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 crate::hir::def::{DefKind, Res};
9 use crate::hir::def_id::{CrateNum, DefId};
11 use crate::hir::{CodegenFnAttrFlags, CodegenFnAttrs};
12 use crate::middle::privacy;
13 use crate::session::config;
14 use crate::ty::query::Providers;
15 use crate::ty::{self, TyCtxt};
16 use crate::util::nodemap::{FxHashSet, HirIdSet};
17 use rustc_data_structures::sync::Lrc;
20 use crate::hir::def_id::LOCAL_CRATE;
21 use crate::hir::intravisit;
22 use crate::hir::intravisit::{NestedVisitorMap, Visitor};
23 use crate::hir::itemlikevisit::ItemLikeVisitor;
24 use rustc_macros::HashStable;
25 use rustc_target::spec::abi::Abi;
27 // Returns true if the given item must be inlined because it may be
28 // monomorphized or it was marked with `#[inline]`. This will only return
29 // true for functions.
30 fn item_might_be_inlined(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>, attrs: CodegenFnAttrs) -> bool {
31 if attrs.requests_inline() {
36 hir::ItemKind::Fn(ref sig, ..) if sig.header.is_const() => {
39 hir::ItemKind::Impl(..) | hir::ItemKind::Fn(..) => {
40 let generics = tcx.generics_of(tcx.hir().local_def_id(item.hir_id));
41 generics.requires_monomorphization(tcx)
47 fn method_might_be_inlined(
49 impl_item: &hir::ImplItem<'_>,
52 let codegen_fn_attrs = tcx.codegen_fn_attrs(impl_item.hir_id.owner_def_id());
53 let generics = tcx.generics_of(tcx.hir().local_def_id(impl_item.hir_id));
54 if codegen_fn_attrs.requests_inline() || generics.requires_monomorphization(tcx) {
57 if let hir::ImplItemKind::Method(method_sig, _) = &impl_item.kind {
58 if method_sig.header.is_const() {
62 if let Some(impl_hir_id) = tcx.hir().as_local_hir_id(impl_src) {
63 match tcx.hir().find(impl_hir_id) {
64 Some(Node::Item(item)) => item_might_be_inlined(tcx, &item, codegen_fn_attrs),
65 Some(..) | None => span_bug!(impl_item.span, "impl did is not an item"),
68 span_bug!(impl_item.span, "found a foreign impl as a parent of a local method")
72 // Information needed while computing reachability.
73 struct ReachableContext<'a, 'tcx> {
76 tables: &'a ty::TypeckTables<'tcx>,
77 // The set of items which must be exported in the linkage sense.
78 reachable_symbols: HirIdSet,
79 // A worklist of item IDs. Each item ID in this worklist will be inlined
80 // and will be scanned for further references.
81 worklist: Vec<hir::HirId>,
82 // Whether any output of this compilation is a library
86 impl<'a, 'tcx> Visitor<'tcx> for ReachableContext<'a, 'tcx> {
87 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
88 NestedVisitorMap::None
91 fn visit_nested_body(&mut self, body: hir::BodyId) {
92 let old_tables = self.tables;
93 self.tables = self.tcx.body_tables(body);
94 let body = self.tcx.hir().body(body);
95 self.visit_body(body);
96 self.tables = old_tables;
99 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
100 let res = match expr.kind {
101 hir::ExprKind::Path(ref qpath) => Some(self.tables.qpath_res(qpath, expr.hir_id)),
102 hir::ExprKind::MethodCall(..) => self
104 .type_dependent_def(expr.hir_id)
105 .map(|(kind, def_id)| Res::Def(kind, def_id)),
110 Some(Res::Local(hir_id)) => {
111 self.reachable_symbols.insert(hir_id);
114 if let Some((hir_id, def_id)) = res.opt_def_id().and_then(|def_id| {
115 self.tcx.hir().as_local_hir_id(def_id).map(|hir_id| (hir_id, def_id))
117 if self.def_id_represents_local_inlined_item(def_id) {
118 self.worklist.push(hir_id);
121 // If this path leads to a constant, then we need to
122 // recurse into the constant to continue finding
123 // items that are reachable.
124 Res::Def(DefKind::Const, _) | Res::Def(DefKind::AssocConst, _) => {
125 self.worklist.push(hir_id);
128 // If this wasn't a static, then the destination is
131 self.reachable_symbols.insert(hir_id);
140 intravisit::walk_expr(self, expr)
144 impl<'a, 'tcx> ReachableContext<'a, 'tcx> {
145 // Returns true if the given def ID represents a local item that is
146 // eligible for inlining and false otherwise.
