Request for comments on overall approach.

runtime/vm/raw_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/raw_object.h"
 
 #include "vm/class_table.h"
 #include "vm/freelist.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
 #include "vm/visitor.h"
 
 
 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)
   if (Object::null_class_ == reinterpret_cast<RawClass*>(kHeapObjectTag)) {
     // Validation relies on properly initialized class classes. Skip if the
     // VM is still being initialized.
     return;
   }
   // All Smi values are valid.
   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
 }
 
 
 intptr_t RawObject::SizeFromClass() const {
   NoHandleScope no_handles(Isolate::Current());
 
   // 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_;
 
   if (instance_size == 0) {
     switch (instance_kind) {
       case kTokenStream: {
         const RawTokenStream* raw_tokens =
             reinterpret_cast<const RawTokenStream*>(this);
         intptr_t tokens_length = Smi::Value(raw_tokens->ptr()->length_);
         instance_size = TokenStream::InstanceSize(tokens_length);
@@ skipping 169 matching lines @@
         const RawJSRegExp* raw_jsregexp =
             reinterpret_cast<const RawJSRegExp*>(this);
         intptr_t data_length = Smi::Value(raw_jsregexp->ptr()->data_length_);
         instance_size = JSRegExp::InstanceSize(data_length);
         break;
       }
       case kFreeListElement: {
         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:
         UNREACHABLE();
         break;
     }
   }
   ASSERT(instance_size != 0);
   uword tags = ptr()->tags_;
   ASSERT((instance_size == SizeTag::decode(tags)) ||
          (SizeTag::decode(tags) == 0) ||
          FreeBit::decode(tags));
   return instance_size;
 }
 
 
 intptr_t RawObject::VisitPointers(ObjectPointerVisitor* visitor) {
   intptr_t size = 0;
   NoHandleScope no_handles(Isolate::Current());
 
   // 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: { \
       Raw##clazz* raw_obj = reinterpret_cast<Raw##clazz*>(this); \
       size = Raw##clazz::Visit##clazz##Pointers(raw_obj, visitor); \
       break; \
     }
     CLASS_LIST_NO_OBJECT(RAW_VISITPOINTERS)
 #undef RAW_VISITPOINTERS
     case kFreeListElement: {
       ASSERT(FreeBit::decode(ptr()->tags_));
       // 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:
       OS::Print("Kind: %d\n", kind);
       UNREACHABLE();
       break;
   }
 
   ASSERT(size != 0);
   ASSERT(size == Size());
@@ skipping 135 matching lines @@
 
 intptr_t RawInstructions::VisitInstructionsPointers(
     RawInstructions* raw_obj, ObjectPointerVisitor* visitor) {
   RawInstructions* obj = raw_obj->ptr();
   visitor->VisitPointer(reinterpret_cast<RawObject**>(&obj->code_));
   return Instructions::InstanceSize(obj->size_);
 }
 
 
 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);
     uword start_pc =
         reinterpret_cast<uword>(raw_instr->ptr()) + Instructions::HeaderSize();
     uword end_pc = start_pc + raw_instr->ptr()->size_;
     ASSERT(end_pc > start_pc);
     if ((pc >= start_pc) && (pc < end_pc)) {
       return true;
     }
   }
   return false;
@@ skipping 102 matching lines @@
     RawUnwindError* raw_obj, ObjectPointerVisitor* visitor) {
   visitor->VisitPointers(raw_obj->from(), raw_obj->to());
   return UnwindError::InstanceSize();
 }
 
 
 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);
   uword from = obj_addr + sizeof(RawObject) + num_native_fields * kWordSize;
   uword to = obj_addr + instance_size - kWordSize;
   visitor->VisitPointers(reinterpret_cast<RawObject**>(from),
                          reinterpret_cast<RawObject**>(to));
   return instance_size;
 }
 
@@ skipping 355 matching lines @@
 intptr_t RawJSRegExp::VisitJSRegExpPointers(RawJSRegExp* raw_obj,
                                             ObjectPointerVisitor* visitor) {
   // Make sure that we got here with the tagged pointer as this.
   ASSERT(raw_obj->IsHeapObject());
   intptr_t length = Smi::Value(raw_obj->ptr()->data_length_);
   visitor->VisitPointers(raw_obj->from(), raw_obj->to());
   return JSRegExp::InstanceSize(length);
 }
 
 }  // namespace dart