--- /dev/null
+use rustc_index::bit_set::BitSet;
+use rustc_middle::mir::{self, Local};
+
+/// 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 always_live_locals = AlwaysLiveLocals(BitSet::new_filled(body.local_decls.len()));
+
+ for block in body.basic_blocks() {
+ for statement in &block.statements {
+ use mir::StatementKind::{StorageDead, StorageLive};
+ if let StorageLive(l) | StorageDead(l) = statement.kind {
+ always_live_locals.0.remove(l);
+ }
+ }
+ }
+
+ always_live_locals
+ }
+
+ pub fn into_inner(self) -> BitSet<Local> {
+ self.0
+ }
+}
+
+impl std::ops::Deref for AlwaysLiveLocals {
+ type Target = BitSet<Local>;
+
+ #[inline]
+ fn deref(&self) -> &Self::Target {
+ &self.0
+ }
+}