(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.


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 (tupleCon UnboxedTuple 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.lhs
        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 (tupleCon UnboxedTuple (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 (tupleCon UnboxedTuple (length args')) args'
  | otherwise            = StgConApp dc args'
    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)
    (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'
    (us1, us2) = splitUniqSupply us
    (alt_ty', alts') = unariseAlts us2 rho alt_ty bndr (repType (idType bndr)) alts

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

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

unariseAlts :: UniqSupply -> UnariseEnv -> AltType -> Id -> RepType -> [StgAlt] -> (AltType, [StgAlt])
unariseAlts us rho alt_ty _ (UnaryRep _) alts
  = (alt_ty, zipWith (\us alt -> unariseAlt us rho alt) (listSplitUniqSupply us) alts)

unariseAlts us rho _ bndr (UbxTupleRep tys) ((DEFAULT, [], [], e) : _)
  = (UbxTupAlt n, [(DataAlt (tupleCon UnboxedTuple n), ys, uses, unariseExpr us2' rho' e)])
    (us2', rho', ys) = unariseIdBinder us rho bndr
    uses = replicate (length ys) (not (isDeadBinder bndr))
    n = length tys

unariseAlts us rho _ bndr (UbxTupleRep _) [(DataAlt _, ys, uses, e)]
  = (UbxTupAlt n, [(DataAlt (tupleCon UnboxedTuple n), ys', uses', unariseExpr us2' rho'' e)])
    (us2', rho', ys', uses') = unariseUsedIdBinders us rho ys uses
    rho'' = extendVarEnv rho' bndr ys'
    n = length ys'

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

unariseAlt :: UniqSupply -> UnariseEnv -> StgAlt -> StgAlt
unariseAlt us rho (con, xs, uses, e)
  = (con, xs', uses', unariseExpr us' rho' e)
    (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)
unariseSRT _   (SRT {})         = panic "unariseSRT"

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 )

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