1 // Finds items that are externally reachable, to determine which items
2 // need to have their metadata (and possibly their AST) serialized.
3 // All items that can be referred to through an exported name are
4 // reachable, and when a reachable thing is inline or generic, it
5 // makes all other generics or inline functions that it references
8 use rustc_data_structures::fx::FxHashSet;
10 use rustc_hir::def::{DefKind, Res};
11 use rustc_hir::def_id::{DefId, LocalDefId};
12 use rustc_hir::intravisit::{self, Visitor};
13 use rustc_hir::itemlikevisit::ItemLikeVisitor;
15 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
16 use rustc_middle::middle::privacy;
17 use rustc_middle::ty::query::Providers;
18 use rustc_middle::ty::{self, DefIdTree, TyCtxt};
19 use rustc_session::config::CrateType;
20 use rustc_target::spec::abi::Abi;
22 // Returns true if the given item must be inlined because it may be
23 // monomorphized or it was marked with `#[inline]`. This will only return
24 // true for functions.
25 fn item_might_be_inlined(tcx: TyCtxt<'_>, item: &hir::Item<'_>, attrs: &CodegenFnAttrs) -> bool {
26 if attrs.requests_inline() {
31 hir::ItemKind::Fn(ref sig, ..) if sig.header.is_const() => true,
32 hir::ItemKind::Impl { .. } | hir::ItemKind::Fn(..) => {
33 let generics = tcx.generics_of(item.def_id);
34 generics.requires_monomorphization(tcx)
40 fn method_might_be_inlined(
42 impl_item: &hir::ImplItem<'_>,
45 let codegen_fn_attrs = tcx.codegen_fn_attrs(impl_item.hir_id().owner.to_def_id());
46 let generics = tcx.generics_of(impl_item.def_id);
47 if codegen_fn_attrs.requests_inline() || generics.requires_monomorphization(tcx) {
50 if let hir::ImplItemKind::Fn(method_sig, _) = &impl_item.kind {
51 if method_sig.header.is_const() {
55 match tcx.hir().find_by_def_id(impl_src) {
56 Some(Node::Item(item)) => item_might_be_inlined(tcx, &item, codegen_fn_attrs),
57 Some(..) | None => span_bug!(impl_item.span, "impl did is not an item"),
61 // Information needed while computing reachability.
62 struct ReachableContext<'tcx> {
65 maybe_typeck_results: Option<&'tcx ty::TypeckResults<'tcx>>,
66 // The set of items which must be exported in the linkage sense.
67 reachable_symbols: FxHashSet<LocalDefId>,
68 // A worklist of item IDs. Each item ID in this worklist will be inlined
69 // and will be scanned for further references.
70 // FIXME(eddyb) benchmark if this would be faster as a `VecDeque`.
71 worklist: Vec<LocalDefId>,
72 // Whether any output of this compilation is a library
76 impl<'tcx> Visitor<'tcx> for ReachableContext<'tcx> {
77 fn visit_nested_body(&mut self, body: hir::BodyId) {
78 let old_maybe_typeck_results =
79 self.maybe_typeck_results.replace(self.tcx.typeck_body(body));
80 let body = self.tcx.hir().body(body);
81 self.visit_body(body);
82 self.maybe_typeck_results = old_maybe_typeck_results;
85 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
86 let res = match expr.kind {
87 hir::ExprKind::Path(ref qpath) => {
88 Some(self.typeck_results().qpath_res(qpath, expr.hir_id))
90 hir::ExprKind::MethodCall(..) => self
92 .type_dependent_def(expr.hir_id)
93 .map(|(kind, def_id)| Res::Def(kind, def_id)),
97 if let Some(res) = res && let Some(def_id) = res.opt_def_id().and_then(|el| el.as_local()) {
98 if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
99 self.worklist.push(def_id);
102 // If this path leads to a constant, then we need to
103 // recurse into the constant to continue finding
104 // items that are reachable.
105 Res::Def(DefKind::Const | DefKind::AssocConst, _) => {
106 self.worklist.push(def_id);
109 // If this wasn't a static, then the destination is
112 self.reachable_symbols.insert(def_id);
118 intravisit::walk_expr(self, expr)
122 impl<'tcx> ReachableContext<'tcx> {
123 /// Gets the type-checking results for the current body.
124 /// As this will ICE if called outside bodies, only call when working with
125 /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
127 fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
128 self.maybe_typeck_results
129 .expect("`ReachableContext::typeck_results` called outside of body")
132 // Returns true if the given def ID represents a local item that is
133 // eligible for inlining and false otherwise.
134 fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
135 let Some(def_id) = def_id.as_local() else {
139 match self.tcx.hir().find_by_def_id(def_id) {
140 Some(Node::Item(item)) => match item.kind {
141 hir::ItemKind::Fn(..) => {
142 item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
146 Some(Node::TraitItem(trait_method)) => match trait_method.kind {
147 hir::TraitItemKind::Const(_, ref default) => default.is_some(),
148 hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)) => true,
149 hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
150 | hir::TraitItemKind::Type(..) => false,
152 Some(Node::ImplItem(impl_item)) => {
153 match impl_item.kind {
154 hir::ImplItemKind::Const(..) => true,
155 hir::ImplItemKind::Fn(..) => {
156 let attrs = self.tcx.codegen_fn_attrs(def_id);
157 let generics = self.tcx.generics_of(def_id);
158 if generics.requires_monomorphization(self.tcx) || attrs.requests_inline() {
161 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
162 let impl_did = self.tcx.hir().get_parent_item(hir_id);
163 // Check the impl. If the generics on the self
164 // type of the impl require inlining, this method
166 match self.tcx.hir().expect_item(impl_did).kind {
167 hir::ItemKind::Impl { .. } => {
168 let generics = self.tcx.generics_of(impl_did);
169 generics.requires_monomorphization(self.tcx)
175 hir::ImplItemKind::TyAlias(_) => false,
179 None => false, // This will happen for default methods.
183 // Step 2: Mark all symbols that the symbols on the worklist touch.
184 fn propagate(&mut self) {
185 let mut scanned = FxHashSet::default();
186 while let Some(search_item) = self.worklist.pop() {
187 if !scanned.insert(search_item) {
191 if let Some(ref item) = self.tcx.hir().find_by_def_id(search_item) {
192 self.propagate_node(item, search_item);
197 fn propagate_node(&mut self, node: &Node<'tcx>, search_item: LocalDefId) {
198 if !self.any_library {
199 // If we are building an executable, only explicitly extern
200 // types need to be exported.
202 if let Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, ..), .. })
203 | Node::ImplItem(hir::ImplItem {
204 kind: hir::ImplItemKind::Fn(sig, ..), ..
207 sig.header.abi != Abi::Rust
211 let codegen_attrs = if self.tcx.def_kind(search_item).has_codegen_attrs() {
212 self.tcx.codegen_fn_attrs(search_item)
214 CodegenFnAttrs::EMPTY
216 let is_extern = codegen_attrs.contains_extern_indicator();
218 codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
219 if reachable || is_extern || std_internal {
220 self.reachable_symbols.insert(search_item);
223 // If we are building a library, then reachable symbols will
224 // continue to participate in linkage after this product is
225 // produced. In this case, we traverse the ast node, recursing on
226 // all reachable nodes from this one.
227 self.reachable_symbols.insert(search_item);
231 Node::Item(item) => {
233 hir::ItemKind::Fn(.., body) => {
234 if item_might_be_inlined(
237 self.tcx.codegen_fn_attrs(item.def_id),
239 self.visit_nested_body(body);
243 // Reachable constants will be inlined into other crates
244 // unconditionally, so we need to make sure that their
245 // contents are also reachable.
246 hir::ItemKind::Const(_, init) | hir::ItemKind::Static(_, _, init) => {
247 self.visit_nested_body(init);
250 // These are normal, nothing reachable about these
251 // inherently and their children are already in the
252 // worklist, as determined by the privacy pass
253 hir::ItemKind::ExternCrate(_)
254 | hir::ItemKind::Use(..)
255 | hir::ItemKind::OpaqueTy(..)
256 | hir::ItemKind::TyAlias(..)
257 | hir::ItemKind::Macro(..)
258 | hir::ItemKind::Mod(..)
259 | hir::ItemKind::ForeignMod { .. }
260 | hir::ItemKind::Impl { .. }
261 | hir::ItemKind::Trait(..)
262 | hir::ItemKind::TraitAlias(..)
263 | hir::ItemKind::Struct(..)
264 | hir::ItemKind::Enum(..)
265 | hir::ItemKind::Union(..)
266 | hir::ItemKind::GlobalAsm(..) => {}
269 Node::TraitItem(trait_method) => {
270 match trait_method.kind {
271 hir::TraitItemKind::Const(_, None)
272 | hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_)) => {
273 // Keep going, nothing to get exported
275 hir::TraitItemKind::Const(_, Some(body_id))
276 | hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)) => {
277 self.visit_nested_body(body_id);
279 hir::TraitItemKind::Type(..) => {}
282 Node::ImplItem(impl_item) => match impl_item.kind {
283 hir::ImplItemKind::Const(_, body) => {
284 self.visit_nested_body(body);
286 hir::ImplItemKind::Fn(_, body) => {
287 let impl_def_id = self.tcx.local_parent(search_item);
288 if method_might_be_inlined(self.tcx, impl_item, impl_def_id) {
289 self.visit_nested_body(body)
292 hir::ImplItemKind::TyAlias(_) => {}
294 Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., body, _, _), .. }) => {
295 self.visit_nested_body(body);
297 // Nothing to recurse on for these
303 | Node::Crate(_) => {}
306 "found unexpected node kind in worklist: {} ({:?})",
309 .node_to_string(self.tcx.hir().local_def_id_to_hir_id(search_item)),
317 // Some methods from non-exported (completely private) trait impls still have to be
318 // reachable if they are called from inlinable code. Generally, it's not known until
319 // monomorphization if a specific trait impl item can be reachable or not. So, we
320 // conservatively mark all of them as reachable.
321 // FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
322 // items of non-exported traits (or maybe all local traits?) unless their respective
323 // trait items are used from inlinable code through method call syntax or UFCS, or their
324 // trait is a lang item.
325 struct CollectPrivateImplItemsVisitor<'a, 'tcx> {
327 access_levels: &'a privacy::AccessLevels,
328 worklist: &'a mut Vec<LocalDefId>,
331 impl CollectPrivateImplItemsVisitor<'_, '_> {
332 fn push_to_worklist_if_has_custom_linkage(&mut self, def_id: LocalDefId) {
333 // Anything which has custom linkage gets thrown on the worklist no
334 // matter where it is in the crate, along with "special std symbols"
335 // which are currently akin to allocator symbols.
336 if self.tcx.def_kind(def_id).has_codegen_attrs() {
337 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
338 if codegen_attrs.contains_extern_indicator()
339 || codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
340 // FIXME(nbdd0121): `#[used]` are marked as reachable here so it's picked up by
341 // `linked_symbols` in cg_ssa. They won't be exported in binary or cdylib due to their
342 // `SymbolExportLevel::Rust` export level but may end up being exported in dylibs.
343 || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED)
344 || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
346 self.worklist.push(def_id);
352 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for CollectPrivateImplItemsVisitor<'a, 'tcx> {
353 fn visit_item(&mut self, item: &hir::Item<'_>) {
354 self.push_to_worklist_if_has_custom_linkage(item.def_id);
356 // We need only trait impls here, not inherent impls, and only non-exported ones
357 if let hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref trait_ref), ref items, .. }) =
360 if !self.access_levels.is_reachable(item.def_id) {
361 // FIXME(#53488) remove `let`
363 self.worklist.extend(items.iter().map(|ii_ref| ii_ref.id.def_id));
365 let Res::Def(DefKind::Trait, trait_def_id) = trait_ref.path.res else {
369 if !trait_def_id.is_local() {
373 self.worklist.extend(
374 tcx.provided_trait_methods(trait_def_id)
375 .map(|assoc| assoc.def_id.expect_local()),
381 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
383 fn visit_impl_item(&mut self, impl_item: &hir::ImplItem<'_>) {
384 self.push_to_worklist_if_has_custom_linkage(impl_item.def_id);
387 fn visit_foreign_item(&mut self, _foreign_item: &hir::ForeignItem<'_>) {
388 // We never export foreign functions as they have no body to export.
392 fn reachable_set<'tcx>(tcx: TyCtxt<'tcx>, (): ()) -> FxHashSet<LocalDefId> {
393 let access_levels = &tcx.privacy_access_levels(());
396 tcx.sess.crate_types().iter().any(|ty| {
397 *ty == CrateType::Rlib || *ty == CrateType::Dylib || *ty == CrateType::ProcMacro
399 let mut reachable_context = ReachableContext {
401 maybe_typeck_results: None,
402 reachable_symbols: Default::default(),
403 worklist: Vec::new(),
407 // Step 1: Seed the worklist with all nodes which were found to be public as
408 // a result of the privacy pass along with all local lang items and impl items.
409 // If other crates link to us, they're going to expect to be able to
410 // use the lang items, so we need to be sure to mark them as
412 reachable_context.worklist.extend(access_levels.map.keys());
413 for item in tcx.lang_items().items().iter() {
414 if let Some(def_id) = *item {
415 if let Some(def_id) = def_id.as_local() {
416 reachable_context.worklist.push(def_id);
421 let mut collect_private_impl_items = CollectPrivateImplItemsVisitor {
424 worklist: &mut reachable_context.worklist,
426 tcx.hir().visit_all_item_likes(&mut collect_private_impl_items);
429 // Step 2: Mark all symbols that the symbols on the worklist touch.
430 reachable_context.propagate();
432 debug!("Inline reachability shows: {:?}", reachable_context.reachable_symbols);
434 // Return the set of reachable symbols.
435 reachable_context.reachable_symbols
438 pub fn provide(providers: &mut Providers) {
439 *providers = Providers { reachable_set, ..*providers };