Aliases.hs

{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-}

-- | A representation where all bindings are annotated with aliasing
-- information.
module Futhark.IR.Aliases
  ( -- * The representation definition
    Aliases,
    AliasDec (..),
    VarAliases,
    ConsumedInExp,
    BodyAliasing,
    module Futhark.IR.Prop.Aliases,

    -- * Module re-exports
    module Futhark.IR.Prop,
    module Futhark.IR.Traversals,
    module Futhark.IR.Pretty,
    module Futhark.IR.Syntax,

    -- * Adding aliases
    addAliasesToPattern,
    mkAliasedLetStm,
    mkAliasedBody,
    mkPatternAliases,
    mkBodyAliases,

    -- * Removing aliases
    removeProgAliases,
    removeFunDefAliases,
    removeExpAliases,
    removeStmAliases,
    removeLambdaAliases,
    removePatternAliases,
    removeScopeAliases,

    -- * Tracking aliases
    AliasesAndConsumed,
    trackAliases,
    mkStmsAliases,
  )
where

import Control.Monad.Identity
import Control.Monad.Reader
import qualified Data.Map.Strict as M
import Data.Maybe
import Futhark.Analysis.Rephrase
import Futhark.Binder
import Futhark.IR.Pretty
import Futhark.IR.Prop
import Futhark.IR.Prop.Aliases
import Futhark.IR.Syntax
import Futhark.IR.Traversals
import Futhark.Transform.Rename
import Futhark.Transform.Substitute
import qualified Futhark.Util.Pretty as PP

-- | The rep for the basic representation.
data Aliases rep

-- | A wrapper around 'AliasDec' to get around the fact that we need an
-- 'Ord' instance, which 'AliasDec does not have.
newtype AliasDec = AliasDec {unAliases :: Names}
  deriving (Show)

instance Semigroup AliasDec where
  x <> y = AliasDec $ unAliases x <> unAliases y

instance Monoid AliasDec where
  mempty = AliasDec mempty

instance Eq AliasDec where
  _ == _ = True

instance Ord AliasDec where
  _ `compare` _ = EQ

instance Rename AliasDec where
  rename (AliasDec names) = AliasDec <$> rename names

instance Substitute AliasDec where
  substituteNames substs (AliasDec names) = AliasDec $ substituteNames substs names

instance FreeIn AliasDec where
  freeIn' = const mempty

instance PP.Pretty AliasDec where
  ppr = PP.braces . PP.commasep . map PP.ppr . namesToList . unAliases

-- | The aliases of the let-bound variable.
type VarAliases = AliasDec

-- | Everything consumed in the expression.
type ConsumedInExp = AliasDec

-- | The aliases of what is returned by the t'Body', and what is
-- consumed inside of it.
type BodyAliasing = ([VarAliases], ConsumedInExp)

instance (RepTypes rep, CanBeAliased (Op rep)) => RepTypes (Aliases rep) where
  type LetDec (Aliases rep) = (VarAliases, LetDec rep)
  type ExpDec (Aliases rep) = (ConsumedInExp, ExpDec rep)
  type BodyDec (Aliases rep) = (BodyAliasing, BodyDec rep)
  type FParamInfo (Aliases rep) = FParamInfo rep
  type LParamInfo (Aliases rep) = LParamInfo rep
  type RetType (Aliases rep) = RetType rep
  type BranchType (Aliases rep) = BranchType rep
  type Op (Aliases rep) = OpWithAliases (Op rep)

instance AliasesOf (VarAliases, dec) where
  aliasesOf = unAliases . fst

instance FreeDec AliasDec

withoutAliases ::
  (HasScope (Aliases rep) m, Monad m) =>
  ReaderT (Scope rep) m a ->
  m a
withoutAliases m = do
  scope <- asksScope removeScopeAliases
  runReaderT m scope

instance (ASTRep rep, CanBeAliased (Op rep)) => ASTRep (Aliases rep) where
  expTypesFromPattern =
    withoutAliases . expTypesFromPattern . removePatternAliases

instance (ASTRep rep, CanBeAliased (Op rep)) => Aliased (Aliases rep) where
  bodyAliases = map unAliases . fst . fst . bodyDec
  consumedInBody = unAliases . snd . fst . bodyDec

instance (ASTRep rep, CanBeAliased (Op rep)) => PrettyRep (Aliases rep) where
  ppExpDec (consumed, inner) e =
    maybeComment $
      catMaybes
        [ exp_dec,
          merge_dec,
          ppExpDec inner $ removeExpAliases e
        ]
    where
      merge_dec =
        case e of
          DoLoop _ merge _ body ->
            let mergeParamAliases fparam als
                  | primType (paramType fparam) =
                    Nothing
                  | otherwise =
                    resultAliasComment (paramName fparam) als
             in maybeComment $
                  catMaybes $
                    zipWith mergeParamAliases (map fst merge) $
                      bodyAliases body
          _ -> Nothing

