Minor change to for-in...

src/x64/full-codegen-x64.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1035 matching lines @@
   __ movq(rcx, Operand(rsp, 4 * kPointerSize));
   __ cmpq(rdx, FieldOperand(rcx, HeapObject::kMapOffset));
   __ j(equal, &update_each);
 
   // Convert the entry to a string or null if it isn't a property
   // anymore. If the property has been removed while iterating, we
   // just skip it.
   __ push(rcx);  // Enumerable.
   __ push(rbx);  // Current entry.
   __ InvokeBuiltin(Builtins::FILTER_KEY, CALL_FUNCTION);
-  __ CompareRoot(rax, Heap::kNullValueRootIndex);
+  __ SmiCompare(rax, Smi::FromInt(0));
   __ j(equal, loop_statement.continue_target());
   __ movq(rbx, rax);
 
   // Update the 'each' property or variable from the possibly filtered
   // entry in register rbx.
   __ bind(&update_each);
   __ movq(result_register(), rbx);
   // Perform the assignment as if via '='.
   EmitAssignment(stmt->each());
 
@@ skipping 2260 matching lines @@
   __ ret(0);
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64