + TwoDigitString(SEC_FROM_TIME(time));
 }
 
 
 function LocalTimezoneString(time) {
   var timezoneOffset =
-      (local_time_offset + DaylightSavingsOffset(time)) / msPerMinute;
+      (DaylightSavingsOffset(time) + local_time_offset) / msPerMinute;
   var sign = (timezoneOffset >= 0) ? 1 : -1;
   var hours = FLOOR((sign * timezoneOffset)/60);
   var min   = FLOOR((sign * timezoneOffset)%60);
   var gmt = ' GMT' + ((sign == 1) ? '+' : '-') +
       TwoDigitString(hours) + TwoDigitString(min);
   return gmt + ' (' +  LocalTimezone(time) + ')';
 }
 
 
 function DatePrintString(time) {
@@ skipping 501 matching lines @@
     "toGMTString", DateToGMTString,
     "toUTCString", DateToUTCString,
     "getYear", DateGetYear,
     "setYear", DateSetYear,
     "toISOString", DateToISOString,
     "toJSON", DateToJSON
   ));
 }
 
 SetupDate();