Some improvement to the garbage collector was done in the last release, and involved moving much of the runtime to Go. Making the compiler into Go, however, is

Some improvement to the garbage collector was done in the last release, and involved moving much of the runtime to Go. Making the compiler into Go, however, is actually only completed in the 1.5 (development) branch, to be released in... August, I think. That'll open up the work on the optimizer (and everything else in the compiler) to be done in Go.