Address review.

5 files changed, 45 insertions, 55 deletions

diff --git a/compiler/rustc_incremental/src/persist/dirty_clean.rs b/compiler/rustc_incremental/src/persist/dirty_clean.rs
index 145c168f8c4..e7bd488af8e 100644
--- a/compiler/rustc_incremental/src/persist/dirty_clean.rs
+++ b/compiler/rustc_incremental/src/persist/dirty_clean.rs
@@ -391,8 +391,6 @@ impl DirtyCleanVisitor<'tcx> {
     fn assert_clean(&self, item_span: Span, dep_node: DepNode) {
         debug!("assert_clean({:?})", dep_node);
 
-        // if the node wasn't previously evaluated and now is (or vice versa),
-        // then the node isn't actually clean or dirty.
         if self.tcx.dep_graph.is_red(&dep_node) {
             let dep_node_str = self.dep_node_str(&dep_node);
             self.tcx
diff --git a/compiler/rustc_incremental/src/persist/save.rs b/compiler/rustc_incremental/src/persist/save.rs
index d80397970ac..23bd63a37d6 100644
--- a/compiler/rustc_incremental/src/persist/save.rs
+++ b/compiler/rustc_incremental/src/persist/save.rs
@@ -34,10 +34,8 @@ pub fn save_dep_graph(tcx: TyCtxt<'_>) {
         let dep_graph_path = dep_graph_path(sess);
         let staging_dep_graph_path = staging_dep_graph_path(sess);
 
-        join(
-            || sess.time("assert_dep_graph", || crate::assert_dep_graph(tcx)),
-            || sess.time("check_dirty_clean", || dirty_clean::check_dirty_clean_annotations(tcx)),
-        );
+        sess.time("assert_dep_graph", || crate::assert_dep_graph(tcx));
+        sess.time("check_dirty_clean", || dirty_clean::check_dirty_clean_annotations(tcx));
 
         if sess.opts.debugging_opts.incremental_info {
             tcx.dep_graph.print_incremental_info()
diff --git a/compiler/rustc_query_system/src/dep_graph/graph.rs b/compiler/rustc_query_system/src/dep_graph/graph.rs
index 295b2a97e4c..04def909131 100644
--- a/compiler/rustc_query_system/src/dep_graph/graph.rs
+++ b/compiler/rustc_query_system/src/dep_graph/graph.rs
@@ -626,11 +626,10 @@ impl<K: DepKind> DepGraph<K> {
 
         // There may be multiple threads trying to mark the same dep node green concurrently
 
-        let dep_node_index = {
-            // We allocating an entry for the node in the current dependency graph and
-            // adding all the appropriate edges imported from the previous graph
-            data.current.intern_dark_green_node(&data.previous, prev_dep_node_index)
-        };
+        // We allocating an entry for the node in the current dependency graph and
+        // adding all the appropriate edges imported from the previous graph
+        let dep_node_index =
+            data.current.promote_node_and_deps_to_current(&data.previous, prev_dep_node_index);
 
         // ... emitting any stored diagnostic ...
 
@@ -713,7 +712,7 @@ impl<K: DepKind> DepGraph<K> {
         }
     }
 
-    // Returns true if the given node has been marked as green during the
+    // Returns true if the given node has been marked as red during the
     // current compilation session. Used in various assertions
     pub fn is_red(&self, dep_node: &DepNode<K>) -> bool {
         self.node_color(dep_node) == Some(DepNodeColor::Red)
@@ -833,17 +832,11 @@ rustc_index::newtype_index! {
 /// will be populated as we run queries or tasks. We never remove nodes from the
 /// graph: they are only added.
 ///
-/// The nodes in it are identified by a `DepNodeIndex`. Internally, this maps to
-/// a `HybridIndex`, which identifies which collection in the `data` field
-/// contains a node's data. Which collection is used for a node depends on
-/// whether the node was present in the `PreviousDepGraph`, and if so, the color
-/// of the node. Each type of node can share more or less data with the previous
-/// graph. When possible, we can store just the index of the node in the
-/// previous graph, rather than duplicating its data in our own collections.
-/// This is important, because these graph structures are some of the largest in
-/// the compiler.
+/// The nodes in it are identified by a `DepNodeIndex`. We avoid keeping the nodes
+/// in memory.  This is important, because these graph structures are some of the
+/// largest in the compiler.
 ///
-/// For the same reason, we also avoid storing `DepNode`s more than once as map
+/// For this reason, we avoid storing `DepNode`s more than once as map
 /// keys. The `new_node_to_index` map only contains nodes not in the previous
 /// graph, and we map nodes in the previous graph to indices via a two-step
 /// mapping. `PreviousDepGraph` maps from `DepNode` to `SerializedDepNodeIndex`,
@@ -939,6 +932,15 @@ impl<K: DepKind> CurrentDepGraph<K> {
         }
     }
 
