If the problem really is that cFloatConv is using the generic
fromRational . toRational implementation, then the correct solution is
to simply _not define cFloatConv_ and use realToFrac everywhere. GHC
already has tons of specialization rules for realToFrac. However,
rewrite rules (which are what is generated by a specialization) are
only syntactic. This, combined with the NOINLINE pragma you have on
cFloatConv, means that they are never allowed to fire.
~d
Quoting Eugene Kirpichov <ekirpic...@gmail.com>:
> Sorry for re-sending, my previous attempt got ignored by gtk2hs-devel
> mailing list as I wasn't subscribed. Now I am.
>
> On Wed, Nov 2, 2011 at 3:14 PM, Eugene Kirpichov <ekirpic...@gmail.com>wrote:
>
>> Yay!!!
>>
>> I made a small change in Types.chs and got my original cairo-binding-based
>> program to be just as blazing fast. The only problem I have with this is
>> that I used multiparameter type classes.
>>
>> Dear gtk2hs team! Is it possible to incorporate my changes? I'm pretty
>> sure people will be happy by an order-of-magnitude speedup. Probably the
>> stuff could be wrapped in #define's for those who aren't using GHC and
>> can't use multiparameter type classes?
>>
>> I am pretty sure I could have done the same with rewrite rules, but I
>> tried for a while and to no avail.
>>
>> FAILED SOLUTION: rewrite rules
>> cFloatConv :: (RealFloat a, RealFloat b) => a -> b
>> cFloatConv = realToFrac
>> {-# NOINLINE cFloatConv #-}
>> {-# RULES "cFloatConv/float2Double" cFloatConv = float2Double #-}
>> {-# RULES "cFloatConv/double2Float" cFloatConv = double2Float #-}
>> {-# RULES "cFloatConv/self" cFloatConv = id #-}
>>
>> For some reason, the rules don't fire. Anyone got an idea why?
>>
>> SUCCEEDED SOLUTION: multiparameter type classes
>>
>> I rewrote cFloatConv like this:
>>
>> import GHC.Float
>> class (RealFloat a, RealFloat b) => CFloatConv a b where
>> cFloatConv :: a -> b
>> cFloatConv = realToFrac
>>
>> instance CFloatConv Double Double where cFloatConv = id
>> instance CFloatConv Double CDouble
>> instance CFloatConv CDouble Double
>> instance CFloatConv Float Float where cFloatConv = id
>> instance CFloatConv Float Double where cFloatConv = float2Double
>> instance CFloatConv Double Float where cFloatConv = double2Float
>>
>> and replaced a couple of constraints in functions below by usage of
>> CFloatConv.
>>
>>
>> On Wed, Nov 2, 2011 at 2:25 PM, Felipe Almeida Lessa <
>> felipe.le...@gmail.com> wrote:
>>
>>> +gtk2hs-devel
>>>
>>> On Wed, Nov 2, 2011 at 8:15 AM, Eugene Kirpichov <ekirpic...@gmail.com>
>>> wrote:
>>> > Any idea how to debug why all the GMP calls?
>>> > I'm looking at even the auto-generated source for cairo bindings, but I
>>> > don't see anything at all that could lead to *thousands* of them.
>>>
>>> Found them. Look at the Types module and you'll see
>>>
>>> cFloatConv :: (RealFloat a, RealFloat b) => a -> b
>>> cFloatConv = realToFrac
>>>
>>> This function (or its cousins peekFloatConv, withFloatConv...) are
>>> used *everywhere*.
>>>
>>> Looking at this module with ghc-core we see that GHC compiled a
>>> generic version of cFloatConv:
>>>
>>> Graphics.Rendering.Cairo.Types.$wcFloatConv
>>> :: forall a_a3TN b_a3TO.
>>> (RealFloat a_a3TN, RealFrac b_a3TO) =>
>>> a_a3TN -> b_a3TO
>>> [GblId,
>>> Arity=3,
>>>
>>> Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=3, Value=True,
>>> ConLike=True, Cheap=True, Expandable=True,
>>> Guidance=IF_ARGS [3 3 0] 12 0}]
>>> Graphics.Rendering.Cairo.Types.$wcFloatConv =
>>> \ (@ a_a3TN)
>>> (@ b_a3TO)
>>> (w_s5zg :: RealFloat a_a3TN)
>>> (ww_s5zj :: RealFrac b_a3TO)
>>> (w1_s5zA :: a_a3TN) ->
>>> fromRational
>>> @ b_a3TO
>>> ($p2RealFrac @ b_a3TO ww_s5zj)
>>> (toRational
>>> @ a_a3TN
>>> ($p1RealFrac
>>> @ a_a3TN ($p1RealFloat @ a_a3TN w_s5zg))
>>> w1_s5zA)
>>>
>>> Note that this is basically cFloatConv = fromRational . toRational.
>>>
>>> *However*, GHC also compiled a Double -> Double specialization:
>>>
>>> Graphics.Rendering.Cairo.Types.cFloatConv1
>>> :: Double -> Double
>>> [GblId,
>>> Arity=1,
>>>
>>> Unf=Unf{Src=InlineStable, TopLvl=True, Arity=1, Value=True,
>>> ConLike=True, Cheap=True, Expandable=True,
>>> Guidance=ALWAYS_IF(unsat_ok=True,boring_ok=False)
>>> Tmpl= \ (eta_B1 [Occ=Once!] :: Double) ->
>>> case eta_B1 of _ { D# ww_a5v3 [Occ=Once] ->
>>> case $w$ctoRational ww_a5v3
>>> of _ { (# ww2_a5v8 [Occ=Once], ww3_a5v9 [Occ=Once] #) ->
>>> $wfromRat ww2_a5v8 ww3_a5v9
>>> }
>>> }}]
>>> Graphics.Rendering.Cairo.Types.cFloatConv1 =
>>> \ (eta_B1 :: Double) ->
>>> case eta_B1 of _ { D# ww_a5v3 ->
>>> case $w$ctoRational ww_a5v3
>>> of _ { (# ww2_a5v8, ww3_a5v9 #) ->
>>> $wfromRat ww2_a5v8 ww3_a5v9
>>> }
>>> }
>>>
>>> ...which is also equivalent to fromRational . toRational however with
>>> the type class inlined! Oh, god...
>>>
>>> Cheers,
>>>
>>> --
>>> Felipe.
>>>
>>> _______________________________________________
>>> Haskell-Cafe mailing list
>>> haskell-c...@haskell.org
>>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>>
>>
>>
>>
>> --
>> Eugene Kirpichov
>> Principal Engineer, Mirantis Inc. http://www.mirantis.com/
>> Editor, http://fprog.ru/
>>
>
>
>
> --
> Eugene Kirpichov
> Principal Engineer, Mirantis Inc. http://www.mirantis.com/
> Editor, http://fprog.ru/
>
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