In generated code for x64 don't load object's class directly from class_ field.

runtime/vm/stub_code_ia32.cc

 // Copyright (c) 2011, 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/globals.h"
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/assembler.h"
 #include "vm/assembler_macros.h"
 #include "vm/code_generator.h"
@@ skipping 1573 matching lines @@
     // 'num_args_tested' is stored as an untagged int.
     __ movl(EBX, FieldAddress(ECX, ICData::num_args_tested_offset()));
     __ cmpl(EBX, Immediate(num_args));
     __ j(EQUAL, &ok, Assembler::kNearJump);
     __ Stop("Incorrect stub for IC data");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
   // Loop that checks if there is an IC data match.
-  // EAX: receiver's class.
   // ECX: IC data object (preserved).
   __ movl(EBX, FieldAddress(ECX, ICData::ic_data_offset()));
   // EBX: ic_data_array with check entries: classes and target functions.
   __ leal(EBX, FieldAddress(EBX, Array::data_offset()));
   // EBX: points directly to the first ic data array element.
   Label loop, found;
   if (num_args == 1) {
     __ call(&get_class);
     // EAX: receiver's class
     __ Bind(&loop);
@@ skipping 287 matching lines @@
 // TOS + 2: instance.
 // TOS + 3: cache array.
 // Result in ECX: null -> not found, otherwise result (true or false).
 void StubCode::GenerateSubtype3TestCacheStub(Assembler* assembler) {
   GenerateSubtypeNTestCacheStub(assembler, 3);
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32