From e7e3001557cc9a2e13bce599e374b474392eb779 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Mon, 20 Apr 2020 10:42:12 -0700
Subject: [PATCH] Remove some allocations in predicate evaluation

---
 src/librustc_infer/traits/util.rs                 |  7 +++----
 src/librustc_trait_selection/traits/auto_trait.rs | 12 +++++++-----
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/src/librustc_infer/traits/util.rs b/src/librustc_infer/traits/util.rs
index 8aacea735f476..55bea57f3e243 100644
--- a/src/librustc_infer/traits/util.rs
+++ b/src/librustc_infer/traits/util.rs
@@ -149,21 +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);
             }
diff --git a/src/librustc_trait_selection/traits/auto_trait.rs b/src/librustc_trait_selection/traits/auto_trait.rs
index b28658e0f1e58..6326a87c5edc3 100644
--- a/src/librustc_trait_selection/traits/auto_trait.rs
+++ b/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();
 
@@ -358,9 +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()).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);
         }
@@ -738,7 +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,