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?
45 import BasicTypes hiding ( TopLevel )
47 import Util ( mapSnd )
53 %************************************************************************
55 \subsection[dsMonoBinds]{Desugaring a @MonoBinds@}
57 %************************************************************************
60 dsTopLHsBinds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
61 dsTopLHsBinds auto_scc binds = ds_lhs_binds auto_scc binds
63 dsLHsBinds :: LHsBinds Id -> DsM [(Id,CoreExpr)]
64 dsLHsBinds binds = ds_lhs_binds NoSccs binds
67 ------------------------
68 ds_lhs_binds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
69 -- scc annotation policy (see below)
70 ds_lhs_binds auto_scc binds = foldM (dsLHsBind auto_scc) [] (bagToList binds)
73 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
75 -> DsM [(Id,CoreExpr)] -- Result
76 dsLHsBind auto_scc rest (L loc bind)
77 = putSrcSpanDs loc $ dsHsBind auto_scc rest bind
80 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
82 -> DsM [(Id,CoreExpr)] -- Result
84 dsHsBind auto_scc rest (VarBind var expr)
85 = dsLExpr expr `thenDs` \ core_expr ->
87 -- Dictionary bindings are always VarMonoBinds, so
88 -- we only need do this here
89 addDictScc var core_expr `thenDs` \ core_expr' ->
90 returnDs ((var, core_expr') : rest)
92 dsHsBind auto_scc rest (FunBind { fun_id = L _ fun, fun_matches = matches, fun_co_fn = co_fn, fun_tick = tick })
93 = matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, body) ->
94 mkOptTickBox tick body `thenDs` \ body' ->
95 dsCoercion co_fn (return (mkLams args body')) `thenDs` \ rhs ->
96 returnDs ((fun,rhs) : rest)
98 dsHsBind auto_scc rest (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty })
99 = dsGuarded grhss ty `thenDs` \ body_expr ->
100 mkSelectorBinds pat body_expr `thenDs` \ sel_binds ->
101 returnDs (sel_binds ++ rest)
103 -- Note [Rules and inlining]
104 -- Common special case: no type or dictionary abstraction
105 -- This is a bit less trivial than you might suppose
106 -- The naive way woudl be to desguar to something like
107 -- f_lcl = ...f_lcl... -- The "binds" from AbsBinds
108 -- M.f = f_lcl -- Generated from "exports"
109 -- But we don't want that, because if M.f isn't exported,
110 -- it'll be inlined unconditionally at every call site (its rhs is
111 -- trivial). That would be ok unless it has RULES, which would
112 -- thereby be completely lost. Bad, bad, bad.
114 -- Instead we want to generate
117 -- Now all is cool. The RULES are attached to M.f (by SimplCore),
118 -- and f_lcl is rapidly inlined away.
120 -- This does not happen in the same way to polymorphic binds,
121 -- because they desugar to
122 -- M.f = /\a. let f_lcl = ...f_lcl... in f_lcl
123 -- Although I'm a bit worried about whether full laziness might
124 -- float the f_lcl binding out and then inline M.f at its call site
126 dsHsBind auto_scc rest (AbsBinds [] [] exports binds)
127 = do { core_prs <- ds_lhs_binds NoSccs binds
128 ; let env = mkABEnv exports
129 do_one (lcl_id, rhs) | Just (gbl_id, prags) <- lookupVarEnv env lcl_id
130 = addInlinePrags prags gbl_id $
131 addAutoScc auto_scc gbl_id rhs
132 | otherwise = (lcl_id, rhs)
133 locals' = [(lcl_id, Var gbl_id) | (_, gbl_id, lcl_id, _) <- exports]
134 ; return (map do_one core_prs ++ locals' ++ rest) }
135 -- No Rec needed here (contrast the other AbsBinds cases)
136 -- because we can rely on the enclosing dsBind to wrap in Rec
138 -- Another common case: one exported variable
139 -- Non-recursive bindings come through this way
140 dsHsBind auto_scc rest
141 (AbsBinds all_tyvars dicts exports@[(tyvars, global, local, prags)] binds)
142 = ASSERT( all (`elem` tyvars) all_tyvars )
143 ds_lhs_binds NoSccs binds `thenDs` \ core_prs ->
145 -- Always treat the binds as recursive, because the typechecker
146 -- makes rather mixed-up dictionary bindings
147 core_bind = Rec core_prs
149 mappM (dsSpec all_tyvars dicts tyvars global local core_bind)
150 prags `thenDs` \ mb_specs ->
152 (spec_binds, rules) = unzip (catMaybes mb_specs)
153 global' = addIdSpecialisations global rules
154 rhs' = mkLams tyvars $ mkLams dicts $ Let core_bind (Var local)
155 bind = addInlinePrags prags global' $ addAutoScc auto_scc global' rhs'
157 returnDs (bind : spec_binds ++ rest)
159 dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports binds)
160 = do { core_prs <- ds_lhs_binds NoSccs binds
161 ; let env = mkABEnv exports
162 do_one (lcl_id,rhs) | Just (gbl_id, prags) <- lookupVarEnv env lcl_id
163 = addInlinePrags prags lcl_id $
164 addAutoScc auto_scc gbl_id rhs
165 | otherwise = (lcl_id,rhs)
167 -- Rec because of mixed-up dictionary bindings
168 core_bind = Rec (map do_one core_prs)
170 tup_expr = mkTupleExpr locals
171 tup_ty = exprType tup_expr
172 poly_tup_expr = mkLams all_tyvars $ mkLams dicts $
173 Let core_bind tup_expr
174 locals = [local | (_, _, local, _) <- exports]
175 local_tys = map idType locals
177 ; poly_tup_id <- newSysLocalDs (exprType poly_tup_expr)
179 ; let dict_args = map Var dicts
181 mk_bind ((tyvars, global, local, prags), n) -- locals !! n == local
182 = -- Need to make fresh locals to bind in the selector, because
183 -- some of the tyvars will be bound to 'Any'
184 do { locals' <- newSysLocalsDs (map substitute local_tys)
185 ; tup_id <- newSysLocalDs (substitute tup_ty)
186 ; mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global local core_bind)
188 ; let (spec_binds, rules) = unzip (catMaybes mb_specs)
189 global' = addIdSpecialisations global rules
190 rhs = mkLams tyvars $ mkLams dicts $
191 mkTupleSelector locals' (locals' !! n) tup_id $
192 mkApps (mkTyApps (Var poly_tup_id) ty_args) dict_args
193 ; returnDs ((global', rhs) : spec_binds) }
195 mk_ty_arg all_tyvar | all_tyvar `elem` tyvars = mkTyVarTy all_tyvar
196 | otherwise = mkArbitraryType all_tyvar
197 ty_args = map mk_ty_arg all_tyvars
198 substitute = substTyWith all_tyvars ty_args
200 ; export_binds_s <- mappM mk_bind (exports `zip` [0..])
201 -- don't scc (auto-)annotate the tuple itself.
203 ; returnDs ((poly_tup_id, poly_tup_expr) :
204 (concat export_binds_s ++ rest)) }
206 mkABEnv :: [([TyVar], Id, Id, [LPrag])] -> VarEnv (Id, [LPrag])
207 -- Takes the exports of a AbsBinds, and returns a mapping
208 -- lcl_id -> (gbl_id, prags)
209 mkABEnv exports = mkVarEnv [ (lcl_id, (gbl_id, prags))
210 | (_, gbl_id, lcl_id, prags) <- exports]
213 dsSpec :: [TyVar] -> [DictId] -> [TyVar]
214 -> Id -> Id -- Global, local
216 -> DsM (Maybe ((Id,CoreExpr), -- Binding for specialised Id
217 CoreRule)) -- Rule for the Global Id
220 -- f :: (Eq a, Ix b) => a -> b -> b
221 -- {-# SPECIALISE f :: Ix b => Int -> b -> b #-}
223 -- AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds
225 -- SpecPrag (/\b.\(d:Ix b). f Int b dInt d)
226 -- (forall b. Ix b => Int -> b -> b)
228 -- Rule: forall b,(d:Ix b). f Int b dInt d = f_spec b d
230 -- Spec bind: f_spec = Let f = /\ab \(d1:Eq a)(d2:Ix b). let binds in f_mono
231 -- /\b.\(d:Ix b). in f Int b dInt d
232 -- The idea is that f occurs just once, so it'll be
233 -- inlined and specialised
235 -- Given SpecPrag (/\as.\ds. f es) t, we have
236 -- the defn f_spec as ds = f es
237 -- and the RULE f es = f_spec as ds
239 -- It is *possible* that 'es' does not mention all of the dictionaries 'ds'
240 -- (a bit silly, because then the
241 dsSpec all_tvs dicts tvs poly_id mono_id mono_bind (L _ (InlinePrag {}))
244 dsSpec all_tvs dicts tvs poly_id mono_id mono_bind
245 (L loc (SpecPrag spec_expr spec_ty _const_dicts inl))
246 -- See Note [Const rule dicts]
248 do { let poly_name = idName poly_id
249 ; spec_name <- newLocalName poly_name
250 ; ds_spec_expr <- dsExpr spec_expr
251 ; let (bndrs, body) = collectBinders (occurAnalyseExpr ds_spec_expr)
252 -- The occurrence-analysis does two things
253 -- (a) identifies unused binders: Note [Unused spec binders]
254 -- (b) sorts dict bindings into NonRecs
255 -- so they can be inlined by decomposeRuleLhs
256 mb_lhs = decomposeRuleLhs body
258 -- Check for dead binders: Note [Unused spec binders]
259 ; case filter isDeadBinder bndrs of {
260 bs | not (null bs) -> do { warnDs (dead_msg bs); return Nothing }
264 Nothing -> do { warnDs decomp_msg; return Nothing }
266 Just (var, args) -> return (Just (addInlineInfo inl spec_id spec_rhs, rule))
268 local_poly = setIdNotExported poly_id
269 -- Very important to make the 'f' non-exported,
270 -- else it won't be inlined!
