1 // This implements the dead-code warning pass. It follows middle::reachable
2 // closely. The idea is that all reachable symbols are live, codes called
3 // from live codes are live, and everything else is dead.
6 use crate::hir::{self, PatKind, TyKind};
7 use crate::hir::intravisit::{self, Visitor, NestedVisitorMap};
8 use crate::hir::itemlikevisit::ItemLikeVisitor;
10 use crate::hir::def::{CtorOf, Def};
11 use crate::hir::CodegenFnAttrFlags;
12 use crate::hir::def_id::{DefId, LOCAL_CRATE};
14 use crate::middle::privacy;
15 use crate::ty::{self, DefIdTree, TyCtxt};
16 use crate::util::nodemap::FxHashSet;
18 use rustc_data_structures::fx::FxHashMap;
20 use syntax::{ast, source_map};
24 // Any local node that may call something in its body block should be
25 // explored. For example, if it's a live Node::Item that is a
26 // function, then we should explore its block to check for codes that
27 // may need to be marked as live.
28 fn should_explore<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
29 hir_id: hir::HirId) -> bool {
30 match tcx.hir().find_by_hir_id(hir_id) {
31 Some(Node::Item(..)) |
32 Some(Node::ImplItem(..)) |
33 Some(Node::ForeignItem(..)) |
34 Some(Node::TraitItem(..)) =>
41 struct MarkSymbolVisitor<'a, 'tcx: 'a> {
42 worklist: Vec<hir::HirId>,
43 tcx: TyCtxt<'a, 'tcx, 'tcx>,
44 tables: &'a ty::TypeckTables<'tcx>,
45 live_symbols: FxHashSet<hir::HirId>,
46 repr_has_repr_c: bool,
48 inherited_pub_visibility: bool,
49 ignore_variant_stack: Vec<DefId>,
50 // maps from tuple struct constructors to tuple struct items
51 struct_constructors: FxHashMap<hir::HirId, hir::HirId>,
54 impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
55 fn check_def_id(&mut self, def_id: DefId) {
56 if let Some(hir_id) = self.tcx.hir().as_local_hir_id(def_id) {
57 if should_explore(self.tcx, hir_id) || self.struct_constructors.contains_key(&hir_id) {
58 self.worklist.push(hir_id);
60 self.live_symbols.insert(hir_id);
64 fn insert_def_id(&mut self, def_id: DefId) {
65 if let Some(hir_id) = self.tcx.hir().as_local_hir_id(def_id) {
66 debug_assert!(!should_explore(self.tcx, hir_id));
67 self.live_symbols.insert(hir_id);
71 fn handle_definition(&mut self, def: Def) {
73 Def::Const(_) | Def::AssociatedConst(..) | Def::TyAlias(_) => {
74 self.check_def_id(def.def_id());
76 _ if self.in_pat => {},
77 Def::PrimTy(..) | Def::SelfTy(..) | Def::SelfCtor(..) |
78 Def::Local(..) | Def::Upvar(..) => {}
79 Def::Ctor(ctor_def_id, CtorOf::Variant, ..) => {
80 let variant_id = self.tcx.parent(ctor_def_id).unwrap();
81 let enum_id = self.tcx.parent(variant_id).unwrap();
82 self.check_def_id(enum_id);
83 if !self.ignore_variant_stack.contains(&ctor_def_id) {
84 self.check_def_id(variant_id);
87 Def::Variant(variant_id) => {
88 let enum_id = self.tcx.parent(variant_id).unwrap();
89 self.check_def_id(enum_id);
90 if !self.ignore_variant_stack.contains(&variant_id) {
91 self.check_def_id(variant_id);
94 Def::ToolMod | Def::NonMacroAttr(..) | Def::Err => {}
96 self.check_def_id(def.def_id());
101 fn lookup_and_handle_method(&mut self, id: hir::HirId) {
102 if let Some(def_id) = self.tables.type_dependent_def_id(id) {
103 self.check_def_id(def_id);
105 bug!("no type-dependent def for method");
109 fn handle_field_access(&mut self, lhs: &hir::Expr, hir_id: hir::HirId) {
110 match self.tables.expr_ty_adjusted(lhs).sty {
112 let index = self.tcx.field_index(hir_id, self.tables);
113 self.insert_def_id(def.non_enum_variant().fields[index].did);
116 _ => span_bug!(lhs.span, "named field access on non-ADT"),
120 fn handle_field_pattern_match(&mut self, lhs: &hir::Pat, def: Def,
121 pats: &[source_map::Spanned<hir::FieldPat>]) {
122 let variant = match self.tables.node_type(lhs.hir_id).sty {
123 ty::Adt(adt, _) => adt.variant_of_def(def),
124 _ => span_bug!(lhs.span, "non-ADT in struct pattern")
