{-|
Copyright : (C) 2017-2022, Google Inc.,
2021-2022, QBayLogic B.V.
License : BSD2 (see the file LICENSE)
Maintainer : QBayLogic B.V. <devops@qbaylogic.com>
Call-by-need evaluator based on the evaluator described in:
Maximilian Bolingbroke, Simon Peyton Jones, "Supercompilation by evaluation",
Haskell '10, Baltimore, Maryland, USA.
-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}
module Clash.GHC.Evaluator where
import Prelude hiding (lookup)
import Control.Concurrent.Supply (Supply, freshId)
import Data.Either (lefts,rights)
import Data.List (foldl',mapAccumL)
import qualified Data.Primitive.ByteArray as BA
import qualified Data.Text as Text
#if MIN_VERSION_base(4,15,0)
import GHC.Num.Integer (Integer (..))
#else
import GHC.Integer.GMP.Internals
(Integer (..), BigNat (..))
#endif
import Clash.Core.DataCon
import Clash.Core.Evaluator.Types
import Clash.Core.HasFreeVars
import Clash.Core.HasType
import Clash.Core.Literal
import Clash.Core.Name
import Clash.Core.Pretty
import Clash.Core.Subst
import Clash.Core.Term
import Clash.Core.TyCon
import Clash.Core.Type
import Clash.Core.Util
import Clash.Core.Var
import Clash.Core.VarEnv
import Clash.Debug
import qualified Clash.Normalize.Primitives as NP (removedArg, undefined, undefinedX)
import Clash.Unique
import Clash.Util (curLoc)
import Clash.GHC.Evaluator.Primitive
evaluator :: Evaluator
evaluator = Evaluator
{ step = ghcStep
, unwind = ghcUnwind
, primStep = ghcPrimStep
, primUnwind = ghcPrimUnwind
}
{- [Note: forcing special primitives]
Clash uses the `whnf` function in two places (for now):
1. The case-of-known-constructor transformation
2. The reduceConstant transformation
The first transformation is needed to reach the required normal form. The
second transformation is more of cleanup transformation, so non-essential.
Normally, `whnf` would force the evaluation of all primitives, which is needed
in the `case-of-known-constructor` transformation. However, there are some
primitives which we want to leave unevaluated in the `reduceConstant`
transformation. Such primitives are:
- Primitives such as `Clash.Sized.Vector.transpose`, `Clash.Sized.Vector.map`,
etc. that do not reduce to an expression in normal form. Where the
`reduceConstant` transformation is supposed to be normal-form preserving.
- Primitives such as `GHC.Int.I8#`, `GHC.Word.W32#`, etc. which seem like
wrappers around a 64-bit literal, but actually perform truncation to the
desired bit-size.
This is why the Primitive Evaluator gets a flag telling whether it should
evaluate these special primitives.
-}
stepVar :: Id -> Step
stepVar i m _
| Just e <- heapLookup LocalId i m
= go LocalId e
| Just e <- heapLookup GlobalId i m
, isGlobalId i
= go GlobalId e
| otherwise
= Nothing
where
go s e =
let term = deShadowTerm (mScopeNames m) (tickExpr e)
in Just . setTerm term . stackPush (Update s i) $ heapDelete s i m
-- Removing the heap-bound value on a force ensures we do not get stuck on
-- expressions such as: "let x = x in x"
tickExpr = Tick (NameMod PrefixName (LitTy . SymTy $ toStr i))
unQualName = snd . Text.breakOnEnd "."
toStr = Text.unpack . unQualName . flip Text.snoc '_' . nameOcc . varName
stepData :: DataCon -> Step
stepData dc = ghcUnwind (DC dc [])
stepLiteral :: Literal -> Step
stepLiteral l = ghcUnwind (Lit l)
stepPrim :: PrimInfo -> Step
stepPrim pInfo m tcm
| primName pInfo == "GHC.Prim.realWorld#" =
ghcUnwind (PrimVal pInfo [] []) m tcm
| otherwise =
case fst $ splitFunForallTy (primType pInfo) of
[] -> ghcPrimStep tcm (forcePrims m) pInfo [] [] m
tys -> newBinder tys (Prim pInfo) m tcm
stepLam :: Id -> Term -> Step
stepLam x e = ghcUnwind (Lambda x e)
stepTyLam :: TyVar -> Term -> Step
stepTyLam x e = ghcUnwind (TyLambda x e)
stepApp :: Term -> Term -> Step
stepApp x y m tcm =
case term of
Data dc ->
let tys = fst $ splitFunForallTy (dcType dc)
in case compare (length args) (length tys) of
EQ -> ghcUnwind (DC dc args) m tcm
LT -> newBinder tys' (App x y) m tcm
GT -> error "Overapplied DC"
Prim p ->
let tys = fst $ splitFunForallTy (primType p)
in case compare (length args) (length tys) of
EQ -> case lefts args of
-- We make boolean conjunction and disjunction extra lazy by
-- deferring the evaluation of the arguments during the evaluation
-- of the primop rule.
--
-- This allows us to implement:
--
-- x && True --> x
-- x && False --> False
-- x || True --> True
-- x || False --> x
--
-- even when that 'x' is _|_. This makes the evaluation
-- rule lazier than the actual Haskel implementations which
-- are strict in the first argument and lazy in the second.
[a0, a1] | primName p `elem` ["GHC.Classes.&&","GHC.Classes.||"] ->
let (m0,i) = newLetBinding tcm m a0
(m1,j) = newLetBinding tcm m0 a1
in ghcPrimStep tcm (forcePrims m) p [] [Suspend (Var i), Suspend (Var j)] m1
(e':es)
| primName p `elem` (undefinedXPrims ++ undefinedPrims)
-- The above primitives are (bottoming) values, whose arguments
-- are never used anywhere in the rest of the compiler. So
-- instead of pushing a PrimApply frame on the stack to evaluate
-- those arguments, we instead just unwind the stack with the
-- primitive value and leave its arguments in an unevaluated
-- state (Suspend).
-> ghcUnwind (PrimVal p (rights args) (map Suspend (e':es))) m tcm
| otherwise
-> Just . setTerm e' $ stackPush (PrimApply p (rights args) [] es) m
_ -> error "internal error"
LT -> newBinder tys' (App x y) m tcm
GT -> let (m0, n) = newLetBinding tcm m y
in Just . setTerm x $ stackPush (Apply n) m0
_ -> let (m0, n) = newLetBinding tcm m y
in Just . setTerm x $ stackPush (Apply n) m0
where
(term, args, _) = collectArgsTicks (App x y)
tys' = fst . splitFunForallTy . inferCoreTypeOf tcm $ App x y
stepTyApp :: Term -> Type -> Step
stepTyApp x ty m tcm =
case term of
Data dc ->
let tys = fst $ splitFunForallTy (dcType dc)
in case compare (length args) (length tys) of
EQ -> ghcUnwind (DC dc args) m tcm
LT -> newBinder tys' (TyApp x ty) m tcm
GT -> error "Overapplied DC"
Prim p ->
let tys = fst $ splitFunForallTy (primType p)
in case compare (length args) (length tys) of
EQ -> case lefts args of
[] | primName p `elem` fmap primName [ NP.removedArg
, NP.undefined
, NP.undefinedX ] ->
ghcUnwind (PrimVal p (rights args) []) m tcm
| otherwise ->
ghcPrimStep tcm (forcePrims m) p (rights args) [] m
(e':es) ->
Just . setTerm e' $ stackPush (PrimApply p (rights args) [] es) m
LT -> newBinder tys' (TyApp x ty) m tcm
GT -> Just . setTerm x $ stackPush (Instantiate ty) m
_ -> Just . setTerm x $ stackPush (Instantiate ty) m
where
(term, args, _) = collectArgsTicks (TyApp x ty)
tys' = fst . splitFunForallTy . inferCoreTypeOf tcm $ TyApp x ty
stepLet :: Bind Term -> Term -> Step
stepLet (NonRec i b) x m _ = Just (allocate [(i,b)] x m)
stepLet (Rec bs) x m _ = Just (allocate bs x m)
stepCase :: Term -> Type -> [Alt] -> Step
stepCase scrut ty alts m _ =
Just . setTerm scrut $ stackPush (Scrutinise ty alts) m
-- TODO Support stepwise evaluation of casts.
