Thread by @smdiehl

LLVM is really great for languages that to first approximation are sugar on top of C (like C++, Rust, Swift etc). If you don't use System V calling convention, have non-standard register use, closures, or objects with dynamic lifetimes then it's basically just a clever assembler.

It's absurd to propose that somehow LLVM has solved compiler backends (because of Rust handwaving), because it absolutely hasn't. It's an amazing toolchain but it is by no means the end of history and most of the interesting work is still open problems for the non-C family.

You can get quite far with the approach where you write the whole runtime in C, compile out to IR and then let the interprocedural optimizer and LTO have at the final artifacts. But that's very brittle about guaranteeing performance and has a ton of compile-time overhead.

Long story short, LLVM is a an optimal backend to Clang. It's a maybe-ish good backend for things that look like C++ if you squint. For anything else you have to ask deeper questions before mangling your language into a form it will accept.

/end of rant