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|
pub use super::*;
use rustc::mir::*;
use rustc::mir::visit::Visitor;
use crate::dataflow::{BitDenotation, GenKillSet};
/// This calculates if any part of a MIR local could have previously been borrowed.
/// This means that once a local has been borrowed, its bit will be set
/// from that point and onwards, until we see a StorageDead statement for the local,
/// at which points there is no memory associated with the local, so it cannot be borrowed.
/// This is used to compute which locals are live during a yield expression for
/// immovable generators.
#[derive(Copy, Clone)]
pub struct HaveBeenBorrowedLocals<'a, 'tcx> {
body: &'a Body<'tcx>,
}
impl<'a, 'tcx> HaveBeenBorrowedLocals<'a, 'tcx> {
pub fn new(body: &'a Body<'tcx>)
-> Self {
HaveBeenBorrowedLocals { body }
}
pub fn body(&self) -> &Body<'tcx> {
self.body
}
}
impl<'a, 'tcx> BitDenotation<'tcx> for HaveBeenBorrowedLocals<'a, 'tcx> {
type Idx = Local;
fn name() -> &'static str { "has_been_borrowed_locals" }
fn bits_per_block(&self) -> usize {
self.body.local_decls.len()
}
fn start_block_effect(&self, _on_entry: &mut BitSet<Local>) {
// Nothing is borrowed on function entry
}
fn statement_effect(&self,
trans: &mut GenKillSet<Local>,
loc: Location) {
let stmt = &self.body[loc.block].statements[loc.statement_index];
BorrowedLocalsVisitor {
trans,
}.visit_statement(stmt, loc);
// StorageDead invalidates all borrows and raw pointers to a local
match stmt.kind {
StatementKind::StorageDead(l) => trans.kill(l),
_ => (),
}
}
fn terminator_effect(&self,
trans: &mut GenKillSet<Local>,
loc: Location) {
let terminator = self.body[loc.block].terminator();
BorrowedLocalsVisitor {
trans,
}.visit_terminator(terminator, loc);
match &terminator.kind {
// Drop terminators borrows the location
TerminatorKind::Drop { location, .. } |
TerminatorKind::DropAndReplace { location, .. } => {
if let Some(local) = find_local(location) {
trans.gen(local);
}
}
_ => (),
}
}
fn propagate_call_return(
&self,
_in_out: &mut BitSet<Local>,
_call_bb: mir::BasicBlock,
_dest_bb: mir::BasicBlock,
_dest_place: &mir::Place<'tcx>,
) {
// Nothing to do when a call returns successfully
}
}
impl<'a, 'tcx> BottomValue for HaveBeenBorrowedLocals<'a, 'tcx> {
// bottom = unborrowed
const BOTTOM_VALUE: bool = false;
}
struct BorrowedLocalsVisitor<'gk> {
trans: &'gk mut GenKillSet<Local>,
}
fn find_local<'tcx>(place: &Place<'tcx>) -> Option<Local> {
place.iterate(|place_base, place_projection| {
for proj in place_projection {
if proj.elem == ProjectionElem::Deref {
return None;
}
}
if let PlaceBase::Local(local) = place_base {
Some(*local)
} else {
None
}
})
}
impl<'tcx> Visitor<'tcx> for BorrowedLocalsVisitor<'_> {
fn visit_rvalue(&mut self,
rvalue: &Rvalue<'tcx>,
location: Location) {
if let Rvalue::Ref(_, _, ref place) = *rvalue {
if let Some(local) = find_local(place) {
self.trans.gen(local);
}
}
self.super_rvalue(rvalue, location)
}
}
|