      exp_dec = case namesToList $ unAliases consumed of
        [] -> Nothing
        als ->
          Just $
            PP.oneLine $
              PP.text "-- Consumes " <> PP.commasep (map PP.ppr als)

maybeComment :: [PP.Doc] -> Maybe PP.Doc
maybeComment [] = Nothing
maybeComment cs = Just $ PP.folddoc (PP.</>) cs

resultAliasComment :: PP.Pretty a => a -> Names -> Maybe PP.Doc
resultAliasComment name als =
  case namesToList als of
    [] -> Nothing
    als' ->
      Just $
        PP.oneLine $
          PP.text "-- Result of " <> PP.ppr name <> PP.text " aliases "
            <> PP.commasep (map PP.ppr als')

removeAliases :: CanBeAliased (Op rep) => Rephraser Identity (Aliases rep) rep
removeAliases =
  Rephraser
    { rephraseExpDec = return . snd,
      rephraseLetBoundDec = return . snd,
      rephraseBodyDec = return . snd,
      rephraseFParamDec = return,
      rephraseLParamDec = return,
      rephraseRetType = return,
      rephraseBranchType = return,
      rephraseOp = return . removeOpAliases
    }

removeScopeAliases :: Scope (Aliases rep) -> Scope rep
removeScopeAliases = M.map unAlias
  where
    unAlias (LetName (_, dec)) = LetName dec
    unAlias (FParamName dec) = FParamName dec
    unAlias (LParamName dec) = LParamName dec
    unAlias (IndexName it) = IndexName it

removeProgAliases ::
  CanBeAliased (Op rep) =>
  Prog (Aliases rep) ->
  Prog rep
removeProgAliases = runIdentity . rephraseProg removeAliases

removeFunDefAliases ::
  CanBeAliased (Op rep) =>
  FunDef (Aliases rep) ->
  FunDef rep
removeFunDefAliases = runIdentity . rephraseFunDef removeAliases

removeExpAliases ::
  CanBeAliased (Op rep) =>
  Exp (Aliases rep) ->
  Exp rep
removeExpAliases = runIdentity . rephraseExp removeAliases

removeStmAliases ::
  CanBeAliased (Op rep) =>
  Stm (Aliases rep) ->
  Stm rep
removeStmAliases = runIdentity . rephraseStm removeAliases

removeLambdaAliases ::
  CanBeAliased (Op rep) =>
  Lambda (Aliases rep) ->
  Lambda rep
removeLambdaAliases = runIdentity . rephraseLambda removeAliases

removePatternAliases ::
  PatternT (AliasDec, a) ->
  PatternT a
removePatternAliases = runIdentity . rephrasePattern (return . snd)

addAliasesToPattern ::
  (ASTRep rep, CanBeAliased (Op rep), Typed dec) =>
  PatternT dec ->
  Exp (Aliases rep) ->
  PatternT (VarAliases, dec)
addAliasesToPattern pat e =
  uncurry Pattern $ mkPatternAliases pat e

mkAliasedBody ::
  (ASTRep rep, CanBeAliased (Op rep)) =>
  BodyDec rep ->
  Stms (Aliases rep) ->
  Result ->
  Body (Aliases rep)
mkAliasedBody dec bnds res =
  Body (mkBodyAliases bnds res, dec) bnds res

mkPatternAliases ::
  (Aliased rep, Typed dec) =>
  PatternT dec ->
  Exp rep ->
  ( [PatElemT (VarAliases, dec)],
    [PatElemT (VarAliases, dec)]
  )
mkPatternAliases pat e =
  -- Some part of the pattern may be the context.  This does not have
  -- aliases from expAliases, so we use a hack to compute aliases of
  -- the context.
  let als = expAliases e ++ repeat mempty -- In case the pattern has
  -- more elements (this
  -- implies a type error).
      context_als = mkContextAliases pat e
   in ( zipWith annotateBindee (patternContextElements pat) context_als,
        zipWith annotateBindee (patternValueElements pat) als
      )
  where
    annotateBindee bindee names =
      bindee `setPatElemDec` (AliasDec names', patElemDec bindee)
      where
        names' =
          case patElemType bindee of
            Array {} -> names
            Mem _ -> names
            _ -> mempty

