Optimization works for Word but not Word32 or Word64
GHC 7.6.1 fails to properly optimize some code when explicitly specifying word size, that optimizes properly for Word.
I have also tested this in 7.4.2 and it works properly.
An example program:
import Criterion.Main
import Control.Monad.Writer
import Data.Bits
import Data.List
import Data.Word
bitByBitCopy :: Word -> Word
bitByBitCopy w = foldl' f 0 [0 .. bitSize w - 1]
where f acc n = if w `testBit` n then acc `setBit` n else acc
bitByBitCopy32 :: Word32 -> Word32
bitByBitCopy32 w = foldl' f 0 [0 .. bitSize w - 1]
where f acc n = if w `testBit` n then acc `setBit` n else acc
bitByBitCopy64 :: Word64 -> Word64
bitByBitCopy64 w = foldl' f 0 [0 .. bitSize w - 1]
where f acc n = if w `testBit` n then acc `setBit` n else acc
-- Bench
wbench :: Benchmarkable b => String -> b -> Writer [Benchmark] ()
wbench s b = tell [bench s b]
main = defaultMain . execWriter $ do
wbench "Word" $ nf bitByBitCopy 0
when (bitSize (0::Word) == 32) $
wbench "Word32" $ nf bitByBitCopy32 0
when (bitSize (0::Word) == 64) $
wbench "Word64" $ nf bitByBitCopy64 0
Trac metadata
Trac field | Value |
---|---|
Version | 7.6.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |