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;
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, DefIdTree, 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: FxHashSet<LocalDefId>,
69 // A worklist of item IDs. Each item ID in this worklist will be inlined
70 // and will be scanned for further references.
71 // FIXME(eddyb) benchmark if this would be faster as a `VecDeque`.
72 worklist: Vec<LocalDefId>,
73 // Whether any output of this compilation is a library
77 impl<'tcx> Visitor<'tcx> for ReachableContext<'tcx> {
78 type Map = intravisit::ErasedMap<'tcx>;
80 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
81 NestedVisitorMap::None
84 fn visit_nested_body(&mut self, body: hir::BodyId) {
85 let old_maybe_typeck_results =
86 self.maybe_typeck_results.replace(self.tcx.typeck_body(body));
87 let body = self.tcx.hir().body(body);
88 self.visit_body(body);
89 self.maybe_typeck_results = old_maybe_typeck_results;
92 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
93 let res = match expr.kind {
94 hir::ExprKind::Path(ref qpath) => {
95 Some(self.typeck_results().qpath_res(qpath, expr.hir_id))
97 hir::ExprKind::MethodCall(..) => self
99 .type_dependent_def(expr.hir_id)
100 .map(|(kind, def_id)| Res::Def(kind, def_id)),
104 if let Some(res) = res {
105 if let Some(def_id) = res.opt_def_id().and_then(|def_id| def_id.as_local()) {
106 if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
107 self.worklist.push(def_id);
110 // If this path leads to a constant, then we need to
111 // recurse into the constant to continue finding
112 // items that are reachable.
113 Res::Def(DefKind::Const | DefKind::AssocConst, _) => {
114 self.worklist.push(def_id);
117 // If this wasn't a static, then the destination is
120 self.reachable_symbols.insert(def_id);
127 intravisit::walk_expr(self, expr)
131 impl<'tcx> ReachableContext<'tcx> {
132 /// Gets the type-checking results for the current body.
133 /// As this will ICE if called outside bodies, only call when working with
134 /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
136 fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
137 self.maybe_typeck_results
138 .expect("`ReachableContext::typeck_results` called outside of body")
141 // Returns true if the given def ID represents a local item that is
142 // eligible for inlining and false otherwise.
143 fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
144 let hir_id = match def_id.as_local() {
145 Some(def_id) => self.tcx.hir().local_def_id_to_hir_id(def_id),
151 match self.tcx.hir().find(hir_id) {
152 Some(Node::Item(item)) => match item.kind {
153 hir::ItemKind::Fn(..) => {
154 item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
158 Some(Node::TraitItem(trait_method)) => match trait_method.kind {
159 hir::TraitItemKind::Const(_, ref default) => default.is_some(),
160 hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)) => true,
161 hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
162 | hir::TraitItemKind::Type(..) => false,
164 Some(Node::ImplItem(impl_item)) => {
165 match impl_item.kind {
166 hir::ImplItemKind::Const(..) => true,
167 hir::ImplItemKind::Fn(..) => {
168 let attrs = self.tcx.codegen_fn_attrs(def_id);
169 let generics = self.tcx.generics_of(def_id);
170 if generics.requires_monomorphization(self.tcx) || attrs.requests_inline() {
173 let impl_did = self.tcx.hir().get_parent_did(hir_id);
174 // Check the impl. If the generics on the self
175 // type of the impl require inlining, this method
177 let impl_hir_id = self.tcx.hir().local_def_id_to_hir_id(impl_did);
178 match self.tcx.hir().expect_item(impl_hir_id).kind {
179 hir::ItemKind::Impl { .. } => {
180 let generics = self.tcx.generics_of(impl_did);
181 generics.requires_monomorphization(self.tcx)
187 hir::ImplItemKind::TyAlias(_) => false,
191 None => false, // This will happen for default methods.
195 // Step 2: Mark all symbols that the symbols on the worklist touch.
196 fn propagate(&mut self) {
197 let mut scanned = FxHashSet::default();
198 while let Some(search_item) = self.worklist.pop() {
199 if !scanned.insert(search_item) {
203 if let Some(ref item) =
204 self.tcx.hir().find(self.tcx.hir().local_def_id_to_hir_id(search_item))
206 self.propagate_node(item, search_item);
211 fn propagate_node(&mut self, node: &Node<'tcx>, search_item: LocalDefId) {
212 if !self.any_library {
213 // If we are building an executable, only explicitly extern
214 // types need to be exported.
215 if let Node::Item(item) = *node {
216 let reachable = if let hir::ItemKind::Fn(ref sig, ..) = item.kind {
217 sig.header.abi != Abi::Rust
221 let def_id = self.tcx.hir().local_def_id(item.hir_id);
222 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
223 let is_extern = codegen_attrs.contains_extern_indicator();
225 codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
226 if reachable || is_extern || std_internal {
227 self.reachable_symbols.insert(search_item);
231 // If we are building a library, then reachable symbols will
232 // continue to participate in linkage after this product is
233 // produced. In this case, we traverse the ast node, recursing on
234 // all reachable nodes from this one.
235 self.reachable_symbols.insert(search_item);
239 Node::Item(item) => {
241 hir::ItemKind::Fn(.., body) => {
242 let def_id = self.tcx.hir().local_def_id(item.hir_id);
243 if item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
245 self.visit_nested_body(body);
249 // Reachable constants will be inlined into other crates
250 // unconditionally, so we need to make sure that their
251 // contents are also reachable.
252 hir::ItemKind::Const(_, init) => {
253 self.visit_nested_body(init);
256 // These are normal, nothing reachable about these
257 // inherently and their children are already in the
258 // worklist, as determined by the privacy pass
259 hir::ItemKind::ExternCrate(_)
260 | hir::ItemKind::Use(..)
