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430 lines
17 KiB
Rust
430 lines
17 KiB
Rust
// Finds items that are externally reachable, to determine which items
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// need to have their metadata (and possibly their AST) serialized.
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// All items that can be referred to through an exported name are
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// reachable, and when a reachable thing is inline or generic, it
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// makes all other generics or inline functions that it references
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// reachable as well.
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use hir::def_id::LocalDefIdSet;
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use rustc_hir as hir;
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use rustc_hir::def::{DefKind, Res};
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use rustc_hir::def_id::{DefId, LocalDefId};
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use rustc_hir::intravisit::{self, Visitor};
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use rustc_hir::Node;
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use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
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use rustc_middle::middle::privacy::{self, Level};
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use rustc_middle::query::Providers;
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use rustc_middle::ty::{self, TyCtxt};
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use rustc_session::config::CrateType;
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use rustc_target::spec::abi::Abi;
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// Returns true if the given item must be inlined because it may be
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// monomorphized or it was marked with `#[inline]`. This will only return
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// true for functions.
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fn item_might_be_inlined(tcx: TyCtxt<'_>, item: &hir::Item<'_>, attrs: &CodegenFnAttrs) -> bool {
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if attrs.requests_inline() {
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return true;
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}
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match item.kind {
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hir::ItemKind::Fn(ref sig, ..) if sig.header.is_const() => true,
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hir::ItemKind::Impl { .. } | hir::ItemKind::Fn(..) => {
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let generics = tcx.generics_of(item.owner_id);
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generics.requires_monomorphization(tcx)
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}
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_ => false,
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}
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}
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fn method_might_be_inlined(
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tcx: TyCtxt<'_>,
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impl_item: &hir::ImplItem<'_>,
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impl_src: LocalDefId,
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) -> bool {
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let codegen_fn_attrs = tcx.codegen_fn_attrs(impl_item.hir_id().owner.to_def_id());
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let generics = tcx.generics_of(impl_item.owner_id);
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if codegen_fn_attrs.requests_inline() || generics.requires_monomorphization(tcx) {
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return true;
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}
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if let hir::ImplItemKind::Fn(method_sig, _) = &impl_item.kind {
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if method_sig.header.is_const() {
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return true;
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}
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}
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match tcx.hir().find_by_def_id(impl_src) {
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Some(Node::Item(item)) => item_might_be_inlined(tcx, &item, codegen_fn_attrs),
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Some(..) | None => span_bug!(impl_item.span, "impl did is not an item"),
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}
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}
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// Information needed while computing reachability.
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struct ReachableContext<'tcx> {
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// The type context.
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tcx: TyCtxt<'tcx>,
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maybe_typeck_results: Option<&'tcx ty::TypeckResults<'tcx>>,
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// The set of items which must be exported in the linkage sense.
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reachable_symbols: LocalDefIdSet,
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// A worklist of item IDs. Each item ID in this worklist will be inlined
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// and will be scanned for further references.
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// FIXME(eddyb) benchmark if this would be faster as a `VecDeque`.
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worklist: Vec<LocalDefId>,
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// Whether any output of this compilation is a library
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any_library: bool,
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}
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impl<'tcx> Visitor<'tcx> for ReachableContext<'tcx> {
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fn visit_nested_body(&mut self, body: hir::BodyId) {
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let old_maybe_typeck_results =
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self.maybe_typeck_results.replace(self.tcx.typeck_body(body));
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let body = self.tcx.hir().body(body);
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self.visit_body(body);
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self.maybe_typeck_results = old_maybe_typeck_results;
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}
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fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
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let res = match expr.kind {
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hir::ExprKind::Path(ref qpath) => {
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Some(self.typeck_results().qpath_res(qpath, expr.hir_id))
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}
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hir::ExprKind::MethodCall(..) => self
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.typeck_results()
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.type_dependent_def(expr.hir_id)
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.map(|(kind, def_id)| Res::Def(kind, def_id)),
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_ => None,
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};
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if let Some(res) = res && let Some(def_id) = res.opt_def_id().and_then(|el| el.as_local()) {
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if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
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self.worklist.push(def_id);
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} else {
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match res {
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// If this path leads to a constant, then we need to
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// recurse into the constant to continue finding
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// items that are reachable.
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Res::Def(DefKind::Const | DefKind::AssocConst, _) => {
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self.worklist.push(def_id);
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}
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// If this wasn't a static, then the destination is
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// surely reachable.
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_ => {
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self.reachable_symbols.insert(def_id);
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}
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}
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}
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}
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intravisit::walk_expr(self, expr)
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}
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fn visit_inline_asm(&mut self, asm: &'tcx hir::InlineAsm<'tcx>, id: hir::HirId) {
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for (op, _) in asm.operands {
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if let hir::InlineAsmOperand::SymStatic { def_id, .. } = op {
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if let Some(def_id) = def_id.as_local() {
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self.reachable_symbols.insert(def_id);
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}
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}
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}
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intravisit::walk_inline_asm(self, asm, id);
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}
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}
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impl<'tcx> ReachableContext<'tcx> {
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/// Gets the type-checking results for the current body.
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/// As this will ICE if called outside bodies, only call when working with
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/// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
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#[track_caller]
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fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
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self.maybe_typeck_results
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.expect("`ReachableContext::typeck_results` called outside of body")
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}
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// Returns true if the given def ID represents a local item that is
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// eligible for inlining and false otherwise.
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fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
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let Some(def_id) = def_id.as_local() else {
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return false;
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};
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match self.tcx.hir().find_by_def_id(def_id) {
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Some(Node::Item(item)) => match item.kind {
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hir::ItemKind::Fn(..) => {
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item_might_be_inlined(self.tcx, &item, self.tcx.codegen_fn_attrs(def_id))
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}
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_ => false,
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},
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Some(Node::TraitItem(trait_method)) => match trait_method.kind {
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hir::TraitItemKind::Const(_, ref default) => default.is_some(),
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hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)) => true,
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hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
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| hir::TraitItemKind::Type(..) => false,
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},
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Some(Node::ImplItem(impl_item)) => match impl_item.kind {
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hir::ImplItemKind::Const(..) => true,
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hir::ImplItemKind::Fn(..) => {
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let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
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let impl_did = self.tcx.hir().get_parent_item(hir_id);
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method_might_be_inlined(self.tcx, impl_item, impl_did.def_id)
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}
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hir::ImplItemKind::Type(_) => false,
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},
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Some(_) => false,
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None => false, // This will happen for default methods.
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}
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}
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// Step 2: Mark all symbols that the symbols on the worklist touch.
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fn propagate(&mut self) {
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let mut scanned = LocalDefIdSet::default();
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while let Some(search_item) = self.worklist.pop() {
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if !scanned.insert(search_item) {
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continue;
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}
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if let Some(ref item) = self.tcx.hir().find_by_def_id(search_item) {
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self.propagate_node(item, search_item);
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}
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}
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}
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fn propagate_node(&mut self, node: &Node<'tcx>, search_item: LocalDefId) {
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if !self.any_library {
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// If we are building an executable, only explicitly extern
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// types need to be exported.
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let reachable =
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if let Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, ..), .. })
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| Node::ImplItem(hir::ImplItem {
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kind: hir::ImplItemKind::Fn(sig, ..), ..
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}) = *node
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{
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sig.header.abi != Abi::Rust
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} else {
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false
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};
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let codegen_attrs = if self.tcx.def_kind(search_item).has_codegen_attrs() {
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self.tcx.codegen_fn_attrs(search_item)
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} else {
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CodegenFnAttrs::EMPTY
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};
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let is_extern = codegen_attrs.contains_extern_indicator();
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let std_internal =
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codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
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if reachable || is_extern || std_internal {
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self.reachable_symbols.insert(search_item);
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}
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} else {
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// If we are building a library, then reachable symbols will
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// continue to participate in linkage after this product is
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// produced. In this case, we traverse the ast node, recursing on
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// all reachable nodes from this one.
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self.reachable_symbols.insert(search_item);
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}
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match *node {
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Node::Item(item) => {
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match item.kind {
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hir::ItemKind::Fn(.., body) => {
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if item_might_be_inlined(
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self.tcx,
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&item,
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self.tcx.codegen_fn_attrs(item.owner_id),
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) {
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self.visit_nested_body(body);
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}
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}
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// Reachable constants will be inlined into other crates
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// unconditionally, so we need to make sure that their
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// contents are also reachable.
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hir::ItemKind::Const(_, _, init) | hir::ItemKind::Static(_, _, init) => {
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self.visit_nested_body(init);
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}
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// These are normal, nothing reachable about these
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// inherently and their children are already in the
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// worklist, as determined by the privacy pass
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hir::ItemKind::ExternCrate(_)
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| hir::ItemKind::Use(..)
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| hir::ItemKind::OpaqueTy(..)
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| hir::ItemKind::TyAlias(..)
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| hir::ItemKind::Macro(..)
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| hir::ItemKind::Mod(..)
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| hir::ItemKind::ForeignMod { .. }
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| hir::ItemKind::Impl { .. }
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| hir::ItemKind::Trait(..)
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| hir::ItemKind::TraitAlias(..)
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| hir::ItemKind::Struct(..)
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| hir::ItemKind::Enum(..)
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| hir::ItemKind::Union(..)
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| hir::ItemKind::GlobalAsm(..) => {}
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}
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}
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Node::TraitItem(trait_method) => {
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match trait_method.kind {
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hir::TraitItemKind::Const(_, None)
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| hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_)) => {
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// Keep going, nothing to get exported
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}
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hir::TraitItemKind::Const(_, Some(body_id))
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| hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)) => {
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self.visit_nested_body(body_id);
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}
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hir::TraitItemKind::Type(..) => {}
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}
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}
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Node::ImplItem(impl_item) => match impl_item.kind {
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hir::ImplItemKind::Const(_, body) => {
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self.visit_nested_body(body);
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}
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hir::ImplItemKind::Fn(_, body) => {
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let impl_def_id = self.tcx.local_parent(search_item);
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if method_might_be_inlined(self.tcx, impl_item, impl_def_id) {
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self.visit_nested_body(body)
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}
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}
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hir::ImplItemKind::Type(_) => {}
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},
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Node::Expr(&hir::Expr {
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kind: hir::ExprKind::Closure(&hir::Closure { body, .. }),
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..
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}) => {
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self.visit_nested_body(body);
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}
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// Nothing to recurse on for these
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Node::ForeignItem(_)
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| Node::Variant(_)
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| Node::Ctor(..)
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| Node::Field(_)
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| Node::Ty(_)
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| Node::Crate(_) => {}
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_ => {
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bug!(
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"found unexpected node kind in worklist: {} ({:?})",
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self.tcx
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.hir()
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.node_to_string(self.tcx.hir().local_def_id_to_hir_id(search_item)),
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node,
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);
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}
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}
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}
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}
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fn check_item<'tcx>(
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tcx: TyCtxt<'tcx>,
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id: hir::ItemId,
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worklist: &mut Vec<LocalDefId>,
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effective_visibilities: &privacy::EffectiveVisibilities,
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) {
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if has_custom_linkage(tcx, id.owner_id.def_id) {
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worklist.push(id.owner_id.def_id);
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}
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if !matches!(tcx.def_kind(id.owner_id), DefKind::Impl { of_trait: true }) {
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return;
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}
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// We need only trait impls here, not inherent impls, and only non-exported ones
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if effective_visibilities.is_reachable(id.owner_id.def_id) {
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return;
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}
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let items = tcx.associated_item_def_ids(id.owner_id);
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worklist.extend(items.iter().map(|ii_ref| ii_ref.expect_local()));
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let Some(trait_def_id) = tcx.trait_id_of_impl(id.owner_id.to_def_id()) else {
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unreachable!();
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};
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if !trait_def_id.is_local() {
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return;
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}
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worklist
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.extend(tcx.provided_trait_methods(trait_def_id).map(|assoc| assoc.def_id.expect_local()));
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}
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fn has_custom_linkage(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
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// Anything which has custom linkage gets thrown on the worklist no
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// matter where it is in the crate, along with "special std symbols"
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// which are currently akin to allocator symbols.
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if !tcx.def_kind(def_id).has_codegen_attrs() {
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return false;
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}
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let codegen_attrs = tcx.codegen_fn_attrs(def_id);
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codegen_attrs.contains_extern_indicator()
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|| codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
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// FIXME(nbdd0121): `#[used]` are marked as reachable here so it's picked up by
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// `linked_symbols` in cg_ssa. They won't be exported in binary or cdylib due to their
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// `SymbolExportLevel::Rust` export level but may end up being exported in dylibs.
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|| codegen_attrs.flags.contains(CodegenFnAttrFlags::USED)
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|| codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
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}
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fn reachable_set(tcx: TyCtxt<'_>, (): ()) -> LocalDefIdSet {
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let effective_visibilities = &tcx.effective_visibilities(());
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let any_library =
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tcx.sess.crate_types().iter().any(|ty| {
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*ty == CrateType::Rlib || *ty == CrateType::Dylib || *ty == CrateType::ProcMacro
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});
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let mut reachable_context = ReachableContext {
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tcx,
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maybe_typeck_results: None,
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reachable_symbols: Default::default(),
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worklist: Vec::new(),
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any_library,
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};
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// Step 1: Seed the worklist with all nodes which were found to be public as
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// a result of the privacy pass along with all local lang items and impl items.
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// If other crates link to us, they're going to expect to be able to
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// use the lang items, so we need to be sure to mark them as
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// exported.
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reachable_context.worklist = effective_visibilities
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.iter()
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.filter_map(|(&id, effective_vis)| {
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effective_vis.is_public_at_level(Level::ReachableThroughImplTrait).then_some(id)
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})
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.collect::<Vec<_>>();
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for (_, def_id) in tcx.lang_items().iter() {
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if let Some(def_id) = def_id.as_local() {
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reachable_context.worklist.push(def_id);
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}
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}
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{
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// Some methods from non-exported (completely private) trait impls still have to be
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// reachable if they are called from inlinable code. Generally, it's not known until
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// monomorphization if a specific trait impl item can be reachable or not. So, we
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// conservatively mark all of them as reachable.
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// FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
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// items of non-exported traits (or maybe all local traits?) unless their respective
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// trait items are used from inlinable code through method call syntax or UFCS, or their
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// trait is a lang item.
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let crate_items = tcx.hir_crate_items(());
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for id in crate_items.items() {
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check_item(tcx, id, &mut reachable_context.worklist, effective_visibilities);
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}
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for id in crate_items.impl_items() {
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if has_custom_linkage(tcx, id.owner_id.def_id) {
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reachable_context.worklist.push(id.owner_id.def_id);
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}
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}
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}
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// Step 2: Mark all symbols that the symbols on the worklist touch.
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reachable_context.propagate();
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debug!("Inline reachability shows: {:?}", reachable_context.reachable_symbols);
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// Return the set of reachable symbols.
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reachable_context.reachable_symbols
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}
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pub fn provide(providers: &mut Providers) {
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*providers = Providers { reachable_set, ..*providers };
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}
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