2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[DsBinds]{Pattern-matching bindings (HsBinds and MonoBinds)}
6 Handles @HsBinds@; those at the top level require different handling,
7 in that the @Rec@/@NonRec@/etc structure is thrown away (whereas at
8 lower levels it is preserved with @let@/@letrec@s).
11 module DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs,
16 #include "HsVersions.h"
19 import {-# SOURCE #-} DsExpr( dsLExpr, dsExpr )
20 import {-# SOURCE #-} Match( matchWrapper )
23 import DsGRHSs ( dsGuarded )
26 import HsSyn -- lots of things
27 import CoreSyn -- lots of things
28 import CoreUtils ( exprType, mkInlineMe, mkSCC )
30 import StaticFlags ( opt_AutoSccsOnAllToplevs,
31 opt_AutoSccsOnExportedToplevs )
32 import OccurAnal ( occurAnalyseExpr )
33 import CostCentre ( mkAutoCC, IsCafCC(..) )
34 import Id ( Id, DictId, idType, idName, isExportedId, mkLocalId, setInlinePragma )
35 import Rules ( addIdSpecialisations, mkLocalRule )
36 import Var ( TyVar, Var, isGlobalId, setIdNotExported )
38 import Type ( mkTyVarTy, substTyWith )
39 import TysWiredIn ( voidTy )
41 import SrcLoc ( Located(..) )
42 import Maybes ( isJust, catMaybes, orElse )
43 import Bag ( bagToList )
44 import BasicTypes ( Activation(..), InlineSpec(..), isAlwaysActive, defaultInlineSpec )
45 import Monad ( foldM )
46 import FastString ( mkFastString )
48 import Util ( mapSnd )
51 %************************************************************************
53 \subsection[dsMonoBinds]{Desugaring a @MonoBinds@}
55 %************************************************************************
58 dsTopLHsBinds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
59 dsTopLHsBinds auto_scc binds = ds_lhs_binds auto_scc binds
61 dsLHsBinds :: LHsBinds Id -> DsM [(Id,CoreExpr)]
62 dsLHsBinds binds = ds_lhs_binds NoSccs binds
65 ------------------------
66 ds_lhs_binds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
67 -- scc annotation policy (see below)
68 ds_lhs_binds auto_scc binds = foldM (dsLHsBind auto_scc) [] (bagToList binds)
71 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
73 -> DsM [(Id,CoreExpr)] -- Result
74 dsLHsBind auto_scc rest (L loc bind)
75 = putSrcSpanDs loc $ dsHsBind auto_scc rest bind
78 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
80 -> DsM [(Id,CoreExpr)] -- Result
82 dsHsBind auto_scc rest (VarBind var expr)
83 = dsLExpr expr `thenDs` \ core_expr ->
85 -- Dictionary bindings are always VarMonoBinds, so
86 -- we only need do this here
87 addDictScc var core_expr `thenDs` \ core_expr' ->
88 returnDs ((var, core_expr') : rest)
90 dsHsBind auto_scc rest (FunBind { fun_id = L _ fun, fun_matches = matches, fun_co_fn = co_fn })
91 = matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, body) ->
92 dsCoercion co_fn (return (mkLams args body)) `thenDs` \ rhs ->
93 addAutoScc auto_scc (fun, rhs) `thenDs` \ pair ->
94 returnDs (pair : rest)
96 dsHsBind auto_scc rest (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty })
97 = dsGuarded grhss ty `thenDs` \ body_expr ->
98 mkSelectorBinds pat body_expr `thenDs` \ sel_binds ->
99 mappM (addAutoScc auto_scc) sel_binds `thenDs` \ sel_binds ->
100 returnDs (sel_binds ++ rest)
102 -- Common special case: no type or dictionary abstraction
103 -- For the (rare) case when there are some mixed-up
104 -- dictionary bindings (for which a Rec is convenient)
105 -- we reply on the enclosing dsBind to wrap a Rec around.
106 dsHsBind auto_scc rest (AbsBinds [] [] exports binds)
107 = ds_lhs_binds (addSccs auto_scc exports) binds `thenDs` \ core_prs ->
109 core_prs' = addLocalInlines exports core_prs
110 exports' = [(global, Var local) | (_, global, local, _) <- exports]
112 returnDs (core_prs' ++ exports' ++ rest)
114 -- Another common case: one exported variable
115 -- Non-recursive bindings come through this way
116 dsHsBind auto_scc rest
117 (AbsBinds all_tyvars dicts exports@[(tyvars, global, local, prags)] binds)
118 = ASSERT( all (`elem` tyvars) all_tyvars )
119 ds_lhs_binds (addSccs auto_scc exports) binds `thenDs` \ core_prs ->
121 -- Always treat the binds as recursive, because the typechecker
122 -- makes rather mixed-up dictionary bindings
123 core_bind = Rec core_prs
125 mappM (dsSpec all_tyvars dicts tyvars global local core_bind)
126 prags `thenDs` \ mb_specs ->
128 (spec_binds, rules) = unzip (catMaybes mb_specs)
129 global' = addIdSpecialisations global rules
130 rhs' = mkLams tyvars $ mkLams dicts $ Let core_bind (Var local)
131 inl = case [inl | InlinePrag inl <- prags] of
132 [] -> defaultInlineSpec
135 returnDs (addInlineInfo inl global' rhs' : spec_binds ++ rest)
137 dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports binds)
138 = ds_lhs_binds (addSccs auto_scc exports) binds `thenDs` \ core_prs ->
140 -- Rec because of mixed-up dictionary bindings
141 core_bind = Rec (addLocalInlines exports core_prs)
143 tup_expr = mkTupleExpr locals
144 tup_ty = exprType tup_expr
145 poly_tup_expr = mkLams all_tyvars $ mkLams dicts $
146 Let core_bind tup_expr
147 locals = [local | (_, _, local, _) <- exports]
148 local_tys = map idType locals
150 newSysLocalDs (exprType poly_tup_expr) `thenDs` \ poly_tup_id ->
152 dict_args = map Var dicts
154 mk_bind ((tyvars, global, local, prags), n) -- locals !! n == local
155 = -- Need to make fresh locals to bind in the selector, because
156 -- some of the tyvars will be bound to voidTy
157 newSysLocalsDs (map substitute local_tys) `thenDs` \ locals' ->
158 newSysLocalDs (substitute tup_ty) `thenDs` \ tup_id ->
159 mapM (dsSpec all_tyvars dicts tyvars global local core_bind)
160 prags `thenDs` \ mb_specs ->
162 (spec_binds, rules) = unzip (catMaybes mb_specs)
163 global' = addIdSpecialisations global rules
164 rhs = mkLams tyvars $ mkLams dicts $
165 mkTupleSelector locals' (locals' !! n) tup_id $
166 mkApps (mkTyApps (Var poly_tup_id) ty_args) dict_args
168 returnDs ((global', rhs) : spec_binds)
170 mk_ty_arg all_tyvar | all_tyvar `elem` tyvars = mkTyVarTy all_tyvar
172 ty_args = map mk_ty_arg all_tyvars
173 substitute = substTyWith all_tyvars ty_args
175 mappM mk_bind (exports `zip` [0..]) `thenDs` \ export_binds_s ->
176 -- don't scc (auto-)annotate the tuple itself.
178 returnDs ((poly_tup_id, poly_tup_expr) : (concat export_binds_s ++ rest))
180 dsSpec :: [TyVar] -> [DictId] -> [TyVar]
181 -> Id -> Id -- Global, local
183 -> DsM (Maybe ((Id,CoreExpr), -- Binding for specialised Id
184 CoreRule)) -- Rule for the Global Id
187 -- f :: (Eq a, Ix b) => a -> b -> b
188 -- {-# SPECIALISE f :: Ix b => Int -> b -> b #-}
190 -- AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds
192 -- SpecPrag (/\b.\(d:Ix b). f Int b dInt d)
193 -- (forall b. Ix b => Int -> b -> b)
195 -- Rule: forall b,(d:Ix b). f Int b dInt d = f_spec b d
197 -- Spec bind: f_spec = Let f = /\ab \(d1:Eq a)(d2:Ix b). let binds in f_mono
198 -- /\b.\(d:Ix b). in f Int b dInt d
199 -- The idea is that f occurs just once, so it'll be
200 -- inlined and specialised
202 dsSpec all_tvs dicts tvs poly_id mono_id mono_bind (InlinePrag {})
205 dsSpec all_tvs dicts tvs poly_id mono_id mono_bind
206 (SpecPrag spec_expr spec_ty const_dicts inl)
207 = do { let poly_name = idName poly_id
208 ; spec_name <- newLocalName poly_name
209 ; ds_spec_expr <- dsExpr spec_expr
210 ; let (bndrs, body) = collectBinders ds_spec_expr
211 mb_lhs = decomposeRuleLhs (bndrs ++ const_dicts) body
214 Nothing -> do { dsWarn msg; return Nothing }
216 Just (bndrs', var, args) -> return (Just (addInlineInfo inl spec_id spec_rhs, rule))
218 local_poly = setIdNotExported poly_id
219 -- Very important to make the 'f' non-exported,
220 -- else it won't be inlined!
