New class for Date objects: caches individual date components.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index f2e35a6b7c422cbaca13a4a8cbb89861ea1f1204..10096426d21c90891620a8858be2e0fc56e146c5 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -64,6 +64,7 @@
 //             - JSBuiltinsObject
 //           - JSGlobalProxy
 //           - JSValue
+//             - JSDate
 //           - JSMessageObject
 //         - JSProxy
 //           - JSFunctionProxy
@@ -295,6 +296,7 @@ const int kVariableSizeSentinel = 0;
   V(JS_MESSAGE_OBJECT_TYPE)                                                    \
                                                                                \
   V(JS_VALUE_TYPE)                                                             \
+  V(JS_DATE_TYPE)                                                              \
   V(JS_OBJECT_TYPE)                                                            \
   V(JS_CONTEXT_EXTENSION_OBJECT_TYPE)                                          \
   V(JS_GLOBAL_OBJECT_TYPE)                                                     \
@@ -610,6 +612,7 @@ enum InstanceType {
   JS_PROXY_TYPE,  // LAST_JS_PROXY_TYPE
 
   JS_VALUE_TYPE,  // FIRST_JS_OBJECT_TYPE
+  JS_DATE_TYPE,
   JS_OBJECT_TYPE,
   JS_CONTEXT_EXTENSION_OBJECT_TYPE,
   JS_GLOBAL_OBJECT_TYPE,
@@ -803,6 +806,7 @@ class MaybeObject BASE_EMBEDDED {
   V(Oddball)                                   \
   V(SharedFunctionInfo)                        \
   V(JSValue)                                   \
+  V(JSDate)                                    \
   V(JSMessageObject)                           \
   V(StringWrapper)                             \
   V(Foreign)                                   \
@@ -5823,7 +5827,7 @@ class JSBuiltinsObject: public GlobalObject {
 };
 
 
-// Representation for JS Wrapper objects, String, Number, Boolean, Date, etc.
+// Representation for JS Wrapper objects, String, Number, Boolean, etc.
 class JSValue: public JSObject {
  public:
   // [value]: the object being wrapped.
@@ -5852,6 +5856,57 @@ class JSValue: public JSObject {
 };
 
 
+// Representation for JS date objects.
+class JSDate: public JSObject {

[ulan, 2012/01/25 13:08:48]

As we discussed offline, all these fields could be packed into few SMIs and we
could designate one bit in each SMI as "the date is a NaN" indicator. A possible
layout would be:

[value]: the time value.

[year_month_day]: SMI that caches the year in bits[31:12], the month in
bits[11:8], the day in bits[7:3], the is_cache_filled flag in bit[2], and the
is_nan flag in bit[1].

[hour_min_sec_ms]: SMI that caches the components similar to [year_month_day].

Advantages of this layout:
- the caches can be filled in lazily;
- less memory usage and CPU cache pressure.

Disadvantage:
- need to check is_nan flag in the getters.

[rossberg, 2012/01/25 15:48:37]

Yeah, I don't want to optimize this prematurely. The whole patch is for
benchmark speed, so I'd like to avoid the extra arithmetic for now and see where
we stand.  Frankly, I don't think space usage matters much for dates anyway, not
on benchmarks and even less so in reality. But let's see.

+ public:
+  // If one component is NaN, all of them are, indicating a NaN time value.
+  // [value]: the time value. Transitional, will disappear.

[ulan, 2012/01/25 13:08:48]

As we discussed offline, the [value] should stay since it's difficult to
reconstruct it.

[rossberg, 2012/01/25 15:48:37]

Done.

+  DECL_ACCESSORS(value, Object)
+  // [year]: caches year.
+  DECL_ACCESSORS(year, Object)
+  // [day]: caches month.
+  DECL_ACCESSORS(month, Object)
+  // [day]: caches day.
+  DECL_ACCESSORS(day, Object)
+  // [day]: caches hours.

[ulan, 2012/01/25 13:08:48]

[day] -> [hour] in the comment.

[rossberg, 2012/01/25 15:48:37]

Done. (And for month above.)

+  DECL_ACCESSORS(hour, Object)
+  // [min]: caches minutes.
+  DECL_ACCESSORS(min, Object)
+  // [sec]: caches seconds.
+  DECL_ACCESSORS(sec, Object)
+  // [ms]: caches milliseconds.
+  DECL_ACCESSORS(ms, Object)
+
+  // Casting.
+  static inline JSDate* cast(Object* obj);
+
+  // Dispatched behavior.
+#ifdef OBJECT_PRINT
+  inline void JSDatePrint() {
+    JSDatePrint(stdout);
+  }
+  void JSDatePrint(FILE* out);
+#endif
+#ifdef DEBUG
+  void JSDateVerify();
+#endif
+
+  // Layout description.
+  static const int kValueOffset = JSObject::kHeaderSize;  // transitional
+  static const int kYearOffset = kValueOffset + kPointerSize;
+  static const int kMonthOffset = kYearOffset + kPointerSize;
+  static const int kDayOffset = kMonthOffset + kPointerSize;
+  static const int kHourOffset = kDayOffset + kPointerSize;
+  static const int kMinOffset = kHourOffset + kPointerSize;
+  static const int kSecOffset = kMinOffset + kPointerSize;
+  static const int kMsOffset = kSecOffset + kPointerSize;
+  static const int kSize = kMsOffset + kPointerSize;
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(JSDate);
+};
+
+
 // Representation of message objects used for error reporting through
 // the API. The messages are formatted in JavaScript so this object is
 // a real JavaScript object. The information used for formatting the