--
stepCast :: Term -> Type -> Type -> Step
stepCast _ _ _ _ _ =
flip trace Nothing $ unlines
[ "WARNING: " <> $(curLoc) <> "Clash can't symbolically evaluate casts"
, "Please file an issue at https://github.com/clash-lang/clash-compiler/issues"
]
stepTick :: TickInfo -> Term -> Step
stepTick tick x m _ =
Just . setTerm x $ stackPush (Tickish tick) m
-- | Small-step operational semantics.
--
ghcStep :: Step
ghcStep m = case mTerm m of
Var i -> stepVar i m
Data dc -> stepData dc m
Literal l -> stepLiteral l m
Prim p -> stepPrim p m
Lam v x -> stepLam v x m
TyLam v x -> stepTyLam v x m
App x y -> stepApp x y m
TyApp x ty -> stepTyApp x ty m
Let bs x -> stepLet bs x m
Case s ty as -> stepCase s ty as m
Cast x a b -> stepCast x a b m
Tick t x -> stepTick t x m
-- | Take a list of types or type variables and create a lambda / type lambda
-- for each one around the given term.
--
newBinder :: [Either TyVar Type] -> Term -> Step
newBinder tys x m tcm =
let (s', iss', x') = mkAbstr (mSupply m, mScopeNames m, x) tys
m' = m { mSupply = s', mScopeNames = iss', mTerm = x' }
in ghcStep m' tcm
where
mkAbstr = foldr go
where
go (Left tv) (s', iss', e') =
(s', iss', TyLam tv (TyApp e' (VarTy tv)))
go (Right ty) (s', iss', e') =
let ((s'', _), n) = mkUniqSystemId (s', iss') ("x", ty)
in (s'', iss' ,Lam n (App e' (Var n)))
newLetBinding
:: TyConMap
-> Machine
-> Term
-> (Machine, Id)
newLetBinding tcm m e
| Var v <- e
, heapContains LocalId v m
= (m, v)
| otherwise
= let m' = heapInsert LocalId id_ e m
in (m' { mSupply = ids', mScopeNames = is1 }, id_)
where
ty = inferCoreTypeOf tcm e
((ids', is1), id_) = mkUniqSystemId (mSupply m, mScopeNames m) ("x", ty)
-- | Unwind the stack by 1
ghcUnwind :: Unwind
ghcUnwind v m tcm = do
(m', kf) <- stackPop m
go kf m'
where
go (Update s x) = return . update s x v
go (Apply x) = return . apply tcm v x
go (Instantiate ty) = return . instantiate tcm v ty
go (PrimApply p tys vs tms) = ghcPrimUnwind tcm p tys vs v tms
go (Scrutinise altTy as) = return . scrutinise v altTy as
go (Tickish _) = return . setTerm (valToTerm v)
-- | Update the Heap with the evaluated term
update :: IdScope -> Id -> Value -> Machine -> Machine
update s x (valToTerm -> term) =
setTerm term . heapInsert s x term
-- | Apply a value to a function
apply :: TyConMap -> Value -> Id -> Machine -> Machine
apply _tcm (Lambda x' e) x m =
setTerm (substTm "Evaluator.apply" subst e) m
where
subst = extendIdSubst subst0 x' (Var x)
subst0 = mkSubst $ extendInScopeSet (mScopeNames m) x
apply tcm pVal@(PrimVal (PrimInfo{primType}) tys vs) x m
| isUndefinedXPrimVal pVal
= setTerm (TyApp (Prim NP.undefinedX) ty) m
| isUndefinedPrimVal pVal
= setTerm (TyApp (Prim NP.undefined) ty) m
where
ty = piResultTys tcm primType (tys ++ map (inferCoreTypeOf tcm . valToTerm) vs ++ [varType x])
apply _ v _ m = error $ "Evaluator.apply: Not a lambda: " ++ show v ++ "\n" ++ show m
-- | Instantiate a type-abstraction
instantiate :: TyConMap -> Value -> Type -> Machine -> Machine
instantiate _tcm (TyLambda x e) ty m =
setTerm (substTm "Evaluator.instantiate1" subst e) m
where
subst = extendTvSubst subst0 x ty
subst0 = mkSubst iss0
iss0 = mkInScopeSet (freeVarsOf e <> freeVarsOf ty)
-- The evaluator is setup in such a way that under normal conditions anything
-- of type 'forall a . ty' must be a ty-lambda.
--
-- However, sometimes we evaluate to an error /value/. When this happens,
-- instead of doing a regural type substitition we:
--
-- 1. Calculate the 'forall a . ty' type of the error value
-- 2. Substitute the 'a' by the applied type.
-- 3. Create a new error value of the shape: 'undefined @substituted_type'
-- Where this particular 'undefined' has type 'forall a . a'. We destinquish
-- between error values throwing X exceptions and other error values, and
-- create appropriate error values that we return. We make this distinctions
-- in onder to enable conversion of X-exception throwing code to undefined
-- bitvectors.
instantiate tcm pVal@(PrimVal (PrimInfo{primType}) tys es) ty m
| isUndefinedXPrimVal pVal
= setTerm (TyApp (Prim NP.undefinedX) primType1) m
| isUndefinedPrimVal pVal
= setTerm (TyApp (Prim NP.undefined) primType1) m
where
esTys = map (inferCoreTypeOf tcm) es
-- Calculate the type of: prim @ty0 .. @tyN e0 .. eN @ty
--
-- This combines the above-mentioned step 1 and 2
primType1 = piResultTys tcm primType (tys ++ esTys ++ [ty])
instantiate _ p _ _ = error $ "Evaluator.instantiate: Not a tylambda: " ++ show p
-- | Evaluate a case-expression
scrutinise :: Value -> Type -> [Alt] -> Machine -> Machine
scrutinise v _altTy [] m = setTerm (valToTerm v) m
-- [Note: empty case expressions]
--
-- Clash does not have empty case-expressions; instead, empty case-expressions
-- are used to indicate that the `whnf` function was called the context of a
-- case-expression, which means certain special primitives must be forced.
-- See also [Note: forcing special primitives]
scrutinise (Lit l) _altTy alts m = case alts of
(DefaultPat, altE):alts1 -> setTerm (go altE alts1) m
_ -> let term = go (error $ "Evaluator.scrutinise: no match "
<> showPpr (Case (valToTerm (Lit l)) (ConstTy Arrow) alts)) alts
in setTerm term m
where
go def [] = def
go _ ((LitPat l1,altE):_) | l1 == l = altE
go _ ((DataPat dc [] [x],altE):_)
| IntegerLiteral l1 <- l
, Just patE <- case dcTag dc of
1 | l1 >= ((-2)^(63::Int)) && l1 < 2^(63::Int) ->
Just (IntLiteral l1)
2 | l1 >= (2^(63::Int)) ->
#if MIN_VERSION_base(4,15,0)
let !(IP ba0) = l1
#else
let !(Jp# !(BN# ba0)) = l1
#endif
ba1 = BA.ByteArray ba0
in Just (ByteArrayLiteral ba1)
3 | l1 < ((-2)^(63::Int)) ->
#if MIN_VERSION_base(4,15,0)
let !(IN ba0) = l1
#else
let !(Jn# !(BN# ba0)) = l1
#endif
ba1 = BA.ByteArray ba0
in Just (ByteArrayLiteral ba1)
_ -> Nothing
= let inScope = freeVarsOf altE
subst0 = mkSubst (mkInScopeSet inScope)
subst1 = extendIdSubst subst0 x (Literal patE)
in substTm "Evaluator.scrutinise" subst1 altE
| NaturalLiteral l1 <- l
, Just patE <- case dcTag dc of
1 | l1 >= 0 && l1 < 2^(64::Int) ->
Just (WordLiteral l1)
2 | l1 >= (2^(64::Int)) ->
#if MIN_VERSION_base(4,15,0)
let !(IP ba0) = l1
#else
let !(Jp# !(BN# ba0)) = l1
#endif
ba1 = BA.ByteArray ba0
in Just (ByteArrayLiteral ba1)
_ -> Nothing
= let inScope = freeVarsOf altE
subst0 = mkSubst (mkInScopeSet inScope)
