Refactoring of snapshots. This simplifies and improves

src/serialize.cc

Index: src/serialize.cc
===================================================================
--- src/serialize.cc	(revision 12497)
+++ src/serialize.cc	(working copy)
@@ -599,109 +599,34 @@
     : isolate_(NULL),
       source_(source),
       external_reference_decoder_(NULL) {
-}
-
-
-// This routine both allocates a new object, and also keeps
-// track of where objects have been allocated so that we can
-// fix back references when deserializing.
-Address Deserializer::Allocate(int space_index, Space* space, int size) {
-  Address address;
-  if (!SpaceIsLarge(space_index)) {
-    ASSERT(!SpaceIsPaged(space_index) ||
-           size <= Page::kPageSize - Page::kObjectStartOffset);
-    MaybeObject* maybe_new_allocation;
-    if (space_index == NEW_SPACE) {
-      maybe_new_allocation =
-          reinterpret_cast<NewSpace*>(space)->AllocateRaw(size);
-    } else {
-      maybe_new_allocation =
-          reinterpret_cast<PagedSpace*>(space)->AllocateRaw(size);
-    }
-    ASSERT(!maybe_new_allocation->IsFailure());
-    Object* new_allocation = maybe_new_allocation->ToObjectUnchecked();
-    HeapObject* new_object = HeapObject::cast(new_allocation);
-    address = new_object->address();
-    high_water_[space_index] = address + size;
-  } else {
-    ASSERT(SpaceIsLarge(space_index));
-    LargeObjectSpace* lo_space = reinterpret_cast<LargeObjectSpace*>(space);
-    Object* new_allocation;
-    if (space_index == kLargeData || space_index == kLargeFixedArray) {
-      new_allocation =
-          lo_space->AllocateRaw(size, NOT_EXECUTABLE)->ToObjectUnchecked();
-    } else {
-      ASSERT_EQ(kLargeCode, space_index);
-      new_allocation =
-          lo_space->AllocateRaw(size, EXECUTABLE)->ToObjectUnchecked();
-    }
-    HeapObject* new_object = HeapObject::cast(new_allocation);
-    // Record all large objects in the same space.
-    address = new_object->address();
-    pages_[LO_SPACE].Add(address);
+  for (int i = 0; i < LAST_SPACE + 1; i++) {
+    reservations_[i] = kUninitializedReservation;
   }
-  last_object_address_ = address;
-  return address;
 }
 
 
-// This returns the address of an object that has been described in the
-// snapshot as being offset bytes back in a particular space.
-HeapObject* Deserializer::GetAddressFromEnd(int space) {
-  int offset = source_->GetInt();
-  ASSERT(!SpaceIsLarge(space));
-  offset <<= kObjectAlignmentBits;
-  return HeapObject::FromAddress(high_water_[space] - offset);
-}
-
-
-// This returns the address of an object that has been described in the
-// snapshot as being offset bytes into a particular space.
-HeapObject* Deserializer::GetAddressFromStart(int space) {
-  int offset = source_->GetInt();
-  if (SpaceIsLarge(space)) {
-    // Large spaces have one object per 'page'.
-    return HeapObject::FromAddress(pages_[LO_SPACE][offset]);
-  }
-  offset <<= kObjectAlignmentBits;
-  if (space == NEW_SPACE) {
-    // New space has only one space - numbered 0.
-    return HeapObject::FromAddress(pages_[space][0] + offset);
-  }
-  ASSERT(SpaceIsPaged(space));
-  int page_of_pointee = offset >> kPageSizeBits;
-  Address object_address = pages_[space][page_of_pointee] +
-                           (offset & Page::kPageAlignmentMask);
-  return HeapObject::FromAddress(object_address);
-}
-
-
 void Deserializer::Deserialize() {
   isolate_ = Isolate::Current();
   ASSERT(isolate_ != NULL);
-  {
-    // Don't GC while deserializing - just expand the heap.
-    AlwaysAllocateScope always_allocate;
-    // Don't use the free lists while deserializing.
-    LinearAllocationScope allocate_linearly;
-    // No active threads.
-    ASSERT_EQ(NULL, isolate_->thread_manager()->FirstThreadStateInUse());
-    // No active handles.
-    ASSERT(isolate_->handle_scope_implementer()->blocks()->is_empty());
-    ASSERT_EQ(NULL, external_reference_decoder_);
-    external_reference_decoder_ = new ExternalReferenceDecoder();
-    isolate_->heap()->IterateStrongRoots(this, VISIT_ONLY_STRONG);
-    isolate_->heap()->IterateWeakRoots(this, VISIT_ALL);
+  isolate_->heap()->ReserveSpace(reservations_, &high_water_[0]);
+  // No active threads.
+  ASSERT_EQ(NULL, isolate_->thread_manager()->FirstThreadStateInUse());
+  // No active handles.
+  ASSERT(isolate_->handle_scope_implementer()->blocks()->is_empty());
+  ASSERT_EQ(NULL, external_reference_decoder_);
+  external_reference_decoder_ = new ExternalReferenceDecoder();
+  isolate_->heap()->IterateStrongRoots(this, VISIT_ONLY_STRONG);
+  isolate_->heap()->RepairFreeListsAfterBoot();
+  isolate_->heap()->IterateWeakRoots(this, VISIT_ALL);
 
-    isolate_->heap()->set_native_contexts_list(
-        isolate_->heap()->undefined_value());
+  isolate_->heap()->set_native_contexts_list(
+      isolate_->heap()->undefined_value());
 
