Shave 39% from snapshot size.

src/serialize.cc

 // Copyright 2011 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 865 matching lines @@
   CASE_STATEMENT(where, how, within, kLargeCode)                               \
   CASE_STATEMENT(where, how, within, kLargeFixedArray)                         \
   CASE_BODY(where, how, within, kAnyOldSpace, kUnknownOffsetFromStart)
 
 #define ONE_PER_CODE_SPACE(where, how, within)                                 \
   CASE_STATEMENT(where, how, within, CODE_SPACE)                               \
   CASE_BODY(where, how, within, CODE_SPACE, kUnknownOffsetFromStart)           \
   CASE_STATEMENT(where, how, within, kLargeCode)                               \
   CASE_BODY(where, how, within, kLargeCode, kUnknownOffsetFromStart)
 
-#define EMIT_COMMON_REFERENCE_PATTERNS(pseudo_space_number,                    \
-                                       space_number,                           \
-                                       offset_from_start)                      \
-  CASE_STATEMENT(kFromStart, kPlain, kStartOfObject, pseudo_space_number)      \
-  CASE_BODY(kFromStart, kPlain, kStartOfObject, space_number, offset_from_start)
+#define FOUR_CASES(byte_code)             \
+  case byte_code:                         \
+  case byte_code + 1:                     \
+  case byte_code + 2:                     \
+  case byte_code + 3:
+
+#define SIXTEEN_CASES(byte_code)          \
+  FOUR_CASES(byte_code)                   \
+  FOUR_CASES(byte_code + 4)               \
+  FOUR_CASES(byte_code + 8)               \
+  FOUR_CASES(byte_code + 12)
 
       // We generate 15 cases and bodies that process special tags that combine
       // the raw data tag and the length into one byte.
 #define RAW_CASE(index, size)                                      \
       case kRawData + index: {                                     \
         byte* raw_data_out = reinterpret_cast<byte*>(current);     \
         source_->CopyRaw(raw_data_out, size);                      \
         current = reinterpret_cast<Object**>(raw_data_out + size); \
         break;                                                     \
       }
       COMMON_RAW_LENGTHS(RAW_CASE)
 #undef RAW_CASE
 
       // Deserialize a chunk of raw data that doesn't have one of the popular
       // lengths.
       case kRawData: {
         int size = source_->GetInt();
         byte* raw_data_out = reinterpret_cast<byte*>(current);
         source_->CopyRaw(raw_data_out, size);
         current = reinterpret_cast<Object**>(raw_data_out + size);
         break;
       }
 
+      SIXTEEN_CASES(kRootArrayLowConstants)
+      SIXTEEN_CASES(kRootArrayHighConstants) {
+        int root_id = RootArrayConstantFromByteCode(data);
+        *current++ = isolate->heap()->roots_address()[root_id];

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

The name roots_address suggests that it returns an Address. Could it be called
roots_array_start or _origin instead?

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

Done.

