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Avoid adding duplicate relations during inference #32042

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Avoid adding duplicate relations during inference #32042

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13 changes: 9 additions & 4 deletions src/librustc/middle/infer/type_variable.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -104,9 +104,13 @@ impl<'tcx> TypeVariableTable<'tcx> {
/// Precondition: neither `a` nor `b` are known.
pub fn relate_vars(&mut self, a: ty::TyVid, dir: RelationDir, b: ty::TyVid) {
if a != b {
self.relations(a).push((dir, b));
self.relations(b).push((dir.opposite(), a));
self.values.record(Relate(a, b));
let new_rel = (dir, b);
// Don't add duplicate relations
if self.relations(a).iter().all(|rel| *rel != new_rel) {
self.relations(a).push(new_rel);
self.relations(b).push((dir.opposite(), a));
self.values.record(Relate(a, b));
}
}
}

Expand All @@ -130,7 +134,8 @@ impl<'tcx> TypeVariableTable<'tcx> {
already instantiated")
};

for &(dir, vid) in &relations {
// Variables which have already been proven to be `ty` does not need to be checked again
for &(dir, vid) in relations.iter().filter(|& &(_, vid)| self.probe(vid) != Some(ty)) {
stack.push((ty, dir, vid));
}

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