147 fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
148 let hir_id = match self.tcx.hir().as_local_hir_id(def_id) {
149 Some(hir_id) => hir_id,
155 match self.tcx.hir().find(hir_id) {
156 Some(Node::Item(item)) => match item.kind {
157 hir::ItemKind::Fn(..) => {
158 item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
162 Some(Node::TraitItem(trait_method)) => match trait_method.kind {
163 hir::TraitItemKind::Const(_, ref default) => default.is_some(),
164 hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(_)) => true,
165 hir::TraitItemKind::Method(_, hir::TraitMethod::Required(_))
166 | hir::TraitItemKind::Type(..) => false,
168 Some(Node::ImplItem(impl_item)) => {
169 match impl_item.kind {
170 hir::ImplItemKind::Const(..) => true,
171 hir::ImplItemKind::Method(..) => {
172 let attrs = self.tcx.codegen_fn_attrs(def_id);
173 let generics = self.tcx.generics_of(def_id);
174 if generics.requires_monomorphization(self.tcx) || attrs.requests_inline() {
177 let impl_did = self.tcx.hir().get_parent_did(hir_id);
178 // Check the impl. If the generics on the self
179 // type of the impl require inlining, this method
181 let impl_hir_id = self.tcx.hir().as_local_hir_id(impl_did).unwrap();
182 match self.tcx.hir().expect_item(impl_hir_id).kind {
183 hir::ItemKind::Impl(..) => {
184 let generics = self.tcx.generics_of(impl_did);
185 generics.requires_monomorphization(self.tcx)
191 hir::ImplItemKind::OpaqueTy(..) | hir::ImplItemKind::TyAlias(_) => false,
195 None => false, // This will happen for default methods.
199 // Step 2: Mark all symbols that the symbols on the worklist touch.
200 fn propagate(&mut self) {
201 let mut scanned = FxHashSet::default();
202 while let Some(search_item) = self.worklist.pop() {
203 if !scanned.insert(search_item) {
207 if let Some(ref item) = self.tcx.hir().find(search_item) {
208 self.propagate_node(item, search_item);
213 fn propagate_node(&mut self, node: &Node<'tcx>, search_item: hir::HirId) {
214 if !self.any_library {
215 // If we are building an executable, only explicitly extern
216 // types need to be exported.
217 if let Node::Item(item) = *node {
218 let reachable = if let hir::ItemKind::Fn(ref sig, ..) = item.kind {
219 sig.header.abi != Abi::Rust
223 let def_id = self.tcx.hir().local_def_id(item.hir_id);
224 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
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);
233 // If we are building a library, then reachable symbols will
234 // continue to participate in linkage after this product is
235 // produced. In this case, we traverse the ast node, recursing on
236 // all reachable nodes from this one.
237 self.reachable_symbols.insert(search_item);
241 Node::Item(item) => {
243 hir::ItemKind::Fn(.., body) => {
244 let def_id = self.tcx.hir().local_def_id(item.hir_id);
245 if item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
247 self.visit_nested_body(body);
251 // Reachable constants will be inlined into other crates
252 // unconditionally, so we need to make sure that their
253 // contents are also reachable.
254 hir::ItemKind::Const(_, init) => {
255 self.visit_nested_body(init);
258 // These are normal, nothing reachable about these
259 // inherently and their children are already in the
260 // worklist, as determined by the privacy pass
261 hir::ItemKind::ExternCrate(_)
262 | hir::ItemKind::Use(..)
263 | hir::ItemKind::OpaqueTy(..)
264 | hir::ItemKind::TyAlias(..)
265 | hir::ItemKind::Static(..)
266 | hir::ItemKind::Mod(..)
267 | hir::ItemKind::ForeignMod(..)
268 | hir::ItemKind::Impl(..)
269 | hir::ItemKind::Trait(..)
270 | hir::ItemKind::TraitAlias(..)
271 | hir::ItemKind::Struct(..)
272 | hir::ItemKind::Enum(..)
273 | hir::ItemKind::Union(..)
