[GHC] #15176: Superclass `Monad m =>` makes program run 100 times slower

[GHC]

#15176: Superclass `Monad m =>` makes program run 100 times slower
-------------------------------------+-------------------------------------
        Reporter:  danilo2           |                Owner:  osa1
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.4.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 No no, don't do that!! Here are the big hitters in the `.ticky` files
 {{{
 ==== Without Monad m (original.ticky) =========

            15000000  984000000          0   2 SS                   vx{v
 s21YX} (main:Main) (fun) in r1YhB
             9000000  520000000          0   4 pSSS
 $w$dLayersFoldableBuilder__{v r1YhB} (main:Main) (fun)
            24000000  320000000          0   3 SpM
 main:Main.$w$sgo1{v r19} (fun)
            16000000  240000000          0   3 SpM
 main:Main.$w$sgo3{v r1a} (fun)
             4000000  232000000          0   2 SS
 sat_s2229{v} (main:Main) (fun) in r1YhB
             3000000  144000000          0   2 SS
 sat_s21Zw{v} (main:Main) (fun) in s21YX
             9000000   72000000          0  46 ++++++++++++++++++++ luna-
 core-0.0.6-inplace:Luna.IR.Term.$fStorable1UniTerm10{v rihy9} (fun)
             1000000   48000000          0   2 SS
 lvl1355{v r1Yhx} (main:Main) (fun)
             2000000   32000000          0   2 SI
 lvl1206{v r1Yf3} (main:Main) (fun)
             2000000   32000000          0   1 M                    luna-
 core-0.0.6-inplace:Luna.IR.Term.$WUniTermVar{v rihwq} (fun)
             1000000   24000000          0   2 SI
 lvl1176{v r1Yez} (main:Main) (fun)
             1000000   24000000          0   1 M                    luna-
 core-0.0.6-inplace:Luna.IR.Term.$WUniTermUnify{v rihwr} (fun)


 =========== With Monad m (patched.ticky) ==============
            60000000 2496000000          0   7 +++++M.              luna-
 core-0.0.6-inplace:Data.Graph.Fold.Deep.$fLayerBuilderDeepmType_$clayerBuild{v
 rGoW} (fun)
            36000000 1584000000          0   3 >S.
 $s$fFunctorStateT_$cfmap{v rmuaf} (luna-
 core-0.0.6-inplace:OCI.Pass.Definition.Class) (fun)
            24000000 1152000000          0   1 S
 sat_s2hor{v} (main:Main) (fun) in r2gUO
            20000000  960000000          0   1 S
 sat_s2hqt{v} (main:Main) (fun) in r2gVh
             6000000  480000000          0   3 pSS                  $wlvl{v
 r2gUO} (main:Main) (fun)
             5000000  400000000          0   3 pSS
 $wlvl3{v r2gVh} (main:Main) (fun)
             8000000  384000000          0   1 S
 sat_s2hoV{v} (main:Main) (fun) in r2gUQ
             6000000  384000000          0   3 SSS
 $s$fReadertlayerm_$cread__3{v r2hmG} (main:Main) (fun)
             6000000  384000000          0   3 SSS
 $s$fReadertlayerm_$cread__2{v r2hmw} (main:Main) (fun)
            24000000  320000000          0   3 SpM
 main:Main.$w$sgo3{v r8e} (fun)
             6000000  288000000          0   3 .SS                  luna-
 core-0.0.6-inplace:OCI.Pass.Definition.Class.$fApplicativePass5{v rmu8N}
 (fun)
            12000000  288000000          0   2 .S                   lvl1{v
 rmual} (luna-core-0.0.6-inplace:OCI.Pass.Definition.Class) (fun)
            16000000  240000000          0   3 SpM
 main:Main.$w$sgo1{v r8b} (fun)
             2000000  160000000          0   3 pSS
 $wlvl1{v r2gUQ} (main:Main) (fun)
             8000000  120000000          0   7 ++++++M
 $w$cbuild1{v riLVV} (luna-core-0.0.6-inplace:Luna.IR.Term) (fun)
             9000000   96000000          0   3 SSM
 sat_sHlw{v} (luna-core-0.0.6-inplace:Data.Graph.Fold.Deep) (fun) in rGoW
             1000000   48000000          0   2 SS
 lvl1702{v r2hn9} (main:Main) (fun)
             2000000   32000000          0   2 SI
 $cpeekByteOff1{v r3Y9N} (luna-core-0.0.6-inplace:Luna.IR.Term.Core) (fun)
             2000000   32000000          0   1 M                    luna-
 core-0.0.6-inplace:Luna.IR.Term.$WUniTermVar{v rihWA} (fun)
             1000000   32000000          0   1 .
 sat_siM5u{v} (luna-core-0.0.6-inplace:Luna.IR.Term) (fun) in riLVV

 }}}
 So we are getting a log of allocation in
 * `luna-
 core-0.0.6-inplace:Data.Graph.Fold.Deep.$fLayerBuilderDeepmType_$clayerBuild`
 * `$s$fFunctorStateT_$cfmap{v rmuaf} (luna-
 core-0.0.6-inplace:OCI.Pass.Definition.Class)`

 Also, in the original version, the big allocation is in Main.

 So I'd generate `Main.stg` and the STG files for `Data.Graph.Fold.Deep,
 and perhaps OCI.Pass.Definition.Class.` to begin with

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15176#comment:14>
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