%
-% (c) The GRASP/AQUA Project, Glasgow University, 1993-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
%
\section[WwLib]{A library for the ``worker/wrapper'' back-end to the strictness analyser}
\begin{code}
-#include "HsVersions.h"
-
module WwLib (
WwBinding(..),
- mkWwBodies, mAX_WORKER_ARGS
+ worthSplitting, setUnpackStrategy,
+ mkWwBodies, mkWrapper
) where
-IMP_Ubiq(){-uitous-}
+#include "HsVersions.h"
import CoreSyn
-import Id ( idType, mkSysLocal, dataConArgTys )
-import IdInfo ( mkStrictnessInfo, nonAbsentArgs, Demand(..) )
+import Id ( Id, idType, mkSysLocal, getIdDemandInfo, setIdDemandInfo )
+import Const ( Con(..) )
+import DataCon ( dataConArgTys )
+import Demand ( Demand(..) )
import PrelVals ( aBSENT_ERROR_ID )
-import SrcLoc ( noSrcLoc )
-import Type ( isPrimType, mkTyVarTys, mkForAllTys, mkFunTys,
- maybeAppDataTyConExpandingDicts
+import TysWiredIn ( unitTy, unitDataCon )
+import Type ( isUnLiftedType, mkTyVarTys, mkTyVarTy, mkFunTys,
+ splitForAllTys, splitFunTys,
+ splitAlgTyConApp_maybe,
+ Type
)
-import UniqSupply ( returnUs, thenUs, thenMaybeUs,
- getUniques, SYN_IE(UniqSM)
- )
-import Util ( zipWithEqual, assertPanic, panic )
+import BasicTypes ( NewOrData(..) )
+import Var ( TyVar )
+import UniqSupply ( returnUs, thenUs, getUniqueUs, getUniquesUs, UniqSM )
+import Util ( zipWithEqual )
+import Outputable
\end{code}
%************************************************************************
\begin{code}
data WwBinding
- = WwLet [CoreBinding]
+ = WwLet [CoreBind]
| WwCase (CoreExpr -> CoreExpr)
-- the "case" will be a "strict let" of the form:
--
same, we ``revise'' the strictness info, so that we won't propagate
the unusable strictness-info into the interfaces.
-==========================
-
-Here's the real fun... The wrapper's ``deconstructing'' of arguments
-and the worker's putting them back together again are ``duals'' in
-some sense.
-What we do is walk along the @Demand@ list, producing two
-expressions (one for wrapper, one for worker...), each with a ``hole''
-in it, where we will later plug in more information. For our previous
-example, the expressions-with-HOLES are:
-\begin{verbatim}
-\ x ys -> -- wrapper
- case x of
- I# x# -> <<HOLE>> x# ys
-
-\ x# ys -> -- worker
- let
- x = I# x#
- in
- <<HOLE>>
-\end{verbatim}
-(Actually, we add the lambda-bound arguments at the end...) (The big
-Lambdas are added on the front later.)
+%************************************************************************
+%* *
+\subsection{Functions over Demands}
+%* *
+%************************************************************************
\begin{code}
-mkWwBodies
- :: Type -- Type of the *body* of the orig
- -- function; i.e. /\ tyvars -> \ vars -> body
- -> [TyVar] -- Type lambda vars of original function
- -> [Id] -- Args of original function
- -> [Demand] -- Strictness info for those args
-
- -> UniqSM (Maybe -- Nothing iff (a) no interesting split possible
- -- (b) any unpack on abstract type
- (Id -> CoreExpr, -- Wrapper expr w/
- -- hole for worker id
- CoreExpr -> CoreExpr, -- Worker expr w/ hole
- -- for original fn body
- StrictnessInfo Id, -- Worker strictness info
- Type -> Type) -- Worker type w/ hole
- ) -- for type of original fn body
-
-
-mkWwBodies body_ty tyvars args arg_infos
- = ASSERT(length args == length arg_infos)
- -- or you can get disastrous user/definer-module mismatches
- if (all_absent_args_and_unboxed_value body_ty arg_infos)
- then returnUs Nothing
-
- else -- the rest...
- mk_ww_arg_processing args arg_infos
- False -- Initialise the "useful-split" flag
- (mAX_WORKER_ARGS - nonAbsentArgs arg_infos)
- `thenMaybeUs` \ (wrap_frag, work_args_info, work_frag) ->
- let
- (work_args, wrkr_demands) = unzip work_args_info
+mAX_WORKER_ARGS :: Int -- ToDo: set via flag
+mAX_WORKER_ARGS = 6
- wrkr_strictness = mkStrictnessInfo wrkr_demands Nothing -- no worker-of-worker...
+setUnpackStrategy :: [Demand] -> [Demand]
+setUnpackStrategy ds
+ = snd (go (mAX_WORKER_ARGS - nonAbsentArgs ds) ds)
+ where
+ go :: Int -- Max number of args available for sub-components of [Demand]
+ -> [Demand]
+ -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
+
+ go n (WwUnpack nd _ cs : ds) | n' >= 0
+ = WwUnpack nd True cs' `cons` go n'' ds
+ | otherwise
+ = WwUnpack nd False cs `cons` go n ds
+ where
+ n' = n + 1 - nonAbsentArgs cs
+ -- Add one because we don't pass the top-level arg any more
+ -- Delete # of non-absent args to which we'll now be committed
+ (n'',cs') = go n' cs
+
+ go n (d:ds) = d `cons` go n ds
+ go n [] = (n,[])
+
+ cons d (n,ds) = (n, d:ds)
- wrapper_w_hole = \ worker_id ->
- mkLam tyvars args (
- wrap_frag (
- mkTyApp (Var worker_id) (mkTyVarTys tyvars)
- ))
+nonAbsentArgs :: [Demand] -> Int
+nonAbsentArgs [] = 0
+nonAbsentArgs (WwLazy True : ds) = nonAbsentArgs ds
+nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
- worker_w_hole = \ orig_body ->
- mkLam tyvars work_args (
- work_frag orig_body
- )
+worthSplitting :: [Demand] -> Bool -- True <=> the wrapper would not be an identity function
+worthSplitting ds = any worth_it ds
+ where
+ worth_it (WwLazy True) = True -- Absent arg
+ worth_it (WwUnpack _ True _) = True -- Arg to unpack
+ worth_it WwStrict = True
+ worth_it other = False
- worker_ty_w_hole = \ body_ty ->
- mkForAllTys tyvars $
- mkFunTys (map idType work_args) body_ty
- in
- returnUs (Just (wrapper_w_hole, worker_w_hole, wrkr_strictness, worker_ty_w_hole))
+allAbsent :: [Demand] -> Bool
+allAbsent ds = all absent ds
where
- -- "all_absent_args_and_unboxed_value":
- -- check for the obscure case of "\ x y z ... -> body" where
- -- (a) *all* of the args x, y, z,... are absent, and
- -- (b) the type of body is unboxed
- -- If these conditions are true, we must *not* play worker/wrapper games!
-
- all_absent_args_and_unboxed_value body_ty arg_infos
- = not (null arg_infos)
- && all is_absent_arg arg_infos
- && isPrimType body_ty
-
- is_absent_arg (WwLazy True) = True
- is_absent_arg _ = False
+ absent (WwLazy is_absent) = is_absent
+ absent (WwUnpack _ True cs) = allAbsent cs
+ absent other = False
\end{code}
-Important: mk_ww_arg_processing doesn't check
-for an "interesting" split. It just races ahead and makes the
-split, even if there's no unpacking at all. This is important for
-when it calls itself recursively.
-It returns Nothing only if it encounters an abstract type in mid-flight.
+%************************************************************************
+%* *
+\subsection{The worker wrapper core}
+%* *
+%************************************************************************
+
+@mkWrapper@ is called when importing a function. We have the type of
+the function and the name of its worker, and we want to make its body (the wrapper).
\begin{code}
-mAX_WORKER_ARGS :: Int -- ToDo: set via flag
-mAX_WORKER_ARGS = 6 -- Hmm... but this is an everything-must-
- -- be-compiled-with-the-same-val thing...
-
-mk_ww_arg_processing
- :: [Id] -- Args of original function
- -> [Demand] -- Strictness info for those args
- -- must be at least as long as args
-
- -> Bool -- False <=> we've done nothing useful in an enclosing call
- -- If this is False when we hit the end of the arg list, we
- -- don't want to do a w/w split... the wrapper would be the identity fn!
- -- So we return Nothing
-
- -> Int -- Number of extra args we are prepared to add.
- -- This prevents over-eager unpacking, leading
- -- to huge-arity functions.
