1 files changed, 12 insertions, 9 deletions
diff --git a/compiler/rustc_middle/src/mir/basic_blocks.rs b/compiler/rustc_middle/src/mir/basic_blocks.rs
index 0ad17e819..3ecd5b9cd 100644
--- a/compiler/rustc_middle/src/mir/basic_blocks.rs
+++ b/compiler/rustc_middle/src/mir/basic_blocks.rs
@@ -5,7 +5,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::graph;
 use rustc_data_structures::graph::dominators::{dominators, Dominators};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-use rustc_data_structures::sync::OnceCell;
+use rustc_data_structures::sync::OnceLock;
 use rustc_index::{IndexSlice, IndexVec};
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use smallvec::SmallVec;
@@ -23,11 +23,11 @@ pub type SwitchSources = FxHashMap<(BasicBlock, BasicBlock), SmallVec<[Option<u1
 
 #[derive(Clone, Default, Debug)]
 struct Cache {
-    predecessors: OnceCell<Predecessors>,
-    switch_sources: OnceCell<SwitchSources>,
-    is_cyclic: OnceCell<bool>,
-    reverse_postorder: OnceCell<Vec<BasicBlock>>,
-    dominators: OnceCell<Dominators<BasicBlock>>,
+    predecessors: OnceLock<Predecessors>,
+    switch_sources: OnceLock<SwitchSources>,
+    is_cyclic: OnceLock<bool>,
+    reverse_postorder: OnceLock<Vec<BasicBlock>>,
+    dominators: OnceLock<Dominators<BasicBlock>>,
 }
 
 impl<'tcx> BasicBlocks<'tcx> {
@@ -63,11 +63,14 @@ impl<'tcx> BasicBlocks<'tcx> {
     }
 
     /// Returns basic blocks in a reverse postorder.
+    ///
+    /// See [`traversal::reverse_postorder`]'s docs to learn what is preorder traversal.
+    ///
+    /// [`traversal::reverse_postorder`]: crate::mir::traversal::reverse_postorder
     #[inline]
     pub fn reverse_postorder(&self) -> &[BasicBlock] {
         self.cache.reverse_postorder.get_or_init(|| {
-            let mut rpo: Vec<_> =
-                Postorder::new(&self.basic_blocks, START_BLOCK).map(|(bb, _)| bb).collect();
+            let mut rpo: Vec<_> = Postorder::new(&self.basic_blocks, START_BLOCK).collect();
             rpo.reverse();
             rpo
         })
@@ -178,7 +181,7 @@ impl<'tcx> graph::WithPredecessors for BasicBlocks<'tcx> {
     }
 }
 
-TrivialTypeTraversalAndLiftImpls! { Cache }
+TrivialTypeTraversalImpls! { Cache }
 
 impl<S: Encoder> Encodable<S> for Cache {
     #[inline]