2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Pattern-matching bindings (HsBinds and MonoBinds)
8 Handles @HsBinds@; those at the top level require different handling,
9 in that the @Rec@/@NonRec@/etc structure is thrown away (whereas at
10 lower levels it is preserved with @let@/@letrec@s).
13 module DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs,
18 #include "HsVersions.h"
20 import {-# SOURCE #-} DsExpr( dsLExpr, dsExpr )
21 import {-# SOURCE #-} Match( matchWrapper )
27 import HsSyn -- lots of things
28 import CoreSyn -- lots of things
31 import TcHsSyn ( mkArbitraryType ) -- Mis-placed?
37 import Var ( TyVar, Var )
45 import BasicTypes hiding ( TopLevel )
47 import Util ( mapSnd )
57 %************************************************************************
59 \subsection[dsMonoBinds]{Desugaring a @MonoBinds@}
61 %************************************************************************
64 dsTopLHsBinds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
65 dsTopLHsBinds auto_scc binds = ds_lhs_binds auto_scc binds
67 dsLHsBinds :: LHsBinds Id -> DsM [(Id,CoreExpr)]
68 dsLHsBinds binds = ds_lhs_binds NoSccs binds
71 ------------------------
72 ds_lhs_binds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
73 -- scc annotation policy (see below)
74 ds_lhs_binds auto_scc binds = foldM (dsLHsBind auto_scc) [] (bagToList binds)
77 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
79 -> DsM [(Id,CoreExpr)] -- Result
80 dsLHsBind auto_scc rest (L loc bind)
81 = putSrcSpanDs loc $ dsHsBind auto_scc rest bind
84 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
86 -> DsM [(Id,CoreExpr)] -- Result
88 dsHsBind auto_scc rest (VarBind var expr)
89 = dsLExpr expr `thenDs` \ core_expr ->
91 -- Dictionary bindings are always VarMonoBinds, so
92 -- we only need do this here
93 addDictScc var core_expr `thenDs` \ core_expr' ->
94 returnDs ((var, core_expr') : rest)
96 dsHsBind auto_scc rest (FunBind { fun_id = L _ fun, fun_matches = matches, fun_co_fn = co_fn, fun_tick = tick })
97 = matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, body) ->
98 mkOptTickBox tick body `thenDs` \ body' ->
99 dsCoercion co_fn (return (mkLams args body')) `thenDs` \ rhs ->
100 returnDs ((fun,rhs) : rest)
102 dsHsBind auto_scc rest (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty })
103 = dsGuarded grhss ty `thenDs` \ body_expr ->
104 mkSelectorBinds pat body_expr `thenDs` \ sel_binds ->
105 returnDs (sel_binds ++ rest)
107 -- Note [Rules and inlining]
108 -- Common special case: no type or dictionary abstraction
109 -- This is a bit less trivial than you might suppose
110 -- The naive way woudl be to desguar to something like
111 -- f_lcl = ...f_lcl... -- The "binds" from AbsBinds
112 -- M.f = f_lcl -- Generated from "exports"
113 -- But we don't want that, because if M.f isn't exported,
114 -- it'll be inlined unconditionally at every call site (its rhs is
115 -- trivial). That would be ok unless it has RULES, which would
116 -- thereby be completely lost. Bad, bad, bad.
118 -- Instead we want to generate
121 -- Now all is cool. The RULES are attached to M.f (by SimplCore),
122 -- and f_lcl is rapidly inlined away.
124 -- This does not happen in the same way to polymorphic binds,
125 -- because they desugar to
126 -- M.f = /\a. let f_lcl = ...f_lcl... in f_lcl
127 -- Although I'm a bit worried about whether full laziness might
128 -- float the f_lcl binding out and then inline M.f at its call site
130 dsHsBind auto_scc rest (AbsBinds [] [] exports binds)
131 = do { core_prs <- ds_lhs_binds NoSccs binds
132 ; let env = mkABEnv exports
133 do_one (lcl_id, rhs) | Just (gbl_id, prags) <- lookupVarEnv env lcl_id
134 = addInlinePrags prags gbl_id $
135 addAutoScc auto_scc gbl_id rhs
136 | otherwise = (lcl_id, rhs)
137 locals' = [(lcl_id, Var gbl_id) | (_, gbl_id, lcl_id, _) <- exports]
138 ; return (map do_one core_prs ++ locals' ++ rest) }
139 -- No Rec needed here (contrast the other AbsBinds cases)
140 -- because we can rely on the enclosing dsBind to wrap in Rec
142 -- Another common case: one exported variable
143 -- Non-recursive bindings come through this way
144 dsHsBind auto_scc rest
145 (AbsBinds all_tyvars dicts exports@[(tyvars, global, local, prags)] binds)
146 = ASSERT( all (`elem` tyvars) all_tyvars )
147 ds_lhs_binds NoSccs binds `thenDs` \ core_prs ->
149 -- Always treat the binds as recursive, because the typechecker
150 -- makes rather mixed-up dictionary bindings
151 core_bind = Rec core_prs
153 mappM (dsSpec all_tyvars dicts tyvars global local core_bind)
154 prags `thenDs` \ mb_specs ->
156 (spec_binds, rules) = unzip (catMaybes mb_specs)
157 global' = addIdSpecialisations global rules
158 rhs' = mkLams tyvars $ mkLams dicts $ Let core_bind (Var local)
159 bind = addInlinePrags prags global' $ addAutoScc auto_scc global' rhs'
161 returnDs (bind : spec_binds ++ rest)
163 dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports binds)
164 = do { core_prs <- ds_lhs_binds NoSccs binds
165 ; let env = mkABEnv exports
166 do_one (lcl_id,rhs) | Just (gbl_id, prags) <- lookupVarEnv env lcl_id
167 = addInlinePrags prags lcl_id $
168 addAutoScc auto_scc gbl_id rhs
169 | otherwise = (lcl_id,rhs)
171 -- Rec because of mixed-up dictionary bindings
172 core_bind = Rec (map do_one core_prs)
174 tup_expr = mkTupleExpr locals
175 tup_ty = exprType tup_expr
176 poly_tup_expr = mkLams all_tyvars $ mkLams dicts $
177 Let core_bind tup_expr
178 locals = [local | (_, _, local, _) <- exports]
179 local_tys = map idType locals
181 ; poly_tup_id <- newSysLocalDs (exprType poly_tup_expr)
183 ; let dict_args = map Var dicts
185 mk_bind ((tyvars, global, local, prags), n) -- locals !! n == local
186 = -- Need to make fresh locals to bind in the selector, because
187 -- some of the tyvars will be bound to 'Any'
188 do { locals' <- newSysLocalsDs (map substitute local_tys)
189 ; tup_id <- newSysLocalDs (substitute tup_ty)
190 ; mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global local core_bind)
192 ; let (spec_binds, rules) = unzip (catMaybes mb_specs)
193 global' = addIdSpecialisations global rules
194 rhs = mkLams tyvars $ mkLams dicts $
195 mkTupleSelector locals' (locals' !! n) tup_id $
196 mkApps (mkTyApps (Var poly_tup_id) ty_args) dict_args
197 ; returnDs ((global', rhs) : spec_binds) }
199 mk_ty_arg all_tyvar | all_tyvar `elem` tyvars = mkTyVarTy all_tyvar
200 | otherwise = mkArbitraryType all_tyvar
201 ty_args = map mk_ty_arg all_tyvars
202 substitute = substTyWith all_tyvars ty_args
204 ; export_binds_s <- mappM mk_bind (exports `zip` [0..])
205 -- don't scc (auto-)annotate the tuple itself.
207 ; returnDs ((poly_tup_id, poly_tup_expr) :
208 (concat export_binds_s ++ rest)) }
210 mkABEnv :: [([TyVar], Id, Id, [Prag])] -> VarEnv (Id, [Prag])
211 -- Takes the exports of a AbsBinds, and returns a mapping
212 -- lcl_id -> (gbl_id, prags)
213 mkABEnv exports = mkVarEnv [ (lcl_id, (gbl_id, prags))
214 | (_, gbl_id, lcl_id, prags) <- exports]
217 dsSpec :: [TyVar] -> [DictId] -> [TyVar]
218 -> Id -> Id -- Global, local
220 -> DsM (Maybe ((Id,CoreExpr), -- Binding for specialised Id
221 CoreRule)) -- Rule for the Global Id
224 -- f :: (Eq a, Ix b) => a -> b -> b
225 -- {-# SPECIALISE f :: Ix b => Int -> b -> b #-}
227 -- AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds
229 -- SpecPrag (/\b.\(d:Ix b). f Int b dInt d)
230 -- (forall b. Ix b => Int -> b -> b)
232 -- Rule: forall b,(d:Ix b). f Int b dInt d = f_spec b d
234 -- Spec bind: f_spec = Let f = /\ab \(d1:Eq a)(d2:Ix b). let binds in f_mono
235 -- /\b.\(d:Ix b). in f Int b dInt d
236 -- The idea is that f occurs just once, so it'll be
237 -- inlined and specialised
239 dsSpec all_tvs dicts tvs poly_id mono_id mono_bind (InlinePrag {})
242 dsSpec all_tvs dicts tvs poly_id mono_id mono_bind
243 (SpecPrag spec_expr spec_ty const_dicts inl)
244 = do { let poly_name = idName poly_id
245 ; spec_name <- newLocalName poly_name
246 ; ds_spec_expr <- dsExpr spec_expr
247 ; let (bndrs, body) = collectBinders ds_spec_expr
248 mb_lhs = decomposeRuleLhs (bndrs ++ const_dicts) body
251 Nothing -> do { warnDs msg; return Nothing }
253 Just (bndrs', var, args) -> return (Just (addInlineInfo inl spec_id spec_rhs, rule))
255 local_poly = setIdNotExported poly_id
256 -- Very important to make the 'f' non-exported,
257 -- else it won't be inlined!
258 spec_id = mkLocalId spec_name spec_ty
259 spec_rhs = Let (NonRec local_poly poly_f_body) ds_spec_expr
260 poly_f_body = mkLams (tvs ++ dicts) $
261 fix_up (Let mono_bind (Var mono_id))
263 -- Quantify over constant dicts on the LHS, since
264 -- their value depends only on their type
265 -- The ones we are interested in may even be imported
266 -- e.g. GHC.Base.dEqInt
268 rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
269 AlwaysActive poly_name
270 bndrs' -- Includes constant dicts
272 (mkVarApps (Var spec_id) bndrs)
275 -- Bind to Any any of all_ptvs that aren't
276 -- relevant for this particular function
277 fix_up body | null void_tvs = body
278 | otherwise = mkTyApps (mkLams void_tvs body)
279 (map mkArbitraryType void_tvs)
280 void_tvs = all_tvs \\ tvs
282 msg = hang (ptext SLIT("Specialisation too complicated to desugar; ignored"))
287 %************************************************************************
289 \subsection{Adding inline pragmas}
291 %************************************************************************
294 decomposeRuleLhs :: [Var] -> CoreExpr -> Maybe ([Var], Id, [CoreExpr])
295 -- Returns Nothing if the LHS isn't of the expected shape
296 -- The argument 'all_bndrs' includes the "constant dicts" of the LHS,
297 -- and they may be GlobalIds, which we can't forall-ify.
298 -- So we substitute them out instead
299 decomposeRuleLhs all_bndrs lhs
300 = go init_env (occurAnalyseExpr lhs) -- Occurrence analysis sorts out the dict
301 -- bindings so we know if they are recursive
304 -- all_bndrs may include top-level imported dicts,
305 -- imported things with a for-all.
306 -- So we localise them and subtitute them out
307 bndr_prs = [ (id, Var (localise id)) | id <- all_bndrs, isGlobalId id ]
308 localise d = mkLocalId (idName d) (idType d)
310 init_env = mkVarEnv bndr_prs
311 all_bndrs' = map subst_bndr all_bndrs
312 subst_bndr bndr = case lookupVarEnv init_env bndr of
313 Just (Var bndr') -> bndr'
314 Just other -> panic "decomposeRuleLhs"
317 -- Substitute dicts in the LHS args, so that there
318 -- aren't any lets getting in the way
319 -- Note that we substitute the function too; we might have this as
320 -- a LHS: let f71 = M.f Int in f71
321 go env (Let (NonRec dict rhs) body)
322 = go (extendVarEnv env dict (simpleSubst env rhs)) body
324 = case collectArgs (simpleSubst env body) of
325 (Var fn, args) -> Just (all_bndrs', fn, args)
328 simpleSubst :: IdEnv CoreExpr -> CoreExpr -> CoreExpr
329 -- Similar to CoreSubst.substExpr, except that
330 -- (a) takes no account of capture; dictionary bindings use new names
331 -- (b) can have a GlobalId (imported) in its domain
332 -- (c) Ids only; no types are substituted
334 simpleSubst subst expr
337 go (Var v) = lookupVarEnv subst v `orElse` Var v
338 go (Cast e co) = Cast (go e) co
339 go (Type ty) = Type ty
340 go (Lit lit) = Lit lit
341 go (App fun arg) = App (go fun) (go arg)
342 go (Note note e) = Note note (go e)
343 go (Lam bndr body) = Lam bndr (go body)
344 go (Let (NonRec bndr rhs) body) = Let (NonRec bndr (go rhs)) (go body)
345 go (Let (Rec pairs) body) = Let (Rec (mapSnd go pairs)) (go body)
346 go (Case scrut bndr ty alts) = Case (go scrut) bndr ty
347 [(c,bs,go r) | (c,bs,r) <- alts]
349 addInlinePrags :: [Prag] -> Id -> CoreExpr -> (Id,CoreExpr)
350 addInlinePrags prags bndr rhs
351 = case [inl | InlinePrag inl <- prags] of
353 (inl:_) -> addInlineInfo inl bndr rhs
355 addInlineInfo :: InlineSpec -> Id -> CoreExpr -> (Id,CoreExpr)
356 addInlineInfo (Inline phase is_inline) bndr rhs
357 = (attach_phase bndr phase, wrap_inline is_inline rhs)
359 attach_phase bndr phase
360 | isAlwaysActive phase = bndr -- Default phase
361 | otherwise = bndr `setInlinePragma` phase
363 wrap_inline True body = mkInlineMe body
364 wrap_inline False body = body
368 %************************************************************************
370 \subsection[addAutoScc]{Adding automatic sccs}
372 %************************************************************************
375 data AutoScc = NoSccs
376 | AddSccs Module (Id -> Bool)
377 -- The (Id->Bool) says which Ids to add SCCs to
379 addAutoScc :: AutoScc
382 -> CoreExpr -- Scc'd Rhs
384 addAutoScc NoSccs _ rhs
386 addAutoScc (AddSccs mod add_scc) id rhs
387 | add_scc id = mkSCC (mkAutoCC id mod NotCafCC) rhs
391 If profiling and dealing with a dict binding,
392 wrap the dict in @_scc_ DICT <dict>@:
395 addDictScc var rhs = returnDs rhs
397 {- DISABLED for now (need to somehow make up a name for the scc) -- SDM
398 | not ( opt_SccProfilingOn && opt_AutoSccsOnDicts)
399 || not (isDictId var)
400 = returnDs rhs -- That's easy: do nothing
403 = getModuleAndGroupDs `thenDs` \ (mod, grp) ->
404 -- ToDo: do -dicts-all flag (mark dict things with individual CCs)
405 returnDs (Note (SCC (mkAllDictsCC mod grp False)) rhs)
410 %************************************************************************
414 %************************************************************************
418 dsCoercion :: HsWrapper -> DsM CoreExpr -> DsM CoreExpr
419 dsCoercion WpHole thing_inside = thing_inside
420 dsCoercion (WpCompose c1 c2) thing_inside = dsCoercion c1 (dsCoercion c2 thing_inside)
421 dsCoercion (WpCo co) thing_inside = do { expr <- thing_inside
422 ; return (Cast expr co) }
423 dsCoercion (WpLam id) thing_inside = do { expr <- thing_inside
424 ; return (Lam id expr) }
425 dsCoercion (WpTyLam tv) thing_inside = do { expr <- thing_inside
426 ; return (Lam tv expr) }
427 dsCoercion (WpApp id) thing_inside = do { expr <- thing_inside
428 ; return (App expr (Var id)) }
429 dsCoercion (WpTyApp ty) thing_inside = do { expr <- thing_inside
430 ; return (App expr (Type ty)) }
431 dsCoercion (WpLet bs) thing_inside = do { prs <- dsLHsBinds bs
432 ; expr <- thing_inside
433 ; return (Let (Rec prs) expr) }