2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
4 \section[WorkWrap]{Worker/wrapper-generating back-end of strictness analyser}
7 module WorkWrap ( wwTopBinds, mkWrapper ) where
9 #include "HsVersions.h"
12 import CoreUnfold ( Unfolding, certainlyWillInline )
13 import CmdLineOpts ( opt_UF_CreationThreshold , opt_D_verbose_core2core,
14 opt_D_dump_worker_wrapper
16 import CoreLint ( beginPass, endPass )
17 import CoreUtils ( exprType, exprArity, exprEtaExpandArity )
18 import DataCon ( DataCon )
19 import MkId ( mkWorkerId )
20 import Id ( Id, idType, idStrictness, setIdArityInfo, isOneShotLambda,
21 setIdStrictness, idInlinePragma,
22 setIdWorkerInfo, idCprInfo, setInlinePragma )
24 import Type ( Type, isNewType, splitForAllTys, splitFunTys )
25 import IdInfo ( mkStrictnessInfo, noStrictnessInfo, StrictnessInfo(..),
26 CprInfo(..), exactArity, InlinePragInfo(..), isNeverInlinePrag,
29 import Demand ( Demand, wwLazy )
31 import UniqSupply ( UniqSupply, initUs_, returnUs, thenUs, mapUs, getUniqueUs, UniqSM )
37 We take Core bindings whose binders have:
41 \item Strictness attached (by the front-end of the strictness
44 \item Constructed Product Result information attached by the CPR
49 and we return some ``plain'' bindings which have been
50 worker/wrapper-ified, meaning:
54 \item Functions have been split into workers and wrappers where
55 appropriate. If a function has both strictness and CPR properties
56 then only one worker/wrapper doing both transformations is produced;
58 \item Binders' @IdInfos@ have been updated to reflect the existence of
59 these workers/wrappers (this is where we get STRICTNESS and CPR pragma
60 info for exported values).
65 wwTopBinds :: UniqSupply
71 beginPass "Worker Wrapper binds";
73 -- Create worker/wrappers, and mark binders with their
74 -- "strictness info" [which encodes their worker/wrapper-ness]
75 let { binds' = workersAndWrappers us binds };
77 endPass "Worker Wrapper binds" (opt_D_dump_worker_wrapper ||
78 opt_D_verbose_core2core) binds'
84 workersAndWrappers :: UniqSupply -> [CoreBind] -> [CoreBind]
86 workersAndWrappers us top_binds
88 mapUs wwBind top_binds `thenUs` \ top_binds' ->
89 returnUs (concat top_binds')
92 %************************************************************************
94 \subsection[wwBind-wwExpr]{@wwBind@ and @wwExpr@}
96 %************************************************************************
98 @wwBind@ works on a binding, trying each \tr{(binder, expr)} pair in
99 turn. Non-recursive case first, then recursive...
103 -> UniqSM [CoreBind] -- returns a WwBinding intermediate form;
104 -- the caller will convert to Expr/Binding,
107 wwBind (NonRec binder rhs)
108 = wwExpr rhs `thenUs` \ new_rhs ->
109 tryWW True {- non-recursive -} binder new_rhs `thenUs` \ new_pairs ->
110 returnUs [NonRec b e | (b,e) <- new_pairs]
111 -- Generated bindings must be non-recursive
112 -- because the original binding was.
114 ------------------------------
117 = mapUs do_one pairs `thenUs` \ new_pairs ->
118 returnUs [Rec (concat new_pairs)]
120 do_one (binder, rhs) = wwExpr rhs `thenUs` \ new_rhs ->
121 tryWW False {- recursive -} binder new_rhs
124 @wwExpr@ basically just walks the tree, looking for appropriate
125 annotations that can be used. Remember it is @wwBind@ that does the
126 matching by looking for strict arguments of the correct type.
127 @wwExpr@ is a version that just returns the ``Plain'' Tree.
130 wwExpr :: CoreExpr -> UniqSM CoreExpr
132 wwExpr e@(Type _) = returnUs e
133 wwExpr e@(Var _) = returnUs e
134 wwExpr e@(Lit _) = returnUs e
136 wwExpr (Lam binder expr)
137 = wwExpr expr `thenUs` \ new_expr ->
138 returnUs (Lam binder new_expr)
141 = wwExpr f `thenUs` \ new_f ->
142 wwExpr a `thenUs` \ new_a ->
143 returnUs (App new_f new_a)
145 wwExpr (Note note expr)
146 = wwExpr expr `thenUs` \ new_expr ->
147 returnUs (Note note new_expr)
149 wwExpr (Let bind expr)
150 = wwBind bind `thenUs` \ intermediate_bind ->
151 wwExpr expr `thenUs` \ new_expr ->
152 returnUs (mkLets intermediate_bind new_expr)
154 wwExpr (Case expr binder alts)
155 = wwExpr expr `thenUs` \ new_expr ->
156 mapUs ww_alt alts `thenUs` \ new_alts ->
157 returnUs (Case new_expr binder new_alts)
159 ww_alt (con, binders, rhs)
160 = wwExpr rhs `thenUs` \ new_rhs ->
161 returnUs (con, binders, new_rhs)
164 %************************************************************************
166 \subsection[tryWW]{@tryWW@: attempt a worker/wrapper pair}
168 %************************************************************************
170 @tryWW@ just accumulates arguments, converts strictness info from the
171 front-end into the proper form, then calls @mkWwBodies@ to do
174 We have to BE CAREFUL that we don't worker-wrapperize an Id that has
175 already been w-w'd! (You can end up with several liked-named Ids
176 bouncing around at the same time---absolute mischief.) So the
177 criterion we use is: if an Id already has an unfolding (for whatever
178 reason), then we don't w-w it.
180 The only reason this is monadised is for the unique supply.
183 tryWW :: Bool -- True <=> a non-recursive binding
184 -> Id -- The fn binder
185 -> CoreExpr -- The bound rhs; its innards
187 -> UniqSM [(Id, CoreExpr)] -- either *one* or *two* pairs;
188 -- if one, then no worker (only
189 -- the orig "wrapper" lives on);
190 -- if two, then a worker and a
192 tryWW non_rec fn_id rhs
193 | isNeverInlinePrag inline_prag
194 = -- Don't split things that will never be inlined
195 returnUs [ (fn_id, rhs) ]
197 | non_rec && certainlyWillInline fn_id
198 -- No point in worker/wrappering something that is going to be
199 -- INLINEd wholesale anyway. If the strictness analyser is run
200 -- twice, this test also prevents wrappers (which are INLINEd)
201 -- from being re-done.
203 -- OUT OF DATE NOTE, kept for info:
204 -- In this case we add an INLINE pragma to the RHS. Why?
207 -- g = \yz -> ... -- And g is strict
208 -- Then f is small, so we don't w/w it. But g is big, and we do, so
209 -- g's wrapper will get inlined in f's RHS, which makes f look big now.
210 -- So f doesn't get inlined, but it is strict and we have failed to w/w it.
211 -- It's out of date because now wrappers look very cheap
212 -- even when they are inlined.
213 = returnUs [ (fn_id, rhs) ]
215 | not (do_strict_ww || do_cpr_ww || do_coerce_ww)
216 = returnUs [ (fn_id, rhs) ]
218 | otherwise -- Do w/w split
219 = mkWwBodies fun_ty arity wrap_dmds result_bot one_shots cpr_info `thenUs` \ (work_demands, wrap_fn, work_fn) ->
220 getUniqueUs `thenUs` \ work_uniq ->
222 work_rhs = work_fn rhs
223 proto_work_id = mkWorkerId work_uniq fn_id (exprType work_rhs)
224 `setInlinePragma` inline_prag
226 work_id | has_strictness = proto_work_id `setIdStrictness` mkStrictnessInfo (work_demands, result_bot)
227 | otherwise = proto_work_id
229 wrap_arity = exprArity wrap_rhs -- Might be greater than the current visible arity
230 -- if the function returns bottom
232 wrap_rhs = wrap_fn work_id
233 wrap_id = fn_id `setIdStrictness` wrapper_strictness
234 `setIdWorkerInfo` HasWorker work_id wrap_arity
235 `setIdArityInfo` exactArity wrap_arity
236 `setInlinePragma` NoInlinePragInfo -- Put it on the worker instead
237 -- Add info to the wrapper:
238 -- (a) we want to set its arity
239 -- (b) we want to pin on its revised strictness info
240 -- (c) we pin on its worker id
242 returnUs ([(work_id, work_rhs), (wrap_id, wrap_rhs)])
243 -- Worker first, because wrapper mentions it
244 -- Arrange to inline the wrapper unconditionally
246 fun_ty = idType fn_id
247 arity = exprEtaExpandArity rhs
249 -- Don't split something which is marked unconditionally NOINLINE
250 inline_prag = idInlinePragma fn_id
252 strictness_info = idStrictness fn_id
253 has_strictness = case strictness_info of
254 StrictnessInfo _ _ -> True
255 NoStrictnessInfo -> False
256 (arg_demands, result_bot) = case strictness_info of
257 StrictnessInfo d r -> (d, r)
258 NoStrictnessInfo -> ([], False)
260 wrap_dmds = setUnpackStrategy arg_demands
261 do_strict_ww = WARN( has_strictness && not result_bot && arity < length arg_demands && worthSplitting wrap_dmds result_bot,
262 text "Insufficient arity" <+> ppr fn_id <+> ppr arity <+> ppr arg_demands )
263 (result_bot || arity >= length arg_demands) -- Only if there's enough visible arity
264 && -- (else strictness info isn't valid)
266 worthSplitting wrap_dmds result_bot -- And it's useful
267 -- worthSplitting returns False for an empty list of demands,
268 -- and hence do_strict_ww is False if arity is zero
269 -- Also it's false if there is no strictness (arg_demands is [])
271 wrapper_strictness | has_strictness = mkStrictnessInfo (wrap_dmds, result_bot)
272 | otherwise = noStrictnessInfo
274 -------------------------------------------------------------
275 cpr_info = idCprInfo fn_id
276 do_cpr_ww = arity > 0 &&
281 -------------------------------------------------------------
282 do_coerce_ww = check_for_coerce arity fun_ty
283 -- We are willing to do a w/w even if the arity is zero.
289 -------------------------------------------------------------
290 one_shots = get_one_shots rhs
292 -- See if there's a Coerce before we run out of arity;
293 -- if so, it's worth trying a w/w split. Reason: we find
294 -- functions like f = coerce (\s -> e)
295 -- and g = \x -> coerce (\s -> e)
296 -- and they may have no useful strictness or cpr info, but if we
297 -- do the w/w thing we get rid of the coerces.
299 check_for_coerce arity ty
300 = length arg_tys <= arity && isNewType res_ty
301 -- Don't look further than arity args,
302 -- but if there are arity or fewer, see if there's
303 -- a newtype in the corner
305 (_, tau) = splitForAllTys ty
306 (arg_tys, res_ty) = splitFunTys tau
308 -- If the original function has one-shot arguments, it is important to
309 -- make the wrapper and worker have corresponding one-shot arguments too.
310 -- Otherwise we spuriously float stuff out of case-expression join points,
311 -- which is very annoying.
312 get_one_shots (Lam b e)
313 | isId b = isOneShotLambda b : get_one_shots e
314 | otherwise = get_one_shots e
315 get_one_shots (Note _ e) = get_one_shots e
316 get_one_shots other = noOneShotInfo
321 %************************************************************************
323 \subsection{The worker wrapper core}
325 %************************************************************************
327 @mkWrapper@ is called when importing a function. We have the type of
328 the function and the name of its worker, and we want to make its body (the wrapper).
331 mkWrapper :: Type -- Wrapper type
333 -> [Demand] -- Wrapper strictness info
334 -> Bool -- Function returns bottom
335 -> CprInfo -- Wrapper cpr info
336 -> UniqSM (Id -> CoreExpr) -- Wrapper body, missing worker Id
338 mkWrapper fun_ty arity demands res_bot cpr_info
339 = mkWwBodies fun_ty arity demands res_bot noOneShotInfo cpr_info `thenUs` \ (_, wrap_fn, _) ->
342 noOneShotInfo = repeat False