Behavior of the inliner on imported class methods

[José Pedro Magalhães]

Hi Roman,

Thanks for the suggestion, but that doesn't seem to change things.


Cheers,
Pedro

2011/1/19 Roman Leshchinskiy <rl at cse.unsw.edu.au>

> Have you tried adding another (dummy) method to the class? GHC used to have
> problems with optimising single-method classes in the past.
>
> Roman
>
>
> On 18 Jan 2011, at 10:33, José Pedro Magalhães <jpm at cs.uu.nl> wrote:
>
> Hello all,
>
> I fail to understand the behavior of the inliner in the following example:
>
> module M1 where
>>
>> class MyEnum a where myEnum :: [a]
>>
>> instance MyEnum () where myEnum = [()]
>>
>
>
>> module M2 where
>>
>> import M1
>>
>> f1 = map (\() -> 'p') [()]
>> f2 = map (\() -> 'q') myEnum
>>
>
> The generated core code for M2 with ghc-7.0.1 -O is:
>
> M2.f22 :: GHC.Types.Char
>> [GblId,
>>  Caf=NoCafRefs,
>>  Str=DmdType m,
>>  Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,
>>          ConLike=True, Cheap=True, Expandable=True,
>>          Guidance=IF_ARGS [] 1 2}]
>> M2.f22 = GHC.Types.C# 'q'
>>
>> M2.f11 :: GHC.Types.Char
>> [GblId,
>>  Caf=NoCafRefs,
>>  Str=DmdType m,
>>  Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,
>>          ConLike=True, Cheap=True, Expandable=True,
>>          Guidance=IF_ARGS [] 1 2}]
>> M2.f11 = GHC.Types.C# 'p'
>>
>> M2.f21 :: () -> GHC.Types.Char
>> [GblId,
>>  Arity=1,
>>  Caf=NoCafRefs,
>>  Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=1, Value=True,
>>          ConLike=True, Cheap=True, Expandable=True,
>>          Guidance=ALWAYS_IF(unsat_ok=True,boring_ok=True)}]
>> M2.f21 =
>>   \ (ds_dch :: ()) -> case ds_dch of _ { () -> M2.f22 }
>>
>> M2.f2 :: [GHC.Types.Char]
>> [GblId,
>>  Str=DmdType,
>>  Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=False,
>>          ConLike=False, Cheap=False, Expandable=False,
>>          Guidance=IF_ARGS [] 3 0}]
>> M2.f2 =
>>   GHC.Base.map
>>     @ () @ GHC.Types.Char M2.f21 M1.$fMyEnum()_$cmyEnum
>>
>> M2.f1 :: [GHC.Types.Char]
>> [GblId,
>>  Caf=NoCafRefs,
>>  Str=DmdType,
>>  Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,
>>          ConLike=True, Cheap=True, Expandable=True,
>>          Guidance=IF_ARGS [] 1 3}]
>> M2.f1 =
>>   GHC.Types.:
>>     @ GHC.Types.Char M2.f11 (GHC.Types.[] @ GHC.Types.Char)
>>
>
> So, why does the inliner fail to get rid of the map in f2, while correctly
> ditching it in f1? Note that using two modules is essential here: if the
> instance is in M2 (and thus becoming orphan), the inliner works "correctly".
> Adding INLINE/INLINABLE pragmas to myEnum doesn't improve things either. Is
> this a bug, or is there a reason for this behavior?
>
>
> Thanks,
> Pedro
>
> _______________________________________________
> Glasgow-haskell-users mailing list
> Glasgow-haskell-users at haskell.org
> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/glasgow-haskell-users/attachments/20110119/392d8241/attachment-0001.htm>