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Don't emit useless vptrs for marker traits

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This commit is contained in:
Maybe Waffle 2023-07-19 11:50:40 +00:00
parent b5d1228508
commit 1f02c75718
4 changed files with 25 additions and 13 deletions
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25
compiler/rustc_trait_selection/src/traits/vtable.rs
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@ -147,9 +147,6 @@ fn prepare_vtable_segments_inner<'tcx, T>(
}
}
// Other than the left-most path, vptr should be emitted for each trait.
emit_vptr_on_new_entry = true;
// emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
while let Some((inner_most_trait_ref, emit_vptr, mut siblings)) = stack.pop() {
segment_visitor(VtblSegment::TraitOwnEntries {
@ -157,6 +154,14 @@ fn prepare_vtable_segments_inner<'tcx, T>(
emit_vptr,
})?;
// If we've emitted (fed to `segment_visitor`) a trait that has methods present in the vtable,
// we'll need to emit vptrs from now on.
if !emit_vptr_on_new_entry
&& has_own_existential_vtable_entries(tcx, inner_most_trait_ref.def_id())
{
emit_vptr_on_new_entry = true;
}
if let Some(next_inner_most_trait_ref) =
siblings.find(|&sibling| visited.insert(sibling.to_predicate(tcx)))
{
@ -196,11 +201,23 @@ fn dump_vtable_entries<'tcx>(
});
}
fn has_own_existential_vtable_entries(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool {
own_existential_vtable_entries_iter(tcx, trait_def_id).next().is_some()
}
fn own_existential_vtable_entries(tcx: TyCtxt<'_>, trait_def_id: DefId) -> &[DefId] {
tcx.arena.alloc_from_iter(own_existential_vtable_entries_iter(tcx, trait_def_id))
}
fn own_existential_vtable_entries_iter(
tcx: TyCtxt<'_>,
trait_def_id: DefId,
) -> impl Iterator<Item = DefId> + '_ {
let trait_methods = tcx
.associated_items(trait_def_id)
.in_definition_order()
.filter(|item| item.kind == ty::AssocKind::Fn);
// Now list each method's DefId (for within its trait).
let own_entries = trait_methods.filter_map(move |&trait_method| {
debug!("own_existential_vtable_entry: trait_method={:?}", trait_method);
@ -215,7 +232,7 @@ fn own_existential_vtable_entries(tcx: TyCtxt<'_>, trait_def_id: DefId) -> &[Def
Some(def_id)
});
tcx.arena.alloc_from_iter(own_entries.into_iter())
own_entries
}
/// Given a trait `trait_ref`, iterates the vtable entries