[GHC] #10527: Panic Simplifier ticks exhausted with type families

[GHC]

#10527: Panic Simplifier ticks exhausted with type families
-------------------------------------+-------------------------------------
        Reporter:  sopvop            |                   Owner:  bgamari
            Type:  bug               |                  Status:  new
        Priority:  highest           |               Milestone:  7.10.2
       Component:  Compiler          |                 Version:  7.10.1-rc1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by bgamari):

 Another thing I have noticed is that the good commit considers some
 inlining contexts to be `RuleArgCtxts` which the bad commits considers
 `BoringCtxt`. This difference may be due to the good commit's eagerness to
 inline `$fFoldableIndentity2` and friends.

 Consider, for instance, this inlinig which occurs in a `RuleArgCtxt`
 (which directly follows an inlining of `fFoldableIdentity2`),

 {{{#!hs
 Considering inlining: $s$crsubset_s2eb
   arg infos [ValueArg, ValueArg, TrivArg]
   interesting continuation RuleArgCtxt
   some_benefit True
   is exp: True
   is work-free: True
   guidance IF_ARGS [30 60 0] 70 0
   discounted size = -105
   ANSWER = YES
 Inlining done: $s$crsubset
     Inlined fn:  \ (@ (g :: * -> *))
                    ($dFunctor_a211 [Occ=Once] :: GHC.Base.Functor g)
                    (eta_B2 [Occ=Once!] :: Bug.Rec '[] -> g (Bug.Rec '[]))
                    (eta_B1 [Occ=OnceL]
                       :: Bug.Rec
                            '["id" Bug.:-> Bug.Expr GHC.Types.Int,
                              "id" Bug.:-> Bug.Expr GHC.Types.Int,
                              "event_type" Bug.:-> Bug.Expr GHC.Types.Int,
                              "field1" Bug.:-> Bug.Expr GHC.Types.Int]) ->
                    GHC.Base.fmap
                      @ g
                      $dFunctor_a211
                      @ (Bug.Rec '[])
                      @ (Bug.Rec
                           '["id" Bug.:-> Bug.Expr GHC.Types.Int,
                             "id" Bug.:-> Bug.Expr GHC.Types.Int,
                             "event_type" Bug.:-> Bug.Expr GHC.Types.Int,
                             "field1" Bug.:-> Bug.Expr GHC.Types.Int])
                      (\ _ [Occ=Dead] -> eta_B1)
                      (eta_B2 Bug.$WRNil)
     Cont:   ApplyToTy Data.Functor.Identity.Identity
             ApplyToVal nodup Data.Functor.Identity.$fFunctorIdentity
             ApplyToVal nodup ((\ _ [Occ=Dead] -> rs `cast` ...) `cast`
 ...)
             ApplyToVal nodup eta_B1
             CastIt Nth:1
                      ((forall a4.
                        <Data.Functor.Identity.Identity a4>_R
                        -> Data.Functor.Identity.NTCo:Identity[0]
 <a4>_R)@Bug.Rec
 '["id"
 Bug.:-> Bug.Expr
 GHC.Types.Int,
 "id"
 Bug.:-> Bug.Expr
 GHC.Types.Int,
 "event_type"
 Bug.:-> Bug.Expr
 GHC.Types.Int,
 "field1"
 Bug.:-> Bug.Expr
 GHC.Types.Int])
             Stop[RuleArgCtxt] Bug.Rec
                                 '["id" Bug.:-> Bug.Expr GHC.Types.Int,
                                   "id" Bug.:-> Bug.Expr GHC.Types.Int,
                                   "event_type" Bug.:-> Bug.Expr
 GHC.Types.Int,
                                   "field1" Bug.:-> Bug.Expr GHC.Types.Int]
 }}}

 Compared to the bad commit, which has not yet inlined
 `$fFoldableIdentity2` and does the same inlining in roughly the same
 context (up to some casts),

 {{{#!hs
 Considering inlining: $s$crsubset_s2eb
   arg infos [ValueArg, ValueArg, TrivArg]
   interesting continuation BoringCtxt
   some_benefit True
   is exp: True
   is work-free: True
   guidance IF_ARGS [30 60 0] 70 0
   discounted size = -105
   ANSWER = YES
 Inlining done: $s$crsubset
     Inlined fn:  \ (@ (g :: * -> *))
                    ($dFunctor_a211 [Occ=Once] :: GHC.Base.Functor g)
                    (eta_B2 [Occ=Once!] :: Bug.Rec '[] -> g (Bug.Rec '[]))
                    (eta_B1 [Occ=OnceL]
                       :: Bug.Rec
                            '["id" Bug.:-> Bug.Expr GHC.Types.Int,
                              "id" Bug.:-> Bug.Expr GHC.Types.Int,
                              "event_type" Bug.:-> Bug.Expr GHC.Types.Int,
                              "field1" Bug.:-> Bug.Expr GHC.Types.Int]) ->
                    GHC.Base.fmap
                      @ g
                      $dFunctor_a211
                      @ (Bug.Rec '[])
                      @ (Bug.Rec
                           '["id" Bug.:-> Bug.Expr GHC.Types.Int,
                             "id" Bug.:-> Bug.Expr GHC.Types.Int,
                             "event_type" Bug.:-> Bug.Expr GHC.Types.Int,
                             "field1" Bug.:-> Bug.Expr GHC.Types.Int])
                      (\ _ [Occ=Dead] -> eta_B1)
                      (eta_B2 Bug.$WRNil)
     Cont:   ApplyToTy Data.Functor.Identity.Identity
             ApplyToVal nodup Data.Functor.Identity.$fFunctorIdentity
             ApplyToVal nodup ((\ _ [Occ=Dead] -> rs) `cast` ...)
             ApplyToVal nodup eta_B1
             Stop[BoringCtxt] Data.Functor.Identity.Identity
                                (Bug.Rec
                                   '["id" Bug.:-> Bug.Expr GHC.Types.Int,
                                     "id" Bug.:-> Bug.Expr GHC.Types.Int,
                                     "event_type" Bug.:-> Bug.Expr
 GHC.Types.Int,
                                     "field1" Bug.:-> Bug.Expr
 GHC.Types.Int])
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10527#comment:16>
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