Implement unary addition in the full (non-optimizing) code generator.

src/x64/full-codegen-x64.cc

 // Copyright 2009 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 1446 matching lines @@
       } else {
         // This expression cannot throw a reference error at the top level.
         VisitForValue(expr->expression(), kStack);
       }
 
       __ CallRuntime(Runtime::kTypeof, 1);
       Apply(context_, rax);
       break;
     }
 
+    case Token::ADD: {
+      Comment cmt(masm_, "[ UnaryOperation (ADD)");
+      VisitForValue(expr->expression(), kAccumulator);
+      Label no_conversion;
+      Condition is_smi;
+      is_smi = masm_->CheckSmi(result_register());
+      __ j(is_smi, &no_conversion);
+      __ push(result_register());
+      __ InvokeBuiltin(Builtins::TO_NUMBER, CALL_FUNCTION);
+      __ bind(&no_conversion);
+      Apply(context_, result_register());
+      break;
+    }
+
     default:
       UNREACHABLE();
   }
 }
 
 
 void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
   Comment cmnt(masm_, "[ CountOperation");
 
   // Expression can only be a property, a global or a (parameter or local)
@@ skipping 352 matching lines @@
   __ movq(Operand(rsp, 0), rdx);
   // And return.
   __ ret(0);
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal