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, NestedVisitorMap, 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<'tcx>, 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(tcx.hir().local_def_id_to_hir_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 type Map = intravisit::ErasedMap<'tcx>;
79 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
80 NestedVisitorMap::None
83 fn visit_nested_body(&mut self, body: hir::BodyId) {
84 let old_maybe_typeck_results =
85 self.maybe_typeck_results.replace(self.tcx.typeck_body(body));
86 let body = self.tcx.hir().body(body);
87 self.visit_body(body);
88 self.maybe_typeck_results = old_maybe_typeck_results;
91 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
92 let res = match expr.kind {
93 hir::ExprKind::Path(ref qpath) => {
94 Some(self.typeck_results().qpath_res(qpath, expr.hir_id))
96 hir::ExprKind::MethodCall(..) => self
98 .type_dependent_def(expr.hir_id)
99 .map(|(kind, def_id)| Res::Def(kind, def_id)),
103 if let Some(res) = res {
104 if let Some(def_id) = res.opt_def_id().and_then(|def_id| def_id.as_local()) {
105 if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
106 self.worklist.push(def_id);
109 // If this path leads to a constant, then we need to
110 // recurse into the constant to continue finding
111 // items that are reachable.
112 Res::Def(DefKind::Const | DefKind::AssocConst, _) => {
113 self.worklist.push(def_id);
116 // If this wasn't a static, then the destination is
119 self.reachable_symbols.insert(def_id);
126 intravisit::walk_expr(self, expr)
130 impl<'tcx> ReachableContext<'tcx> {
131 /// Gets the type-checking results for the current body.
132 /// As this will ICE if called outside bodies, only call when working with
133 /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
135 fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
136 self.maybe_typeck_results
137 .expect("`ReachableContext::typeck_results` called outside of body")
140 // Returns true if the given def ID represents a local item that is
141 // eligible for inlining and false otherwise.
142 fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
143 let hir_id = match def_id.as_local() {
144 Some(def_id) => self.tcx.hir().local_def_id_to_hir_id(def_id),
150 match self.tcx.hir().find(hir_id) {
151 Some(Node::Item(item)) => match item.kind {
152 hir::ItemKind::Fn(..) => {
153 item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
157 Some(Node::TraitItem(trait_method)) => match trait_method.kind {
158 hir::TraitItemKind::Const(_, ref default) => default.is_some(),
159 hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)) => true,
160 hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
161 | hir::TraitItemKind::Type(..) => false,
163 Some(Node::ImplItem(impl_item)) => {
164 match impl_item.kind {
165 hir::ImplItemKind::Const(..) => true,
166 hir::ImplItemKind::Fn(..) => {
167 let attrs = self.tcx.codegen_fn_attrs(def_id);
168 let generics = self.tcx.generics_of(def_id);
169 if generics.requires_monomorphization(self.tcx) || attrs.requests_inline() {
172 let impl_did = self.tcx.hir().get_parent_did(hir_id);
173 // Check the impl. If the generics on the self
174 // type of the impl require inlining, this method
176 let impl_hir_id = self.tcx.hir().local_def_id_to_hir_id(impl_did);
177 match self.tcx.hir().expect_item(impl_hir_id).kind {
178 hir::ItemKind::Impl { .. } => {
179 let generics = self.tcx.generics_of(impl_did);
180 generics.requires_monomorphization(self.tcx)
186 hir::ImplItemKind::TyAlias(_) => false,
190 None => false, // This will happen for default methods.
194 // Step 2: Mark all symbols that the symbols on the worklist touch.
195 fn propagate(&mut self) {
196 let mut scanned = FxHashSet::default();
197 while let Some(search_item) = self.worklist.pop() {
198 if !scanned.insert(search_item) {
202 if let Some(ref item) =
203 self.tcx.hir().find(self.tcx.hir().local_def_id_to_hir_id(search_item))
205 self.propagate_node(item, search_item);
210 fn propagate_node(&mut self, node: &Node<'tcx>, search_item: LocalDefId) {
211 if !self.any_library {
212 // If we are building an executable, only explicitly extern
213 // types need to be exported.
215 if let Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, ..), .. })
216 | Node::ImplItem(hir::ImplItem {
217 kind: hir::ImplItemKind::Fn(sig, ..), ..
220 sig.header.abi != Abi::Rust
224 let codegen_attrs = self.tcx.codegen_fn_attrs(search_item);
225 let is_extern = codegen_attrs.contains_extern_indicator();
227 codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
228 if reachable || is_extern || std_internal {
229 self.reachable_symbols.insert(search_item);
232 // If we are building a library, then reachable symbols will
233 // continue to participate in linkage after this product is
234 // produced. In this case, we traverse the ast node, recursing on
235 // all reachable nodes from this one.
236 self.reachable_symbols.insert(search_item);
240 Node::Item(item) => {
242 hir::ItemKind::Fn(.., body) => {
243 if item_might_be_inlined(
246 self.tcx.codegen_fn_attrs(item.def_id),
248 self.visit_nested_body(body);
252 // Reachable constants will be inlined into other crates
253 // unconditionally, so we need to make sure that their
254 // contents are also reachable.
255 hir::ItemKind::Const(_, init) | hir::ItemKind::Static(_, _, init) => {
256 self.visit_nested_body(init);
259 // These are normal, nothing reachable about these
260 // inherently and their children are already in the
261 // worklist, as determined by the privacy pass
262 hir::ItemKind::ExternCrate(_)
263 | hir::ItemKind::Use(..)
264 | hir::ItemKind::OpaqueTy(..)
265 | hir::ItemKind::TyAlias(..)
266 | hir::ItemKind::Macro(..)
