2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1995
4 \section[WorkWrap]{Worker/wrapper-generating back-end of strictness analyser}
7 #include "HsVersions.h"
9 module WorkWrap ( workersAndWrappers ) where
15 import Id ( idType, addIdStrictness, getIdStrictness,
16 getIdUnfolding, mkWorkerId,
17 replaceIdInfo, getIdInfo, idWantsToBeINLINEd
19 import IdInfo -- bits and pieces
20 import Maybes ( maybeToBool, Maybe(..) )
22 import SrcLoc ( mkUnknownSrcLoc, SrcLoc )
27 We take Core bindings whose binders have their strictness attached (by
28 the front-end of the strictness analyser), and we return some
29 ``plain'' bindings which have been worker/wrapper-ified, meaning:
32 Functions have been split into workers and wrappers where appropriate;
34 Binders' @IdInfos@ have been updated to reflect the existence
35 of these workers/wrappers (this is where we get STRICTNESS pragma
36 info for exported values).
40 workersAndWrappers :: [CoreBinding] -> WwM [CoreBinding]
42 workersAndWrappers top_binds
43 = mapWw (wwBind True{-top-level-}) top_binds `thenWw` \ top_binds2 ->
45 top_binds3 = map make_top_binding top_binds2
47 returnWw (concat top_binds3)
49 make_top_binding :: WwBinding -> [CoreBinding]
51 make_top_binding (WwLet binds) = binds
54 %************************************************************************
56 \subsection[wwBind-wwExpr]{@wwBind@ and @wwExpr@}
58 %************************************************************************
60 @wwBind@ works on a binding, trying each \tr{(binder, expr)} pair in
61 turn. Non-recursive case first, then recursive...
64 wwBind :: Bool -- True <=> top-level binding
66 -> WwM WwBinding -- returns a WwBinding intermediate form;
67 -- the caller will convert to Expr/Binding,
70 wwBind top_level (NonRec binder rhs)
71 = wwExpr rhs `thenWw` \ new_rhs ->
72 tryWW binder new_rhs `thenWw` \ new_pairs ->
73 returnWw (WwLet [NonRec b e | (b,e) <- new_pairs])
74 -- Generated bindings must be non-recursive
75 -- because the original binding was.
77 ------------------------------
79 wwBind top_level (Rec pairs)
80 = mapWw do_one pairs `thenWw` \ new_pairs ->
81 returnWw (WwLet [Rec (concat new_pairs)])
83 do_one (binder, rhs) = wwExpr rhs `thenWw` \ new_rhs ->
87 @wwExpr@ basically just walks the tree, looking for appropriate
88 annotations that can be used. Remember it is @wwBind@ that does the
89 matching by looking for strict arguments of the correct type.
90 @wwExpr@ is a version that just returns the ``Plain'' Tree.
94 wwExpr :: CoreExpr -> WwM CoreExpr
96 wwExpr e@(Var _) = returnWw e
97 wwExpr e@(Lit _) = returnWw e
98 wwExpr e@(Con _ _ _) = returnWw e
99 wwExpr e@(Prim _ _ _) = returnWw e
101 wwExpr (Lam binders expr)
102 = wwExpr expr `thenWw` \ new_expr ->
103 returnWw (Lam binders new_expr)
105 wwExpr (CoTyLam ty expr)
106 = wwExpr expr `thenWw` \ new_expr ->
107 returnWw (CoTyLam ty new_expr)
110 = wwExpr e1 `thenWw` \ new_e1 ->
111 returnWw (App new_e1 e2)
113 wwExpr (CoTyApp expr ty)
114 = wwExpr expr `thenWw` \ new_expr ->
115 returnWw (CoTyApp new_expr ty)
118 = wwExpr expr `thenWw` \ new_expr ->
119 returnWw (SCC cc new_expr)
121 wwExpr (Let bind expr)
122 = wwBind False{-not top-level-} bind `thenWw` \ intermediate_bind ->
123 wwExpr expr `thenWw` \ new_expr ->
124 returnWw (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 `thenWw` \ new_expr ->
131 ww_alts alts `thenWw` \ new_alts ->
132 returnWw (Case new_expr new_alts)
134 ww_alts (AlgAlts alts deflt)
135 = mapWw ww_alg_alt alts `thenWw` \ new_alts ->
136 ww_deflt deflt `thenWw` \ new_deflt ->
137 returnWw (AlgAlts new_alts new_deflt)
139 ww_alts (PrimAlts alts deflt)
140 = mapWw ww_prim_alt alts `thenWw` \ new_alts ->
141 ww_deflt deflt `thenWw` \ new_deflt ->
142 returnWw (PrimAlts new_alts new_deflt)
144 ww_alg_alt (con, binders, rhs)
145 = wwExpr rhs `thenWw` \ new_rhs ->
146 returnWw (con, binders, new_rhs)
148 ww_prim_alt (lit, rhs)
149 = wwExpr rhs `thenWw` \ new_rhs ->
150 returnWw (lit, new_rhs)
155 ww_deflt (BindDefault binder rhs)
156 = wwExpr rhs `thenWw` \ new_rhs ->
157 returnWw (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 -> WwM [(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) = digForLambdas rhs
210 body_ty = coreExprType body
212 uniqSMtoWwM (mkWwBodies body_ty tyvars args args_info) `thenWw` \ 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 getUniqueWw `thenWw` \ 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 returnWw [ (worker_id, worker_rhs), -- worker comes first
250 (wrapper_id, wrapper_rhs) ] -- because wrapper mentions it
252 do_nothing = returnWw [ (fn_id, rhs) ]