#2463: unsafePerformIO in unused record field affects optimisations
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Reporter: claus | Owner:
Type: run-time performance bug | Status: closed
Priority: normal | Milestone:
Component: Compiler | Version: 6.9
Severity: normal | Resolution: invalid
Keywords: | Testcase:
Architecture: Unknown | Os: Unknown
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Changes (by claus):
* status: new => closed
* resolution: => invalid
Comment:
Going through the output of `-ddump-simpl`, it appears that just
mentioning `unsafePerformIO` in the slow version instead of `undefined` in
the fast version is sufficient to prevent a worker/wrapper split for
`mkQ`.
Adding an `{-# INLINE mkQ #-}` pragma makes the "slow" version as fast as
the "fast" one. GHC can't really see that the record field is unused, but
it can see that `undefined` is a lot smaller than anything else, so this
is probably not a bug, just unexpected behaviour (I used `undefined` as a
placeholder, not as a blackhole that would swallow its context; will have
to use something else next time;-).
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2463#comment:1>
GHC <http://www.haskell.org/ghc/>
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