mkContextAliases ::
  Aliased rep =>
  PatternT dec ->
  Exp rep ->
  [Names]
mkContextAliases pat (DoLoop ctxmerge valmerge _ body) =
  let ctx = map fst ctxmerge
      init_als = zip mergenames $ map (subExpAliases . snd) $ ctxmerge ++ valmerge
      expand als = als <> mconcat (mapMaybe (`lookup` init_als) (namesToList als))
      merge_als =
        zip mergenames $
          map ((`namesSubtract` mergenames_set) . expand) $
            bodyAliases body
   in if length ctx == length (patternContextElements pat)
        then map (fromMaybe mempty . flip lookup merge_als . paramName) ctx
        else map (const mempty) $ patternContextElements pat
  where
    mergenames = map (paramName . fst) $ ctxmerge ++ valmerge
    mergenames_set = namesFromList mergenames
mkContextAliases pat (If _ tbranch fbranch _) =
  take (length $ patternContextNames pat) $
    zipWith (<>) (bodyAliases tbranch) (bodyAliases fbranch)
mkContextAliases pat _ =
  replicate (length $ patternContextElements pat) mempty

mkBodyAliases ::
  Aliased rep =>
  Stms rep ->
  Result ->
  BodyAliasing
mkBodyAliases bnds res =
  -- We need to remove the names that are bound in bnds from the alias
  -- and consumption sets.  We do this by computing the transitive
  -- closure of the alias map (within bnds), then removing anything
  -- bound in bnds.
  let (aliases, consumed) = mkStmsAliases bnds res
      boundNames =
        foldMap (namesFromList . patternNames . stmPattern) bnds
      aliases' = map (`namesSubtract` boundNames) aliases
      consumed' = consumed `namesSubtract` boundNames
   in (map AliasDec aliases', AliasDec consumed')

-- | The aliases of the result and everything consumed in the given
-- statements.
mkStmsAliases ::
  Aliased rep =>
  Stms rep ->
  [SubExp] ->
  ([Names], Names)
mkStmsAliases bnds res = delve mempty $ stmsToList bnds
  where
    delve (aliasmap, consumed) [] =
      ( map (aliasClosure aliasmap . subExpAliases) res,
        consumed
      )
    delve (aliasmap, consumed) (bnd : bnds') =
      delve (trackAliases (aliasmap, consumed) bnd) bnds'
    aliasClosure aliasmap names =
      names <> mconcat (map look $ namesToList names)
      where
        look k = M.findWithDefault mempty k aliasmap

type AliasesAndConsumed =
  ( M.Map VName Names,
    Names
  )

trackAliases ::
  Aliased rep =>
  AliasesAndConsumed ->
  Stm rep ->
  AliasesAndConsumed
trackAliases (aliasmap, consumed) stm =
  let pat = stmPattern stm
      pe_als =
        zip (patternNames pat) $ map addAliasesOfAliases $ patternAliases pat
      als = M.fromList pe_als
      rev_als = foldMap revAls pe_als
      revAls (v, v_als) =
        M.fromList $ map (,oneName v) $ namesToList v_als
      comb = M.unionWith (<>)
      aliasmap' = rev_als `comb` als `comb` aliasmap
      consumed' = consumed <> addAliasesOfAliases (consumedInStm stm)
   in (aliasmap', consumed')
  where
    addAliasesOfAliases names = names <> aliasesOfAliases names
    aliasesOfAliases = mconcat . map look . namesToList
    look k = M.findWithDefault mempty k aliasmap

mkAliasedLetStm ::
  (ASTRep rep, CanBeAliased (Op rep)) =>
  Pattern rep ->
  StmAux (ExpDec rep) ->
  Exp (Aliases rep) ->
  Stm (Aliases rep)
mkAliasedLetStm pat (StmAux cs attrs dec) e =
  Let
    (addAliasesToPattern pat e)
    (StmAux cs attrs (AliasDec $ consumedInExp e, dec))
    e

instance (Bindable rep, CanBeAliased (Op rep)) => Bindable (Aliases rep) where
  mkExpDec pat e =
    let dec = mkExpDec (removePatternAliases pat) $ removeExpAliases e
     in (AliasDec $ consumedInExp e, dec)

  mkExpPat ctx val e =
    addAliasesToPattern (mkExpPat ctx val $ removeExpAliases e) e

  mkLetNames names e = do
    env <- asksScope removeScopeAliases
    flip runReaderT env $ do
      Let pat dec _ <- mkLetNames names $ removeExpAliases e
      return $ mkAliasedLetStm pat dec e

  mkBody bnds res =
    let Body bodyrep _ _ = mkBody (fmap removeStmAliases bnds) res
     in mkAliasedBody bodyrep bnds res

instance (ASTRep (Aliases rep), Bindable (Aliases rep)) => BinderOps (Aliases rep)