simplStg/UnariseStg.hs

    {-
    (c) The GRASP/AQUA Project, Glasgow University, 1992-2012

    Note [Unarisation]
    ~~~~~~~~~~~~~~~~~~

    The idea of this pass is to translate away *all* unboxed-tuple binders. So for example:

    f (x :: (# Int, Bool #)) = f x + f (# 1, True #)
     ==>
    f (x1 :: Int) (x2 :: Bool) = f x1 x2 + f 1 True

    It is important that we do this at the STG level and NOT at the core level
    because it would be very hard to make this pass Core-type-preserving.

    STG fed to the code generators *must* be unarised because the code generators do
    not support unboxed tuple binders natively.

    Note [Unarisation and arity]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    Because of unarisation, the arity that will be recorded in the generated info table
    for an Id may be larger than the idArity. Instead we record what we call the RepArity,
    which is the Arity taking into account any expanded arguments, and corresponds to
    the number of (possibly-void) *registers* arguments will arrive in.
    -}

    {-# LANGUAGE CPP #-}

    module UnariseStg (unarise) where

    #include "HsVersions.h"

    import CoreSyn
    import StgSyn
    import VarEnv
    import UniqSupply
    import Id
    import MkId (realWorldPrimId)
    import Type
    import TysWiredIn
    import DataCon
    import VarSet
    import OccName
    import Name
    import Util
    import Outputable
    import BasicTypes

    -- | A mapping from unboxed-tuple binders to the Ids they were expanded to.
    --
    -- INVARIANT: Ids in the range don't have unboxed tuple types.
    --
    -- Those in-scope variables without unboxed-tuple types are not present in
    -- the domain of the mapping at all.
    type UnariseEnv = VarEnv [Id]

    ubxTupleId0 :: Id
    ubxTupleId0 = dataConWorkId (tupleDataCon Unboxed 0)

    unarise :: UniqSupply -> [StgBinding] -> [StgBinding]
    unarise us binds = zipWith (\us -> unariseBinding us init_env) (listSplitUniqSupply us) binds
      where -- See Note [Nullary unboxed tuple] in Type.hs
            init_env = unitVarEnv ubxTupleId0 [realWorldPrimId]

    unariseBinding :: UniqSupply -> UnariseEnv -> StgBinding -> StgBinding
    unariseBinding us rho bind = case bind of
      StgNonRec x rhs -> StgNonRec x (unariseRhs us rho rhs)
      StgRec xrhss    -> StgRec $ zipWith (\us (x, rhs) -> (x, unariseRhs us rho rhs))
                                          (listSplitUniqSupply us) xrhss

    unariseRhs :: UniqSupply -> UnariseEnv -> StgRhs -> StgRhs
    unariseRhs us rho rhs = case rhs of
      StgRhsClosure ccs b_info fvs update_flag srt args expr
        -> StgRhsClosure ccs b_info (unariseIds rho fvs) update_flag
                         (unariseSRT rho srt) args' (unariseExpr us' rho' expr)
        where (us', rho', args') = unariseIdBinders us rho args
      StgRhsCon ccs con args
        -> StgRhsCon ccs con (unariseArgs rho args)

    ------------------------
    unariseExpr :: UniqSupply -> UnariseEnv -> StgExpr -> StgExpr
    unariseExpr _ rho (StgApp f args)
      | null args
      , UbxTupleRep tys <- repType (idType f)
      =  -- Particularly important where (##) is concerned
         -- See Note [Nullary unboxed tuple]
        StgConApp (tupleDataCon Unboxed (length tys))
                  (map StgVarArg (unariseId rho f))

      | otherwise
      = StgApp f (unariseArgs rho args)

    unariseExpr _ _ (StgLit l)
      = StgLit l

    unariseExpr _ rho (StgConApp dc args)
      | isUnboxedTupleCon dc = StgConApp (tupleDataCon Unboxed (length args')) args'
      | otherwise            = StgConApp dc args'
      where
        args' = unariseArgs rho args

    unariseExpr _ rho (StgOpApp op args ty)
      = StgOpApp op (unariseArgs rho args) ty

    unariseExpr us rho (StgLam xs e)
      = StgLam xs' (unariseExpr us' rho' e)
      where
        (us', rho', xs') = unariseIdBinders us rho xs

    unariseExpr us rho (StgCase e case_lives alts_lives bndr srt alt_ty alts)
      = StgCase (unariseExpr us1 rho e) (unariseLives rho case_lives)
                (unariseLives rho alts_lives) bndr (unariseSRT rho srt)
                alt_ty alts'
     where
        (us1, us2) = splitUniqSupply us
        alts'      = unariseAlts us2 rho alt_ty bndr alts

    unariseExpr us rho (StgLet bind e)
      = StgLet (unariseBinding us1 rho bind) (unariseExpr us2 rho e)
      where
        (us1, us2) = splitUniqSupply us

    unariseExpr us rho (StgLetNoEscape live_in_let live_in_bind bind e)
      = StgLetNoEscape (unariseLives rho live_in_let) (unariseLives rho live_in_bind)
                       (unariseBinding us1 rho bind) (unariseExpr us2 rho e)
      where
        (us1, us2) = splitUniqSupply us

    unariseExpr us rho (StgTick tick e)
      = StgTick tick (unariseExpr us rho e)

    ------------------------
    unariseAlts :: UniqSupply -> UnariseEnv -> AltType -> Id -> [StgAlt] -> [StgAlt]
    unariseAlts us rho (UbxTupAlt n) bndr [(DEFAULT, [], [], e)]
      = [(DataAlt (tupleDataCon Unboxed n), ys, uses, unariseExpr us2' rho' e)]
      where
        (us2', rho', ys) = unariseIdBinder us rho bndr
        uses = replicate (length ys) (not (isDeadBinder bndr))

    unariseAlts us rho (UbxTupAlt n) bndr [(DataAlt _, ys, uses, e)]
      = [(DataAlt (tupleDataCon Unboxed n), ys', uses', unariseExpr us2' rho'' e)]
      where
        (us2', rho', ys', uses') = unariseUsedIdBinders us rho ys uses
        rho'' = extendVarEnv rho' bndr ys'

    unariseAlts _ _ (UbxTupAlt _) _ alts
      = pprPanic "unariseExpr: strange unboxed tuple alts" (ppr alts)

    unariseAlts us rho _ _ alts
      = zipWith (\us alt -> unariseAlt us rho alt) (listSplitUniqSupply us) alts

    --------------------------
    unariseAlt :: UniqSupply -> UnariseEnv -> StgAlt -> StgAlt
    unariseAlt us rho (con, xs, uses, e)
      = (con, xs', uses', unariseExpr us' rho' e)
      where
        (us', rho', xs', uses') = unariseUsedIdBinders us rho xs uses

    ------------------------
    unariseSRT :: UnariseEnv -> SRT -> SRT
    unariseSRT _   NoSRT            = NoSRT
    unariseSRT rho (SRTEntries ids) = SRTEntries (concatMapVarSet (unariseId rho) ids)

    unariseLives :: UnariseEnv -> StgLiveVars -> StgLiveVars
    unariseLives rho ids = concatMapVarSet (unariseId rho) ids

    unariseArgs :: UnariseEnv -> [StgArg] -> [StgArg]
    unariseArgs rho = concatMap (unariseArg rho)

    unariseArg :: UnariseEnv -> StgArg -> [StgArg]
    unariseArg rho (StgVarArg x) = map StgVarArg (unariseId rho x)
    unariseArg _   (StgLitArg l) = [StgLitArg l]

    unariseIds :: UnariseEnv -> [Id] -> [Id]
    unariseIds rho = concatMap (unariseId rho)

    unariseId :: UnariseEnv -> Id -> [Id]
    unariseId rho x
      | Just ys <- lookupVarEnv rho x
      = ASSERT2( case repType (idType x) of UbxTupleRep _ -> True; _ -> x == ubxTupleId0
               , text "unariseId: not unboxed tuple" <+> ppr x )
        ys

      | otherwise
      = ASSERT2( case repType (idType x) of UbxTupleRep _ -> False; _ -> True
               , text "unariseId: was unboxed tuple" <+> ppr x )
        [x]

    unariseUsedIdBinders :: UniqSupply -> UnariseEnv -> [Id] -> [Bool]
                         -> (UniqSupply, UnariseEnv, [Id], [Bool])
    unariseUsedIdBinders us rho xs uses
      = case mapAccumL2 do_one us rho (zipEqual "unariseUsedIdBinders" xs uses) of
          (us', rho', xs_usess) -> uncurry ((,,,) us' rho') (unzip (concat xs_usess))
      where
        do_one us rho (x, use) = third3 (map (flip (,) use)) (unariseIdBinder us rho x)

    unariseIdBinders :: UniqSupply -> UnariseEnv -> [Id] -> (UniqSupply, UnariseEnv, [Id])
    unariseIdBinders us rho xs = third3 concat $ mapAccumL2 unariseIdBinder us rho xs

    unariseIdBinder :: UniqSupply -> UnariseEnv -> Id -> (UniqSupply, UnariseEnv, [Id])
    unariseIdBinder us rho x = case repType (idType x) of
        UnaryRep _      -> (us, rho, [x])
        UbxTupleRep tys -> let (us0, us1) = splitUniqSupply us
                               ys   = unboxedTupleBindersFrom us0 x tys
                               rho' = extendVarEnv rho x ys
                           in (us1, rho', ys)

    unboxedTupleBindersFrom :: UniqSupply -> Id -> [UnaryType] -> [Id]
    unboxedTupleBindersFrom us x tys = zipWith (mkSysLocalOrCoVar fs) (uniqsFromSupply us) tys
      where fs = occNameFS (getOccName x)

    concatMapVarSet :: (Var -> [Var]) -> VarSet -> VarSet
    concatMapVarSet f xs = mkVarSet [x' | x <- varSetElems xs, x' <- f x]