basicTypes/IdInfo.hs

    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1993-1998

    \section[IdInfo]{@IdInfos@: Non-essential information about @Ids@}

    (And a pretty good illustration of quite a few things wrong with
    Haskell. [WDP 94/11])
    -}

    {-# LANGUAGE CPP #-}
    {-# LANGUAGE FlexibleContexts #-}

    module IdInfo (
            -- * The IdDetails type
            IdDetails(..), pprIdDetails, coVarDetails, isCoVarDetails,
            JoinArity, isJoinIdDetails_maybe,
            RecSelParent(..),

            -- * The IdInfo type
            IdInfo,         -- Abstract
            vanillaIdInfo, noCafIdInfo,

            -- ** The OneShotInfo type
            OneShotInfo(..),
            oneShotInfo, noOneShotInfo, hasNoOneShotInfo,
            setOneShotInfo,

            -- ** Zapping various forms of Info
            zapLamInfo, zapFragileInfo,
            zapDemandInfo, zapUsageInfo, zapUsageEnvInfo, zapUsedOnceInfo,
            zapTailCallInfo, zapCallArityInfo,

            -- ** The ArityInfo type
            ArityInfo,
            unknownArity,
            arityInfo, setArityInfo, ppArityInfo,

            callArityInfo, setCallArityInfo,

            -- ** Demand and strictness Info
            strictnessInfo, setStrictnessInfo,
            demandInfo, setDemandInfo, pprStrictness,

            -- ** Unfolding Info
            unfoldingInfo, setUnfoldingInfo,

            -- ** The InlinePragInfo type
            InlinePragInfo,
            inlinePragInfo, setInlinePragInfo,

            -- ** The OccInfo type
            OccInfo(..),
            isDeadOcc, isStrongLoopBreaker, isWeakLoopBreaker,
            occInfo, setOccInfo,

            InsideLam, OneBranch,
            insideLam, notInsideLam, oneBranch, notOneBranch,

            TailCallInfo(..),
            tailCallInfo, isAlwaysTailCalled,

            -- ** The RuleInfo type
            RuleInfo(..),
            emptyRuleInfo,
            isEmptyRuleInfo, ruleInfoFreeVars,
            ruleInfoRules, setRuleInfoHead,
            ruleInfo, setRuleInfo,

            -- ** The CAFInfo type
            CafInfo(..),
            ppCafInfo, mayHaveCafRefs,
            cafInfo, setCafInfo,

            -- ** Tick-box Info
            TickBoxOp(..), TickBoxId,

            -- ** Levity info
            LevityInfo, levityInfo, setNeverLevPoly, setLevityInfoWithType,
            isNeverLevPolyIdInfo
        ) where

    #include "HsVersions.h"

    import GhcPrelude

    import CoreSyn

    import Class
    import {-# SOURCE #-} PrimOp (PrimOp)
    import Name
    import VarSet
    import BasicTypes
    import DataCon
    import TyCon
    import PatSyn
    import Type
    import ForeignCall
    import Outputable
    import Module
    import Demand
    import Util

    -- infixl so you can say (id `set` a `set` b)
    infixl  1 `setRuleInfo`,
              `setArityInfo`,
              `setInlinePragInfo`,
              `setUnfoldingInfo`,
              `setOneShotInfo`,
              `setOccInfo`,
              `setCafInfo`,
              `setStrictnessInfo`,
              `setDemandInfo`,
              `setNeverLevPoly`,
              `setLevityInfoWithType`

    {-
    ************************************************************************
    *                                                                      *
                         IdDetails
    *                                                                      *
    ************************************************************************
    -}

    -- | Identifier Details
    --
    -- The 'IdDetails' of an 'Id' give stable, and necessary,
    -- information about the Id.
    data IdDetails
      = VanillaId

      -- | The 'Id' for a record selector
      | RecSelId
        { sel_tycon   :: RecSelParent
        , sel_naughty :: Bool       -- True <=> a "naughty" selector which can't actually exist, for example @x@ in:
                                    --    data T = forall a. MkT { x :: a }
        }                           -- See Note [Naughty record selectors] in TcTyClsDecls

      | DataConWorkId DataCon       -- ^ The 'Id' is for a data constructor /worker/
      | DataConWrapId DataCon       -- ^ The 'Id' is for a data constructor /wrapper/

                                    -- [the only reasons we need to know is so that
                                    --  a) to support isImplicitId
                                    --  b) when desugaring a RecordCon we can get
                                    --     from the Id back to the data con]
      | ClassOpId Class             -- ^ The 'Id' is a superclass selector,
                                    -- or class operation of a class

      | PrimOpId PrimOp             -- ^ The 'Id' is for a primitive operator
      | FCallId ForeignCall         -- ^ The 'Id' is for a foreign call.
                                    -- Type will be simple: no type families, newtypes, etc

      | TickBoxOpId TickBoxOp       -- ^ The 'Id' is for a HPC tick box (both traditional and binary)

      | DFunId Bool                 -- ^ A dictionary function.
           -- Bool = True <=> the class has only one method, so may be
           --                  implemented with a newtype, so it might be bad
           --                  to be strict on this dictionary

      | CoVarId    -- ^ A coercion variable
                   -- This only covers /un-lifted/ coercions, of type
                   -- (t1 ~# t2) or (t1 ~R# t2), not their lifted variants
      | JoinId JoinArity           -- ^ An 'Id' for a join point taking n arguments
           -- Note [Join points] in CoreSyn

    -- | Recursive Selector Parent
    data RecSelParent = RecSelData TyCon | RecSelPatSyn PatSyn deriving Eq
      -- Either `TyCon` or `PatSyn` depending
      -- on the origin of the record selector.
      -- For a data type family, this is the
      -- /instance/ 'TyCon' not the family 'TyCon'

    instance Outputable RecSelParent where
      ppr p = case p of
                RecSelData ty_con -> ppr ty_con
                RecSelPatSyn ps   -> ppr ps

    -- | Just a synonym for 'CoVarId'. Written separately so it can be
    -- exported in the hs-boot file.
    coVarDetails :: IdDetails
    coVarDetails = CoVarId

    -- | Check if an 'IdDetails' says 'CoVarId'.
    isCoVarDetails :: IdDetails -> Bool
    isCoVarDetails CoVarId = True
    isCoVarDetails _       = False

    isJoinIdDetails_maybe :: IdDetails -> Maybe JoinArity
    isJoinIdDetails_maybe (JoinId join_arity) = Just join_arity
    isJoinIdDetails_maybe _                   = Nothing

    instance Outputable IdDetails where
        ppr = pprIdDetails

    pprIdDetails :: IdDetails -> SDoc
    pprIdDetails VanillaId = empty
    pprIdDetails other     = brackets (pp other)
     where
       pp VanillaId               = panic "pprIdDetails"
       pp (DataConWorkId _)       = text "DataCon"
       pp (DataConWrapId _)       = text "DataConWrapper"
       pp (ClassOpId {})          = text "ClassOp"
       pp (PrimOpId _)            = text "PrimOp"
       pp (FCallId _)             = text "ForeignCall"
       pp (TickBoxOpId _)         = text "TickBoxOp"
       pp (DFunId nt)             = text "DFunId" <> ppWhen nt (text "(nt)")
       pp (RecSelId { sel_naughty = is_naughty })
                                  = brackets $ text "RecSel" <>
                                               ppWhen is_naughty (text "(naughty)")
       pp CoVarId                 = text "CoVarId"
       pp (JoinId arity)          = text "JoinId" <> parens (int arity)

    {-
    ************************************************************************
    *                                                                      *
    \subsection{The main IdInfo type}
    *                                                                      *
    ************************************************************************
    -}

    -- | Identifier Information
    --
    -- An 'IdInfo' gives /optional/ information about an 'Id'.  If
    -- present it never lies, but it may not be present, in which case there
    -- is always a conservative assumption which can be made.
    --
    -- Two 'Id's may have different info even though they have the same
    -- 'Unique' (and are hence the same 'Id'); for example, one might lack
    -- the properties attached to the other.
    --
    -- Most of the 'IdInfo' gives information about the value, or definition, of
    -- the 'Id', independent of its usage. Exceptions to this
    -- are 'demandInfo', 'occInfo', 'oneShotInfo' and 'callArityInfo'.
    --
    -- Performance note: when we update 'IdInfo', we have to reallocate this
    -- entire record, so it is a good idea not to let this data structure get
    -- too big.
    data IdInfo
      = IdInfo {
            arityInfo       :: !ArityInfo,          -- ^ 'Id' arity
            ruleInfo        :: RuleInfo,            -- ^ Specialisations of the 'Id's function which exist
                                                    -- See Note [Specialisations and RULES in IdInfo]
            unfoldingInfo   :: Unfolding,           -- ^ The 'Id's unfolding
            cafInfo         :: CafInfo,             -- ^ 'Id' CAF info
            oneShotInfo     :: OneShotInfo,         -- ^ Info about a lambda-bound variable, if the 'Id' is one
            inlinePragInfo  :: InlinePragma,        -- ^ Any inline pragma atached to the 'Id'
            occInfo         :: OccInfo,             -- ^ How the 'Id' occurs in the program

            strictnessInfo  :: StrictSig,      --  ^ A strictness signature

            demandInfo      :: Demand,       -- ^ ID demand information
            callArityInfo   :: !ArityInfo,   -- ^ How this is called.
                                             -- n <=> all calls have at least n arguments

            levityInfo      :: LevityInfo    -- ^ when applied, will this Id ever have a levity-polymorphic type?
        }

    -- Setters

    setRuleInfo :: IdInfo -> RuleInfo -> IdInfo
    setRuleInfo       info sp = sp `seq` info { ruleInfo = sp }
    setInlinePragInfo :: IdInfo -> InlinePragma -> IdInfo
    setInlinePragInfo info pr = pr `seq` info { inlinePragInfo = pr }
    setOccInfo :: IdInfo -> OccInfo -> IdInfo
    setOccInfo        info oc = oc `seq` info { occInfo = oc }
            -- Try to avoid spack leaks by seq'ing

    setUnfoldingInfo :: IdInfo -> Unfolding -> IdInfo
    setUnfoldingInfo info uf
      = -- We don't seq the unfolding, as we generate intermediate
        -- unfoldings which are just thrown away, so evaluating them is a
        -- waste of time.
        -- seqUnfolding uf `seq`
        info { unfoldingInfo = uf }

    setArityInfo :: IdInfo -> ArityInfo -> IdInfo
    setArityInfo      info ar  = info { arityInfo = ar  }
    setCallArityInfo :: IdInfo -> ArityInfo -> IdInfo
    setCallArityInfo info ar  = info { callArityInfo = ar  }
    setCafInfo :: IdInfo -> CafInfo -> IdInfo
    setCafInfo        info caf = info { cafInfo = caf }

    setOneShotInfo :: IdInfo -> OneShotInfo -> IdInfo
    setOneShotInfo      info lb = {-lb `seq`-} info { oneShotInfo = lb }

    setDemandInfo :: IdInfo -> Demand -> IdInfo
    setDemandInfo info dd = dd `seq` info { demandInfo = dd }

    setStrictnessInfo :: IdInfo -> StrictSig -> IdInfo
    setStrictnessInfo info dd = dd `seq` info { strictnessInfo = dd }

    -- | Basic 'IdInfo' that carries no useful information whatsoever
    vanillaIdInfo :: IdInfo
    vanillaIdInfo
      = IdInfo {
                cafInfo             = vanillaCafInfo,
                arityInfo           = unknownArity,
                ruleInfo            = emptyRuleInfo,
                unfoldingInfo       = noUnfolding,
                oneShotInfo         = NoOneShotInfo,
                inlinePragInfo      = defaultInlinePragma,
                occInfo             = noOccInfo,
                demandInfo          = topDmd,
                strictnessInfo      = nopSig,
                callArityInfo       = unknownArity,
                levityInfo          = NoLevityInfo
               }

    -- | More informative 'IdInfo' we can use when we know the 'Id' has no CAF references
    noCafIdInfo :: IdInfo
    noCafIdInfo  = vanillaIdInfo `setCafInfo`    NoCafRefs
            -- Used for built-in type Ids in MkId.

    {-
    ************************************************************************
    *                                                                      *
    \subsection[arity-IdInfo]{Arity info about an @Id@}
    *                                                                      *
    ************************************************************************

    For locally-defined Ids, the code generator maintains its own notion
    of their arities; so it should not be asking...  (but other things
    besides the code-generator need arity info!)
    -}

    -- | Arity Information
    --
    -- An 'ArityInfo' of @n@ tells us that partial application of this
    -- 'Id' to up to @n-1@ value arguments does essentially no work.
    --
    -- That is not necessarily the same as saying that it has @n@ leading
    -- lambdas, because coerces may get in the way.
    --
    -- The arity might increase later in the compilation process, if
    -- an extra lambda floats up to the binding site.
    type ArityInfo = Arity

    -- | It is always safe to assume that an 'Id' has an arity of 0
    unknownArity :: Arity
    unknownArity = 0

    ppArityInfo :: Int -> SDoc
    ppArityInfo 0 = empty
    ppArityInfo n = hsep [text "Arity", int n]

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Inline-pragma information}
    *                                                                      *
    ************************************************************************
    -}

    -- | Inline Pragma Information
    --
    -- Tells when the inlining is active.
    -- When it is active the thing may be inlined, depending on how
    -- big it is.
    --
    -- If there was an @INLINE@ pragma, then as a separate matter, the
    -- RHS will have been made to look small with a Core inline 'Note'
    --
    -- The default 'InlinePragInfo' is 'AlwaysActive', so the info serves
    -- entirely as a way to inhibit inlining until we want it
    type InlinePragInfo = InlinePragma

    {-
    ************************************************************************
    *                                                                      *
                   Strictness
    *                                                                      *
    ************************************************************************
    -}

    pprStrictness :: StrictSig -> SDoc
    pprStrictness sig = ppr sig

    {-
    ************************************************************************
    *                                                                      *
            RuleInfo
    *                                                                      *
    ************************************************************************

    Note [Specialisations and RULES in IdInfo]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Generally speaking, a GlobalId has an *empty* RuleInfo.  All their
    RULES are contained in the globally-built rule-base.  In principle,
    one could attach the to M.f the RULES for M.f that are defined in M.
    But we don't do that for instance declarations and so we just treat
    them all uniformly.

    The EXCEPTION is PrimOpIds, which do have rules in their IdInfo. That is
    jsut for convenience really.

    However, LocalIds may have non-empty RuleInfo.  We treat them
    differently because:
      a) they might be nested, in which case a global table won't work
      b) the RULE might mention free variables, which we use to keep things alive

    In TidyPgm, when the LocalId becomes a GlobalId, its RULES are stripped off
    and put in the global list.
    -}

    -- | Rule Information
    --
    -- Records the specializations of this 'Id' that we know about
    -- in the form of rewrite 'CoreRule's that target them
    data RuleInfo
      = RuleInfo
            [CoreRule]
            DVarSet         -- Locally-defined free vars of *both* LHS and RHS
                            -- of rules.  I don't think it needs to include the
                            -- ru_fn though.
                            -- Note [Rule dependency info] in OccurAnal

    -- | Assume that no specilizations exist: always safe
    emptyRuleInfo :: RuleInfo
    emptyRuleInfo = RuleInfo [] emptyDVarSet

    isEmptyRuleInfo :: RuleInfo -> Bool
    isEmptyRuleInfo (RuleInfo rs _) = null rs

