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

module GHC.Types.RepType
  (
    -- * Code generator views onto Types
    UnaryType, NvUnaryType, isNvUnaryType,
    unwrapType,

    -- * Predicates on types
    isVoidTy,

    -- * Type representation for the code generator
    typePrimRep, typePrimRep1,
    runtimeRepPrimRep, typePrimRepArgs,
    PrimRep(..), primRepToType,
    countFunRepArgs, countConRepArgs, tyConPrimRep, tyConPrimRep1,

    -- * Unboxed sum representation type
    ubxSumRepType, layoutUbxSum, typeSlotTy, SlotTy (..),
    slotPrimRep, primRepSlot
  ) where

#include "HsVersions.h"

import GHC.Prelude

import GHC.Types.Basic (Arity, RepArity)
import GHC.Core.DataCon
import GHC.Builtin.Names
import GHC.Core.Coercion
import GHC.Core.TyCon
import GHC.Core.TyCon.RecWalk
import GHC.Core.TyCo.Rep
import GHC.Core.Type
import GHC.Builtin.Types.Prim
import {-# SOURCE #-} GHC.Builtin.Types ( anyTypeOfKind )

import GHC.Utils.Misc
import GHC.Utils.Outputable
import GHC.Utils.Panic

import Data.List (sort)
import qualified Data.IntSet as IS

{- **********************************************************************
*                                                                       *
                Representation types
*                                                                       *
********************************************************************** -}

type NvUnaryType = Type
type UnaryType   = Type
     -- Both are always a value type; i.e. its kind is TYPE rr
     -- for some rr; moreover the rr is never a variable.
     --
     --   NvUnaryType : never an unboxed tuple or sum, or void
     --
     --   UnaryType   : never an unboxed tuple or sum;
     --                 can be Void# or (# #)

isNvUnaryType :: Type -> Bool
isNvUnaryType :: Type -> Bool
isNvUnaryType Type
ty
  | [PrimRep
_] <- HasDebugCallStack => Type -> [PrimRep]
Type -> [PrimRep]
typePrimRep Type
ty
  = Bool
True
  | Bool
otherwise
  = Bool
False

-- INVARIANT: the result list is never empty.
typePrimRepArgs :: HasDebugCallStack => Type -> [PrimRep]
typePrimRepArgs :: HasDebugCallStack => Type -> [PrimRep]
typePrimRepArgs Type
ty
  | [] <- [PrimRep]
reps
  = [PrimRep
VoidRep]
  | Bool
otherwise
  = [PrimRep]
reps
  where
    reps :: [PrimRep]
reps = HasDebugCallStack => Type -> [PrimRep]
Type -> [PrimRep]
typePrimRep Type
ty

-- | Gets rid of the stuff that prevents us from understanding the
-- runtime representation of a type. Including:
--   1. Casts
--   2. Newtypes
--   3. Foralls
--   4. Synonyms
-- But not type/data families, because we don't have the envs to hand.
unwrapType :: Type -> Type
unwrapType :: Type -> Type
unwrapType Type
ty
  | Just (()
_, Type
unwrapped)
      <- NormaliseStepper () -> (() -> () -> ()) -> Type -> Maybe ((), Type)
forall ev.
NormaliseStepper ev -> (ev -> ev -> ev) -> Type -> Maybe (ev, Type)
topNormaliseTypeX NormaliseStepper ()
stepper () -> () -> ()
forall a. Monoid a => a -> a -> a
mappend Type
inner_ty
  = Type
unwrapped
  | Bool
otherwise
  = Type
inner_ty
  where
    inner_ty :: Type
inner_ty = Type -> Type
go Type
ty

    go :: Type -> Type
go Type
t | Just Type
t' <- Type -> Maybe Type
coreView Type
t = Type -> Type
go Type
t'
    go (ForAllTy TyCoVarBinder
_ Type
t)            = Type -> Type
go Type
t
    go (CastTy Type
t KindCoercion
_)              = Type -> Type
go Type
t
    go Type
t                         = Type
t

     -- cf. Coercion.unwrapNewTypeStepper
    stepper :: NormaliseStepper ()
stepper RecTcChecker
rec_nts TyCon
tc [Type]
tys
      | Just (Type
ty', KindCoercion
_) <- TyCon -> [Type] -> Maybe (Type, KindCoercion)
instNewTyCon_maybe TyCon
tc [Type]
tys
      = case RecTcChecker -> TyCon -> Maybe RecTcChecker
checkRecTc RecTcChecker
rec_nts TyCon
tc of
          Just RecTcChecker
rec_nts' -> RecTcChecker -> Type -> () -> NormaliseStepResult ()
forall ev. RecTcChecker -> Type -> ev -> NormaliseStepResult ev
NS_Step RecTcChecker
rec_nts' (Type -> Type
go Type
ty') ()
          Maybe RecTcChecker
Nothing       -> NormaliseStepResult ()
forall ev. NormaliseStepResult ev
NS_Abort   -- infinite newtypes
      | Bool
otherwise
      = NormaliseStepResult ()
forall ev. NormaliseStepResult ev
NS_Done

