patch applied (ghc-6.8/ghc): MERGED: Improve the treatment of 'seq' (Trac #2273)

[Ian Lynagh]

Wed May 21 14:20:31 PDT 2008  Ian Lynagh <igloo at earth.li>
  * MERGED: 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.
   
  simonpj at microsoft.com**20080516085149

    M ./compiler/basicTypes/MkId.lhs -6 +14
    M ./compiler/deSugar/DsUtils.lhs -9 +44
    M ./compiler/simplCore/Simplify.lhs -12 +15

View patch online:
http://darcs.haskell.org/ghc-6.8/ghc/_darcs/patches/20080521212031-3fd76-e9d9c167c83ec99b60bcf0f792ce9ff57bf4c81a.gz