Request for comments on overall approach.

runtime/vm/assembler_ia32.h

Index: runtime/vm/assembler_ia32.h
diff --git a/runtime/vm/assembler_ia32.h b/runtime/vm/assembler_ia32.h
index 1cb69eccc3ae2796b2e5192d6cefa27f87cd2fac..e681d0859bde4287e51c266cf8545a83da3a30b0 100644
--- a/runtime/vm/assembler_ia32.h
+++ b/runtime/vm/assembler_ia32.h
@@ -529,6 +529,19 @@ class Assembler : public ValueObject {
   void CallRuntime(const RuntimeEntry& entry);
 
   /*
+   * Loading and comparing classes of objects
+   */
+  void GetClassOf(Register result, Register object, Register scratch);
+
+  void LoadObjectClassId(Register result, Register object);
+
+  void CompareClassOf(Register object, const Class& clazz, Register scratch);

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

When do you ever have to compare classes? Or asked differently: In which
situation are classids not good enough?

[Vyacheslav Egorov (Google), 2012/05/26 16:48:22]

This macros was introduced initially to cover a very common code pattern that
loads class and then compares to some constant. 

This does compare class ids internally. 

I can expand it in places where it is used but it seems cleaner when it's
collapsed.

+
+  void CompareClassId(Register clsid, const Class& cls) {
+    cmpl(clsid, Immediate(cls.index()));
+  }
+
+  /*
    * Misc. functionality
    */
   void SmiTag(Register reg) {