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).
14 -- The above warning supression flag is a temporary kludge.
15 -- While working on this module you are encouraged to remove it and fix
16 -- any warnings in the module. See
17 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
20 module DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs,
25 #include "HsVersions.h"
27 import {-# SOURCE #-} DsExpr( dsLExpr, dsExpr )
28 import {-# SOURCE #-} Match( matchWrapper )
34 import HsSyn -- lots of things
35 import CoreSyn -- lots of things
38 import TcHsSyn ( mkArbitraryType ) -- Mis-placed?
52 import BasicTypes hiding ( TopLevel )
54 import Util ( mapSnd )
60 %************************************************************************
62 \subsection[dsMonoBinds]{Desugaring a @MonoBinds@}
64 %************************************************************************
67 dsTopLHsBinds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
68 dsTopLHsBinds auto_scc binds = ds_lhs_binds auto_scc binds
70 dsLHsBinds :: LHsBinds Id -> DsM [(Id,CoreExpr)]
71 dsLHsBinds binds = ds_lhs_binds NoSccs binds
74 ------------------------
75 ds_lhs_binds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
76 -- scc annotation policy (see below)
77 ds_lhs_binds auto_scc binds = foldM (dsLHsBind auto_scc) [] (bagToList binds)
80 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
82 -> DsM [(Id,CoreExpr)] -- Result
83 dsLHsBind auto_scc rest (L loc bind)
84 = putSrcSpanDs loc $ dsHsBind auto_scc rest bind
87 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
89 -> DsM [(Id,CoreExpr)] -- Result
91 dsHsBind auto_scc rest (VarBind var expr)
92 = dsLExpr expr `thenDs` \ core_expr ->
94 -- Dictionary bindings are always VarMonoBinds, so
95 -- we only need do this here
96 addDictScc var core_expr `thenDs` \ core_expr' ->
97 returnDs ((var, core_expr') : rest)
99 dsHsBind auto_scc rest (FunBind { fun_id = L _ fun, fun_matches = matches,
100 fun_co_fn = co_fn, fun_tick = tick, fun_infix = inf })
101 = matchWrapper (FunRhs (idName fun) inf) matches `thenDs` \ (args, body) ->
102 mkOptTickBox tick body `thenDs` \ body' ->
103 dsCoercion co_fn (return (mkLams args body')) `thenDs` \ rhs ->
104 returnDs ((fun,rhs) : rest)
106 dsHsBind auto_scc rest (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty })
107 = dsGuarded grhss ty `thenDs` \ body_expr ->
108 mkSelectorBinds pat body_expr `thenDs` \ sel_binds ->
109 returnDs (sel_binds ++ rest)
111 -- Note [Rules and inlining]
112 -- Common special case: no type or dictionary abstraction
113 -- This is a bit less trivial than you might suppose
114 -- The naive way woudl be to desguar to something like
115 -- f_lcl = ...f_lcl... -- The "binds" from AbsBinds
116 -- M.f = f_lcl -- Generated from "exports"
117 -- But we don't want that, because if M.f isn't exported,
118 -- it'll be inlined unconditionally at every call site (its rhs is
119 -- trivial). That would be ok unless it has RULES, which would
120 -- thereby be completely lost. Bad, bad, bad.
122 -- Instead we want to generate
125 -- Now all is cool. The RULES are attached to M.f (by SimplCore),
126 -- and f_lcl is rapidly inlined away.
128 -- This does not happen in the same way to polymorphic binds,
129 -- because they desugar to
130 -- M.f = /\a. let f_lcl = ...f_lcl... in f_lcl
131 -- Although I'm a bit worried about whether full laziness might
132 -- float the f_lcl binding out and then inline M.f at its call site
134 dsHsBind auto_scc rest (AbsBinds [] [] exports binds)
135 = do { core_prs <- ds_lhs_binds NoSccs binds
136 ; let env = mkABEnv exports
137 do_one (lcl_id, rhs) | Just (gbl_id, prags) <- lookupVarEnv env lcl_id
138 = addInlinePrags prags gbl_id $
139 addAutoScc auto_scc gbl_id rhs
140 | otherwise = (lcl_id, rhs)
141 locals' = [(lcl_id, Var gbl_id) | (_, gbl_id, lcl_id, _) <- exports]
142 ; return (map do_one core_prs ++ locals' ++ rest) }
143 -- No Rec needed here (contrast the other AbsBinds cases)
144 -- because we can rely on the enclosing dsBind to wrap in Rec
146 -- Another common case: one exported variable
147 -- Non-recursive bindings come through this way
148 dsHsBind auto_scc rest
149 (AbsBinds all_tyvars dicts exports@[(tyvars, global, local, prags)] binds)
150 = ASSERT( all (`elem` tyvars) all_tyvars )
151 ds_lhs_binds NoSccs binds `thenDs` \ core_prs ->
153 -- Always treat the binds as recursive, because the typechecker
154 -- makes rather mixed-up dictionary bindings
155 core_bind = Rec core_prs
157 mappM (dsSpec all_tyvars dicts tyvars global local core_bind)
158 prags `thenDs` \ mb_specs ->
160 (spec_binds, rules) = unzip (catMaybes mb_specs)
161 global' = addIdSpecialisations global rules
162 rhs' = mkLams tyvars $ mkLams dicts $ Let core_bind (Var local)
163 bind = addInlinePrags prags global' $ addAutoScc auto_scc global' rhs'
165 returnDs (bind : spec_binds ++ rest)
167 dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports binds)
168 = do { core_prs <- ds_lhs_binds NoSccs binds
169 ; let env = mkABEnv exports
170 do_one (lcl_id,rhs) | Just (gbl_id, prags) <- lookupVarEnv env lcl_id
171 = addInlinePrags prags lcl_id $
172 addAutoScc auto_scc gbl_id rhs
173 | otherwise = (lcl_id,rhs)
175 -- Rec because of mixed-up dictionary bindings
176 core_bind = Rec (map do_one core_prs)
178 tup_expr = mkTupleExpr locals
179 tup_ty = exprType tup_expr
180 poly_tup_expr = mkLams all_tyvars $ mkLams dicts $
181 Let core_bind tup_expr
182 locals = [local | (_, _, local, _) <- exports]
183 local_tys = map idType locals
185 ; poly_tup_id <- newSysLocalDs (exprType poly_tup_expr)
187 ; let dict_args = map Var dicts
189 mk_bind ((tyvars, global, local, prags), n) -- locals !! n == local
190 = -- Need to make fresh locals to bind in the selector, because
191 -- some of the tyvars will be bound to 'Any'
192 do { locals' <- newSysLocalsDs (map substitute local_tys)
193 ; tup_id <- newSysLocalDs (substitute tup_ty)
194 ; mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global local core_bind)
196 ; let (spec_binds, rules) = unzip (catMaybes mb_specs)
197 global' = addIdSpecialisations global rules
198 rhs = mkLams tyvars $ mkLams dicts $
199 mkTupleSelector locals' (locals' !! n) tup_id $
200 mkApps (mkTyApps (Var poly_tup_id) ty_args) dict_args
201 ; returnDs ((global', rhs) : spec_binds) }
203 mk_ty_arg all_tyvar | all_tyvar `elem` tyvars = mkTyVarTy all_tyvar
204 | otherwise = mkArbitraryType all_tyvar
205 ty_args = map mk_ty_arg all_tyvars
206 substitute = substTyWith all_tyvars ty_args
208 ; export_binds_s <- mappM mk_bind (exports `zip` [0..])
209 -- don't scc (auto-)annotate the tuple itself.
211 ; returnDs ((poly_tup_id, poly_tup_expr) :
212 (concat export_binds_s ++ rest)) }
214 mkABEnv :: [([TyVar], Id, Id, [LPrag])] -> VarEnv (Id, [LPrag])
215 -- Takes the exports of a AbsBinds, and returns a mapping
216 -- lcl_id -> (gbl_id, prags)
217 mkABEnv exports = mkVarEnv [ (lcl_id, (gbl_id, prags))
218 | (_, gbl_id, lcl_id, prags) <- exports]
221 dsSpec :: [TyVar] -> [DictId] -> [TyVar]
222 -> Id -> Id -- Global, local
224 -> DsM (Maybe ((Id,CoreExpr), -- Binding for specialised Id
225 CoreRule)) -- Rule for the Global Id
228 -- f :: (Eq a, Ix b) => a -> b -> b
229 -- {-# SPECIALISE f :: Ix b => Int -> b -> b #-}
231 -- AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds
233 -- SpecPrag (/\b.\(d:Ix b). f Int b dInt d)
234 -- (forall b. Ix b => Int -> b -> b)
236 -- Rule: forall b,(d:Ix b). f Int b dInt d = f_spec b d
238 -- Spec bind: f_spec = Let f = /\ab \(d1:Eq a)(d2:Ix b). let binds in f_mono
239 -- /\b.\(d:Ix b). in f Int b dInt d
240 -- The idea is that f occurs just once, so it'll be
241 -- inlined and specialised
243 -- Given SpecPrag (/\as.\ds. f es) t, we have
244 -- the defn f_spec as ds = f es
245 -- and the RULE f es = f_spec as ds
247 -- It is *possible* that 'es' does not mention all of the dictionaries 'ds'
248 -- (a bit silly, because then the
249 dsSpec all_tvs dicts tvs poly_id mono_id mono_bind (L _ (InlinePrag {}))
252 dsSpec all_tvs dicts tvs poly_id mono_id mono_bind
253 (L loc (SpecPrag spec_expr spec_ty _const_dicts inl))
254 -- See Note [Const rule dicts]
256 do { let poly_name = idName poly_id
257 ; spec_name <- newLocalName poly_name
258 ; ds_spec_expr <- dsExpr spec_expr
259 ; let (bndrs, body) = collectBinders (occurAnalyseExpr ds_spec_expr)
260 -- The occurrence-analysis does two things
261 -- (a) identifies unused binders: Note [Unused spec binders]
262 -- (b) sorts dict bindings into NonRecs
263 -- so they can be inlined by decomposeRuleLhs
264 mb_lhs = decomposeRuleLhs body
266 -- Check for dead binders: Note [Unused spec binders]
267 ; case filter isDeadBinder bndrs of {
268 bs | not (null bs) -> do { warnDs (dead_msg bs); return Nothing }
272 Nothing -> do { warnDs decomp_msg; return Nothing }
274 Just (var, args) -> return (Just (addInlineInfo inl spec_id spec_rhs, rule))
276 local_poly = setIdNotExported poly_id
277 -- Very important to make the 'f' non-exported,
278 -- else it won't be inlined!
279 spec_id = mkLocalId spec_name spec_ty
280 spec_rhs = Let (NonRec local_poly poly_f_body) ds_spec_expr
281 poly_f_body = mkLams (tvs ++ dicts) $
282 fix_up (Let mono_bind (Var mono_id))
284 rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
285 AlwaysActive poly_name
287 (mkVarApps (Var spec_id) bndrs)
290 -- Bind to Any any of all_ptvs that aren't
291 -- relevant for this particular function
292 fix_up body | null void_tvs = body
293 | otherwise = mkTyApps (mkLams void_tvs body)
294 (map mkArbitraryType void_tvs)
295 void_tvs = all_tvs \\ tvs
297 dead_msg bs = vcat [ sep [ptext SLIT("Useless constraint") <> plural bs
298 <+> ptext SLIT("in specialied type:"),
299 nest 2 (pprTheta (map get_pred bs))]
300 , ptext SLIT("SPECIALISE pragma ignored")]
301 get_pred b = ASSERT( isId b ) expectJust "dsSpec" (tcSplitPredTy_maybe (idType b))
303 decomp_msg = hang (ptext SLIT("Specialisation too complicated to desugar; ignored"))
307 Note [Unused spec binders]
308 ~~~~~~~~~~~~~~~~~~~~~~~~~~
311 {-# SPECIALISE f :: Eq a => a -> a #-}
312 It's true that this *is* a more specialised type, but the rule
313 we get is something like this:
316 Note that the rule is bogus, becuase it mentions a 'd' that is
317 not bound on the LHS! But it's a silly specialisation anyway, becuase
318 the constraint is unused. We could bind 'd' to (error "unused")
319 but it seems better to reject the program because it's almost certainly
320 a mistake. That's what the isDeadBinder call detects.
322 Note [Const rule dicts]
323 ~~~~~~~~~~~~~~~~~~~~~~~
324 A SpecPrag has a field for "constant dicts" in the RULE, but I think
325 it's pretty useless. See the place where it's generated in TcBinds.
326 TcSimplify will discharge a constraint by binding it to, say,
327 GHC.Base.$f2 :: Eq Int, withour putting anything in the LIE, so this
328 dict won't show up in the const-dicts field. It probably doesn't matter,
329 because the rule will end up being something like
330 f Int GHC.Base.$f2 = ...
332 forall d. f Int d = ...
