Remove some Vec allocations to improve performance

src/librustc_infer/infer/outlives/verify.rs

@@ -223,7 +223,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         // like `T` and `T::Item`. It may not work as well for things
         // like `<T as Foo<'a>>::Item`.
         let c_b = self.param_env.caller_bounds;
-        let param_bounds = self.collect_outlives_from_predicate_list(&compare_ty, c_b);
+        let param_bounds = self.collect_outlives_from_predicate_list(&compare_ty, c_b.into_iter());
 
         // Next, collect regions we scraped from the well-formedness
         // constraints in the fn signature. To do that, we walk the list
@@ -315,15 +315,12 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         let tcx = self.tcx;
         let assoc_item = tcx.associated_item(assoc_item_def_id);
         let trait_def_id = assoc_item.container.assert_trait();
-        let trait_predicates =
-            tcx.predicates_of(trait_def_id).predicates.iter().map(|(p, _)| *p).collect();
+        let trait_predicates = tcx.predicates_of(trait_def_id).predicates.iter().map(|(p, _)| *p);
         let identity_substs = InternalSubsts::identity_for_item(tcx, assoc_item_def_id);
         let identity_proj = tcx.mk_projection(assoc_item_def_id, identity_substs);
         self.collect_outlives_from_predicate_list(
             move |ty| ty == identity_proj,
-            traits::elaborate_predicates(tcx, trait_predicates)
-                .map(|o| o.predicate)
-                .collect::<Vec<_>>(),
+            traits::elaborate_predicates(tcx, trait_predicates).map(|o| o.predicate),
         )
         .map(|b| b.1)
     }
@@ -337,10 +334,9 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     fn collect_outlives_from_predicate_list(
         &self,
         compare_ty: impl Fn(Ty<'tcx>) -> bool,
-        predicates: impl IntoIterator<Item = impl AsRef<ty::Predicate<'tcx>>>,
+        predicates: impl Iterator<Item = impl AsRef<ty::Predicate<'tcx>>>,
     ) -> impl Iterator<Item = ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>> {
         predicates
-            .into_iter()
             .filter_map(|p| p.as_ref().to_opt_type_outlives())
             .filter_map(|p| p.no_bound_vars())
             .filter(move |p| compare_ty(p.0))

src/librustc_infer/traits/util.rs

@@ -97,24 +97,22 @@ pub fn elaborate_trait_ref<'tcx>(
     tcx: TyCtxt<'tcx>,
     trait_ref: ty::PolyTraitRef<'tcx>,
 ) -> Elaborator<'tcx> {
-    elaborate_predicates(tcx, vec![trait_ref.without_const().to_predicate()])
+    elaborate_predicates(tcx, std::iter::once(trait_ref.without_const().to_predicate()))
 }
 
 pub fn elaborate_trait_refs<'tcx>(
     tcx: TyCtxt<'tcx>,
     trait_refs: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
 ) -> Elaborator<'tcx> {
-    let predicates = trait_refs.map(|trait_ref| trait_ref.without_const().to_predicate()).collect();
+    let predicates = trait_refs.map(|trait_ref| trait_ref.without_const().to_predicate());
     elaborate_predicates(tcx, predicates)
 }
 
 pub fn elaborate_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
-    mut predicates: Vec<ty::Predicate<'tcx>>,
+    predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
 ) -> Elaborator<'tcx> {
-    let mut visited = PredicateSet::new(tcx);
-    predicates.retain(|pred| visited.insert(pred));
-    let obligations: Vec<_> =
+    let obligations =
         predicates.into_iter().map(|predicate| predicate_obligation(predicate, None)).collect();
     elaborate_obligations(tcx, obligations)
 }
@@ -151,21 +149,20 @@ impl Elaborator<'tcx> {
                 // Get predicates declared on the trait.
                 let predicates = tcx.super_predicates_of(data.def_id());
 
-                let obligations = predicates.predicates.iter().map(|(pred, span)| {
+                let obligations = predicates.predicates.into_iter().map(|(pred, span)| {
                     predicate_obligation(
                         pred.subst_supertrait(tcx, &data.to_poly_trait_ref()),
                         Some(*span),
                     )
                 });
-                debug!("super_predicates: data={:?} predicates={:?}", data, &obligations);
+                debug!("super_predicates: data={:?}", data);
 
