#5779: SPECIALISE pragma generates wrong activations
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Reporter: rl | Owner:
Type: bug | Status: closed
Priority: normal | Milestone:
Component: Compiler | Version: 7.5
Resolution: invalid | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: Runtime performance bug | Difficulty: Unknown
Testcase: | Blockedby:
Blocking: | Related:
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Changes (by simonpj):
* status: new => closed
* difficulty: => Unknown
* resolution: => invalid
Comment:
On the contrary it's vital that specialisations don't kick in too early.
Imagine that `foo` had a rule
{{{
RULE "foo/bar" forall x. foo (bar x) = x
}}}
You put a NOINLINE pragma on `foo` to make sure it isn't inlined too
early, to make sure that the RULE gets to fire. But you'd be annoyed if
the SPECIALISE pragma rewrite `foo` to `foo_spec`, and thereby stopped the
RULE firing!
Happily you can add a phase to the SPECIALISE pragma, thus:
{{{
{-# SPECIALISE [1] foo :: Int -> Int #-}
}}}
which should let you do as you want. This behaviour, and the override
mechanism, are documented:
http://www.haskell.org/ghc/dist/current/docs/html/users_guide/pragmas.html
#specialize-pragma. If the documenation is unclear (all too possible)
could you suggest better wording? Thanks.
Simon
Yell if that doesn't do the job
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5779#comment:1>
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