#3717: Superfluous seq no eliminated
---------------------------------+------------------------------------------
Reporter: rl | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.13 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
---------------------------------+------------------------------------------
Program:
{{{
foo :: Int -> Int
foo 0 = 0
foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
}}}
GHC generates this code:
{{{
T.$wfoo =
\ (ww_slm :: GHC.Prim.Int#) ->
case ww_slm of ds_XkE {
__DEFAULT ->
case case GHC.Prim.<# ds_XkE 5 of _ {
GHC.Bool.False -> lvl1_rlG; GHC.Bool.True -> lvl_rlE
}
of _ { __DEFAULT ->
T.$wfoo (GHC.Prim.-# ds_XkE 1)
};
0 -> 0
}
}}}
Note that the seq is still there although it is a nop. This actually
occurs in stream fusion code.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3717>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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