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().as_local_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_tables: Option<&'tcx ty::TypeckTables<'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_tables = self.maybe_typeck_tables.replace(self.tcx.body_tables(body));
85 let body = self.tcx.hir().body(body);
86 self.visit_body(body);
87 self.maybe_typeck_tables = old_maybe_typeck_tables;
90 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
91 let res = match expr.kind {
92 hir::ExprKind::Path(ref qpath) => Some(self.tables().qpath_res(qpath, expr.hir_id)),
93 hir::ExprKind::MethodCall(..) => self
95 .type_dependent_def(expr.hir_id)
96 .map(|(kind, def_id)| Res::Def(kind, def_id)),
101 Some(Res::Local(hir_id)) => {
102 self.reachable_symbols.insert(hir_id);
105 if let Some((hir_id, def_id)) = res.opt_def_id().and_then(|def_id| {
106 def_id.as_local().map(|def_id| (self.tcx.hir().as_local_hir_id(def_id), def_id))
108 if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
109 self.worklist.push(hir_id);
112 // If this path leads to a constant, then we need to
113 // recurse into the constant to continue finding
114 // items that are reachable.
115 Res::Def(DefKind::Const | DefKind::AssocConst, _) => {
116 self.worklist.push(hir_id);
119 // If this wasn't a static, then the destination is
122 self.reachable_symbols.insert(hir_id);
131 intravisit::walk_expr(self, expr)
135 impl<'tcx> ReachableContext<'tcx> {
136 /// Gets the type-checking side-tables for the current body.
137 /// As this will ICE if called outside bodies, only call when working with
138 /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
140 fn tables(&self) -> &'tcx ty::TypeckTables<'tcx> {
141 self.maybe_typeck_tables.expect("`ReachableContext::tables` called outside of body")
144 // Returns true if the given def ID represents a local item that is
145 // eligible for inlining and false otherwise.
146 fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
147 let hir_id = match def_id.as_local() {
148 Some(def_id) => self.tcx.hir().as_local_hir_id(def_id),
154 match self.tcx.hir().find(hir_id) {
155 Some(Node::Item(item)) => match item.kind {
156 hir::ItemKind::Fn(..) => {
157 item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
161 Some(Node::TraitItem(trait_method)) => match trait_method.kind {
162 hir::TraitItemKind::Const(_, ref default) => default.is_some(),
163 hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)) => true,
164 hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
165 | hir::TraitItemKind::Type(..) => false,
167 Some(Node::ImplItem(impl_item)) => {
168 match impl_item.kind {
169 hir::ImplItemKind::Const(..) => true,
170 hir::ImplItemKind::Fn(..) => {
171 let attrs = self.tcx.codegen_fn_attrs(def_id);
172 let generics = self.tcx.generics_of(def_id);
173 if generics.requires_monomorphization(self.tcx) || attrs.requests_inline() {
176 let impl_did = self.tcx.hir().get_parent_did(hir_id);
177 // Check the impl. If the generics on the self
178 // type of the impl require inlining, this method
180 let impl_hir_id = self.tcx.hir().as_local_hir_id(impl_did);
181 match self.tcx.hir().expect_item(impl_hir_id).kind {
182 hir::ItemKind::Impl { .. } => {
183 let generics = self.tcx.generics_of(impl_did);
184 generics.requires_monomorphization(self.tcx)
190 hir::ImplItemKind::TyAlias(_) => false,
194 None => false, // This will happen for default methods.
198 // Step 2: Mark all symbols that the symbols on the worklist touch.
199 fn propagate(&mut self) {
200 let mut scanned = FxHashSet::default();
201 while let Some(search_item) = self.worklist.pop() {
202 if !scanned.insert(search_item) {
206 if let Some(ref item) = self.tcx.hir().find(search_item) {
207 self.propagate_node(item, search_item);
212 fn propagate_node(&mut self, node: &Node<'tcx>, search_item: hir::HirId) {
213 if !self.any_library {
214 // If we are building an executable, only explicitly extern
215 // types need to be exported.
216 if let Node::Item(item) = *node {
217 let reachable = if let hir::ItemKind::Fn(ref sig, ..) = item.kind {
218 sig.header.abi != Abi::Rust
222 let def_id = self.tcx.hir().local_def_id(item.hir_id);
223 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
224 let is_extern = codegen_attrs.contains_extern_indicator();
226 codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
227 if reachable || is_extern || std_internal {
228 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 let def_id = self.tcx.hir().local_def_id(item.hir_id);
244 if item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
246 self.visit_nested_body(body);
250 // Reachable constants will be inlined into other crates
251 // unconditionally, so we need to make sure that their
252 // contents are also reachable.
253 hir::ItemKind::Const(_, init) => {
254 self.visit_nested_body(init);
257 // These are normal, nothing reachable about these
258 // inherently and their children are already in the
259 // worklist, as determined by the privacy pass
260 hir::ItemKind::ExternCrate(_)
261 | hir::ItemKind::Use(..)
262 | hir::ItemKind::OpaqueTy(..)
263 | hir::ItemKind::TyAlias(..)
264 | hir::ItemKind::Static(..)
265 | hir::ItemKind::Mod(..)
266 | hir::ItemKind::ForeignMod(..)
267 | hir::ItemKind::Impl { .. }
268 | hir::ItemKind::Trait(..)
269 | hir::ItemKind::TraitAlias(..)
270 | hir::ItemKind::Struct(..)
271 | hir::ItemKind::Enum(..)
272 | hir::ItemKind::Union(..)
273 | hir::ItemKind::GlobalAsm(..) => {}
276 Node::TraitItem(trait_method) => {
277 match trait_method.kind {
278 hir::TraitItemKind::Const(_, None)
279 | hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_)) => {
280 // Keep going, nothing to get exported
282 hir::TraitItemKind::Const(_, Some(body_id))
283 | hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)) => {
284 self.visit_nested_body(body_id);
286 hir::TraitItemKind::Type(..) => {}
289 Node::ImplItem(impl_item) => match impl_item.kind {
290 hir::ImplItemKind::Const(_, body) => {
291 self.visit_nested_body(body);
293 hir::ImplItemKind::Fn(_, body) => {
294 let did = self.tcx.hir().get_parent_did(search_item);
295 if method_might_be_inlined(self.tcx, impl_item, did) {
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: {} ({:?})",
314 self.tcx.hir().node_to_string(search_item),
322 // Some methods from non-exported (completely private) trait impls still have to be
323 // reachable if they are called from inlinable code. Generally, it's not known until
324 // monomorphization if a specific trait impl item can be reachable or not. So, we
325 // conservatively mark all of them as reachable.
326 // FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
327 // items of non-exported traits (or maybe all local traits?) unless their respective
328 // trait items are used from inlinable code through method call syntax or UFCS, or their
329 // trait is a lang item.
330 struct CollectPrivateImplItemsVisitor<'a, 'tcx> {
332 access_levels: &'a privacy::AccessLevels,
333 worklist: &'a mut Vec<hir::HirId>,
336 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for CollectPrivateImplItemsVisitor<'a, 'tcx> {
337 fn visit_item(&mut self, item: &hir::Item<'_>) {
338 // Anything which has custom linkage gets thrown on the worklist no
339 // matter where it is in the crate, along with "special std symbols"
340 // which are currently akin to allocator symbols.
341 let def_id = self.tcx.hir().local_def_id(item.hir_id);
342 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
343 if codegen_attrs.contains_extern_indicator()
344 || codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
346 self.worklist.push(item.hir_id);
349 // We need only trait impls here, not inherent impls, and only non-exported ones
350 if let hir::ItemKind::Impl { of_trait: Some(ref trait_ref), ref items, .. } = item.kind {
351 if !self.access_levels.is_reachable(item.hir_id) {
352 self.worklist.extend(items.iter().map(|ii_ref| ii_ref.id.hir_id));
354 let trait_def_id = match trait_ref.path.res {
355 Res::Def(DefKind::Trait, def_id) => def_id,
359 if !trait_def_id.is_local() {
363 // FIXME(#53488) remove `let`
365 self.worklist.extend(
366 tcx.provided_trait_methods(trait_def_id)
367 .map(|assoc| tcx.hir().as_local_hir_id(assoc.def_id.expect_local())),
373 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
375 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {
376 // processed in visit_item above
380 fn reachable_set<'tcx>(tcx: TyCtxt<'tcx>, crate_num: CrateNum) -> &'tcx HirIdSet {
381 debug_assert!(crate_num == LOCAL_CRATE);
383 let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
386 tcx.sess.crate_types().iter().any(|ty| {
387 *ty == CrateType::Rlib || *ty == CrateType::Dylib || *ty == CrateType::ProcMacro
389 let mut reachable_context = ReachableContext {
391 maybe_typeck_tables: None,
392 reachable_symbols: Default::default(),
393 worklist: Vec::new(),
397 // Step 1: Seed the worklist with all nodes which were found to be public as
398 // a result of the privacy pass along with all local lang items and impl items.
399 // If other crates link to us, they're going to expect to be able to
400 // use the lang items, so we need to be sure to mark them as
402 reachable_context.worklist.extend(access_levels.map.iter().map(|(id, _)| *id));
403 for item in tcx.lang_items().items().iter() {
404 if let Some(did) = *item {
405 if let Some(hir_id) = did.as_local().map(|did| tcx.hir().as_local_hir_id(did)) {
406 reachable_context.worklist.push(hir_id);
411 let mut collect_private_impl_items = CollectPrivateImplItemsVisitor {
414 worklist: &mut reachable_context.worklist,
416 tcx.hir().krate().visit_all_item_likes(&mut collect_private_impl_items);
419 // Step 2: Mark all symbols that the symbols on the worklist touch.
420 reachable_context.propagate();
422 debug!("Inline reachability shows: {:?}", reachable_context.reachable_symbols);
424 // Return the set of reachable symbols.
425 tcx.arena.alloc(reachable_context.reachable_symbols)
428 pub fn provide(providers: &mut Providers<'_>) {
429 *providers = Providers { reachable_set, ..*providers };