Use the previous context link when checking context extension objects.

src/x64/lithium-codegen-x64.cc

 // Copyright 2011 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 2664 matching lines @@
 void LCodeGen::DoContext(LContext* instr) {
   Register result = ToRegister(instr->result());
   __ movq(result, rsi);
 }
 
 
 void LCodeGen::DoOuterContext(LOuterContext* instr) {
   Register context = ToRegister(instr->context());
   Register result = ToRegister(instr->result());
   __ movq(result,
-          Operand(context, Context::SlotOffset(Context::CLOSURE_INDEX)));
-  __ movq(result, FieldOperand(result, JSFunction::kContextOffset));
+          Operand(context, Context::SlotOffset(Context::PREVIOUS_INDEX)));
 }
 
 
 void LCodeGen::DoGlobalObject(LGlobalObject* instr) {
   Register result = ToRegister(instr->result());
   __ movq(result, GlobalObjectOperand());
 }
 
 
 void LCodeGen::DoGlobalReceiver(LGlobalReceiver* instr) {
@@ skipping 1571 matching lines @@
   RegisterEnvironmentForDeoptimization(environment);
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64