patch applied (ghc): Don't build unnecessary lets in knownCon

[Simon Peyton Jones]

Wed Aug 16 03:48:31 PDT 2006  simonpj at microsoft.com
  * Don't build unnecessary lets in knownCon
  
  Faced with
  	case x of y { (a,b) -> rhs }
  
  where x is bound to (c,d), we were generating
  	
  	let y = (c,d) in rhs
  
  and thenn hoping to get rid of the y binding by CSE or some such.  It's
  better simply not to build it in the first place, by generating
  
  	let y = x in rhs
  
  This patch does the job.
  

    M ./compiler/simplCore/Simplify.lhs -15 +21