Parallelize codegen #445
Description
I'm struggling with iteration because my crate already takes 30s+ to compile even after minor incremental changes. The process is clearly single-threaded, with remaining 63 threads available on my CPU contributing nothing. And it gets even slower as I add more code to it.
I do not know why it is single-threaded today, but it would be a big improvement if compile times were significantly shortened using parallelism.