1 //! This pass adds validation calls (AcquireValid, ReleaseValid) where appropriate.
2 //! It has to be run really early, before transformations like inlining, because
3 //! introducing these calls *adds* UB -- so, conceptually, this pass is actually part
4 //! of MIR building, and only after this pass we think of the program has having the
5 //! normal MIR semantics.
8 use rustc_middle::mir::*;
9 use rustc_middle::ty::{self, Ty, TyCtxt};
13 /// Determines whether this place is "stable": Whether, if we evaluate it again
14 /// after the assignment, we can be sure to obtain the same place value.
15 /// (Concurrent accesses by other threads are no problem as these are anyway non-atomic
16 /// copies. Data races are UB.)
17 fn is_stable(place: PlaceRef<'_>) -> bool {
18 // Which place this evaluates to can change with any memory write,
19 // so cannot assume deref to be stable.
23 /// Determine whether this type may contain a reference (or box), and thus needs retagging.
24 /// We will only recurse `depth` times into Tuples/ADTs to bound the cost of this.
25 fn may_contain_reference<'tcx>(ty: Ty<'tcx>, depth: u32, tcx: TyCtxt<'tcx>) -> bool {
27 // Primitive types that are not references
40 ty::Adt(..) if ty.is_box() => true,
41 // Compound types: recurse
42 ty::Array(ty, _) | ty::Slice(ty) => {
43 // This does not branch so we keep the depth the same.
44 may_contain_reference(*ty, depth, tcx)
47 depth == 0 || tys.iter().any(|ty| may_contain_reference(ty, depth - 1, tcx))
49 ty::Adt(adt, subst) => {
51 || adt.variants().iter().any(|v| {
52 v.fields.iter().any(|f| may_contain_reference(f.ty(tcx, subst), depth - 1, tcx))
55 // Conservative fallback
60 impl<'tcx> MirPass<'tcx> for AddRetag {
61 fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
62 sess.opts.unstable_opts.mir_emit_retag
65 fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
66 // We need an `AllCallEdges` pass before we can do any work.
67 super::add_call_guards::AllCallEdges.run_pass(tcx, body);
69 let basic_blocks = body.basic_blocks.as_mut();
70 let local_decls = &body.local_decls;
71 let needs_retag = |place: &Place<'tcx>| {
72 // FIXME: Instead of giving up for unstable places, we should introduce
73 // a temporary and retag on that.
74 is_stable(place.as_ref())
75 && may_contain_reference(place.ty(&*local_decls, tcx).ty, /*depth*/ 3, tcx)
76 && !local_decls[place.local].is_deref_temp()
78 let place_base_raw = |place: &Place<'tcx>| {
79 // If this is a `Deref`, get the type of what we are deref'ing.
80 if place.has_deref() {
81 let ty = &local_decls[place.local].ty;
84 // Not a deref, and thus not raw.
90 // Retag arguments at the beginning of the start block.
92 // Gather all arguments, skip return value.
93 let places = local_decls.iter_enumerated().skip(1).take(body.arg_count).filter_map(
95 let place = Place::from(local);
96 needs_retag(&place).then_some((place, decl.source_info))
100 // Emit their retags.
101 basic_blocks[START_BLOCK].statements.splice(
103 places.map(|(place, source_info)| Statement {
105 kind: StatementKind::Retag(RetagKind::FnEntry, Box::new(place)),
111 // Retag return values of functions. Also escape-to-raw the argument of `drop`.
112 // We collect the return destinations because we cannot mutate while iterating.
113 let returns = basic_blocks
115 .filter_map(|block_data| {
116 match block_data.terminator().kind {
117 TerminatorKind::Call { target: Some(target), destination, .. }
118 if needs_retag(&destination) =>
120 // Remember the return destination for later
121 Some((block_data.terminator().source_info, destination, target))
124 // `Drop` is also a call, but it doesn't return anything so we are good.
125 TerminatorKind::Drop { .. } | TerminatorKind::DropAndReplace { .. } => None,
126 // Not a block ending in a Call -> ignore.
130 .collect::<Vec<_>>();
131 // Now we go over the returns we collected to retag the return values.
132 for (source_info, dest_place, dest_block) in returns {
133 basic_blocks[dest_block].statements.insert(
137 kind: StatementKind::Retag(RetagKind::Default, Box::new(dest_place)),
143 // Add retag after assignment.
144 for block_data in basic_blocks {
145 // We want to insert statements as we iterate. To this end, we
146 // iterate backwards using indices.
147 for i in (0..block_data.statements.len()).rev() {
148 let (retag_kind, place) = match block_data.statements[i].kind {
149 // Retag-as-raw after escaping to a raw pointer, if the referent
150 // is not already a raw pointer.
151 StatementKind::Assign(box (lplace, Rvalue::AddressOf(_, ref rplace)))
152 if !place_base_raw(rplace) =>
154 (RetagKind::Raw, lplace)
156 // Retag after assignments of reference type.
157 StatementKind::Assign(box (ref place, ref rvalue)) if needs_retag(place) => {
158 let kind = match rvalue {
159 Rvalue::Ref(_, borrow_kind, _)
160 if borrow_kind.allows_two_phase_borrow() =>
164 _ => RetagKind::Default,
168 // Do nothing for the rest
171 // Insert a retag after the statement.
172 let source_info = block_data.statements[i].source_info;
173 block_data.statements.insert(
177 kind: StatementKind::Retag(retag_kind, Box::new(place)),