5% smaller snapshots by omitting object ids when possible

runtime/vm/dart_api_message.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bigint_operations.h"
 #include "vm/dart_api_message.h"
 #include "vm/object.h"
 #include "vm/snapshot_ids.h"
 #include "vm/symbols.h"
 #include "vm/unicode.h"
@@ skipping 362 matching lines @@
   object = AllocateDartCObjectString(len);
   char* p = object->value.as_string;
   memmove(p, str->ptr()->data(), len);
   p[len] = '\0';
   ASSERT(vm_symbol_references_[symbol_id] == NULL);
   vm_symbol_references_[symbol_id] = object;
   return object;
 }
 
 
+intptr_t ApiMessageReader::NextAvailableObjectId() const {
+  return backward_references_.length() + kMaxPredefinedObjectIds;
+}
+
+
 Dart_CObject* ApiMessageReader::ReadObjectRef() {
   int64_t value64 = Read<int64_t>();
   if ((value64 & kSmiTagMask) == 0) {
     int64_t untagged_value = value64 >> kSmiTagShift;
     if ((kMinInt32 <= untagged_value) && (untagged_value <= kMaxInt32)) {
       return AllocateDartCObjectInt32(static_cast<int32_t>(untagged_value));
     } else {
       return AllocateDartCObjectInt64(untagged_value);
     }
   }
   ASSERT((value64 <= kIntptrMax) && (value64 >= kIntptrMin));
   intptr_t value = static_cast<intptr_t>(value64);
   if (IsVMIsolateObject(value)) {
     return ReadVMIsolateObject(value);
   }
   if (SerializedHeaderTag::decode(value) == kObjectId) {
     return ReadIndexedObject(SerializedHeaderData::decode(value));
   }
   ASSERT(SerializedHeaderTag::decode(value) == kInlined);
   // Read the class header information and lookup the class.
   intptr_t class_header = ReadIntptrValue();
 
+  intptr_t object_id = SerializedHeaderData::decode(value);
+  if (object_id == kOmittedObjectId) {
+    object_id = NextAvailableObjectId();
+  }
+
   // Reading of regular dart instances has limited support in order to
   // read typed data views.
   if (SerializedHeaderData::decode(class_header) == kInstanceObjectId) {
-    intptr_t object_id = SerializedHeaderData::decode(value);
     Dart_CObject_Internal* object =
         AllocateDartCObjectInternal(Dart_CObject_Internal::kUninitialized);
     AddBackRef(object_id, object, kIsNotDeserialized);
     // Read class of object.
     object->cls = reinterpret_cast<Dart_CObject_Internal*>(ReadObjectImpl());
     ASSERT(object->cls->type ==
            static_cast<Dart_CObject_Type>(Dart_CObject_Internal::kClass));
     return object;
   }
   ASSERT((class_header & kSmiTagMask) != 0);
-  intptr_t object_id = SerializedHeaderData::decode(value);
   intptr_t class_id = LookupInternalClass(class_header);
   if ((class_id == kArrayCid) || (class_id == kImmutableArrayCid)) {
     ASSERT(GetBackRef(object_id) == NULL);
     intptr_t len = ReadSmiValue();
     Dart_CObject* value = AllocateDartCObjectArray(len);
     AddBackRef(object_id, value, kIsNotDeserialized);
     return value;
   }
 
   intptr_t tags = ReadTags();
@@ skipping 314 matching lines @@
   }
   ASSERT((value64 <= kIntptrMax) && (value64 >= kIntptrMin));
   intptr_t value = static_cast<intptr_t>(value64);
   if (IsVMIsolateObject(value)) {
     return ReadVMIsolateObject(value);
   }
   if (SerializedHeaderTag::decode(value) == kObjectId) {
     return ReadIndexedObject(SerializedHeaderData::decode(value));
   }
   ASSERT(SerializedHeaderTag::decode(value) == kInlined);
-  return ReadInlinedObject(SerializedHeaderData::decode(value));
+
+  intptr_t object_id = SerializedHeaderData::decode(value);
+  if (object_id == kOmittedObjectId) {
+    object_id = NextAvailableObjectId();
+  }
+  return ReadInlinedObject(object_id);
 }
 
 
 void ApiMessageReader::AddBackRef(intptr_t id,
                                   Dart_CObject* obj,
                                   DeserializeState state) {
   intptr_t index = (id - kMaxPredefinedObjectIds);
   ASSERT(index == backward_references_.length());
   BackRefNode* node = AllocateBackRefNode(obj, state);
   ASSERT(node != NULL);
@@ skipping 416 matching lines @@
     if (!success) {
       UnmarkAllCObjects(object);
       return false;
     }
   }
   UnmarkAllCObjects(object);
   return true;
 }
 
 }  // namespace dart