Inline instance object hash code into object header on 64 bit.

runtime/vm/object.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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/become.h"
@@ skipping 893 matching lines @@
   cls.set_is_finalized();
   cls.set_is_type_finalized();
   cls.set_is_cycle_free();
 
   cls = dynamic_class_;
   *dynamic_type_ = Type::NewNonParameterizedType(cls);
 
   cls = void_class_;
   *void_type_ = Type::NewNonParameterizedType(cls);
 
+#if defined(HASH_IN_OBJECT_HEADER)

[Vyacheslav Egorov (Google), 2017/05/30 15:25:00]

How do we make sure that this list is exhaustive? 

For example what happens if I call:

(1).runtimeType.hash

?

[erikcorry, 2017/06/02 15:34:04]

Good point that does not work.

Instead, the new version uses the visitor to give hash codes to all objects in
the VM isolate.  PTAL.

+  // These need to be set now because they can end up in read-only memory where
+  // they can't be overwritten.  Some of them actually have hashCode methods,
+  // so the value won't be used once the VM is fully booted.
+  Object::SetCachedHash(sentinel_->raw(), 1);
+  Object::SetCachedHash(transition_sentinel_->raw(), 2);
+  Object::SetCachedHash(unknown_constant_->raw(), 3);
+  Object::SetCachedHash(non_constant_->raw(), 4);
+  Object::SetCachedHash(empty_array_->raw(), 256);
+  Object::SetCachedHash(zero_array_->raw(), 257);
+  Object::SetCachedHash(dynamic_type_->raw(), 103);
+  Object::SetCachedHash(void_type_->raw(), 104);
+  Object::SetCachedHash(null_instance_->raw(), 42);
+#endif
+
   // Allocate and initialize singleton true and false boolean objects.
   cls = Class::New<Bool>();
   isolate->object_store()->set_bool_class(cls);
   *bool_true_ = Bool::New(true);
   *bool_false_ = Bool::New(false);
 
   *smi_illegal_cid_ = Smi::New(kIllegalCid);
 
   String& error_str = String::Handle();
   error_str = String::New("SnapshotWriter Error", Heap::kOld);
@@ skipping 22429 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart