[GHC] #991: -O option doesn't deal with par well

[GHC]

#991: -O option doesn't deal with par well
------------------------------------------------+---------------------------
    Reporter:  shelarcy at capella.freemail.ne.jp  |       Owner:                  
        Type:  bug                              |      Status:  new             
    Priority:  normal                           |   Milestone:                  
   Component:  Compiler                         |     Version:  6.6             
    Severity:  normal                           |    Keywords:  Parallel Haskell
  Difficulty:  Unknown                          |    Testcase:                  
Architecture:  Unknown                          |          Os:  Unknown         
------------------------------------------------+---------------------------
I tried to parallelize below code.

 {{{
 circleReg1 :: Frac -> Region
 circleReg1 r (Pt x y) = x*x + y*y < r*r
 }}}

 I use -threaded option with dual-CPU machine. So I saw these code upgrade
 performance very much.

 {{{
 [circleReg2] r (Pt x y) =
   let x' = (x*x)
       y' = y*y
       r' = r*r
   in
     x' `par` y' `par` r' `seq`  x' + y' < r'

 circleReg3 r (Pt x y) =
   let x' = (x*x)
       y' = y*y
       r' = r*r
       strategy = rnf x' `par` rnf y' `par` rnf r'
   in
     x' + y' < r' `demanding` strategy
 }}}

 But ... If I want to optimise my code by ghc using -O option,
 ghc notice error message like this;

 circleReg2:
 {{{
 C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ghc1572_0\ghc1572_0.hc: In function
 `scmg_entry':
 C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ghc1572_0\ghc1572_0.hc:1102: warning:
 implicit declaration of function `newSpark'
 }}}

 circleReg3:
 {{{
 C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ghc980_0\ghc980_0.hc: In function
 `Main_lvl_entry':
 C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ghc980_0\ghc980_0.hc:1097: warning:
 implicit declaration of function `newSpark'
 }}}

 and -O option makes slower above code.
 It seems that performance goes back to before parallelize, or more slowly.

 I saw this error on Windows. Power PC Mac with GHC 6.4.1 doesn't cause
 this problem ... but I don't test GHC 6.6 on Mac, so I don't know this bug
 cause only Windows or not.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/991>
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