If the compiler is optimising code away, it's optimising away its copy of code that the diligent programmer has already written. ie. the implied assertion that

If the compiler is optimising code away, it's optimising away its copy of code that the diligent programmer has already written. ie. the implied assertion that the check is not performed at all is not true. The check is not performed twice. Of course programmers are not always diligent but perhaps in that case a language which unconditionally demands diligence is not the right choice. > It also adds a very sub­tle, ex­cep­tional case to sev­eral very com­mon func­tions, bur­den­ing pro­gram­mers. Dealing with the burden of subtle and/or exceptional cases is the price of using a low-level language. If the price is unacceptable, don't buy the product.