subst1 = extendIdSubst subst0 x (Literal patE)
in substTm "Evaluator.scrutinise" subst1 altE
go def (_:alts1) = go def alts1
scrutinise (DC dc xs) _altTy alts m
| altE:_ <- [substInAlt altDc tvs pxs xs altE
| (DataPat altDc tvs pxs,altE) <- alts, altDc == dc ] ++
[altE | (DefaultPat,altE) <- alts ]
= setTerm altE m
scrutinise v@(PrimVal p _ vs) altTy alts m
| isUndefinedXPrimVal v
= setTerm (TyApp (Prim NP.undefinedX) altTy) m
| isUndefinedPrimVal v
= setTerm (TyApp (Prim NP.undefined) altTy) m
| any (\case {(LitPat {},_) -> True; _ -> False}) alts
= case alts of
((DefaultPat,altE):alts1) -> setTerm (go altE alts1) m
_ -> let term = go (error $ "Evaluator.scrutinise: no match "
<> showPpr (Case (valToTerm v) (ConstTy Arrow) alts)) alts
in setTerm term m
where
go def [] = def
go _ ((LitPat l1,altE):_) | l1 == l = altE
go def (_:alts1) = go def alts1
l = case primName p of
"Clash.Sized.Internal.BitVector.fromInteger##"
| [Lit (WordLiteral 0), Lit l0] <- vs -> l0
"Clash.Sized.Internal.BitVector.fromInteger#"
| [_,Lit (NaturalLiteral 0),Lit l0] <- vs -> l0
"Clash.Sized.Internal.Index.fromInteger#"
| [_,Lit l0] <- vs -> l0
"Clash.Sized.Internal.Signed.fromInteger#"
| [_,Lit l0] <- vs -> l0
"Clash.Sized.Internal.Unsigned.fromInteger#"
| [_,Lit l0] <- vs -> l0
_ -> error ("scrutinise: " ++ showPpr (Case (valToTerm v) (ConstTy Arrow) alts))
scrutinise v _altTy alts _ =
error ("scrutinise: " ++ showPpr (Case (valToTerm v) (ConstTy Arrow) alts))
substInAlt :: DataCon -> [TyVar] -> [Id] -> [Either Term Type] -> Term -> Term
substInAlt dc tvs xs args e = substTm "Evaluator.substInAlt" subst e
where
tys = rights args
tms = lefts args
substTyMap = zip tvs (drop (length (dcUnivTyVars dc)) tys)
substTmMap = zip xs tms
inScope = freeVarsOf tys `unionVarSet` freeVarsOf (e:tms)
subst = extendTvSubstList (extendIdSubstList subst0 substTmMap) substTyMap
subst0 = mkSubst (mkInScopeSet inScope)
-- | Allocate let-bindings on the heap
allocate :: [LetBinding] -> Term -> Machine -> Machine
allocate xes e m =
m { mHeapLocal = extendVarEnvList (mHeapLocal m) xes'
, mSupply = ids'
, mScopeNames = isN
, mTerm = e'
}
where
xNms = fmap fst xes
is1 = extendInScopeSetList (mScopeNames m) xNms
(ids', s) = mapAccumL (letSubst (mHeapLocal m)) (mSupply m) xNms
(nms, s') = unzip s
isN = extendInScopeSetList is1 nms
subst = extendIdSubstList subst0 s'
subst0 = mkSubst (foldl' extendInScopeSet is1 nms)
xes' = zip nms (fmap (substTm "Evaluator.allocate0" subst . snd) xes)
e' = substTm "Evaluator.allocate1" subst e
-- | Create a unique name and substitution for a let-binder
letSubst
:: PureHeap
-> Supply
-> Id
-> (Supply, (Id, (Id, Term)))
letSubst h acc id0 =
let (acc',id1) = mkUniqueHeapId h acc id0
in (acc',(id1,(id0,Var id1)))
where
mkUniqueHeapId :: PureHeap -> Supply -> Id -> (Supply, Id)
mkUniqueHeapId h' ids x =
maybe (ids', x') (const $ mkUniqueHeapId h' ids' x) (lookupVarEnv x' h')
where
(i,ids') = freshId ids
x' = modifyVarName (`setUnique` i) x