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use rustc_index::bit_set::BitSet;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::{self, Local, Location};
/// The set of locals in a MIR body that do not have `StorageLive`/`StorageDead` annotations.
///
/// These locals have fixed storage for the duration of the body.
//
// FIXME: Currently, we need to traverse the entire MIR to compute this. We should instead store it
// as a field in the `LocalDecl` for each `Local`.
#[derive(Debug, Clone)]
pub struct AlwaysLiveLocals(BitSet<Local>);
impl AlwaysLiveLocals {
pub fn new(body: &mir::Body<'tcx>) -> Self {
let mut ret = AlwaysLiveLocals(BitSet::new_filled(body.local_decls.len()));
let mut vis = StorageAnnotationVisitor(&mut ret);
vis.visit_body(body);
ret
}
pub fn into_inner(self) -> BitSet<Local> {
self.0
}
}
impl std::ops::Deref for AlwaysLiveLocals {
type Target = BitSet<Local>;
fn deref(&self) -> &Self::Target {
&self.0
}
}
/// Removes locals that have `Storage*` annotations from `AlwaysLiveLocals`.
struct StorageAnnotationVisitor<'a>(&'a mut AlwaysLiveLocals);
impl Visitor<'tcx> for StorageAnnotationVisitor<'_> {
fn visit_statement(&mut self, statement: &mir::Statement<'tcx>, _location: Location) {
use mir::StatementKind::{StorageDead, StorageLive};
if let StorageLive(l) | StorageDead(l) = statement.kind {
(self.0).0.remove(l);
}
}
}
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