221 spec_id = mkLocalId spec_name spec_ty
222 spec_rhs = Let (NonRec local_poly poly_f_body) ds_spec_expr
223 poly_f_body = mkLams (tvs ++ dicts) $
224 fix_up (Let mono_bind (Var mono_id))
226 -- Quantify over constant dicts on the LHS, since
227 -- their value depends only on their type
228 -- The ones we are interested in may even be imported
229 -- e.g. GHC.Base.dEqInt
231 rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
232 AlwaysActive poly_name
233 bndrs' -- Includes constant dicts
235 (mkVarApps (Var spec_id) bndrs)
238 -- Bind to voidTy any of all_ptvs that aren't
239 -- relevant for this particular function
240 fix_up body | null void_tvs = body
241 | otherwise = mkTyApps (mkLams void_tvs body)
242 (map (const voidTy) void_tvs)
243 void_tvs = all_tvs \\ tvs
245 msg = hang (ptext SLIT("Specialisation too complicated to desugar; ignored"))
250 %************************************************************************
252 \subsection{Adding inline pragmas}
254 %************************************************************************
257 decomposeRuleLhs :: [Var] -> CoreExpr -> Maybe ([Var], Id, [CoreExpr])
258 -- Returns Nothing if the LHS isn't of the expected shape
259 -- The argument 'all_bndrs' includes the "constant dicts" of the LHS,
260 -- and they may be GlobalIds, which we can't forall-ify.
261 -- So we substitute them out instead
262 decomposeRuleLhs all_bndrs lhs
263 = go init_env (occurAnalyseExpr lhs) -- Occurrence analysis sorts out the dict
264 -- bindings so we know if they are recursive
267 -- all_bndrs may include top-level imported dicts,
268 -- imported things with a for-all.
269 -- So we localise them and subtitute them out
270 bndr_prs = [ (id, Var (localise id)) | id <- all_bndrs, isGlobalId id ]
271 localise d = mkLocalId (idName d) (idType d)
273 init_env = mkVarEnv bndr_prs
274 all_bndrs' = map subst_bndr all_bndrs
275 subst_bndr bndr = case lookupVarEnv init_env bndr of
276 Just (Var bndr') -> bndr'
277 Just other -> panic "decomposeRuleLhs"
280 -- Substitute dicts in the LHS args, so that there
281 -- aren't any lets getting in the way
282 -- Note that we substitute the function too; we might have this as
283 -- a LHS: let f71 = M.f Int in f71
284 go env (Let (NonRec dict rhs) body)
285 = go (extendVarEnv env dict (simpleSubst env rhs)) body
287 = case collectArgs (simpleSubst env body) of
288 (Var fn, args) -> Just (all_bndrs', fn, args)
291 simpleSubst :: IdEnv CoreExpr -> CoreExpr -> CoreExpr
292 -- Similar to CoreSubst.substExpr, except that
293 -- (a) takes no account of capture; dictionary bindings use new names
294 -- (b) can have a GlobalId (imported) in its domain
295 -- (c) Ids only; no types are substituted
297 simpleSubst subst expr
300 go (Var v) = lookupVarEnv subst v `orElse` Var v
301 go (Type ty) = Type ty
302 go (Lit lit) = Lit lit
303 go (App fun arg) = App (go fun) (go arg)
304 go (Note note e) = Note note (go e)
305 go (Lam bndr body) = Lam bndr (go body)
306 go (Let (NonRec bndr rhs) body) = Let (NonRec bndr (go rhs)) (go body)
307 go (Let (Rec pairs) body) = Let (Rec (mapSnd go pairs)) (go body)
308 go (Case scrut bndr ty alts) = Case (go scrut) bndr ty
