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rewrite: flip inner/outer loops of mut_repo.new_parents()

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This is basically a DFS to find leaf nodes. It will help omit duplicated
parent ids early.
This commit is contained in:
Yuya Nishihara 2024-08-28 19:21:38 +09:00
parent 8b6bebad40
commit d76d4a90a7
1 changed files with 27 additions and 40 deletions
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67
lib/src/repo.rs
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@ -989,50 +989,37 @@ impl MutableRepo {
///
/// Panics if `parent_mapping` contains cycles
pub fn new_parents(&self, old_ids: Vec<CommitId>) -> Vec<CommitId> {
fn single_substitution_round(
parent_mapping: &HashMap<CommitId, Rewrite>,
ids: Vec<CommitId>,
) -> (Vec<CommitId>, bool) {
let mut made_replacements = false;
let mut new_ids = vec![];
// TODO(ilyagr): (Maybe?) optimize common case of replacements all
// being singletons. If CommitId-s were Copy. no allocations would be needed in
// that case, but it probably doesn't matter much while they are Vec<u8>-s.
for id in ids.into_iter() {
match parent_mapping.get(&id) {
None | Some(Rewrite::Divergent(_)) => {
new_ids.push(id);
}
Some(Rewrite::Rewritten(replacement)) => {
made_replacements = true;
new_ids.push(replacement.clone())
}
Some(Rewrite::Abandoned(replacements)) => {
assert!(
// Each commit must have a parent, so a parent can
// not just be mapped to nothing. This assertion
// could be removed if this function is used for
// mapping something other than a commit's parents.
!replacements.is_empty(),
"Found empty value for key {id:?} in the parent mapping",
);
made_replacements = true;
new_ids.extend(replacements.iter().cloned())
}
};
}
(new_ids, made_replacements)
}
let mut new_ids = old_ids;
let mut new_ids = Vec::with_capacity(old_ids.len());
// The longest possible non-cycle substitution sequence goes through each key of
// parent_mapping once.
let mut allowed_iterations = 0..self.parent_mapping.len();
loop {
let made_replacements;
(new_ids, made_replacements) = single_substitution_round(&self.parent_mapping, new_ids);
let mut to_visit = old_ids.iter().rev().collect_vec();
while let Some(id) = to_visit.pop() {
let mut made_replacements = false;
match self.parent_mapping.get(id) {
None | Some(Rewrite::Divergent(_)) => {
new_ids.push(id.clone());
}
Some(Rewrite::Rewritten(replacement)) => {
made_replacements = true;
to_visit.push(replacement);
}
Some(Rewrite::Abandoned(replacements)) => {
assert!(
// Each commit must have a parent, so a parent can
// not just be mapped to nothing. This assertion
// could be removed if this function is used for
// mapping something other than a commit's parents.
!replacements.is_empty(),
"Found empty value for key {id:?} in the parent mapping",
);
made_replacements = true;
to_visit.extend(replacements.iter().rev());
}
}
if !made_replacements {
break;
allowed_iterations = 0..self.parent_mapping.len();
continue;
}
allowed_iterations
.next()