127 if let PatKind::Wild = pat.node.pat.node {
130 let index = self.tcx.field_index(pat.node.hir_id, self.tables);
131 self.insert_def_id(variant.fields[index].did);
135 fn mark_live_symbols(&mut self) {
136 let mut scanned = FxHashSet::default();
137 while let Some(id) = self.worklist.pop() {
138 if !scanned.insert(id) {
142 // in the case of tuple struct constructors we want to check the item, not the generated
143 // tuple struct constructor function
144 let id = self.struct_constructors.get(&id).cloned().unwrap_or(id);
146 if let Some(node) = self.tcx.hir().find_by_hir_id(id) {
147 self.live_symbols.insert(id);
148 self.visit_node(node);
153 fn visit_node(&mut self, node: Node<'tcx>) {
154 let had_repr_c = self.repr_has_repr_c;
155 self.repr_has_repr_c = false;
156 let had_inherited_pub_visibility = self.inherited_pub_visibility;
157 self.inherited_pub_visibility = false;
159 Node::Item(item) => {
161 hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) => {
162 let def_id = self.tcx.hir().local_def_id_from_hir_id(item.hir_id);
163 let def = self.tcx.adt_def(def_id);
164 self.repr_has_repr_c = def.repr.c();
166 intravisit::walk_item(self, &item);
168 hir::ItemKind::Enum(..) => {
169 self.inherited_pub_visibility = item.vis.node.is_pub();
171 intravisit::walk_item(self, &item);
173 hir::ItemKind::ForeignMod(..) => {}
175 intravisit::walk_item(self, &item);
179 Node::TraitItem(trait_item) => {
180 intravisit::walk_trait_item(self, trait_item);
182 Node::ImplItem(impl_item) => {
183 intravisit::walk_impl_item(self, impl_item);
185 Node::ForeignItem(foreign_item) => {
186 intravisit::walk_foreign_item(self, &foreign_item);
190 self.repr_has_repr_c = had_repr_c;
191 self.inherited_pub_visibility = had_inherited_pub_visibility;
194 fn mark_as_used_if_union(&mut self, adt: &ty::AdtDef, fields: &hir::HirVec<hir::Field>) {
195 if adt.is_union() && adt.non_enum_variant().fields.len() > 1 && adt.did.is_local() {
196 for field in fields {
197 let index = self.tcx.field_index(field.hir_id, self.tables);
198 self.insert_def_id(adt.non_enum_variant().fields[index].did);
204 impl<'a, 'tcx> Visitor<'tcx> for MarkSymbolVisitor<'a, 'tcx> {
205 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
206 NestedVisitorMap::None
209 fn visit_nested_body(&mut self, body: hir::BodyId) {
210 let old_tables = self.tables;
211 self.tables = self.tcx.body_tables(body);
212 let body = self.tcx.hir().body(body);
213 self.visit_body(body);
214 self.tables = old_tables;
217 fn visit_variant_data(&mut self, def: &'tcx hir::VariantData, _: ast::Name,
218 _: &hir::Generics, _: hir::HirId, _: syntax_pos::Span) {
219 let has_repr_c = self.repr_has_repr_c;
220 let inherited_pub_visibility = self.inherited_pub_visibility;
221 let live_fields = def.fields().iter().filter(|f| {
222 has_repr_c || inherited_pub_visibility || f.vis.node.is_pub()
224 self.live_symbols.extend(live_fields.map(|f| f.hir_id));
226 intravisit::walk_struct_def(self, def);
229 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
231 hir::ExprKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
232 let def = self.tables.qpath_def(qpath, expr.hir_id);
233 self.handle_definition(def);
235 hir::ExprKind::MethodCall(..) => {
236 self.lookup_and_handle_method(expr.hir_id);
238 hir::ExprKind::Field(ref lhs, ..) => {
239 self.handle_field_access(&lhs, expr.hir_id);
241 hir::ExprKind::Struct(_, ref fields, _) => {
242 if let ty::Adt(ref adt, _) = self.tables.expr_ty(expr).sty {
243 self.mark_as_used_if_union(adt, fields);
249 intravisit::walk_expr(self, expr);
252 fn visit_arm(&mut self, arm: &'tcx hir::Arm) {
253 if arm.pats.len() == 1 {
254 let variants = arm.pats[0].necessary_variants();
256 // Inside the body, ignore constructions of variants
257 // necessary for the pattern to match. Those construction sites
258 // can't be reached unless the variant is constructed elsewhere.
259 let len = self.ignore_variant_stack.len();
260 self.ignore_variant_stack.extend_from_slice(&variants);
261 intravisit::walk_arm(self, arm);
262 self.ignore_variant_stack.truncate(len);
264 intravisit::walk_arm(self, arm);
268 fn visit_pat(&mut self, pat: &'tcx hir::Pat) {
270 PatKind::Struct(hir::QPath::Resolved(_, ref path), ref fields, _) => {
271 self.handle_field_pattern_match(pat, path.def, fields);
273 PatKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
274 let def = self.tables.qpath_def(qpath, pat.hir_id);
275 self.handle_definition(def);
281 intravisit::walk_pat(self, pat);
285 fn visit_path(&mut self, path: &'tcx hir::Path, _: hir::HirId) {
286 self.handle_definition(path.def);
287 intravisit::walk_path(self, path);
290 fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
292 TyKind::Def(item_id, _) => {
293 let item = self.tcx.hir().expect_item_by_hir_id(item_id.id);
294 intravisit::walk_item(self, item);
298 intravisit::walk_ty(self, ty);
302 fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt<'_, '_, '_>,
304 attrs: &[ast::Attribute]) -> bool {
305 if attr::contains_name(attrs, "lang") {
309 // Stable attribute for #[lang = "panic_impl"]
310 if attr::contains_name(attrs, "panic_handler") {
314 // (To be) stable attribute for #[lang = "oom"]
315 if attr::contains_name(attrs, "alloc_error_handler") {
319 // Don't lint about global allocators
320 if attr::contains_name(attrs, "global_allocator") {
324 let def_id = tcx.hir().local_def_id_from_hir_id(id);
325 let cg_attrs = tcx.codegen_fn_attrs(def_id);
327 // #[used], #[no_mangle], #[export_name], etc also keeps the item alive
328 // forcefully, e.g., for placing it in a specific section.
329 if cg_attrs.contains_extern_indicator() ||
330 cg_attrs.flags.contains(CodegenFnAttrFlags::USED) {
334 tcx.lint_level_at_node(lint::builtin::DEAD_CODE, id).0 == lint::Allow
337 // This visitor seeds items that
338 // 1) We want to explicitly consider as live:
339 // * Item annotated with #[allow(dead_code)]
340 // - This is done so that if we want to suppress warnings for a
341 // group of dead functions, we only have to annotate the "root".
342 // For example, if both `f` and `g` are dead and `f` calls `g`,
343 // then annotating `f` with `#[allow(dead_code)]` will suppress
344 // warning for both `f` and `g`.
345 // * Item annotated with #[lang=".."]
346 // - This is because lang items are always callable from elsewhere.
348 // 2) We are not sure to be live or not
349 // * Implementation of a trait method
350 struct LifeSeeder<'k, 'tcx: 'k> {
351 worklist: Vec<hir::HirId>,
352 krate: &'k hir::Crate,
353 tcx: TyCtxt<'k, 'tcx, 'tcx>,
354 // see `MarkSymbolVisitor::struct_constructors`
355 struct_constructors: FxHashMap<hir::HirId, hir::HirId>,
358 impl<'v, 'k, 'tcx> ItemLikeVisitor<'v> for LifeSeeder<'k, 'tcx> {
359 fn visit_item(&mut self, item: &hir::Item) {
360 let allow_dead_code = has_allow_dead_code_or_lang_attr(self.tcx,
364 self.worklist.push(item.hir_id);
367 hir::ItemKind::Enum(ref enum_def, _) => {
369 self.worklist.extend(enum_def.variants.iter().map(|variant| variant.node.id));
372 for variant in &enum_def.variants {
373 if let Some(ctor_hir_id) = variant.node.data.ctor_hir_id() {
374 self.struct_constructors.insert(ctor_hir_id, variant.node.id);
378 hir::ItemKind::Trait(.., ref trait_item_refs) => {
379 for trait_item_ref in trait_item_refs {
380 let trait_item = self.krate.trait_item(trait_item_ref.id);
381 match trait_item.node {
382 hir::TraitItemKind::Const(_, Some(_)) |
383 hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(_)) => {
384 if has_allow_dead_code_or_lang_attr(self.tcx,
387 self.worklist.push(trait_item.hir_id);
394 hir::ItemKind::Impl(.., ref opt_trait, _, ref impl_item_refs) => {
395 for impl_item_ref in impl_item_refs {
396 let impl_item = self.krate.impl_item(impl_item_ref.id);
397 if opt_trait.is_some() ||
398 has_allow_dead_code_or_lang_attr(self.tcx,
401 self.worklist.push(impl_item_ref.id.hir_id);
405 hir::ItemKind::Struct(ref variant_data, _) => {
406 if let Some(ctor_hir_id) = variant_data.ctor_hir_id() {
407 self.struct_constructors.insert(ctor_hir_id, item.hir_id);
414 fn visit_trait_item(&mut self, _item: &hir::TraitItem) {
415 // ignore: we are handling this in `visit_item` above
418 fn visit_impl_item(&mut self, _item: &hir::ImplItem) {
419 // ignore: we are handling this in `visit_item` above
423 fn create_and_seed_worklist<'a, 'tcx>(
424 tcx: TyCtxt<'a, 'tcx, 'tcx>,
425 access_levels: &privacy::AccessLevels,
427 ) -> (Vec<hir::HirId>, FxHashMap<hir::HirId, hir::HirId>) {
428 let worklist = access_levels.map.iter().filter_map(|(&id, level)| {
429 if level >= &privacy::AccessLevel::Reachable {
436 tcx.entry_fn(LOCAL_CRATE).map(|(def_id, _)| tcx.hir().as_local_hir_id(def_id).unwrap())
437 ).collect::<Vec<_>>();
439 // Seed implemented trait items
440 let mut life_seeder = LifeSeeder {
444 struct_constructors: Default::default(),
446 krate.visit_all_item_likes(&mut life_seeder);
448 (life_seeder.worklist, life_seeder.struct_constructors)
451 fn find_live<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
452 access_levels: &privacy::AccessLevels,
454 -> FxHashSet<hir::HirId> {
455 let (worklist, struct_constructors) = create_and_seed_worklist(tcx, access_levels, krate);
456 let mut symbol_visitor = MarkSymbolVisitor {
459 tables: &ty::TypeckTables::empty(None),
460 live_symbols: Default::default(),
461 repr_has_repr_c: false,
463 inherited_pub_visibility: false,
464 ignore_variant_stack: vec![],
467 symbol_visitor.mark_live_symbols();
468 symbol_visitor.live_symbols
471 struct DeadVisitor<'a, 'tcx: 'a> {
472 tcx: TyCtxt<'a, 'tcx, 'tcx>,
473 live_symbols: FxHashSet<hir::HirId>,
476 impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
477 fn should_warn_about_item(&mut self, item: &hir::Item) -> bool {
478 let should_warn = match item.node {
479 hir::ItemKind::Static(..)
480 | hir::ItemKind::Const(..)
481 | hir::ItemKind::Fn(..)
482 | hir::ItemKind::Ty(..)
483 | hir::ItemKind::Enum(..)
484 | hir::ItemKind::Struct(..)
485 | hir::ItemKind::Union(..) => true,
488 should_warn && !self.symbol_is_live(item.hir_id)
491 fn should_warn_about_field(&mut self, field: &hir::StructField) -> bool {
492 let field_type = self.tcx.type_of(self.tcx.hir().local_def_id_from_hir_id(field.hir_id));
493 !field.is_positional()
494 && !self.symbol_is_live(field.hir_id)
495 && !field_type.is_phantom_data()
496 && !has_allow_dead_code_or_lang_attr(self.tcx, field.hir_id, &field.attrs)
499 fn should_warn_about_variant(&mut self, variant: &hir::VariantKind) -> bool {
500 !self.symbol_is_live(variant.id)
501 && !has_allow_dead_code_or_lang_attr(self.tcx,
506 fn should_warn_about_foreign_item(&mut self, fi: &hir::ForeignItem) -> bool {
507 !self.symbol_is_live(fi.hir_id)
508 && !has_allow_dead_code_or_lang_attr(self.tcx, fi.hir_id, &fi.attrs)
511 // id := HIR id of an item's definition.
516 if self.live_symbols.contains(&id) {
519 // If it's a type whose items are live, then it's live, too.
520 // This is done to handle the case where, for example, the static
521 // method of a private type is used, but the type itself is never
523 let def_id = self.tcx.hir().local_def_id_from_hir_id(id);
524 let inherent_impls = self.tcx.inherent_impls(def_id);
525 for &impl_did in inherent_impls.iter() {
526 for &item_did in &self.tcx.associated_item_def_ids(impl_did)[..] {
527 if let Some(item_hir_id) = self.tcx.hir().as_local_hir_id(item_did) {
528 if self.live_symbols.contains(&item_hir_id) {
537 fn warn_dead_code(&mut self,
539 span: syntax_pos::Span,
543 if !name.as_str().starts_with("_") {
545 .lint_hir(lint::builtin::DEAD_CODE,
548 &format!("{} is never {}: `{}`",
549 node_type, participle, name));
554 impl<'a, 'tcx> Visitor<'tcx> for DeadVisitor<'a, 'tcx> {
555 /// Walk nested items in place so that we don't report dead-code
556 /// on inner functions when the outer function is already getting
557 /// an error. We could do this also by checking the parents, but
558 /// this is how the code is setup and it seems harmless enough.
559 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
560 NestedVisitorMap::All(&self.tcx.hir())
563 fn visit_item(&mut self, item: &'tcx hir::Item) {
564 if self.should_warn_about_item(item) {
565 // For items that have a definition with a signature followed by a
566 // block, point only at the signature.
567 let span = match item.node {
568 hir::ItemKind::Fn(..) |
569 hir::ItemKind::Mod(..) |
570 hir::ItemKind::Enum(..) |
571 hir::ItemKind::Struct(..) |
572 hir::ItemKind::Union(..) |
573 hir::ItemKind::Trait(..) |
574 hir::ItemKind::Impl(..) => self.tcx.sess.source_map().def_span(item.span),
577 let participle = match item.node {
578 hir::ItemKind::Struct(..) => "constructed", // Issue #52325
585 item.node.descriptive_variant(),
589 // Only continue if we didn't warn
590 intravisit::walk_item(self, item);
594 fn visit_variant(&mut self,
595 variant: &'tcx hir::Variant,
596 g: &'tcx hir::Generics,
598 if self.should_warn_about_variant(&variant.node) {
599 self.warn_dead_code(variant.node.id, variant.span, variant.node.ident.name,
600 "variant", "constructed");
602 intravisit::walk_variant(self, variant, g, id);
606 fn visit_foreign_item(&mut self, fi: &'tcx hir::ForeignItem) {
607 if self.should_warn_about_foreign_item(fi) {
608 self.warn_dead_code(fi.hir_id, fi.span, fi.ident.name,
609 fi.node.descriptive_variant(), "used");
611 intravisit::walk_foreign_item(self, fi);
614 fn visit_struct_field(&mut self, field: &'tcx hir::StructField) {
615 if self.should_warn_about_field(&field) {
616 self.warn_dead_code(field.hir_id, field.span, field.ident.name, "field", "used");
618 intravisit::walk_struct_field(self, field);
621 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
622 match impl_item.node {
623 hir::ImplItemKind::Const(_, body_id) => {
624 if !self.symbol_is_live(impl_item.hir_id) {
625 self.warn_dead_code(impl_item.hir_id,
627 impl_item.ident.name,
631 self.visit_nested_body(body_id)
633 hir::ImplItemKind::Method(_, body_id) => {
634 if !self.symbol_is_live(impl_item.hir_id) {
635 let span = self.tcx.sess.source_map().def_span(impl_item.span);
636 self.warn_dead_code(impl_item.hir_id, span, impl_item.ident.name, "method",
639 self.visit_nested_body(body_id)
641 hir::ImplItemKind::Existential(..) |
642 hir::ImplItemKind::Type(..) => {}
646 // Overwrite so that we don't warn the trait item itself.
647 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
648 match trait_item.node {
649 hir::TraitItemKind::Const(_, Some(body_id)) |
650 hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(body_id)) => {
651 self.visit_nested_body(body_id)
653 hir::TraitItemKind::Const(_, None) |
654 hir::TraitItemKind::Method(_, hir::TraitMethod::Required(_)) |
655 hir::TraitItemKind::Type(..) => {}
660 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
661 let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
662 let krate = tcx.hir().krate();
663 let live_symbols = find_live(tcx, access_levels, krate);
664 let mut visitor = DeadVisitor {
668 intravisit::walk_crate(&mut visitor, krate);