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, certainlySmallEnoughToInline, calcUnfoldingGuidance )
13 import CmdLineOpts ( opt_UF_CreationThreshold , opt_D_verbose_core2core,
14 opt_D_dump_worker_wrapper
16 import CoreLint ( beginPass, endPass )
17 import CoreUtils ( coreExprType, exprEtaExpandArity )
18 import Const ( Con(..) )
19 import DataCon ( DataCon )
20 import MkId ( mkWorkerId )
21 import Id ( Id, idType, getIdStrictness, setIdArity, isOneShotLambda,
22 setIdStrictness, getIdDemandInfo, getInlinePragma,
23 setIdWorkerInfo, getIdCprInfo )
25 import Type ( Type, isNewType, splitForAllTys, splitFunTys )
26 import IdInfo ( mkStrictnessInfo, noStrictnessInfo, StrictnessInfo(..),
27 CprInfo(..), exactArity, InlinePragInfo(..)
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.
128 ???????????????? ToDo
131 wwExpr :: CoreExpr -> UniqSM CoreExpr
133 wwExpr e@(Type _) = returnUs e
134 wwExpr e@(Var _) = returnUs e
136 wwExpr e@(Con con args)
137 = mapUs wwExpr args `thenUs` \ args' ->
138 returnUs (Con con args')
140 wwExpr (Lam binder expr)
141 = wwExpr expr `thenUs` \ new_expr ->
142 returnUs (Lam binder new_expr)
145 = wwExpr f `thenUs` \ new_f ->
146 wwExpr a `thenUs` \ new_a ->
147 returnUs (App new_f new_a)
149 wwExpr (Note note expr)
150 = wwExpr expr `thenUs` \ new_expr ->
151 returnUs (Note note new_expr)
153 wwExpr (Let bind expr)
154 = wwBind bind `thenUs` \ intermediate_bind ->
155 wwExpr expr `thenUs` \ new_expr ->
156 returnUs (mkLets intermediate_bind new_expr)
158 wwExpr (Case expr binder alts)
159 = wwExpr expr `thenUs` \ new_expr ->
160 mapUs ww_alt alts `thenUs` \ new_alts ->
161 returnUs (Case new_expr binder new_alts)
163 ww_alt (con, binders, rhs)
164 = wwExpr rhs `thenUs` \ new_rhs ->
165 returnUs (con, binders, new_rhs)
168 %************************************************************************
170 \subsection[tryWW]{@tryWW@: attempt a worker/wrapper pair}
172 %************************************************************************
174 @tryWW@ just accumulates arguments, converts strictness info from the
175 front-end into the proper form, then calls @mkWwBodies@ to do
178 We have to BE CAREFUL that we don't worker-wrapperize an Id that has
179 already been w-w'd! (You can end up with several liked-named Ids
180 bouncing around at the same time---absolute mischief.) So the
181 criterion we use is: if an Id already has an unfolding (for whatever
182 reason), then we don't w-w it.
184 The only reason this is monadised is for the unique supply.
187 tryWW :: Bool -- True <=> a non-recursive binding
188 -> Id -- The fn binder
189 -> CoreExpr -- The bound rhs; its innards
191 -> UniqSM [(Id, CoreExpr)] -- either *one* or *two* pairs;
192 -- if one, then no worker (only
193 -- the orig "wrapper" lives on);
194 -- if two, then a worker and a
196 tryWW non_rec fn_id rhs
197 | (non_rec && -- Don't split if its non-recursive and small
198 certainlySmallEnoughToInline (calcUnfoldingGuidance opt_UF_CreationThreshold rhs)
199 -- No point in worker/wrappering something that is going to be
200 -- INLINEd wholesale anyway. If the strictness analyser is run
201 -- twice, this test also prevents wrappers (which are INLINEd)
202 -- from being re-done.
