Use FxHashSet instead of Vec for well formed tys

compiler/rustc_borrowck/src/type_check/free_region_relations.rs

@@ -259,7 +259,7 @@ impl UniversalRegionRelationsBuilder<'cx, 'tcx> {
                 // We add implied bounds from both the unnormalized and normalized ty
                 // See issue #87748
                 let constraints_implied_1 = self.add_implied_bounds(ty);
-                let TypeOpOutput { output: ty, constraints: constraints1, .. } = self
+                let TypeOpOutput { output: norm_ty, constraints: constraints1, .. } = self
                     .param_env
                     .and(type_op::normalize::Normalize::new(ty))
                     .fully_perform(self.infcx)
@@ -286,8 +286,9 @@ impl UniversalRegionRelationsBuilder<'cx, 'tcx> {
                 // }
                 // ```
                 // Both &Self::Bar and &() are WF
-                let constraints_implied_2 = self.add_implied_bounds(ty);
-                normalized_inputs_and_output.push(ty);
+                let constraints_implied_2 =
+                    if ty != norm_ty { self.add_implied_bounds(norm_ty) } else { None };
+                normalized_inputs_and_output.push(norm_ty);
                 constraints1.into_iter().chain(constraints_implied_1).chain(constraints_implied_2)
             })
             .collect();

compiler/rustc_trait_selection/src/infer.rs

@@ -2,6 +2,7 @@ use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
 use crate::traits::query::outlives_bounds::InferCtxtExt as _;
 use crate::traits::{self, TraitEngine, TraitEngineExt};
 
+use rustc_data_structures::stable_set::FxHashSet;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
@@ -184,7 +185,7 @@ pub trait OutlivesEnvironmentExt<'tcx> {
     fn add_implied_bounds(
         &mut self,
         infcx: &InferCtxt<'a, 'tcx>,
-        fn_sig_tys: &[Ty<'tcx>],
+        fn_sig_tys: FxHashSet<Ty<'tcx>>,
         body_id: hir::HirId,
         span: Span,
     );
@@ -210,13 +211,13 @@ impl<'tcx> OutlivesEnvironmentExt<'tcx> for OutlivesEnvironment<'tcx> {
     fn add_implied_bounds(
         &mut self,
         infcx: &InferCtxt<'a, 'tcx>,
-        fn_sig_tys: &[Ty<'tcx>],
+        fn_sig_tys: FxHashSet<Ty<'tcx>>,
         body_id: hir::HirId,
         span: Span,
     ) {
         debug!("add_implied_bounds()");
 
-        for &ty in fn_sig_tys {
+        for ty in fn_sig_tys {
             let ty = infcx.resolve_vars_if_possible(ty);
             debug!("add_implied_bounds: ty = {}", ty);
             let implied_bounds = infcx.implied_outlives_bounds(self.param_env, body_id, ty, span);

compiler/rustc_typeck/src/check/check.rs

@@ -688,7 +688,7 @@ fn check_opaque_meets_bounds<'tcx>(
         // Finally, resolve all regions. This catches wily misuses of
         // lifetime parameters.
         let fcx = FnCtxt::new(&inh, param_env, hir_id);
-        fcx.regionck_item(hir_id, span, &[]);
+        fcx.regionck_item(hir_id, span, FxHashSet::default());
     });
 }
 

compiler/rustc_typeck/src/check/compare_method.rs

@@ -1,4 +1,5 @@
 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
+use rustc_data_structures::stable_set::FxHashSet;
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorReported};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
@@ -250,7 +251,7 @@ fn compare_predicate_entailment<'tcx>(
         // Compute placeholder form of impl and trait method tys.
         let tcx = infcx.tcx;
 
-        let mut wf_tys = vec![];
+        let mut wf_tys = FxHashSet::default();
 
         let (impl_sig, _) = infcx.replace_bound_vars_with_fresh_vars(
             impl_m_span,
@@ -398,7 +399,7 @@ fn compare_predicate_entailment<'tcx>(
         // Finally, resolve all regions. This catches wily misuses of
         // lifetime parameters.
         let fcx = FnCtxt::new(&inh, param_env, impl_m_hir_id);
-        fcx.regionck_item(impl_m_hir_id, impl_m_span, &wf_tys);
+        fcx.regionck_item(impl_m_hir_id, impl_m_span, wf_tys);
 
         Ok(())
     })
@@ -1098,7 +1099,7 @@ crate fn compare_const_impl<'tcx>(
         }
 
         let fcx = FnCtxt::new(&inh, param_env, impl_c_hir_id);
-        fcx.regionck_item(impl_c_hir_id, impl_c_span, &[]);
+        fcx.regionck_item(impl_c_hir_id, impl_c_span, FxHashSet::default());
     });
 }
 
@@ -1216,7 +1217,7 @@ fn compare_type_predicate_entailment<'tcx>(
         // Finally, resolve all regions. This catches wily misuses of
         // lifetime parameters.
         let fcx = FnCtxt::new(&inh, param_env, impl_ty_hir_id);
-        fcx.regionck_item(impl_ty_hir_id, impl_ty_span, &[]);
+        fcx.regionck_item(impl_ty_hir_id, impl_ty_span, FxHashSet::default());
 
         Ok(())
     })
@@ -1436,10 +1437,10 @@ pub fn check_type_bounds<'tcx>(
         // lifetime parameters.
         let fcx = FnCtxt::new(&inh, param_env, impl_ty_hir_id);
         let implied_bounds = match impl_ty.container {
-            ty::TraitContainer(_) => vec![],
+            ty::TraitContainer(_) => FxHashSet::default(),
             ty::ImplContainer(def_id) => fcx.impl_implied_bounds(def_id, impl_ty_span),
         };
-        fcx.regionck_item(impl_ty_hir_id, impl_ty_span, &implied_bounds);
+        fcx.regionck_item(impl_ty_hir_id, impl_ty_span, implied_bounds);
 
         Ok(())
     })

compiler/rustc_typeck/src/check/mod.rs

@@ -388,7 +388,7 @@ fn typeck_with_fallback<'tcx>(
             // from normalization. We could just discard these, but to align with
             // compare_method and elsewhere, we just add implied bounds for
             // these types.
-            let mut wf_tys = vec![];
+            let mut wf_tys = FxHashSet::default();
             // Compute the fty from point of view of inside the fn.
             let fn_sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), fn_sig);
             wf_tys.extend(fn_sig.inputs_and_output.iter());
@@ -451,7 +451,7 @@ fn typeck_with_fallback<'tcx>(
 
             fcx.write_ty(id, expected_type);
 
-            (fcx, vec![])
+            (fcx, FxHashSet::default())
         };
 
         let fallback_has_occurred = fcx.type_inference_fallback();
@@ -475,7 +475,7 @@ fn typeck_with_fallback<'tcx>(
         fcx.select_all_obligations_or_error();
 
         if fn_sig.is_some() {
-            fcx.regionck_fn(id, body, span, &wf_tys);
+            fcx.regionck_fn(id, body, span, wf_tys);
         } else {
             fcx.regionck_expr(body);
         }

compiler/rustc_typeck/src/check/regionck.rs

@@ -76,6 +76,7 @@ use crate::check::dropck;
 use crate::check::FnCtxt;
 use crate::mem_categorization as mc;
 use crate::middle::region;
+use rustc_data_structures::stable_set::FxHashSet;
 use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
@@ -126,7 +127,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
     /// Region checking during the WF phase for items. `wf_tys` are the
     /// types from which we should derive implied bounds, if any.
-    pub fn regionck_item(&self, item_id: hir::HirId, span: Span, wf_tys: &[Ty<'tcx>]) {
+    pub fn regionck_item(&self, item_id: hir::HirId, span: Span, wf_tys: FxHashSet<Ty<'tcx>>) {
         debug!("regionck_item(item.id={:?}, wf_tys={:?})", item_id, wf_tys);
         let subject = self.tcx.hir().local_def_id(item_id);
         let mut rcx = RegionCtxt::new(self, item_id, Subject(subject), self.param_env);
@@ -149,7 +150,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         fn_id: hir::HirId,
         body: &'tcx hir::Body<'tcx>,
         span: Span,
-        wf_tys: &[Ty<'tcx>],
+        wf_tys: FxHashSet<Ty<'tcx>>,
     ) {
         debug!("regionck_fn(id={})", fn_id);
         let subject = self.tcx.hir().body_owner_def_id(body.id());
@@ -286,15 +287,10 @@ impl<'a, 'tcx> RegionCtxt<'a, 'tcx> {
         // because it will have no effect.
         //
         // FIXME(#27579) return types should not be implied bounds
-        let fn_sig_tys: Vec<_> =
+        let fn_sig_tys: FxHashSet<_> =
             fn_sig.inputs().iter().cloned().chain(Some(fn_sig.output())).collect();
 
