1 files changed, 47 insertions, 0 deletions
diff --git a/compiler/rustc_mir/src/util/storage.rs b/compiler/rustc_mir/src/util/storage.rs
new file mode 100644
index 00000000000..0b7b1c29537
--- /dev/null
+++ b/compiler/rustc_mir/src/util/storage.rs
@@ -0,0 +1,47 @@
+use rustc_index::bit_set::BitSet;
+use rustc_middle::mir::visit::Visitor;
+use rustc_middle::mir::{self, Local, Location};
+
+/// The set of locals in a MIR body that do not have `StorageLive`/`StorageDead` annotations.
+///
+/// These locals have fixed storage for the duration of the body.
+//
+// FIXME: Currently, we need to traverse the entire MIR to compute this. We should instead store it
+// as a field in the `LocalDecl` for each `Local`.
+#[derive(Debug, Clone)]
+pub struct AlwaysLiveLocals(BitSet<Local>);
+
+impl AlwaysLiveLocals {
+    pub fn new(body: &mir::Body<'tcx>) -> Self {
+        let mut ret = AlwaysLiveLocals(BitSet::new_filled(body.local_decls.len()));
+
+        let mut vis = StorageAnnotationVisitor(&mut ret);
+        vis.visit_body(body);
+
+        ret
+    }
+
+    pub fn into_inner(self) -> BitSet<Local> {
+        self.0
+    }
+}
+
+impl std::ops::Deref for AlwaysLiveLocals {
+    type Target = BitSet<Local>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+/// Removes locals that have `Storage*` annotations from `AlwaysLiveLocals`.
+struct StorageAnnotationVisitor<'a>(&'a mut AlwaysLiveLocals);
+
+impl Visitor<'tcx> for StorageAnnotationVisitor<'_> {
+    fn visit_statement(&mut self, statement: &mir::Statement<'tcx>, _location: Location) {
+        use mir::StatementKind::{StorageDead, StorageLive};
+        if let StorageLive(l) | StorageDead(l) = statement.kind {
+            (self.0).0.remove(l);
+        }
+    }
+}