    -- | Retrieve the locally-defined free variables of both the left and
    -- right hand sides of the specialization rules
    ruleInfoFreeVars :: RuleInfo -> DVarSet
    ruleInfoFreeVars (RuleInfo _ fvs) = fvs

    ruleInfoRules :: RuleInfo -> [CoreRule]
    ruleInfoRules (RuleInfo rules _) = rules

    -- | Change the name of the function the rule is keyed on on all of the 'CoreRule's
    setRuleInfoHead :: Name -> RuleInfo -> RuleInfo
    setRuleInfoHead fn (RuleInfo rules fvs)
      = RuleInfo (map (setRuleIdName fn) rules) fvs

    {-
    ************************************************************************
    *                                                                      *
    \subsection[CG-IdInfo]{Code generator-related information}
    *                                                                      *
    ************************************************************************
    -}

    -- CafInfo is used to build Static Reference Tables (see simplStg/SRT.hs).

    -- | Constant applicative form Information
    --
    -- Records whether an 'Id' makes Constant Applicative Form references
    data CafInfo
            = MayHaveCafRefs                -- ^ Indicates that the 'Id' is for either:
                                            --
                                            -- 1. A function or static constructor
                                            --    that refers to one or more CAFs, or
                                            --
                                            -- 2. A real live CAF

            | NoCafRefs                     -- ^ A function or static constructor
                                            -- that refers to no CAFs.
            deriving (Eq, Ord)

    -- | Assumes that the 'Id' has CAF references: definitely safe
    vanillaCafInfo :: CafInfo
    vanillaCafInfo = MayHaveCafRefs

    mayHaveCafRefs :: CafInfo -> Bool
    mayHaveCafRefs  MayHaveCafRefs = True
    mayHaveCafRefs _               = False

    instance Outputable CafInfo where
       ppr = ppCafInfo

    ppCafInfo :: CafInfo -> SDoc
    ppCafInfo NoCafRefs = text "NoCafRefs"
    ppCafInfo MayHaveCafRefs = empty

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Bulk operations on IdInfo}
    *                                                                      *
    ************************************************************************
    -}

    -- | This is used to remove information on lambda binders that we have
    -- setup as part of a lambda group, assuming they will be applied all at once,
    -- but turn out to be part of an unsaturated lambda as in e.g:
    --
    -- > (\x1. \x2. e) arg1
    zapLamInfo :: IdInfo -> Maybe IdInfo
    zapLamInfo info@(IdInfo {occInfo = occ, demandInfo = demand})
      | is_safe_occ occ && is_safe_dmd demand
      = Nothing
      | otherwise
      = Just (info {occInfo = safe_occ, demandInfo = topDmd})
      where
            -- The "unsafe" occ info is the ones that say I'm not in a lambda
            -- because that might not be true for an unsaturated lambda
        is_safe_occ occ | isAlwaysTailCalled occ     = False
        is_safe_occ (OneOcc { occ_in_lam = in_lam }) = in_lam
        is_safe_occ _other                           = True

        safe_occ = case occ of
                     OneOcc{} -> occ { occ_in_lam = True
                                     , occ_tail   = NoTailCallInfo }
                     IAmALoopBreaker{}
                              -> occ { occ_tail   = NoTailCallInfo }
                     _other   -> occ

        is_safe_dmd dmd = not (isStrictDmd dmd)

    -- | Remove all demand info on the 'IdInfo'
    zapDemandInfo :: IdInfo -> Maybe IdInfo
    zapDemandInfo info = Just (info {demandInfo = topDmd})

    -- | Remove usage (but not strictness) info on the 'IdInfo'
    zapUsageInfo :: IdInfo -> Maybe IdInfo
    zapUsageInfo info = Just (info {demandInfo = zapUsageDemand (demandInfo info)})

