Wrap some query results in `Lrc`.

So that the frequent clones in `try_get` are cheaper.

Fixes #54274.

14 files changed, 73 insertions, 69 deletions

diff --git a/src/librustc/infer/outlives/verify.rs b/src/librustc/infer/outlives/verify.rs
index a7a79dd2e65..5fee04341b6 100644
--- a/src/librustc/infer/outlives/verify.rs
+++ b/src/librustc/infer/outlives/verify.rs
@@ -299,8 +299,8 @@ impl<'cx, 'gcx, 'tcx> VerifyBoundCx<'cx, 'gcx, '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
-            .into_iter()
-            .map(|(p, _)| p)
+            .iter()
+            .map(|(p, _)| *p)
             .collect();
         let identity_substs = Substs::identity_for_item(tcx, assoc_item_def_id);
         let identity_proj = tcx.mk_projection(assoc_item_def_id, identity_substs);
diff --git a/src/librustc/traits/object_safety.rs b/src/librustc/traits/object_safety.rs
index 1d76ccdca31..715ce0d7e80 100644
--- a/src/librustc/traits/object_safety.rs
+++ b/src/librustc/traits/object_safety.rs
@@ -182,7 +182,7 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
         };
         predicates
             .predicates
-            .into_iter()
+            .iter()
             .map(|(predicate, _)| predicate.subst_supertrait(self, &trait_ref))
             .any(|predicate| {
                 match predicate {
@@ -302,9 +302,10 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
             return Some(MethodViolationCode::Generic);
         }
 
-        if self.predicates_of(method.def_id).predicates.into_iter()
+        if self.predicates_of(method.def_id).predicates.iter()
                 // A trait object can't claim to live more than the concrete type,
                 // so outlives predicates will always hold.
+                .cloned()
                 .filter(|(p, _)| p.to_opt_type_outlives().is_none())
                 .collect::<Vec<_>>()
                 // Do a shallow visit so that `contains_illegal_self_type_reference`
diff --git a/src/librustc/traits/specialize/mod.rs b/src/librustc/traits/specialize/mod.rs
index d7b5dd049e3..d3dc1655b0d 100644
--- a/src/librustc/traits/specialize/mod.rs
+++ b/src/librustc/traits/specialize/mod.rs
@@ -407,7 +407,7 @@ fn to_pretty_impl_header(tcx: TyCtxt<'_, '_, '_>, impl_def_id: DefId) -> Option<
 
     // The predicates will contain default bounds like `T: Sized`. We need to
     // remove these bounds, and add `T: ?Sized` to any untouched type parameters.
-    let predicates = tcx.predicates_of(impl_def_id).predicates;
+    let predicates = &tcx.predicates_of(impl_def_id).predicates;
     let mut pretty_predicates = Vec::with_capacity(
         predicates.len() + types_without_default_bounds.len());
 
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 83feadd50d7..4472f23b2c4 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -2126,7 +2126,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
     }
 
     #[inline]
-    pub fn predicates(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> GenericPredicates<'gcx> {
+    pub fn predicates(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Lrc<GenericPredicates<'gcx>> {
         tcx.predicates_of(self.did)
     }
 
@@ -2369,8 +2369,8 @@ impl<'a, 'gcx, 'tcx> AdtDef {
                     def_id: sized_trait,
                     substs: tcx.mk_substs_trait(ty, &[])
                 }).to_predicate();
-                let predicates = tcx.predicates_of(self.did).predicates;
-                if predicates.into_iter().any(|(p, _)| p == sized_predicate) {
+                let predicates = &tcx.predicates_of(self.did).predicates;
+                if predicates.iter().any(|(p, _)| *p == sized_predicate) {
                     vec![]
                 } else {
                     vec![ty]
diff --git a/src/librustc/ty/query/mod.rs b/src/librustc/ty/query/mod.rs
index c834166e67d..0052628e12a 100644
--- a/src/librustc/ty/query/mod.rs
+++ b/src/librustc/ty/query/mod.rs
@@ -127,17 +127,18 @@ define_queries! { <'tcx>
         /// predicate gets in the way of some checks, which are intended
         /// to operate over only the actual where-clauses written by the
         /// user.)
-        [] fn predicates_of: PredicatesOfItem(DefId) -> ty::GenericPredicates<'tcx>,
+        [] fn predicates_of: PredicatesOfItem(DefId) -> Lrc<ty::GenericPredicates<'tcx>>,
 
         /// Maps from the def-id of an item (trait/struct/enum/fn) to the
         /// predicates (where clauses) directly defined on it. This is
         /// equal to the `explicit_predicates_of` predicates plus the
         /// `inferred_outlives_of` predicates.
-        [] fn predicates_defined_on: PredicatesDefinedOnItem(DefId) -> ty::GenericPredicates<'tcx>,
+        [] fn predicates_defined_on: PredicatesDefinedOnItem(DefId)
+            -> Lrc<ty::GenericPredicates<'tcx>>,
 
         /// Returns the predicates written explicit by the user.
         [] fn explicit_predicates_of: ExplicitPredicatesOfItem(DefId)
-            -> ty::GenericPredicates<'tcx>,
+            -> Lrc<ty::GenericPredicates<'tcx>>,
 
         /// Returns the inferred outlives predicates (e.g., for `struct
         /// Foo<'a, T> { x: &'a T }`, this would return `T: 'a`).
@@ -149,12 +150,12 @@ define_queries! { <'tcx>
         /// evaluate them even during type conversion, often before the
         /// full predicates are available (note that supertraits have
         /// additional acyclicity requirements).
-        [] fn super_predicates_of: SuperPredicatesOfItem(DefId) -> ty::GenericPredicates<'tcx>,
+        [] fn super_predicates_of: SuperPredicatesOfItem(DefId) -> Lrc<ty::GenericPredicates<'tcx>>,
 
         /// To avoid cycles within the predicates of a single item we compute
         /// per-type-parameter predicates for resolving `T::AssocTy`.
         [] fn type_param_predicates: type_param_predicates((DefId, DefId))
-            -> ty::GenericPredicates<'tcx>,
+            -> Lrc<ty::GenericPredicates<'tcx>>,
 
         [] fn trait_def: TraitDefOfItem(DefId) -> &'tcx ty::TraitDef,
         [] fn adt_def: AdtDefOfItem(DefId) -> &'tcx ty::AdtDef,
diff --git a/src/librustc_metadata/cstore_impl.rs b/src/librustc_metadata/cstore_impl.rs
index e6e1367b592..e1d9ca5339e 100644
--- a/src/librustc_metadata/cstore_impl.rs
+++ b/src/librustc_metadata/cstore_impl.rs
@@ -103,9 +103,9 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     generics_of => {
         tcx.alloc_generics(cdata.get_generics(def_id.index, tcx.sess))
     }
-    predicates_of => { cdata.get_predicates(def_id.index, tcx) }
-    predicates_defined_on => { cdata.get_predicates_defined_on(def_id.index, tcx) }
-    super_predicates_of => { cdata.get_super_predicates(def_id.index, tcx) }
+    predicates_of => { Lrc::new(cdata.get_predicates(def_id.index, tcx)) }
+    predicates_defined_on => { Lrc::new(cdata.get_predicates_defined_on(def_id.index, tcx)) }
+    super_predicates_of => { Lrc::new(cdata.get_super_predicates(def_id.index, tcx)) }
     trait_def => {
         tcx.alloc_trait_def(cdata.get_trait_def(def_id.index, tcx.sess))
     }
diff --git a/src/librustc_traits/lowering/mod.rs b/src/librustc_traits/lowering/mod.rs
index 471c0e7abbc..dc47b15a68f 100644
--- a/src/librustc_traits/lowering/mod.rs
+++ b/src/librustc_traits/lowering/mod.rs
@@ -217,8 +217,9 @@ fn program_clauses_for_trait<'a, 'tcx>(
 
     let implemented_from_env = Clause::ForAll(ty::Binder::bind(implemented_from_env));
 
-    let where_clauses = &tcx.predicates_defined_on(def_id).predicates
-        .into_iter()
+    let predicates = &tcx.predicates_defined_on(def_id).predicates;
+    let where_clauses = &predicates
+        .iter()
         .map(|(wc, _)| wc.lower())
         .map(|wc| wc.subst(tcx, bound_vars))
         .collect::<Vec<_>>();
@@ -314,8 +315,9 @@ fn program_clauses_for_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId
     let trait_pred = ty::TraitPredicate { trait_ref }.lower();
 
     // `WC`
-    let where_clauses = tcx.predicates_of(def_id).predicates
-        .into_iter()
+    let predicates = &tcx.predicates_of(def_id).predicates;
+    let where_clauses = predicates
+        .iter()
         .map(|(wc, _)| wc.lower())
         .map(|wc| wc.subst(tcx, bound_vars));
 
@@ -352,7 +354,7 @@ pub fn program_clauses_for_type_def<'a, 'tcx>(
 
     // `WC`
     let where_clauses = tcx.predicates_of(def_id).predicates
-        .into_iter()
+        .iter()
         .map(|(wc, _)| wc.lower())
         .map(|wc| wc.subst(tcx, bound_vars))
         .collect::<Vec<_>>();
diff --git a/src/librustc_typeck/astconv.rs b/src/librustc_typeck/astconv.rs
index 572e79407a1..d388d756438 100644
--- a/src/librustc_typeck/astconv.rs
+++ b/src/librustc_typeck/astconv.rs
@@ -24,6 +24,7 @@ use rustc::traits;
 use rustc::ty::{self, Ty, TyCtxt, ToPredicate, TypeFoldable};
 use rustc::ty::{GenericParamDef, GenericParamDefKind};
 use rustc::ty::wf::object_region_bounds;
+use rustc_data_structures::sync::Lrc;
 use rustc_target::spec::abi;
 use std::collections::BTreeSet;
 use std::slice;
@@ -45,7 +46,7 @@ pub trait AstConv<'gcx, 'tcx> {
     /// Returns the set of bounds in scope for the type parameter with
     /// the given id.
     fn get_type_parameter_bounds(&self, span: Span, def_id: DefId)
-                                 -> ty::GenericPredicates<'tcx>;
+                                 -> Lrc<ty::GenericPredicates<'tcx>>;
 
     /// What lifetime should we use when a lifetime is omitted (and not elided)?
     fn re_infer(&self, span: Span, _def: Option<&ty::GenericParamDef>)
@@ -1119,8 +1120,8 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx>+'o {
     {
         let tcx = self.tcx();
 
-        let bounds = self.get_type_parameter_bounds(span, ty_param_def_id)
-            .predicates.into_iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref());
+        let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
+        let bounds = predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref());
 
         // Check that there is exactly one way to find an associated type with the
         // correct name.
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 41e0c6c0a19..c936e0833c0 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -1869,7 +1869,7 @@ impl<'a, 'gcx, 'tcx> AstConv<'gcx, 'tcx> for FnCtxt<'a, 'gcx, 'tcx> {
     fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
 
     fn get_type_parameter_bounds(&self, _: Span, def_id: DefId)
-                                 -> ty::GenericPredicates<'tcx>
+                                 -> Lrc<ty::GenericPredicates<'tcx>>
     {
         let tcx = self.tcx;
         let node_id = tcx.hir.as_local_node_id(def_id).unwrap();
@@ -1877,7 +1877,7 @@ impl<'a, 'gcx, 'tcx> AstConv<'gcx, 'tcx> for FnCtxt<'a, 'gcx, 'tcx> {
         let item_def_id = tcx.hir.local_def_id(item_id);
         let generics = tcx.generics_of(item_def_id);
         let index = generics.param_def_id_to_index[&def_id];
-        ty::GenericPredicates {
+        Lrc::new(ty::GenericPredicates {
             parent: None,
             predicates: self.param_env.caller_bounds.iter().filter_map(|&predicate| {
                 match predicate {
@@ -1890,7 +1890,7 @@ impl<'a, 'gcx, 'tcx> AstConv<'gcx, 'tcx> for FnCtxt<'a, 'gcx, 'tcx> {
                     _ => None
                 }
             }).collect()
-        }
+        })
     }
 
     fn re_infer(&self, span: Span, def: Option<&ty::GenericParamDef>)
diff --git a/src/librustc_typeck/check/wfcheck.rs b/src/librustc_typeck/check/wfcheck.rs
index 8574443190d..b5addbd18d2 100644
--- a/src/librustc_typeck/check/wfcheck.rs
+++ b/src/librustc_typeck/check/wfcheck.rs
@@ -910,8 +910,8 @@ fn check_false_global_bounds<'a, 'gcx, 'tcx>(
 
     let def_id = fcx.tcx.hir.local_def_id(id);
     let predicates = fcx.tcx.predicates_of(def_id).predicates
-        .into_iter()
-        .map(|(p, _)| p)
+        .iter()
+        .map(|(p, _)| *p)
         .collect();
     // Check elaborated bounds
     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
diff --git a/src/librustc_typeck/collect.rs b/src/librustc_typeck/collect.rs
index d2dc226aca2..6ef09d96fd1 100644
--- a/src/librustc_typeck/collect.rs
+++ b/src/librustc_typeck/collect.rs
@@ -39,6 +39,7 @@ use rustc::ty::{self, AdtKind, ToPolyTraitRef, Ty, TyCtxt};
 use rustc::ty::{ReprOptions, ToPredicate};
 use rustc::util::captures::Captures;
 use rustc::util::nodemap::FxHashMap;
+use rustc_data_structures::sync::Lrc;
 use rustc_target::spec::abi;
 
 use syntax::ast;
@@ -178,7 +179,8 @@ impl<'a, 'tcx> AstConv<'tcx, 'tcx> for ItemCtxt<'a, 'tcx> {
         self.tcx
     }
 
-    fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx> {
+    fn get_type_parameter_bounds(&self, span: Span, def_id: DefId)
+                                 -> Lrc<ty::GenericPredicates<'tcx>> {
         self.tcx
             .at(span)
             .type_param_predicates((self.item_def_id, def_id))
@@ -243,7 +245,7 @@ impl<'a, 'tcx> AstConv<'tcx, 'tcx> for ItemCtxt<'a, 'tcx> {
 fn type_param_predicates<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     (item_def_id, def_id): (DefId, DefId),
-) -> ty::GenericPredicates<'tcx> {
+) -> Lrc<ty::GenericPredicates<'tcx>> {
     use rustc::hir::*;
 
     // In the AST, bounds can derive from two places. Either
@@ -264,11 +266,11 @@ fn type_param_predicates<'a, 'tcx>(
         tcx.generics_of(item_def_id).parent
     };
 
-    let mut result = parent.map_or(
-        ty::GenericPredicates {
+    let mut result = parent.map_or_else(
+        || Lrc::new(ty::GenericPredicates {
             parent: None,
             predicates: vec![],
-        },
+        }),
         |parent| {
             let icx = ItemCtxt::new(tcx, parent);
             icx.get_type_parameter_bounds(DUMMY_SP, def_id)
@@ -298,7 +300,7 @@ fn type_param_predicates<'a, 'tcx>(
                     // Implied `Self: Trait` and supertrait bounds.
                     if param_id == item_node_id {
                         let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id);
-                        result
+                        Lrc::make_mut(&mut result)
                             .predicates
                             .push((identity_trait_ref.to_predicate(), item.span));
                     }
@@ -317,7 +319,7 @@ fn type_param_predicates<'a, 'tcx>(
     };
 
     let icx = ItemCtxt::new(tcx, item_def_id);
-    result
+    Lrc::make_mut(&mut result)
         .predicates
         .extend(icx.type_parameter_bounds_in_generics(ast_generics, param_id, ty,
             OnlySelfBounds(true)));
@@ -685,7 +687,7 @@ fn adt_def<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx ty::Ad
 fn super_predicates_of<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     trait_def_id: DefId,
-) -> ty::GenericPredicates<'tcx> {
+) -> Lrc<ty::GenericPredicates<'tcx>> {
     debug!("super_predicates(trait_def_id={:?})", trait_def_id);
     let trait_node_id = tcx.hir.as_local_node_id(trait_def_id).unwrap();
 
@@ -729,10 +731,10 @@ fn super_predicates_of<'a, 'tcx>(
         }
     }
 
-    ty::GenericPredicates {
+    Lrc::new(ty::GenericPredicates {
         parent: None,
         predicates: superbounds,
-    }
+    })
 }
 
 fn trait_def<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx ty::TraitDef {
@@ -1605,27 +1607,23 @@ fn early_bound_lifetimes_from_generics<'a, 'tcx>(
 fn predicates_defined_on<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     def_id: DefId,
-) -> ty::GenericPredicates<'tcx> {
-    let explicit = tcx.explicit_predicates_of(def_id);
-    let span = tcx.def_span(def_id);
-    let predicates = explicit.predicates.into_iter().chain(
-        tcx.inferred_outlives_of(def_id).iter().map(|&p| (p, span))
-    ).collect();
-
-    ty::GenericPredicates {
-        parent: explicit.parent,
-        predicates: predicates,
+) -> Lrc<ty::GenericPredicates<'tcx>> {
+    let mut result = tcx.explicit_predicates_of(def_id);
+    let inferred_outlives = tcx.inferred_outlives_of(def_id);
+    if !inferred_outlives.is_empty() {
+        let span = tcx.def_span(def_id);
+        Lrc::make_mut(&mut result)
+            .predicates
+            .extend(inferred_outlives.iter().map(|&p| (p, span)));
     }
+    result
 }
 
 fn predicates_of<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     def_id: DefId,
-) -> ty::GenericPredicates<'tcx> {
-    let ty::GenericPredicates {
-        parent,
-        mut predicates,
-    } = tcx.predicates_defined_on(def_id);
+) -> Lrc<ty::GenericPredicates<'tcx>> {
+    let mut result = tcx.predicates_defined_on(def_id);
 
     if tcx.is_trait(def_id) {
         // For traits, add `Self: Trait` predicate. This is
@@ -1641,16 +1639,17 @@ fn predicates_of<'a, 'tcx>(
         // used, and adding the predicate into this list ensures
         // that this is done.
         let span = tcx.def_span(def_id);
-        predicates.push((ty::TraitRef::identity(tcx, def_id).to_predicate(), span));
+        Lrc::make_mut(&mut result)
+            .predicates
+            .push((ty::TraitRef::identity(tcx, def_id).to_predicate(), span));
     }
-
-    ty::GenericPredicates { parent, predicates }
+    result
 }
 
 fn explicit_predicates_of<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     def_id: DefId,
-) -> ty::GenericPredicates<'tcx> {
+) -> Lrc<ty::GenericPredicates<'tcx>> {
     use rustc::hir::*;
     use rustc_data_structures::fx::FxHashSet;
 
@@ -1761,10 +1760,10 @@ fn explicit_predicates_of<'a, 'tcx>(
 
                     if impl_trait_fn.is_some() {
                         // impl Trait
-                        return ty::GenericPredicates {
+                        return Lrc::new(ty::GenericPredicates {
                             parent: None,
                             predicates: bounds.predicates(tcx, opaque_ty),
-                        };
+                        });
                     } else {
                         // named existential types
                         predicates.extend(bounds.predicates(tcx, opaque_ty));
@@ -1794,7 +1793,7 @@ fn explicit_predicates_of<'a, 'tcx>(
     // on a trait we need to add in the supertrait bounds and bounds found on
     // associated types.
     if let Some((_trait_ref, _)) = is_trait {
-        predicates.extend(tcx.super_predicates_of(def_id).predicates);
+        predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
     }
 
     // In default impls, we can assume that the self type implements
@@ -1971,10 +1970,10 @@ fn explicit_predicates_of<'a, 'tcx>(
         );
     }
 
-    ty::GenericPredicates {
+    Lrc::new(ty::GenericPredicates {
         parent: generics.parent,
         predicates,
-    }
+    })
 }
 
 pub enum SizedByDefault {
diff --git a/src/librustc_typeck/outlives/explicit.rs b/src/librustc_typeck/outlives/explicit.rs
index 75f8b78b9ec..9b374cf932f 100644
--- a/src/librustc_typeck/outlives/explicit.rs
+++ b/src/librustc_typeck/outlives/explicit.rs
@@ -33,14 +33,14 @@ impl<'tcx> ExplicitPredicatesMap<'tcx> {
     ) -> &RequiredPredicates<'tcx> {
         self.map.entry(def_id).or_insert_with(|| {
             let predicates = if def_id.is_local() {
-                tcx.explicit_predicates_of(def_id).predicates
+                tcx.explicit_predicates_of(def_id)
             } else {
-                tcx.predicates_of(def_id).predicates
+                tcx.predicates_of(def_id)
             };
             let mut required_predicates = RequiredPredicates::default();
 
             // process predicates and convert to `RequiredPredicates` entry, see below
-            for (pred, _) in predicates.into_iter() {
+            for (pred, _) in predicates.predicates.iter() {
                 match pred {
                     ty::Predicate::TypeOutlives(predicate) => {
                         let OutlivesPredicate(ref ty, ref reg) = predicate.skip_binder();
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 77782c19b72..924c86ba56f 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -1563,7 +1563,7 @@ impl Clean<Generics> for hir::Generics {
 }
 
 impl<'a, 'tcx> Clean<Generics> for (&'a ty::Generics,
-                                    &'a ty::GenericPredicates<'tcx>) {
+                                    &'a Lrc<ty::GenericPredicates<'tcx>>) {
     fn clean(&self, cx: &DocContext) -> Generics {
         use self::WherePredicate as WP;
 
diff --git a/src/librustdoc/clean/simplify.rs b/src/librustdoc/clean/simplify.rs
index eda522af922..635608d140d 100644
--- a/src/librustdoc/clean/simplify.rs
+++ b/src/librustdoc/clean/simplify.rs
@@ -156,8 +156,8 @@ fn trait_is_same_or_supertrait(cx: &DocContext, child: DefId,
     if child == trait_ {
         return true
     }
-    let predicates = cx.tcx.super_predicates_of(child).predicates;
-    predicates.iter().filter_map(|(pred, _)| {
+    let predicates = cx.tcx.super_predicates_of(child);
+    predicates.predicates.iter().filter_map(|(pred, _)| {
         if let ty::Predicate::Trait(ref pred) = *pred {
             if pred.skip_binder().trait_ref.self_ty().is_self() {
                 Some(pred.def_id())