Preserve DebugInfo in DeadStoreElimination.

compiler/rustc_mir_dataflow/src/debuginfo.rs

@@ -0,0 +1,20 @@
+use rustc_index::bit_set::BitSet;
+use rustc_middle::mir::visit::*;
+use rustc_middle::mir::*;
+
+/// Return the set of locals that appear in debuginfo.
+pub fn debuginfo_locals(body: &Body<'_>) -> BitSet<Local> {
+    let mut visitor = DebuginfoLocals(BitSet::new_empty(body.local_decls.len()));
+    for debuginfo in body.var_debug_info.iter() {
+        visitor.visit_var_debug_info(debuginfo);
+    }
+    visitor.0
+}
+
+struct DebuginfoLocals(BitSet<Local>);
+
+impl Visitor<'_> for DebuginfoLocals {
+    fn visit_local(&mut self, local: Local, _: PlaceContext, _: Location) {
+        self.0.insert(local);
+    }
+}

compiler/rustc_mir_dataflow/src/lib.rs

@@ -35,6 +35,7 @@ pub use self::framework::{
 
 use self::move_paths::MoveData;
 
+pub mod debuginfo;
 pub mod drop_flag_effects;
 pub mod elaborate_drops;
 mod errors;