In background compilation make a copy of Field in order to freeze its state

runtime/vm/object.h

 // 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.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 2863 matching lines @@
 
   FINAL_HEAP_OBJECT_IMPLEMENTATION(RedirectionData, Object);
   friend class Class;
   friend class Function;
   friend class HeapProfiler;
 };
 
 
 class Field : public Object {
  public:
+  RawField* Original() const;
+  Field* OriginalAsHandle(Zone* zone = NULL) const {
+    if (zone == NULL) {
+      zone = Thread::Current()->zone();
+    }
+    return &Field::ZoneHandle(zone, Original());
+  }

[siva, 2016/02/25 23:38:33]

Can this function be moved to the callers (e.g ast.h) instead of here. We have
been consistent of having all methods in this file return pointer to raw
objects.

[srdjan, 2016/02/26 00:40:43]

Removed function.

+  void SetOriginal(const Field& value) const;
+  bool IsOriginal() const {
+    return Original() == this->raw();

[siva, 2016/02/25 23:38:33]

Wouldn't it be easier to just do:
{
  if (IsNull()) {
    return true;
  }
  NoSafepointScope no_safepoint;
  return this->raw() != this->raw_ptr()->owner_;
}

[srdjan, 2016/02/26 00:40:43]

Adapted:
  bool IsOriginal() const {
    if (IsNull()) {
      return true;
    }
    NoSafepointScope no_safepoint;
    return !raw_ptr()->owner_->IsField();
  }

+  }
+
+  // Returns ZoneHandle of a field cloned from 'this'. 'this' is set as the
+  // original field of result.
+  Field* CloneFromOriginal() const;

[siva, 2016/02/25 23:38:33]

RawField* CloneFromOriginal() const;

(See comment in MayCloneField() - ast.cc)

[srdjan, 2016/02/26 00:40:43]

Returning RawField*

+
   RawString* name() const { return raw_ptr()->name_; }
   RawString* UserVisibleName() const;  // Same as scrubbed name.
   virtual RawString* DictionaryName() const { return name(); }
 
   bool is_static() const { return StaticBit::decode(raw_ptr()->kind_bits_); }
   bool is_final() const { return FinalBit::decode(raw_ptr()->kind_bits_); }
   bool is_const() const { return ConstBit::decode(raw_ptr()->kind_bits_); }
   bool is_reflectable() const {
     return ReflectableBit::decode(raw_ptr()->kind_bits_);
   }
   void set_is_reflectable(bool value) const {
+    ASSERT(IsOriginal());
     set_kind_bits(ReflectableBit::update(value, raw_ptr()->kind_bits_));
   }
   bool is_double_initialized() const {
     return DoubleInitializedBit::decode(raw_ptr()->kind_bits_);
   }
   // Called in parser after allocating field, immutable property otherwise.
   // Marks fields that are initialized with a simple double constant.
   void set_is_double_initialized(bool value) const {
     ASSERT(Thread::Current()->IsMutatorThread());
+    ASSERT(IsOriginal());
     set_kind_bits(DoubleInitializedBit::update(value, raw_ptr()->kind_bits_));
   }
 
   inline intptr_t Offset() const;
   // Called during class finalization.
   inline void SetOffset(intptr_t offset_in_bytes) const;
 
   inline RawInstance* StaticValue() const;
   inline void SetStaticValue(const Instance& value,
                              bool save_initial_value = false) const;
 
-  RawClass* owner() const;
-  RawClass* origin() const;  // Either mixin class, or same as owner().
-  RawScript* script() const;
-  RawObject* RawOwner() const { return raw_ptr()->owner_; }
+  RawClass* Owner() const;
+  RawClass* Origin() const;  // Either mixin class, or same as owner().
+  RawScript* Script() const;
+  RawObject* RawOwner() const;
 
   RawAbstractType* type() const  { return raw_ptr()->type_; }
   // Used by class finalizer, otherwise initialized in constructor.
   void SetFieldType(const AbstractType& value) const;
 
   static intptr_t InstanceSize() {
     return RoundedAllocationSize(sizeof(RawField));
   }
 
   static RawField* New(const String& name,
                        bool is_static,
                        bool is_final,
                        bool is_const,
                        bool is_reflectable,
                        const Class& owner,
                        const AbstractType& type,
                        TokenPosition token_pos);
 
   static RawField* NewTopLevel(const String& name,
                                bool is_final,
                                bool is_const,
                                const Object& owner,
                                TokenPosition token_pos);
 
   // Allocate new field object, clone values from this field. The
   // owner of the clone is new_owner.
   RawField* Clone(const Class& new_owner) const;
+  // Allocate new field object, clone values from this field. The
+  // original is specified.
+  RawField* Clone(const Field& original) const;
 
   static intptr_t instance_field_offset() {
     return OFFSET_OF(RawField, value_.offset_);
   }
   static intptr_t static_value_offset() {
     return OFFSET_OF(RawField, value_.static_value_);
   }
 
   static intptr_t kind_bits_offset() { return OFFSET_OF(RawField, kind_bits_); }
 
   TokenPosition token_pos() const { return raw_ptr()->token_pos_; }
 
   bool has_initializer() const {
     return HasInitializerBit::decode(raw_ptr()->kind_bits_);
   }
   // Called by parser after allocating field.
   void set_has_initializer(bool has_initializer) const {
+    ASSERT(IsOriginal());
     ASSERT(Thread::Current()->IsMutatorThread());
     set_kind_bits(HasInitializerBit::update(has_initializer,
                                             raw_ptr()->kind_bits_));
   }
 
   // Return class id that any non-null value read from this field is guaranteed
   // to have or kDynamicCid if such class id is not known.
   // Stores to this field must update this information hence the name.
   intptr_t guarded_cid() const { return raw_ptr()->guarded_cid_; }
 
   void set_guarded_cid(intptr_t cid) const {
+    ASSERT(IsOriginal());
     ASSERT(Thread::Current()->IsMutatorThread());
     StoreNonPointer(&raw_ptr()->guarded_cid_, cid);
   }
   static intptr_t guarded_cid_offset() {
     return OFFSET_OF(RawField, guarded_cid_);
   }
   // Return the list length that any list stored in this field is guaranteed
   // to have. If length is kUnknownFixedLength the length has not
   // been determined. If length is kNoFixedLength this field has multiple
   // list lengths associated with it and cannot be predicted.
@@ skipping 19 matching lines @@
   intptr_t UnboxedFieldCid() const {
     return guarded_cid();
   }
 
   bool is_unboxing_candidate() const {
     return UnboxingCandidateBit::decode(raw_ptr()->kind_bits_);
   }
   // Default 'true', set to false once optimizing compiler determines it should
   // be boxed.
   void set_is_unboxing_candidate(bool b) const {
+    ASSERT(IsOriginal());
     set_kind_bits(UnboxingCandidateBit::update(b, raw_ptr()->kind_bits_));
   }
 
   static bool IsExternalizableCid(intptr_t cid) {
     return (cid == kOneByteStringCid) || (cid == kTwoByteStringCid);
   }
 
   enum {
     kUnknownLengthOffset = -1,
     kUnknownFixedLength = -1,
     kNoFixedLength = -2,
   };
   // Returns false if any value read from this field is guaranteed to be
   // not null.
   // Internally we is_nullable_ field contains either kNullCid (nullable) or
   // any other value (non-nullable) instead of boolean. This is done to simplify
   // guarding sequence in the generated code.
   bool is_nullable() const {
     return raw_ptr()->is_nullable_ == kNullCid;
   }
   void set_is_nullable(bool val) const {
+    ASSERT(IsOriginal());
     ASSERT(Thread::Current()->IsMutatorThread());
     StoreNonPointer(&raw_ptr()->is_nullable_, val ? kNullCid : kIllegalCid);
   }
   static intptr_t is_nullable_offset() {
     return OFFSET_OF(RawField, is_nullable_);
   }
 
   // Record store of the given value into this field. May trigger
   // deoptimization of dependent optimized code.
   void RecordStore(const Object& value) const;
@@ skipping 5368 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_