[GHC] #13694: CSE runs before SpecConstr

[GHC]

#13694: CSE runs before SpecConstr
-------------------------------------+-------------------------------------
           Reporter:  mpickering     |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:  SpecConstr,    |  Operating System:  Unknown/Multiple
  cse                                |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 SpecConstr can lead to more CSE opportunities. Currently CSE is run only
 once after the full laziness transformation but then not again later in
 the pipeline. Running it again after the final clean-up simplification
 might lead to smaller programs.

 One example with `-fspec-constr-keen`.

 {{{
 module Foo where

 main :: [Int]
 main = drop 1 [1,2]

 mainMODULE :: [Int]
 mainMODULE = mydrop 1 [1,2]

 mydrop :: Int -> [a] -> [a]
 mydrop 0 xs = xs
 mydrop n (x:xs) = mydrop (n-1) xs
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13694>
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