The main difficulty in support isn't actually making the changes (which is going to be largely defining various tables and other boilerplate, unless your ISA is really weird and does something unusual), it's in doing all of the politics necessary to get those changes committed upstream.
replyMaintining this type of long time fork is the kind of mind numbing, tedious thing LLMs are actually exceptionally good at. I did some backend work on Lean4 compiler and then they switched out parts of the codegen, it took Codex less than an hour to recover the feature set I had implemented but on the new backend.
reply> and it was pretty much trivial to spit out support not just in gcc and llvm, but I also, for fun, made WATCOM backends and a few other things
replyNo links? You may have dreamt about it instead.