Stop considering moved-out locals when computing auto traits for generators

Author: nbdd0121

compiler/rustc_mir_transform/src/coroutine.rs

@@ -69,10 +69,11 @@ use rustc_middle::ty::{
 };
 use rustc_middle::{bug, span_bug};
 use rustc_mir_dataflow::impls::{
- MaybeBorrowedLocals, MaybeLiveLocals, MaybeRequiresStorage, MaybeStorageLive,
- always_storage_live_locals,
+ MaybeBorrowedLocals, MaybeInitializedPlaces, MaybeLiveLocals, MaybeRequiresStorage,
+ MaybeStorageLive, always_storage_live_locals,
 };
-use rustc_mir_dataflow::{Analysis, Results, ResultsVisitor};
+use rustc_mir_dataflow::move_paths::MoveData;
+use rustc_mir_dataflow::{self, Analysis, MaybeReachable, Results, ResultsVisitor};
 use rustc_span::def_id::{DefId, LocalDefId};
 use rustc_span::{Span, sym};
 use rustc_target::spec::PanicStrategy;
@@ -633,6 +634,12 @@ struct LivenessInfo {
  /// Which locals are live across any suspension point.
  saved_locals: CoroutineSavedLocals,
 
+ /// Which locals are live *and* initialized across any suspension point.
+ ///
+ /// A local that is live but is not initialized (i.e. it has been moved out of) does
+ /// not need to be accounted for in auto trait checking.
+ init_locals: DenseBitSet<Local>,
+
  /// The set of saved locals live at each suspension point.
  live_locals_at_suspension_points: Vec<DenseBitSet<CoroutineSavedLocal>>,
 
@@ -686,10 +693,18 @@ fn locals_live_across_suspend_points<'tcx>(
  let mut liveness =
  MaybeLiveLocals.iterate_to_fixpoint(tcx, body, Some("coroutine")).into_results_cursor(body);
 
+ let move_data = MoveData::gather_moves(body, tcx, |_| true);
+
+ // Calculate the set of locals which are initialized
+ let mut inits = MaybeInitializedPlaces::new(tcx, body, &move_data)
+ .iterate_to_fixpoint(tcx, body, Some("coroutine"))
+ .into_results_cursor(body);
+
  let mut storage_liveness_map = IndexVec::from_elem(None, &body.basic_blocks);
  let mut live_locals_at_suspension_points = Vec::new();
  let mut source_info_at_suspension_points = Vec::new();
  let mut live_locals_at_any_suspension_point = DenseBitSet::new_empty(body.local_decls.len());
+ let mut init_locals_at_any_suspension_point = DenseBitSet::new_empty(body.local_decls.len());
 
  for (block, data) in body.basic_blocks.iter_enumerated() {
  if let TerminatorKind::Yield { .. } = data.terminator().kind {
@@ -727,12 +742,26 @@ fn locals_live_across_suspend_points<'tcx>(
  // The coroutine argument is ignored.
  live_locals.remove(SELF_ARG);
 
- debug!("loc = {:?}, live_locals = {:?}", loc, live_locals);
+ inits.seek_to_block_end(block);
+ let mut init_locals: DenseBitSet<_> = DenseBitSet::new_empty(body.local_decls.len());
+ if let MaybeReachable::Reachable(bitset) = inits.get() {
+ for move_path_index in bitset.iter() {
+ if let Some(local) = move_data.move_paths[move_path_index].place.as_local() {
+ init_locals.insert(local);
+ }
+ }
+ }
+ init_locals.intersect(&live_locals);
+
+ debug!(
+ "loc = {:?}, live_locals = {:?}, init_locals = {:?}",
+ loc, live_locals, init_locals
+ );
 
  // Add the locals live at this suspension point to the set of locals which live across
  // any suspension points
  live_locals_at_any_suspension_point.union(&live_locals);
-
+ init_locals_at_any_suspension_point.union(&init_locals);
  live_locals_at_suspension_points.push(live_locals);
  source_info_at_suspension_points.push(data.terminator().source_info);
  }
@@ -757,6 +786,7 @@ fn locals_live_across_suspend_points<'tcx>(
 
  LivenessInfo {
  saved_locals,
+ init_locals: init_locals_at_any_suspension_point,
  live_locals_at_suspension_points,
  source_info_at_suspension_points,
  storage_conflicts,
@@ -929,6 +959,7 @@ fn compute_layout<'tcx>(
 ) {
  let LivenessInfo {
  saved_locals,
+ init_locals,
  live_locals_at_suspension_points,
  source_info_at_suspension_points,
  storage_conflicts,
@@ -950,6 +981,9 @@ fn compute_layout<'tcx>(
  // this code runs on pre-cleanup MIR, and `ignore_for_traits = false` is the safer
  // default.
  let ignore_for_traits = match decl.local_info {
+ // If only the storage is required to be live, but local is not initialized,
+ // then we can ignore such type for auto trait purposes.
+ _ if !init_locals.contains(local) => true,
  // Do not include raw pointers created from accessing `static` items, as those could
  // well be re-created by another access to the same static.
  ClearCrossCrate::Set(box LocalInfo::StaticRef { is_thread_local, .. }) => {

tests/ui/async-await/field-assign-nonsend.stderr

@@ -5,14 +5,11 @@ LL | assert_send(agent.handle());
  | ^^^^^^^^^^^^^^ future returned by `handle` is not `Send`
  |
  = help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `Rc<String>`
-note: future is not `Send` as this value is used across an await
- --> $DIR/field-assign-nonsend.rs:20:39
+note: captured value is not `Send` because `&mut` references cannot be sent unless their referent is `Send`
+ --> $DIR/field-assign-nonsend.rs:16:21
  |
-LL | let mut info = self.info_result.clone();
- | -------- has type `InfoResult` which is not `Send`
-...
-LL | let _ = send_element(element).await;
- | ^^^^^ await occurs here, with `mut info` maybe used later
+LL | async fn handle(&mut self) {
+ | ^^^^^^^^^ has type `&mut Agent` which is not `Send`, because `Agent` is not `Send`
 note: required by a bound in `assert_send`
  --> $DIR/field-assign-nonsend.rs:37:19
  |

tests/ui/async-await/temp-borrow-nonsend.rs

@@ -0,0 +1,23 @@
+//@ check-pass
+//@ edition:2021
+
+use core::marker::PhantomData;
+
+struct B(PhantomData<*const ()>);
+
+fn do_sth(_: &B) {}
+
+async fn foo() {}
+
+async fn test() {
+ let b = B(PhantomData);
+ do_sth(&b);
+ drop(b);
+ foo().await;
+}
+
+fn assert_send<T: Send>(_: T) {}
+
+fn main() {
+ assert_send(test());
+}