Auto merge of #130821 - lcnr:nalgebra-hang-2, r=<try>

caching? CACHING!

Fixes the new minimization of the hang in nalgebra and nalgebra itself :3

this is a bit iffy, especially the cache in `TypeRelating`. I believe all the caches are correct, but would like to provide an easily verifiable abstraction for caching visitors if possible. Don't think I can extend that one to `TypeRelating` however.

The first commit removes region uniquification, reintroducing the ICE from rust-lang/trait-system-refactor-initiative#27. This does not affect coherence and I would like to fix this by introducing OR-region constraints

- [ ] add test of the new nalgebra minimization, it's different from this
- [ ] add an abstraction for caching type visitors

r? `@compiler-errors`

compiler/rustc_infer/src/infer/relate/type_relating.rs

@@ -1,3 +1,4 @@
+use rustc_data_structures::sso::SsoHashSet;
 use rustc_middle::traits::solve::Goal;
 use rustc_middle::ty::relate::{
     Relate, RelateResult, TypeRelation, relate_args_invariantly, relate_args_with_variances,
@@ -16,6 +17,7 @@ pub struct TypeRelating<'combine, 'a, 'tcx> {
     fields: &'combine mut CombineFields<'a, 'tcx>,
     structurally_relate_aliases: StructurallyRelateAliases,
     ambient_variance: ty::Variance,
+    cache: SsoHashSet<(ty::Variance, Ty<'tcx>, Ty<'tcx>)>,
 }
 
 impl<'combine, 'infcx, 'tcx> TypeRelating<'combine, 'infcx, 'tcx> {
@@ -24,7 +26,12 @@ impl<'combine, 'infcx, 'tcx> TypeRelating<'combine, 'infcx, 'tcx> {
         structurally_relate_aliases: StructurallyRelateAliases,
         ambient_variance: ty::Variance,
     ) -> TypeRelating<'combine, 'infcx, 'tcx> {
-        TypeRelating { fields: f, structurally_relate_aliases, ambient_variance }
+        TypeRelating {
+            fields: f,
+            structurally_relate_aliases,
+            ambient_variance,
+            cache: Default::default(),
+        }
     }
 }
 
@@ -78,6 +85,10 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for TypeRelating<'_, '_, 'tcx> {
         let a = infcx.shallow_resolve(a);
         let b = infcx.shallow_resolve(b);
 
+        if self.cache.contains(&(self.ambient_variance, a, b)) {
+            return Ok(a);
+        }
+
         match (a.kind(), b.kind()) {
             (&ty::Infer(TyVar(a_id)), &ty::Infer(TyVar(b_id))) => {
                 match self.ambient_variance {
@@ -160,6 +171,8 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for TypeRelating<'_, '_, 'tcx> {
             }
         }
 
+        assert!(self.cache.insert((self.ambient_variance, a, b)));
+
         Ok(a)
     }
 

compiler/rustc_infer/src/infer/resolve.rs

@@ -1,3 +1,4 @@
+use rustc_data_structures::sso::SsoHashMap;
 use rustc_middle::bug;
 use rustc_middle::ty::fold::{FallibleTypeFolder, TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::visit::TypeVisitableExt;
@@ -15,12 +16,13 @@ use super::{FixupError, FixupResult, InferCtxt};
 /// points for correctness.
 pub struct OpportunisticVarResolver<'a, 'tcx> {
     infcx: &'a InferCtxt<'tcx>,
+    cache: SsoHashMap<Ty<'tcx>, Ty<'tcx>>,
 }
 
 impl<'a, 'tcx> OpportunisticVarResolver<'a, 'tcx> {
     #[inline]
     pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
-        OpportunisticVarResolver { infcx }
+        OpportunisticVarResolver { infcx, cache: Default::default() }
     }
 }
 
@@ -31,12 +33,19 @@ impl<'a, 'tcx> TypeFolder<TyCtxt<'tcx>> for OpportunisticVarResolver<'a, 'tcx> {
 
     #[inline]
     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
-        if !t.has_non_region_infer() {
+        if let Some(&ty) = self.cache.get(&t) {
+            return ty;
+        }
+
+        let res = if !t.has_non_region_infer() {
             t // micro-optimize -- if there is nothing in this type that this fold affects...
         } else {
             let t = self.infcx.shallow_resolve(t);
             t.super_fold_with(self)
-        }
+        };
+
+        assert!(self.cache.insert(t, res).is_none());
+        res
     }
 
     fn fold_const(&mut self, ct: Const<'tcx>) -> Const<'tcx> {

compiler/rustc_middle/src/ty/fold.rs

@@ -1,4 +1,5 @@
 use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::sso::SsoHashMap;
 use rustc_hir::def_id::DefId;
 pub use rustc_type_ir::fold::{
     FallibleTypeFolder, TypeFoldable, TypeFolder, TypeSuperFoldable, shift_region, shift_vars,
@@ -164,11 +165,13 @@ struct BoundVarReplacer<'tcx, D> {
     current_index: ty::DebruijnIndex,
 
     delegate: D,
+
+    cache: SsoHashMap<(ty::DebruijnIndex, Ty<'tcx>), Ty<'tcx>>,
 }
 
 impl<'tcx, D: BoundVarReplacerDelegate<'tcx>> BoundVarReplacer<'tcx, D> {
     fn new(tcx: TyCtxt<'tcx>, delegate: D) -> Self {
-        BoundVarReplacer { tcx, current_index: ty::INNERMOST, delegate }
+        BoundVarReplacer { tcx, current_index: ty::INNERMOST, delegate, cache: Default::default() }
     }
 }
 
@@ -191,15 +194,22 @@ where
     }
 
     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
-        match *t.kind() {
+        if let Some(&ty) = self.cache.get(&(self.current_index, t)) {
+            return ty;
+        }
+
+        let res = match *t.kind() {
             ty::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::fold::shift_vars(self.tcx, ty, self.current_index.as_u32())
             }
             _ if t.has_vars_bound_at_or_above(self.current_index) => t.super_fold_with(self),
             _ => t,
-        }
+        };
+
+        assert!(self.cache.insert((self.current_index, t), res).is_none());
+        res
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {