Match on GADT triggers -dstg-lint panic when -fcatch-bottoms is enabled
GHC panics when compiling the following program with `-dstg-lint -fcatch-bottoms`:
```haskell
{-# LANGUAGE GADTs #-}
module M where
data T a where
A :: T Int
B :: T Bool
f :: T Int -> ()
f A = ()
```
```
$ ghc -dstg-lint -fcatch-bottoms M.hs
[1 of 1] Compiling M ( M.hs, M.o )
ghc: panic! (the 'impossible' happened)
(GHC version 8.10.0.20191210:
assertConsistentCafInfo
f :: T Int -> ()
[GblId, Arity=1, Caf=NoCafRefs, Unf=OtherCon []] =
\r [ds_sHF]
case ds_sHF of {
__DEFAULT -> runtimeError "Bottoming expression returned"#;
A co_aAp -> () [];
};
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler/utils/Outputable.hs:1179:37 in ghc:Outputable
pprPanic, called at compiler/stgSyn/CoreToStg.hs:309:39 in ghc:CoreToStg
```
I have reproduced this on both 8.8.1 and 8.10.1-alpha2. The error occurs regardless of optimization flags.
issue