[GHC] #7542: GHC doesn't optimize (strict) composition with id

[GHC]

#7542: GHC doesn't optimize (strict) composition with id
---------------------------------+------------------------------------------
    Reporter:  shachaf           |       Owner:                         
        Type:  bug               |      Status:  new                    
    Priority:  normal            |   Milestone:                         
   Component:  Compiler          |     Version:  7.6.1                  
    Keywords:                    |          Os:  Unknown/Multiple       
Architecture:  Unknown/Multiple  |     Failure:  Runtime performance bug
  Difficulty:  Unknown           |    Testcase:                         
   Blockedby:                    |    Blocking:                         
     Related:                    |  
---------------------------------+------------------------------------------

Comment(by simonpj):

 The previous two commits improve the situation a bit; both were triggered
 by looking at the code from this example, thanks.

 I'm far from sure that we get perfect code now.  But I'm also convinced
 that this is the wrong way to solve this problem: check out
 [wiki:NewtypeWrappers].

 Meanwhile do have a go with HEAD and see if you get better code now.

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7542#comment:9>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler