llvm 20 is out but unlike in earlier versions of ghc moving to it means you can no longer use llvm:

compiling:

ghc -fllvm hello.hs
Loaded package environment from /Users/avie/.ghc/aarch64-darwin-9.12.2/environments/default
[1 of 2] Compiling Main ( hello.hs, hello.o )
<no location info>: error: [GHC-66599]
GHC was not configured with a supported LLVM toolchain
Make sure you have installed LLVM between [13 and 20) and reinstall GHC to make -fllvm work

from configure:

configure: We only support llvm 13 upto 20 (non-inclusive) (found 20.1.1).

Can we move to llvm 20 on HEAD and can we revert to the old behavior on ghc 9.12.3?

Should I file an ER?

Thanks