[GHC] #2273: inlining defeats seq

[GHC]

#2273: inlining defeats seq
----------------------+-----------------------------------------------------
 Reporter:  igloo     |          Owner:  igloo  
     Type:  merge     |         Status:  new    
 Priority:  normal    |      Milestone:         
Component:  Compiler  |        Version:  6.9    
 Severity:  normal    |     Resolution:         
 Keywords:            |     Difficulty:  Unknown
 Testcase:            |   Architecture:  Unknown
       Os:  Unknown   |  
----------------------+-----------------------------------------------------
Changes (by simonpj):

  * owner:  => igloo
  * type:  bug => merge

Comment:

 Fixed by
 {{{
 Fri May 16 09:51:49 GMT Daylight Time 2008  simonpj at microsoft.com
   * Improve the treatment of 'seq' (Trac #2273)

   Trac #2273 showed a case in which 'seq' didn't cure the space leak
   it was supposed to.  This patch does two things to help

   a) It removes a now-redundant special case in Simplify, which
      switched off the case-binder-swap in the early stages.  This
      isn't necessary any more because FloatOut has improved since
      the Simplify code was written.  And switching off the binder-swap
      is harmful for seq.

   However fix (a) is a bit fragile, so I did (b) too:

   b) Desugar 'seq' specially.  See Note [Desugaring seq (2)] in DsUtils
      This isn't very robust either, since it's defeated by abstraction,
      but that's not something GHC can fix; the programmer should use
      a let! instead.


     M ./compiler/basicTypes/MkId.lhs -6 +14
     M ./compiler/deSugar/DsUtils.lhs -9 +44
     M ./compiler/simplCore/Simplify.lhs -12 +15
 }}}
 Most of the new lines are comments!

 I believe this could usefully be moved to the branch too.

 I wonder if it'd be worth a test in `eyeball`?

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2273#comment:2>
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