#3501: Error thunks not being exposed with "B" strictness
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Reporter: simonpj | Owner:
Type: run-time performance bug | Status: new
Priority: normal | Milestone: 6.14 branch
Component: Compiler | Version: 6.11
Severity: normal | Keywords:
Difficulty: Unknown | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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At the moment GHC often floats `error "urk"` to the top level (which it
should), after the strictness analyser. But since it's ''after''
strictness analysis, the exported thing doesn't have a strictness
signature saying "I am a diverging term", which in turn loses useful
optimisations in importing modules.
An example is test T3286. If you compile it with `-O --ddump-simpl`,
you'll see stuff like
{{{
case T3286b.$fFractionalLogFloat3
`cast` (CoUnsafe T3286b.LogFloat GHC.Prim.Double#
:: T3286b.LogFloat ~ GHC.Prim.Double#)
of ww2_aGk { __DEFAULT ->
(GHC.Types.D# ww2_aGk)
`cast` (sym T3286b.NTCo:LogFloat
:: GHC.Types.Double ~ T3286b.LogFloat)
}}}
But if you look at `T3286b.$fFractionalLogFloat3`, it turns out to be
bottom, so the case should be eliminated.
This is a long-standing infelicity; I'm making a ticket so I don't forget
it.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3501>
GHC <http://www.haskell.org/ghc/>
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