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Avoid vacuous Constraint::{VarSubVar,RegSubReg} constraints.

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If the two regions are the same, we can skip it. This is a small perf win.
This commit is contained in:
Nicholas Nethercote
2025-07-25 19:52:08 +10:00
parent 606dcc0d2e
commit 75a1f47750
1 changed files with 6 additions and 2 deletions
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8
compiler/rustc_infer/src/infer/region_constraints/mod.rs
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@@ -471,7 +471,9 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
// all regions are subregions of static, so we can ignore this // all regions are subregions of static, so we can ignore this
} }
(ReVar(sub_id), ReVar(sup_id)) => { (ReVar(sub_id), ReVar(sup_id)) => {
self.add_constraint(Constraint::VarSubVar(sub_id, sup_id), origin); if sub_id != sup_id {
self.add_constraint(Constraint::VarSubVar(sub_id, sup_id), origin);
}
} }
(_, ReVar(sup_id)) => { (_, ReVar(sup_id)) => {
self.add_constraint(Constraint::RegSubVar(sub, sup_id), origin); self.add_constraint(Constraint::RegSubVar(sub, sup_id), origin);
@@ -480,7 +482,9 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
self.add_constraint(Constraint::VarSubReg(sub_id, sup), origin); self.add_constraint(Constraint::VarSubReg(sub_id, sup), origin);
} }
_ => { _ => {
self.add_constraint(Constraint::RegSubReg(sub, sup), origin); if sub != sup {
self.add_constraint(Constraint::RegSubReg(sub, sup), origin);
}
} }
} }
} }