countFunRepArgs :: Arity -> Type -> RepArity
countFunRepArgs :: Int -> Type -> Int
countFunRepArgs Int
0 Type
_
  = Int
0
countFunRepArgs Int
n Type
ty
  | FunTy AnonArgFlag
_ Type
_ Type
arg Type
res <- Type -> Type
unwrapType Type
ty
  = [PrimRep] -> Int
forall (t :: * -> *) a. Foldable t => t a -> Int
length (HasDebugCallStack => Type -> [PrimRep]
Type -> [PrimRep]
typePrimRepArgs Type
arg) Int -> Int -> Int
forall a. Num a => a -> a -> a
+ Int -> Type -> Int
countFunRepArgs (Int
n Int -> Int -> Int
forall a. Num a => a -> a -> a
- Int
1) Type
res
  | Bool
otherwise
  = String -> SDoc -> Int
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"countFunRepArgs: arity greater than type can handle" ((Int, Type, [PrimRep]) -> SDoc
forall a. Outputable a => a -> SDoc
ppr (Int
n, Type
ty, HasDebugCallStack => Type -> [PrimRep]
Type -> [PrimRep]
typePrimRep Type
ty))

countConRepArgs :: DataCon -> RepArity
countConRepArgs :: DataCon -> Int
countConRepArgs DataCon
dc = Int -> Type -> Int
go (DataCon -> Int
dataConRepArity DataCon
dc) (DataCon -> Type
dataConRepType DataCon
dc)
  where
    go :: Arity -> Type -> RepArity
    go :: Int -> Type -> Int
go Int
0 Type
_
      = Int
0
    go Int
n Type
ty
      | FunTy AnonArgFlag
_ Type
_ Type
arg Type
res <- Type -> Type
unwrapType Type
ty
      = [PrimRep] -> Int
forall (t :: * -> *) a. Foldable t => t a -> Int
length (HasDebugCallStack => Type -> [PrimRep]
Type -> [PrimRep]
typePrimRep Type
arg) Int -> Int -> Int
forall a. Num a => a -> a -> a
+ Int -> Type -> Int
go (Int
n Int -> Int -> Int
forall a. Num a => a -> a -> a
- Int
1) Type
res
      | Bool
otherwise
      = String -> SDoc -> Int
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"countConRepArgs: arity greater than type can handle" ((Int, Type, [PrimRep]) -> SDoc
forall a. Outputable a => a -> SDoc
ppr (Int
n, Type
ty, HasDebugCallStack => Type -> [PrimRep]
Type -> [PrimRep]
typePrimRep Type
ty))

-- | True if the type has zero width.
isVoidTy :: Type -> Bool
isVoidTy :: Type -> Bool
isVoidTy = [PrimRep] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null ([PrimRep] -> Bool) -> (Type -> [PrimRep]) -> Type -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. HasDebugCallStack => Type -> [PrimRep]
Type -> [PrimRep]
typePrimRep


{- **********************************************************************
*                                                                       *
                Unboxed sums
 See Note [Translating unboxed sums to unboxed tuples] in GHC.Stg.Unarise
*                                                                       *
********************************************************************** -}

type SortedSlotTys = [SlotTy]

-- | Given the arguments of a sum type constructor application,
--   return the unboxed sum rep type.
--
-- E.g.
--
--   (# Int# | Maybe Int | (# Int#, Float# #) #)
--
-- We call `ubxSumRepType [ [IntRep], [LiftedRep], [IntRep, FloatRep] ]`,
-- which returns [WordSlot, PtrSlot, WordSlot, FloatSlot]
--
-- INVARIANT: Result slots are sorted (via Ord SlotTy), except that at the head
-- of the list we have the slot for the tag.
ubxSumRepType :: [[PrimRep]] -> [SlotTy]
ubxSumRepType :: [[PrimRep]] -> SortedSlotTys
ubxSumRepType [[PrimRep]]
constrs0
  -- These first two cases never classify an actual unboxed sum, which always
  -- has at least two disjuncts. But it could happen if a user writes, e.g.,
  -- forall (a :: TYPE (SumRep [IntRep])). ...
  -- which could never be instantiated. We still don't want to panic.
  | [[PrimRep]]
constrs0 [[PrimRep]] -> Int -> Bool
forall a. [a] -> Int -> Bool
`lengthLessThan` Int
2
  = [SlotTy
WordSlot]

  | Bool
otherwise
  = let
      combine_alts :: [SortedSlotTys]  -- slots of constructors
                   -> SortedSlotTys    -- final slots
      combine_alts :: [SortedSlotTys] -> SortedSlotTys
combine_alts [SortedSlotTys]
constrs = (SortedSlotTys -> SortedSlotTys -> SortedSlotTys)
-> SortedSlotTys -> [SortedSlotTys] -> SortedSlotTys
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' SortedSlotTys -> SortedSlotTys -> SortedSlotTys
merge [] [SortedSlotTys]
constrs

