Having it as default on todays hardware is a non-starter. Few would pay say a 200% perf penalty for arithmetic unless it's on a security critical path. So opt-i

Having it as default on todays hardware is a non-starter. Few would pay say a 200% perf penalty for arithmetic unless it's on a security critical path. So opt-in it is. And almost all languages already support that type of opt in at the global level or smaller scope.