cvs commit: fptools/ghc/compiler/simplCore CSE.lhs

[Simon Peyton Jones]

simonpj     2004/01/08 03:53:30 PST

  Modified files:
    ghc/compiler/simplCore CSE.lhs 
  Log:
  	  ---------------------------------------
  	Fix a long-standing CSE bug with unboxed tuples
  	  ---------------------------------------
  
  		Merge to stable
  
  Consider
          case f x of
  	  (# a,b #) -> if a>0
  		       then f x -- CSE opportunity
  		       else (# b,a #)
  
   GHC 6.2's CSE pass wrongly optimised this to:
  
  	case f x of t
  	  (# a,b #) -> if a>0 then
  			  t	-- WRONG
  			else (# b,a #)
  
  (Wrong because we aren't allowed to mention a case binder for
  an unboxed-tuple case.)
  
  This commit fixes the problem.
  
  Revision  Changes    Path
  1.15      +55 -30    fptools/ghc/compiler/simplCore/CSE.lhs