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#![deny(rustc::untranslatable_diagnostic)]
#![deny(rustc::diagnostic_outside_of_impl)]
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::{
Body, Local, Location, Place, PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind,
Terminator, TerminatorKind,
};
use rustc_middle::ty::TyCtxt;
use crate::{borrow_set::BorrowSet, facts::AllFacts, location::LocationTable, places_conflict};
/// Emit `loan_killed_at` and `cfg_edge` facts at the same time.
pub(super) fn emit_loan_kills<'tcx>(
tcx: TyCtxt<'tcx>,
all_facts: &mut AllFacts,
location_table: &LocationTable,
body: &Body<'tcx>,
borrow_set: &BorrowSet<'tcx>,
) {
let mut visitor = LoanKillsGenerator { borrow_set, tcx, location_table, all_facts, body };
for (bb, data) in body.basic_blocks.iter_enumerated() {
visitor.visit_basic_block_data(bb, data);
}
}
struct LoanKillsGenerator<'cx, 'tcx> {
tcx: TyCtxt<'tcx>,
all_facts: &'cx mut AllFacts,
location_table: &'cx LocationTable,
borrow_set: &'cx BorrowSet<'tcx>,
body: &'cx Body<'tcx>,
}
impl<'cx, 'tcx> Visitor<'tcx> for LoanKillsGenerator<'cx, 'tcx> {
fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
// Also record CFG facts here.
self.all_facts.cfg_edge.push((
self.location_table.start_index(location),
self.location_table.mid_index(location),
));
self.all_facts.cfg_edge.push((
self.location_table.mid_index(location),
self.location_table.start_index(location.successor_within_block()),
));
// If there are borrows on this now dead local, we need to record them as `killed`.
if let StatementKind::StorageDead(local) = statement.kind {
self.record_killed_borrows_for_local(local, location);
}
self.super_statement(statement, location);
}
fn visit_assign(&mut self, place: &Place<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
// When we see `X = ...`, then kill borrows of
// `(*X).foo` and so forth.
self.record_killed_borrows_for_place(*place, location);
self.super_assign(place, rvalue, location);
}
fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
// Also record CFG facts here.
self.all_facts.cfg_edge.push((
self.location_table.start_index(location),
self.location_table.mid_index(location),
));
let successor_blocks = terminator.successors();
self.all_facts.cfg_edge.reserve(successor_blocks.size_hint().0);
for successor_block in successor_blocks {
self.all_facts.cfg_edge.push((
self.location_table.mid_index(location),
self.location_table.start_index(successor_block.start_location()),
));
}
// A `Call` terminator's return value can be a local which has borrows,
// so we need to record those as `killed` as well.
if let TerminatorKind::Call { destination, .. } = terminator.kind {
self.record_killed_borrows_for_place(destination, location);
}
self.super_terminator(terminator, location);
}
}
impl<'tcx> LoanKillsGenerator<'_, 'tcx> {
/// Records the borrows on the specified place as `killed`. For example, when assigning to a
/// local, or on a call's return destination.
fn record_killed_borrows_for_place(&mut self, place: Place<'tcx>, location: Location) {
// Depending on the `Place` we're killing:
// - if it's a local, or a single deref of a local,
// we kill all the borrows on the local.
// - if it's a deeper projection, we have to filter which
// of the borrows are killed: the ones whose `borrowed_place`
// conflicts with the `place`.
match place.as_ref() {
PlaceRef { local, projection: &[] }
| PlaceRef { local, projection: &[ProjectionElem::Deref] } => {
debug!(
"Recording `killed` facts for borrows of local={:?} at location={:?}",
local, location
);
self.record_killed_borrows_for_local(local, location);
}
PlaceRef { local, projection: &[.., _] } => {
// Kill conflicting borrows of the innermost local.
debug!(
"Recording `killed` facts for borrows of \
innermost projected local={:?} at location={:?}",
local, location
);
if let Some(borrow_indices) = self.borrow_set.local_map.get(&local) {
for &borrow_index in borrow_indices {
let places_conflict = places_conflict::places_conflict(
self.tcx,
self.body,
self.borrow_set[borrow_index].borrowed_place,
place,
places_conflict::PlaceConflictBias::NoOverlap,
);
if places_conflict {
let location_index = self.location_table.mid_index(location);
self.all_facts.loan_killed_at.push((borrow_index, location_index));
}
}
}
}
}
}
/// Records the borrows on the specified local as `killed`.
fn record_killed_borrows_for_local(&mut self, local: Local, location: Location) {
if let Some(borrow_indices) = self.borrow_set.local_map.get(&local) {
let location_index = self.location_table.mid_index(location);
self.all_facts.loan_killed_at.reserve(borrow_indices.len());
for &borrow_index in borrow_indices {
self.all_facts.loan_killed_at.push((borrow_index, location_index));
}
}
}
}
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