261 | hir::ItemKind::OpaqueTy(..)
262 | hir::ItemKind::TyAlias(..)
263 | hir::ItemKind::Static(..)
264 | hir::ItemKind::Mod(..)
265 | hir::ItemKind::ForeignMod(..)
266 | hir::ItemKind::Impl { .. }
267 | hir::ItemKind::Trait(..)
268 | hir::ItemKind::TraitAlias(..)
269 | hir::ItemKind::Struct(..)
270 | hir::ItemKind::Enum(..)
271 | hir::ItemKind::Union(..)
272 | hir::ItemKind::GlobalAsm(..) => {}
275 Node::TraitItem(trait_method) => {
276 match trait_method.kind {
277 hir::TraitItemKind::Const(_, None)
278 | hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_)) => {
279 // Keep going, nothing to get exported
281 hir::TraitItemKind::Const(_, Some(body_id))
282 | hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)) => {
283 self.visit_nested_body(body_id);
285 hir::TraitItemKind::Type(..) => {}
288 Node::ImplItem(impl_item) => match impl_item.kind {
289 hir::ImplItemKind::Const(_, body) => {
290 self.visit_nested_body(body);
292 hir::ImplItemKind::Fn(_, body) => {
294 self.tcx.parent(search_item.to_def_id()).unwrap().expect_local();
295 if method_might_be_inlined(self.tcx, impl_item, impl_def_id) {
296 self.visit_nested_body(body)
299 hir::ImplItemKind::TyAlias(_) => {}
301 Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., body, _, _), .. }) => {
302 self.visit_nested_body(body);
304 // Nothing to recurse on for these
310 | Node::MacroDef(_) => {}
313 "found unexpected node kind in worklist: {} ({:?})",
316 .node_to_string(self.tcx.hir().local_def_id_to_hir_id(search_item)),
324 // Some methods from non-exported (completely private) trait impls still have to be
325 // reachable if they are called from inlinable code. Generally, it's not known until
326 // monomorphization if a specific trait impl item can be reachable or not. So, we
327 // conservatively mark all of them as reachable.
328 // FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
329 // items of non-exported traits (or maybe all local traits?) unless their respective
330 // trait items are used from inlinable code through method call syntax or UFCS, or their
331 // trait is a lang item.
332 struct CollectPrivateImplItemsVisitor<'a, 'tcx> {
334 access_levels: &'a privacy::AccessLevels,
335 worklist: &'a mut Vec<LocalDefId>,
338 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for CollectPrivateImplItemsVisitor<'a, 'tcx> {
339 fn visit_item(&mut self, item: &hir::Item<'_>) {
340 // Anything which has custom linkage gets thrown on the worklist no
341 // matter where it is in the crate, along with "special std symbols"
342 // which are currently akin to allocator symbols.
343 let def_id = self.tcx.hir().local_def_id(item.hir_id);
344 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
345 if codegen_attrs.contains_extern_indicator()
346 || codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
348 self.worklist.push(def_id);
351 // We need only trait impls here, not inherent impls, and only non-exported ones
352 if let hir::ItemKind::Impl { of_trait: Some(ref trait_ref), ref items, .. } = item.kind {
353 if !self.access_levels.is_reachable(item.hir_id) {
354 // FIXME(#53488) remove `let`
357 .extend(items.iter().map(|ii_ref| tcx.hir().local_def_id(ii_ref.id.hir_id)));
359 let trait_def_id = match trait_ref.path.res {
360 Res::Def(DefKind::Trait, def_id) => def_id,
364 if !trait_def_id.is_local() {
368 self.worklist.extend(
369 tcx.provided_trait_methods(trait_def_id)
370 .map(|assoc| assoc.def_id.expect_local()),
376 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
378 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {
379 // processed in visit_item above
383 fn reachable_set<'tcx>(tcx: TyCtxt<'tcx>, crate_num: CrateNum) -> FxHashSet<LocalDefId> {
384 debug_assert!(crate_num == LOCAL_CRATE);
386 let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
389 tcx.sess.crate_types().iter().any(|ty| {
390 *ty == CrateType::Rlib || *ty == CrateType::Dylib || *ty == CrateType::ProcMacro
392 let mut reachable_context = ReachableContext {
394 maybe_typeck_results: None,
395 reachable_symbols: Default::default(),
396 worklist: Vec::new(),
400 // Step 1: Seed the worklist with all nodes which were found to be public as
401 // a result of the privacy pass along with all local lang items and impl items.
402 // If other crates link to us, they're going to expect to be able to
403 // use the lang items, so we need to be sure to mark them as
407 .extend(access_levels.map.iter().map(|(id, _)| tcx.hir().local_def_id(*id)));
408 for item in tcx.lang_items().items().iter() {
409 if let Some(def_id) = *item {
410 if let Some(def_id) = def_id.as_local() {
411 reachable_context.worklist.push(def_id);
416 let mut collect_private_impl_items = CollectPrivateImplItemsVisitor {
419 worklist: &mut reachable_context.worklist,
421 tcx.hir().krate().visit_all_item_likes(&mut collect_private_impl_items);
424 // Step 2: Mark all symbols that the symbols on the worklist touch.
425 reachable_context.propagate();
427 debug!("Inline reachability shows: {:?}", reachable_context.reachable_symbols);
429 // Return the set of reachable symbols.
430 reachable_context.reachable_symbols
433 pub fn provide(providers: &mut Providers) {
434 *providers = Providers { reachable_set, ..*providers };