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

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

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

        pprUniqueAlways,

        mkUniqueGrimily,
        getKey,
        mkUnique, unpkUnique,
        eqUnique, ltUnique,
        incrUnique, stepUnique,

        newTagUnique,
        nonDetCmpUnique,
        isValidKnownKeyUnique,

        -- ** Local uniques
        -- | These are exposed exclusively for use by 'GHC.Types.Var.Env.uniqAway', which
        -- has rather peculiar needs. See Note [Local uniques].
        mkLocalUnique, minLocalUnique, maxLocalUnique,
    ) where

#include "Unique.h"

import GHC.Prelude

import GHC.Data.FastString
import GHC.Utils.Outputable
import GHC.Utils.Panic.Plain

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

import Data.Char        ( chr, ord )

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

Note [Uniques and masks]
~~~~~~~~~~~~~~~~~~~~~~~~
A `Unique` in GHC is a Word-sized value composed of two pieces:
* A "mask", of width `UNIQUE_TAG_BITS`, in the high order bits
* A number, of width `uNIQUE_BITS`, which fills up the remainder of the Word

The mask is typically an ASCII character.  It is typically used to make it easier
to distinguish uniques constructed by different parts of the compiler.
There is a (potentially incomplete) list of unique masks used given in
GHC.Builtin.Uniques. See Note [Uniques-prelude - Uniques for wired-in Prelude things]

`mkUnique` constructs a `Unique` from its pieces
  mkUnique :: Char -> Int -> Unique

-}

-- | Unique identifier.
--
-- 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
--
-- These are sometimes also referred to as \"keys\" in comments in GHC.
newtype Unique = MkUnique Int

{-# INLINE uNIQUE_BITS #-}
uNIQUE_BITS :: Int
uNIQUE_BITS :: Int
uNIQUE_BITS = Int -> Int
forall b. FiniteBits b => b -> Int
finiteBitSize (Int
0 :: Int) Int -> Int -> Int
forall a. Num a => a -> a -> a
- UNIQUE_TAG_BITS

{-
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
newTagUnique :: Unique -> Char -> Unique

mkUniqueGrimily :: Int -> Unique
mkUniqueGrimily = Int -> Unique
MkUnique

{-# INLINE getKey #-}
getKey :: Unique -> Int
getKey (MkUnique Int
x) = Int
x

incrUnique :: Unique -> Unique
incrUnique (MkUnique Int
i) = Int -> Unique
MkUnique (Int
i Int -> Int -> Int
forall a. Num a => a -> a -> a
+ Int
1)
stepUnique :: Unique -> Int -> Unique
stepUnique (MkUnique Int
i) Int
n = Int -> Unique
MkUnique (Int
i Int -> Int -> Int
forall a. Num a => a -> a -> a
+ Int
n)

mkLocalUnique :: Int -> Unique
mkLocalUnique :: Int -> Unique
mkLocalUnique Int
i = Char -> Int -> Unique
mkUnique Char
'X' Int
i

minLocalUnique :: Unique
minLocalUnique :: Unique
minLocalUnique = Int -> Unique
mkLocalUnique Int
0

maxLocalUnique :: Unique
maxLocalUnique :: Unique
maxLocalUnique = Int -> Unique
mkLocalUnique Int
uniqueMask

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

-- | How many bits are devoted to the unique index (as opposed to the class
-- character).
uniqueMask :: Int
uniqueMask :: Int
uniqueMask = (Int
1 Int -> Int -> Int
forall a. Bits a => a -> Int -> a
`shiftL` Int
uNIQUE_BITS) Int -> Int -> Int
forall a. Num a => a -> a -> a
- Int
1

-- 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
-- EXPORTED and used only in GHC.Builtin.Uniques
mkUnique :: Char -> Int -> Unique
mkUnique Char
c Int
i
  = Int -> Unique
MkUnique (Int
tag Int -> Int -> Int
forall a. Bits a => a -> a -> a
.|. Int
bits)
  where
    tag :: Int
tag  = Char -> Int
ord Char
c Int -> Int -> Int
forall a. Bits a => a -> Int -> a
`shiftL` Int
uNIQUE_BITS
    bits :: Int
bits = Int
i Int -> Int -> Int
forall a. Bits a => a -> a -> a
.&. Int
uniqueMask

unpkUnique :: Unique -> (Char, Int)
unpkUnique (MkUnique Int
u)
  = let
        -- as long as the Char may have its eighth bit set, we
        -- really do need the logical right-shift here!
        tag :: Char
tag = Int -> Char
chr (Int
u Int -> Int -> Int
forall a. Bits a => a -> Int -> a
`shiftR` Int
uNIQUE_BITS)
        i :: Int
i   = Int
u Int -> Int -> Int
forall a. Bits a => a -> a -> a
.&. Int
uniqueMask
    in
    (Char
tag, Int
i)

-- | The interface file symbol-table encoding assumes that known-key uniques fit
-- in 30-bits; verify this.
--
-- See Note [Symbol table representation of names] in "GHC.Iface.Binary" for details.
isValidKnownKeyUnique :: Unique -> Bool
isValidKnownKeyUnique :: Unique -> Bool
isValidKnownKeyUnique Unique
u =
    case Unique -> (Char, Int)
unpkUnique Unique
u of
      (Char
c, Int
x) -> Char -> Int
ord Char
c Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
< Int
0xff Bool -> Bool -> Bool
&& Int
x Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
<= (Int
1 Int -> Int -> Int
forall a. Bits a => a -> Int -> a
`shiftL` Int
22)

{-
************************************************************************
*                                                                      *
\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
a
x hasKey :: forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
k    = a -> Unique
forall a. Uniquable a => a -> Unique
getUnique a
x Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
k

instance Uniquable FastString where
 getUnique :: FastString -> Unique
getUnique FastString
fs = Int -> Unique
mkUniqueGrimily (FastString -> Int
uniqueOfFS FastString
fs)

instance Uniquable Int where
 getUnique :: Int -> Unique
getUnique Int
i = Int -> Unique
mkUniqueGrimily Int
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).
-}

-- 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/deterministic-builds
--
-- Note [Unique Determinism and code generation]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- The goal of the deterministic builds (wiki/deterministic-builds, #4012)
-- is to get ABI compatible binaries given the same inputs and environment.
-- The motivation behind that is that if the ABI doesn't change the
-- binaries can be safely reused.
-- Note that this is weaker than bit-for-bit identical binaries and getting
-- bit-for-bit identical binaries is not a goal for now.
-- This means that we don't care about nondeterminism that happens after
-- the interface files are created, in particular we don't care about
-- register allocation and code generation.
-- To track progress on bit-for-bit determinism see #12262.

eqUnique :: Unique -> Unique -> Bool
eqUnique :: Unique -> Unique -> Bool
eqUnique (MkUnique Int
u1) (MkUnique Int
u2) = Int
u1 Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
== Int
u2

ltUnique :: Unique -> Unique -> Bool
ltUnique :: Unique -> Unique -> Bool
ltUnique (MkUnique Int
u1) (MkUnique Int
u2) = Int
u1 Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
< Int
u2

-- Provided here to make it explicit at the call-site that it can
-- introduce non-determinism.
-- See Note [Unique Determinism]
-- See Note [No Ord for Unique]
nonDetCmpUnique :: Unique -> Unique -> Ordering
nonDetCmpUnique :: Unique -> Unique -> Ordering
nonDetCmpUnique (MkUnique Int
u1) (MkUnique Int
u2)
  = if Int
u1 Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
== Int
u2 then Ordering
EQ else if Int
u1 Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
< Int
u2 then Ordering
LT else Ordering
GT

{-
Note [No Ord for Unique]
~~~~~~~~~~~~~~~~~~~~~~~~~~
As explained in Note [Unique Determinism] the relative order of Uniques
is nondeterministic. To prevent from accidental use the Ord Unique
instance has been removed.
This makes it easier to maintain deterministic builds, but comes with some
drawbacks.
The biggest drawback is that Maps keyed by Uniques can't directly be used.
The alternatives are:

  1) Use UniqFM or UniqDFM, see Note [Deterministic UniqFM] to decide which
  2) Create a newtype wrapper based on Unique ordering where nondeterminism
     is controlled. See Module.ModuleEnv
  3) Change the algorithm to use nonDetCmpUnique and document why it's still
     deterministic
  4) Use TrieMap as done in GHC.Cmm.CommonBlockElim.groupByLabel
-}

instance Eq Unique where
    Unique
a == :: Unique -> Unique -> Bool
== Unique
b = Unique -> Unique -> Bool
eqUnique Unique
a Unique
b
    Unique
a /= :: Unique -> Unique -> Bool
/= Unique
b = Bool -> Bool
not (Unique -> Unique -> Bool
eqUnique Unique
a Unique
b)

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

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

showUnique :: Unique -> String
showUnique :: Unique -> String
showUnique Unique
uniq
  = case Unique -> (Char, Int)
unpkUnique Unique
uniq of
      (Char
tag, Int
u) -> Char
tag Char -> String -> String
forall a. a -> [a] -> [a]
: Int -> String
iToBase62 Int
u

pprUniqueAlways :: Unique -> SDoc
-- The "always" means regardless of -dsuppress-uniques
-- It replaces the old pprUnique to remind callers that
-- they should consider whether they want to consult
-- Opt_SuppressUniques
pprUniqueAlways :: Unique -> SDoc
pprUniqueAlways Unique
u
  = String -> SDoc
text (Unique -> String
showUnique Unique
u)

instance Outputable Unique where
    ppr :: Unique -> SDoc
ppr = Unique -> SDoc
pprUniqueAlways

instance Show Unique where
    show :: Unique -> String
show Unique
uniq = Unique -> String
showUnique Unique
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 :: Int -> String
iToBase62 Int
n_
  = Bool -> String -> String
forall a. HasCallStack => Bool -> a -> a
assert (Int
n_ Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
>= Int
0) (String -> String) -> String -> String
forall a b. (a -> b) -> a -> b
$ Int -> String -> String
go Int
n_ String
""
  where
    go :: Int -> String -> String
go Int
n String
cs | Int
n Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
< Int
62
            = let !c :: Char
c = Int -> Char
chooseChar62 Int
n in Char
c Char -> String -> String
forall a. a -> [a] -> [a]
: String
cs
            | Bool
otherwise
            = Int -> String -> String
go Int
q (Char
c Char -> String -> String
forall a. a -> [a] -> [a]
: String
cs) where (!Int
q, Int
r) = Int -> Int -> (Int, Int)
forall a. Integral a => a -> a -> (a, a)
quotRem Int
n Int
62
                                  !c :: Char
c = Int -> Char
chooseChar62 Int
r

    chooseChar62 :: Int -> Char
    {-# INLINE chooseChar62 #-}
    chooseChar62 :: Int -> Char
chooseChar62 (I# Int#
n) = Char# -> Char
C# (Addr# -> Int# -> Char#
indexCharOffAddr# Addr#
chars62 Int#
n)
    chars62 :: Addr#
chars62 = Addr#
"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"#