309 [(c,bs,go r) | (c,bs,r) <- alts]
311 addLocalInlines exports core_prs
312 = map add_inline core_prs
314 add_inline (bndr,rhs) | Just inl <- lookupVarEnv inline_env bndr
315 = addInlineInfo inl bndr rhs
318 inline_env = mkVarEnv [(mono_id, prag)
319 | (_, _, mono_id, prags) <- exports,
320 InlinePrag prag <- prags]
322 addInlineInfo :: InlineSpec -> Id -> CoreExpr -> (Id,CoreExpr)
323 addInlineInfo (Inline phase is_inline) bndr rhs
324 = (attach_phase bndr phase, wrap_inline is_inline rhs)
326 attach_phase bndr phase
327 | isAlwaysActive phase = bndr -- Default phase
328 | otherwise = bndr `setInlinePragma` phase
330 wrap_inline True body = mkInlineMe body
331 wrap_inline False body = body
335 %************************************************************************
337 \subsection[addAutoScc]{Adding automatic sccs}
339 %************************************************************************
344 | TopLevelAddSccs (Id -> Maybe Id)
347 addSccs :: AutoScc -> [(a,Id,Id,[Prag])] -> AutoScc
348 addSccs auto_scc@(TopLevelAddSccs _) exports = auto_scc
349 addSccs NoSccs exports = NoSccs
350 addSccs TopLevel exports
351 = TopLevelAddSccs (\id -> case [ exp | (_,exp,loc,_) <- exports, loc == id ] of
352 (exp:_) | opt_AutoSccsOnAllToplevs ||
354 opt_AutoSccsOnExportedToplevs)
358 addAutoScc :: AutoScc -- if needs be, decorate toplevs?
360 -> DsM (Id, CoreExpr)
362 addAutoScc (TopLevelAddSccs auto_scc_fn) pair@(bndr, core_expr)
364 = getModuleDs `thenDs` \ mod ->
365 returnDs (bndr, mkSCC (mkAutoCC top_bndr mod NotCafCC) core_expr)
366 where do_auto_scc = isJust maybe_auto_scc
367 maybe_auto_scc = auto_scc_fn bndr
368 (Just top_bndr) = maybe_auto_scc
374 If profiling and dealing with a dict binding,
375 wrap the dict in @_scc_ DICT <dict>@:
378 addDictScc var rhs = returnDs rhs
380 {- DISABLED for now (need to somehow make up a name for the scc) -- SDM
381 | not ( opt_SccProfilingOn && opt_AutoSccsOnDicts)
382 || not (isDictId var)
383 = returnDs rhs -- That's easy: do nothing
386 = getModuleAndGroupDs `thenDs` \ (mod, grp) ->
387 -- ToDo: do -dicts-all flag (mark dict things with individual CCs)
388 returnDs (Note (SCC (mkAllDictsCC mod grp False)) rhs)
393 %************************************************************************
397 %************************************************************************
401 dsCoercion :: ExprCoFn -> DsM CoreExpr -> DsM CoreExpr
402 dsCoercion CoHole thing_inside = thing_inside
403 dsCoercion (CoCompose c1 c2) thing_inside = dsCoercion c1 (dsCoercion c2 thing_inside)
404 dsCoercion (CoLams ids c) thing_inside = do { expr <- dsCoercion c thing_inside
405 ; return (mkLams ids expr) }
406 dsCoercion (CoTyLams tvs c) thing_inside = do { expr <- dsCoercion c thing_inside
407 ; return (mkLams tvs expr) }
408 dsCoercion (CoApps c ids) thing_inside = do { expr <- dsCoercion c thing_inside
409 ; return (mkVarApps expr ids) }
410 dsCoercion (CoTyApps c tys) thing_inside = do { expr <- dsCoercion c thing_inside
411 ; return (mkTyApps expr tys) }
412 dsCoercion (CoLet bs c) thing_inside = do { prs <- dsLHsBinds bs
413 ; expr <- dsCoercion c thing_inside
414 ; return (Let (Rec prs) expr) }