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.
7 use crate::transform::{MirPass, MirSource};
9 use rustc::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 intersting, 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<'tcx>(ty: Ty<'tcx>) -> 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 run_pass(&self, tcx: TyCtxt<'tcx>, _src: MirSource<'tcx>, body: &mut BodyAndCache<'tcx>) {
62 if !tcx.sess.opts.debugging_opts.mir_emit_retag {
65 let (span, arg_count) = (body.span, body.arg_count);
66 let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
67 let needs_retag = |place: &Place<'tcx>| {
68 // FIXME: Instead of giving up for unstable places, we should introduce
69 // a temporary and retag on that.
70 is_stable(place.as_ref()) && may_be_reference(place.ty(&*local_decls, tcx).ty)
74 // Retag arguments at the beginning of the start block.
76 let source_info = SourceInfo {
77 scope: OUTERMOST_SOURCE_SCOPE,
78 span: span, // FIXME: Consider using just the span covering the function
79 // argument declaration.
81 // Gather all arguments, skip return value.
82 let places = local_decls
86 .map(|(local, _)| Place::from(local))
90 basic_blocks[START_BLOCK].statements.splice(
92 places.into_iter().map(|place| Statement {
94 kind: StatementKind::Retag(RetagKind::FnEntry, box (place)),
100 // Retag return values of functions. Also escape-to-raw the argument of `drop`.
101 // We collect the return destinations because we cannot mutate while iterating.
102 let mut returns: Vec<(SourceInfo, Place<'tcx>, BasicBlock)> = Vec::new();
103 for block_data in basic_blocks.iter_mut() {
104 match block_data.terminator().kind {
105 TerminatorKind::Call { ref destination, .. } => {
106 // Remember the return destination for later
107 if let Some(ref destination) = destination {
108 if needs_retag(&destination.0) {
110 block_data.terminator().source_info,
111 destination.0.clone(),
117 TerminatorKind::Drop { .. } | TerminatorKind::DropAndReplace { .. } => {
118 // `Drop` is also a call, but it doesn't return anything so we are good.
121 // Not a block ending in a Call -> ignore.
125 // Now we go over the returns we collected to retag the return values.
126 for (source_info, dest_place, dest_block) in returns {
127 basic_blocks[dest_block].statements.insert(
131 kind: StatementKind::Retag(RetagKind::Default, box (dest_place)),
137 // Add retag after assignment.
138 for block_data in basic_blocks {
139 // We want to insert statements as we iterate. To this end, we
140 // iterate backwards using indices.
141 for i in (0..block_data.statements.len()).rev() {
142 let (retag_kind, place) = match block_data.statements[i].kind {
143 // Retag-as-raw after escaping to a raw pointer.
144 StatementKind::Assign(box (ref place, Rvalue::AddressOf(..))) => {
145 (RetagKind::Raw, place.clone())
147 // Assignments of reference or ptr type are the ones where we may have
148 // to update tags. This includes `x = &[mut] ...` and hence
149 // we also retag after taking a reference!
150 StatementKind::Assign(box (ref place, ref rvalue)) if needs_retag(place) => {
151 let kind = match rvalue {
152 Rvalue::Ref(_, borrow_kind, _)
153 if borrow_kind.allows_two_phase_borrow() =>
157 _ => RetagKind::Default,
159 (kind, place.clone())
161 // Do nothing for the rest
164 // Insert a retag after the statement.
165 let source_info = block_data.statements[i].source_info;
166 block_data.statements.insert(
168 Statement { source_info, kind: StatementKind::Retag(retag_kind, box (place)) },