[GHC] #10148: Optimization causes repeated computation

[GHC]

#10148: Optimization causes repeated computation
-------------------------------------+-------------------------------------
        Reporter:  akio              |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1-rc1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by simonpj):

 Akio, good work.  But I would be reluctant to zap demand info:
  * Occurrence info is syntactic, and changes often, so needs to be zapped
  * Demand info is (supposed to be) semantic, and so should not change,
 except that the demand might get stronger; it is a static analysis after
 all.

 So my diagnosis is that the demand analyser is wrong.  Consider

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10148#comment:9>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler