[GHC] #14079: Failure to do CPR in the presence of a local letrec

[GHC]

#14079: Failure to do CPR in the presence of a local letrec
-------------------------------------+-------------------------------------
        Reporter:  nomeata           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.3
      Resolution:                    |             Keywords:  JoinPoints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 Ah, in this case, this is because `certainlyWillInline` returns `True` for
 `e`, so `tryWW` will refrain from W/W’ing this function. If I mark it as
 `NOINLINE` then we get the desired code (note that the join-point has it’s
 return type changes as well:)

 {{{
 $we [InlPrag=NOINLINE] :: Int -> Int -> Int# -> Int -> (# Int, Int #)
 [LclId, Arity=4, Str=<L,U><L,U><S,U><L,U(U)>,
  Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(arity=4,unsat_ok=True,boring_ok=True)}]
 $we
   = \ (ww :: Int)
       (ww :: Int)
       (ww [Dmd=<S,U>] :: Int#)
       (w [Dmd=<L,U(U)>] :: Int) ->
       joinrec {
         $wje [InlPrag=[0], Occ=LoopBreaker] :: Int -> Int -> Int# -> (#
 Int, Int #)
         [LclId[JoinId(3)], Arity=3, Str=<L,U><L,U><S,U>,
          Unf=Unf{Src=<vanilla>, TopLvl=False, Value=True, ConLike=True,
                  WorkFree=True, Expandable=True,
 Guidance=ALWAYS_IF(arity=3,unsat_ok=True,boring_ok=True)}]
         $wje (ww :: Int) (ww :: Int) (ww [Dmd=<S,U>] :: Int#)
           = case ># ww 0# of {
               __DEFAULT -> case w of { I# y [Dmd=<S,U>] -> jump $wje ww ww
 (+# ww y) };
               1# -> (# ww, ww #)
             }; } in
       jump $wje ww ww ww
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14079#comment:1>
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