2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1996
4 \section[WorkWrap]{Worker/wrapper-generating back-end of strictness analyser}
7 #include "HsVersions.h"
9 module WorkWrap ( workersAndWrappers ) where
14 import CoreUnfold ( UnfoldingGuidance(..) )
15 import CoreUtils ( coreExprType )
16 import Id ( idWantsToBeINLINEd, getIdStrictness, mkWorkerId,
19 import IdInfo ( noIdInfo, addInfo_UF, indicatesWorker,
20 mkStrictnessInfo, StrictnessInfo(..)
23 import UniqSupply ( returnUs, thenUs, mapUs, getUnique, UniqSM(..) )
25 import Util ( panic{-ToDo:rm-} )
27 replaceIdInfo = panic "WorkWrap.replaceIdInfo (ToDo)"
28 iWantToBeINLINEd = panic "WorkWrap.iWantToBeINLINEd (ToDo)"
31 We take Core bindings whose binders have their strictness attached (by
32 the front-end of the strictness analyser), and we return some
33 ``plain'' bindings which have been worker/wrapper-ified, meaning:
36 Functions have been split into workers and wrappers where appropriate;
38 Binders' @IdInfos@ have been updated to reflect the existence
39 of these workers/wrappers (this is where we get STRICTNESS pragma
40 info for exported values).
44 workersAndWrappers :: [CoreBinding] -> UniqSM [CoreBinding]
46 workersAndWrappers top_binds
47 = mapUs (wwBind True{-top-level-}) top_binds `thenUs` \ top_binds2 ->
49 top_binds3 = map make_top_binding top_binds2
51 returnUs (concat top_binds3)
53 make_top_binding :: WwBinding -> [CoreBinding]
55 make_top_binding (WwLet binds) = binds
58 %************************************************************************
60 \subsection[wwBind-wwExpr]{@wwBind@ and @wwExpr@}
62 %************************************************************************
64 @wwBind@ works on a binding, trying each \tr{(binder, expr)} pair in
65 turn. Non-recursive case first, then recursive...
68 wwBind :: Bool -- True <=> top-level binding
70 -> UniqSM WwBinding -- returns a WwBinding intermediate form;
71 -- the caller will convert to Expr/Binding,
74 wwBind top_level (NonRec binder rhs)
75 = wwExpr rhs `thenUs` \ new_rhs ->
76 tryWW binder new_rhs `thenUs` \ new_pairs ->
77 returnUs (WwLet [NonRec b e | (b,e) <- new_pairs])
78 -- Generated bindings must be non-recursive
79 -- because the original binding was.
81 ------------------------------
83 wwBind top_level (Rec pairs)
84 = mapUs do_one pairs `thenUs` \ new_pairs ->
85 returnUs (WwLet [Rec (concat new_pairs)])
87 do_one (binder, rhs) = wwExpr rhs `thenUs` \ new_rhs ->
91 @wwExpr@ basically just walks the tree, looking for appropriate
92 annotations that can be used. Remember it is @wwBind@ that does the
93 matching by looking for strict arguments of the correct type.
94 @wwExpr@ is a version that just returns the ``Plain'' Tree.
98 wwExpr :: CoreExpr -> UniqSM CoreExpr
100 wwExpr e@(Var _) = returnUs e
101 wwExpr e@(Lit _) = returnUs e
102 wwExpr e@(Con _ _) = returnUs e
103 wwExpr e@(Prim _ _) = returnUs e
105 wwExpr (Lam binder expr)
106 = wwExpr expr `thenUs` \ new_expr ->
107 returnUs (Lam binder new_expr)
110 = wwExpr f `thenUs` \ new_f ->
111 returnUs (App new_f a)
114 = wwExpr expr `thenUs` \ new_expr ->
115 returnUs (SCC cc new_expr)
117 wwExpr (Coerce c ty expr)
118 = wwExpr expr `thenUs` \ new_expr ->
119 returnUs (Coerce c ty new_expr)
121 wwExpr (Let bind expr)
122 = wwBind False{-not top-level-} bind `thenUs` \ intermediate_bind ->
123 wwExpr expr `thenUs` \ new_expr ->
124 returnUs (mash_ww_bind intermediate_bind new_expr)
126 mash_ww_bind (WwLet binds) body = mkCoLetsNoUnboxed binds body
127 mash_ww_bind (WwCase case_fn) body = case_fn body
129 wwExpr (Case expr alts)
130 = wwExpr expr `thenUs` \ new_expr ->
131 ww_alts alts `thenUs` \ new_alts ->
132 returnUs (Case new_expr new_alts)
134 ww_alts (AlgAlts alts deflt)
135 = mapUs ww_alg_alt alts `thenUs` \ new_alts ->
136 ww_deflt deflt `thenUs` \ new_deflt ->
137 returnUs (AlgAlts new_alts new_deflt)
139 ww_alts (PrimAlts alts deflt)
140 = mapUs ww_prim_alt alts `thenUs` \ new_alts ->
141 ww_deflt deflt `thenUs` \ new_deflt ->
142 returnUs (PrimAlts new_alts new_deflt)
144 ww_alg_alt (con, binders, rhs)
145 = wwExpr rhs `thenUs` \ new_rhs ->
146 returnUs (con, binders, new_rhs)
148 ww_prim_alt (lit, rhs)
149 = wwExpr rhs `thenUs` \ new_rhs ->
150 returnUs (lit, new_rhs)
155 ww_deflt (BindDefault binder rhs)
156 = wwExpr rhs `thenUs` \ new_rhs ->
157 returnUs (BindDefault binder new_rhs)
160 %************************************************************************
162 \subsection[tryWW]{@tryWW@: attempt a worker/wrapper pair}
164 %************************************************************************
166 @tryWW@ just accumulates arguments, converts strictness info from the
167 front-end into the proper form, then calls @mkWwBodies@ to do
170 We have to BE CAREFUL that we don't worker-wrapperize an Id that has
171 already been w-w'd! (You can end up with several liked-named Ids
172 bouncing around at the same time---absolute mischief.) So the
173 criterion we use is: if an Id already has an unfolding (for whatever
174 reason), then we don't w-w it.
176 The only reason this is monadised is for the unique supply.
179 tryWW :: Id -- the fn binder
180 -> CoreExpr -- the bound rhs; its innards
182 -> UniqSM [(Id, CoreExpr)] -- either *one* or *two* pairs;
183 -- if one, then no worker (only
184 -- the orig "wrapper" lives on);
185 -- if two, then a worker and a
188 | idWantsToBeINLINEd fn_id
189 -- No point in worker/wrappering something that is going to be
190 -- INLINEd wholesale anyway. If the strictness analyser is run
191 -- twice, this test also prevents wrappers (which are INLINEd)
192 -- from being re-done.
196 = case (getIdStrictness fn_id) of
198 NoStrictnessInfo -> do_nothing
199 BottomGuaranteed -> do_nothing
200 StrictnessInfo [] _ -> do_nothing -- V weird (but possible?)
202 StrictnessInfo args_info _ ->
203 if not (indicatesWorker args_info) then
207 -- OK, it looks as if a worker is worth a try
209 (uvars, tyvars, args, body) = collectBinders rhs
210 body_ty = coreExprType body
212 mkWwBodies body_ty tyvars args args_info `thenUs` \ result ->
215 Nothing -> -- Very peculiar. This can only happen if we hit an
216 -- abstract type, which we shouldn't have since we've
217 -- constructed the args_info in this module!
219 -- False. We might hit the all-args-absent-and-the-
220 -- body-is-unboxed case. A Nothing is legit. (WDP 94/10)
223 Just (wrapper_w_hole, worker_w_hole, worker_strictness, worker_ty_w_hole) ->
225 -- Terrific! It worked!
226 getUnique `thenUs` \ worker_uniq ->
228 worker_ty = worker_ty_w_hole body_ty
230 worker_id = mkWorkerId worker_uniq fn_id worker_ty
231 (noIdInfo `addInfo` worker_strictness)
233 wrapper_rhs = wrapper_w_hole worker_id
234 worker_rhs = worker_w_hole body
236 revised_strictness_info
237 = -- We know the basic strictness info already, but
238 -- we need to slam in the exact identity of the
240 mkStrictnessInfo args_info (Just worker_id)
242 wrapper_id = fn_id `replaceIdInfo`
243 (getIdInfo fn_id `addInfo`
244 revised_strictness_info `addInfo_UF`
245 iWantToBeINLINEd UnfoldAlways)
246 -- NB! the "iWantToBeINLINEd" part adds an INLINE pragma to
247 -- the wrapper, which is of course what we want.
249 returnUs [ (worker_id, worker_rhs), -- worker comes first
250 (wrapper_id, wrapper_rhs) ] -- because wrapper mentions it
252 do_nothing = returnUs [ (fn_id, rhs) ]