1 files changed, 43 insertions, 4 deletions

diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index fe3fa024cd5..1b89a49cf98 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,
         }
     }
 }