#4924: bizarre strictness analysis bug
---------------------------------+------------------------------------------
Reporter: simonmar | Owner:
Type: bug | Status: new
Priority: high | Milestone: 7.2.1
Component: Compiler | Version: 7.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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This module:
{{{
module Test where
f :: Int -> Int -> Int
f 0 t = t
f i t = f (i-1) (t+1)
g :: Int -> Int -> Int
g 0 t = t
g i t = g (i-1) (t+1)
}}}
contains two identical functions, `f` and `g`. If we compile with `-O2
-dverbose-core2core` using HEAD, GHC derives different strictness for
them:
{{{
Test.f [Occ=LoopBreaker]
:: GHC.Types.Int -> GHC.Types.Int -> GHC.Types.Int
...
Str=DmdType U(L)U(L)m,
Test.g [Occ=LoopBreaker]
:: GHC.Types.Int -> GHC.Types.Int -> GHC.Types.Int
...
Str=DmdType U(L)L,
}}}
The strictness on `g` is wrong (it should be strict in both arguments).
What is even more bizarre is that if you DELETE `f`, then `g` gets the
correct strictness!
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4924>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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