-    // Update data pointers to the external strings containing natives sources.
-    for (int i = 0; i < Natives::GetBuiltinsCount(); i++) {
-      Object* source = isolate_->heap()->natives_source_cache()->get(i);
-      if (!source->IsUndefined()) {
-        ExternalAsciiString::cast(source)->update_data_cache();
-      }
+  // Update data pointers to the external strings containing natives sources.
+  for (int i = 0; i < Natives::GetBuiltinsCount(); i++) {
+    Object* source = isolate_->heap()->natives_source_cache()->get(i);
+    if (!source->IsUndefined()) {
+      ExternalAsciiString::cast(source)->update_data_cache();
     }
   }
 
@@ -713,10 +638,10 @@
 
 void Deserializer::DeserializePartial(Object** root) {
   isolate_ = Isolate::Current();
-  // Don't GC while deserializing - just expand the heap.
-  AlwaysAllocateScope always_allocate;
-  // Don't use the free lists while deserializing.
-  LinearAllocationScope allocate_linearly;
+  for (int i = NEW_SPACE; i < kNumberOfSpaces; i++) {
+    ASSERT(reservations_[i] != kUninitializedReservation);
+  }
+  isolate_->heap()->ReserveSpace(reservations_, &high_water_[0]);
   if (external_reference_decoder_ == NULL) {
     external_reference_decoder_ = new ExternalReferenceDecoder();
   }
@@ -758,10 +683,9 @@
 // written very late, which means the FreeSpace map is not set up by the
 // time we need to use it to mark the space at the end of a page free.
 void Deserializer::ReadObject(int space_number,
-                              Space* space,
                               Object** write_back) {
   int size = source_->GetInt() << kObjectAlignmentBits;
-  Address address = Allocate(space_number, space, size);
+  Address address = Allocate(space_number, size);
   *write_back = HeapObject::FromAddress(address);
   Object** current = reinterpret_cast<Object**>(address);
   Object** limit = current + (size >> kPointerSizeLog2);
@@ -770,44 +694,19 @@
   }
   ReadChunk(current, limit, space_number, address);
 #ifdef DEBUG
-  bool is_codespace = (space == HEAP->code_space()) ||
-      ((space == HEAP->lo_space()) && (space_number == kLargeCode));
+  bool is_codespace = (space_number == CODE_SPACE);
   ASSERT(HeapObject::FromAddress(address)->IsCode() == is_codespace);
 #endif
 }
 
-
-// This macro is always used with a constant argument so it should all fold
-// away to almost nothing in the generated code.  It might be nicer to do this
-// with the ternary operator but there are type issues with that.
-#define ASSIGN_DEST_SPACE(space_number)                                        \
-  Space* dest_space;                                                           \
-  if (space_number == NEW_SPACE) {                                             \
-    dest_space = isolate->heap()->new_space();                                \
-  } else if (space_number == OLD_POINTER_SPACE) {                              \
-    dest_space = isolate->heap()->old_pointer_space();                         \
-  } else if (space_number == OLD_DATA_SPACE) {                                 \
-    dest_space = isolate->heap()->old_data_space();                            \
-  } else if (space_number == CODE_SPACE) {                                     \
-    dest_space = isolate->heap()->code_space();                                \
-  } else if (space_number == MAP_SPACE) {                                      \
-    dest_space = isolate->heap()->map_space();                                 \
-  } else if (space_number == CELL_SPACE) {                                     \
-    dest_space = isolate->heap()->cell_space();                                \
-  } else {                                                                     \
-    ASSERT(space_number >= LO_SPACE);                                          \
-    dest_space = isolate->heap()->lo_space();                                  \
-  }
-
-
-static const int kUnknownOffsetFromStart = -1;
-
-
 void Deserializer::ReadChunk(Object** current,
                              Object** limit,
                              int source_space,
                              Address current_object_address) {
   Isolate* const isolate = isolate_;
+  // Write barrier support costs around 1% in startup time.  In fact there
+  // are no new space objects in current boot snapshots, so it's not needed,
+  // but that may change.
   bool write_barrier_needed = (current_object_address != NULL &&
                                source_space != NEW_SPACE &&
                                source_space != CELL_SPACE &&
@@ -823,21 +722,19 @@
       ASSERT((within & ~kWhereToPointMask) == 0);                              \
       ASSERT((space_number & ~kSpaceMask) == 0);
 
-#define CASE_BODY(where, how, within, space_number_if_any, offset_from_start)  \
+#define CASE_BODY(where, how, within, space_number_if_any)                     \
       {                                                                        \
         bool emit_write_barrier = false;                                       \
         bool current_was_incremented = false;                                  \
         int space_number =  space_number_if_any == kAnyOldSpace ?              \
                             (data & kSpaceMask) : space_number_if_any;         \
         if (where == kNewObject && how == kPlain && within == kStartOfObject) {\
-          ASSIGN_DEST_SPACE(space_number)                                      \
-          ReadObject(space_number, dest_space, current);                       \
+          ReadObject(space_number, current);                                   \
           emit_write_barrier = (space_number == NEW_SPACE);                    \
         } else {                                                               \
           Object* new_object = NULL;  /* May not be a real Object pointer. */  \
           if (where == kNewObject) {                                           \
-            ASSIGN_DEST_SPACE(space_number)                                    \
-            ReadObject(space_number, dest_space, &new_object);                 \
+            ReadObject(space_number, &new_object);                             \
           } else if (where == kRootArray) {                                    \
             int root_id = source_->GetInt();                                   \
             new_object = isolate->heap()->roots_array_start()[root_id];        \
@@ -848,6 +745,9 @@
                 [cache_index];                                                 \
             emit_write_barrier = isolate->heap()->InNewSpace(new_object);      \
           } else if (where == kExternalReference) {                            \
+            int skip = source_->GetInt();                                      \
+            current = reinterpret_cast<Object**>(reinterpret_cast<Address>(    \
+                current) + skip);                                              \
             int reference_id = source_->GetInt();                              \
             Address address = external_reference_decoder_->                    \
                 Decode(reference_id);                                          \
@@ -856,15 +756,12 @@
             emit_write_barrier = (space_number == NEW_SPACE);                  \
             new_object = GetAddressFromEnd(data & kSpaceMask);                 \
           } else {                                                             \
-            ASSERT(where == kFromStart);                                       \
-            if (offset_from_start == kUnknownOffsetFromStart) {                \
-              emit_write_barrier = (space_number == NEW_SPACE);                \
-              new_object = GetAddressFromStart(data & kSpaceMask);             \
-            } else {                                                           \
-              Address object_address = pages_[space_number][0] +               \
-                  (offset_from_start << kObjectAlignmentBits);                 \
-              new_object = HeapObject::FromAddress(object_address);            \
-            }                                                                  \
+            ASSERT(where == kBackrefWithSkip);                                 \
+            int skip = source_->GetInt();                                      \
+            current = reinterpret_cast<Object**>(                              \
+                reinterpret_cast<Address>(current) + skip);                    \
+            emit_write_barrier = (space_number == NEW_SPACE);                  \
+            new_object = GetAddressFromEnd(data & kSpaceMask);                 \
           }                                                                    \
           if (within == kInnerPointer) {                                       \
             if (space_number != CODE_SPACE || new_object->IsCode()) {          \
@@ -872,7 +769,7 @@
               new_object = reinterpret_cast<Object*>(                          \
                   new_code_object->instruction_start());                       \
             } else {                                                           \
-              ASSERT(space_number == CODE_SPACE || space_number == kLargeCode);\
+              ASSERT(space_number == CODE_SPACE);                              \
               JSGlobalPropertyCell* cell =                                     \
                   JSGlobalPropertyCell::cast(new_object);                      \
               new_object = reinterpret_cast<Object*>(                          \
@@ -904,48 +801,19 @@
         break;                                                                 \
       }                                                                        \
 
-// This generates a case and a body for each space.  The large object spaces are
-// very rare in snapshots so they are grouped in one body.
-#define ONE_PER_SPACE(where, how, within)                                      \
-  CASE_STATEMENT(where, how, within, NEW_SPACE)                                \
-  CASE_BODY(where, how, within, NEW_SPACE, kUnknownOffsetFromStart)            \
-  CASE_STATEMENT(where, how, within, OLD_DATA_SPACE)                           \
-  CASE_BODY(where, how, within, OLD_DATA_SPACE, kUnknownOffsetFromStart)       \
-  CASE_STATEMENT(where, how, within, OLD_POINTER_SPACE)                        \
-  CASE_BODY(where, how, within, OLD_POINTER_SPACE, kUnknownOffsetFromStart)    \
-  CASE_STATEMENT(where, how, within, CODE_SPACE)                               \
-  CASE_BODY(where, how, within, CODE_SPACE, kUnknownOffsetFromStart)           \
-  CASE_STATEMENT(where, how, within, CELL_SPACE)                               \
-  CASE_BODY(where, how, within, CELL_SPACE, kUnknownOffsetFromStart)           \
-  CASE_STATEMENT(where, how, within, MAP_SPACE)                                \
-  CASE_BODY(where, how, within, MAP_SPACE, kUnknownOffsetFromStart)            \
-  CASE_STATEMENT(where, how, within, kLargeData)                               \
-  CASE_STATEMENT(where, how, within, kLargeCode)                               \
-  CASE_STATEMENT(where, how, within, kLargeFixedArray)                         \
-  CASE_BODY(where, how, within, kAnyOldSpace, kUnknownOffsetFromStart)
-
 // This generates a case and a body for the new space (which has to do extra
 // write barrier handling) and handles the other spaces with 8 fall-through
 // cases and one body.
 #define ALL_SPACES(where, how, within)                                         \
   CASE_STATEMENT(where, how, within, NEW_SPACE)                                \
-  CASE_BODY(where, how, within, NEW_SPACE, kUnknownOffsetFromStart)            \
+  CASE_BODY(where, how, within, NEW_SPACE)                                     \
   CASE_STATEMENT(where, how, within, OLD_DATA_SPACE)                           \
   CASE_STATEMENT(where, how, within, OLD_POINTER_SPACE)                        \
   CASE_STATEMENT(where, how, within, CODE_SPACE)                               \
   CASE_STATEMENT(where, how, within, CELL_SPACE)                               \
   CASE_STATEMENT(where, how, within, MAP_SPACE)                                \
-  CASE_STATEMENT(where, how, within, kLargeData)                               \
-  CASE_STATEMENT(where, how, within, kLargeCode)                               \
-  CASE_STATEMENT(where, how, within, kLargeFixedArray)                         \
-  CASE_BODY(where, how, within, kAnyOldSpace, kUnknownOffsetFromStart)
+  CASE_BODY(where, how, within, kAnyOldSpace)
 
-#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 FOUR_CASES(byte_code)             \
   case byte_code:                         \
   case byte_code + 1:                     \
@@ -958,14 +826,48 @@
   FOUR_CASES(byte_code + 8)               \
   FOUR_CASES(byte_code + 12)
 
