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::LOCAL_CRATE;
12 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
13 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
14 use rustc_hir::itemlikevisit::ItemLikeVisitor;
15 use rustc_hir::{HirIdSet, Node};
16 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
17 use rustc_middle::middle::privacy;
18 use rustc_middle::ty::query::Providers;
19 use rustc_middle::ty::{self, TyCtxt};
20 use rustc_session::config::CrateType;
21 use rustc_target::spec::abi::Abi;
23 // Returns true if the given item must be inlined because it may be
24 // monomorphized or it was marked with `#[inline]`. This will only return
25 // true for functions.
26 fn item_might_be_inlined(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>, attrs: &CodegenFnAttrs) -> bool {
27 if attrs.requests_inline() {
32 hir::ItemKind::Fn(ref sig, ..) if sig.header.is_const() => true,
33 hir::ItemKind::Impl { .. } | hir::ItemKind::Fn(..) => {
34 let generics = tcx.generics_of(tcx.hir().local_def_id(item.hir_id));
35 generics.requires_monomorphization(tcx)
41 fn method_might_be_inlined(
43 impl_item: &hir::ImplItem<'_>,
46 let codegen_fn_attrs = tcx.codegen_fn_attrs(impl_item.hir_id.owner.to_def_id());
47 let generics = tcx.generics_of(tcx.hir().local_def_id(impl_item.hir_id));
48 if codegen_fn_attrs.requests_inline() || generics.requires_monomorphization(tcx) {
51 if let hir::ImplItemKind::Fn(method_sig, _) = &impl_item.kind {
52 if method_sig.header.is_const() {
56 match tcx.hir().find(tcx.hir().local_def_id_to_hir_id(impl_src)) {
57 Some(Node::Item(item)) => item_might_be_inlined(tcx, &item, codegen_fn_attrs),
58 Some(..) | None => span_bug!(impl_item.span, "impl did is not an item"),
62 // Information needed while computing reachability.
63 struct ReachableContext<'tcx> {
66 maybe_typeck_results: Option<&'tcx ty::TypeckResults<'tcx>>,
67 // The set of items which must be exported in the linkage sense.
68 reachable_symbols: HirIdSet,
69 // A worklist of item IDs. Each item ID in this worklist will be inlined
70 // and will be scanned for further references.
71 worklist: Vec<hir::HirId>,
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)),
104 Some(Res::Local(hir_id)) => {
105 self.reachable_symbols.insert(hir_id);
108 if let Some((hir_id, def_id)) = res.opt_def_id().and_then(|def_id| {
111 .map(|def_id| (self.tcx.hir().local_def_id_to_hir_id(def_id), def_id))
113 if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
114 self.worklist.push(hir_id);
117 // If this path leads to a constant, then we need to
118 // recurse into the constant to continue finding
119 // items that are reachable.
120 Res::Def(DefKind::Const | DefKind::AssocConst, _) => {
121 self.worklist.push(hir_id);
124 // If this wasn't a static, then the destination is
127 self.reachable_symbols.insert(hir_id);
136 intravisit::walk_expr(self, expr)
140 impl<'tcx> ReachableContext<'tcx> {
141 /// Gets the type-checking results for the current body.
142 /// As this will ICE if called outside bodies, only call when working with
143 /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
145 fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
146 self.maybe_typeck_results
147 .expect("`ReachableContext::typeck_results` called outside of body")
150 // Returns true if the given def ID represents a local item that is
151 // eligible for inlining and false otherwise.
152 fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
153 let hir_id = match def_id.as_local() {
154 Some(def_id) => self.tcx.hir().local_def_id_to_hir_id(def_id),
160 match self.tcx.hir().find(hir_id) {
161 Some(Node::Item(item)) => match item.kind {
162 hir::ItemKind::Fn(..) => {
163 item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
167 Some(Node::TraitItem(trait_method)) => match trait_method.kind {
168 hir::TraitItemKind::Const(_, ref default) => default.is_some(),
169 hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)) => true,
170 hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
171 | hir::TraitItemKind::Type(..) => false,
173 Some(Node::ImplItem(impl_item)) => {
174 match impl_item.kind {
175 hir::ImplItemKind::Const(..) => true,
176 hir::ImplItemKind::Fn(..) => {
177 let attrs = self.tcx.codegen_fn_attrs(def_id);
178 let generics = self.tcx.generics_of(def_id);
179 if generics.requires_monomorphization(self.tcx) || attrs.requests_inline() {
182 let impl_did = self.tcx.hir().get_parent_did(hir_id);
183 // Check the impl. If the generics on the self
184 // type of the impl require inlining, this method
186 let impl_hir_id = self.tcx.hir().local_def_id_to_hir_id(impl_did);
187 match self.tcx.hir().expect_item(impl_hir_id).kind {
188 hir::ItemKind::Impl { .. } => {
189 let generics = self.tcx.generics_of(impl_did);
190 generics.requires_monomorphization(self.tcx)
196 hir::ImplItemKind::TyAlias(_) => false,
200 None => false, // This will happen for default methods.
204 // Step 2: Mark all symbols that the symbols on the worklist touch.
205 fn propagate(&mut self) {
206 let mut scanned = FxHashSet::default();
207 while let Some(search_item) = self.worklist.pop() {
208 if !scanned.insert(search_item) {
212 if let Some(ref item) = self.tcx.hir().find(search_item) {
213 self.propagate_node(item, search_item);
218 fn propagate_node(&mut self, node: &Node<'tcx>, search_item: hir::HirId) {
219 if !self.any_library {
220 // If we are building an executable, only explicitly extern
221 // types need to be exported.
222 if let Node::Item(item) = *node {
223 let reachable = if let hir::ItemKind::Fn(ref sig, ..) = item.kind {
224 sig.header.abi != Abi::Rust
228 let def_id = self.tcx.hir().local_def_id(item.hir_id);
229 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
230 let is_extern = codegen_attrs.contains_extern_indicator();
232 codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
233 if reachable || is_extern || std_internal {
234 self.reachable_symbols.insert(search_item);
238 // If we are building a library, then reachable symbols will
239 // continue to participate in linkage after this product is
240 // produced. In this case, we traverse the ast node, recursing on
241 // all reachable nodes from this one.
242 self.reachable_symbols.insert(search_item);
246 Node::Item(item) => {
248 hir::ItemKind::Fn(.., body) => {
249 let def_id = self.tcx.hir().local_def_id(item.hir_id);
250 if item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
252 self.visit_nested_body(body);
256 // Reachable constants will be inlined into other crates
257 // unconditionally, so we need to make sure that their
258 // contents are also reachable.
259 hir::ItemKind::Const(_, init) => {
260 self.visit_nested_body(init);
263 // These are normal, nothing reachable about these
264 // inherently and their children are already in the
265 // worklist, as determined by the privacy pass
266 hir::ItemKind::ExternCrate(_)
267 | hir::ItemKind::Use(..)
268 | hir::ItemKind::OpaqueTy(..)
269 | hir::ItemKind::TyAlias(..)
270 | hir::ItemKind::Static(..)
271 | hir::ItemKind::Mod(..)
272 | hir::ItemKind::ForeignMod(..)
273 | hir::ItemKind::Impl { .. }
274 | hir::ItemKind::Trait(..)
275 | hir::ItemKind::TraitAlias(..)
276 | hir::ItemKind::Struct(..)
277 | hir::ItemKind::Enum(..)
278 | hir::ItemKind::Union(..)
279 | hir::ItemKind::GlobalAsm(..) => {}
282 Node::TraitItem(trait_method) => {
283 match trait_method.kind {
284 hir::TraitItemKind::Const(_, None)
285 | hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_)) => {
286 // Keep going, nothing to get exported
288 hir::TraitItemKind::Const(_, Some(body_id))
289 | hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)) => {
290 self.visit_nested_body(body_id);
292 hir::TraitItemKind::Type(..) => {}
295 Node::ImplItem(impl_item) => match impl_item.kind {
296 hir::ImplItemKind::Const(_, body) => {
297 self.visit_nested_body(body);
299 hir::ImplItemKind::Fn(_, body) => {
300 let did = self.tcx.hir().get_parent_did(search_item);
301 if method_might_be_inlined(self.tcx, impl_item, did) {
302 self.visit_nested_body(body)
305 hir::ImplItemKind::TyAlias(_) => {}
307 Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., body, _, _), .. }) => {
308 self.visit_nested_body(body);
310 // Nothing to recurse on for these
316 | Node::MacroDef(_) => {}
319 "found unexpected node kind in worklist: {} ({:?})",
320 self.tcx.hir().node_to_string(search_item),
328 // Some methods from non-exported (completely private) trait impls still have to be
329 // reachable if they are called from inlinable code. Generally, it's not known until
330 // monomorphization if a specific trait impl item can be reachable or not. So, we
331 // conservatively mark all of them as reachable.