                 // Only keep those bounds that we haven't already seen.
                 // This is necessary to prevent infinite recursion in some
                 // cases. One common case is when people define
                 // `trait Sized: Sized { }` rather than `trait Sized { }`.
                 let visited = &mut self.visited;
-                let obligations =
-                    obligations.filter(|obligation| visited.insert(&obligation.predicate));
+                let obligations = obligations.filter(|o| visited.insert(&o.predicate));
 
                 self.stack.extend(obligations);
             }

src/librustc_middle/ty/trait_def.rs

@@ -168,15 +168,13 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     /// Returns a vector containing all impls
-    pub fn all_impls(self, def_id: DefId) -> Vec<DefId> {
-        let impls = self.trait_impls_of(def_id);
+    pub fn all_impls(self, def_id: DefId) -> impl Iterator<Item = DefId> + 'tcx {
+        let TraitImpls { blanket_impls, non_blanket_impls } = self.trait_impls_of(def_id);
 
-        impls
-            .blanket_impls
-            .iter()
-            .chain(impls.non_blanket_impls.values().flatten())
+        blanket_impls
+            .into_iter()
+            .chain(non_blanket_impls.into_iter().map(|(_, v)| v).flatten())
             .cloned()
-            .collect()
     }
 }
 

src/librustc_mir/transform/const_prop.rs

@@ -122,8 +122,7 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
             .predicates_of(source.def_id())
             .predicates
             .iter()
-            .filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None })
-            .collect();
+            .filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
         if !traits::normalize_and_test_predicates(
             tcx,
             traits::elaborate_predicates(tcx, predicates).map(|o| o.predicate).collect(),

src/librustc_trait_selection/opaque_types.rs

@@ -418,7 +418,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             let opaque_type = tcx.mk_opaque(def_id, opaque_defn.substs);
 
             let required_region_bounds =
-                required_region_bounds(tcx, opaque_type, bounds.predicates);
+                required_region_bounds(tcx, opaque_type, bounds.predicates.into_iter());
             debug_assert!(!required_region_bounds.is_empty());
 
             for required_region in required_region_bounds {
@@ -1127,7 +1127,8 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
 
         debug!("instantiate_opaque_types: bounds={:?}", bounds);
 
-        let required_region_bounds = required_region_bounds(tcx, ty, bounds.predicates.clone());
+        let required_region_bounds =
+            required_region_bounds(tcx, ty, bounds.predicates.iter().cloned());
         debug!("instantiate_opaque_types: required_region_bounds={:?}", required_region_bounds);
 
         // Make sure that we are in fact defining the *entire* type
@@ -1245,17 +1246,15 @@ pub fn may_define_opaque_type(tcx: TyCtxt<'_>, def_id: DefId, opaque_hir_id: hir
 crate fn required_region_bounds(
     tcx: TyCtxt<'tcx>,
     erased_self_ty: Ty<'tcx>,
-    predicates: Vec<ty::Predicate<'tcx>>,
+    predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
 ) -> Vec<ty::Region<'tcx>> {
-    debug!(
-        "required_region_bounds(erased_self_ty={:?}, predicates={:?})",
-        erased_self_ty, predicates
-    );
+    debug!("required_region_bounds(erased_self_ty={:?})", erased_self_ty);
 
     assert!(!erased_self_ty.has_escaping_bound_vars());
 
     traits::elaborate_predicates(tcx, predicates)
         .filter_map(|obligation| {
+            debug!("required_region_bounds(obligation={:?})", obligation);
             match obligation.predicate {
                 ty::Predicate::Projection(..)
                 | ty::Predicate::Trait(..)

src/librustc_trait_selection/traits/auto_trait.rs

@@ -281,7 +281,7 @@ impl AutoTraitFinder<'tcx> {
             },
         }));
 
-        let mut computed_preds: FxHashSet<_> = param_env.caller_bounds.iter().cloned().collect();
+        let computed_preds = param_env.caller_bounds.iter().cloned();
         let mut user_computed_preds: FxHashSet<_> =
             user_env.caller_bounds.iter().cloned().collect();
 
@@ -358,10 +358,11 @@ impl AutoTraitFinder<'tcx> {
                 _ => panic!("Unexpected error for '{:?}': {:?}", ty, result),
             };
 
-            computed_preds.extend(user_computed_preds.iter().cloned());
-            let normalized_preds =
-                elaborate_predicates(tcx, computed_preds.iter().cloned().collect())
-                    .map(|o| o.predicate);
+            let normalized_preds = elaborate_predicates(
+                tcx,
+                computed_preds.clone().chain(user_computed_preds.iter().cloned()),
+            )
+            .map(|o| o.predicate);
             new_env =
                 ty::ParamEnv::new(tcx.mk_predicates(normalized_preds), param_env.reveal, None);
         }
@@ -739,7 +740,7 @@ impl AutoTraitFinder<'tcx> {
                             if p.ty().skip_binder().has_infer_types() {
                                 if !self.evaluate_nested_obligations(
                                     ty,
-                                    v.clone().iter().cloned(),
+                                    v.into_iter(),
                                     computed_preds,
                                     fresh_preds,
                                     predicates,

src/librustc_trait_selection/traits/error_reporting/mod.rs

@@ -1007,7 +1007,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
             }
         };
 
-        for obligation in super::elaborate_predicates(self.tcx, vec![*cond]) {
+        for obligation in super::elaborate_predicates(self.tcx, std::iter::once(*cond)) {
             if let ty::Predicate::Trait(implication, _) = obligation.predicate {
                 let error = error.to_poly_trait_ref();
                 let implication = implication.to_poly_trait_ref();
@@ -1208,22 +1208,18 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
 
         match simp {
             Some(simp) => all_impls
-                .iter()
-                .filter_map(|&def_id| {
+                .filter_map(|def_id| {
                     let imp = self.tcx.impl_trait_ref(def_id).unwrap();
                     let imp_simp = fast_reject::simplify_type(self.tcx, imp.self_ty(), true);
                     if let Some(imp_simp) = imp_simp {
                         if simp != imp_simp {
                             return None;
                         }
                     }
-
                     Some(imp)
                 })
                 .collect(),
-            None => {
-                all_impls.iter().map(|&def_id| self.tcx.impl_trait_ref(def_id).unwrap()).collect()
-            }
+            None => all_impls.map(|def_id| self.tcx.impl_trait_ref(def_id).unwrap()).collect(),
         }
     }
 

src/librustc_trait_selection/traits/mod.rs

@@ -110,8 +110,8 @@ pub enum TraitQueryMode {
 pub fn predicates_for_generics<'tcx>(
     cause: ObligationCause<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    generic_bounds: &ty::InstantiatedPredicates<'tcx>,
-) -> PredicateObligations<'tcx> {
+    generic_bounds: ty::InstantiatedPredicates<'tcx>,
+) -> impl Iterator<Item = PredicateObligation<'tcx>> {
     util::predicates_for_generics(cause, 0, param_env, generic_bounds)
 }
 
@@ -297,7 +297,7 @@ pub fn normalize_param_env_or_error<'tcx>(
     );
 
     let mut predicates: Vec<_> =
-        util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec())
+        util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.into_iter().cloned())
             .map(|obligation| obligation.predicate)
             .collect();
 

src/librustc_trait_selection/traits/object_safety.rs

@@ -302,7 +302,7 @@ fn generics_require_sized_self(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
     // Search for a predicate like `Self : Sized` amongst the trait bounds.
     let predicates = tcx.predicates_of(def_id);
     let predicates = predicates.instantiate_identity(tcx).predicates;
-    elaborate_predicates(tcx, predicates).any(|obligation| match obligation.predicate {
+    elaborate_predicates(tcx, predicates.into_iter()).any(|obligation| match obligation.predicate {
         ty::Predicate::Trait(ref trait_pred, _) => {
             trait_pred.def_id() == sized_def_id && trait_pred.skip_binder().self_ty().is_param(0)
         }

src/librustc_trait_selection/traits/project.rs

@@ -900,7 +900,7 @@ fn assemble_candidates_from_trait_def<'cx, 'tcx>(
     // If so, extract what we know from the trait and try to come up with a good answer.
     let trait_predicates = tcx.predicates_of(def_id);
     let bounds = trait_predicates.instantiate(tcx, substs);
-    let bounds = elaborate_predicates(tcx, bounds.predicates).map(|o| o.predicate);
+    let bounds = elaborate_predicates(tcx, bounds.predicates.into_iter()).map(|o| o.predicate);
     assemble_candidates_from_predicates(
         selcx,
         obligation,
@@ -911,16 +911,14 @@ fn assemble_candidates_from_trait_def<'cx, 'tcx>(
     )
 }
 