+#define COMMON_RAW_LENGTHS(f)        \
+  f(1)  \
+  f(2)  \
+  f(3)  \
+  f(4)  \
+  f(5)  \
+  f(6)  \
+  f(7)  \
+  f(8)  \
+  f(9)  \
+  f(10) \
+  f(11) \
+  f(12) \
+  f(13) \
+  f(14) \
+  f(15) \
+  f(16) \
+  f(17) \
+  f(18) \
+  f(19) \
+  f(20) \
+  f(21) \
+  f(22) \
+  f(23) \
+  f(24) \
+  f(25) \
+  f(26) \
+  f(27) \
+  f(28) \
+  f(29) \
+  f(30) \
+  f(31)
+
       // 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;                                                     \
+#define RAW_CASE(index)                                                      \
+      case kRawData + index: {                                               \
+        byte* raw_data_out = reinterpret_cast<byte*>(current);               \
+        source_->CopyRaw(raw_data_out, index * kPointerSize);                \
+        current =                                                            \
+            reinterpret_cast<Object**>(raw_data_out + index * kPointerSize); \
+        break;                                                               \
       }
       COMMON_RAW_LENGTHS(RAW_CASE)
 #undef RAW_CASE
@@ -976,12 +878,11 @@
         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) {
+      SIXTEEN_CASES(kRootArrayConstants + kNoSkipDistance)
+      SIXTEEN_CASES(kRootArrayConstants + kNoSkipDistance + 16) {
         int root_id = RootArrayConstantFromByteCode(data);
         Object* object = isolate->heap()->roots_array_start()[root_id];
         ASSERT(!isolate->heap()->InNewSpace(object));
@@ -989,6 +890,18 @@
         break;
       }
 
+      SIXTEEN_CASES(kRootArrayConstants + kHasSkipDistance)
+      SIXTEEN_CASES(kRootArrayConstants + kHasSkipDistance + 16) {
+        int root_id = RootArrayConstantFromByteCode(data);
+        int skip = source_->GetInt();
+        current = reinterpret_cast<Object**>(
+            reinterpret_cast<intptr_t>(current) + skip);
+        Object* object = isolate->heap()->roots_array_start()[root_id];
+        ASSERT(!isolate->heap()->InNewSpace(object));
+        *current++ = object;
+        break;
+      }
+
       case kRepeat: {
         int repeats = source_->GetInt();
         Object* object = current[-1];
@@ -1000,10 +913,11 @@
 
       STATIC_ASSERT(kRootArrayNumberOfConstantEncodings ==
                     Heap::kOldSpaceRoots);
-      STATIC_ASSERT(kMaxRepeats == 12);
-      FOUR_CASES(kConstantRepeat)
-      FOUR_CASES(kConstantRepeat + 4)
-      FOUR_CASES(kConstantRepeat + 8) {
+      STATIC_ASSERT(kMaxRepeats == 13);
+      case kConstantRepeat:
+      FOUR_CASES(kConstantRepeat + 1)
+      FOUR_CASES(kConstantRepeat + 5)
+      FOUR_CASES(kConstantRepeat + 9) {
         int repeats = RepeatsForCode(data);
         Object* object = current[-1];
         ASSERT(!isolate->heap()->InNewSpace(object));
@@ -1014,100 +928,80 @@
 
       // Deserialize a new object and write a pointer to it to the current
       // object.
-      ONE_PER_SPACE(kNewObject, kPlain, kStartOfObject)
+      ALL_SPACES(kNewObject, kPlain, kStartOfObject)
       // Support for direct instruction pointers in functions.  It's an inner
       // pointer because it points at the entry point, not at the start of the
       // code object.
-      ONE_PER_CODE_SPACE(kNewObject, kPlain, kInnerPointer)
+      CASE_STATEMENT(kNewObject, kPlain, kInnerPointer, CODE_SPACE)
+      CASE_BODY(kNewObject, kPlain, kInnerPointer, CODE_SPACE)
       // Deserialize a new code object and write a pointer to its first
       // instruction to the current code object.
-      ONE_PER_SPACE(kNewObject, kFromCode, kInnerPointer)
+      ALL_SPACES(kNewObject, kFromCode, kInnerPointer)
       // 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)
+      ALL_SPACES(kBackrefWithSkip, kPlain, kStartOfObject)
 #if V8_TARGET_ARCH_MIPS
       // Deserialize a new object from pointer found in code and write
       // a pointer to it to the current object. Required only for MIPS, and
       // omitted on the other architectures because it is fully unrolled and
       // would cause bloat.
-      ONE_PER_SPACE(kNewObject, kFromCode, kStartOfObject)
+      ALL_SPACES(kNewObject, kFromCode, kStartOfObject)
       // Find a recently deserialized code object using its offset from the
       // current allocation point and write a pointer to it to the current
       // object. Required only for MIPS.
       ALL_SPACES(kBackref, kFromCode, kStartOfObject)
-      // Find an already deserialized code object using its offset from
-      // the start and write a pointer to it to the current object.
-      // Required only for MIPS.
-      ALL_SPACES(kFromStart, kFromCode, kStartOfObject)
+      ALL_SPACES(kBackrefWithSkip, kFromCode, kStartOfObject)
 #endif
       // 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, kInnerPointer)
+      ALL_SPACES(kBackrefWithSkip, kFromCode, kInnerPointer)
       ALL_SPACES(kBackref, kPlain, kInnerPointer)
-      // 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, kInnerPointer)
-      // 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, kInnerPointer)
+      ALL_SPACES(kBackrefWithSkip, kPlain, kInnerPointer)
       // 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)
+      CASE_BODY(kRootArray, kPlain, kStartOfObject, 0)
       // 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,
-                0,
-                kUnknownOffsetFromStart)
+                0)
       // Find an code entry in the partial snapshots cache and
       // write a pointer to it to the current object.
       CASE_STATEMENT(kPartialSnapshotCache, kPlain, kInnerPointer, 0)
       CASE_BODY(kPartialSnapshotCache,
                 kPlain,
                 kInnerPointer,
-                0,
-                kUnknownOffsetFromStart)
+                0)
       // Find an external reference and write a pointer to it to the current
       // object.
       CASE_STATEMENT(kExternalReference, kPlain, kStartOfObject, 0)
       CASE_BODY(kExternalReference,
                 kPlain,
                 kStartOfObject,
-                0,
-                kUnknownOffsetFromStart)
+                0)
       // Find an external reference and write a pointer to it in the current
       // code object.
       CASE_STATEMENT(kExternalReference, kFromCode, kStartOfObject, 0)
       CASE_BODY(kExternalReference,
                 kFromCode,
                 kStartOfObject,
-                0,
-                kUnknownOffsetFromStart)
+                0)
 
 #undef CASE_STATEMENT
 #undef CASE_BODY
-#undef ONE_PER_SPACE
 #undef ALL_SPACES
-#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;
-      }
-
       case kSkip: {
-        current++;
+        int size = source_->GetInt();
+        current = reinterpret_cast<Object**>(
+            reinterpret_cast<intptr_t>(current) + size);
         break;
       }
 
@@ -1132,18 +1026,20 @@
         UNREACHABLE();
     }
   }
-  ASSERT_EQ(current, limit);
+  ASSERT_EQ(limit, current);
 }
 
 
 void SnapshotByteSink::PutInt(uintptr_t integer, const char* description) {
-  const int max_shift = ((kPointerSize * kBitsPerByte) / 7) * 7;
-  for (int shift = max_shift; shift > 0; shift -= 7) {
-    if (integer >= static_cast<uintptr_t>(1u) << shift) {
-      Put((static_cast<int>((integer >> shift)) & 0x7f) | 0x80, "IntPart");
-    }
-  }
-  PutSection(static_cast<int>(integer & 0x7f), "IntLastPart");
+  ASSERT(integer < 1 << 22);
+  integer <<= 2;
+  int bytes = 1;
+  if (integer > 0xff) bytes = 2;
+  if (integer > 0xffff) bytes = 3;
+  integer |= bytes;
+  Put(static_cast<int>(integer & 0xff), "IntPart1");
+  if (bytes > 1) Put(static_cast<int>((integer >> 8) & 0xff), "IntPart2");
+  if (bytes > 2) Put(static_cast<int>((integer >> 16) & 0xff), "IntPart3");
 }
 
 
@@ -1151,7 +1047,6 @@
     : sink_(sink),
       current_root_index_(0),
       external_reference_encoder_(new ExternalReferenceEncoder),
-      large_object_total_(0),
       root_index_wave_front_(0) {
   isolate_ = Isolate::Current();
   // The serializer is meant to be used only to generate initial heap images
@@ -1184,6 +1079,7 @@
 
 void PartialSerializer::Serialize(Object** object) {
   this->VisitPointer(object);
+  Pad();
 }
 
 
@@ -1198,14 +1094,14 @@
     if (reinterpret_cast<Address>(current) ==
         isolate->heap()->store_buffer()->TopAddress()) {
       sink_->Put(kSkip, "Skip");
+      sink_->PutInt(kPointerSize, "SkipOneWord");
     } else if ((*current)->IsSmi()) {
-      sink_->Put(kRawData, "RawData");
-      sink_->PutInt(kPointerSize, "length");
+      sink_->Put(kRawData + 1, "Smi");
       for (int i = 0; i < kPointerSize; i++) {
         sink_->Put(reinterpret_cast<byte*>(current)[i], "Byte");
       }
     } else {
-      SerializeObject(*current, kPlain, kStartOfObject);
+      SerializeObject(*current, kPlain, kStartOfObject, 0);
     }
   }
 }
@@ -1292,58 +1188,50 @@
     int space,
     int address,
     HowToCode how_to_code,
-    WhereToPoint where_to_point) {
+    WhereToPoint where_to_point,
+    int skip) {
   int offset = CurrentAllocationAddress(space) - address;
-  bool from_start = true;
-  if (SpaceIsPaged(space)) {
-    // For paged space it is simple to encode back from current allocation if
-    // the object is on the same page as the current allocation pointer.
-    if ((CurrentAllocationAddress(space) >> kPageSizeBits) ==
-        (address >> kPageSizeBits)) {
-      from_start = false;
-      address = offset;
-    }
-  } else if (space == NEW_SPACE) {
-    // 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) {
-    sink_->Put(kFromStart + how_to_code + where_to_point + space, "RefSer");
-    sink_->PutInt(address, "address");
-  } else {
+  // Shift out the bits that are always 0.
+  offset >>= kObjectAlignmentBits;
+  if (skip == 0) {
     sink_->Put(kBackref + how_to_code + where_to_point + space, "BackRefSer");
-    sink_->PutInt(address, "address");
+  } else {
+    sink_->Put(kBackrefWithSkip + how_to_code + where_to_point + space,
+               "BackRefSerWithSkip");
+    sink_->PutInt(skip, "BackRefSkipDistance");
   }
+  sink_->PutInt(offset, "offset");
 }
 
 
 void StartupSerializer::SerializeObject(
     Object* o,
     HowToCode how_to_code,
-    WhereToPoint where_to_point) {
+    WhereToPoint where_to_point,
+    int skip) {
   CHECK(o->IsHeapObject());
   HeapObject* heap_object = HeapObject::cast(o);
 
   int root_index;
   if ((root_index = RootIndex(heap_object, how_to_code)) != kInvalidRootIndex) {
-    PutRoot(root_index, heap_object, how_to_code, where_to_point);
+    PutRoot(root_index, heap_object, how_to_code, where_to_point, skip);
     return;
   }
 
   if (address_mapper_.IsMapped(heap_object)) {
-    int space = SpaceOfAlreadySerializedObject(heap_object);
+    int space = SpaceOfObject(heap_object);
     int address = address_mapper_.MappedTo(heap_object);
     SerializeReferenceToPreviousObject(space,
                                        address,
                                        how_to_code,
-                                       where_to_point);
+                                       where_to_point,
+                                       skip);
   } else {
+    if (skip != 0) {
+      sink_->Put(kSkip, "FlushPendingSkip");
+      sink_->PutInt(skip, "SkipDistance");
+    }
+
     // Object has not yet been serialized.  Serialize it here.
     ObjectSerializer object_serializer(this,
                                        heap_object,
@@ -1365,25 +1253,32 @@
   Object* undefined = isolate->heap()->undefined_value();
   VisitPointer(&undefined);
   HEAP->IterateWeakRoots(this, VISIT_ALL);
+  Pad();
 }
 
 
 void Serializer::PutRoot(int root_index,
                          HeapObject* object,
                          SerializerDeserializer::HowToCode how_to_code,
-                         SerializerDeserializer::WhereToPoint where_to_point) {
+                         SerializerDeserializer::WhereToPoint where_to_point,
+                         int skip) {
   if (how_to_code == kPlain &&
       where_to_point == kStartOfObject &&
       root_index < kRootArrayNumberOfConstantEncodings &&
       !HEAP->InNewSpace(object)) {
-    if (root_index < kRootArrayNumberOfLowConstantEncodings) {
-      sink_->Put(kRootArrayLowConstants + root_index, "RootLoConstant");
+    if (skip == 0) {
+      sink_->Put(kRootArrayConstants + kNoSkipDistance + root_index,
+                 "RootConstant");
     } else {
-      sink_->Put(kRootArrayHighConstants + root_index -
-                     kRootArrayNumberOfLowConstantEncodings,
-                 "RootHiConstant");
+      sink_->Put(kRootArrayConstants + kHasSkipDistance + root_index,
+                 "RootConstant");
+      sink_->PutInt(skip, "SkipInPutRoot");
     }
   } else {
+    if (skip != 0) {
+      sink_->Put(kSkip, "SkipFromPutRoot");
+      sink_->PutInt(skip, "SkipFromPutRootDistance");
+    }
     sink_->Put(kRootArray + how_to_code + where_to_point, "RootSerialization");
     sink_->PutInt(root_index, "root_index");
   }
@@ -1393,7 +1288,8 @@
 void PartialSerializer::SerializeObject(
     Object* o,
     HowToCode how_to_code,
-    WhereToPoint where_to_point) {
+    WhereToPoint where_to_point,
+    int skip) {
   CHECK(o->IsHeapObject());
   HeapObject* heap_object = HeapObject::cast(o);
 
@@ -1406,11 +1302,16 @@
 
   int root_index;
   if ((root_index = RootIndex(heap_object, how_to_code)) != kInvalidRootIndex) {
-    PutRoot(root_index, heap_object, how_to_code, where_to_point);
+    PutRoot(root_index, heap_object, how_to_code, where_to_point, skip);
     return;
   }
 
   if (ShouldBeInThePartialSnapshotCache(heap_object)) {
+    if (skip != 0) {
+      sink_->Put(kSkip, "SkipFromSerializeObject");
+      sink_->PutInt(skip, "SkipDistanceFromSerializeObject");
+    }
+
     int cache_index = PartialSnapshotCacheIndex(heap_object);
     sink_->Put(kPartialSnapshotCache + how_to_code + where_to_point,
                "PartialSnapshotCache");
@@ -1427,13 +1328,18 @@
   ASSERT(!heap_object->IsSymbol());
 
   if (address_mapper_.IsMapped(heap_object)) {
-    int space = SpaceOfAlreadySerializedObject(heap_object);
+    int space = SpaceOfObject(heap_object);
     int address = address_mapper_.MappedTo(heap_object);
     SerializeReferenceToPreviousObject(space,
                                        address,
                                        how_to_code,
-                                       where_to_point);
+                                       where_to_point,
+                                       skip);
   } else {
+    if (skip != 0) {
+      sink_->Put(kSkip, "SkipFromSerializeObject");
+      sink_->PutInt(skip, "SkipDistanceFromSerializeObject");
+    }
     // Object has not yet been serialized.  Serialize it here.
     ObjectSerializer serializer(this,
                                 heap_object,
@@ -1457,16 +1363,11 @@
       SnapshotPositionEvent(object_->address(), sink_->Position()));
 
   // Mark this object as already serialized.
-  bool start_new_page;
-  int offset = serializer_->Allocate(space, size, &start_new_page);
+  int offset = serializer_->Allocate(space, size);
   serializer_->address_mapper()->AddMapping(object_, offset);
-  if (start_new_page) {
-    sink_->Put(kNewPage, "NewPage");
-    sink_->PutSection(space, "NewPageSpace");
-  }
 
   // Serialize the map (first word of the object).
-  serializer_->SerializeObject(object_->map(), kPlain, kStartOfObject);
+  serializer_->SerializeObject(object_->map(), kPlain, kStartOfObject, 0);
 
   // Serialize the rest of the object.
   CHECK_EQ(0, bytes_processed_so_far_);
@@ -1507,7 +1408,8 @@
           sink_->Put(CodeForRepeats(repeat_count), "SerializeRepeats");
         }
       } else {
-        serializer_->SerializeObject(current_contents, kPlain, kStartOfObject);
+        serializer_->SerializeObject(
+                current_contents, kPlain, kStartOfObject, 0);
         bytes_processed_so_far_ += kPointerSize;
         current++;
       }
@@ -1519,9 +1421,10 @@
 void Serializer::ObjectSerializer::VisitEmbeddedPointer(RelocInfo* rinfo) {
   Object** current = rinfo->target_object_address();
 
-  OutputRawData(rinfo->target_address_address());
+  int skip = OutputRawData(rinfo->target_address_address(),
+                           kCanReturnSkipInsteadOfSkipping);
   HowToCode representation = rinfo->IsCodedSpecially() ? kFromCode : kPlain;
-  serializer_->SerializeObject(*current, representation, kStartOfObject);
+  serializer_->SerializeObject(*current, representation, kStartOfObject, skip);
   bytes_processed_so_far_ += rinfo->target_address_size();
 }
 
@@ -1529,10 +1432,12 @@
 void Serializer::ObjectSerializer::VisitExternalReferences(Address* start,
                                                            Address* end) {
   Address references_start = reinterpret_cast<Address>(start);
-  OutputRawData(references_start);
+  int skip = OutputRawData(references_start, kCanReturnSkipInsteadOfSkipping);
 
   for (Address* current = start; current < end; current++) {
     sink_->Put(kExternalReference + kPlain + kStartOfObject, "ExternalRef");
+    sink_->PutInt(skip, "SkipB4ExternalRef");
+    skip = 0;
     int reference_id = serializer_->EncodeExternalReference(*current);
     sink_->PutInt(reference_id, "reference id");
   }
@@ -1542,12 +1447,13 @@
 
 void Serializer::ObjectSerializer::VisitExternalReference(RelocInfo* rinfo) {
   Address references_start = rinfo->target_address_address();
-  OutputRawData(references_start);
+  int skip = OutputRawData(references_start, kCanReturnSkipInsteadOfSkipping);
 
   Address* current = rinfo->target_reference_address();
   int representation = rinfo->IsCodedSpecially() ?
                        kFromCode + kStartOfObject : kPlain + kStartOfObject;
   sink_->Put(kExternalReference + representation, "ExternalRef");
+  sink_->PutInt(skip, "SkipB4ExternalRef");
   int reference_id = serializer_->EncodeExternalReference(*current);
   sink_->PutInt(reference_id, "reference id");
   bytes_processed_so_far_ += rinfo->target_address_size();
@@ -1556,7 +1462,7 @@
 
 void Serializer::ObjectSerializer::VisitRuntimeEntry(RelocInfo* rinfo) {
   Address target_start = rinfo->target_address_address();
-  OutputRawData(target_start);
+  int skip = OutputRawData(target_start, kCanReturnSkipInsteadOfSkipping);
   Address target = rinfo->target_address();
   uint32_t encoding = serializer_->EncodeExternalReference(target);
   CHECK(target == NULL ? encoding == 0 : encoding != 0);
@@ -1568,6 +1474,7 @@
     representation = kStartOfObject + kPlain;
   }
   sink_->Put(kExternalReference + representation, "ExternalReference");
+  sink_->PutInt(skip, "SkipB4ExternalRef");
   sink_->PutInt(encoding, "reference id");
   bytes_processed_so_far_ += rinfo->target_address_size();
 }
@@ -1576,17 +1483,17 @@
 void Serializer::ObjectSerializer::VisitCodeTarget(RelocInfo* rinfo) {
   CHECK(RelocInfo::IsCodeTarget(rinfo->rmode()));
   Address target_start = rinfo->target_address_address();
-  OutputRawData(target_start);
+  int skip = OutputRawData(target_start, kCanReturnSkipInsteadOfSkipping);
   Code* target = Code::GetCodeFromTargetAddress(rinfo->target_address());
-  serializer_->SerializeObject(target, kFromCode, kInnerPointer);
+  serializer_->SerializeObject(target, kFromCode, kInnerPointer, skip);
   bytes_processed_so_far_ += rinfo->target_address_size();
 }
 
 
 void Serializer::ObjectSerializer::VisitCodeEntry(Address entry_address) {
   Code* target = Code::cast(Code::GetObjectFromEntryAddress(entry_address));
-  OutputRawData(entry_address);
-  serializer_->SerializeObject(target, kPlain, kInnerPointer);
+  int skip = OutputRawData(entry_address, kCanReturnSkipInsteadOfSkipping);
+  serializer_->SerializeObject(target, kPlain, kInnerPointer, skip);
   bytes_processed_so_far_ += kPointerSize;
 }
 
@@ -1595,8 +1502,8 @@
   ASSERT(rinfo->rmode() == RelocInfo::GLOBAL_PROPERTY_CELL);
   JSGlobalPropertyCell* cell =
       JSGlobalPropertyCell::cast(rinfo->target_cell());
-  OutputRawData(rinfo->pc());
-  serializer_->SerializeObject(cell, kPlain, kInnerPointer);
+  int skip = OutputRawData(rinfo->pc(), kCanReturnSkipInsteadOfSkipping);
+  serializer_->SerializeObject(cell, kPlain, kInnerPointer, skip);
 }
 
 
@@ -1624,31 +1531,50 @@
 }
 
 
-void Serializer::ObjectSerializer::OutputRawData(Address up_to) {
+int Serializer::ObjectSerializer::OutputRawData(
+    Address up_to, Serializer::ObjectSerializer::ReturnSkip return_skip) {
   Address object_start = object_->address();
+  Address base = object_start + bytes_processed_so_far_;
   int up_to_offset = static_cast<int>(up_to - object_start);
-  int skipped = up_to_offset - bytes_processed_so_far_;
+  int to_skip = up_to_offset - bytes_processed_so_far_;
+  int bytes_to_output = to_skip;
+  bytes_processed_so_far_ +=  to_skip;
   // This assert will fail if the reloc info gives us the target_address_address
   // locations in a non-ascending order.  Luckily that doesn't happen.
-  ASSERT(skipped >= 0);
-  if (skipped != 0) {
-    Address base = object_start + bytes_processed_so_far_;
-#define RAW_CASE(index, length)                                                \
-    if (skipped == length) {                                                   \
+  ASSERT(to_skip >= 0);
+  bool outputting_code = false;
+  if (to_skip != 0 && code_object_ && !code_has_been_output_) {
+    // Output the code all at once and fix later.
+    bytes_to_output = object_->Size() + to_skip - bytes_processed_so_far_;
+    outputting_code = true;
+    code_has_been_output_ = true;
+  }
+  if (bytes_to_output != 0 &&
+      (!code_object_ || outputting_code)) {
+#define RAW_CASE(index)                                                        \
+    if (!outputting_code && bytes_to_output == index * kPointerSize &&         \
+        index * kPointerSize == to_skip) {                                     \
       sink_->PutSection(kRawData + index, "RawDataFixed");                     \
+      to_skip = 0;  /* This insn already skips. */                             \
     } else  /* NOLINT */
     COMMON_RAW_LENGTHS(RAW_CASE)
 #undef RAW_CASE
     {  /* NOLINT */
+      // We always end up here if we are outputting the code of a code object.
       sink_->Put(kRawData, "RawData");
-      sink_->PutInt(skipped, "length");
+      sink_->PutInt(bytes_to_output, "length");
     }
-    for (int i = 0; i < skipped; i++) {
+    for (int i = 0; i < bytes_to_output; i++) {
       unsigned int data = base[i];
       sink_->PutSection(data, "Byte");
     }
-    bytes_processed_so_far_ += skipped;
   }
+  if (to_skip != 0 && return_skip == kIgnoringReturn) {
+    sink_->Put(kSkip, "Skip");
+    sink_->PutInt(to_skip, "SkipDistance");
+    to_skip = 0;
+  }
+  return to_skip;
 }
 
 
@@ -1656,15 +1582,7 @@
   for (int i = FIRST_SPACE; i <= LAST_SPACE; i++) {
     AllocationSpace s = static_cast<AllocationSpace>(i);
     if (HEAP->InSpace(object, s)) {
-      if (i == LO_SPACE) {
-        if (object->IsCode()) {
-          return kLargeCode;
-        } else if (object->IsFixedArray()) {
-          return kLargeFixedArray;
-        } else {
-          return kLargeData;
-        }
-      }
+      ASSERT(i < kNumberOfSpaces);
       return i;
     }
   }
@@ -1673,46 +1591,8 @@
 }
 
 
-int Serializer::SpaceOfAlreadySerializedObject(HeapObject* object) {
-  for (int i = FIRST_SPACE; i <= LAST_SPACE; i++) {
-    AllocationSpace s = static_cast<AllocationSpace>(i);
-    if (HEAP->InSpace(object, s)) {
-      return i;
-    }
-  }
-  UNREACHABLE();
-  return 0;
-}
-
-
-int Serializer::Allocate(int space, int size, bool* new_page) {
+int Serializer::Allocate(int space, int size) {
   CHECK(space >= 0 && space < kNumberOfSpaces);
-  if (SpaceIsLarge(space)) {
-    // In large object space we merely number the objects instead of trying to
-    // determine some sort of address.
-    *new_page = true;
-    large_object_total_ += size;
-    return fullness_[LO_SPACE]++;
-  }
-  *new_page = false;
-  if (fullness_[space] == 0) {
-    *new_page = true;
-  }
-  if (SpaceIsPaged(space)) {
-    // Paged spaces are a little special.  We encode their addresses as if the
-    // pages were all contiguous and each page were filled up in the range
-    // 0 - Page::kObjectAreaSize.  In practice the pages may not be contiguous
-    // and allocation does not start at offset 0 in the page, but this scheme
-    // means the deserializer can get the page number quickly by shifting the
-    // serialized address.
-    CHECK(IsPowerOf2(Page::kPageSize));
-    int used_in_this_page = (fullness_[space] & (Page::kPageSize - 1));
-    CHECK(size <= SpaceAreaSize(space));
-    if (used_in_this_page + size > SpaceAreaSize(space)) {
-      *new_page = true;
-      fullness_[space] = RoundUp(fullness_[space], Page::kPageSize);
-    }
-  }
   int allocation_address = fullness_[space];
   fullness_[space] = allocation_address + size;
   return allocation_address;
@@ -1728,4 +1608,21 @@
 }
 
 
+void Serializer::Pad() {
+  // The non-branching GetInt will read up to 3 bytes too far, so we need
+  // to pad the snapshot to make sure we don't read over the end.
+  for (unsigned i = 0; i < sizeof(int32_t) - 1; i++) {
+    sink_->Put(kNop, "Padding");
+  }
+}
+
+
+bool SnapshotByteSource::AtEOF() {
+  if (0u + length_ - position_ > sizeof(uint32_t)) return false;
+  for (int x = position_; x < length_; x++) {
+    if (data_[x] != SerializerDeserializer::nop()) return false;
+  }
+  return true;
+}
+
 } }  // namespace v8::internal