[GHC] #14596: Remove uses of unsafeGlobalDynFlags for state hack

[GHC]

#14596: Remove uses of unsafeGlobalDynFlags for state hack
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4265
       Wiki Page:                    |
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Comment (by simonpj):

 > It seems like the logical place to put this is as a flag in TyCon.

 Yes...

 * The flag is only needed in `PrimTyCon`
 * And only used for `statePrimTyCon` (see `Id.isStateHackType`)

 The trouble is, if `statePrimTyCon` is dependent on `DynFlags`, it can't
 be top-level defines (as it is now).
 Does that matter?  Turns out that `statePrimTyCon` is used

 * In `MkId.runRWId`.  I think I can elimiante this top-level Id altogether

 * In `TysPrim.mkStatePrimTy`...

 * ...which in turn is used in `PrelRules.seqRule`.  That is easy to
 elminate; I'll submit a patch shortly.

 * ...and `TysPrim.realWorldStatePrimTy` and `MkId.realWorldPrimId`.  This
 is a bit harder; it they are used in:
   * a bunch of cases in `DsCCall`, but there is a monad to hand there, so
 that's easy to fix.
   * a couple of places in `eqType realWorldStatePrimTy`, but that doesn't
 need the tycon, only the unique
   * in `CorePrep` and `ByteCodeGen` where we are inlining `runRWId`.  I'm
 sure these would be do-able because we have an argument of type `State#`
 so the relevant `TyCon` is in there.

 In short, I think this could be done with minimal plumbing.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14596#comment:3>
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