+        break;
+      }
+
+      case kRepeat: {
+        int repeats = source_->GetInt();
+        Object* object = current[-1];
+        for (int i = 0; i < repeats; i++) current[i] = object;
+        current += repeats;
+        break;
+      }
+
+      STATIC_ASSERT(kMaxRepeats == 12);
+      FOUR_CASES(kConstantRepeat)
+      FOUR_CASES(kConstantRepeat + 4)
+      FOUR_CASES(kConstantRepeat + 8) {
+        int repeats = RepeatsForCode(data);
+        Object* object = current[-1];
+        for (int i = 0; i < repeats; i++) current[i] = object;
+        current += repeats;
+        break;
+      }
+
       // Deserialize a new object and write a pointer to it to the current
       // object.
       ONE_PER_SPACE(kNewObject, kPlain, kStartOfObject)
       // Support for direct instruction pointers in functions
       ONE_PER_CODE_SPACE(kNewObject, kPlain, kFirstInstruction)
       // Deserialize a new code object and write a pointer to its first
       // instruction to the current code object.
       ONE_PER_SPACE(kNewObject, kFromCode, kFirstInstruction)
       // Find a recently deserialized object using its offset from the current
       // allocation point and write a pointer to it to the current object.
       ALL_SPACES(kBackref, kPlain, kStartOfObject)
       // Find a recently deserialized code object using its offset from the
       // current allocation point and write a pointer to its first instruction
       // to the current code object or the instruction pointer in a function
       // object.
       ALL_SPACES(kBackref, kFromCode, kFirstInstruction)
       ALL_SPACES(kBackref, kPlain, kFirstInstruction)
       // Find an already deserialized object using its offset from the start
       // and write a pointer to it to the current object.
       ALL_SPACES(kFromStart, kPlain, kStartOfObject)
       ALL_SPACES(kFromStart, kPlain, kFirstInstruction)
       // Find an already deserialized code object using its offset from the
       // start and write a pointer to its first instruction to the current code
       // object.
       ALL_SPACES(kFromStart, kFromCode, kFirstInstruction)
-      // Find an already deserialized object at one of the predetermined popular
-      // offsets from the start and write a pointer to it in the current object.
-      COMMON_REFERENCE_PATTERNS(EMIT_COMMON_REFERENCE_PATTERNS)
       // Find an object in the roots array and write a pointer to it to the
       // current object.
       CASE_STATEMENT(kRootArray, kPlain, kStartOfObject, 0)
       CASE_BODY(kRootArray, kPlain, kStartOfObject, 0, kUnknownOffsetFromStart)
       // Find an object in the partial snapshots cache and write a pointer to it
       // to the current object.
       CASE_STATEMENT(kPartialSnapshotCache, kPlain, kStartOfObject, 0)
       CASE_BODY(kPartialSnapshotCache,
                 kPlain,
                 kStartOfObject,
@@ skipping 21 matching lines @@
       CASE_BODY(kExternalReference,
                 kFromCode,
                 kStartOfObject,
                 0,
                 kUnknownOffsetFromStart)
 
 #undef CASE_STATEMENT
 #undef CASE_BODY
 #undef ONE_PER_SPACE
 #undef ALL_SPACES
-#undef EMIT_COMMON_REFERENCE_PATTERNS
 #undef ASSIGN_DEST_SPACE
 
       case kNewPage: {
         int space = source_->Get();
         pages_[space].Add(last_object_address_);
         if (space == CODE_SPACE) {
           CPU::FlushICache(last_object_address_, Page::kPageSize);
         }
         break;
       }
@@ skipping 66 matching lines @@
     sink_->PutSection(character, "TagCharacter");
   } while (character != 0);
 }
 
 #endif
 
 Serializer::Serializer(SnapshotByteSink* sink)
     : sink_(sink),
       current_root_index_(0),
       external_reference_encoder_(new ExternalReferenceEncoder),
-      large_object_total_(0) {
+      large_object_total_(0),
+      root_index_wave_front_(0) {
   // The serializer is meant to be used only to generate initial heap images
   // from a context in which there is only one isolate.
   ASSERT(Isolate::Current()->IsDefaultIsolate());
   for (int i = 0; i <= LAST_SPACE; i++) {
     fullness_[i] = 0;
   }
 }
 
 
 Serializer::~Serializer() {
@@ skipping 36 matching lines @@
   }
   isolate->set_serialize_partial_snapshot_cache_length(
       Isolate::kPartialSnapshotCacheCapacity);
 }
 
 
 void Serializer::VisitPointers(Object** start, Object** end) {
   Isolate* isolate = Isolate::Current();
 
   for (Object** current = start; current < end; current++) {
+    if (start == isolate->heap()->roots_address()) {
+      root_index_wave_front_ = Max(root_index_wave_front_, current - start);
+    }
     if (reinterpret_cast<Address>(current) ==
         isolate->heap()->store_buffer()->TopAddress()) {
       sink_->Put(kSkip, "Skip");
     } else if ((*current)->IsSmi()) {
       sink_->Put(kRawData, "RawData");
       sink_->PutInt(kPointerSize, "length");
       for (int i = 0; i < kPointerSize; i++) {
         sink_->Put(reinterpret_cast<byte*>(current)[i], "Byte");
       }
     } else {
@@ skipping 47 matching lines @@
   startup_serializer_->VisitPointer(
       &isolate->serialize_partial_snapshot_cache()[length]);
   // We don't recurse from the startup snapshot generator into the partial
   // snapshot generator.
   ASSERT(length == isolate->serialize_partial_snapshot_cache_length());
   isolate->set_serialize_partial_snapshot_cache_length(length + 1);
   return length;
 }
 
