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 (Let bind expr)
118 = wwBind False{-not top-level-} bind `thenUs` \ intermediate_bind ->
119 wwExpr expr `thenUs` \ new_expr ->
120 returnUs (mash_ww_bind intermediate_bind new_expr)
122 mash_ww_bind (WwLet binds) body = mkCoLetsNoUnboxed binds body
123 mash_ww_bind (WwCase case_fn) body = case_fn body
125 wwExpr (Case expr alts)
126 = wwExpr expr `thenUs` \ new_expr ->
127 ww_alts alts `thenUs` \ new_alts ->
128 returnUs (Case new_expr new_alts)
130 ww_alts (AlgAlts alts deflt)
131 = mapUs ww_alg_alt alts `thenUs` \ new_alts ->
132 ww_deflt deflt `thenUs` \ new_deflt ->
133 returnUs (AlgAlts new_alts new_deflt)
135 ww_alts (PrimAlts alts deflt)
136 = mapUs ww_prim_alt alts `thenUs` \ new_alts ->
137 ww_deflt deflt `thenUs` \ new_deflt ->
138 returnUs (PrimAlts new_alts new_deflt)
140 ww_alg_alt (con, binders, rhs)
141 = wwExpr rhs `thenUs` \ new_rhs ->
142 returnUs (con, binders, new_rhs)
144 ww_prim_alt (lit, rhs)
145 = wwExpr rhs `thenUs` \ new_rhs ->
146 returnUs (lit, new_rhs)
151 ww_deflt (BindDefault binder rhs)
152 = wwExpr rhs `thenUs` \ new_rhs ->
153 returnUs (BindDefault binder new_rhs)
156 %************************************************************************
158 \subsection[tryWW]{@tryWW@: attempt a worker/wrapper pair}
160 %************************************************************************
162 @tryWW@ just accumulates arguments, converts strictness info from the
163 front-end into the proper form, then calls @mkWwBodies@ to do
166 We have to BE CAREFUL that we don't worker-wrapperize an Id that has
167 already been w-w'd! (You can end up with several liked-named Ids
168 bouncing around at the same time---absolute mischief.) So the
169 criterion we use is: if an Id already has an unfolding (for whatever
170 reason), then we don't w-w it.
172 The only reason this is monadised is for the unique supply.
175 tryWW :: Id -- the fn binder
176 -> CoreExpr -- the bound rhs; its innards
178 -> UniqSM [(Id, CoreExpr)] -- either *one* or *two* pairs;
179 -- if one, then no worker (only
180 -- the orig "wrapper" lives on);
181 -- if two, then a worker and a
184 | idWantsToBeINLINEd fn_id
185 -- No point in worker/wrappering something that is going to be
186 -- INLINEd wholesale anyway. If the strictness analyser is run
187 -- twice, this test also prevents wrappers (which are INLINEd)
188 -- from being re-done.
192 = case (getIdStrictness fn_id) of
194 NoStrictnessInfo -> do_nothing
195 BottomGuaranteed -> do_nothing
196 StrictnessInfo [] _ -> do_nothing -- V weird (but possible?)
198 StrictnessInfo args_info _ ->
199 if not (indicatesWorker args_info) then
203 -- OK, it looks as if a worker is worth a try
205 (uvars, tyvars, args, body) = collectBinders rhs
206 body_ty = coreExprType body
208 mkWwBodies body_ty tyvars args args_info `thenUs` \ result ->
211 Nothing -> -- Very peculiar. This can only happen if we hit an
212 -- abstract type, which we shouldn't have since we've
213 -- constructed the args_info in this module!
215 -- False. We might hit the all-args-absent-and-the-
216 -- body-is-unboxed case. A Nothing is legit. (WDP 94/10)
219 Just (wrapper_w_hole, worker_w_hole, worker_strictness, worker_ty_w_hole) ->
221 -- Terrific! It worked!
222 getUnique `thenUs` \ worker_uniq ->
224 worker_ty = worker_ty_w_hole body_ty
226 worker_id = mkWorkerId worker_uniq fn_id worker_ty
227 (noIdInfo `addInfo` worker_strictness)
229 wrapper_rhs = wrapper_w_hole worker_id
230 worker_rhs = worker_w_hole body
232 revised_strictness_info
233 = -- We know the basic strictness info already, but
234 -- we need to slam in the exact identity of the
236 mkStrictnessInfo args_info (Just worker_id)
238 wrapper_id = fn_id `replaceIdInfo`
239 (getIdInfo fn_id `addInfo`
240 revised_strictness_info `addInfo_UF`
241 iWantToBeINLINEd UnfoldAlways)
242 -- NB! the "iWantToBeINLINEd" part adds an INLINE pragma to
243 -- the wrapper, which is of course what we want.
245 returnUs [ (worker_id, worker_rhs), -- worker comes first
246 (wrapper_id, wrapper_rhs) ] -- because wrapper mentions it
248 do_nothing = returnUs [ (fn_id, rhs) ]