[GHC] #14649: ghc panic: mergeSATInfo

[GHC]

#14649: ghc panic: mergeSATInfo
-------------------------------------+-------------------------------------
           Reporter:  tianxiaogu     |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 ghc panic with option `-O` and `-fstatic-argument-transformation`.
 Affected versions include 8.2.2 and HEAD (8.5.20180108)

 {{{#!hs
 {-# LANGUAGE DataKinds             #-}
 {-# LANGUAGE PartialTypeSignatures #-}
 {-# LANGUAGE PolyKinds             #-}
 {-# LANGUAGE TypeFamilies          #-}
 {-# LANGUAGE TypeOperators         #-}

 module T12844 where

 barWraper :: ('(r,r') ~ Head rngs, Foo rngs) => FooData rngs
 barWraper = bar

 bar :: (_) => FooData rngs
 bar = barWraper

 data FooData rngs

 class Foo xs where foo :: (Head xs ~ '(r,r')) => FooData xs

 type family Head (xs :: [k]) where Head (x ': xs) = x
 }}}

 Log:

 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.5.20180108 for x86_64-unknown-linux):
         mergeSATInfo
   Left:STSTSTSTSTSVSV, Right:STSTSTSTSTSVSC
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in
 ghc:Outputable
         pprPanic, called at compiler/simplCore/SAT.hs:152:20 in ghc:SAT

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

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14649>
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