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add_retag: ensure box-to-raw-ptr casts are preserved for Miri

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This commit is contained in:
Ralf Jung 2024-03-17 17:02:38 +01:00
parent a42873e85b
commit c96fa5e143
10 changed files with 91 additions and 33 deletions
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36
compiler/rustc_mir_transform/src/add_retag.rs
View file

@ -24,7 +24,7 @@ fn may_contain_reference<'tcx>(ty: Ty<'tcx>, depth: u32, tcx: TyCtxt<'tcx>) -> b
| ty::Str
| ty::FnDef(..)
| ty::Never => false,
// References
// References and Boxes (`noalias` sources)
ty::Ref(..) => true,
ty::Adt(..) if ty.is_box() => true,
ty::Adt(adt, _) if Some(adt.did()) == tcx.lang_items().ptr_unique() => true,
@ -125,15 +125,39 @@ impl<'tcx> MirPass<'tcx> for AddRetag {
for i in (0..block_data.statements.len()).rev() {
let (retag_kind, place) = match block_data.statements[i].kind {
// Retag after assignments of reference type.
StatementKind::Assign(box (ref place, ref rvalue)) if needs_retag(place) => {
StatementKind::Assign(box (ref place, ref rvalue)) => {
let add_retag = match rvalue {
// Ptr-creating operations already do their own internal retagging, no
// need to also add a retag statement.
Rvalue::Ref(..) | Rvalue::AddressOf(..) => false,
_ => true,
// *Except* if we are deref'ing a Box, because those get desugared to directly working
// with the inner raw pointer! That's relevant for `AddressOf` as Miri otherwise makes it
// a NOP when the original pointer is already raw.
Rvalue::AddressOf(_mutbl, place) => {
// Using `is_box_global` here is a bit sketchy: if this code is
// generic over the allocator, we'll not add a retag! This is a hack
// to make Stacked Borrows compatible with custom allocator code.
// Long-term, we'll want to move to an aliasing model where "cast to
// raw pointer" is a complete NOP, and then this will no longer be
// an issue.
if place.is_indirect_first_projection()
&& body.local_decls[place.local].ty.is_box_global(tcx)
{
Some(RetagKind::Raw)
} else {
None
}
}
Rvalue::Ref(..) => None,
_ => {
if needs_retag(place) {
Some(RetagKind::Default)
} else {
None
}
}
};
if add_retag {
(RetagKind::Default, *place)
if let Some(kind) = add_retag {
(kind, *place)
} else {
continue;
}

4
compiler/rustc_mir_transform/src/lib.rs
View file

@ -529,11 +529,11 @@ fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
// AddMovesForPackedDrops needs to run after drop
// elaboration.
&add_moves_for_packed_drops::AddMovesForPackedDrops,
// `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
// `AddRetag` needs to run after `ElaborateDrops` but before `ElaborateBoxDerefs`. Otherwise it should run fairly late,
// but before optimizations begin.
&add_retag::AddRetag,
&elaborate_box_derefs::ElaborateBoxDerefs,
&coroutine::StateTransform,
&add_retag::AddRetag,
&Lint(known_panics_lint::KnownPanicsLint),
];
pm::run_passes_no_validate(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::Initial)));