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rewrite: do not resolve transitive parents repeatedly when updating refs

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This was quadratic before, and was super slow if thousands of commits were
abandoned.

#4352
This commit is contained in:
Yuya Nishihara 2024-08-30 20:01:03 +09:00
parent cb16b5afd0
commit 8e500c0182
1 changed files with 36 additions and 7 deletions
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43
lib/src/repo.rs
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@ -1032,6 +1032,40 @@ impl MutableRepo {
new_ids
}
/// Fully resolves transitive replacements in `parent_mapping`.
///
/// If `parent_mapping` contains cycles, this function will panic.
fn resolve_rewrite_mapping_with(
&self,
mut predicate: impl FnMut(&Rewrite) -> bool,
) -> HashMap<CommitId, Vec<CommitId>> {
let sorted_ids = dag_walk::topo_order_forward(
self.parent_mapping.keys(),
|&id| id,
|&id| match self.parent_mapping.get(id).filter(|&v| predicate(v)) {
None => &[],
Some(rewrite) => rewrite.new_parent_ids(),
},
);
let mut new_mapping: HashMap<CommitId, Vec<CommitId>> = HashMap::new();
for old_id in sorted_ids {
let Some(rewrite) = self.parent_mapping.get(old_id).filter(|&v| predicate(v)) else {
continue;
};
let lookup = |id| new_mapping.get(id).map_or(slice::from_ref(id), |ids| ids);
let new_ids = match rewrite.new_parent_ids() {
[id] => lookup(id).to_vec(), // unique() not needed
ids => ids.iter().flat_map(lookup).unique().cloned().collect(),
};
debug_assert_eq!(
new_ids,
self.rewritten_ids_with(slice::from_ref(old_id), &mut predicate)
);
new_mapping.insert(old_id.clone(), new_ids);
}
new_mapping
}
/// Updates branches, working copies, and anonymous heads after rewriting
/// and/or abandoning commits.
pub fn update_rewritten_references(&mut self, settings: &UserSettings) -> BackendResult<()> {
@ -1041,13 +1075,8 @@ impl MutableRepo {
}
fn update_all_references(&mut self, settings: &UserSettings) -> BackendResult<()> {
for (old_parent_id, _rewrite) in self.parent_mapping.clone() {
// Call `rewritten_ids_with()` here since `parent_mapping` only contains direct
// mappings, not transitive ones.
// TODO: keep parent_mapping updated with transitive mappings so we don't need
// to call `rewritten_ids_with()` here.
let new_parent_ids = self.rewritten_ids_with(slice::from_ref(&old_parent_id), |_| true);
self.update_references(settings, old_parent_id, new_parent_ids)?;
for (old_id, new_ids) in self.resolve_rewrite_mapping_with(|_| true) {
self.update_references(settings, old_id, new_ids)?;
}
Ok(())
}