diff --git a/src/librustc/ty/inhabitedness/def_id_forest.rs b/src/librustc/ty/inhabitedness/def_id_forest.rs
index 9c12d736a30..7bc77e1b1a1 100644
--- a/src/librustc/ty/inhabitedness/def_id_forest.rs
+++ b/src/librustc/ty/inhabitedness/def_id_forest.rs
@@ -87,11 +87,7 @@ impl<'a, 'gcx, 'tcx> DefIdForest {
             }
             ret.root_ids.extend(old_ret.drain());
 
-            for id in next_forest.root_ids {
-                if ret.contains(tcx, id) {
-                    next_ret.push(id);
-                }
-            }
+            next_ret.extend(next_forest.root_ids.into_iter().filter(|&id| ret.contains(tcx, id)));
 
             mem::swap(&mut next_ret, &mut ret.root_ids);
             next_ret.drain();
@@ -107,11 +103,7 @@ impl<'a, 'gcx, 'tcx> DefIdForest {
         let mut ret = DefIdForest::empty();
         let mut next_ret = SmallVec::new();
         for next_forest in iter {
-            for id in ret.root_ids.drain() {
-                if !next_forest.contains(tcx, id) {
-                    next_ret.push(id);
-                }
-            }
+            next_ret.extend(ret.root_ids.drain().filter(|&id| !next_forest.contains(tcx, id)));
 
             for id in next_forest.root_ids {
                 if !next_ret.contains(&id) {
diff --git a/src/librustc/ty/query/job.rs b/src/librustc/ty/query/job.rs
index d07891fca12..a1dc4f16ce9 100644
--- a/src/librustc/ty/query/job.rs
+++ b/src/librustc/ty/query/job.rs
@@ -388,7 +388,7 @@ fn remove_cycle<'tcx>(
 
         // Find the queries in the cycle which are
         // connected to queries outside the cycle
-        let entry_points: Vec<Lrc<QueryJob<'tcx>>> = stack.iter().filter_map(|query| {
+        let entry_points = stack.iter().filter_map(|query| {
             // Mark all the other queries in the cycle as already visited
             let mut visited = FxHashSet::from_iter(stack.iter().filter_map(|q| {
                 if q.1.as_ptr() != query.1.as_ptr() {
@@ -403,12 +403,12 @@ fn remove_cycle<'tcx>(
             } else {
                 None
             }
-        }).collect();
+        });
 
         // Deterministically pick an entry point
         // FIXME: Sort this instead
         let mut hcx = tcx.create_stable_hashing_context();
-        let entry_point = entry_points.iter().min_by_key(|q| {
+        let entry_point = entry_points.min_by_key(|q| {
             let mut stable_hasher = StableHasher::<u64>::new();
             q.info.query.hash_stable(&mut hcx, &mut stable_hasher);
             stable_hasher.finish()
diff --git a/src/librustc/ty/query/on_disk_cache.rs b/src/librustc/ty/query/on_disk_cache.rs
index 66e38fb218a..ce580c78033 100644
--- a/src/librustc/ty/query/on_disk_cache.rs
+++ b/src/librustc/ty/query/on_disk_cache.rs
@@ -254,23 +254,19 @@ impl<'sess> OnDiskCache<'sess> {
             })?;
 
             // Encode diagnostics
-            let diagnostics_index = {
-                let mut diagnostics_index = EncodedDiagnosticsIndex::new();
+            let diagnostics_index: EncodedDiagnosticsIndex = self.current_diagnostics.borrow()
+                .iter()
+                .map(|(dep_node_index, diagnostics)|
+            {
+                let pos = AbsoluteBytePos::new(encoder.position());
+                // Let's make sure we get the expected type here:
+                let diagnostics: &EncodedDiagnostics = diagnostics;
+                let dep_node_index = SerializedDepNodeIndex::new(dep_node_index.index());
+                encoder.encode_tagged(dep_node_index, diagnostics)?;
 
-                for (dep_node_index, diagnostics) in self.current_diagnostics
-                                                        .borrow()
-                                                        .iter() {
-                    let pos = AbsoluteBytePos::new(encoder.position());
-                    // Let's make sure we get the expected type here:
-                    let diagnostics: &EncodedDiagnostics = diagnostics;
-                    let dep_node_index =
-                        SerializedDepNodeIndex::new(dep_node_index.index());
-                    encoder.encode_tagged(dep_node_index, diagnostics)?;
-                    diagnostics_index.push((dep_node_index, pos));
-                }
-
-                diagnostics_index
-            };
+                Ok((dep_node_index, pos))
+            })
+            .collect::<Result<_, _>>()?;
 
             let interpret_alloc_index = {
                 let mut interpret_alloc_index = Vec::new();
@@ -282,6 +278,7 @@ impl<'sess> OnDiskCache<'sess> {
                         // otherwise, abort
                         break;
                     }
+                    interpret_alloc_index.reserve(new_n);
                     for idx in n..new_n {
                         let id = encoder.interpret_allocs_inverse[idx];
                         let pos = encoder.position() as u32;
diff --git a/src/librustc/ty/query/plumbing.rs b/src/librustc/ty/query/plumbing.rs
index 15e692fd984..39a59cf090e 100644
--- a/src/librustc/ty/query/plumbing.rs
+++ b/src/librustc/ty/query/plumbing.rs
@@ -709,14 +709,19 @@ macro_rules! define_queries_inner {
 
                 // We use try_lock here since we are only called from the
                 // deadlock handler, and this shouldn't be locked
-                $(for v in self.$name.try_lock().unwrap().active.values() {
-                    match *v {
-                        QueryResult::Started(ref job) => jobs.push(job.clone()),
-                        _ => (),
-                    }
-                })*
+                $(
+                    jobs.extend(
+                        self.$name.try_lock().unwrap().active.values().filter_map(|v|
+                            if let QueryResult::Started(ref job) = *v {
+                                Some(job.clone())
+                            } else {
+                                None
+                            }
+                        )
+                    );
+                )*
 
-                return jobs;
+                jobs
             }
         }