GHC produces incorrect coercions in hairy code
Andres Löh has been working with an optimized version of generics-sop, and ran into segfaults. He was able to reduce the test case to the attached (still not tiny) one, and could reduce it no further. He discovered the following utterly bogus definition in -ddump-simpl (with -O):
Main.gshowP_$dAll :: All MyShow GHC.Exts.Any
[GblId,
Unf=Unf{Src=<vanilla>, TopLvl=True, Value=False, ConLike=False,
WorkFree=False, Expandable=True, Guidance=IF_ARGS [] 20 0}]
Main.gshowP_$dAll
= ghc-prim-0.5.0.0:GHC.Classes.$p1(%,%)
@ (All MyShow GHC.Exts.Any)
@ (All (All MyShow) GHC.Exts.Any)
(ghc-prim-0.5.0.0:GHC.Classes.C:(%%)
`cast` (Sub (Sym (Main.D:R:AllFk_c[][0] <[*]>_N <All MyShow>_N))
; Sym (Main.N:All[0] <[*]>_N <All MyShow>_N <'[]>_N)
; Sub
(Nth:1
(Sub
(Sym
(Main.D:R:AllFkc:[0] <[*]>_N <All MyShow>_N <'[Char]>_N <'[]>_N))
; (AllF
<[*]>_N
<All MyShow>_N
((':)
<[*]>_N
(UnsafeCo nominal '[Char] GHC.Exts.Any)
(UnsafeCo nominal '[] GHC.Exts.Any))_N)_R
; Sub
(Main.D:R:AllFkc:[0]
<[*]>_N <All MyShow>_N <GHC.Exts.Any>_N <GHC.Exts.Any>_N)))
; Main.N:All[0]
<[*]>_N
<All MyShow>_N
(UnsafeCo nominal GHC.Exts.Any (GHC.Exts.Any : GHC.Exts.Any))
; Sub
(Main.D:R:AllFkc:[0]
<[*]>_N <All MyShow>_N <GHC.Exts.Any>_N <GHC.Exts.Any>_N)
:: (() :: Constraint :: Constraint)
~R#
((All MyShow GHC.Exts.Any,
All (All MyShow) GHC.Exts.Any) :: Constraint)))Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | kosmikus |
| Operating system | |
| Architecture |