use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
use rustc_middle::ty::{self, adjustment::PointerCast, Instance, InstanceDef, Ty, TyCtxt};
use rustc_middle::ty::{Binder, TraitPredicate, TraitRef};
-use rustc_mir_dataflow::impls::MaybeMutBorrowedLocals;
use rustc_mir_dataflow::{self, Analysis};
use rustc_span::{sym, Span, Symbol};
use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
use super::{is_lang_panic_fn, is_lang_special_const_fn, ConstCx, Qualif};
use crate::const_eval::is_unstable_const_fn;
-// We are using `MaybeMutBorrowedLocals` as a proxy for whether an item may have been mutated
-// through a pointer prior to the given point. This is okay even though `MaybeMutBorrowedLocals`
-// kills locals upon `StorageDead` because a local will never be used after a `StorageDead`.
-type IndirectlyMutableResults<'mir, 'tcx> =
- rustc_mir_dataflow::ResultsCursor<'mir, 'tcx, MaybeMutBorrowedLocals<'mir, 'tcx>>;
-
type QualifResults<'mir, 'tcx, Q> =
rustc_mir_dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'mir, 'mir, 'tcx, Q>>;
has_mut_interior: Option<QualifResults<'mir, 'tcx, HasMutInterior>>,
needs_drop: Option<QualifResults<'mir, 'tcx, NeedsDrop>>,
needs_non_const_drop: Option<QualifResults<'mir, 'tcx, NeedsNonConstDrop>>,
- indirectly_mutable: Option<IndirectlyMutableResults<'mir, 'tcx>>,
}
impl Qualifs<'mir, 'tcx> {
- pub fn indirectly_mutable(
- &mut self,
- ccx: &'mir ConstCx<'mir, 'tcx>,
- local: Local,
- location: Location,
- ) -> bool {
- let indirectly_mutable = self.indirectly_mutable.get_or_insert_with(|| {
- let ConstCx { tcx, body, param_env, .. } = *ccx;
-
- // We can use `unsound_ignore_borrow_on_drop` here because custom drop impls are not
- // allowed in a const.
- //
- // FIXME(ecstaticmorse): Someday we want to allow custom drop impls. How do we do this
- // without breaking stable code?
- MaybeMutBorrowedLocals::mut_borrows_only(tcx, &body, param_env)
- .unsound_ignore_borrow_on_drop()
- .into_engine(tcx, &body)
- .pass_name("const_qualification")
- .iterate_to_fixpoint()
- .into_results_cursor(&body)
- });
-
- indirectly_mutable.seek_before_primary_effect(location);
- indirectly_mutable.get().contains(local)
- }
-
/// Returns `true` if `local` is `NeedsDrop` at the given `Location`.
///
/// Only updates the cursor if absolutely necessary
});
needs_drop.seek_before_primary_effect(location);
- needs_drop.get().contains(local) || self.indirectly_mutable(ccx, local, location)
+ needs_drop.get().contains(local)
}
/// Returns `true` if `local` is `NeedsNonConstDrop` at the given `Location`.
});
needs_non_const_drop.seek_before_primary_effect(location);
- needs_non_const_drop.get().contains(local) || self.indirectly_mutable(ccx, local, location)
+ needs_non_const_drop.get().contains(local)
}
/// Returns `true` if `local` is `HasMutInterior` at the given `Location`.
});
has_mut_interior.seek_before_primary_effect(location);
- has_mut_interior.get().contains(local) || self.indirectly_mutable(ccx, local, location)
+ has_mut_interior.get().contains(local)
}
fn in_return_place(
.into_results_cursor(&ccx.body);
cursor.seek_after_primary_effect(return_loc);
- cursor.contains(RETURN_PLACE)
+ cursor.get().contains(RETURN_PLACE)
}
};
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::{self, BasicBlock, Local, Location, Statement, StatementKind};
+use rustc_mir_dataflow::fmt::DebugWithContext;
+use rustc_mir_dataflow::JoinSemiLattice;
+use rustc_span::DUMMY_SP;
+use std::fmt;
use std::marker::PhantomData;
use super::{qualifs, ConstCx, Qualif};
/// A `Visitor` that propagates qualifs between locals. This defines the transfer function of
/// `FlowSensitiveAnalysis`.
///
-/// This transfer does nothing when encountering an indirect assignment. Consumers should rely on
-/// the `MaybeMutBorrowedLocals` dataflow pass to see if a `Local` may have become qualified via
-/// an indirect assignment or function call.
+/// To account for indirect assignments, data flow conservatively assumes that local becomes
+/// qualified immediately after it is borrowed or its address escapes. The borrow must allow for
+/// mutation, which includes shared borrows of places with interior mutability. The type of
+/// borrowed place must contain the qualif.
struct TransferFunction<'a, 'mir, 'tcx, Q> {
ccx: &'a ConstCx<'mir, 'tcx>,
- qualifs_per_local: &'a mut BitSet<Local>,
-
+ state: &'a mut State,
_qualif: PhantomData<Q>,
}
where
Q: Qualif,
{
- fn new(ccx: &'a ConstCx<'mir, 'tcx>, qualifs_per_local: &'a mut BitSet<Local>) -> Self {
- TransferFunction { ccx, qualifs_per_local, _qualif: PhantomData }
+ fn new(ccx: &'a ConstCx<'mir, 'tcx>, state: &'a mut State) -> Self {
+ TransferFunction { ccx, state, _qualif: PhantomData }
}
fn initialize_state(&mut self) {
- self.qualifs_per_local.clear();
+ self.state.qualif.clear();
+ self.state.borrow.clear();
for arg in self.ccx.body.args_iter() {
let arg_ty = self.ccx.body.local_decls[arg].ty;
if Q::in_any_value_of_ty(self.ccx, arg_ty) {
- self.qualifs_per_local.insert(arg);
+ self.state.qualif.insert(arg);
}
}
}
match (value, place.as_ref()) {
(true, mir::PlaceRef { local, .. }) => {
- self.qualifs_per_local.insert(local);
+ self.state.qualif.insert(local);
}
// For now, we do not clear the qualif if a local is overwritten in full by
// with aggregates where we overwrite all fields with assignments, which would not
// get this feature.
(false, mir::PlaceRef { local: _, projection: &[] }) => {
- // self.qualifs_per_local.remove(*local);
+ // self.state.qualif.remove(*local);
}
_ => {}
self.assign_qualif_direct(&return_place, qualif);
}
}
+
+ fn address_of_allows_mutation(&self, mt: mir::Mutability, place: mir::Place<'tcx>) -> bool {
+ match mt {
+ mir::Mutability::Mut => true,
+ mir::Mutability::Not => self.shared_borrow_allows_mutation(place),
+ }
+ }
+
+ fn ref_allows_mutation(&self, kind: mir::BorrowKind, place: mir::Place<'tcx>) -> bool {
+ match kind {
+ mir::BorrowKind::Mut { .. } => true,
+ mir::BorrowKind::Shared | mir::BorrowKind::Shallow | mir::BorrowKind::Unique => {
+ self.shared_borrow_allows_mutation(place)
+ }
+ }
+ }
+
+ fn shared_borrow_allows_mutation(&self, place: mir::Place<'tcx>) -> bool {
+ !place
+ .ty(self.ccx.body, self.ccx.tcx)
+ .ty
+ .is_freeze(self.ccx.tcx.at(DUMMY_SP), self.ccx.param_env)
+ }
}
impl<Q> Visitor<'tcx> for TransferFunction<'_, '_, 'tcx, Q>
// it no longer needs to be dropped.
if let mir::Operand::Move(place) = operand {
if let Some(local) = place.as_local() {
- self.qualifs_per_local.remove(local);
+ // For backward compatibility with the MaybeMutBorrowedLocals used in an earlier
+ // implementation we retain qualif if a local had been borrowed before. This might
+ // not be strictly necessary since the local is no longer initialized.
+ if !self.state.borrow.contains(local) {
+ self.state.qualif.remove(local);
+ }
}
}
}
rvalue: &mir::Rvalue<'tcx>,
location: Location,
) {
- let qualif = qualifs::in_rvalue::<Q, _>(
- self.ccx,
- &mut |l| self.qualifs_per_local.contains(l),
- rvalue,
- );
+ let qualif =
+ qualifs::in_rvalue::<Q, _>(self.ccx, &mut |l| self.state.qualif.contains(l), rvalue);
if !place.is_indirect() {
self.assign_qualif_direct(place, qualif);
}
self.super_assign(place, rvalue, location);
}
+ fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
+ self.super_rvalue(rvalue, location);
+
+ match rvalue {
+ mir::Rvalue::AddressOf(mt, borrowed_place) => {
+ if !borrowed_place.is_indirect()
+ && self.address_of_allows_mutation(*mt, *borrowed_place)
+ {
+ let place_ty = borrowed_place.ty(self.ccx.body, self.ccx.tcx).ty;
+ if Q::in_any_value_of_ty(self.ccx, place_ty) {
+ self.state.qualif.insert(borrowed_place.local);
+ self.state.borrow.insert(borrowed_place.local);
+ }
+ }
+ }
+
+ mir::Rvalue::Ref(_, kind, borrowed_place) => {
+ if !borrowed_place.is_indirect() && self.ref_allows_mutation(*kind, *borrowed_place)
+ {
+ let place_ty = borrowed_place.ty(self.ccx.body, self.ccx.tcx).ty;
+ if Q::in_any_value_of_ty(self.ccx, place_ty) {
+ self.state.qualif.insert(borrowed_place.local);
+ self.state.borrow.insert(borrowed_place.local);
+ }
+ }
+ }
+
+ mir::Rvalue::Cast(..)
