Request for comments on overall approach.

runtime/vm/flow_graph_compiler_x64.cc

Index: runtime/vm/flow_graph_compiler_x64.cc
diff --git a/runtime/vm/flow_graph_compiler_x64.cc b/runtime/vm/flow_graph_compiler_x64.cc
index 426f7069b005235ba51a598cb5a70c7fd46e8ae3..0ed629bcf635b9282f8805bb2ec295bdd381fc78 100644
--- a/runtime/vm/flow_graph_compiler_x64.cc
+++ b/runtime/vm/flow_graph_compiler_x64.cc
@@ -124,7 +124,7 @@ FlowGraphCompiler::GenerateInstantiatedTypeWithArgumentsTest(
   if (is_raw_type) {
     // Dynamic type argument, check only classes.
     // List is a very common case.
-    __ movq(R10, FieldAddress(RAX, Object::class_offset()));
+    __ GetClassOf(R10, RAX);
     if (!type_class.is_interface()) {
       __ CompareObject(R10, type_class);
       __ j(EQUAL, is_instance_lbl);
@@ -232,7 +232,7 @@ void FlowGraphCompiler::GenerateInstantiatedTypeNoArgumentsTest(
   ObjectStore* object_store = Isolate::Current()->object_store();
   // Compare if the classes are equal. Instance is not Smi.
   __ Bind(&compare_classes);
-  __ movq(R10, FieldAddress(RAX, Object::class_offset()));
+  __ GetClassOf(R10, RAX);
   // If type is an interface, we can skip the class equality check.
   if (!type_class.is_interface()) {
     __ CompareObject(R10, type_class);
@@ -320,7 +320,7 @@ RawSubtypeTestCache* FlowGraphCompiler::GenerateSubtype1TestCacheLookup(
   const Bool& bool_true = Bool::ZoneHandle(Bool::True());
   const Immediate raw_null =
       Immediate(reinterpret_cast<intptr_t>(Object::null()));
-  __ movq(R10, FieldAddress(RAX, Object::class_offset()));
+  __ GetClassOf(R10, RAX);
   // Check immediate superclass equality.
   __ movq(R13, FieldAddress(R10, Class::super_type_offset()));
   __ movq(R13, FieldAddress(R13, Type::type_class_offset()));
@@ -369,7 +369,7 @@ RawSubtypeTestCache* FlowGraphCompiler::GenerateUninstantiatedTypeTest(
     // Can handle only type arguments that are instances of TypeArguments.
     // (runtime checks canonicalize type arguments).
     Label fall_through;
-    __ movq(R10, FieldAddress(RDX, Object::class_offset()));
+    __ GetClassOf(R10, RDX);
     __ CompareObject(R10, Object::ZoneHandle(Object::type_arguments_class()));
     __ j(NOT_EQUAL, &fall_through);
     __ movq(RDI,
@@ -1145,8 +1145,8 @@ void FlowGraphCompiler::VisitInstantiateTypeArguments(
     // matching length and, if so, use it as the instantiated type_arguments.
     // No need to check the instantiator (RAX) for null here, because a null
     // instantiator will have the wrong class (Null instead of TypeArguments).
-    __ LoadObject(RCX, Class::ZoneHandle(Object::type_arguments_class()));
-    __ cmpq(RCX, FieldAddress(RAX, Object::class_offset()));
+    __ GetClassOf(R10, RAX);
+    __ CompareObject(R10, Class::ZoneHandle(Object::type_arguments_class()));
     __ j(NOT_EQUAL, &type_arguments_uninstantiated, Assembler::kNearJump);
     Immediate arguments_length =
         Immediate(Smi::RawValue(comp->type_arguments().Length()));
@@ -1194,8 +1194,8 @@ void FlowGraphCompiler::VisitExtractConstructorTypeArguments(
     // No need to check the instantiator (RAX) for null here, because a null
     // instantiator will have the wrong class (Null instead of TypeArguments).
     Label type_arguments_uninstantiated;
-    __ LoadObject(RCX, Class::ZoneHandle(Object::type_arguments_class()));
-    __ cmpq(RCX, FieldAddress(RAX, Object::class_offset()));
+    __ GetClassOf(R10, RAX);
+    __ CompareObject(R10, Class::ZoneHandle(Object::type_arguments_class()));
     __ j(NOT_EQUAL, &type_arguments_uninstantiated, Assembler::kNearJump);
     Immediate arguments_length =
         Immediate(Smi::RawValue(comp->type_arguments().Length()));
@@ -1248,8 +1248,8 @@ void FlowGraphCompiler::VisitExtractConstructorInstantiator(
     // matching length and, if so, use it as the instantiated type_arguments.
     // No need to check the instantiator (RAX) for null here, because a null
     // instantiator will have the wrong class (Null instead of TypeArguments).
-    __ LoadObject(RCX, Class::ZoneHandle(Object::type_arguments_class()));
-    __ cmpq(RCX, FieldAddress(RAX, Object::class_offset()));
+    __ GetClassOf(R10, RAX);
+    __ CompareObject(R10, Class::ZoneHandle(Object::type_arguments_class()));
     __ j(NOT_EQUAL, &done, Assembler::kNearJump);
     Immediate arguments_length =
         Immediate(Smi::RawValue(comp->type_arguments().Length()));