#5550: GHC infinite loop when compiling vector
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Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.2.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by rl):
Here is what the #4448 example would look like with !ForceSpecConstr:
{{{
import GHC.Exts ( SpecConstrAnnotation(..) )
data SPEC = SPEC | SPEC2
{-# ANN type SPEC ForceSpecConstr #-}
foo :: Int -> Int -> Int -> (Int,Int)
foo !a !b !c = loop SPEC (Left (a,b))
where
loop :: SPEC -> Either (Int,Int) (Int, (Int,Int)) -> (Int,Int)
loop SPEC (Left (!x,!n))
| n > 0 = loop SPEC (Right (x,(x+c,n-1)))
| otherwise = (x,n)
loop SPEC (Right (i,t))
| i < c = loop SPEC (Right (i+1,t))
| otherwise = loop SPEC (Left t)
}}}
I think there is a misunderstanding here. Specialising on `SPEC` isn't the
problem, that happens anyway. It's specialising on other arguments that's
problematic. I also suggest a type-specific approach: only turn off
condition (3) for non-recursive types.
Perhaps you mean that we should use !ForceSpecConstr to mark individual
arguments? That doesn't work for a variety of reasons.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5550#comment:12>
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