id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
7292,Optimization works for Word but not Word32 or Word64,zuserm,igloo,"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
}}}
 ",bug,closed,high,7.8.1,Compiler,7.6.1,fixed,,,Unknown/Multiple,Unknown/Multiple,Runtime performance bug,Unknown,,,,