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Do not use prepend to avoid quadratic behaviour.

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This commit is contained in:
Camille Gillot
2025-08-22 20:51:46 +00:00
parent de7c633ee5
commit 4e9dd1b67b
2 changed files with 37 additions and 58 deletions
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44
compiler/rustc_index/src/interval.rs
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@@ -140,42 +140,20 @@ impl<I: Idx> IntervalSet<I> {
result
}
/// Specialized version of `insert` when we know that the inserted point is *before* any
/// contained.
pub fn prepend(&mut self, point: I) {
let point = point.index() as u32;
if let Some((first_start, _)) = self.map.first_mut() {
assert!(point <= *first_start);
if point == *first_start {
// The point is already present in the set.
} else if point + 1 == *first_start {
// Just extend the first range.
*first_start = point;
} else {
self.map.insert(0, (point, point));
}
} else {
// If the map is empty, push is faster than insert.
self.map.push((point, point));
}
debug_assert!(
self.check_invariants(),
"wrong intervals after prepend {point:?} to {self:?}"
);
}
/// Specialized version of `insert` when we know that the inserted point is *after* any
/// contained.
pub fn append(&mut self, point: I) {
let point = point.index() as u32;
if let Some((_, last_end)) = self.map.last_mut()
&& let _ = assert!(*last_end < point)
&& point == *last_end + 1
{
*last_end = point;
if let Some((_, last_end)) = self.map.last_mut() {
assert!(*last_end <= point);
if point == *last_end {
// The point is already in the set.
} else if point == *last_end + 1 {
*last_end = point;
} else {
self.map.push((point, point));
}
} else {
self.map.push((point, point));
}
@@ -397,10 +375,6 @@ impl<R: Idx, C: Step + Idx> SparseIntervalMatrix<R, C> {
self.ensure_row(row).insert(point)
}
pub fn prepend(&mut self, row: R, point: C) {
self.ensure_row(row).prepend(point)
}
pub fn append(&mut self, row: R, point: C) {
self.ensure_row(row).append(point)
}