Auto merge of #106395 - compiler-errors:rework-predicates, r=eholk

Rework some `predicates_of`/`{Generic,Instantiated}Predicates` code

1. Make `instantiate_own` return an iterator, since it's a bit more efficient and easier to work with
2. Remove `bound_{explicit,}_predicates_of` -- these `bound_` methods in particular were a bit awkward to work with since `ty::GenericPredicates` *already* acts kinda like an `EarlyBinder` with its own `instantiate_*` methods, and had only a few call sites anyways.
3. Implement `IntoIterator` for `InstantiatedPredicates`, since it's *very* commonly being `zip`'d together.

22 files changed, 155 insertions, 156 deletions

diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index 968c1f49b95..e512099b93b 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -673,40 +673,34 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let tcx = self.infcx.tcx;
 
         // Find out if the predicates show that the type is a Fn or FnMut
-        let find_fn_kind_from_did = |predicates: ty::EarlyBinder<
-            &[(ty::Predicate<'tcx>, Span)],
-        >,
-                                     substs| {
-            predicates.0.iter().find_map(|(pred, _)| {
-                    let pred = if let Some(substs) = substs {
-                        predicates.rebind(*pred).subst(tcx, substs).kind().skip_binder()
-                    } else {
-                        pred.kind().skip_binder()
-                    };
-                    if let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = pred && pred.self_ty() == ty {
-                    if Some(pred.def_id()) == tcx.lang_items().fn_trait() {
-                        return Some(hir::Mutability::Not);
-                    } else if Some(pred.def_id()) == tcx.lang_items().fn_mut_trait() {
-                        return Some(hir::Mutability::Mut);
-                    }
+        let find_fn_kind_from_did = |(pred, _): (ty::Predicate<'tcx>, _)| {
+            if let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = pred.kind().skip_binder()
+                && pred.self_ty() == ty
+            {
+                if Some(pred.def_id()) == tcx.lang_items().fn_trait() {
+                    return Some(hir::Mutability::Not);
+                } else if Some(pred.def_id()) == tcx.lang_items().fn_mut_trait() {
+                    return Some(hir::Mutability::Mut);
                 }
-                    None
-                })
+            }
+            None
         };
 
         // If the type is opaque/param/closure, and it is Fn or FnMut, let's suggest (mutably)
         // borrowing the type, since `&mut F: FnMut` iff `F: FnMut` and similarly for `Fn`.
         // These types seem reasonably opaque enough that they could be substituted with their
         // borrowed variants in a function body when we see a move error.
-        let borrow_level = match ty.kind() {
-            ty::Param(_) => find_fn_kind_from_did(
-                tcx.bound_explicit_predicates_of(self.mir_def_id().to_def_id())
-                    .map_bound(|p| p.predicates),
-                None,
-            ),
-            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
-                find_fn_kind_from_did(tcx.bound_explicit_item_bounds(*def_id), Some(*substs))
-            }
+        let borrow_level = match *ty.kind() {
+            ty::Param(_) => tcx
+                .explicit_predicates_of(self.mir_def_id().to_def_id())
+                .predicates
+                .iter()
+                .copied()
+                .find_map(find_fn_kind_from_did),
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => tcx
+                .bound_explicit_item_bounds(def_id)
+                .subst_iter_copied(tcx, substs)
+                .find_map(find_fn_kind_from_did),
             ty::Closure(_, substs) => match substs.as_closure().kind() {
                 ty::ClosureKind::Fn => Some(hir::Mutability::Not),
                 ty::ClosureKind::FnMut => Some(hir::Mutability::Mut),
diff --git a/compiler/rustc_borrowck/src/type_check/canonical.rs b/compiler/rustc_borrowck/src/type_check/canonical.rs
index 02222c0a03c..11729e2c83f 100644
--- a/compiler/rustc_borrowck/src/type_check/canonical.rs
+++ b/compiler/rustc_borrowck/src/type_check/canonical.rs
@@ -107,11 +107,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         instantiated_predicates: ty::InstantiatedPredicates<'tcx>,
         locations: Locations,
     ) {
-        for (predicate, span) in instantiated_predicates
-            .predicates
-            .into_iter()
-            .zip(instantiated_predicates.spans.into_iter())
-        {
+        for (predicate, span) in instantiated_predicates {
             debug!(?predicate);
             let category = ConstraintCategory::Predicate(span);
             let predicate = self.normalize_with_category(predicate, locations, category);
diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
index 770d7b6f927..c43bfd16ab1 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -209,9 +209,11 @@ fn compare_method_predicate_entailment<'tcx>(
     //
     // We then register the obligations from the impl_m and check to see
     // if all constraints hold.
-    hybrid_preds
-        .predicates
-        .extend(trait_m_predicates.instantiate_own(tcx, trait_to_placeholder_substs).predicates);
+    hybrid_preds.predicates.extend(
+        trait_m_predicates
+            .instantiate_own(tcx, trait_to_placeholder_substs)
+            .map(|(predicate, _)| predicate),
+    );
 
     // Construct trait parameter environment and then shift it into the placeholder viewpoint.
     // The key step here is to update the caller_bounds's predicates to be
@@ -230,7 +232,7 @@ fn compare_method_predicate_entailment<'tcx>(
     debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds());
 
     let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs);
-    for (predicate, span) in iter::zip(impl_m_own_bounds.predicates, impl_m_own_bounds.spans) {
+    for (predicate, span) in impl_m_own_bounds {
         let normalize_cause = traits::ObligationCause::misc(span, impl_m_hir_id);
         let predicate = ocx.normalize(&normalize_cause, param_env, predicate);
 
@@ -1828,8 +1830,7 @@ fn compare_type_predicate_entailment<'tcx>(
     check_region_bounds_on_impl_item(tcx, impl_ty, trait_ty, false)?;
 
     let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
-
-    if impl_ty_own_bounds.is_empty() {
+    if impl_ty_own_bounds.len() == 0 {
         // Nothing to check.
         return Ok(());
     }
@@ -1844,9 +1845,11 @@ fn compare_type_predicate_entailment<'tcx>(
     // associated type in the trait are assumed.
     let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
     let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
-    hybrid_preds
-        .predicates
-        .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
+    hybrid_preds.predicates.extend(
+        trait_ty_predicates
+            .instantiate_own(tcx, trait_to_impl_substs)
+            .map(|(predicate, _)| predicate),
+    );
 
     debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
 
@@ -1862,9 +1865,7 @@ fn compare_type_predicate_entailment<'tcx>(
 
     debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds());
 
-    assert_eq!(impl_ty_own_bounds.predicates.len(), impl_ty_own_bounds.spans.len());
-    for (span, predicate) in std::iter::zip(impl_ty_own_bounds.spans, impl_ty_own_bounds.predicates)
-    {
+    for (predicate, span) in impl_ty_own_bounds {
         let cause = ObligationCause::misc(span, impl_ty_hir_id);
         let predicate = ocx.normalize(&cause, param_env, predicate);
 
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index 912e0ec560b..49dd1eb22f7 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -32,7 +32,6 @@ use rustc_trait_selection::traits::{
 };
 
 use std::cell::LazyCell;
-use std::iter;
 use std::ops::{ControlFlow, Deref};
 
 pub(super) struct WfCheckingCtxt<'a, 'tcx> {
@@ -1310,7 +1309,7 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
     let infcx = wfcx.infcx;
     let tcx = wfcx.tcx();
 
-    let predicates = tcx.bound_predicates_of(def_id.to_def_id());
+    let predicates = tcx.predicates_of(def_id.to_def_id());
     let generics = tcx.generics_of(def_id);
 
     let is_our_default = |def: &ty::GenericParamDef| match def.kind {
@@ -1411,7 +1410,6 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
 
     // Now we build the substituted predicates.
     let default_obligations = predicates
-        .0
         .predicates
         .iter()
         .flat_map(|&(pred, sp)| {
@@ -1442,13 +1440,13 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
             }
             let mut param_count = CountParams::default();
             let has_region = pred.visit_with(&mut param_count).is_break();
-            let substituted_pred = predicates.rebind(pred).subst(tcx, substs);
+            let substituted_pred = ty::EarlyBinder(pred).subst(tcx, substs);
             // Don't check non-defaulted params, dependent defaults (including lifetimes)
             // or preds with multiple params.
             if substituted_pred.has_non_region_param() || param_count.params.len() > 1 || has_region
             {
                 None
-            } else if predicates.0.predicates.iter().any(|&(p, _)| p == substituted_pred) {
+            } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
                 // Avoid duplication of predicates that contain no parameters, for example.
                 None
             } else {
@@ -1474,22 +1472,21 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
             traits::Obligation::new(tcx, cause, wfcx.param_env, pred)
         });
 
-    let predicates = predicates.0.instantiate_identity(tcx);
+    let predicates = predicates.instantiate_identity(tcx);
 
     let predicates = wfcx.normalize(span, None, predicates);
 
     debug!(?predicates.predicates);
     assert_eq!(predicates.predicates.len(), predicates.spans.len());
-    let wf_obligations =
-        iter::zip(&predicates.predicates, &predicates.spans).flat_map(|(&p, &sp)| {
-            traits::wf::predicate_obligations(
-                infcx,
-                wfcx.param_env.without_const(),
-                wfcx.body_id,
-                p,
-                sp,
-            )
-        });
+    let wf_obligations = predicates.into_iter().flat_map(|(p, sp)| {
+        traits::wf::predicate_obligations(
+            infcx,
+            wfcx.param_env.without_const(),
+            wfcx.body_id,
+            p,
+            sp,
+        )
+    });
 
     let obligations: Vec<_> = wf_obligations.chain(default_obligations).collect();
     wfcx.register_obligations(obligations);
diff --git a/compiler/rustc_hir_typeck/src/callee.rs b/compiler/rustc_hir_typeck/src/callee.rs
index f1a4f94cd01..b617821fbd6 100644
--- a/compiler/rustc_hir_typeck/src/callee.rs
+++ b/compiler/rustc_hir_typeck/src/callee.rs
@@ -375,14 +375,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 if self.tcx.has_attr(def_id, sym::rustc_evaluate_where_clauses) {
                     let predicates = self.tcx.predicates_of(def_id);
                     let predicates = predicates.instantiate(self.tcx, subst);
-                    for (predicate, predicate_span) in
-                        predicates.predicates.iter().zip(&predicates.spans)
-                    {
+                    for (predicate, predicate_span) in predicates {
                         let obligation = Obligation::new(
                             self.tcx,
                             ObligationCause::dummy_with_span(callee_expr.span),
                             self.param_env,
-                            *predicate,
+                            predicate,
                         );
                         let result = self.evaluate_obligation(&obligation);
                         self.tcx
@@ -391,7 +389,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 callee_expr.span,
                                 &format!("evaluate({:?}) = {:?}", predicate, result),
                             )
-                            .span_label(*predicate_span, "predicate")
+                            .span_label(predicate_span, "predicate")
                             .emit();
                     }
                 }
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
index b9e13fd2009..c9609e69439 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
@@ -2140,8 +2140,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         // FIXME(compiler-errors): This could be problematic if something has two
                         // fn-like predicates with different args, but callable types really never
                         // do that, so it's OK.
-                        for (predicate, span) in
-                            std::iter::zip(instantiated.predicates, instantiated.spans)
+                        for (predicate, span) in instantiated
                         {
                             if let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = predicate.kind().skip_binder()
                                 && pred.self_ty().peel_refs() == callee_ty
diff --git a/compiler/rustc_hir_typeck/src/method/confirm.rs b/compiler/rustc_hir_typeck/src/method/confirm.rs
index 4a33a791e1b..372ea30ebd0 100644
--- a/compiler/rustc_hir_typeck/src/method/confirm.rs
+++ b/compiler/rustc_hir_typeck/src/method/confirm.rs
@@ -19,7 +19,6 @@ use rustc_middle::ty::{InternalSubsts, UserSubsts, UserType};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_trait_selection::traits;
 
-use std::iter;
 use std::ops::Deref;
 
 struct ConfirmContext<'a, 'tcx> {
@@ -101,7 +100,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         let filler_substs = rcvr_substs
             .extend_to(self.tcx, pick.item.def_id, |def, _| self.tcx.mk_param_from_def(def));
         let illegal_sized_bound = self.predicates_require_illegal_sized_bound(
-            &self.tcx.predicates_of(pick.item.def_id).instantiate(self.tcx, filler_substs),
+            self.tcx.predicates_of(pick.item.def_id).instantiate(self.tcx, filler_substs),
         );
 
         // Unify the (adjusted) self type with what the method expects.
@@ -565,7 +564,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
 
     fn predicates_require_illegal_sized_bound(
         &self,
-        predicates: &ty::InstantiatedPredicates<'tcx>,
+        predicates: ty::InstantiatedPredicates<'tcx>,
     ) -> Option<Span> {
         let sized_def_id = self.tcx.lang_items().sized_trait()?;
 
@@ -575,10 +574,11 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                 ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred))
                     if trait_pred.def_id() == sized_def_id =>
                 {
-                    let span = iter::zip(&predicates.predicates, &predicates.spans)
+                    let span = predicates
+                        .iter()
                         .find_map(
                             |(p, span)| {
-                                if *p == obligation.predicate { Some(*span) } else { None }
+                                if p == obligation.predicate { Some(span) } else { None }
                             },
                         )
                         .unwrap_or(rustc_span::DUMMY_SP);
diff --git a/compiler/rustc_infer/src/infer/error_reporting/note.rs b/compiler/rustc_infer/src/infer/error_reporting/note.rs
index 021e741ee2f..b18cbd404d4 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/note.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/note.rs
@@ -330,9 +330,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
         let Ok(trait_predicates) = self
             .tcx
-            .bound_explicit_predicates_of(trait_item_def_id)
-            .map_bound(|p| p.predicates)
-            .subst_iter_copied(self.tcx, trait_item_substs)
+            .explicit_predicates_of(trait_item_def_id)
+            .instantiate_own(self.tcx, trait_item_substs)
             .map(|(pred, _)| {
                 if pred.is_suggestable(self.tcx, false) {
                     Ok(pred.to_string())
diff --git a/compiler/rustc_middle/src/ty/generics.rs b/compiler/rustc_middle/src/ty/generics.rs
index 8a5e765b9a3..801ca600445 100644
--- a/compiler/rustc_middle/src/ty/generics.rs
+++ b/compiler/rustc_middle/src/ty/generics.rs
@@ -341,15 +341,9 @@ impl<'tcx> GenericPredicates<'tcx> {
         &self,
         tcx: TyCtxt<'tcx>,
         substs: SubstsRef<'tcx>,
-    ) -> InstantiatedPredicates<'tcx> {
-        InstantiatedPredicates {
-            predicates: self
-                .predicates
-                .iter()
-                .map(|(p, _)| EarlyBinder(*p).subst(tcx, substs))
-                .collect(),
-            spans: self.predicates.iter().map(|(_, sp)| *sp).collect(),
-        }
+    ) -> impl Iterator<Item = (Predicate<'tcx>, Span)> + DoubleEndedIterator + ExactSizeIterator
+    {
+        EarlyBinder(self.predicates).subst_iter_copied(tcx, substs)
     }
 
     #[instrument(level = "debug", skip(self, tcx))]
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index e9bd0e9866f..bf8f45c50a3 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1252,6 +1252,35 @@ impl<'tcx> InstantiatedPredicates<'tcx> {
     pub fn is_empty(&self) -> bool {
         self.predicates.is_empty()
     }
+
+    pub fn iter(&self) -> <&Self as IntoIterator>::IntoIter {
+        (&self).into_iter()
+    }
+}
+
+impl<'tcx> IntoIterator for InstantiatedPredicates<'tcx> {
+    type Item = (Predicate<'tcx>, Span);
+
+    type IntoIter = std::iter::Zip<std::vec::IntoIter<Predicate<'tcx>>, std::vec::IntoIter<Span>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        debug_assert_eq!(self.predicates.len(), self.spans.len());
+        std::iter::zip(self.predicates, self.spans)
+    }
+}
+
+impl<'a, 'tcx> IntoIterator for &'a InstantiatedPredicates<'tcx> {
+    type Item = (Predicate<'tcx>, Span);
+
+    type IntoIter = std::iter::Zip<
+        std::iter::Copied<std::slice::Iter<'a, Predicate<'tcx>>>,
+        std::iter::Copied<std::slice::Iter<'a, Span>>,
+    >;
+
+    fn into_iter(self) -> Self::IntoIter {
+        debug_assert_eq!(self.predicates.len(), self.spans.len());
+        std::iter::zip(self.predicates.iter().copied(), self.spans.iter().copied())
+    }
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable, TyEncodable, TyDecodable, Lift)]
diff --git a/compiler/rustc_middle/src/ty/subst.rs b/compiler/rustc_middle/src/ty/subst.rs
index 8f764011d0a..5dc9e311bf6 100644
--- a/compiler/rustc_middle/src/ty/subst.rs
+++ b/compiler/rustc_middle/src/ty/subst.rs
@@ -639,6 +639,13 @@ where
     }
 }
 
+impl<'tcx, I: IntoIterator> ExactSizeIterator for SubstIter<'_, 'tcx, I>
+where
+    I::IntoIter: ExactSizeIterator,
+    I::Item: TypeFoldable<'tcx>,
+{
+}
+
 impl<'tcx, 's, I: IntoIterator> EarlyBinder<I>
 where
     I::Item: Deref,
@@ -686,6 +693,14 @@ where
     }
 }
 
+impl<'tcx, I: IntoIterator> ExactSizeIterator for SubstIterCopied<'_, 'tcx, I>
+where
+    I::IntoIter: ExactSizeIterator,
+    I::Item: Deref,
+    <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
+{
+}
+
 pub struct EarlyBinderIter<T> {
     t: T,
 }
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index 1286a5253c0..37d3e12a667 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -666,20 +666,6 @@ impl<'tcx> TyCtxt<'tcx> {
         ty::EarlyBinder(self.item_bounds(def_id))
     }
 
-    pub fn bound_predicates_of(
-        self,
-        def_id: DefId,
-    ) -> ty::EarlyBinder<ty::generics::GenericPredicates<'tcx>> {
-        ty::EarlyBinder(self.predicates_of(def_id))
-    }
-
-    pub fn bound_explicit_predicates_of(
-        self,
-        def_id: DefId,
-    ) -> ty::EarlyBinder<ty::generics::GenericPredicates<'tcx>> {
-        ty::EarlyBinder(self.explicit_predicates_of(def_id))
-    }
-
     pub fn bound_impl_subject(self, def_id: DefId) -> ty::EarlyBinder<ty::ImplSubject<'tcx>> {
         ty::EarlyBinder(self.impl_subject(def_id))
     }
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
index df57c0f60fa..0419bb3f724 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
@@ -82,9 +82,7 @@ pub fn recompute_applicable_impls<'tcx>(
 
     let predicates =
         tcx.predicates_of(obligation.cause.body_id.owner.to_def_id()).instantiate_identity(tcx);
-    for obligation in
-        elaborate_predicates_with_span(tcx, std::iter::zip(predicates.predicates, predicates.spans))
-    {
+    for obligation in elaborate_predicates_with_span(tcx, predicates.into_iter()) {
         let kind = obligation.predicate.kind();
         if let ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) = kind.skip_binder()
             && param_env_candidate_may_apply(kind.rebind(trait_pred))
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 5211f873a1e..6e2341a823b 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -2070,7 +2070,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
             // Find another predicate whose self-type is equal to the expected self type,
             // but whose substs don't match.
-            let other_pred = std::iter::zip(&predicates.predicates, &predicates.spans)
+            let other_pred = predicates.into_iter()
                 .enumerate()
                 .find(|(other_idx, (pred, _))| match pred.kind().skip_binder() {
                     ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred))
@@ -2095,7 +2095,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             // If we found one, then it's very likely the cause of the error.
             if let Some((_, (_, other_pred_span))) = other_pred {
                 err.span_note(
-                    *other_pred_span,
+                    other_pred_span,
                     "closure inferred to have a different signature due to this bound",
                 );
             }
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 13aa067844a..531aa23d6ea 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -115,14 +115,12 @@ pub fn predicates_for_generics<'tcx>(
     param_env: ty::ParamEnv<'tcx>,
     generic_bounds: ty::InstantiatedPredicates<'tcx>,
 ) -> impl Iterator<Item = PredicateObligation<'tcx>> {
-    std::iter::zip(generic_bounds.predicates, generic_bounds.spans).enumerate().map(
-        move |(idx, (predicate, span))| Obligation {
-            cause: cause(idx, span),
-            recursion_depth: 0,
-            param_env,
-            predicate,
-        },
-    )
+    generic_bounds.into_iter().enumerate().map(move |(idx, (predicate, span))| Obligation {
+        cause: cause(idx, span),
+        recursion_depth: 0,
+        param_env,
+        predicate,
+    })
 }
 
 /// Determines whether the type `ty` is known to meet `bound` and
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 81966f3fcb2..9c655aff0ba 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -2259,25 +2259,23 @@ fn confirm_impl_trait_in_trait_candidate<'tcx>(
         tcx.predicates_of(impl_fn_def_id).instantiate(tcx, impl_fn_substs),
         &mut obligations,
     );
-    obligations.extend(std::iter::zip(predicates.predicates, predicates.spans).map(
-        |(pred, span)| {
-            Obligation::with_depth(
-                tcx,
-                ObligationCause::new(
-                    obligation.cause.span,
-                    obligation.cause.body_id,
-                    if span.is_dummy() {
-                        super::ItemObligation(impl_fn_def_id)
-                    } else {
-                        super::BindingObligation(impl_fn_def_id, span)
-                    },
-                ),
-                obligation.recursion_depth + 1,
-                obligation.param_env,
-                pred,
-            )
-        },
-    ));
+    obligations.extend(predicates.into_iter().map(|(pred, span)| {
+        Obligation::with_depth(
+            tcx,
+            ObligationCause::new(
+                obligation.cause.span,
+                obligation.cause.body_id,
+                if span.is_dummy() {
+                    super::ItemObligation(impl_fn_def_id)
+                } else {
+                    super::BindingObligation(impl_fn_def_id, span)
+                },
+            ),
+            obligation.recursion_depth + 1,
+            obligation.param_env,
+            pred,
+        )
+    }));
 
     let ty = normalize_with_depth_to(
         selcx,
@@ -2303,10 +2301,10 @@ fn assoc_ty_own_obligations<'cx, 'tcx>(
     nested: &mut Vec<PredicateObligation<'tcx>>,
 ) {
     let tcx = selcx.tcx();
-    let own = tcx
+    let predicates = tcx
         .predicates_of(obligation.predicate.def_id)
         .instantiate_own(tcx, obligation.predicate.substs);
-    for (predicate, span) in std::iter::zip(own.predicates, own.spans) {
+    for (predicate, span) in predicates {
         let normalized = normalize_with_depth_to(
             selcx,
             obligation.param_env,
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index a41d10f1043..d4ac461690c 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -185,9 +185,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         })?);
 
         if let ty::Alias(ty::Projection, ..) = placeholder_self_ty.kind() {
-            let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs).predicates;
-            debug!(?predicates, "projection predicates");
-            for predicate in predicates {
+            let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
+            for (predicate, _) in predicates {
                 let normalized = normalize_with_depth_to(
                     self,
                     obligation.param_env,
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index ba4e668f52d..95c269d1b78 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -2558,12 +2558,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // obligation will normalize to `<$0 as Iterator>::Item = $1` and
         // `$1: Copy`, so we must ensure the obligations are emitted in
         // that order.
-        let predicates = tcx.bound_predicates_of(def_id);
-        debug!(?predicates);
-        assert_eq!(predicates.0.parent, None);
-        let mut obligations = Vec::with_capacity(predicates.0.predicates.len());
-        for (predicate, span) in predicates.0.predicates {
-            let span = *span;
+        let predicates = tcx.predicates_of(def_id);
+        assert_eq!(predicates.parent, None);
+        let predicates = predicates.instantiate_own(tcx, substs);
+        let mut obligations = Vec::with_capacity(predicates.len());
+        for (predicate, span) in predicates {
             let cause = cause.clone().derived_cause(parent_trait_pred, |derived| {
                 ImplDerivedObligation(Box::new(ImplDerivedObligationCause {
                     derived,
@@ -2576,7 +2575,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 param_env,
                 cause.clone(),
                 recursion_depth,
-                predicates.rebind(*predicate).subst(tcx, substs),
+                predicate,
                 &mut obligations,
             );
             obligations.push(Obligation { cause, recursion_depth, param_env, predicate });
diff --git a/compiler/rustc_trait_selection/src/traits/vtable.rs b/compiler/rustc_trait_selection/src/traits/vtable.rs
index 5ec9c2a24cd..64daca714c3 100644
--- a/compiler/rustc_trait_selection/src/traits/vtable.rs
+++ b/compiler/rustc_trait_selection/src/traits/vtable.rs
@@ -261,7 +261,10 @@ fn vtable_entries<'tcx>(
                     // Note that this method could then never be called, so we
                     // do not want to try and codegen it, in that case (see #23435).
                     let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
-                    if impossible_predicates(tcx, predicates.predicates) {
+                    if impossible_predicates(
+                        tcx,
+                        predicates.map(|(predicate, _)| predicate).collect(),
+                    ) {
                         debug!("vtable_entries: predicates do not hold");
                         return VtblEntry::Vacant;
                     }
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index fec4047ff49..2cebad64c43 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -736,7 +736,7 @@ impl<'tcx> WfPredicates<'tcx> {
         trace!("{:#?}", predicates);
         debug_assert_eq!(predicates.predicates.len(), origins.len());
 
