Use the previous context link when checking context extension objects.

src/x64/full-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 1071 matching lines @@
   Scope* s = scope();
   while (s != NULL) {
     if (s->num_heap_slots() > 0) {
       if (s->calls_eval()) {
         // Check that extension is NULL.
         __ cmpq(ContextOperand(context, Context::EXTENSION_INDEX),
                 Immediate(0));
         __ j(not_equal, slow);
       }
       // Load next context in chain.
-      __ movq(temp, ContextOperand(context, Context::CLOSURE_INDEX));
-      __ movq(temp, FieldOperand(temp, JSFunction::kContextOffset));
+      __ movq(temp, ContextOperand(context, Context::PREVIOUS_INDEX));
       // Walk the rest of the chain without clobbering rsi.
       context = temp;
     }
     // If no outer scope calls eval, we do not need to check more
     // context extensions.  If we have reached an eval scope, we check
     // all extensions from this point.
     if (!s->outer_scope_calls_eval() || s->is_eval_scope()) break;
     s = s->outer_scope();
   }
 
   if (s != NULL && s->is_eval_scope()) {
     // Loop up the context chain.  There is no frame effect so it is
     // safe to use raw labels here.
     Label next, fast;
     if (!context.is(temp)) {
       __ movq(temp, context);
     }
     // Load map for comparison into register, outside loop.
     __ LoadRoot(kScratchRegister, Heap::kGlobalContextMapRootIndex);
     __ bind(&next);
     // Terminate at global context.
     __ cmpq(kScratchRegister, FieldOperand(temp, HeapObject::kMapOffset));
     __ j(equal, &fast, Label::kNear);
     // Check that extension is NULL.
     __ cmpq(ContextOperand(temp, Context::EXTENSION_INDEX), Immediate(0));
     __ j(not_equal, slow);
     // Load next context in chain.
-    __ movq(temp, ContextOperand(temp, Context::CLOSURE_INDEX));
-    __ movq(temp, FieldOperand(temp, JSFunction::kContextOffset));
+    __ movq(temp, ContextOperand(temp, Context::PREVIOUS_INDEX));
     __ jmp(&next);
     __ bind(&fast);
   }
 
   // All extension objects were empty and it is safe to use a global
   // load IC call.
   __ movq(rax, GlobalObjectOperand());
   __ Move(rcx, slot->var()->name());
   Handle<Code> ic = isolate()->builtins()->LoadIC_Initialize();
   RelocInfo::Mode mode = (typeof_state == INSIDE_TYPEOF)
@@ skipping 11 matching lines @@
   Register temp = rbx;
 
   for (Scope* s = scope(); s != slot->var()->scope(); s = s->outer_scope()) {
     if (s->num_heap_slots() > 0) {
       if (s->calls_eval()) {
         // Check that extension is NULL.
         __ cmpq(ContextOperand(context, Context::EXTENSION_INDEX),
                 Immediate(0));
         __ j(not_equal, slow);
       }
-      __ movq(temp, ContextOperand(context, Context::CLOSURE_INDEX));
-      __ movq(temp, FieldOperand(temp, JSFunction::kContextOffset));
+      __ movq(temp, ContextOperand(context, Context::PREVIOUS_INDEX));
       // Walk the rest of the chain without clobbering rsi.
       context = temp;
     }
   }
   // Check that last extension is NULL.
   __ cmpq(ContextOperand(context, Context::EXTENSION_INDEX), Immediate(0));
   __ j(not_equal, slow);
 
   // This function is used only for loads, not stores, so it's safe to
   // return an rsi-based operand (the write barrier cannot be allowed to
@@ skipping 3145 matching lines @@
   __ ret(0);
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64