The increase was caused during 1.4->1.5 by translating the whole compiler toolchain from C to Go. The core devs focussed on correctness over performance on the

The increase was caused during 1.4->1.5 by translating the whole compiler toolchain from C to Go. The core devs focussed on correctness over performance on the first pass. They clawed back a lot of the performance already, and though it is slower than it used to be, it isn't at all bad compared with C++ and other languages I've used.