@@ -333,7 +333,7 @@ pub fn simplify_locals<'tcx>(body: &mut Body<'tcx>, tcx: TyCtxt<'tcx>) {
333333 // count. For example, if we removed `_2 = discriminant(_1)`, then we'll subtract one from
334334 // `use_counts[_1]`. That in turn might make `_1` unused, so we loop until we hit a
335335 // fixedpoint where there are no more unused locals.
336- remove_unused_definitions ( & mut used_locals, body) ;
336+ remove_unused_definitions ( & mut used_locals, body, tcx ) ;
337337
338338 // Finally, we'll actually do the work of shrinking `body.local_decls` and remapping the `Local`s.
339339 let map = make_local_map ( & mut body. local_decls , & used_locals) ;
@@ -462,12 +462,22 @@ impl Visitor<'_> for UsedLocals {
462462}
463463
464464/// Removes unused definitions. Updates the used locals to reflect the changes made.
465- fn remove_unused_definitions < ' a , ' tcx > ( used_locals : & ' a mut UsedLocals , body : & mut Body < ' tcx > ) {
465+ fn remove_unused_definitions < ' a , ' tcx > (
466+ used_locals : & ' a mut UsedLocals ,
467+ body : & mut Body < ' tcx > ,
468+ tcx : TyCtxt < ' tcx > ,
469+ ) {
466470 // The use counts are updated as we remove the statements. A local might become unused
467471 // during the retain operation, leading to a temporary inconsistency (storage statements or
468472 // definitions referencing the local might remain). For correctness it is crucial that this
469473 // computation reaches a fixed point.
470474
475+ let def_id = body. source . def_id ( ) ;
476+ let is_static = tcx. is_static ( def_id) ;
477+ let param_env = tcx. param_env ( def_id) ;
478+
479+ let local_decls = body. local_decls . clone ( ) ;
480+
471481 let mut modified = true ;
472482 while modified {
473483 modified = false ;
@@ -479,7 +489,21 @@ fn remove_unused_definitions<'a, 'tcx>(used_locals: &'a mut UsedLocals, body: &m
479489 StatementKind :: StorageLive ( local) | StatementKind :: StorageDead ( local) => {
480490 used_locals. is_used ( * local)
481491 }
482- StatementKind :: Assign ( box ( place, _) ) => used_locals. is_used ( place. local ) ,
492+ StatementKind :: Assign ( box ( place, _) ) => {
493+ let used = used_locals. is_used ( place. local ) ;
494+ let mut is_zst = false ;
495+
496+ // ZST locals can be removed
497+ if used && !is_static {
498+ let ty = local_decls[ place. local ] . ty ;
499+ let param_env_and = param_env. and ( ty) ;
500+ if let Ok ( layout) = tcx. layout_of ( param_env_and) {
501+ is_zst = layout. is_zst ( ) ;
502+ }
503+ }
504+
505+ used && !is_zst
506+ }
483507
484508 StatementKind :: SetDiscriminant { ref place, .. } => {
485509 used_locals. is_used ( place. local )
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