205 || arity == 0 -- Don't split if it's not a function
206 || never_inline fn_id
208 || not (do_strict_ww || do_cpr_ww || do_coerce_ww)
209 = returnUs [ (fn_id, rhs) ]
211 | otherwise -- Do w/w split
212 = mkWwBodies fun_ty arity wrap_dmds one_shots cpr_info `thenUs` \ (work_args, wrap_fn, work_fn) ->
213 getUniqueUs `thenUs` \ work_uniq ->
215 work_rhs = work_fn rhs
216 work_demands = [getIdDemandInfo v | v <- work_args, isId v]
217 proto_work_id = mkWorkerId work_uniq fn_id (coreExprType work_rhs)
218 work_id | has_strictness = proto_work_id `setIdStrictness` mkStrictnessInfo (work_demands, result_bot)
219 | otherwise = proto_work_id
221 wrap_rhs = wrap_fn work_id
222 wrap_id = fn_id `setIdStrictness` wrapper_strictness
223 `setIdWorkerInfo` Just work_id
224 `setIdArity` exactArity arity
225 -- Add info to the wrapper:
226 -- (a) we want to set its arity
227 -- (b) we want to pin on its revised strictness info
228 -- (c) we pin on its worker id
230 returnUs ([(work_id, work_rhs), (wrap_id, wrap_rhs)])
231 -- Worker first, because wrapper mentions it
233 fun_ty = idType fn_id
234 arity = exprEtaExpandArity rhs
236 -- Don't split something which is marked unconditionally NOINLINE
237 never_inline fn_id = case getInlinePragma fn_id of
238 IMustNotBeINLINEd False Nothing -> True
241 strictness_info = getIdStrictness fn_id
242 StrictnessInfo arg_demands result_bot = strictness_info
243 has_strictness = case strictness_info of
244 StrictnessInfo _ _ -> True
247 do_strict_ww = has_strictness && worthSplitting wrap_dmds result_bot
249 -- NB: There maybe be more items in arg_demands than arity, because
250 -- the strictness info is semantic and looks through InlineMe and Scc Notes,
251 -- whereas arity does not
252 demands_for_visible_args = take arity arg_demands
253 remaining_arg_demands = drop arity arg_demands
255 wrap_dmds | has_strictness = setUnpackStrategy demands_for_visible_args
256 | otherwise = take arity (repeat wwLazy)
258 wrapper_strictness | has_strictness = mkStrictnessInfo (wrap_dmds ++ remaining_arg_demands, result_bot)
259 | otherwise = noStrictnessInfo
261 -------------------------------------------------------------
262 cpr_info = getIdCprInfo fn_id
263 do_cpr_ww = case cpr_info of
267 -------------------------------------------------------------
268 do_coerce_ww = check_for_coerce arity fun_ty
270 -------------------------------------------------------------
271 one_shots = get_one_shots rhs
273 -- See if there's a Coerce before we run out of arity;
274 -- if so, it's worth trying a w/w split. Reason: we find
275 -- functions like f = coerce (\s -> e)
276 -- and g = \x -> coerce (\s -> e)
277 -- and they may have no useful strictness or cpr info, but if we
278 -- do the w/w thing we get rid of the coerces.
280 check_for_coerce arity ty
281 = length arg_tys <= arity && isNewType res_ty
282 -- Don't look further than arity args,
283 -- but if there are arity or fewer, see if there's
284 -- a newtype in the corner
286 (_, tau) = splitForAllTys ty
287 (arg_tys, res_ty) = splitFunTys tau
289 -- If the original function has one-shot arguments, it is important to
290 -- make the wrapper and worker have corresponding one-shot arguments too.
291 -- Otherwise we spuriously float stuff out of case-expression join points,
292 -- which is very annoying.
293 get_one_shots (Lam b e)
294 | isId b = isOneShotLambda b : get_one_shots e
295 | otherwise = get_one_shots e
296 get_one_shots (Note _ e) = get_one_shots e
297 get_one_shots other = noOneShotInfo
302 %************************************************************************
304 \subsection{The worker wrapper core}
306 %************************************************************************
308 @mkWrapper@ is called when importing a function. We have the type of
309 the function and the name of its worker, and we want to make its body (the wrapper).
312 mkWrapper :: Type -- Wrapper type
314 -> [Demand] -- Wrapper strictness info
315 -> CprInfo -- Wrapper cpr info
316 -> UniqSM (Id -> CoreExpr) -- Wrapper body, missing worker Id
318 mkWrapper fun_ty arity demands cpr_info
319 = mkWwBodies fun_ty arity demands noOneShotInfo cpr_info `thenUs` \ (_, wrap_fn, _) ->
322 noOneShotInfo = repeat False