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Try speeding up weeder with a bloom filter #186

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Try speeding up weeder with a bloom filter #186

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5 changes: 5 additions & 0 deletions src/Weeder.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,7 @@ import Data.Set ( Set )
import qualified Data.Set as Set
import Data.Tree (Tree)
import qualified Data.Tree as Tree
import Data.BloomFilter.Hash

-- generic-lens
import Data.Generics.Labels ()
Expand Down Expand Up @@ -139,6 +140,10 @@ instance Show Declaration where
declarationStableName


-- TODO maybe we can make this faster by only hashing the location.
instance Hashable Declaration where
hashIO32 d s = hashIO32 (declarationStableName d) s
Comment on lines +143 to +145
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This is definitely not fast, and could be why this approach doesn't work.

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Could be worth trying the Uniquable instance of Module and OccName to produce hashes.

Note [The Unique of an OccName]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
They are efficient, because FastStrings have unique Int# keys.  We assume
this key is less than 2^24, and indeed FastStrings are allocated keys
sequentially starting at 0.

So we can make a Unique using
        mkUnique ns key  :: Unique
where 'ns' is a Char representing the name space.  This in turn makes it
easy to build an OccEnv.
-}

(or maybe even better: the Uniquable instance of the original Names we derive the declarations from with nameToDeclaration)


declarationStableName :: Declaration -> String
declarationStableName Declaration { declModule, declOccName } =
let
Expand Down
19 changes: 18 additions & 1 deletion src/Weeder/Run.hs
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Expand Up @@ -17,6 +17,7 @@ import Data.Function ( (&) )
import Data.Set ( Set )
import qualified Data.Set as Set
import qualified Data.Map.Strict as Map
import qualified Data.BloomFilter.Easy as BloomFilter

-- ghc
import GHC.Plugins
Expand Down Expand Up @@ -117,7 +118,9 @@ runWeeder weederConfig@Config{ rootPatterns, typeClassRoots, rootInstances, root
-- We only care about dead declarations if they have a span assigned,
-- since they don't show up in the output otherwise
dead =
outputableDeclarations analysis Set.\\ reachableSet
fastSpecialSetDifference
(outputableDeclarations analysis)
reachableSet

warnings =
Map.unionsWith (++) $
Expand Down Expand Up @@ -173,3 +176,17 @@ runWeeder weederConfig@Config{ rootPatterns, typeClassRoots, rootInstances, root
displayDeclaration :: Declaration -> String
displayDeclaration d =
moduleNameString ( moduleName ( declModule d ) ) <> "." <> occNameString ( declOccName d )

-- | This computes the same as (Set.\\) but is faster by assuming that the set difference will be small.
-- I.e. there will be more non-weeds than weeds.
--
fastSpecialSetDifference :: Set Declaration -> Set Declaration -> Set Declaration
fastSpecialSetDifference allDecls usedDecls =
let bloom = BloomFilter.easyList 0.05 (Set.toList usedDecls)
-- The elem docs say:
-- @
-- If the value is present, return True. If the value is not present, there is still some possibility that True will be returned.
-- @
-- I.e. if some declaration is a weed, it will definitely show up in the result, but also some weeds will show up in the result.
-- So we need to do another set difference afterwards, but with a much smaller set.
in Set.difference (Set.filter (not . (`BloomFilter.elem` bloom)) allDecls) usedDecls
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I'm about 50% sure I got this backward in some way, so that might be part of the issue as well.

1 change: 1 addition & 0 deletions weeder.cabal
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Expand Up @@ -40,6 +40,7 @@ library
, text ^>= 2.0.1 || ^>= 2.1
, toml-reader ^>= 0.2.0.0
, transformers ^>= 0.5.6.2 || ^>= 0.6
, bloomfilter ^>= 2.0.1.2
hs-source-dirs: src
exposed-modules:
Weeder
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