It's actually faster to separate things, because you will be able to implement them cleanly. Having a good pipeline such as "text -> AST -> typed AST -> IR -> .

It's actually faster to separate things, because you will be able to implement them cleanly. Having a good pipeline such as "text -> AST -> typed AST -> IR -> .... -> ASM/VM code" is very valuable. The costy parts are the middle layer optimization anyway. Typechecking time, for a well written type checker, is not that big.