completeCall failure while building stringsearch

While benchmarking #19557 (closed) I noticed that GHC 7bc7eea3 fails to compile stringsearch-0.3.6.6 due to a simplifier crash:

[10 of 15] Compiling Data.ByteString.Search.DFA ( Data/ByteString/Search/DFA.hs, dist/build/Data/ByteString/Search/DFA.o, dist/build/Data/ByteString/Search/DFA.dyn_o )
ghc: panic! (the 'impossible' happened)
  (GHC version 9.3.20210422:
        completeCall
  $s$j_skZJ
  Stop[BoringCtxt] ByteString -> [Int]
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/GHC/Utils/Panic.hs:181:37 in ghc:GHC.Utils.Panic
        pprPanic, called at compiler/GHC/Core/Opt/Simplify.hs:1823:9 in ghc:GHC.Core.Opt.Simplify

Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug

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