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_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| {
109 def_id.as_local().map(|def_id| (self.tcx.hir().as_local_hir_id(def_id), def_id))
111 if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
112 self.worklist.push(hir_id);
115 // If this path leads to a constant, then we need to
116 // recurse into the constant to continue finding
117 // items that are reachable.
118 Res::Def(DefKind::Const | DefKind::AssocConst, _) => {
119 self.worklist.push(hir_id);
122 // If this wasn't a static, then the destination is
125 self.reachable_symbols.insert(hir_id);
134 intravisit::walk_expr(self, expr)
138 impl<'tcx> ReachableContext<'tcx> {
139 /// Gets the type-checking results for the current body.
140 /// As this will ICE if called outside bodies, only call when working with
141 /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
143 fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
144 self.maybe_typeck_results
145 .expect("`ReachableContext::typeck_results` called outside of body")
148 // Returns true if the given def ID represents a local item that is
149 // eligible for inlining and false otherwise.
150 fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
151 let hir_id = match def_id.as_local() {
152 Some(def_id) => self.tcx.hir().as_local_hir_id(def_id),
158 match self.tcx.hir().find(hir_id) {
159 Some(Node::Item(item)) => match item.kind {
160 hir::ItemKind::Fn(..) => {
161 item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
165 Some(Node::TraitItem(trait_method)) => match trait_method.kind {
166 hir::TraitItemKind::Const(_, ref default) => default.is_some(),
167 hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)) => true,
168 hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
169 | hir::TraitItemKind::Type(..) => false,
171 Some(Node::ImplItem(impl_item)) => {
172 match impl_item.kind {
173 hir::ImplItemKind::Const(..) => true,
174 hir::ImplItemKind::Fn(..) => {
175 let attrs = self.tcx.codegen_fn_attrs(def_id);
176 let generics = self.tcx.generics_of(def_id);
177 if generics.requires_monomorphization(self.tcx) || attrs.requests_inline() {
180 let impl_did = self.tcx.hir().get_parent_did(hir_id);
181 // Check the impl. If the generics on the self
182 // type of the impl require inlining, this method
184 let impl_hir_id = self.tcx.hir().as_local_hir_id(impl_did);
185 match self.tcx.hir().expect_item(impl_hir_id).kind {
186 hir::ItemKind::Impl { .. } => {
187 let generics = self.tcx.generics_of(impl_did);
188 generics.requires_monomorphization(self.tcx)
194 hir::ImplItemKind::TyAlias(_) => false,
198 None => false, // This will happen for default methods.
202 // Step 2: Mark all symbols that the symbols on the worklist touch.
203 fn propagate(&mut self) {
204 let mut scanned = FxHashSet::default();
205 while let Some(search_item) = self.worklist.pop() {
206 if !scanned.insert(search_item) {
210 if let Some(ref item) = self.tcx.hir().find(search_item) {
211 self.propagate_node(item, search_item);
216 fn propagate_node(&mut self, node: &Node<'tcx>, search_item: hir::HirId) {
217 if !self.any_library {
218 // If we are building an executable, only explicitly extern
219 // types need to be exported.
220 if let Node::Item(item) = *node {
221 let reachable = if let hir::ItemKind::Fn(ref sig, ..) = item.kind {
222 sig.header.abi != Abi::Rust
226 let def_id = self.tcx.hir().local_def_id(item.hir_id);
227 let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
228 let is_extern = codegen_attrs.contains_extern_indicator();
230 codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
231 if reachable || is_extern || std_internal {
232 self.reachable_symbols.insert(search_item);
236 // If we are building a library, then reachable symbols will
237 // continue to participate in linkage after this product is
238 // produced. In this case, we traverse the ast node, recursing on
239 // all reachable nodes from this one.
240 self.reachable_symbols.insert(search_item);
244 Node::Item(item) => {
246 hir::ItemKind::Fn(.., body) => {
247 let def_id = self.tcx.hir().local_def_id(item.hir_id);
248 if item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
250 self.visit_nested_body(body);
254 // Reachable constants will be inlined into other crates
255 // unconditionally, so we need to make sure that their
256 // contents are also reachable.
257 hir::ItemKind::Const(_, init) => {
258 self.visit_nested_body(init);
261 // These are normal, nothing reachable about these
262 // inherently and their children are already in the
263 // worklist, as determined by the privacy pass
264 hir::ItemKind::ExternCrate(_)
265 | hir::ItemKind::Use(..)
266 | hir::ItemKind::OpaqueTy(..)
267 | hir::ItemKind::TyAlias(..)
268 | hir::ItemKind::Static(..)
269 | hir::ItemKind::Mod(..)
270 | hir::ItemKind::ForeignMod(..)
271 | hir::ItemKind::Impl { .. }
272 | hir::ItemKind::Trait(..)
273 | hir::ItemKind::TraitAlias(..)
274 | hir::ItemKind::Struct(..)
275 | hir::ItemKind::Enum(..)
276 | hir::ItemKind::Union(..)
277 | hir::ItemKind::GlobalAsm(..) => {}
280 Node::TraitItem(trait_method) => {
281 match trait_method.kind {
282 hir::TraitItemKind::Const(_, None)
283 | hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_)) => {
284 // Keep going, nothing to get exported
286 hir::TraitItemKind::Const(_, Some(body_id))
287 | hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)) => {
288 self.visit_nested_body(body_id);
290 hir::TraitItemKind::Type(..) => {}
293 Node::ImplItem(impl_item) => match impl_item.kind {
294 hir::ImplItemKind::Const(_, body) => {
295 self.visit_nested_body(body);
297 hir::ImplItemKind::Fn(_, body) => {
298 let did = self.tcx.hir().get_parent_did(search_item);
299 if method_might_be_inlined(self.tcx, impl_item, did) {
300 self.visit_nested_body(body)
303 hir::ImplItemKind::TyAlias(_) => {}
305 Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., body, _, _), .. }) => {
306 self.visit_nested_body(body);
308 // Nothing to recurse on for these
314 | Node::MacroDef(_) => {}
317 "found unexpected node kind in worklist: {} ({:?})",
318 self.tcx.hir().node_to_string(search_item),
326 // Some methods from non-exported (completely private) trait impls still have to be
327 // reachable if they are called from inlinable code. Generally, it's not known until
328 // monomorphization if a specific trait impl item can be reachable or not. So, we
329 // conservatively mark all of them as reachable.
330 // FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
331 // items of non-exported traits (or maybe all local traits?) unless their respective
332 // trait items are used from inlinable code through method call syntax or UFCS, or their
333 // trait is a lang item.
334 struct CollectPrivateImplItemsVisitor<'a, 'tcx> {
336 access_levels: &'a privacy::AccessLevels,
337 worklist: &'a mut Vec<hir::HirId>,
340 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for CollectPrivateImplItemsVisitor<'a, 'tcx> {
341 fn visit_item(&mut self, item: &hir::Item<'_>) {
342 // Anything which has custom linkage gets thrown on the worklist no
343 // matter where it is in the crate, along with "special std symbols"
344 // which are currently akin to allocator symbols.
345 let def_id = self.tcx.hir().local_def_id(item.hir_id);
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(item.hir_id);
353 // We need only trait impls here, not inherent impls, and only non-exported ones
354 if let hir::ItemKind::Impl { of_trait: Some(ref trait_ref), ref items, .. } = item.kind {
355 if !self.access_levels.is_reachable(item.hir_id) {
356 self.worklist.extend(items.iter().map(|ii_ref| ii_ref.id.hir_id));
358 let trait_def_id = match trait_ref.path.res {
359 Res::Def(DefKind::Trait, def_id) => def_id,
363 if !trait_def_id.is_local() {
367 // FIXME(#53488) remove `let`
369 self.worklist.extend(
370 tcx.provided_trait_methods(trait_def_id)
371 .map(|assoc| tcx.hir().as_local_hir_id(assoc.def_id.expect_local())),
377 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
379 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {
380 // processed in visit_item above
384 fn reachable_set<'tcx>(tcx: TyCtxt<'tcx>, crate_num: CrateNum) -> &'tcx HirIdSet {
385 debug_assert!(crate_num == LOCAL_CRATE);
387 let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
390 tcx.sess.crate_types().iter().any(|ty| {
391 *ty == CrateType::Rlib || *ty == CrateType::Dylib || *ty == CrateType::ProcMacro
393 let mut reachable_context = ReachableContext {
395 maybe_typeck_results: None,
396 reachable_symbols: Default::default(),
397 worklist: Vec::new(),
401 // Step 1: Seed the worklist with all nodes which were found to be public as
402 // a result of the privacy pass along with all local lang items and impl items.
403 // If other crates link to us, they're going to expect to be able to
404 // use the lang items, so we need to be sure to mark them as
406 reachable_context.worklist.extend(access_levels.map.iter().map(|(id, _)| *id));
407 for item in tcx.lang_items().items().iter() {
408 if let Some(did) = *item {
409 if let Some(hir_id) = did.as_local().map(|did| tcx.hir().as_local_hir_id(did)) {
410 reachable_context.worklist.push(hir_id);
415 let mut collect_private_impl_items = CollectPrivateImplItemsVisitor {
418 worklist: &mut reachable_context.worklist,
420 tcx.hir().krate().visit_all_item_likes(&mut collect_private_impl_items);
423 // Step 2: Mark all symbols that the symbols on the worklist touch.
424 reachable_context.propagate();
426 debug!("Inline reachability shows: {:?}", reachable_context.reachable_symbols);
428 // Return the set of reachable symbols.
429 tcx.arena.alloc(reachable_context.reachable_symbols)
432 pub fn provide(providers: &mut Providers) {
433 *providers = Providers { reachable_set, ..*providers };