274 | hir::ItemKind::GlobalAsm(..) => {}
277 Node::TraitItem(trait_method) => {
278 match trait_method.kind {
279 hir::TraitItemKind::Const(_, None)
280 | hir::TraitItemKind::Method(_, hir::TraitMethod::Required(_)) => {
281 // Keep going, nothing to get exported
283 hir::TraitItemKind::Const(_, Some(body_id))
284 | hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(body_id)) => {
285 self.visit_nested_body(body_id);
287 hir::TraitItemKind::Type(..) => {}
290 Node::ImplItem(impl_item) => match impl_item.kind {
291 hir::ImplItemKind::Const(_, body) => {
292 self.visit_nested_body(body);
294 hir::ImplItemKind::Method(_, body) => {
295 let did = self.tcx.hir().get_parent_did(search_item);
296 if method_might_be_inlined(self.tcx, impl_item, did) {
297 self.visit_nested_body(body)
300 hir::ImplItemKind::OpaqueTy(..) | hir::ImplItemKind::TyAlias(_) => {}
302 Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., body, _, _), .. }) => {
303 self.visit_nested_body(body);
305 // Nothing to recurse on for these
311 | Node::MacroDef(_) => {}
314 "found unexpected node kind in worklist: {} ({:?})",
315 self.tcx.hir().node_to_string(search_item),
323 // Some methods from non-exported (completely private) trait impls still have to be
324 // reachable if they are called from inlinable code. Generally, it's not known until
325 // monomorphization if a specific trait impl item can be reachable or not. So, we
326 // conservatively mark all of them as reachable.
327 // FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
328 // items of non-exported traits (or maybe all local traits?) unless their respective
329 // trait items are used from inlinable code through method call syntax or UFCS, or their
330 // trait is a lang item.
331 struct CollectPrivateImplItemsVisitor<'a, 'tcx> {
333 access_levels: &'a privacy::AccessLevels,
334 worklist: &'a mut Vec<hir::HirId>,
337 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for CollectPrivateImplItemsVisitor<'a, 'tcx> {
338 fn visit_item(&mut self, item: &hir::Item<'_>) {
339 // Anything which has custom linkage gets thrown on the worklist no
340 // matter where it is in the crate, along with "special std symbols"
341 // which are currently akin to allocator symbols.
342 let def_id = self.tcx.hir().local_def_id(item.hir_id);
343 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
344 if codegen_attrs.contains_extern_indicator()
345 || codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
347 self.worklist.push(item.hir_id);
350 // We need only trait impls here, not inherent impls, and only non-exported ones
351 if let hir::ItemKind::Impl(.., Some(ref trait_ref), _, ref impl_item_refs) = item.kind {
352 if !self.access_levels.is_reachable(item.hir_id) {
353 self.worklist.extend(impl_item_refs.iter().map(|ii_ref| ii_ref.id.hir_id));
355 let trait_def_id = match trait_ref.path.res {
356 Res::Def(DefKind::Trait, def_id) => def_id,
360 if !trait_def_id.is_local() {
364 let provided_trait_methods = self.tcx.provided_trait_methods(trait_def_id);
365 self.worklist.reserve(provided_trait_methods.len());
366 for default_method in provided_trait_methods {
367 let hir_id = self.tcx.hir().as_local_hir_id(default_method.def_id).unwrap();
368 self.worklist.push(hir_id);
374 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
376 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {
377 // processed in visit_item above
381 // We introduce a new-type here, so we can have a specialized HashStable
382 // implementation for it.
383 #[derive(Clone, HashStable)]
384 pub struct ReachableSet(pub Lrc<HirIdSet>);
386 fn reachable_set(tcx: TyCtxt<'_>, crate_num: CrateNum) -> ReachableSet {
387 debug_assert!(crate_num == LOCAL_CRATE);
389 let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
391 let any_library = tcx.sess.crate_types.borrow().iter().any(|ty| {
392 *ty == config::CrateType::Rlib
393 || *ty == config::CrateType::Dylib
394 || *ty == config::CrateType::ProcMacro
396 let mut reachable_context = ReachableContext {
398 tables: &ty::TypeckTables::empty(None),
399 reachable_symbols: Default::default(),
400 worklist: Vec::new(),
404 // Step 1: Seed the worklist with all nodes which were found to be public as
405 // a result of the privacy pass along with all local lang items and impl items.
406 // If other crates link to us, they're going to expect to be able to
407 // use the lang items, so we need to be sure to mark them as
409 reachable_context.worklist.extend(access_levels.map.iter().map(|(id, _)| *id));
410 for item in tcx.lang_items().items().iter() {
411 if let Some(did) = *item {
412 if let Some(hir_id) = tcx.hir().as_local_hir_id(did) {
413 reachable_context.worklist.push(hir_id);
418 let mut collect_private_impl_items = CollectPrivateImplItemsVisitor {
421 worklist: &mut reachable_context.worklist,
423 tcx.hir().krate().visit_all_item_likes(&mut collect_private_impl_items);
426 // Step 2: Mark all symbols that the symbols on the worklist touch.
427 reachable_context.propagate();
429 debug!("Inline reachability shows: {:?}", reachable_context.reachable_symbols);
431 // Return the set of reachable symbols.
432 ReachableSet(Lrc::new(reachable_context.reachable_symbols))
435 pub fn provide(providers: &mut Providers<'_>) {
436 *providers = Providers { reachable_set, ..*providers };