-        iter::zip(iter::zip(predicates.predicates, predicates.spans), origins.into_iter().rev())
+        iter::zip(predicates, origins.into_iter().rev())
             .map(|((mut pred, span), origin_def_id)| {
                 let code = if span.is_dummy() {
                     traits::ItemObligation(origin_def_id)
diff --git a/compiler/rustc_traits/src/chalk/db.rs b/compiler/rustc_traits/src/chalk/db.rs
index 7c0cae1e7bd..f146de3966b 100644
--- a/compiler/rustc_traits/src/chalk/db.rs
+++ b/compiler/rustc_traits/src/chalk/db.rs
@@ -7,7 +7,7 @@
 //! `crate::chalk::lowering` (to lower rustc types into Chalk types).
 
 use rustc_middle::traits::ChalkRustInterner as RustInterner;
-use rustc_middle::ty::{self, AssocKind, EarlyBinder, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable};
+use rustc_middle::ty::{self, AssocKind, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable};
 use rustc_middle::ty::{InternalSubsts, SubstsRef};
 use rustc_target::abi::{Integer, IntegerType};
 
@@ -38,13 +38,12 @@ impl<'tcx> RustIrDatabase<'tcx> {
         def_id: DefId,
         bound_vars: SubstsRef<'tcx>,
     ) -> Vec<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>> {
-        let predicates = self.interner.tcx.predicates_defined_on(def_id).predicates;
-        predicates
-            .iter()
-            .map(|(wc, _)| EarlyBinder(*wc).subst(self.interner.tcx, bound_vars))
-            .filter_map(|wc| LowerInto::<
-                    Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>>
-                    >::lower_into(wc, self.interner)).collect()
+        self.interner
+            .tcx
+            .predicates_defined_on(def_id)
+            .instantiate_own(self.interner.tcx, bound_vars)
+            .filter_map(|(wc, _)| LowerInto::lower_into(wc, self.interner))
+            .collect()
     }
 
     fn bounds_for<T>(&self, def_id: DefId, bound_vars: SubstsRef<'tcx>) -> Vec<T>
diff --git a/compiler/rustc_traits/src/type_op.rs b/compiler/rustc_traits/src/type_op.rs
index aa5c83ac2e6..f35c5e44882 100644
--- a/compiler/rustc_traits/src/type_op.rs
+++ b/compiler/rustc_traits/src/type_op.rs
@@ -17,7 +17,6 @@ use rustc_trait_selection::traits::query::type_op::subtype::Subtype;
 use rustc_trait_selection::traits::query::{Fallible, NoSolution};
 use rustc_trait_selection::traits::{Normalized, Obligation, ObligationCause, ObligationCtxt};
 use std::fmt;
-use std::iter::zip;
 
 pub(crate) fn provide(p: &mut Providers) {
     *p = Providers {
@@ -108,9 +107,7 @@ fn relate_mir_and_user_substs<'tcx>(
     let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
 
     debug!(?instantiated_predicates);
-    for (instantiated_predicate, predicate_span) in
-        zip(instantiated_predicates.predicates, instantiated_predicates.spans)
-    {
+    for (instantiated_predicate, predicate_span) in instantiated_predicates {
         let span = if span == DUMMY_SP { predicate_span } else { span };
         let cause = ObligationCause::new(
             span,