      merge :: SortedSlotTys -> SortedSlotTys -> SortedSlotTys
      merge :: SortedSlotTys -> SortedSlotTys -> SortedSlotTys
merge SortedSlotTys
existing_slots []
        = SortedSlotTys
existing_slots
      merge [] SortedSlotTys
needed_slots
        = SortedSlotTys
needed_slots
      merge (SlotTy
es : SortedSlotTys
ess) (SlotTy
s : SortedSlotTys
ss)
        | Just SlotTy
s' <- SlotTy
s SlotTy -> SlotTy -> Maybe SlotTy
`fitsIn` SlotTy
es
        = -- found a slot, use it
          SlotTy
s' SlotTy -> SortedSlotTys -> SortedSlotTys
forall a. a -> [a] -> [a]
: SortedSlotTys -> SortedSlotTys -> SortedSlotTys
merge SortedSlotTys
ess SortedSlotTys
ss
        | SlotTy
s SlotTy -> SlotTy -> Bool
forall a. Ord a => a -> a -> Bool
< SlotTy
es
        = -- we need a new slot and this is the right place for it
          SlotTy
s SlotTy -> SortedSlotTys -> SortedSlotTys
forall a. a -> [a] -> [a]
: SortedSlotTys -> SortedSlotTys -> SortedSlotTys
merge (SlotTy
es SlotTy -> SortedSlotTys -> SortedSlotTys
forall a. a -> [a] -> [a]
: SortedSlotTys
ess) SortedSlotTys
ss
        | Bool
otherwise
        = -- keep searching for a slot
          SlotTy
es SlotTy -> SortedSlotTys -> SortedSlotTys
forall a. a -> [a] -> [a]
: SortedSlotTys -> SortedSlotTys -> SortedSlotTys
merge SortedSlotTys
ess (SlotTy
s SlotTy -> SortedSlotTys -> SortedSlotTys
forall a. a -> [a] -> [a]
: SortedSlotTys
ss)

      -- Nesting unboxed tuples and sums is OK, so we need to flatten first.
      rep :: [PrimRep] -> SortedSlotTys
      rep :: [PrimRep] -> SortedSlotTys
rep [PrimRep]
ty = SortedSlotTys -> SortedSlotTys
forall a. Ord a => [a] -> [a]
sort ((PrimRep -> SlotTy) -> [PrimRep] -> SortedSlotTys
forall a b. (a -> b) -> [a] -> [b]
map PrimRep -> SlotTy
primRepSlot [PrimRep]
ty)

      sumRep :: SortedSlotTys
sumRep = SlotTy
WordSlot SlotTy -> SortedSlotTys -> SortedSlotTys
forall a. a -> [a] -> [a]
: [SortedSlotTys] -> SortedSlotTys
combine_alts (([PrimRep] -> SortedSlotTys) -> [[PrimRep]] -> [SortedSlotTys]
forall a b. (a -> b) -> [a] -> [b]
map [PrimRep] -> SortedSlotTys
rep [[PrimRep]]
constrs0)
               -- WordSlot: for the tag of the sum
    in
      SortedSlotTys
sumRep

layoutUbxSum :: SortedSlotTys -- Layout of sum. Does not include tag.
                              -- We assume that they are in increasing order
             -> [SlotTy]      -- Slot types of things we want to map to locations in the
                              -- sum layout
             -> [Int]         -- Where to map 'things' in the sum layout
layoutUbxSum :: SortedSlotTys -> SortedSlotTys -> [Int]
layoutUbxSum SortedSlotTys
sum_slots0 SortedSlotTys
arg_slots0 =
    SortedSlotTys -> IntSet -> [Int]
go SortedSlotTys
arg_slots0 IntSet
IS.empty
  where
    go :: [SlotTy] -> IS.IntSet -> [Int]
    go :: SortedSlotTys -> IntSet -> [Int]
go [] IntSet
_
      = []
    go (SlotTy
arg : SortedSlotTys
args) IntSet
used
      = let slot_idx :: Int
slot_idx = SlotTy -> Int -> SortedSlotTys -> IntSet -> Int
findSlot SlotTy
arg Int
0 SortedSlotTys
sum_slots0 IntSet
used
         in Int
slot_idx Int -> [Int] -> [Int]
forall a. a -> [a] -> [a]
: SortedSlotTys -> IntSet -> [Int]
go SortedSlotTys
args (Int -> IntSet -> IntSet
IS.insert Int
slot_idx IntSet
used)

    findSlot :: SlotTy -> Int -> SortedSlotTys -> IS.IntSet -> Int
    findSlot :: SlotTy -> Int -> SortedSlotTys -> IntSet -> Int
findSlot SlotTy
arg Int
slot_idx (SlotTy
slot : SortedSlotTys
slots) IntSet
useds
      | Bool -> Bool
not (Int -> IntSet -> Bool
IS.member Int
slot_idx IntSet
useds)
      , SlotTy -> Maybe SlotTy
forall a. a -> Maybe a
Just SlotTy
slot Maybe SlotTy -> Maybe SlotTy -> Bool
forall a. Eq a => a -> a -> Bool
== SlotTy
arg SlotTy -> SlotTy -> Maybe SlotTy
`fitsIn` SlotTy
slot
      = Int
slot_idx
      | Bool
otherwise
      = SlotTy -> Int -> SortedSlotTys -> IntSet -> Int
findSlot SlotTy
arg (Int
slot_idx Int -> Int -> Int
forall a. Num a => a -> a -> a
+ Int
1) SortedSlotTys
slots IntSet
useds
    findSlot SlotTy
_ Int
_ [] IntSet
_
      = String -> SDoc -> Int
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"findSlot" (String -> SDoc
text String
"Can't find slot" SDoc -> SDoc -> SDoc
$$ SortedSlotTys -> SDoc
forall a. Outputable a => a -> SDoc
ppr SortedSlotTys
sum_slots0 SDoc -> SDoc -> SDoc
$$ SortedSlotTys -> SDoc
forall a. Outputable a => a -> SDoc
ppr SortedSlotTys
arg_slots0)

--------------------------------------------------------------------------------

-- We have 3 kinds of slots:
--
--   - Pointer slot: Only shared between actual pointers to Haskell heap (i.e.
--     boxed objects). These come in two variants: Lifted and unlifted (see
--     #19645).
--
--   - Word slots: Shared between IntRep, WordRep, Int64Rep, Word64Rep, AddrRep.
--
--   - Float slots: Shared between floating point types.
--
--   - Void slots: Shared between void types. Not used in sums.
--
-- TODO(michalt): We should probably introduce `SlotTy`s for 8-/16-/32-bit
-- values, so that we can pack things more tightly.
data SlotTy = PtrLiftedSlot | PtrUnliftedSlot | WordSlot | Word64Slot | FloatSlot | DoubleSlot
  deriving (SlotTy -> SlotTy -> Bool
(SlotTy -> SlotTy -> Bool)
-> (SlotTy -> SlotTy -> Bool) -> Eq SlotTy
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
/= :: SlotTy -> SlotTy -> Bool
$c/= :: SlotTy -> SlotTy -> Bool
== :: SlotTy -> SlotTy -> Bool
$c== :: SlotTy -> SlotTy -> Bool
Eq, Eq SlotTy
Eq SlotTy
-> (SlotTy -> SlotTy -> Ordering)
-> (SlotTy -> SlotTy -> Bool)
-> (SlotTy -> SlotTy -> Bool)
-> (SlotTy -> SlotTy -> Bool)
-> (SlotTy -> SlotTy -> Bool)
-> (SlotTy -> SlotTy -> SlotTy)
-> (SlotTy -> SlotTy -> SlotTy)
-> Ord SlotTy
SlotTy -> SlotTy -> Bool
SlotTy -> SlotTy -> Ordering
SlotTy -> SlotTy -> SlotTy
forall a.
Eq a
-> (a -> a -> Ordering)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> a)
-> (a -> a -> a)
-> Ord a
min :: SlotTy -> SlotTy -> SlotTy
$cmin :: SlotTy -> SlotTy -> SlotTy
max :: SlotTy -> SlotTy -> SlotTy
$cmax :: SlotTy -> SlotTy -> SlotTy
>= :: SlotTy -> SlotTy -> Bool
$c>= :: SlotTy -> SlotTy -> Bool
> :: SlotTy -> SlotTy -> Bool
$c> :: SlotTy -> SlotTy -> Bool
<= :: SlotTy -> SlotTy -> Bool
$c<= :: SlotTy -> SlotTy -> Bool
< :: SlotTy -> SlotTy -> Bool
$c< :: SlotTy -> SlotTy -> Bool
compare :: SlotTy -> SlotTy -> Ordering
$ccompare :: SlotTy -> SlotTy -> Ordering
Ord)
    -- Constructor order is important! If slot A could fit into slot B
    -- then slot A must occur first.  E.g.  FloatSlot before DoubleSlot
    --
    -- We are assuming that WordSlot is smaller than or equal to Word64Slot
    -- (would not be true on a 128-bit machine)

instance Outputable SlotTy where
  ppr :: SlotTy -> SDoc
ppr SlotTy
PtrLiftedSlot   = String -> SDoc
text String
"PtrLiftedSlot"
  ppr SlotTy
PtrUnliftedSlot = String -> SDoc
text String
"PtrUnliftedSlot"
  ppr SlotTy
Word64Slot      = String -> SDoc
text String
"Word64Slot"
  ppr SlotTy
WordSlot        = String -> SDoc
text String
"WordSlot"
  ppr SlotTy
DoubleSlot      = String -> SDoc
text String
"DoubleSlot"
  ppr SlotTy
FloatSlot       = String -> SDoc
text String
"FloatSlot"