+    #[cfg(debug_assertions)]
+    fn record_edge(&self, dep_node_index: DepNodeIndex, key: DepNode<K>) {
+        if let Some(forbidden_edge) = &self.forbidden_edge {
+            forbidden_edge.index_to_node.lock().insert(dep_node_index, key);
+        }
+    }
+
+    /// Writes the node to the current dep-graph and allocates a `DepNodeIndex` for it.
+    /// Assumes that this is a node that has no equivalent in the previous dep-graph.
     fn intern_new_node(
         &self,
         key: DepNode<K>,
@@ -951,9 +953,7 @@ impl<K: DepKind> CurrentDepGraph<K> {
                 let dep_node_index = self.encoder.borrow().send(key, current_fingerprint, edges);
                 entry.insert(dep_node_index);
                 #[cfg(debug_assertions)]
-                if let Some(forbidden_edge) = &self.forbidden_edge {
-                    forbidden_edge.index_to_node.lock().insert(dep_node_index, key);
-                }
+                self.record_edge(dep_node_index, key);
                 dep_node_index
             }
         }
@@ -964,20 +964,20 @@ impl<K: DepKind> CurrentDepGraph<K> {
         prev_graph: &PreviousDepGraph<K>,
         key: DepNode<K>,
         edges: EdgesVec,
-        current_fingerprint: Option<Fingerprint>,
+        fingerprint: Option<Fingerprint>,
         print_status: bool,
     ) -> (DepNodeIndex, Option<(SerializedDepNodeIndex, DepNodeColor)>) {
         let print_status = cfg!(debug_assertions) && print_status;
 
         if let Some(prev_index) = prev_graph.node_to_index_opt(&key) {
             // Determine the color and index of the new `DepNode`.
-            if let Some(current_fingerprint) = current_fingerprint {
-                if current_fingerprint == prev_graph.fingerprint_by_index(prev_index) {
+            if let Some(fingerprint) = fingerprint {
+                if fingerprint == prev_graph.fingerprint_by_index(prev_index) {
                     if print_status {
                         eprintln!("[task::green] {:?}", key);
                     }
 
-                    // This is a light green node: it existed in the previous compilation,
+                    // This is a green node: it existed in the previous compilation,
                     // its query was re-executed, and it has the same result as before.
                     let mut prev_index_to_index = self.prev_index_to_index.lock();
 
@@ -985,16 +985,14 @@ impl<K: DepKind> CurrentDepGraph<K> {
                         Some(dep_node_index) => dep_node_index,
                         None => {
                             let dep_node_index =
-                                self.encoder.borrow().send(key, current_fingerprint, edges);
+                                self.encoder.borrow().send(key, fingerprint, edges);
                             prev_index_to_index[prev_index] = Some(dep_node_index);
                             dep_node_index
                         }
                     };
 
                     #[cfg(debug_assertions)]
-                    if let Some(forbidden_edge) = &self.forbidden_edge {
-                        forbidden_edge.index_to_node.lock().insert(dep_node_index, key);
-                    }
+                    self.record_edge(dep_node_index, key);
                     (dep_node_index, Some((prev_index, DepNodeColor::Green(dep_node_index))))
                 } else {
                     if print_status {
@@ -1009,16 +1007,14 @@ impl<K: DepKind> CurrentDepGraph<K> {
                         Some(dep_node_index) => dep_node_index,
                         None => {
                             let dep_node_index =
-                                self.encoder.borrow().send(key, current_fingerprint, edges);
+                                self.encoder.borrow().send(key, fingerprint, edges);
                             prev_index_to_index[prev_index] = Some(dep_node_index);
                             dep_node_index
                         }
                     };
 
                     #[cfg(debug_assertions)]
-                    if let Some(forbidden_edge) = &self.forbidden_edge {
-                        forbidden_edge.index_to_node.lock().insert(dep_node_index, key);
-                    }
+                    self.record_edge(dep_node_index, key);
                     (dep_node_index, Some((prev_index, DepNodeColor::Red)))
                 }
             } else {
@@ -1043,9 +1039,7 @@ impl<K: DepKind> CurrentDepGraph<K> {
                 };
 
                 #[cfg(debug_assertions)]
-                if let Some(forbidden_edge) = &self.forbidden_edge {
-                    forbidden_edge.index_to_node.lock().insert(dep_node_index, key);
-                }
+                self.record_edge(dep_node_index, key);
                 (dep_node_index, Some((prev_index, DepNodeColor::Red)))
             }
         } else {
@@ -1053,16 +1047,16 @@ impl<K: DepKind> CurrentDepGraph<K> {
                 eprintln!("[task::new] {:?}", key);
             }
 
-            let current_fingerprint = current_fingerprint.unwrap_or(Fingerprint::ZERO);
+            let fingerprint = fingerprint.unwrap_or(Fingerprint::ZERO);
 
             // This is a new node: it didn't exist in the previous compilation session.
-            let dep_node_index = self.intern_new_node(key, edges, current_fingerprint);
+            let dep_node_index = self.intern_new_node(key, edges, fingerprint);
 
             (dep_node_index, None)
         }
     }
 
-    fn intern_dark_green_node(
+    fn promote_node_and_deps_to_current(
         &self,
         prev_graph: &PreviousDepGraph<K>,
         prev_index: SerializedDepNodeIndex,
@@ -1086,9 +1080,7 @@ impl<K: DepKind> CurrentDepGraph<K> {
                 );
                 prev_index_to_index[prev_index] = Some(dep_node_index);
                 #[cfg(debug_assertions)]
-                if let Some(forbidden_edge) = &self.forbidden_edge {
-                    forbidden_edge.index_to_node.lock().insert(dep_node_index, key);
-                }
+                self.record_edge(dep_node_index, key);
                 dep_node_index
             }
         }
diff --git a/compiler/rustc_query_system/src/dep_graph/query.rs b/compiler/rustc_query_system/src/dep_graph/query.rs
index 0fe3748e386..27b3b5e1366 100644
--- a/compiler/rustc_query_system/src/dep_graph/query.rs
+++ b/compiler/rustc_query_system/src/dep_graph/query.rs
@@ -32,7 +32,8 @@ impl<K: DepKind> DepGraphQuery<K> {
 
         for &target in edges.iter() {
             let target = self.dep_index_to_index[target];
-            // Skip missing edges.
+            // We may miss the edges that are pushed while the `DepGraphQuery` is being accessed.
+            // Skip them to issues.
             if let Some(target) = target {
                 self.graph.add_edge(source, target, ());
             }
diff --git a/compiler/rustc_query_system/src/dep_graph/serialized.rs b/compiler/rustc_query_system/src/dep_graph/serialized.rs
index 663113543fc..aeb0e2b0da1 100644
--- a/compiler/rustc_query_system/src/dep_graph/serialized.rs
+++ b/compiler/rustc_query_system/src/dep_graph/serialized.rs
@@ -73,7 +73,7 @@ impl<'a, K: DepKind + Decodable<opaque::Decoder<'a>>> Decodable<opaque::Decoder<
 {
     #[instrument(skip(d))]
     fn decode(d: &mut opaque::Decoder<'a>) -> Result<SerializedDepGraph<K>, String> {
-        let position = d.position();
+        let start_position = d.position();
 
         // The last 16 bytes are the node count and edge count.
         debug!("position: {:?}", d.position());
@@ -85,7 +85,7 @@ impl<'a, K: DepKind + Decodable<opaque::Decoder<'a>>> Decodable<opaque::Decoder<
         debug!(?node_count, ?edge_count);
 
         debug!("position: {:?}", d.position());
-        d.set_position(position);
+        d.set_position(start_position);
         debug!("position: {:?}", d.position());
 
         let mut nodes = IndexVec::with_capacity(node_count);
@@ -137,7 +137,7 @@ struct Stat<K: DepKind> {
     edge_counter: u64,
 }
 
-struct EncodingStatus<K: DepKind> {
+struct EncoderState<K: DepKind> {
     encoder: FileEncoder,
     total_node_count: usize,
     total_edge_count: usize,
@@ -145,7 +145,7 @@ struct EncodingStatus<K: DepKind> {
     stats: Option<FxHashMap<K, Stat<K>>>,
 }
 
-impl<K: DepKind> EncodingStatus<K> {
+impl<K: DepKind> EncoderState<K> {
     fn new(encoder: FileEncoder, record_stats: bool) -> Self {
         Self {
             encoder,
@@ -186,8 +186,9 @@ impl<K: DepKind> EncodingStatus<K> {
 
         debug!(?index, ?node);
         let encoder = &mut self.encoder;
-        self.result =
-            std::mem::replace(&mut self.result, Ok(())).and_then(|()| node.encode(encoder));
+        if self.result.is_ok() {
+            self.result = node.encode(encoder);
+        }
         index
     }
 
@@ -209,7 +210,7 @@ impl<K: DepKind> EncodingStatus<K> {
 }
 
 pub struct GraphEncoder<K: DepKind> {
-    status: Lock<EncodingStatus<K>>,
+    status: Lock<EncoderState<K>>,
     record_graph: Option<Lock<DepGraphQuery<K>>>,
 }
 
@@ -225,7 +226,7 @@ impl<K: DepKind + Encodable<FileEncoder>> GraphEncoder<K> {
         } else {
             None
         };
-        let status = Lock::new(EncodingStatus::new(encoder, record_stats));
+        let status = Lock::new(EncoderState::new(encoder, record_stats));
         GraphEncoder { status, record_graph }
     }