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|
//! This pass adds validation calls (AcquireValid, ReleaseValid) where appropriate.
//! It has to be run really early, before transformations like inlining, because
//! introducing these calls *adds* UB -- so, conceptually, this pass is actually part
//! of MIR building, and only after this pass we think of the program has having the
//! normal MIR semantics.
use crate::MirPass;
use rustc_middle::mir::*;
use rustc_middle::ty::{self, Ty, TyCtxt};
pub struct AddRetag;
/// Determines whether this place is "stable": Whether, if we evaluate it again
/// after the assignment, we can be sure to obtain the same place value.
/// (Concurrent accesses by other threads are no problem as these are anyway non-atomic
/// copies. Data races are UB.)
fn is_stable(place: PlaceRef<'_>) -> bool {
// Which place this evaluates to can change with any memory write,
// so cannot assume deref to be stable.
!place.has_deref()
}
/// Determine whether this type may contain a reference (or box), and thus needs retagging.
/// We will only recurse `depth` times into Tuples/ADTs to bound the cost of this.
fn may_contain_reference<'tcx>(ty: Ty<'tcx>, depth: u32, tcx: TyCtxt<'tcx>) -> bool {
match ty.kind() {
// Primitive types that are not references
ty::Bool
| ty::Char
| ty::Float(_)
| ty::Int(_)
| ty::Uint(_)
| ty::RawPtr(..)
| ty::FnPtr(..)
| ty::Str
| ty::FnDef(..)
| ty::Never => false,
// References
ty::Ref(..) => true,
ty::Adt(..) if ty.is_box() => true,
// Compound types: recurse
ty::Array(ty, _) | ty::Slice(ty) => {
// This does not branch so we keep the depth the same.
may_contain_reference(*ty, depth, tcx)
}
ty::Tuple(tys) => {
depth == 0 || tys.iter().any(|ty| may_contain_reference(ty, depth - 1, tcx))
}
ty::Adt(adt, subst) => {
depth == 0
|| adt.variants().iter().any(|v| {
v.fields.iter().any(|f| may_contain_reference(f.ty(tcx, subst), depth - 1, tcx))
})
}
// Conservative fallback
_ => true,
}
}
impl<'tcx> MirPass<'tcx> for AddRetag {
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
sess.opts.unstable_opts.mir_emit_retag
}
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
// We need an `AllCallEdges` pass before we can do any work.
super::add_call_guards::AllCallEdges.run_pass(tcx, body);
let (span, arg_count) = (body.span, body.arg_count);
let basic_blocks = body.basic_blocks.as_mut();
let local_decls = &body.local_decls;
let needs_retag = |place: &Place<'tcx>| {
// FIXME: Instead of giving up for unstable places, we should introduce
// a temporary and retag on that.
is_stable(place.as_ref())
&& may_contain_reference(place.ty(&*local_decls, tcx).ty, /*depth*/ 3, tcx)
&& !local_decls[place.local].is_deref_temp()
};
let place_base_raw = |place: &Place<'tcx>| {
// If this is a `Deref`, get the type of what we are deref'ing.
if place.has_deref() {
let ty = &local_decls[place.local].ty;
ty.is_unsafe_ptr()
} else {
// Not a deref, and thus not raw.
false
}
};
// PART 1
// Retag arguments at the beginning of the start block.
{
// FIXME: Consider using just the span covering the function
// argument declaration.
let source_info = SourceInfo::outermost(span);
// Gather all arguments, skip return value.
let places = local_decls
.iter_enumerated()
.skip(1)
.take(arg_count)
.map(|(local, _)| Place::from(local))
.filter(needs_retag);
// Emit their retags.
basic_blocks[START_BLOCK].statements.splice(
0..0,
places.map(|place| Statement {
source_info,
kind: StatementKind::Retag(RetagKind::FnEntry, Box::new(place)),
}),
);
}
// PART 2
// Retag return values of functions. Also escape-to-raw the argument of `drop`.
// We collect the return destinations because we cannot mutate while iterating.
let returns = basic_blocks
.iter_mut()
.filter_map(|block_data| {
match block_data.terminator().kind {
TerminatorKind::Call { target: Some(target), destination, .. }
if needs_retag(&destination) =>
{
// Remember the return destination for later
Some((block_data.terminator().source_info, destination, target))
}
// `Drop` is also a call, but it doesn't return anything so we are good.
TerminatorKind::Drop { .. } | TerminatorKind::DropAndReplace { .. } => None,
// Not a block ending in a Call -> ignore.
_ => None,
}
})
.collect::<Vec<_>>();
// Now we go over the returns we collected to retag the return values.
for (source_info, dest_place, dest_block) in returns {
basic_blocks[dest_block].statements.insert(
0,
Statement {
source_info,
kind: StatementKind::Retag(RetagKind::Default, Box::new(dest_place)),
},
);
}
// PART 3
// Add retag after assignment.
for block_data in basic_blocks {
// We want to insert statements as we iterate. To this end, we
// iterate backwards using indices.
for i in (0..block_data.statements.len()).rev() {
let (retag_kind, place) = match block_data.statements[i].kind {
// Retag-as-raw after escaping to a raw pointer, if the referent
// is not already a raw pointer.
StatementKind::Assign(box (lplace, Rvalue::AddressOf(_, ref rplace)))
if !place_base_raw(rplace) =>
{
(RetagKind::Raw, lplace)
}
// Retag after assignments of reference type.
StatementKind::Assign(box (ref place, ref rvalue)) if needs_retag(place) => {
let kind = match rvalue {
Rvalue::Ref(_, borrow_kind, _)
if borrow_kind.allows_two_phase_borrow() =>
{
RetagKind::TwoPhase
}
_ => RetagKind::Default,
};
(kind, *place)
}
// Do nothing for the rest
_ => continue,
};
// Insert a retag after the statement.
let source_info = block_data.statements[i].source_info;
block_data.statements.insert(
i + 1,
Statement {
source_info,
kind: StatementKind::Retag(retag_kind, Box::new(place)),
},
);
}
}
}
}
|
