Re: [GHC] #1957: Program that runs slower with optimizations on

[GHC]

#1957: Program that runs slower with optimizations on
--+-
 Reporter:  clanehin  |  Owner:   
 Type:  bug   | Status:  closed   
 Priority:  normal|  Milestone:   
Component:  Compiler  |Version:  6.8.1
 Severity:  normal| Resolution:  duplicate
 Keywords:| Difficulty:  Unknown  
 Testcase:|   Architecture:  x86  
   Os:  Linux |  
--+-
Comment (by igloo):

 `-fno-state-hack` does cure it:
 {{{
 -O0: 15.91s
 -O2: 60.95s
 -O2 -fno-state-hack: 6.23s
 }}}

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Re: [GHC] #1957: Program that runs slower with optimizations on

[GHC]

#1957: Program that runs slower with optimizations on
--+-
 Reporter:  clanehin  |  Owner:   
 Type:  bug   | Status:  closed   
 Priority:  normal|  Milestone:   
Component:  Compiler  |Version:  6.8.1
 Severity:  normal| Resolution:  duplicate
 Keywords:| Difficulty:  Unknown  
 Testcase:|   Architecture:  x86  
   Os:  Linux |  
--+-
Comment (by simonpj):

 Trying with `-fno-state-hack` (a static flag) would tell you if this was
 the same as #1168. Does that cure it?

 Simon

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Re: [GHC] #1957: Program that runs slower with optimizations on

[GHC]

#1957: Program that runs slower with optimizations on
--+-
 Reporter:  clanehin  |  Owner:   
 Type:  bug   | Status:  closed   
 Priority:  normal|  Milestone:   
Component:  Compiler  |Version:  6.8.1
 Severity:  normal| Resolution:  duplicate
 Keywords:| Difficulty:  Unknown  
 Testcase:|   Architecture:  x86  
   Os:  Linux |  
--+-
Changes (by simonmar):

  * status:  new => closed
  * resolution:  => duplicate

Comment:

 This is the same as #1168 (but I'll add an xref from there, more examples
 are always useful).

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Re: [GHC] #1957: Program that runs slower with optimizations on

[GHC]

#1957: Program that runs slower with optimizations on
--+-
 Reporter:  clanehin  |  Owner: 
 Type:  bug   | Status:  new
 Priority:  normal|  Milestone: 
Component:  Compiler  |Version:  6.8.1  
 Severity:  normal| Resolution: 
 Keywords:| Difficulty:  Unknown
 Testcase:|   Architecture:  x86
   Os:  Linux |  
--+-
Comment (by dons):

 Looks like the printFib is messing with the inlining:

 Across 2 modules, -O2 and -O are 5x slower than -Onot.
 In a single module, -O2 wins easily.

 Something fishy going on.

 Looking at the unfolding in the .hi file for NaiveFib.hs:

 {{{
 interface main:NaiveFib 3 608120071117 where
 export main:NaiveFib naiveFib printFib
 module dependencies:
 package dependencies: base
 orphans: base:GHC.Base
 family instance modules:
 3 printFib :: GHC.Num.Integer -> GHC.IOBase.IO ()
 {- Arity: 2 Strictness: LL
Unfolding: (NaiveFib.a
  `cast`
(GHC.Num.Integer -> sym ((GHC.IOBase.:CoIO) ( -}
 3 naiveFib :: GHC.Num.Integer -> GHC.Num.Integer
 {- Arity: 1 HasNoCafRefs Strictness: S -}
 3 a :: GHC.Num.Integer
-> GHC.Prim.State# GHC.Prim.RealWorld
-> (# GHC.Prim.State# GHC.Prim.RealWorld, () #)
 {- Arity: 2 Strictness: LL
Unfolding: (\ x :: GHC.Num.Integer eta :: GHC.Prim.State#
 GHC.Prim.RealWorld ->
case @ (# GHC.Prim.State# GHC.Prim.RealWorld, () #)
 GHC.IO.a24
 GHC.Handle.stdout
 (GHC.Num.$wshowsPrec
 0
 (NaiveFib.naiveFib x)
 (GHC.Base.[] @ GHC.Base.Char))
 eta of wild { (# new_s, a59 #) ->
GHC.IO.$wa9 GHC.Handle.stdout '\n' new_s }) -}
 vectorised variables:
 vectorised tycons:
 vectorised reused tycons:
 }}}

 Looks like the print is mucking up the optimiser a bit?
 Let's try moving the printFib line into Main.hs:

 {{{
 $ time ./Main-O2
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 ./Main-O2  2.99s user 0.01s system 99% cpu 3.028 total
 }}}

 And, its fixed if we inline printFib too:

 {{{
  printFib = print . naiveFib
  {-# INLINE printFib #-}
 }}}

 Simon, what's going on with the optimiser here?

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Re: [GHC] #1957: Program that runs slower with optimizations on

[GHC]

#1957: Program that runs slower with optimizations on
--+-
 Reporter:  clanehin  |  Owner: 
 Type:  bug   | Status:  new
 Priority:  normal|  Milestone: 
Component:  Compiler  |Version:  6.8.1  
 Severity:  normal| Resolution: 
 Keywords:| Difficulty:  Unknown
 Testcase:|   Architecture:  x86
   Os:  Linux |  
--+-
Comment (by clanehin):

 Forgot to preview.  Sorry.

 {{{

 [EMAIL PROTECTED]:~/test/optimizer-bug$ more Main.hs NaiveFib.hs
 ::
 Main.hs
 ::
 module Main
 (main)
 where

 import NaiveFib
 import Control.Monad

 main :: IO ()
 main = replicateM_ 10 (printFib 37)
 ::
 NaiveFib.hs
 ::
 module NaiveFib
 (printFib,naiveFib)
 where

 printFib :: Integer -> IO ()
 printFib = print . naiveFib

 naiveFib :: Integer -> Integer
 naiveFib 0 = 0
 naiveFib 1 = 1
 naiveFib n = naiveFib (n-1) + naiveFib (n-2)



 [EMAIL PROTECTED]:~/test/optimizer-bug$ make main-O0
 ghc-6.8.1 -O0 --make Main.hs -o main-O0
 [1 of 2] Compiling NaiveFib ( NaiveFib.hs, NaiveFib.o )
 [2 of 2] Compiling Main ( Main.hs, Main.o )
 Linking main-O0 ...
 [EMAIL PROTECTED]:~/test/optimizer-bug$ time ./main-O0
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817

 real0m34.491s
 user0m25.982s
 sys 0m0.564s
 [EMAIL PROTECTED]:~/test/optimizer-bug$ make clean
 rm -f *.hi
 rm -f *.o
 rm -f main-O2
 rm -f main-O0
 [EMAIL PROTECTED]:~/test/optimizer-bug$ make main-O2
 ghc-6.8.1 -O2 --make Main.hs -o main-O2
 [1 of 2] Compiling NaiveFib ( NaiveFib.hs, NaiveFib.o )
 [2 of 2] Compiling Main ( Main.hs, Main.o )
 Linking main-O2 ...
 [EMAIL PROTECTED]:~/test/optimizer-bug$ time ./main-O2
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817

 real1m50.331s
 user1m23.641s
 sys 0m1.008s

 }}}

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[GHC] #1957: Program that runs slower with optimizations on

[GHC]

#1957: Program that runs slower with optimizations on
-+--
Reporter:  clanehin  |   Owner:   
Type:  bug   |  Status:  new  
Priority:  normal|   Milestone:   
   Component:  Compiler  | Version:  6.8.1
Severity:  normal|Keywords:   
  Difficulty:  Unknown   |Testcase:   
Architecture:  x86   |  Os:  Linux
-+--
 This program runs significantly slower with optimization than without.

 I need two modules to manifest this bug.

 Is this a duplicate of 917/1945?  Using -fno-full-laziness does not
 mitigate the problem.

 This seems to be the opposite of 1945.  Without optimizations, there is a
 long delay and then all 10 results print at once.  With optimizations,
 there is a shorter delay between each print statement.

 module Main
 (main)
 where

 import NaiveFib
 import Control.Monad

 main :: IO ()
 main = replicateM_ 10 (printFib 37)

 module NaiveFib
 (printFib,naiveFib)
 where

 printFib :: Integer -> IO ()
 printFib = print . naiveFib

 naiveFib :: Integer -> Integer
 naiveFib 0 = 0
 naiveFib 1 = 1
 naiveFib n = naiveFib (n-1) + naiveFib (n-2)

 [EMAIL PROTECTED]:~/test/optimizer-bug$ make main-O0
 ghc-6.8.1 -O0 --make Main.hs -o main-O0
 [1 of 2] Compiling NaiveFib ( NaiveFib.hs, NaiveFib.o )
 [2 of 2] Compiling Main ( Main.hs, Main.o )
 Linking main-O0 ...
 [EMAIL PROTECTED]:~/test/optimizer-bug$ time ./main-O0
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817

 real0m34.491s
 user0m25.982s
 sys 0m0.564s

 [EMAIL PROTECTED]:~/test/optimizer-bug$ make main-O2
 ghc-6.8.1 -O2 --make Main.hs -o main-O2
 [1 of 2] Compiling NaiveFib ( NaiveFib.hs, NaiveFib.o )
 [2 of 2] Compiling Main ( Main.hs, Main.o )
 Linking main-O2 ...
 [EMAIL PROTECTED]:~/test/optimizer-bug$ time ./main-O2
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817
 24157817

 real1m50.331s
 user1m23.641s
 sys 0m1.008s

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