\begin{code}
module CoreUtils (
-- Construction
- mkNote, mkInlineMe, mkSCC, mkCoerce,
+ mkNote, mkInlineMe, mkSCC, mkCoerce, mkCoerce2,
bindNonRec, needsCaseBinding,
mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes,
#include "HsVersions.h"
-import GlaExts -- For `xori`
+import GLAEXTS -- For `xori`
import CoreSyn
import PprCore ( pprCoreExpr )
import Outputable
import TysPrim ( alphaTy ) -- Debugging only
import Util ( equalLength, lengthAtLeast )
+import TysPrim ( statePrimTyCon )
\end{code}
\begin{code}
mkNote :: Note -> CoreExpr -> CoreExpr
-mkNote (Coerce to_ty from_ty) expr = mkCoerce to_ty from_ty expr
+mkNote (Coerce to_ty from_ty) expr = mkCoerce2 to_ty from_ty expr
mkNote (SCC cc) expr = mkSCC cc expr
mkNote InlineMe expr = mkInlineMe expr
mkNote note expr = Note note expr
\begin{code}
-mkCoerce :: Type -> Type -> CoreExpr -> CoreExpr
+mkCoerce :: Type -> CoreExpr -> CoreExpr
+mkCoerce to_ty expr = mkCoerce2 to_ty (exprType expr) expr
-mkCoerce to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr)
+mkCoerce2 :: Type -> Type -> CoreExpr -> CoreExpr
+mkCoerce2 to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr)
= ASSERT( from_ty `eqType` to_ty2 )
- mkCoerce to_ty from_ty2 expr
+ mkCoerce2 to_ty from_ty2 expr
-mkCoerce to_ty from_ty expr
+mkCoerce2 to_ty from_ty expr
| to_ty `eqType` from_ty = expr
| otherwise = ASSERT( from_ty `eqType` exprType expr )
Note (Coerce to_ty from_ty) expr
\begin{code}
exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
-exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind
- -- copying them
-exprIsValue (Lit l) = True
-exprIsValue (Lam b e) = isRuntimeVar b || exprIsValue e
-exprIsValue (Note _ e) = exprIsValue e
-exprIsValue (Var v) = idArity v > 0 || isEvaldUnfolding (idUnfolding v)
- -- The idArity case catches data cons and primops that
- -- don't have unfoldings
+exprIsValue (Var v) -- NB: There are no value args at this point
+ = isDataConId v -- Catches nullary constructors,
+ -- so that [] and () are values, for example
+ || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
+ || isEvaldUnfolding (idUnfolding v)
+ -- Check the thing's unfolding; it might be bound to a value
-- A worry: what if an Id's unfolding is just itself:
-- then we could get an infinite loop...
-exprIsValue other_expr
- | (Var fun, args) <- collectArgs other_expr,
- isDataConId fun || valArgCount args < idArity fun
- = check (idType fun) args
- | otherwise
- = False
+
+exprIsValue (Lit l) = True
+exprIsValue (Type ty) = True -- Types are honorary Values;
+ -- we don't mind copying them
+exprIsValue (Lam b e) = isRuntimeVar b || exprIsValue e
+exprIsValue (Note _ e) = exprIsValue e
+exprIsValue (App e (Type _)) = exprIsValue e
+exprIsValue (App e a) = app_is_value e [a]
+exprIsValue other = False
+
+-- There is at least one value argument
+app_is_value (Var fun) args
+ | isDataConId fun -- Constructor apps are values
+ || idArity fun > valArgCount args -- Under-applied function
+ = check_args (idType fun) args
+app_is_value (App f a) as = app_is_value f (a:as)
+app_is_value other as = False
+
+ -- 'check_args' checks that unlifted-type args
+ -- are in fact guaranteed non-divergent
+check_args fun_ty [] = True
+check_args fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
+ Just (_, ty) -> check_args ty args
+check_args fun_ty (arg : args)
+ | isUnLiftedType arg_ty = exprOkForSpeculation arg
+ | otherwise = check_args res_ty args
where
- -- 'check' checks that unlifted-type args are in
- -- fact guaranteed non-divergent
- check fun_ty [] = True
- check fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
- Just (_, ty) -> check ty args
- check fun_ty (arg : args)
- | isUnLiftedType arg_ty = exprOkForSpeculation arg
- | otherwise = check res_ty args
- where
- (arg_ty, res_ty) = splitFunTy fun_ty
+ (arg_ty, res_ty) = splitFunTy fun_ty
\end{code}
\begin{code}
arity = tyConArity tc
val_args = drop arity args
to_arg_tys = dataConArgTys dc tc_arg_tys
- mk_coerce ty arg = mkCoerce ty (exprType arg) arg
+ mk_coerce ty arg = mkCoerce ty arg
new_val_args = zipWith mk_coerce to_arg_tys val_args
in
ASSERT( all isTypeArg (take arity args) )
-- use the idinfo here
-- Lambdas; increase arity
-arityType (Lam x e) | isId x = AFun (isOneShotLambda x) (arityType e)
+arityType (Lam x e) | isId x = AFun (isOneShotLambda x || isStateHack x) (arityType e)
| otherwise = arityType e
-- Applications; decrease arity
arityType (App f (Type _)) = arityType f
arityType (App f a) = case arityType f of
- AFun one_shot xs | one_shot -> xs
- | exprIsCheap a -> xs
+ AFun one_shot xs | exprIsCheap a -> xs
other -> ATop
-- Case/Let; keep arity if either the expression is cheap
arityType other = ATop
+isStateHack id = case splitTyConApp_maybe (idType id) of
+ Just (tycon,_) | tycon == statePrimTyCon -> True
+ other -> False
+
+ -- The last clause is a gross hack. It claims that
+ -- every function over realWorldStatePrimTy is a one-shot
+ -- function. This is pretty true in practice, and makes a big
+ -- difference. For example, consider
+ -- a `thenST` \ r -> ...E...
