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 /// Determines whether or not this LocalDecl is temp, if not it needs retagging.
61 fn is_not_temp<'tcx>(local_decl: &LocalDecl<'tcx>) -> bool {
62 if let Some(local_info) = &local_decl.local_info {
63 match local_info.as_ref() {
64 LocalInfo::DerefTemp => return false,
71 impl<'tcx> MirPass<'tcx> for AddRetag {
72 fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
73 sess.opts.debugging_opts.mir_emit_retag
76 fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
77 // We need an `AllCallEdges` pass before we can do any work.
78 super::add_call_guards::AllCallEdges.run_pass(tcx, body);
80 let (span, arg_count) = (body.span, body.arg_count);
81 let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
82 let needs_retag = |place: &Place<'tcx>| {
83 // FIXME: Instead of giving up for unstable places, we should introduce
84 // a temporary and retag on that.
85 is_stable(place.as_ref())
86 && may_be_reference(place.ty(&*local_decls, tcx).ty)
87 && is_not_temp(&local_decls[place.local])
89 let place_base_raw = |place: &Place<'tcx>| {
90 // If this is a `Deref`, get the type of what we are deref'ing.
92 place.projection.iter().rposition(|p| matches!(p, ProjectionElem::Deref));
93 if let Some(deref_base) = deref_base {
94 let base_proj = &place.projection[..deref_base];
95 let ty = Place::ty_from(place.local, base_proj, &*local_decls, tcx).ty;
98 // Not a deref, and thus not raw.
104 // Retag arguments at the beginning of the start block.
106 // FIXME: Consider using just the span covering the function
107 // argument declaration.
108 let source_info = SourceInfo::outermost(span);
109 // Gather all arguments, skip return value.
110 let places = local_decls
114 .map(|(local, _)| Place::from(local))
115 .filter(needs_retag);
116 // Emit their retags.
117 basic_blocks[START_BLOCK].statements.splice(
119 places.map(|place| Statement {
121 kind: StatementKind::Retag(RetagKind::FnEntry, Box::new(place)),
127 // Retag return values of functions. Also escape-to-raw the argument of `drop`.
128 // We collect the return destinations because we cannot mutate while iterating.
129 let returns = basic_blocks
131 .filter_map(|block_data| {
132 match block_data.terminator().kind {
133 TerminatorKind::Call { target: Some(target), destination, .. }
134 if needs_retag(&destination) =>
136 // Remember the return destination for later
137 Some((block_data.terminator().source_info, destination, target))
140 // `Drop` is also a call, but it doesn't return anything so we are good.
141 TerminatorKind::Drop { .. } | TerminatorKind::DropAndReplace { .. } => None,
142 // Not a block ending in a Call -> ignore.
146 .collect::<Vec<_>>();
147 // Now we go over the returns we collected to retag the return values.
148 for (source_info, dest_place, dest_block) in returns {
149 basic_blocks[dest_block].statements.insert(
153 kind: StatementKind::Retag(RetagKind::Default, Box::new(dest_place)),
159 // Add retag after assignment.
160 for block_data in basic_blocks {
161 // We want to insert statements as we iterate. To this end, we
162 // iterate backwards using indices.
163 for i in (0..block_data.statements.len()).rev() {
164 let (retag_kind, place) = match block_data.statements[i].kind {
165 // Retag-as-raw after escaping to a raw pointer, if the referent
166 // is not already a raw pointer.
167 StatementKind::Assign(box (lplace, Rvalue::AddressOf(_, ref rplace)))
168 if !place_base_raw(rplace) =>
170 (RetagKind::Raw, lplace)
172 // Retag after assignments of reference type.
173 StatementKind::Assign(box (ref place, ref rvalue)) if needs_retag(place) => {
174 let kind = match rvalue {
175 Rvalue::Ref(_, borrow_kind, _)
176 if borrow_kind.allows_two_phase_borrow() =>
180 _ => RetagKind::Default,
184 // Do nothing for the rest
187 // Insert a retag after the statement.
188 let source_info = block_data.statements[i].source_info;
189 block_data.statements.insert(
193 kind: StatementKind::Retag(retag_kind, Box::new(place)),