333 The latter is more general, but in practice I think it won't make any
337 %************************************************************************
339 \subsection{Adding inline pragmas}
341 %************************************************************************
344 decomposeRuleLhs :: CoreExpr -> Maybe (Id, [CoreExpr])
345 -- Returns Nothing if the LHS isn't of the expected shape
347 = go emptyVarEnv (occurAnalyseExpr lhs) -- Occurrence analysis sorts out the dict
348 -- bindings so we know if they are recursive
350 -- Substitute dicts in the LHS args, so that there
351 -- aren't any lets getting in the way
352 -- Note that we substitute the function too; we might have this as
353 -- a LHS: let f71 = M.f Int in f71
354 go env (Let (NonRec dict rhs) body)
355 = go (extendVarEnv env dict (simpleSubst env rhs)) body
357 = case collectArgs (simpleSubst env body) of
358 (Var fn, args) -> Just (fn, args)
361 simpleSubst :: IdEnv CoreExpr -> CoreExpr -> CoreExpr
362 -- Similar to CoreSubst.substExpr, except that
363 -- (a) takes no account of capture; dictionary bindings use new names
364 -- (b) can have a GlobalId (imported) in its domain
365 -- (c) Ids only; no types are substituted
367 -- (b) is the reason we can't use CoreSubst... and it's no longer relevant
368 -- so really we should replace simpleSubst
369 simpleSubst subst expr
372 go (Var v) = lookupVarEnv subst v `orElse` Var v
373 go (Cast e co) = Cast (go e) co
374 go (Type ty) = Type ty
375 go (Lit lit) = Lit lit
376 go (App fun arg) = App (go fun) (go arg)
377 go (Note note e) = Note note (go e)
378 go (Lam bndr body) = Lam bndr (go body)
379 go (Let (NonRec bndr rhs) body) = Let (NonRec bndr (go rhs)) (go body)
380 go (Let (Rec pairs) body) = Let (Rec (mapSnd go pairs)) (go body)
381 go (Case scrut bndr ty alts) = Case (go scrut) bndr ty
382 [(c,bs,go r) | (c,bs,r) <- alts]
384 addInlinePrags :: [LPrag] -> Id -> CoreExpr -> (Id,CoreExpr)
385 addInlinePrags prags bndr rhs
386 = case [inl | L _ (InlinePrag inl) <- prags] of
388 (inl:_) -> addInlineInfo inl bndr rhs
390 addInlineInfo :: InlineSpec -> Id -> CoreExpr -> (Id,CoreExpr)
391 addInlineInfo (Inline phase is_inline) bndr rhs
392 = (attach_phase bndr phase, wrap_inline is_inline rhs)
394 attach_phase bndr phase
395 | isAlwaysActive phase = bndr -- Default phase
396 | otherwise = bndr `setInlinePragma` phase
398 wrap_inline True body = mkInlineMe body
399 wrap_inline False body = body
403 %************************************************************************
405 \subsection[addAutoScc]{Adding automatic sccs}
407 %************************************************************************
410 data AutoScc = NoSccs
411 | AddSccs Module (Id -> Bool)
412 -- The (Id->Bool) says which Ids to add SCCs to
414 addAutoScc :: AutoScc
417 -> CoreExpr -- Scc'd Rhs
419 addAutoScc NoSccs _ rhs
421 addAutoScc (AddSccs mod add_scc) id rhs
422 | add_scc id = mkSCC (mkAutoCC id mod NotCafCC) rhs
426 If profiling and dealing with a dict binding,
427 wrap the dict in @_scc_ DICT <dict>@:
430 addDictScc var rhs = returnDs rhs
432 {- DISABLED for now (need to somehow make up a name for the scc) -- SDM
433 | not ( opt_SccProfilingOn && opt_AutoSccsOnDicts)
434 || not (isDictId var)
435 = returnDs rhs -- That's easy: do nothing
438 = getModuleAndGroupDs `thenDs` \ (mod, grp) ->
439 -- ToDo: do -dicts-all flag (mark dict things with individual CCs)
440 returnDs (Note (SCC (mkAllDictsCC mod grp False)) rhs)
445 %************************************************************************
449 %************************************************************************
453 dsCoercion :: HsWrapper -> DsM CoreExpr -> DsM CoreExpr
454 dsCoercion WpHole thing_inside = thing_inside
455 dsCoercion (WpCompose c1 c2) thing_inside = dsCoercion c1 (dsCoercion c2 thing_inside)
456 dsCoercion (WpCo co) thing_inside = do { expr <- thing_inside
457 ; return (Cast expr co) }
458 dsCoercion (WpLam id) thing_inside = do { expr <- thing_inside
459 ; return (Lam id expr) }
460 dsCoercion (WpTyLam tv) thing_inside = do { expr <- thing_inside
461 ; return (Lam tv expr) }
462 dsCoercion (WpApp id) thing_inside = do { expr <- thing_inside
463 ; return (App expr (Var id)) }
464 dsCoercion (WpTyApp ty) thing_inside = do { expr <- thing_inside
465 ; return (App expr (Type ty)) }
466 dsCoercion (WpLet bs) thing_inside = do { prs <- dsLHsBinds bs
467 ; expr <- thing_inside
468 ; return (Let (Rec prs) expr) }