Compilers can typically reason fairly well about tail recursion like this. In this case the compiler cannot remove the assertion because you could pass in 0. Bu

Compilers can typically reason fairly well about tail recursion like this. In this case the compiler cannot remove the assertion because you could pass in 0. But if you change the assert to be a >= 0 (which is vacuously true, as the warning indicates) it will optimize the code to "return 1" and eliminate the recursive call: https://godbolt.org/z/jad3Eh9Pf https://godbolt.org/z/jad3Eh9Pf