Shave 39% from snapshot size.

src/serialize.h

 // Copyright 2006-2009 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 169 matching lines @@
 
   int position() { return position_; }
 
  private:
   const byte* data_;
   int length_;
   int position_;
 };
 
 
-// It is very common to have a reference to objects at certain offsets in the
-// heap.  These offsets have been determined experimentally.  We code
-// references to such objects in a single byte that encodes the way the pointer
-// is written (only plain pointers allowed), the space number and the offset.
-// This only works for objects in the first page of a space.  Don't use this for
-// things in newspace since it bypasses the write barrier.
-
-static const int k64 = (sizeof(uintptr_t) - 4) / 4;
-
-#define COMMON_REFERENCE_PATTERNS(f)                               \
-  f(kNumberOfSpaces, 2, (11 - k64))                                \
-  f((kNumberOfSpaces + 1), 2, 0)                                   \
-  f((kNumberOfSpaces + 2), 2, (142 - 16 * k64))                    \
-  f((kNumberOfSpaces + 3), 2, (74 - 15 * k64))                     \
-  f((kNumberOfSpaces + 4), 2, 5)                                   \
-  f((kNumberOfSpaces + 5), 1, 135)                                 \
-  f((kNumberOfSpaces + 6), 2, (228 - 39 * k64))
-
 #define COMMON_RAW_LENGTHS(f)        \
   f(1, 1)  \
   f(2, 2)  \
   f(3, 3)  \
   f(4, 4)  \
   f(5, 5)  \
   f(6, 6)  \
   f(7, 7)  \
   f(8, 8)  \
   f(9, 12)  \
@@ skipping 17 matching lines @@
   enum Where {
     kNewObject = 0,                 // Object is next in snapshot.
     // 1-8                             One per space.
     kRootArray = 0x9,               // Object is found in root array.
     kPartialSnapshotCache = 0xa,    // Object is in the cache.
     kExternalReference = 0xb,       // Pointer to an external reference.
     kSkip = 0xc,                    // Skip a pointer sized cell.
     // 0xd-0xf                         Free.
     kBackref = 0x10,                 // Object is described relative to end.
     // 0x11-0x18                       One per space.
-    // 0x19-0x1f                       Common backref offsets.
+    // 0x19-0x1f                       Free.
     kFromStart = 0x20,              // Object is described relative to start.
     // 0x21-0x28                       One per space.
     // 0x29-0x2f                       Free.
     // 0x30-0x3f                       Used by misc tags below.
     kPointedToMask = 0x3f
   };
 
   // How to code the pointer to the object.
   enum HowToCode {
     kPlain = 0,                          // Straight pointer.
@@ skipping 16 matching lines @@
   // A tag emitted at strategic points in the snapshot to delineate sections.
   // If the deserializer does not find these at the expected moments then it
   // is an indication that the snapshot and the VM do not fit together.
   // Examine the build process for architecture, version or configuration
   // mismatches.
   static const int kSynchronize = 0x70;
   // Used for the source code of the natives, which is in the executable, but
   // is referred to from external strings in the snapshot.
   static const int kNativesStringResource = 0x71;
   static const int kNewPage = 0x72;
-  // 0x73-0x7f                            Free.
-  // 0xb0-0xbf                            Free.
-  // 0xf0-0xff                            Free.
+  static const int kRepeat = 0x73;
+  static const int kConstantRepeat = 0x74;
+  // 0x74-0x7f            Repeat last word (subtract 0x73 to get the count).
+  static const int kMaxRepeats = 0x7f - 0x73;
+  static int CodeForRepeats(int repeats) {
+    ASSERT(repeats >= 1 && repeats <= kMaxRepeats);
+    return 0x73 + repeats;
+  }
+  static int RepeatsForCode(int byte_code) {
+    ASSERT(byte_code >= kConstantRepeat && byte_code <= 0x7f);
+    return byte_code - 0x73;
+  }
+  static const int kRootArrayLowConstants = 0xb0;
+  // 0xb0-0xbf            Things from the first 16 elements of the root array.
+  static const int kRootArrayHighConstants = 0xf0;
+  // 0xf0-0xff            Things from the next 16 elements of the root array.
+  static int RootArrayConstantFromByteCode(int byte_code) {
+    return (byte_code & 0xf) | ((byte_code & 0x40) >> 2);
+  }
 
 
   static const int kLargeData = LAST_SPACE;
   static const int kLargeCode = kLargeData + 1;
   static const int kLargeFixedArray = kLargeCode + 1;
   static const int kNumberOfSpaces = kLargeFixedArray + 1;
   static const int kAnyOldSpace = -1;
 
