ghc panic using SIMD types with unboxed sums

{-# language MagicHash,UnboxedSums #-} 
module Test where
import GHC.Prim

foo :: (# Int8X16# | () #) -> ()
foo _ = ()

building with -fllvm yields:

<no location info>: error:
    panic! (the 'impossible' happened)
  GHC version 9.4.2:
	primRepSlot
  No slot for VecRep
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/GHC/Utils/Panic.hs:182:37 in ghc:GHC.Utils.Panic
        pprPanic, called at compiler/GHC/Types/RepType.hs:329:27 in ghc:GHC.Types.RepType

This appears to happen for all SIMD types.

Other combinations of SIMD types (eg in an unboxed tuple) are working fine.