[GHC] #7619: Make worker-wrapper unbox data families

[GHC]

#7619: Make worker-wrapper unbox data families
-------------------------------------+------------------------------------
        Reporter:  akio              |            Owner:  nomeata
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.7
      Resolution:                    |         Keywords:  type family
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by nomeata):

 This is actually simple to implement (see [a1ddb71/ghc] on branch
 `wip/T7619`), but rather ugly due to the additional passing of the
 FamInstEnv everywhere. That’s why I did not push to master yet.

 There are types `FamInstEnvs` and `FamInstEnv`, but it is not well-
 explained, only
 {{{
 type FamInstEnvs = (FamInstEnv, FamInstEnv)
      -- External package inst-env, Home-package inst-env
 }}}

 Note that `topNormaliseType_maybe` takes a `FamInstEnvs`, and I can get a
 `FamInstEnv` from the `ModGuts` and from `ExternalPackageState`.

 If I combine these as follows, am I doing the right thing?
 {{{
 doPassDFU :: (DynFlags -> FamInstEnvs -> UniqSupply -> CoreProgram ->
 CoreProgram) -> ModGuts -> CoreM ModGuts
 doPassDFU do_pass guts = do
     dflags <- getDynFlags
     us     <- getUniqueSupplyM
     hsc_env <- getHscEnv
     eps <- liftIO $ hscEPS hsc_env
     let fam_envs = (eps_fam_inst_env eps, mg_fam_inst_env guts)
     doPass (do_pass dflags fam_envs us) guts
 }}}

 And why do we need to make that distinction in the first place – it seems
 that `topNormaliseType_maybe` does not treat them differently.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7619#comment:6>
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