--- /dev/null
+use super::TrackedValue;
+use crate::{
+ expr_use_visitor::{self, ExprUseVisitor},
+ FnCtxt,
+};
+use hir::{def_id::DefId, Body, HirId, HirIdMap};
+use rustc_data_structures::fx::FxHashSet;
+use rustc_hir as hir;
+use rustc_middle::ty::{ParamEnv, TyCtxt};
+use rustc_middle::{
+ hir::place::{PlaceBase, Projection, ProjectionKind},
+ ty::TypeVisitable,
+};
+
+pub(super) fn find_consumed_and_borrowed<'a, 'tcx>(
+ fcx: &'a FnCtxt<'a, 'tcx>,
+ def_id: DefId,
+ body: &'tcx Body<'tcx>,
+) -> ConsumedAndBorrowedPlaces {
+ let mut expr_use_visitor = ExprUseDelegate::new(fcx.tcx, fcx.param_env);
+ expr_use_visitor.consume_body(fcx, def_id, body);
+ expr_use_visitor.places
+}
+
+pub(super) struct ConsumedAndBorrowedPlaces {
+ /// Records the variables/expressions that are dropped by a given expression.
+ ///
+ /// The key is the hir-id of the expression, and the value is a set or hir-ids for variables
+ /// or values that are consumed by that expression.
+ ///
+ /// Note that this set excludes "partial drops" -- for example, a statement like `drop(x.y)` is
+ /// not considered a drop of `x`, although it would be a drop of `x.y`.
+ pub(super) consumed: HirIdMap<FxHashSet<TrackedValue>>,
+
+ /// A set of hir-ids of values or variables that are borrowed at some point within the body.
+ pub(super) borrowed: FxHashSet<TrackedValue>,
+
+ /// A set of hir-ids of values or variables that are borrowed at some point within the body.
+ pub(super) borrowed_temporaries: FxHashSet<HirId>,
+}
+
+/// Works with ExprUseVisitor to find interesting values for the drop range analysis.
+///
+/// Interesting values are those that are either dropped or borrowed. For dropped values, we also
+/// record the parent expression, which is the point where the drop actually takes place.
+struct ExprUseDelegate<'tcx> {
+ tcx: TyCtxt<'tcx>,
+ param_env: ParamEnv<'tcx>,
+ places: ConsumedAndBorrowedPlaces,
+}
+
+impl<'tcx> ExprUseDelegate<'tcx> {
+ fn new(tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Self {
+ Self {
+ tcx,
+ param_env,
+ places: ConsumedAndBorrowedPlaces {
+ consumed: <_>::default(),
+ borrowed: <_>::default(),
+ borrowed_temporaries: <_>::default(),
+ },
+ }
+ }
+
+ fn consume_body(&mut self, fcx: &'_ FnCtxt<'_, 'tcx>, def_id: DefId, body: &'tcx Body<'tcx>) {
+ // Run ExprUseVisitor to find where values are consumed.
+ ExprUseVisitor::new(
+ self,
+ &fcx.infcx,
+ def_id.expect_local(),
+ fcx.param_env,
+ &fcx.typeck_results.borrow(),
+ )
+ .consume_body(body);
+ }
+
+ fn mark_consumed(&mut self, consumer: HirId, target: TrackedValue) {
+ self.places.consumed.entry(consumer).or_insert_with(|| <_>::default());
+
+ debug!(?consumer, ?target, "mark_consumed");
+ self.places.consumed.get_mut(&consumer).map(|places| places.insert(target));
+ }
+
+ fn borrow_place(&mut self, place_with_id: &expr_use_visitor::PlaceWithHirId<'tcx>) {
+ self.places
+ .borrowed
+ .insert(TrackedValue::from_place_with_projections_allowed(place_with_id));
+
+ // Ordinarily a value is consumed by it's parent, but in the special case of a
+ // borrowed RValue, we create a reference that lives as long as the temporary scope
+ // for that expression (typically, the innermost statement, but sometimes the enclosing
+ // block). We record this fact here so that later in generator_interior
+ // we can use the correct scope.
+ //
+ // We special case borrows through a dereference (`&*x`, `&mut *x` where `x` is
+ // some rvalue expression), since these are essentially a copy of a pointer.
+ // In other words, this borrow does not refer to the
+ // temporary (`*x`), but to the referent (whatever `x` is a borrow of).
+ //
+ // We were considering that we might encounter problems down the line if somehow,
+ // some part of the compiler were to look at this result and try to use it to
+ // drive a borrowck-like analysis (this does not currently happen, as of this writing).
+ // But even this should be fine, because the lifetime of the dereferenced reference
+ // found in the rvalue is only significant as an intermediate 'link' to the value we
+ // are producing, and we separately track whether that value is live over a yield.