typeSlotTy :: UnaryType -> Maybe SlotTy
typeSlotTy :: Type -> Maybe SlotTy
typeSlotTy Type
ty
  | Type -> Bool
isVoidTy Type
ty
  = Maybe SlotTy
forall a. Maybe a
Nothing
  | Bool
otherwise
  = SlotTy -> Maybe SlotTy
forall a. a -> Maybe a
Just (PrimRep -> SlotTy
primRepSlot (HasDebugCallStack => Type -> PrimRep
Type -> PrimRep
typePrimRep1 Type
ty))

primRepSlot :: PrimRep -> SlotTy
primRepSlot :: PrimRep -> SlotTy
primRepSlot PrimRep
VoidRep     = String -> SDoc -> SlotTy
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"primRepSlot" (String -> SDoc
text String
"No slot for VoidRep")
primRepSlot PrimRep
LiftedRep   = SlotTy
PtrLiftedSlot
primRepSlot PrimRep
UnliftedRep = SlotTy
PtrUnliftedSlot
primRepSlot PrimRep
IntRep      = SlotTy
WordSlot
primRepSlot PrimRep
Int8Rep     = SlotTy
WordSlot
primRepSlot PrimRep
Int16Rep    = SlotTy
WordSlot
primRepSlot PrimRep
Int32Rep    = SlotTy
WordSlot
primRepSlot PrimRep
Int64Rep    = SlotTy
Word64Slot
primRepSlot PrimRep
WordRep     = SlotTy
WordSlot
primRepSlot PrimRep
Word8Rep    = SlotTy
WordSlot
primRepSlot PrimRep
Word16Rep   = SlotTy
WordSlot
primRepSlot PrimRep
Word32Rep   = SlotTy
WordSlot
primRepSlot PrimRep
Word64Rep   = SlotTy
Word64Slot
primRepSlot PrimRep
AddrRep     = SlotTy
WordSlot
primRepSlot PrimRep
FloatRep    = SlotTy
FloatSlot
primRepSlot PrimRep
DoubleRep   = SlotTy
DoubleSlot
primRepSlot VecRep{}    = String -> SDoc -> SlotTy
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"primRepSlot" (String -> SDoc
text String
"No slot for VecRep")

slotPrimRep :: SlotTy -> PrimRep
slotPrimRep :: SlotTy -> PrimRep
slotPrimRep SlotTy
PtrLiftedSlot   = PrimRep
LiftedRep
slotPrimRep SlotTy
PtrUnliftedSlot = PrimRep
UnliftedRep
slotPrimRep SlotTy
Word64Slot      = PrimRep
Word64Rep
slotPrimRep SlotTy
WordSlot        = PrimRep
WordRep
slotPrimRep SlotTy
DoubleSlot      = PrimRep
DoubleRep
slotPrimRep SlotTy
FloatSlot       = PrimRep
FloatRep

-- | Returns the bigger type if one fits into the other. (commutative)
fitsIn :: SlotTy -> SlotTy -> Maybe SlotTy
fitsIn :: SlotTy -> SlotTy -> Maybe SlotTy
fitsIn SlotTy
ty1 SlotTy
ty2
  | SlotTy
ty1 SlotTy -> SlotTy -> Bool
forall a. Eq a => a -> a -> Bool
== SlotTy
ty2
  = SlotTy -> Maybe SlotTy
forall a. a -> Maybe a
Just SlotTy
ty1
  | SlotTy -> Bool
isWordSlot SlotTy
ty1 Bool -> Bool -> Bool
&& SlotTy -> Bool
isWordSlot SlotTy
ty2
  = SlotTy -> Maybe SlotTy
forall a. a -> Maybe a
Just (SlotTy -> SlotTy -> SlotTy
forall a. Ord a => a -> a -> a
max SlotTy
ty1 SlotTy
ty2)
  | SlotTy -> Bool
isFloatSlot SlotTy
ty1 Bool -> Bool -> Bool
&& SlotTy -> Bool
isFloatSlot SlotTy
ty2
  = SlotTy -> Maybe SlotTy
forall a. a -> Maybe a
Just (SlotTy -> SlotTy -> SlotTy
forall a. Ord a => a -> a -> a
max SlotTy
ty1 SlotTy
ty2)
  | Bool
otherwise
  = Maybe SlotTy
forall a. Maybe a
Nothing
  where
    isWordSlot :: SlotTy -> Bool
isWordSlot SlotTy
Word64Slot = Bool
True
    isWordSlot SlotTy
WordSlot   = Bool
True
    isWordSlot SlotTy
_          = Bool
False

    isFloatSlot :: SlotTy -> Bool
isFloatSlot SlotTy
DoubleSlot = Bool
True
    isFloatSlot SlotTy
FloatSlot  = Bool
True
    isFloatSlot SlotTy
_          = Bool
False


{- **********************************************************************
*                                                                       *
                   PrimRep
*                                                                       *
*************************************************************************

Note [RuntimeRep and PrimRep]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This Note describes the relationship between GHC.Types.RuntimeRep
(of levity-polymorphism fame) and GHC.Core.TyCon.PrimRep, as these types
are closely related.

A "primitive entity" is one that can be
 * stored in one register
 * manipulated with one machine instruction


Examples include:
 * a 32-bit integer
 * a 32-bit float
 * a 64-bit float
 * a machine address (heap pointer), etc.
 * a quad-float (on a machine with SIMD register and instructions)
 * ...etc...

The "representation or a primitive entity" specifies what kind of register is
needed and how many bits are required. The data type GHC.Core.TyCon.PrimRep
enumerates all the possibilities.

data PrimRep
  = VoidRep
  | LiftedRep     -- ^ Lifted pointer
  | UnliftedRep   -- ^ Unlifted pointer
  | Int8Rep       -- ^ Signed, 8-bit value
  | Int16Rep      -- ^ Signed, 16-bit value
  ...etc...
  | VecRep Int PrimElemRep  -- ^ SIMD fixed-width vector

The Haskell source language is a bit more flexible: a single value may need multiple PrimReps.
For example

  utup :: (# Int, Int #) -> Bool
  utup x = ...

Here x :: (# Int, Int #), and that takes two registers, and two instructions to move around.
Unboxed sums are similar.

Every Haskell expression e has a type ty, whose kind is of form TYPE rep
   e :: ty :: TYPE rep
where rep :: RuntimeRep. Here rep describes the runtime representation for e's value,
but RuntimeRep has some extra cases:

data RuntimeRep = VecRep VecCount VecElem   -- ^ a SIMD vector type
                | TupleRep [RuntimeRep]     -- ^ An unboxed tuple of the given reps
                | SumRep [RuntimeRep]       -- ^ An unboxed sum of the given reps
                | BoxedRep Levity -- ^ boxed; represented by a pointer
                | IntRep          -- ^ signed, word-sized value
                ...etc...
data Levity     = Lifted
                | Unlifted

It's all in 1-1 correspondence with PrimRep except for TupleRep and SumRep,
which describe unboxed products and sums respectively. RuntimeRep is defined
in the library ghc-prim:GHC.Types. It is also "wired-in" to GHC: see
GHC.Builtin.Types.runtimeRepTyCon. The unarisation pass, in GHC.Stg.Unarise, transforms the
program, so that every variable has a type that has a PrimRep. For
example, unarisation transforms our utup function above, to take two Int
arguments instead of one (# Int, Int #) argument.

Also, note that boxed types are represented slightly differently in RuntimeRep
and PrimRep. PrimRep just has the nullary LiftedRep and UnliftedRep data
constructors. RuntimeRep has a BoxedRep data constructor, which accepts a
Levity. The subtle distinction is that since BoxedRep can accept a variable
argument, RuntimeRep can talk about levity polymorphic types. PrimRep, by
contrast, cannot.

See also Note [Getting from RuntimeRep to PrimRep] and Note [VoidRep].

Note [VoidRep]
~~~~~~~~~~~~~~
PrimRep contains a constructor VoidRep, while RuntimeRep does
not. Yet representations are often characterised by a list of PrimReps,
where a void would be denoted as []. (See also Note [RuntimeRep and PrimRep].)

However, after the unariser, all identifiers have exactly one PrimRep, but
void arguments still exist. Thus, PrimRep includes VoidRep to describe these
binders. Perhaps post-unariser representations (which need VoidRep) should be
a different type than pre-unariser representations (which use a list and do
not need VoidRep), but we have what we have.

RuntimeRep instead uses TupleRep '[] to denote a void argument. When
converting a TupleRep '[] into a list of PrimReps, we get an empty list.

Note [Getting from RuntimeRep to PrimRep]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
General info on RuntimeRep and PrimRep is in Note [RuntimeRep and PrimRep].

How do we get from an Id to the list or PrimReps used to store it? We get
the Id's type ty (using idType), then ty's kind ki (using typeKind), then
pattern-match on ki to extract rep (in kindPrimRep), then extract the PrimRep
from the RuntimeRep (in runtimeRepPrimRep).

We now must convert the RuntimeRep to a list of PrimReps. Let's look at two
examples:

  1. x :: Int#
  2. y :: (# Int, Word# #)

With these types, we can extract these kinds:

  1. Int# :: TYPE IntRep
  2. (# Int, Word# #) :: TYPE (TupleRep [LiftedRep, WordRep])

In the end, we will get these PrimReps:

  1. [IntRep]
  2. [LiftedRep, WordRep]

It would thus seem that we should have a function somewhere of
type `RuntimeRep -> [PrimRep]`. This doesn't work though: when we
look at the argument of TYPE, we get something of type Type (of course).
RuntimeRep exists in the user's program, but not in GHC as such.
Instead, we must decompose the Type of kind RuntimeRep into tycons and
extract the PrimReps from the TyCons. This is what runtimeRepPrimRep does:
it takes a Type and returns a [PrimRep]

runtimeRepPrimRep works by using tyConRuntimeRepInfo. That function
should be passed the TyCon produced by promoting one of the constructors
of RuntimeRep into type-level data. The RuntimeRep promoted datacons are
associated with a RuntimeRepInfo (stored directly in the PromotedDataCon
constructor of TyCon). This pairing happens in GHC.Builtin.Types. A RuntimeRepInfo
usually(*) contains a function from [Type] to [PrimRep]: the [Type] are
the arguments to the promoted datacon. These arguments are necessary
for the TupleRep and SumRep constructors, so that this process can recur,
producing a flattened list of PrimReps. Calling this extracted function
happens in runtimeRepPrimRep; the functions themselves are defined in
tupleRepDataCon and sumRepDataCon, both in GHC.Builtin.Types.

The (*) above is to support vector representations. RuntimeRep refers
to VecCount and VecElem, whose promoted datacons have nuggets of information
related to vectors; these form the other alternatives for RuntimeRepInfo.

Returning to our examples, the Types we get (after stripping off TYPE) are

  1. TyConApp (PromotedDataCon "IntRep") []
  2. TyConApp (PromotedDataCon "TupleRep")
              [TyConApp (PromotedDataCon ":")
                        [ TyConApp (AlgTyCon "RuntimeRep") []
                        , TyConApp (PromotedDataCon "LiftedRep") []
                        , TyConApp (PromotedDataCon ":")
                                   [ TyConApp (AlgTyCon "RuntimeRep") []
                                   , TyConApp (PromotedDataCon "WordRep") []
                                   , TyConApp (PromotedDataCon "'[]")
                                              [TyConApp (AlgTyCon "RuntimeRep") []]]]]

runtimeRepPrimRep calls tyConRuntimeRepInfo on (PromotedDataCon "IntRep"), resp.
(PromotedDataCon "TupleRep"), extracting a function that will produce the PrimReps.
In example 1, this function is passed an empty list (the empty list of args to IntRep)
and returns the PrimRep IntRep. (See the definition of runtimeRepSimpleDataCons in
GHC.Builtin.Types and its helper function mk_runtime_rep_dc.) Example 2 passes the promoted
list as the one argument to the extracted function. The extracted function is defined
as prim_rep_fun within tupleRepDataCon in GHC.Builtin.Types. It takes one argument, decomposes
the promoted list (with extractPromotedList), and then recurs back to runtimeRepPrimRep
to process the LiftedRep and WordRep, concatentating the results.

-}

-- | Discovers the primitive representation of a 'Type'. Returns
-- a list of 'PrimRep': it's a list because of the possibility of
-- no runtime representation (void) or multiple (unboxed tuple/sum)
-- See also Note [Getting from RuntimeRep to PrimRep]
typePrimRep :: HasDebugCallStack => Type -> [PrimRep]
typePrimRep :: HasDebugCallStack => Type -> [PrimRep]
typePrimRep Type
ty = HasDebugCallStack => SDoc -> Type -> [PrimRep]
SDoc -> Type -> [PrimRep]
kindPrimRep (String -> SDoc
text String
"typePrimRep" SDoc -> SDoc -> SDoc
<+>
                              SDoc -> SDoc
parens (Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