+ -- The early full laziness pass, if it doesn't know that r is one-shot
+ -- will pull out E (let's say it doesn't mention r) to give
+ -- let lvl = E in a `thenST` \ r -> ...lvl...
+ -- When `thenST` gets inlined, we end up with
+ -- let lvl = E in \s -> case a s of (r, s') -> ...lvl...
+ -- and we don't re-inline E.
+ --
+ -- It would be better to spot that r was one-shot to start with, but
+ -- I don't want to rely on that.
+ --
+ -- Another good example is in fill_in in PrelPack.lhs. We should be able to
+ -- spot that fill_in has arity 2 (and when Keith is done, we will) but we can't yet.
+
{- NOT NEEDED ANY MORE: etaExpand is cleverer
ok_note InlineMe = False
ok_note other = True
-- Given e' = etaExpand n us e ty
-- We should have
-- ty = exprType e = exprType e'
+--
+-- Note that SCCs are not treated specially. If we have
+-- etaExpand 2 (\x -> scc "foo" e)
+-- = (\xy -> (scc "foo" e) y)
+-- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
etaExpand n us expr ty
| manifestArity expr >= n = expr -- The no-op case
-- The ILX code generator requires eta expansion for type arguments
-- too, but alas the 'n' doesn't tell us how many of them there
-- may be. So we eagerly eta expand any big lambdas, and just
- -- cross our fingers about possible loss of sharing in the
- -- ILX case.
+ -- cross our fingers about possible loss of sharing in the ILX case.
-- The Right Thing is probably to make 'arity' include
-- type variables throughout the compiler. (ToDo.)
not (isForAllTy ty)
-- Saturated, so nothing to do
= expr
-eta_expand n us (Note note@(Coerce _ ty) e) _
- = Note note (eta_expand n us e ty)
-
- -- Use mkNote so that _scc_s get pushed inside any lambdas that
- -- are generated as part of the eta expansion. We rely on this
- -- behaviour in CorePrep, when we eta expand an already-prepped RHS.
-eta_expand n us (Note note e) ty
- = mkNote note (eta_expand n us e ty)
-
-- Short cut for the case where there already
-- is a lambda; no point in gratuitously adding more
eta_expand n us (Lam v body) ty
| otherwise
= Lam v (eta_expand (n-1) us body (funResultTy ty))
+-- We used to have a special case that stepped inside Coerces here,
+-- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
+-- = Note note (eta_expand n us e ty)
+-- BUT this led to an infinite loop
+-- Example: newtype T = MkT (Int -> Int)
+-- eta_expand 1 (coerce (Int->Int) e)
+-- --> coerce (Int->Int) (eta_expand 1 T e)
+-- by the bogus eqn
+-- --> coerce (Int->Int) (coerce T
+-- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
+-- by the splitNewType_maybe case below
+-- and round we go
+
eta_expand n us expr ty
= case splitForAllTy_maybe ty of {
Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty')
case splitFunTy_maybe ty of {
Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
where
- arg1 = mkSysLocal SLIT("eta") uniq arg_ty
+ arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
(uniq:us2) = us
; Nothing ->
+ -- Given this:
+ -- newtype T = MkT (Int -> Int)
+ -- Consider eta-expanding this
+ -- eta_expand 1 e T
+ -- We want to get
+ -- coerce T (\x::Int -> (coerce (Int->Int) e) x)
+
case splitNewType_maybe ty of {
- Just ty' -> mkCoerce ty ty' (eta_expand n us (mkCoerce ty' ty expr) ty') ;
+ Just ty' -> mkCoerce2 ty ty' (eta_expand n us (mkCoerce2 ty' ty expr) ty') ;
Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr
}}}
\end{code}
projects / ghc-hetmet.git / blobdiff