GHC 8.4.1-alpha panics when optimizing function using getTag and tagToEnum#
I originally observed this panic in this Travis build. The panic can be reduced to this file:
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE TypeFamilies #-}
module Bug where
import GHC.Base (getTag)
import GHC.Exts (Int(..), tagToEnum#)
data family TyFamilyEnum
data instance TyFamilyEnum = TyFamilyEnum1 | TyFamilyEnum2 | TyFamilyEnum3
suc :: TyFamilyEnum -> TyFamilyEnum
suc a_aaf8
= case getTag a_aaf8 of
a_aaf9
-> if 2 == I# a_aaf9
then error "succ{TyFamilyEnum}: tried to take `succ' of last tag in enumeration"
else case I# a_aaf9 + 1 of
I# i_aafa -> tagToEnum# i_aafa :: TyFamilyEnum
In GHC 8.2.2, compiling this with optimization works fine. But in GHC 8.4.1-alpha, it panics:
$ /opt/ghc/8.4.1/bin/ghc -fforce-recomp -O1 Bug.hs
[1 of 1] Compiling Bug ( Bug.hs, Bug.o )
ghc: panic! (the 'impossible' happened)
(GHC version 8.4.0.20171222 for x86_64-unknown-linux):
Prelude.!!: index too large
Trac metadata
Trac field | Value |
---|---|
Version | 8.4.1-alpha1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | highest |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |