Fix a bug in delete for lookup slots.

src/x64/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 7217 matching lines @@
       Slot* slot = variable->AsSlot();
       if (variable->is_global()) {
         LoadGlobal();
         frame_->Push(variable->name());
         Result answer = frame_->InvokeBuiltin(Builtins::DELETE,
                                               CALL_FUNCTION, 2);
         frame_->Push(&answer);
         return;
 
       } else if (slot != NULL && slot->type() == Slot::LOOKUP) {
-        // Call the runtime to look up the context holding the named
+        // Call the runtime to delete from the context holding the named
         // variable.  Sync the virtual frame eagerly so we can push the
         // arguments directly into place.
         frame_->SyncRange(0, frame_->element_count() - 1);
         frame_->EmitPush(rsi);
         frame_->EmitPush(variable->name());
-        Result context = frame_->CallRuntime(Runtime::kLookupContext, 2);
-        ASSERT(context.is_register());
-        frame_->EmitPush(context.reg());
-        context.Unuse();
-        frame_->EmitPush(variable->name());
-        Result answer = frame_->InvokeBuiltin(Builtins::DELETE,
-                                              CALL_FUNCTION, 2);
+        Result answer = frame_->CallRuntime(Runtime::kDeleteContextSlot, 2);
         frame_->Push(&answer);
         return;
       }
 
       // Default: Result of deleting non-global, not dynamically
       // introduced variables is false.
       frame_->Push(Factory::false_value());
 
     } else {
       // Default: Result of deleting expressions is true.
@@ skipping 1543 matching lines @@
 }
 
 #endif
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64