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, destructors and operations on 'Unique's
            hasKey, cmpByUnique,

            pprUnique,

            mkUniqueGrimily,                -- Used in UniqSupply only!
            getKey,                         -- 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,
            mkCTupleTyConUnique,
            mkPreludeMiscIdUnique, mkPreludeDataConUnique,
            mkPreludeTyConUnique, mkPreludeClassUnique,
            mkPArrDataConUnique, mkCoVarUnique,

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

            tyConRepNameUnique,
            dataConWorkerUnique, dataConRepNameUnique,

            mkBuiltinUnique,
            mkPseudoUniqueD,
            mkPseudoUniqueE,
            mkPseudoUniqueH
        ) where

    #include "HsVersions.h"

    import BasicTypes
    import FastString
    import Outputable
    import Util

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

    import Data.Char        ( chr, ord )
    import Data.Bits

    {-
    ************************************************************************
    *                                                                      *
    \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 {-# UNPACK #-} !Int

    {-
    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

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

    mkUniqueGrimily = MkUnique

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

    incrUnique (MkUnique i) = MkUnique (i + 1)
    stepUnique (MkUnique i) n = MkUnique (i + n)

    -- deriveUnique uses an 'X' tag so that it won't clash with
    -- any of the uniques produced any other way
    -- SPJ says: this looks terribly smelly to me!
    deriveUnique (MkUnique i) delta = mkUnique 'X' (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 .|. bits)
      where
        tag  = ord c `shiftL` 24
        bits = i .&. 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 = chr (u `shiftR` 24)
            i   = u .&. 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 (uniqueOfFS fs)

    instance Uniquable Int where
     getUnique i = mkUniqueGrimily i

    cmpByUnique :: Uniquable a => a -> a -> Ordering
    cmpByUnique x y = (getUnique x) `cmpUnique` (getUnique y)

    {-
    ************************************************************************
    *                                                                      *
    \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).
    -}

    -- Note [Unique Determinism]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~
    -- The order of allocated @Uniques@ is not stable across rebuilds.
    -- The main reason for that is that typechecking interface files pulls
    -- @Uniques@ from @UniqSupply@ and the interface file for the module being
    -- currently compiled can, but doesn't have to exist.
    --
    -- It gets more complicated if you take into account that the interface
    -- files are loaded lazily and that building multiple files at once has to
    -- work for any subset of interface files present. When you add parallelism
    -- this makes @Uniques@ hopelessly random.
    --
    -- As such, to get deterministic builds, the order of the allocated
    -- @Uniques@ should not affect the final result.
    -- see also wiki/DeterministicBuilds

    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 n_ ""
      where
        go n cs | n < 62
                = let !c = chooseChar62 n in c : cs
                | otherwise
                = go q (c : cs) where (q, r) = quotRem n 62
                                      !c = chooseChar62 r

        chooseChar62 :: Int -> Char
        {-# INLINE chooseChar62 #-}
        chooseChar62 (I# 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     :: Boxity -> Arity -> Unique
    mkCTupleTyConUnique    :: Arity -> Unique
    mkPreludeDataConUnique :: Arity -> Unique
    mkTupleDataConUnique   :: Boxity -> Arity -> Unique
    mkPrimOpIdUnique       :: Int -> Unique
    mkPreludeMiscIdUnique  :: Int -> Unique
    mkPArrDataConUnique    :: Int -> Unique
    mkCoVarUnique          :: Int -> Unique

    mkAlphaTyVarUnique   i = mkUnique '1' i
    mkCoVarUnique        i = mkUnique 'g' i
    mkPreludeClassUnique i = mkUnique '2' i

    --------------------------------------------------
    -- Wired-in type constructor keys occupy *two* slots:
    --    * u: the TyCon itself
    --    * u+1: the TyConRepName of the TyCon
    mkPreludeTyConUnique i                = mkUnique '3' (2*i)
    mkTupleTyConUnique Boxed           a  = mkUnique '4' (2*a)
    mkTupleTyConUnique Unboxed         a  = mkUnique '5' (2*a)
    mkCTupleTyConUnique                a  = mkUnique 'k' (2*a)

    tyConRepNameUnique :: Unique -> Unique
    tyConRepNameUnique  u = incrUnique u

    -- 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).

    --------------------------------------------------
    -- Wired-in data constructor keys occupy *three* slots:
    --    * u: the DataCon itself
    --    * u+1: its worker Id
    --    * u+2: the TyConRepName of the promoted TyCon
    -- Prelude data constructors are too simple to need wrappers.

    mkPreludeDataConUnique i              = mkUnique '6' (3*i)    -- Must be alphabetic
    mkTupleDataConUnique Boxed          a = mkUnique '7' (3*a)    -- ditto (*may* be used in C labels)
    mkTupleDataConUnique Unboxed        a = mkUnique '8' (3*a)

    dataConRepNameUnique, dataConWorkerUnique :: Unique -> Unique
    dataConWorkerUnique  u = incrUnique u
    dataConRepNameUnique u = stepUnique u 2

    --------------------------------------------------
    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' (uniqueOfFS fs)
    mkDataOccUnique fs = mkUnique 'd' (uniqueOfFS fs)
    mkTvOccUnique   fs = mkUnique 'v' (uniqueOfFS fs)
    mkTcOccUnique   fs = mkUnique 'c' (uniqueOfFS fs)