[GHC] #13623: join points produce bad code for stream fusion

[GHC]

#13623: join points produce bad code for stream fusion
-------------------------------------+-------------------------------------
        Reporter:  choenerzs         |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.2.1-rc1
      Resolution:                    |             Keywords:  JoinPoints
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 choenerzs):

 Pure conjecture: `$wfoldlM'_loop_s1U8` takes `SPEC` and should probably
 then not be a join point. On the other hand, the `vector` people probably
 need join points to happen if they want to remove `Skip` from from the
 `Step` data type.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13623#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler