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 OccurAnal ( occurAnalyseExpr )
31 import CostCentre ( mkAutoCC, IsCafCC(..) )
32 import Id ( Id, DictId, idType, idName, mkLocalId, setInlinePragma )
33 import Rules ( addIdSpecialisations, mkLocalRule )
34 import Var ( TyVar, Var, isGlobalId, setIdNotExported )
36 import Type ( mkTyVarTy, substTyWith )
37 import TysWiredIn ( voidTy )
38 import Module ( Module )
40 import SrcLoc ( Located(..) )
41 import Maybes ( catMaybes, orElse )
42 import Bag ( bagToList )
43 import BasicTypes ( Activation(..), InlineSpec(..), isAlwaysActive )
44 import Monad ( foldM )
45 import FastString ( mkFastString )
47 import Util ( mapSnd )
50 %************************************************************************
52 \subsection[dsMonoBinds]{Desugaring a @MonoBinds@}
54 %************************************************************************
57 dsTopLHsBinds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
58 dsTopLHsBinds auto_scc binds = ds_lhs_binds auto_scc binds
60 dsLHsBinds :: LHsBinds Id -> DsM [(Id,CoreExpr)]
61 dsLHsBinds binds = ds_lhs_binds NoSccs binds
64 ------------------------
65 ds_lhs_binds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
66 -- scc annotation policy (see below)
67 ds_lhs_binds auto_scc binds = foldM (dsLHsBind auto_scc) [] (bagToList binds)
70 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
72 -> DsM [(Id,CoreExpr)] -- Result
73 dsLHsBind auto_scc rest (L loc bind)
74 = putSrcSpanDs loc $ dsHsBind auto_scc rest bind
77 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
79 -> DsM [(Id,CoreExpr)] -- Result
81 dsHsBind auto_scc rest (VarBind var expr)
82 = dsLExpr expr `thenDs` \ core_expr ->
84 -- Dictionary bindings are always VarMonoBinds, so
85 -- we only need do this here
86 addDictScc var core_expr `thenDs` \ core_expr' ->
87 returnDs ((var, core_expr') : rest)
89 dsHsBind auto_scc rest (FunBind { fun_id = L _ fun, fun_matches = matches, fun_co_fn = co_fn })
90 = matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, body) ->
91 dsCoercion co_fn (return (mkLams args body)) `thenDs` \ rhs ->
92 returnDs ((fun,rhs) : rest)
94 dsHsBind auto_scc rest (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty })
95 = dsGuarded grhss ty `thenDs` \ body_expr ->
96 mkSelectorBinds pat body_expr `thenDs` \ sel_binds ->
97 returnDs (sel_binds ++ rest)
99 -- Note [Rules and inlining]
100 -- Common special case: no type or dictionary abstraction
101 -- This is a bit less trivial than you might suppose
102 -- The naive way woudl be to desguar to something like
103 -- f_lcl = ...f_lcl... -- The "binds" from AbsBinds
104 -- M.f = f_lcl -- Generated from "exports"
105 -- But we don't want that, because if M.f isn't exported,
106 -- it'll be inlined unconditionally at every call site (its rhs is
107 -- trivial). That would be ok unless it has RULES, which would
108 -- thereby be completely lost. Bad, bad, bad.
110 -- Instead we want to generate
113 -- Now all is cool. The RULES are attached to M.f (by SimplCore),
114 -- and f_lcl is rapidly inlined away.
