#4930: Case-of-case not eliminated when it could be
---------------------------------+------------------------------------------
Reporter: rl | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.1 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
---------------------------------+------------------------------------------
Small example:
{{{
foo :: Int -> Int
foo n = (if n < 5 then error "Too small" else n+2) `seq` n+5
}}}
GHC produces this:
{{{
foo =
\ (w_slQ :: Int) ->
case w_slQ of _ { I# ww_slT ->
case case <# ww_slT 5 of _ {
False -> case +# ww_slT 2 of sat_sm1 { __DEFAULT -> I# sat_sm1
};
True -> foo1
}
of _ { I# _ ->
case +# ww_slT 5 of sat_sm4 { __DEFAULT -> I# sat_sm4 }
}
}
}}}
It ought to produce something like this instead:
{{{
foo n = case n of I# n# ->
case n# <# 5 of
True -> foo1
False -> I# (n# +# 5)
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4930>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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