Re: [GHC] #15725: Core Lint error: Trans coercion mis-match

9 Oct 2018

      #15725: Core Lint error: Trans coercion mis-match
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.6.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #15703            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Some slightly more precise tracing reveals the following:

 {{{
 opt_co4_wrap }
   Co: GRefl nominal x_X1Gk (Sym (D:R:Rep1Identity[0]) _N)
   coercionType(Co): (x_X1Gk :: Par1 a_a1FN)
                     ~# ((x_X1Gk |> Sym (D:R:Rep1Identity[0]) _N)
 :: Rep1
 Identity a_a1FN)
   ---
   Result: Sym (GRefl nominal (From1 Identity a_a1FN x_a1FO)
                    ((D:R:Rep1Identity[0] _N ; Sym (Sym
 (D:R:Rep1Identity[0]) _N)) ; Sym (D:R:Rep1Identity[0])
 _N))
   coercionType(Result): (From1 Identity a_a1FN x_a1FO :: Rep1
                                                            Identity
 a_a1FN)
                         ~# (From1 Identity a_a1FN x_a1FO :: Rep1 Identity
 a_a1FN)
 }}}

 Next step: figure out why `GRefl` is being optimized so crap-tacularly.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15725#comment:2
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