Auto merge of #135592 - matthiaskrgr:rollup-4t69l7i, r=matthiaskrgr

Rollup of 7 pull requests

Successful merges:

 - #134754 (Implement `use` associated items of traits)
 - #135481 (coverage: Completely overhaul counter assignment, using node-flow graphs)
 - #135504 (Allow coercing safe-to-call target_feature functions to safe fn pointers)
 - #135561 (Update docs for `-Clink-dead-code` to discourage its use)
 - #135574 (ci: mirror ubuntu:22.04 to ghcr.io)
 - #135585 (resolve symlinks of LLVM tool binaries before copying them)
 - #135588 (Add license-metadata.json to rustc-src tarball.)

r? `@ghost`
`@rustbot` modify labels: rollup

3 files changed, 53 insertions, 0 deletions

diff --git a/compiler/rustc_data_structures/src/graph/iterate/mod.rs b/compiler/rustc_data_structures/src/graph/iterate/mod.rs
index ecda7d3fba8..7b4573d7a84 100644
--- a/compiler/rustc_data_structures/src/graph/iterate/mod.rs
+++ b/compiler/rustc_data_structures/src/graph/iterate/mod.rs
@@ -125,6 +125,16 @@ where
     pub fn visited(&self, node: G::Node) -> bool {
         self.visited.contains(node)
     }
+
+    /// Returns a reference to the set of nodes that have been visited, with
+    /// the same caveats as [`Self::visited`].
+    ///
+    /// When incorporating the visited nodes into another bitset, using bulk
+    /// operations like `union` or `intersect` can be more efficient than
+    /// processing each node individually.
+    pub fn visited_set(&self) -> &DenseBitSet<G::Node> {
+        &self.visited
+    }
 }
 
 impl<G> std::fmt::Debug for DepthFirstSearch<G>
diff --git a/compiler/rustc_data_structures/src/graph/mod.rs b/compiler/rustc_data_structures/src/graph/mod.rs
index 103ddd917bf..92035e8bc48 100644
--- a/compiler/rustc_data_structures/src/graph/mod.rs
+++ b/compiler/rustc_data_structures/src/graph/mod.rs
@@ -4,6 +4,7 @@ pub mod dominators;
 pub mod implementation;
 pub mod iterate;
 mod reference;
+pub mod reversed;
 pub mod scc;
 pub mod vec_graph;
 
diff --git a/compiler/rustc_data_structures/src/graph/reversed.rs b/compiler/rustc_data_structures/src/graph/reversed.rs
new file mode 100644
index 00000000000..9b726deaa15
--- /dev/null
+++ b/compiler/rustc_data_structures/src/graph/reversed.rs
@@ -0,0 +1,42 @@
+use crate::graph::{DirectedGraph, Predecessors, Successors};
+
+/// View that reverses the direction of edges in its underlying graph, so that
+/// successors become predecessors and vice-versa.
+///
+/// Because of `impl<G: Graph> Graph for &G`, the underlying graph can be
+/// wrapped by-reference instead of by-value if desired.
+#[derive(Clone, Copy, Debug)]
+pub struct ReversedGraph<G> {
+    pub inner: G,
+}
+
+impl<G> ReversedGraph<G> {
+    pub fn new(inner: G) -> Self {
+        Self { inner }
+    }
+}
+
+impl<G: DirectedGraph> DirectedGraph for ReversedGraph<G> {
+    type Node = G::Node;
+
+    fn num_nodes(&self) -> usize {
+        self.inner.num_nodes()
+    }
+}
+
+// Implementing `StartNode` is not possible in general, because the start node
+// of an underlying graph is instead an _end_ node in the reversed graph.
+// But would be possible to define another wrapper type that adds an explicit
+// start node to its underlying graph, if desired.
+
+impl<G: Predecessors> Successors for ReversedGraph<G> {
+    fn successors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node> {
+        self.inner.predecessors(node)
+    }
+}
+
+impl<G: Successors> Predecessors for ReversedGraph<G> {
+    fn predecessors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node> {
+        self.inner.successors(node)
+    }
+}