Comment by codebje

The CE-dev community's LLVM back-end for the (e)Z80 'panned out' in that it produced pretty decent Z80 assembly code, but like most hobby-level back-ends the effort to keep up to date with LLVM's changes overwhelmed the few contributors active and it's now three years since the last release. It still works, so long as you're OK using the older LLVM (and clang).

This is why these back-ends aren't accepted by the LLVM project: without a significant commitment to supporting them, they're a liability for LLVM.