use Vec for region constraints instead of BTreeMap

compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs

@@ -408,30 +408,35 @@ fn try_extract_error_from_region_constraints<'tcx>(
     mut region_var_origin: impl FnMut(RegionVid) -> RegionVariableOrigin,
     mut universe_of_region: impl FnMut(RegionVid) -> UniverseIndex,
 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
+    let placeholder_universe = match placeholder_region.kind() {
+        ty::RePlaceholder(p) => p.universe,
+        ty::ReVar(vid) => universe_of_region(vid),
+        _ => ty::UniverseIndex::ROOT,
+    };
     let matches =
         |a_region: Region<'tcx>, b_region: Region<'tcx>| match (a_region.kind(), b_region.kind()) {
             (RePlaceholder(a_p), RePlaceholder(b_p)) => a_p.bound == b_p.bound,
             _ => a_region == b_region,
         };
-    let check = |constraint: &Constraint<'tcx>, cause: &SubregionOrigin<'tcx>, exact| {
-        match *constraint {
+    let mut check =
+        |constraint: &Constraint<'tcx>, cause: &SubregionOrigin<'tcx>, exact| match *constraint {
             Constraint::RegSubReg(sub, sup)
                 if ((exact && sup == placeholder_region)
                     || (!exact && matches(sup, placeholder_region)))
                     && sup != sub =>
             {
                 Some((sub, cause.clone()))
             }
-            // FIXME: Should this check the universe of the var?
             Constraint::VarSubReg(vid, sup)
-                if ((exact && sup == placeholder_region)
-                    || (!exact && matches(sup, placeholder_region))) =>
+                if (exact
+                    && sup == placeholder_region
+                    && !universe_of_region(vid).can_name(placeholder_universe))
+                    || (!exact && matches(sup, placeholder_region)) =>
             {
                 Some((ty::Region::new_var(infcx.tcx, vid), cause.clone()))
             }
             _ => None,
-        }
-    };
+        };
     let mut info = region_constraints
         .constraints
         .iter()

compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs

@@ -137,6 +137,10 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
     ) -> LexicalRegionResolutions<'tcx> {
         let mut var_data = self.construct_var_data();
 
+        // Deduplicating constraints is shown to have a positive perf impact.
+        self.data.constraints.sort_by_key(|(constraint, _)| *constraint);
+        self.data.constraints.dedup_by_key(|(constraint, _)| *constraint);
+
         if cfg!(debug_assertions) {
             self.dump_constraints();
         }
@@ -183,7 +187,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         let mut constraints = IndexVec::from_elem(Vec::new(), &var_values.values);
         // Tracks the changed region vids.
         let mut changes = Vec::new();
-        for constraint in self.data.constraints.keys() {
+        for (constraint, _) in &self.data.constraints {
             match *constraint {
                 Constraint::RegSubVar(a_region, b_vid) => {
                     let b_data = var_values.value_mut(b_vid);
@@ -678,7 +682,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         let dummy_source = graph.add_node(());
         let dummy_sink = graph.add_node(());
 
-        for constraint in self.data.constraints.keys() {
+        for (constraint, _) in &self.data.constraints {
             match *constraint {
                 Constraint::VarSubVar(a_id, b_id) => {
                     graph.add_edge(NodeIndex(a_id.index()), NodeIndex(b_id.index()), *constraint);
@@ -885,9 +889,11 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                     }
 
                     Constraint::RegSubVar(region, _) | Constraint::VarSubReg(_, region) => {
+                        let constraint_idx =
+                            this.constraints.binary_search_by(|(c, _)| c.cmp(&edge.data)).unwrap();
                         state.result.push(RegionAndOrigin {
                             region,
-                            origin: this.constraints.get(&edge.data).unwrap().clone(),
+                            origin: this.constraints[constraint_idx].1.clone(),
                         });
                     }
 

compiler/rustc_infer/src/infer/region_constraints/leak_check.rs

@@ -416,8 +416,8 @@ impl<'tcx> MiniGraph<'tcx> {
                 region_constraints.undo_log.region_constraints_in_snapshot(&snapshot.undo_snapshot)
             {
                 match undo_entry {
-                    AddConstraint(constraint) => {
-                        each_constraint(constraint);
+                    &AddConstraint(i) => {
+                        each_constraint(&region_constraints.data().constraints[i].0);
                     }
                     &AddVerify(i) => span_bug!(
                         region_constraints.data().verifys[i].origin.span(),
@@ -430,8 +430,8 @@ impl<'tcx> MiniGraph<'tcx> {
             region_constraints
                 .data()
                 .constraints
-                .keys()
-                .for_each(|constraint| each_constraint(constraint));
+                .iter()
+                .for_each(|(constraint, _)| each_constraint(constraint));
         }
     }
 

compiler/rustc_infer/src/infer/region_constraints/mod.rs

@@ -20,7 +20,6 @@ use rustc_middle::ty::{ReBound, ReVar};
 use rustc_middle::ty::{Region, RegionVid};
 use rustc_span::Span;
 
-use std::collections::BTreeMap;
 use std::ops::Range;
 use std::{cmp, fmt, mem};
 
@@ -90,7 +89,7 @@ pub type VarInfos = IndexVec<RegionVid, RegionVariableInfo>;
 pub struct RegionConstraintData<'tcx> {
     /// Constraints of the form `A <= B`, where either `A` or `B` can
     /// be a region variable (or neither, as it happens).
-    pub constraints: BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
+    pub constraints: Vec<(Constraint<'tcx>, SubregionOrigin<'tcx>)>,
 
     /// Constraints of the form `R0 member of [R1, ..., Rn]`, meaning that
     /// `R0` must be equal to one of the regions `R1..Rn`. These occur
@@ -273,7 +272,7 @@ pub(crate) enum UndoLog<'tcx> {
     AddVar(RegionVid),
 
     /// We added the given `constraint`.
-    AddConstraint(Constraint<'tcx>),
+    AddConstraint(usize),
 
     /// We added the given `verify`.
     AddVerify(usize),
@@ -319,8 +318,9 @@ impl<'tcx> RegionConstraintStorage<'tcx> {
                 self.var_infos.pop().unwrap();
                 assert_eq!(self.var_infos.len(), vid.index());
             }
-            AddConstraint(ref constraint) => {
-                self.data.constraints.remove(constraint);
+            AddConstraint(index) => {
+                self.data.constraints.pop().unwrap();
+                assert_eq!(self.data.constraints.len(), index);
             }
             AddVerify(index) => {
                 self.data.verifys.pop();
@@ -443,14 +443,9 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
         // cannot add constraints once regions are resolved
         debug!("RegionConstraintCollector: add_constraint({:?})", constraint);
 
-        // never overwrite an existing (constraint, origin) - only insert one if it isn't
-        // present in the map yet. This prevents origins from outside the snapshot being
-        // replaced with "less informative" origins e.g., during calls to `can_eq`
-        let undo_log = &mut self.undo_log;
-        self.storage.data.constraints.entry(constraint).or_insert_with(|| {
-            undo_log.push(AddConstraint(constraint));
-            origin
-        });
+        let index = self.storage.data.constraints.len();
+        self.storage.data.constraints.push((constraint, origin));
+        self.undo_log.push(AddConstraint(index));
     }
 
     fn add_verify(&mut self, verify: Verify<'tcx>) {

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -477,7 +477,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
         let mut vid_map: FxHashMap<RegionTarget<'cx>, RegionDeps<'cx>> = FxHashMap::default();
         let mut finished_map = FxHashMap::default();
 
-        for constraint in regions.constraints.keys() {
+        for (constraint, _) in &regions.constraints {
             match constraint {
                 &Constraint::VarSubVar(r1, r2) => {
                     {

src/librustdoc/clean/auto_trait.rs

@@ -195,7 +195,7 @@ where
         // into a map. Each RegionTarget (either a RegionVid or a Region) maps
         // to its smaller and larger regions. Note that 'larger' regions correspond
         // to sub-regions in Rust code (e.g., in 'a: 'b, 'a is the larger region).
-        for constraint in regions.constraints.keys() {
+        for (constraint, _) in &regions.constraints {
             match *constraint {
                 Constraint::VarSubVar(r1, r2) => {
                     {

tests/ui/higher-ranked/higher-ranked-lifetime-error.stderr

@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |     assert_all::<_, &String>(id);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
    |
-   = note: expected reference `&String`
-              found reference `&String`
+   = note: expected trait `for<'a> <for<'a> fn(&'a String) -> &'a String {id} as FnMut<(&'a String,)>>`
+              found trait `for<'a> <for<'a> fn(&'a String) -> &'a String {id} as FnMut<(&'a String,)>>`
 
 error: aborting due to 1 previous error