 
-int PartialSerializer::RootIndex(HeapObject* heap_object) {
-  for (int i = 0; i < Heap::kRootListLength; i++) {
-    Object* root = HEAP->roots_address()[i];
-    if (root == heap_object) return i;
+int Serializer::RootIndex(HeapObject* heap_object) {
+  Heap* heap = HEAP;
+  if (heap->InNewSpace(heap_object)) return kInvalidRootIndex;
+  for (int i = 0; i < root_index_wave_front_; i++) {
+    Object* root = heap->roots_address()[i];
+    if (!root->IsSmi() && root == heap_object) return i;
   }
   return kInvalidRootIndex;
 }
 
 
 // Encode the location of an already deserialized object in order to write its
 // location into a later object.  We can encode the location as an offset from
 // the start of the deserialized objects or as an offset backwards from the
 // current allocation pointer.
 void Serializer::SerializeReferenceToPreviousObject(
@@ skipping 15 matching lines @@
     // For new space it is always simple to encode back from current allocation.
     if (offset < address) {
       from_start = false;
       address = offset;
     }
   }
   // If we are actually dealing with real offsets (and not a numbering of
   // all objects) then we should shift out the bits that are always 0.
   if (!SpaceIsLarge(space)) address >>= kObjectAlignmentBits;
   if (from_start) {
-#define COMMON_REFS_CASE(pseudo_space, actual_space, offset)                   \
-    if (space == actual_space && address == offset &&                          \
-        how_to_code == kPlain && where_to_point == kStartOfObject) {           \
-      sink_->Put(kFromStart + how_to_code + where_to_point +                   \
-                 pseudo_space, "RefSer");                                      \
-    } else  /* NOLINT */
-    COMMON_REFERENCE_PATTERNS(COMMON_REFS_CASE)
-#undef COMMON_REFS_CASE
-    {  /* NOLINT */
-      sink_->Put(kFromStart + how_to_code + where_to_point + space, "RefSer");
-      sink_->PutInt(address, "address");
-    }
+    sink_->Put(kFromStart + how_to_code + where_to_point + space, "RefSer");
+    sink_->PutInt(address, "address");
   } else {
     sink_->Put(kBackref + how_to_code + where_to_point + space, "BackRefSer");
     sink_->PutInt(address, "address");
   }
 }
 
 
 void StartupSerializer::SerializeObject(
     Object* o,
     HowToCode how_to_code,
     WhereToPoint where_to_point) {
   CHECK(o->IsHeapObject());
   HeapObject* heap_object = HeapObject::cast(o);
 
+  int root_index;
+  if ((root_index = RootIndex(heap_object)) != kInvalidRootIndex) {
+    PutRoot(root_index, heap_object, how_to_code, where_to_point);
+    return;
+  }
+
   if (address_mapper_.IsMapped(heap_object)) {
     int space = SpaceOfAlreadySerializedObject(heap_object);
     int address = address_mapper_.MappedTo(heap_object);
     SerializeReferenceToPreviousObject(space,
                                        address,
                                        how_to_code,
                                        where_to_point);
   } else {
     // Object has not yet been serialized.  Serialize it here.
     ObjectSerializer object_serializer(this,
@@ skipping 10 matching lines @@
   for (int i = Isolate::Current()->serialize_partial_snapshot_cache_length();
        i < Isolate::kPartialSnapshotCacheCapacity;
        i++) {
     sink_->Put(kRootArray + kPlain + kStartOfObject, "RootSerialization");
     sink_->PutInt(Heap::kUndefinedValueRootIndex, "root_index");
   }
   HEAP->IterateWeakRoots(this, VISIT_ALL);
 }
 
 
+void Serializer::PutRoot(int root_index,
+                         HeapObject* object,
+                         SerializerDeserializer::HowToCode how_to_code,
+                         SerializerDeserializer::WhereToPoint where_to_point) {
+  if (how_to_code == kPlain &&
+      where_to_point == kStartOfObject &&
+      root_index < 0x20 &&

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

Name the constants.

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

Done.

+      !HEAP->InNewSpace(object)) {
+    if (root_index < 0x10) {
+      sink_->Put(kRootArrayLowConstants + root_index, "RootLoConstant");
+    } else {
+      sink_->Put(kRootArrayHighConstants + root_index - 0x10, "RootHiConstant");
+    }
+  } else {
+    sink_->Put(kRootArray + how_to_code + where_to_point, "RootSerialization");
+    sink_->PutInt(root_index, "root_index");
+  }
+}
+
+
 void PartialSerializer::SerializeObject(
     Object* o,
     HowToCode how_to_code,
     WhereToPoint where_to_point) {
   CHECK(o->IsHeapObject());
   HeapObject* heap_object = HeapObject::cast(o);
 
   int root_index;
   if ((root_index = RootIndex(heap_object)) != kInvalidRootIndex) {
-    sink_->Put(kRootArray + how_to_code + where_to_point, "RootSerialization");
-    sink_->PutInt(root_index, "root_index");
+    PutRoot(root_index, heap_object, how_to_code, where_to_point);
     return;
   }
 
   if (ShouldBeInThePartialSnapshotCache(heap_object)) {
     int cache_index = PartialSnapshotCacheIndex(heap_object);
     sink_->Put(kPartialSnapshotCache + how_to_code + where_to_point,
                "PartialSnapshotCache");
     sink_->PutInt(cache_index, "partial_snapshot_cache_index");
     return;
   }
@@ skipping 57 matching lines @@
 
 
 void Serializer::ObjectSerializer::VisitPointers(Object** start,
                                                  Object** end) {
   Object** current = start;
   while (current < end) {
     while (current < end && (*current)->IsSmi()) current++;
     if (current < end) OutputRawData(reinterpret_cast<Address>(current));
 
     while (current < end && !(*current)->IsSmi()) {
-      serializer_->SerializeObject(*current, kPlain, kStartOfObject);
-      bytes_processed_so_far_ += kPointerSize;
-      current++;
+      if (current != start &&
+          current[0] == current[-1] &&
+          !HEAP->InNewSpace(*current)) {
+        int repeat_count = 1;
+        while (current < end - 1 && current[repeat_count] == current[0]) {
+          repeat_count++;
+        }
+        current += repeat_count;
+        bytes_processed_so_far_ += repeat_count * kPointerSize;
+        if (repeat_count > kMaxRepeats) {

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

A generic repeat takes five bytes. Up to 4*kMaxRepeats, it's smaller to do
repeated constant repeats.

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

No, a generic repeat takes 2 bytes if the repeat count is less than 128.

+          sink_->Put(kRepeat, "SerializeRepeats");
+          sink_->PutInt(repeat_count, "SerializeRepeats");
+        } else {
+          sink_->Put(CodeForRepeats(repeat_count), "SerializeRepeats");
+        }
+      } else {
+        serializer_->SerializeObject(*current, kPlain, kStartOfObject);
+        bytes_processed_so_far_ += kPointerSize;
+        current++;
+      }
     }
   }
 }
 
 
 void Serializer::ObjectSerializer::VisitExternalReferences(Address* start,
                                                            Address* end) {
   Address references_start = reinterpret_cast<Address>(start);
   OutputRawData(references_start);
 
@@ skipping 163 matching lines @@
       fullness_[space] = RoundUp(fullness_[space], Page::kPageSize);
     }
   }
   int allocation_address = fullness_[space];
   fullness_[space] = allocation_address + size;
   return allocation_address;
 }
 
 
 } }  // namespace v8::internal