2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 Taken quite directly from the Peyton Jones/Lester paper.
9 exprFreeVars, -- CoreExpr -> VarSet -- Find all locally-defined free Ids or tyvars
10 exprsFreeVars, -- [CoreExpr] -> VarSet
11 bindFreeVars, -- CoreBind -> VarSet
13 exprSomeFreeVars, exprsSomeFreeVars,
14 exprFreeNames, exprsFreeNames,
16 idRuleVars, idFreeVars, varTypeTyVars,
17 ruleRhsFreeVars, rulesRhsFreeVars,
18 ruleLhsFreeNames, ruleLhsFreeIds,
20 CoreExprWithFVs, -- = AnnExpr Id VarSet
21 CoreBindWithFVs, -- = AnnBind Id VarSet
22 freeVars, -- CoreExpr -> CoreExprWithFVs
23 freeVarsOf -- CoreExprWithFVs -> IdSet
26 #include "HsVersions.h"
42 %************************************************************************
44 \section{Finding the free variables of an expression}
46 %************************************************************************
48 This function simply finds the free variables of an expression.
49 So far as type variables are concerned, it only finds tyvars that are
51 * free in type arguments,
52 * free in the type of a binder,
54 but not those that are free in the type of variable occurrence.
57 exprFreeVars :: CoreExpr -> VarSet -- Find all locally-defined free Ids or tyvars
58 exprFreeVars = exprSomeFreeVars isLocalVar
60 exprsFreeVars :: [CoreExpr] -> VarSet
61 exprsFreeVars = foldr (unionVarSet . exprFreeVars) emptyVarSet
63 bindFreeVars :: CoreBind -> VarSet
64 bindFreeVars (NonRec b r) = exprFreeVars r
65 bindFreeVars (Rec prs) = addBndrs (map fst prs)
66 (foldr (union . rhs_fvs) noVars prs)
67 isLocalVar emptyVarSet
69 exprSomeFreeVars :: InterestingVarFun -- Says which Vars are interesting
72 exprSomeFreeVars fv_cand e = expr_fvs e fv_cand emptyVarSet
74 exprsSomeFreeVars :: InterestingVarFun -- Says which Vars are interesting
77 exprsSomeFreeVars fv_cand = foldr (unionVarSet . exprSomeFreeVars fv_cand) emptyVarSet
79 type InterestingVarFun = Var -> Bool -- True <=> interesting
84 type FV = InterestingVarFun
86 -> VarSet -- Free vars
88 union :: FV -> FV -> FV
89 union fv1 fv2 fv_cand in_scope = fv1 fv_cand in_scope `unionVarSet` fv2 fv_cand in_scope
92 noVars fv_cand in_scope = emptyVarSet
94 -- Comment about obselete code
95 -- We used to gather the free variables the RULES at a variable occurrence
96 -- with the following cryptic comment:
97 -- "At a variable occurrence, add in any free variables of its rule rhss
98 -- Curiously, we gather the Id's free *type* variables from its binding
99 -- site, but its free *rule-rhs* variables from its usage sites. This
100 -- is a little weird. The reason is that the former is more efficient,
101 -- but the latter is more fine grained, and a makes a difference when
102 -- a variable mentions itself one of its own rule RHSs"
103 -- Not only is this "weird", but it's also pretty bad because it can make
104 -- a function seem more recursive than it is. Suppose
107 -- RULE g x = ...f...
108 -- Then f is not mentioned in its own RHS, and needn't be a loop breaker
109 -- (though g may be). But if we collect the rule fvs from g's occurrence,
110 -- it looks as if f mentions itself. (This bites in the eftInt/eftIntFB
111 -- code in GHC.Enum.)
113 -- Anyway, it seems plain wrong. The RULE is like an extra RHS for the
114 -- function, so its free variables belong at the definition site.
116 -- Deleted code looked like
117 -- foldVarSet add_rule_var var_itself_set (idRuleVars var)
118 -- add_rule_var var set | keep_it fv_cand in_scope var = extendVarSet set var
123 oneVar var fv_cand in_scope
125 if keep_it fv_cand in_scope var
129 someVars :: VarSet -> FV
130 someVars vars fv_cand in_scope
131 = filterVarSet (keep_it fv_cand in_scope) vars
133 keep_it fv_cand in_scope var
134 | var `elemVarSet` in_scope = False
139 addBndr :: CoreBndr -> FV -> FV
140 addBndr bndr fv fv_cand in_scope
141 = someVars (varTypeTyVars bndr) fv_cand in_scope
142 -- Include type varibles in the binder's type
143 -- (not just Ids; coercion variables too!)
144 `unionVarSet` fv fv_cand (in_scope `extendVarSet` bndr)
146 addBndrs :: [CoreBndr] -> FV -> FV
147 addBndrs bndrs fv = foldr addBndr fv bndrs
152 expr_fvs :: CoreExpr -> FV
154 expr_fvs (Type ty) = someVars (tyVarsOfType ty)
155 expr_fvs (Var var) = oneVar var
156 expr_fvs (Lit lit) = noVars
157 expr_fvs (Note _ expr) = expr_fvs expr
158 expr_fvs (App fun arg) = expr_fvs fun `union` expr_fvs arg
159 expr_fvs (Lam bndr body) = addBndr bndr (expr_fvs body)
160 expr_fvs (Cast expr co) = expr_fvs expr `union` someVars (tyVarsOfType co)
162 expr_fvs (Case scrut bndr ty alts)
163 = expr_fvs scrut `union` someVars (tyVarsOfType ty) `union` addBndr bndr
164 (foldr (union . alt_fvs) noVars alts)
166 alt_fvs (con, bndrs, rhs) = addBndrs bndrs (expr_fvs rhs)
168 expr_fvs (Let (NonRec bndr rhs) body)
169 = rhs_fvs (bndr, rhs) `union` addBndr bndr (expr_fvs body)
171 expr_fvs (Let (Rec pairs) body)
172 = addBndrs (map fst pairs)
173 (foldr (union . rhs_fvs) (expr_fvs body) pairs)
176 rhs_fvs (bndr, rhs) = expr_fvs rhs `union` someVars (idRuleVars bndr)
177 -- Treat any RULES as extra RHSs of the binding
180 exprs_fvs exprs = foldr (union . expr_fvs) noVars exprs
184 %************************************************************************
188 %************************************************************************
190 exprFreeNames finds the free *external* *names* of an expression, notably
191 including the names of type constructors (which of course do not show
192 up in exprFreeVars). Similarly ruleLhsFreeNames. The latter is used
193 when deciding whether a rule is an orphan. In particular, suppose that
194 T is defined in this module; we want to avoid declaring that a rule like
195 fromIntegral T = fromIntegral_T
196 is an orphan. Of course it isn't, an declaring it an orphan would
197 make the whole module an orphan module, which is bad.
199 There's no need to delete local binders, because they will all
203 ruleLhsFreeNames :: CoreRule -> NameSet
204 ruleLhsFreeNames (BuiltinRule { ru_fn = fn }) = unitNameSet fn
205 ruleLhsFreeNames (Rule { ru_fn = fn, ru_bndrs = tpl_vars, ru_args = tpl_args })
206 = addOneToNameSet (exprsFreeNames tpl_args) fn
208 exprFreeNames :: CoreExpr -> NameSet
209 -- Find the free *external* names of an expression
214 | isExternalName n = unitNameSet n
215 | otherwise = emptyNameSet
217 go (Lit _) = emptyNameSet
218 go (Type ty) = tyClsNamesOfType ty -- Don't need free tyvars
219 go (App e1 e2) = go e1 `unionNameSets` go e2
220 go (Lam v e) = go e `delFromNameSet` idName v
222 go (Cast e co) = go e `unionNameSets` tyClsNamesOfType co
223 go (Let (NonRec b r) e) = go e `unionNameSets` go r
224 go (Let (Rec prs) e) = exprsFreeNames (map snd prs) `unionNameSets` go e
225 go (Case e b ty as) = go e `unionNameSets` tyClsNamesOfType ty
226 `unionNameSets` unionManyNameSets (map go_alt as)
228 go_alt (_,_,r) = go r
230 exprsFreeNames es = foldr (unionNameSets . exprFreeNames) emptyNameSet es
233 %************************************************************************
235 \section[freevars-everywhere]{Attaching free variables to every sub-expression}
237 %************************************************************************
241 ruleRhsFreeVars :: CoreRule -> VarSet
242 ruleRhsFreeVars (BuiltinRule {}) = noFVs
243 ruleRhsFreeVars (Rule { ru_fn = fn, ru_bndrs = bndrs, ru_rhs = rhs })
246 -- Don't include the Id in its own rhs free-var set.
247 -- Otherwise the occurrence analyser makes bindings recursive
248 -- that shoudn't be. E.g.
249 -- RULE: f (f x y) z ==> f x (f y z)
251 fvs = addBndrs bndrs (expr_fvs rhs) isLocalVar emptyVarSet
253 rulesRhsFreeVars :: [CoreRule] -> VarSet
254 rulesRhsFreeVars rules
255 = foldr (unionVarSet . ruleRhsFreeVars) emptyVarSet rules
257 ruleLhsFreeIds :: CoreRule -> VarSet
258 -- This finds all locally-defined free Ids on the LHS of the rule
259 ruleLhsFreeIds (BuiltinRule {}) = noFVs
260 ruleLhsFreeIds (Rule { ru_bndrs = bndrs, ru_args = args })
261 = addBndrs bndrs (exprs_fvs args) isLocalId emptyVarSet
265 %************************************************************************
267 \section[freevars-everywhere]{Attaching free variables to every sub-expression}
269 %************************************************************************
271 The free variable pass annotates every node in the expression with its
272 NON-GLOBAL free variables and type variables.
275 type CoreBindWithFVs = AnnBind Id VarSet
276 type CoreExprWithFVs = AnnExpr Id VarSet
277 -- Every node annotated with its free variables,
278 -- both Ids and TyVars
280 freeVarsOf :: CoreExprWithFVs -> IdSet
281 freeVarsOf (free_vars, _) = free_vars
284 aFreeVar = unitVarSet
285 unionFVs = unionVarSet
287 delBindersFV :: [Var] -> VarSet -> VarSet
288 delBindersFV bs fvs = foldr delBinderFV fvs bs
290 delBinderFV :: Var -> VarSet -> VarSet
291 -- This way round, so we can do it multiple times using foldr
293 -- (b `delBinderFV` s) removes the binder b from the free variable set s,
295 -- (a) the free variables of b's type
296 -- (b) the idSpecVars of b
298 -- This is really important for some lambdas:
299 -- In (\x::a -> x) the only mention of "a" is in the binder.
302 -- let x::a = b in ...
303 -- we should really note that "a" is free in this expression.
304 -- It'll be pinned inside the /\a by the binding for b, but
305 -- it seems cleaner to make sure that a is in the free-var set
306 -- when it is mentioned.
308 -- This also shows up in recursive bindings. Consider:
309 -- /\a -> letrec x::a = x in E
310 -- Now, there are no explicit free type variables in the RHS of x,
311 -- but nevertheless "a" is free in its definition. So we add in
312 -- the free tyvars of the types of the binders, and include these in the
313 -- free vars of the group, attached to the top level of each RHS.
315 -- This actually happened in the defn of errorIO in IOBase.lhs:
316 -- errorIO (ST io) = case (errorIO# io) of
319 -- bottom = bottom -- Never evaluated
321 delBinderFV b s = (s `delVarSet` b) `unionFVs` varTypeTyVars b
322 -- Include coercion variables too!
324 varTypeTyVars :: Var -> TyVarSet
325 -- Find the type variables free in the type of the variable
326 -- Remember, coercion variables can mention type variables...
328 | isLocalId var || isCoVar var = tyVarsOfType (idType var)
329 | otherwise = emptyVarSet -- Global Ids and non-coercion TyVars
331 idFreeVars :: Id -> VarSet
332 idFreeVars id = ASSERT( isId id) idRuleVars id `unionVarSet` varTypeTyVars id
334 idRuleVars ::Id -> VarSet
335 idRuleVars id = ASSERT( isId id) specInfoFreeVars (idSpecialisation id)
339 %************************************************************************
341 \subsection{Free variables (and types)}
343 %************************************************************************
346 freeVars :: CoreExpr -> CoreExprWithFVs
351 -- ToDo: insert motivating example for why we *need*
352 -- to include the idSpecVars in the FV list.
353 -- Actually [June 98] I don't think it's necessary
354 -- fvs = fvs_v `unionVarSet` idSpecVars v
356 fvs | isLocalVar v = aFreeVar v
359 freeVars (Lit lit) = (noFVs, AnnLit lit)
360 freeVars (Lam b body)
361 = (b `delBinderFV` freeVarsOf body', AnnLam b body')
363 body' = freeVars body
365 freeVars (App fun arg)
366 = (freeVarsOf fun2 `unionFVs` freeVarsOf arg2, AnnApp fun2 arg2)
371 freeVars (Case scrut bndr ty alts)
372 = ((bndr `delBinderFV` alts_fvs) `unionFVs` freeVarsOf scrut2 `unionFVs` tyVarsOfType ty,
373 AnnCase scrut2 bndr ty alts2)
375 scrut2 = freeVars scrut
377 (alts_fvs_s, alts2) = mapAndUnzip fv_alt alts
378 alts_fvs = foldr1 unionFVs alts_fvs_s
380 fv_alt (con,args,rhs) = (delBindersFV args (freeVarsOf rhs2),
385 freeVars (Let (NonRec binder rhs) body)
386 = (freeVarsOf rhs2 `unionFVs` body_fvs `unionFVs` idRuleVars binder,
387 -- Remember any rules; cf rhs_fvs above
388 AnnLet (AnnNonRec binder rhs2) body2)
391 body2 = freeVars body
392 body_fvs = binder `delBinderFV` freeVarsOf body2
394 freeVars (Let (Rec binds) body)
395 = (delBindersFV binders all_fvs,
396 AnnLet (AnnRec (binders `zip` rhss2)) body2)
398 (binders, rhss) = unzip binds
400 rhss2 = map freeVars rhss
401 rhs_body_fvs = foldr (unionFVs . freeVarsOf) body_fvs rhss2
402 all_fvs = foldr (unionFVs . idRuleVars) rhs_body_fvs binders
403 -- The "delBinderFV" happens after adding the idSpecVars,
404 -- since the latter may add some of the binders as fvs
406 body2 = freeVars body
407 body_fvs = freeVarsOf body2
410 freeVars (Cast expr co)
411 = (freeVarsOf expr2 `unionFVs` cfvs, AnnCast expr2 co)
413 expr2 = freeVars expr
414 cfvs = tyVarsOfType co
416 freeVars (Note other_note expr)
417 = (freeVarsOf expr2, AnnNote other_note expr2)
419 expr2 = freeVars expr
421 freeVars (Type ty) = (tyVarsOfType ty, AnnType ty)