    -- | Remove usage environment info from the strictness signature on the 'IdInfo'
    zapUsageEnvInfo :: IdInfo -> Maybe IdInfo
    zapUsageEnvInfo info
        | hasDemandEnvSig (strictnessInfo info)
        = Just (info {strictnessInfo = zapUsageEnvSig (strictnessInfo info)})
        | otherwise
        = Nothing

    zapUsedOnceInfo :: IdInfo -> Maybe IdInfo
    zapUsedOnceInfo info
        = Just $ info { strictnessInfo = zapUsedOnceSig    (strictnessInfo info)
                      , demandInfo     = zapUsedOnceDemand (demandInfo     info) }

    zapFragileInfo :: IdInfo -> Maybe IdInfo
    -- ^ Zap info that depends on free variables
    zapFragileInfo info@(IdInfo { occInfo = occ, unfoldingInfo = unf })
      = new_unf `seq`  -- The unfolding field is not (currently) strict, so we
                       -- force it here to avoid a (zapFragileUnfolding unf) thunk
                       -- which might leak space
        Just (info `setRuleInfo` emptyRuleInfo
                   `setUnfoldingInfo` new_unf
                   `setOccInfo`       zapFragileOcc occ)
      where
        new_unf = zapFragileUnfolding unf

    zapFragileUnfolding :: Unfolding -> Unfolding
    zapFragileUnfolding unf
     | isFragileUnfolding unf = noUnfolding
     | otherwise              = unf

    zapTailCallInfo :: IdInfo -> Maybe IdInfo
    zapTailCallInfo info
      = case occInfo info of
          occ | isAlwaysTailCalled occ -> Just (info `setOccInfo` safe_occ)
              | otherwise              -> Nothing
            where
              safe_occ = occ { occ_tail = NoTailCallInfo }

    zapCallArityInfo :: IdInfo -> IdInfo
    zapCallArityInfo info = setCallArityInfo info 0

    {-
    ************************************************************************
    *                                                                      *
    \subsection{TickBoxOp}
    *                                                                      *
    ************************************************************************
    -}

    type TickBoxId = Int

    -- | Tick box for Hpc-style coverage
    data TickBoxOp
       = TickBox Module {-# UNPACK #-} !TickBoxId

    instance Outputable TickBoxOp where
        ppr (TickBox mod n)         = text "tick" <+> ppr (mod,n)

    {-
    ************************************************************************
    *                                                                      *
       Levity
    *                                                                      *
    ************************************************************************

    Note [Levity info]
    ~~~~~~~~~~~~~~~~~~

    Ids store whether or not they can be levity-polymorphic at any amount
    of saturation. This is helpful in optimizing the levity-polymorphism check
    done in the desugarer, where we can usually learn that something is not
    levity-polymorphic without actually figuring out its type. See
    isExprLevPoly in CoreUtils for where this info is used. Storing
    this is required to prevent perf/compiler/T5631 from blowing up.

    -}

    -- See Note [Levity info]
    data LevityInfo = NoLevityInfo  -- always safe
                    | NeverLevityPolymorphic
      deriving Eq

    instance Outputable LevityInfo where
      ppr NoLevityInfo           = text "NoLevityInfo"
      ppr NeverLevityPolymorphic = text "NeverLevityPolymorphic"

    -- | Marks an IdInfo describing an Id that is never levity polymorphic (even when
    -- applied). The Type is only there for checking that it's really never levity
    -- polymorphic
    setNeverLevPoly :: HasDebugCallStack => IdInfo -> Type -> IdInfo
    setNeverLevPoly info ty
      = ASSERT2( not (resultIsLevPoly ty), ppr ty )
        info { levityInfo = NeverLevityPolymorphic }

    setLevityInfoWithType :: IdInfo -> Type -> IdInfo
    setLevityInfoWithType info ty
      | not (resultIsLevPoly ty)
      = info { levityInfo = NeverLevityPolymorphic }
      | otherwise
      = info

    isNeverLevPolyIdInfo :: IdInfo -> Bool
    isNeverLevPolyIdInfo info
      | NeverLevityPolymorphic <- levityInfo info = True
      | otherwise                                 = False