basicTypes/Unique.hs

    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998

    @Uniques@ are used to distinguish entities in the compiler (@Ids@,
    @Classes@, etc.) from each other.  Thus, @Uniques@ are the basic
    comparison key in the compiler.

    If there is any single operation that needs to be fast, it is @Unique@
    comparison.  Unsurprisingly, there is quite a bit of huff-and-puff
    directed to that end.

    Some of the other hair in this code is to be able to use a
    ``splittable @UniqueSupply@'' if requested/possible (not standard
    Haskell).
    -}

    {-# LANGUAGE CPP, BangPatterns, MagicHash #-}

    module Unique (
            -- * Main data types
            Unique, Uniquable(..),

            -- ** Constructors, desctructors and operations on 'Unique's
            hasKey,

            pprUnique,

            mkUniqueGrimily,                -- Used in UniqSupply only!
            getKey, getKeyFastInt,          -- Used in Var, UniqFM, Name only!
            mkUnique, unpkUnique,           -- Used in BinIface only

            incrUnique,                     -- Used for renumbering
            deriveUnique,                   -- Ditto
            newTagUnique,                   -- Used in CgCase
            initTyVarUnique,

            -- ** Making built-in uniques

            -- now all the built-in Uniques (and functions to make them)
            -- [the Oh-So-Wonderful Haskell module system wins again...]
            mkAlphaTyVarUnique,
            mkPrimOpIdUnique,
            mkTupleTyConUnique, mkTupleDataConUnique,
            mkPreludeMiscIdUnique, mkPreludeDataConUnique,
            mkPreludeTyConUnique, mkPreludeClassUnique,
            mkPArrDataConUnique,

        mkVarOccUnique, mkDataOccUnique, mkTvOccUnique, mkTcOccUnique,
            mkRegSingleUnique, mkRegPairUnique, mkRegClassUnique, mkRegSubUnique,
            mkCostCentreUnique,

            mkBuiltinUnique,
            mkPseudoUniqueD,
            mkPseudoUniqueE,
            mkPseudoUniqueH
        ) where

    #include "HsVersions.h"

    import BasicTypes
    import FastTypes
    import FastString
    import Outputable
    -- import StaticFlags
    import Util

    --just for implementing a fast [0,61) -> Char function
    import GHC.Exts (indexCharOffAddr#, Char(..))

    import Data.Char        ( chr, ord )

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Unique-type]{@Unique@ type and operations}
    *                                                                      *
    ************************************************************************

    The @Chars@ are ``tag letters'' that identify the @UniqueSupply@.
    Fast comparison is everything on @Uniques@:
    -}

    --why not newtype Int?

    -- | The type of unique identifiers that are used in many places in GHC
    -- for fast ordering and equality tests. You should generate these with
    -- the functions from the 'UniqSupply' module
    data Unique = MkUnique FastInt

    {-
    Now come the functions which construct uniques from their pieces, and vice versa.
    The stuff about unique *supplies* is handled further down this module.
    -}

    unpkUnique      :: Unique -> (Char, Int)        -- The reverse

    mkUniqueGrimily :: Int -> Unique                -- A trap-door for UniqSupply
    getKey          :: Unique -> Int                -- for Var
    getKeyFastInt   :: Unique -> FastInt            -- for Var

    incrUnique      :: Unique -> Unique
    deriveUnique    :: Unique -> Int -> Unique
    newTagUnique    :: Unique -> Char -> Unique

    mkUniqueGrimily x = MkUnique (iUnbox x)

    {-# INLINE getKey #-}
    getKey (MkUnique x) = iBox x
    {-# INLINE getKeyFastInt #-}
    getKeyFastInt (MkUnique x) = x

    incrUnique (MkUnique i) = MkUnique (i +# _ILIT(1))

    -- deriveUnique uses an 'X' tag so that it won't clash with
    -- any of the uniques produced any other way
    deriveUnique (MkUnique i) delta = mkUnique 'X' (iBox i + delta)

    -- newTagUnique changes the "domain" of a unique to a different char
    newTagUnique u c = mkUnique c i where (_,i) = unpkUnique u

    -- pop the Char in the top 8 bits of the Unique(Supply)

    -- No 64-bit bugs here, as long as we have at least 32 bits. --JSM

    -- and as long as the Char fits in 8 bits, which we assume anyway!

    mkUnique :: Char -> Int -> Unique       -- Builds a unique from pieces
    -- NOT EXPORTED, so that we can see all the Chars that
    --               are used in this one module
    mkUnique c i
      = MkUnique (tag `bitOrFastInt` bits)
      where
        !tag  = fastOrd (cUnbox c) `shiftLFastInt` _ILIT(24)
        !bits = iUnbox i `bitAndFastInt` _ILIT(16777215){-``0x00ffffff''-}

    unpkUnique (MkUnique u)
      = let
            -- as long as the Char may have its eighth bit set, we
            -- really do need the logical right-shift here!
            tag = cBox (fastChr (u `shiftRLFastInt` _ILIT(24)))
            i   = iBox (u `bitAndFastInt` _ILIT(16777215){-``0x00ffffff''-})
        in
        (tag, i)

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Uniquable-class]{The @Uniquable@ class}
    *                                                                      *
    ************************************************************************
    -}

    -- | Class of things that we can obtain a 'Unique' from
    class Uniquable a where
        getUnique :: a -> Unique

    hasKey          :: Uniquable a => a -> Unique -> Bool
    x `hasKey` k    = getUnique x == k

    instance Uniquable FastString where
     getUnique fs = mkUniqueGrimily (iBox (uniqueOfFS fs))

    instance Uniquable Int where
     getUnique i = mkUniqueGrimily i

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Unique-instances]{Instance declarations for @Unique@}
    *                                                                      *
    ************************************************************************

    And the whole point (besides uniqueness) is fast equality.  We don't
    use `deriving' because we want {\em precise} control of ordering
    (equality on @Uniques@ is v common).
    -}

    eqUnique, ltUnique, leUnique :: Unique -> Unique -> Bool
    eqUnique (MkUnique u1) (MkUnique u2) = u1 ==# u2
    ltUnique (MkUnique u1) (MkUnique u2) = u1 <#  u2
    leUnique (MkUnique u1) (MkUnique u2) = u1 <=# u2

    cmpUnique :: Unique -> Unique -> Ordering
    cmpUnique (MkUnique u1) (MkUnique u2)
      = if u1 ==# u2 then EQ else if u1 <# u2 then LT else GT

    instance Eq Unique where
        a == b = eqUnique a b
        a /= b = not (eqUnique a b)

    instance Ord Unique where
        a  < b = ltUnique a b
        a <= b = leUnique a b
        a  > b = not (leUnique a b)
        a >= b = not (ltUnique a b)
        compare a b = cmpUnique a b

    -----------------
    instance Uniquable Unique where
        getUnique u = u

    -- We do sometimes make strings with @Uniques@ in them:

    showUnique :: Unique -> String
    showUnique uniq
      = case unpkUnique uniq of
          (tag, u) -> finish_show tag u (iToBase62 u)

    finish_show :: Char -> Int -> String -> String
    finish_show 't' u _pp_u | u < 26
      = -- Special case to make v common tyvars, t1, t2, ...
        -- come out as a, b, ... (shorter, easier to read)
        [chr (ord 'a' + u)]
    finish_show tag _ pp_u = tag : pp_u

    pprUnique :: Unique -> SDoc
    pprUnique u = text (showUnique u)

    instance Outputable Unique where
        ppr = pprUnique

    instance Show Unique where
        show uniq = showUnique uniq

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Utils-base62]{Base-62 numbers}
    *                                                                      *
    ************************************************************************

    A character-stingy way to read/write numbers (notably Uniques).
    The ``62-its'' are \tr{[0-9a-zA-Z]}.  We don't handle negative Ints.
    Code stolen from Lennart.
    -}

    iToBase62 :: Int -> String
    iToBase62 n_
      = ASSERT(n_ >= 0) go (iUnbox n_) ""
      where
        go n cs | n <# _ILIT(62)
                 = case chooseChar62 n of { c -> c `seq` (c : cs) }
                 | otherwise
                 =  case (quotRem (iBox n) 62) of { (q_, r_) ->
                    case iUnbox q_ of { q -> case iUnbox r_ of { r ->
                    case (chooseChar62 r) of { c -> c `seq`
                    (go q (c : cs)) }}}}

        chooseChar62 :: FastInt -> Char
        {-# INLINE chooseChar62 #-}
        chooseChar62 n = C# (indexCharOffAddr# chars62 n)
        !chars62 = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"#

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Uniques-prelude]{@Uniques@ for wired-in Prelude things}
    *                                                                      *
    ************************************************************************