116 -- This does not happen in the same way to polymorphic binds,
117 -- because they desugar to
118 -- M.f = /\a. let f_lcl = ...f_lcl... in f_lcl
119 -- Although I'm a bit worried about whether full laziness might
120 -- float the f_lcl binding out and then inline M.f at its call site
122 dsHsBind auto_scc rest (AbsBinds [] [] exports binds)
123 = do { core_prs <- ds_lhs_binds NoSccs binds
124 ; let env = mkABEnv exports
125 do_one (lcl_id, rhs) | Just (gbl_id, prags) <- lookupVarEnv env lcl_id
126 = addInlinePrags prags gbl_id $
127 addAutoScc auto_scc gbl_id rhs
128 | otherwise = (lcl_id, rhs)
129 locals' = [(lcl_id, Var gbl_id) | (_, gbl_id, lcl_id, _) <- exports]
130 ; return (map do_one core_prs ++ locals' ++ rest) }
131 -- No Rec needed here (contrast the other AbsBinds cases)
132 -- because we can rely on the enclosing dsBind to wrap in Rec
134 -- Another common case: one exported variable
135 -- Non-recursive bindings come through this way
136 dsHsBind auto_scc rest
137 (AbsBinds all_tyvars dicts exports@[(tyvars, global, local, prags)] binds)
138 = ASSERT( all (`elem` tyvars) all_tyvars )
139 ds_lhs_binds NoSccs binds `thenDs` \ core_prs ->
141 -- Always treat the binds as recursive, because the typechecker
142 -- makes rather mixed-up dictionary bindings
143 core_bind = Rec core_prs
145 mappM (dsSpec all_tyvars dicts tyvars global local core_bind)
146 prags `thenDs` \ mb_specs ->
148 (spec_binds, rules) = unzip (catMaybes mb_specs)
149 global' = addIdSpecialisations global rules
150 rhs' = mkLams tyvars $ mkLams dicts $ Let core_bind (Var local)
151 bind = addInlinePrags prags global' $ addAutoScc auto_scc global' rhs'
153 returnDs (bind : spec_binds ++ rest)
155 dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports binds)
156 = do { core_prs <- ds_lhs_binds NoSccs binds
157 ; let env = mkABEnv exports
158 do_one (lcl_id,rhs) | Just (gbl_id, prags) <- lookupVarEnv env lcl_id
159 = addInlinePrags prags lcl_id $
160 addAutoScc auto_scc gbl_id rhs
161 | otherwise = (lcl_id,rhs)
163 -- Rec because of mixed-up dictionary bindings
164 core_bind = Rec (map do_one core_prs)
166 tup_expr = mkTupleExpr locals
167 tup_ty = exprType tup_expr
168 poly_tup_expr = mkLams all_tyvars $ mkLams dicts $
169 Let core_bind tup_expr
170 locals = [local | (_, _, local, _) <- exports]
171 local_tys = map idType locals
173 ; poly_tup_id <- newSysLocalDs (exprType poly_tup_expr)
175 ; let dict_args = map Var dicts
177 mk_bind ((tyvars, global, local, prags), n) -- locals !! n == local
178 = -- Need to make fresh locals to bind in the selector, because
179 -- some of the tyvars will be bound to voidTy
180 do { locals' <- newSysLocalsDs (map substitute local_tys)
181 ; tup_id <- newSysLocalDs (substitute tup_ty)
182 ; mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global local core_bind)
184 ; let (spec_binds, rules) = unzip (catMaybes mb_specs)
185 global' = addIdSpecialisations global rules
186 rhs = mkLams tyvars $ mkLams dicts $
187 mkTupleSelector locals' (locals' !! n) tup_id $
188 mkApps (mkTyApps (Var poly_tup_id) ty_args) dict_args
189 ; returnDs ((global', rhs) : spec_binds) }
191 mk_ty_arg all_tyvar | all_tyvar `elem` tyvars = mkTyVarTy all_tyvar
193 ty_args = map mk_ty_arg all_tyvars
194 substitute = substTyWith all_tyvars ty_args
196 ; export_binds_s <- mappM mk_bind (exports `zip` [0..])
197 -- don't scc (auto-)annotate the tuple itself.
199 ; returnDs ((poly_tup_id, poly_tup_expr) :
200 (concat export_binds_s ++ rest)) }
202 mkABEnv :: [([TyVar], Id, Id, [Prag])] -> VarEnv (Id, [Prag])
203 -- Takes the exports of a AbsBinds, and returns a mapping
204 -- lcl_id -> (gbl_id, prags)
205 mkABEnv exports = mkVarEnv [ (lcl_id, (gbl_id, prags))
206 | (_, gbl_id, lcl_id, prags) <- exports]
209 dsSpec :: [TyVar] -> [DictId] -> [TyVar]
210 -> Id -> Id -- Global, local
212 -> DsM (Maybe ((Id,CoreExpr), -- Binding for specialised Id
213 CoreRule)) -- Rule for the Global Id
216 -- f :: (Eq a, Ix b) => a -> b -> b
217 -- {-# SPECIALISE f :: Ix b => Int -> b -> b #-}
219 -- AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds
221 -- SpecPrag (/\b.\(d:Ix b). f Int b dInt d)
222 -- (forall b. Ix b => Int -> b -> b)
224 -- Rule: forall b,(d:Ix b). f Int b dInt d = f_spec b d
226 -- Spec bind: f_spec = Let f = /\ab \(d1:Eq a)(d2:Ix b). let binds in f_mono
227 -- /\b.\(d:Ix b). in f Int b dInt d
228 -- The idea is that f occurs just once, so it'll be
229 -- inlined and specialised
231 dsSpec all_tvs dicts tvs poly_id mono_id mono_bind (InlinePrag {})
234 dsSpec all_tvs dicts tvs poly_id mono_id mono_bind
235 (SpecPrag spec_expr spec_ty const_dicts inl)
236 = do { let poly_name = idName poly_id
237 ; spec_name <- newLocalName poly_name
238 ; ds_spec_expr <- dsExpr spec_expr
239 ; let (bndrs, body) = collectBinders ds_spec_expr
240 mb_lhs = decomposeRuleLhs (bndrs ++ const_dicts) body
243 Nothing -> do { warnDs msg; return Nothing }
245 Just (bndrs', var, args) -> return (Just (addInlineInfo inl spec_id spec_rhs, rule))
247 local_poly = setIdNotExported poly_id
248 -- Very important to make the 'f' non-exported,
249 -- else it won't be inlined!
250 spec_id = mkLocalId spec_name spec_ty
251 spec_rhs = Let (NonRec local_poly poly_f_body) ds_spec_expr
252 poly_f_body = mkLams (tvs ++ dicts) $
253 fix_up (Let mono_bind (Var mono_id))
255 -- Quantify over constant dicts on the LHS, since
256 -- their value depends only on their type
257 -- The ones we are interested in may even be imported
258 -- e.g. GHC.Base.dEqInt
260 rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
261 AlwaysActive poly_name
262 bndrs' -- Includes constant dicts
264 (mkVarApps (Var spec_id) bndrs)
267 -- Bind to voidTy any of all_ptvs that aren't
268 -- relevant for this particular function
269 fix_up body | null void_tvs = body
270 | otherwise = mkTyApps (mkLams void_tvs body)
271 (map (const voidTy) void_tvs)
272 void_tvs = all_tvs \\ tvs
274 msg = hang (ptext SLIT("Specialisation too complicated to desugar; ignored"))
279 %************************************************************************
281 \subsection{Adding inline pragmas}
283 %************************************************************************
286 decomposeRuleLhs :: [Var] -> CoreExpr -> Maybe ([Var], Id, [CoreExpr])
287 -- Returns Nothing if the LHS isn't of the expected shape
288 -- The argument 'all_bndrs' includes the "constant dicts" of the LHS,
289 -- and they may be GlobalIds, which we can't forall-ify.
290 -- So we substitute them out instead
291 decomposeRuleLhs all_bndrs lhs
292 = go init_env (occurAnalyseExpr lhs) -- Occurrence analysis sorts out the dict
293 -- bindings so we know if they are recursive
296 -- all_bndrs may include top-level imported dicts,
297 -- imported things with a for-all.
298 -- So we localise them and subtitute them out
299 bndr_prs = [ (id, Var (localise id)) | id <- all_bndrs, isGlobalId id ]
300 localise d = mkLocalId (idName d) (idType d)
302 init_env = mkVarEnv bndr_prs
303 all_bndrs' = map subst_bndr all_bndrs
304 subst_bndr bndr = case lookupVarEnv init_env bndr of
305 Just (Var bndr') -> bndr'
306 Just other -> panic "decomposeRuleLhs"
309 -- Substitute dicts in the LHS args, so that there
310 -- aren't any lets getting in the way
311 -- Note that we substitute the function too; we might have this as
312 -- a LHS: let f71 = M.f Int in f71
313 go env (Let (NonRec dict rhs) body)
314 = go (extendVarEnv env dict (simpleSubst env rhs)) body
316 = case collectArgs (simpleSubst env body) of
317 (Var fn, args) -> Just (all_bndrs', fn, args)
320 simpleSubst :: IdEnv CoreExpr -> CoreExpr -> CoreExpr
321 -- Similar to CoreSubst.substExpr, except that
322 -- (a) takes no account of capture; dictionary bindings use new names
323 -- (b) can have a GlobalId (imported) in its domain
324 -- (c) Ids only; no types are substituted
326 simpleSubst subst expr
329 go (Var v) = lookupVarEnv subst v `orElse` Var v
330 go (Cast e co) = Cast (go e) co
331 go (Type ty) = Type ty
332 go (Lit lit) = Lit lit
333 go (App fun arg) = App (go fun) (go arg)
334 go (Note note e) = Note note (go e)
335 go (Lam bndr body) = Lam bndr (go body)
336 go (Let (NonRec bndr rhs) body) = Let (NonRec bndr (go rhs)) (go body)
337 go (Let (Rec pairs) body) = Let (Rec (mapSnd go pairs)) (go body)
338 go (Case scrut bndr ty alts) = Case (go scrut) bndr ty
339 [(c,bs,go r) | (c,bs,r) <- alts]
341 addInlinePrags :: [Prag] -> Id -> CoreExpr -> (Id,CoreExpr)
342 addInlinePrags prags bndr rhs
343 = case [inl | InlinePrag inl <- prags] of
345 (inl:_) -> addInlineInfo inl bndr rhs
347 addInlineInfo :: InlineSpec -> Id -> CoreExpr -> (Id,CoreExpr)
348 addInlineInfo (Inline phase is_inline) bndr rhs
349 = (attach_phase bndr phase, wrap_inline is_inline rhs)
351 attach_phase bndr phase
352 | isAlwaysActive phase = bndr -- Default phase
353 | otherwise = bndr `setInlinePragma` phase
355 wrap_inline True body = mkInlineMe body
356 wrap_inline False body = body
360 %************************************************************************
362 \subsection[addAutoScc]{Adding automatic sccs}
364 %************************************************************************
367 data AutoScc = NoSccs
368 | AddSccs Module (Id -> Bool)
369 -- The (Id->Bool) says which Ids to add SCCs to
371 addAutoScc :: AutoScc
374 -> CoreExpr -- Scc'd Rhs
376 addAutoScc NoSccs _ rhs
378 addAutoScc (AddSccs mod add_scc) id rhs
379 | add_scc id = mkSCC (mkAutoCC id mod NotCafCC) rhs
383 If profiling and dealing with a dict binding,
384 wrap the dict in @_scc_ DICT <dict>@:
387 addDictScc var rhs = returnDs rhs
389 {- DISABLED for now (need to somehow make up a name for the scc) -- SDM
390 | not ( opt_SccProfilingOn && opt_AutoSccsOnDicts)
391 || not (isDictId var)
392 = returnDs rhs -- That's easy: do nothing
395 = getModuleAndGroupDs `thenDs` \ (mod, grp) ->
396 -- ToDo: do -dicts-all flag (mark dict things with individual CCs)
397 returnDs (Note (SCC (mkAllDictsCC mod grp False)) rhs)
402 %************************************************************************
406 %************************************************************************
410 dsCoercion :: HsWrapper -> DsM CoreExpr -> DsM CoreExpr
411 dsCoercion WpHole thing_inside = thing_inside
412 dsCoercion (WpCompose c1 c2) thing_inside = dsCoercion c1 (dsCoercion c2 thing_inside)
413 dsCoercion (WpCo co) thing_inside = do { expr <- thing_inside
414 ; return (Cast expr co) }
415 dsCoercion (WpLam id) thing_inside = do { expr <- thing_inside
416 ; return (Lam id expr) }
417 dsCoercion (WpTyLam tv) thing_inside = do { expr <- thing_inside
418 ; return (Lam tv expr) }
419 dsCoercion (WpApp id) thing_inside = do { expr <- thing_inside
420 ; return (App expr (Var id)) }
421 dsCoercion (WpTyApp ty) thing_inside = do { expr <- thing_inside
422 ; return (App expr (Type ty)) }
423 dsCoercion (WpLet bs) thing_inside = do { prs <- dsLHsBinds bs
424 ; expr <- thing_inside
425 ; return (Let (Rec prs) expr) }