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Slightly refactor 'exiting_out loop in `prepare_vtable_segments` 

1. Hide the option as an iterator, so it's nicer to work with
2. Replace a loop with `find`
This commit is contained in:
Maybe Waffle 2023-07-19 10:19:12 +00:00
parent 364fc444a5
commit d567f0fc68
1 changed files with 22 additions and 20 deletions
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42
compiler/rustc_trait_selection/src/traits/vtable.rs
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@ -87,7 +87,7 @@ fn prepare_vtable_segments_inner<'tcx, T>(
let mut visited = PredicateSet::new(tcx);
let predicate = trait_ref.without_const().to_predicate(tcx);
let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> =
smallvec![(trait_ref, emit_vptr_on_new_entry, None)];
smallvec![(trait_ref, emit_vptr_on_new_entry, maybe_iter(None))];
visited.insert(predicate);
// the main traversal loop:
@ -138,7 +138,7 @@ fn prepare_vtable_segments_inner<'tcx, T>(
stack.push((
next_super_trait,
emit_vptr_on_new_entry,
Some(direct_super_traits_iter),
maybe_iter(Some(direct_super_traits_iter)),
))
}
@ -152,30 +152,26 @@ fn prepare_vtable_segments_inner<'tcx, T>(
// emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
'exiting_out: loop {
if let Some((inner_most_trait_ref, emit_vptr, siblings_opt)) = stack.last_mut() {
if let Some((inner_most_trait_ref, emit_vptr, siblings)) = stack.last_mut() {
segment_visitor(VtblSegment::TraitOwnEntries {
trait_ref: *inner_most_trait_ref,
emit_vptr: *emit_vptr,
})?;
'exiting_out_skip_visited_traits: loop {
if let Some(siblings) = siblings_opt {
if let Some(next_inner_most_trait_ref) = siblings.next() {
if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) {
// We're throwing away potential constness of super traits here.
// FIXME: handle ~const super traits
let next_inner_most_trait_ref =
next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
*inner_most_trait_ref = next_inner_most_trait_ref;
*emit_vptr = emit_vptr_on_new_entry;
break 'exiting_out;
} else {
continue 'exiting_out_skip_visited_traits;
}
}
match siblings.find(|&sibling| visited.insert(sibling.to_predicate(tcx))) {
Some(next_inner_most_trait_ref) => {
// We're throwing away potential constness of super traits here.
// FIXME: handle ~const super traits
let next_inner_most_trait_ref =
next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
*inner_most_trait_ref = next_inner_most_trait_ref;
*emit_vptr = emit_vptr_on_new_entry;
break 'exiting_out;
}
None => {
stack.pop();
continue 'exiting_out;
}
stack.pop();
continue 'exiting_out;
}
}
// all done
@ -184,6 +180,12 @@ fn prepare_vtable_segments_inner<'tcx, T>(
}
}
/// Turns option of iterator into an iterator (this is just flatten)
fn maybe_iter<I: Iterator>(i: Option<I>) -> impl Iterator<Item = I::Item> {
// Flatten is bad perf-vise, we could probably implement a special case here that is better
i.into_iter().flatten()
}
fn dump_vtable_entries<'tcx>(
tcx: TyCtxt<'tcx>,
sp: Span,