rust/compiler/rustc_passes/src/reachable.rs
2023-07-28 22:21:40 +02:00

430 lines
17 KiB
Rust

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