+ | mir::Rvalue::ShallowInitBox(..)
+ | mir::Rvalue::Use(..)
+ | mir::Rvalue::ThreadLocalRef(..)
+ | mir::Rvalue::Repeat(..)
+ | mir::Rvalue::Len(..)
+ | mir::Rvalue::BinaryOp(..)
+ | mir::Rvalue::CheckedBinaryOp(..)
+ | mir::Rvalue::NullaryOp(..)
+ | mir::Rvalue::UnaryOp(..)
+ | mir::Rvalue::Discriminant(..)
+ | mir::Rvalue::Aggregate(..) => {}
+ }
+ }
+
fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
match statement.kind {
StatementKind::StorageDead(local) => {
- self.qualifs_per_local.remove(local);
+ self.state.qualif.remove(local);
+ self.state.borrow.remove(local);
}
_ => self.super_statement(statement, location),
}
if let mir::TerminatorKind::DropAndReplace { value, place, .. } = &terminator.kind {
let qualif = qualifs::in_operand::<Q, _>(
self.ccx,
- &mut |l| self.qualifs_per_local.contains(l),
+ &mut |l| self.state.qualif.contains(l),
value,
);
}
}
+ // We ignore borrow on drop because custom drop impls are not allowed in consts.
+ // FIXME: Reconsider if accounting for borrows in drops is necessary for const drop.
+
// We need to assign qualifs to the dropped location before visiting the operand that
// replaces it since qualifs can be cleared on move.
self.super_terminator(terminator, location);
FlowSensitiveAnalysis { ccx, _qualif: PhantomData }
}
- fn transfer_function(
- &self,
- state: &'a mut BitSet<Local>,
- ) -> TransferFunction<'a, 'mir, 'tcx, Q> {
+ fn transfer_function(&self, state: &'a mut State) -> TransferFunction<'a, 'mir, 'tcx, Q> {
TransferFunction::<Q>::new(self.ccx, state)
}
}
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(super) struct State {
+ /// Describes whether a local contains qualif.
+ pub qualif: BitSet<Local>,
+ /// Describes whether a local's address escaped and it might become qualified as a result an
+ /// indirect mutation.
+ pub borrow: BitSet<Local>,
+}
+
+impl State {
+ #[inline]
+ pub(super) fn contains(&self, local: Local) -> bool {
+ self.qualif.contains(local)
+ }
+}
+
+impl<C> DebugWithContext<C> for State {
+ fn fmt_with(&self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.write_str("qualif: ")?;
+ self.qualif.fmt_with(ctxt, f)?;
+ f.write_str(" borrow: ")?;
+ self.borrow.fmt_with(ctxt, f)?;
+ Ok(())
+ }
+
+ fn fmt_diff_with(&self, old: &Self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ if self == old {
+ return Ok(());
+ }
+
+ if self.qualif != old.qualif {
+ f.write_str("qualif: ")?;
+ self.qualif.fmt_diff_with(&old.qualif, ctxt, f)?;
+ f.write_str("\n")?;
+ }
+
+ if self.borrow != old.borrow {
+ f.write_str("borrow: ")?;
+ self.qualif.fmt_diff_with(&old.borrow, ctxt, f)?;
+ f.write_str("\n")?;
+ }
+
+ Ok(())
+ }
+}
+
+impl JoinSemiLattice for State {
+ fn join(&mut self, other: &Self) -> bool {
+ self.qualif.join(&other.qualif) || self.borrow.join(&other.borrow)
+ }
+}
+
impl<Q> rustc_mir_dataflow::AnalysisDomain<'tcx> for FlowSensitiveAnalysis<'_, '_, 'tcx, Q>
where
Q: Qualif,
{
- type Domain = BitSet<Local>;
+ type Domain = State;
const NAME: &'static str = Q::ANALYSIS_NAME;
fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain {
- BitSet::new_empty(body.local_decls.len())
+ State {
+ qualif: BitSet::new_empty(body.local_decls.len()),
+ borrow: BitSet::new_empty(body.local_decls.len()),
+ }
}
fn initialize_start_block(&self, _body: &mir::Body<'tcx>, state: &mut Self::Domain) {
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