#2439: Missed optimisation with dictionaries and loops
--------------------------------------+-------------------------------------
Reporter: rl | Owner: simonpj
Type: bug | Status: new
Priority: normal | Milestone: 6.12 branch
Component: Compiler | Version: 6.9
Resolution: | Keywords:
Difficulty: Unknown | Os: Unknown/Multiple
Testcase: | Architecture: Unknown/Multiple
Failure: Runtime performance bug |
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Comment (by rl):
I'm not sure how this translates to the new inliner. This is code that is
generated now:
{{{
Foo.sum' =
\ (@ a_aj6) ($dNum_aje :: GHC.Num.Num a_aj6) ->
let {
lit_skO [Dmd=Just L] :: a_aj6
[LclId, Str=DmdType]
lit_skO = GHC.Num.fromInteger @ a_aj6 $dNum_aje Foo.sum'1 } in
letrec {
loop_skM [Occ=LoopBreaker] :: a_aj6 -> [a_aj6] -> a_aj6
[LclId, Arity=2, Str=DmdType SS]
loop_skM =
\ (z_afp :: a_aj6) (ds_djs :: [a_aj6]) ->
case z_afp of z1_XfG { __DEFAULT ->
case ds_djs of _ {
[] -> z1_XfG;
: x_afr xs_afs ->
loop_skM (GHC.Num.+ @ a_aj6 $dNum_aje z1_XfG x_afr) xs_afs
}
}; } in
\ (xs_afu :: [a_aj6]) -> loop_skM lit_skO xs_afu
}}}
Instead of scrutinising the dictionary, we are now calling the method
selector in every iteration. Is this even worse than before?
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2439#comment:6>
GHC <http://www.haskell.org/ghc/>
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