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}
10 worthSplitting, setUnpackStrategy,
14 #include "HsVersions.h"
17 import Id ( GenId, idType, mkSysLocal, dataConArgTys, isDataCon, isNewCon, Id )
18 import IdInfo ( mkStrictnessInfo, {-??nonAbsentArgs,-} Demand(..) )
19 import PrelVals ( aBSENT_ERROR_ID, voidId )
20 import TysPrim ( voidTy )
21 import SrcLoc ( noSrcLoc )
22 import Type ( isUnpointedType, mkTyVarTys, mkForAllTys, mkFunTys,
23 splitForAllTys, splitFunTys,
24 splitAlgTyConApp_maybe,
27 import TyCon ( isNewTyCon, isDataTyCon )
28 import BasicTypes ( NewOrData(..) )
29 import TyVar ( TyVar )
30 import PprType ( GenType, GenTyVar )
31 import UniqSupply ( returnUs, thenUs, thenMaybeUs,
32 getUniques, getUnique, UniqSM
34 import Util ( zipWithEqual, zipEqual )
39 %************************************************************************
41 \subsection[datatype-WwLib]{@WwBinding@: a datatype for worker/wrapper-ing}
43 %************************************************************************
45 In the worker/wrapper stuff, we want to carry around @CoreBindings@ in
46 an ``intermediate form'' that can later be turned into a \tr{let} or
47 \tr{case} (depending on strictness info).
52 | WwCase (CoreExpr -> CoreExpr)
53 -- the "case" will be a "strict let" of the form:
58 -- (instead of "let <blah> = rhs in body")
60 -- The expr you pass to the function is "body" (the
61 -- expression that goes "in the corner").
64 %************************************************************************
66 \subsection[mkWrapperAndWorker]{@mkWrapperAndWorker@}
68 %************************************************************************
70 ************ WARNING ******************
71 these comments are rather out of date
72 *****************************************
74 @mkWrapperAndWorker@ is given:
77 The {\em original function} \tr{f}, of the form:
79 f = /\ tyvars -> \ args -> body
81 The original-binder \tr{f}, the \tr{tyvars}, \tr{args}, and \tr{body}
84 We use the Id \tr{f} mostly to get its type.
87 Strictness information about \tr{f}, in the form of a list of
94 @mkWrapperAndWorker@ produces (A BIT OUT-OF-DATE...):
97 Maybe @Nothing@: no worker/wrappering going on in this case. This can
98 happen (a)~if the strictness info says that there is nothing
99 interesting to do or (b)~if *any* of the argument types corresponding
100 to ``active'' arg postitions is abstract or will be to the outside
101 world (i.e., {\em this} module can see the constructors, but nobody
102 else will be able to). An ``active'' arg position is one which the
103 wrapper has to unpack. An importing module can't do this unpacking,
104 so it simply has to give up and call the wrapper only.
107 Maybe \tr{Just (wrapper_Id, wrapper_body, worker_Id, worker_body)}.
109 The @wrapper_Id@ is just the one that was passed in, with its
110 strictness IdInfo updated.
113 The \tr{body} of the original function may not be given (i.e., it's
114 BOTTOM), in which case you'd jolly well better not tug on the
117 Here's an example. The original function is:
119 g :: forall a . Int -> [a] -> a
121 g = /\ a -> \ x ys ->
127 From this, we want to produce:
129 -- wrapper (an unfolding)
130 g :: forall a . Int -> [a] -> a
132 g = /\ a -> \ x ys ->
134 I# x# -> g.wrk a x# ys
135 -- call the worker; don't forget the type args!
138 g.wrk :: forall a . Int# -> [a] -> a
140 g.wrk = /\ a -> \ x# ys ->
144 case x of -- note: body of g moved intact
149 Something we have to be careful about: Here's an example:
151 -- "f" strictness: U(P)U(P)
152 f (I# a) (I# b) = a +# b
154 g = f -- "g" strictness same as "f"
156 \tr{f} will get a worker all nice and friendly-like; that's good.
157 {\em But we don't want a worker for \tr{g}}, even though it has the
158 same strictness as \tr{f}. Doing so could break laziness, at best.
160 Consequently, we insist that the number of strictness-info items is
161 exactly the same as the number of lambda-bound arguments. (This is
162 probably slightly paranoid, but OK in practice.) If it isn't the
163 same, we ``revise'' the strictness info, so that we won't propagate
164 the unusable strictness-info into the interfaces.
167 %************************************************************************
169 \subsection{Functions over Demands}
171 %************************************************************************
174 mAX_WORKER_ARGS :: Int -- ToDo: set via flag
177 setUnpackStrategy :: [Demand] -> [Demand]
179 = snd (go (mAX_WORKER_ARGS - nonAbsentArgs ds) ds)
181 go :: Int -- Max number of args available for sub-components of [Demand]
183 -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
185 go n (WwUnpack nd _ cs : ds) | n' >= 0
186 = WwUnpack nd True cs' `cons` go n'' ds
188 = WwUnpack nd False cs `cons` go n ds
190 n' = n + 1 - nonAbsentArgs cs
191 -- Add one because we don't pass the top-level arg any more
192 -- Delete # of non-absent args to which we'll now be committed
195 go n (d:ds) = d `cons` go n ds
198 cons d (n,ds) = (n, d:ds)
200 nonAbsentArgs :: [Demand] -> Int
202 nonAbsentArgs (WwLazy True : ds) = nonAbsentArgs ds
203 nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
205 worthSplitting :: [Demand] -> Bool -- True <=> the wrapper would not be an identity function
206 worthSplitting [] = False
207 worthSplitting (WwLazy True : ds) = True -- Absent arg
208 worthSplitting (WwUnpack _ True _ : ds) = True -- Arg to unpack
209 worthSplitting (d : ds) = worthSplitting ds
211 allAbsent :: [Demand] -> Bool
212 allAbsent (WwLazy True : ds) = allAbsent ds
213 allAbsent (WwUnpack _ True cs : ds) = allAbsent cs && allAbsent ds
214 allAbsent (d : ds) = False
219 %************************************************************************
221 \subsection{The worker wrapper core}
223 %************************************************************************
225 @mkWrapper@ is called when importing a function. We have the type of
226 the function and the name of its worker, and we want to make its body (the wrapper).
229 mkWrapper :: Type -- Wrapper type
230 -> [Demand] -- Wrapper strictness info
231 -> UniqSM (Id -> CoreExpr) -- Wrapper body, missing worker Id
233 mkWrapper fun_ty demands
235 n_wrap_args = length demands
237 getUniques n_wrap_args `thenUs` \ wrap_uniqs ->
239 (tyvars, tau_ty) = splitForAllTys fun_ty
240 (arg_tys, body_ty) = splitFunTys tau_ty
241 -- The "expanding dicts" part here is important, even for the splitForAll
242 -- The imported thing might be a dictionary, such as Functor Foo
243 -- But Functor Foo = forall a b. (a->b) -> Foo a -> Foo b
244 -- and as such might have some strictness info attached.
245 -- Then we need to have enough args to zip to the strictness info
247 wrap_args = zipWith mk_ww_local wrap_uniqs arg_tys
248 leftover_arg_tys = drop n_wrap_args arg_tys
249 final_body_ty = mkFunTys leftover_arg_tys body_ty
251 mkWwBodies tyvars wrap_args final_body_ty demands `thenUs` \ (wrap_fn, _, _) ->
255 @mkWwBodies@ is called when doing the worker/wrapper split inside a module.
258 mkWwBodies :: [TyVar] -> [Id] -> Type -- Original fn args and body type
259 -> [Demand] -- Strictness info for original fn; corresp 1-1 with args
260 -> UniqSM (Id -> CoreExpr, -- Wrapper body, lacking only the worker Id
261 CoreExpr -> CoreExpr, -- Worker body, lacking the original function body
262 [Demand]) -- Strictness info for worker
264 mkWwBodies tyvars args body_ty demands
265 | allAbsent demands &&
266 isUnpointedType body_ty
267 = -- Horrid special case. If the worker would have no arguments, and the
268 -- function returns a primitive type value, that would make the worker into
269 -- an unboxed value. We box it by passing a dummy void argument, thus:
271 -- f = /\abc. \xyz. fw abc void
272 -- fw = /\abc. \v. body
274 getUnique `thenUs` \ void_arg_uniq ->
276 void_arg = mk_ww_local void_arg_uniq voidTy
278 returnUs (\ work_id -> mkLam tyvars args (App (mkTyApp (Var work_id) (mkTyVarTys tyvars)) (VarArg voidId)),
279 \ body -> mkLam tyvars [void_arg] body,
282 mkWwBodies tyvars args body_ty demands
285 args_w_demands = zipEqual "mkWwBodies" args demands
287 mkWW args_w_demands `thenUs` \ (wrap_fn, work_args_w_demands, work_fn) ->
289 (work_args, work_demands) = unzip work_args_w_demands
291 returnUs (\ work_id -> mkLam tyvars args (wrap_fn (mkTyApp (Var work_id) (mkTyVarTys tyvars))),
292 \ body -> mkLam tyvars work_args (work_fn body),
298 mkWW :: [(Id,Demand)]
299 -> UniqSM (CoreExpr -> CoreExpr, -- Wrapper body, lacking the inner call to the worker
300 -- and without its lambdas
301 [(Id,Demand)], -- Worker args and their demand infos
302 CoreExpr -> CoreExpr) -- Worker body, lacking the original body of the function
307 = returnUs (\ wrapper_body -> wrapper_body,
309 \ worker_body -> worker_body)
313 mkWW ((arg,WwLazy True) : ds)
314 = mkWW ds `thenUs` \ (wrap_fn, worker_args, work_fn) ->
315 returnUs (\ wrapper_body -> wrap_fn wrapper_body,
317 \ worker_body -> mk_absent_let arg (work_fn worker_body))
321 mkWW ((arg,WwUnpack new_or_data True cs) : ds)
322 = getUniques (length inst_con_arg_tys) `thenUs` \ uniqs ->
324 unpk_args = zipWith mk_ww_local uniqs inst_con_arg_tys
325 unpk_args_w_ds = zipEqual "mkWW" unpk_args cs
327 mkWW (unpk_args_w_ds ++ ds) `thenUs` \ (wrap_fn, worker_args, work_fn) ->
328 returnUs (\ wrapper_body -> mk_unpk_case new_or_data arg unpk_args data_con arg_tycon (wrap_fn wrapper_body),
330 \ worker_body -> work_fn (mk_pk_let new_or_data arg data_con tycon_arg_tys unpk_args worker_body))
332 inst_con_arg_tys = dataConArgTys data_con tycon_arg_tys
333 (arg_tycon, tycon_arg_tys, data_con)
334 = case (splitAlgTyConApp_maybe (idType arg)) of
336 Just (arg_tycon, tycon_arg_tys, [data_con]) ->
337 -- The main event: a single-constructor data type
338 (arg_tycon, tycon_arg_tys, data_con)
340 Just (_, _, data_cons) -> pprPanic "mk_ww_arg_processing: not one constr (interface files not consistent/up to date ?)" ((ppr arg) <+> (ppr (idType arg)))
341 Nothing -> panic "mk_ww_arg_processing: not datatype"
345 mkWW ((arg,other_demand) : ds)
346 = mkWW ds `thenUs` \ (wrap_fn, worker_args, work_fn) ->
347 returnUs (\ wrapper_body -> wrap_fn (App wrapper_body (VarArg arg)),
348 (arg,other_demand) : worker_args,
353 %************************************************************************
355 \subsection{Utilities}
357 %************************************************************************
361 mk_absent_let arg body
362 | not (isUnpointedType arg_ty)
363 = Let (NonRec arg (mkTyApp (Var aBSENT_ERROR_ID) [arg_ty])) body
365 = panic "WwLib: haven't done mk_absent_let for primitives yet"
369 mk_unpk_case NewType arg unpk_args boxing_con boxing_tycon body
370 -- A newtype! Use a coercion not a case
371 = ASSERT( null other_args && isNewTyCon boxing_tycon )
372 Let (NonRec unpk_arg (Coerce (CoerceOut boxing_con) (idType unpk_arg) (Var arg)))
375 (unpk_arg:other_args) = unpk_args
377 mk_unpk_case DataType arg unpk_args boxing_con boxing_tycon body
379 = ASSERT( isDataTyCon boxing_tycon )
381 (AlgAlts [(boxing_con, unpk_args, body)]
385 mk_pk_let NewType arg boxing_con con_tys unpk_args body
386 = ASSERT( null other_args && isNewCon boxing_con )
387 Let (NonRec arg (Coerce (CoerceIn boxing_con) (idType arg) (Var unpk_arg))) body
389 (unpk_arg:other_args) = unpk_args
391 mk_pk_let DataType arg boxing_con con_tys unpk_args body
392 = ASSERT( isDataCon boxing_con )
393 Let (NonRec arg (Con boxing_con con_args)) body
395 con_args = map TyArg con_tys ++ map VarArg unpk_args
399 = mkSysLocal SLIT("ww") uniq ty noSrcLoc