On Wed, Nov 2, 2011 at 3:14 PM, Eugene Kirpichov <ekirpichov@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.lessa@gmail.com> wrote:

+gtk2hs-devel

On Wed, Nov 2, 2011 at 8:15 AM, Eugene Kirpichov <ekirpichov@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-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

--
Eugene Kirpichov
Principal Engineer, Mirantis Inc. http://www.mirantis.com/
Editor, http://fprog.ru/