[GHC] #11644: Core lint error in result of Specialise for TEST=T3220 WAY=profasm

25 Feb 2016

      #11644: Core lint error in result of Specialise for TEST=T3220 WAY=profasm
-------------------------------------+-------------------------------------
           Reporter:  thomie         |             Owner:
               Type:  bug            |            Status:  new
           Priority:  highest        |         Milestone:  8.0.1
          Component:  Compiler       |           Version:  8.0.1-rc2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:  indexed-       |        Blocked By:
  types/should_compile/T3220         |
           Blocking:                 |   Related Tickets:  #11371, #11643
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 This is the code:
 {{{
 {-# LANGUAGE TypeFamilies, ScopedTypeVariables#-}

 module T3220 where

 class Foo m where
     type Bar m :: *
     action :: m -> Bar m -> m

 right x m = action m (Right x)

 right' :: (Either a b ~ Bar m, Foo m) => b -> m -> m
 right' x m = action m (Right x)

 instance Foo Int where
     type Bar Int = Either Int Int
     action m a = either (*) (+) a m

 instance Foo Float where
     type Bar Float = Either Float Float
     action m a = either (*) (+) a m

 foo = print $ right (1::Int) (3 :: Int)
 bar = print $ right (1::Float) (3 :: Float)
 }}}

 Invocation:
 {{{
 $ ghc-8.0.1 T3220.hs -prof -O -dcore-lint
 }}}

 {{{
 [1 of 1] Compiling T3220            ( T3220.hs, T3220.o )
 *** Core Lint errors : in result of Specialise ***
 <no location info>: warning:
     In the expression: action
                          @ Float
                          $fFooFloat
                          m_ayb
                          ((Right @ Float @ Float x_aya)
                           `cast` (Sub (Sym cobox_aUe) :: Either a_aU3
 b_aU4 ~R# Bar m_aU1))
     cobox_aUe :: Bar m_aU1 ~# Either a_aU3 b_aU4
     [LclId[CoVarId], Str=DmdType] is out of scope
 }}}

 Interestingly, with HEAD (2aee41960aa00fe09a2cd1983e02c15e06013037), it
 hits an assert from #11371.
 {{{
 =====> T3220(profasm) 12 of 21 [0, 11, 0]
 cd ./indexed-types/should_compile &&  "/home/thomas/ghc-
 validate/inplace/test   spaces/ghc-stage2" -c T3220.hs -fforce-recomp
 -dcore-lint -dcmm-lint -dno-debug-output -no-user-package-db -rtsopts
 -fno-warn-tabs -fno-warn-missed-specialisations -fno-ghci-history  -O
 -prof -static -auto-all  > T3220.comp.stderr 2>&1
 Compile failed (status 256) errors were:
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.1.20160221 for x86_64-unknown-linux):
         ASSERT failed!
   CallStack (from HasCallStack):
   assertPprPanic, called at compiler/types/TyCoRep.hs:1942:51 in
 ghc:TyCoRep
   checkValidSubst, called at compiler/types/TyCoRep.hs:2076:17 in
 ghc:TyCoRep
   substCo, called at compiler/coreSyn/CoreSubst.hs:605:20 in ghc:CoreSubst
   in_scope InScope {x_axS m_axT $caction_a1dp $caction_a1dR right
                     right' foo bar $tcFoo $tc'C:Foo $fFooFloat $fFooInt
 $trModule
                     a_s1fZ a_s1g0 a_s1g1 a_s1g2}
   tenv [aTT :-> Float, aTV :-> Float, aTW :-> Float]
   cenv []
   tys []
   cos [Sub (Sym cobox_aU6)]
   needInScope [aU6 :-> cobox_aU6]

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

 This is a regression from 7.10.3. Setting priority=highest.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11644
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