2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1996
4 \section[WwLib]{A library for the ``worker/wrapper'' back-end to the strictness analyser}
7 #include "HsVersions.h"
12 worthSplitting, setUnpackStrategy,
20 import Id ( GenId, idType, mkSysLocal, dataConArgTys, isDataCon, isNewCon, SYN_IE(Id) )
21 import IdInfo ( mkStrictnessInfo, {-??nonAbsentArgs,-} Demand(..) )
22 import PrelVals ( aBSENT_ERROR_ID, voidId )
23 import TysPrim ( voidTy )
24 import SrcLoc ( noSrcLoc )
25 import Type ( isPrimType, mkTyVarTys, mkForAllTys, mkFunTys,
26 splitForAllTyExpandingDicts, splitForAllTy, splitFunTyExpandingDicts,
27 maybeAppDataTyConExpandingDicts,
30 import TyCon ( isNewTyCon, isDataTyCon )
31 import BasicTypes ( NewOrData(..) )
32 import TyVar ( SYN_IE(TyVar) )
33 import PprType ( GenType, GenTyVar )
34 import UniqSupply ( returnUs, thenUs, thenMaybeUs,
35 getUniques, getUnique, SYN_IE(UniqSM)
37 import Util ( zipWithEqual, zipEqual, assertPanic, panic, pprPanic )
42 %************************************************************************
44 \subsection[datatype-WwLib]{@WwBinding@: a datatype for worker/wrapper-ing}
46 %************************************************************************
48 In the worker/wrapper stuff, we want to carry around @CoreBindings@ in
49 an ``intermediate form'' that can later be turned into a \tr{let} or
50 \tr{case} (depending on strictness info).
55 | WwCase (CoreExpr -> CoreExpr)
56 -- the "case" will be a "strict let" of the form:
61 -- (instead of "let <blah> = rhs in body")
63 -- The expr you pass to the function is "body" (the
64 -- expression that goes "in the corner").
67 %************************************************************************
69 \subsection[mkWrapperAndWorker]{@mkWrapperAndWorker@}
71 %************************************************************************
73 ************ WARNING ******************
74 these comments are rather out of date
75 *****************************************
77 @mkWrapperAndWorker@ is given:
80 The {\em original function} \tr{f}, of the form:
82 f = /\ tyvars -> \ args -> body
84 The original-binder \tr{f}, the \tr{tyvars}, \tr{args}, and \tr{body}
87 We use the Id \tr{f} mostly to get its type.
90 Strictness information about \tr{f}, in the form of a list of
97 @mkWrapperAndWorker@ produces (A BIT OUT-OF-DATE...):
100 Maybe @Nothing@: no worker/wrappering going on in this case. This can
101 happen (a)~if the strictness info says that there is nothing
102 interesting to do or (b)~if *any* of the argument types corresponding
103 to ``active'' arg postitions is abstract or will be to the outside
104 world (i.e., {\em this} module can see the constructors, but nobody
105 else will be able to). An ``active'' arg position is one which the
106 wrapper has to unpack. An importing module can't do this unpacking,
107 so it simply has to give up and call the wrapper only.
110 Maybe \tr{Just (wrapper_Id, wrapper_body, worker_Id, worker_body)}.
112 The @wrapper_Id@ is just the one that was passed in, with its
113 strictness IdInfo updated.
116 The \tr{body} of the original function may not be given (i.e., it's
117 BOTTOM), in which case you'd jolly well better not tug on the
120 Here's an example. The original function is:
122 g :: forall a . Int -> [a] -> a
124 g = /\ a -> \ x ys ->
130 From this, we want to produce:
132 -- wrapper (an unfolding)
133 g :: forall a . Int -> [a] -> a
135 g = /\ a -> \ x ys ->
137 I# x# -> g.wrk a x# ys
138 -- call the worker; don't forget the type args!
141 g.wrk :: forall a . Int# -> [a] -> a
143 g.wrk = /\ a -> \ x# ys ->
147 case x of -- note: body of g moved intact
152 Something we have to be careful about: Here's an example:
154 -- "f" strictness: U(P)U(P)
155 f (I# a) (I# b) = a +# b
157 g = f -- "g" strictness same as "f"
159 \tr{f} will get a worker all nice and friendly-like; that's good.
160 {\em But we don't want a worker for \tr{g}}, even though it has the
161 same strictness as \tr{f}. Doing so could break laziness, at best.
163 Consequently, we insist that the number of strictness-info items is
164 exactly the same as the number of lambda-bound arguments. (This is
165 probably slightly paranoid, but OK in practice.) If it isn't the
166 same, we ``revise'' the strictness info, so that we won't propagate
167 the unusable strictness-info into the interfaces.
170 %************************************************************************
172 \subsection{Functions over Demands}
174 %************************************************************************
177 mAX_WORKER_ARGS :: Int -- ToDo: set via flag
180 setUnpackStrategy :: [Demand] -> [Demand]
182 = snd (go (mAX_WORKER_ARGS - nonAbsentArgs ds) ds)
184 go :: Int -- Max number of args available for sub-components of [Demand]
186 -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
188 go n (WwUnpack nd _ cs : ds) | n' >= 0
189 = WwUnpack nd True cs' `cons` go n'' ds
191 = WwUnpack nd False cs `cons` go n ds
193 n' = n + 1 - nonAbsentArgs cs
194 -- Add one because we don't pass the top-level arg any more
195 -- Delete # of non-absent args to which we'll now be committed
198 go n (d:ds) = d `cons` go n ds
201 cons d (n,ds) = (n, d:ds)
203 nonAbsentArgs :: [Demand] -> Int
205 nonAbsentArgs (WwLazy True : ds) = nonAbsentArgs ds
206 nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
208 worthSplitting :: [Demand] -> Bool -- True <=> the wrapper would not be an identity function
209 worthSplitting [] = False
210 worthSplitting (WwLazy True : ds) = True -- Absent arg
211 worthSplitting (WwUnpack _ True _ : ds) = True -- Arg to unpack
212 worthSplitting (d : ds) = worthSplitting ds
214 allAbsent :: [Demand] -> Bool
215 allAbsent (WwLazy True : ds) = allAbsent ds
216 allAbsent (WwUnpack _ True cs : ds) = allAbsent cs && allAbsent ds
217 allAbsent (d : ds) = False
222 %************************************************************************
224 \subsection{The worker wrapper core}
226 %************************************************************************
228 @mkWrapper@ is called when importing a function. We have the type of
229 the function and the name of its worker, and we want to make its body (the wrapper).
232 mkWrapper :: Type -- Wrapper type
233 -> [Demand] -- Wrapper strictness info
234 -> UniqSM (Id -> CoreExpr) -- Wrapper body, missing worker Id
236 mkWrapper fun_ty demands
238 n_wrap_args = length demands
240 getUniques n_wrap_args `thenUs` \ wrap_uniqs ->
242 (tyvars, tau_ty) = splitForAllTyExpandingDicts fun_ty
243 (arg_tys, body_ty) = splitFunTyExpandingDicts tau_ty
244 -- The "expanding dicts" part here is important, even for the splitForAll
245 -- The imported thing might be a dictionary, such as Functor Foo
246 -- But Functor Foo = forall a b. (a->b) -> Foo a -> Foo b
247 -- and as such might have some strictness info attached.
248 -- Then we need to have enough args to zip to the strictness info
250 wrap_args = zipWith mk_ww_local wrap_uniqs arg_tys
251 leftover_arg_tys = drop n_wrap_args arg_tys
252 final_body_ty = mkFunTys leftover_arg_tys body_ty
254 mkWwBodies tyvars wrap_args final_body_ty demands `thenUs` \ (wrap_fn, _, _) ->
258 @mkWwBodies@ is called when doing the worker/wrapper split inside a module.
261 mkWwBodies :: [TyVar] -> [Id] -> Type -- Original fn args and body type
262 -> [Demand] -- Strictness info for original fn; corresp 1-1 with args
263 -> UniqSM (Id -> CoreExpr, -- Wrapper body, lacking only the worker Id
264 CoreExpr -> CoreExpr, -- Worker body, lacking the original function body
265 [Demand]) -- Strictness info for worker
267 mkWwBodies tyvars args body_ty demands
268 | allAbsent demands &&
270 = -- Horrid special case. If the worker would have no arguments, and the
271 -- function returns a primitive type value, that would make the worker into
272 -- an unboxed value. We box it by passing a dummy void argument, thus:
274 -- f = /\abc. \xyz. fw abc void
275 -- fw = /\abc. \v. body
277 getUnique `thenUs` \ void_arg_uniq ->
279 void_arg = mk_ww_local void_arg_uniq voidTy
281 returnUs (\ work_id -> mkLam tyvars args (App (mkTyApp (Var work_id) (mkTyVarTys tyvars)) (VarArg voidId)),
282 \ body -> mkLam tyvars [void_arg] body,
285 mkWwBodies tyvars args body_ty demands
288 args_w_demands = zipEqual "mkWwBodies" args demands
290 mkWW args_w_demands `thenUs` \ (wrap_fn, work_args_w_demands, work_fn) ->
292 (work_args, work_demands) = unzip work_args_w_demands
294 returnUs (\ work_id -> mkLam tyvars args (wrap_fn (mkTyApp (Var work_id) (mkTyVarTys tyvars))),
295 \ body -> mkLam tyvars work_args (work_fn body),
301 mkWW :: [(Id,Demand)]
302 -> UniqSM (CoreExpr -> CoreExpr, -- Wrapper body, lacking the inner call to the worker
303 -- and without its lambdas
304 [(Id,Demand)], -- Worker args and their demand infos
305 CoreExpr -> CoreExpr) -- Worker body, lacking the original body of the function
310 = returnUs (\ wrapper_body -> wrapper_body,
312 \ worker_body -> worker_body)
316 mkWW ((arg,WwLazy True) : ds)
317 = mkWW ds `thenUs` \ (wrap_fn, worker_args, work_fn) ->
318 returnUs (\ wrapper_body -> wrap_fn wrapper_body,
320 \ worker_body -> mk_absent_let arg (work_fn worker_body))
324 mkWW ((arg,WwUnpack new_or_data True cs) : ds)
325 = getUniques (length inst_con_arg_tys) `thenUs` \ uniqs ->
327 unpk_args = zipWith mk_ww_local uniqs inst_con_arg_tys
328 unpk_args_w_ds = zipEqual "mkWW" unpk_args cs
330 mkWW (unpk_args_w_ds ++ ds) `thenUs` \ (wrap_fn, worker_args, work_fn) ->
331 returnUs (\ wrapper_body -> mk_unpk_case new_or_data arg unpk_args data_con arg_tycon (wrap_fn wrapper_body),
333 \ worker_body -> work_fn (mk_pk_let new_or_data arg data_con tycon_arg_tys unpk_args worker_body))
335 inst_con_arg_tys = dataConArgTys data_con tycon_arg_tys
336 (arg_tycon, tycon_arg_tys, data_con)
337 = case (maybeAppDataTyConExpandingDicts (idType arg)) of
339 Just (arg_tycon, tycon_arg_tys, [data_con]) ->
340 -- The main event: a single-constructor data type
341 (arg_tycon, tycon_arg_tys, data_con)
343 Just (_, _, data_cons) -> pprPanic "mk_ww_arg_processing: not one constr (interface files not consistent/up to date ?)" ((ppr PprDebug arg) <+> (ppr PprDebug (idType arg)))
344 Nothing -> panic "mk_ww_arg_processing: not datatype"
348 mkWW ((arg,other_demand) : ds)
349 = mkWW ds `thenUs` \ (wrap_fn, worker_args, work_fn) ->
350 returnUs (\ wrapper_body -> wrap_fn (App wrapper_body (VarArg arg)),
351 (arg,other_demand) : worker_args,
356 %************************************************************************
358 \subsection{Utilities}
360 %************************************************************************
364 mk_absent_let arg body
365 | not (isPrimType arg_ty)
366 = Let (NonRec arg (mkTyApp (Var aBSENT_ERROR_ID) [arg_ty])) body
368 = panic "WwLib: haven't done mk_absent_let for primitives yet"
372 mk_unpk_case NewType arg unpk_args boxing_con boxing_tycon body
373 -- A newtype! Use a coercion not a case
374 = ASSERT( null other_args && isNewTyCon boxing_tycon )
375 Let (NonRec unpk_arg (Coerce (CoerceOut boxing_con) (idType unpk_arg) (Var arg)))
378 (unpk_arg:other_args) = unpk_args
380 mk_unpk_case DataType arg unpk_args boxing_con boxing_tycon body
382 = ASSERT( isDataTyCon boxing_tycon )
384 (AlgAlts [(boxing_con, unpk_args, body)]
388 mk_pk_let NewType arg boxing_con con_tys unpk_args body
389 = ASSERT( null other_args && isNewCon boxing_con )
390 Let (NonRec arg (Coerce (CoerceIn boxing_con) (idType arg) (Var unpk_arg))) body
392 (unpk_arg:other_args) = unpk_args
394 mk_pk_let DataType arg boxing_con con_tys unpk_args body
395 = ASSERT( isDataCon boxing_con )
396 Let (NonRec arg (Con boxing_con con_args)) body
398 con_args = map TyArg con_tys ++ map VarArg unpk_args
402 = mkSysLocal SLIT("ww") uniq ty noSrcLoc