271 spec_id = mkLocalId spec_name spec_ty
272 spec_rhs = Let (NonRec local_poly poly_f_body) ds_spec_expr
273 poly_f_body = mkLams (tvs ++ dicts) $
274 fix_up (Let mono_bind (Var mono_id))
276 rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
277 AlwaysActive poly_name
279 (mkVarApps (Var spec_id) bndrs)
282 -- Bind to Any any of all_ptvs that aren't
283 -- relevant for this particular function
284 fix_up body | null void_tvs = body
285 | otherwise = mkTyApps (mkLams void_tvs body)
286 (map mkArbitraryType void_tvs)
287 void_tvs = all_tvs \\ tvs
289 dead_msg bs = vcat [ sep [ptext SLIT("Useless constraint") <> plural bs
290 <+> ptext SLIT("in specialied type:"),
291 nest 2 (pprTheta (map get_pred bs))]
292 , ptext SLIT("SPECIALISE pragma ignored")]
293 get_pred b = ASSERT( isId b ) expectJust "dsSpec" (tcSplitPredTy_maybe (idType b))
295 decomp_msg = hang (ptext SLIT("Specialisation too complicated to desugar; ignored"))
299 Note [Unused spec binders]
300 ~~~~~~~~~~~~~~~~~~~~~~~~~~
303 {-# SPECIALISE f :: Eq a => a -> a #-}
304 It's true that this *is* a more specialised type, but the rule
305 we get is something like this:
308 Note that the rule is bogus, becuase it mentions a 'd' that is
309 not bound on the LHS! But it's a silly specialisation anyway, becuase
310 the constraint is unused. We could bind 'd' to (error "unused")
311 but it seems better to reject the program because it's almost certainly
312 a mistake. That's what the isDeadBinder call detects.
314 Note [Const rule dicts]
315 ~~~~~~~~~~~~~~~~~~~~~~~
316 A SpecPrag has a field for "constant dicts" in the RULE, but I think
317 it's pretty useless. See the place where it's generated in TcBinds.
318 TcSimplify will discharge a constraint by binding it to, say,
319 GHC.Base.$f2 :: Eq Int, withour putting anything in the LIE, so this
320 dict won't show up in the const-dicts field. It probably doesn't matter,
321 because the rule will end up being something like
322 f Int GHC.Base.$f2 = ...
324 forall d. f Int d = ...
325 The latter is more general, but in practice I think it won't make any
329 %************************************************************************
331 \subsection{Adding inline pragmas}
333 %************************************************************************
336 decomposeRuleLhs :: CoreExpr -> Maybe (Id, [CoreExpr])
337 -- Returns Nothing if the LHS isn't of the expected shape
339 = go emptyVarEnv (occurAnalyseExpr lhs) -- Occurrence analysis sorts out the dict
340 -- bindings so we know if they are recursive
342 -- Substitute dicts in the LHS args, so that there
343 -- aren't any lets getting in the way
344 -- Note that we substitute the function too; we might have this as
345 -- a LHS: let f71 = M.f Int in f71
346 go env (Let (NonRec dict rhs) body)
347 = go (extendVarEnv env dict (simpleSubst env rhs)) body
349 = case collectArgs (simpleSubst env body) of
350 (Var fn, args) -> Just (fn, args)
353 simpleSubst :: IdEnv CoreExpr -> CoreExpr -> CoreExpr
354 -- Similar to CoreSubst.substExpr, except that
355 -- (a) takes no account of capture; dictionary bindings use new names
356 -- (b) can have a GlobalId (imported) in its domain
357 -- (c) Ids only; no types are substituted
359 -- (b) is the reason we can't use CoreSubst... and it's no longer relevant
360 -- so really we should replace simpleSubst
361 simpleSubst subst expr
364 go (Var v) = lookupVarEnv subst v `orElse` Var v
365 go (Cast e co) = Cast (go e) co
366 go (Type ty) = Type ty
367 go (Lit lit) = Lit lit
368 go (App fun arg) = App (go fun) (go arg)
369 go (Note note e) = Note note (go e)
370 go (Lam bndr body) = Lam bndr (go body)
371 go (Let (NonRec bndr rhs) body) = Let (NonRec bndr (go rhs)) (go body)
372 go (Let (Rec pairs) body) = Let (Rec (mapSnd go pairs)) (go body)
373 go (Case scrut bndr ty alts) = Case (go scrut) bndr ty
374 [(c,bs,go r) | (c,bs,r) <- alts]
376 addInlinePrags :: [LPrag] -> Id -> CoreExpr -> (Id,CoreExpr)
377 addInlinePrags prags bndr rhs
378 = case [inl | L _ (InlinePrag inl) <- prags] of
380 (inl:_) -> addInlineInfo inl bndr rhs
382 addInlineInfo :: InlineSpec -> Id -> CoreExpr -> (Id,CoreExpr)
383 addInlineInfo (Inline phase is_inline) bndr rhs
384 = (attach_phase bndr phase, wrap_inline is_inline rhs)
386 attach_phase bndr phase
387 | isAlwaysActive phase = bndr -- Default phase
388 | otherwise = bndr `setInlinePragma` phase
390 wrap_inline True body = mkInlineMe body
391 wrap_inline False body = body
395 %************************************************************************
397 \subsection[addAutoScc]{Adding automatic sccs}
399 %************************************************************************
402 data AutoScc = NoSccs
403 | AddSccs Module (Id -> Bool)
404 -- The (Id->Bool) says which Ids to add SCCs to
406 addAutoScc :: AutoScc
409 -> CoreExpr -- Scc'd Rhs
411 addAutoScc NoSccs _ rhs
413 addAutoScc (AddSccs mod add_scc) id rhs
414 | add_scc id = mkSCC (mkAutoCC id mod NotCafCC) rhs
418 If profiling and dealing with a dict binding,
419 wrap the dict in @_scc_ DICT <dict>@:
422 addDictScc var rhs = returnDs rhs
424 {- DISABLED for now (need to somehow make up a name for the scc) -- SDM
425 | not ( opt_SccProfilingOn && opt_AutoSccsOnDicts)
426 || not (isDictId var)
427 = returnDs rhs -- That's easy: do nothing
430 = getModuleAndGroupDs `thenDs` \ (mod, grp) ->
431 -- ToDo: do -dicts-all flag (mark dict things with individual CCs)
432 returnDs (Note (SCC (mkAllDictsCC mod grp False)) rhs)
437 %************************************************************************
441 %************************************************************************
445 dsCoercion :: HsWrapper -> DsM CoreExpr -> DsM CoreExpr
446 dsCoercion WpHole thing_inside = thing_inside
447 dsCoercion (WpCompose c1 c2) thing_inside = dsCoercion c1 (dsCoercion c2 thing_inside)
448 dsCoercion (WpCo co) thing_inside = do { expr <- thing_inside
449 ; return (Cast expr co) }
450 dsCoercion (WpLam id) thing_inside = do { expr <- thing_inside
451 ; return (Lam id expr) }
452 dsCoercion (WpTyLam tv) thing_inside = do { expr <- thing_inside
453 ; return (Lam tv expr) }
454 dsCoercion (WpApp id) thing_inside = do { expr <- thing_inside
455 ; return (App expr (Var id)) }
456 dsCoercion (WpTyApp ty) thing_inside = do { expr <- thing_inside
457 ; return (App expr (Type ty)) }
458 dsCoercion (WpLet bs) thing_inside = do { prs <- dsLHsBinds bs
459 ; expr <- thing_inside
460 ; return (Let (Rec prs) expr) }