1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 // This implements the dead-code warning pass. It follows middle::reachable
12 // closely. The idea is that all reachable symbols are live, codes called
13 // from live codes are live, and everything else is dead.
16 use hir::{self, PatKind};
17 use hir::intravisit::{self, Visitor, NestedVisitorMap};
18 use hir::itemlikevisit::ItemLikeVisitor;
21 use hir::CodegenFnAttrFlags;
22 use hir::def_id::{DefId, LOCAL_CRATE};
25 use ty::{self, TyCtxt};
26 use util::nodemap::FxHashSet;
28 use syntax::{ast, source_map};
32 // Any local node that may call something in its body block should be
33 // explored. For example, if it's a live Node::Item that is a
34 // function, then we should explore its block to check for codes that
35 // may need to be marked as live.
36 fn should_explore<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
37 node_id: ast::NodeId) -> bool {
38 match tcx.hir.find(node_id) {
39 Some(Node::Item(..)) |
40 Some(Node::ImplItem(..)) |
41 Some(Node::ForeignItem(..)) |
42 Some(Node::TraitItem(..)) =>
49 struct MarkSymbolVisitor<'a, 'tcx: 'a> {
50 worklist: Vec<ast::NodeId>,
51 tcx: TyCtxt<'a, 'tcx, 'tcx>,
52 tables: &'a ty::TypeckTables<'tcx>,
53 live_symbols: FxHashSet<ast::NodeId>,
54 repr_has_repr_c: bool,
56 inherited_pub_visibility: bool,
57 ignore_variant_stack: Vec<DefId>,
60 impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
61 fn check_def_id(&mut self, def_id: DefId) {
62 if let Some(node_id) = self.tcx.hir.as_local_node_id(def_id) {
63 if should_explore(self.tcx, node_id) {
64 self.worklist.push(node_id);
66 self.live_symbols.insert(node_id);
70 fn insert_def_id(&mut self, def_id: DefId) {
71 if let Some(node_id) = self.tcx.hir.as_local_node_id(def_id) {
72 debug_assert!(!should_explore(self.tcx, node_id));
73 self.live_symbols.insert(node_id);
77 fn handle_definition(&mut self, def: Def) {
79 Def::Const(_) | Def::AssociatedConst(..) | Def::TyAlias(_) => {
80 self.check_def_id(def.def_id());
82 _ if self.in_pat => (),
83 Def::PrimTy(..) | Def::SelfTy(..) | Def::SelfCtor(..) |
84 Def::Local(..) | Def::Upvar(..) => {}
85 Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
86 if let Some(enum_id) = self.tcx.parent_def_id(variant_id) {
87 self.check_def_id(enum_id);
89 if !self.ignore_variant_stack.contains(&variant_id) {
90 self.check_def_id(variant_id);
94 self.check_def_id(def.def_id());
99 fn lookup_and_handle_method(&mut self, id: hir::HirId) {
100 if let Some(def) = self.tables.type_dependent_defs().get(id) {
101 self.check_def_id(def.def_id());
103 bug!("no type-dependent def for method");
107 fn handle_field_access(&mut self, lhs: &hir::Expr, node_id: ast::NodeId) {
108 match self.tables.expr_ty_adjusted(lhs).sty {
110 let index = self.tcx.field_index(node_id, self.tables);
111 self.insert_def_id(def.non_enum_variant().fields[index].did);
114 _ => span_bug!(lhs.span, "named field access on non-ADT"),
118 fn handle_field_pattern_match(&mut self, lhs: &hir::Pat, def: Def,
119 pats: &[source_map::Spanned<hir::FieldPat>]) {
120 let variant = match self.tables.node_id_to_type(lhs.hir_id).sty {
121 ty::Adt(adt, _) => adt.variant_of_def(def),
122 _ => span_bug!(lhs.span, "non-ADT in struct pattern")
125 if let PatKind::Wild = pat.node.pat.node {
128 let index = self.tcx.field_index(pat.node.id, self.tables);
129 self.insert_def_id(variant.fields[index].did);
133 fn mark_live_symbols(&mut self) {
134 let mut scanned = FxHashSet::default();
135 while let Some(id) = self.worklist.pop() {
136 if !scanned.insert(id) {
140 if let Some(ref node) = self.tcx.hir.find(id) {
141 self.live_symbols.insert(id);
142 self.visit_node(node);
147 fn visit_node(&mut self, node: &Node<'tcx>) {
148 let had_repr_c = self.repr_has_repr_c;
149 self.repr_has_repr_c = false;
150 let had_inherited_pub_visibility = self.inherited_pub_visibility;
151 self.inherited_pub_visibility = false;
153 Node::Item(item) => {
155 hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) => {
156 let def_id = self.tcx.hir.local_def_id(item.id);
157 let def = self.tcx.adt_def(def_id);
158 self.repr_has_repr_c = def.repr.c();
160 intravisit::walk_item(self, &item);
162 hir::ItemKind::Enum(..) => {
163 self.inherited_pub_visibility = item.vis.node.is_pub();
164 intravisit::walk_item(self, &item);
166 hir::ItemKind::Fn(..)
167 | hir::ItemKind::Ty(..)
168 | hir::ItemKind::Static(..)
169 | hir::ItemKind::Existential(..)
170 | hir::ItemKind::Const(..) => {
171 intravisit::walk_item(self, &item);
176 Node::TraitItem(trait_item) => {
177 intravisit::walk_trait_item(self, trait_item);
179 Node::ImplItem(impl_item) => {
180 intravisit::walk_impl_item(self, impl_item);
182 Node::ForeignItem(foreign_item) => {
183 intravisit::walk_foreign_item(self, &foreign_item);
187 self.repr_has_repr_c = had_repr_c;
188 self.inherited_pub_visibility = had_inherited_pub_visibility;
191 fn mark_as_used_if_union(&mut self, adt: &ty::AdtDef, fields: &hir::HirVec<hir::Field>) {
192 if adt.is_union() && adt.non_enum_variant().fields.len() > 1 && adt.did.is_local() {
193 for field in fields {
194 let index = self.tcx.field_index(field.id, self.tables);
195 self.insert_def_id(adt.non_enum_variant().fields[index].did);
201 impl<'a, 'tcx> Visitor<'tcx> for MarkSymbolVisitor<'a, 'tcx> {
202 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
203 NestedVisitorMap::None
206 fn visit_nested_body(&mut self, body: hir::BodyId) {
207 let old_tables = self.tables;
208 self.tables = self.tcx.body_tables(body);
209 let body = self.tcx.hir.body(body);
210 self.visit_body(body);
211 self.tables = old_tables;
214 fn visit_variant_data(&mut self, def: &'tcx hir::VariantData, _: ast::Name,
215 _: &hir::Generics, _: ast::NodeId, _: syntax_pos::Span) {
216 let has_repr_c = self.repr_has_repr_c;
217 let inherited_pub_visibility = self.inherited_pub_visibility;
218 let live_fields = def.fields().iter().filter(|f| {
219 has_repr_c || inherited_pub_visibility || f.vis.node.is_pub()
221 self.live_symbols.extend(live_fields.map(|f| f.id));
223 intravisit::walk_struct_def(self, def);
226 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
228 hir::ExprKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
229 let def = self.tables.qpath_def(qpath, expr.hir_id);
230 self.handle_definition(def);
232 hir::ExprKind::MethodCall(..) => {
233 self.lookup_and_handle_method(expr.hir_id);
235 hir::ExprKind::Field(ref lhs, ..) => {
236 self.handle_field_access(&lhs, expr.id);
238 hir::ExprKind::Struct(_, ref fields, _) => {
239 if let ty::Adt(ref adt, _) = self.tables.expr_ty(expr).sty {
240 self.mark_as_used_if_union(adt, fields);
246 intravisit::walk_expr(self, expr);
249 fn visit_arm(&mut self, arm: &'tcx hir::Arm) {
250 if arm.pats.len() == 1 {
251 let variants = arm.pats[0].necessary_variants();
253 // Inside the body, ignore constructions of variants
254 // necessary for the pattern to match. Those construction sites
255 // can't be reached unless the variant is constructed elsewhere.
256 let len = self.ignore_variant_stack.len();
257 self.ignore_variant_stack.extend_from_slice(&variants);
258 intravisit::walk_arm(self, arm);
259 self.ignore_variant_stack.truncate(len);
261 intravisit::walk_arm(self, arm);
265 fn visit_pat(&mut self, pat: &'tcx hir::Pat) {
267 PatKind::Struct(hir::QPath::Resolved(_, ref path), ref fields, _) => {
268 self.handle_field_pattern_match(pat, path.def, fields);
270 PatKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
271 let def = self.tables.qpath_def(qpath, pat.hir_id);
272 self.handle_definition(def);
278 intravisit::walk_pat(self, pat);
282 fn visit_path(&mut self, path: &'tcx hir::Path, _: hir::HirId) {
283 self.handle_definition(path.def);
284 intravisit::walk_path(self, path);
288 fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt<'_, '_, '_>,
290 attrs: &[ast::Attribute]) -> bool {
291 if attr::contains_name(attrs, "lang") {
295 // Stable attribute for #[lang = "panic_impl"]
296 if attr::contains_name(attrs, "panic_handler") {
300 // (To be) stable attribute for #[lang = "oom"]
301 if attr::contains_name(attrs, "alloc_error_handler") {
305 // Don't lint about global allocators
306 if attr::contains_name(attrs, "global_allocator") {
310 let def_id = tcx.hir.local_def_id(id);
311 let cg_attrs = tcx.codegen_fn_attrs(def_id);
313 // #[used], #[no_mangle], #[export_name], etc also keeps the item alive
314 // forcefully, e.g. for placing it in a specific section.
315 if cg_attrs.contains_extern_indicator() ||
316 cg_attrs.flags.contains(CodegenFnAttrFlags::USED) {
320 tcx.lint_level_at_node(lint::builtin::DEAD_CODE, id).0 == lint::Allow
323 // This visitor seeds items that
324 // 1) We want to explicitly consider as live:
325 // * Item annotated with #[allow(dead_code)]
326 // - This is done so that if we want to suppress warnings for a
327 // group of dead functions, we only have to annotate the "root".
328 // For example, if both `f` and `g` are dead and `f` calls `g`,
329 // then annotating `f` with `#[allow(dead_code)]` will suppress
330 // warning for both `f` and `g`.
331 // * Item annotated with #[lang=".."]
332 // - This is because lang items are always callable from elsewhere.
334 // 2) We are not sure to be live or not
335 // * Implementation of a trait method
336 struct LifeSeeder<'k, 'tcx: 'k> {
337 worklist: Vec<ast::NodeId>,
338 krate: &'k hir::Crate,
339 tcx: TyCtxt<'k, 'tcx, 'tcx>,
342 impl<'v, 'k, 'tcx> ItemLikeVisitor<'v> for LifeSeeder<'k, 'tcx> {
343 fn visit_item(&mut self, item: &hir::Item) {
344 let allow_dead_code = has_allow_dead_code_or_lang_attr(self.tcx,
348 self.worklist.push(item.id);
351 hir::ItemKind::Enum(ref enum_def, _) if allow_dead_code => {
352 self.worklist.extend(enum_def.variants.iter()
353 .map(|variant| variant.node.data.id()));
355 hir::ItemKind::Trait(.., ref trait_item_refs) => {
356 for trait_item_ref in trait_item_refs {
357 let trait_item = self.krate.trait_item(trait_item_ref.id);
358 match trait_item.node {
359 hir::TraitItemKind::Const(_, Some(_)) |
360 hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(_)) => {
361 if has_allow_dead_code_or_lang_attr(self.tcx,
364 self.worklist.push(trait_item.id);
371 hir::ItemKind::Impl(.., ref opt_trait, _, ref impl_item_refs) => {
372 for impl_item_ref in impl_item_refs {
373 let impl_item = self.krate.impl_item(impl_item_ref.id);
374 if opt_trait.is_some() ||
375 has_allow_dead_code_or_lang_attr(self.tcx,
378 self.worklist.push(impl_item_ref.id.node_id);
386 fn visit_trait_item(&mut self, _item: &hir::TraitItem) {
387 // ignore: we are handling this in `visit_item` above
390 fn visit_impl_item(&mut self, _item: &hir::ImplItem) {
391 // ignore: we are handling this in `visit_item` above
395 fn create_and_seed_worklist<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
396 access_levels: &privacy::AccessLevels,
400 let worklist = access_levels.map.iter().filter_map(|(&id, level)| {
401 if level >= &privacy::AccessLevel::Reachable {
408 tcx.sess.entry_fn.borrow().map(|(id, _, _)| id)
409 ).collect::<Vec<_>>();
411 // Seed implemented trait items
412 let mut life_seeder = LifeSeeder {
417 krate.visit_all_item_likes(&mut life_seeder);
419 return life_seeder.worklist;
422 fn find_live<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
423 access_levels: &privacy::AccessLevels,
425 -> FxHashSet<ast::NodeId> {
426 let worklist = create_and_seed_worklist(tcx, access_levels, krate);
427 let mut symbol_visitor = MarkSymbolVisitor {
430 tables: &ty::TypeckTables::empty(None),
431 live_symbols: Default::default(),
432 repr_has_repr_c: false,
434 inherited_pub_visibility: false,
435 ignore_variant_stack: vec![],
437 symbol_visitor.mark_live_symbols();
438 symbol_visitor.live_symbols
441 fn get_struct_ctor_id(item: &hir::Item) -> Option<ast::NodeId> {
443 hir::ItemKind::Struct(ref struct_def, _) if !struct_def.is_struct() => {
444 Some(struct_def.id())
450 struct DeadVisitor<'a, 'tcx: 'a> {
451 tcx: TyCtxt<'a, 'tcx, 'tcx>,
452 live_symbols: FxHashSet<ast::NodeId>,
455 impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
456 fn should_warn_about_item(&mut self, item: &hir::Item) -> bool {
457 let should_warn = match item.node {
458 hir::ItemKind::Static(..)
459 | hir::ItemKind::Const(..)
460 | hir::ItemKind::Fn(..)
461 | hir::ItemKind::Ty(..)
462 | hir::ItemKind::Enum(..)
463 | hir::ItemKind::Struct(..)
464 | hir::ItemKind::Union(..) => true,
467 let ctor_id = get_struct_ctor_id(item);
468 should_warn && !self.symbol_is_live(item.id, ctor_id)
471 fn should_warn_about_field(&mut self, field: &hir::StructField) -> bool {
472 let field_type = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
473 !field.is_positional()
474 && !self.symbol_is_live(field.id, None)
475 && !field_type.is_phantom_data()
476 && !has_allow_dead_code_or_lang_attr(self.tcx, field.id, &field.attrs)
479 fn should_warn_about_variant(&mut self, variant: &hir::VariantKind) -> bool {
480 !self.symbol_is_live(variant.data.id(), None)
481 && !has_allow_dead_code_or_lang_attr(self.tcx,
486 fn should_warn_about_foreign_item(&mut self, fi: &hir::ForeignItem) -> bool {
487 !self.symbol_is_live(fi.id, None)
488 && !has_allow_dead_code_or_lang_attr(self.tcx, fi.id, &fi.attrs)
491 // id := node id of an item's definition.
492 // ctor_id := `Some` if the item is a struct_ctor (tuple struct),
494 // If the item is a struct_ctor, then either its `id` or
495 // `ctor_id` (unwrapped) is in the live_symbols set. More specifically,
496 // DefMap maps the ExprKind::Path of a struct_ctor to the node referred by
497 // `ctor_id`. On the other hand, in a statement like
498 // `type <ident> <generics> = <ty>;` where <ty> refers to a struct_ctor,
499 // DefMap maps <ty> to `id` instead.
500 fn symbol_is_live(&mut self,
502 ctor_id: Option<ast::NodeId>)
504 if self.live_symbols.contains(&id)
505 || ctor_id.map_or(false, |ctor| self.live_symbols.contains(&ctor))
509 // If it's a type whose items are live, then it's live, too.