-
- -> UniqSM (Maybe -- Nothing iff any unpack on abstract type
- -- or if the wrapper would be the identity fn (can happen if we unpack
- -- a huge structure, and decide not to do it)
-
- (CoreExpr -> CoreExpr, -- Wrapper expr w/
- -- hole for worker id
- -- applied to types
- [(Id,Demand)], -- Worker's args
- -- and their strictness info
- CoreExpr -> CoreExpr) -- Worker body expr w/ hole
- ) -- for original fn body
-
-mk_ww_arg_processing [] _ useful_split _ = if useful_split then
- returnUs (Just (id, [], id))
- else
- returnUs Nothing
-
-mk_ww_arg_processing (arg : args) (WwLazy True : infos) useful_split max_extra_args
- = -- Absent argument
- -- So, finish args to the right...
- --pprTrace "Absent; num_wrkr_args=" (ppInt num_wrkr_args) (
+mkWrapper :: Type -- Wrapper type
+ -> [Demand] -- Wrapper strictness info
+ -> UniqSM (Id -> CoreExpr) -- Wrapper body, missing worker Id
+
+mkWrapper fun_ty demands
+ = let
+ n_wrap_args = length demands
+ in
+ getUniquesUs n_wrap_args `thenUs` \ wrap_uniqs ->
let
- arg_ty = idType arg
+ (tyvars, tau_ty) = splitForAllTys fun_ty
+ (arg_tys, body_ty) = splitFunTys tau_ty
+ -- The "expanding dicts" part here is important, even for the splitForAll
+ -- The imported thing might be a dictionary, such as Functor Foo
+ -- But Functor Foo = forall a b. (a->b) -> Foo a -> Foo b
+ -- and as such might have some strictness info attached.
+ -- Then we need to have enough args to zip to the strictness info
+
+ wrap_args = ASSERT( n_wrap_args <= length arg_tys )
+ zipWith mk_ww_local wrap_uniqs arg_tys
+
+ leftover_arg_tys = drop n_wrap_args arg_tys
+ final_body_ty = mkFunTys leftover_arg_tys body_ty
in
- mk_ww_arg_processing args infos True {- useful split -} max_extra_args
- -- We've already discounted for absent args,
- -- so we don't change max_extra_args
- `thenMaybeUs` \ (wrap_rest, work_args_info, work_rest) ->
-
- -- wrapper doesn't pass this arg to worker:
- returnUs (Just (
- -- wrapper:
- \ hole -> wrap_rest hole,
-
- -- worker:
- work_args_info, -- NB: no argument added
- \ hole -> mk_absent_let arg arg_ty (work_rest hole)
- ))
- --)
- where
- mk_absent_let arg arg_ty body
- = if not (isPrimType arg_ty) then
- Let (NonRec arg (mkTyApp (Var aBSENT_ERROR_ID) [arg_ty])) body
- else -- quite horrible
- panic "WwLib: haven't done mk_absent_let for primitives yet"
-
-
-mk_ww_arg_processing (arg : args) (WwUnpack cmpnt_infos : infos) useful_split max_extra_args
- | new_max_extra_args > 0 -- Check that we are prepared to add arguments
- = -- this is the complicated one.
- --pprTrace "Unpack; num_wrkr_args=" (ppCat [ppInt num_wrkr_args, ppStr "; new_max=", ppInt new_num_wrkr_args, ppStr "; arg=", ppr PprDebug arg, ppr PprDebug (WwUnpack cmpnt_infos)]) $
-
- case (maybeAppDataTyConExpandingDicts arg_ty) of
-
- Nothing -> -- Not a data type
- panic "mk_ww_arg_processing: not datatype"
-
- Just (_, _, []) -> -- An abstract type
- -- We have to give up on the whole idea
- returnUs Nothing
-
- Just (_, _, (_:_:_)) -> -- Two or more constructors; that's odd
- panic "mk_ww_arg_processing: multi-constr"
-
- Just (arg_tycon, tycon_arg_tys, [data_con]) ->
- -- The main event: a single-constructor data type
-
- let
- inst_con_arg_tys = dataConArgTys data_con tycon_arg_tys
- in
- getUniques (length inst_con_arg_tys) `thenUs` \ uniqs ->
-
- let
- unpk_args = zipWithEqual "mk_ww_arg_processing"
- (\ u t -> mkSysLocal SLIT("upk") u t noSrcLoc)
- uniqs inst_con_arg_tys
- in
- -- In processing the rest, push the sub-component args
- -- and infos on the front of the current bunch
- mk_ww_arg_processing (unpk_args ++ args) (cmpnt_infos ++ infos) True {- useful split -} new_max_extra_args
- `thenMaybeUs` \ (wrap_rest, work_args_info, work_rest) ->
-
- returnUs (Just (
- -- wrapper: unpack the value
- \ hole -> mk_unpk_case arg unpk_args
- data_con arg_tycon
- (wrap_rest hole),
-
- -- worker: expect the unpacked value;
- -- reconstruct the orig value with a "let"
- work_args_info,
- \ hole -> work_rest (mk_pk_let arg data_con tycon_arg_tys unpk_args hole)
- ))
- where
- arg_ty = idType arg
+ mkWwBodies tyvars wrap_args final_body_ty demands `thenUs` \ (wrap_fn, _, _) ->
+ returnUs wrap_fn
+\end{code}
- new_max_extra_args
- = max_extra_args
- + 1 -- We won't pass the original arg now
- - nonAbsentArgs cmpnt_infos -- But we will pass an arg for each cmpt
+@mkWwBodies@ is called when doing the worker/wrapper split inside a module.
- mk_unpk_case arg unpk_args boxing_con boxing_tycon body
- = Case (Var arg) (
- AlgAlts [(boxing_con, unpk_args, body)]
- NoDefault
- )
+\begin{code}
+mkWwBodies :: [TyVar] -> [Id] -> Type -- Original fn args and body type
+ -> [Demand] -- Strictness info for original fn; corresp 1-1 with args
+ -> UniqSM (Id -> CoreExpr, -- Wrapper body, lacking only the worker Id
+ CoreExpr -> CoreExpr, -- Worker body, lacking the original function body
+ [Demand]) -- Strictness info for worker
+
+mkWwBodies tyvars args body_ty demands
+ | allAbsent demands &&
+ isUnLiftedType body_ty
+ = -- Horrid special case. If the worker would have no arguments, and the
+ -- function returns a primitive type value, that would make the worker into
+ -- an unboxed value. We box it by passing a dummy void argument, thus:
+ --
+ -- f = /\abc. \xyz. fw abc void
+ -- fw = /\abc. \v. body
+ --
+ getUniqueUs `thenUs` \ void_arg_uniq ->
+ let
+ void_arg = mk_ww_local void_arg_uniq unitTy
+ in
+ returnUs (\ work_id -> mkLams tyvars $ mkLams args $
+ mkApps (Var work_id)
+ (map (Type . mkTyVarTy) tyvars ++ [mkConApp unitDataCon []]),
+ \ body -> mkLams (tyvars ++ [void_arg]) body,
+ [WwLazy True])
+
+mkWwBodies tyvars wrap_args body_ty demands
+ | otherwise
+ = let
+ wrap_args_w_demands = zipWithEqual "mkWwBodies" setIdDemandInfo wrap_args demands
+ in
+ mkWW wrap_args_w_demands `thenUs` \ (wrap_fn, work_args_w_demands, work_fn) ->
+ returnUs (\ work_id -> mkLams tyvars $ mkLams wrap_args_w_demands $
+ wrap_fn (mkTyApps (Var work_id) (mkTyVarTys tyvars)),
+
+ \ body -> mkLams tyvars $ mkLams work_args_w_demands $
+ work_fn body,
+
+ map getIdDemandInfo work_args_w_demands)
+\end{code}
+
+
+\begin{code}
+mkWW :: [Id] -- Wrapper args; have their demand info on them
+ -> UniqSM (CoreExpr -> CoreExpr, -- Wrapper body, lacking the inner call to the worker
+ -- and without its lambdas
+ [Id], -- Worker args; have their demand info on them
+ CoreExpr -> CoreExpr) -- Worker body, lacking the original body of the function
+
+
+ -- Empty case
+mkWW []
+ = returnUs (\ wrapper_body -> wrapper_body,
+ [],
+ \ worker_body -> worker_body)
+
+
+mkWW (arg : ds)
+ = case getIdDemandInfo arg of
- mk_pk_let arg boxing_con con_tys unpk_args body
- = Let (NonRec arg (Con boxing_con
- (map TyArg con_tys ++ map VarArg unpk_args)))
- body
+ -- Absent case
+ WwLazy True ->
+ mkWW ds `thenUs` \ (wrap_fn, worker_args, work_fn) ->
+ returnUs (\ wrapper_body -> wrap_fn wrapper_body,
+ worker_args,
+ \ worker_body -> mk_absent_let arg (work_fn worker_body))
-mk_ww_arg_processing (arg : args) (arg_demand : infos) useful_split max_extra_args
+
+ -- Unpack case
+ WwUnpack new_or_data True cs ->
+ getUniquesUs (length inst_con_arg_tys) `thenUs` \ uniqs ->
+ let
+ unpk_args = zipWith mk_ww_local uniqs inst_con_arg_tys
+ unpk_args_w_ds = zipWithEqual "mkWW" setIdDemandInfo unpk_args cs
+ in
+ mkWW (unpk_args_w_ds ++ ds) `thenUs` \ (wrap_fn, worker_args, work_fn) ->
+ returnUs (\ wrapper_body -> mk_unpk_case new_or_data arg unpk_args data_con arg_tycon
+ (wrap_fn wrapper_body),
+ worker_args,
+ \ worker_body -> work_fn (mk_pk_let new_or_data arg data_con
+ tycon_arg_tys unpk_args worker_body))
+ where
+ inst_con_arg_tys = dataConArgTys data_con tycon_arg_tys
+ (arg_tycon, tycon_arg_tys, data_con)
+ = case (splitAlgTyConApp_maybe (idType arg)) of
+
+ Just (arg_tycon, tycon_arg_tys, [data_con]) ->
+ -- The main event: a single-constructor data type
+ (arg_tycon, tycon_arg_tys, data_con)
+
+ Just (_, _, data_cons) ->
+ pprPanic "mk_ww_arg_processing:"
+ (text "not one constr (interface files not consistent/up to date?)"
+ $$ (ppr arg <+> ppr (idType arg)))
+
+ Nothing ->
+ panic "mk_ww_arg_processing: not datatype"
+
+
+ -- Other cases
+ other_demand ->
+ mkWW ds `thenUs` \ (wrap_fn, worker_args, work_fn) ->
+ returnUs (\ wrapper_body -> wrap_fn (App wrapper_body (Var arg)),
+ arg : worker_args,
+ work_fn)
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Utilities}
+%* *
+%************************************************************************
+
+
+\begin{code}
+mk_absent_let arg body
+ | not (isUnLiftedType arg_ty)
+ = Let (NonRec arg (mkTyApps (Var aBSENT_ERROR_ID) [arg_ty])) body
| otherwise
- = -- For all others at the moment, we just
- -- pass them to the worker unchanged.
- --pprTrace "Other; num_wrkr_args=" (ppCat [ppInt num_wrkr_args, ppStr ";arg=", ppr PprDebug arg, ppr PprDebug arg_demand]) (
+ = panic "WwLib: haven't done mk_absent_let for primitives yet"
+ where
+ arg_ty = idType arg
+
+mk_unpk_case NewType arg unpk_args boxing_con boxing_tycon body
+ -- A newtype! Use a coercion not a case
+ = ASSERT( null other_args )
+ Case (Note (Coerce (idType unpk_arg) (idType arg)) (Var arg))
+ unpk_arg
+ [(DEFAULT,[],body)]
+ where
+ (unpk_arg:other_args) = unpk_args
- -- Finish args to the right...
- mk_ww_arg_processing args infos useful_split max_extra_args
- `thenMaybeUs` \ (wrap_rest, work_args_info, work_rest) ->
+mk_unpk_case DataType arg unpk_args boxing_con boxing_tycon body
+ -- A data type
+ = Case (Var arg) arg [(DataCon boxing_con, unpk_args, body)]
- returnUs (Just (
- -- wrapper:
- \ hole -> wrap_rest (App hole (VarArg arg)),
+mk_pk_let NewType arg boxing_con con_tys unpk_args body
+ = ASSERT( null other_args )
+ Let (NonRec arg (Note (Coerce (idType arg) (idType unpk_arg)) (Var unpk_arg))) body
+ where
+ (unpk_arg:other_args) = unpk_args
+
+mk_pk_let DataType arg boxing_con con_tys unpk_args body
+ = Let (NonRec arg (Con (DataCon boxing_con) con_args)) body
+ where
+ con_args = map Type con_tys ++ map Var unpk_args
- -- worker:
- (arg, arg_demand) : work_args_info,
- \ hole -> work_rest hole
- ))
- --)
-nonAbsentArgs :: [Demand] -> Int
-nonAbsentArgs cmpts = length [() | WwLazy True <- cmpts]
+mk_ww_local uniq ty = mkSysLocal uniq ty
\end{code}
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