Local wrapper function remains in final program; result = extra closure allocation

I have a strange problem with a local function binding that is not being inlined. I've attached the repro code, build it like this:

$ ghc -O2 Haxl/Core/Monad.hs

There are several modules, but the one with the problem is Haxl/Core/Monad.hs. In particular Haxl.Core.Monad.$fApplicativeGenHaxl2, which contains this fragment:

            let {
              $wa4_s6YQ
              $wa4_s6YQ =
                \ w_s6YF _ ww1_s6YM _ _ w1_s6YI ->
                  case GHC.Prim.readMutVar# ipv7_X5Ne w1_s6YI
                  of _ { (# ipv10_X5QO, ipv11_X5QQ #) ->
                  case ipv11_X5QQ of _ {
                    Haxl.Core.Monad.IVarFull a2_a3kK -> case lvl6_r7qi of wild3_00 { };
                    Haxl.Core.Monad.IVarEmpty dt2_d4Vs ->
                      case GHC.Prim.writeMutVar#
                             ipv7_X5Ne (Haxl.Core.Monad.IVarFull w_s6YF) ipv10_X5QO
                      of s2#_a5OR { __DEFAULT ->
                      case GHC.Prim.readMutVar# dt2_d4Vs s2#_a5OR
                      of _ { (# ipv12_X5R0, ipv13_X5R2 #) ->
                      case GHC.Prim.readMutVar# ww1_s6YM ipv12_X5R0
                      of _ { (# ipv14_X5SS, ipv15_X5SU #) ->
                      letrec {
                        go_a5ti
                        go_a5ti =
                          \ ds10_a5tj ->
                            case ds10_a5tj of _ {
                              [] -> ipv15_X5SU;
                              : y_a5to ys_a5tp -> GHC.Types.: (y_a5to w_s6YF) (go_a5ti ys_a5tp)
                            }; } in
                      case go_a5ti ipv13_X5R2 of x'_a5P6 { __DEFAULT ->
                      case GHC.Prim.writeMutVar# ww1_s6YM x'_a5P6 ipv14_X5SS
                      of s2#1_a5P7 { __DEFAULT ->
                      (# s2#1_a5P7, Haxl.Core.Monad.cacheRequest6 #)
                      }
                      }
                      }
                      }
                      }
                  }
                  } } in
            let {
              a2_s6lH
              a2_s6lH =
                \ w_s6YF _ w2_s6YH w3_s6YI ->
                  case w2_s6YH
                  of _
                  { Haxl.Core.Monad.SchedState ww1_s6YL ww2_s6YM ww3_s6YN ww4_s6YO ->
                  $wa4_s6YQ w_s6YF ww1_s6YL ww2_s6YM ww3_s6YN ww4_s6YO w3_s6YI
                  } } in

I want $wa4 to be inlined at its single occurrence in a2. I believe the reason it is not being inlined is that a2 is a wrapper, but the situation seems silly because the wrapper isn't going away either, so we have a redundant closure being built (this is in my inner loop).

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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