ty SDoc -> SDoc -> SDoc
<+> SDoc
dcolon SDoc -> SDoc -> SDoc
<+> Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr (HasDebugCallStack => Type -> Type
Type -> Type
typeKind Type
ty)))
                             (HasDebugCallStack => Type -> Type
Type -> Type
typeKind Type
ty)

-- | Like 'typePrimRep', but assumes that there is precisely one 'PrimRep' output;
-- an empty list of PrimReps becomes a VoidRep.
-- This assumption holds after unarise, see Note [Post-unarisation invariants].
-- Before unarise it may or may not hold.
-- See also Note [RuntimeRep and PrimRep] and Note [VoidRep]
typePrimRep1 :: HasDebugCallStack => UnaryType -> PrimRep
typePrimRep1 :: HasDebugCallStack => Type -> PrimRep
typePrimRep1 Type
ty = case HasDebugCallStack => Type -> [PrimRep]
Type -> [PrimRep]
typePrimRep Type
ty of
  []    -> PrimRep
VoidRep
  [PrimRep
rep] -> PrimRep
rep
  [PrimRep]
_     -> String -> SDoc -> PrimRep
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"typePrimRep1" (Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
ty SDoc -> SDoc -> SDoc
$$ [PrimRep] -> SDoc
forall a. Outputable a => a -> SDoc
ppr (HasDebugCallStack => Type -> [PrimRep]
Type -> [PrimRep]
typePrimRep Type
ty))

-- | Find the runtime representation of a 'TyCon'. Defined here to
-- avoid module loops. Returns a list of the register shapes necessary.
-- See also Note [Getting from RuntimeRep to PrimRep]
tyConPrimRep :: HasDebugCallStack => TyCon -> [PrimRep]
tyConPrimRep :: HasDebugCallStack => TyCon -> [PrimRep]
tyConPrimRep TyCon
tc
  = HasDebugCallStack => SDoc -> Type -> [PrimRep]
SDoc -> Type -> [PrimRep]
kindPrimRep (String -> SDoc
text String
"kindRep tc" SDoc -> SDoc -> SDoc
<+> TyCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr TyCon
tc SDoc -> SDoc -> SDoc
$$ Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
res_kind)
                Type
res_kind
  where
    res_kind :: Type
res_kind = TyCon -> Type
tyConResKind TyCon
tc

-- | Like 'tyConPrimRep', but assumed that there is precisely zero or
-- one 'PrimRep' output
-- See also Note [Getting from RuntimeRep to PrimRep] and Note [VoidRep]
tyConPrimRep1 :: HasDebugCallStack => TyCon -> PrimRep
tyConPrimRep1 :: HasDebugCallStack => TyCon -> PrimRep
tyConPrimRep1 TyCon
tc = case HasDebugCallStack => TyCon -> [PrimRep]
TyCon -> [PrimRep]
tyConPrimRep TyCon
tc of
  []    -> PrimRep
VoidRep
  [PrimRep
rep] -> PrimRep
rep
  [PrimRep]
_     -> String -> SDoc -> PrimRep
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"tyConPrimRep1" (TyCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr TyCon
tc SDoc -> SDoc -> SDoc
$$ [PrimRep] -> SDoc
forall a. Outputable a => a -> SDoc
ppr (HasDebugCallStack => TyCon -> [PrimRep]
TyCon -> [PrimRep]
tyConPrimRep TyCon
tc))

-- | Take a kind (of shape @TYPE rr@) and produce the 'PrimRep's
-- of values of types of this kind.
-- See also Note [Getting from RuntimeRep to PrimRep]
kindPrimRep :: HasDebugCallStack => SDoc -> Kind -> [PrimRep]
kindPrimRep :: HasDebugCallStack => SDoc -> Type -> [PrimRep]
kindPrimRep SDoc
doc Type
ki
  | Just Type
ki' <- Type -> Maybe Type
coreView Type
ki
  = HasDebugCallStack => SDoc -> Type -> [PrimRep]
SDoc -> Type -> [PrimRep]
kindPrimRep SDoc
doc Type
ki'
kindPrimRep SDoc
doc (TyConApp TyCon
typ [Type
runtime_rep])
  = ASSERT( typ `hasKey` tYPETyConKey )
    HasDebugCallStack => SDoc -> Type -> [PrimRep]
SDoc -> Type -> [PrimRep]
runtimeRepPrimRep SDoc
doc Type
runtime_rep
kindPrimRep SDoc
doc Type
ki
  = String -> SDoc -> [PrimRep]
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"kindPrimRep" (Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
ki SDoc -> SDoc -> SDoc
$$ SDoc
doc)

-- | Take a type of kind RuntimeRep and extract the list of 'PrimRep' that
-- it encodes. See also Note [Getting from RuntimeRep to PrimRep]
runtimeRepPrimRep :: HasDebugCallStack => SDoc -> Type -> [PrimRep]
runtimeRepPrimRep :: HasDebugCallStack => SDoc -> Type -> [PrimRep]
runtimeRepPrimRep SDoc
doc Type
rr_ty
  | Just Type
rr_ty' <- Type -> Maybe Type
coreView Type
rr_ty
  = HasDebugCallStack => SDoc -> Type -> [PrimRep]
SDoc -> Type -> [PrimRep]
runtimeRepPrimRep SDoc
doc Type
rr_ty'
  | TyConApp TyCon
rr_dc [Type]
args <- Type
rr_ty
  , RuntimeRep [Type] -> [PrimRep]
fun <- TyCon -> RuntimeRepInfo
tyConRuntimeRepInfo TyCon
rr_dc
  = [Type] -> [PrimRep]
fun [Type]
args
  | Bool
otherwise
  = String -> SDoc -> [PrimRep]
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"runtimeRepPrimRep" (SDoc
doc SDoc -> SDoc -> SDoc
$$ Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
rr_ty)

-- | Convert a PrimRep back to a Type. Used only in the unariser to give types
-- to fresh Ids. Really, only the type's representation matters.
-- See also Note [RuntimeRep and PrimRep]
primRepToType :: PrimRep -> Type
primRepToType :: PrimRep -> Type
primRepToType = Type -> Type
anyTypeOfKind (Type -> Type) -> (PrimRep -> Type) -> PrimRep -> Type
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Type -> Type
tYPE (Type -> Type) -> (PrimRep -> Type) -> PrimRep -> Type
forall b c a. (b -> c) -> (a -> b) -> a -> c
. PrimRep -> Type
primRepToRuntimeRep