arithmetic mode for LE from vhdl

Why? Cause I want so and i have no table with results to compare.

I know about adding a constant to register. will it better to change to 4 input LUT-function only without Carry-propagate function and use register feedback? are there any benifits from normal mode when doing arithmetic operation with constant? What about "use more resources" -> quantity of LE remains for normal or for arithmetic mode, does'nt matter. LE becomes 2 separate 3inputLUT for sum and for carry but is still in one LE.

but my main idea was "quartus able to turn on arithmetic mode for LE from processing vhdl code". It definitly turns on arithmetic mode with non-constant drivers when using arithmetic operaions <- counter outputs is good candidates to unstabe category.