Auto merge of rust-lang#133566 - lcnr:fast-reject-perf, r=<try>

fast-reject: add counter to avoid hangs

alternative approach to rust-lang#133524

r? `@compiler-errors`

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -98,7 +98,7 @@ pub fn overlapping_impls(
     // Before doing expensive operations like entering an inference context, do
     // a quick check via fast_reject to tell if the impl headers could possibly
     // unify.
-    let drcx = DeepRejectCtxt::relate_infer_infer(tcx);
+    let mut drcx = DeepRejectCtxt::relate_infer_infer(tcx);
     let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
     let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
     let may_overlap = match (impl1_ref, impl2_ref) {

compiler/rustc_trait_selection/src/traits/effects.rs

@@ -79,7 +79,7 @@ fn evaluate_host_effect_from_bounds<'tcx>(
     obligation: &HostEffectObligation<'tcx>,
 ) -> Result<ThinVec<PredicateObligation<'tcx>>, EvaluationFailure> {
     let infcx = selcx.infcx;
-    let drcx = DeepRejectCtxt::relate_rigid_rigid(selcx.tcx());
+    let mut drcx = DeepRejectCtxt::relate_rigid_rigid(selcx.tcx());
     let mut candidate = None;
 
     for predicate in obligation.param_env.caller_bounds() {

compiler/rustc_trait_selection/src/traits/project.rs

@@ -866,7 +866,7 @@ fn assemble_candidates_from_predicates<'cx, 'tcx>(
     potentially_unnormalized_candidates: bool,
 ) {
     let infcx = selcx.infcx;
-    let drcx = DeepRejectCtxt::relate_rigid_rigid(selcx.tcx());
+    let mut drcx = DeepRejectCtxt::relate_rigid_rigid(selcx.tcx());
     for predicate in env_predicates {
         let bound_predicate = predicate.kind();
         if let ty::ClauseKind::Projection(data) = predicate.kind().skip_binder() {

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -232,7 +232,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .filter(|p| p.def_id() == stack.obligation.predicate.def_id())
             .filter(|p| p.polarity() == stack.obligation.predicate.polarity());
 
-        let drcx = DeepRejectCtxt::relate_rigid_rigid(self.tcx());
+        let mut drcx = DeepRejectCtxt::relate_rigid_rigid(self.tcx());
         let obligation_args = stack.obligation.predicate.skip_binder().trait_ref.args;
         // Keep only those bounds which may apply, and propagate overflow if it occurs.
         for bound in bounds {
@@ -548,7 +548,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligation: &PolyTraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) {
-        let drcx = DeepRejectCtxt::relate_rigid_infer(self.tcx());
+        let mut drcx = DeepRejectCtxt::relate_rigid_infer(self.tcx());
         let obligation_args = obligation.predicate.skip_binder().trait_ref.args;
         self.tcx().for_each_relevant_impl(
             obligation.predicate.def_id(),

compiler/rustc_type_ir/src/fast_reject.rs

@@ -181,41 +181,46 @@ impl<DefId> SimplifiedType<DefId> {
 /// We also use this function during coherence. For coherence the
 /// impls only have to overlap for some value, so we treat parameters
 /// on both sides like inference variables.
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone)]
 pub struct DeepRejectCtxt<
     I: Interner,
     const INSTANTIATE_LHS_WITH_INFER: bool,
     const INSTANTIATE_RHS_WITH_INFER: bool,
 > {
     _interner: PhantomData<I>,
+    /// We bail if the walked types are too big to avoid hangs.
+    ///
+    /// We could alternatively use a cache to deduplicate types but this
+    /// feels like unnecessary effort.
+    num_non_trivial_types: usize,
 }
 
 impl<I: Interner> DeepRejectCtxt<I, false, false> {
     /// Treat parameters in both the lhs and the rhs as rigid.
     pub fn relate_rigid_rigid(_interner: I) -> DeepRejectCtxt<I, false, false> {
-        DeepRejectCtxt { _interner: PhantomData }
+        DeepRejectCtxt { _interner: PhantomData, num_non_trivial_types: 0 }
     }
 }
 
 impl<I: Interner> DeepRejectCtxt<I, true, true> {
     /// Treat parameters in both the lhs and the rhs as infer vars.
     pub fn relate_infer_infer(_interner: I) -> DeepRejectCtxt<I, true, true> {
-        DeepRejectCtxt { _interner: PhantomData }
+        DeepRejectCtxt { _interner: PhantomData, num_non_trivial_types: 0 }
     }
 }
 
 impl<I: Interner> DeepRejectCtxt<I, false, true> {
     /// Treat parameters in the lhs as rigid, and in rhs as infer vars.
     pub fn relate_rigid_infer(_interner: I) -> DeepRejectCtxt<I, false, true> {
-        DeepRejectCtxt { _interner: PhantomData }
+        DeepRejectCtxt { _interner: PhantomData, num_non_trivial_types: 0 }
     }
 }
 
 impl<I: Interner, const INSTANTIATE_LHS_WITH_INFER: bool, const INSTANTIATE_RHS_WITH_INFER: bool>
     DeepRejectCtxt<I, INSTANTIATE_LHS_WITH_INFER, INSTANTIATE_RHS_WITH_INFER>
 {
     pub fn args_may_unify(
-        self,
+        &mut self,
         obligation_args: I::GenericArgs,
         impl_args: I::GenericArgs,
     ) -> bool {
@@ -234,7 +239,7 @@ impl<I: Interner, const INSTANTIATE_LHS_WITH_INFER: bool, const INSTANTIATE_RHS_
         })
     }
 
-    pub fn types_may_unify(self, lhs: I::Ty, rhs: I::Ty) -> bool {
+    pub fn types_may_unify(&mut self, lhs: I::Ty, rhs: I::Ty) -> bool {
         match rhs.kind() {
             // Start by checking whether the `rhs` type may unify with
             // pretty much everything. Just return `true` in that case.
@@ -273,6 +278,12 @@ impl<I: Interner, const INSTANTIATE_LHS_WITH_INFER: bool, const INSTANTIATE_RHS_
             | ty::Placeholder(_) => {}
         };
 
+        self.num_non_trivial_types += 1;
+        // Arbitrary cutoff.
+        if self.num_non_trivial_types >= 1024 {
+            return true;
+        }
+
         // For purely rigid types, use structural equivalence.
         match lhs.kind() {
             ty::Ref(_, lhs_ty, lhs_mutbl) => match rhs.kind() {
@@ -417,7 +428,7 @@ impl<I: Interner, const INSTANTIATE_LHS_WITH_INFER: bool, const INSTANTIATE_RHS_
         }
     }
 
-    pub fn consts_may_unify(self, lhs: I::Const, rhs: I::Const) -> bool {
+    pub fn consts_may_unify(&mut self, lhs: I::Const, rhs: I::Const) -> bool {
         match rhs.kind() {
             ty::ConstKind::Param(_) => {
                 if INSTANTIATE_RHS_WITH_INFER {
@@ -465,7 +476,7 @@ impl<I: Interner, const INSTANTIATE_LHS_WITH_INFER: bool, const INSTANTIATE_RHS_
         }
     }
 
-    fn var_and_ty_may_unify(self, var: ty::InferTy, ty: I::Ty) -> bool {
+    fn var_and_ty_may_unify(&mut self, var: ty::InferTy, ty: I::Ty) -> bool {
         if !ty.is_known_rigid() {
             return true;
         }

src/librustdoc/html/render/write_shared.rs

@@ -918,8 +918,8 @@ impl<'item> DocVisitor<'item> for TypeImplCollector<'_, '_, 'item> {
             // Be aware of `tests/rustdoc/type-alias/deeply-nested-112515.rs` which might regress.
             let Some(impl_did) = impl_item_id.as_def_id() else { continue };
             let for_ty = self.cx.tcx().type_of(impl_did).skip_binder();
-            let reject_cx = DeepRejectCtxt::relate_infer_infer(self.cx.tcx());
-            if !reject_cx.types_may_unify(aliased_ty, for_ty) {
+            let mut drcx = DeepRejectCtxt::relate_infer_infer(self.cx.tcx());
+            if !drcx.types_may_unify(aliased_ty, for_ty) {
                 continue;
             }
             // Avoid duplicates