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Optimize IntMap.alter using unboxed sums. #523

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Optimize IntMap.alter using unboxed sums. #523

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50 changes: 50 additions & 0 deletions Data/IntMap/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,10 @@
#if __GLASGOW_HASKELL__ >= 708
{-# LANGUAGE TypeFamilies #-}
#endif
#if __GLASGOW_HASKELL__ >= 802
{-# LANGUAGE UnboxedSums #-}
{-# LANGUAGE UnboxedTuples #-}
#endif

{-# OPTIONS_HADDOCK not-home #-}

Expand Down Expand Up @@ -311,6 +315,9 @@ import Prelude hiding (lookup, map, filter, foldr, foldl, null)
import Data.IntSet.Internal (Key)
import qualified Data.IntSet.Internal as IntSet
import Utils.Containers.Internal.BitUtil
#if __GLASGOW_HASKELL__ >= 802
import Utils.Containers.Internal.PtrEquality (ptrEq)
#endif
import Utils.Containers.Internal.StrictFold
import Utils.Containers.Internal.StrictPair

Expand Down Expand Up @@ -937,6 +944,48 @@ updateLookupWithKey _ _ Nil = (Nothing,Nil)
-- | /O(min(n,W))/. The expression (@'alter' f k map@) alters the value @x@ at @k@, or absence thereof.
-- 'alter' can be used to insert, delete, or update a value in an 'IntMap'.
-- In short : @'lookup' k ('alter' f k m) = f ('lookup' k m)@.

#if __GLASGOW_HASKELL__ >= 802
alter :: (Maybe a -> Maybe a) -> Key -> IntMap a -> IntMap a
alter f !k t = case alter# f k t of
(# (# #) | #) -> t
(# | t' #) -> t'
{-# INLINE alter #-}


-- Internal implementation which keeps track of whether or not the intmap was
-- modified using an unboxed sum (Maybe).
--
-- If no modifications are made to the map (# (# #) | #) is returned, otherwise
-- (# | newMap #) is returned.
alter# :: (Maybe a -> Maybe a) -> Key -> IntMap a -> (# (# #) | IntMap a #)
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What happens if you make the function have type Maybe# a -> Maybe# a, where Maybe# is the unboxed version of Maybe? Couldn't we often avoid the Maybe allocation that way? Benchmark!

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That function is user defined (passed to alter) so at some point you would have to do the conversion from Maybe to Maybe#. As far as I know coerce wouldn't work for f because they have different representations (Maybe and Maybe# that is), but there may be another way that I'm unaware of. Did you have a specific approach in mind?

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I think it's a decent bet that the function we're passed will be small enough to inline. So calling alter# with

\ p -> fromMaybe (f (toMaybe p))

(essentially) should usually avoid any actual Maybes. Or so I imagine.

alter# f !k t@(Bin p m l r)
| nomatch k p m = case f Nothing of
Nothing -> (# (# #) | #)
Just x -> (# | link k (Tip k x) p t #)
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I don't think you're being strict enough with your return values.

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Do you mean something like the following?

let !t' = link k (Tip k x) p t in (# | t' #)

Or something else?

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Yes, but see the link below for a clearer way.

| zero k m = case alter# f k l of
(# (# #) | #) -> (# (# #) | #)
(# | l' #) -> (# | binCheckLeft p m l' r #)

| otherwise = case alter# f k r of
(# (# #) | #) -> (# (# #) | #)
(# | r' #) -> (# | binCheckRight p m l r' #)

alter# f k t@(Tip ky y)
| k==ky = case f (Just y) of
Just x -> if x `ptrEq` y
then (# (# #) | #)
else (# | Tip ky x #)
Nothing -> (# | Nil #)
| otherwise = case f Nothing of
Just x -> (# | link k (Tip k x) ky t #)
Nothing -> (# (# #) | #)
alter# f k Nil = case f Nothing of
Just x -> (# | Tip k x #)
Nothing -> (# (# #) | #)
{-# INLINABLE alter# #-}

