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  • Glasgow Haskell CompilerGlasgow Haskell Compiler
  • GHCGHC
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  • #10215
Closed
Open
Issue created Mar 29, 2015 by Levent Erkök@LeventErkokReporter

Optimizer has bugs regarding handling of -0.0

This is most likely related to #9238 (closed)

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:

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.

Trac metadata
Trac field Value
Version 7.8.3
Type Bug
TypeOfFailure OtherFailure
Priority high
Resolution Unresolved
Component Compiler
Test case
Differential revisions
BlockedBy
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Blocking
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