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 place.projection.iter().all(|elem| {
20 // Which place this evaluates to can change with any memory write,
21 // so cannot assume this to be stable.
22 ProjectionElem::Deref => false,
23 // Array indices are interesting, but MIR building generates a *fresh*
24 // temporary for every array access, so the index cannot be changed as
26 ProjectionElem::Index { .. } |
27 // The rest is completely boring, they just offset by a constant.
28 ProjectionElem::Field { .. } |
29 ProjectionElem::ConstantIndex { .. } |
30 ProjectionElem::Subslice { .. } |
31 ProjectionElem::Downcast { .. } => true,
36 /// Determine whether this type may be a reference (or box), and thus needs retagging.
37 fn may_be_reference(ty: Ty<'_>) -> bool {
39 // Primitive types that are not references
52 ty::Adt(..) if ty.is_box() => true,
53 // Compound types are not references
54 ty::Array(..) | ty::Slice(..) | ty::Tuple(..) | ty::Adt(..) => false,
55 // Conservative fallback
60 impl<'tcx> MirPass<'tcx> for AddRetag {
61 fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
62 sess.opts.debugging_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 (span, arg_count) = (body.span, body.arg_count);
70 let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
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()) && may_be_reference(place.ty(&*local_decls, tcx).ty)
76 let place_base_raw = |place: &Place<'tcx>| {
77 // If this is a `Deref`, get the type of what we are deref'ing.
79 place.projection.iter().rposition(|p| matches!(p, ProjectionElem::Deref));
80 if let Some(deref_base) = deref_base {
81 let base_proj = &place.projection[..deref_base];
82 let ty = Place::ty_from(place.local, base_proj, &*local_decls, tcx).ty;
85 // Not a deref, and thus not raw.
91 // Retag arguments at the beginning of the start block.
93 // FIXME: Consider using just the span covering the function
94 // argument declaration.
95 let source_info = SourceInfo::outermost(span);
96 // Gather all arguments, skip return value.
97 let places = local_decls
101 .map(|(local, _)| Place::from(local))
102 .filter(needs_retag);
103 // Emit their retags.
104 basic_blocks[START_BLOCK].statements.splice(
106 places.map(|place| Statement {
108 kind: StatementKind::Retag(RetagKind::FnEntry, Box::new(place)),
114 // Retag return values of functions. Also escape-to-raw the argument of `drop`.
115 // We collect the return destinations because we cannot mutate while iterating.
116 let returns = basic_blocks
118 .filter_map(|block_data| {
119 match block_data.terminator().kind {
120 TerminatorKind::Call { destination: Some(ref destination), .. }
121 if needs_retag(&destination.0) =>
123 // Remember the return destination for later
124 Some((block_data.terminator().source_info, destination.0, destination.1))
127 // `Drop` is also a call, but it doesn't return anything so we are good.
128 TerminatorKind::Drop { .. } | TerminatorKind::DropAndReplace { .. } => None,
129 // Not a block ending in a Call -> ignore.
133 .collect::<Vec<_>>();
134 // Now we go over the returns we collected to retag the return values.
135 for (source_info, dest_place, dest_block) in returns {
136 basic_blocks[dest_block].statements.insert(
140 kind: StatementKind::Retag(RetagKind::Default, Box::new(dest_place)),
146 // Add retag after assignment.
147 for block_data in basic_blocks {
148 // We want to insert statements as we iterate. To this end, we
149 // iterate backwards using indices.
150 for i in (0..block_data.statements.len()).rev() {
151 let (retag_kind, place) = match block_data.statements[i].kind {
152 // Retag-as-raw after escaping to a raw pointer, if the referent
153 // is not already a raw pointer.
154 StatementKind::Assign(box (lplace, Rvalue::AddressOf(_, ref rplace)))
155 if !place_base_raw(rplace) =>
157 (RetagKind::Raw, lplace)
159 // Retag after assignments of reference type.
160 StatementKind::Assign(box (ref place, ref rvalue)) if needs_retag(place) => {
161 let kind = match rvalue {
162 Rvalue::Ref(_, borrow_kind, _)
163 if borrow_kind.allows_two_phase_borrow() =>
167 _ => RetagKind::Default,
171 // Do nothing for the rest
174 // Insert a retag after the statement.
175 let source_info = block_data.statements[i].source_info;
176 block_data.statements.insert(
180 kind: StatementKind::Retag(retag_kind, Box::new(place)),