-        self.outlives_environment.add_implied_bounds(
-            self.fcx,
-            &fn_sig_tys[..],
-            body_id.hir_id,
-            span,
-        );
+        self.outlives_environment.add_implied_bounds(self.fcx, fn_sig_tys, body_id.hir_id, span);
         self.outlives_environment.save_implied_bounds(body_id.hir_id);
         self.link_fn_params(&body.params);
         self.visit_body(body);

compiler/rustc_typeck/src/check/wfcheck.rs

@@ -44,7 +44,7 @@ struct CheckWfFcxBuilder<'tcx> {
 impl<'tcx> CheckWfFcxBuilder<'tcx> {
     fn with_fcx<F>(&mut self, f: F)
     where
-        F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>) -> Vec<Ty<'tcx>>,
+        F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>) -> FxHashSet<Ty<'tcx>>,
     {
         let id = self.id;
         let span = self.span;
@@ -59,7 +59,7 @@ impl<'tcx> CheckWfFcxBuilder<'tcx> {
             }
             let wf_tys = f(&fcx);
             fcx.select_all_obligations_or_error();
-            fcx.regionck_item(id, span, &wf_tys);
+            fcx.regionck_item(id, span, wf_tys);
         });
     }
 }
@@ -394,7 +394,7 @@ fn check_associated_item(
         let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
 
         let (mut implied_bounds, self_ty) = match item.container {
-            ty::TraitContainer(_) => (vec![], fcx.tcx.types.self_param),
+            ty::TraitContainer(_) => (FxHashSet::default(), fcx.tcx.types.self_param),
             ty::ImplContainer(def_id) => {
                 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
             }
@@ -553,7 +553,7 @@ fn check_type_defn<'tcx, F>(
         check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
 
         // No implied bounds in a struct definition.
-        vec![]
+        FxHashSet::default()
     });
 }
 
@@ -579,7 +579,7 @@ fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
     for_item(tcx, item).with_fcx(|fcx| {
         check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
 
-        vec![]
+        FxHashSet::default()
     });
 }
 
@@ -620,7 +620,7 @@ fn check_item_fn(
     for_id(tcx, item_id, span).with_fcx(|fcx| {
         let def_id = tcx.hir().local_def_id(item_id);
         let sig = tcx.fn_sig(def_id);
-        let mut implied_bounds = vec![];
+        let mut implied_bounds = FxHashSet::default();
         check_fn_or_method(fcx, ident.span, sig, decl, def_id.to_def_id(), &mut implied_bounds);
         implied_bounds
     })
@@ -659,7 +659,7 @@ fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_fo
         }
 
         // No implied bounds in a const, etc.
-        vec![]
+        FxHashSet::default()
     });
 }
 
@@ -918,14 +918,14 @@ fn check_fn_or_method<'fcx, 'tcx>(
     sig: ty::PolyFnSig<'tcx>,
     hir_decl: &hir::FnDecl<'_>,
     def_id: DefId,
-    implied_bounds: &mut Vec<Ty<'tcx>>,
+    implied_bounds: &mut FxHashSet<Ty<'tcx>>,
 ) {
     let sig = fcx.tcx.liberate_late_bound_regions(def_id, sig);
 
     // Unnormalized types in signature are WF too
     implied_bounds.extend(sig.inputs());
     // FIXME(#27579) return types should not be implied bounds
-    implied_bounds.push(sig.output());
+    implied_bounds.insert(sig.output());
 
     // Normalize the input and output types one at a time, using a different
     // `WellFormedLoc` for each. We cannot call `normalize_associated_types`
@@ -977,7 +977,7 @@ fn check_fn_or_method<'fcx, 'tcx>(
     );
 
     // FIXME(#27579) return types should not be implied bounds
-    implied_bounds.push(sig.output());
+    implied_bounds.insert(sig.output());
 
     debug!(?implied_bounds);
 
@@ -1513,7 +1513,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .collect()
     }
 
-    pub(super) fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
+    pub(super) fn impl_implied_bounds(
+        &self,
+        impl_def_id: DefId,
+        span: Span,
+    ) -> FxHashSet<Ty<'tcx>> {
         match self.tcx.impl_trait_ref(impl_def_id) {
             Some(trait_ref) => {
                 // Trait impl: take implied bounds from all types that
@@ -1526,7 +1530,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // Inherent impl: take implied bounds from the `self` type.
                 let self_ty = self.tcx.type_of(impl_def_id);
                 let self_ty = self.normalize_associated_types_in(span, self_ty);
-                vec![self_ty]
+                std::array::IntoIter::new([self_ty]).collect()
             }
         }
     }