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Short-circuit DefIdForest::intersection() #57060

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Merged
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Dec 22, 2018
Merged

Short-circuit DefIdForest::intersection() #57060

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13 changes: 12 additions & 1 deletion src/librustc/ty/inhabitedness/def_id_forest.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -74,10 +74,21 @@ impl<'a, 'gcx, 'tcx> DefIdForest {
iter: I) -> DefIdForest
where I: IntoIterator<Item=DefIdForest>
{
let mut ret = DefIdForest::full(tcx);
let mut iter = iter.into_iter();
let mut ret = if let Some(first) = iter.next() {
first
} else {
return DefIdForest::full(tcx);
};

let mut next_ret = SmallVec::new();
let mut old_ret: SmallVec<[DefId; 1]> = SmallVec::new();
for next_forest in iter {
// No need to continue if the intersection is already empty.
if ret.is_empty() {
break;
}

for id in ret.root_ids.drain() {
if next_forest.contains(tcx, id) {
next_ret.push(id);
Expand Down