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

[GHC]

#11644: Core lint error in result of Specialise for TEST=T3220 WAY=optasm
-------------------------------------+-------------------------------------
        Reporter:  thomie            |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.0.1-rc2
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Compile-time      |            Test Case:
  crash                              |  simplCore/should_compile/T11644,
                                     |  indexed-
                                     |  types/should_compile/ColInference3
      Blocked By:                    |             Blocking:
 Related Tickets:  #11371, #11643    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * status:  merge => closed
 * failure:  None/Unknown => Compile-time crash
 * resolution:   => fixed


@@ -2,1 +2,1 @@
- {{{
+ {{{#!hs

New description:

 This is the code:
 {{{#!hs
 {-# 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 -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.

--

Comment:

 Merged to `ghc-8.0` as c12ae2f986d4cd59e38752da7fd7b597d6ba903e.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11644#comment:9>
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