Request for comments on overall approach.

runtime/vm/raw_object.cc

Index: runtime/vm/raw_object.cc
diff --git a/runtime/vm/raw_object.cc b/runtime/vm/raw_object.cc
index 649d6e69e7cc7784f7886b5a92958728dac7e1aa..0e45a773f9c9930d8ad04c574f5ac08d61cb2891 100644
--- a/runtime/vm/raw_object.cc
+++ b/runtime/vm/raw_object.cc
@@ -13,6 +13,18 @@
 
 namespace dart {
 
+
+
+RawClass* RawObject::GetClass(uword tags) {
+  if (FreeBit::decode(tags)) {
+    return FreeListElement::freelist_class();
+  } else {
+    return Isolate::Current()->class_table()->At(
+        ClassTag::decode(tags));
+  }
+}
+
+
 void RawObject::Validate(Isolate* isolate) const {
   // Validation only happens in DEBUG builds.
 #if defined(DEBUG)
@@ -25,19 +37,13 @@ void RawObject::Validate(Isolate* isolate) const {
   if (!IsHeapObject()) {
     return;
   }
-  // Validate that the class_ field is sensible.
-  RawClass* raw_class = ptr()->class_;
-  ASSERT(raw_class->IsHeapObject());
-  RawClass* raw_class_class = raw_class->ptr()->class_;
-  ASSERT(raw_class_class->IsHeapObject());
-  ASSERT(raw_class_class->ptr()->instance_kind_ == kClass);
 
   // Validate that the tags_ field is sensible.
   uword tags = ptr()->tags_;
   ASSERT((tags & 0x000000f0) == 0);
   intptr_t cid = ClassTag::decode(tags);
-  RawClass* tag_class = isolate->class_table()->At(cid);
-  ASSERT(tag_class == raw_class);
+  RawClass* raw_class = isolate->class_table()->At(cid);
+  ASSERT(raw_class->IsHeapObject());
 #endif
 }
 
@@ -48,7 +54,7 @@ intptr_t RawObject::SizeFromClass() const {
   // Only reasonable to be called on heap objects.
   ASSERT(IsHeapObject());
 
-  RawClass* raw_class = ptr()->class_;
+  RawClass* raw_class = GetClass();
   intptr_t instance_size = raw_class->ptr()->instance_size_;
   ObjectKind instance_kind = raw_class->ptr()->instance_kind_;
 
@@ -238,7 +244,7 @@ intptr_t RawObject::SizeFromClass() const {
         ASSERT(FreeBit::decode(ptr()->tags_));
         uword addr = RawObject::ToAddr(const_cast<RawObject*>(this));
         FreeListElement* element = reinterpret_cast<FreeListElement*>(addr);
-        instance_size = element->Size();
+        instance_size = element->size();
         break;
       }
       default:
@@ -262,13 +268,10 @@ intptr_t RawObject::VisitPointers(ObjectPointerVisitor* visitor) {
   // Only reasonable to be called on heap objects.
   ASSERT(IsHeapObject());
 
-  // Read the necessary data out of the class before visting the class itself.
-  RawClass* raw_class = ptr()->class_;
+  // Read the necessary data out of the class before visiting the class itself.
+  RawClass* raw_class = GetClass();

[Ivan Posva, 2012/05/26 04:34:46]

The ObjectKind is equivalent to the instance_kind_ for all ids less than
kFreeListElement. All ids greater than kNumPredefineKinds are either Instance or
Closure, which we plan to resolve in a different manner with Siva.

   ObjectKind kind = raw_class->ptr()->instance_kind_;
 
-  // Visit the class before visting the fields.
-  visitor->VisitPointer(reinterpret_cast<RawObject**>(&ptr()->class_));
-
   switch (kind) {
 #define RAW_VISITPOINTERS(clazz) \
     case clazz::kInstanceKind: { \
@@ -283,7 +286,7 @@ intptr_t RawObject::VisitPointers(ObjectPointerVisitor* visitor) {
       // Nothing to visit for free list elements.
       uword addr = RawObject::ToAddr(this);
       FreeListElement* element = reinterpret_cast<FreeListElement*>(addr);
-      size = element->Size();
+      size = element->size();
       break;
     }
     default:
@@ -439,7 +442,7 @@ intptr_t RawInstructions::VisitInstructionsPointers(
 
 
 bool RawInstructions::ContainsPC(RawObject* raw_obj, uword pc) {
-  RawClass* raw_class = raw_obj->ptr()->class_;
+  RawClass* raw_class = raw_obj->GetClass();
   ObjectKind instance_kind = raw_class->ptr()->instance_kind_;
   if (instance_kind == kInstructions) {

[Ivan Posva, 2012/05/26 04:34:46]

Just use the class id field here.

     RawInstructions* raw_instr = reinterpret_cast<RawInstructions*>(raw_obj);
@@ -564,9 +567,9 @@ intptr_t RawInstance::VisitInstancePointers(RawInstance* raw_obj,
                                             ObjectPointerVisitor* visitor) {
   // Make sure that we got here with the tagged pointer as this.
   ASSERT(raw_obj->IsHeapObject());
-  RawInstance* obj = raw_obj->ptr();
-  intptr_t instance_size = obj->class_->ptr()->instance_size_;
-  intptr_t num_native_fields = obj->class_->ptr()->num_native_fields_;
+  RawClass* raw_class = raw_obj->GetClass();
+  intptr_t instance_size = raw_class->ptr()->instance_size_;
+  intptr_t num_native_fields = raw_class->ptr()->num_native_fields_;
 
   // Calculate the first and last raw object pointer fields.
   uword obj_addr = RawObject::ToAddr(raw_obj);