1 files changed, 53 insertions, 0 deletions
diff --git a/compiler/rustc_query_system/src/cache.rs b/compiler/rustc_query_system/src/cache.rs
new file mode 100644
index 000000000..d592812f7
--- /dev/null
+++ b/compiler/rustc_query_system/src/cache.rs
@@ -0,0 +1,53 @@
+//! Cache for candidate selection.
+
+use crate::dep_graph::{DepContext, DepNodeIndex};
+
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::sync::Lock;
+
+use std::hash::Hash;
+
+#[derive(Clone)]
+pub struct Cache<Key, Value> {
+    hashmap: Lock<FxHashMap<Key, WithDepNode<Value>>>,
+}
+
+impl<Key, Value> Default for Cache<Key, Value> {
+    fn default() -> Self {
+        Self { hashmap: Default::default() }
+    }
+}
+
+impl<Key, Value> Cache<Key, Value> {
+    /// Actually frees the underlying memory in contrast to what stdlib containers do on `clear`
+    pub fn clear(&self) {
+        *self.hashmap.borrow_mut() = Default::default();
+    }
+}
+
+impl<Key: Eq + Hash, Value: Clone> Cache<Key, Value> {
+    pub fn get<CTX: DepContext>(&self, key: &Key, tcx: CTX) -> Option<Value> {
+        Some(self.hashmap.borrow().get(key)?.get(tcx))
+    }
+
+    pub fn insert(&self, key: Key, dep_node: DepNodeIndex, value: Value) {
+        self.hashmap.borrow_mut().insert(key, WithDepNode::new(dep_node, value));
+    }
+}
+
+#[derive(Clone, Eq, PartialEq)]
+pub struct WithDepNode<T> {
+    dep_node: DepNodeIndex,
+    cached_value: T,
+}
+
+impl<T: Clone> WithDepNode<T> {
+    pub fn new(dep_node: DepNodeIndex, cached_value: T) -> Self {
+        WithDepNode { dep_node, cached_value }
+    }
+
+    pub fn get<CTX: DepContext>(&self, tcx: CTX) -> T {
+        tcx.dep_graph().read_index(self.dep_node);
+        self.cached_value.clone()
+    }
+}