Re: [Haskell-cafe] Re: Profiling nested case
Done. http://hackage.haskell.org/trac/ghc/ticket/2465 -- ryan On 7/23/08, Simon Peyton-Jones [EMAIL PROTECTED] wrote: | I had similar experiences as you when attempting to write high | performance Haskell; the language makes you want to use high-level | abstracted functions but the optimizer (while amazing, to be honest) | seems to miss a few cases that it seems like it should hit. Ryan, if you find any of these, do please submit them to GHC's Trac bug-tracker. There's a special category for performance bugs. Small programs of the form GHC should hit this, but doesn't are incredibly useful. Thanks Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Re: Profiling nested case
| I had similar experiences as you when attempting to write high | performance Haskell; the language makes you want to use high-level | abstracted functions but the optimizer (while amazing, to be honest) | seems to miss a few cases that it seems like it should hit. Ryan, if you find any of these, do please submit them to GHC's Trac bug-tracker. There's a special category for performance bugs. Small programs of the form GHC should hit this, but doesn't are incredibly useful. Thanks Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Profiling nested case
I had similar experiences as you when attempting to write high performance Haskell; the language makes you want to use high-level abstracted functions but the optimizer (while amazing, to be honest) seems to miss a few cases that it seems like it should hit. The problem seems to be that the compiler is extremely good at optimizing systems-level code, but that any control-structure function needs to be extremely inlined to be successful. You might try re-writing sequence or foldM a few different ways using the same test function and see what you can get. One thing that I notice about this code is that if you switch Right and Left you will get the default behavior for the Either monad: worldSceneSwitch point = case redSphere (0,50,0) 50 point of v@(Left _) - v Right d1 - case greenSphere (25,-250,0) 50 point of v@(Left _) - v Right d2 - Right $ d1 `min` d2 is the same as worldSceneSwitch point = do d1 - redSphere (0, 50, 0) 50 point d2 - greenSphere (25, -250, 0) 50 point Right (d1 `min` d2) Here is the same concept using foldM: minimumM (x : xs) = do v0 - x foldM (return . min) v0 xs worldSceneSwitch point = minimumM [ redSphere (0, 50, 0) 50 point, greenSphere (25, -250, 0) 50 point ] However, the performance here will be terrible if minimumM and foldM do not get sufficiently inlined; you do not want to be allocating list thunks just to execute them shortly thereafter. -- ryan On Sat, Jul 19, 2008 at 6:48 AM, Mitar [EMAIL PROTECTED] wrote: Hi! I had to change code somewhat. Now I have a function like: worldScene point = case redSphere (0,50,0) 50 point of v@(Right _) - v Left d1 - case greenSphere (25,-250,0) 50 point of v@(Right _) - v Left d2 - Left $ d1 `min` d2 (Of course there could be more objects.) Any suggestion how could I make this less hard-coded? Something which would take a list of objects (object functions) and then return a Right if any object function return Right or a minimum value of all Lefts. But that it would have similar performance? If not on my GHC version (6.8.3) on something newer (which uses fusion or something). Is there some standard function for this or should I write my own recursive function to run over a list of object functions? But I am afraid that this will be hard to optimize for compiler. (It is important to notice that the order of executing object functions is not important so it could be a good candidate for parallelism.) Mitar ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Profiling nested case
Hi! I had to change code somewhat. Now I have a function like: worldScene point = case redSphere (0,50,0) 50 point of v@(Right _) - v Left d1 - case greenSphere (25,-250,0) 50 point of v@(Right _) - v Left d2 - Left $ d1 `min` d2 (Of course there could be more objects.) Any suggestion how could I make this less hard-coded? Something which would take a list of objects (object functions) and then return a Right if any object function return Right or a minimum value of all Lefts. But that it would have similar performance? If not on my GHC version (6.8.3) on something newer (which uses fusion or something). Is there some standard function for this or should I write my own recursive function to run over a list of object functions? But I am afraid that this will be hard to optimize for compiler. (It is important to notice that the order of executing object functions is not important so it could be a good candidate for parallelism.) Mitar ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Profiling nested case
Mitar wrote: On Fri, Jul 18, 2008 at 3:54 PM, Chaddaï Fouché [EMAIL PROTECTED] wrote: So that I can easily change the type everywhere. But it would be much nicer to write: data Quaternion a = Q !a !a !a !a deriving (Eq,Show) Only the performance of Num instance functions of Quaternion is then quite worse. You can probably use a specialization pragma to get around that. But why is this not automatic? If I use Quaternions of only one type in the whole program then why it does not make specialized version for it? At least with -O2 switch. You could try jhc: it does whole program optimization. Ghc compiles each module separately. Cheers Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Profiling nested case
ben.franksen: Mitar wrote: On Fri, Jul 18, 2008 at 3:54 PM, Chaddaï Fouché [EMAIL PROTECTED] wrote: So that I can easily change the type everywhere. But it would be much nicer to write: data Quaternion a = Q !a !a !a !a deriving (Eq,Show) Only the performance of Num instance functions of Quaternion is then quite worse. You can probably use a specialization pragma to get around that. But why is this not automatic? If I use Quaternions of only one type in the whole program then why it does not make specialized version for it? At least with -O2 switch. You could try jhc: it does whole program optimization. Ghc compiles each module separately. No need to switch compilers. GHC is able to do a pretty good job. Consider, data Q a = Q !a !a !a !a deriving (Eq,Show) -- yeah, polymorphic go :: Num a = Q a - Q a go (Q 0 0 0 0) = Q 1 2 3 4 go (Q a b c d) = go $! Q (a * a) (b * b) (c * c) (d * d) -- ah, but we fix it. type QI = Q Int -- and try that: main = print (go (Q 2 3 7 13 :: QI)) GHC specialises and gives us, $wgo :: Int# - Int# - Int# - Int# - Q Int So just use ghc-core to check what you're getting. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