    Allocation of unique supply characters:
            v,t,u : for renumbering value-, type- and usage- vars.
            B:   builtin
            C-E: pseudo uniques     (used in native-code generator)
            X:   uniques derived by deriveUnique
            _:   unifiable tyvars   (above)
            0-9: prelude things below
                 (no numbers left any more..)
            ::   (prelude) parallel array data constructors

            other a-z: lower case chars for unique supplies.  Used so far:

            d       desugarer
            f       AbsC flattener
            g       SimplStg
            n       Native codegen
            r       Hsc name cache
            s       simplifier
    -}

    mkAlphaTyVarUnique     :: Int -> Unique
    mkPreludeClassUnique   :: Int -> Unique
    mkPreludeTyConUnique   :: Int -> Unique
    mkTupleTyConUnique     :: TupleSort -> Int -> Unique
    mkPreludeDataConUnique :: Int -> Unique
    mkTupleDataConUnique   :: TupleSort -> Int -> Unique
    mkPrimOpIdUnique       :: Int -> Unique
    mkPreludeMiscIdUnique  :: Int -> Unique
    mkPArrDataConUnique    :: Int -> Unique

    mkAlphaTyVarUnique i            = mkUnique '1' i

    mkPreludeClassUnique i          = mkUnique '2' i

    -- Prelude type constructors occupy *three* slots.
    -- The first is for the tycon itself; the latter two
    -- are for the generic to/from Ids.  See TysWiredIn.mk_tc_gen_info.

    mkPreludeTyConUnique i          = mkUnique '3' (3*i)
    mkTupleTyConUnique BoxedTuple   a       = mkUnique '4' (3*a)
    mkTupleTyConUnique UnboxedTuple a       = mkUnique '5' (3*a)
    mkTupleTyConUnique ConstraintTuple a    = mkUnique 'k' (3*a)

    -- Data constructor keys occupy *two* slots.  The first is used for the
    -- data constructor itself and its wrapper function (the function that
    -- evaluates arguments as necessary and calls the worker). The second is
    -- used for the worker function (the function that builds the constructor
    -- representation).

    mkPreludeDataConUnique i        = mkUnique '6' (2*i)    -- Must be alphabetic
    mkTupleDataConUnique BoxedTuple   a = mkUnique '7' (2*a)        -- ditto (*may* be used in C labels)
    mkTupleDataConUnique UnboxedTuple    a = mkUnique '8' (2*a)
    mkTupleDataConUnique ConstraintTuple a = mkUnique 'h' (2*a)

    mkPrimOpIdUnique op         = mkUnique '9' op
    mkPreludeMiscIdUnique  i    = mkUnique '0' i

    -- No numbers left anymore, so I pick something different for the character tag
    mkPArrDataConUnique a           = mkUnique ':' (2*a)

    -- The "tyvar uniques" print specially nicely: a, b, c, etc.
    -- See pprUnique for details

    initTyVarUnique :: Unique
    initTyVarUnique = mkUnique 't' 0

    mkPseudoUniqueD, mkPseudoUniqueE, mkPseudoUniqueH,
       mkBuiltinUnique :: Int -> Unique

    mkBuiltinUnique i = mkUnique 'B' i
    mkPseudoUniqueD i = mkUnique 'D' i -- used in NCG for getUnique on RealRegs
    mkPseudoUniqueE i = mkUnique 'E' i -- used in NCG spiller to create spill VirtualRegs
    mkPseudoUniqueH i = mkUnique 'H' i -- used in NCG spiller to create spill VirtualRegs

    mkRegSingleUnique, mkRegPairUnique, mkRegSubUnique, mkRegClassUnique :: Int -> Unique
    mkRegSingleUnique = mkUnique 'R'
    mkRegSubUnique    = mkUnique 'S'
    mkRegPairUnique   = mkUnique 'P'
    mkRegClassUnique  = mkUnique 'L'

    mkCostCentreUnique :: Int -> Unique
    mkCostCentreUnique = mkUnique 'C'

    mkVarOccUnique, mkDataOccUnique, mkTvOccUnique, mkTcOccUnique :: FastString -> Unique
    -- See Note [The Unique of an OccName] in OccName
    mkVarOccUnique  fs = mkUnique 'i' (iBox (uniqueOfFS fs))
    mkDataOccUnique fs = mkUnique 'd' (iBox (uniqueOfFS fs))
    mkTvOccUnique   fs = mkUnique 'v' (iBox (uniqueOfFS fs))
    mkTcOccUnique   fs = mkUnique 'c' (iBox (uniqueOfFS fs))