   // A bitmask for getting the space out of an instruction.
   static const int kSpaceMask = 15;
@@ skipping 173 matching lines @@
     }
     serialization_enabled_ = true;
   }
 
   static void Disable() { serialization_enabled_ = false; }
   // Call this when you have made use of the fact that there is no serialization
   // going on.
   static void TooLateToEnableNow() { too_late_to_enable_now_ = true; }
   static bool enabled() { return serialization_enabled_; }
   SerializationAddressMapper* address_mapper() { return &address_mapper_; }
+  void PutRoot(
+      int index, HeapObject* object, HowToCode how, WhereToPoint where);
 #ifdef DEBUG
   virtual void Synchronize(const char* tag);
 #endif
 
  protected:
   static const int kInvalidRootIndex = -1;
-  virtual int RootIndex(HeapObject* heap_object) = 0;
+
+  int RootIndex(HeapObject* heap_object);
   virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) = 0;
+  int root_index_wave_front() { return root_index_wave_front_; }
+  void set_root_index_wave_front(int value) { root_index_wave_front_ = value; }

[Lasse Reichstein, 2011/10/20 10:06:54]

Assert that the wave-front moves forward?

[Erik Corry, 2011/10/20 11:01:42]

Done.

 
   class ObjectSerializer : public ObjectVisitor {
    public:
     ObjectSerializer(Serializer* serializer,
                      Object* o,
                      SnapshotByteSink* sink,
                      HowToCode how_to_code,
                      WhereToPoint where_to_point)
       : serializer_(serializer),
         object_(HeapObject::cast(o)),
@@ skipping 55 matching lines @@
   // sense in large object space.
   int fullness_[LAST_SPACE + 1];
   SnapshotByteSink* sink_;
   int current_root_index_;
   ExternalReferenceEncoder* external_reference_encoder_;
   static bool serialization_enabled_;
   // Did we already make use of the fact that serialization was not enabled?
   static bool too_late_to_enable_now_;
   int large_object_total_;
   SerializationAddressMapper address_mapper_;
+  int root_index_wave_front_;
 
   friend class ObjectSerializer;
   friend class Deserializer;
 
   DISALLOW_COPY_AND_ASSIGN(Serializer);
 };
 
 
 class PartialSerializer : public Serializer {
  public:
   PartialSerializer(Serializer* startup_snapshot_serializer,
                     SnapshotByteSink* sink)
     : Serializer(sink),
       startup_serializer_(startup_snapshot_serializer) {
+    set_root_index_wave_front(Heap::kStrongRootListLength);
   }
 
   // Serialize the objects reachable from a single object pointer.
   virtual void Serialize(Object** o);
   virtual void SerializeObject(Object* o,
                                HowToCode how_to_code,
                                WhereToPoint where_to_point);
 
  protected:
-  virtual int RootIndex(HeapObject* o);
   virtual int PartialSnapshotCacheIndex(HeapObject* o);
   virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) {
     // Scripts should be referred only through shared function infos.  We can't
     // allow them to be part of the partial snapshot because they contain a
     // unique ID, and deserializing several partial snapshots containing script
     // would cause dupes.
     ASSERT(!o->IsScript());
     return o->IsString() || o->IsSharedFunctionInfo() ||
            o->IsHeapNumber() || o->IsCode() ||
            o->IsSerializedScopeInfo() ||
            o->map() == HEAP->fixed_cow_array_map();
   }
 
  private:
   Serializer* startup_serializer_;
   DISALLOW_COPY_AND_ASSIGN(PartialSerializer);
 };
 
 
 class StartupSerializer : public Serializer {
  public:
   explicit StartupSerializer(SnapshotByteSink* sink) : Serializer(sink) {
     // Clear the cache of objects used by the partial snapshot.  After the
     // strong roots have been serialized we can create a partial snapshot
-    // which will repopulate the cache with objects neede by that partial
+    // which will repopulate the cache with objects needed by that partial
     // snapshot.
     Isolate::Current()->set_serialize_partial_snapshot_cache_length(0);
   }
   // Serialize the current state of the heap.  The order is:
   // 1) Strong references.
   // 2) Partial snapshot cache.
   // 3) Weak references (eg the symbol table).
   virtual void SerializeStrongReferences();
   virtual void SerializeObject(Object* o,
                                HowToCode how_to_code,
                                WhereToPoint where_to_point);
   void SerializeWeakReferences();
   void Serialize() {
     SerializeStrongReferences();
     SerializeWeakReferences();
   }
 
  private:
-  virtual int RootIndex(HeapObject* o) { return kInvalidRootIndex; }
   virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) {
     return false;
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SERIALIZE_H_