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-rw-r--r--compiler/rustc_middle/src/ty/consts.rs14
-rw-r--r--compiler/rustc_middle/src/ty/context.rs47
-rw-r--r--compiler/rustc_middle/src/ty/fold.rs14
-rw-r--r--compiler/rustc_middle/src/ty/print/pretty.rs4
-rw-r--r--compiler/rustc_middle/src/ty/region.rs36
-rw-r--r--compiler/rustc_middle/src/ty/sty.rs22
-rw-r--r--compiler/rustc_middle/src/ty/typeck_results.rs12
-rw-r--r--compiler/rustc_middle/src/ty/visit.rs6
8 files changed, 130 insertions, 25 deletions
diff --git a/compiler/rustc_middle/src/ty/consts.rs b/compiler/rustc_middle/src/ty/consts.rs
index 614b6471f18..95adb561c70 100644
--- a/compiler/rustc_middle/src/ty/consts.rs
+++ b/compiler/rustc_middle/src/ty/consts.rs
@@ -95,7 +95,15 @@ impl<'tcx> Const<'tcx> {
         debruijn: ty::DebruijnIndex,
         bound_const: ty::BoundConst,
     ) -> Const<'tcx> {
-        Const::new(tcx, ty::ConstKind::Bound(debruijn, bound_const))
+        Const::new(tcx, ty::ConstKind::Bound(ty::BoundVarIndexKind::Bound(debruijn), bound_const))
+    }
+
+    #[inline]
+    pub fn new_canonical_bound(tcx: TyCtxt<'tcx>, var: ty::BoundVar) -> Const<'tcx> {
+        Const::new(
+            tcx,
+            ty::ConstKind::Bound(ty::BoundVarIndexKind::Canonical, ty::BoundConst { var }),
+        )
     }
 
     #[inline]
@@ -180,6 +188,10 @@ impl<'tcx> rustc_type_ir::inherent::Const<TyCtxt<'tcx>> for Const<'tcx> {
         Const::new_bound(tcx, debruijn, ty::BoundConst { var })
     }
 
+    fn new_canonical_bound(tcx: TyCtxt<'tcx>, var: rustc_type_ir::BoundVar) -> Self {
+        Const::new_canonical_bound(tcx, var)
+    }
+
     fn new_placeholder(tcx: TyCtxt<'tcx>, placeholder: ty::PlaceholderConst) -> Self {
         Const::new_placeholder(tcx, placeholder)
     }
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 7d3e2c9965d..161fec9245a 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -1110,6 +1110,15 @@ const NUM_PREINTERNED_FRESH_TYS: u32 = 20;
 const NUM_PREINTERNED_FRESH_INT_TYS: u32 = 3;
 const NUM_PREINTERNED_FRESH_FLOAT_TYS: u32 = 3;
 const NUM_PREINTERNED_ANON_BOUND_TYS_I: u32 = 3;
+
+// From general profiling of the *max vars during canonicalization* of a value:
+// - about 90% of the time, there are no canonical vars
+// - about 9% of the time, there is only one canonical var
+// - there are rarely more than 3-5 canonical vars (with exceptions in particularly pathological cases)
+// This may not match the number of bound vars found in `for`s.
+// Given that this is all heap interned, it seems likely that interning fewer
+// vars here won't make an appreciable difference. Though, if we were to inline the data (in an array),
+// we may want to consider reducing the number for canonicalized vars down to 4 or so.
 const NUM_PREINTERNED_ANON_BOUND_TYS_V: u32 = 20;
 
 // This number may seem high, but it is reached in all but the smallest crates.
@@ -1160,9 +1169,14 @@ pub struct CommonTypes<'tcx> {
     pub fresh_float_tys: Vec<Ty<'tcx>>,
 
     /// Pre-interned values of the form:
-    /// `Bound(DebruijnIndex(i), BoundTy { var: v, kind: BoundTyKind::Anon})`
+    /// `Bound(BoundVarIndexKind::Bound(DebruijnIndex(i)), BoundTy { var: v, kind: BoundTyKind::Anon})`
     /// for small values of `i` and `v`.
     pub anon_bound_tys: Vec<Vec<Ty<'tcx>>>,
+
+    // Pre-interned values of the form:
+    // `Bound(BoundVarIndexKind::Canonical, BoundTy { var: v, kind: BoundTyKind::Anon })`
+    // for small values of `v`.
+    pub anon_canonical_bound_tys: Vec<Ty<'tcx>>,
 }
 
 pub struct CommonLifetimes<'tcx> {
@@ -1176,9 +1190,14 @@ pub struct CommonLifetimes<'tcx> {
     pub re_vars: Vec<Region<'tcx>>,
 
     /// Pre-interned values of the form:
-    /// `ReBound(DebruijnIndex(i), BoundRegion { var: v, kind: BoundRegionKind::Anon })`
+    /// `ReBound(BoundVarIndexKind::Bound(DebruijnIndex(i)), BoundRegion { var: v, kind: BoundRegionKind::Anon })`
     /// for small values of `i` and `v`.
     pub anon_re_bounds: Vec<Vec<Region<'tcx>>>,
+
+    // Pre-interned values of the form:
+    // `ReBound(BoundVarIndexKind::Canonical, BoundRegion { var: v, kind: BoundRegionKind::Anon })`
+    // for small values of `v`.
+    pub anon_re_canonical_bounds: Vec<Region<'tcx>>,
 }
 
 pub struct CommonConsts<'tcx> {
@@ -1211,7 +1230,7 @@ impl<'tcx> CommonTypes<'tcx> {
                 (0..NUM_PREINTERNED_ANON_BOUND_TYS_V)
                     .map(|v| {
                         mk(ty::Bound(
-                            ty::DebruijnIndex::from(i),
+                            ty::BoundVarIndexKind::Bound(ty::DebruijnIndex::from(i)),
                             ty::BoundTy { var: ty::BoundVar::from(v), kind: ty::BoundTyKind::Anon },
                         ))
                     })
@@ -1219,6 +1238,15 @@ impl<'tcx> CommonTypes<'tcx> {
             })
             .collect();
 
+        let anon_canonical_bound_tys = (0..NUM_PREINTERNED_ANON_BOUND_TYS_V)
+            .map(|v| {
+                mk(ty::Bound(
+                    ty::BoundVarIndexKind::Canonical,
+                    ty::BoundTy { var: ty::BoundVar::from(v), kind: ty::BoundTyKind::Anon },
+                ))
+            })
+            .collect();
+
         CommonTypes {
             unit: mk(Tuple(List::empty())),
             bool: mk(Bool),
@@ -1250,6 +1278,7 @@ impl<'tcx> CommonTypes<'tcx> {
             fresh_int_tys,
             fresh_float_tys,
             anon_bound_tys,
+            anon_canonical_bound_tys,
         }
     }
 }
@@ -1270,7 +1299,7 @@ impl<'tcx> CommonLifetimes<'tcx> {
                 (0..NUM_PREINTERNED_ANON_RE_BOUNDS_V)
                     .map(|v| {
                         mk(ty::ReBound(
-                            ty::DebruijnIndex::from(i),
+                            ty::BoundVarIndexKind::Bound(ty::DebruijnIndex::from(i)),
                             ty::BoundRegion {
                                 var: ty::BoundVar::from(v),
                                 kind: ty::BoundRegionKind::Anon,
@@ -1281,11 +1310,21 @@ impl<'tcx> CommonLifetimes<'tcx> {
             })
             .collect();
 
+        let anon_re_canonical_bounds = (0..NUM_PREINTERNED_ANON_RE_BOUNDS_V)
+            .map(|v| {
+                mk(ty::ReBound(
+                    ty::BoundVarIndexKind::Canonical,
+                    ty::BoundRegion { var: ty::BoundVar::from(v), kind: ty::BoundRegionKind::Anon },
+                ))
+            })
+            .collect();
+
         CommonLifetimes {
             re_static: mk(ty::ReStatic),
             re_erased: mk(ty::ReErased),
             re_vars,
             anon_re_bounds,
+            anon_re_canonical_bounds,
         }
     }
 }
diff --git a/compiler/rustc_middle/src/ty/fold.rs b/compiler/rustc_middle/src/ty/fold.rs
index 7d56ec1635f..ee29afcff63 100644
--- a/compiler/rustc_middle/src/ty/fold.rs
+++ b/compiler/rustc_middle/src/ty/fold.rs
@@ -125,7 +125,9 @@ where
 
     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
         match *t.kind() {
-            ty::Bound(debruijn, bound_ty) if debruijn == self.current_index => {
+            ty::Bound(ty::BoundVarIndexKind::Bound(debruijn), bound_ty)
+                if debruijn == self.current_index =>
+            {
                 let ty = self.delegate.replace_ty(bound_ty);
                 debug_assert!(!ty.has_vars_bound_above(ty::INNERMOST));
                 ty::shift_vars(self.tcx, ty, self.current_index.as_u32())
@@ -146,9 +148,11 @@ where
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
         match r.kind() {
-            ty::ReBound(debruijn, br) if debruijn == self.current_index => {
+            ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn), br)
+                if debruijn == self.current_index =>
+            {
                 let region = self.delegate.replace_region(br);
-                if let ty::ReBound(debruijn1, br) = region.kind() {
+                if let ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn1), br) = region.kind() {
                     // If the callback returns a bound region,
                     // that region should always use the INNERMOST
                     // debruijn index. Then we adjust it to the
@@ -165,7 +169,9 @@ where
 
     fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
         match ct.kind() {
-            ty::ConstKind::Bound(debruijn, bound_const) if debruijn == self.current_index => {
+            ty::ConstKind::Bound(ty::BoundVarIndexKind::Bound(debruijn), bound_const)
+                if debruijn == self.current_index =>
+            {
                 let ct = self.delegate.replace_const(bound_const);
                 debug_assert!(!ct.has_vars_bound_above(ty::INNERMOST));
                 ty::shift_vars(self.tcx, ct, self.current_index.as_u32())
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 8f7c8170f7a..4d1fcaeda5e 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -2664,7 +2664,7 @@ impl<'a, 'tcx> ty::TypeFolder<TyCtxt<'tcx>> for RegionFolder<'a, 'tcx> {
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
         let name = &mut self.name;
         let region = match r.kind() {
-            ty::ReBound(db, br) if db >= self.current_index => {
+            ty::ReBound(ty::BoundVarIndexKind::Bound(db), br) if db >= self.current_index => {
                 *self.region_map.entry(br).or_insert_with(|| name(Some(db), self.current_index, br))
             }
             ty::RePlaceholder(ty::PlaceholderRegion {
@@ -2687,7 +2687,7 @@ impl<'a, 'tcx> ty::TypeFolder<TyCtxt<'tcx>> for RegionFolder<'a, 'tcx> {
             }
             _ => return r,
         };
-        if let ty::ReBound(debruijn1, br) = region.kind() {
+        if let ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn1), br) = region.kind() {
             assert_eq!(debruijn1, ty::INNERMOST);
             ty::Region::new_bound(self.tcx, self.current_index, br)
         } else {
diff --git a/compiler/rustc_middle/src/ty/region.rs b/compiler/rustc_middle/src/ty/region.rs
index 3a7852dea06..f0687f2bc72 100644
--- a/compiler/rustc_middle/src/ty/region.rs
+++ b/compiler/rustc_middle/src/ty/region.rs
@@ -31,7 +31,7 @@ impl<'tcx> rustc_type_ir::Flags for Region<'tcx> {
 
     fn outer_exclusive_binder(&self) -> ty::DebruijnIndex {
         match self.kind() {
-            ty::ReBound(debruijn, _) => debruijn.shifted_in(1),
+            ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn), _) => debruijn.shifted_in(1),
             _ => ty::INNERMOST,
         }
     }
@@ -59,7 +59,20 @@ impl<'tcx> Region<'tcx> {
         {
             re
         } else {
-            tcx.intern_region(ty::ReBound(debruijn, bound_region))
+            tcx.intern_region(ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn), bound_region))
+        }
+    }
+
+    #[inline]
+    pub fn new_canonical_bound(tcx: TyCtxt<'tcx>, var: ty::BoundVar) -> Region<'tcx> {
+        // Use a pre-interned one when possible.
+        if let Some(re) = tcx.lifetimes.anon_re_canonical_bounds.get(var.as_usize()).copied() {
+            re
+        } else {
+            tcx.intern_region(ty::ReBound(
+                ty::BoundVarIndexKind::Canonical,
+                ty::BoundRegion { var, kind: ty::BoundRegionKind::Anon },
+            ))
         }
     }
 
@@ -122,7 +135,12 @@ impl<'tcx> Region<'tcx> {
     pub fn new_from_kind(tcx: TyCtxt<'tcx>, kind: RegionKind<'tcx>) -> Region<'tcx> {
         match kind {
             ty::ReEarlyParam(region) => Region::new_early_param(tcx, region),
-            ty::ReBound(debruijn, region) => Region::new_bound(tcx, debruijn, region),
+            ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn), region) => {
+                Region::new_bound(tcx, debruijn, region)
+            }
+            ty::ReBound(ty::BoundVarIndexKind::Canonical, region) => {
+                Region::new_canonical_bound(tcx, region.var)
+            }
             ty::ReLateParam(ty::LateParamRegion { scope, kind }) => {
                 Region::new_late_param(tcx, scope, kind)
             }
@@ -148,6 +166,10 @@ impl<'tcx> rustc_type_ir::inherent::Region<TyCtxt<'tcx>> for Region<'tcx> {
         Region::new_bound(tcx, debruijn, ty::BoundRegion { var, kind: ty::BoundRegionKind::Anon })
     }
 
+    fn new_canonical_bound(tcx: TyCtxt<'tcx>, var: rustc_type_ir::BoundVar) -> Self {
+        Region::new_canonical_bound(tcx, var)
+    }
+
     fn new_placeholder(tcx: TyCtxt<'tcx>, placeholder: ty::PlaceholderRegion) -> Self {
         Region::new_placeholder(tcx, placeholder)
     }
@@ -223,7 +245,7 @@ impl<'tcx> Region<'tcx> {
     #[inline]
     pub fn bound_at_or_above_binder(self, index: ty::DebruijnIndex) -> bool {
         match self.kind() {
-            ty::ReBound(debruijn, _) => debruijn >= index,
+            ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn), _) => debruijn >= index,
             _ => false,
         }
     }
@@ -254,7 +276,11 @@ impl<'tcx> Region<'tcx> {
             ty::ReStatic => {
                 flags = flags | TypeFlags::HAS_FREE_REGIONS;
             }
-            ty::ReBound(..) => {
+            ty::ReBound(ty::BoundVarIndexKind::Canonical, _) => {
+                flags = flags | TypeFlags::HAS_RE_BOUND;
+                flags = flags | TypeFlags::HAS_CANONICAL_BOUND;
+            }
+            ty::ReBound(ty::BoundVarIndexKind::Bound(..), _) => {
                 flags = flags | TypeFlags::HAS_RE_BOUND;
             }
             ty::ReErased => {
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index de35e5e847c..a3fdd4e35b6 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -487,7 +487,23 @@ impl<'tcx> Ty<'tcx> {
         {
             ty
         } else {
-            Ty::new(tcx, Bound(index, bound_ty))
+            Ty::new(tcx, Bound(ty::BoundVarIndexKind::Bound(index), bound_ty))
+        }
+    }
+
+    #[inline]
+    pub fn new_canonical_bound(tcx: TyCtxt<'tcx>, var: BoundVar) -> Ty<'tcx> {
+        // Use a pre-interned one when possible.
+        if let Some(ty) = tcx.types.anon_canonical_bound_tys.get(var.as_usize()).copied() {
+            ty
+        } else {
+            Ty::new(
+                tcx,
+                Bound(
+                    ty::BoundVarIndexKind::Canonical,
+                    ty::BoundTy { var, kind: ty::BoundTyKind::Anon },
+                ),
+            )
         }
     }
 
@@ -952,6 +968,10 @@ impl<'tcx> rustc_type_ir::inherent::Ty<TyCtxt<'tcx>> for Ty<'tcx> {
         Ty::new_bound(tcx, debruijn, ty::BoundTy { var, kind: ty::BoundTyKind::Anon })
     }
 
+    fn new_canonical_bound(tcx: TyCtxt<'tcx>, var: ty::BoundVar) -> Self {
+        Ty::new_canonical_bound(tcx, var)
+    }
+
     fn new_alias(
         interner: TyCtxt<'tcx>,
         kind: ty::AliasTyKind,
diff --git a/compiler/rustc_middle/src/ty/typeck_results.rs b/compiler/rustc_middle/src/ty/typeck_results.rs
index 8dd80aab946..370ef364bf5 100644
--- a/compiler/rustc_middle/src/ty/typeck_results.rs
+++ b/compiler/rustc_middle/src/ty/typeck_results.rs
@@ -798,8 +798,8 @@ impl<'tcx> IsIdentity for CanonicalUserType<'tcx> {
                     match arg.kind() {
                         GenericArgKind::Type(ty) => match ty.kind() {
                             ty::Bound(debruijn, b) => {
-                                // We only allow a `ty::INNERMOST` index in generic parameters.
-                                assert_eq!(*debruijn, ty::INNERMOST);
+                                // We only allow a `ty::BoundVarIndexKind::Canonical` index in generic parameters.
+                                assert_eq!(*debruijn, ty::BoundVarIndexKind::Canonical);
                                 cvar == b.var
                             }
                             _ => false,
@@ -807,8 +807,8 @@ impl<'tcx> IsIdentity for CanonicalUserType<'tcx> {
 
                         GenericArgKind::Lifetime(r) => match r.kind() {
                             ty::ReBound(debruijn, b) => {
-                                // We only allow a `ty::INNERMOST` index in generic parameters.
-                                assert_eq!(debruijn, ty::INNERMOST);
+                                // We only allow a `ty::BoundVarIndexKind::Canonical` index in generic parameters.
+                                assert_eq!(debruijn, ty::BoundVarIndexKind::Canonical);
                                 cvar == b.var
                             }
                             _ => false,
@@ -816,8 +816,8 @@ impl<'tcx> IsIdentity for CanonicalUserType<'tcx> {
 
                         GenericArgKind::Const(ct) => match ct.kind() {
                             ty::ConstKind::Bound(debruijn, b) => {
-                                // We only allow a `ty::INNERMOST` index in generic parameters.
-                                assert_eq!(debruijn, ty::INNERMOST);
+                                // We only allow a `ty::BoundVarIndexKind::Canonical` index in generic parameters.
+                                assert_eq!(debruijn, ty::BoundVarIndexKind::Canonical);
                                 cvar == b.var
                             }
                             _ => false,
diff --git a/compiler/rustc_middle/src/ty/visit.rs b/compiler/rustc_middle/src/ty/visit.rs
index f0c47f257cc..e84ac56b31d 100644
--- a/compiler/rustc_middle/src/ty/visit.rs
+++ b/compiler/rustc_middle/src/ty/visit.rs
@@ -78,7 +78,9 @@ impl<'tcx> TyCtxt<'tcx> {
 
             fn visit_region(&mut self, r: ty::Region<'tcx>) -> Self::Result {
                 match r.kind() {
-                    ty::ReBound(debruijn, _) if debruijn < self.outer_index => {
+                    ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn), _)
+                        if debruijn < self.outer_index =>
+                    {
                         ControlFlow::Continue(())
                     }
                     _ => {
@@ -205,7 +207,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for LateBoundRegionsCollector {
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) {
-        if let ty::ReBound(debruijn, br) = r.kind() {
+        if let ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn), br) = r.kind() {
             if debruijn == self.current_index {
                 self.regions.insert(br.kind);
             }