Re: [GHC] #5889: -fno-prof-count-entries leads to linking errors

12 Jan 2018

      #5889: -fno-prof-count-entries leads to linking errors
-------------------------------------+-------------------------------------
        Reporter:  akio              |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.3
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:  x86_64
                                     |  (amd64)
 Type of failure:  GHC rejects       |            Test Case:
  valid program                      |  profiling/should_compile/T5889
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by osa1):

 I just checked what simplifier pass optimizes these cost centers in the
 definition site, and then checked why the same pass does not optimize the
 same way in the use site. The pass is `post-worker-wrapper`. Before the
 pass `bar` looks like this:

 {{{
 bar
   = \ (n_a1Gx :: Integer) (m_a1Gy [Dmd=] :: Maybe Integer) ->
       scc<bar>
       let {
         ds_s2rs [Dmd=] :: (Integer, Integer)
         [LclId,
          Unf=Unf{Src=<vanilla>, TopLvl=False, Value=False, ConLike=False,
                  WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 30
 0}]
         ds_s2rs
           = let {
               ds_s2rs [Dmd=] :: (Integer, Integer)
               [LclId,
                Unf=Unf{Src=<vanilla>, TopLvl=False, Value=False,
 ConLike=False,
                        WorkFree=False, Expandable=False, Guidance=IF_ARGS
 [] 30 0}]
               ds_s2rs = scc split n_a1Gx m_a1Gy } in
             case ds_s2rs of ww_s2sc
             { (ww_s2sd [Dmd=], ww_s2se [Dmd=]) ->
                 (ww_s2sd, ww_s2se)
             } in
       plus_noinline
         (scc
          case ds_s2rs of { (y_a2pz [Dmd=], z_a2pB [Dmd=]) ->
          y_a2pz
          })
         (scc
          case ds_s2rs of { (y_a2pz [Dmd=], z_a2pB [Dmd=]) ->
          z_a2pB
          })
 }}}

 after:

 {{{
 bar
   = \ (n_a1Gx :: Integer) (m_a1Gy :: Maybe Integer) ->
       scc<bar>
       case scc split n_a1Gx m_a1Gy of
       { (ww_s2sd [Dmd=], ww_s2se [Dmd=]) ->
       plus_noinline ww_s2sd ww_s2se
       }
 }}}

 The same pass in `A` does nothing. The program before and after the pass
 looks like this:

 {{{
 ds_s4uU :: (Integer, Integer)
 [LclId,
  Unf=Unf{Src=<vanilla>, TopLvl=True, Value=False, ConLike=False,
          WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 50 30}]
 ds_s4uU
   = scc<bar>
     scc
     case B.$wsplit n_s4uS (GHC.Base.Nothing @ Integer) of
     { (# ww1_s2sg, ww2_s2sh #) ->
     (ww1_s2sg, ww2_s2sh)
     }

 main_s37c :: String
 [LclId,
  Unf=Unf{Src=<vanilla>, TopLvl=True, Value=False, ConLike=False,
          WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 110 30}]
 main_s37c
   = case GHC.Show.$w$cshowsPrec4
            0#
            (scc<bar>
             plus_noinline
               (scc
                case ds_s4uU of { (y_a2pz [Dmd=], z_a2pB [Dmd=])
 ->
                y_a2pz
                })
               (scc
                case ds_s4uU of { (y_a2pz [Dmd=], z_a2pB [Dmd=])
 ->
                z_a2pB
                }))
            (GHC.Types.[] @ Char)
     of
     { (# ww3_a376, ww4_a377 #) ->
     GHC.Types.: @ Char ww3_a376 ww4_a377
     }
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/5889#comment:20
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