#else
alter :: (Maybe a -> Maybe a) -> Key -> IntMap a -> IntMap a
alter f !k t@(Bin p m l r)
| nomatch k p m = case f Nothing of
Expand All @@ -954,6 +1003,7 @@ alter f k t@(Tip ky y)
alter f k Nil = case f Nothing of
Just x -> Tip k x
Nothing -> Nil
#endif

-- | /O(log n)/. The expression (@'alterF' f k map@) alters the value @x@ at
-- @k@, or absence thereof. 'alterF' can be used to inspect, insert, delete,
Expand Down
49 changes: 49 additions & 0 deletions Data/IntMap/Strict.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,11 @@
#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
{-# LANGUAGE Trustworthy #-}
#endif
#if __GLASGOW_HASKELL__ >= 802
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE UnboxedSums #-}
{-# LANGUAGE UnboxedTuples #-}
#endif

#include "containers.h"

Expand Down Expand Up @@ -303,6 +308,9 @@ import Data.IntMap.Internal
import Data.IntMap.Internal.DeprecatedDebug (showTree, showTreeWith)
import qualified Data.IntSet.Internal as IntSet
import Utils.Containers.Internal.BitUtil
#if __GLASGOW_HASKELL__ >= 802
import Utils.Containers.Internal.PtrEquality (ptrEq)
#endif
import Utils.Containers.Internal.StrictFold
import Utils.Containers.Internal.StrictPair
#if !MIN_VERSION_base(4,8,0)
Expand Down Expand Up @@ -559,6 +567,46 @@ updateLookupWithKey f0 !k0 t0 = toPair $ go f0 k0 t0
-- | /O(min(n,W))/. The expression (@'alter' f k map@) alters the value @x@ at @k@, or absence thereof.
-- 'alter' can be used to insert, delete, or update a value in an 'IntMap'.
-- In short : @'lookup' k ('alter' f k m) = f ('lookup' k m)@.
#if __GLASGOW_HASKELL__ >= 802
alter :: (Maybe a -> Maybe a) -> Key -> IntMap a -> IntMap a
alter f !k t = case alter# f k t of
(# (# #) | #) -> t
(# | t' #) -> t'
{-# INLINE alter #-}


-- Internal implementation which keeps track of whether or not the intmap was
-- modified using an unboxed sum (Maybe).
--
-- If no modifications are made to the map (# (# #) | #) is returned, otherwise
-- (# | newMap #) is returned.
alter# :: (Maybe a -> Maybe a) -> Key -> IntMap a -> (# (# #) | IntMap a #)
alter# f !k t@(Bin p m l r)
| nomatch k p m = case f Nothing of
Nothing -> (# (# #) | #)
Just !x -> (# | link k (Tip k x) p t #)
| zero k m = case alter# f k l of
(# (# #) | #) -> (# (# #) | #)
(# | l' #) -> (# | binCheckLeft p m l' r #)

| otherwise = case alter# f k r of
(# (# #) | #) -> (# (# #) | #)
(# | r' #) -> (# | binCheckRight p m l r' #)

alter# f k t@(Tip ky y)
| k==ky = case f (Just y) of
Just x -> if x `ptrEq` y
then (# (# #) | #)
else (# | Tip ky x #)
Nothing -> (# | Nil #)
| otherwise = case f Nothing of
Just !x -> (# | link k (Tip k x) ky t #)
Nothing -> (# (# #) | #)
alter# f k Nil = case f Nothing of
Just !x -> (# | Tip k x #)
Nothing -> (# (# #) | #)

#else
alter :: (Maybe a -> Maybe a) -> Key -> IntMap a -> IntMap a
alter f !k t =
case t of
Expand All @@ -578,6 +626,7 @@ alter f !k t =
Nil -> case f Nothing of
Just !x -> Tip k x
Nothing -> Nil
#endif

-- | /O(log n)/. The expression (@'alterF' f k map@) alters the value @x@ at
-- @k@, or absence thereof. 'alterF' can be used to inspect, insert, delete,
Expand Down