ghc 8.4.1 and trac 13930
ben at smart-cactus.org
Wed May 2 04:58:21 UTC 2018
Evan Laforge <qdunkan at gmail.com> writes:
> I recently noticed that with -O1, ghc was optimizing some code
> if Trace.traceShowId "b" $ True
> then return $ Left $ Serialize.BadMagic (Serialize.magicBytes
> magic) file_magic
> else first Serialize.UnserializeError <$> Exception.evaluate
> (Serialize.decode rest)
> to always evaluate the 'else' branch. This is fixed in 8.4.2, so I'm
> pretty sure it's https://ghc.haskell.org/trac/ghc/ticket/13930
> I assume there's no point trying to get a minimal reproduction, since
> it's a known issue and fixed. Still,
> says "incorrectly optimised, resulting in space leaks".
> Maybe it should instead say "incorrectly optimised, resulting in
> taking the wrong branch in 'if' expressions"? That's a bit more
> alarming, and is a stronger "upgrade to 8.4.2" signal.
Yes, I suppose the language in the release notes does rather understate
the degree of the incorrectness.
I'll push a new version of the manual with some stronger language
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