It's not
that bad, all x86 processors have the BSR instruction which can be mapped to LZCNT semantics with just a few extra instructions.
Left to right - modern x86-64, baseline x86-64, baseline i686:
https://rust.godbolt.org/z/nGsM35TEo
Maybe you're thinking of POPCNT, which hurts a lot more if it doesn't compile down to the native instruction:
https://rust.godbolt.org/z/xcxG3v4Mn
