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[WIP] Use unboxed sums for change / no-change tracking #461

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[WIP] Use unboxed sums for change / no-change tracking #461

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7f017fe
Try something else for avoiding allocations on no-ops
sjakobi May 11, 2022
2e0014e
Avoid re-allocating NoChanges
sjakobi May 11, 2022
2cc5d07
Changed is strict now
sjakobi May 11, 2022
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50 changes: 32 additions & 18 deletions Data/HashMap/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE PatternGuards #-}
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE RoleAnnotations #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE StandaloneDeriving #-}
Expand Down Expand Up @@ -803,37 +804,38 @@ insert k v m = insert' (hash k) k v m
{-# INLINABLE insert #-}

insert' :: Eq k => Hash -> k -> v -> HashMap k v -> HashMap k v
insert' h0 k0 v0 m0 = go h0 k0 v0 0 m0
insert' h0 k0 v0 m0 =
case go h0 k0 v0 0 m0 of
NoChange -> m0
Changed m -> m
where
go !h !k x !_ Empty = Leaf h (L k x)
go !h !k x !_ Empty = Changed (Leaf h (L k x))
go h k x s t@(Leaf hy l@(L ky y))
| hy == h = if ky == k
then if x `ptrEq` y
then t
else Leaf h (L k x)
else collision h l (L k x)
| otherwise = runST (two s h k x hy t)
go h k x s t@(BitmapIndexed b ary)
then NoChange
else Changed (Leaf h (L k x))
else Changed $ collision h l (L k x)
| otherwise = Changed $ runST (two s h k x hy t)
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I suspect that we're less lazy in the result of two now, and that this is the actual source of the minor performance improvements.

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I should try to make two itself more strict: Force the result of the recursive application of go, force the returned BitmapIndexed nodes.

go h k x s (BitmapIndexed b ary)
| b .&. m == 0 =
let !ary' = A.insert ary i $! Leaf h (L k x)
in bitmapIndexedOrFull (b .|. m) ary'
in Changed $ bitmapIndexedOrFull (b .|. m) ary'
| otherwise =
let !st = A.index ary i
!st' = go h k x (nextShift s) st
in if st' `ptrEq` st
then t
else BitmapIndexed b (A.update ary i st')
in case go h k x (nextShift s) st of
Changed st' -> Changed $ BitmapIndexed b (A.update ary i st')
noChange -> noChange
where m = mask h s
i = sparseIndex b m
go h k x s t@(Full ary) =
go h k x s (Full ary) =
let !st = A.index ary i
!st' = go h k x (nextShift s) st
in if st' `ptrEq` st
then t
else Full (update32 ary i st')
in case go h k x (nextShift s) st of
Changed st' -> Changed $ Full (update32 ary i st')
noChange -> noChange
where i = index h s
go h k x s t@(Collision hy v)
| h == hy = Collision h (updateOrSnocWith (\a _ -> (# a #)) k x v)
| h == hy = Changed $ Collision h (updateOrSnocWith (\a _ -> (# a #)) k x v) -- TODO: Improve
| otherwise = go h k x s $ BitmapIndexed (mask hy s) (A.singleton t)
{-# INLINABLE insert' #-}

Expand Down Expand Up @@ -2502,6 +2504,18 @@ ptrEq :: a -> a -> Bool
ptrEq x y = Exts.isTrue# (Exts.reallyUnsafePtrEquality# x y ==# 1#)
{-# INLINE ptrEq #-}

type Change a = (# (# #) | a #)

pattern NoChange :: Change a
pattern NoChange <- (# (# #) | #)
where NoChange = (# (# #) | #)

pattern Changed :: a -> Change a
pattern Changed a <- (# | a #) where
Changed !a = (# | a #)

{-# COMPLETE NoChange, Changed #-}

------------------------------------------------------------------------
-- IsList instance
instance (Eq k, Hashable k) => Exts.IsList (HashMap k v) where
Expand Down