[GHC] #10215: Optimizer has bugs regarding handling of -0.0
GHC
ghc-devs at haskell.org
Sun Mar 29 23:28:18 UTC 2015
#10215: Optimizer has bugs regarding handling of -0.0
-------------------------------------+-------------------------------------
Reporter: lerkok | Owner:
Type: bug | Status: new
Priority: high | Milestone:
Component: Compiler | Version: 7.8.3
Keywords: | Operating System: Unknown/Multiple
Architecture: | Type of failure: Incorrect result
Unknown/Multiple | at runtime
Test Case: | Blocked By:
Blocking: | Related Tickets: #9238
Differential Revisions: |
-------------------------------------+-------------------------------------
This is most likely related to
https://ghc.haskell.org/trac/ghc/ticket/9238
Perhaps it can be merged into that if it is indeed the case, though it'd
be good for an expert to take a look and make sure first that the culprit
is indeed the same. In any case, the program in this ticket can at least
serve as a test-case.
I observed this on 7.8.3; though I suspect the same holds in the just
released 7.10.1 as well.
For the following program:
{{{#!hs
testF :: Float -> Bool
testF x = x == 0 && not (isNegativeZero x)
testD :: Double -> Bool
testD x = x == 0 && not (isNegativeZero x)
main :: IO ()
main = do print $ testF (-0.0)
print $ testD (-0.0)
}}}
If I compile with no optimizations, then I get the correct answers:
{{{
$ /bin/rm -f a.hi a.o a; ghc -O0 a; ./a
[1 of 1] Compiling Main ( a.hs, a.o )
Linking a ...
False
False
}}}
But if I turn optimizations on, then I get:
{{{
$ /bin/rm -f a.hi a.o a; ghc -O2 a; ./a
[1 of 1] Compiling Main ( a.hs, a.o )
Linking a ...
True
True
}}}
which is just plain wrong.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10215>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
More information about the ghc-tickets
mailing list