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|
use rustc_data_structures::fx::FxHashSet;
use rustc_middle::mir::visit::{PlaceContext, Visitor};
use rustc_middle::mir::{
Local, Location, Place, Statement, StatementKind, Terminator, TerminatorKind,
};
use crate::MirBorrowckCtxt;
impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
/// Walks the MIR adding to the set of `used_mut` locals that will be ignored for the purposes
/// of the `unused_mut` lint.
///
/// `temporary_used_locals` should contain locals that were found to be temporary, mutable and
/// used from borrow checking. This function looks for assignments into these locals from
/// user-declared locals and adds those user-defined locals to the `used_mut` set. This can
/// occur due to a rare case involving upvars in closures.
///
/// `never_initialized_mut_locals` should contain the set of user-declared mutable locals
/// (not arguments) that have not already been marked as being used.
/// This function then looks for assignments from statements or the terminator into the locals
/// from this set and removes them from the set. This leaves only those locals that have not
/// been assigned to - this set is used as a proxy for locals that were not initialized due to
/// unreachable code. These locals are then considered "used" to silence the lint for them.
/// See #55344 for context.
pub(crate) fn gather_used_muts(
&mut self,
temporary_used_locals: FxHashSet<Local>,
mut never_initialized_mut_locals: FxHashSet<Local>,
) {
{
let mut visitor = GatherUsedMutsVisitor {
temporary_used_locals,
never_initialized_mut_locals: &mut never_initialized_mut_locals,
mbcx: self,
};
visitor.visit_body(&visitor.mbcx.body);
}
// Take the union of the existed `used_mut` set with those variables we've found were
// never initialized.
debug!("gather_used_muts: never_initialized_mut_locals={:?}", never_initialized_mut_locals);
self.used_mut = self.used_mut.union(&never_initialized_mut_locals).cloned().collect();
}
}
/// MIR visitor for collecting used mutable variables.
/// The 'visit lifetime represents the duration of the MIR walk.
struct GatherUsedMutsVisitor<'visit, 'cx, 'tcx> {
temporary_used_locals: FxHashSet<Local>,
never_initialized_mut_locals: &'visit mut FxHashSet<Local>,
mbcx: &'visit mut MirBorrowckCtxt<'cx, 'tcx>,
}
impl GatherUsedMutsVisitor<'_, '_, '_> {
fn remove_never_initialized_mut_locals(&mut self, into: Place<'_>) {
// Remove any locals that we found were initialized from the
// `never_initialized_mut_locals` set. At the end, the only remaining locals will
// be those that were never initialized - we will consider those as being used as
// they will either have been removed by unreachable code optimizations; or linted
// as unused variables.
self.never_initialized_mut_locals.remove(&into.local);
}
}
impl<'visit, 'cx, 'tcx> Visitor<'tcx> for GatherUsedMutsVisitor<'visit, 'cx, 'tcx> {
fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
debug!("visit_terminator: terminator={:?}", terminator);
match &terminator.kind {
TerminatorKind::Call { destination, .. } => {
self.remove_never_initialized_mut_locals(*destination);
}
TerminatorKind::DropAndReplace { place, .. } => {
self.remove_never_initialized_mut_locals(*place);
}
_ => {}
}
self.super_terminator(terminator, location);
}
fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
if let StatementKind::Assign(box (into, _)) = &statement.kind {
debug!(
"visit_statement: statement={:?} local={:?} \
never_initialized_mut_locals={:?}",
statement, into.local, self.never_initialized_mut_locals
);
self.remove_never_initialized_mut_locals(*into);
}
self.super_statement(statement, location);
}
fn visit_local(&mut self, local: Local, place_context: PlaceContext, location: Location) {
if place_context.is_place_assignment() && self.temporary_used_locals.contains(&local) {
// Propagate the Local assigned at this Location as a used mutable local variable
for moi in &self.mbcx.move_data.loc_map[location] {
let mpi = &self.mbcx.move_data.moves[*moi].path;
let path = &self.mbcx.move_data.move_paths[*mpi];
debug!(
"assignment of {:?} to {:?}, adding {:?} to used mutable set",
path.place, local, path.place
);
if let Some(user_local) = path.place.as_local() {
self.mbcx.used_mut.insert(user_local);
}
}
}
}
}
|
