Create a forever red node and use it to force side effects.

1 files changed, 20 insertions, 2 deletions

diff --git a/compiler/rustc_query_system/src/dep_graph/graph.rs b/compiler/rustc_query_system/src/dep_graph/graph.rs
index 0e1419f8a48..d218e3b7753 100644
--- a/compiler/rustc_query_system/src/dep_graph/graph.rs
+++ b/compiler/rustc_query_system/src/dep_graph/graph.rs
@@ -43,6 +43,7 @@ rustc_index::newtype_index! {
 impl DepNodeIndex {
     pub const INVALID: DepNodeIndex = DepNodeIndex::MAX;
     pub const SINGLETON_DEPENDENCYLESS_ANON_NODE: DepNodeIndex = DepNodeIndex::from_u32(0);
+    pub const FOREVER_RED_NODE: DepNodeIndex = DepNodeIndex::from_u32(1);
 }
 
 impl std::convert::From<DepNodeIndex> for QueryInvocationId {
@@ -124,6 +125,8 @@ impl<K: DepKind> DepGraph<K> {
             record_stats,
         );
 
+        let colors = DepNodeColorMap::new(prev_graph_node_count);
+
         // Instantiate a dependy-less node only once for anonymous queries.
         let _green_node_index = current.intern_new_node(
             profiler,
@@ -133,6 +136,18 @@ impl<K: DepKind> DepGraph<K> {
         );
         debug_assert_eq!(_green_node_index, DepNodeIndex::SINGLETON_DEPENDENCYLESS_ANON_NODE);
 
+        // Instantiate a dependy-less red node only once for anonymous queries.
+        let (_red_node_index, _prev_and_index) = current.intern_node(
+            profiler,
+            &prev_graph,
+            DepNode { kind: DepKind::NULL, hash: Fingerprint::ZERO.into() },
+            smallvec![],
+            None,
+            false,
+        );
+        debug_assert_eq!(_red_node_index, DepNodeIndex::FOREVER_RED_NODE);
+        debug_assert!(matches!(_prev_and_index, None | Some((_, DepNodeColor::Red))));
+
         DepGraph {
             data: Some(Lrc::new(DepGraphData {
                 previous_work_products: prev_work_products,
@@ -140,7 +155,7 @@ impl<K: DepKind> DepGraph<K> {
                 current,
                 processed_side_effects: Default::default(),
                 previous: prev_graph,
-                colors: DepNodeColorMap::new(prev_graph_node_count),
+                colors,
                 debug_loaded_from_disk: Default::default(),
             })),
             virtual_dep_node_index: Lrc::new(AtomicU32::new(0)),
@@ -965,6 +980,9 @@ impl<K: DepKind> CurrentDepGraph<K> {
         let nanos = duration.as_secs() * 1_000_000_000 + duration.subsec_nanos() as u64;
         let mut stable_hasher = StableHasher::new();
         nanos.hash(&mut stable_hasher);
+        let anon_id_seed = stable_hasher.finish();
+        // We rely on the fact that `anon_id_seed` is not zero when creating static nodes.
+        debug_assert_ne!(anon_id_seed, Fingerprint::ZERO);
 
         #[cfg(debug_assertions)]
         let forbidden_edge = match env::var("RUST_FORBID_DEP_GRAPH_EDGE") {
@@ -1000,7 +1018,7 @@ impl<K: DepKind> CurrentDepGraph<K> {
                 )
             }),
             prev_index_to_index: Lock::new(IndexVec::from_elem_n(None, prev_graph_node_count)),
-            anon_id_seed: stable_hasher.finish(),
+            anon_id_seed,
             #[cfg(debug_assertions)]
             forbidden_edge,
             total_read_count: AtomicU64::new(0),