267 | hir::ItemKind::Mod(..)
268 | hir::ItemKind::ForeignMod { .. }
269 | hir::ItemKind::Impl { .. }
270 | hir::ItemKind::Trait(..)
271 | hir::ItemKind::TraitAlias(..)
272 | hir::ItemKind::Struct(..)
273 | hir::ItemKind::Enum(..)
274 | hir::ItemKind::Union(..)
275 | hir::ItemKind::GlobalAsm(..) => {}
278 Node::TraitItem(trait_method) => {
279 match trait_method.kind {
280 hir::TraitItemKind::Const(_, None)
281 | hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_)) => {
282 // Keep going, nothing to get exported
284 hir::TraitItemKind::Const(_, Some(body_id))
285 | hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)) => {
286 self.visit_nested_body(body_id);
288 hir::TraitItemKind::Type(..) => {}
291 Node::ImplItem(impl_item) => match impl_item.kind {
292 hir::ImplItemKind::Const(_, body) => {
293 self.visit_nested_body(body);
295 hir::ImplItemKind::Fn(_, body) => {
297 self.tcx.parent(search_item.to_def_id()).unwrap().expect_local();
298 if method_might_be_inlined(self.tcx, impl_item, impl_def_id) {
299 self.visit_nested_body(body)
302 hir::ImplItemKind::TyAlias(_) => {}
304 Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., body, _, _), .. }) => {
305 self.visit_nested_body(body);
307 // Nothing to recurse on for these
313 | Node::Crate(_) => {}
316 "found unexpected node kind in worklist: {} ({:?})",
319 .node_to_string(self.tcx.hir().local_def_id_to_hir_id(search_item)),
327 // Some methods from non-exported (completely private) trait impls still have to be
328 // reachable if they are called from inlinable code. Generally, it's not known until
329 // monomorphization if a specific trait impl item can be reachable or not. So, we
330 // conservatively mark all of them as reachable.
331 // FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
332 // items of non-exported traits (or maybe all local traits?) unless their respective
333 // trait items are used from inlinable code through method call syntax or UFCS, or their
334 // trait is a lang item.
335 struct CollectPrivateImplItemsVisitor<'a, 'tcx> {
337 access_levels: &'a privacy::AccessLevels,
338 worklist: &'a mut Vec<LocalDefId>,
341 impl CollectPrivateImplItemsVisitor<'_, '_> {
342 fn push_to_worklist_if_has_custom_linkage(&mut self, def_id: LocalDefId) {
343 // Anything which has custom linkage gets thrown on the worklist no
344 // matter where it is in the crate, along with "special std symbols"
345 // which are currently akin to allocator symbols.
346 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
347 if codegen_attrs.contains_extern_indicator()
348 || codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
350 self.worklist.push(def_id);
355 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for CollectPrivateImplItemsVisitor<'a, 'tcx> {
356 fn visit_item(&mut self, item: &hir::Item<'_>) {
357 self.push_to_worklist_if_has_custom_linkage(item.def_id);
359 // We need only trait impls here, not inherent impls, and only non-exported ones
360 if let hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref trait_ref), ref items, .. }) =
363 if !self.access_levels.is_reachable(item.def_id) {
364 // FIXME(#53488) remove `let`
366 self.worklist.extend(items.iter().map(|ii_ref| ii_ref.id.def_id));
368 let trait_def_id = match trait_ref.path.res {
369 Res::Def(DefKind::Trait, def_id) => def_id,
373 if !trait_def_id.is_local() {
377 self.worklist.extend(
378 tcx.provided_trait_methods(trait_def_id)
379 .map(|assoc| assoc.def_id.expect_local()),
385 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
387 fn visit_impl_item(&mut self, impl_item: &hir::ImplItem<'_>) {
388 self.push_to_worklist_if_has_custom_linkage(impl_item.def_id);
391 fn visit_foreign_item(&mut self, _foreign_item: &hir::ForeignItem<'_>) {
392 // We never export foreign functions as they have no body to export.
396 fn reachable_set<'tcx>(tcx: TyCtxt<'tcx>, (): ()) -> FxHashSet<LocalDefId> {
397 let access_levels = &tcx.privacy_access_levels(());
400 tcx.sess.crate_types().iter().any(|ty| {
401 *ty == CrateType::Rlib || *ty == CrateType::Dylib || *ty == CrateType::ProcMacro
403 let mut reachable_context = ReachableContext {
405 maybe_typeck_results: None,
406 reachable_symbols: Default::default(),
407 worklist: Vec::new(),
411 // Step 1: Seed the worklist with all nodes which were found to be public as
412 // a result of the privacy pass along with all local lang items and impl items.
413 // If other crates link to us, they're going to expect to be able to
414 // use the lang items, so we need to be sure to mark them as
416 reachable_context.worklist.extend(access_levels.map.keys());
417 for item in tcx.lang_items().items().iter() {
418 if let Some(def_id) = *item {
419 if let Some(def_id) = def_id.as_local() {
420 reachable_context.worklist.push(def_id);
425 let mut collect_private_impl_items = CollectPrivateImplItemsVisitor {
428 worklist: &mut reachable_context.worklist,
430 tcx.hir().visit_all_item_likes(&mut collect_private_impl_items);
433 // Step 2: Mark all symbols that the symbols on the worklist touch.
434 reachable_context.propagate();
436 debug!("Inline reachability shows: {:?}", reachable_context.reachable_symbols);
438 // Return the set of reachable symbols.
439 reachable_context.reachable_symbols
442 pub fn provide(providers: &mut Providers) {
443 *providers = Providers { reachable_set, ..*providers };