[GHC] #2328: Compiling DoCon with 6.8.3 has 3x slow-down compared with 6.8.2

[GHC]

#2328: Compiling DoCon with 6.8.3 has 3x slow-down compared with 6.8.2
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 Reporter:  simonpj                       |          Owner:         
     Type:  compile-time performance bug  |         Status:  new    
 Priority:  normal                        |      Milestone:  6.8.3  
Component:  Compiler                      |        Version:  6.8.2  
 Severity:  normal                        |     Resolution:         
 Keywords:                                |     Difficulty:  Unknown
 Testcase:                                |   Architecture:  Unknown
       Os:  Unknown                       |  
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Comment (by igloo):

 The problem seems to be that this patch:
 {{{
 [MERGED: Inline implication constraints
 Ian Lynagh <igloo at earth.li>**20071215163315
  Mon Nov  5 22:08:07 GMT 2007  simonpj at microsoft.com

    This patch fixes Trac #1643, where Lennart found that GHC was
 generating
    code with unnecessary dictionaries.  The reason was that we were
 getting
    an implication constraint floated out of an INLINE (actually an
 instance
    decl), and the implication constraint therefore wasn't inlined even
    though it was used only once (but inside the INLINE).  Thus we were
    getting:

          ic = \d -> <stuff>
          foo = _inline_me_ (...ic...)

    Then 'foo' gets inlined in lots of places, but 'ic' now looks a bit
    big.

    But implication constraints should *always* be inlined; they are just
    artefacts of the constraint simplifier.

    This patch solves the problem, by adding a WpInline form to the HsWrap
    type.
 }}}
 makes more things inlinable, and thus requires more space. Reverting the
 patch gets us back to 6.8.2 performance. Should I revert it in the 6.8
 branch, Simon?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2328#comment:3>
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