510 // This is done to handle the case where, for example, the static
511 // method of a private type is used, but the type itself is never
513 let def_id = self.tcx.hir.local_def_id(id);
514 let inherent_impls = self.tcx.inherent_impls(def_id);
515 for &impl_did in inherent_impls.iter() {
516 for &item_did in &self.tcx.associated_item_def_ids(impl_did)[..] {
517 if let Some(item_node_id) = self.tcx.hir.as_local_node_id(item_did) {
518 if self.live_symbols.contains(&item_node_id) {
527 fn warn_dead_code(&mut self,
529 span: syntax_pos::Span,
533 if !name.as_str().starts_with("_") {
535 .lint_node(lint::builtin::DEAD_CODE,
538 &format!("{} is never {}: `{}`",
539 node_type, participle, name));
544 impl<'a, 'tcx> Visitor<'tcx> for DeadVisitor<'a, 'tcx> {
545 /// Walk nested items in place so that we don't report dead-code
546 /// on inner functions when the outer function is already getting
547 /// an error. We could do this also by checking the parents, but
548 /// this is how the code is setup and it seems harmless enough.
549 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
550 NestedVisitorMap::All(&self.tcx.hir)
553 fn visit_item(&mut self, item: &'tcx hir::Item) {
554 if self.should_warn_about_item(item) {
555 // For items that have a definition with a signature followed by a
556 // block, point only at the signature.
557 let span = match item.node {
558 hir::ItemKind::Fn(..) |
559 hir::ItemKind::Mod(..) |
560 hir::ItemKind::Enum(..) |
561 hir::ItemKind::Struct(..) |
562 hir::ItemKind::Union(..) |
563 hir::ItemKind::Trait(..) |
564 hir::ItemKind::Impl(..) => self.tcx.sess.source_map().def_span(item.span),
567 let participle = match item.node {
568 hir::ItemKind::Struct(..) => "constructed", // Issue #52325
575 item.node.descriptive_variant(),
579 // Only continue if we didn't warn
580 intravisit::walk_item(self, item);
584 fn visit_variant(&mut self,
585 variant: &'tcx hir::Variant,
586 g: &'tcx hir::Generics,
588 if self.should_warn_about_variant(&variant.node) {
589 self.warn_dead_code(variant.node.data.id(), variant.span, variant.node.name,
590 "variant", "constructed");
592 intravisit::walk_variant(self, variant, g, id);
596 fn visit_foreign_item(&mut self, fi: &'tcx hir::ForeignItem) {
597 if self.should_warn_about_foreign_item(fi) {
598 self.warn_dead_code(fi.id, fi.span, fi.name,
599 fi.node.descriptive_variant(), "used");
601 intravisit::walk_foreign_item(self, fi);
604 fn visit_struct_field(&mut self, field: &'tcx hir::StructField) {
605 if self.should_warn_about_field(&field) {
606 self.warn_dead_code(field.id, field.span, field.ident.name, "field", "used");
608 intravisit::walk_struct_field(self, field);
611 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
612 match impl_item.node {
613 hir::ImplItemKind::Const(_, body_id) => {
614 if !self.symbol_is_live(impl_item.id, None) {
615 self.warn_dead_code(impl_item.id,
617 impl_item.ident.name,
621 self.visit_nested_body(body_id)
623 hir::ImplItemKind::Method(_, body_id) => {
624 if !self.symbol_is_live(impl_item.id, None) {
625 let span = self.tcx.sess.source_map().def_span(impl_item.span);
626 self.warn_dead_code(impl_item.id, span, impl_item.ident.name, "method", "used");
628 self.visit_nested_body(body_id)
630 hir::ImplItemKind::Existential(..) |
631 hir::ImplItemKind::Type(..) => {}
635 // Overwrite so that we don't warn the trait item itself.
636 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
637 match trait_item.node {
638 hir::TraitItemKind::Const(_, Some(body_id)) |
639 hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(body_id)) => {
640 self.visit_nested_body(body_id)
642 hir::TraitItemKind::Const(_, None) |
643 hir::TraitItemKind::Method(_, hir::TraitMethod::Required(_)) |
644 hir::TraitItemKind::Type(..) => {}
649 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
650 let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
651 let krate = tcx.hir.krate();
652 let live_symbols = find_live(tcx, access_levels, krate);
653 let mut visitor = DeadVisitor {
657 intravisit::walk_crate(&mut visitor, krate);