-fn assemble_candidates_from_predicates<'cx, 'tcx, I>(
+fn assemble_candidates_from_predicates<'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligation: &ProjectionTyObligation<'tcx>,
     obligation_trait_ref: &ty::TraitRef<'tcx>,
     candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
     ctor: fn(ty::PolyProjectionPredicate<'tcx>) -> ProjectionTyCandidate<'tcx>,
-    env_predicates: I,
-) where
-    I: IntoIterator<Item = ty::Predicate<'tcx>>,
-{
+    env_predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
+) {
     debug!("assemble_candidates_from_predicates(obligation={:?})", obligation);
     let infcx = selcx.infcx();
     for predicate in env_predicates {
@@ -1153,10 +1151,8 @@ fn confirm_object_candidate<'cx, 'tcx>(
             object_ty
         ),
     };
-    let env_predicates = data
-        .projection_bounds()
-        .map(|p| p.with_self_ty(selcx.tcx(), object_ty).to_predicate())
-        .collect();
+    let env_predicates =
+        data.projection_bounds().map(|p| p.with_self_ty(selcx.tcx(), object_ty).to_predicate());
     let env_predicate = {
         let env_predicates = elaborate_predicates(selcx.tcx(), env_predicates);
 

src/librustc_trait_selection/traits/select.rs

@@ -1443,7 +1443,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             bounds
         );
 
-        let elaborated_predicates = util::elaborate_predicates(self.tcx(), bounds.predicates);
+        let elaborated_predicates =
+            util::elaborate_predicates(self.tcx(), bounds.predicates.into_iter());
         let matching_bound = elaborated_predicates.filter_to_traits().find(|bound| {
             self.infcx.probe(|_| {
                 self.match_projection(

src/librustc_trait_selection/traits/specialize/mod.rs

@@ -189,26 +189,22 @@ fn fulfill_implication<'a, 'tcx>(
 
     let selcx = &mut SelectionContext::new(&infcx);
     let target_substs = infcx.fresh_substs_for_item(DUMMY_SP, target_impl);
-    let (target_trait_ref, mut obligations) =
+    let (target_trait_ref, obligations) =
         impl_trait_ref_and_oblig(selcx, param_env, target_impl, target_substs);
-    debug!(
-        "fulfill_implication: target_trait_ref={:?}, obligations={:?}",
-        target_trait_ref, obligations
-    );
 
     // do the impls unify? If not, no specialization.
-    match infcx.at(&ObligationCause::dummy(), param_env).eq(source_trait_ref, target_trait_ref) {
-        Ok(InferOk { obligations: o, .. }) => {
-            obligations.extend(o);
-        }
-        Err(_) => {
-            debug!(
-                "fulfill_implication: {:?} does not unify with {:?}",
-                source_trait_ref, target_trait_ref
-            );
-            return Err(());
-        }
-    }
+    let more_obligations =
+        match infcx.at(&ObligationCause::dummy(), param_env).eq(source_trait_ref, target_trait_ref)
+        {
+            Ok(InferOk { obligations, .. }) => obligations,
+            Err(_) => {
+                debug!(
+                    "fulfill_implication: {:?} does not unify with {:?}",
+                    source_trait_ref, target_trait_ref
+                );
+                return Err(());
+            }
+        };
 
     // attempt to prove all of the predicates for impl2 given those for impl1
     // (which are packed up in penv)
@@ -226,7 +222,7 @@ fn fulfill_implication<'a, 'tcx>(
         // we already make a mockery out of the region system, so
         // why not ignore them a bit earlier?
         let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
-        for oblig in obligations.into_iter() {
+        for oblig in obligations.chain(more_obligations) {
             fulfill_cx.register_predicate_obligation(&infcx, oblig);
         }
         match fulfill_cx.select_all_or_error(infcx) {
@@ -261,7 +257,7 @@ pub(super) fn specialization_graph_provider(
 ) -> &specialization_graph::Graph {
     let mut sg = specialization_graph::Graph::new();
 
-    let mut trait_impls = tcx.all_impls(trait_id);
+    let mut trait_impls: Vec<_> = tcx.all_impls(trait_id).collect();
 
     // The coherence checking implementation seems to rely on impls being
     // iterated over (roughly) in definition order, so we are sorting by