lazily init SolverRegionConstraintStorage on access

Author: khyperia

compiler/rustc_infer/src/infer/solver_region_constraints.rs

@@ -8,24 +8,24 @@ use super::InferCtxt;
 pub type SolverRegionConstraint<'tcx> = RegionConstraint<TyCtxt<'tcx>, Span>;
 
 #[derive(Clone, Debug)]
-pub(crate) struct SolverRegionConstraintStorage<'tcx>(SolverRegionConstraint<'tcx>);
+pub(crate) struct SolverRegionConstraintStorage<'tcx>(Option<SolverRegionConstraint<'tcx>>);
 
 impl<'tcx> SolverRegionConstraintStorage<'tcx> {
     pub(crate) fn new() -> Self {
-        Self(SolverRegionConstraint::new_true())
+        Self(None)
     }
 
     pub(crate) fn get_constraint(&self) -> SolverRegionConstraint<'tcx> {
-        self.0.clone()
+        self.0.clone().unwrap_or_default()
     }
 
     pub(crate) fn take(&mut self) -> SolverRegionConstraint<'tcx> {
-        core::mem::replace(&mut self.0, SolverRegionConstraint::new_true())
+        self.0.take().unwrap_or_default()
     }
 
     #[instrument(level = "debug", skip(self))]
     pub(crate) fn overwrite(&mut self, constraint: SolverRegionConstraint<'tcx>) {
-        self.0 = constraint;
+        self.0 = Some(constraint);
     }
 }
 

compiler/rustc_type_ir/src/region_constraint.rs

@@ -481,7 +481,9 @@ impl<I: Interner, S: Clone + std::fmt::Debug + Eq + std::hash::Hash> RegionConst
     }
 }
 
-impl<I: Interner> Default for RegionConstraint<I> {
+impl<I: Interner, S: Clone + std::fmt::Debug + Eq + std::hash::Hash> Default
+    for RegionConstraint<I, S>
+{
     fn default() -> Self {
         Self::new_true()
     }