Only nuke storage for mapped locals, don't rebuild it

Author: Amanieu

compiler/rustc_mir_transform/src/move_elimination.rs

@@ -55,7 +55,7 @@ impl<'tcx> crate::MirPass<'tcx> for MoveElimination {
 
         apply_mappings(tcx, body, &remapped_locals);
 
-        if tcx.sess.emit_lifetime_markers() {
+        if false && tcx.sess.emit_lifetime_markers() {
             reconstruct_storage(body, &points, &liveness_matrix);
         }
 
@@ -388,13 +388,22 @@ fn apply_mappings<'tcx>(
     body: &mut Body<'tcx>,
     remapped_locals: &IndexVec<Local, Option<Place<'tcx>>>,
 ) {
-    let mut rewriter = PlaceUpdater { tcx, remapped_locals };
+    let mut mapped_locals = DenseBitSet::new_empty(body.local_decls.len());
+    for (src, dst) in remapped_locals.iter_enumerated() {
+        if let Some(dst_place) = dst {
+            mapped_locals.insert(src);
+            mapped_locals.insert(dst_place.local);
+        }
+    }
+
+    let mut rewriter = PlaceUpdater { tcx, remapped_locals, mapped_locals };
     rewriter.visit_body_preserves_cfg(body);
 }
 
 struct PlaceUpdater<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
     remapped_locals: &'a IndexVec<Local, Option<Place<'tcx>>>,
+    mapped_locals: DenseBitSet<Local>,
 }
 
 impl<'tcx> MutVisitor<'tcx> for PlaceUpdater<'_, 'tcx> {
@@ -422,11 +431,14 @@ impl<'tcx> MutVisitor<'tcx> for PlaceUpdater<'_, 'tcx> {
     }
 
     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
-        // Remove all storage statements: we will be reconstructing them
-        // directly from liveness information.
-        if let StatementKind::StorageDead(_) | StatementKind::StorageLive(_) = statement.kind {
-            statement.make_nop(true);
-            return;
+        match statement.kind {
+            StatementKind::StorageDead(local) | StatementKind::StorageLive(local)
+                if self.mapped_locals.contains(local) =>
+            {
+                statement.make_nop(true);
+                return;
+            }
+            _ => {}
         }
 
         self.super_statement(statement, location);