[es6] Fix prototype chain walk for instanceof.

src/crankshaft/x64/lithium-codegen-x64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/crankshaft/x64/lithium-codegen-x64.h"
 
 #include "src/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 2439 matching lines @@
   if (instr->hydrogen()->ObjectNeedsSmiCheck()) {
     Condition is_smi = __ CheckSmi(object);
     EmitFalseBranch(instr, is_smi);
   }
 
   // Loop through the {object}s prototype chain looking for the {prototype}.
   __ movp(object_map, FieldOperand(object, HeapObject::kMapOffset));
   Label loop;
   __ bind(&loop);
 
-
   // Deoptimize if the object needs to be access checked.
   __ testb(FieldOperand(object_map, Map::kBitFieldOffset),
            Immediate(1 << Map::kIsAccessCheckNeeded));
   DeoptimizeIf(not_zero, instr, Deoptimizer::kAccessCheck);
   // Deoptimize for proxies.
   __ CmpInstanceType(object_map, JS_PROXY_TYPE);
   DeoptimizeIf(equal, instr, Deoptimizer::kProxy);
 
   __ movp(object_prototype, FieldOperand(object_map, Map::kPrototypeOffset));
+  __ CompareRoot(object_prototype, Heap::kNullValueRootIndex);
+  EmitFalseBranch(instr, equal);
   __ cmpp(object_prototype, prototype);
   EmitTrueBranch(instr, equal);
-  __ CompareRoot(object_prototype, Heap::kNullValueRootIndex);
-  EmitFalseBranch(instr, equal);
   __ movp(object_map, FieldOperand(object_prototype, HeapObject::kMapOffset));
   __ jmp(&loop);
 }
 
 
 void LCodeGen::DoCmpT(LCmpT* instr) {
   DCHECK(ToRegister(instr->context()).is(rsi));
   Token::Value op = instr->op();
 
   Handle<Code> ic = CodeFactory::CompareIC(isolate(), op).code();
@@ skipping 3141 matching lines @@
   __ bind(deferred->exit());
   __ bind(&done);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64