Faulty Word64 arithmetic if optimized
The following program produces different results depending on optimization:
Checked.hs:
module Checked ((.-.)) where
(.-.) :: (Bounded a, Integral a) => a -> a -> Maybe a
x .-. y | x >= 0 && y < 0 = if z > x then Just z
else Nothing
| x >= 0 = if z <= x then Just z
else Nothing
| x < 0 && y > 0 = if z < x then Just z
else Nothing
| otherwise = Just z
where z = x - y
Main.hs:
module Main (main) where
import Data.Maybe
import Data.Word
import Numeric
import Checked
main :: IO ()
main = print $ showHex (fromJust ((0xFFFFFFFF00000000 :: Word64) .-. 0x00000000FFFFFFFF)) ""
D:\dev\haskell\ch1>ghc --make Checked.hs Main.hs
[1 of 2] Compiling Checked ( Checked.hs, Checked.o )
[2 of 2] Compiling Main ( Main.hs, Main.o )
Linking Main.exe ...
D:\dev\haskell\ch1>Main.exe
"fffffffe00000001"
D:\dev\haskell\ch1>del *.hi *.o *.exe
D:\dev\haskell\ch1>ghc --make -O2 Checked.hs Main.hs
[1 of 2] Compiling Checked ( Checked.hs, Checked.o )
[2 of 2] Compiling Main ( Main.hs, Main.o )
Linking Main.exe ...
D:\dev\haskell\ch1>Main.exe
"fffe00000001"
D:\dev\haskell\ch1>
The bug disappears if definition and usage of (.-.) are in the same module.
Trac metadata
Trac field | Value |
---|---|
Version | 7.4.2 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |