Implement patch records to patch canonical objects.

runtime/vm/snapshot.h

Index: runtime/vm/snapshot.h
diff --git a/runtime/vm/snapshot.h b/runtime/vm/snapshot.h
index 1989c7b495f10b4832cd7edd3648ad9ec069e443..b6a7b202d5955ea253502a392ba825ff9511ae4c 100644
--- a/runtime/vm/snapshot.h
+++ b/runtime/vm/snapshot.h
@@ -97,6 +97,7 @@ enum SerializedHeaderType {
 static const int8_t kHeaderTagBits = 2;
 static const int8_t kObjectIdBits = (kBitsPerInt32 - (kHeaderTagBits + 1));
 static const intptr_t kMaxObjectId = (kMaxUint32 >> (kHeaderTagBits + 1));
+static const intptr_t kInvalidPatchIndex = -1;
 
 
 class SerializedHeaderTag : public BitField<enum SerializedHeaderType,
@@ -248,21 +249,42 @@ class BaseReader {
 
 class BackRefNode : public ValueObject {
  public:
-  BackRefNode(Object* reference, DeserializeState state)
-      : reference_(reference), state_(state) {}
+  BackRefNode(Object* reference,
+              DeserializeState state,
+              bool defer_canonicalization)
+      : reference_(reference),
+        state_(state),
+        defer_canonicalization_(defer_canonicalization),
+        patch_records_(NULL) {}
   Object* reference() const { return reference_; }
   bool is_deserialized() const { return state_ == kIsDeserialized; }
   void set_state(DeserializeState state) { state_ = state; }
+  bool defer_canonicalization() const { return defer_canonicalization_; }
+  ZoneGrowableArray<intptr_t>* patch_records() const { return patch_records_; }
 
   BackRefNode& operator=(const BackRefNode& other) {
     reference_ = other.reference_;
     state_ = other.state_;
+    defer_canonicalization_ = other.defer_canonicalization_;
+    patch_records_ = other.patch_records_;
     return *this;
   }
 
+  void AddPatchRecord(intptr_t patch_object_id, intptr_t patch_offset) {
+    if (defer_canonicalization_) {
+      if (patch_records_ == NULL) {
+        patch_records_ = new ZoneGrowableArray<intptr_t>();
+      }
+      patch_records_->Add(patch_object_id);
+      patch_records_->Add(patch_offset);
+    }
+  }
+
  private:
   Object* reference_;
   DeserializeState state_;
+  bool defer_canonicalization_;
+  ZoneGrowableArray<intptr_t>* patch_records_;
 };
 
 
@@ -290,7 +312,10 @@ class SnapshotReader : public BaseReader {
   RawObject* ReadObject();
 
   // Add object to backward references.
-  void AddBackRef(intptr_t id, Object* obj, DeserializeState state);
+  void AddBackRef(intptr_t id,
+                  Object* obj,
+                  DeserializeState state,
+                  bool defer_canonicalization = false);
 
   // Get an object from the backward references list.
   Object* GetBackRef(intptr_t id);
@@ -367,24 +392,44 @@ class SnapshotReader : public BaseReader {
 
   RawClass* ReadClassId(intptr_t object_id);
   RawObject* ReadStaticImplicitClosure(intptr_t object_id, intptr_t cls_header);
-  RawObject* ReadObjectImpl();
-  RawObject* ReadObjectImpl(intptr_t header);
-  RawObject* ReadObjectRef();
+  RawObject* ReadObjectImpl(intptr_t patch_object_id = kInvalidPatchIndex,
+                            intptr_t patch_offset = 0);
+  RawObject* ReadObjectImpl(intptr_t header,
+                            intptr_t patch_object_id,
+                            intptr_t patch_offset);
+  RawObject* ReadObjectRef(intptr_t patch_object_id = kInvalidPatchIndex,
+                           intptr_t patch_offset = 0);
 
   // Read a VM isolate object that was serialized as an Id.
   RawObject* ReadVMIsolateObject(intptr_t object_id);
 
   // Read an object that was serialized as an Id (singleton in object store,
   // or an object that was already serialized before).
-  RawObject* ReadIndexedObject(intptr_t object_id);
+  RawObject* ReadIndexedObject(intptr_t object_id,
+                               intptr_t patch_object_id,
+                               intptr_t patch_offset);
 
   // Read an inlined object from the stream.
-  RawObject* ReadInlinedObject(intptr_t object_id);
+  RawObject* ReadInlinedObject(intptr_t object_id,
+                               intptr_t patch_object_id,
+                               intptr_t patch_offset);
+
+  // Add a patch record for the object so that objects whose canonicalization
+  // is deferred can be back patched after they are canonicalized.
+  void AddPatchRecord(intptr_t object_id,
+                      intptr_t patch_object_id,
+                      intptr_t patch_offset);
+
+  // Process all the deferred canonicalization entries and patch all references.
+  void ProcessDeferredCanonicalizations();
 
   // Decode class id from the header field.
   intptr_t LookupInternalClass(intptr_t class_header);
 
-  void ArrayReadFrom(const Array& result, intptr_t len, intptr_t tags);
+  void ArrayReadFrom(intptr_t object_id,
+                     const Array& result,
+                     intptr_t len,
+                     intptr_t tags);
 
   intptr_t NextAvailableObjectId() const;