It looks more like the JIT improvements made it profitable to manually unroll some loops in the base64 module: https://github.com/erlang/otp/commit/a03cf1601605

It looks more like the JIT improvements made it profitable to manually unroll some loops in the base64 module: https://github.com/erlang/otp/commit/a03cf1601605dee767cd9d5f18fc44fc39148795 https://github.com/erlang/otp/commit/a03cf1601605dee767cd9d5... IOW, the 4x improvement seems to largely come from a refactor of the base64 module, not from compiler improvements per se.