#4223: LLVM slower then NCG, C example
-------------------------------+--------------------------------------------
Reporter: dterei | Owner: dterei
Type: bug | Status: new
Priority: normal | Component: Compiler (LLVM)
Version: 6.12.3 | Keywords:
Os: Linux | Testcase:
Architecture: x86_64 (amd64) | Failure: Runtime performance bug
-------------------------------+--------------------------------------------
The following program is slower when compiled via the LLVM backend then
when compiled via C or NCG.
{{{
{-# LANGUAGE BangPatterns #-}
{-
ghc 6.12.1 -O2
1.752
-}
import Data.Vector.Storable
import qualified Data.Vector.Storable as V
import Foreign
import Foreign.C.Types
-- Define a 4 element vector type
data Vec4 = Vec4 {-# UNPACK #-} !CFloat
{-# UNPACK #-} !CFloat
{-# UNPACK #-} !CFloat
{-# UNPACK #-} !CFloat
------------------------------------------------------------------------
-- Ensure we can store it in an array
instance Storable Vec4 where
sizeOf _ = sizeOf (undefined :: CFloat) * 4
alignment _ = alignment (undefined :: CFloat)
{-# INLINE peek #-}
peek p = do
a <- peekElemOff q 0
b <- peekElemOff q 1
c <- peekElemOff q 2
d <- peekElemOff q 3
return (Vec4 a b c d)
where
q = castPtr p
{-# INLINE poke #-}
poke p (Vec4 a b c d) = do
pokeElemOff q 0 a
pokeElemOff q 1 b
pokeElemOff q 2 c
pokeElemOff q 3 d
where
q = castPtr p
------------------------------------------------------------------------
a = Vec4 0.2 0.1 0.6 1.0
m = Vec4 0.99 0.7 0.8 0.6
add :: Vec4 -> Vec4 -> Vec4
{-# INLINE add #-}
add (Vec4 a b c d) (Vec4 a' b' c' d') = Vec4 (a+a') (b+b') (c+c') (d+d')
mult :: Vec4 -> Vec4 -> Vec4
{-# INLINE mult #-}
mult (Vec4 a b c d) (Vec4 a' b' c' d') = Vec4 (a*a') (b*b') (c*c') (d*d')
vsum :: Vec4 -> CFloat
{-# INLINE vsum #-}
vsum (Vec4 a b c d) = a+b+c+d
multList :: Int -> Vector Vec4 -> Vector Vec4
multList !count !src
| count <= 0 = src
| otherwise = multList (count-1) $ V.map (\v -> add (mult v m) a)
src
main = do
print $ Data.Vector.Storable.sum
$ Data.Vector.Storable.map vsum
$ multList repCount
$ Data.Vector.Storable.replicate arraySize (Vec4 0 0 0 0)
repCount, arraySize :: Int
repCount = 10000
arraySize = 20000
}}}
Timings under Linux/64bit:
{{{
* fasm: 1.502s
* viac: 1.525s
* llvm: 1.853s
}}}
This isn't universal though (as in across all targets), for example we get
the following timings under these other targets:
Windows/32bit:
{{{
* fasm: 3.279s
* viac: 3.997s
* llvm: 1.932s
}}}
As for if its the 32bit or the fact that its Windows isn't known yet.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4223>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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