+ // Example:
+ //
+ // ```notrust
+ // fn identity<T>(x: &mut T) -> &mut T { x }
+ // let a: A = ...;
+ // let y: &'y mut A = &mut *identity(&'a mut a);
+ // ^^^^^^^^^^^^^^^^^^^^^^^^^ the borrow we are talking about
+ // ```
+ //
+ // The expression `*identity(...)` is a deref of an rvalue,
+ // where the `identity(...)` (the rvalue) produces a return type
+ // of `&'rv mut A`, where `'a: 'rv`. We then assign this result to
+ // `'y`, resulting in (transitively) `'a: 'y` (i.e., while `y` is in use,
+ // `a` will be considered borrowed). Other parts of the code will ensure
+ // that if `y` is live over a yield, `&'y mut A` appears in the generator
+ // state. If `'y` is live, then any sound region analysis must conclude
+ // that `'a` is also live. So if this causes a bug, blame some other
+ // part of the code!
+ let is_deref = place_with_id
+ .place
+ .projections
+ .iter()
+ .any(|Projection { kind, .. }| *kind == ProjectionKind::Deref);
+
+ if let (false, PlaceBase::Rvalue) = (is_deref, place_with_id.place.base) {
+ self.places.borrowed_temporaries.insert(place_with_id.hir_id);
+ }
+ }
+}
+
+impl<'tcx> expr_use_visitor::Delegate<'tcx> for ExprUseDelegate<'tcx> {
+ fn consume(
+ &mut self,
+ place_with_id: &expr_use_visitor::PlaceWithHirId<'tcx>,
+ diag_expr_id: HirId,
+ ) {
+ let hir = self.tcx.hir();
+ let parent = match hir.find_parent_node(place_with_id.hir_id) {
+ Some(parent) => parent,
+ None => place_with_id.hir_id,
+ };
+ debug!(
+ "consume {:?}; diag_expr_id={}, using parent {}",
+ place_with_id,
+ hir.node_to_string(diag_expr_id),
+ hir.node_to_string(parent)
+ );
+ place_with_id
+ .try_into()
+ .map_or((), |tracked_value| self.mark_consumed(parent, tracked_value));
+ }
+
+ fn borrow(
+ &mut self,
+ place_with_id: &expr_use_visitor::PlaceWithHirId<'tcx>,
+ diag_expr_id: HirId,
+ bk: rustc_middle::ty::BorrowKind,
+ ) {
+ debug!(
+ "borrow: place_with_id = {place_with_id:#?}, diag_expr_id={diag_expr_id:#?}, \
+ borrow_kind={bk:#?}"
+ );
+
+ self.borrow_place(place_with_id);
+ }
+
+ fn copy(
+ &mut self,
+ place_with_id: &expr_use_visitor::PlaceWithHirId<'tcx>,
+ _diag_expr_id: HirId,
+ ) {
+ debug!("copy: place_with_id = {place_with_id:?}");
+
+ self.places
+ .borrowed
+ .insert(TrackedValue::from_place_with_projections_allowed(place_with_id));
+
+ // For copied we treat this mostly like a borrow except that we don't add the place
+ // to borrowed_temporaries because the copy is consumed.
+ }
+
+ fn mutate(
+ &mut self,
+ assignee_place: &expr_use_visitor::PlaceWithHirId<'tcx>,
+ diag_expr_id: HirId,
+ ) {
+ debug!("mutate {assignee_place:?}; diag_expr_id={diag_expr_id:?}");
+
+ if assignee_place.place.base == PlaceBase::Rvalue
+ && assignee_place.place.projections.is_empty()
+ {
+ // Assigning to an Rvalue is illegal unless done through a dereference. We would have
+ // already gotten a type error, so we will just return here.
+ return;
+ }
+
+ // If the type being assigned needs dropped, then the mutation counts as a borrow
+ // since it is essentially doing `Drop::drop(&mut x); x = new_value;`.
+ let ty = self.tcx.erase_regions(assignee_place.place.base_ty);
+ if ty.needs_infer() {
+ self.tcx.sess.delay_span_bug(
+ self.tcx.hir().span(assignee_place.hir_id),
+ &format!("inference variables in {ty}"),
+ );
+ } else if ty.needs_drop(self.tcx, self.param_env) {
+ self.places
+ .borrowed
+ .insert(TrackedValue::from_place_with_projections_allowed(assignee_place));
+ }
+ }
+
+ fn bind(
+ &mut self,
+ binding_place: &expr_use_visitor::PlaceWithHirId<'tcx>,
+ diag_expr_id: HirId,
+ ) {
+ debug!("bind {binding_place:?}; diag_expr_id={diag_expr_id:?}");
+ }
+
+ fn fake_read(
+ &mut self,
+ place_with_id: &expr_use_visitor::PlaceWithHirId<'tcx>,
+ cause: rustc_middle::mir::FakeReadCause,
+ diag_expr_id: HirId,
+ ) {
+ debug!(
+ "fake_read place_with_id={place_with_id:?}; cause={cause:?}; diag_expr_id={diag_expr_id:?}"
+ );
+
+ // fake reads happen in places like the scrutinee of a match expression.
+ // we treat those as a borrow, much like a copy: the idea is that we are
+ // transiently creating a `&T` ref that we can read from to observe the current
+ // value (this `&T` is immediately dropped afterwards).
+ self.borrow_place(place_with_id);
+ }
+}
projects / rustc.git / blobdiff