332 // FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
333 // items of non-exported traits (or maybe all local traits?) unless their respective
334 // trait items are used from inlinable code through method call syntax or UFCS, or their
335 // trait is a lang item.
336 struct CollectPrivateImplItemsVisitor<'a, 'tcx> {
338 access_levels: &'a privacy::AccessLevels,
339 worklist: &'a mut Vec<hir::HirId>,
342 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for CollectPrivateImplItemsVisitor<'a, 'tcx> {
343 fn visit_item(&mut self, item: &hir::Item<'_>) {
344 // Anything which has custom linkage gets thrown on the worklist no
345 // matter where it is in the crate, along with "special std symbols"
346 // which are currently akin to allocator symbols.
347 let def_id = self.tcx.hir().local_def_id(item.hir_id);
348 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
349 if codegen_attrs.contains_extern_indicator()
350 || codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
352 self.worklist.push(item.hir_id);
355 // We need only trait impls here, not inherent impls, and only non-exported ones
356 if let hir::ItemKind::Impl { of_trait: Some(ref trait_ref), ref items, .. } = item.kind {
357 if !self.access_levels.is_reachable(item.hir_id) {
358 self.worklist.extend(items.iter().map(|ii_ref| ii_ref.id.hir_id));
360 let trait_def_id = match trait_ref.path.res {
361 Res::Def(DefKind::Trait, def_id) => def_id,
365 if !trait_def_id.is_local() {
369 // FIXME(#53488) remove `let`
372 .extend(tcx.provided_trait_methods(trait_def_id).map(|assoc| {
373 tcx.hir().local_def_id_to_hir_id(assoc.def_id.expect_local())
379 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
381 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {
382 // processed in visit_item above
386 fn reachable_set<'tcx>(tcx: TyCtxt<'tcx>, crate_num: CrateNum) -> &'tcx HirIdSet {
387 debug_assert!(crate_num == LOCAL_CRATE);
389 let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
392 tcx.sess.crate_types().iter().any(|ty| {
393 *ty == CrateType::Rlib || *ty == CrateType::Dylib || *ty == CrateType::ProcMacro
395 let mut reachable_context = ReachableContext {
397 maybe_typeck_results: None,
398 reachable_symbols: Default::default(),
399 worklist: Vec::new(),
403 // Step 1: Seed the worklist with all nodes which were found to be public as
404 // a result of the privacy pass along with all local lang items and impl items.
405 // If other crates link to us, they're going to expect to be able to
406 // use the lang items, so we need to be sure to mark them as
408 reachable_context.worklist.extend(access_levels.map.iter().map(|(id, _)| *id));
409 for item in tcx.lang_items().items().iter() {
410 if let Some(did) = *item {
411 if let Some(hir_id) = did.as_local().map(|did| tcx.hir().local_def_id_to_hir_id(did)) {
412 reachable_context.worklist.push(hir_id);
417 let mut collect_private_impl_items = CollectPrivateImplItemsVisitor {
420 worklist: &mut reachable_context.worklist,
422 tcx.hir().krate().visit_all_item_likes(&mut collect_private_impl_items);
425 // Step 2: Mark all symbols that the symbols on the worklist touch.
426 reachable_context.propagate();
428 debug!("Inline reachability shows: {:?}", reachable_context.reachable_symbols);
430 // Return the set of reachable symbols.
431 tcx.arena.alloc(reachable_context.reachable_symbols)
434 pub fn provide(providers: &mut Providers) {
435 *providers = Providers { reachable_set, ..*providers };